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Biological Denitrification System for Industrial Wastewater

Permanent Link: http://ufdc.ufl.edu/UFE0024688/00001

Material Information

Title: Biological Denitrification System for Industrial Wastewater
Physical Description: 1 online resource (53 p.)
Language: english
Creator: Kapadi, Shourie
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2009

Subjects

Subjects / Keywords: aeration, attached, biological, bioreactor, biotreatability, carbon, column, compounds, continuous, denitrification, exchange, growth, industrial, ion, nitrate, organic, packed, pretreatment, reactor, source, stirred, stripping, suspended, tank, vocs, volatile, wastewater
Chemical Engineering -- Dissertations, Academic -- UF
Genre: Chemical Engineering thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: The purpose of this project was to investigate the suitability of a biological system for treating a high nitrate industrial process stream (IPS). The main focus will be on the required pretreatment of the IPS. Earlier research carried out by a graduate student Sherin Peter on denitrification of the IPS has proved that VOCs present in it hinder bacterial growth. During this project, attempts were made to minimize the VOC content of the IPS so that denitrification process is not hindered. Aeration with compressed air was used as a method of stripping VOCs out of the IPS. Experiments to find out the optimized method of aeration were carried out during this project. Presence of metal ions was also found to be a hindering factor in previous research carried out on the IPS and ion-exchanging the IPS was found to be effective in dealing with this problem. However the large volumetric flow rate of the IPS makes ion-exchanging cost prohibitive. It was ascertained that ion-exchanging certainly helps but is not essential. Denitrifying bacteria require carbon for their growth and adequate quantities of carbon are absolutely essential. Carbon contained in the IPS was first choice since it eliminates the extra cost external carbon source. It was found that carbon in the IPS is sufficient for significant nitrate removal (around 70%). Effectiveness of the two waste carbon process streams (CPS) available at the industry manufacturing site was also checked as probable additional carbon sources. Performance of an attached growth bioreactor for denitrification of nigh nitrate content wastewater was also studied during this project. It was found that the attached growth bioreactor is able to obtain 100% denitrification of synthetic nitrate sample but the pH in the bioreactor often falls below 7 during continuous operation which has a potential of killing all the bacterial culture and therefore the bioreactor. pH drop results because the feed of synthetic sample used was at pH 5. Using synthetic feed at pH 7 could eliminate this problem but at a considerable expense.
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 Shourie Kapadi.
Thesis: Thesis (M.S.)--University of Florida, 2009.
Local: Adviser: Svoronos, Spyros.
Local: Co-adviser: Koopman, Ben L.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2009
System ID: UFE0024688:00001

Permanent Link: http://ufdc.ufl.edu/UFE0024688/00001

Material Information

Title: Biological Denitrification System for Industrial Wastewater
Physical Description: 1 online resource (53 p.)
Language: english
Creator: Kapadi, Shourie
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2009

Subjects

Subjects / Keywords: aeration, attached, biological, bioreactor, biotreatability, carbon, column, compounds, continuous, denitrification, exchange, growth, industrial, ion, nitrate, organic, packed, pretreatment, reactor, source, stirred, stripping, suspended, tank, vocs, volatile, wastewater
Chemical Engineering -- Dissertations, Academic -- UF
Genre: Chemical Engineering thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: The purpose of this project was to investigate the suitability of a biological system for treating a high nitrate industrial process stream (IPS). The main focus will be on the required pretreatment of the IPS. Earlier research carried out by a graduate student Sherin Peter on denitrification of the IPS has proved that VOCs present in it hinder bacterial growth. During this project, attempts were made to minimize the VOC content of the IPS so that denitrification process is not hindered. Aeration with compressed air was used as a method of stripping VOCs out of the IPS. Experiments to find out the optimized method of aeration were carried out during this project. Presence of metal ions was also found to be a hindering factor in previous research carried out on the IPS and ion-exchanging the IPS was found to be effective in dealing with this problem. However the large volumetric flow rate of the IPS makes ion-exchanging cost prohibitive. It was ascertained that ion-exchanging certainly helps but is not essential. Denitrifying bacteria require carbon for their growth and adequate quantities of carbon are absolutely essential. Carbon contained in the IPS was first choice since it eliminates the extra cost external carbon source. It was found that carbon in the IPS is sufficient for significant nitrate removal (around 70%). Effectiveness of the two waste carbon process streams (CPS) available at the industry manufacturing site was also checked as probable additional carbon sources. Performance of an attached growth bioreactor for denitrification of nigh nitrate content wastewater was also studied during this project. It was found that the attached growth bioreactor is able to obtain 100% denitrification of synthetic nitrate sample but the pH in the bioreactor often falls below 7 during continuous operation which has a potential of killing all the bacterial culture and therefore the bioreactor. pH drop results because the feed of synthetic sample used was at pH 5. Using synthetic feed at pH 7 could eliminate this problem but at a considerable expense.
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 Shourie Kapadi.
Thesis: Thesis (M.S.)--University of Florida, 2009.
Local: Adviser: Svoronos, Spyros.
Local: Co-adviser: Koopman, Ben L.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2009
System ID: UFE0024688:00001


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1 BIOLOGICAL DENITRIFICATION SYSTEM FOR INDUSTRIAL WASTEWATER By SHOURIE KAPADI 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

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2 2009 Shourie Kapadi

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3 To my parents and family members

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4 ACKNOWLEDGMENTS I gratefully acknowledge my advisor, Dr. Spyros Svoronos, for his guidance and support. I th ank my co -chair, Dr. Ben Koopman, for his valuable advice through the course of the experiments. I also acknowledge Kiranmai Durvasula and Vijay Krishna for their guidance and advice in experimental work. I am also grateful to Chris Buechler and Darrick Elmore for their guidance and providing industrial samples and material used in the experiments. I thank Solutions Defined team members, Danyal Turkoglu, Sergio Posada, Eric Staunton, Julie Mammino, Cherona Levy, Paul Lang, Kelly Hodoval, Rosalynn Gaffne y and Allen Tam, for working with me on this project. Finally, I thank my parents and family members for their endless support and advice throughout my studies.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS .................................................................................................................... 4 LIST OF FIGURES .............................................................................................................................. 7 ABSTRACT .......................................................................................................................................... 9 CHAPTER 1 INTRODUCTION ....................................................................................................................... 11 Need for Denitrification .............................................................................................................. 11 Description of Denitrification Systems ...................................................................................... 11 Advantages and Disad vantages of Biological Denitrification .................................................. 12 Denitrification Chemical Equation [2] ....................................................................................... 13 Previous Research on Denitrification of the I ndustrial Process Stream (IPS) ........................ 15 Goal of This Project .................................................................................................................... 15 2 BIOTREATABILITY TEST ...................................................................................................... 16 Introduction ................................................................................................................................. 16 Procedure ..................................................................................................................................... 16 3 PRETREATMENT TO THE INDUSTRIAL PROCESS STREAM ...................................... 19 Aeration ....................................................................................................................................... 19 Introduction .......................................................................................................................... 19 Experimental Set up for Aeration Pretreatment ................................................................ 19 Biotreatability Tests to Optimize Pretreatment .................................................................. 20 Aeration of IPS at pH 2 and at pH 2 & 8 .................................................................... 20 Aeration of IPS at pH 5 and at pH 8 ........................................................................... 22 6 Hours of Aeration at pH 2 & 5 ................................................................................. 23 1 hr Aeration at pH 2 and at Air Flow Pr essure of 16 Lpm ...................................... 24 Aeration at pH 2 at 16 Lpm for Different Time Intervals ......................................... 25 Ion -exchange ............................................................................................................................... 29 Introduction .......................................................................................................................... 29 Biotreatability Tests ............................................................................................................. 29 Ion Exchanged vs. Non Ion Exchanged Sample 2 ..................................................... 29 Ion Exchanged vs. Non Ion Exchanged Sample 3 ..................................................... 30 4 CARBON SOURCE FOR DENITRIFICATION ..................................................................... 32 Introduction ................................................................................................................................. 32 Biotreatability Tests .................................................................................................................... 32 Ion Exchanged vs. Non Ion Exchanged Sample 2 without External Carbon Sou rce ...... 32

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6 Ion Exchanged vs. Non Ion Exchanged Sample 3 Without External Carbon Source ..... 34 Investigation on Other Waste Streams as Pr obable Carbon Sources ....................................... 36 5 OPTIMIZATION OF AERATION PRETREATMENT .......................................................... 42 Packed C olumn A eration ............................................................................................................ 42 Introduction .......................................................................................................................... 42 Aeration Experiment to Optimize Aeration Pretreatment ................................................. 42 6 ATTACHED GROWTH BIOREACTOR ................................................................................. 47 Introduction ................................................................................................................................. 47 Materials and methods ................................................................................................................ 47 Feed Preparation and Sampling .................................................................................................. 49 Results ad Conclusion ................................................................................................................. 50 LIST OF REFERENCES ................................................................................................................... 52 BIOGRAPHICAL SKETCH ............................................................................................................. 53

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7 LIST OF FIGURES Figure page 3 1 Assembly for aeration of the IPS .......................................................................................... 20 3 2 Absorbance results for no aeration, aeration at pH 2 and pH 2 & 8 ................................... 21 3 3 BI of IPS with no aeration, aeration at pH 2 and pH 2 & 8 ................................................. 21 3 4 Absorbance results for aeration of pH 5 and pH 8. .............................................................. 22 3 5 BI of IPS with aeration at pH 5 and pH 8 ............................................................................. 22 3 6 A bsorbance results for aeration at pH 2 & 5 for 6 hours each ............................................ 23 3 7 BI of IPS with aeration at pH 2 & 5 for 6 hrs each .............................................................. 24 3 8 Abs orbance results for aeration at pH 2 at 16 lpm for 1 hour ............................................. 25 3 9 BI of IPS with aeration for 1 hr at pH 2 and at 16 lpm ........................................................ 25 3 10 Absorbance results for aeration at pH 2 for 10 and 60 minutes. ......................................... 26 3 11 BI of IPS with aeration for different time intervals at pH 2 and at 16 lpm ...................... 266 3 12 Absorbance results for aeration IPS samples 2 and 3 .......................................................... 27 3 13 BI for aeration IPS samples 2 ................................................................................................ 28 3 14 BI f or aeration IPS samples 3 ................................................................................................ 28 3 15 Absorbance results ion exchanged and non ion exchanged sample 2 ................................ 29 3 16 BI for ion exchanged a nd non ion exchanged sample 2 ...................................................... 30 3 17 Absorbance results ion exchanged and non ion exchanged sample 3 ................................ 31 3 18 BI for ion exchanged and non ion exchanged sample 3 ...................................................... 31 4 1 Absorbance values of ion exchanged and non ion exchanged sample 2 without external carbon ....................................................................................................................... 33 4 2 BI of ion exchanged and non ion exchanged sample 2 without external carbon ............... 33 4 3 Absorbance values of ion exchanged and non ion exchanged sample 3 without external carbon ....................................................................................................................... 34 4 4 BI of ion exchanged and non ion exchanged sample 3 without external carbon ............... 35

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8 4 5 Absorbance values during biotreatability of inves tigation on other waste streams as probable carbon sources ......................................................................................................... 37 4 6 BI values during biotreatability of investigation on other waste streams as probable carbon sources ........................................................................................................................ 37 4 7 Absorbance values during biotreatability of CPS1 as a Carbon Source ............................. 38 4 8 BI values during biotreatability of CPS1 as a Carbon Source ............................................. 38 4 9 Absorbance values during biotreatability of CPS1 as a Carbon Source with and without pretreatment .............................................................................................................. 39 4 10 BI values during biotreatability of CPS1 as a Carbon Source with and without pretreatment ............................................................................................................................ 39 4 11 Absorbance during biotreatability of CPS2 as a Carbon Source ........................................ 40 4 12 BI during biotreatability of CPS2 as a Carbon Source ........................................................ 41 5 1 Packed column for aeration experiments .............................................................................. 42 5 2 Absorbance during biotreatability of aeration experiment to optimize aeration pretreatment ............................................................................................................................ 43 5 3 BI during biotreatability of aeration experiment to optimize aeration pretreatment ......... 43 5 4 Absorbance during biotreatability of aeration experiment to optimize aeration .............. 443 5 5 BI during biotreatability of aeration experiment to optim ize aeration pretreatment ......... 44 5 6 Absorbance during biotreatability of aeration experiment to optimize aeration pretreatment ............................................................................................................................ 45 5 7 BI during biotreatability of aeration experiment to optimize aeration pretreatment ....... 454 6 1 Experiment setup for attached growth reactor ...................................................................... 47 6 2 Block diagram of the attached growth reactor assembly ..................................................... 48 6 3 Performance of attached growth bioreactor (pH vs. time) .................................................. 50 6 4 Performance of attached growth bioreactor (% nitrate reduction vs. time) ........................ 50

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9 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requi rements for the Degree of Master of Science BIOLOGICAL DENITRIFICATION SYSTEM FOR INDUSTRIAL WASTEWATER By Shourie Kapadi August 2009 Chair: Spyros Svoronos Cochair: Ben Koopman Major: Chemical Engineering The purpose of this project was to investigate t he suitability of a biological system for treating a high nitrate industrial process stream (IPS). The main focus will be on the required pretreatment of the IPS. Earlier research carried out by a graduate student Sherin Peter on denitrification of the I PS has pro ved that VOCs present in it hinder bacterial growth. During this project, a ttempts were made to minimize the VOC content of the IPS so that denitrification process is not hindered. Aeration with compressed air was used as a method of stripping VO Cs out of the I PS. Experiments to find out the optimized method of aeration were carried out during this project. Presence of metal ions was also found to be a hindering factor in previous research carried out on the IPS and ion -exchanging the IPS was fou nd to be effective in dealing with this problem. However the large volumetric flow rate of the IPS makes ionexchanging cost prohibitive. It was ascertained that ion -exchanging certainly helps but is not essential. Denitrifying bacteria require carbon for their growth and adequate quantities of carbon are absolutely essential. Carbon contained in the IPS was first choice since it eliminates the extra cost external carbon source. It was found that carbon in the IPS is sufficient for significant nitrate

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10 remov al (around 70%). Effectiveness of the two waste carbon process streams (CPS) available at the industry manufacturing site was also checked as probable additional carbon sources. Performance of an attached growth bioreactor for denitrification of nigh nitr ate content wastewater was also studied during this project. It was found that the attached growth bioreactor is able to obtain 100% denitrification of synthetic nitrate sample but the pH in the bioreactor often falls below 7 during continuous operation wh ich has a potential of killing all the bacterial culture and therefore the bioreactor. pH drop results because the feed of synthetic sample used was at pH 5. Using synthetic feed at pH 7 could eliminate this problem but at a considerable expense.

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11 CHAPTER 1 INTRODUCTION Need for D enitrification Nitrate present in water can act as a fertilizer to aquatic weeds, grasses and algae H igh nitrate levels in water reservoirs can lead to their excessive growth. This leads to eutrophication and reduced oxygen level which is harmful to fish present in aquatic biosphere and hence can be a cause of ecological imbalance. It is, therefore, essential to ensure sufficient removal of nitrate [1]. EPA has strict regulations to avoid high nitrate wastes being discharged in wa ter reservoirs. Availability of nitrate can be minimized by discharging it as nitrogen gas through the application of biological denitrification. [2] Domestic wastewater contains 0 20 mg/lit of NO3 -N. [6] Industrial wastewater, on the other hand, can contain much more concentration of NO3 -N. Metal processing industries and industries manufacturing plastics and resins, explosives and fertilizers produce high nitrate content waste. [3] Description of D enitrification S ystems Denitrification involves r eduction of nitrate nitrogen ( NO3 -N) which acts as a terminal electron acceptor. The process takes place in anaerobic conditions and is alternative to reduction of oxygen. Microorganisms responsible for denitrification are facultative anaerobes. The proc ess can be carried out by a large number of microbial genre commonly found in wastewater treatment system. This includes Achromobacter, Aerobacter, Alcaligenes, Bacillus, Flavobacterium, Micrococcus, Proteus and Pseudomonas. [2] There are 2 types of enzyme systems involved with the reduction of NO3-N. [2] 1 Assimilatory: nitrate nitrogen is converted to ammonia nitrogen 2 Dissimilatory: nitrate nitrogen is converted to nitrogen gas.

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12 The Steps in the Reduction of Nitrate are g iven as [2] : NO32 2O 2 Any one of Nitric Oxide (NO), Nitrous Oxide (N2O) and nitrogen gas (N2) can be released as a gaseous end product of the process. Final end product formed depends on the type of organism and pH. N2 is the major product formed by the m ixed cultures used in wastewater treatment. [2] The process uses nitrate nitrogen as the nitrogen source for bacterial cell synthesis and as the terminal electron acceptor. Proteins, Carbohydrates, Acetate, Propionate and Benzoate etc. can be used as a car bon source. [2] Advantages and Disadvantages of Biological Denitrification Biological denitrification is a stable highly efficient and reliable method of nitrate removal The process has easy process control and can be run on a continuous basis and is th us useful in dealing with large quantities of process streams to be treated. [2] Generation of non hazardous residues is one of the most important features of biological denitrification. [4] Denitrification process can be carried out either in slurry reac tors or fixed film reactors. Both types of reactors have capability of producing quality effluents in a cost effective manner. Attached film bioreactors allow for short hydraulic residence times with high solids retention times and low solids waste after d enitrification. Slurry reactors give better process control and possess greater adaptive potential. [2] Selection of proper media size and minimization of increase in head loss throughout the system are two important problems faced in designing of attached film reactors. On the other hand, ensuring reliable settling in CSTRs with cell recycle is the problem associated with the use of slurry reactors. [2]

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13 Studies on denitrification process carried out in attached growth bioreactors showed that biomass of de nitrifying bacteria grows on the packing media. Increase in nitrate content of the wastewater fed to the bioreactor leads to increase in the biomass that gets developed on the media. This phenomenon is accompanied by the increase in pressure drop which ind icates accumulation of excessive biomass on the packed media. Increase in the pressure drop adversely affects the performance of the reactor and thus needs to be avoided. One way of regaining efficiency is to flush out the biomass using high water flow. [4] Typical values of effluent pH observed in this type of bioreactors are in 7 to 8. This pH range does not have any significant effect on rate of denitrification. High rates of denitrification were observed up to effluent pH above 9 but effluent pH more th an 9.5 seem to adversely affect the denitrification process. Use of external carbon source has proved to be effective in obtaining high nitrate removal rates for synthetic nitrate solutions. 70 80% nitrate reduction is claimed by this process. [4] Denitrif ication Chemical Equation [2] 1] Reaction for bacterial cell synthesis (Rc): 2] Reaction for electron acceptor with nitrate as the terminal electron acceptor (Ra): 3] Reaction for electron donor with acetate as the carbon source (Rd): The overall mol ar -based equation for bacterial growth can be obtained as,

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14 R = Rd + fe x Ra + fs x Rc Where, fe = fraction of electrons used for energy and fs = fraction of electrons used for biosynthesis and fe + fs = 1 Calculation of fs: fs = (growth yield) x (appropriate conversion factor) Denitrification with acetate as electron donor yields about 15 to 18 g dry matter per mole acetate. [5] We will consider 16.5 g dry matter per mole of acetate for our calculation. That is, 16.5 g dry matter per 98 g of acetate ( potassium acetate is considered here) From equation Rc, it can be said that (1/28) moles of biomass = 4.0357 grams of biomass is produced per eequivalent. From equation Rd, 8 g COD = 1 eequivalent. Therefore, gVSS equivalent e x equivalent e gCOD x gCOD gVSS fs 0357 4 8 98 5 16 Therefore, fs = 0. 33 Therefore, fe = 0.67 Final equation fir denitrification can be obtained by putting values of fs and fe in the formula for overall rate equation ( R) stated above.

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15 Previous R esearch on D enitrification of the Industrial Process Stream (IPS) A graduate stud ent, Sherin Peter, proved in her research that biological denitrification of the IPS is possible after removal of VOCs present in it by aeration of the IPS. She also proved that, higher denitrification rates can be obtained by cation exchanging the IPS a nd thereby minimizing the metal ions present in it. Desired rate of denitrification of the IPS can be obtained after providing it with pretreatment of aeration (to remove VOCs) and ion -exchange (to minimize metal ions) and with the use of external carbon s ource in the form of Potassium Acetate. It was possible to get denitrification rate of around 2 mg NO3N/L/min and an overall denitrification of 98%. Investigation of available carbon process streams (CPS) with the industry as alternate carbon sources was not done. It was found that micronutrients should be directly added to the reactor since precipitation of micronutrients in feed creates deficiency of micronutrients in the reactor which affects the rate of denitrification. Goal of T his P roject The main fo cus of this research work was to determine and optimize a pretreatment to the IPS which can be implemented on an industrial scale. This included optimization of aeration required to strip off the VOCs present in the IPS and investigation of the necessity o f ion exchanging the IPS. Selection of cost efficient carbon source was also an important area to be researched. Performance of attached film bioreactor for denitrification of high nitrate synthetic wastewater was also studied.

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16 CHAPTER 2 BIOTREATABILITY TEST Introduction Earlier research on denitrification on the industrial process stream (IPS) has proved that presence of Volatile Organic Compounds (VOCs) and metal ions present in the IPS affect the growth of denitrifying bacteria. Designing of pretreat ment which makes IPS more suitable for denitrifying bacteria was essential. To verify if pretreatment provided to the IPS is good enough to sustain bacterial growth in it, a batch test was developed during previous research. This test provides us with Bio logical Treatability Index (BI) which is a comparison of the maximum specific growth rate ( max) of denitrifying bacteria grown in an IPS sample to that of denitrifying bacteria grown in a synthetic nitrate sample of the same nitrate -nitrogen concentration: Treatable nitrate solutions will have a value close to 1. While BI of 0 indicates that the sample can not be denitrified biologically. Procedure 1] NO3-N content of the IPS sample is measured using HACH NitraVer Test N Tube test kits. 2] A synthetic nitrate solution of about the same NO3--N content is prepared by adding concentrated nitri c acid to DI water. Approximately 250 ml of synthetic nitrate solution is prepared to carry out each test. 3] 4:1 ratio of carbon to NO3--N is used in all the samples used in this test. Potassium acetate is used as a carbon source. 4] Following chemicals are added to support bacterial growth and metabolism:

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17 a 0.5 g/L potassium phosphate as phosphorus source b 0.1 g/L magnesium sulfate heptahydrate as magnesium source c 0.3 g/L ammonium chloride as the ammonium source 5] Synthetic nitrate solution and the IPS sa mple are neutralized to pH 8 using NaOH pallets. 6] Well stirred samples of synthetic nitrate solution and the IPS separated in three parts of volume 60 ml each are put in three125 ml Erlenmeyer Flasks. 7] 10 ml of denitrifying bacterial culture, grown in a high synthetic nitrate stream, is added to each flask. 8] 0.2 ml micronutrient solution (prepared using instructions for trace element solution by Vishniac & Santer) is also added to each flask. Addition of micronutrient solution is critical for bacteri al growth during the experiment. 9] 5 ml sample is collected from each flask and flasks are stoppered immediately with solid rubber stoppers. Initial (time = 0 hrs) readings of NO3-N, pH, and absorbance are obtained using 5 ml samples drawn out. The NO3 -N concentration is measured after filtering the sample from each flask using 0.45 m filters, and diluting the samples to appropriate concentrations. 10] All the flasks are kept in a shaking incubator set at 37 11] pH, and absorbance readi ngs of one flask of each sample (Synthetic nitrate solution and IPS) are measured at around 3 4 and 78 hrs. 12] Final NO3-N concentration, pH and absorbance are measured at 2224 hrs. 13] To calculate maximum specific growth rate of denitrifying bacteri a in a sample, a graph of [ln (absorbance)] vs. time was plotted. It was proved in earlier research that, the slope of a trend

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18 line which shows the best fit of the data points gives the maximum specific growth rate for the sample. Final value of BI was the n calculated as ( _max) sample / ( _max) synthetic solution

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19 CHAPTER 3 PRETREATMENT TO THE INDUSTRIAL PROCESS S TREAM Aeration Introduction Previous studies on the industrial process stream (IPS) proved that presence of volatile organic compounds (VOCs) pr esent in it hinder the growth of denitrifying bacteria and aeration of the IPS can be used as a pretreatment before it is used for the process of denitrification. It was essential to optimize the pretreatment so that it can be implemented on industrial sca le in a cost effective way. Various factors which affect the performance of aeration pretreatment were considered. Aeration of the IPS at different pH, different time durations and air flow rate were tried to find out the best trade -off between the cost a nd the effectiveness of the pretreatment. Packed column aeration was also used in order to achieve efficient removal of VOCs. Experimental Set up for A eration P retreatment 1] Aeration was performed in stirred vessel Specifications: Made by New Brunswic k Scientific C o ., I nc and the specific machine used was BIOFLO 110 Fermentor/Bioreactor 2] The aeration pretreatment to the IPS was carried out in a chemical hood. This is because VOCs getting stripped out of the IPS were assumed to be harmful to the human body. 3] Five hundred milliliters of sample is poured into the vessel Agitation is set to 550 rpm. 4] Air from a compressed air tank is passed through a flowmeter and then sent into vessel right below the rotating blades. Air flow rate was adjust ed as per the pretreatment requirements of individual experiment. Air flow rate was measured by the flowmeter.

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20 5] Duration of the aeration was also determined by the pretreatment requirements of individual experiment. Samples obtained after this pretreatment were used in biotreatability tests. Figure showing air tank, vessel used for aeration is shown below. Fig ure 3 1. Assembly for aeration of the IPS Bio treatability T ests to Optimize Pretreatment 1] Aeration of IPS at pH 2 and at pH 2 & 8 In order t o remove weakly acidic VOCs, it was essential to aerate the IPS at low pH. IPS was therefore aerated at pH 2. It was also hypothesized that the IPS may contain some basic VOCs. To get rid of those VOCs, IPS was aerated at pH 8. First biotreatability test c onducted used following three different IPS samples: 1] Aeration at pH 2 for 2 hours and at air pressure of 1.6 lpm. 10 corresponds to 1.6 L/min and the volume of the sample aerated was 500 ml. 2] Aeration at pH 2 and 8 for 2 hours each and at air pressure of 1.6 lpm.

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21 3] No pretreatment. Results of the experiment are shown in graphs below: Figure 3 2 Absorbance results for no aeration, aeration at pH 2 and pH 2 & 8 Figure 3 3 BI of IPS with no aeration, aeration at pH 2 and pH 2 & 8 1] Aeration a t pH 2 for 2 hours = 0.27 2] Aeration at pH 2 & 8 for 2 hours each = 0.77 3] No pretreatment, BI = 0.04

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22 Low BI value for the sample without any pretreatment ascertained previous findings that pretreatment of the IPS is certainly required. It was also foun d that aeration of the IPS at pH 2 and pH 8 is more effective than aeration at pH 2. 2] Aera tion of IPS at pH 5 and at pH 8 Raising pH of the IPS to 8 is cost prohibitive and therefore it was decided to find out the BI value of the IPS at slightly lower p H. Another experiment was carried out in which following pretreatments were considered: 1] Aeration at pH 5 for 2 hours and at air pressure of 1.6 lpm 2] Aeration at pH 8 for 2 hours and at air pressure of 1.6 lpm Results of the experiment are shown in g raphs below: Figure 3 4 Absorbance results for aeration of pH 5 and pH 8. Figure 3 5 BI of IPS with aeration at pH 5 and pH 8

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23 1] Aeration at pH 5 for 2 hours, BI = 0.11 2] Aeration at pH 8 for 2 hours, BI = 0.03 Low BI values from this experimen t proved that it is essential to aerate the IPS at pH 2 to remove acidic VOCs. But last experiment showed low BI value for aeration the IPS sample aerated at pH 2. Therefore it was concluded that aeration for 2 hours at 1.6 lpm of air flow pressure is not enough pretreatment to the IPS and it is essential to find out a better way to aerate the IPS more efficiently. 3] 6 H ours of A eration at pH 2 & 5 In order to achieve more efficient aeration, the IPS sample was aerated for 6 hours at pH 2 and 5 each. The air flow pressure was set at 1.6 lpm. Following graphs show the result of this experiment. Figure 3 6 Absorbance results for aerati on at pH 2 & 5 for 6 hours each

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24 Figure 3 7 BI of IPS with aeration at pH 2 & 5 for 6 hrs each BI value in this case was found to be equal to 0.85. This is significantly greater than previous BI values obtained for aeration of the IPS for 2 hours. High BI value obtained from this experiment showed that pretreatment of the IPS was successful. But again, raising pH of t he IPS to 5 is not cost efficient as far as implementing it on the industrial scale is concerned. It was thus essential to examine if aeration at pH 2 can give good BI values. 4] 1 -hr A eration at pH 2 and at A ir F low P ressure of 16 L pm In an attempt to ge t high BI value (i.e. efficient pretreatment) to the IPS at pH 2, an experiment was carried out in which the IPS was aerated for 1 hour at pH 2 and at air flow pressure of 16 lpm. Following graphs show the result of this experiment.

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25 Figure 3 8 Absorbance results for aeration at pH 2 at 16 lpm for 1 hour Figure 3 9 BI of IPS with aeration for 1 hr at pH 2 and at 16 lpm BI for this experiment is 1.06 which is in the limits of experimental error. This result shows that 1 -hr aeration to the IPS at pH 2 and at air flow pressure of 16 lpm makes the IPS treatable by the denitrifying bacteria. Air flow rate was measured as 16 liters/min. 5] Aeration at pH 2 at 16 L pm for D ifferent Time I ntervals Having found that aeration at pH 2 can work great with highe r air flow rates, it was essential to figure out if aeration conducted for lesser period of time can serve as a sufficient pretreatment for the practical applications.

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26 An experiment was therefore conducted to optimize aeration. Pretreatment conditions are as listed below: 1] Aeration at pH 2 at 100 for 10 minutes 2] Aeration at pH 2 at 100 for 60 minutes Following graphs show the result of this experiment. Figure 3 10. Absorbance results for aeration at pH 2 for 10 and 60 minutes. Figure 3 11. BI of IPS with aeration for different time intervals at pH 2 and at 16 lpm

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27 BI for the IPS sample aerated for 10 minutes was found to be equal to 0.27 and that of the IPS sample aerated for 1 hr was found to be equal to 0.77. All the experiments performed til l now were performed on sample 1. It was known that the IPS has variability in its composition. Sample 3 had NO3-N of approximately 2600 mg/lit. To verify if the method of biological denitrification works at such a high nitrate level, a biotreatability te st conducted was conducted on 1] Sample 2 with NO3-N content of 1100 mg/lit and 2] Sample 3 with NO3-N of 2600 mg/lit Both the samples were aerated at pH 2 for 1 hour and at 16 lpm It should be noted that the ratio of potassium acetate to nitrate nitr ogen used for the IPS sample 3 is maintained between 2.5 to 3 is to 1. This is done because high levels of carbon corresponding to exceptionally high NO3N levels in IPS sample 3 were assumed to be harmful for the growth of denitrifying bacteria. The same ratio is used whenever IPS sample 3 during an experiment. Following graphs show the result of this experiment. Figure 3 12. Absorbance results for aeration IPS samples 2 and 3

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28 Figure 3 13. BI for aeration IPS samples 2 Figure 3 14. BI for aerati on IPS samples 3 BI of sample 2 was found to be approxmitely equal to 0.6 and that of sample 3 was 0.96. There results proved that the denitrifying bacteria work well even at very high nitrate content. These results also conclude that, variability of the IPS will not have adverse effect on the process of denitrification if the IPS is pretreated properly.

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29 Ion -exchang e Introduction Previous studies on the IPS have proved that ion -exchanging the IPS helps to increase the rate of denitrification. Although it was a useful finding, it was impractical to implement it on a industrial scale. It was therefore necessary to find out if ion -exchanging IPS is absolutely essential. Biotreatability Tests 1] Ion Exchanged vs. N on I on E xchanged S ample 2 Ion -exchanged sampl e 2 and non -ion exchanged sample 2 were used to carry out biotreatability test. Both the samples were aerated for 1 hr at pH 2 at 16 lpm Following graphs show the result of this experiment. Figure 3 15. Absorbance results ion exchanged and non ion ex changed sample 2

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30 Figure 3 16. BI for ion exchanged and non ion exchanged sample 2 Results of the biotreatability test showed that BI of the ion -exchanged sample is 0.99 and that of non ion -exchanged sample is 1.28. Although a BI value of 1.28 is on a h igher side, it is within the limits of experimental error. But this experiment proves that both the samples are well treated and are good to be used for the process of denitrification and non ion -exchanged sample is certainly treatable. 2] Ion Exchanged vs N on I on E xchanged S ample 3 Ion -exchanged and non ion exchanged sample 3 were used to in a biotreatability test to account for the variability in constitution of the IPS. Sample 3 has exceptionally high nitrate content. Both the samples were aerated for 1 hr at pH 2 at 16 lpm.

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31 Following graphs show the result of this experiment. Figure 3 17. Absorbance results ion exchanged and non ion exchanged sample 3 Figure 3 18. BI for ion exchanged and non ion exchanged sample 3 The BI of the ion exchanged s ample was found to be equal to 0.4 and that of non ion exchanged sample was found to be equal to 0.7. Therefore, it is confirmed that non ion exchanged sample can work well.

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32 CHAPTER 4 CARBON SOURCE FOR DE NITRIFICATION Introduction After pretreatment was designed and optimized, it was essential to find out if the carbon content of the IPS is enough carbon source for the process of denitrification. Carbon contained in the IPS was the first choice because it eliminates the cost associated with using external carbon source. Biotreatability tests were thus performed on the samples of the IPS to figure out if the use of external carbon source can be avoided. It should be noted that the use of external carbon source is essential in case of the synthetic nitrate s ample used in the biotreatability test. Synthetic nitrate solution is made by adding small amount of conc. nitric acid to water and thus can not possibly have carbon present in it. Biotreatability Tests 1] Ion Exchanged vs. N on I on E xchanged S ample 2 w itho ut E xternal C arbon S ource All the procedure of biotreatability test previously described remains the same except that no potassium acetate is added to the IPS samples. Ion -exchanged sample 2 and non -ion exchanged sample 2 were aerated at pH 2 at 100 lpm. B oth these samples are devoid of external carbon source. Following graphs show the result of this experiment.

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33 Figure 4 1 Absorbance values of ion exchanged and non ion exchanged sample 2 without external carbon Figure 4 2 BI of ion exchanged and n on ion exchanged sample 2 without external carbon IPS without external Carbon has initial nitrate nitrogen of 820 mg/lit and final nitrate nitrogen of 246 mg/lit. This is 70% reduction. When synthetic sample had 730 mg/lit of initial nitrate nitrogen and 2 0 mg/lit of final nitrate nitrogen. This is 97.3 % reduction. Nitrate nitrogen reduction obtained at the end of BI test (24 hrs) on sample 2 gave 70% nitrate reduction. The BI value of ion exchanged sample is 0.82 and that of non ion exchanged

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34 sample is ar ound 1. The excellent BI does indicate that the carbon is available. Also the fact that synthetic and IPS stopped being exponential at the same time indicates that the carbon contained in the IPS may be sufficient. These ion exchanged and non ion exchanged sample BI values seem to refute previous findings that metal ions hinder the growth of denitrifying bacteria. But the laboratory analysis of ion exchanged and non ion changed IPS sample 2 shows that there is little difference between metal ion content of both the samples and both the samples have very low copper content. 2 ] Ion Exchanged vs. N on I on E xchanged S ample 3 Without E xternal C arbon S ource The same experiment was carried out on ion -exchanged sample 3 and nonion exchanged sample 3. Pretreatment used was aeration at pH 2 for 1 hour at 16 lpm Following graphs show the result of this experiment. Figure 4 3 Absorbance values of ion exchanged and non ion exchanged sample 3 without external carbon

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35 Figure 4 4 BI of ion exchanged and non ion exc hanged sample 3 without external carbon Since the IPS sample 3 had exceptionally high nitrate content, final reading of the experiment was taken at 38.5 hrs. In general, last reading was taken at around 3639 hrs in all those experiments in which sample 3 was used. But in some cases it was observed that absorbance of synthetic nitrate solution started dropping after 24 hrs which as indicated by the nitrate test showed that the NO3 -N of the synthetic nitrate sample got eaten up by the bacteria and hence ba cteria started dying. In such cases, therefore, final reading of 36 39 hrs had to be dropped and results are based on reading obtained after 24 hrs. The BI of ion -exchanged and non ion -exchanged sample was measured to be 0.79 and 0.82. This experiment shows that the IPS without external carbon exhausted carbon much earlier than the synthetic sample. Therefore, when nitrate nitrogen levels are very high, addition of external carbon will be beneficial. Again, these ion exchanged and non ion exchanged sample BI values seem to refute previous findings that metal ions hinder the growth of denitrifying bacteria. But the laboratory analysis of ion exchanged and non ion changed IPS sample 3 shows that there is little difference

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36 between metal ion content of both th e samples and both the samples have very low copper content. Investigation on Other Waste Streams as Probable C arbon S ources It may be questioned that if carbon present in the IPS is found to be sufficient for carrying out denitrification process then investigation on other carbon sources is not justified. Reasons to investigate CPS are as follows: 1] 2 Waste Carbon Process Streams are available and need treatment. If one or both of those can be used in this process and treated then cost of treating the m separately may be avoided. Results obtained from these experiments can serve as data for the cost -benefit optimization problem. 2] The IPS is highly variable in NO3-N content and contents of other constituents like the carbon source. It will be therefor e worth investigating if CPS available can be used as additional carbon source so that the denitrification process under consideration is invulnerable against changes in composition of the IPS. It should be noted that, these experiments were carried out co nsidering constraints on availability of waste carbon process streams. In all the experiments performed on CPS 1 and CPS 2, therefore, the ratio of volume of CPS used to that of IPS used is maintained the same as per those constraints and carbon to NO3 -N ratio is not guaranteed as 4:1. Two industrial waste streams were available as probable carbon sources. It was required to find out if any of those can be used as a carbon source for denitrification process. A biotreatability experiment was therefore conducted with the first carbon source. Following four samples were used to carry out the test: 1] Synthetic 2] IPS (aerated at pH = 2 at 100 for 1 hour) + Synthetic Carbon 3] CPS 1 (aerated at pH = 4.75 at 16 lpm for 1 hour) + synthetic nitrate

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37 4] IPS (aerat ed at pH = 2 at 100 for 1 hour) + CPS 1 (aerated at pH = 4.75 at 16 lpm for 1 hour) Figure 4 5 Absorbance values during biotreatability of investigation on other waste streams as probable carbon sources Figure 4 6 BI values during biotreatability of investigation on other waste streams as probable carbon sources Results of the experiment are: 1] IPS + synthetic carbon, BI = 0.86 2] CPS 1 + synthetic nitrate, BI = 0.46 3] IPS + CPS 1, BI = 0.11 The experiment shows that CPS1 can not be used as a carbon source since BI is very low. Another experiment was carried out in which CPS1 was used as a carbon source and synthetic nitrate was used as a NO3-N source. Results of the experiment are shown in the figure.

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38 Figure 4 7 Absorbance values during biotreatability of CPS1 as a Carbon Source Figure 4 8 BI values during biotreatability of CPS1 as a Carbon Source From the graph, it can be seen that the BI of CPS1+ Synthetic Nitrate solution is 0.45. It can be concluded from this experiment that CPS1 (without pretreatment) is not a good carbon source for the denitrification process. To check if CPS1 can serve as a good carbon source after aeration as a pretreatment, an experiment was performed in which an aerated sample of CPS1 was compared to the nonaerated sample of CPS1. 500 ml of CPS1 was aerated for 1 hour. Results of the experiment are shown in the graphs below:

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39 Figure 4 9 Absorbance values during biotreatability of CPS1 as a Carbon Source with and without pretreatment Figure 4 10. BI val ues during biotreatability of CPS1 as a Carbon Source with and without pretreatment Results are: 1] Non aerated CPS1 + synthetic nitrate, BI = 0.32

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40 2] Aerated CPS1 + synthetic nitrate, BI = 0.31 It can be seen that there is no significant difference in pe rformance of aerated and non aerated CPS1 as a carbon source. Also, both the samples showed low value of BI. It can be concluded that the CPS1 is not a good carbon source of the denitrification process under consideration. Investigation of CPS2 as a carbon source for denitrification process: 500ml of CPS2 was aerated at pH = 1.5 at 16lit/min for 2 hours. The sample obtained after this pretreatment is used as a carbon source for the biotreatability experiment. Following samples are used in this experiment: 1] IPS (aerated for 1 hr at pH =2 and at 16 lit/min) + Synthetic carbon 2] CPS 2 (aerated for 2 hrs at pH = 1.6 and at 16 lit/min) + Synthetic Nitrate 3] IPS (aerated for 1 hr at pH =2 and at 16 lit/min) + CPS 2 (aerated for 2 hrs at pH = 1.6 and at 16 li t/min) Figure 4 11. Absorbance during biotreatability of CPS2 as a Carbon Source

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41 Figure 4 12. BI during biotreatability of CPS2 as a Carbon Source Results are given below: 1] Aerated IPS + Synthetic Carbon, BI = 0.745 2] Aerated CPS 2 + Synthetic Nitrate, BI = 0.166 3] Aerated IPS + Aerated CPS 2, BI = 0.021 Since BI values of all the samples in which CPS 2 was used as a carbon source are low, we can conclude that CPS 2 is not a good carbon source for the denitrification process under consideration.

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42 CHAPTER 5 OPTIMIZATION OF AERA TION PRETREATMENT Packed C olumn A eration Introduction In order to achieve aeration in more efficient manner, packed column aeration was used. P acking increase the contact area between air and the IPS and the air residenc e time; leading to more efficient VOC removal. In order to maintain safe working conditions in the lab, counter current aeration was avoided. Air was passed from the bottom to the top of the packed column against the stagnant volume of IPS. Figure 5 1. Packed column for aeration experiments Aeration E xperiment to O ptimize A eration P retreatment To optimize aeration, an experiment was performed in which the IPS was pretreated using the packed column. 500 ml of nonion exchanged sample 3 was used in each of the following samples of this experiment: 1] Aeration for 15 min at 16 lpm 2] Aeration for 30 min at 16 lpm

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43 3] Aeration for 60 min at 16 lpm 4] Aeration for 60 min at 8 lpm 5] Aeration for 60 min at 4 lpm Figure 5 2 Absorbance during biotreatability of aeration experiment to optimize aeration pretreatment Figure 5 3 BI during biotreatability of aeration experiment to optimize aeration pretreatment

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44 Figure 5 4 Absorbance during biotreatability of aeration experiment to optimize aeration pretre atment Figure 5 5 BI during biotreatability of aeration experiment to optimize aeration pretreatment

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45 Figure 5 6 Absorbance during biotreatability of aeration experiment to optimize aeration pretreatment Figure 5 7 BI during biotreatability of aeration experiment to optimize aeration pretreatment The results of biotreatability of these samples are: 1] Aeration for 15 min at 16 lpm ( 100 kPa), BI = 0.65 2] Aeration for 30 min at 16 lpm ( 100 kPa), BI = 0.75 3] Aeration for 60 min at 16 lpm ( 1 00 kPa), BI = 0.73 4] Aeration for 60 min at 8 lpm ( 50 kPa), BI = 0.70 5] Aeration for 60 min at 4 lpm ( 25 kPa), BI = 0.59

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46 This experiment proved that packed column aeration for lesser period of time and at lesser pressure of air flow provide good pret reatment to the IPS. These results provide useful data for optimization during process designing. But as a result of packed column aeration, it was concluded that efficient aeration method can reduce the time duration of the pretreatment and air flow rate required to achieve efficient aeration.

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47 CHAPTER 6 ATTACHED GROWTH BIOREACTOR Introduction Attached growth bioreactors are reactors in which bacteria attach on solid immobile packing medium like rock, slag, ceramic or plastic. In order to maintain anoxic c onditions in the reactor, media is kept submerged. Recirculation makes the system homogeneous. Attached growth bioreactors allow for short hydraulic residence times with high solids retention times and low solids waste after denitrification. Materials an d methods Gas Outlet released in water to maintain anaerobic conditions Recycle Stream Gas Outlet EffluentTank Feed Tank Figure 6 1 Experiment setup for attached growth reactor

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48 Effluent Recycled Reactor Nitrate Synthetic Gas Outlet Tank Stream Feed Nitrate T ank Stream Figure 6 2 Block diagram of the attached growth reactor assembly A 3.78 L HDPE bottle was used to construct the attached growth bioreactor. The set up of the bioreactor is shown in figure 6.1. It was filled to 3/4th of its volume by rock media from Biomax and a culture of denitrifying bacteria grown on high synthetic nitrate stream. About 2 liters of denitrifying bacterial culture was used. The working volume of the bioreactor was ar ound 3.5 liters. This media provided high surface area for the attached growth of bacterial cells. Denitrifying bacteria were allowed to attach to the rock media by not starting either recycle or fresh feed pump for the first day. The reactor content was j ust recirculated on the second day. This was done to homogenize the reactor content. Fresh feed pump was kept off for first couple of days. The bioreactor was provided with 8 inlet ports at the bottom to avoid channeling of the inlet feed. An outlet port w as provided at a level of upper end of the rock packings. Bioreactor content was pumped out of this end (recycled) and was mixed with a stream of high synthetic

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49 nitrate content. Flow rates of the recycled bioreactor effluent and the synthetic nitrate feed stream were adjusted such that the pH of the combined stream is around 7. Flow rate of the recycled stream was maintained at 9.45 ml/min and that of the synthetic nitrate feed stream was maintained at 0.7 ml/min. The reactor was therefore operated at a rec ycle rate of 13.5. The combined feed stream was pumped from the bottom of the bioreactor to its top. Effluent outlet was provided at a level slightly higher than the recycle outlet. This means that, a small volume of the reactor in its upper portion does n ot have any rock media. This ensures the maintenance of anaerobic conditions in the reactor volume. Effluent receiving tank was adjusted in such a way that the effluent moves to the receiving tank under gravity. One end of the effluent tube was inserted in to the effluent port while the other end was place in water to prevent air entering into the bioreactor through effluent tube. Denitrification process produces carbon dioxide ( CO2) and Nitrogen ( N2) gases. It is, therefore, essential to provide a bioreacto r with a gas outlet. One end of the gas outlet was provided at the top of the bioreactor while the other end of the gas outlet was placed in a beaker filled with water. This was done to maintain anoxic conditions into the bioreactor. Feed P reparation and S ampling Synthetic nitrate solution with high NO3 --N content was made by adding concentrated nitric acid to DI water. Concentration of NO3 -N in the synthetic nitrate feed was set to around 1000 mg/lit of NO3 -N. Potassium acetate was added as a carbon sour ce. A carbon to nitrate nitrogen ratio of 4:1 was maintained in the feed. 0.024 g/lit of potassium phosphate was added as a source of phosphorus. 0.01 g/lit of yeast extract and 0.03 ml/lit of molybdic acid solution prepared by adding 1.1 g of molybdic aci d dissolved in 1000 ml of DI water. 4 drops/lit of micronutrients were added to the feed. The resulting synthetic nitrate solution has a pH of around 5.

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50 Sample of the bioreactor content were obtained from the effluent outlet tube. pH and NO3 -N were measu red once a day. NO3 -N was measured using HACH NitraVer test kits and a spectrophotometer. Figure 6 3 Performance of attached growth bioreactor (pH vs. time) Figure 6 4 Performance of attached growth bioreactor (% nitrate reduction vs. time) R esults ad Conclusion It was observed that the pH of the effluent of attached growth bioreactor remains in the range of 7 to 8. Even though optimal growth of denitrifying bacteria is observed in the pH range of 8 to 9.5, 100% reduction of NO3 -N was noted e ven in this pH range. The reactor was run for around 5 weeks and maximum NO3 -N reduction of 0.7 mg/min i.e. 0.35 mg/ (lit.min) was obtained.

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51 Previous research carried out by a graduate student Sherin Peter studied denitrification of synthetic nitrate s olution in a suspended growth bioreactor run as a CSTR. It was found that, NO3 -N reduction of 4 mg/ (lit. min) is achievable on a synthetic nitrate solution. This rate of denitrification is much higher than the rate of denitrification obtained by an atta ched growth reactor. Fluctuating values of pH was the most important reason why higher flow rates of fresh nitrate feed were not opted for. pH of the reactor below 7 has the ability of killing the bacterial culture and thereby entire reactor. Feed at pH 7 can be used to keep the bioreactor operational in pH level of 7 to 9.5. In conclusion, 100% denitrification obtained in the attached growth bioreactor was an encouraging fact about the performance of this reactor. Difficulty in controlling the pH fluctua tions was a hindering factor in achieving higher rates of nitrate reduction.

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52 LIST OF REFERENCES 1] Tchobanoglous G., Burton F.L. & Stensel, D.H. (2003). Wastewater Engineering: Treatment and Reuse Boston: McGraw -Hill, c2003. 2] Leslie Grady C.P., Daigger, G.T., and Lim, H.C. (1980). Biological Wastewater Treatment: theory and applications New York: M. Dekker, c1980. 3] Nemerow N.L. (1978). Industrial Water Pollution: Origins, Characteristics and Treatment Reading, Mass.: Addison-We sley Pub. Co., c1978. 4] Gabaldn, C. Izquierdo M., MartnezSoria V. Marzal P., & Alvarez Hornos F.J. (2007) Biological nitrate removal from wastewater of a metal -finishing industry. Journal of Hazardous M aterials 148, 485490 5] Strohm, T.O., Gri ffin, B., Zumft, W G. & Schink B (2007). Growth Yields in Bacterial Denitrification and Nitrate Ammonification Appl Environ Microbiol 73(5), 1420 1424 6] Fresenius W., Deutsche Gesellschaft fr Technische Zusammenarbeit (1989). Waste water technology: origin, collect ion, treatment, and analysis of waste water Berlin; New York: Springer -Verlag, c1989.

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53 BIOGRAPHICAL SKETCH Author, Shourie Kapadi, has completed his Bachelors Degree in Chemical Engineering at the University of Mumbai. He then pursued his masters degree in Chemical Engineering at the University of Florida. He received his degree in August 2009. This thesis was a part of his research work conducted while studying as a graduate student at the University of Florida. The inspiration to pursue work on denitri fication came from his interest in the area of Biological Wastewater Treatment.