Anaerobic Digestion of Yard Waste and Biogas Purification by Removal of Hydrogen Sulfide ...

103 Pages·2012·4.93 MB·English

Anaerobic Digestion of Yard Waste and Biogas Purification by Removal of
Hydrogen Sulfide

Thesis

Presented in Partial Fulfillment of the Requirements for the Degree Master of
Science in the Graduate School of The Ohio State University
By
Phillip B. Cherosky
Graduate Program in Food, Agricultural and Biological Engineering

The Ohio State University
2012

Master's Examination Committee:
Dr. Yebo Li, Advisor
Dr. Jay F. Martin
Dr. Frederick C. Michel
Copyright by
Phillip B. Cherosky
2012
Abstract
Lignocellulosic biomass feedstocks, in particular yard waste, are highly
desired for anaerobic digestion as they are widely available and tipping fees are
commonly associated with disposal. The high concentration of lignin presents a
major challenge for utilizing yard wastes as a feedstock for anaerobic digestion.
Therefore, additional steps are necessary to increase the biodegradability of yard
waste.
The initial focus of this study was to test two potential methods for
increasing the methane production of yard waste: pretreatment and co-digestion.
Sodium hydroxide (NaOH) pretreatment was studied at NaOH concentrations of 3%
and 5%. It was found that 3% NaOH pretreatment had no significant improvement
on methane production while 5% NaOH pretreatment had a significant negative
effect on methane production. The second method studied was co-digestion of yard
waste and food waste. Co-digestion at a ratio of 75% food waste and 25% yard
waste showed a four-fold increase in methane yield compared to digestion of 50%
food waste and 50% yard waste and a two-fold increase in methane production
compared to digestion of 100% food waste.
Anaerobic digestion of food waste containing protein and other sulfur
containing substances produces hydrogen sulfide in biogas. Hydrogen sulfide (H S)
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in biogas causes corrosion of metal components such as regulators, gas meters,
valves, and mountings. Combustion of biogas containing H S produces poisonous
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sulfur dioxide (SO ). The SO also dissolves in engine oil causing the oil to become
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acidic and lose its ability to lubricate. One method for H S removal involves using
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hydrated iron oxides supported on a media comprised of wood chips or wood
shavings. The iron oxide reacts with the H S in the gas to form iron sulfide and
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water. This method is called an iron sponge.
The second focus of this study was to test hydrogen sulfide removal using the
iron sponge method. The first goal was to determine the optimum operating
parameters of an iron sponge system. Using ground yard waste, ideal operating
parameters for the iron sponge were determined to be 0.1875” particle size and
15%-25% moisture content. Moisture was found to be a critical factor in the
operation of the H S scrubber system. Optimum moisture content varies with
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particle size and the materials’ ability to absorb water. The iron sponge needs water
to properly facilitate H S conversion to Fe S , but high moisture can be problematic.
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The second and primary goal of this research was to develop and test iron
sponge materials using alternative media to the commercial material, SulfaMaster™,
and to identify those with equal or superior performance. An iron sponge using
digested yard waste from an anaerobic digester as a media material at 25%
moisture was determined to be an ideal alternative to the SulfaMaster™ material
removing 90% of the hydrogen sulfide in biogas at initial levels near 1000ppm H S.
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The digested yard waste had similar performance to SulfaMaster™ and is an
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inexpensive substitute. Ground yard waste at 0.1875” particle size performed
similarly but results were more erratic. Spent tobacco was not an effective medium
for the iron sponge.

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Dedication

This document is dedicated to my friends and family.
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Acknowledgments
I would like to express my appreciation to my advisor, Dr. Yebo Li for the
support, guidance and patience that he has provided throughout my graduate study.
I would also like to thank my committee members: Dr. Jay F. Martin and Dr.
Frederick C. Michel for the time they have taken to be on my examination
committee.
I would also like to express gratitude to members of the Food, Agricultural
and Biological Engineering Department including: Mike Klingman, Mary Wicks,
Peggy Christman and Candy McBride for all of their help.
I would also like to thank to my fellow lab members: Stephen Park, Dr. Jian
Shi, Ting Cai, Shenjun Hu and Xiaolan Lu for all of their help over the past year. I
would especially like to thank Dr. Zhongjiang Wang for helping design and run my
experiments.
Finally, I would like to thank Quasar Energy Group who generously
sponsored my research and provided materials and equipment.

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Vita

February 1988 ..........................................................Born Mt. Vernon, OH
June 2010 ....................................................................B.S. in Food, Agricultural and Biological
Engineering, The Ohio State University
June 2010 to June 2011 ........................................Graduate Teaching Associate, Department
of Food, Agricultural and Biological
Engineering, The Ohio State University
June 2011 to present ............................................Graduate Research Assistant, Department
of Food, Agricultural and Biological
Engineering, The Ohio State University

Field of Study

Major Field: Food, Agricultural and Biological Engineering

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Table of Contents

Abstract ..............................................................................................................................................................ii
Acknowledgments ....................................................................................................................................... vi
Vita ..................................................................................................................................................................... vii
List of Tables .................................................................................................................................................... x
List of Figures .................................................................................................................................................xi
Chapter 1: Introduction ..............................................................................................................................1
Chapter 2: Literature Review ...................................................................................................................4
2.1 Anaerobic Digestion .........................................................................................................................4
2.2 Hydrogen Sulfide Removal ......................................................................................................... 15
2.2.1 H S Removal Methods .......................................................................................................... 17
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2.3 Iron Sponge........................................................................................................................................ 29
Chapter 3: Anaerobic Digestion of Yard Waste ............................................................................ 37
3.1 Introduction ...................................................................................................................................... 37
3.2 Methods and Materials................................................................................................................. 38
3.2.1 Substrates and Inoculum .................................................................................................... 38
3.2.2 Anaerobic Digestion of Yard Waste with NaOH Pretreatment ........................ 40
3.2.3 Anaerobic Co-Digestion of Yard Waste and Food Waste .................................... 41
3.2.4 Analytical Methods ................................................................................................................ 43
3.3 Results and Discussion................................................................................................................. 45
3.3.1 Effect of S/I Ratio and Particle Size ............................................................................... 45
3.3.2 Effect of NaOH Pretreatment ............................................................................................ 48
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3.3.3 Effect of Co-digestion of Food Waste and Yard Waste on Biogas
Production ........................................................................................................................................... 56
3.4 Conclusions ........................................................................................................................................ 62
Chapter 4: Hydrogen Sulfide Removal from Biogas Using Iron Sponge
Technologies ................................................................................................................................................. 63
4.1 Introduction ...................................................................................................................................... 63
4.2 Materials and Methods................................................................................................................. 64
4.2.1 Experimental Setup ............................................................................................................... 64
4.2.2 Media Creation ........................................................................................................................ 66
4.2.3 Analytical Methods ................................................................................................................ 68
4.3 Results .................................................................................................................................................. 69
4.3.1 Effects of Moisture Level on SulfaMaster™ Material ............................................. 69
4.3.2 Effect of Particle Size and Moisture Content on H S Reduction ...................... 70
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4.3.3 Effect of Media Material on H S Reduction ................................................................ 74
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4.3.4 Effect of H S Concentration on H S Reduction ......................................................... 77
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4.3.5 Full Scale Comparison .......................................................................................................... 78
4.3.6 Cost Analysis of Digested Yard Waste Iron Sponge ............................................... 80
4.4 Conclusion .......................................................................................................................................... 82
Chapter 5: Conclusions and Suggestions for Future Research ............................................. 83
References ...................................................................................................................................................... 85

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