<%BANNER%>

High Solids Anaerobic Digestion for the Long Term Exploratory Nasa Lunar Space Missions

Permanent Link: http://ufdc.ufl.edu/UFE0041041/00001

Material Information

Title: High Solids Anaerobic Digestion for the Long Term Exploratory Nasa Lunar Space Missions
Physical Description: 1 online resource (129 p.)
Language: english
Creator: Dhoble, Abhishek
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2009

Subjects

Subjects / Keywords: als, anaerobic, biogas, biogasification, digestion, lunar, methane, nasa, spacewaste, thermophilic, waste
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

Abstract: Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science HIGH SOLIDS ANAEROBIC DIGESTION FOR THE LONG TERM EXPLORATORY NASA LUNAR SPACE MISSIONS By Abhishek Dhoble December 2009 Chair: Pratap C. Pullammanappallil Major: Agricultural and Biological Engineering 'What would it be like to live on the moon?' The National Aeronautical and Space Administration (NASA) solidified its goal of a Colonization of the Moon as a reality in the near future. The Lunar outpost will be an inhabited facility on the surface of the Moon which NASA currently proposes to construct over five years between 2019 and 2024. In a confined environment away from Earth s surface, regeneration of resources including air, water, and nutrients is essential for the crew to survive. NASA is currently funding research for a variety of solid waste resource recovery technologies that may provide useful alternatives to the current method of waste management. One of the biological technologies being tested is a type of anaerobic digestion named high-solids anaerobic digestion. The technical feasibility of applying high-solids anaerobic digestion for reduction and stabilization of the organic fraction of solid wastes generated during Lunar space missions was investigated. Anaerobic biochemical methane potential assays run on several individual waste feedstocks expected to be produced during Lunar space missions resulted in ultimate methane yields ranging from 0.01 to 0.846L g-1 solids added. Two batch systems were tested, one of which had no agitation of solids during digestion of materials and the other was mixed continuously at 180 RPM. The unmixed digester performed better than the agitated digester. The anaerobic biodegradation performance of the NASA Lunar mission waste stream was characterized in a two stage hybrid system under thermophilic conditions. Based on these characteristics, a prototype digester was designed and sized for a space mission with a four-person crew during a one year exploratory Lunar space mission. With a view to increasing methane yield and decreasing undigested solids, two options were investigated: heat treatment of waste and replacement of current plastic packaging material with biodegradable polymers. Steam heat treatment did not show any significant effect in terms of methane potential or degradation. Four different brands of compostable/biodegradable polymers available in the market were tested for their biodegradability and biochemical methane potential. The Bio Bagregistered trademark showed the most promise. Incorporating biodegradable materials could potentially enhance methane yield by 24% and reduce solid residues by 70%. Research presented here supports the use of high-solids anaerobic digestion for bioregenerative reduction and stabilization of organic components of solid wastes during extended Lunar space missions.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Abhishek Dhoble.
Thesis: Thesis (M.S.)--University of Florida, 2009.
Local: Adviser: Pullammanappallil, Pratap C.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2009
System ID: UFE0041041:00001

Permanent Link: http://ufdc.ufl.edu/UFE0041041/00001

Material Information

Title: High Solids Anaerobic Digestion for the Long Term Exploratory Nasa Lunar Space Missions
Physical Description: 1 online resource (129 p.)
Language: english
Creator: Dhoble, Abhishek
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2009

Subjects

Subjects / Keywords: als, anaerobic, biogas, biogasification, digestion, lunar, methane, nasa, spacewaste, thermophilic, waste
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

Abstract: Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science HIGH SOLIDS ANAEROBIC DIGESTION FOR THE LONG TERM EXPLORATORY NASA LUNAR SPACE MISSIONS By Abhishek Dhoble December 2009 Chair: Pratap C. Pullammanappallil Major: Agricultural and Biological Engineering 'What would it be like to live on the moon?' The National Aeronautical and Space Administration (NASA) solidified its goal of a Colonization of the Moon as a reality in the near future. The Lunar outpost will be an inhabited facility on the surface of the Moon which NASA currently proposes to construct over five years between 2019 and 2024. In a confined environment away from Earth s surface, regeneration of resources including air, water, and nutrients is essential for the crew to survive. NASA is currently funding research for a variety of solid waste resource recovery technologies that may provide useful alternatives to the current method of waste management. One of the biological technologies being tested is a type of anaerobic digestion named high-solids anaerobic digestion. The technical feasibility of applying high-solids anaerobic digestion for reduction and stabilization of the organic fraction of solid wastes generated during Lunar space missions was investigated. Anaerobic biochemical methane potential assays run on several individual waste feedstocks expected to be produced during Lunar space missions resulted in ultimate methane yields ranging from 0.01 to 0.846L g-1 solids added. Two batch systems were tested, one of which had no agitation of solids during digestion of materials and the other was mixed continuously at 180 RPM. The unmixed digester performed better than the agitated digester. The anaerobic biodegradation performance of the NASA Lunar mission waste stream was characterized in a two stage hybrid system under thermophilic conditions. Based on these characteristics, a prototype digester was designed and sized for a space mission with a four-person crew during a one year exploratory Lunar space mission. With a view to increasing methane yield and decreasing undigested solids, two options were investigated: heat treatment of waste and replacement of current plastic packaging material with biodegradable polymers. Steam heat treatment did not show any significant effect in terms of methane potential or degradation. Four different brands of compostable/biodegradable polymers available in the market were tested for their biodegradability and biochemical methane potential. The Bio Bagregistered trademark showed the most promise. Incorporating biodegradable materials could potentially enhance methane yield by 24% and reduce solid residues by 70%. Research presented here supports the use of high-solids anaerobic digestion for bioregenerative reduction and stabilization of organic components of solid wastes during extended Lunar space missions.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Abhishek Dhoble.
Thesis: Thesis (M.S.)--University of Florida, 2009.
Local: Adviser: Pullammanappallil, Pratap C.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2009
System ID: UFE0041041:00001


This item has the following downloads:


Full Text

PAGE 1

1 HIGH SOLIDS ANAEROBIC DIGESTION FOR THE LONG TERM EXPLORATORY NASA LUNAR SPACE MISSIONS By ABHISHEK DHOBLE A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2009

PAGE 2

2 2009 Abhishek Dhoble

PAGE 3

3 To the farmers of my country awaiting bioenergy revolution next decade & their service: my sole inspi ration to carry out this study

PAGE 4

4 ACKNOWLEDGMENTS I would like thank the many individuals that have contributed to make this project a success and my educational experience so enjoyable. Specifically, I would like to express my great apprec iation to Dr. Pratap C Pullammanappallil, my academic advisor and c ommittee chair, for his continual support and guidance during my time at the University of Florida. I would like to thank Dr. Ben Koopman, my committee member and professor for minor in Environmental Engineering Sciences for his insightful ideas and concepts in the field of Bioenvironmental Engineering and in taking the time to elaborate on his experiences and suggestions on my project. I would like to thank Dr Arthur A. Teixeira, my committee member for his comments and suggestions in my experiments and thesis I also owe a lot of gratitude to Sachin Gadekar for presenting me with the opportunity of meeting Dr. Pullammanappallil and encouraging me to tak e on a promising career path in Bioprocess Engineering. On a more personal note I would like to thank all of my family; without them, this would never have been possible. I would like to also thank all of my friends at the University of Florida who supported me during my studies as well. This research was supported by a gr ant from the NASA/UF Environmental Systems Commercial Space Technology Center.

PAGE 5

5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ...................................................................................................... 4 LIST OF TABLES ................................................................................................................ 8 LIST OF FIGURES ............................................................................................................ 10 LIST OF ABBREVIATIONS .............................................................................................. 12 ABSTRACT ........................................................................................................................ 14 CHAPTER 1 INTRODUCTION ........................................................................................................ 16 1.1 Backgr ound and Justification ............................................................................ 16 1.2 Objectives .......................................................................................................... 17 1.3 Thesis Organization ........................................................................................... 18 2 ANAEROBIC DIGESTION OF SOLID WASTES: A REVIEW .................................. 20 2.1 Introduction ........................................................................................................ 20 2.2 Anaerobic Digestion of Biomass ....................................................................... 22 2.3 Factors affecting Anaerobic Digestion .............................................................. 24 2.3.1 Temperature ........................................................................................... 24 2.3.2 pH ................................................................................................... 26 2.3.3 Pretreatment ........................................................................................... 27 2.3.4 Digester Designs .................................................................................... 28 2.4. Comparison of mixed and unmixed systems ................................................... 31 2.4.1 One Stage Mixed Systems ..................................................................... 31 2. 4.2 One Stage Unmixed systems ................................................................. 32 2.4.3 Comparison ............................................................................................. 32 2.4.5 Two Stage Systems ................................................................................ 33 2.4.6 Hy brid Systems ....................................................................................... 35 2.5 Conclusion ......................................................................................................... 37 3 MATERIALS & METHODS ......................................................................................... 46 3.1 Introduction ........................................................................................................ 46 3.2 Component Samples ......................................................................................... 46 3.2.1 Human Wastes ....................................................................................... 46 3.2.2 Packaging ............................................................................................... 47 3.2.3 Adhered and Uneaten Food ................................................................... 47 3.2.4 MAGS ................................................................................................... 47 3.2.5 Gray Tape ............................................................................................... 48

PAGE 6

6 3.2.6 Papers ................................................................................................... 48 3.2.7 Towels, Washcloths and Fire Retardant Clothing ................................. 48 3.2.8 Biodegradable Packaging Materials ...................................................... 48 3.3 Feedstock Preparation ....................................................................................... 48 3.4 Set Up of Biochemical Methane Potential Assays ............................................ 49 3.5 Biogasification System Set Up .......................................................................... 51 3.5.1 Anaerobic Digester ................................................................................. 51 3.5.2 Bi ogas Flow Measurement ..................................................................... 51 3.5.3 Biogas meter operation .......................................................................... 52 3.5.4 Calibration of biogas meter .................................................................... 52 3.5.5 Positive Pressure Testing ....................................................................... 54 3.6 Analysis ................................................................................................................. 55 3.6.1 Gas Analysis ........................................................................................... 55 3.6.2 Liquid A nalysis ........................................................................................ 56 3.6.2.1 pH ............................................................................................... 56 3.6.2.2 Soluble chemical oxygen demand ............................................ 56 3.6.3 Solids Analysis .......................................................................................... 56 Moisture content ..................................................................................... 56 Volatile solids .......................................................................................... 57 4 BIOCHEMICAL METHANE POTENTIAL STUDIES ................................................. 63 4.1 Introduction ........................................................................................................ 63 4.2 Biochemical Methane Potential of Lunar Wastes ............................................. 63 4.2.1 Background ............................................................................................. 63 4.2.2 Results and Discussion .......................................................................... 64 4.3 Biochemical Methane Potential of Biodegradable Packaging Material ........... 67 4.3.1 Background ............................................................................................. 67 4.3.2 Results ................................................................................................... 69 4.3.3 Discussion ............................................................................................... 69 4.3.4 Conclusions .............................................................................................. 72 5 SINGLE STAGE BIOGASIFICATION STUDIES ....................................................... 85 5.1 Introduction ........................................................................................................ 85 5.2 Background ........................................................................................................ 85 5.3 Results & Discussion ......................................................................................... 86 5.4 One Stage Biogasification of Bio Bag ............................................................... 88 5.5 Conclusions ........................................................................................................ 89 6 TWO STAGE BIOGASIFICATION STUDIES AND CONCEPTUAL DESIGN ......... 97 6.1 Introduction ........................................................................................................ 97 6.2 Two Stage Bi ogasification Studies .................................................................... 97 6.2.1 Background ............................................................................................. 97 6.2.2 Results and Discussion .......................................................................... 98

PAGE 7

7 6.3 Full Scale Conceptual Design ......................................................................... 100 6.3.1 Background ........................................................................................... 100 6.3.2 Reactor Volume Calculations ............................................................... 100 6.3.4 Sizing the second stage of two stage system ...................................... 101 6.3.5 Digester Operations .............................................................................. 102 6.3.5.1 Thermophilic System ............................................................... 102 6.3.5.2 Mesophilic System .................................................................. 103 6.4 En ergy Potential of Anaerobic Digestion Operations During 1 Year Exploratory Lunar Space Mission ........................................................ 105 6.5 Energy Requirements ........................................................................... 106 6.5.1 Energy Required for the Digester Start -Up ............................ 106 6.5.2 Heat Losses from Insulation ................................................... 107 6.5.3 Heat of Vaporization ................................................................ 107 6.5.4 Energy Requirement of Pump................................................. 108 6.6 Comparison of Lunar mission wastes digesters with Mars mission wastes ................................................................................................... 110 6.7 Conclusion ............................................................................................ 112 7 CONCLUSIONS AND FUTURE WORK .................................................................. 115 7.1 Conclusions ...................................................................................................... 115 7.2 Future Work ..................................................................................................... 116 APPENDIX A BIOGASI FICATION STUDIES FOR NASA: JOHNSON SPACE CENTER HOUSTON ................................................................................................................ 118 B PILOT SCALE STUDEY: OPERATION OF A SEMI -CONTINUOUS ANAEROBIC D IGESTER UNDER THERMOPHILIC CONDITIONS ..................... 121 LIST OF REFERENCES ................................................................................................. 125 BIOGRAPHICAL SKETCH .............................................................................................. 129

PAGE 8

8 LIST OF TABLES Table page 2 -1 Digester performance for one stage mixed system .............................................. 38 2 -2 Digester performance for one stage Unmixed system .......................................... 41 2 -3 Digester performance for multi stage system ........................................................ 44 3 -2 Formulation of Simulated Synthetic Human Feces ............................................... 58 3 -3 Description of biodegradable bags ........................................................................ 59 3 -4 Composition of stock solutions .............................................................................. 59 4 -1 Biochemical Methane Potentials of Lunar Wastes ................................................ 74 4 -2 Comparison of theoretical and experimental methane yields for Lunar wast es .. 75 4 -3 Comparison of theoretical and experimental methane potentials for Lunar wastes ..................................................................................................................... 76 4 -4 Mathis Steam Treatment Results .......................................................................... 77 4 -5 Biochemical Methane Potentials of Steam Treated Lunar Wastes ...................... 78 4 -6 Biochemical methane potential of biodegradable bags ........................................ 79 4 -7 Improved methane potential of Lunar wastes with biodegradable packaging ..... 80 5 -1 Single Stage Biogasification of Lunar Wastes ...................................................... 91 5 -2 Biogasification of Bio Bag ...................................................................................... 91 6 -1 Energy Consumption for Lunar Digesters ........................................................... 109 6 -2 Net Energy Gain for Lunar Digesters .................................................................. 109 6 -3 Initial water requirement for Lunar Digesters ...................................................... 110 6 -4 Estimates of daily solid waste stream for Mars mission (source: Haley et al 2002) ..................................................................................................................... 111 6 -5 Two stage biogasification of Lunar wastes ......................................................... 113 A-1 NASA JSC Landscape waste compositon .......................................................... 118 A-2 NASA JSC Office waste compositon ................................................................... 119

PAGE 9

9 A-3 NASA JSC Cafeteria waste compositon ............................................................. 120 A-4 NASA JSC Cumulative Methane Yield Results .................................................. 120 B-1 Feed analysis of Citrus waste .............................................................................. 124

PAGE 10

10 LIST OF FIGURES Figure page 1 -1 NASA Lunar colony pictures (Source: http://www.nasa.gov/) .............................. 19 2 -1 Simplified process steps for anaerobic digestion .................................................. 23 2 -2 Types anaerobic digestion processes ................................................................... 29 2 -3 Anaerobic digestion process .................................................................................. 30 2 -4 The scheme of the laboratory -scale one stage mixed anaerobic biogas digester. Q=Quality of a measured valu e; M=motor; T=Temperature; R=recorded values; I=instrument C=controller. (Source: Demirel et al. 2009) .... 31 2 -5 One stage unmixed syst em demonstrated by Charles for MSW (Source: Charles et al 2009 ) .............................................................................................. 32 2 -6 Two stage biogasification of Indian MSW (Source: Vietez et al 1999) .............. 34 2 -7 SEBAC system (Source: Chynoweth et al 1993) ................................................ 36 3 -1 Canisters used for steam pretreatment studies .................................................... 60 3 -2 Digester setup for biogasification studies .............................................................. 60 3 -3 Biogas U tube meter .............................................................................................. 61 3 -4 Soda Lime Scrubber .............................................................................................. 61 3 -5 Mathis Labomat used for steam treatment studies ............................................... 62 4 -1 Biochemical Methane Potentials of Individual Lunar Waste Components ........... 81 4 -2 Biochemical Methane Potentials of Steam Treated Lunar Waste Components .. 81 4 -3 Biochemical Methane Potentials of Biodegradable Bags ..................................... 82 4 -4 Steam treated Lunar waste components exposed for A)2 hours B) 1 hour C)30 min D) 15 min ................................................................................................ 83 4 -5 Degraded biodegradable bags A)Bio Bag B)Bag-to -Nature C)Eco Film D)Eco Saf e ......................................................................................................................... 84 5 -1 Comparison of Mixed and Unmixed System for Lunar Waste Biogasification ..... 92 5 -2 COD/pH variations in Mixed and Unmixed System .............................................. 92

PAGE 11

11 5 -3 Methane Yield/COD variations in Mixed and Unmixed System ........................... 93 5 -4 Cumulative Methane Yield for Biogasification of Bio Bag ..................................... 93 5 -5 COD/pH Variations in the Biogasifica tion of Bio Bag ............................................ 94 5 -6 Methane Yield/COD Variations in the Biogasification of Bio Bag ......................... 94 5 -7 Degraded samples from single stage biogasification of Lunar wastes : A) Packaging material B) Clothes C) Wipes D) Grey Tape ....................................... 95 5 -8 Degraded Bio Bag from single stage biogasification ............................................ 96 6 -1 Thermophilic Digester Operation ......................................................................... 102 6 -2 NASA Lunar Thermophilic Digesters: 3 dimensional view ................................. 103 6 -3 NASA LunarThermophilic Digesters: Top view ................................................... 103 6 -4 Mesophilic Digeste r Operation ............................................................................. 104 6 -5 NASA Lunar Mesophilic Digesters: 3 dimensional view ..................................... 105 6 -6 NASA Lunar Mesophilic Digesters: Top view ...................................................... 105 6 -7 Space Mission Waste Composition (source: Haley et al 2002) ........................ 110 6 -8 Cumulative Methane Potential of Two Stage System ......................................... 114 6 -9 Variation of cumulative methane yiedl and SCOD in digester for two stage system (Run1) ..................................................................................................... 114 B-1 Digester set up for pilot scale studies .................................................................. 123

PAGE 12

12 LIST OF ABBREVIATION S AFR Anaerobic filter reactor ALS Advance life support system ARS Air revitalization system ATCS Active thermal control system BVAD Baseline values and assumptions document BMP Biochemical methane potential BPS Biogas production system CH4 Chemical formula for methane CM Crew Member COD Chemical oxygen demand CSTR Continuous stirred tank reactor ECLSS Environmental control and life support system ESCSTC Environmental systems commercial space technology center ESM Equivalent s ystems mass EVA Extra vehicular activity FPS Food production system GC Gas chromatograph GMO Genetically Modified Organisms HAS Human accommodation system HRT Hydraulic retention time HSLAD High solids leachbed anaerobic digestion IFAS Institute of food and agricultural sciences ISS International space station IVA Internal vehicular activity

PAGE 13

13 LSS Life support system MAGS Maximum Absorption Garments MSW Municipal solid waste NASA National Aeronautical and Space Administration OFMSW Orga nic fraction of municipal solid waste OLR Organic Loading Rate OLF Organic Loading Factor RT Retention Time STP Standard Temperature and Pressure SBR Sequencing batch reactor SCOD Soluble chemical oxygen demand SEBAC Sequential batch anaerobic composting SS Suspended solids STR Stirred tank reactor TS Total solids UASB Up -flow anaerobic sludge blanket VFA Volatile fatty acids VS Volatile solids VSS Volatile suspended solids

PAGE 14

14 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science HIGH SOLIDS ANAEROBIC DIGESTION FOR THE LONG TERM EXPLORATORY NASA LUNAR SPACE MISSIONS By Abhishek Dhoble December 2009 Chair: Pratap C. Pullammanappallil Major: Agricultural and Biological Engineering What would it be like to live on the moon?" The National Aeronautical and Space Administration (NASA) solidified its goal of a C olonization of the Moon as a reality in the near future. T he Lunar outpost will be an inhabited facility on the surface of the Moon which NASA currently proposes to construct over five years between 2019 and 2024. In a confined environment away from E arths surface, regeneration of resources including air, water, and nutrients is essential for the crew to survive. NASA is currently funding research for a variety of solid waste resource recovery technologies that may provide useful alternatives to the cur rent method of waste management One of the biologi cal technologies being tested is a type of anaerobic digestion named high-solids anaerobic digestion. The tec hnical feasibility of applying high-solids anaerobic digestion for reduction and stabilization of the organic fraction of solid wastes generated during Lunar space missions was investigated. Anaerobic biochemical methane potential assays run on several individual waste feedstocks expected to be produced during Lunar space missions resulted in ultimate methane yields ranging from 0.01 to 0.846 L g1 so lids

PAGE 15

15 added. Two batch systems were tested, one of which had no agitation of solids during digestion of materials and the other was mixed continuously at 180 RPM. The u nmixed digester performed better than the agitated digester. T he an aerobic biodegradation performance of the NASA Lunar mission waste stream was characterized in a two stage hybrid system under thermophilic conditions Based on these characteristics, a prototype digester was designed and sized for a space mission with a four person crew during a one year exploratory Lunar space mission. With a view to increasing methane yield and decreasing undigested solids, two options were investigated: heat treatment of waste and replacement of curren t plastic packaging material with biodegradable polymers. Steam heat treatment did not show an y significant effect in terms of me thane potential or degradation. F our different brands of compostable/biodegradable polymers available in the market were tested for their biodegradability and biochemical methane potential The Bio Bag showed the most promise. Incorporating biodegradable materials could potentially enhance methane yield by 24% and reduce solid residues by 70%. Research presented here supports th e use of high-solids anaerobic digestion for bioregenerative reduction and stabilization of organic components of solid wastes during extended Lunar space missions

PAGE 16

16 CHAPTER 1 INTRODUCTION 1.1 Background and Justification Since the beginning of time, a human has been fascinated by the moon. The National Aeronautical and Space Administration (NASA) solidified its goal of a C olonization of the Moon as a reality in the near future. T he Lunar outpost will be an inhabited facility on the surface of the Moon which NASA currently proposes to construct over the five years between 2019 and 2024. Waste treatment and removal for missions to moon will be more challenging due to the longer mission duration regardless of complications from the environment. Waste management for such missions may employ more efficient versions of technologies than developed for Shuttle or completely different approaches may be more cost effective D epending on the mission protocols, indefinite stable storage for the end products of any waste processing scheme will be necessary. Historically wastes generated during human spaceflight are materials with no further utility requiring onl y storage until missions end. However, Exploration Waste Subsystems may reclaim resources from input wastes allowing greater closure within the overall life support system. The waste subsystem collects waste materials from life support subsystems and inter faces. Current NASA spacecraft waste handling approaches essentially rely on dumping and/or storage. For future long duration Lunar mission, it is practically impossible to get all the stored wastes back to the earth and the waste generated over a year can not be dumped in Lunar surface. The present studies highlights the importance of a tech nology called Anaerobic Digestion which not only reduces the wastes on the Lunar surface, but may provide significant fuel out of it during

PAGE 17

17 a year of exploration. An aerobic Digestion (AD) or biogasification i s a biological process in which microorganisms break dow n organic matter into methane and carbon di oxide under anaerobic ( or no oxygen) conditions The technology is ideally suited for space mission, as it does no t require oxygen. 1.2 Objectives The goal of this research was to effectively carry out bench-scale studies on the anaerobic digestion (also known biogasification) of NASA long term Lunar mission waste stream in an effort to identify critical factors and performance measures during batch operation. The research findings would ultimately lead to a proposal of a system design and operation concept for full -scale application of biogasification. This goal was chosen as a sub study on an on-going project (Biog asification Studies for Johnson Space Center, NASA: High Solids Technology) carried out over twelve months in the Bioprocess Engineering Research Laboratory, Agricultural and Biological Engineering Department, University of Florida, Gainesville. The goals of this res ea rch work were divided into four objectives. Objective 1: Determine the biochemical methane potential of NASA Luna r waste stream and the effect of pretreatment. Objective 2 : Determine the biochemical methane potentials of biodegradable ma terials as an alternative for Lunar waste packaging. Objective 3 : Evaluate appropriate process designs for anaerobically digesting Lunar mission wastes Objective 4 : Propose a full scale design for anaerobic digestion of Lunar mission waste and carry out mass and energy balances for this system.

PAGE 18

18 1.3 Thesis Organization This thesis is divided into seven Chapters Following this Chapter, the Chapter 2 reviews anaerobic digester designs used for high solids feedstocks like solid wastes and biomass. The purpose of this review was to identify process designs that would be most applicable for Lunar wastes which were then tested in laboratory scale apparat us. Chapter 3 Materials and Methods, includes description of the materials and methods employed to meet the objectives. It lists the assumptions made during the entire analysis and describes the procedures followed during the implementation. Chapters 4, 5 and 6 describe and discuss the results of the experiments that determined the biochemical methane potential assays as well as the performance of process designs tested for biogasificat ion of Lunar wastes. Chapter 6 also proposes a full scale design for Lunar mission and presents mass and energy balance for this design. Conclusions and Fu ture work, is the Chapter 7 and discusses the future work that is possible in this area.

PAGE 19

19 A B C D Figure 11 NASA Lunar colony pictures (Source: http://www.nasa.gov/ )

PAGE 20

20 CHAPTER 2 ANAEROBIC DIGESTION OF SOLID WASTES: A R EVIEW 2.1 Introduction The recent oil crisis global warming concerns and the consequent price rises have spawned considerable interest in the exploration of ren ewable ener gy sources. Biomass will be the most significant renewable energy source in the next few decades until solar or wind power production offers an economically attractive large -scale alternative. Biomass may be converted to a variety of energy forms including thermal steam, electricity, hydrogen, ethanol, methanol, and methane. Selection of the energy form is dependent upon a number of factors, including need for direct heat or steam conversion e ffi ciencies, energy transport, conversion process and hardware, economies of scale, and environmental impact of conversion process waste streams. Under most circumstances methane is an ideal fuel. Currently it represents about 20% of the US energy supply in the form of natural gas (Chynoweth et al 2001) Related to t his, an extensive pipeline distribution system and a variety of hardware are in place for its domestic, municipal, and industrial use. Compared to other fossil fuels, methane produces few atmospheric pollutants and generates less carbon dioxide per unit en ergy. Because methane is comparatively a clean fuel, the trend is toward its increased use for appliances, vehicles, industrial applications, and power generation. Although some applications require high purity methane, it can be used in a variety of stage s of purity and e ffi ciencies of transport and energy from conversion are good. (De Baere et al 1984). Other fuels such as methanol and hydrogen are not well developed commercially for production and use and are more diff icult to produce from biomass. Eth anol is becoming a popular biomass derived fuel. Although it has the advantage of easy

PAGE 21

21 storage and transport, the fermentation process for its production requires extensive feedstock pretreatment and pure culture maintenance, and energy requirements assoc iated with feed processing and product separation result in overall low process e ffi ciencies. These problems are not characteristic of processes for biological conversion of biomass t o methane. T he literature on anaerobic digestion of solid wastes may at times appear confusing or difficult to summarize, one likely reason is that it is hard to find papers with similar experimental set ups. In fact, it is precisely the appropriateness of a given reactor design for the treatment of particular organic wastes w hich forms the focus of most research papers. The comparison of research data and drawing of co n clusions is difficult because the great diversity of reactor designs is matched by an as large variability of waste composition and choice of operational parameters (retention time, solids content, mixing, recirculation, inoculation, number of stages, te mperature). Empirical knowhow is the rule and there certainly does not exist a consensus over the optimal reactor design to treat solid wastes. The reason m ost likely lies in the complexity of the biochemical pathways involved and the novelty of the technology as quoted in Vandevivere et al (2002) The focus of the present review is to categorize the rector designs used for solid feedstocks to delineate the effect of mixing, temperatu re, pH control and retention time etc on the rate of biogasification, extent of degradation and methane yields. This Chapter surveys the primary biomass sources for methane (CH4,) production reported in the literature. The vari ous operational factors like type of digester, scale of operation, mode of operation, pretreatment, HRT (Hydraulic Retention Time) OLR

PAGE 22

22 (Organic Loading Rate), pH control, methane yield and VS (Volatile Solids) reduction is tabulated for different types of feedstocks. Animal manures, sewage sl u dges and liquid effluents (<10% solids) from biomass -based industries, which are secondarily derived from the vegetation, are outside the scope of this review In this review, the extensive literature data have been t abulated and ranked under various categories and the influence of several parameters on the methane potential of the feedstocks are presented. Most of the data reported do not contain any statistical information on variability of methane yield, HRT and OLR etc., only the mean values have been reported. A few of the data from the literature lack homogeneity in conditions of measurement, units, etc. and, in some cases, the data given by individual research groups are inadequate and are not included in this ou tline. 2.2 Anaerobic Digestion of Biomass The term biomass would apply to agricultural (or forest) residues, any garbage, refuse, sludge and other discarded material resulting from community activities or commercial operations. Solid waste management has become a major concern in the world recently due to the huge quantities generated worldwide. Anaerobic diges tion is a process in which syntropic consortia of microorganisms break down organic mat erial in the absence of oxygen to produce biogas a mixture of methane and carbon dioxide. Large organic chain molecules such as cellulose and starch are broken down into simpler sugars and monomers. Non -methanogenic populations depolymerize organic polymers and ferment them to acetate, hydrogen, and carbon dioxide. M ethanogenic bacteria convert acetic acid, hydrogen, and carbon dioxide to methane (Boone et al., 1993; Smith & Frank, 1988). The digestion process begins with bacterial hydrolysis of the input materials in order to break down insoluble

PAGE 23

23 organic polymers such as carbohydrates and make them available for utilization by microbial consortia. Acidogenic bacteria then convert the sugars and amino acids into carbon dioxide, hydrogen, ammonia, and organic acids. Acetogenic bacteria then convert these resulting organic acids into acetic acid, along with additional ammoni a, hydrogen, and carbon dioxide as shown in Figure 2 1 In the absence of methanogens, fermentation products, volatile organic acids and hydrogen build up. This build-up retards the overall degradative process causing a decrease in pH which inhibits growth and stops fermentation. The overall role of methanogenesis in the biosphere is to complete the degradation process by removal of inhibitory fermentation products (Chynoweth and Pullammanappallil, 1996). Figure 21 Simplified process steps for anaerobic digestion

PAGE 24

24 Anaerobic digestion of solid waste is becoming a popular method to treat these wastes because it can generate biogas as an energy resource. For example, Canada generates approximately 1.45 x 108 t of biomass per year. Anaerobic digestion of these biomass using conventional technologies could g enerate 1.14 x 1010 m3/year of CH4 with a heating value of 4.56 x 108 GJ, which is equivalent to about 4.4 % of Canada's current annual energy use (Levin et al 2007). At the same time, the digested residue from anaerobic digestion could serve as fertilizer for plant growth (Svensson et al., 2004). Moreover, anaerobic digestion has limited impact for our environment (MataAlvarez et al., 2000). 2. 3 Factors affecting Anaerobic Digestion The common factors affecti ng anaerobic digestion process are basically temperature, pH, pretreatment of feedstock and digester design. The performance of the process and the methane yield varies considerably depen ding on these process factors 2.3.1 Temperature Anaerobic digestion may be operated in psychrophilic (12-16 oC), mesophilic (3537 oC) or thermophilic conditions (55 -60 oC). From the present survey, it was found that 88% of the literature prefered mesophlic operations. However thermophilic temperatures, the rates of degrad ation and biogasification are faster, and have greater potential to destroy weed seeds and plant and human pathogens, which is especially beneficial for reapplying the digested residue with little post treatment back on to the fields to recycle nutrients ( Koppar and Pullammanappallil, 2007). For example, in Mace et al (2003 ) found that biodegradability of municipal solid waste could be enhanced by thermophilic operation and the corresponding ultimate methane yield was about 10%

PAGE 25

25 higher The greater energy d emand for thermophilic temperature is approximately the same as the excess energy produced in the process in many cases. All the benefits of thermophilic digestion outlined above are not necessarily ap plicable under all situations. It appears the feedstoc k may have an impact on the choice of temperature. Lee et al (2009) investigated the effect of mesophilic, thermophilic and psychrophilic temperature conditions on anaerobic digestion of kitchen waste. Mesophlic system showed 24% more VS reduction than t hermophilic system. While psychrophilic system showed lowest VS degradation. In terms of methane yield, thermophilic system showed the highest followed by mesophilc and psychrophilic. It appears that a greater extent of hydrolysis or solubilization occurr ed during mesophilic digestion as inferred from the higher VS reduction, but it is likely that not all the hydrolyzed product was converted to methane as inferred from the lower methane yield compared to thermophilic temperature. The nature of inoculum ha s a bigger impact on the performance of thermophilic digester. Most thermophilic digestion studies ( Rich et al 1995 ) (Pullammanappallil et al 200) utilized an inoculum (or starter culture) that was obtained from mesophilic digester. Mesophilic digest ers are more prevalent and it is easier to obtain this inoculum. Since dominant species required for thermophilic digestion is not usually found in large numbers in a mesophilic inoculum, this leads to slower kinetics of degradation until the inoculum is well adapted for thermophilic conditions. However, studies in literature do not take into account this adaptation period. For instance, in the studies carried out by Rich et al (1995), MSW was used as a feedstock in a stirred thermophilic digester operated in batch mode. The process had to be operated for 90 days to obtain a methane yield of 0.398L/g Vs at STP. However,

PAGE 26

26 Rivard et al (1990), obtained the same methane yield in semicontinuously fed stirred mesophilic digester at a HRT of 20 days. The a pparent lack of process stability attributed to thermophilic digestion (Gallert and Winter, 1997) could be due to use of improper inoculum. Therefore, provided thermophilic inoculum is available, the applicability of thermophilic digestion for the feedst ock under consideration should be investigated as the benefits of this process temperature range outweigh that at mesophilic temperature 2.3.2 pH The effect of pH on anaerobic digestion varies between different groups of microorganisms in the digester. pH of 6.8 to 8 is optimum for methanogenesis while a broader pH range from 5 to 8 is optimum for acidogenesis (Anaerobic digestion website www.anaerobic -digestion.com/ accessed on 10/25/09 ). It should be not ed that pH is not the only cause of inhibition and indeed other substances if present above certain concentrations can inhibit t he digestion process (Frostell et al 1984). Lai (1999) clearly demonstrated that methanogenesis can be initiated fairly quickl y in a bed of MSW by providing adequate pH buffer to an extent that prevented significant drops in pH. This was more critical than supplying inoculum to start the digestion process. A deliberately pH inhibited digester was activated quickly by raising th e pH above 6.5 (Lai 1999). It is necessary to maintain pH at an appropriate set point for optimum digestion. Typically the tendency is for the pH to drop below neutral levels due to accumulation of organic acids. To some extent the process itself is ab le to generate alkalinity/buffer to maintain pH close to neutral levels. This is due to dissolution of carbon dioxide produced in the process, which dissociates to bicarbonate and carbonate ions in turning providing pH buffering capacity. To take advantage of this ability it is necessary to carefully

PAGE 27

27 manipulate the feed and recirculate leachate so as to prevent an excessive accumulation of organic acids or significant drop in pH. Leachate recirculation has been used as a means for pH control. For instanc e, Chugh et al (1989) and Charles et al (2009) demonstrated recirculation of anaerobic digester liquor as a quality pH control measure during anaerobic digestion of MSW. Many commercial te chnologies (e.g. DRANCO ) ( Citrus Summary 2004 05 ) employ leachat e recirculation as well as mixing digested residue with feed to provide alkalinity and incoulum during digestion of MSW. The other option is to maintain pH by dosing chemicals like NaOH (Yoshiyukiueno et al ., 2007; Shanmugam et al ., 2009; Wilkie et al ., 1986), HCl (Gunasselan 1998), KHCO3 (Demiral et al ., 2009; Rich et al. 1995) and Ca(OH)2 (Sharma et al ,1988; Saini et al. 1989). Systems employing pH control by dosing chemicals can be operated at greater organic loading rate (OLR). For instance, durin g anaerobic digestion of MSW, Rich et al (1995) employed pH control by bicarbonate addition to maintain pH between 7.37.4. They were able to achieve OLR of 7.8 g VS/L/d, while studies carried out by Cecchi et al (1990) on similar feedstock and digester design without any pH control could achieve OLR only up to 2.1 g VS/L/d. Even though pH control by chemical dosing may be advantageous for terrestrial applications, choice of an appropriate design that is able to manipulate pH by controlling feed rate or leachate recirculation may be economical for non-terrestrial applications as this approach does not require hauling chemicals to the lunar base. 2.3.3 Pretreatment Necessary physical pretreatment steps may include magnetic separation, comminution in a rotatating drum or shredder, screening, pulping, gravity separation etc. Ensiling reported to be an advantageous pretreatment for sugar beets (Svensson et al.

PAGE 28

28 2005). Alkali pretreatment is the most common type of pretreatment for biomass digestion to maint ain the optimal pH in the digester (Dar et al. 1987) Thermal hydrolysis or steam hydrolysis is a most common type of pretreatment for synthetic feedstock (Vargas et al. 2009) which has been also used in carrying out the studies on Lunar waste stream in later chapters. Most of the MSW feedstock were shredded before putting into the digesters. Rich et al. (1995 ) found that shredding to 0.8mm size is optimal for pilot scale batch stirred tank anaerobic digestion of MSW. Rivard et al. (1990 ) found out the ef fect of yeast extraction as a pretreatment on anaerobic digestion of MSW. In the present studies, pretreatment/preprocessing did not seem to have much more effect on methane yield. For instance, in the anaerobic digestion of MSW, Rich et a l ( 1995 ) used the shredded samples for the anaerobic digestion got the methane yield of 0.398 L/g VS which is at par of what Cecchi et al. (1990 ) got for MSW without any pretreatment and preprocessing. Pretreatment/preprocessing seemed to do well in terms of OLR. Preprocess ed MSW samples achieved 70% OLR than the unprocessed in the studies mentioned above. Pretreatment/preprocessing is the unnecessary investment of capital as it has no significant effect on methane yield. 2.3.4 Digester Designs T he anaerobic digestion proces ses used for biomass feedstock can be broadly classified into t h ree categories: one stage systems, multistage systems and hybrid systems. The biomethanization of organic wastes is accomplished by a series of biochemical transformations, which can be roughl y separated into a first step where

PAGE 29

29 hydrolysis, acidification and liquefaction take place and a second step where acetate, hydrogen and carbon dioxide are transformed into methane. In one-stage system, all these reactions take place sim ultaneously in a single reactor, whereas in twoor multi stage systems, the reactions take place sequentially in at least two reactors Figure 22. Types anaerobic digestion processes One stage systems can be operated in dry and wet mode. The system with feed having 10-15% TS are termed as Wet systems. The required TS is generally attained by dilution with water. For the systems having more than 15%TS in feed are categorized as Dry systems. Generally MSW are digested in dry systems. Anaer obic digestion occurs primarily in two steps as shown in Figure 2 -3: acid formation and methane formation. Types of Anaerobic Digesters for Solid Wastes One -Stage Systems One Stage Mixed Systems One Stage Unmixed Systems Two Stage Systems Hybrid Systems

PAGE 30

30 Figure 23. Anaerobic digestion process These processes are mediated by different groups of microorganisms, which require different nutritional compounds and environmental conditions. This could lead to some problems of stability and control if the whole process occurs in one reactor (Demirel and Yenigun, 2002; Pohland and Ghosh, 1971). Therefore, at present more researchers put their efforts into a two phase anaerobic digestion process, which means a physical separation of acid-for mers and methane-formers in two separate reactors. In this case, optimum environmental conditions for each group of microorganisms could be provided separately to improve the whole process (Demirel and Yenigun, 2002). Ghosh et al. (2000) showed that given the same operating conditions, the two-phase anaerobic digestion of municipal solid wastes exhibited 18% higher methane yield, 22% higher methane production rate and 13% higher methane concentration than the corresponding performance parameters for one-stage operation. However, others (Weiland et al., 1990) believed that it was unnecessary to treat all kinds of solid wastes in two separate reactors; it depends on the physical and chemical properties of biodegradable wastes. They recommended that one-stage ope ration could be used to treat solid waste with low protein content such as beet pulp (Weiland et al 1990). Wastes (lignocellulosics, carbohydrates, proteins, fats) Volatile organic acids (acetic, propionic, butyric, valeric acids) Biogas (methane, carbon dioxide)

PAGE 31

31 2.4. Comparison of mixed and unmixed systems 2.4.1 One Stage Mixed Systems Figur e 2 4 The scheme of the laboratory -scale one stage mixed anaerobic biogas digester. Q = Quality of a measured value; M = motor; T =T emperature; R = recorded values; I = instrument C = controller. (Source: Demirel et al ., 2009 ) One stage mixed systems are the one in which the solids are stirred continuously. Stirring is usu ally done using agitators, mechanical stirrers, magnetic stirrers etc. The systems in which whole mass of solids are stirred will be termed as mixed systems. If the solids are stationary inside the reactor and only the leachate is being stirred, such syste ms may not be classified as mixed systems. The mixed system employed by Demirel et al. (2009 ) for the biogasification of sugar beet silage is shown above.

PAGE 32

32 2.4.2 One Stage Unmixed s ystems Figure 25 One stage unmixed system demonstrated by Charles for MSW (Source: Charles et al 2009 ) One stage unmixed systems are the one in which solids are not being stirred in during the course of digestion. Unmixed systems have advantage over mixed one in terms of capital investment and energy requirement. The wet one stage unmixed system used by Charles for anaerobic digestion of MSW is shown above. 2.4.3 Compari son The important outcomes are: unmixed system seems to do better than mixed system. For instance, biogasification studies carried out on MSW showed 81.25% more methane yield in unmixed system than mixed system under same biogasification conditions. In terms of OLR, mixed system seemed to do better than unmixed one. For instance, one stage mixed system studies carried out by Cecchi et al. (1990 ) on MSW achieved OLR of 2.1 g VS/L/d while the same studies carried out by Stenstorm et al under unmixed conditions achieved OLR of 1.04 g VS/L/d.

PAGE 33

33 2. 4. 5 Two Stage Systems The rationale of twoand multi -stage s ystems is that the overall conversion process of OFMSW to biogas is mediated by a sequence of biochemical reactions which do not necessarily share the same optimal environmental conditions (Vendevivere et al., 2002) Optimizing these reactions separately in different stages or reactors may lead to a larger overall reaction rate and biogas yield (Ghosh et al., 1999). Typically, two stages are used where the first one harbors the liquefaction acidification reactions, with a rate limited by the hydrolysis of ce llulose, and the second one harbours the acetogenesis and methanogenesis, with a rate limited by the slow microbial growth rate (Liu and Ghosh, 1997; Palmowski and Miiller, 1999). With these two steps occurring in distinct reactors, it becomes possible to increase the rate of methanogenesis by designing the second reactor with a biomass retention scheme or other means (Weiland, 1992; Kiibler and Wild, 1992). In parallel, it is possible to increase the rate of hydrolysis in the first stage by using inicroaer ophilic conditions or other means (Capela et al., 1999; Wellinger et al., 1999). The application of these principles has led to a great variety of two -stage designs. The increased technical complexity of two -stage relative to single -stage systems has not, however, always been translated in the expected higher rates and yields (Weiland, 1992). In fact, the main advantage of two-stage systems is not a putative higher reaction rate, but rather a greater biological reliability for wastes which cause unstable pe rformance in one -stage systems. It should be noted however that, in the context of industrial applications, even for the challenging treatment of highly degradable biowastes, preference is given to technically -simpler one-stage plants. Biological reliabili ty is then achieved by adequate buffering and mixing of incoming wastes, by precisely controlled feeding rate and, if

PAGE 34

34 possible, by resorting to co -digestion with other types of wastes (Weiland, 2000). Industrial applications have up to now displayed little acceptance for two-stage systems as these represent only ca. 10 % of the current treatment capacity (De Baere, 1999). Figure 26 Two stage biogasification of Indian MSW (Source: Vietez et al 1999) In the two stage biogasification studies carried out on simulated Indian MSW by Vieitez et al (1999 ), solid bed reactor was used packed with a density of 160 kg/m3. The reactor was charged with 1.227 kg (dry) waste. The waste was chopped into the 2cm size pieces. Fermentation reaction stopped after about 2.5 months of solid bed fermentation at which time total volatile fatty acids concentration accumulate. It demonstrated the methane yield of 0.27 L/g VS after HRT of 295 days and 30% reduction in VS. In another kind of two stage biogasification studies carr ied out by Chug et al 1999, two solid leachbed digesters were used. Unsorted MSW shredded to 10cm was fed in

PAGE 35

35 the batch mode at pilot scale in 200 L digester demonstrated the methane yield of 0.18 L/gVS at STP with 54.7% reduction in VS. In a two phase mesophilic biogasification studies carried out on fruit and vegetable wastes by Bouallagui et al. 2004, the anaerobic sequencing batch reactor (ASBR) was used. The reactor was fed semi continuously with shredded feed. It achieved 0.337 L /g VS of methane yield at STP. The HRT varied between acidification and methane reactor by 7 days. 2. 4. 6 Hybrid Systems Hybrid systems are multistage system. All the reactors in the hybrid system act methanogenic reactor. Hydrolysis, acidification and liquefaction as well as methane formation takes place in all the digesters of the system. SEBAC is an example of hybrid system. The SEBAC system is an anaerobic sequential batch digestion process designed to overcome inoculation, mixing and instability problems common of anaerobi c reactor designs. A liquid recycle method is used to provide water, nutrients and bacteria to the fresh feedstock. Fermentation products such as volatile acids formed during start up are removed via the liquid handling system to a mature reactor where they are converted to methane. In doing so, the instability in the start up reactor is eliminated, as is the need for mixing feed and effluent. Organic matter is decomposed primarily to methane, carbon dioxide, and compost over a residence time of 1030 days. The SEBAC system requires a minimum of 3 bioreactors linked through a leachate handling, piping and pumping system. As illustrated in Figure, the anaerobic digestion process used in the SEBAC design involves three stages of digestion that occur sequentially as conversion proceeds. The feedstock is not removed, but passes through different stages over time in the same reactor vessel. In stage 1 of anaerobic digestion,

PAGE 36

36 after the shredded waste is placed into a new stage reactor, leachate will be circulated, providing inoculum, moisture, nutrients and bacteria from the nearly completed mature reactor to the new reactor. The circulation of leachate also removes volatile organic acids (VOA) formed in the new reactor during start -up and conveys them to the matur e reactor for conversion to methane and carbon dioxide (biogas). In stage 2, the activated stage, the reactor is methanogenic, and is maintained by recycling leachate upon itself. In stage 3, the mature stage, the reactor acts as a mature reactor and its l eachate is recycled with a new reactor for startup. Figure 27 SEBAC system (Source: Chynoweth et al 1993) The SEBAC process has the advantages of simple operation, low energy requirements and working conditions of low temperature and pressure, while producing methane, carbon dioxide, nutrients, and compost as valuable products. This design of SEBAC was origina lly intended for terrestrial operation with high solids feeds, such as municipal solid waste. For that application, gravity was relied upon to bring cascading liquid leachate in contact with the organic feedstock by pumping leachate into the top of

PAGE 37

37 the rea ctor and allowing it to flow by gravity and collect at the bottom for subsequent recycling. In addition, bulk density of solid wastes in the leachbed was kept low to assure sufficient permeability and enhance the leachate percolation rates. 2.5 Conclusion An extensive literature data on High Solids Anaerobic Digestion has been tabulated and the studies here form the basis for the high solids anaerobic digestion for NASA Lunar wastes. Though most of the literature on anaerobic digesion highlights the use of mesophilic system, the studies on Lunar wastes are carried out at thermophilic conditions as the acclimatized thermophilic inoculum in our lab showed better process performance and stable operations for sugar beet biogasification. The literature review hig hlights the importance of pH control in improving OLR, but in terms of space operations for future Lunar missions, it will be difficult to carry out chemicals to the Lunar base for pH control. So, Lunar wastes were biogasified with no pH control. Pretreatm ent did not seem to have much effect in terms of methane potential and it will be difficult in terms of transportation and more capital investment to carry out pretreatment/preprocessing device to the Lunar base. So, no pretreatment or preprocessing was used for anaerobic digestion of Lunar wastes. Lunar wastes were also tested for the one stage mixed and unmixed conditions as well as two stage hybrid operations. Two stage hybrid operations were chosen as it can handle any fluctuations in pH and there was need for pH control during those operations.

PAGE 38

38 Table 2 1 Digester performance for one stage mixed system Type of Waste Digester Sca l e Mode Temp (C) Pre treatment HRT (days) OLR kg VS/m 3/d pH pH Control CH4 yield (m3 /kg VS) Biogasificatio n Efficiency % VS red % Ref MSW CSTR P B 55 Shredding 90 7.8 7.3 7.4 NaHCO 3 Addition 0.398 91.97 NR Rich et al. 1995 Sugar beet silage CSTR L C 41 42 Dilution (tap water) 25 7.41 NR Daily Addition of 1 M KHCO3 NR NR NR Demiral e.al. 2009 Sunflower Oil Cake Erlenmeyer Flasks (250ml) L B 35 None NR NR 7.1 7.6 None NR NR NR Raposo et al. 2009 OFMSW CSTR (300 L) P S 35 None 25 2.1 NR None 0.399 98.24 69 Cecchi et al. 1990 MSW CSTR (3.5 L) L S 37 Yeast extraction 20 NR 7.9 KOH addition 0.324 79.26 NR Rivard et al.1990 Bermuda Grass CSTR (7 L) L S 35 Grinding (<0.5mm) 12 1.6 NR None 0.219 53.92 37.5 Ghosh et al, 1985 Fruit & Vegetable Waste CSTR (5 L) L S 35 Drying (60 C) & Grinding (2mm) 20 2.0 7.8 None 0.400 98.48 NR Gunaseela n 2004

PAGE 39

39 Table 2 1. Continued Jatropha Curcus CSTR (5 L) L S 35 Drying (60 C) & Grinding (2mm) 20 2.0 7.8 None 0.350 86.17 NR Gunaseela n 2004 OFMSW CSTR (300 l) P B 35 None 14 4.3 6.9 7.3 None NR NR NR Cecchi et al. 1998 Woody biomass CSTR (5 L) L B 35 Size reduction(0.8 mm) 20 1.6 6.8 7.1 None 0.39 96.02 NR Turick et al. 1991 Fruit & Vegetable Waste CSTR (10 L) with solid recycling L C 35 37 Hammer milling NR 3.87 6.2 8.0 NaHCO 3 Addition 0.335 82.48 93.2 Lane 1984 Fruit & Vegetable Waste CSTR (60 L) L S 28 30 Sun drying & Grinding 20 40 NR Adjustin g OLR 0.600 150.17 NR Viswanath et al ,. 1 992 Jerusalem Artichoke CSTR (10 L) P S 37 Ensiling 46 2.6 NR None 0.307 75.10 61.00 Gunnarso nt et al. 1985 Gliricidia Leaves Aspirator Bottles (magnetic stirring) (3 L) L B 29 35 None NR NR 6.2 None 0.181 44.56 37.50 Gunaseela n, 1998

PAGE 40

40 Table 2 1. Continued Napier Grass CSTR (4 L) L S 35 Drying 20 1.23 7.0 NaOH Addition 0.113 27.82 NR Wilkie et al. 1986 Beet Pulp STR P S 55 Milling 27 5.7 NR None 0.358 82.00 81.00 Frostell et al. 1984 Water Hycinth Uplflow STR (5 L) L S 25 Size reduction 15 1.6 NR None 0.420 106.88 NR Chynowet h et al 1982 Poultry slaughterhou se waste Stirred acrylic digester L S 31 None 50 2.1 NR None 0.550 137.19 64.00 Salminen et al. Vine shoots CSTR (2 L) L S 55 NaCl treatment 20 1.0 7.2 None 0.315 72.83 NR Jimenez et al.,1 990 Note:

PAGE 41

41 Table 2 2 Digester performance for one stage Unmixed system Type of Waste Digester S c a l e M o d e Te mp. (C) Pretreatment HRT days OLR kg VS/m 3/d pH pH Control CH4 yield (m3 /kg VS) Biogasifi cation Efficienc y % VS red % Ref Sugar beet tops & wheat straw Solid phase reactor L B 35 Ensiling 62 NR NR None 0.259 63.76 NR Svensson et al., 2005 Floating lid reactor (259 m3) P B 35 Ensiling 40 1.06 8 NR None 0.381 93.81 NR Korean food waste Serum Bottle (500 ml) L B 35 Crush/screw press 28 NR 7.8 None 0.403 99.22 NR Lee et al.,2009 Solid municipal sludge NR P B 36 Thermal hydrolysis (170 C) 15 NR 7.8 None 0.580 142.34 53.50 Jolis, 2009 NR P B 55 Thermal hydrolysis (170 C) 5 NR 7.5 None 0.860 198.83 61.60 Swine waste ASBR (5 L) L S 25 Dilution (tap water) 98 2.20 7.5 7.9 None 0.310 78.89 NR Garcia et al, 2009 Leather fleshing with MSW Duran bottles L B 35 Minces & homogenized with a commercial blender 35 NR 6.5 addition of either 6 N NaOH or 1 N HCl. 0.457 112.52 68.60 Shanmugam et al.,2009 MSW Di COM reactor (7 L) L B 55 Pre aeration (48 hrs) 70 7.00 6.5 recirculation of leachate/anaero bic liquor NR NR 41.00 Charles et al.,2009

PAGE 42

42 Table 2 2 Continued Mixture of fresh sugar beet leaves & e ley crop Water jacketed Plexiglas column reactor L S 33 Ensiling NR 2.00 NR None 0.360 89.22 NR Svensson et al. 2007 Beet tops Stratified bed P S 35 Crushing & Ensiling NR 2.05 NR None 0.330 81.25 NR Svensson et al. 2007 Beet silage NR L C 35 Dilution (tap water) 24.8 2.6 7.12 None NR NR NR Demirel, 2009 Tomato processing wastes Mini B (5 L) L S 35 Air drying & powdering 24 4.3 7.0 None 0.420 103.41 NR Sarada et al. 1994 Silk worm pupae waste Bioreactor (1.5 L) L B 32 Defattation 30 1.0 7.95 None 0.380 95.10 51.00 Viswanath et al.,1994 Straw Serum Bottle (120 ml) L B 35 Ball milling, dilution (tap water) NR NR 7.6 7.9 None 0.033 8.13 NR Hashimoto, 19 89 Terrestrial weed Aspirator Bottle (2 L) L B 28 Homogenizati on in blender (0.5 mm sieve size) pretreatment with HCl or NaOH NR NR 7.8 8.0 None 0.236 59.46 65.90 Gunaseelan, 1995 Sorghum Cultivars BMP assay L B 35 Grinding (0.8 mm) NR NR 7.3 7.5 None 0.400 98.48 92.00 Chynoweth et al.,1 987 Lantana Camera Winchester bottles (3 L) L B 31 Alkali pretreatment NR NR NR None 0.241 60.12 NR Dar et al.,1987 Mirabilis leaves Erlenmeyer conical flasks (1 L) L B 36 Drying 56 NR 5.4 6.8 None 0.242 59.39 42.60 Sharma et al. 1987

PAGE 43

43 Table 2 2 Continued Lignocellulosic materials BMP assay (260 ml) L B 35 Shredding NR NR NR None 0.333 81.99 NR Tong et al. 1990 Agricultural & Forest residues Aspirator bottle (5 L) L B 37 Grinding NR NR 6.7 7.2 using calcium hydroxide (Glaxo). 0.249 60.91 38.7 Sharma et al. 1988 Woody biomass Aspirator bottle (5 L) L B 37 None NR NR 6.5 7.1 using Ca(OH)2 slurry 0.426 104.21 59.10 Sainai et al 1989 Calotropis procera leaves Glass vials (0.1 L) L B 35 Shredding & grinding NR NR 7.1 8.1 None 0.280 68.94 64.50 Mahamat 1989 Spent sugar beet pulp Non stirred reactor L B 55 None 7 4.0 NR None 0.336 77.00 96.00 Koppar et al.,2008 MSW Solid bed digester (50 G) P t B 35 Magnetic separation 30 1.04 NR None 0.560 137.88 NR Stenstrom et al. Sugar beet press pulp Solid Bed Digester (24000 m3) F B 37 Pulping NR 9.5 NR None 0.072 20.00 75.00 Brooks et al. 2008 Sorghum, corn, cellulose mixture Digester (20 L) L B 55 None 16.7 10.0 NR None 0.380 87.86 90.70 Richards et al. 1992 Office paper Serum bottles (160 ml) B B 35 Alkali pretreatment 200 NR NR None 0.300 83.33 80.00 Clarkson et al. Dairy manure Non stirred tanks L C 36 None 2 6 NR None 0.150 50.00 NR Jewell et al. Parthenium solids NR L B 24.2 Drying, homogenizati on 20 2.06 8.1 Addition of 0.8 N HCl 0.173 44.14 62.42 Gunaseelan 1998 Cattle manure slurry Bioreactor (10 L) L B 35 Size reduction 10 NR NR None NR NR NR Ong et al. 2000

PAGE 44

44 Table 2 3 Digester performance for multi stage system Type of Waste Digester S c a l e M o d e Temp (C) Pretreatment HRT (days) OLR (kg VS/m3 /d) pH pH Control CH4 yield (m3 /kg VS) Biogasificat ion Efficiency % VS red % Ref Unsorted MSW Solid leachbed (200 L) P B 35 Stredding (10 cm) 18 NR 7.0 Leachate recirculation 0.180 50.00 54.70 Chug et al. 1999 Unscreened dairy manure Non stirred tanks L C 36 None NR 6.0 NR None 0.151 50.00 NR Demirer et al. 2005 Solid poultry slaughterhous e waste Stirred acrylic digester L S 31 None 100 2.1 NR None 0.550 137.20 64.00 Salminen et al .,2002 Mixed unsorted MSW Solid leachbed (42 L) P B 38 Shredding 21 NR NR None 0.180 50.00 NR Clarke et al.,1999 Agricultural residues Solid bed UASB (Stage 1: 7.6 L) (Stage 2: 2.6 L) P B 35 Size reduction 36 4.1 NR None 0.204 56.67 NR Parawira et al.,2008 Fruit & Vegetable waste ASBR L S 35 Shredding 3 & 10 1.27 NR None 0.337 93.61 95.00 Boullagui et al.,2004 Grass Solid bed upflow P B 25 None 190 0.11 NR None 0.145 40.27 67.00 Yu et al.

PAGE 45

45 Table 2 3 Continued Potato waste Solid bed for stage 1 & UASB for stage 2 L B 37 Size reduction to small pieces in kitchen blender 50 1.26 NR None 0.390 95.22 95.00 Parawira et al.,2005 White cabbage leaves Digester (3 L) L B 35 None NR NR NR None 0.382 94.05 NR Zubr, 1986 Fruit & vegetable waste Up flow sludge bed reactor L C 35 None NR NR NR None 0.383 94.30 90.00 Viturtia et al.,1989 Garbage and paper wastes CSTR (200 L)for stage 1 & IRPR (500 L) for stage 2 P C 60 & 55 Pulverization & shredding 8 15.7 5.8 6.0 6.25N NaOH Addition NR NR 87.80 Yoshiyukiueno et al.,2007 Simulated Indian MSW Solid bed reactor L B 25 & 35 Chopping into 2cm size pieces 295 NR NR None 0.270 75.00 30.00 Vietez et al.,1999 Kitchen garbage CSTR L C 70 & 35 None 4 1.99 7.84 Leachate recirculation 0.306 75.34 61.3 Lee et al. 2009 55 4 1.01 8.03 0.351 81.15 49.6 65 4 1.01 8.00 0.293 65.74 31.8 Note: L=Lab Scale, P=Pilot Scale=Full Scale, B=Batch, C=Continuous, S=Semi continuous, Temp=Temperature Red.=Reduction, Ref=Reference

PAGE 46

46 CHAPTER 3 MATERIALS & METHODS 3.1 Introduction In this Chapter the materials used to simulate the solid waste stream for long term NASA lunar space missions are described. Two types of experiments were carried out: the biochemical methane potential assay and biogasification studies. The setup for both type of studie s are explained along with their operation. The Chapter proceeds in describing the details of the procedure used to carry out various analyses during present studies. The biochemical methane potential studies were carried out in a small serum bottles while biogasification studies were carried out in a 5 liter bioreactor. To see the effect of heat on the biodegradability and methane potential of the samples, steam treatment experiments were carried out. For the steam treatment Experiment the Mathis equipment shown in Figure 3 5 was used. The Chapter concludes by describing the analytical techniques used to carry out measurements on critical biogasification parameters. 3.2 Component Samples Based on the Historical Values from previous Shuttle and ISS miss ion, predicted useful waste products that could be generated from a Lunar mission were simulated in our laboratory. The components of this waste stream is as described in Table 3-1. The description of each component is as follows: 3.2.1 Human Wastes Form ulation of synthetic human waste was adopted from Simulated Human Feces for Testing Human Waste Processing Technologies in Space Systems, Kanapathipillai Wignarajah and Eric Litwiller, Enterprise Advisory Services Inc., NASA -Ames Research

PAGE 47

47 Center (2006-01 -2 180) as shown in Table 3.2. The goals were to mimic the true water retention properties of feces and to best fit the chemical composition and consistency reported in literature. By critically evaluating previously used formulations and the composition, both physical and chemical, the stimulant was prepared as reported in Simulated Human Feces for Testing Human Waste Processing Technologies in Space Systems (Wignarajah et al 2006). The starting chemicals in the synthesis were: Cellulose CnH2n 2On Polyet hylene glycol H(OCH2CH2)n OH Peanut oil CH COOH Psyllium powder Dietary fiber CnH2n 2On Miso (Soya powder product) 38% proteins; 21% Fats; 20% fiber; 4% minerals 3.2.2 Packaging Historical data from previous missions suggests that packaging includes 50% polyethylene and 50% polystyrene materials (Exploration Life Support Baseline Values And Assumptions Document, JSC 64367, DRART July2, 2008). Polyethylene was simulated using an empty milk can while polystyrene was simulated with commercial styrofoa m cups 3.2.3 Adhered and Uneaten Food Adhered and Uneaten food was quantified to have 27.5% Glucose, 22.5% Fat and 50% Protein. Glucose was simulated with dextrose, fat with squalene and protein with L -isoleucine ((Exploration Life Support Baseline Valu es And Assumptions Document, JSC -64367, DRART July2, 2008). 3.2.4 MAGS MAGS are Maximum Absorption Garments to catch metabolic wastes. MAGS were simulated with the wet wipes sent by NASA (catalog No.USAW1070NSDS)

PAGE 48

48 3.2.5 Gray Tape Gray tapes are made up of 8 0% polyethylene polymer and 20% butadiene polymer. Scotch electrical gray tapes available in the local stores were used to simulate this. 3.2.6 Papers Composition of the paper includes cellulose (glucose polymer), wood fiber( with 65.8% glucose, 19.8% xylose, 12.5% galactose and 1.3% mannose). A4 size printing office papers were used to simulate this. 3.2.7 Towels, Washcloths and Fire Retardant Clothing Towels were simulated with the cotton. Clothes were simulated with the Sears Fire Ret ardant Welding Cloth having 95% cellulose with polybenzimidazole as fire retardant. 3.2.8 Biodegradable Packaging Materials There are various types of biodegradable plastic materials available in the market. A few of these materials for example, poly lactic acid based packaging materials have already been tested in our laboratory for its anaerobic biodegradability (Moreira, 2009). Therefore, other types of biodegradable materials were tested in this study. The materials were tested were in the form of compostable garb age bags as these were easy to obtain. The biodegradable plastic bags samples used for the present studies are those recommended by Biodegradable Products Institute. The description of the products is listed in Table 3-3. 3.3 Feedstock Preparation Each of the chemicals used for the simulation of lunar waste stream were stored at normal room temperature away from direct exposure to sunlight. MAGS were stored in

PAGE 49

49 the zip lock bags to avoid evaporation of the moisture. Each of the biodegradable garbage bag sample received from the provider was stored at normal room temperature. Samples were shredded into 1mm x 1mm pieces before transferring into the assay bottles for biochemical methane potential studies. No pretreatment or shredding was done for both si ngle stage and two-stage biogasification studies. For the steam pretreatment experiments, steel canisters as shown in the Figure 31 were used. Unshredded sample was fed into each canister with 150 ml of distilled water. The steam treatment at 160oC was carried out in the Mathis equipment shown in Figure 35. Canisters were removed from the Mathis at the time intervals of 15 min, 30 min, 1 hr and 2 hrs. Canisters were then allowed to cool to room temperature, all the gases were vented off in the fume h ood and the samples were filtered using Whatman filter paper. The samples were air dried for 24 hours and then transferred into the assay bottles. 3.4 Set Up of Biochemical Methane Potential Assays The Biochemical Methane Potential procedures employed w ere developed from the anaerobic Warburg test combined with serum bottle techniques by Owen et al. (1979). Modifications to these procedures are also outlined in ASTM (1992) and examples of results can be found in Owens and Chynoweth (1993). The BMP assay was conducted with Corning No.1460, 500 ml serum bottle. Each bottle was fed with 5 g (total weight) of the shredded samples. In each serum bottle, 200 ml of inoculated media (inoculum and nutrient solution) was added to the 5 g of sample. Bottles were sealed with rubber serum caps of appropriate size. Sealed bottles were inverted and incubated at 55oC. Each assay was accompanied with blank controls containing only inoculated medium. Each component

PAGE 50

50 of the Lunar waste mix was tested. Shredded samples o f feedstocks were anaerobically incubated, in a sealed serum bottle, with the standard media and inoculum until gas production had ceased. Each solution used to make the anaerobic media possess a specific function for the overall success of creating an ideal anaerobic environment. Stock solution (S 1) containing resazurin, a redox indicator, assures the media is in the reduced state and turns the media pink when oxygen is present (Chynoweth and Owens, 2000). Stock solution (S -2) contains macronutrients that assure nitrogen, phosphorus and potassium are not limiting. Stock solution (S 3) contains micronutrients that assure appropriate trace metals are available in the final media. Previously, the micronutrient solution lacked a source for nickel (Owen et al., 1979) but studies showing the importance of nickel in methanogen metabolism resulted in its addition to the defined media (Chynoweth and Owens, 2000). Sodium sulfide solution, a reducing agent, is included in another stock solution (S -4) and serves to rem ove any remaining available oxygen in the media after preparation. Sodium bicarbonate, the final chemical added, provides pH buffering to assure acidification of the substrate does not cause an inhibitory pH drop. Concentrated stock solutions were used for preparing the defined media as suggested by Owen et al (1979) and are stored at 4C. The defined media contains nutrients and vitamins for mixed anaerobic cultures. The composition is tabulated in Table 34. This process can take up to 30 days for simple substrates, such as sugars and starches, and up to 120 days for recalcitrant lignocellulosic substrates, such as cypress (Chynoweth and Owens, 2000). Single bottles of Bio Bag, Bag -to Nature and Eco

PAGE 51

51 Film while duplicate bottles of Eco -Safe were a ssayed for biochemical methane potential. 3.5 Biogasification System Set Up 3.5.1 Anaerobic Digester Two types of digesters were used in these experiments: mixed and unmixed. A digester was constructed by modifying a Pyrex glass jar. The volume of the dige ster was 5 liters. The digester was sealed with a top lid, using an O -ring fitted for gas and liquid tightness and clamped with a stainless steel clamp. Three ports were provided at the top of the lid, one for gas outlet, and others for sample withdrawal. The digester was also equipped with an outlet at the bottom from which liquid samples were collected. No additional mixing device was applied for the unmixed system. Magnetic stirrer was used for mixed stirred reactor system. The digester was placed in an incubator where the temperature was maintained at 55oC. The digester set -up is shown in Figure 3-2. 3.5.2 Biogas Flow Measurement Many conventional technologies exist when gas flow measurement is a parameter of interest. Diaphragm, rotary and turbine gas m eters are common in many industrial and commercial applications, but are limited for high and steady flow conditions. In these studies, the biogas flow rate is low which is not detected by these flow meters. Raw biogas produced from anaerobic digestion of organic matter can cause erroneous flow readings on conventional devices due to moisture and other impurities in the biogas and flow that is intermittent and delivered in packets. For such a purpose, a special U -tube gas meter was used to efficiently meas ure the gas flow by liquid displacement. (Figure 33).

PAGE 52

52 3.5.3 Biogas meter operation A liquid displacement flow meter (U tube design) was used to measure biogas flow from digester. This design circumvents the deficiencies of the conventional meters by havin g error free operation even if gas flow is intermittent, high in moisture and contains impurities and also for low flow rate. The active components of the circuit include a 3way solenoid valve, a float switch, an electromechanical counter, a time delay relay 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 second leg rose to a certain level, the float switch tripped, causing three events to occur simultaneously: a signal was sent to the counter 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 the vent line open long enough to equilibrate the levels. During the vent cycle, the reactors biogas was isolated from the gas meter. With each switch closure, the counter continued to increment the amount of gas flowing through the meter; cumulative counts per given period would yield a volumetric gas flow rate. 3.5.4 Calibration of biogas meter Biogas flow was measured by determining the relationship between the counter increment and t he volume of incoming gas required to trigger 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 syrin ge of known volume and accuracy (100 1 mL) was used to determine the amount of simulated biogas required to induce one counter increment.

PAGE 53

53 Calibration protocol included injecting a series 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 (standalone gas meter) and on line mode (gas meter connected to reactor vessel) during low or no biogas production. The final result of the calibration was an input output relationship, called a calibration factor with units mL of gas/count. The precision of calibration factors were characterized by reporting the standard deviation of a population of repeated measurements. Typically, a series of ten injections were deemed as adequate population for determining a gas calibration factor. Values of 55 3.2 mL per count were obtained regularly during calibration protocols. This level of measured resolution (one gas click) on each gas meter was sufficient to provi de insight about biogas production trends within a period of study (7-120 days). In gas measurement applications, the relationship between intensive properties (e.g.,temperature and pressure) and gas behavior were considered. The ideal gas law can be appli ed to real gases when absolute 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 characterizing and predicting the behavior of biogas. The strong relationship between gas temperature and volume received attention during calibration of biogas meters. During experimentation, biogas was produced at 55C in each vessel and measured externally at a lower temperature. 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 cooling, a

PAGE 54

54 conservative correction factor was 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 factor was multiplied by a correction factor (= 273.15 328.15 C ) to conservatively estimate gas produced in each biogasification vessel. 3.5.5 Positive Pressure Testing The performance of biogasification experiments was initially evaluated by the quantity of biogas produced per given time. Biomass is mineralized to a methane and carbon dioxide gas mixture from available substrate (solid feedstock and soluble constituents) and released from the bed by buoyancy; subsequently, measurements of gas mixture volumes and composition provide explicit insight to biogas production rate and implicit insight to biochemical progression, respectively. With performance measure being so highly dependent on gas collection, efforts were taken to correctly seal and minimize gas leaks. Possible leak areas considered were as follows: Fitt ings for gas outlet (at top of lid) U -tube meter Biogas tubing (vessel -to meter line) Top -lid gasket The leak test consisted of pressurizing the vessel and gas meter system to comparable values seen during biogasification experiments. Each system was 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 i n going column was marked to detect changes over time; liquid soap was applied at the aforementioned leak areas to detect any leaks.

PAGE 55

55 3.6 Analysis 3.6.1 Gas Analysis Assay bottles were periodically analyzed for gas production and composition for more than 120 days. Gas volume sampling and removal during incubation was performed with glass syringes (5 -30 ml depending on gas volume) equipped with 23gauge needles. Readings are taken at the room temperature and the syringe is held horizontal for measurement. Volume determinations are made by allowing the syringe plunger to move (gently twirling to provide freedom of movement) and equilibrate between bottle and atmospheric pressure. The gas samples were analyzed with a Model 1200 Fisher Gas Partitioner. The GC wa s fitted with two 6-feet Haysep 80/100 mesh columns containing Porapak Q support. Ultra high purity Helium (99.99%) was used as the carrier gas at an operating head pressure of 15 psi. The gas was analyzed for its methane, carbon dioxide, nitrogen and oxyg en content. The GC was calibrated with an external standard containing N2:CH4:CO2 in volume ratio of 25:45:30. Calculations After each sampling, the value of the measured volume of methane produced by the bottles was converted to dry gas at 1 atm and 0oC (STP) and added to the previous measurements. This cumulative methane volume removed was added to the methane (dry at STP) present in the headspace of the bottle to determine the total cumulative methane volume of the sampling time. The total cumulative m ethane volumes were corrected for methane production attributed to the medium and inoculum by subtracting the averaged blank control volume from each bottles total cumulative methane volume. Finally, the corrected cumulative methane yield was calculated by dividing the corrected volume by the weight of sample added to each bottle.

PAGE 56

56 3.6.2 Liquid Analysis 3.6.2.1 pH The analysis of pH was conducted using the Campbell Scientific pH probe. 3.6.2.2 Soluble chemical oxygen demand The soluble chemical oxygen demand (SCOD) analysis was carried out using HACHs United States Environmental Protection Agency (USEPA) approved dichromate method. The method utilized small micro vials that contained the necessary reagents (silver, chromium and mercury) to carry out the an alysis. Mixed culture samples were taken at the beginning and the end of the run; each sample was centrifuged (Fisher for COD analysis Vials (HACH COD of range: 2 to 150 0 mg/L) were filled with mixed culture 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 samples were estimated by measuring its color intensity usi ng a colorimeter (HACH, DR/890) against a blank. Average error of colorimetric COD analysis was quantified as 4 % for samples that range 0 to 20,000 mg/L. 3.6.3 Solids Analysis Moisture content The moisture content of each aliquot was determined by placi ng 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 temperature and weighed with an analytical balance. The percent total solids and moisture was calculated by mass difference.

PAGE 57

57 Volatile solids After a sample was dried for moisture content and total solids, the volatile solids content was determined. Each sample was placed in an evaporation 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 temperature in a desiccator, before being weighed. The volatile solids content was calculated by mass difference.

PAGE 58

58 Table 3 1. Quantification of NASA Lunar wast e stream S.N. Type of Waste Dry Weight kg/(CM D) Water Content kg/(CM D) 1 Human Wastes 0.123 0.090 2 Packaging 0.220 -3 Adhered Food 0.098 0.070 4 Uneaten Food 0.249 0.210 5 MAGS 0.173 0.058 6 Gray Tape 0.033 -7 Paper 0.105 0.08 8 Towels & Washcloths 0.100 0.009 CM = crew member; D = day Table 3 2. Formulation of Simulated Synthetic Human Feces S.N. Component % weight Weight in grams 1 Yeast Extract 30 1.4850 2 Cellulose 15 0.7425 3 Polyethylene Glycol 20 0.9900 4 Psyllium Husk 5 0.2475 5 Peanut Oil 20 0.9900 6 Miso 5 0.2475 Proteins (38%) Fats (21%) Fiber (20%) Minerals (4%) 7 Inorganics 5 KCl (40%) 0.0990 NaCl (40%) 0.0990 CaCl2 (20%) 0.0495 8 Dried Coarse Vegetable Matter 0.0500

PAGE 59

59 Table 3 3. Description of biodegradable bags S.N. Sample Dimension Weight 1 Bio Bag 37 in x 13 in 30.5 g 2 Bag to Nature 24 in x 30 in 3.19 g 3 Eco Film 17 in x 16 in 9.6 g 4 Eco Safe 38 in x 15 in 40.3 g Table 3 4 Composition of stock solutions Stock Solution Composition Concentration(g/L) Volume S1 S1 sample 2 S2 Resazurin 1 1.80 mL S3 (NH 4 ) 2 HPO4 26.7 5.40 mL S4 S4 1 CaCl 2 .2H 2 O 16.7 27.00 mL NH 4 Cl 26.6 MgCl 2 .6H 2 O 120 KCl 86.7 MnCl 2 .4H 2 O 1.33 CoCl 2 .6H 2 O 2 S4 2 H 3 BO 3 0.38 2.70 mL CuCl 2 .2H 2 O 0.18 Na 2 MoO 4 .2H 2 O 0.17 ZnCl 2 0.14 NiCl 2 6H 2 O 0.05 NaVO 3 nH 2 O 0.05 S4 3 H 2 WO 4 0.007 0.27 mL S5 S5 FeCl 2 .4H 2 O 370 18.00 mL S6 S6 Na 2 S.9H 2 O 500 18.00 mL S7 S7 1 Biotin 0.002 1.80 mL Folic Acid 0.002 0.90 mL Pyridoxine hydrochloride 0.01 Riboflavin 0.005 Thiamin 0.005 Nicotinic acid 0.005 Pantothenic acid 0.005 p aminobezoic acid 0.005 Thioctic acid 0.005 S7 2 B12 0.0001 0.18 mL Sodium bicarbonate 8.40 g

PAGE 60

60 Figure 3 1. Canisters used for steam pretreatment studies Figure 32. Digester setup for biogasification studies

PAGE 61

61 Figure 33. Biogas U -tube meter Figure 34. Soda Lime Scrubber

PAGE 62

62 Figure 35. Mathis Labomat used for steam treatment studies

PAGE 63

63 CHAPTER 4 BIOCHEMICAL METHANE POTENTIAL STUDIES 4.1 Introduction The first stu dy of the research work was to determine biochemical methane potential of the individual componen ts in Lunar waste stream at thermophilic conditions. The aim o f this study was to analyze the anaerobic biochemical methane assays to determine extent and rate of bioconversion. Further, f our different brands of compostable/ biodegradable garbage bags available in the market namely Bio Bag, Bagto -Nature, Eco Film and Eco Safe were t ested for their biodegradability and biochemical methane potential under anaerobic condition. These bags represented biodegradable packaging materials that could potentially replace some of the current plastics used in a Lunar mission. 4.2 Biochemical M ethane Potential of Lunar Wastes 4.2 .1 Background Biochemical methane potential is a measure of sample biodegradability under anaerobic digestion conditions B ioassay techniques are essential for determining biodegradability since no chemical procedure is available which distinguishes between biodegradable and nonbiodegradable organics. Bioassay techniques can also measur e the presence or absence of inhibitory substances and offer the most promise for resolving anaerobic treatment problems because they ar e relatively simple and inexpensive and do not require knowledge of specific inhibitory substances. Both continuous (and semi -continuous) and batch feed techniques have been used to evaluate biodegradability. The continuous procedures closely simulate full -scale anaerobic operation; however they are costly in terms of facilities, equipment, time, and

PAGE 64

64 personnel. Batch bioassay techniques do not have these limitations and thus permit the evaluation of a wide range of variables. Batch techniques can evaluate t he influence of shock loads, but, in general do not simulate the effects of real systems as well. Anaerobic serum bottles containing samples, defined media, and seed inocula are incubated at the desired temperature, and respective gas productions are monit ored volumetrically using the syringe method of Nottingham & Hungate (1969). The liquid and gas phases can be sampled periodically by syringe extraction for subsequent analyses 4. 2 2 Results and Discussion The biochemical methane potential assays were carried out on individual NASA Lunar waste components as described in Chapter 3 with 5 g of each component and 200 ml of mixed culture together with nutrient media. The profiles of cumulative methane yield of i ndividual NASA Lunar w aste components are shown in Figure 4 1 and the results tabulated in Table 4 -1. Human waste and the f ood w aste seem to be two major components having highest methane potential. The cumulative methane potential of h uman w aste was 0.856 liters of methane per gram dry weight of waste at standard condition of temperature and pressure. Food w aste followed the same trend with 0.481 liters of methane per gram dry weight of waste at standard c onditions. Packaging m aterials ( which includes main ly polyethylene and polystyrene), w ipes and g rey t ape did not seem to have any significant methane potential. Papers, cotton and Lunar clothing showed methane potentials of 0.237, 0.046 and 0.013 liters of methane per gram of waste at standard conditions, respectively. It took 54 days for human w aste to achieve 95% of its methane yield and 78 days for food waste. Cotton and clothing seemed to degrade faster compared to other Lunar

PAGE 65

65 waste components achieving 95% of their methane potential in 29 days and 20 days respectively. Papers and wipes took significant time to degrade and demonstrated 95% of their methane yield in 66 and 54 days respectively. The undigested samples from the assay were filtered, dried at ambient temper ature for 24 hours and weighed. The degradation was calculated based on the amount of undigested sample recovered compared to what was fed. Human waste and food waste were the only soluble components in the Lunar waste stream and showed 100% degradation af ter digestion. Papers and cotton showed degradation of 98% and 96% respectively. The r est of the components did not show any significant degradation. Human waste and food waste seemed to degrade all their Soluble Chemical Oxygen Demands ( SCOD ) at par of wh at is predicted theoretically and demonstrated their suitability for anaerobic digestion. Papers and clothing most of which primarily made up of ce llulose, also showed good performance in anaerobic digestion process. As tabulated in Table 4 -1. Theoretical COD of all Lunar waste components and the comparison of theoretical and experimental methane yields are reported in Table 4 -2. The basis for theoretical COD estimation wa s that nearly all organic compounds can be fully oxidized to carbon dioxide The amoun t of oxygen required to oxidize an organic compound to carbon dioxide, ammonia, and water is given by: COD was estimated using the Equation: COD=(Moles of O2 required)*(Molecular Weight of O2)/(Molecular Weight of Sample)

PAGE 66

66 Human waste has a theoretical methane yield of 0.686 L/g, but experimental methane yield for human waste was 0.856 L/g. The reason for experimental methane yield to be more than theoretical yield may be because of the empirical formula predicted for human waste was not indicative of th e actual one. For food waste the theoretical and experimental methane yields were 0.507 and 0.481 L/g respectively, which represents some components in food waste wer e not completely degraded during the duration of the assay. Packaging material and grey tape seems to have very high methane yield of 1.148 L/g theoretically because of the long polymeric chain they, but experimentally (as expected) there was no significant methane production from these assays. Papers and cotton sh owed the methane yield at par with their theoretically predicted methane yields. The methane potentials for the Lunar wastes components are tabulated in Table 4 -3 and compared with the theoretical predictions. Experimental methane potentials of all the components added up to 315.81 L/C M -D compared to the theoretically predicted 681.88 L/CM -D. Steam treatment of the Lunar waste components was carried out as described in Chapter 3. Each of 5 g of undigested and a digested sample recovered from single stage anaerobic digestion were steam treated for a period of 15 min, 30 min, 1 hour and 2 hours. The steam treated samples are shown in Figure 4 2. The profiles of the cumulative methane yield of the steam treated Lunar waste components is shown in Figure 4 2. T here was 3840% solubilization for undigested samples after steam treatment. This was not the total mass reduction but the particulate matter solubilization. The SCOD of the undigested samples after steam treatment was very high in the range of 1 7 .4 -2 1 2 g/L and the pH was in the range o f 6.06 -6.74. One

PAGE 67

67 imp ortant observation was that higher the treatment time less is the SCOD and pH. This was probably because the longer exposure to steam might have hydrolyzed the waste. These results were at par of the cumulative methane potential studies in which the sample steam exposed for 15 min showed 86.27% more methane yield than that with 2 hours of steam exposure. The cumulative methane yield for the undigested steam treated samples was in the range of 0.014-0.102 liters of methane per gram of sam ple at standard conditions of temperature and pressure. The steam treated digested residues from the digester was tested for its degradability and methane potential in the biochemical methane potential assays. The opposite trend was observed in terms of w eigh t reduction in steam treatment experiments. Solubilization increased with exposure time. Extent of solubilization was in the range of 2-14% The steam t reated samples released less SCOD in the range of 1.123.08 g/L which was consistent with extent of solids solubilization. The methane potential of the steam treated digested residues was not more than 0.001 liters of methane per gram of sample at standard condition of temperature and pressure which demonstrates that solid residues coming out of the digester did not have much methane potential and some alternative methods must be developed to degrade it and recover energy out of it. 4.3 Biochemical Methan e Potential of Biodegradable Packaging Material 4.3 .1 Background As discussed in the biochemical methane potential studies of individual Lunar waste components, packaging material did not degrade and contribute to methane potential. It is possible that t he packaging material s in L unar waste stream could be replaced with various biodegradable polymeric material s. Other studies in our lab oratory

PAGE 68

68 have determined the extent of degradabil ity and methane potential of poly lactic acid material s under anaerobic digestion conditions To test the biodegradability and methane poten tials of other biodegradable polymeric materials, compostable biodegradable garbage bags were used as representative of such materials. The studies carried out here may be useful for the terrestrial MSW facilities also. Synthetic polymeric plastic material s accumulate in the environment at a rate of 25 million metric tons per annum. Polyethylene (PEs) represent 64% of plastic materials produced as packaging and bottles, which are usually discarded after only brief use Plastic bags accumulate in the environm ent due to their low degradability, generating pollution and taking space in landfills. Also, because they have very small masses and are usually contaminated, recycling is economically unfeasible. Their elimination at composting plants is not complete; th erefore fragments of bags end up contaminating the compost and ultimately require screening or othe r processes for their removal. (Scott et al ). Consequently, they are not suitable for recovering energy by incineration, because the heat is lost in evaporating the water instead of producing electricity. The compostable fraction of M.S.W. (Municipal Solid Waste) such as kitchen scraps, grass cuttings, waste from canteens, restaurants, the organic part of solid urban waste (also known as the "wet part") pac ked in the normal polythene bags is not exposed to the microbial population in the landfill unless the bags are shredded before landfilling. Recently there are a few brands of biodegradable garbage bags available in the market. These biodegradable garbage bags will biodegrade completely and safely leaving no residues and are certified for their biodegradability by ASTM D6400 standards. As the conditions in land filling process are similar to that of anaerobic digestion process, these

PAGE 69

69 biodegradable garbage b ags are tested for the degradability and energy potential under anaerobic conditions in the present studies. Now a days, anaerobic digestion is becoming a preferred option for MSW management Therefore, it is important to investigate the degradability of t hese compostable materials under anaerobic conditions. 4.3.2 Results Table 4 4 summarizes the performance of BMP assays in terms of corrected cumulative methane yield (expressed as liters of methane gas produced at STP per grams of the garbage bag sample f ed). Duration of the assays varied from 106 to 172 days. Each of assay was fed with 5 g of sample initially. The amount of the sample degraded and the percentage of degradation is reported in Table 4 4 The initial SCOD was 5.0 g/L. The residual SCOD at the end of the run and the final pH is also reported. Table 4 4 also summarizes the duration to produce 95% m ethane yield potential of each sample as well mass of biogas recovered. Figure 43 shows the plot of cumulative methane yield values versus duration of assays for all the samples. 4.3.3 Discussion The results highlight the agreement between the amounts of biogas produced to the amount of substrate solubilized which validated the mass balance of the process. For instance, 5 g of Bio Bag fed in the pr ocess was solubilzed completely. Mass of biogas recovered was 5.74 g. About 1.70 g of Bag -to -Nature sample from which 1.90 g of biogas was produced. 1.20 g degraded for Eco Film giving 1.26 g of biogas and 2.30 g of Eco Safe degraded yielding 3.29 g of b iogas. Its interesting to note that in all the cases amount of biogas recovered is more than the amount of substrate degraded.

PAGE 70

70 Post run liquid analysis suggests that pH values of all the assays were almost in the range of 7.0 to 8.0 which is the optimal range for methanogenasis. Also, the residual SCOD from all the assays were in the range of 2.48 g/L to 6.54 g/L which highlights that there was no unusually high accumulation of Volatile Fatty Acids (VFAs) indicating stable digestion in all the assays. Am ongst the samples used for the biochemical methane potential analysis, Bio Bag had the most methane potential. The methane potential of Bio Bag is 0.344 L/g while those of the others ranged between 0.084 to 0.146 L/g which is far lower than Bio Bag. Corres pondingly extent of solubilization of Bio Bag (95%)was more than that of other samples (23 34%). The manufacturer of Bio Bag claims to be the worlds largest brand of 100% biodegradable and 100% compostable bags which was validated in the present study. Next best product in terms of met hane potential and degradation wa s Bag-to Nature with methane potential of 0.146 g/L and 34% degradation in 127 days In terms of rate of methane production also Bio Bag seems to do well than others. Duration to achiev e 95% methane potential for Bio Bag was 45 days while for others it was observed in the range of 118165 days. ASTM standards for compostable plastics (ASTM D 6400 -04) requires plastic to degrade more than 90% under controlled conditions. Bio Bag seems to meet those standards even under anaerobic digestion conditions. Bio Bag is a blend of GMO (Genetically Modified Organisms) free starch polymer and other renewable resources. Other products like Bag-to Nature, Eco Film, and Eco Safe even though meets ASTM D 6400 standards for compostability it does not degrade very well under anaerobic digestion conditions. Bag-To Nature is made

PAGE 71

71 from a blend of organic biopolymers which apparently degrade s completely leaving no residues when composted. But, the present studies highlights that 66% of the Bag -to Nature sample was still undegraded even after 127 days of digestion. Eco Film contains no polyethylene and is heat and m oisture s table. Still, Eco Film seems to degrade 24% in thermophilic conditions. Eco Safe claim s that its Compostable trash bags are specifically engineered to quickly degrade in 10 to 45 days and fully biodegrade in less than 6 months It seems to degrade only 23% even after 172 days of digestion. An interesting trend was observed in the cumulati ve methane yield profile of Bio Bag, Bag -to -Nature and Eco Safe assays. There is a continual increase in methane production for 10 20 days following a decrease in methane production for 3 -5 days. Again methane production continues to increase for next 1020 days. While in case of Eco Film assay the methane yield profile increases constantly. The reason for the trend may be due the presence different kind of additives, fillers, copolymers etc used in the production of these bags. Accessibility to the degradable components may require solubilization or degradation of other components. So once a component is degraded it is followed by a lag phase while the other component is exposed for microbial attack. Another reason could be that microbial growth on degradable components may follow diauxic profiles where degradation of one component is initiated after the degradation of another component. Since the exact composition of these bags was not revealed by the manufacturers it was difficult to pinpoint the reasons for the observed profiles. In some cases d egradation is activated by heat, UV light and enhanced by mechanical action. (Vargas et al. ) showed that PLA pretreatment by irradiation (gamma source and e beam) or steam (120C for 3 h) enhanced its degradation under composting

PAGE 72

7 2 conditions. Likewise, to promote anaerobic degradability it may be necessary to subject these materials to some form of pretreatment. It should be noted that under current waste management practices where the MSW is mostly landfilled, these biodegradable materials may not degrade completely. The present studies also aim to serve high solids anaerobic digestion systems for NASA Long T erm Lunar Space Missions. With no oxygen condition on the lunar surface, anaerobic digestion is an option for treating solid wastes. Bio Bag being the most biodegradable plastic that was tested and with the highest methane potential, can be recommended f or the use as packaging material, trash collector as well for coatings on paper and other degradable substrate in long duration space missions. Substitution of packaging materials with Bio Bag type material, the methane potential of a Lunar waste stream c an be improved by 24% as demonstrated in Table 47. 4.3.4 Conclusions Individual Lunar waste components were tested for their biodegradability and methane potential. Human waste and food waste demonstrated highest methane potential of 0.856 and 0.481 L/g at STP and complete biodegradability. Paper, cotton and clothing also showed good methane potentials and biodegradability. Other components such as packaging materials, wipes, grey tapes etc did not degrade. Steam treatment did not show any significant effe ct in terms on methane potential or degradation. Solid residues from the digester did not have much methane potential and some alternative methods must be developed to degrade it and recover additional energy. Four different brands of biodegradable garbage bags available in the market namely Bio Bag, Bagto -Nature, Eco Film and Eco Safe were tested for their

PAGE 73

73 biodegradability and biochemical methane potential under anaerobic digestion condition. Bio Bag observed to be best amongst the four in terms of methan e potential, biodegradation and rate of methane production. The amount of biogas produced seems to be in correlation with the amount of material biodegraded under balanced digestion condition. Bio Bag achieves 0.344 L/g of methane yield under standard con dition of temperature and pressure with 95% degradation in 106 days under anaerobic condition which seem to be in accordance with ASTM D 640004 standards for Compostable Plastics. Bio Bag type material when incorporated in long term space missions for pa ckaging could increase the methane potential of lunar waste by 24%

PAGE 74

74 Table 4 1 Biochemical Methane Potentials of Lunar Wastes S.N. Sample Gas Analysis Solids Analysis Liquid Analysis Duration to produce 95%CH4 yield potential (Days) Cumulative CH4 Yield (L/g)@STP Solubilization/ Degradation (g) Soulubilzation/ Degradation (%) Residual SCOD (g/L) Final pH 1. Human Waste 0.856 5.0 100% 12 .56 8.01 5 4 2. Uneaten/Adhered Food 0.481 5.0 100% 12.32 8.41 78 3. Packaging 0.000 0.1 2% 5.36 7.96 NA 4. Wet Wipes 0.037 0.3 6% 4.50 8.20 54 5. Dry Wipes 0.000 0.1 2% 4.20 7.86 NA 6. Grey Tape 0.004 0.1 2% 3.54 8.02 15 7. Papers 0.237 4.9 98 % 3.12 7.80 66 8 Cotton 0. 231 4.8 96% 7.04 7.69 29 9 Clothing 0.013 1.7 34% 3.80 7.87 20

PAGE 75

75 Table 4 2 Comparison of theoretical and experimental methane yields for Lunar w astes S.N. Sample Molecular Formula Molecular Weight (g) Theoretical COD (g O2/g sample) Theoretical CH4 yield (L/g) Experimental CH4 yield (L/g) 1 Human Waste C 42 H 69 O 13 N 5 921 2.049 0.68 6 0.856 2 Uneaten/Adhered Food C 6 H 12 O 6 C5H9O2 C 6 H 15 O 2 N 2 150.57 1.515 0.507 0.481 3 Packaging C n H 2n 14 3.428 1.148 0.000 4 MAGS CH 2 CH(COONa) 93 0.946 0.317 0.037 5 Gray Tape C 2 H 4 +C 5 H 10 49 3.428 1.148 0.004 6 Papers C 6 H 12 O 6 C 5 H 10 O 5 170.55 1.065 0.357 0.237 7 Cotton (C 6 H 10 O 5 ) n 162 1.185 0.397 0.231 8 Clothing C 6 H 12 O 6 C 11 H 15 N 2 181.15 1.132 0.379 0.013

PAGE 76

76 Table 4 3 Comparison of theoretical and experimental methane potentials for Lunar wastes S.N. Sample Expected Dry W t ( k g /CM D ) Theoretical CH4 Potential (L/CM D ) Experimental CH4 Potential (L/CM D ) 1 Human Waste 0.123 84.38 105.28 2 Uneaten/Adhered Food 0.347 175.93 166.91 3 Packaging 0.220 252.56 0 4 MAGS 0.173 54.84 6.40 5 Gray Tape 0.033 37.88 0.13 6 Papers 0.105 37.49 24.89 7 Cotton & Clothing 0.100 38.80 12.20 TOTAL 681.88 315.81

PAGE 77

77 Table 4 4 Mathis Steam Treatment Results S. N. Sample Treatment Period Solids Analysis Liquid Analysis Original Weight Wt of the solids remaining Solubilization Solubilization % pH COD (min) (g) (g) (g) (g/L) 1 Undigested 1 15 5.0 2.9 2.1 42% 6.74 21 28 2 Undigested 2 30 5.0 3.1 1.9 38% 6.48 19 96 3 Undigested 3 60 5.0 3.0 2.0 40% 6.28 19 32 4 Undigested 4 120 5.0 3.1 1.9 38% 6.06 17 48 5 Digested 1 15 5.0 4.9 0.1 2% 8.05 3 08 6 Digested 2 30 5.0 4.7 0.3 6% 7.43 2 12 7 Digested 3 60 5.0 4.6 0.4 8% 7.15 1 12 8 Digested 4 120 5.0 4.3 0.7 14% 6.43 0 00

PAGE 78

78 Table 4 5 Biochemical Methane Potentials of Steam Treated Lunar Wastes S.N Sample Gas Analysis Solid Analysis Liquid Analysis Duration to produce 95%CH4 yield potential Cumulative CH4 yield @STP Solubilization Solubilization % Residual SCOD Final pH (L/g) (g) (g/L) (Days) 1 Undigested 1 0. 210 3.20 64% 3.80 6.70 45 2 Undigested 2 0. 130 3.05 61% 3.54 6.52 45 3 Undigested 3 0. 065 3.24 64% 3.80 6.43 45 4 Undigested 4 0. 028 3.18 63% 3.12 6.15 45 5 Digested 1 0.001 1.20 24% 2.12 7.98 25 6 Digested 2 0.001 1.48 29% 2.08 7.92 25 7 Digested 3 0.001 1.34 26% 2.24 7.56 25 8 Digested 4 0.001 1.68 33% 2.80 7.23 25

PAGE 79

79 Table 4 6 Biochemical methane potential of biodegradable bags S N Sample Duration (Days) Gas Analysis Solids Analysis Liquid Analysis Duration to produce 95% methane yield potential (Days) Mass of Biogas recovered (g) Cumulative CH4 Yield (L/g) @STP Degradation (g) Degradation (%) Residual SCOD (g/L) Final pH 1 Bio Bag 106 0.344 4.75 95% 5.72 8.09 45 5.74 2 Bag to Nature 127 0.146 1.70 34% 6.54 7.86 118 1.90 3 Eco Film 127 0.084 1.20 24% 2.48 7.87 120 1.26 4 Eco Safe 172 0.136 2.30 23% 3.54 8.29 165 3.29

PAGE 80

80 Table 4 7 Improved methane potential of Lunar wastes with biodegradable packaging S.N. Sample Experimental CH4 Potential (L/CM D ) Improved CH4 Potential with Biodegradable Packaging (L/CM D ) 1 Human Waste 105.28 105.28 2 Uneaten/Adhered Food 166.91 166.91 3 Packaging 0 75.68 4 MAGS 6.40 6.40 5 Gray Tape 0.13 0.13 6 Papers 24.89 24.89 7 Cotton & Clothing 12.20 12.20 TOTAL 315.81 391.49

PAGE 81

81 Figure 41. Biochemical Methane Potentials of Individual Lunar Waste Components Figure 42 Biochemical Methane Potentials of Steam Treated Lunar Waste Components 0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0 10 20 30 40 50 60 70 80 90 100Cumulative Methane Yield (L/g) @STPCumulative Time (Days) Human Waste Food Waste Packaging Wet Wipes Dry Wipes Grey Tape Cotton Clothing Papers 0 0.05 0.1 0.15 0.2 0.25 0 20 40 60 80Cumulative CH4 Yield @ STP (L/g)Cumulative Time (Days) Undigested (15min) Undigested (30min) Undigested (60min) Undigested (120min) Dig Solids (15min) Dig Solids (30min) Dig Solids (60min) Dig Solids (120min)

PAGE 82

82 Figure 4 3. Biochemical Methane Potentials of Biodegradable Bags 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0 50 100 150 200Cumulative Methane Yield (L/g)@STPCumulative Time (Days) BIO BAG BAG TO NATURE ECO FILM ECO SAFE

PAGE 83

83 A B C D Figure 44 Steam treated Lunar waste components exposed for A)2 hours B) 1 hour C)30 min D) 15 min

PAGE 84

84 A B C D Figure 4 5 Degraded biodegradable bags A)Bio Bag B)Bagto -Nature C)Eco Film D)Eco Safe

PAGE 85

85 CHAPTER 5 SINGLE STAGE BIOGASI FICATION STUDIES 5.1 Introduction This part of the study involves batch, single stage, and thermophilic anaerobic digestion of NASA Lunar waste stream. This first iteration of experiments was chosen for its simplistic design and operation. Two batch systems were introduced, one of which had no agitation of solids during digestion materials and the other was mixed continuously at 180 RPM The progression of an Experiment was measured by the evolution of methane with time. After the feedstock was degraded the reactor was opened and the residue removed and analyzed. The aim of this study was to characterize the anaerobic biodegradation potential of NASA Lunar waste stream as well Biodegradable bags and its metha ne potential (measured as methane yield) 5.2 Background Among various technologies that are available for anaerobic digestion, continuously stirred tank reactors (CSTR) are typically used to process high solid materials. Thorough mixing of the content in the digester distributes microorganism uniformly and im proves mass and heat transfer, and therefore is regarded as essential in high rate anaerobic digestion. Furthermore, agitation helps particle size reduction and release of produced biogas from the digester contents. Mixing is usually accomplished by mechan ical mixers, slurry recirculation or biogas recirculation. The significance of mixing in anaerobic digestion has been reported by many researchers (Kim et al., Mcmahon et al., Smith et al., Stroot et al.), though contradiction is found in determining the e ffect of mixing duration and intensity on anaerobic digester performance. Nevertheless, most studies agreed that high intensity mixing had an adverse effect on

PAGE 86

86 digester performance ( Kaparaju et al., 2008; McMahon et al., 2001; Stroot et al., 2001; Vavilli n et al. 2004.). Batch process offers advantages that mixing process does not have. Batch process is considered energy conserving for it does not require fine shredding of substrates or agitating of digester contents. Anaerobic digestion in batch system ca n be carried out at ambient pressure and at mesophilic and thermophilic temperatures both. Studies had showed vigorous mixing was harmful to anaerobic digestion (Kaparaju et al., 2008; McMahon et al., 2001; Stroot et al., 2001.) and the negative effect was interpreted as high shear forces disrupting microbial flock structures and disturbing syntrophic relationship between microbes (Vavillin et al. 2004). Therefore, appropriate m ixing rate need to be maintained. 5.3 Results & Discussion The profiles of cumulative methane yield for NASA Lunar waste stream in mixed and unmixed digester is shown in the Figure 5 1. Run1 for both mixed and unmixed system was started with the 100 g dry weight of the Lunar waste combination as mentioned in Chapter 2.Working volume of 4 liters was maintained in both the digesters. The methane production rate and the methane flow rate were monitored for 12 days of digestion. Total methane obtained at standard conditions of temperature and pressure at the end of the r un was 1.76 liters for mixed system and 3.46 liters for unmixed system. Cumulative methane yield at the standard conditions of temperature and pressure was 0.035 liters of methane per gram dry weight for mixed system and 0.039 liters of methane per gram dry weight for unmixed system. Daily methane production rate picked at 0.490 m3 m3 d1 for mixed digester on day 9 and 1.36 m3 m3 d1 for mixed digester on day 6. The daily methane production rate dropped to 0.04 m3 m3 d1 for mixed digester and 0. 1 6 m3 m3 d1 for unmixed digester when Run 1 was completed

PAGE 87

87 For m ixed di gester to achieve its 95% of methane yield potential required 6 days while that for unmixed digester required 5 days. Run 2 was started with the fresh inoculum for both mixed and unmixed system with the 25 g dry weight of the Lunar waste combination. Working volume of 2 liters was maintained in both the digesters. The methane production rate and the methane flow rate were monitored for 28 days of digestion. Total methane obtained at standa rd conditions of temperature and pressure at the end of the run was 3.12 liters for mixed system and 4.55 liters for unmixed system. Cumulative methane yield at the standard conditions of temperature and pressure was 0.12 liters of methane per gram dry wei ght for mixed system and 0.18 liters of methane per gram dry weight for unmixed system. Daily methane production rate picked at 0.130 m3 m3 d1 for mixed digester on day 21 and 1.915 m3 m3 d1 for mixed digester on day 2. The daily methane production rate dropped to 0.025 m3 m3 d1 on day 10 f or mixed digester and 0. 024 m3 m3 d1 for unmixed digester when Run 2 was completed For mixed digester to achieve its 95% of methane yield potential required 17 days while that for unmixed digester r equired 3 days. In all two runs, unmixed digester exhibited higher methane yield and methane production rate than mixed digester. Only difference was that run1 showed unstable digestion because of overloading compared to run2. In run1, unmixed digester ach ieved 11.43% more methane yield than mixed digester, while in run 2 unmixed digester achieved 50% more methane yield than mixed digester. In run 1, the degradation of solids obtained in the mixed and the unmixed digesters were 44.80% and 42.00% respective ly. While that in the run 2, it was 57.20% and 56.40% respectively. The

PAGE 88

88 results highlights the direct correlation between the amounts of biogas produced to the amount of substrate degraded which validates the mass balance of the process. T he validation of mass balance justif ies the validation of the biogasification The profiles for SCOD for mixed as well as unmixed digesters for run 2 are shown in the Figure 5 3. SCOD concentration in both the digesters initially accumulated, reached the maximum and decrea sed linearly to a minimum. Mixed digester showed a significantly higher SCOD than unmixed digester. The higher degradation rate of SCOD in unmixed digester is consistent with the higher daily methane production rate. The pH of all the digesters was well in between the range of 7.84 9.12 which signified there was no accumulation of any volatile organic acids. 5.4 One Stage Biogasification of Bio Bag Two experimental runs were conducted in this study. In run1 digester was loaded with 50 g (wet weight) of Bio Bag and maintained at 55 C during the run. 2 kg of bulking materials ((lava rocks from landscaping supplier, 0.025 m in average size) was added into digester along with the feedstock to prevent compaction and floatation. The digester was inoculated with mixed culture as mentioned in Chapter 3. The first run was ended when the gas production was low enough. The digesters were emptied and washed thoroughly. Residual Bio Bag was discarded, and the digester liquor was kept for the second run. Run 2 was s tarted with the digester liquor from the first run and the digester was loaded with 20 g (wet weight) of Bio Bag sample. The profiles of cumulative methane yield for the biogasification of Bio Bag is shown in the Figure 5 -4 Working volume of 3.5 liters wa s maintained in both the runs The methane production rate and the methane flow rate were moni tored for 60 days of digestion for run 1 and 30 days for run 2. Total methane obtained at standard conditions

PAGE 89

89 of temperature and pr essure was 7.18 liters and 3.18 liters at the end of run 1 and run 2 respectively Cumulative methane yield at the standard conditions of temperature and pressure was 0. 14 liters of methane per gram wet weight for run 1 and 0.15 liters of methane per gram wet weight for run 2 Daily met hane production rate picked at 0.245 m3 m3 d1 for mixed digeste r on day 40 in run 1 and 0.195 m3 m3 d1 for run2 on day 2 The daily methane production rate dropped to 0.008 m3 m3 d1 and 0. 011 m3 m3 d1 f or run 1 and run 2 respectively at the end of the run. Run 1 required 34 days to achieve 95% of its methane yield potential while run 2 required 7 days for the same. The results highlights the direct correlation between the amounts of biogas produced to the amount of substrate degraded which validates the mass balance of the process. The pH of all the runs were in the range of 7.08.0. T he validation of mass balance and the pH range justif ies the validation of the biogasification and a stable digestion. Th e profile of SCOD for run 1 is shown in Figure 5 -4 SCOD concentration initially accumulated reached a maximum and decreased to minimum around 4.5 g L1. The digesters in run 1 showed significantly higher SCOD than other runs due to the use of inoculumn w ith high SCOD. The higher degradation rate of SCOD in run 1 was consistent with the higher daily methane production rate seen in Figure 5 -4. Run 2 a started with low initial SCOD. As the SCOD concentration decreases, cumulative methane yield increases acc ordantly. 5.5 Conclusions NASA Lunar waste stream was biogasified in single -stage, b atch anaerobic digesters under mixed and unmixed condition respectively for 2 runs. The digester at bulking condition produced 11.43% and 50 % more methane than the digester at mixing

PAGE 90

90 condition in run 1 and 2 respectively after the same digestion time. In a ddition, the digester at unmixed condition also exhibited higher organic matter degradation rate. Unmixed system seems to do better than mixed system for NASA Lunar waste stream. Biogasification of Bio Bag suggests that adopted inoculum gives better methane yield than the fresh culture.

PAGE 91

91 Table 5 1 Single Stage Biogasification of Lunar Waste s S N Sample Dry Weight (g) Working Volume (L) Total Methane @ STP (L) Gas Analysis Solids Analysis Liquid Analysis Duration to produce 95% methane yield potential (Days) Mass of Biogas recovere d (g) Cumulative CH4 Yield (L/g) @STP Degradation (g) Degradation (%) Residual SCOD (g/L) Final pH 1 Mixed 1 100 4.0 1.76 0.03 5 44.80 44.80% 8.40 7. 20 6 4.71 2 Mixed 2 25 2 .0 3.12 0.12 14.3 0 57.20% 7.84 8.66 16 8.36 3 Unmixed 1 100 4.0 3.46 0.03 9 42.00 42.00% 9.12 7.53 5 9.27 4 Unmixed 2 25 2.0 4.55 0.18 14.1 0 56.40% 8.10 8.86 24 12.19 Table 5 2 Biogasification of Bio -Bag S N Sample Dry Weight (g) Duration (Days) Total Methane (L) Gas Analysis Solids Analysis Liquid Analysis Duration to produce 95% methane yield potential (Days) Mass of Biogas recovered (g) Cumulative CH4 Yield (L/g) @STP Degradation (g) Degradation (%) Residual SCOD (g/L) Final pH 1 Run 1 50 64 7.18 0.14 32 64% 5.90 8.53 34 19.23 2 Run 2 20 70 6.10 0.15 45 90% 4.54 8.59 63 19.00

PAGE 92

92 Figure 51 Comparison of Mixed and Unmixed System for Lunar Waste Biogasification Figure 52 COD/pH variations in Mixed and Unmixed System 0.02 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0 5 10 15 20 25 30 35Cumulative Methane Yield(L/g)@STPCumulative Time (Days) Mixed2 Unmixed2 Mixed1 Unmixed1

PAGE 93

93 Figure 53 Methane Yield/COD variations in Mixed and Unmixed System Figure 54 Cumulative Methane Yield for Biogasification of Bio Bag 0 2000 4000 6000 8000 10000 12000 14000 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0 5 10 15 20 25 30COD (mg/L) Cumulative Methane Yield @ STP (L/g)Cumulative TIme (Days) Methane Yild (Mx) Methane Yield(Umx)

PAGE 94

94 Figure 55 COD/pH Variations in the Biogasification of Bio Bag Figure 56 Methane Yield/COD Variations in the Biogasification of Bio Bag 8.1 8.15 8.2 8.25 8.3 8.35 8.4 8.45 8.5 8.55 8.6 8.65 0 1000 2000 3000 4000 5000 6000 7000 8000 0 5 10 15 20 25 30pH COD (mg/L)Cumulative Time (Days) COD pH 0 1000 2000 3000 4000 5000 6000 7000 8000 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0 5 10 15 20 25 30COD (mg/L) Cumulative Methane Yield @ STP (L/g)Cumulative Time (Days) Cumulative Methane Yield

PAGE 95

95 A B C D Figure 57 Degraded samples from single stage biogasification of Lunar wastes : A) Packaging material B) Clothes C) Wipes D) Grey Tape

PAGE 96

96 Figure 58 Degraded Bio Bag from single stage biogasification

PAGE 97

97 CHAPTER 6 TWO STAGE BIOGASIFIC ATION STUDIES AND CO NCE PTUAL DESIGN 6.1 Introduction This part of the study demonstrates two stage biogasification of NASA Lunar wastes. Two stage operation was carried out, one of which acted as a main digester having 2 L working volume into which the waste was loaded and the other was a mixed digester having a 3.5 L working volume to digest soluble organic matter produced in the first stage. About 600 ml of liquid was transferred from first stage to second and vice a versa daily. The progression of an Experiment was measured by the evolution of methane with time. After the feedstock was degraded the reactor was opened and the residue removed and analyzed. The aim of this study was to demonstrate an appropriate digester design that could be used for efficiently biogasifying Lunar mission waste. From this information a prototype digester was designed sized for a four person crew on a one year exploratory Lunar space mission. Research presented here supports the use of high-solids anaerobic digestion for bioregenerative purposes an d stabilization of the organic components of solid wastes during extended Lunar space missions. 6.2 Two Stage Biogasification Studies 6.2.1 Background Typically, when a two stage system is used, the first one harbors the liquefactionacidification reactions, with a rate limited by the hydrolysis of cellulose, and the second one harbors the acetogenesis and methanogenesis, with a rate limited by the slow microbial growth rate (Liu and Ghosh, 1997; Palmowski and Miiller, 1999). With these two steps occurring in distinct reactors, it becomes possible to increase the rate of

PAGE 98

98 methanogenesis by designing the second reactor with a biomass retention scheme or other means (Weiland, 1992; Kiibler and Wild, 1992). In parallel, it is possible to increase the rate of hy drolysis in the first stage by using microaerophilic conditions or other means (Capela et al., 1999; Wellinger et al., 1999). The application of these principles has led to a great variety of two -stage designs. However, in the hybrid two stage system emp loyed in this study, methanogenesis occurs in both digesters. The purpose of the second stage is to degrade readily solubilized organic matter from the first stage and convert it to methane. It was found that waste generated in a lunar mission contains a large fraction of readily solubilizable organic matter. If this is not quickly removed from the first stage, it has the potential to acidify rapidly, causing the pH to drop and inhibiting further degradation. The design for second stage of the system c ould be any one of the many designs commonly used for anaerobically digesting wastewater. For simplicity a stirred tank digester was used in this study. 6.2.2 Results and Discussion The profile of cumulative methane potential of NASA Lunar waste in two stage system is shown in Figure 66. Run1 started with 25 g of the waste gave total 5.56 L of methane in 18 days out of which 2.08 L generated from the first stage and 3.48 L generated from the second stage. Total cumulative methane yield for run1 was 0.200 liters of methane per gram of waste at the standard condition of temperature and pressure. Run2 was started with 50 g of the waste gave total 5.70 L of methane in 8 days out of which 3.79 L generated from the first stage and 1.95 L generated from the second stage. Total cumulative methane yield for run1 was 0.210 liters of methane per gram of waste at the standard condition of temperature and pressure. It is interesting to note that run2 achieved the same cumulative methane yield as run1 in less time.

PAGE 99

99 Duration for run2 was 10 days less than run1. This could be because of the adaptation of microbial consortia in the digester to the substrates in the waste stream during run1. Daily met hane production rate peaked at 0.239 m3 m3 d1 for digester on day 2 in run 1 and 0.735 m3 m3 d1 for run2 on day 2. The daily methane production rate dropped to 0.017 m3 m3 d1 and 0.051 m3 m3 d1 for run 1 and run 2 respectively at the end of the run. Run 1 required 15 days to achieve 95% of its methane yield potential while run 2 required 6 days for the same. The results highlights the direct correlation between the amounts of biogas produced to the amount of substrate degraded which validates the m ass balance of the process. The pH of all the runs were maintained in the range of 7.08.0 without addition of any chemicals indicating stable digestion. The profile of SCOD for run 1 is shown in Figure 6 -9. SCOD concentration initially accumulated reac hed a maximum to and de creased to minimum around 5.5g/L The digesters in run2 showed significantly higher SCOD of 16.8 g/L because of the larger quantity of waste loaded into the digester. The higher degradation rate of SCOD in run 2 was consistent with t he higher daily methane production rate seen in Figure 6 7. Run 1 started with low initial SCOD of 10.2 g/L. The rate of degradation in the two stage system is higher than one stage system d iscussed in Chapter 5. For the same amount of feedstock, two stag e system achieved the methane potential 55.55% faster than the one stage system. About 6% more solids degradation was achieved in two stage system compared to single stage system. It was

PAGE 100

100 possible to apply a higher organic loading of 25 g/L in the two stage system as compared to 12.5 g/L in one stage. 6.3 Full Scale Conceptual Design 6.3.1 Background For lunar applications, a two stage system was envisioned. The system was designed so that feed would be collected, coarsely shredded, mixed with recycled diges ter effluent to give the desired concentration of solids, and compacted to a density of 200 kg/m3. The digestion time was forecasted to be 8 days per batch. The energy potential for one year exploratory lunar mission was calculated based on the laboratory scale experimental data. Biogas from anaerobic digester would be treated to recover carbon dioxide and remove hydrogen sulfide and other contaminants. The methane could be used as fuel. The residue from the digester was readily dewatered as it contained only non degradable plastic material. Pathogens would also be inactivated during the anaerobic process as the digestion was carried out at thermophilic con ditions (Bendixen, 1994; Engeli, 1993). 6.3.2 Reactor Volume Calculations The expected amount of waste entering the anaerobic digestion system would be that generated by 4 person crew. For typical 8days anaerobic digestion cycle as demonstrated in two st age work above each reactor would contain 8days worth of solid waste. Individual lunar waste components add to 1.101 kg/(CM -D). Considering the crew of 4 astronauts, the amount of waste generated will be 1.101*4 = 4.404 kg/D.

PAGE 101

101 Over 8 days, 35.23 kg (4.404 8 = 35.23) of waste would be generated. This would collected in one vessel over 8 days. After the dry waste is placed in the digester and compacted to 200 kg/m3, recycled digester effluent must be added to initiate anaerobic digestion. As demonstrated above for the two stage system for 50 g of the Lunar waste 2.00 L of inoculum was added Hence, to digest 35.23 kg of the waste it would require 1.5863 m3 of liquid (or recycled digested effluent) for a total volume of 1.41 m3. Assuming the reactor is c ylindrical -shaped and assuming no headspace (due to low gravity application). The dimensions of the reactor can be calculated as follows: V = R2 H [6 1] If the radii of the vessel is 0.502 m (R), the height would be 1.78 m (H) for a volume of VP = 1.41 m3 6.3.4 Sizing the second stage of two stage system Upon addition of liquid into digester the readily solubilized organic matter leaches out and within a few hours the soluble organic content increases to 16.8 g COD/L. In experiments here the volume of second stage was 87.5% more than the first stage but as noted earlier the second stage design was not optimal. Under optimized conditions an anaerobic filt er (the design employed for second stage) can be sized to handle 8 g COD/L/day ( Lee et al. 2009). Assuming that as in the experiments if liquid volume equal to 30% of total volume of first digester is transferred to second stage every 24 hours, the size of the second stage works out to be 0.846 m3. The volume of the anaerobic filter= 0.846 m3

PAGE 102

102 R = 0.502 m H = 1.0686 m Surface Area= 4.9539 m2 6.3.5 Digester Operations 6.3.5.1 Thermophilic System The Digester -1 will be filled with the solid wastes and will be operated for 8 days. Simultaneously, the Digester 2 will act as the trash collector during these 8 days. At the end of digestion in Digester 1, liquid from Digester 1 will be transferred to Digester 2 initiating the digestion process in Digester 2. Digest er -1 will be emptied, and will act as trash collector. This process will be repeated. A total of 46 batches of waste will be treated over a year. Figure 61. Thermophilic Digester Operation Stage two

PAGE 103

103 Figure 62. NASA Lunar Thermophilic Digesters: 3 dimensional view Figure 63. NASA LunarThermophilic Digesters: Top view 6.3.5.2 Mesophilic System It was seen that the rate of degradation under mesophilic conditions is half as that achieved under thermophilic conditions. Therefore, period of digestion of a batch of Pump Manifold Pump Digester 1 Stage Two Digester2 Digester2 Digester1 Stage Two

PAGE 104

104 waste will be 16 days and 3 digesters will be required if similar vessel volumes as t hat used for thermophilic digestion is employed. Digester -1 will be filled with the solid wastes over eight days and operated for 16 days. From day 9, Digester 2 will act as the trash collector for the next eight days. On day 17 the process will be initi ated in digester -2 and digester 3 will now serve as trash collector for the next 8 days. By day 24, Digester -1 will become available for trash collection. In total the vessels will be loaded 46 times. The anaerobic filter (or second stage) will be requir ed to treat liquid streams from two digesters. Since typical loading rates for anaerobic filter under mesophilic conditions are half as that for thermophilic digester, the volume requirements will be four -fold for this vessel, i.e. 3.384 m3. Figure 64. Mesophilic Digester Operation Stag e two

PAGE 105

105 Figure 65. NASA Lunar Mesophilic Digesters: 3 dimensional view Figure 66. NASA Lunar Mesophilic Digesters: Top view 6.4 Energy Potential of Anaerobic Digestion Operations During 1 Year Exploratory Lunar Space Mission Experimental Methane Potential = 200 L/(CM -D) For a crew of 4 astronauts= 200 4 = 800 L/D/kg Pump Manifold Pump Stage Two Digester3 Digester1 Digester2 Stage Two Digester2 Digester1 Digester3

PAGE 106

106 Total methane potential = 800 1.101 = 880.8 L/D For a Batch of 8 Days = 880.8 8 = 7046.4 L =7.046 m3 Calorific Value of Methane = 37,000 KJ/m3 Total Energy potential of Lunar Wastes = 260,716 KJ for a batch of 8 days For a 1 year exploratory lu nar space mission, there will be 46 such batch digestions. Energy potential for 1 year Lunar Wastes= 11,992,972 KJ which is almost 12 M KJ. In the units of power=0.3824 kW 6.5 Energy Requirements 6.5.1 Energy Required for the Digester Start Up The amount of heat needed to heat a subject from one temperature level to another can be expressed as: Q = cp m dT [6 2] where Q = amount of heat (kJ) cp = specif ic heat capacity (kJ/kg.K) m = mass (kg) dT = temperature difference between hot and cold side (K) For Thermophilic (55 C) Operation: Q=4.19 (KJ/kg.K) (1410+1410+846) kg (328-298) K Q= 460,816 KJ for start up For Mesophilic (38 C) Operation: Q=4.19 (KJ/kg.K) (1410*3+3384) kg (311298) K Q= 414,735 KJ for start up

PAGE 107

107 6.5.2 Heat Losses from Insulation (Source: Thermalinc website, http://www.thermalinc.com/math/insulation.htm accessed on 10/25/09) For Thermophilic (55 C) Operation: Required heat for maintaining the temperature in the tank= 0.1656 W/m2oC = 0.1656 17.7661* 30 =88.2366 W =2,782,631 KJ per year For Mesophilic (38 C) Operation: Required heat for maintaining the temperat ure in the tank= 0.1656 W/m2oC = 0.1656 34.2838* 13 =73.8062 W = 2,327,551 KJ 6.5.3 Heat of Vaporization For Thermophilic (55 C) Operation: Biogas moles for a batch=524.28 moles Water moles=12.5% Biogas Moles G=0.125 G + 524.28 Heat of Vaporization = 2370.8 1.34 = 3176.87 KJ per Batch For Mesophilic (38 C) Operation: Biogas moles for a batch=524.28 moles Water moles=6.54% Biogas Moles

PAGE 108

108 G=0.0654 G + 629.14 Heat of Vaporization = 2411.7 0.79 = 1911.15 KJ per Batch 6.5.4 Energy Requirement of Pump To recirculate the leachate within the digester and to transfer liquid between stage 1 and stage 2 a pump must be used. As calculated earlier, for one digester, the required leachate volume is 1.413 m3. It is assumed that the total leachate recirculation/transferred volume per day is 10 times the leachate volume in digester, i.e., 14.13 m3 and the pumps work 20 minutes per 2 hours. So, the leachate recirculation flow rate is: Q = 10 1.413 (m3/d) / (24/2) 20 (min/d) = 0.0588m3/min According to Energy Conser vation Law, the energy required can be calculated as follows: ET = 0.5 m v2 + m g H [6 -3] v = Q/D2 [6 -4] Hence, Pump energy = 51,038 J per day So, its 18,629 KJ per year for Thermophilic (55 C). It will be twice this for mesophilic system as liq uid needs to be recirculated between two digesters and anaerobic filter. Tables 6 -1 and 62 summarizes the energy consumption for operation of thermophilic and mesophilic digester systems. The net energy gain is 72% and 76% for thermophilic and mesophilic operation respectively. Most of the energy is consumed for maintaining the temperature in the vessels. If temperature losses can be minimized with better insulation then net energy gain would be even higher. Table 63 lists the

PAGE 109

109 initial amount of water r equired to start up the digestion process. Due to the larger volumes mesophilic operation requires more water. After start up the effluent from digester will be recycled and no further make up water will be required. Taking into consideration the increased water requirement for mesophilic operation and given that excess net energy gain is small, thermophilc operation is recommended. More thermophilic operation has the added advantage of higher levels of pathogen inactivation. Table 6 1. Energy Consum ption for Lunar Digesters S.N. Type of Energy Thermophilic (55 C) System (KJ) Mesophilic (38 C) System (KJ) 1 Energy for digester start up 460,816 414,735 2 Energy to compensate heat losses from insulation 2,782,631 2,327,551 3 Energy to compensate heat of vaporization 146,136 87,913 4 Energy consumed for pumping operation 18,629 37,258 Total 3,408,212 2,867,457 Table 6 2. Net Energy Gain for Lunar Digesters S.N. Type of Energy Thermophilic (55 C) System (KJ) Mesophilic (38 C) System (KJ) 1 Energy Potential of Lunar Wastes 11,992,972 11,992,972 2 Energy Consumption during digestion operation 3,408,212 2,867,457 Net Gain 8,584,760 9,125,515

PAGE 110

110 Table 6 3. Initial water requirement for Lunar Digesters S.N. Water Requirement Thermophilic (55 C) System (L) Mesophilic (38 C) System (L) 1 Water requirement for the digesters 2820 4,230 2 Water requirement for the anaerobic filter 846 3,384 TOTAL 3,666 7,614 6.6 Comparison of Lunar mission wastes digesters with Mars mission wastes Previously Haley et al (2002) developed a design for high solids anaerobic digestion of wastes generated during long term Mars mission. The wastes generated during a long term Mars mission are quite different from that generated in a Lunar base. The composition of Mars mission waste is as follows: Figure 67. Space Mission Waste Composition (source: Haley et al, 2002)

PAGE 111

111 The daily solid waste streams for a 6person crew during a 600day exploratory mission to Mars were estimated as follows: Table 6 4. Estimates of daily solid waste stream for Mars mission (source: Haley et al 2002) Waste Component Dry Wt., Kg Percent of total Ash% Organic Matter, Kg Moisture, % Dry human waste 0.72 9.4 5 0.68 85 Inedible plant biomass 5.45 51.4 5 5.2 75 Trash 0.56 5.3 5 0.53 10 Paper 1.16 10.9 5 1.1 10 Packaging materials 2.02 19.0 Tape 0.25 2.4 Filters 0.33 3.1 Misc. 0.07 0.7 Total 10.6 100 7.5 For these wastes Haley et al (2002) had developed a 5vessel (used as trash collectors and digesters) and 2-reservior system with the volume of each digester equal to 0.125 m3 while that of reservoirs was 0.062 m3. This system handles 7.5 kg of waste/day in a batch of 5 days. The to tal size of the reactors for Mars mission wastes reported by Haley et al (2002) was 0.749 m3 to treat 37.5 kg of waste per batch. While, for treating a batch of 35.23 kg of Lunar mission wastes, the total size of the reactors was estimated to be 4.94 m3. The difference in sizes is mainly because of the difference in the composition of waste streams for Lunar mission and Mars mission. Lunar mission waste components, as reported in Table 31, has 61.30% of the organic matter of the waste stream, while Mars m ission waste components has 70.75% of the organic matter of the total waste stream. Human wastes, adhered food, uneaten food form the soluble part of the organic waste component which is 40% of total organic matter present. While, Mars mission waste has only human wastes as the soluble part

PAGE 112

112 of the organic waste which forms 9% of total organic matter present. As Lunar mission wastes has more soluble organic matter compared to Mars mission wastes, the leachate turns acidic quickly upon water addition. To handle this acidic leachate a separate anaerobic filter digester is required. This was not a necessity for wastes generated in Mars as most of the organic component is plant biomass which does not solubilize quickly. Hence the volume of the digester is mor e for the Lunar mission wastes compared to Mars mission wastes. 6.7 Conclusion The conceptual design for the NASA Lunar waste digesters has been developed based on results from pilot scale studies. Thermophilic system seems to do better than mesophilic in terms of mass of the equipment and water requirement. Thermophilic system requires 50% less water than mesophilic system which will be an important consideration for long term space mission. Mesophilic system does slightly better in terms of net energy gai n, producing 4% more. Both energy and water are the crucial entities for the long duration space missions, but in terms of cost of transportations of equipment and reactors, thermophilic system should be a good choice.

PAGE 113

113 Table 6 5. Two stage biogasification of Lunar wastes S N Sample Dry Weight (g) Duration (Days) Total CH4 (L) CH4 from stage1 CH4 from stage2 Gas Analysis Solids Analysis Liquid Analysis Duration to produce 95% methane yield potential (Days) Mass of Biogas recovered (g) Cumulative CH4 Yield (L/g) @STP Degradation (g) Degradation (%) Residual SCOD (g/L) Final pH 1 Run 1 25 18 5.56 2.08 3.48 0.200 15.1 60.40 5.55 8.23 15 14.89 2 Run 2 50 8 5.70 3.79 1.95 0.210 33.5 67.00 3.12 7.97 6 15.27

PAGE 114

114 Figure 68. Cumulative Methane Potential of Two Stage System Figure 69. Variation of cumulative methane yiedl and SCOD in digester for two stage system (Run1) 0.02 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0 5 10 15 20Cumulative CH4 Yield @ STP (L/g)Cumulative Time (Days) Run 1 Stage 1 Run 1 Stage 2 Run 2 Stage 1 Run 2 Stage 2 0 2000 4000 6000 8000 10000 12000 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0 2 4 6 8 10 12COD (mg/L) Cumulative Methane Yield @ STP (L/g)Cumulative Time (Days) Cumulative Methane Yield SCOD

PAGE 115

115 CHAPTER 7 CONCLUSIONS AND FUTURE WORK 7.1 Conclusions Research presented here supports the use of high-solids leachbed anaerobic digestion for bioregenerative reduction and stabil ization of the organic components of solid wastes during one year exploratory Lunar space missions. Initial biochemical methane potential studies and one stage as well as two stage studies followed by conceptual prototype reactor have shown positive result s for decreased retention time and increased reduction of biomass in the modified anaerobic digestion system The critical findings in the study are as follows: 1. Human w aste and f ood w aste demonstrated highest methane potenti al of 0.856 and 0.481 L/g at standard condition of temperature and pressure (STP) and complete biodegradability. Paper cotton and clothing also showed good methane potentials and biodegradability. Other components such as packaging materials, wipes, grey tapes etc did not degrade m uch. The s team treatment did not show an y significant effect in terms of methane potential on degradation. Solid residues coming out of the digester did not have much methane potential and some alternative methods must be developed to degrade it and recover energy out of it. 2. Another interesting finding was Bio Bag achieved 0.344 L/g of methane yield under standard condition of temperature and pressure (STP) with 95% degradation in 106 days under anaerobic condition which seem to be in accordance with ASTM D 6400 -04 standards for Compostable Plastics. Repeated biogasification of Bio Bag showed that adapted inoculum gives better methane yield than the fresh culture. The Bio Bag also

PAGE 116

116 seems to prove its merit in long term space missions for use in advan ced life support system (ALS). 3. The unmixed digester at bulking condition produced 11.43% and 50% more methane than the digeste r at mixing condition in two replicate runs after the same digestion time. In addition, the digester at unmixed condition also exhibited a higher organic matter degradation rate. A t wo stage system seemed to work faster and better than a one stage system. For the same amount of feedstock, a two stage system achieved the targeted methane potential 55.55% faster than the one -stage system. In terms of solids degradation, the two stage system degraded 6% more solids than the single stage sy stem. A two stage hybrid design digested 25 g/L of waste in 8 days. 4. Conceptual designs based on thermophilic and mesophilic operations wer e compared. The t hermophilic system required 50 % less water than the mesophilic system which will be an important consideration for long term space mission. Mesophilic system seem ed to do better in terms of energy potential of the system. Mesophilic system produced 4 % more energy than the thermophilic system. Both energy and water are the crucial entities for long duration space missions, but in terms of cost of transportation of equipment and reactors, a thermophilic system should be a good option. 7.2 Future Work This work was preliminary and should continue so the following topics of interest can be addressed: 1 The residues coming out of the digester has some moisture content which can be air dried within 24 hours. The experiments here suggest that it d oes not have any more methane potential. NASA should consider thermal treatment on those residues to get the maximum energy out of it.

PAGE 117

117 2 NASA should consider of developing fully degradable materials for Lunar mission including clothing to enhance anaerobic d igestion of entire waste. 3 Optimization of two stage operation to get maximum methane yield and highest degradation in optimized HRT and OLR. 4 Nutrient balances for N, P, and K; need to be determined, with identification of their concentrations in feeds and effluent liquid, so lid, and gas streams. 5 Improvement of biogas quality including trace contaminants (like hydrogen sulfide, nitrogenous compounds and volatile organic chemicals) 6 A rough estimate of capital and operating costs for the systems

PAGE 118

118 APPENDIX A BIOGASI FICATION STUDIES FOR NASA: JOHNSON SPACE CENTER -HOUSTON COOLER: 1 NASA JSC LANDSCAPE WASTE Total weight of the sample received= 7.62 kg Overall Bulk Density= 0.194 kg/L Average Bulk Density=0.089 KG/L Table A-1 NASA JSC Landscape waste compositon S.N. Components Wt(kg) Bulk Density (kg/L) Vol (L) Wt Fr Wt% Vol Fr Vol% 1 Grass Clippings 0.03 0.03 0.0009 0.029 2.91 0.003 0.33 2 Weeds 0.05 0.056 0.0028 0.049 4.85 0.01 1.04 3 Leaves (Green) 0.1 0.03 0.003 0.097 9.71 0.011 1.11 4 Leaves (Brown) Dried 0.03 0.032 0.001 0.029 2.91 0.004 0.36 5 Trimmings 0.02 0.02 0.0004 0.019 1.94 0.001 0.15 6 Mulch 0.1 0.1 0.01 0.097 9.71 0.037 3.70 7 Soil 0.7 0.36 0.252 0.68 67.96 0.933 93.31 Total 1.03 0.089714286 0.2701 1 100 1 100

PAGE 119

119 COOLER: 2 NASA JSC OFFICE WASTE Total weight of the sample received= 4.49 kg Overall Bulk Density= 0.116 kg/L Average Bulk Density=0.209 KG/L Table A-2 NASA JSC Office waste compositon S.N. Components Wt(kg) Bulk Density (kg/L) Vol (L) Wt Fr Wt% Vol Fr Vol % 1 Paper Bags 0.17 0.10 0.017 0.0417 4.17 0.0069 0.69 2 Cotton 0.22 0.12 0.0264 0.0540 5.40 0.0108 1.08 3 Dirty Clothes 0.02 0.20 0.004 0.0049 0.49 0.0016 0.16 4 Empty Gatorade Bottle 0.05 0.05 0.0025 0.0123 1.23 0.0010 0.10 5 Empty Cans 0.02 0.02 0.0004 0.0049 0.49 0.0002 0.02 6 Carpet 1.7 0.90 1.53 0.4175 41.75 0.6250 62.50 7 Trash Bag (Polythene) 0.005 0.09 0.00045 0.0012 0.12 0.0002 0.02 8 Thermocol 0.03 0.08 0.0024 0.0074 0.74 0.0010 0.10 9 Office Papers 0.02 0.40 0.008 0.0049 0.49 0.0033 0.33 10 Paper Towels 0.02 0.11 0.0022 0.0049 0.49 0.0009 0.09 11 Paper Glasses 0.03 0.03 0.0009 0.0074 0.74 0.0004 0.04 12 Cups 0.02 0.02 0.0004 0.0049 0.49 0.0002 0.02 13 Straw 0.01 0.01 0.0001 0.0025 0.25 0.0000 0.00 14 Plastic Food Container 0.3 0.30 0.09 0.0737 7.37 0.0368 3.68 15 Cardboard 0.6 0.60 0.36 0.1473 14.73 0.1471 14.71 16 Food Box 0.2 0.20 0.04 0.0491 4.91 0.0163 1.63 17 Cardboard Food Box 0.6 0.60 0.36 0.1473 14.73 0.1471 14.71 18 Cigarette Box 0.05 0.05 0.0025 0.0123 1.23 0.0010 0.10 19 Tissue Paper 0.007 0.10 0.0007 0.0017 0.17 0.0003 0.03 TOTAL 4.072 2.44795 1 100 1 100

PAGE 120

120 COOLER: 3 NASA JSC CAFETERIA WASTE Total weight of the sample received= 2.90 kg Overall Bulk Density= 0.112 kg/L Average Bulk Density=0.160 kg/L Table A-3 NASA JSC Cafeteria waste compositon S.N. Components Wt (kg) Bulk Density (kg/L) Vol (L) Wt fr Wt % Vol fr Vol % 1 Cardboards 0.57 0.60 0.342 0.2027 20.27 0.746 74.64 2 Big Plastic Bag 0.19 0.09 0.017 0.067 6.75 0.03 3.73 3 Plastic Food Containers 0.21 0.03 0.006 0.0746 7.46 0.014 1.375 4 Uneated/Adhered Food 1.83 0.05 0.091 0.650 65.0 0.2 19.9 5 Tissue Paper 0.005 0.10 0.000 0.001 0.17 0.00 0.10 6 Paper Towels 0.007 0.11 0.000 0.0024 0.24 0.00 0.16 Total 2.81 0.458 1 100 1 100 Table A-4 NASA JSC Cumulative Methane Yield Results Type of Waste Dry Weight (g) VS (g) Total Methane (L) Cumulative Methane Yield (L CH4/g VS) thermophilic Cumulative Methane Yield (L CH4/g VS) @ STP Office Papers Run1 98.41 57.49 22.12 0.3848 0.32 Office Papers Run2 98.41 57.49 16.35 0.28 0.24 Cardboard Run1 59.90 55.00 16.15 0.2936 0.24 Cardboard Run2 98.04 90.02 15.14 0.17 0.14 Paper Towels Run1 98.10 89.07 16.84 0.19 0.16 NASA JSC Low Mix Combination 98.50 65.80 7.48 0.11 0.09 NASA JSC Landscaping Waste 4.70 4.124 0.87 0.17 0.14

PAGE 121

121 APPENDIX B PILOT SCALE STUDEY: OPERATION OF A SEMI -CONTINUOUS ANAEROBIC DIGESTER UNDER THERMOPHILIC CONDITIONS The digester set up is shown in Figure B -1. A stainless steel conical bottom digester was constructed with a total volume of 45 gallons. The height and inner diameter of the cylindrical section were 0.74 m (29 inches) and 0.4 m (16 inches), respectively. The height and diameter of conical secti on were 0.558 m (22 inches) and 0.4 m (16 inches), respectively. Conical section was modified to achieve easy separation of digested solids from bottom of the digester. Modified conical section is as shown in Figure B-1 Cylindrical and conical sections were bolted together by using a gasket. A heating jacket was constructed by winding a copper coil around the cylindrical section. Hot water from an electrical heater was recirculated through the copper coil. Complete digester was insulated using kjsdhfjkhsdak foam. Ports for recirculation were constructed at different heights on cylindrical and conical sections. For the present study, recirculation of the leachate was done as shown in Fig. B1 which was the only mode of mixing in the digester. Solids were fed to the digesters by operating the knife gate valves at the top. Top gate valve (# 8) was opened first and the chamber was filled with the solids. Then, this valve was closed and valve 7 was opened which allowed solids to fall in the digester; thus making sure no air got into the system. Digested solids were withdrawn from the bottom in a similar way. A gas port was provided at the top of digester. A gas sampling port with rubber septa was made in the gas line from the digester to the U -tube gas meter. Gas production from the digesters was measured using a positive displacement gas meter.

PAGE 122

122 The device consisted of a clear PVC U -tube filled with anti -freeze solution, a float switch (Grainger), a counter (Redington Inc.) and a solenoid valve (Fabco Air). The U -tube gas meter was calibrated in-line to determine volume of biogas per count. A count was considered as that amount of gas read on syringe (in milliliters) for which the gas meter completes one whole number count (e.g. one count = 0.25 L, then two counts = 0.5 L and continued on). The pH in the digester was measured daily using pH meter (Accumet pH meter, Model 805 MP). The feedstock was provided by Tropicana, company based in Tampa. It consisted of citrus seeds, peels and pulp after juicing operation. The feedstock was frozen at 20oC and fed directly to the digester whenever needed without bringing it to the room temperature. No pretreatment was given to the feedstock. Different characteristics of the feed are provided later. Average nutrient composition of dried citrus pulp is given in Table B1. Analyses were obtained by the Feed Laboratory, Division of Chemistry, Florida Department of Agriculture, Tallahassee. All mineral values are expressed on a dry matter basis. Initially, the anaerobic digester was run on sugar beet tailings from American Crystal Sugar. About 1 kg of solid feed was added once a week for a month. After consistency in biogas production, citrus waste was fed to the digester at a consistent feed rate. Initially, 1 kg of wet citrus waste was fed to get an idea of total biogas which could be produced by complete digestion. I t is reported that anaerobic digestion of citrus pulp is not a common practice because of the toxic effect of peel oils on anaerobic bacteria. If the waste stream is

PAGE 123

123 s ufficiently stripped off d -limonene, an anaerobic digester can reduce the BOD by 90% with methane content in the biogas ranging from 60 70 %. Figure B 1 Digester set up for pilot scale studies

PAGE 124

124 Table B-1 Feed analysis of Citrus waste Nutrient Content Moisture, % 8.58 Ash, % 4.68 Ether extract, % 3.74 Crude protein, % 6.16 Crude fiber, % 12.28 N.F.E., % 64.56 Calcium, % 1.43 Phosphorus, % 0.11 Magnesium, % 0.12 Potassium, % 1.09 Sodium, % 0.096 Sulfur, % 0.066 Iron, ppm 98.72 Copper, ppm 6.19 Zinc, ppm 9.94 Manganese, ppm 5.7 Cobalt, ppm 0.073

PAGE 125

125 LIST OF REFERENCES American Society for Testing and Materials ASTM D6400 04 Standard Specification for Compostable Plastics American Society for Testing and Materials ASTM D6868 03 Standard Specification for Biodegradable Plastics Used as Coatings on Paper and Other Compostable Substrates Badger, D. M., Bogue, M J. and Stewart, D. J., Biogas production from crops and organic wastes. 1. Results of batch digestions. New Z ealand .I. Sci., 1979, 22, 1 t 20. Botelho G, Queiro s A, Machado A, Frangiosa P, Ferreira J. Enhancement of the thermooxidative degradability of polystyrene by chemical modification. Polym Degrad Stab 2004,86:493 7. Cecchi, F., Traverso, P. G. and Cescon, P., Anaerobic digestion of organic fraction of municipal solid waste digester performance. Sci. of Total Env., 1986, 56, 183197. Cecchi, F., Traverso, P G., Vallini, G. and Prescimone V., Codigestione anaerobic di rifiuti solidi urbani provenienti da raccolta differenziata efanghi di supero. In RiJiuli urban speciali tossici e nocivi, ed. A. Frigerio. CI, ESSE. I. Milano, Italy, 1988, pp. 7890. Cecchi, F., Vallini, G., Pavan, P., Bassetti, A. and Mata-Alvarez, J. Management of macroalgae from Venice lagoon thr ough anaerobic co digestion and co composting wi th municipal solid waste (MSW). War. Sci. Tech., 1993, 27, 159 168. Chugh, S., Chynoweth, D.P., Clarke, W.P., Pullammanappallil, P., Rudolph, V., (1999). Degradation of unsorted municipal solid wast e by a leachbed process. Bioresour. Technol. 69, 103 115. Chynoweth, D.P., Bosch, G., Earle, J.F.K., Owens, J., Legrand, R., 1992. Sequential batch anaerobic compos ting of the organic fraction of municipal solid waste. Water Sci. Technol. 25, 327 339. Chyn oweth, D. P., Jerger, D. E. and Srivastava. V. J., Biological gasification of woody biomass. In Proceed ings af the 20th Intersociety Energy Conversion Engineering Conference, Vol. 1, Society of Automotive Engineers, Inc., Warrendale, PA, USA, 1985, pp. 573-579. Chynoweth, D. P., Turic k, C. E., Owens, J. M., Jerger, D. E. and Peck, M. W., Biochemical methane potential of biomass and waste feedstocks. Biomass and Bioenergy, 1993, 5, 95l 1 I.

PAGE 126

126 Chynoweth, D., Legrand, R., Apparatus and Method for Sequential Batch Anaerobic Composting of High Solids Organic Feedst ock, U.S. Patent 5269634, 1993 Citrus Summary 2004 05. Orlando, FL: Florida Dept. of Agriculture and Consumer Services and USDA National Agriculture Statistics Service; 2006. p. 53. De Baere, L., High r ate dry anaerobic composting process for the organic fraction of solid waste, 7thSymp. on Biotechnology for Fuels and Chemicals,Gatlinburg, Tennessee, 1984. DE Baere, L. and Verstraete, W., High rate anaerobic composting with biogas recovery. Biocycle, 1984, 25, 3c 31. Environmental Systems (ICES) and European Symposium on space EnvironmentalControl Systems, July 11-14, Rome, Italy. Exploration Life Support Baseline Values and Assumptions Doc ument, JSC 64367, June 30, 2008 Frank, J. R. an d Smith, W. H., In troduction to methane from biomass: a systems approach, In Methane.from Biomass. A Systems Approach (W. H. Smith and J. R. Frank, eds). Elsevier Avvlied Science. London, 1988. Frostell, B., Sointio, J., Bonkoski, W., 1984. Methane Generation from the Anaer obic Digestion of Bee t Pulp. Energy from Biomass and Wastes, vol. VIII. Wiley, pp. 903 922. Garcia, J.L., Labat, M., Meyer, F., Deschamps, F., 1984. Anaerobic digestion of sugar beet pulps. Biotechnol. Lett. 6 (6), 379 384. Ghanem, K.M., El -Refai, A.H., E l -Gazaerly, M.A., 1992. Methane production from beet pulp. Resour. Conserv. Recycling 6, 267 275. Gross RA, Kalra B. Biodegradable polymers for the environment. Science 2002, 297:803 7. Hansen, K.H., Angelidaki, I., Ahring, B.K ., 1998. Anaerobic digestion of swine manure: inhibition by ammonia. Water Res. 32, 5 12. Hashimoto, A. G., Pre treatment of wheat of straw for fermentation to methane. Biotechnology and Bioengineering, 1986, 28, 1857-1866. Hegde, G., Pullammanappallil, P., 2007. Comparison of thermo ph ilic and mesophilic one-stage, batch, high -solid s anaerobic digestion. Environ. Technol. 28, 361 369. J. Szikriszt, B. Frostel l, J. Normann and R. Bergstrom, Pilot scale anaerobic digestion of municipal solid w aste after a nova1 pretreatment, In Anaerobic D igestion (E. R. Hall and P N. Hobson, eds), pp. 375-382. Pergamon Press, Oxford (1988).

PAGE 127

127 Klass, D. L., G hosh, S. and Conrad, J. R., The conversion of grass to fuel for captive use. Paper presented at Symposium on Clean Fuels from Biomass, Sewage, Urban Refuse and Agricultural Wastes, pp. 229 -252. Institute of Gas Technolog y, Chicago, IL, 1976. Knol, W., van der Most, M. M. and de Waart, J., Biogas production by a naerobic digestion of fruit and vegetable waste. A preliminary study. J. Sci. Fd Agric., 1978, 29, 822830. Mata -Alvarez, J., Cecchi, F., Pavan, P. and Bassetti, A., Semi -dry thermophil ic anaerobic digestion of fresh and pre-composted organic fraction of municipal solid waste (MSW): Digester performance. Wat. Sci. Tech., 1993, 27, 8796. Marty, T. B., Ragot, M., Ballester, J. M., Ballester, M. and Giallo, J., Semi -solid state thermophilic digestion of urban wastes, EEC Contractor Meeting Anaerobic Digestion, Villeneuve DAscq (Lille), France (1986). OKeefe, D. M., Chy noweth, D. P., Barkdoll, A. W. Nordstedt, R. A., Owens, J. M. and Sifontes, J., Sequential batch an aerobic composting of municipal solid waste (MSW) and yard waste. War. Sci. Tech., 1993, 21, 7786. 0. Begotten, E. Thiebaut, A. Pavia and J. P. Peillex, Thermophilic anaerob ic digestion of municipal solid wastes by the Valorga process, In Ftfth Int. Symp. On Anaerobic digestion -poster papers, (A. Tilche and A. Rozzi, eds), pp.789-792. Monduzzi. Bologna, Italy (1988). Owen,W.F. Stucky D.C.,Healy, J.B., Jr., Young L.Y., and Mc Carty P.L. (1979). Bioassay for monitoring biochemical methane potential and anaerobic toxicity. Water Reaserch 13, 485492. Parawira, W., Murto, M., Zvauya, R. and Mattiasson, B., 2004. Anaerobic batch digestion of solid potato waste alone and in combinat ion with sugar beet leaves. Rewewable Energy 29, 18111823. Pind, P. F., Angellidaki, I. and Ahring, B. K., 2003. Dynamics of the anaerobic process: effects of volatile fatty acids. Wiley Periodicals, Inc. 1-11. Pullammanappallil, P., Clarke, W., Rudolf, V ., Chynoweth, D., Chugh, S., Nopharatana, A., Lai, T., Nair, S. Hegde, S., 2005. High-solids, leachbed anaerobic digestion of organic fraction of municipal solid waste. In: Proceedings of 4th Inter national Symposium on Anaerobic Digestion of Solid Waste, 31 Aug 2 Sept, Copenhagen. Scott G. Polymers and the environment. Cambridge: RSC Paperbacks; 1999, 80. Scott G. Green polymers. Polym Degrad Stab 2000,68:1 7. Richards, B. K., Cum mings, R. J., Jewell, W. J. and Herndon, F. G. High solids anaerobic methane fermentation of sorghum and cellulose. Biomass and Bioenergy, 1991, 1, 4753.

PAGE 128

128 Sudhakar M, Doble M, Murthy PS, Venkatesan R. Marine microbe-mediated biodegradation of low and highdensity polyethylenes. Int Biodeterior Biodegradation 2008, 61:203 13. Sarada, R. and Joseph, R., 1996. A comparative study of single and two stage processes for methane production from tomato processing waste. Process Biochemistry 31 (4), 337340. Stewart, D. J., Bogue, M. J. and Badger, D. M., Biogas production from crops and organic wastes. 2. Results of continuous digestion tests. New Zealand J. Sci., 1984, 27, 285-294. Svensson, L. M., Bjornsson, L. and Mattiasson, B., 2007. Enhancing performance in anaerobic high-solids stratified bed digesters by straw bed implementati on. Bioresource Technology98, 47 52. Teixeira, A., Chynoweth, D.P., Owens, J.M., and Pullamman appallil, P., 2005. Space based SEBAC -II Solid Waste Management Technology for Commercial Application to Beet Sugar Industry. Paper No. 2005013026. Proceedings of Internation al Conference on Environmental Systems (ICES) and European S ymposium on space Environmental Control Systems, July 11 -14, Rome, Italy. Valorga, Waste recovery as a source of methane and fertilizer -The Valorga process. 2nd Annual Int. Symp on Ind. Resource Managem., Philadelphia, U.S.A., (1985). Vargas L. F, Welt ., B. A., Teixeira A., Pullammanappallil P., Balaban M., Beatty C Biodegradation Of Treated Polylactic Acid (Pla) Under Anaerobic Conditions, Transaction of the ASABE 2009, vol.52. Issue 3, 1025 -1030. Vieitez E.R., Ghosh s., Biogasification of solid wastes by two phase anaerobic ferementation, Biomass and Bioenergy 16 (1999) 299309. Wingarajah K., Litwiller E., Fisher J., Hogan J., 2006, Simulated Human Feces for Testing Human Waste Processing Technologies in Space Systems Yang, K., Yu, Y. and Hwang, S., 2003. Selective optimization in thermophilic acidogenesis ofcheese whey wastewater to acetic and butyric acids: partial acidification and methanation.Water Research 37, 2467-2477. Yan g, P. Y., Wei tzenhoff, M. H. and Moy, J. H., Biogasification of papaya processing wastes. Trans. ASAE., 1984, 27, 840 -843.

PAGE 129

129 BIOGRAPHICAL SKETCH Abhishek Dhoble was born in Nagpur in Maharashtra, India. He received his Bachelor of Technology in Chemic al Engineering from Nagpur University, India, in June 2008. In August 2008, he came to University of Florida to pursue his m asters in Chemical Engineering; thereafter he shifted to Agricultural and Biological Engineering Department to pursue his m asters with thesis under the supervision of Dr. Pullammanappallil After completing his gr aduate studies, he aspires to join Administrative Services back home to be a part of Bioenergy Revolution serving poor and needy people, especially the farmers, using his te ch nical skills acquired during the studies and experiences as a graduate student