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Record for a UF thesis. Title & abstract won't display until thesis is accessible after 2008-02-29.

Permanent Link: http://ufdc.ufl.edu/UFE0021414/00001

Material Information

Title: Record for a UF thesis. Title & abstract won't display until thesis is accessible after 2008-02-29.
Physical Description: Book
Language: english
Creator: Polematidis, Ioannis M
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2007

Subjects

Subjects / Keywords: Agricultural and Biological Engineering -- Dissertations, Academic -- UF
Genre: Agricultural and Biological Engineering thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Statement of Responsibility: by Ioannis M Polematidis.
Thesis: Thesis (M.S.)--University of Florida, 2007.
Local: Adviser: Pullammanappallil, Pratap C.
Electronic Access: INACCESSIBLE UNTIL 2008-02-29

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2007
System ID: UFE0021414:00001

Permanent Link: http://ufdc.ufl.edu/UFE0021414/00001

Material Information

Title: Record for a UF thesis. Title & abstract won't display until thesis is accessible after 2008-02-29.
Physical Description: Book
Language: english
Creator: Polematidis, Ioannis M
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2007

Subjects

Subjects / Keywords: Agricultural and Biological Engineering -- Dissertations, Academic -- UF
Genre: Agricultural and Biological Engineering thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Statement of Responsibility: by Ioannis M Polematidis.
Thesis: Thesis (M.S.)--University of Florida, 2007.
Local: Adviser: Pullammanappallil, Pratap C.
Electronic Access: INACCESSIBLE UNTIL 2008-02-29

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2007
System ID: UFE0021414:00001


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1 THERMOPHILIC, BATCH, HIGH-SOLIDS BIOGASIFICATION OF SUGAR BEET TAILINGS By IOANNIS M. POLEMATIDIS A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2007

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2 2007 Ioannis M. Polematidis

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3 To my mother who has always been supportive of my education

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4 ACKNOWLEDGMENTS I thank the many individuals that have contri buted to make this project a success and my graduate experience so enjoyable. Specifical ly, I express my grea t appreciation to Dr. Pullammanappallil, my academic advisor and committee chair, for his flexibility, continual support and guidance during my time at the University of Florida. I give special thanks to Dr. Spyros Svoronos for presenting me with the opp ortunity of meeting Dr. Pullammanappallil and encouraging me to take on a promising career path in Bioprocess Engineering. I also owe a lot of gratitude to Dr. Arthur Teixeira for his devotion and patience during my program, as well as his inspirational lectures. I would like to thank Dr. John M. Owens and Dr. David Chynoweth for their insightful ideas and concepts in the fiel d of anaerobic digestion and in taking the time to elaborate on their experiences as students. In addition, I would like to thank Mr. Bob Tonkinson, Mr Larry Miller and Mr. Abhay Kopp ar for assisting me with mechanical and analytical issues. One a more personal note I would like to tha nk all of my family; w ithout them, this would never have been possible. I would like to also th ank all of my friends at the University of Florida who supported me during my studies as well.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS...............................................................................................................4 LIST OF TABLES................................................................................................................. ..........8 LIST OF FIGURES................................................................................................................ .........9 LIST OF ABBREVIATIONS........................................................................................................12 ABSTRACT....................................................................................................................... ............14 CHAPTER 1 INTRODUCTION..................................................................................................................16 1.1 Background................................................................................................................ ......16 1.2 Objective................................................................................................................. .........19 2 MATERIALS AND METHODS...........................................................................................22 2.1 Introduction.............................................................................................................. ........22 2.2 Reactor Design............................................................................................................ .....22 2.3 Instrumentation and Equipment.......................................................................................25 2.3.1 Introduction...........................................................................................................25 2.3.2 Datalogger and Controller.....................................................................................25 2.3.3 Datalogger Support Software................................................................................26 2.3.4 Sensor for Biogas Production................................................................................27 2.3.4.1 Biogas meter operation................................................................................28 2.3.4.2 Calibration of biogas meter.........................................................................28 2.3.4.3 Connection to data acquisition....................................................................30 2.3.5 Sensor for pH.........................................................................................................30 2.3.6 Sensor Temperature...............................................................................................32 2.4 Temperature Control....................................................................................................... .33 2.4.1 Heating Hardware..................................................................................................33 2.4.2 Temperature Control..............................................................................................34 2.4.3 System Temperature Profiling................................................................................35 2.4.4 Temperature Fail-Safe Protocol.............................................................................36 2.5 Pressure Testing.......................................................................................................... .....37 2.5.1 Positive Pressure Testing.......................................................................................37 2.6 Liquid Storage Vessels....................................................................................................38 2.6.1 Inoculum Storage Tank.........................................................................................38 2.6.2 High COD Liquid Storage.....................................................................................39 2.7 Biogasification System Setup...........................................................................................39 2.8 Feedstock Preparation..................................................................................................... .40 2.9 Protocol for Solids Reactor Loading................................................................................40

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6 2.9.1 Pre-Loading Protocol..............................................................................................40 2.9.2 Un-Bulked Experiments Loading...........................................................................40 2.9.3 Bulked Experiments Loading.................................................................................41 2.9.4 Reactor Start-Up.....................................................................................................41 2.9.5 Reactor Un-Loading..............................................................................................42 2.10 Protocol for AFR......................................................................................................... ..42 2.10.1 Reactor Start-Up..................................................................................................42 2.10.2 Feeding................................................................................................................42 2.11 Protocol for Sequencing Experiments...........................................................................43 2.12 Inoculum Development.................................................................................................43 2.13 Design of Experiments..................................................................................................44 2.14 Analytical Methods........................................................................................................ .45 2.14.1 Gas Analysis.........................................................................................................45 2.14.2 Liquid Analysis...................................................................................................45 2.14.2.1 pH................................................................................................................... ..45 2.14.2.2 Soluble chemical oxygen demand....................................................................45 2.14.2.3 Volatile fatty acids............................................................................................46 2.14.3 Solids Analysis.....................................................................................................47 2.14.3.1 Moisture content........................................................................................47 2.14.3.2 Volatile solids............................................................................................47 2.14.3.3 Solids composition calculation..................................................................47 Solids chemical characteristics.................................................................................47 2.15 Performance Analysis.....................................................................................................48 3 STUDY I RESULTS: SINGLE-STAGE BIOGASIFICATION............................................70 3.1 Introduction.............................................................................................................. ........70 3.2 Background................................................................................................................ ......70 3.3 Results................................................................................................................... ...........72 3.4 Discussion................................................................................................................ ........77 3.5 Conclusions............................................................................................................... .......81 4 STUDY II RESULTS: LEACHING AND TREATMENT OF READILY SOLUBLE FRACTION OF SUGAR BEET TAILINGS.........................................................................86 4.1 Introduction.............................................................................................................. ........86 4.2 Results.................................................................................................................... ...........86 4.3 Discussion................................................................................................................. ........89 4.4 Conclusions................................................................................................................ .......93 5 STUDY III RESULTS: THE EFFECT OF BULKING ON THE BIOGASIFICATION OF SUGAR BEET TAILINGS............................................................................................101 5.1 Introduction.............................................................................................................. ......101 5.2 Background................................................................................................................ ....102 5.3 Results................................................................................................................... .........104 5.4 Discussion................................................................................................................. ......109

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7 5.5 Conclusions............................................................................................................... .....113 6 STUDY IV RESULTS: THE EFFECT OF TWO-STAGE OPERATION ON THE BIOGASIFICATION OF SU GAR BEET TAILINGS........................................................121 6.1 Introduction.............................................................................................................. ......121 6.2 Background................................................................................................................ ....122 6.4 Discussion................................................................................................................ ......130 6.5 Conclusions................................................................................................................ .....133 7 CONCLUSIONS AND FUTURE WORK...........................................................................144 7.1 Conclusions................................................................................................................ .....144 7.2 Future Work................................................................................................................ ....146 APPENDIX A PROGRAM CODE for cr10X..............................................................................................149 B THE EFFECT OF MACERATION ON BIOGASIFICATION OF SUGAR BEET TAILINGS....................................................................................................................... .....155 C ACTIVITY TEST ON DORMANT INOCULUM..............................................................157 LIST OF REFERENCES.............................................................................................................158 BIOGRAPHICAL SKETCH.......................................................................................................161

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8 LIST OF TABLES Table page 2-1 Constituents tested by Dairy One on so lids fraction of sugar beet tailings.......................69 3-1 Sugar beet tailings characteristics......................................................................................83 3-2 Loading and unloading data for Study I experiments........................................................83 3-3 Summary of biogasification perf ormance in Study I experiments....................................84 4-1 Leaching experiments fo r sugar beet tailings....................................................................96 4-2 Summary of parameters from biogasi fication of wash water in the AFR.......................100 5-1 Loading and unloading data for bulked and un-bulked experiments...............................118 5-2 Summary of performance in Study III experiments........................................................118 5-3 Summary of methane potential distribution in Study III.................................................119 5-4 Chemical characteristics of tailings and digested residue................................................119 5-5 Mineral compositions in suga r beet tailings and residue.................................................120 6-1 Loading and unloading data for Experiments IV.1 to IV.4.............................................142 6-2 Summary of operation times for two-stage experiments.................................................142 6-3 Summary of cumulative methane yield di stribution in two-stage biogasification..........143

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9 LIST OF FIGURES Figure page 2-1 Construction of biogasification ve ssels from 5-gallon carboy bottle................................49 2-2 Lid components and sealing m echanism for biogasification vessels.................................50 2-3 Lid specifications and components for bi ogasification vessels.........................................51 2-4 Custom-build tripod stand for biogasification vessels.......................................................52 2-5 Controller panel C1 and C2...............................................................................................53 2-6 Biogas U-tube meter........................................................................................................ ..54 2-7 pH flow cell system for biogasification system.................................................................54 2-8 Temperature compensation calibration of pH sensor........................................................55 2-9 Heating tape attachment to vessel wall..............................................................................56 2-10 Circuit diagram for heating band.......................................................................................56 2-11 Schematic for vessel temperature profiling.......................................................................57 2-12 Spatial temperature profil es in biogasification vessel.......................................................58 2-13 On/off controller tuning of h eating to biogasification vessel........................................... 59 2-14 Liquid re-circulation eff ect on temperature control...........................................................60 2-15 Temperature profile within biogasifica tion vessel during on/off re-circulation mode......60 2-16 Temperature profile within biogasifica tion vessel during up-flow and down-flow recirculation.................................................................................................................... ......61 2-17 Comparison of re-circulation modes on biogasification vessel temperature.....................61 2-18 Inoculum storage vessel................................................................................................... ..62 2-19 Wash water cold storage bag.............................................................................................62 2-20 Solids biogasification reactor schematic (ABCR).............................................................63 2-21 Liquids biogasification reactor (AFR) schematic..............................................................64 2-22 Complete biogasifica tion experiment station.....................................................................65

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10 2-23 Bulking agent layers in s ugar beet tailings waste bed.......................................................66 2-24 Inoculum acclimatization experiments..............................................................................67 2-25 Design of experiments for sugar beet tailings bi ogasification...........................................68 3-1 Sugar beet tailings residue................................................................................................ .82 3-2 Comparison of cumulative methane production from experiments in Study I..................84 3-3 Profiles of biogasification parame ters from experiments in Study I.................................85 4-1 In-situ leaching of sugar beet tailings................................................................................95 4-2 Performance profiles from wash water biogasification.....................................................97 4-3 COD balance from wash wate r biogasification in the AFR..............................................99 5-1 Comparison of cumulative methan e production from bulked and un-bulked experiments.................................................................................................................... ..115 5-2 Comparison of biogasification para meter profiles for bulked and un-bulked experiments.................................................................................................................... ..116 5-3 Comparison of VFA profiles for bulked and un bulked experiments.............................117 6-1 Two-phase/stage block flow diagrams.............................................................................134 6-2 Two-stage system for the biogasi fication of sugar beet tailings......................................135 6-3 Cumulative methane yields from ABCR and AFR in Experiment IV.1..........................136 6-4 Cumulative methane yields from ABCR and AFR in Experiment IV.2..........................136 6-5 Cumulative methane yields from ABCR and AFR in Experiment IV.3..........................137 6-6 Cumulative methane yields from ABCR and AFR in Experiment IV.4..........................137 6-7 Biogasification parameter profiles fr om ABCR and AFR in Experiment IV.1...............138 6-8 Biogasification parameter profiles fr om ABCR and AFR in Experiment IV.2...............139 6-9 Biogasification parameter profiles fr om ABCR and AFR in Experiment IV.3...............140 6-10 Biogasification parameter profiles fr om ABCR and AFR in Experiment IV.4...............141 7-1 Summary of different mode s investigated in biogasifyi ng sugar beet tailings ..............147

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11 7-2 Performance comparison for mode of opera tion on the biogasification of sugar beet tailings....................................................................................................................... ...... 148 B-1 Cumulative methane yield of macerated sugar beet tailings...........................................155 B-2 Biogasification parameters for macerated sugar beet tailings.........................................156 C-1 Inoculum activity test run................................................................................................157

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12 LIST OF ABBREVIATIONS ABCR Anaerobic batch composting reactor ACSC American Crystal Sugar Company ADF Acid detergent fiber AFR Anaerobic filter reactor ARS Analytical research systems BMP Biochemical methane potential C1 CR10X 1 controller C2 CR10X 2 controller C/N Carbon-to-nitrogen ratio COD Chemical oxygen demand CSTR Continuous stirred tank reactor DM Dry matter FID Flame ionization detector GC Gas chromatograph HRT Hydraulic retention time ISR Inoculum-to-substrate ratio MSW Municipal solid waste NDF Neutral detergent fiber NFC Non-structural carbohydrates OFMSW Organic fraction of municipal solid waste SBR Sequencing batch reactor SCOD Soluble chemical oxygen demand SEBAC Sequential batch anaerobic composting SS Suspended solids

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13 SSR Solid state relay SWWT Separate wash water treatment STR Stirred tank reactor TS Total solids UASB Up-flow anaerobic sludge blanket VFA Volatile fatty acids VS Volatile solids VSS Volatile suspended solids

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14 Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science THERMOPHILIC, BATCH, HIGH-SOLIDS BIOGASIFICATION OF SUGAR BEET TAILINGS By Ioannis M. Polematidis August 2007 Chair: Pratap C. Pullammanappallil Major: Agricultural and Biological Engineering Tailings from sugar beet processing are currently managed by landfilling or land application. For example, American Crystal Suga r Company generates 400 tons per day of sugar beet tailings and spends close to $1 milli on dollars per year disposing them. Anaerobic conversion of sugar beet tailings into energy woul d not only generate biogas for energy, but also reduce the quantity of waste stre am that requires disposal. The concept of flooded Sequential batch an aerobic composting (SEBAC-2) technology, developed at the University of Florida was ini tially implemented for the biogasification of sugar beet tailings. Preliminary experiments were cond ucted at mesophilic (37C) temperatures and it was found that daily methane produc tion rates and methane yield fail ed to increase even after 40 days of digestion. Persistent high volatile fatty acids build up and high soluble COD during biogasification were perceived to be significant reason for the failure. This thesis presents findings related to th e implementation of single-stage and two-stage thermophilic high-solids systems for enhanced bioga sification of sugar beet tailings. The single stage system was operated in different mode s: no pre-treatment, pre-treatment, no bulking, bulking and maceration. The methane yi elds varied between 170 to 285 L kg VS-1 and time required to achieve 95% of methane potential vari ed between 8 to 15 days. Single-stage with pre-

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15 treatment and bulking showed the highest methane potential, the shortest retention time and low volatile fatty acids accumulation. Two-stage sy stem was operated by sequencing a single-stage high solids system with an anaerob ic filter reactor. The methan e yields varied between 293 to 315 L kg VS-1 and time required to achieve 95% of me thane potential varied between 7.5 to 10 days. The volatile fatty acid accumulation was also found to be low. The advantages of operating a two-stage system was the elimination of pre-treatment, and bulking, in addition to reduced retention times and higher loading ra tes. The retention time in the two-stage thermophilic system was reduced to almost 1/ 3 from previously operated SEBAC-2 mesophilic system.

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16 CHAPTER 1 INTRODUCTION 1.1 Background Management of organic wastes generated by hu man activities is increasingly one the most pressing concerns confronting a developing society. Increas ed awareness and stricter environmental policies and regul ations have translated to re-examining and enhancing conventional practices. High demands to establish an environmentally-acceptable and sustainable technology platform fo r organic wastes has prompted the interest of research, development and commercialization sectors. Indus tries producing significant organic wastes as part of their processing practices are becomi ng in tune with modern waste management strategies. In-vessel conversi on technologies provide a sensible on-site solution to organic waste management, especially in many nations where it is becoming increasingly difficult to landfill biologically degradable waste (Fricke et al., 2005). The sugar beet industry (American Crystal Sugar Company, ACSC) was recently targeted as a promising candidate for implementing a sustainable technol ogical solution to their sign ificant sugar refining organic byproduct: sugar beet tailings. Nearly forty percent of all refined sugar cons umed in the USA annually is made from beets grown in the north central and nor th western regions of the United States. Sugar beet processing generates significant quantities of both solid an d liquid organic waste. Post-harvest operation begins when beets are brought into the processing plant from storage in outdoor stockpiles and are washed; sugar beet tailings, which mainly consist of sugar beet (10-30%), weeds, sugar beet tops, debris and soil are dislodged from sugar beets during this washing process. Subsequently, sugar beet tailings are stockpiled outside the processing plant and are hauled away for disposal into landfills or applied on nearby farmland at a cost to the plant. For example,

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17 ACSC spends approximately $1 million per year di sposing 400 tons of tailings that are generated daily at its East Grand Forks, Minnesota processing plant (Teixeira et al., 2005). Organic waste management begins with identifying feedstock characteristics and evaluating plausible conversion technologies for handling such feed stock. Commercial conversion processes include combustion, ther mochemical gasification, thermochemical liquefaction, aerobic com posting and anaerobic digestion. Th ese processes yield conversion to various products which include electrical/heat energy, steam, low-to-hi gh energy gases, liquid fuels and chemical feedstocks. If the orga nic waste is abundant, and if collection and transportation is economically feasible, majo r criteria for the selection of conversion technologies include (Chynoweth et al., 1980): Feedstock characteristics such as mo isture content or biodegradability Energy product desired Effluent streams (byproducts, residues) Environmental impact Economics A lack of literature on the disposal of sugar be et tailings indicated that not much attention had been devoted towards processing this wast e residue for value addition. Selection among the available residual waste conversi on technologies was evaluated in itially based on the intrinsic moisture. Appearing as a solid, su gar beet tailings (Figure 1-1) actually have a moisture content of 84 to 87 %, and a biodegradable fraction approximately 80 to 90 % of dry matter content. Generally, a feed moisture content of more th an 50% is not preferred for thermal conversion processes; implementation of conventional com bustion, liquefaction or gasification would be practical only if a vigorous and costly pre-drying stage was implemented into the overall waste management scheme.

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18 Biological conversion technologi es provide a conventional approach to management of high moisture and biodegradable feedstocks and ar e generally classified as either aerobic or anaerobic processes. Aerobic processing (compos ting) is the biological transformation in the presence of oxygen whereas anaerob ic processes (anaerobic digesti on or biogasification) occurs in the absence of oxygen and also yields a valuable product: bioga s fuel (a mixture of methane and carbon dioxide). Practical bi odegradability of an organic f eedstock utilizing each process may vary under similar conditions: particle size, time, and envi ronmental conditions (temperature, nutrient requirements, etc.) wi ll influence the outcom e of biodegradation (Kayhanian, 1995). Though waste mi nimization and recycling can be fully exploited with both biological transformation schemes, there is still a residual fraction which has to be disposed of (Fricke et al., 2004). Biological gasification (bi ogasification) of sugar beet taili ngs via the anaerobic process is a very attractive method that would not only genera te biogas, but also redu ce the volume of waste stream that requires disposal Preliminary studies on feasibility of biogasification were conducted at the University of Florida. Bioche mical methane potential (BMP) assays of sugar beet tailings yielded 250 L of methane/kg VS. Based on this methane yield, a simple economic analysis showed that taking into account the reduced cost of dis posal, electricity revenues, and natural gas savings, a conservative net savings from biogasifying 400 tons/day of tailings was $4,873 per day (Teixeira et al., 2005). Among the various technologies that are availa ble for anaerobic dige stion, the Sequential Batch Anaerobic Composting (SEBAC) was initially chosen for the biogasification of sugar beet tailings. The SEBAC process is a patented hi gh solids, batch, leachbed process that uses a combination of solid state fermentation and leach ate recycle to provide a simple and reliable

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19 process (Chugh et al., 1999; Chynoweth and Le grand, 1993; Chynoweth et al., 1992). As compared to other waste management technolog ies, SEBAC offers numerous technical and economic advantages, which include: Simple operation protocols Flexible designs, such as tanks, trench or cells Relatively low initial capital investments The SEBAC process has been tested on organic fraction of municipal solid waste (OFMSW), woody biomass, yard wastes and mixtures of ya rd wastes and biosolid s. Recently, the SEBAC process was modified (termed SEBAC-2) for improved kinetics and reduced solids processing time by incorporating flooded operation and periodic redirection of leachate flow (Luniya et al., 2005). In preliminary experiments, sugar beet taili ngs were anaerobically digested using SEBAC2 at mesophilic conditions; findings showed that the methane generation rates were poorer compared to that from digestion of other orga nic residues (Chynoweth et al., 2002). Persistently high volatile organic acid concentrations were measured in leachate and daily methane production rates failed to increase even after 40 da ys of digestion. Therefore, if biogasification of tailings were to be successfully implemented at full-scale there was need for further investigations to determine the factors affecting the degradation of tailings and to develop a scalable process. These investigations and their outcomes are presented here. 1.2 Objective The objective of this research was to eff ectively carry out bench-scale studies on the biogasification (also known as anaerobi c digestion) of sugar beet taili ngs in an effort to identify critical factors and performan ce measures during batch operation. The research findings would ultimately lead to a proposal of a system desi gn and operation concept for full-scale application

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20 of biogasification. This objectiv e was chosen as a point of study on an on-going industriallyoriented project (Conversion of Biomass into Energy and Compost through Sequential Batch Anaerobic Composting) at the University of Fl orida in partnership with Xcel Energy and American Crystal Sugar Company. The goals of this research work were divided into six objectives. Objective 1 : Design, construct, and successfully operate a bench-scale system for batch, high-solids biogasification of sugar beet tailings. Objective 2 : Investigate the effect of single st age operation on sugar beet tailings Objective 3 : Investigate the leaching and pre-treatment of readily soluble fraction of sugar beet tailings Objective 4 : Investigate the effect of bulking on the biogasification of sugar beet tailings Objective 5 : Investigate the effect of two-stage operation on the biogasification of sugar beet tailings Objective 6 : Achieve accelerated biogasification of sugar beet tailings and highlight operation techniques that can be im plemented in scale-up studies.

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21 Figure 1-1. Raw sugar beet tailings recei ved from American Crystal Sugar Company

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22 CHAPTER 2 MATERIALS AND METHODS 2.1 Introduction In this chapter, the systems that were empl oyed to perform well-controlled experiments in biogasification of sugarbeet tailings are descri bed. The design, fabr ication and operation of reactors, the instrumentation and software, the operation of gas meters, the implementation of temperature control, and supporting equipment ar e described in detail. Protocols followed regarding preparation of feedst ock, reactor loading, unloading a nd operational schemes are also described in detail. The chapter proceeds in describing the prel iminary acclimatization stage of building a microbial population necessary to carry out well-controlled experime nts. Thereafter, a platform of four studies was designed to address key fact ors affecting high-solids biogasification digestion of sugar beet tailings. The chapter concludes by describing the analytical techniques used to carry out measurements on critical biogasificatio n parameters; this includes the work conducted by an external laborato ry Dairy One Forage Lab (Ithaca, New York). 2.2 Reactor Design Experiments were carried out in three, 20-liter Pyrex glass carboy bottles converted specifically to meet the design needs of batch anaerobic leachbed/ high-s olids reactors. Two vessels were designated for solids digestion, na med as anaerobic batch composting reactors 1 and 2 (ABCR1 & 2). The third vessel for liq uid digestion was named anaerobic filter reactor (AFR). Design issues addressed included: the need for a large cr oss-sectional opening to facilitate solids loading and unloading efficien tly; the need for an adjustable bed volume to experiment with a range of bulking densities; Adju stable leachate re-circulation lines to account for level increases/decreases of settled solids and working liquid volumes; the need for a top-

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23 plate lid that would keep the vessel gas-tight ; and an efficient st rategy for flushing and performing maintenance on the vessel. To adeq uately tailor a vessel with such needs, collaborative design and custom fabrication was provided by Analytical Research Systems (Micanopy, FL, USA) in conjunction with University of Florida s Agricultural and Biological Engineering machine shop. Solids handling during loading and unloading of vessels recei ved forefront attention in design considerations. Each carboy bottle was ther mally cut at its base and a flanged lip was curled, resulting in an inverted carboy bottle with a complete cr oss-sectional opening. The neck of the bottle was adjusted by thermally fusing a glass flange and couple to increase overall length. A custom-build glass Duran O-ring flan ge bottom (ABCRs only) was machined to fit the carboy flange, secured by a stainless steel, quick-release clamp. Carboy modifications (Figure 2-1) to construct bior eactors were regarded as simp le and low-cost solutions to constructing lab-scale anaerobic equimpment. To facilitate easy loading and unloading of sugar beet tailings, the next phase of design focused on a top lid adequate to seal each vessel. Several design concepts were drafted for a toplid to cover the cross-sectional area of the modi fied carboy bottle. The glass flange design on the carboy bottle gave impetus to a clamp-seal strate gy; clearance on the glass flange (0.75 inches) provided enough surface area for a gask et to sit in between the propos ed lid and glass flange. A flange ring was conceptualized and fabricated to press against the underside of the carboy flange, whereas the lid would press on the upside of the glass flange. Th e lid would clamp to the flange ring at twelve points; bolts and wing nuts were used to fasten th e parts together (Figure 2-2). Aluminum was chosen as the material of cons truction for the top lid. This versatile metal provided certain beneficial propert ies such as; strong metal charac teristics which made it suitable

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24 for clamping; a light weight, minimizing force on the glass structure; and metal with low oxidative properties to withstand humid environmen ts. The lid included ports and an adjustable perforated plate suspended on the in side of th e lid; tapered holes were fabricated to meet the needs of four ports (1/2 inch NPT-F) and three support-rod holes (Figure 2-3). Ports were fitted with fluid system piping components, which included Swagelok press fittings for inch tubes (liquid inlets) and hose barbs for 3/8 inch si licon tubing (gas outlet); additional holes were plugged with appropriate brass caps. Three 6-in ch stainless steel suppor t rods were screwed on the inside part of the lid; a 1/ 8 inch 316 stainless steel perforat ed plate (11 inches in diameter) was suspended from the rods and served as the ad justable top barrier for the leach bed. A similar perforated plate was machined as a bottom barrier of the leach bed, sitting on the shoulders of the glass carboy. Finally, a Viton ga sket was cut to 1 inches in area (twice as wide as the glass carboy flange) to serve as the sealant between the lid and gasket. A high he at, inert and chemical resistant silicone lubricant (Dow Corning High V acuum Grease) was applied to both sides of the gasket to assure proper sealing. The lubri cant was re-applied af ter each experiment. Support stands were fabricated by ARS to ad equately erect each biogasification vessel. Design criteria that were considered included: A stand that can support a 20-kg load A glass-friendly material that would support the full weight of the carboy, lid and contents sufficiently A stand that would enable easy access to sample/process ports and maintenance A stand that would not impede lo ading and unloading of vessels. A custom tri-pod support stand was tailored to the de sign criteria for each vessel. Each consisted of an adjustable UHMW-PE base support ring wi th an 11-inch ID chamfered hole and three

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25 hollow aluminum legs; base mounts (Base Flange #4UG93, Grainger) were fitted on the ends of each leg to secure to a base plate (Figure 2-4). Slight modifications in design were impleme nted on the AFR, fabricated by ARS. A short-neck, 20-L Pyrex carboy bot tle (CLS 15955, Sigma-Aldrich ) was ordered specifically for this vessel. A special request was made to ARS glass-blower to minimize the volume of reactor below the bottoms perforated plate. This de sign modification translated to minimal dead volume that would not contribute to the active reactor volume; in contrast, solids reactors were designed with long necks to accommodate particulat es to accumulate during degradation without clogging re-circulation lines. Th e Duran o-ring flange design wa s substituted by Teflon widemouth threaded plug. Finally, four press-fitt ings (SAF 2507 Swagelok) were machined and screwed into the Teflon plug to serve as inlet/outlet ports. 2.3 Instrumentation and Equipment 2.3.1 Introduction In order to achieve proper understanding of the process characteristics in anaerobic digestion, each biogasification vessel was instru mented for data acquisition of biogas production rate, temperature and pH; Logger Net (v 3.1) software and CR10-X measurement/controller module (products of Campbell Scien tific Inc, USA) were used to monitor such parameters. The effects of variation of measur ed parameters would help to optimize the system performance within the systems operation boundaries. 2.3.2 Datalogger and Controller The CR10-X is a compact, modular datalogger with a measurement and control module, external power supply and keyboard display. Th e low-power design allows it to operate up to one year on a 7 Amp-hr, unregulated 12 Vdc s ource. It is designed for unattended network applications and can measure, record and display data (62000 non-vol atile points) without

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26 operator or computer intervention. In addition, th e CR10-Xs built-in intel ligence helps to setup test routines and specify the parameters of each channel. The channels available include: 12 single-ended or 6 differential, individually configured; two pul se counters; switched voltage excitations; and eight control/dig ital ports. A wide range of sens ors compatible with the CR10X were available on the market to m eet the specific needs of measur ing or controlling experimental parameters. Two CR10X controllers were available for th is biogasification studyC1 and C2. With three units constructed for bi ogasification experiments, C1 would serve ABCR 1 whereas C2 would serve ABCR 2 and AFR. This arrangemen t was especially beneficial when dual-stage experimentation was conducted on the latter part of this work (Chapter 6). Two, 12-V batteries supplied power to both controllers; each day th ey were closely monitored, measured and recharged if voltage fell belo w 11.8 volts. Controllers left on line with a power source of < 11.5 volts would shift to an indete rminate state and malfunction. Th is led to potential loss of temperature control in reactors a nd datalogging failure. A fail-safe diagnostic was coded in the CR10X program (Appendix A) in the event of power supply outage to prevent the worse case scenario when heating tape fails to turn-off wh en set point is exceeded. This would lead to temperatures above the thermophilic range in th e reactor causing irrevers ible inactivation of microorganisms. Controllers C1 and C2 were encased in a wiring panel (Figure 2-5) for protection of any outside inte rferences or liquid spills.. 2.3.3 Datalogger Support Software LoggerNet 3.2-series software was used in conjunction with the CR10X datalogger and control module. It supports programming, comm unication, and data retrieval between Campbell Scientific dataloggers an d a PC. It is considered the standard software package recommended

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27 for those who have single or network dataloggers that do not require the more advanced features offered by competitors (e.g. Labview). Some software features include the ability to: Create custom datalogger programs using Edlog compiler Display or graphs real-time or historic data Build custom display screens to vi ew data or control flags/ports Collect data on demand or schedule Retrieve data using various telecommunications options Processe data in LoggerNets Split program Export data to third party analysis package In this project, LoggerNet served well in handling programs needed to monitor, log and control biogasification experiments. Edlog is the program ming tool for Campbell Scientific mixed-array and table-data dataloggers. It was used to create new programs, edit existing programs, or convert existing code into a file th at could be edited. It provided the necessary tools to write execution files that enabled meas urements of temperature, pH, biogas production as well as frequency of sampling and final data storage allocation. Case-specific programs for biogasification ex periments were written and compiled in Edlog; the execution and sampling interval for ad equate resolution was c hosen as one minute. Programs were then uploaded from the PCs CS I/O 9-pin port via a cable to the CR10X datalogger, and initiated to run. Within 24-36 ho urs, data would be manually downloaded from each controller and parametrically sorted into arra y tables. Microsoft Xcel was used as an offline, third-party data base for analysis of parameters and system operation. 2.3.4 Sensor for Biogas Production Many conventional technologies exist when ga s flow measurement is a parameter of interest. Diaphragm, rotary and turbine gas meters are common in many industrial and commercial applications, but are limited for high and steady flow conditions. Raw biogas produced from anaerobic digestion of organic ma tter can cause erroneous flow readings on

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28 conventional devices due to moisture and othe r impurities in the bioga s and flow that is intermittent and delivered in packets. For such a purpose, a special U-tube gas meter was used to efficiently measure the gas flow by liquid displacement (Figure 2-6). 2.3.4.1 Biogas meter operation A liquid displacement flow meter (U-tube desi gn) was used to measure gas flow through a process line. This design circumvents the de ficiencies of the conventional meters by having error free operation even if gas flow is interm ittent, high in moisture and contains impurities. The active components of the circuit include a 3-way solenoid valve, a float switch, an electromechanical counter, a time delay rela y and a U-tube monometer component. A low volatility fluid antifreeze brand was filled inside the u-tube and the entire apparatus was sealed properly. The biogas from the reactor accumulated in one limb of the U-tube and displaced the liquid inside; when the liquid in the s econd leg rose to a certain level, the float switch tripped, causing three events to occur simultaneou sly: a signal was sent to the c ounter to record the reading for display; the biogas from the first leg was vented into the atmosphere, causing a reset of both liquid levels in both legs; and a timer kept th e vent line open long enough to equilibrate the levels. During the vent cycle, the reactors biog as was isolated from the gas meter. With each switch closure, the counter continued to increm ent the amount of gas flowing through the meter; cumulative counts per given period woul d yield a volumetric gas flow rate. 2.3.4.2 Calibration of biogas meter Biogas flow was measured by determining the relationship between the counter increment and the volume of incoming gas required to trigge r one counter increment. To simulate biogas, which primarily consists of two gas-phase components (methane and carbon dioxide), a specialty, high purity standard was used; 60.00% CH4 and 40.00% CO2. A glass syringe of

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29 known volume and accuracy (100 1 mL) was used to determine the amount of simulated biogas required to induce one counter increment. Calibration protocol included injecting a seri es of simulated biogas doses into a biogas meter via a sealed septum and observing at what volume switch closures occurred. Protocol was conducted in both off-line mode (stand-alone gas meter) and on-line mode (gas meter connected to reactor vessel) during low or no biogas production. The final re sult of the calibration was an input-output relationship, called a calibration factor w ith unitsmL of gas/count. The precision of calibration factors were char acterized by reporting the standard deviati on of a population of repeated measurements. Typically, a series of ten injections were deemed as adequate population for determining a gas cali bration factor. Values of 55 3.2 mL per count were obtained regularly during calibration protocols. This level of meas ured resolution (one gas click) on each gas meter was sufficient to provide in sight about biogas production trends within a period of study (100 minutes). In gas measurement applications, the rela tionship between intensive properties (e.g., temperature and pressure) and gas behavior were considered. Th e ideal gas law can be applied to real gases when pressures are lower than an atmosphere and when temperatures are not close to the liquefaction point. With near ambient pressures and a 55C operating temperature, this equation of state was adequate in characterizi ng and predicting the behavior of biogas. The strong relationship between gas temperat ure and volume received attention during calibration of biogas meters. During experime ntation, Biogas was produced at 55 C in each vessel and measured externally at a lower temperatur e. As a result, a cooling affect translated to a variable delivery of volume of gas than what actually was produced in each vessel. To take account of measurement errors due to gas c ooling, a conservative co rrection factor was

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30 implemented in all measurements: normalizing measured gas to standard temperature and pressure (STP) conditions. This factor was conservative because it assumed that gas was collected at 55 C. The final calibration f actor was multiplied by a correction factor (273.15/328.15 C) to conservatively estimate ga s produced in each biogasification vessel. 2.3.4.3 Connection to data acquisition Previous biogas monitoring (SEBAC) was condu cted by off-line measurements with the U-tube gas meter. Counts were typically cumu lated for an extended inte rval of time (typically one day) and a cumulative gas production rate was calculated only the n. To better study the evolution of intermittent gas in each vessel, a real-time gas generation concept was implemented to read counts every minute of operation. This real-time measurement a pproach probed further into the dynamics of gas rele ase during biogasification and map out periods of high/low productivity at a higher resolution. The U-tube meter operated on a switch-closure mechanism that was actuated by a float switch trigger. When the trigger is activated, a change in voltage was expressed across the two terminals on the 11-pin time relay socket; this sw itch closure could be pick ed up as a pulse input ( 2.5 V) by the CR10X datalogger A dual-wire line was used to connect the datalogger with the gas meter to precisely measure the switch cl osure. Hence, each count was logged through a pulse port and stored in the final storage. The datalogger provided switch closure resolutions of 1.2 s for signals up to 400 kHz. 2.3.5 Sensor for pH The use of a real-time sensor suitable to m easure the pH of leachate during biogasification was incorporated into each system. Luniya 2005 adapted an off-line method of measuring pH to depict the progression of biogasi fication; one sample was taken each day for measurement. However, further resolution in pH profiling would enhance the in sight into the dynamics of pH

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31 change, and become useful in process control appl ications. This gave impetus to find a pH probe suitable for robust, biological applications that can interface with the CR10X datalogger. The CSIM 11 pH probe (manufactured by Innova tive Sensors, Inc.) was found to be the most appropriate for experiment al conditions in biogasification. The probe was built for field and industrial use; it contains a pre-amplifier that practically eliminates the hypersensitive characteristics of ion specific probes. Some important specifications include: A 0C to 80C temperature range A 0 to 100 psig pressure range Accuracy of 0.1% over full range Response time as 95% of reading in 10 seconds Drift less than 2 mV per week Mounting at any angle The CSIM11 pH sensor was incorporated to measure the pH of di gester and anaerobic filter effluent via an external flow-cell method; liquid leachate was pumped from the bottom of each vessel, allowed to flow through a flow ce ll containing the pH probe, and subsequently returned to the top of the reacto r. A bypass line was incorporated in the pH flow cell to assist in inspection, maintenance and calibrati on of sensors. As a result the flow cell concept (Figure 2-7) circumvented any re-circulation downtim e during routine checks on the pH probe The CSIM 11 pH probe was connected to the CR10Xs analog differential channels and was set to measure and store pH every minute during experiments. Temperature compensation of pH measurements was programmed into Edlog code; the pH value was adjusted in real time by using the measured vessel temperature. A ppendix A includes the program code that was written to program the pH sensor. Calibration was carried out on pH sensors on a regular basis to ensure accurate measurements. The frequency of calibration de pended on the level of accuracy required and the coating/fouling nature of the samples measure d. A trial operation that was conducted revealed

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32 the need to check electrodes that were con tinuously monitoring leachate checked about once a week. The inspection process included: cleaning th e electrode to remove any bacterial films or hard coatings; visually inspecting the reference junction inside the prob e; confirming that the bulb was filled with reference so lution; and a ca libration check. Calibration check of the pH sensor was conducted by measuring pH of three buffer solutionspH of 4, 7 and 10. The datalogger was programmed to read pH in each buffer solution and their temperatures. The Nernst temperatur e compensation was calculated for the probe and an appropriate value of multiplier was used in the datalogger measurement to correct for temperature (Figure 2-8). Each buffe r solution was measured within pH 0.2. If a drift was observed, then the value of multiplier was ad justed accordingly. Once the protocol was completed, the pH probe was screwed back into the flow cell to begin monitoring leachate; necessary changes were made to compensate for possible offsets in the program compiler. 2.3.6 Sensor Temperature Temperature monitoring and control was c onducted by T-type thermocouples. The CR10X had the capabilities of connecting either six thermocouples (differentia l channels) or twelve (single-ended channels). Each thermocoupl e contained two dissimilar metals (copper and constantan) that produced a volta ge drop when subjected to diffe rent thermal contact. Edlogs control toolbox provided a template for readi ng T-type thermocouple voltage output and converting into a temperature. Thermocouple designs used included extension thermocouple wire and a 1/8 inch junction probe thermocouple manufactured by Omega Scientific, Inc. Thermocouples were tested for accuracy a nd precision of measurement. The CR10X internally contains a thermocoupl e reference that was suitable to use as a standard. To make a thermocouple measurement, the controller referen ce temperature was converted to equivalent TC

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33 voltage relative to 0 C, and then added to the measured TC voltage; the sum is the reported output temperature, with a polynomial linearization error of < 0.2 C from 0C to + 60 C. 2.4 Temperature Control 2.4.1 Heating Hardware Sustaining thermophilic conditions (55C) in each vessel was addressed after design and fabrication. Heat delivery options that were considered includ ed both internal and external devices; a heating element with in the reactor or a leachat e re-circulation method which exchanges heat with a warm water bath. The in ternal heating element option was eliminated on the basis that a completely filled solids bed would impede convection of heat. Also, the possibilities of fouling a nd scaling heating elements (as seen in SEBAC-2 heating vessels, UF Energy Park Site) during prolonged operation were anticipated. The external heating option proved viable for delivery of a thermophili c leachate, but introduced undesired high recirculation rates (~ 1.5 L/min) to su stain in-vessel thermophilic conditions. Thermolyne heating tapes (SIL HTQ TP series type, manufactured by Barnstead International) provided trouble-free heating op eration for vessels to sustain thermophilic conditions. They are constructed of high quality resistance wire and braided insulation and are designed to provide the user with long life and high performance. Measuring 1 inch wide and 6 feet in length, each vessel was wrapped with two heating tapes in parallel along its exterior glass wall; tape was used to adequately secure each band firmly on the glass (Figure 2-9). To minimize radial heat losses, flexible-fiber insu lation was applied over the heating tape. Each vessel was subsequently wrapped with aluminum heating duct to firmly hold the insulation in place. A view window was left un-insulated to serve as a level indicator for filling and dispensing during vessel loading and unloading.

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34 Each heating band had the capability of de livering 418 Watts of pow er with a 120 V AC requirement; regulation of heat delivery from each band was addressed by conventional control accessories. Solid state relays (SSR) are norma lly open switching devices with no moving parts, capable of millions of cycles of operation. The SSRL series of solid state relays (manufactured by Omega Engineering, Inc) were used to c ontrol the large resist ance heating bands in conjunction with the CR10 X dattalogger and cont roller. Each SSR was equipped with Vdc input/Vac output terminals, which sufficiently li nked with the CR10Xs pulse terminals. When called upon by a program, the normally open SSR woul d be triggered by a 5 Vdc control signal from the CR10X; subsequently the SSR would cl ose and complete the circuit, providing 120 Vac to each heating band. An LED status input indica tor provided visual confirmation of the state each relay was in. Circuit connections between the datalogger, SSR and heating band (Figure 210) provided a simple electrical solution to heating la b-scale vessels with adequate control. To dissipate heat, each SSR was mounted on an aluminum plate, which conducted heat away, circumventing any overloads or failures of the device. All SSRs were monitored using a multimeter on a regular basis to assure that they were functioning normally. A checkpoint inspection of critical locations within the circ uit enabled positive iden tification of faulty performance (e.g, controller failure to excite 5 Vdc or SSR failures to actuate VAC terminals). 2.4.2 Temperature Control Sustaining thermophilic conditions in each vessel with the aforementioned heating hardware was addressed by a temperature profiling of the system. The simplest form of control (on/off control) was deemed suffi cient for robust batch studies. On-off control is usually used where precise control is not necessary, or wher e the mass of the system is so large that temperatures change very slowly. Some of the observations taken into consideration, while deciding on a control strategy included:

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35 Temperature and spatial variations (if any) within each vessel Acceptable high/low set points for on/off control Single, dual-direction an d no liquid re-circulation on temperature control Warm-up time Temperature profiling was conducted initially by placing six thermocouples (type-T) at multiple radial and axial positions in conjunction with a liquid re-circulation mode for mild mixing; Rachig rings were packed into the bed area to simulate biomass solids and 12-L of water was poured into the reactor to flood the bed (Figure 2-11). An on-off controller will switc h the output (on or off) only wh en the temperature crosses a set point. Since the temperature crosses the set point to change the out put state, the process temperature will be cycling continually, going from below setpoint to above, and back below. As a result, the turn-on and turn-off temperatur es were deliberately made to differ by small amounts to prevent noise from switching the hea ting band rapidly and un necessarily when the temperature was near the set point. The appropr iate Edlog program was coded (Appendix A) for on/off control of the heating bands around a ve ssel; open loop control tuning was done to determine the optimum on/off set-points within system constraints (packed bed media and constant re-circulation rate). A total of nine profile studies (Figures 2-12 to 2-17) were conducted for development of an ad equate heating control strategy. 2.4.3 System Temperature Profiling The temperature profile studies conducted se rved as indicators of system performance under experimental conditions; the studies revealed the following: The first profile study (Figure 2-12) was conduc ted to characterize a ny spatial temperature variations in the vessel. Th e six thermocouples indicated that it took approximately 230 minutes to elevate the vessel temperature from 25C to ~ 55C. Moreover, the difference in temperature after a steady-state on/o ff control between each thermocouple was 2 C. Such small temperature gradients were deemed tolerable spatially; subsequently, a thermocouple position in the center of the bed was assigned for temperature control.

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36 The second profile study (Figure 2-13) was ai med at determining the on/off set points for heating. At a one-minute interval resoluti on on data acquisition and a constant recirculation rate (~ 0.42 L/min), the on/off set-range boundaries were toggled at four different settings. The aim of each study was to converge and confine the bed temperature to or near 55C. The outcomes demonstrated an inherent lag a ssociated with on/off control. As a result, the minimum amplitude for the saw-tooth profiles under a spatiallycentered thermocouple position was approximately 1.5C. The third profile study (Figures 2-14 and 215) aimed to characterize the dependency of liquid re-circulation on temperature control. With no re-circulation, the saw-tooth temperature profiles were confined within 54-55.5C shifted to 54.5-56C, resulting in a less desired control profile. Spatially, a gradient of approxi mately 20C (after 800 minutes) existed from the center of the bed to the re-circulation ports at the bottom of the reactor. The last profile study (Figures 2-16 and 217) was conducted to validate whether a toggling re-circulation schedul e for mixing would sustain or improve the temperature control observed in Figure 2-13(D). The incen tives for toggle-mixing were justified during high solids mesophilic digestion of simulate d solid waste (Luniya, 2005). In that work, compaction of solid waste bed in a reactor during biogasification was alleviated and dislodged by a toggle re-circula tion mode. Five minute cycles were exercised in each direction of re-circulation. Within a 100-minute steady-stea dy state thermophilic control trial, the toggle-mixing scheme increased the amplitude of the saw-tooth profile to 2C and introduced sharp changes in temperature/time. From all the temperature characterization studies conducted, profile study Fi gure 2-13 (D) was the most appealing for on/off control. 2.4.4 Temperature Fail-Safe Protocol Other matters pertaining to temperature contro l in each biogasification vessel were also considered. Typically, automated control systems that rely on a power source employ a fail-safe mechanism for managing sudden changes to control or operation. In the case of this work both C1 and C2 depended on a constant power suppl y provided by two 12-V batteries. Each unit would function optimally when the input source voltage ranged from 11.5 to 12.5 VDC. However, if the voltage power supply fell be low 11.5 V, each controller would go into an indeterminate state; the data logging capabilitie s would become limited and the actuation ports (which controlled heating) would be locked into either an on or o ff state. Implications of such failure included: Temperature control failure in off mode, resu lting in decreased temperature and kinetics.

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37 Temperature control failure in on mode, resu lting in exceeding the tolerable temperature limits of the microbial culture (cell death). Failure to log other system parameters, resulti ng in loss of viable data for biogasification In addition to daily voltage inspections on both batteries, a fail-safe program was also devised to address the potentia l consequences of an indeterminate datalogger. Several commands were coded (Appendix A) to systematic ally check the voltage of each battery and appropriately respond. The primar y concern in this work (or fo r that matter in any anaerobic reactor) was preservation of the microbial culture. As discussed temperature control failure in the on mode would result in the destructi on of the inoculum, when subjected to high temperature for a prolonged period of time. T hus, a fail-safe command was coded that read the voltage of a battery and systematically command ed actuator ports; if vol tage fell below 11.8 V, the program would automatically turn off actuator ports for hea ting. Justification in kinetic losses outweighed the potential ri sk of loosing batches of inoc ulum by subjecting to thermal shocks. 2.5 Pressure Testing 2.5.1 Positive Pressure Testing The performance of biogasifica tion experiments was initially evaluated by the quantity of biogas produced per given time. Biomass is mineralized to a methane and carbon dioxide gasmixture from available substrate (solid feedstock and soluble cons tituents) and released from the bed by buoyancy; subsequently, measurements of gas mixture volumes and composition provide explicit insight to biogas produc tion rate and imp licit insight to bioc hemical progression, respectively. With performan ce measure being so highly depe ndent on gas collection, efforts were taken to correctly seal and minimize gas leaks.

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38 Each vessel was fabricated to accommodate approximately 2 psi according to ARS engineers; the allowable pressure accumulation (before exhaust) in each vessel when connected to the U-tube displacement meter was approximately 0.25 psi. A protocol was devised that would systematically check if the system leaked. Possible leak areas cons idered were as follows: Brass fittings for re-circulation, th ermocouple, and gas outlet (Atop lid) U-tube meter Biogas tubing (vessel-to-meter line) Top-lid gasket The leak test consisted of pressurizing th e vessel and gas meter system to comparable values seen during biogasificati on experiments. Each system wa s injected with air through the biogas sampling septum and the liquid-level in the biogas meter was monitored. Enough air was injected to enable the displaced liquid column to just fall short of tripping the float switch. The level of the fluid in the in-goi ng column was marked to detect changes over time; liquid soap was applied at the aforementioned l eak areas to detect any leaks. The level of the gas meter was examined after 24 hrs to quantify any pressure loss; typical liquid-leve l changes observed over that period were approximately 1-inch of water (0.04 psi). W ith expected biogas production of 500 mL per day, 0.04 psi loss translated to about 25 mL/day of biogas ( 4.8% of average daily biogas production). 2.6 Liquid Storage Vessels 2.6.1 Inoculum Storage Tank A storage tank (Figure 2-18) was fabricated for storage of accumulated or excess inoculum produced during biogasification experiments. A simple vessel in design, the storage tank makeup comprised of a cylindrical PVC body, 18 inches in diameter and was placed horizontally. Two PVC caps were glued to each end of the body, completely enclosing the 100-L vessel. Five bulk-head fittings were placed on one face of the vessel and valves were fitted appropriately;

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39 four ports on the top for liquid inlets/gas outlets and one at the bottom as a liquid outlet port. With the nature of contents being thermophilic anaerobic inoculum, each vessel was kept anaerobic. A 40-L collapsible gas bag was fitted on one valve to monitor any gas production and supply oxygen free gas in cases of vacuum. 2.6.2 High COD Liquid Storage A storage vessel (Figure 2-19) for wastewater generated from pre-treatment of sugar beet tailings was also constructed. To avoid fermenta tion of wash water, a re frigeration unit was put in place. A collapsible, 20-L st orage bag was suspended inside th e refrigeration unit, with inlet and outlet ports at the bottom. This collapsible bag concept provided the means of storing highly degradable liquid feedstocks in oxygen-free and cold environments (4 C). Liquid was delivered to the storage bag via a -inch tube drilled through the refrige rator insulation, which connected to outlet ports on biogasification units. In e xperiments where liquid st ream was biogasified, a Cole Parmer peristaltic pump was used to pump out contents and deliver th em to the appropriate vessel. 2.7 Biogasification System Setup An operational schematic of th e setup of solids (Figure 2-20 ) and liquids (Figure 2-21) biogasification reactors used in this research aided the constr uction phase of the project. Schematics highlighted the dimensions of each unit, the reactor sectional volumes and positions of sampling and outlet ports. The re-circulation system in both cases was driven by Masterflex peristaltic pump using Master felx Tygon (15) tubing, which ha s very low oxygen diffusivity. For sequencing-experiments (Chapter 6), an L/S Masterflex programmable pump was used to exchange leachate between the solids and liqui d reactor. The complete biogasification experiment station (Figure 2-22) was optimally positioned on a lab bench to facilitate easy loading/un-loading of solids, daily sampling and safety considerations.

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40 2.8 Feedstock Preparation Sugar beet tailings were collected by AC SC during the 2005-2006 processing campaign at East Grand Forks Plant, Minnesota A total of 525 kg of sugar b eet tailings were stored in 35 pails and kept in a freezer unit by ACSC. Upon re quest, feedstock was shippe d in five liter pails (frozen) to the University of Florida. Pails of tailings received were mixed together thoroughly to yield a homogenous feedstock sample. Tailings were then packaged in 1.5, 3 or 5-kg aliquots and stored at 0C in a freezer. 2.9 Protocol for Solids Reactor Loading 2.9.1 Pre-Loading Protocol Prior to loading a reactor with sugar beet tailings, the empty reactor was thoroughly cleaned. Additionally, the peristaltic pump tubi ng was replaced, the pH probe was tested for accuracy and all the re-circulati on lines were checked for any damage and valves were rinsed free of any particulates or debris. A spot calibration was conducted on the biogas meter to confirm that volumetric counts of gas did not ch ange. Thereafter, a pr essure test was also conducted on each reactor before start-up to al so assure proper sealing. With satisfactory compliance to pre-loading protocol, each reactor wa s ready for loading of sugar beet tailings. 2.9.2 Un-Bulked Experiments Loading The allowable quantity of sugar beet tailings that could be loaded in each reactor permitting a 1.8-L headspace was shown to be appr oximately 6 kg wet weight. Pre-packaged aliquots of tailings were poured into each reactor with no external compaction applied, to form a bed of tailings. The top-lid su spended perforated plate was adju sted adequately to intimately make contact with the top of the filled waste bed and the occupied volume was recorded. The packing density of un-bulked experiments ranged from 450 to 650 kg/m3 (wet basis).

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41 2.9.3 Bulked Experiments Loading Bulked experiments (Chapter 5) were c onducted by spatially arranging a bulking agent inside the sugar beet tailings waste bed. Between 1-2 kg of Pumice stones (landscaping rocks, 25 mm in average size obtained from Lowes, Ga inesville) were strate gically placed in monolayers during the feedstock loading procedure (F igure 2-23). The aliquot of tailings was divided into 4 sub-samples to assure homogeneous la yers between each bulking agent layer. The top-lid suspended perforated plate was adju sted adequately to intimately make contact with the top-most layer of bulking agent. Th e packing density of bulked experiments ranged from 250 to 450 kg/m3. 2.9.4 Reactor Start-Up The reactor was sealed once the loading pro cess was completed. A thin layer of Dow Corning high vacuum grease (976-V) was applied on the glass-flange lip and adjoining gasket. The top lid was brought into position and was fastened in a cross-direction fashion. A thermocouple probe was inserted from the top of the lid into the bed of biomass. Connections between the reactor and gas meter and liquid re -circulation lines were made by Tygon 3/8-inch and hard plastic tubing, respectiv ely. Digester liquor (from prev ious batch run) was pumped inside to the level of the top pe rforated plate. The volume of this typically ranged from 8.5 to 12-L, depending on the packing density of an ex periment. A viewing glass was used to guide fill-up progress. Sodium bicarbonate was added at 5 g/L to sufficient buffer the system during biogasification. The entire system wa s pressure tested once more using CH4/CO2 gas mixture (60:40 in volume ratio) and the pressure level wa s monitored over a period of a few hours. The temperature control was then turned on and the reactor was gradually heated until the set range (54.5 to 55C); this process took approximately 230 minutes. Once the temperature of the reactor had reached the desired te mperature range, the experiment was then recorded as being at

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42 day zero and the initial gas meter counter noted; datalogging was subsequently initiated by the CR10-X. 2.9.5 Reactor Un-Loading Upon completion of biogasification, reactor s were unplugged from heating and biogas monitoring. Liquid was drained fr om the bottom, while solids were removed manually from the top. The residue collected was dewatered by gr avity and was ready for analysis (see Solids Analysis section). A sample of liquid was test ed for analytical parameters and the rest was stored in the inoculum storage vessel. 2.10 Protocol for AFR 2.10.1 Reactor Start-Up The AFR was constructed for the purpose of treating liquid organic streams, namely CODrich wastewater produced in the so lubilization experiments of sugar beet tailings (Chapter 4). A pre-loading protocol was administ ered in the loading of the liqui ds digester, analogous to solids loading. Approximately 10 kg of pumice stones (s imilar to the ones used for bulking the solids in the solids digester) filled the entire available volume above the perforated plate (approximately 16 L). The pumice stones served as a support for growth media to encourage the growth of biofilms. Approximately 1 kg of sugar beet tailings was also added as part of this packed bed, serving as a way to start up the digester. With no t op-perforated plat e, the reactor was greased and sealed. Start-up was initiate d by gradual heating until the thermophilic set range was attained similar to solids reactor s. Datalogging was subsequently initiated. 2.10.2 Feeding Experiments conducted with liquid streams we re conducted in both batch and fed-batch feeding options. In batch feeding mode, wastew ater aliquots subjected to treatment were pumped into the system by the AFR e-circulation pump. Firstly, the specified feed volume was

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43 drained from the reactor into the inoculum storage vessel (Fi gure 2-18); next, the AFR recirculation pump was disconnected from its mi xing duties and used for pumping fresh feed. During the procedure, the reactor was vented to atmosphere to avoid any biogas meter failures as a result of not maintaining reactor volume. Fi nally, the reactor was sealed and injected with CH4/CO2 mixture to purge any air out of the system. In semi-batch feeding mode, an L/S brushles s programmable Masterflex pump was used to make scheduled deliveries of fee d. A dual-peristaltic head was used to adequately add feed at the top of the reactor while rem oving effluent liquid at the bottom of the vessel; influent wash water was pumped from the cold liquid storage bag whereas the effluent was pumped into the inoculum storage vessel. With the proximity of 2 feet between liquid storage and reactor, a minimum dose rate (100 ml/min) and dose durati on (1 minute) was established for delivery of fresh feed to the system. The mechanism of simultaneous feeding and removal permitted the volume of reactor to remain constant. 2.11 Protocol for Sequencing Experiments A total of 15 experiments were carried out in this research study. Ou t of these 15 studies, 4 of them involved the exchange of leachate between the ABCR and AFR. The exchange of leachate between the two reactors is termed as a sequencing pr ocess. Sequencing was provided by using the L/S Masterflex programmable pump set a specific delivery schedule; adjustments were made to sequencing throughou t the during of studies. Detail s of the sequencing protocol are further discussed in Chapter 6. 2.12 Inoculum Development Microbial populations necessary for biogasi fication were cultured during a 12-month, ongoing acclimatization process. In addition, this extended stu dy time served as a shake-down phase in understanding system responses, tende ncies and limitations. It was found that the

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44 appropriate microbial populations required for biogasification were naturally present within the tailings; no external so urce of inoculum was needed to initiate methanogenesis. A simple incubator method was used to cultivate the present microorganisms by supplying them with appropriate conditions for growth. Sugar beet tailings were init ially placed in two, 5-L glass bottles and flooded with water containing sodium bicarbonate. The bottles were placed in an incubator controlled at 55 1C. Biogasification parameters were monitored on a daily basis. The process was scaled to the 20-L solids reacto rs (ABCR 1 & 2) after th ree generations of 5-L incubator trials. A total of 15 acclimatization tr ials (Figure 2-24) were conducted, resulting in 24 L of a 10th generation microbial population suitable fo r conducting well-controlled experiments in biogasification. All subsequent experiments were started by using the 24-L inoculum derived from Experiments 15 and 16. 2.13 Design of Experiments An experimental design was dr afted to effectively carry ou t bench-scale biogasification studies with scopes of ascertaini ng how quickly sugar beet tailings biodegrade and mineralize to methane and developing methods to accelerate th e biodegradation rate. During the inoculumbuilding process, observations made on biogasi fication and solubilization characteristics, behavior of the bed of tailings during degrad ation and other phenomen a, gave direction in choosing the appropriate e xperiments. A total of four studies were chosen as areas of research interest addressed in th e design of experiments: Study I : Single-stage, high solids biogasification of sugar beet tailings Study II : Pre-treatment effects (solubilization) to enhance single-stage biogasification of sugar beet tailings Study III : The effect of bulking on the biogasi fication of sugar beet tailings Study IV : The effect of two-stage operation on th e biogasification of sugar beet tailings

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45 The design of experiments (Figure 2-25) carried out on sugar beet ta ilings was a systematic tool used to develop a strategy for enhanced biogasification by elimination of unnecessary experiments. 2.14 Analytical Methods 2.14.1 Gas Analysis Gas samples were taken daily from each reacto r using a 20-mL gas tight syringe fitted with an air-tight tee valve. The gas samples were anal yzed with a Model 1200 Fi sher Gas Partitioner. The GC was fitted with two 6-feet Haysep 80/100 mesh columns containing Porapak Q support. Ultra high purity Helium (99.99%) was used as the ca rrier gas at an operating head pressure of 15 psi. The gas was analyzed for its methane, carbon dioxide, nitrogen and oxygen content. The GC was calibrated with an ex ternal standard containing N2:CH4:CO2 in volume ratio of 25:45:30. Gas chromatographs were processed and record ed using a SP 4290 Spectra Physics Integrator. 2.14.2 Liquid Analysis 2.14.2.1 pH The analysis of pH was conducted using the Campbell Scientific on-line pH probes discussed earlier (S ee section 2.3.5). 2.14.2.2 Soluble chemical oxygen demand The soluble chemical oxygen demand (SCOD) analysis was carried out using HACHs United States Environmental Protection Agen cy (USEPA)-approved dichromate method. The method utilized small micro vials that contained the necessary reagents (silver, chromium and mercury) to carry out the analysis. Leachate sa mples were withdrawn from each reactor daily; each sample was centrifuged (Fisher Marathon mi cro H centrifuge), filtered (Whatman micro filter paper, 45 m) and stored for COD analysis. Precautions were taken to minimize the vaporization of VFAs, which accounted for a frac tion of the total SCOD to be measured. Vials

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46 (HACH COD of range: 2 to 1500 mg/L) were filled with leachate sample (diluted if estimated detection limit was approached) and digested for 2 hours at 150C in a COD reactor (HACH, Model 45600). The SCOD of the digested samp les were estimated by measuring their color using a colorimeter (HACH, DR /890) against a blank. Averag e error of colorimetric COD analysis was quantified as 4 % for samples that range 0 to 20,000 mg/L. 2.14.2.3 Volatile fatty acids The volatile fatty acids (VFAs) were anal yzed on Shimadzu GC9AM with a Flame Ionisation Detector (FID) gas chromatograph. The GC-FID was equipped a 1.7 m long by 3 mm inner diameter glass column packed with 100/ 120 chromosorb WAW coated with 1% phosphoric acid. High purity nitrogen (99.9%) was used as the carrier gas at a flow rate of 20 ml/min. Hydrogen and air were used as the combus tion gases, flowing at 0.6 and 1.0 ml/min, respectively. Temperatures of injector, column and detector were 180 C, 145C and 200C respectively. Four standard solutions were prepared w ith a fixed concentration (50, 100, 200 and 500 mg/L) of all six VFAs (acetic ac id, propionic acid, butyric acid, iso-butytic acid, valeric acid, and iso-valeric acid) to be analyz ed. All the standards were stor ed in air-tight glass jars under refrigeration to prevent VFA breakdown. For the range of interest (50 500 mg/L), VFA peak response was shown to be linear; subsequentl y, calibration was conducted only at 100 mg/L. Analysis of the standard solution yielded acetic acid at 108 mg/L 12%; propionic acid at 104 mg/L 9%; butyric acid at 99 mg/L 8%; iso-butyric acid at 96 mg/L 8%; valeric acid at 93 mg/L 9%; and iso-valeric at 96 mg/L 9%. The GC-FID was calibrated with standard solution prior to analysis of liquid samples. Liquid samples were withdrawn daily from each reactor; each sa mple was centrifuged (Fisher Marathon micro H centrifuge), filte red (Whatman micro filter paper, 45 m) and stored

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47 (4C). Sample preparation for analysis of VFA consisted of mixing a 1-mL solution of centrifuged and filtered sample a nd 20% (by volume) of phosphoric acid for acidification. The solution mixture of 2 L volume was then injected into th e GC-FID (after calibration). 2.14.3 Solids Analysis 2.14.3.1 Moisture content Aliquots of fresh sugarbeet tail ings ( 0.5 to 1 kg) and digested residue (0.3 to 1.5 kg) were set aside for solids analysis. The moisture cont ent of each aliquot was determined by placing the sample in a constant temperature oven at 105 1C for a period of 24 hours. Subsequently, each sample was allowed to cool down to room temperat ure and weighed with an analytical balance. The percent total solids and moistu re was calculated by mass difference. 2.14.3.2 Volatile solids After a sample was dried for moisture conten t and total solids, the volatile solids content was determined. Each sample was placed in an ev aporation tray (aluminum) or crucible and then placed inside a furnace at 550 5C for two hours. After heat treatment, each sample was removed and allowed to cool down at room temper ature in a desiccator, before being weighed. The volatile solids content was calculated by mass difference. 2.14.3.3 Solids composition calculation Calculations for % solids, % volatiles and % fixed solids we re carried out according to standard methods (APHA, 1992) Solids chemical characteristics The chemical composition of raw sugarbeet tai lings and digested residues were tested. Sample aliquots (50 g) were stor ed in air-tight bags and packed in an insulated envelope for shipment to a forage testing laboratory (Dairy One, Inc., Ithaca, New York). The components tested on the wet and dry matter basis are listed in Table 2-1. Upon receiving forage labs results,

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48 calculations were performed to determine th e % solubilization and degradation of the aforementioned components as a result of biogasi fication. The pertinent definitions regarding components tested were given by Dairy One fact sheet. The definitions for carbohydrates are as follows: Neutral detergent fiber (NDF): is a measure of hemi cellulose, cellulose and lignin representing the fibrous bulk of the forage Acid detergent fiber (ADF): is a measure of cellulose and lignin 2.15 Performance Analysis The performance of the biogasificati on reactors was evaluated by fitting the cumulative methane production data to the modified Gomper tz equation (Lay et al., 1998). The Gompertz equation describes cumulative me thane production from batch digesters assuming that methane production is a function of bacter ial growth. The modified Gomper tz equation is presented as 1 exp exp t P e R P Mm (1-1) where M is the cumulative methane production, L (kg VS)-1 at any time t, P is the methane yield potential, L (kg VS)-1, Rm is the maximum methane production rate, L (kg VS)-1 d-1, is the duration of lag phase in days (d), and t is th e time (in days) at which cumulative methane production M is calculated. The parameters P, and Rm were estimated data sets by using the Solve r feature in MSExcel. The value of parameters which minimized th e sum of the square of errors between fit and experimental data were determined.

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49 Figure 2-1. Construction of biogasification vessels from 5-gallon carboy bottle

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50 Figure 2-2. Lid components and seali ng mechanism for biogasification vessels

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51 Figure 2-3. Lid specifica tions and components for biogasification vessels

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52 Figure 2-4. Custom-build tripod stand for biogasification vessels

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53 Figure 2-5. Controller panel C1 and C2

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54 Figure 2-6. Biogas U-tube meter Figure 2-7. pH flow cell syst em for biogasification system

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55 Figure 2-8. Temperature compensa tion calibration of pH sensor

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56 Figure 2-9. Heating tape attachment to vessel wall Figure 2-10. Circuit diagram for heating band

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57 Figure 2-11. Schematic for vessel temperature profiling

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58 Figure 2-12. Spatial temperature profiles in biogasification vessel

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59 Figure 2-13. On/off controller t uning of heating to biogasificati on vessel. A) Set-range from 53 to 57 C. B) Set-range from 55 to 56 C. C) Set-range from 55 to 55.5 C and D) Set range from 54.5 to 55 C

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60 Figure 2-14. Liquid re-circulati on effect on temperature control Figure 2-15. Temperature profil e within biogasification vessel during on/off re-circulation mode

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61 Figure 2-16. Temperature profil e within biogasification vessel during up-flow and down-flow re-circulation Figure 2-17. Comparison of re-circulation modes on biogasification vessel temperature

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62 Figure 2-18. Inoculum storage vessel Figure 2-19. Wash water cold storage bag

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63 Figure 2-20. Solids biogasification reactor schematic (ABCR)

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64 Figure 2-21. Liquids biogasif ication reactor (AFR) schematic

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65 Figure 2-22. Complete biogasi fication experiment station

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66 Figure 2-23. Bulking agent layers in sugar beet tailings waste bed

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67 Figure 2-24. Inoculum acclimatization experiments

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68 Figure 2-25. Design of experiments for sugar beet tailings biogasification

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69 Table 2-1. Constituents tested by Dairy One on solids fraction of sugar beet tailings Component Measured (% DM) Moisture Crude protein Adjusted crude protein Soluble protein Acid detergent fiber (ADF) Neutral detergent fiber (NDF) Non-fibrous carbohydrates (NFC) Lignin Potassium Sodium Sulfur Calcium Phosphorus Magnesium Iron Zinc Copper Manganese Molybdenum

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70 CHAPTER 3 STUDY I RESULTS: SINGLE-STAGE BIOGASIFICATION 3.1 Introduction The first study of the research work involved batch, single-stage thermophilic biogasification of raw sugar beet tailings usi ng a flooded unmixed digester. The aim of this study was to characterize the aneo robic biodegradation potential of sugar beet tailings and its methane potential (measured as methane yield) us ing different organic lo adings. This first iteration of experiments was chosen for its simpli stic design and operation ; sugar beet tailings were loaded as received from ACSC, flooded with the active thermophilic inoculum and digested in batch mode. The progression of an experime nt was measured by the evolution of methane with time. After the tailings were degraded the reactor was opened and the residue removed. There was no agitation of solids during digestion except for re-circulation of the liquid. 3.2 Background Successful application of anaer obic technology to the treatment of solids is dependent on development of a reactor that can achieve high rates. The evaluation of reactor designs for anaerobic digestion generally depends on biolog ical, technical and economical aspects. Two main parameters considered in making decisi ons impingent on design in cludes the number of stages and the concentration of so lids in the reactor. About 90% of the full scale plants currently in Europe treating organic fr action of municipal solid waste (OFMSW) rely on a one-stage system (Lissens et al., 2001). Primary modes of operation for one-stage systems are batch, semicontinuous and continuous. Batch systems have up to now not been succe ssful in taking up a considerable market share. However, specific features such as a simple design and process control, robustness and lower investments make them attractive for de veloping countries (Boualla gui et al., 2005). For

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71 example in Asia, most of the biogasification plan ts digesting agricultural and animal wastes are simple, single stage bioreactors without any auxiliary mixing (Ong et. al, 2000). Anaerobic batch digestion has proven to be useful because they can be performed simply, with inexpensive equipment. In addition, batch systems are partic ularly useful in assessing the rate at which a material can be digested (Parawira, et al., 2004) Anaerobic digestion systems exhibiting < 20 % TS are usually referred to as wet systems whereas 20 to 40 % TS systems are considered as dry. Conventional wet systems are performed in a single-stage reactor, where homogen eity is obtained by co ntinuous stirring of a 3 to 8 % TS slurry (Svensson et. al 2006, Hart mann and Ahring, 2006). Slurries rely on high consumption of process water necessary to dilu te waste streams, are usually carried out in CSTR-type systems. They are pa rticularly seen advantageous because of their readily easy pumping of solids throughout a sy stem. In dry anaerobic designs, high-solids concentrations are attained with minimal external water necessity; wastes move in a plug flow inside a reactor (Lissens et al., 2001). The advant age of high-solids dry fermentati on is that organic loading rates of 10 kg VS m-3 d-1 and higher can be applied. Howeve r, the full contact of biomass and substrate is not guaranteed; in dividual processes can be obser ved spatially, which limits an optimal co-operation of the microbial groups i nvolved in anaerobic digestion (Hartmann and Ahring, 2006). Regardless of solids concentration in digesti on systems, reaction rate is also greatly influenced by temperature. All digestion plants were initially operated at mesophilic temperatures (27 to 38C). However, as of 1992-1993, thermophilic (50 to 58C) operation has been established as an acceptable mode of fe rmentation. Using thermophilic temperatures in

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72 preference to mesophilic have been shown to have higher degradat ion rates and better sanitation effect (Nielse et al., 200 3 and L. De Baere, 2000) A lack of literature on the disposal of sugar be et tailings indicated that not much attention had been devoted towards anaerobic digestion of this organic waste. The unique physical properties of tailings includes having high-solids bulking capabiliti es but low TS content (13 to 17 %). This unique composition makes a mixed slu rry reactor difficult to operate mechanically. Likewise, a dry digestion system would not be efficient with a hi gh-moisture feedstock such as tailings. A flooded, batch, process seemed the most prom ising for characterizi ng biogasification of sugar beet tailings. Conventiona lly, a high-solids process is a one -stage process that does not require feedstock pre-treatment, mixing, agitation or movement of reactor contents. It also requires minimal water addition and does not requ ire bulky, expensive, high pressure vessels (Hedge and Pullammanappallil, 2007). A flooded operation of a leach-bed process was recently applied to the SEBAC process; it yielded im proved kinetics (Luniya et al., 2005). It was speculated that the re-circulation of liquid contents was beneficial for the bacterial distribution in the whole system. 3.3 Results Experiments: Three experiments (I.1, I.2, and I.3) were conducted consecutively to digest raw sugar beet tailings in a single-stage mode at thermophilic conditions. Organic loading was varied in each case by changing th e amount of tailings that was c onfined in the reactor -low, medium and high total occupied volumes; visually th at translated to tailin gs beds that occupied one-third, half and three-fourths of the total working reactor volume; the active volume of each reactor was maintained between 12 to 13 L. Du e to the high moisture content, the amount of tailings loaded in each experi ment (1.1, 3.0 and 5.0 kg) translated to 1.3%, 2.9 % and 5.3% of

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73 total solids in the system. Though seemingly low pe rcentage of solids, it was validated that the 5.3% solid slurry of sugar beet tailings could not be mixed wi th a stir rod. Varying the organic loading translated to identifying the boundaries of under-loaded and over-loaded reactor in light of vol umetric efficiencies. The perfo rmance of each experiment was monitored by analysis of biogasification para meters on a daily basis (methane rate, gas composition, methane yield, pH, etc). The dur ation time for biogasification was held until evidence of stagnation was dete cted (decreases in methane pr oduction, high levels of VFAs, etc.). Starting with experiment I.1, fresh inocul um (pH of 8.1) was doped with 5 g/L of sodium bicarbonate to assure proper bu ffering during biogasification. Subsequently, Experiments I.2 and I.3 were buffered similarly. The protocol fo r loading each reactor for each experiment was followed according to 2.8.2. Characteristics of feed and digested residue: The characteristics of sugar beet tailings (Table 3-2) and loading/unloading parameters (Table 3-3) for experiments conducted were determined experimentally. The total and volat ile solids loaded in each experiment were on average 15% total solids and 91 % volatile solids. Therefore, upon loading Experiments I.1 to I.3, the available solids for de gradation were 0.16, 0.42 and 0.68 kg, re spectively; the subsequent corresponding (compaction-free) dry matter bulk densities lo aded were 60, 70, and 75 kg/m3, respectively. Residue samples were collected at the end of each experiment by draining away reactor liquor from the waste bed. It was estimated that the total suspended solids in the drained liquor from the biogasification of sugar beet tailings didnt vary much, ranging from 1 to 3 g/L. After biogasification, the residue appeared as fibrous and homogene ous and visually indicated a 70 to 80% volume decrease from what was loaded (Figure 3-1). In biogasifying sugar beet tailings, the volatile soli ds reduction for Experiments I.1 and I.2 were 90 and 78 %, respectively;

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74 I.3 was treated as a recovery experiment with AFR and percent volatile solids degradation was not calculated until after post-sequenced tim e period (Chapter 6, Experiment IV.4). Physical observations: An increase in liquid height in the headspace of each experiment was observed during the first 2-3 days of bioga sification. In I.3 liqui d level overwhelmingly increased to beyond the confines of the reactor headspace; appr oximately 1 liter was captured externally, stored and added back after 3 days. In the case of both I.2 and I.3, compaction was observed on the top-most perforated plate c oncurrently during the liquid level increases. Biogasification of sugar beet tailings: The biogasification parameters measured were plotted (Figures 3-2 and 3-3) during each experi ment. To eliminate the variations due to differences in wet tailings loaded, cumulative methane production values were normalized on the basis of kg VS loaded in each experiment. Th e lag periods (Figure 3-2) at the start of biogasification for all three experiments were between 0.1 to 0.3 days, which corresponded to < 1% of digestion time for I.1-2 and ~ 1.5% of biogasification time for I.3. By 0.5 days into biogasification, the rate of methane for I.1 reached 0.3 L-1L-1d-1 whereas I.2 and I.3 mimicked each other and peaked at 1.8 L-1L-1d-1. The biogas methane compositions at that time were also 25%, 17% and 10% for I.1-3, respectively. Su ch responses indicated a quick onset of methanogenesis. However, after 2 days, stagnati on in I.3 was evident by th e lack of increase in methane composition; only a 11% methane compos ition increase was obser ved in I.3 from 2.0 < t < 6.7 days, whereas I.1 and I.2 increased by 31% and 48%, respectively. At 6.7 days, the methane production rates began decreasing steadily ; I.2 and I.3 both leveled off to 0.13 and 0.40 L-1L-1d-1, respectively; I.1, which was discontinued from digestion at 6.7 days, exhibited a 0.11 L-1L-1d-1 final methane production rate. The ultimate methane yields in all three consecutive experiments were 170, 171 and 35 L/kg VS at STP, respectively.

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75 The trends in pH and volatile organic acids (F igure 3-3) revealed st ability of anaerobic process in Experiments I.1 to I.3. Experiment I.1 initially started at pH of 8 and decreased to 7.7 in 2.4 days. Notably, acetic acid was the only orga nic acid that accumulated significantly; with a concentration of 624 mg/L at time 0, acetic ac id accumulated to 1220 mg/L within 1.3 days of start up, and subsequently degraded to 500mg/L. Propionic, butyric and valeric acids did not show substantial accumulation, as they all degraded to less than 100 mg/L by end of biogasification. The pH profile of I.2 was quite similar to I.1, starting a little highe r at 8.4 and decreasing to 7.5 by 2.3 days of the start-up. A pH of 8 wa s observed at the end of biogasification. Unlike I.1, all organic acids accumulated collectively in I.2; acetic acid accumulated up to 3900 mg/L after 3.4 days of start-up and degraded to 1640 mg/L; propionic and butyric acids both accumulated to 400 mg/L and 680 mg/L within the first 4 days before degrading to approximately 350 mg/L and 315 mg/L, respectively; valeric acid concentrati ons were quite low, evolving within 50 to 100 mg/L during biogasifica tion. In general, a 3.8 fold increase was observed in peak organic acid concentrations fo r the major VFA acids (acetic and propionic) when comparing I.1 with I.2. Experiment I.3 indicated the most rapid accumulation of VFA and consecutive pH drops during biogasification. The starting pH of reactor liquor was 7.5 and continually declined to 6.1, where the experiment was stopped at 6.7 days. Acetic and butyric acid concentrations accumulated dramatically during the start-up of I. 3. Within 2.4 days of start-up, acetic and butyric acids accumulated to 4000 mg/L and 2500 mg /L, respectively. Thereafter, acetic acid continued to increase to a peak value of 5050 mg/L, whereas butyr ic negligibly degraded to 2460 mg/L. The concentrations of acetic and butyric acids at the end of experiment (10.5 days)

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76 showed a degradation of 40% and 55% of observe d peak values. The remaining acids, propionic and valeric exhibited rapid accumulation reachi ng peak values of 431 mg/L and 135 mg/L midway though biogasification, before degrading to the final values of 320 mg/l and 55 mg/l within 10.5 days. In all, the total VFA concentrations for I.1 to I.3 at the termination point of each experiment were 650, 2398 and 4514 mg/L, respectively. Soluble COD (SCOD) profiles (Figure 3-3) we re also examined during biogasification for each experiment. In general, as the organic loading in each experiment was increased, an elevated SCOD was observed. In I.1, the SCOD at started at 5 g/L, peaked at 15 g/L and degraded to 8.3 g/L at the end of digestion. I.2 exhibited an in creased concentration of SCOD, exhibiting oscillatory concentrations of SCOD du ring digestion; a start of 12.4 g/L, followed by three consecutive saddle peak points at 23, 25, an d 21 g/L. Thereafter, the SCOD proceeded to degrade to 14 g/L, converging to within error ( 0.4% for COD 0 to 20 g/L) of the start value. Finally, I.3 exhibited a first or der saturation profile of SCOD in solution. Within 0.5 days, the SCOD value increased from 9 g/l to 34 g/l. By the end of the experiment, the SCOD continued to increase to a value of 41 g/L, where it appeared to remain fixed. At the termination of I.1, I.2 and I.3, the total VFA fractions with respect to total soluble COD were 7%, 17% and 11% percent, respectively. The modified Gompertz model equation (Eq.11) was fit to I.1 and I.2s cumulative methane yield data (continued digestion of I.3 wa s further investigated after termination at 6.7 days in Study IV) A reasonable fit was esta blished when this model was applied to both experiments. It should be noted that even though experiments in this study were not taken to completion, the cumulative methane yield could be extrapolated by using the Gompertz model equation (Hedge and Pullammanappallil, 2007). The performance parameters (Table 4-3)

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77 between experimentally-determined values a nd Gompertz model equation was analyzed for Experiments I.1 and I.2. 3.4 Discussion Employing a single-stage, batch, high-solids biog asification of raw suga r beet tailings as received provided valuable insights into pr ocess and performance dynamics. The volumetric efficiency and biogasification performance were scrutinized to ascertai n their relationship. Typically, high-solids biogasifica tion systems employ high volumetri c efficiencies (i.e higher bulk densities) for increased throughput. Comp action to higher densities (~300 kg/m3) is considered a major parameter influencing th e reactor size (Chynoweth and Pullammanappallil, 1996). The best case scenario would be a high volumetric efficiency coupled with rapid mineralization to methane. In the case of tailin gs, as the organic loading was increased in each batch experiment (i.e. volumetric efficiency incr eased), the cumulative methane yield decreased; this was especially evident with in the first six days of bioga sification. This trend appears consistent in the VS reduction as well, decrea sing from 90 to 78% for I.1 and I.2, respectively. Additional observations noted during batch operation included a flot ation and compaction phenomena of tailings. It was suspected that cont act inaccessibility of liquid to solids may have had an impact in the degradation decline from I.1 to I.2. This led to the possibility of trapped gases in the bed during methanogenesis, causing delays in gas evolut ion and disrupting bed homogeneity. Preliminary biochemical methane potential (BMP) assays conducted by Teixeira et al., 2005 on sugar beet tailings indicated that a yi eld of 250 L/kg VS was ach ievable after about 30 days under mesophilic conditions (38 oC). In general, a bench mark of 20 days or less to attain 95% of biochemical methane potential was used to evaluate if enhancements to previous work by Teixeira et al., 2005 were attained here. Th e methane yield of all three organic loading

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78 experiments conducted far exceeded the potentia l of the SEBAC-2 mesophilic experiment in Teixeira et al., 2005, which yielde d 40 L CH4/kg VS after 30 days of biogasification. However, all three experiments did not at tain the biochemical methane pot ential exhibited by BMP studies, when Gompertz model extrapolation was used. From looking at SCOD profiles (Figure 3-3) it was speculated that sugar beet tailings contain a large fraction of read ily soluble organic content. This was seen by rapid SCOD increase within less than half a day, part icularly in Experime nts I.2 and I.3; SCOD concentrations in both I.2 and I.3 increased two a nd three-fold during that time. It was suspected that physical solubilization rather than hydrolysis was responsible for th is occurrence. First order hydrolysis of biopolymer s found in OFMSW suggested k values of 0.5 to 0.63 d-1 (Chynoweth and Pullammanappallil, 1996). The SCOD increases witnessed here would correlate to k > 1 d-1. Therefore, it was suggested that this readily soluble fraction became inhibitory (at some SCOD concen tration) to hydrolysis of solids and diminished the biochemical methane potential as organic loading was increa sed. Through modeling, it was shown that that beyond a concentration of 20 g/L SCOD there wa s (OFMSW biogasification) an on-set of inhibition (Lai, 2001). Previous ly, it was shown that SEBAC could initiate methanogenesis rapidly in feedstocks such as organic fraction of municipal solid waste (OFMSW), yard waste, mixtures of biosolids and simulated solid waste. For example, soluble COD of reactor liquids from flooded vegetable waste bed was 8 g/L (He dge and Pullammanappallil, 2007) and that from OFMSW was 12 g/L (Lai 2001). W ith the exception of I.1, sugar beet tailings at increased organic loads produced much higher SCOD fractions, ranging 14 to 41 g/L SCOD. Studies have shown retardation can occur in single-stage anaerobic systems that fail to meet an inoculum-to-substrate ratio (ISR) at start-up. No strategic accommodations where made

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79 in this study to assure that the kg VS loaded to liquid inoculum was maintained constant; rather, the working volume of the reactor was held fixed. As a rule of thumb, the proper choice of ISR will depend on the final objective: methane or in termediate compounds production. In the case of normal single-stage operation, the rate of VF A due to hydrolysis and fermentation of macromolecules (acidogenic stage) should be sy nchronous with the rate of VFA conversion to methane via methanogenic stage (Sarada and Jo seph, 1995). Increased an aerobic degradability usually depends on high ISR value, whereas spec ific methane productivity maximums depend on small ISRs (Fernandez et al., 2001 ). This is confirmed with I.2, where higher initial methane rates (with respect to I.1) were observed, but overall anaerobic de gradability at the end of the experiment was reduced. Thus, it is speculated th at the extensive release of readily soluble COD (substrate), started having a more pronounced effect on synchrony in acetoclastic and methanogenic activities, for loadings > 0.42 kg VS per 12 L of reactor volume. The VFA accumulation and degradation trends observed in the three experiments bring additional insight to the progr ession of biogasification. Rese archers have found that VFA concentrations are the most important parameters in anaerobic digestion (Babel, et al., 2004; Pind 2002; Kim 2002). Under normal or balanced operation, the rate of production of VFA should be matched by their consumption rates; he nce there should be very little accumulation. In a continuous single-stage operation, it has been re ported that VFA < 500 mg /L is indicative of stable performance (Chynoweth and Pullammana ppallil, 1996). In the present study, trends reveal VFA accumulation levels beyond 500 mg/L, followed by different extents of degradation. In general, degradation of peak values for VFAs in all the experiments showed improvements by the termination. However, as the organic loading was increased, the final extent of degradation was diminish ed. With increased va lues of VFAs, the rate of mineralization

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80 to methane declined. This was especially exhibited in I.3, where the final total VFA concentration represented 25% of the soluble COD. Hence a considerable fraction had the potential of degrading, but was unable to do so due to unfavorable cond itions in the reactor. Accumulation and persistence of VFAs is typicall y inhibitory, if pH of system falls below pH 6.5; at low pH values, un-ionized species of VFAs are formed and have been found to be toxic to methane formers (McCarty 1964; Chugh 1999). This phenomenon was consistent in how the pH and VFA trends behaved in I.3; VFAs accumu lating beyond certain peak values (5000 mg/L total VFA) inherently decreased the pH to levels below the 6. 5 threshold, producing inhibitory forms of acids and diminishing th e potential for conversion. It is suggested that an adjustment in the amount of inoculum to VS loaded in biogasification of sugar beet taili ngs need to be considered for enhanced performance. To sustain sufficient volumetric efficiencies and optimal cu mulative methane yields, it is therefore proposed that biogasification of sugar beet tailings incl ude a pre-treatment step to remove the readily soluble organic matter. This appr oach will be considered in Study II. It is hypothesized that pretreatment removal and separate treatment of r eadily soluble organic matter would enhance the rate of the current batch operation. The liquid rise and compaction observed in E xperiments I.2 and I.3 ga ve great insight to some possible physical limitations when employing biogasification at +400 kg/m3 (wet) bulking densities. It was speculated th at biogas produced in the waste bed in I.2 and I.3 significantly excluded liquid out of the waste bed, causing liquid to rise. Fr equent perturbations (vigorous shaking) increased the rate at which biogas was measured by the ga s meter. Exclusion of liquid was suspected to have an adverse effect on biogas ification performance, as the availability of inoculum to utilize substrate was diminished. Chapter 5 addresses th e addition of a bulking

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81 agent to alleviate compaction of the waste be d and promote separation by increased hydraulic porosity. 3.5 Conclusions It was possible to anaerobically biogasify suga r beet tailings usi ng a flooded, high solids process at thermophilic temperatures, but with poor efficiency. As loading was increased from 0.16 to 0.68 kg VS, a decrease was seen in the % VS reduction and evolution of methane. Sugar beet tailings are composed of a high am ounts of readily soluble organic components. At increasing solids loading, an incr ease in SCOD accumulation was observed. Subsequently, overwhelming production of inte rmediate VFAs imbalanced the synchrony between acidogenesis and methanoge nesis, which caused inhibition. Flotation and compaction of tailings was obser ved. It was speculated that this action reduced the contact of liquid to substrate, in addition to pe rcolation of product gases from the waste bed.

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82 Figure 3-1. Sugar beet tailings residue

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83 Table 3-1. Sugar beet ta ilings characteristics Tailings characteristics Moisture (%) 83 87 Total solids (%) 13 17 Volatile solids (%) 80 92 Table 3-2. Loading and unloading data for Study I experiments Experiments I.1 I.2 *I.3 Wet tailings weight (kg) 1.1 3 5 Total solids (kg) 0.18 0.45 0.77 Volatile solids (kg) 0.16 0.42 0.68 Inoculum added (L) 12 11.5 10.0 Packing density (kg wet/m3) 416 465 491 Packing density (kg dry/m3) 66 70 75 Loading Total solids in reactor (%) 1.3 2.9 5.3 Wet residue weight (kg) 0.82 2.30 Un-loading Total solids (kg) 0.03 0.12 Volatile solids (kg) 0.0170.090Total solids reduction (%) 82 74 Volatile solids reduction (%) 74 78 Un-loading of I.3 is conducted after sequencing experiments in Study V

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84 Table 3-3. Summary of bi ogasification performance in Study I experiments aGompertz parameters (model) Experiment Final cumulative methane yield (experimental ) bP bRm b Duration to produce 95% methane yield potential L CH4 kg VS-1 L CH4 kg VS-1 L kg VS-1 d-1 days days I.1 170 168 23 0.1 10.7 I.2 171 204 21 0.6 14.9 I.3 36 a Gompertz parameters derived by fitting experiment data into Modified Gompertz Model. b Symbols have their usual meaning Time elapsed (days) 02468101214 Cumulative methane yield (L CH4 @ STP / kg VS) 0 20 40 60 80 100 120 140 160 180 Experiment I.1 Experiment I.2 Experiment I.3 Figure 3-2. Comparison of cumulative meth ane production from experiments in Study I

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85 Figure 3-3. Profiles of biogasifi cation parameters from experiments in Study I. A) Methane production rate. B) Methane fraction in biogas. C) The pH profile in re actor. D) Soluble COD in reactor. E) Acetic acid concentration prof ile. F) Propionic acid co ncentration profile. G) Butyric acid concentration profile. H) Valeric acid concentration profile. Methane Production Rate (L/L/d) 0.0 0.5 1.0 1.5 2.0 Methane fraction in biogas pH 0.0 0.2 0.4 0.6 0.8 6.0 6.5 7.0 7.5 8.0 8.5 Acetic acid (mg/L) 1000 2000 3000 4000 5000 Propionic acid(mg/L) 0 100 200 300 400 500 Butyric acid (mg/L) 500 1000 1500 2000 2500 Time elapsed (Days) 024681012Valeric acid (mg/L) 0 20 40 60 80 100 120 140 Time elapsed (Days) 024681012Soluble COD (mg/L) 0 10 20 30 40 50 Experiment I.1 Experiment I.2 Experiment I.3 A B C D E F G H

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86 CHAPTER 4 STUDY II RESULTS: LEACHING AND TREATMENT OF READILY SOLUBLE FRACTION OF SUGAR BEET TAILINGS 4.1 Introduction In Study I (Chapter 3), it was speculated th at raw sugar beet tailings contained a considerable fraction of readily -soluble organic compounds. Part icularly, Experiments I.2 and I.3 showed dramatic increases in the concentr ation of SCOD accumulating in a short amount of time -0.5 days. It was unclear to what extent this accumulation was due to solids hydrolysis or readily soluble constituents. High levels of soluble chemical oxygen demand (SCOD) in solution that is derived from readily soluble components can be removed by a simple leaching (washing) procedure. It was speculated the pre-tr eatment of raw sugar beet tailings will enhance the biogasification of solids by minimizing the subs trate concentrations in a fixed liquid volume, while attaining a realistic volum etric efficiency. Wastewater effluent (wash water) generated during pre-treatment could contri bute significantly to the overall biochemical methane potential of sugar beet tailings. The aims of this study were to: 1. Pre-treat and quantify readily -soluble organic content in raw sugar beet tailings 2. Treat leached tailings effluent wash water in the AFR to assess the methane contribution of the readily soluble fraction of tailings 4.2 Results Washing: A set of five washing experiments we re conducted to ascertain the amount of readily-soluble organics in raw sugar beet tailings. In-situ wash ing experiments were carried out in ABCR 1 and 2 at thermophilic temperatures w ith liquid re-circulation for mixing. Loading of tailings and unloading of wash water were followed according to the loading procedure for bulked experiments (2.9.3) and storage of li quid feeds (2.6), respectively. Bulking agent (pumice stones) was used to avoid flotation and compaction, which was observed in Study I.

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87 Also, to assure adequate removal of readily so luble organics, each experiment was treated to a secondary wash. Readily soluble COD profiles (Fig ure 4-1) and experiment para meters (Table 4-1) for insitu washing of sugar beet tailings. The contac t time was held arbitrarily at 10 hours and samples were withdrawn from each unit at fixed intervals and analyzed for their TCOD content. The first wash revealed a first-order rate (k = 0.99 hr-1) behavior, as concentrations approached 24.5 3.6 g COD/L; a second pass in washing resulted in a substantially lower so luble COD concentration of 4.0 1.1 g COD/L. On average, over 85% of the total readily so luble COD fraction in tailings was removed in the first wash. A total of 20 liters of wash wate r with an average SCOD of 13.9 1.3 g/L COD was generated from the combined wash 1 and 2 in each experiment. Physical and chemical constituents of wash wate r resulted in < 1g/L total suspended solids, total VFAs < 200 mg/L, and 0.4% simple sugars; analysis for other components, such as crude protein, degradable and soluble proteins where below detection limits for measurement. The readily solubilized organic fr action for sugar beet tailings was approximately 0.54 0.07 g COD/g VS. Wash water treatment: Biogasification experiments (II.6 to II.10) were conducted on the wash water effluents incurred from leaching stud ies. Wash water aliquots containing 11 to 14 g/L COD were processed in a se quencing-batch mode in the AFR to experimentally determine their methane potential. The loading and perfor mance parameters (Table 4-2) for each wash water experiment and the biogasification parame ter profiles (Figure 4-2) and soluble COD balances in the AFR (Figure 4-3) were experime ntally determined and compared. Feed volumes delivered for experiments II.6 to II.10 corresponde d to 1.5, 2, 3, 4 and 2 liters, respectively. This

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88 resulted in displacing 14 to 36 % of reactor liq uid contents upon additions at the start of experiment (reactor volume was held constant). Two initiation experiments were conducted in the AFR to acclimatize the microorganisms to wash water. In general, the progression of experiments show that the AFR was able to biogasify aliquots of wash water generated duri ng leaching. In the case of experiments I.6, I.7 and I.8, a proportional increase in the daily methan e rate was observed, while hydraulic retention time (HRT) decreased from 37, 30 and 22 days, re spectively. For sequencing batch reactors (SBR), the HRT is defined as the active volume of reactor divided by the feed rate; feed rate was calculated by the volume of feed over the batc h-time duration in which it is treated. The cumulative methane yield also increased during th e series additions, rang ing from 0.23 to 0.28 L CH4 g COD-1 added. However, upon the addition of 4 L feed volume in II.9, a decrease was observed in the peak methane producti on rate, falling from 0.64 to 0.44 L L-1d-1. The duration to attain 95% of methane yield also increased mo st drastically during II.9 addition, increasing on average by 1 day. The pH profiles showed increa singly sharp decreases in itially as hydraulic loading was increased, but never fell below 6.8; the total VFA concentration was sustained below 200 mg/L, but increased to 325 mg/L after II.9 addition into the AFR. It was observed that the SCOD concentration fell with each addition of wash water; starting at 2.4 g/L COD, a mos tly linear drop relationship was s een as wash water was pushed through the AFR. Dotted marks on the SCOD profile plot on Figure 4-2 (B) indicate the initial concentration of SCOD in the AFR upon addition of wash water; it wa s unclear whether the degradation to the final SCOD va lue was linear or non-linear. So luble COD balances (Figure 43) for each batch-fed experiment were conducte d for validation of experimentally-determined quantities. Calculations we re conducted according to co mmonly-accepted stoichiometric

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89 relationships in anaerobic di gestion. For a given batch e xperiment, a COD balance was performed at the start and end of a run; start-va lues presented the residual and feed fraction of COD; end-values presented the fractions for measured COD mineralized to methane, COD discarded as effluent, COD consumed for bioma ss growth and the final residual remaining in reactor. The COD going towards biomass was shown to be 9% of the COD added as feed; biomass COD is usually considered a negligib le term, and usually no t considered in COD balances. The effluent exhausted after each feed addition accounted for only 9% of methane COD In general, the sum of components maki ng up COD at the start of a batch balanced with the measurement error with end value; II.6 fell short by 2.6 g COD or 9% of total COD added. The relative reproducibility in cl osing the COD balance (within error) fortif ied the analytical techniques used for measuring critical parameters. The modified Gompertz model equation (Eq. 11) was fit to all five experiments to determine the critical biogasific ation parameters. In general, each fit was very precise and indicated remarkable reproducibility of a typical batch growth rate curve. Final experimental cumulative methane values were within each other when the biogas measurement error was attributed; values were averaged since the degree of sensitivity dismissed any detectable differences in yields in lieu of differences in organic loading. Both Gompertz and experimental values revealed that the cumulative methane yiel d of sugar beet tailings wash water was 0.25 0.02 L CH4 g-1 COD added. In addition, the lag phase in all experiments was < 0.1 days and with the exception to II.9, th e duration to produce 95% of th e methane yield potential was approximately 1.5 days. 4.3 Discussion It was concluded through experimentation that sugar beet tailings contain a significant amount of readily soluble fractions that can be degraded by anaerobic dige stion in an anaerobic

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90 filter reactor. The readily-soluble organic matter derived from in-situ washing experiments was 0.54 g COD/g VS; 86% of solubilized organic matte r was achieved within 5 hours of the first wash. Therefore, the readily solubilized COD am ounts suspected of inhibitory affects in I.2 and I.3 of Study I were 86, 227 and 367 g, respectivel y. The corresponding total increase in COD concentrations experienced in I.1 to I.3 were 6.5, 17.4 and 36.7 g/L COD, respectively. It was quite evident from these findings that the rem oval of readily soluble components on sugar beet tailings was a critical step in mitig ating COD levels for batch operation. Volumetric efficiency can be de fined as a ratio loaded material to available reactor volume. Qualitatively speaking, this parameter can be used to assess how efficiently reactor volume is used. In experiment I.1, it was shown that 1.1 kg of sugar beet tailings were loaded in 12 L working volume; un-compacted tailings occu pied only 23% of the working volume (low volumetric efficiency). A pre-treatment wash ing step would theref ore improve volumetric efficiencies in batch reactors by increasing volume occupied by sugar beet tailings From stoichiometry, the readily so luble content per kg VS loaded of tailings translated to a 118 L CH4 kg VS-1 (assuming 75% degradation of readily soluble COD). Biochemical methane potential (BMP) values for sugar beet tailings were reported as 250 L CH4 kg VS-1 (Teixeira et al., 2005), which implied that readily soluble fr action accounted for 47% of total biochemical methane potential; Methanogenesis from the solid fraction of tailings should account for the remaining 53% of methane potential, or approximately 132 L CH4 kg VS-1. Therefore, a twofold increase in total solids loaded in a single batch reactor could be accommodated if pretreatment was employed. At a bulking density of 465 kg/m3 for sugar beet tailings inside a reactor, approximately 2.2 L or 15% of the work ing volume would be additionally occupied with tailings subjected to washing. For example, in looking at experiment I.1, the corresponding

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91 equivalent soluble COD would be produced in bioga sifying 2 kg of washed tailings, rather than 1.1 kg of raw tailings. In general, experiment I.1 (ISR = 0.04 L g SCOD-1) provided adequate biogasification start-up and minimal accumulation of intermediates; pre-treatment in such case would not only increase total solids loaded, but maintain a ISR value sufficient for acceptable biogasification outcomes. It is speculated that removi ng readily soluble organic substrate could even enhance the rate of solids degr adation to methane (Chapter 5). The production of an additional waste stream (tailings wash water) was not optimized to minimize quantities generated; two washes provided adequate removal of readily soluble COD. During the process, the total VFA of < 200 mg/L indicated that aci dogenesis did not occur naturally under the wash conditi ons; any presence of indigenous microorganisms on tailings did not promote biogasification at detectable levels Furthermore, the washing process produced very low concentrations of suspended solids (< 1g /L) and did not require a ny clarification before treatment in the AFR. The time reserved for pre-treatment was regarded a crucial parameter. For a complete biogasification cycle of 20 days, pre-treatment employed here accounted for 4% of the cycle time. Therefore, pr e-treatment of sugar beet taili ngs via in-situ washing could be afforded given that time spent for washing would be outweighed by increase d degradation rates. Assessment of the biochemical methane potential of wash water containing readily soluble organic compounds from tailings was conducted in the AFR reactor in batch mode. The simple start-up and operation of this unit provided a se nsible outlook operating combined suspended and attached growth rate system on the lab scale. The treatment of wastew ater is a conventional practice and is not disputed or re searched extensively in this wor k. In general, wash water from pre-treated tailings had a sol ubilized organic content of 13.9 g/ L COD; by convention, this is considered a moderate-strength wa stewater and can be treated in high-rate AF (anaerobic filter)

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92 or Upflow Anaerobic Sludge Blanket systems (UASB), at 5 to 40 g COD L-1 d-1. In experiments II.6 to II.10, low rate process (< 5 g COD L-1 d-1) was adapted to determine the potential generated by wash water. It was shown that wash water had a biogasification potential of 0.25 0.02 L CH4 g COD-1 added. Therefore, 71% efficiency in the mineralization of readily soluble COD to methane was experimentally determined. Biogasification of wash water provided insight to the operational characteristics of the AFR. It was speculated that SCOD residuals pres ent in AFR reactor were driven to further degradation once plug additions of wash water were added (Figure 4.2 (C)). The initial start of experiments in AFR was a result of priming the unit for about 15 days with mild wastewater (~ .25 g COD L-1 d-1). Thereafter, the COD leveled around 2 g/L COD and it was assumed that this would be a non-degradable residual (where to tal VFAs were < 0.03 g/L COD). Conventional practices typically use aerobic cu ltures to treat wastewater st rength between 0.05 to 1.5 g/L COD and anaerobic if wastewater is between 1.5 to 50 g/L COD. From initiation experiments to the end of II.9, it was shown that additions of wash water COD facilitated the decrease of residual concentration of solubilized orga nic content in the reactor. The AFR system operated as low as 0.57 0.02 g/L COD before SCOD started accumulating. Characterization of the process during the batch feedings of wash water also revealed that increasing the haudralic and organic loading rate caused an increase in the duration to produce 95% of the methane yield potentia l. In particular, the extreme case was seen when the liquid addition of 4 L or 36% of the working liquid volu me in the AFR was displaced with wash water (experiment II.9). The duration to produce 95% of the methane yield was increased by one day. This suggested that a significant part of the microbial growth in the reactor was suspended, rather than attached on the bulking media. Therefore, c onsiderable removal in the percentage of active

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93 microorganisms diminished the methane rate in II.9 and washout of microorganisms was becoming apparent. But by reducing hydraulic lo ading to 3L in II.10, kinetics of methane production was improved. Visual inspection of bulking media (after Study II experiments) confirmed that no biofilms were present. This was logical considering that the AFR syst em was only operated for 35 days and was initiated with suspended growth inocul um (generated in a re-circulated system) and trace amount of sugar beet tailings. Moreover, it was reasone d that the mode of operation in the AFR most likely didnt promote the formation of biofilms. At a 0.42 L/ min re-circulation rate, the working liquid volume was turn ed over every 26 minutes; this wa s necessary to assure proper temperature control in the vessel. Therefore, it was suspecte d that the vessel during Study II experimentation acted as a Stirre d Tank Reactor with bulking medi a, rather than an ideal AFR reactor; bulking media seemed to mainly facilitate liquid ga s separation, which was indicated by continuity in methane production rates. From such experiments, it was projected that the AFR would operate satisfactorily up to a hydraulic loading rate of 3 L d-1 (HRT = 21 days) for the wash wa ter concentrations presented in Chapter 4. Further maturation of this unit c ould sufficiently bring down the HRT to lower values, increasing the throughput of wash water. However, this exploration was beyond the scope of this work, as anaerobi c processes operating at HRT of 5 days are conventionally and commercially used for moderate-strengt h, low suspended solids, wastewaters. 4.4 Conclusions Sugar beet tailings can be leached of their r eadily soluble COD content by in-situ solid-bed leaching. The readily soluble fraction was calculated as 0.54 0.07 g COD/g VS 85% of the readily solubilized fraction of sugar beet tailings leached within 5 hours of the first wash

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94 With a BMP value of 250 L/kg VS, it was estimated that 53% of the methane yield would come from solid fraction of sugar beet tail ings; the remaining 47% would be contributed from biogasification of wash water Wash water generated yielded 0.25 L CH4 at STP g COD-1 added in the AFR; the COD-tomethane mineralization efficiency was estimated as 71% The lab-scale AFR behaved more as a batch STR; it was suspected that very little attached growth was present during the 20-day st udy and the mode of operation promoted suspended growth

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95 Contact time (hours) 024681012 Soluble COD (g/L) 0 5 10 15 20 25 30 Wash 1 Wash 2 Wash 1 Fit Wash 2 Fit Figure 4-1. In-situ leaching of sugar beet tailings

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96 Table 4-1. Leaching experiments for sugar beet tailings Experiments II.1 to II.5 Wet tailings weight (kg) 3.0 Total solids (kg) 0.52 0.05 Volatile solids (kg) 0.48 0.05 Packing density (kg wet/m3) 650 Loading Bulking agent (kg) 2.5 H2O added (L) 10 Contact time (hr) 10 Temperature (C) 55 2 Saturated concentration (g/L COD) 24.5 3.6 Wash 1 Rate constant, k (hr-1) 0.99 H2O added (L) 10 Contact time (hr) 10 Temperature (C) 55 2 Saturated concentration (g/L COD) 4.0 1.1 Wash 2 Rate constant, k (hr-1) 0.20 Total wash water (L) 18.6 0.34 Total suspended solids (g/L) 1.0 Wash water concentration (g/L COD) 13.9 1.3 Wash total Readily-solubilized fraction (g COD/ g VS) 0.54 0.07

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97 Cumulative methane yield (L CH4 @ STP/ g COD added) 0.0 0.1 0.2 0.3 Methane Production Rate (L/L/day) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Time elapsed (Days) 02468101214161820Methane fraction in biogas (% vol) 0.0 0.2 0.4 0.6 0.8 1.0 Initiation II.6 II.7 II.8 II.9 II.10A B C Figure 4-2. Performance profile s from wash water biogasification. A) Cumulative methane yield. B) Methane production rate. C) Meth ane production rate. D) Profile of pH. E) SCOD profile. F) Total VFA profile.

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98 pH 6.8 7.0 7.2 7.4 7.6 Soluble COD (g/L) 0.0 0.5 1.0 1.5 2.0 2.5 Time elapsed (Days) 02468101214161820Total VFA (mg/L) 0 50 100 150 200 250 300 350 Initiation II.6 II.7 II.8 II.9 II.10D E F Figure 4-2. Continued

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99 Figure 4-3. COD balance from wash water biogasification in the AFR

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100 Table 4-2. Summary of para meters from biogasification of wash water in the AFR aGompertz parameters (model) Experiment Loading rate HRT Final cumulative methane yield (experimental) bP bRm b Duration to produce 95% of methane yield potential g COD L-1 d-1 days L CH4 g COD-1 L CH4 g COD-1 L g COD-1 d-1 days days II.6 0.5 0.02 37 0.23 0.02 0.23 0.24 0.1 1.4 II.7 0.6 0.03 30 0.24 0.03 0.27 0.24 0.1 1.5 II.8 0.6 0.03 22 0.28 0.03 0.27 0.24 0.1 1.7 II.9 1.6 0.08 19 0.26 0.02 0.25 0.30 0.1 2.7 II.10 1.2 0.06 21 0.26 0.02 0.22 0.29 0.1 1.5 c0.25 0.02 a Gompertz parameters derived by fitting experiment data into Modified Gompertz Model. b Symbols have their usual meaning. c Average and standard deviation of Gompertz P-values.

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101 CHAPTER 5 STUDY III RESULTS: THE EFFECT OF BU LKING ON THE BIOGASIFICATION OF SUGAR BEET TAILINGS 5.1 Introduction In study I, experiments revealed that single-stage batch biogas ification of raw sugar beet tailings may require pre-treatment to mutually sustain high concentration of solids and balanced biogasification. Moreover, cert ain physical phenomena that were observed to occur, like compaction and flotation, were regarded as possi ble kinetic-limiting culprits. It was observed that once the reactor was loaded with tailings and liquid added; the liqui d level rises by 15 to 20% during the first 1 to 3 days of biogasification. It was speculated that this rise in liquid level was due to compaction of bed with concomitant expulsion of liquid from the bed. In addition, gas builds up within the bed as the wetted s ubstrate undergoes fermentation; localized VFA accumulation and pH drops would become imminent. When the reactors were subjected to frequent physical perturbations (like vigorous shaking) a s udden release of overwhelming amounts of biogas (> 0.11 L/min) was observed and liquid level fell as a result of such perturbations. The goal of this study was to examine the effect of bulking the tailings on the biogasification performance of sugar beet taili ngs. It was important to overcome the above physical limitations for the development of a bi ogasification strategy that promoted faster degradation of solids and maximi zed ultimate methane potential. The strategy tested in this study involved addition of an inert bulking agent to the tailings bed that would prevent compaction and allow movement of gas from the bed and liq uid in and out of the bed; liquid movement would bring buffer and methanogenic inoculum to more areas and buffer against pH changes and mediate degradation of VFA. Further understandi ng was also needed in characterizing feedstock

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102 transformation. The extent of degradation or solubilization of chemical components (liqnin, cellulose, hemicellulose, etc) during biogasi fication was also analyzed in this study. 5.2 Background The addition of a bulking agent in a batch, singl e-stage biogasfication of sugar beet tailings was believed to alleviate the flotation and compacti on of the tailings and f acilitate the percolation of trapped biogas. Limited literature was avai lable on the use of bulking agents to remedy these physical limitations. Notably, the addition of a bu lking agent to enhance anaerobic digestion in vessels system has been reported in very few studies. In Hegde and Pullammanappallil (2007), a feedstock comprising of vegetable waste and woodchips was anaerobically digested at mesophillic and thermophillic temperatures in a single-stage, batch, high-solids system. The addition of wood chips was suggested to improve the structural strength of the waste bed and imparted bulking properties. A similar approach was also taken with the anaerobic digestion of organic fraction of municipal solid waste (OFM SW) by Adhikari, 2003. In that work, shredded OFMSW was loaded with bamboo cutlets to a bulking density of 600 kg/m3 in a flooded reactor. However, neither work mentioned the effect of bulking on the biogasification performance. Typically, since high-solids anaer obic digestion is carried out on feedstocks that are naturally bulked (for example unsorted municipal solid wast e or un-shredded organi c fraction of municipal solid waste, yard waste, and mixtures of manure and straw), not much attention has been paid to understand the effect of bulki ng in these digesters. Based on physical observations in Study I, it was proposed that the exclusion of liquid inoculum by trapped biogas and subsequent co mpaction could be addressed by constructing a structured matrix within the bed using landscapin g rocks as a bulking agent. As the onset of methanogenesis would produce biogas, gas-liquid/so lid separation would be facilitated by a more porous structure; biogas bubbles woul d overcome cohesive forces from the surfaces of tailings or

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103 other boundaries impeding gas separation. Efficien t biogas expulsion (upon generation) in waste beds was hypothesized to minimize compacti on/flotation caused by trapped bubbles and maximize the intimate liquid-solid contact. Ther efore, the biogasification progression would not be limited by physical boundaries between active organisms and substrate surfaces. The concept behind this reasoning was take n somewhat analogously from mechanisms inherent in aerobic composting. It has been s hown that adjusting the ra tio of organic waste: bulking agent has had beneficial effects in developing high rates of respiration (Boen et al., 2003; Aasen et al., 2003; Pagans et al., 2005). St udies there have demonstrated the importance of the interaction of compaction and moisture in lieu of porosity and permeability of composting matrices. In general, the rate-limiting parame ter for respiration oxygen uptake was enhanced by having optimized pile configurations (Malin ska and Richard, 2003). Bulking agents provide certain waste bed structure to encourage porosit y for efficient permeation of oxygen to surfaces, whereupon aerobic degradation can occur. The lack of sufficient bulking in aerobic systems has been widely accepted to cause compaction. A downstream implication of this phenomenon included increased concentrations of organic acids as a result of poor aerobic respiration rates (Aasen 2003). Furthermore, it has been suggest ed that metabolically active organisms could be located on the surface of a bulking agent, where they might be less exposed to high concentrations of acids on substrate su rfaces during a process (Boen et al., 2003). Using this as an analogy to anaerobic diges tion of flooded waste beds, it can be concluded that,sufficient porosity is needed to expel biogas formed and allow liquid to percolate into the bed. Chen and Chynoweth (1994) addressed hydra ulic conductivity of municipal solid waste (MSW) under various degrees of compaction for leachate re-circulation improvements in landfill applications. Hydraulic conductivity is defined as a measure of the abil ity of porous media to

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104 conduct liquid. In such work, MSW waste beds underwent changing degrees of moisture content as a result of metabolic gas production. It was observed that gas cont inued to exclude water from the pore spaces within the matrix, which caused a decline in hydraulic conductivity. Once easily fermentable substrates of MSW were depleted, gas formation diminished and the hydraulic conductivity increas ed and eventually leveled off. Due to degradation, it was reasoned that hydraulic conductivity becomes a time-depe ndent parameter, as structure constantly degrades. It was reasonable based on Study I observati ons to investigate the effect of bulking on biogasification performance be investigated. Ex tensive experimentation regarding the changes in hydraulic conductivity or efficien cy in gas-liquid/solid separation is beyond the scope of this work. However, quantifying possible improveme nts offered by bulking tailings in flooded operation could have design implications on the larger scale. 5.3 Results Experiments: A total of six experiments were co nducted consecutively to digest 3 kg aliquot of sugar beet tailings. Experiment s III.1 to III.3 were unbulked trials, whereas Experiments III.4 to III.6 were bulked trials. The decision to conduct experiments with 3kg batch samples was decided by two factors: 1. Bulking agent and 3 kg of raw tailings was the maximum (un-compacted) volumetric load that could be confined to a 12-L working volume and 2. The 3-kg load in Study I (Chapt er 3) did not breech headspace tolerance during liquid exclusion from the waste bed. The protocol for loading un-bulked and bulked experiments was followed according to 2.9.2 and 2.9.3, respectively. To extract the re adily soluble organic fraction fr om sugar beet tailings, each experiment was subjected to in-situ pre-treatment described in Study II.

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105 The performance of each experiment was monitored by analysis of biogasification parameters on a daily basis. Observations we re focused during start-up to characterize liquidlevel increases (or decreases). The biogasifica tion experiments were carried out until evidence of a stagnation or slow-down in the methane production rate was observed. Experiment III.1 and III.4 were inoculated with fresh stock inoculum, followed by re-use within their respected sets. Bicarbonate buffering was provi ded similar to Study I. Characteristics of feed and digested residue: The loading and unloading data of Study III (Table 5-1) were experimentally determined and recorded. As seen, the un-compacted packing density (dry basis) from bulked to unbulked experiments was almost tripled; the volume fraction taken up by landscaping rocks wa s considerable, therefore increasing demand for volume usage. Moreover, it was observed th at feedstock used for experiments in Study III were on the low end of the range of total solids at 13%. Any sampling procedures for collecting sugar beet tailings at EGF was conducted externally and therefore not contro lled or scrutinized. Pre-cautions were taken to al ways homogenize samples receiv ed (by thorough mixing), but variations were present from shipment to shipment. Residue samples from each experiment were unloaded and measured for TS and VS reduction. Upon opening bulked react ors, it was clearly visible th at rocks and residue where intermittently mixed with each other. External washing of residue fixed on rocks was conducted followed by filtration. On average, it was show n that the TS reduction for bulked runs was 86 4 % whereas un-bulked runs yielded 76 3 % TS reduction; a narrower margin was seen in VS reduction, where bulked and unbulked runs showed 85 2% and 85 1% reductions, respectively (It is suspected that the VS meas ured was actually VSS). Additionally, chemical characteristics of tailings and residue were analyzed by Dairy One Forage Lab (2.14.3.4)

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106 Physical observations: The rise of liquid level inside the reactor for both sets of experiments was observed during th e duration of biogasification. As expected, the rise in the liquid level for un-bulked was higher than that of bulked runs. From the headspace viewing window, the average maximum excluded volumes obs erved for bulked and un-bulked trials were 1 to 1.5 L and 2.5 to 3 L, respectively. The leve l in both sets began to fall during progression of digestion, notably faster in the bulked reactor. Biogasification of sugar beet tailings: The biogasification parameters measured during each experiment (Figures 5-1 to 5-3) were plo tted side-by-side to highlight differences in magnitude. In general, all the profiles within a set exhibited reproducibility. From the cumulative methane yield plots, it is evident that bulked experiments resembled more closely the shape of a typical growth curve; plots of un-bul ked experiments exhibited an irregular inflection point, occurring between days 4-6. Scrutiny of inflection points revealed that methane composition increased only 7% during the two-da y spans. On average, the experimentallydetermined cumulative methane yields of bulke d and un-bulked runs were 137 9 and 127 6 L kg VS-1, respectively. Considerable differences were exhibited in the methane producti on rates between bulked and un-bulked schemes. In general,un-bulked plots exhibited oscillat ory behavior ;initial increases to 0.5 l l-1day-1 by the first day, fell to 0.2 to 0.35 between days 4 to 6. Thereafter, the methane production rate increased again to levels 0.4 to 0.5 L L-1d-1; finally, the rates fell to below 0.1 L L-1d-1 after 15 days. In the bulked experiments, rates were seen to increase up to 1 L L-1d-1 after 2 days (except for III.6, where the rate reached this value after 3.5 days) and thereafter decreased and approached 0.25 L L-1d-1 after 6 to 7 days. Differences were also seen in the duration by when each experiment attained a particular methane composition. In general,

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107 bulked experiments rapidly attained a 60% meth ane composition after 4 days whereas un-bulked experiment took twice as long. Un-bulked tria ls experienced stagnation early on, as methane compositions hovered between 20 to 30 % for a tw o-day duration. On average, the highest methane compositions attained in bulked a nd un-bulked experiments were 68% and 80%, respectively. The pH profiles for both sets of experiment s display a similar trend; at the start of experiments, the pH drops to a minimum value, before making an eventual rise. Bulked experiments decreased on average up to 0.5 pH units with the first two days, and steadily increased thereafter, leveling off at approxima tely 7.3. Un-bulked trials showed similar behavior, but maintained the low-end values (~ pH of 7.5) for duration of 3 to 4 days before making the climb. The final pH level-off fo r un-bulked experiments occurred between 7.8 and 8.4, and was speculated due to higher concentrati ons of carbon dioxide gas in the liquid phase. The contrast in SCOD profiles between bulked and un-bulked runs was not as distinct as the aforementioned parameters. Both sets of experiments started at SCOD values below 5 g/L COD and accumulated to values less than 12 g/ L; bulked experiments accumulated a to their maximum values of 5 to 8 g/L COD within 2 to 3 days, before leveling off; un-bulked experiments attained increased max values within 6 days of biogasification. At the termination of the experiment, neither set decayed back to the starting SCOD levels. The VFA profiles (Figure 5-3) for both sets of experiments were examined and plotted during biogasification. In general it can be seen that all four VFA aci ds accumulated to higher levels in un-bulked experiments as compared to bulked experiments. The most notable difference is in acetic acid concentrations; bul ked concentrations accumulated only as high as 800 mg/L in two days before degrading belo w 100 mg/L in 7 days; un-bulked experiments

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108 reached as high as 2000 mg/L and sustained aceti c levels between 900 and 1600 mg/L for 3 days before degrading below 300 mg/L. With the excepti on of acetic acid in both sets of experiments, no other VFAs accumulated to values > 500 mg/L The summary of performance for bulked and unbulked experiments (Table 5-2) was used to make notable comparisons between the two modes of operation. Th e modified Gompertz model equation (Eq 1-1) was applied to bulked experiments to determine critical model parameters. Un-bulked experime nts were shown to deviate from a classical growth curve, and were not reasonably ideal for Gompertz fitting. The duration to produce 95% of methane yield potentials for bulked and un-bulked experiments was 6.7 1 and 14.5 1.6 days, respectively. Gompertz P and Rm values for bulked experiments yielded 148 5 L CH4 kg VS-1 and 27 7 kg VS L-1 d-1. The methane potential distribution between wa sh water and solids biogasification (Table 53) combined the effects of both solid and liq uid fractions in biogasification. Wash water generated from in-situ solubili zation produced concentrations between 0.52 and 0.58 g COD g VS-1; the average reported in Study II was 0.54 0.07 g COD g VS-1. Using the experimentallydetermined yield coefficient for wash water (0.25 0.02 L CH4 g COD-1 added), wash water methane potentials were calculated for bulked and un-bulked experiments as 145 32 and 131 23 L CH4 g COD-1, respectively. Thus, the combined soli ds and wash water contributions to cumulative methane yields for bulked and un-bulked experiments were 282 22 and 258 27 L CH4 kg VS-1, respectively. The % VS of major components (Table 5-4) considered in degradation of plant-based organic matter measured by Dairy One were also examined. Clea rly, % NFC (non-fibrous carbohydrates) was the largest VS fraction of ta ilings, at 44.9%. Other critical component

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109 fractions included: cellulose at 21.8 %; hemi cellulose at 14.3%; li gnin at 5.1 %; cr ude protein at 7.3 %; and soluble protein at 1.2%. Residue take n from Expirment III.6 was also measured for the same components. The % degradation (VS basis) of NFC was the highest, at 92%. Degradation of other components in cluded: cellulose at 87%; hemi cellulose at 84%; lignin at 42%; and crude protein at 52%. Ex perimentally, solids unloading an alysis indicated that the % VS of total dry matter of sugar beet tailings and residue was 93% and 60 %, respectively. The mineral components (considered no n-volatile solids) of sugar beet tailings and residue were measured (Table 5-5); results showed that mine rals account for 3.1 and 6.8% of the total sugar beet tailings and residue dry matter content, respectively. Th e experimentally-determined ash content of III.6 residue was 40% of the dry-matt er unloaded from the reactor. The discussion describes discrepancies between component-derived balances and experimental observations. 5.4 Discussion By implementing a second iteration (pre-tr eatment and bulking) in process methodology, clear improvements in biogasification performance we re attained. In general, batch experiments in Study III resulted in lower accumulation of SC OD and VFAs and higher degradation rates, as compared to Study I and mesophilic SEBAC-2 wo rk, (Teixeira et al., 2005). A biochemical methane potential of > 250 L kg VS-1 was achieved in 15 (un-bulked runs) or 10 (bulked runs) days, provided that a high-rate wastewater reactor could concurrently treat wash water generated in the pre-treatment stage. Enhancing th e waste bed structure by adding a bulking agent minimized the overall residence time for the biogasif ication of sugar beet tailings (bulked vs. unbulked experiments). The theory that bulking would diminish th e liquid exclusion and compaction phenomena and enhance biogasification was confirmed visually in Study II. Within the first few days of biogasification, bulked experiments showed less th an half of the excluded fluid in un-bulked

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110 experiments. Therefore, more liquid was avai lable for interaction with tailings, and biogas generated had improved passage through the solid bed. It was speculated that increased levels of VFA accumulation in un-bulked experiments occurre d from localized isolation of tailings from bulk fluid, encapsulated in trapped biogas. As acidification occurred, insufficient methanogens were present locally to convert VFAs or inhib itory concentrations of the VFAs restricted methanogenic growth. The stagnation in % methan e between day 2 and 3 can be used as further evidence to this claim. However, as biogasi fication progressed, the volume of excluded liquid minimized and improvements in methane composition, VFA concentrations and pH were seen after the sixth day. As of late, no literature references in anaer obic digestion have been found to support or refute the postulated mechanism aforementioned. The % VS reduction for bulked and un-bulked runs was experimentally determined to be 85 2 and 81 2 %, respectively. Discrepanc ies however exist betwee n measured cumulative methane yields and %VS reduction recorded. Fr om stoichiometry, a 100 % VS reduction (i.e. all of material digests) should yield 350 L CH4 kg VS-1. Along that basis, an 85 and 81% VS reduction in sugar beet tailings wo uld correlate to 284 and 298 L kg VS-1. Differences between the measured and stoichiometric yields were 5 an d 9%, and suggested that not all of the VS was degraded or accounted by solids analysis and methane measured. As a case study, experiment III.6 was used in lieu of components analysis to help explain discrepancies between measured cumulative meth ane yields and % VS reduction values. From analysis, 279 g of VS was lost in the biogasification process; experimental methane yield of 247 L kg VS-1 corresponded to 218 g VS, therefore 61 g of VS remained un-accounted for. At the end of experiment III.6, a positiv e 1.86g/L SCOD difference was meas ured from start and finish liquid samples. If the end solids concentration in the liquid is assumed to be 1% (close to what

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111 was measured in Study I), then 54 g VS would be additionally accounted for by both soluble and suspended volatile solids. By scrutinizing the effluent solid recovery, the balance on missing VS was accounted to within 12%. If suspended soli ds (SS) and volatile suspended solids (VSS) were accounted for, then the VS reduction re ported for bulked and un-bulked would have been close to what experimental values correspond to. Typically, VS reductions above 85% were seen in feedstocks such as sorghum halapense, or a mixture of wheat straw and dairy manure (J erger et al, 1987). Su ch feedstocks were typically operated in reactors with HRTs of 50 days, whereas tailings were shown to be successfully degraded at HRT < 10 days (bul ked experiments only). Degradation rates normalized across the entire batch duration indi cated improved volume usage efficiency. On average, bulked experiments de graded tailings at 3.1 kg VS m-3 d-1 and un-bulked experiments were measured to 1.4 kg VS m-3 d-1. In experiments I.1 and I.2 of Study I, degradation rates across a batch study averaged to 1.1 and 2.5 kg VS m-3 d-1, respectively. Therefore, pretreatment and bulking effect produced 2-fold increase in degradation efficiency per m3 of reactor volume. The extent of degradation of individual com ponents also provided insight to composition and biodegradability of sugar beet tailings. In general, the retardant component for biodegradation lignin was only 4.7% (DM) of tailings. Increased amounts of lignin are usually retardant to biodegradation by sheathing cellulose from microbial attack (Chynoweth and Pullammanappallil, 1996). In Jerger et al 1987, the lignin concentration ranged from 5 to 10% (dry matter), which suggested that most of th e cellulose, hemi cellulose and non-structural carbohydrates (NFC) fractions were converted to methane and car bon dioxide. In the case of sugar beet tailings, it was shown that NFCs (sta rch, sugar, pectin and fermentation acids) had

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112 the greatest degradation at 92% The NFCs are composed of non-cell wall carbohydrates and are readily biodegradable (Dairy One). The fibrous bulk of the forage of sugar beet tailings was the measure of hemi cellulose, cellulose and li gnin; these components ma de up the cell wall or structural carbohydrates. Through analysis, over 87% of the cellulose and 84% of hemi cellulose where found to be degraded; hemi cellulose is us ually more readily biodegradable than cellulose by anaerobic microbes (Chynoweth and Pulla mmanappallil, 1996; Tsao 1984) Lignin was thought to only solubilize by 42%, as digestibility to methane was considered limited (Odier and Artaud, 1992). Any residual un-degraded carbohydrates were assumed to have been intertwined with lignin, which prevented their degradation. The mineral compositions presented (Table 5-5) suggest that sugar beet tailings harnessed many of the nutrients required for microbi al growth. Apart from carbon, nitrogen and phosphorus are the major nutrients required for anaerobic digestion. Approximately 1.2% and 0.024% of biodegradable volatile matter is required for cell biomass nitrogen and phosphorus requirement, respectively (Chynoweth and Pullammana ppallil, 1996). From analysis, this crucial requirement was met in excess from a batch of ta ilings; nitrogen was assumed to be in sufficient ratio by observing that the extent of degradation of crude protein (various essential amino acids) was 41.3%. The recycle of inoculum from experi ment to experiment was also suspected to contribute to the overall nitrogen and phosphor us concentration. Nutrients needed in intermediate concentrations (sodium, potassium, calcium, magnesium, sulfur, etc) were also met by natural concentrations of s ugar beet tailings themselves. In Experiment III.6, an ash balance was c onducted for all the non-volatile components (i.e. minerals). Analysis determined that only 6.8% of the residue dry matter was composed of nonvolatiles; VS calculations confirme d that 60% of the dry matter lo aded was volatile, therefore an

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113 unknown was suspected. Sugar beet tailings co ntain a considerable portion of sand, which typically is characterized as SiO2. Therefore, it was speculate d that 83% of ash measured experimentally accounted for sand contained on sugar beet tailings; this component was not picked up by Dairy One, Study III further established that sugar beet ta ilings can be operated in a robust mode, requiring minimal supplements. Biomethanogenesis is known to be sensitive to several groups of inhibitors, namely to su lfides, heavy metals, halogen, hydrocarbons, VFAs, ammonia and cations (Chynoweth and Pullammanappallil 1996; Speece 1987b). The parameters that influence digester performance (VFAs and pH) were show n to be within the acceptable ranges (pH > 6.8, total VFA < 500 mg/L). The presence of inhi bitors or overloading was not suspected as experiments in series within each set did not show significant deviation in trends as a result of accumulation or toxicity. The preliminary approach to Study III as a mean s to classify the extent of biodegradation and improve on rate of conversion was sufficiently met as seen by the results. A more detailed analysis on parameters not mentioned but cons idered important in anaerobic biogasification (alkalinity, C/N ratio, to tal and free ammonia) should be ad dressed in the future. From the aforementioned findings, implications to design, operation and material handling for large scale applications in sugar beet processing should also be addr essed (Chapter 7). 5.5 Conclusions The effect of pre-treatment was shown to decrease the SCOD accumulation levels during biogasification of a 3-kg un-bulked wa ste bed of sugar beet tailings. The effect of bulking on pre-treated sugar beet tailings was show n to increase the degradation rate 3-fold; the duration to achie ve 95% of the methane potential in bulked experiments was les than 7 days whereas un-bulked experiments took nearly 15 days.

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114 The addition of a bulking agent decreased th e volume of excluded liquid inside a reactor by more than 50% during the start-up phase ; no appreciable compaction, as observed in Study I was detected in Study III. Based on the VS reduction after digestion ( 86 2 when bulked; 81 2 when un-bulked) sugar beet tailings were considered to be a highly degradable feedstock Over 90% of the NFCs in sugar beet tailings were readily degradable. The % degradation for cellulose and hemi cellulose was 87 and 84%. Robust operation of biogasification on sugar beet tailings was attained with minimal addition of supplements or minerals. Accu mulation of toxins or inhibitors was not detected at sensitivity levels that would indicate diminish ed biogasification performance.

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115 Time elapsed (days) 02468101214161820 Cumulative methane yiel d (L CH4 @ STP / kg VS) 0 20 40 60 80 100 120 140 160 Bulked Experiments (III.1-3) Un-bulked Experiments (III.4-6) Figure 5-1. Comparison of cumulative me thane production from bulked and un-bulked experiments

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116 pH 6.5 7.0 7.5 8.0 8.5 Methane Production Rate (L/L/day) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Methane fraction in biogas 0.0 0.2 0.4 0.6 0.8 1.0 pH 6.5 7.0 7.5 8.0 8.5 Time elapsed (Days) 0246810Soluble COD (mg/L) 0 2000 4000 6000 8000 10000 Methane Production Rate (L/L/d) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Methane fraction in biogas 0.0 0.2 0.4 0.6 0.8 1.0 Time elapsed (Days) 02468101214161820Soluble COD (mg/L) 2000 4000 6000 8000 10000 12000 14000 Un-Bulked Experiments Bulked Experiments Figure 5-2. Comparison of bi ogasification parameter profiles for bulked and un-bulked experiments

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117 Acetic acid (mg/L) 0 400 800 1200 1600 2000 2400 Propionic acid (mg/L) Butyric acid (mg/L) 0 100 200 300 400 500 0 50 100 150 200 Acetic acid (mg/L) 0 400 800 1200 1600 2000 2400 Propionic acid(mg/L) 0 100 200 300 400 500 Butyric acid (mg/L) 0 50 100 150 200 Time elapsed (Days) 0246810Valeric acid (mg/L) 0 50 100 150 200 Time elapsed (Days) 02468101214161820Valeric acid (mg/L) 0 50 100 150 200 Un-Bulked Experiments Bulked Experiments Figure 5-3. Comparison of VF A profiles for bulked and un-bulked experiments

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118 Table 5-1. Loading and unloading data for bulked and un-bulked experiments Experiments III.1 to III.3 (Bulked) III.4 to III.6 (Un-bulked) Wet tailings weight (kg) 3 3 Total solids (kg) 0.38 0.02 0.38 0.02 Volatile solids (kg) 0.33 0.06 0.34 0.02 Inoculum added (L) 9.0 0.5 11.8 1.2 Packing density (kg wet/m3) 250 650 Packing density (kg dry/m3) 32 2 81 4 Loading Total solids in reactor (%) 3.3 0.2 2.6 0.4 Wet residue weight (kg) 0.67 0.05 0.88 0.3 Unloading Total solids (kg) 0.050 0.01 0.09 0.02 Volatile solids (kg) 0.047 0.01 0.06 0.01 Total solids reduction (%) 86 4 76 3 Volatile solids reduction (%) 86 2 81 2 Table 5-2. Summary of perfor mance in Study III experiments aGompertz parameters (model) Experiment Final cumulative methane (experimental) bP bRm b Duration to produce 95% methane yield potential (L CH4 kg VS-1) (L CH4 kg VS-1) (L kg VS-1 d-1) (days) (days) Bulked III.1 148 153 28 0.8 7.8 III.2 130 143 20 0.7 6.7 III.3 133 149 33 0.9 5.6 c137 9 148 5 27 7 0.8 0.1 6.7 1 Un-bulked III.4 120 12.7 III.5 132 15.0 III.6 130 15.8 127 6 14.5 1.6 a Gompertz parameters derived by fitting experiment data into Modified Gompertz Model. b Symbols have their usual meaning. c Mean standard deviation of three experiments.

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119 Table 5-3. Summary of methane potential distribution in Study III Experiment Readily-solubilized fraction a Wash water methane yield bTotal cumulative methane yield (g COD/g VS) (L CH4 kg VS-1) (L CH4 kg VS-1) Bulked III.1 0.44 109 257 III.2 0.67 167 297 III.3 0.64 160 293 c 0.58 0.12 145 32 282 22 Un-bulked III.4 0.48 120 240 III.5 0.63 158 290 III.6 0.47 117 247 0.52 0.09 131 23 258 27 a Wash water biogasification potential determined from experimental efficiency in Study II. b Sum of methane potential from readily soluble fraction and solids degradation. c Mean standard deviation of three experiments Table 5-4. Chemical characteristic s of tailings and digested residue Chemical component Tailings (% VS) Residue (% VS) Extend of degradation or solubilization (% VS) Crude protein 7.3 22.8 52 Soluble protein 1.2 3.9 0 NFC 44.9 22.9 92 Lignin 5.1 19.1 42 Hemi cellulose 14.3 14.7 84 Cellulose 21.8 18.0 87

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120 Table 5-5. Mineral compositions in sugar beet tailings and residue Minerals Tailings (% DM) Residue (% DM) Calcium 1.23 2.82 Phosphorus 0.12 0.23 Magnesium 0.41 0.51 Potassium 0.92 0.60 Sodium 0.229 2.277 Sulfur 0.09 0.36 Iron 6.0 x 10-4 7.0 x 10-3 Zinc 5.9 x 10-4 5.4 x 10-4 Copper 2.7 x 10-4 2.0 x 10-4 Manganese 2.7 x 10-4 2.9 x 10-4 Molybdenum 2.7 x 10-4 7.9 x 10-4

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121 CHAPTER 6 STUDY IV RESULTS: THE EFFECT OF TWO-STAGE OPERATION ON THE BIOGASIFICATION OF SU GAR BEET TAILINGS 6.1 Introduction In Study III, it was shown that performance of single-stage biogasifi cation of sugar beet tailings can be enhanced by wash ing and bulking the solid-bed. Nota bly, a three-fold increase in degradation kinetics was obtai ned and the duration to produce 95% of the cumulative methane potential was reduced to less than 7 days (bul ked experiments only). Such kinetics were significant outcomes when compared to Study I results. The implication of accelerated biogasification was estimated to translate directly into reducing the numbe r of reactors by more than one half in commercial applications However, the application of a bulking agent to in-vessel biogasific ation technologies was regarded unconventional and efficiency of material handling operations during loading/unloading and separation of residue and bulking agent (if recycled) were challenged. Furthermore, the higher volume occupancy of a bulking agent would increase volume requirements to accommodate critical throughputs. For example, in Study III, the dry matter packing density was halved from un-bulked to bulked experiments. Therefore, any kinetic improvements offered by bulking would have to supercede practical design and economic tolerances. Study IV implemented a two-st age approach to biogasifyi ng sugar beet tailings by incorporating a sequence operation between the solids containing reactors and the anaerobic filter reactor (AFR) used to treat wash water. It was speculated that a separate second stage would have a considerable impact in alleviat ing certain limitations of single-stage batch operation (VFA accumulation, high SCOD levels, un-synchronized cooperation of microbial groups ) that were observed in Study I and Study III (un-bulked runs). The goals of Study IV

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122 were to conduct two-stage experiments on un-bulk ed tailings (with and without pre-treatment), with the exclusion of a bulking agent. It was believed that improve ments in biogasification would justify the utilization of a two-stage system (with attached film or high rate reactor) as an additional option for biogasifying of sugar beet tailings. 6.2 Background The designs and strategies employed to enhan ce biogasification of or ganic feedstocks has been thoroughly researched in the last two d ecades. Among design options, each has its own set of benefits and constraints and the selection process is usually dependent upon feedstock characterizations and/or personal preference. De signs usually depend on factors such as reactor solids concentration, mixing strategy, temperatur e and number of stages (Pullammanappallil and Chynoweth, 1996; Gunaseelan 1997 ; Mata-Alvarez and Llabres, 2000). Single-stage biogasification quite commonly is limited in or ganic loading (especially when TS> 20%); the rate of volatile acid formation due to hydrolysis and fermentati on of macromolecules (acidogenic stage) is often not synchronous with the ra te of volatile acid conversion to methane (methanogenic phase). When the acidogenic an d methanogenic processe s are not synchronized, the maximal methane gas yield is only achieved after longer retention ti mes (Sarada and Joseph, 1995). Two-phase and two-stage systems permit much higher loads and have been proven to run at lower retention times than single-stage (combi ned) systems. Figure 61 shows the block-flow diagrams comparing two-phase and two-stage syst ems (Azbar and Speece, 2001). In literature, these terms tend to be used interchangeably. For the purposes of this research, the two-phase and two-stage will be treated as separate processes. Two-phase system usually refers to the de velopment of unique biomasses in separate reactors. In this process, fermentation and methanogenesis ar e separated by using different

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123 retention times; usually, only acidogens are found in the first phase, while primarily methanogens are found in the longer SRT of the second phase (Azbar and Speece, 2001; Gunaseelan 1997; Yang et al., 2002). Phased syst ems, which produce substrate gradients and in turn metabolic intermediates (V FAs), have been found to enha nce the methanogenic conversion in the second reactor. Therefore, phase sepa ration promotes biogas formation in the second reactor for the most part; attached film reactor s are typically employed as second reactors for their ability to digest high quant ities of wastewater at low HRTs (< 10 days) without the fear of washout (Mata-Alvar ez and Llabres, 2000). In a two-stage system, acidogenic and methanoge nic reactions occur in both reactors but are operated at a different retention time. For ra pidly fermentable wastes, it has been shown that a two stage reactor can lower the overall retention time compar ed to a single stage system (Gunaseelan, 1997). The initial a pproach to biogasifying sugar be et tailings (T eixeira et al., 2005) was to use a two-stage mesophilic system in flooded mode referred to as SEBAC-2. The original SEBAC process was a dry-digestion concep t developed at the Univ ersity of Florida for bioconversion of OFMSW. The process used a leachate management strategy that provided microorganisms, moisture and nutrients for ra pid conversion of OFMS W and the removal of inhibitory fermentative products during start-up. A mature bioreactor wo uld take the leachate containing inhibitory fermentative products (such as VFAs) from the fres hly-started bioreactor and convert them to methane (Chynoweth et al., 1992; Chugh et al., 1995). This operation was called sequencing. The treated leachate was then fed back to the bior eactor containing fresh waste. The freshly-started wa ste reactor achieving pH > 6.5 and a methane composition of > 30% after a certain duration of sequencing would be considered balanced and self-sustaining and sequencing would be disengaged.

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124 Implementing SEBAC for the biogasification of raw sugar beet tailings was suspected to be limiting due to feedstock characteristics. Su ccess of SEBAC depends on the availability of a mature reactor containing a bed of degraded so lids. As leachate passes through the bed, VFAs are degraded and microorganisms, buffer and othe r nutrients are picked up. However, Study III showed degradation greater than 80% for sugar beet tailings and hardly any residue was left at the end of the run, Residue settling at the bottom was suspected to diminish the contact between microorganisms and fresh incoming leachate. Fu rthermore, the highly soluble COD component of tailings was assumed to exceed the assimilation cap acity of stabilized wast e bed in Teixiera et al., 2005. Previously, SEBAC was shown to initiate methanogenesis rapidly in feedstocks such as organic fraction of municipal solid waste, yard waste, mixtures of biosolids and yard wastes, where COD values are typically < 20 g/L (Chynoweth et al 2002). Biogasification of sugar beet tailings was speculated to be enhanced using a two-stage concept, by implementing the AFR previously used for wash water treatment (Study II). It should be noted that other high-ra te wastewater anaerobic systems could have been used as well instead of AFR. The system considered (Figure 6-2) for two-stage biogasi fication of sugar beet tailings was constructed without pr evious sizing of vessels with re spect to each other. The solids reactor (ABCR) and liquid reactor (AFR) we re operated at 12 and 18 L working volumes, corresponding to 5 and 7.5 day HRT, respectively. Bulking media in the AFR was speculated to harness sufficient attached growth for rapid conversion of incoming streams for the solids reactor; both reactors were contributors to biogas formation. 6.3 Results Experiments: A total of four experiments were c onducted consecutively in a sequenced mode with the AFR. Sugar beet tailings in E xperiments IV.1 and IV.2 were loaded in ABCRs

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125 and pre-treated exactly as un-bul ked experiments in Study III. The AFR was used intermittently to process wash water generated from pre-treat ment or sequenced with ABCR during the early stages of biogasification. Si milarly, Experiment IV.3 was also loaded with 3-kg of raw sugar beet tailings, but in-situ pre-treatment to re move the readily solubl e fraction was bypassed; biogasification and sequencing with the AFR were initiated immediately upon start-up. Lastly, experiment IV.4 was conducted to demonstrate th e utility of having an AFR when single-stage systems are overloaded; Experiment I.3 in Study I (5-kg raw tailings) was sequenced with the AFR after the termination poi nt reported in Study I. As reported in Study I and III, the performa nce of each experiment in Study IV was monitored by analysis of biogasification paramete rs. Treatment of wash water in the AFR and sequencing between AFR and ABCR for the aforemen tioned experiments is described in sections 2.10 and 2.11, respectively. Sequencing between the AFR and ABCR was carried out until process performance (methane yield, % CH4 composition, pH, decline if VFA concentration) in first stage (ABCR) showed improvements. Bi carbonate buffering was provided similar to Study I and III. Characteristics of feed and digested residue: Table 6-1 lists the loading and unloading data for the experiments in Study IV. The un-co mpacted packing density (dry basis) for all Experiments (IV.1 to IV.4) ranged between 75 to 100 kg/m3. The visible volume usage for loading 3 and 5 kg of tailings in experiments wa s approximately half and three-quarters of the working volume (12 L), respectively. Similar pr ocedures addressed in Study III were used to collect and homogenize sugar beet tailings samp les before loading each reactor. Upon loading raw tailings to digesters and flooding the TS concentration in side the 3 and 5 kg experiments were approximately 3.3 and 5.3 % TS, respectively.

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126 Residue samples from each experiment were unloaded and measured for TS and VS reduction. In opening reactors, it was observed that Experiment IV.4 had the highest visible volume reduction, approximately 80 to 90%; Experime nts IV.1 to IV.3 were visually observed to have reduced between 70 to 80%. On average, TS and VS reduction for Experiments IV.1 to IV3 were 82 2 and 88 2 %, respectively; Expe riment IV.4 yielded a TS reduction of 86% and VS reduction of 93%. Physical observations: The rise of liquid in all four experiments due to the mechanism proposed in Study III was observed during Study IV as well. However, during sequencing with the AFR, the excluded liquid level in the ABCR reduced at a rate mu ch faster rate than excluded liquid level in the un-bulked runs of Study III. It was suspected that additional hydraulic injections and withdrawals due to sequencing pr omoted separation of accumulated biogas from the waste bed. Biogasification of sugar beet tailings: The cumulative methane yield profiles for the AFR and ABCR in Experiments IV.1 to IV.4 (Figur es 6-3 to 6-6) were plotted together to highlight progression with respect to one another. The plots are also sectioned off to illustrate regions were AFR was either sequenced with an ABCR or used to trea t wash water generated from pre-treatment. The abbreviations ww a nd seq (Figures 6-3 to 6-6) symbolize regions where wash water was being treated by the AF R and sequencing between the AFR and ABCR commenced, respectively. All un-marked regions indicated that both the AFR and ABCR were operating in a solo mode. The complete su mmary of operation times (Table 6-2), and experimental cumulative methane distributions (Table 6-3) was constructed as a basis for comparison between experiments.

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127 In Experiments IV.1 and IV.2, sugar beet tail ings generated approxi mately 0.5 g COD/gVS when pre-treated with in-situ method (Study II ). Only one pass of washing was implemented, generating 12 L of 15 to 17 g/L SCOD strength wa sh water. The availability of the AFR to process the wash water was dependent the biogas ification progression in the ABCR; precedence was put on AFR sequencing with ABCR during the star t-up stages of biogasif ication to alleviate accumulation of intermediates. In Experiment IV.1, wash water was processed at the beginning of biogasification (0.7 to 2 days ) and after sequencing duties (6.1 to 10.9 days). Wash water treatment in experiment IV.2 was implemente d only after AFR sequenced operation with ABCR was halted. The processing of wash water in the packed bed was conducted at an HRT of 7.5 days in both experiments. The implementation of sequenced operation in Experiments IV.1 and IV.2 was dictated by what was observed in Study III; un-bulked experime nts exhibited poor increases in methane rate and composition between days 4 to 6. Both E xperiments IV.1 and IV.2 were operated in a twostage sequenced operation for 4.1 and 5.1 days, respectively. The on-set of sequencing on the performance parameters of both the ABCR and AF R (Figures 6-7 and 6-10) was considered an important response factor. In general, methan e production rate in the ABCR reactor was shown to improve by 0.4 to 0.6 L L-1 d-1 after a lag time (~ 2 days). The methane fraction in biogas showed dramatic increases, spanning from 25% to 55% within three days in both experiments. Similarly, the pH profiles exhibited in both ABCR and AFR showed increases at varying degrees; sequenced operation caused an increase from pH 7.8 to 8.1 in IV.1 and 7.2 to 8.1 in IV.2. The pH trends observed during the treatment of wash water in the AFR decreased to from 8.1 down to 7.4, before leveling off in to mid-range pH values (7.4 to 7.8) after four days.

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128 Soluble COD and VFA concentrations in E xperiments IV.1 and IV.2 exhibited similar trend behaviors. The SCOD concentrations in the ABCR increased as high as 10 to 14 g/L during the first three days of biogasification. U pon sequencing, a short lag time (1 to 3 days) was followed by a rapid decay of SCOD; concentrations reduced by 6 g/L SCOD in 3 days, before leveling off to values < 8 g/L SCOD. The SCOD levels in the AFR showed an increase only when effluent from ABCR was treated; concentr ations reached as high as 7 g/L SCOD before gradually falling to concentrati ons as low as 1.3 g/L SCOD within 8 days. Wash water treatment did not contribute to any increa ses to the SCOD concentration in the AFR. The total VFA concentration in the ABCR reached as high 2260 and 1600 mg/L within 1 to 3 days in both Experiments IV.1 and IV.2, respectively. Next, th e rapid decay of VFAs was observed after a 2-day lag in the sequencing stag e, where concentrations fell on average by 1000 to 1500 mg/L within 4 days and leveling off under 500 mg/L at the end of biogasification. The total VFA concentrations in the AFR during sequencing and wash water treatment were maintained below 500 mg/L during the complete duration. Experiments IV.1 and IV.2 yielded a total cumulative yield of 293 and 315 L CH4 kg VS-1, respectively. Approximately 66 % of the total cumulative yield in both stages evolved in the AFR and the remaining 34% from the ABCR; the duration to produced 95% of the total methane potential in both units was in th e range of 9.2 to 9.8 days. The two-stage concept of operating at different retention times was exercised; ABCR and AFR opera ted at 7.5 and 5 day HRTs, respectively. In Experiment IV.3, pre-treatment was bypassed on the 3 kg sample of sugar beet tailings. The AFR was sequenced with the ABCR (at HRT s mentioned in Experiments IV.2 and IV.3) immediately at the start of the run. Unlike Experiments IV.1 and IV.2, the duration to produce

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129 95% of the cumulative methane potential was lower at 7.4 days ; the total cumulative methane produced, 303 L CH4 kg VS-1. More equal distribution of me thane was observed, as 54% of the total cumulative yield evolved from the AFR and 46% from the ABCR. From start-up, Experiment IV.3 showed rapi d increases in methan e production rate and methane fraction in the biogas. In the ABCR, methane production increased to 1.6 L L-1 d-1 within 0.5 days and methane composition reache d 50% after only 3.5 days of operation. The AFR similarly achieved a max rate of 0.9 L L-1 d-1 after 1 day and reached 60% methane after 1.75 days. As biogasification progressed, the meth ane production rate in both units declined daily by 0.4 L L-1 d-1 and the methane composition increased, leveling off at 70% methane. At 4.5 days, 90% of the liquid contents in the A BCR were sequenced out and replenished by AFR liquid contents; the pH values at this point we re both at 8.05. Sequencing was terminated at 6.7 days, as methane production rate in the AFR fell to 0.1 L L-1 d-1. Experiment IV.3 SCOD profile increased to 19 g/L SCOD by the first day; the daily ABCR decay of SCOD in the sequenced stage oc curred was 3.1 g/L SCOD. After 6.7 days, the SCOD level in the leveled off just below 5 g /l SCOD. The AFR SCOD concentrations also never exceeded 5 g/L and hovered at 4.5 g/L by end of sequencing. Total VFA concentrations in the ABCR reached as high as 2200 mg/L in 2.5 da ys; rapid decay observed in IV.1 and IV.2 was consistent in IV.3 as well, where the total VFA concentration fell below 500 mg/L after 7 days of biogasification. The AFR total VFA concentra tions were also below 500 mg/L throughout sequencing duration. Figures 6-6 and 6-10 show the biogasification parameter profiles for Experiment IV.4. The start-up of this experiment was originally established in Ch apter 3, as Experiment I.3. The accumulation SCOD and VFA intermediates diminished the progression of cumulative methane

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130 yield after 6.6 days in single-stage biogasifi cation. In Study IV seque ncing with the AFR was conducted between 6.6 days and 10.5 days to revive and activate the pickle d reactor. Following a 1.5-day lag, biogasification para meters rapidly incr eased from day 8 to day 10.5: the methane production rates in the ABCR increased from 0.5 to 2.5 L L-1 d-1; the methane composition increased from 35% to 64%; and the pH increa sed from 6.6 to 7.3. Moreover, the SCOD and VFA profiles during the sequenci ng duration decreased significan tly by 16 g/L and 3000 mg/L, respectively. After the 10.5-day mark, single stage biogasification was re-instated; SCOD and VFA fell to final values of 11 g/L and 1,500 mg/L after 7 days. The total cumulative methane yield for experime nt IV.4 was experimentally determined as 319 L CH4 kg VS-1. Approximately 57% of the total cumula tive yield in both stages evolved in the ABCR and the remaining 43% from the AFR; the duration to produced 95% of the total methane potential in both units was 15.2 days. A sequencing duration of only 3.8 days was applied towards reviving the inhibited single-stage experiment aforementioned. 6.4 Discussion The problems associated with volatile fatty acids and high levels of soluble COD were shown to impede the rates of de gradation in Experiments I.3, III.4 to III.6 (Studies I and III). Implementing a two-stage operation for the biogasifi cation of sugar beet ta ilings translated to enhancing the rate at which accumulated cons tituents (SCOD and VFA) where removed and degraded; the AFR provided the necessary repl enishment of micro-org anisms, and buffer necessary for methanogenic start-up support in th e ABCR reactor; it did not rely on a certain % of digested residue Increases in the TS and VS reduction in Study IV confirmed that a substantial portion of degradable matter residing in the liquid was capable of being degraded further. From un-bulked experiments in Study III, a VS reduction of 85 1% did not coincide with the total measured

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131 cumulative methane yield, 258 27 L CH4 kg VS-1; effluent solid recovery was shown to unaccount for 12% of un-degraded VS. In un-bul ked sequenced Experiments IV.1 to IV.3, the discrepancy between the total experimentally measured yield and % VS reduction was greatly reduced. The average experimental cumulative methane yield measured was 304 11 L CH4 kg VS-1, which theoretically corresponded to 88 4% VS reduction; residue VS analysis for Experiments IV.1 to IV.3 yielded 88 2 % VS reduction. It is specu lated that sequencing increased the retention of contributing constitu ents within the AFR that would otherwise not break down as rapidly in a single-stage solids reac tor; total suspended solids in wash water and VS locked-up in reactor liquor were mineralized to methane more readily. Further evidence of increased degradation was indicated by the SCOD profiles in both ABCR and AFR, where accumulated concentrations returned or fell be low the typical starti ng values (5 g/L). The effect of sequencing in Experiments IV.1 and IV.2 circumvented the sluggish behavior observed in Experiments III.4 to III.6 betw een the second and the fourth day. Methane production rate was increased by 0.2 L L-1 d-1 and yield was improved by 10 L kg VS-1 d-1 when sequenced. It is suspected that the balance between acidogenic and methanogenic groups in the ABCR during that time was improved addition of microorganisms and removal of VFAs and SCOD. Experiment IV.3 showed that pre-treatment was not a n ecessary step implementing twostage operation with the AFR used in the research work. At a p eak organic loading rate of 2.5 g COD L-1 d-1 on the first day of sequencing, the AFRs methane production rate increased to 0.9 L L-1 d-1 with no signs of sluggish behavior. In Experi ment IV.4, the organic loading rate delivered varied between 5.3 and 3.3 g COD L-1 d-1 for the first two days of sequencing. The AFR sustained a methane production rate of 0.9 L L-1 d-1 and VFA concentrations climbed to 670 mg/L before falling below 500 mg/L. Thus, the AF R demonstrated its potential to effectively

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132 treat effluents between 5 to 40 g/L at an HRT of 7.5 days without major complications during sequencing. On the contrary, the spent digester in th e two-stage flooded mesophilic SEBAC-2 reported Teixeira et al., 2005 showed poor performance because of the process inability to treat the high amount of readily soluble organi c compounds that formed initiall y. In a SEBAC process, the leachate re-circulation strategy ensures that read ily soluble COD generated in a fresh waste bed (1st stage) would be converted to methane in th e second stage and that microorganisms, buffer and nutrients would be recycle back; this was con tingent on the basis that a significant amount of residue remains in the mature reactor, harbor ing the necessary microorganisms to carry-out degradation of incoming intermed iates (Chynoweth et al, 2002). Th e AFR used in Study IV was independent of feedstock residue; it provided a consistent centra lized treatment option that can handle high SCOD liquor from a solids reactor. However, it should be noted that thermophilic operation was a critical factor that improved the rates of degradation in the two-stage implemented in this work; the mesophilic kinetic rates of SEBAC-2 are therefore expected to be lower than thermophilic operation. The effect s of sizing the ABCR and AFR accordingly to attain optimum loading and ch aracterize boundaries should be a ddressed in the future. The concept of running two-stage sequential ba tch biogasification on su gar beet tailings with a high-rate anaerobic wastewater reactor su ggests that pre-treatment could be avoided and that higher bulking densities may be afforded in the first stage. The physical limitations of trapped biogas however may limit the latter. Experiment IV. 3, which had an in-vessel bulking density of 75 kg/m3 (dry basis), occupied 83% of the work ing volume. Therefore, the savings in pre-treatment on account of incor porating the AFR as a supporting unit process to the treatment of raw sugar beet tailings was a considerable accomplishment. High rate systems such as

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133 anaerobic filter (AF) or H ybrid UASB/AF are known to tr eat wastewaters > 5 g COD L-1 d-1. Thus, practical outlooks of incr easing the compaction density and attaining high degradation of sugar beet tailings seem promising. 6.5 Conclusions The cumulative methane potential and VS reduction in the combined two-stage ABCR/AFR system for the biogasification of su gar beet tailings were found to be 304 L kg VS-1 and 88 2%. On average, the overall methane yield cont ributions of the ABCR and AFR during twostage operation were 116 L CH4 kg VS-1 (38%) and 188 L CH4 kg VS-1(62%), respectively. The recovery of a single-stage inhibited re actor was fulfilled by sequencing with the AFR at an HRT of 7.5 days; cumulative methane yi eld and VS reduction for 5 kg of un-washed sugar beet tailings were 319 L kg VS-1 and 93% Expulsion of a pre-treatment step to remove readily soluble fraction of tailings was justified by the AFRs ability to process or ganic loading rates between 2.5 and 5.3 g COD L-1 d-1. This resulted in reducing th e total process time by 0.5 1 days The two-stage system concept of using seque ncing between a solid and liquid reactor was shown decrease the duration to produce 95% of the methane yield less than 10 days consistently.

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134 Figure 6-1. Two-phase/stage block flow diagrams

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135 Figure 6-2. Two-stage system for the bi ogasification of sugar beet tailings

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136 Time elapsed (days) 02468101214 Cumulative methane yield (L CH4 @ STP / kg VS) 0 50 100 150 200 250 ABCR: Exp IV.1 AFR: Exp IV.1 AFR wash water treatment ABCR AFR sequencing AFR wash water treatment Figure 6-3. Cumulative methane yields from ABCR and AFR in Experiment IV.1 Time elapsed (days) 02468101214 Cumulative methane yield (L CH4 @ STP / kg VS) 0 50 100 150 200 250 ABCR: Exp IV.2 AFR: Exp IV.2 ABCR AFR sequencing AFR wash water treatment Figure 6-4. Cumulative methane yields from ABCR and AFR in Experiment IV.2

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137 Time elapsed (days) 024681012 Cumulative methane yield (L CH4 @ STP / kg VS) 0 50 100 150 200 250 ABCR: Exp IV.3 AFR: Exp IV.3 ABCR AFR sequencing Figure 6-5. Cumulative methane yields from ABCR and AFR in Experiment IV.3 Time elapsed (days) 024681012141618 Cumulative methane yield (L CH4 @ STP / kg VS) 0 50 100 150 200 250 ABCR: Exp IV.4 AFR: Exp IV.4 ABCR AFR sequencing Figure 6-6. Cumulative methane yields from ABCR and AFR in Experiment IV.4

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138 Methane Production Rate (L/L/d) 0.0 0.2 0.4 0.6 0.8 1.0 Methane fraction in biogas pH 0.0 0.2 0.4 0.6 0.8 1.0 Time elapsed (Days) 024681012 7.2 7.4 7.6 7.8 8.0 8.2 8.4 8.6 Soluble COD (g/L) 0 2 4 6 8 10 12 14 16 18 Time elapsed (Days) 024681012Total VFA (mg/L) 0 500 1000 1500 2000 2500 ABCR: Exp IV.1 AFR: Exp IV.1 ww seq ww ww seq ww Figure 6-7. Biogasification parameter profile s from ABCR and AFR in Experiment IV.1

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139 Methane Production Rate (L/L/d) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Methane fraction in biogas pH 0.0 0.2 0.4 0.6 0.8 Time elapsed (Days) 024681012 7.2 7.4 7.6 7.8 8.0 8.2 8.4 Soluble COD (g/L) 0 2 4 6 8 10 12 Time elapsed (Days) 024681012Total VFA (mg/L) 0 500 1000 1500 2000 ABCR: Exp IV.2 AFR: Exp IV.2 seq ww seq ww Figure 6-8. Biogasification parameter profile s from ABCR and AFR in Experiment IV.2

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140 Methane Production Rate (L/L/d) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 Methane fraction in biogas pH 0.0 0.2 0.4 0.6 0.8 1.0 Time elapsed (Days) 024681012 7.4 7.6 7.8 8.0 8.2 8.4 8.6 Soluble COD (g/L) 0 5 10 15 20 25 Time elapsed (Days) 024681012Total VFA (mg/L) 0 500 1000 1500 2000 2500 ABCR: Exp IV.3 AFR: Exp IV.3 seq seq Figure 6-9. Biogasification parameter profile s from ABCR and AFR in Experiment IV.3

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141 Methane Production Rate (L/L/d) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Methane fraction in biogas pH 0.0 0.2 0.4 0.6 0.8 Time elapsed (Days) 02468101214161820 6.0 6.5 7.0 7.5 8.0 8.5 Soluble COD (g/L) 0 10 20 30 40 50 Time elapsed (Days) 02468101214161820Total VFA (mg/L) 0 2000 4000 6000 8000 ABCR: Exp IV.4 AFR: Exp IV.4 seq seq Figure 6-10. Biogasification parameter prof iles from ABCR and AFR in Experiment IV.4

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142 Table 6-1. Loading and unloading da ta for Experiments IV.1 to IV.4 Experiments IV.1 to IV.3 IV.4 Wet tailings weight (kg) 3 5 Total solids (kg) 0.48 0.02 0.77 Volatile solids (kg) 0.43 0.02 0.68 Inoculum added (L) 12 10 Packing density (kg wet/m3) 470 490 Packing density (kg dry/m3) 97 11 75 Loading Total solids in reactor (%) 3.3 0.1 5.3 Wet residue weight (kg) 0.93 0.2 2.25 Unloading Total solids (kg) 0.050 0.01 0.088 Volatile solids (kg) 0.05 0.05 0.047 Total solids reduction (%) 82 2 86 Volatile solids reduction (%) 88 2 93 Table 6-2. Summary of operation times for two-stage experiments Experiment Readilysolubilized fraction Wash time Sequencing duration Biogasification duration in ABCR Biogasification duration in AFR Sequencing HRT in ABCR Sequencing HRT in AFR Total process time (g COD/g VS) (Days) (Days) (Days) (Days) (Days) (Days) (Days) Two-stage IV.1 0.51 0.5 4.1 10.9 12.0 5 7.5 12.5 IV.2 0.50 0.5 5.1 10.6 10.6 5 7.5 11.1 IV.3 6.7 10.5 6.7 5 7.5 10.4 aSingle/Two-stage IV.4 3.8 17.4 4.1 5 7.5 17.4 a Refers to recovery operation of a single-stage unit sequenced with the AFR

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143 Table 6-3. Summary of cumulative methane yi eld distribution in two-stage biogasification Total Cumulative Methane Yield Duration to produce 95% methane yield potential Experiment ABCR Cumulative Methane Yield (L CH4 kg VS-1) AFR Cumulative Methane Yield (L CH4 kg VS-1) (L CH4 kg VS-1) (Days) Two-stage IV.1 101 192 293 9.8 IV.2 108 207 315 9.2 IV.3 138 165 303 7.4 Single/Two-stage IV.4 181 138 319 15.2

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144 CHAPTER 7 CONCLUSIONS AND FUTURE WORK 7.1 Conclusions The conclusions to this research work were all based on the findings from experimental studies on the biogasification of sugar beet tailings. The object ive to carry out bench-scale studies in an effort to identify critical fact ors and performance measur es during batch operation was fulfilled. Design of experiments established that feedstock characteristics and mode of operation were critical factors that influenced the rate and extent of biogasification. The implications of improved biogasification will ultima tely lead to the development of a scalable process for application to th e sugar beet industry. At the start of this research, sugar beet tailings biogasification was implemented only on mesophilic SEBAC-2 and rates of methane genera tion were poorer to that of other organic residues; cumulative methane yield and daily methane production from mesophilic SEBAC-2 did not meet expectations. To progr ess previous accomplishments, th is research tailored design and operation in flooded mode to the unique requireme nts of sugar beet tailings in thermophilic conditions. Table 7.1 and Figure 7.1 depict a final summary of data from different modes of biogasification and the corresponding cumulative me thane yield plots, respectively. Each mode was represented by the best experimental tr ial obtained on bench-sc ale. Single-stage experiments that implemented in -situ solubilization were subject ed to separate wash water treatment (SWWT) in an AFR; a lag was added to justify the time for washing. Two additional experiments not mentioned in this thesis that we re conducted included inves tigating the effect of maceration and long-term storage of inoculum on the start-up and biogasification of sugar beet tailings. Such studies provided valuable insight as to potenti al benefits of additional pre-

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145 treatment (maceration) or inocul um viability after long storage time (6 months). Appendices B and C show the biogasification performance prof iles of the aforementioned additional studies, respectively. Critical findings on the charac teristics of sugar beet tail ings and performance of highsolids, batch, thermophilic biogasification experiments were: Performance and efficiency of single-stage biogasification was limite d by organic loading. Sugar beet tailings contain a significant fraction of readily solubilizable organic matter ( ~ 0.54 g COD/g VS). Wash water generated from leaching of this organic matter yielded 0.25 L CH4 @ STP g COD-1 in a lab-scale wastewater digester (AFR) and was estimated to contribute 47% of the total methane available from tailings. Compaction of sugar beet taili ngs and exclusion of liquid from the waste bed retarded the biogasification rate during single-stage operation. The addition of a bulking ag ent overcame compaction, decreased liquid exclusion from the waste bed and tripled the biogasification kinetics. Particle-size reduction by maceration did not si gnificantly improve the reactor performance or efficiency Robust operation was attained with the re-u se of inoculum without any addition of nutrients or supplements. Storage of inoculum at room temperature for up to six months did not significantly affect the biogasification activity Two-stage biogasification using a wastewater reactor was shown to improve breakdown of VS matter locked-up in liquid phase; cumula tive methane yield was increased by 17% as compared to single-stage achievements and re sidual volatile organic acids were low. Biogasification of tailings in both single and two-stage systems showed a volume reduction between 70 to 90%. Based on the findings presented, two different de sign options can be considered for scale-up applications on the biogasificat ion of sugar beet tailings: 1. Single-stage biogasifica tion process which would take up both the duties of biogasifying sugar beet tailings and processing any wash wa ter generated from pre-treatment. System analysis would have to evaluate whether the improved kinetics ve rsus efficient volume usage would justify adding a bulking agent

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146 2. Two-stage biogasification process consisting of a solids reactor and a high-rate wastewater reactor. Sequencing between the two vessels would bypass pre-treatm ent altogether and encourage increased loading rates. This proce ss established a 3-fold increase in the rate of conversion; solids retention time was improved from 20 days to 7.4 days. The accelerated degradation observed with th e two-stage system presents significant implications for scale-up system for the sugar b eet industry. Tripling the kinetics of degradation would translate to almost a 2/3 reduction in vol ume needed for the solids vessel. Therefore, economic and technological in centives of implementing mesophilic SEBAC-2 addressed in Teixeira et al, 2005 are speculated to have im proved by incorporation a modified thermophilic two-stage system tailored to the needs of sugar beet tailings. Investigations into economic improvements however are beyond th e scope of this thesis. 7.2 Future Work This research work was the jump-off point in establishing a basis for understanding biogasification of sugar beet tailings. Considerable efforts went into fabrication and design of an experiment station to carry out batch experime nts for operating well-controlled experiments. The studies presented here open some areas of e xpansion for this research. The following topics of interest can be addressed: Recognizing that further improvements in kineti cs are possible, more iterations of process and design changes can be investigated. Fo r example, bulked and sequenced experiments could improve the rate of degradation even further. Investigating how continuous versus batc h feed operation affects the throughput and biogasification rate of sugar beet tailings. Continuous feeding could decrease the required solids reactor volume by 50% and improve solids handling issues faced in batch systems Designing gas-liquid/solid separa tion system inside the waste bed of a reactor as to circumvent biogas entrapment during the start-up of biogasification Formulate dynamic modeling and simulation on sugar beet tailings biogasification. Modeling single and two-stage system for sugar beet tailings as a validation process for experiments conducted here.

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147 Figure 7-1. Summary of different modes investigated in bi ogasifying sugar beet tailings. M ode 1: Single-stag e (no washing; no bulking; no maceration). Mode 2: Singlestage with SWWT (washing; no bulking; no maceration). Mode 3: Single-stage with SWWT (washing; bulking; no maceration). Mode 4: Si ngle-stage with SWWT (washing; bulking; maceration). Mode 5: Two-stage (no washing; no bul king; no maceration). Mode 6: Mesophi lic SEBAC-2 (no washing; no bulking, no maceration)

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148 Time elapsed (Days) 051015202530 Cumulative methane yield (L CH4 @ STP/ kg VS) 0 50 100 150 200 250 300 350 1: Mode 1 2: Mode 2 3: Mode 3 4: Mode 4 5: Mode 5 6: Mode 6 ( Mesophilic SEBAC -2) 5 6 3 4 2 1 Figure 7-2. Performance comparison for mode of operation on the biogasification of sugar beet tailings. Mode 1: Single-stage (no washi ng; no bulking; no maceration). Mode 2: Single-stage with SWWT (washing; no bul king; no maceration). Mode 3: Singlestage with SWWT (washing; bulking; no maceration). Mode 4: Single-stage with SWWT (washing; bulking; maceration). Mode 5: Two-stage (no washing; no bulking; no maceration). Mode 6: Mes ophilic SEBAC-2 (no wa shing; no bulking, no maceration)

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149 APPENDIX A PROGRAM CODE FOR CR10X ;{CR10X} ;ABCR 2 + AFR Progam ;Version 1 ;Date: February 16, 2007 ;Programmer: Ioannis M. Polematidis ;Comments: ; 1) Temperature Monitoring (Type-T Thermocouple Probe) ; 2) pH Monitoring (Campbell Sci CSIM11 pH Sensor) ; 3) Heating System (Thermolyne Briskheat Heating Tape) ; 4) Biogas Rate ;-------------------------------------------------------------------------------------------;Flag/Port/Channel Usage ;Port 1: Used to Control Heating Coil in AFR ;Port 2: Used to Control Heation Coil in ABCR_2 ;Pulse Port 1: Used to Monitor Gas Meter 3 (AFR) ;Pulse Port 2: Used to Montior Gas Meter 2 (ABCR_2) ;Diff Channel 1: Used to Monitor Temperature in AFR ;Diff Channel 2: Used to Monitor Temperature in ABCR_2 ;Diff Channel 3: Used to Monitor pH Sensor in AFR ;Diff Channel 4: Used to Monitor pH Sensor in ABCR_2 ;Flags: Set Output Flags High => Final Monitored Values are Calculated Externally ;---------------------------------------------------------------------------------------------;======================== ==================== ======================= ;*********************PROGRAM START********************************* ;======================== ==================== ======================== ;{CR10X} ;-----------------------------------------------------------------; Execution Intervals, Sa mpling and Flag Status ;-----------------------------------------------------------------1: Batt Voltage (P10) 1: 1 Loc [ Voltage ] 2: Internal Temperature (P17) 1: 2 Loc [ CR10XTemp ] ;------------------------------------------------------------------; Fail-Safe

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150 ;------------------------------------------------------------------3: If (X<=>F) (P89) 1: 1 X Loc [ Voltage ] 2: 4 < 3: 11.5 F 4: 51 Set Port 1 Low 4: If (X<=>F) (P89) 1: 1 X Loc [ Voltage ] 2: 4 < 3: 11.5 F 4: 51 Set Port 1 Low 5: If (X<=>F) (P89) 1: 1 X Loc [ Voltage ] 2: 4 < 3: 11.5 F 4: 57 Set Port 7 Low 6: If (X<=>F) (P89) 1: 1 X Loc [ Voltage ] 2: 4 < 3: 11.5 F 4: 57 Set Port 7 Low ;------------------------------------------------------------------;Temperature Control ;------------------------------------------------------------------7: Thermocouple Temp (DIFF) (P14) 1: 2 Reps 2: 1 2.5 mV Slow Range 3: 1 DIFF Channel 4: 1 Type T (Copper-Constantan) 5: 2 Ref Temp (Deg. C) Loc [ CR10XTemp ] 6: 3 Loc [ T_1 ]

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151 7: 1.0 Mult 8: 0.0 Offset 8: If (X<=>F) (P89) 1: 3 X Loc [ T_1 ] 2: 3 >= 3: 56 F 4: 51 Set Port 1 Low 9: If (X<=>F) (P89) 1: 3 X Loc [ T_1 ] 2: 4 < 3: 54 F 4: 41 Set Port 1 High 10: If (X<=>F) (P89) 1: 4 X Loc [ T_2 ] 2: 4 < 3: 54 F 4: 42 Set Port 2 High 11: If (X<=>F) (P89) 1: 4 X Loc [ T_2 ] 2: 3 >= 3: 56 F 4: 52 Set Port 2 Low ;----------------------------------------------------------------; Feeding Schedule (AFR) ;----------------------------------------------------------------12: Thermocouple Temp (DIFF) (P14) 1: 1 Reps 2: 1 2.5 mV Slow Range 3: 5 DIFF Channel 4: 1 Type T (Copper-Constantan) 5: 2 Ref Temp (Deg. C) Loc [ CR10XTemp ] 6: 20 Loc [ Tfeed ] 7: 1.0 Mult 8: 0.0 Offset 13: If time is (P92)

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152 1: 59 Minutes (Seconds --) into a 2: 60 Interval (same units as above) 3: 47 Set Port 7 High 14: If time is (P92) 1: 0 Minutes (Seconds --) into a 2: 60 Interval (same units as above) 3: 57 Set Port 7 Low ;----------------------------------------------------------------; pH Monitor Protocol (AFR + ABCR_2) ;----------------------------------------------------------------pHMult_1 = -1/(((T_1+273)/298)*58.7) pHMult_2 = -1/(((T_2 + 273)/298)*58.7) 15: Volt (Diff) (P2) 1: 2 Reps 2: 5 2500 mV Slow Range 3: 3 DIFF Channel 4: 5 Loc [ pH_1 ] 5: 1.0 Mult 6: 0.0 Offset pH_1 = pH_1*pHMult_1 pH_2 = pH_2*pHMult_ 16: Z=X+F (P34) 1: 5 X Loc [ pH_1 ] 2: 7 F 3: 5 Z Loc [ pH_1 ] 17: Z=X+F (P34) 1: 6 X Loc [ pH_2 ] 2: 7 F 3: 6 Z Loc [ pH_2 ] ;-----------------------------------------------------------------; Gas Meter Monitoring ;-----------------------------------------------------------------

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153 18: Pulse (P3) 1: 2 Reps 2: 1 Pulse Channel 1 3: 2 Switch Closure, All Counts 4: 7 Loc [ Click_1 ] 5: 1.0 Mult 6: 0.0 Offset 19: If time is (P92) 1: 0 Minutes (Seconds --) into a 2: 1 Interval (same units as above) 3: 10 Set Output Flag High (Flag 0) 20: Set Active Storage Area (P80) 1: 3 Input Storage Area 2: 9 Loc [ min_tot ] 21: Totalize (P72) 1: 2 Reps 2: 7 Loc [ Click_1 ] Q_1 = (Click_1*0.055)/1 Q_2 = (Click_2*0.055)/1 22: Set Active Storage Area (P80) 1: 1 Final Storage Area 1 2: 1 Array ID 23: Sample (P70) 1: 1 Reps 2: 9 Loc [ min_tot ] 24: Sample (P70) 1: 1 Reps 2: 10 Loc [ Q_1 ] 25: Sample (P70) 1: 1 Reps 2: 11 Loc [ Q_2 ]

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154 26: Sample (P70) 1: 11 Reps 2: 1 Loc [ Voltage ] ;-----------------------------------------------------------------; Execution Intervals, Sa mpling and Flag Status ;-----------------------------------------------------------------27: Do (P86) 1: 10 Set Output Flag High (Flag 0) 28: Real Time (P77) 1: 220 Day,Hour/Minute (midnight = 2400) 29: Sample (P70) 1: 13 Reps 2: 1 Loc [ Voltage ] 30: Sample (P70) 1: 2 Reps 2: 20 Loc [ Tfeed ] End Program

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155 APPENDIX B THE EFFECT OF MACERATION ON BIOGAS IFICATION OF SUGAR BEET TAILINGS Time elapsed (Days) 02468101214161820 Cumulative methane yiel d (L CH4 @ STP/kg VS) 0 20 40 60 80 100 120 140 160 180 200 Macerated Run 1 (VS loaded, 0.54 kg) Macerated Run 2 (VS loaded, 0.28 kg) Figure B-1. Cumulative methane yield of macerated sugar beet tailings

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156 Figure B-2. Biogasification parameters for macerated sugar beet tailings Methane Production Rate (L/L/d) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Methane fraction in biogas 0.0 0.2 0.4 0.6 0.8 1.0 pH 6.8 7.2 7.6 8.0 8.4 Time elapsed (Days) 02468101214161820Soluble COD (mg/L) 0 5000 10000 15000 20000 25000 30000 Acetic acid (mg/L) 0 1000 2000 3000 4000 Propionic acid (mg/L) 0 100 200 300 400 500 Butyric acid (mg/L) 0 200 400 600 800 1000 Time elapsed (Days) 02468101214161820Valeric acid (mg/L) 0 20 40 60 80 100 120

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157APPENDIX C ACTIVITY TEST ON DORMANT INOCULUM 0.0 15.0 30.0 45.0 60.0 75.0 90.0 105.0 120.0 135.0 150.0 01234567891011121314151617181920Time elapsed (Days)Cumulative Methane Yield L/kg VS0.000 0.500 1.000 1.500CH4 Rate L/L/day CH4 Yield @ STP CH4 Rate L/L/daySolids Methane Yield: 143 L/kg VS SWWT Methane Yield: 119 L/kg VS Figure C-1. Inoculum activity test run

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158 LIST OF REFERENCES APHA-AWWA-WPCF, 1992. Standards methods for the examination of water and wastewater, 18th edition. American Public Health Association, Ameri can Water Works Association and Water Environment Fe deration, Washington DC. Aasen, R., Boen, A.,Bergersen, O., 2006. Effect of increased porosity on short organic acids, bacterial counts and respira tion rate during composting of acidic organic waste. Proceedings of the International Conference Orbit, September 13-16, Weimar, Germany. Azbar, N., Speece, R. E., 2001. Two-phase, tw o-stage and single-stage anaerobic process comparison. Journal of Environm ental Engineering, 127 (3), 240-248. Babel, S., Fukushi, K., Sitanrassamee, B., 2004. Effect of acid speciation on solid waste liquefaction in an anaero bic acid digester. Water Research 38, 2417-2423. Boen, A., Aasen, R., Bergersen, O., 2006. Strate gies for quick establishment of high-rate composting in acidic household waste. Proceedings of the International Conference Orbit, September 13-16, Weimar, Germany. Bouallagui H., Touhami, Y., Ben Cheikh R., Ha mdi, M., 2005. Bioreactor performance in anaerobic digestion of fruit and vegetabl e wastes. Process Biochemistry 40, 989-995. Chen, Ten-hong, Chynoweth, D.P., 1995. Hydraulic conductivity of compacted municipal solid waste. Bioresource Technology 51, 205-212. Chugh, S., Chynoweth, D.P., Clarke W.P ., Pullammanappallil, P., Rudolph, V., 1999. Degradation of unsorted municipal solid wast e by a leach-bed process. Bioresource Tehchnology 69, 103-115. Chugh, S., Clarke, W., Nopharatana, A., Pullamm anappallil, P., Rudolph, V., 1995. Degradation of unsorted MSW by sequential ba tch anaerobic reactor. In Sardinia 95, Fifth International L andfill Symposium Cagliari, Italy, 66-77. Chynoweth, D. P., Srivastava, V. J., Henry, M. P., Tarman, P. B., 1980. Biothermal gasification of biomass. Energy from Biomass and Wa stes IV, Lake Buena Vista, FL, 527-554. Chynoweth, D. P., Pullammanappallil P., 1996. Anaerobic Digestion of Municipal Solid Wastes. In Palmisano, A.C. and Barlaz, M.A. eds. Mi crobiology of Solid Waste. CRC Press, Inc. Boca Raton, FL, p. 71-113. Chynoweth, D.P., Bosch, G., Earle, J.F.K., Ow ens, J., Legrand R., 1992. Sequential batch anaerobic composting of the organic fraction of municipal solid waste. Water Science Technology 25, 327-339. Chynoweth, D. P., Haley, P., Owens, J., Rich, E ., Teixeira, Welt, B., Townsend, T., Choi, H., 2002. Anaerobic composting for recovery of nutrients, compost, and energy from solid wastes during space missions Paper No. 2002-01-2351. International Conference on Environmental Systems (ICES). Chynoweth, D.P., Legrand, R., 1993. Apparatus and method for sequent ial batch anaerobic compositing of high solids organic feedstock, U.S. Patent 5269634. De Baere, L., 2000. Anaerobic digestion of solid waste: state-of-the-art Water Science and Technology 41 (3), 283-290. Fernandez, B., Porrier, P., Chamy, R., 2001. Effect of inoculum-substrate ratio on the start-up of solid waste anaerobic dige sters. Water Science a nd Technology 44 (4), 103-108.

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159 Gunaseelan, V. N., 1997. Anaer obic digestion of biomass for methane production A review. Biomass and Bioenergy 13, 83-114. Fricke, K., Santen, H., Wallman, R., 2005. Comp arison of selected aerobic and anaerobic procedures for MSW treatment. Wast e Management, Article in Press. Hartman, H., Ahring, B.K., 2006. Strategies for th e anaerobic digestion of organic fraction of municipal solid waste An overview. Water Science and Technology, 53 (8), 7-22. Hegde, G., Pullammanappallil, P., 2007. Compar ison of thermophilic and mesophilic one-stage, batch, high-solids anaerobi c digestion. Environmental Technology 28, 361-369. Jerger, D. E., Chynoweth, D. P., 1987. Anaerobi c digestion of sorghum biomass. Biomass 14, 99-113. Kayhanian, M., 1994. Biodegradability of the orga nic fraction of munici pal solid waste in a high-solids anaerobic digester. Wast e Management and Research 13, 123-136. Kim, M., Ahn, Y., Speece, R. E., 2002. Compara tive process stability and efficiency of anaerobic digestion; mesophilic vs. thermophilic. Water Research 36, 4369-4385. Lai T. E., 2001. Rate limiting factors of the an aerobic digestion of municipal solid waste in bioreactor landfills. PhD Dissertation, Departme nt of Chemical Engineering, University of Queensland, Brisbane, Australia. Lay, J-J., Li, Y-Y., Noike, T., 1998. Mathematic al model for methane production from landfill bioreactor. Journal of Environm ental Engineering 124 (8),730-736. Lissens, G., Vandavivere, L., De Baere, Biey, E. M., Verstraete, W., 2001. Solid waste digestor: process performance and practice for munici pal solid waste digest ion. Water Science Technology 44 (8), 91-102. Luniya, S., 2005. Automation of prototype soli d waste system for long-term NASA space missions. M.S. Thesis, Department of Agricu ltural and Biological Engineering. University of Florida, United States of America. Luniya, S. S.,Teixeira, A. A., Owens, J. M., Pullammanappallil, P. C. and Liu, W., 2005. Automated SEBAC-II prototype solid waste management system for long term space mission. Paper No. 2005-01-3025, Proceedings of International Conference on Environmental Systems (ICES) and Europ ean Symposium on Space Environmental Control Systems, July 11-14, Rome, Italy. Malinska, K. A. and Richard, T. L., 2006. The impact of physical properties and compaction on biodegradation kinetics during composting. Proceedings of the International Conference Orbit, September 13-16, Weimar, Germany. Mata-Alvarez, J., Mace, S., Llabres, P., 2000. Anaer obic digestion of organic solid wastes. An overview of research achievements and pe rspectives.. Bioresource. Technology 74, 3-16. Nielsen, H.B., Mladenovska, Z., Westermann, B. And Ahring, K., 2004. Comparison of twostage thermophilic (68C/55C) anaerobic dige stion with one-stage thermophilic (55C) digestion of cattle manure. Biotechno logy and Bioengineering, 86 (3), 291-300. Ong, H., Greenfield, P., Pullammanappallil, P ., 2000. An operational strategy for improved biomethanation of cattle-manure slurry in an unmixed, single-stage, digester. Bioresource Technology. 73, 87-89. Pagans, E., Barrena, R., Font, X. and Sanc hez, A., 2006. Ammonia emissions from the composting of different organic wastes Dependency on process temperature. Chemosphere 62, 1534 1542.

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160 Parawira, W., Murto, M., Zvauya, R. and Mat tiasson, B., 2004. Anaerobic batch digestion of solid potato waste alone and in combination with sugar beet leaves. Rewewable Energy 29, 1811-1823. Pind, P. F., Angellidaki, I. and Ahring, B. K., 20 03. Dynamics of the anaerobic process: effects of volatile fatty acids. Wiley Periodicals, Inc. 1-11. Sarada, R. and Joseph, R., 1996. A comparativ e study of single and two stage processes for methane production from tomato processing wast e. Process Biochemistry 31 (4), 337-340. Svensson, L. M., Bjornsson, L. and Mattiasson, B., 2007. Enhancing performance in anaerobic high-solids stratified bed dige sters by straw bed implementa tion. Bioresource Technology 98, 47-52. Teixeira, A., Chynoweth, D.P., Owens, J.M., and Pullammanappallil, P., 2005. Space-based SEBAC-II Solid Waste Management Technolog y for Commercial A pplication to Beet Sugar Industry. Paper No. 2005-01-3026. Proceedings of International Conference on Environmental Systems (ICES) and Europ ean Symposium on space Environmental Control Systems, July 11-14, Rome, Italy. Yang, K., Yu, Y. and Hwang, S., 2003. Selective optimization in thermophilic acidogenesis of cheese-whey wastewater to acetic and butyric acids: partial acidification and methanation. Water Research 37, 2467-2477.

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161 BIOGRAPHICAL SKETCH Ioannis M. Polematidis was born (on December 17, 1981) in Athens, Greece and immigrated to the United States with his mother in 1990. He received his Bachelor of Science degree in chemical engineering (graduating magna cum laude) from the University of Florida in April 2005. Thereafter, he worked as a research assi stant for 2 months in the Bioprocesses lab aiding Dr. Pullammanappallil on an on-going biofuels project, before enroll ing in the graduate school at the University of Fl orida. He obtained a Master of Science degree in agricultural and biological e ngineering in August 2007. After comple ting his graduate studies, he plans to work in the field of environmental engineering that will use the technical sk ills acquired during his studies and experiences as a student.