Solid- State Anaerobic Digestion of Lignocellulosic

92 Pages·2011·1.38 MB·English

Solid- State Anaerobic Digestion of Lignocellulosic Biomass for Biogas Production

Thesis

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

The Ohio State University
2011

Thesis Committee:
Dr. Yebo Li, Advisor
Dr. Jay F. Martin
Dr. Frederick C. Michel

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Copyright by
Lo Niee Liew
2011

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Abstract
The anaerobic digestion (AD) process can generally be classified into two
categories based on the total solids (TS) content of material in the digester: solid-state
anaerobic digestion (SS-AD) which has TS content of 20% and higher, and liquid AD
which has TS content of 15% and lower. SS-AD has the advantages of using a smaller
reactor volume and less moving parts as agitation is generally not required. Energy
demand for heating the material in digester is therefore reduced with a smaller volume of
materials to be heated.
Lignocellulosic biomass has been considered as one of the suitable feedstock for
SS-AD as it is easily available and issues encountered in liquid AD such as stratification
can be avoided. The challenge of utilizing lignocellulosic biomass in AD is the
recalcitrant properties of such material. Pretreatment is therefore necessary to improve
the biodegradability of lignocellulosic biomass.
In this study, SS-AD of four types of feedstocks was tested under batch operation.
The SS-AD was conducted under 37C for 30 days. The feedstocks selected were corn
stover, wheat straw, fallen tree leaves, and yard waste. As inoculation is essential in SS-
AD, effect of substrate to inoculum (S/I) ratio (volatile solids of substrate to volatile
solids of inoculum) on methane yield was investigated. For all feedstocks tested, the
highest methane yield was obtained at S/I ratio of 2. The highest methane yield of 81.2
L/kg volatile solids (VS) was obtained from SS-AD of corn stover followed by wheat
straw (66.9 L/kg VS), leaves (55.4 L/kg VS) and yard waste (40.8 L/kg VS). An inverse
linear relationship was obtained between the methane yield and lignin content of
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lignocellulosic biomass. The methane production of the feedstock in SS-AD fits the
simple first-order kinetic model.
SS-AD of leaves with simulatanoues alkaline (NaOH) treatment was further
studied to improve the methane production. The highest methane yield of 81.8 L/kg
volatile solids (VS) was obtained at NaOH loading of 3.5% and S/I ratio of 4.1. However,
it was not significantly different from that of control (without NaOH addition). At S/I
ratio of 6.2, NaOH loading of 3.5% enhanced the methane yield by 24-fold over the
control. The AD process at S/I ratio of 8.2 were failed. In addition, increasing the total
solid (TS) content from 20% to 26% reduced biogas yield by 35% in reactors at S/I ratio
of 6.2 and NaOH loading of 3.5%. Cellulose and hemicellulose degradation and methane
yields during the 30-day AD process are highly related.
The results obtained from this study showed the feasibility of utilizing
lignocellulosic biomass as feedstock in SS-AD for biogas production. In addition,
alkaline pretreatment with NaOH was also shown to enhance methane production from
leaves in SS-AD.

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Dedication
This document is dedicated to my family

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Acknowledgments

My most sincere appreciation and gratitude to my advisor, Dr. Yebo Li for his
infinite support and guidance provided throughout my graduate study. I would also like to
gratefully thank professors serving as my dissertation committee: Dr. Jay F. Martin and
Dr. Frederick C. Michel for their time.
I would also like to express thanks to the staff members of Food, Agricultural and
Biological Engineering Department: Mike Klingmans for his dedication in providing the
engineering assistance needed whenever required, Mary wicks for her enthusiasm in
proof reading the thesis and both Peggy Christman and Candy McBride for their prompt
response to all the administrative supports I needed.
I am also indebted to my lab members: Dr. Ellen Wan, Stephen Park, Dr. Jian Shi,
Dr. ZhiFang Cui, Dr. Guiming Fu and Stephanie Xu, for their attentiveness in providing
the supports and encouragements throughout my stay in Wooster, OH
Lastly, I would like to express my deepest gratitude to my family members for
their constant understanding, patience and encouragement in all the undertakings I
pursue.

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Vita

March, 1981 …...…………………………..Born – Johor, Malaysia.
December, 2004 .............................................B.S. in Agricultural and Biological
Engineering, Purdue University.
December, 2006 .............................................Food Technologist, Cadbury
Confectioneries, Shah Alam, Malaysia.
April, 2008 .....................................................Operational Auditor, Nestlé, Petaling Jaya,
Malaysia.
July, 2009 .......................................................Project Engineer, Nestlé, Petaling Jaya,
Malaysia.
August, 2009 to present .................................Graduate Research Associate, Department
of Food, Agricultural and Biological
Engineering , The Ohio State University.

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Table of Content
Abstract iii
Acknowledgments.............................................................................................................. vi
Vita……………….. .......................................................................................................... vii
List of Tables ..................................................................................................................... xi
List of Figures ................................................................................................................... xii
Chapter 1 Introduction ........................................................................................................ 1
Chapter 2 Literature Review ............................................................................................... 6
2.1. Lignocellulosic Biomass as Feedstock for Anaerobic Digestion ......................... 6
2.1.1. Crop residues ............................................................................................. 8
2.1.2. Yard waste ............................................................................................... 12
2.2. Pretreatment of Lignocellulosic Biomass for Anaerobic Digestion ................... 17
2.3. Operation of SS-AD ........................................................................................... 39
Chapter 3 Effect of Substrate to Inoculum Ratio on Methane Production in Solid-State
Anaerobic Digestion of Lignocellulosic Biomass ............................................ 42
3.1. Introduction ........................................................................................................ 42
3.2. Materials and Methods ....................................................................................... 44
3.2.1. Feedstock and inoculum .......................................................................... 44
3.2.2. Solid-state anaerobic digestion ................................................................ 44
3.2.3. Analytical methods .................................................................................. 46
3.2.4. Statistical analysis .................................................................................... 47
3.3. Results and discussion ........................................................................................ 48
3.3.1. Composition analysis of inoculum and lignocellulosic biomass ............. 48
3.3.2. Biogas production .................................................................................... 49
3.3.3. Relationship between biogas production and lignin content ................... 57
3.3.4. Degradation of holocellulose and extractives .......................................... 58
3.4. Conclusion .......................................................................................................... 60
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Chapter 4 Enhancing the Solid-state Anaerobic Digestion of Fallen Leaves through
Simultaneous Alkaline Treatment .................................................................... 62
4.1. Introduction ........................................................................................................ 62
4.2. Materials and methods ........................................................................................ 65
4.2.1. Feedstock and inoculum .......................................................................... 65
4.2.2 Solid-state anaerobic digestion with simultaneous NaOH treatment ....... 66
4.2.3. Analytical methods .................................................................................. 67
4.2.4. Statistical analysis .................................................................................... 68
4.3. Results and discussion ........................................................................................ 68
4.3.1. Biogas production .................................................................................... 68
4.3.2 Variation of pH, total volatile fatty acids (TVFAs) and alkalinity ........... 73
4.3.3. Degradation of cellulose and hemicellulose ............................................ 76
4.4. Conclusions ........................................................................................................ 78
Chapter 5 Conclusions and Suggestions for Future Research .......................................... 80
Reference…………. ......................................................................................................... 82

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List of Tables

Table 2.1 Methane yield from various crop residues tested with anaerobic digestion

Table 2.2 Methane yield from various wood and forestry waste tested with anaerobic
digestion

Table 2.3 Various pretreatment methods applied on lignocellulosic biomass in anaerobic
digestion

Table 2.4 Alkaline pretreatment of lignocellulosic biomass in anaerobic digestion

Table 3.1. Design of reactors using four different feedstocks

Table 3.2 Characteristics of inoculum and lignocellulosic biomass

Table 3.3 Correlation coefficients of lignocellulosic biomass using first-order kinetic

Table 4.1 Characteristics of leaves and inoculum

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