Optimum Production of Biogas from Bio-Municipal Solid Wastes Using Two Stages Anaerobic

110 Pages·2011·1.41 MB·English

ADDIS ABABA UNIVERSITY
SCHOOL OF GRADUATE STUDIES
ADDIS ABABA INSITUTE OF TECHNOLOGY
DEPARTMENT OF CHEMICAL ENGINEERING

Optimum Production of Biogas from Bio-Municipal Solid
Wastes Using Two Stages Anaerobic Digester

__________________________________________________________________________________ 

By
Gizachew Assefa Kerga

JUNE 2011
ADDIS ABABA, ETHIOPIA
ADDIS ABABA UNIVERSITY
SCHOOL OF GRADUATE STUDIES
ADDIS ABABA INSITUTE OF TECHNOLOGY
DEPARTMENT OF CHEMICAL ENGINEERING

Optimum Production of Biogas from Bio-Municipal Solid
Wastes Using Two Stages Anaerobic Digester

A thesis Submitted to the Research and Graduate School of Addis Ababa
University, Addis Ababa Institute of Technology, Department of Chemical
Engineering in partial fulfillment of the requirements for the attainment of the
Degree of Masters of Science in Chemical Engineering under Environmental
Engineering Stream.

By: Gizachew Assefa Kerga

Advisor: Dr.Ing Birhanu Assefa

JUNE 2011
ADDIS ABABA, ETHIOPIA
ADDIS ABABA UNIVERSITY
SCHOOL OF GRADUATE STUDIES
ADDIS ABABA INSITUTE OF TECHNOLOGY
DEPARTMENT OF CHEMICAL ENGINEERING

Optimum Production of Biogas from Bio-Municipal Solid Wastes
Using Two Stages Anaerobic Digester 

A thesis submitted to the Research and Graduate School of Addis Ababa University, Addis
Ababa Institute of Technology, Department of Chemical Engineering in partial fulfillment of the
requirements for the attainment of the Degree of Masters of Science in Chemical Engineering
under Environmental Engineering Stream.

By: Gizachew Assefa Kerga

Approved by the Examining Board:

Dr. Ing Zebene Kiflie
Chairman, Department’s Graduate committee

Dr.Ing Birhanu Assefa
Advisor

Internal Examiner

External Examiner
Acknowledgement

I wish to express my deepest appreciation to Dr.Ing Birhanu Assefa, my
advisor, for his invaluable comments and excellent supervision. I must also
thank him for the warm relations showed towards me, which was very helpful
and very much cherished.

I also extend my appreciation to Environmental Engineering Laboratory
assistants, Ato Yosan Teshome and Ato Tewabe Amsalu for their assistance,
Further; I wish to thank Ato Hintsa-Selassie Seifu, Ato Alemayehu Mengiste,
Ato Biruk Tefera, Ato Biruk Yohannes, and Ato Nebiyu Getachew to support me
in one way or the other in realizing this thesis.
I would also like to thank Addis Ababa University Science Faculty,
Environmental Science Department for their technical lab support on the
thesis, I exceptional grateful to Marta Yishak. IGNIS Project office generously
sponsored my research and provided equipments. I appreciate the persons that
helping me from IGNIS Project office such as Fisum, Nebiyu also including my
advisor Dr.Ing Birhanu Assefa. Many “thank-you” to my colleagues and friends
in masters Program for being helpful in many ways.
My special thanks go to my families specially Mrs. Belay Assefa and Mr. Degif
Barega for their encouragement and support towards my thesis and academic
career.
The last but the most, I thank the highest and merciful God for the strength
and the calm through the perplexing times during my study.

i
Table of Contents 
Contents 
Acknowledgement ............................................................................................ i 
Table of Contents ............................................................................................ ii 
List of Tables................................................................................................... v 
List of Figures ................................................................................................ vi 
List of Abbreviations ......................................................................................vii 
Abstract ........................................................................................................ viii 
1.  INTRODUCTION ....................................................................................... 1 
1.1  Background ......................................................................................... 1 
1.2  Problem Statement .............................................................................. 2 
1.3  Objective of the Research ..................................................................... 4 
2.  LITERATURE REVIEW .............................................................................. 5 
2.1  Historical Background: ........................................................................ 5 
2.2  Biogas composition .............................................................................. 7 
2.3  Biogas characteristics .......................................................................... 8 
2.4  Advantages and Disadvantages of AD System ...................................... 9 
2.5  General Anaerobic Digestion (AD) process description ........................ 10 
2.5.1  Pretreatment of feed stock ............................................................ 10 
2.5.2  Process and mechanism of bio-methanation................................. 11 
2.5.3  Post treatment of residual fraction from AD.................................. 14 
2.6  Operational Parameters for Biogas Production ................................... 16 
2.6.1  Temperature ................................................................................ 17 
2.6.2  Hydraulic Retention time ............................................................. 18 
2.6.3  Type of substrates........................................................................ 19 
2.6.4  pH: .............................................................................................. 21 
2.6.5  Carbon: Nitrogen C/N ratio .......................................................... 22 
2.6.6  Organic loading rate .................................................................... 24 
2.6.7  Mixing ......................................................................................... 24 
2.7  Toxicity ............................................................................................. 25 
ii
2.8  Co- digestion ..................................................................................... 25 
2.9  Seeding ............................................................................................. 26 
2.10  Compost ............................................................................................ 26 
2.11  Types of anaerobic digestion systems ................................................. 26 
2.11.1  Continuous versus batch process .............................................. 27 
2.11.2  Mesophilic versus thermophilic digestion .................................. 28 
2.11.3  Single stage versus multi stage digestion ................................... 30 
2.12  Current Status of AD Treatment Processes ........................................ 31 
2.13  Two-Stage AD Systems ...................................................................... 33 
2.14  Performance Parameters .................................................................... 36 
3.  METHODOLOGY ..................................................................................... 37 
3.1  Materials ........................................................................................... 37 
3.2  Measurements and Equipments ........................................................ 38 
3.3  Methods ............................................................................................ 39 
3.3.1  Study variables ............................................................................ 39 
3.3.2  Study design ................................................................................ 39 
3.3.3  Sample analysis ........................................................................... 40 
3.4  Statistical analysis ............................................................................ 41 
3.5  Experimental set up .......................................................................... 43 
4.  RESULTS AND DISCUSSION .................................................................. 45 
4.1  Results and Discussion on Performance of hydrolysis stage ............... 45 
4.2  Results and Discussion on Methanogenic stage ................................. 47 
4.2.1  Characteristics of the substrates used in the batch tests .............. 47 
4.2.2  Determination of digestate characteristics .................................... 50 
4.2.3  COD: BOD ratio ........................................................................... 51 
4.2.4  Rate of Biogas production ............................................................ 51 
4.2.5  Identification of maximum mix ratio for highest biogas production52 
4.2.6  Identification of maximum mix ratio for highest CH production .. 54 
4
4.2.7  COD, VS and TS Removal Efficiency............................................. 57 
4.2.8  Methane yield and VS removal ..................................................... 60 
iii
4.2.9  Overall performance of the reactors .............................................. 63 
5.  CONCLUSION AND RECOMMENDATIONS .............................................. 65 
5.1  Conclusion ........................................................................................ 65 
5.2  Recommendations for further study ................................................... 67 
REFERENCES ............................................................................................... 68 
ANNEX.......................................................................................................... 76 
Annex 1: Laboratory procedures................................................................. 76 
Annex 2: Statistical analysis ...................................................................... 84 
Annex 3: Experimental setups and Equipments ......................................... 87 
Annex 4: Experimental Results .................................................................. 91 

iv
List of Tables

Table 2.2. Approximate composition of Biogas ................................................. 7 
Table 2.3.1 Physical and Chemical Characteristics .......................................... 8 
Table 2.3.2 Theoretical CH and CO composition in three main organic groups.
4 2
....................................................................................................................... 8 
Table 2.4 Advantages of anaerobic digestion process ....................................... 9 
Table 2.5.3 Maximum gas yield per kg VS for different organic wastes. .......... 21 
Table 2.5.5 Typical C/N ratios of different materials ...................................... 23 
Table 2.10.2 Mesophilic and Thermophilic Anaerobic Digestion ..................... 29 
Table 2.10.3 Advantages and disadvantages of single and two stages ............ 31 
Table 2.12 Methane yield from OFMSW (RISE-AT, 1998) ............................... 32 
Table 3.5.1 Sampling analysis and analytical parameters .............................. 41 
Table 3.1 sample Analysis parameters ........................................................... 42 
Table 4.2.1 Characteristics of the substrates used in the batch tests ............. 48 
Table 4.2.2 Feedstock characteristics after digestion ..................................... 50 
Table 4.2.5 Cumulative biogas production and composition .......................... 54 
Table 4.2.5 (A) COD removal efficiency analysis for batch experiments .......... 58 
Table 4.2.6 (B) TS and VS removal efficiency analysis .................................... 59 
Table 4.2.7 Methane yields and VS removal rates for the batch tests ............. 60 

v
List of Figures

Figure 2.4.2 Anaerobic digestion process (Evans, 2001) ................................. 14 
Figure 2.10 Classification of anaerobic digestion by operational criteria (Evans,
2001) .............................................................................................. 27 
Figure 2.11 Two stage anaerobic digestion process ........................................ 35 
Figure 3.3 Experimental setup ...................................................................... 43 
Figure 4.1 Leachate BOD (mg/L) increment per days..................................... 46 
Figure 4.2 BOD input for the reactors (A), COD input for the reactors (B), Total
Nitrogen (TKN) input for the reactors (C), C/N ratio of substrate input
for the reactors (D). ......................................................................... 49 
Figure 4.2.4 (A) Gas Production rate for different mix ratio (in m3/day) .......... 52 
Figure 4.2.4 (B) Cumulative Gas Production for different mix ratio (in m3) ..... 53 
Fig.4.2.5 (B) Daily methane production from batch reactors m3/day .............. 56 
Figure 4.2.5(C) Cumulative methane Production for different mix ratio (in m3)
....................................................................................................... 57 
Figure 4.2.6 Removal Efficency (cid:31) (%), TS, VS, COD ....................................... 59 
Figure 4.2.5(E) Cumulative Specific Methane Production for different mix ratio
(in m3) ............................................................................................. 61 
Figure 4.2.7 (A), methane production per VS removed ................................... 62 
Figure 4.20.7 (B) cumulative methane produced per VS removed .................. 62 
Figure 4.2.8 (A) Overall performance by total CH production per kg of VS ,
4 added
....................................................................................................... 64 
Figure 4.2.8 (B) Overall performance by total CH production per kg of
4
VS , ........................................................................................ 64 
Removed

vi
List of Abbreviations

AD Anaerobic Digestion
BMSW Biodegradable Municipal Solid Waste
COD Chemical Oxygen Demand
C/N Carbon to Nitrogen ratio
DCAD Dry Continuous Anaerobic Digestion
DC Developing Countries
HS High Solids
ISWM Integrated Solid Waste Management
LFG Landfill Gases
LS Low Solids
M Mesophilic
MBT Mechanical Biological Treatment
MC Moisture Content
MS Multi Stage
MSW Municipal Solid Waste
MS-OFMSW Manually sorted Organic Fraction of Municipal Solid waste
n.a. No data available
OFMSW Organic Fraction of Municipal Solid waste
OLR Organic Loading Rate
OM Organic Matter
RT Retention Time
SRT Solid Retention Time
SS Single Stage
SS-OFMSW Source-Sorted Organic Fraction of Municipal Solid Waste
STP Standard Temperature Pressure
SWM Solid Waste Management
T Thermophilic
TKN Total Kjeldahl Nitrogen
TS Total Solids
VFA Volatile Fatty Acids
VS Volatile Solid

vii