dry anaerobic digestion of municipal solid waste and digestate management strategies

145 Pages·2012·2.84 MB·English

DRY ANAEROBIC DIGESTION OF MUNICIPAL SOLID
WASTE AND DIGESTATE MANAGEMENT STRATEGIES
by
Zeshan
A dissertation submitted in partial fulfillment of the requirements for
the degree of Doctor of Philosophy in
Environmental Engineering and Management
Examination Committee: Prof. Chettiyappan Visvanathan(Chairperson)
Prof. AjitP.Annachhatre
Dr.P.AbdulSalam
External Examiner: Dr. Yasumasa Tojo
Laboratory of Solid Waste Disposal
Engineering
Division of Environmental Engineering
Hokkaido University, Japan
Nationality: Pakistani
Previous Degree: Master of Science (Honors) Agriculture
(Soil and Environmental Sciences)
University of Agriculture, Faisalabad
Scholarship donor: Higher Education Commission (HEC)
Pakistan-AIT Fellowship
Asian Institute of Technology
School of Environment, Resources and Development
Thailand
December2012
i
Acknowledgements
First of all, the author would like to thank Allah, the most gracious, the most beneficent,
for giving him the opportunity to achieve higher education at this level and giving him the
courage and the patience during the course of his Ph.D. study at AIT.
The author would like to express his profound gratitude to his adviser Prof. C. Visvanathan
for kindly giving valuable guidance, stimulating suggestions and ample encouragement
during the study at AIT. The author is deeply indebted to Prof. Ajit Annachhatre and Dr.
Abdul Salam for their valuable comments, suggestions and support and serving as
members of the examination committee.
A special thank is addressed to Dr. Yasumasa TOJO for kindly accepting to serve as the
external examiner. His constructive and professional comments will be highly appreciated.
A special note of appreciation is extended to Dr. Obuli P. Karthikeyan for his help and
great interest in this research including valuable comments and suggestions during various
phases. Special thanks to Dr. Romchat Rattanaoudom for her help and guide as a senior
and a colleague.
Sincere thanks are given to Ms. Phonthida Sensai, Mr. Supawat Chaikasem, Mr.
Muhammad Zeeshan Ali Khan and Mr. Amila Abeynayaka as helping friends. The author
would also like to thank all friends, EEM staff, laboratory colleagues and technicians for
their help, moral support and cooperation which contributed in various ways to the
completion of this dissertation.
The author gratefully acknowledges Higher Education Commission (HEC) of Pakistan and
AIT for the joint scholarship for the Ph.D. study at AIT.
The author would like to dedicate this piece of work to his beloved brother who passed
away during the course of this study. His long lasting love and prayers always inspired and
encouragedauthorto fulfill his desires.
Deepest and sincere gratitude goes to his beloved parents (Mr. and Mrs. Sheikh
Muhammad Ramzan) for their endless love, encouragement and prayers. The author
wishes to express his deepest appreciation to his siblings for their prayers, patience and
understanding throughout the entire period of this study.
ii
Abstract
Global solid waste generation is continuously rising. Improper disposal of the gigantic
amount of solid waste seriously affects the environment and contributes to climate change
by release of green house gases (GHGs). Practicing anaerobic digestion for organic
fraction of municipal solid waste (OFMSW) can reduce emissions to environment and
thereby alleviate theenvironmental problemstogether with production of biogas, an energy
source, and digestate, a soil amendment. Dry anaerobic digestion has gained much
attention because of its advantages of lesser water addition, lower reactor volume and
higher volumetric biogas production than wet digestion. However, one of its problems is
accumulation of ammonia which is more common in digesters fed with improper C/N ratio
wastes and needs to be corrected.
This study was carried out to evaluate the performance of a pilot-scale thermophilic dry
anaerobic reactor for biogas production and to analyze the management options for the
digestate. This was achieved by investigating substrates of different C/N ratio to get a
correct feedstock for dry anaerobic digestion (to minimize ammonia accumulation) and by
investigating different organic loading rates (OLRs) of the correct feedstock. Moreover,
GHG emission potential of digestate was calculated (based on its characteristics) with and
without storage and curing and different digestate management options were analyzed.
In first experiment, the effect of C/N ratio and total ammonia-N accumulation in a dry
anaerobic digestion was studied effectively. Two simulations of OFMSW were preparedto
attain C/N ratio 27 and C/N ratio 32 using biodegradable feedstocks such as food waste,
fruit and vegetable waste, leaf waste and paper waste. Results showed that the simulation
with C/N ratio 32 had about 30% less ammonia-N in digestate as compared to that with
C/N ratio 27. Moreover, a free ammonia accumulation/inhibition effect was documented
and methods to overcome the adverse effects were discussed.
In another experiment, correct feedstock from the first experiment (C/N ratio 32) was used
as substrate to improve the performance of the same reactor. The effect of different OLRs,
such as 4.55, 6.30 and 8.50 kg VS/m3d, was studied on the parameters like biogas
production, VS removal and VFA accumulation. Results showed that increase in OLR
proportionally increased the gas production rate (5, 6.37 and 7.55 m3/m3 /d for three
reactor vol
OLRs respectively) of reactor, but the specific methane production reduced (330, 320 and
266 L CH /kg VS). Similarly, VS removal also reduced (78, 75 and 67%) with increase in
4
OLR. The system performed well at OLR and RT of 6.40 kg VS/m3d and 24 days
respectively, however, purpose of treatment also determines the optimum operating
conditions.
Digestate from the reactor was characterized and its C/N ratio and GHG emission potential
was calculated. It was found that the C/N ratio of digestate was 15-20 for most of the study
period, which is safe range for its application to agricultural land without further treatment.
The GHG potential calculation shows that storage of the digestate for 2 months decreased
its GHG potential by 10%, hence, storage was found to be a source of GHG emission.
Moreover, application of digestate directly to land has minimum net GHG emission (i.e. -
11 gCO -eq/kg digestate). Therefore, digestate should be applied to land immediately after
2
digestion to minimize GHG emission from the storage system.
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Table ofContents
Chapter Title Page
Title page i
Acknowledgements ii
Abstract iii
Table of Contents iv
List of Tables vii
List of Figures viii
List of Abbreviations x
1 Introduction 1
1.1 Background 1
1.2 Objectives of the Study 2
1.3 Scope of the Study 3
2 Literature Review 4
2.1 Introductionof Dry Anaerobic Digestion 4
2.2 Process of Anaerobic Digestion: The Fundamentals 5
2.2.1 Hydrolysis 5
2.2.2 Acidogenesis 6
2.2.3 Acetogenesis 6
2.2.4 Methanogenesis 7
2.3 Inhibition of Dry Anaerobic Digestion 8
2.3.1 Volatile fatty acids (VFA) 8
2.3.2 Ammonia 9
2.4 Optimization of Factors Affecting Dry Anaerobic Digestion 11
2.4.1 pH 11
2.4.2 Solids content 11
2.4.3 C/N ratio 13
2.4.4 Temperature 14
2.4.5 Mixing 16
2.4.6 Retention time 17
2.4.7 Organic loading rate 18
2.5 Other techniques to Optimize Dry Anaerobic Digestion 19
2.5.1 Physical pretreatment 19
2.5.2 Chemical pretreatment 19
2.5.3Biological pretreatment (inoculation) 20
2.5.4 Co-digestion 20
2.6 Reactor Design for Dry Anaerobic Digestion 21
2.6.1 Single-stage batch systems 22
2.6.2 Single-stage continuous systems 23
2.6.3 Multi-stagecontinuous systems 23
2.6.4 Design of available technologies for dry anaerobic digestion 25
2.7 Research Progress and Research Needs of Dry Anaerobic Digestion 27
2.8 Anaerobic Digestion and Digestate Management 30
2.8.1 Need ofdigestate management and digestate utilization 30
2.8.2 Effect of prior digestion on properties of digestate 31
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2.9 Characteristics of Digestates 33
2.9.1 Characteristics of solid digestates 33
2.9.2 Characteristics of liquid digestates 35
2.9.3 Presence of organic pollutants 37
2.9.4 Presence of heavy metals 38
2.9.5 GHG emission potential of digestate 38
2.10 Management Aspects of Anaerobic Digestate 39
2.10.1 Separation of liquid and soliddigestate 39
2.10.2 Direct land application of liquid digestate 40
2.10.3 Aerobic post-treatment of solid digestate and its effects on 40
quality
2.10.4 Digestate storage and its effects on characteristics 41
2.11 PostUtilization MonitoringIssues of Anaerobic Digestate 42
2.11.1 Effect of digestate application on soil 42
2.11.2 Influence of digestate application on plant growth and health 42
2.12 Research Needs for the Dissertation 43
3 Methodology 44
3.1 Inoculum and Simulations of Waste 45
3.1.1 Inoculum for anaerobic digestion experiments 45
3.1.2 Simulations of waste 45
3.2 Experimental Set-up 46
3.2.1 Experimental set-up for gasformation potential test 46
3.2.2 Experimental set-up for pilot-scale experiments 46
3.3 Experimental Conditions 47
3.3.1 Experimental conditions for gas formation potential test 47
3.3.2 Experimental conditions for Phase I pilotexperiment 48
3.3.3 Experimental conditions for Phase II pilot experiment 50
3.4 Digestate Management and GHG Emissions Estimation (Phase III) 51
3.4.1 Storage of digestate 52
3.4.2 Dewatering of digestate 52
3.4.3 Curing ofdewatered digestate 53
3.4.4 Estimation of GHG emissions in the digestate management 55
system
3.5 Analytical Methods 58
4 Results and Discussion 60
4.1 GasFormation Potential of Waste 60
4.2 Effect of C/NRatio and Ammonia-N Accumulation on ITDAR 62
(Resultsof Phase I Pilot Experiment)
4.2.1Performance of ITDAR during start-up and continuous 63
operations
4.2.2 Effect of C/N ratio and ammonia-N accumulation in ITDAR 65
4.2.3 Summary of the effect of ammonia-N accumulation in ITDAR 68
4.2.4 Energy balance of ITDAR in Phase I pilot experiment 70
4.3 Optimization of a Pilot-Scale Thermophilic Dry Anaerobic Digester 71
(Results of Phase II Pilot Experiment)
4.3.1 Start-up of ITDAR in phase II pilot experiment 71
4.3.2 Stability parameters of ITDAR: Effect oforganic loading rate 74
v
4.3.3 Effect oforganic loading rateon performance parameters of 76
ITDAR
4.4 Digestate Managementand GHGEmissions (Phase III) 79
4.4.1 Characteristics of raw digestate 79
4.4.2 Characteristics of stored, dewatered and cured digestate 81
4.4.3 Digestate management from perspectives of GHG emissions 83
4.5Decentralized Dry AnaerobicDigestion of OFMSW for a Community 86
of 5000 People
4.5.1 Design of the decentralized AD system 86
4.5.2 Preparation of feedstock for dry AD (Pre-treatment) 86
4.5.3 Operation of decentralized AD system 87
4.5.4 Generation of methane and energy 88
4.5.5 Digestate management 88
4.5.6 Reduction of GHG emissions 90
4.5.7 Material flow (VS balance) 90
5 Conclusions and Recommendations 91
5.1 Conclusions 91
5.2 Recommendations 93
References 95
Appendices 110
Appendix A 110
Appendix B 114
Appendix C 122
Appendix D 127
Appendix E 130
Appendix F 134
vi
List of Tables
Table Title Page
2.1 Biomethanization Inhibitors and their Inhibitory Concentration 8
2.2 Change in TAN Inhibitory Concentration with Feed TS and Temperature 10
2.3 Typical C/N Ratios of Different Materials 13
2.4 High Gas Production Rate in Relation to High Organic Loading Rate in
Dry Anaerobic Digestion 18
2.5 Performance ofVarious Kinds of Dry Anaerobic Digesters 28
2.6 Effect of Digestion on Properties of Waste 32
2.7 Characteristics of Solid Digestate in Dry Anaerobic Digestion Systems 34
2.8 Characteristics of Separated Liquid Digestates from Different Digestion
Systems 36
2.9 Concentration of Organic Pollutants in Digesates and Composts (µg/kg 37
DM)
2.10 Heavy Metal Content in Different Types of Digestates (mg/kg DM) 38
2.11 Regulations of Nutrient Loading on Agricultural Land 40
3.1 Composition and Characteristics of Simulated Feedstock 45
3.2 Characteristics of Substrate and Inoculum Used in Gas Formation Potential
Test 48
3.3 Operating Conditions of ITDAR for Phase I Pilot Experiment 49
3.4 Forms and Sources of GHGContributed and GHG Avoided 56
3.5 Analytical Methods for Various Parameters of Anaerobic Digestion of
OFMSW 59
4.1 Digestion Parameters and Methane Yield of ITDAR 66
4.2 Surplus Energy of ITDAR During Various Runs 71
4.3 Percentage ofVS Removaland Specific Methane Production in ITDAR 77
4.4 Comparison of Digestate Characteristics and Guidelines 82
4.5 Characteristics of Digestate at Different Stages of Management 82
4.6 Net GHG Emissions from All Scenarios of DigestateManagement 85
4.7 Technical Details of Proposed AD Plant and its Comparison to Pilot Plant 87
4.8 Technical Data of Sand Drying Bed for Digestate Dewatering 88
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List ofFigures
Figure Title Page
2.1 Trend of low solids and high solids anaerobic digestion plants in Europe 5
2.2 Main stages of anaerobic digestion process 6
2.3 Graphical representation of temperature ranges for anaerobic digestion 14
2.4 Capacity of mesophilic versus thermophilic digestion operation in Europe 15
2.5 General methods of mixing in dry anaerobic digestion, a) digestate
recirculation, b) biogas recirculation and c) mechanical mixer 16
2.6 Classes of dry anaerobic digestion by operational criteria 22
2.7 Comparison between one stage and two stage process in Europe 24
2.8 Designs of single-stage dry anaerobic digesters 26
2.9 Emissions from soil applied digestate to environments 30
2.10 Liquid-solid separation of digestate with production of useful products 39
2.11 Changing parameters during aerobic post-treatment 41
3.1 Phases of overall research study 44
3.2 Experimental set-up for gas formation potentialtest 46
3.3 Pilot-scale experimental setup of inclined thermophilic dry anaerobic
digester 47
3.4 Method steps for gas formation potential test 48
3.5 Operating conditions of ITDAR for Phase II pilot experiment 51
3.6 Possible unit processes of digestate management system 52
3.7 Plastic drums for storage of digestate 53
3.8 Sand drying bed: Top view 54
3.9 Sand bed for digestate dewatering, A-A cross-sectional view 54
3.10 Comparative scenarios of digestate management 56
4.1 Cumulative and specific biogas production by feedstock 1 61
4.2 Cumulative and specific biogas production by feedstock 2 62
4.3 Time course of dry anaerobic digestion with various parameters in 64
ITDAR
4.4 Interaction of ammonia and VFA in ITDAR 67
4.5 Variation of total ammonia-N concentration andTAN/TKN ratio with
feed C/N ratio in ITDAR 69
4.6 pH profile of ITDAR during start-up 72
4.7 Profile of VFA and VFA/Alk ratio during start-up 73
4.8 CH , CO and GPR fluctuation during start-up phase 74
4 2
4.9 Evolution of pH in ITDAR during continuous loading 75
4.10 Concentration of VFA in ITDAR during continuous loading 75
4.11 VFA/Alk ratio in ITDAR during continuous loading 76
4.12 Gas production rate of ITDAR during different OLRs 77
4.13 Cumulative methane perliter of reactor volume in ITDAR 78
4.14 Selection of operating conditions based on purpose of waste treatment 78
4.15 Comparison of feed and digestate regarding total solids in phase I 80
experiment
4.16 TKN and C/N ratio of the digestate in phase I experiment 80
4.17 TS and VS content of digestate in phase II experiment 81
4.18 GHG emission potential of OFMSW and digestates 83
4.19 Net GHG emissions from all scenarios of digestate management 86
viii
4.20 Layout of conceptualdecentralized AD plant for a community 89
4.21 Conceptual mass balance for VS of the proposed decentralized system 90
ix
List ofAbbreviations
AD Anaerobic Digestion
AIT Asian Institute of Technology
APHA American Public Health Association
BVS Biodegradable Volatile Solids
COD Chemical Oxygen Demand
DAD Dry Anaerobic Digestion
DEHP Di-2-ethylhexyl Phthalates
Dig Digestate Recirculation Rate
rr
DM Dry Matter
DOC Dissolved Organic Carbon
DRANCO Dry Anaerobic Compostig
EU European Union
FID Flame Ionization Detector
FM Fresh Matter
GC Gas Chromatography
GHG Greenhouse Gas
GP Gas Potential
HRT Hydraulic Retention Time
MS-OFMSW Mechanically Separated Organic Fraction of Municipal Solid Waste
MSW Municipal Solid Waste
NP Nonyl Phenol
OFMSW Organic Fraction of Municipal Solid Waste
OLR Organic Loading Rate
OM Organic Matter
ORP Oxidation Reduction Potential
PAH Polycyclic Aromatic Hydrocarbon
PBDE Polybrominated Diphenyl Ethers
PCB Polychlorinated Biphenyl
PCDD Polychlorinated Dibenzo-p-Dioxin
PCDF Polychlorinated Dibenzo Furans
RT Retention Time
RVS Refractory Volatile Solids
SDB Sand Drying Bed
SEBAC Sequential Batch Anaerobic Composting
SSHS Single Stage High Solid
SS-OFMSW Source Separated OFMSW
SRT Solids Retention Time
STP Standard Temperature and Pressure
TCD Thermal Conductivity Detector
TS Total Solids
UASB Upflow Anaerobic Sludge Blanket
VFA Volatile Fatty Acid
VS Volatile Solids
WM Wet Mass
x