SUPPRESSION OF SULFATE REDUCING BACTERIA DURING ANAEROBIC TREATMENT by SK. ZIAUDDIN AHAMMAD DEPARTMENT OF BIOCHEMICAL ENGINEERING AND BIOTECHNOLOGY Submitted in fulfillment of the requirements of the degree of DOCTOR OF PHILOSOPHY to the INDIAN INSTITUTE OF TECHNOLOGY DELHI NEW DELHI - 110016, INDIA JULY 2009
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SUPPRESSION OF SULFATE REDUCING
BACTERIA DURING ANAEROBIC TREATMENT
by
SK. ZIAUDDIN AHAMMAD DEPARTMENT OF BIOCHEMICAL ENGINEERING AND BIOTECHNOLOGY
Submitted
in fulfillment of the requirements of the degree of
DOCTOR OF PHILOSOPHY
to the
INDIAN INSTITUTE OF TECHNOLOGY DELHI NEW DELHI - 110016, INDIA
JULY 2009
ti\J2.41 kA,(.
I. L., ill
Acc.
Certificate
This is to certify that the thesis entitled "Suppression of Sulfate Reducing Bacteria
during Anaerobic Treatment" being submitted by Sk. Ziauddin Ahammad is worthy of
consideration for the award of the degree of Doctor of Philosophy. The thesis has been
prepared under my supervision and guidance in conformity with the rules and regulations
of Indian Institute of Technology Delhi and is a record of the original bonafide research
work. The results presented in this thesis have not been submitted in part or full to any
other universities or institutes for the award of any other degree or diploma.
Dr. T.R. Sreekrishnan Dr. James Gomes Professor Associate Professor Department of Biochemical Engineering and Biotechnology School of Biological Sciences Indian Institute of Technology Delhi Indian Institute of Technology Delhi
Acknowledgements
I am extremely grateful to my supervisors Prof. T. R. Sreekrishnan and Dr. James Gomes
for their expert guidance and constant encouragement throughout my project. It would not
have been possible at all to complete my thesis successfully, without their continuous support
and motivation. I am highly indebted to them for their patience and devoting their valuable
time throughout my work.
I am very thankful to Prof. G. P. Agarwal, Prof. J. K. Deb, Prof. Sunil Nath, Dr. P.K.
Roychoudhuri, Dr. A.K. Mittal and Prof. Mukesh Khare for their valuable suggestions and
encouragements.
My indebted thanks to Dr. Russell Davenport, Mrs. Fiona Read, Prof. Thomas Curtis of
CEG, Newcastle University for their expert guidance and teaching, which helped me to learn
molecular biology techniques applied in Environmental Engineering.
I am very much thankful to Mr. J. A. Khan, Mr. D.B. Sharma for their technical support and
cooperation.
I am grateful to the authorities of Indian Institute of Technology, Delhi for the facilities
received, to the All India Council of Technical Education, New Delhi for financial assistance
through National Doctoral Fellowship to carry out the research work.
My heartfelt thanks to my lab mates Dr. Mukesh Goel, Mr. Ramesh Motipalli, Mr. Dileep
P.V. for their ever-helping hands. I express my gratitude to my friends Mr. A.Remesh, Mr.
Mohit Naresh, Ms Meenu Chhabra, Mr. Muthu M., Mr. Javed Equbal, for their wholehearted
support throughout my stay in IIT.
It is not possible to express in word the support and love I received from my parents and
other family members. ‘x .21'444444- A-kuwb.A31 Dated, IIT Delhi
(Sk. Ziauddin Ahammad) Hauz Khas, New Delhi, The 8th July, 2009
ii
Abstract
In anaerobic wastewater treatment processes, the sulfate-reducing bacteria (SRB), which
coexist with methanogens, produces hydrogen sulfide (H2S). Though several techniques
are being used to remove H2S from biogas to obtain H2S-free biogas, none of those are
cost effective. This study was taken up to attempt the suppression of SRB in anaerobic
reactors using modifications in process as well as reactor operating conditions.
The effects of different parameters like temperature, volatile fatty acids (VFA)
concentration and reactor dilution rate on the growth of SRB in these reactors were
studied. Complete suppression of SRB with H2S free biogas containing 72 and 76%
methane was achieved at 55°C in batch reactor and in continuous stirred tank reactor
(HRT 3.8 d) respectively. The effect of immobilization on the suppression of SRB was
also studied with different support materials. Bio-film immobilized on nylon granules
produced H2S free biogas containing 68% methane in an anaerobic fluidized bed reactor
(HRT 0.55 d). Anaerobic RBC having acrylic discs favored the methanogens over SRB
to form bio-film on the disc resulting in H2S free biogas containing 53 % methane. SRB
suppression was found to be independent of VFA concentration in both batch and
continuous processes. A mathematical model has been developed and simulated with the
experimental observations to predict the interaction behavior of SRB and methanogens in
the mixed culture system.
The results of this research show for the first time that it is possible to eliminate SRB
from anaerobic cultures to produce H2S-free methane by manipulating the operational
iii
parameters. Consequently, the process technology based on these findings will be placed
economically at a significantly advantageous position compared to existing technologies
for the removal of H2S from biogas.
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CONTENTS Page No.
Certificate
Acknowledgements ii
Abstract iii
Contents v
List of Figures x
List of Tables xviii
Nomenclature xx
1 INTRODUCTION AND OBJECTIVES 1-4 1.1. Introduction 1
1.2 Objectives 3
2 LITERATURE REVIEW 5-38 2.1 Background 5
2.2 Anaerobic wastewater treatment process 7
2.3 Biogas- a degradation byproduct 10
2.4 Characteristics of methanogens and SRB 12
2.4.1 Methanogens 12
2.4.2 Sulfate reducing bacteria (SRB) 14
2.5 Competition between sulfate reducers, methanogens
and acetogens 17
2.5.1 Hydrogen 17
2.5.2 Acetate 18
2.5.3 Propionate 18
2.5.4 Butyrate 19
2.6 Commonly used reactors in anaerobic process 20
v
2.7 Parameters affecting the reactor performances
during anaerobic treatment 21
2.7.1 pH 22
2.7.2 Waste composition 23
2.7.3 Temperature 23
2.7.4 Loading rate 24
2.7.5 Retention time 24
2.7.6 Toxicity 24
2.7.7 Granule deterioration 27
2.8 Problems associated with SRB 27
2.9 Industries prone to MIC by SRB 29
2.10 Containment of H2S to control MIC 31
2.10.1 Growth inhibition of SRB in the treatment system 32
2.10.1.1 Growth inhibition using biocides 32
2.10.1.2 Prevention of anaerobic activity by changing
terminal electron acceptor 33
2.10.2 Removal of H2S from the biogas produced in the