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D E V E L O P M E N T O F A H I G H R A T E 
B I O M E T H A N A T I O N R E A C T O R S Y S T E M : 
A P I L O T S T U D Y O F A N I N D U S T R I A L W A S T E 
S T R E A M 
By 
PUSHPANJALIIRANGA JAYASURIYA 
B.Sc.Eng. (Hons.) THE UNIVERSITY OF MORATUWA. SRI LANKA, 1998 
A thesis submitted in fulfillment 
of the requirement for the degree 
of Master of Engineering 
in 
Energy Technology 
62-1 u OZ 
©©logo S^ o© 8^)@o. @ 
DEPARTMENT OF MECHANICAL ENGINEERING 
FACULTY OF ENGINEERING 
UNIVERSITY OF MORATUWA 
\ \ \ 
SRI LANKA 
JVtarch, 2002 
074681 
University of Moratuwa 
74681* 
11f- 6 SI 
DECLARATION 
" I certify that this thesis does not incorporate without acknowledge any material 
previously submitted for a degree or diploma in any university or higher 
educational institution in Sri Lanka or abroad and to the best of my knowledge 
and belief it does not contain any material previously published or written by 
another person except where due reference is made in the text". 
lya 
u 
Abstract 
A pilot scale two-phase anaerobic reactor system was constructed and the 
feasibility of Biomethanation using two-phase systems was evaluated. As the raw 
materials, a batter mixture washing effluent from a wafer biscuit manufacturing 
plant was used. This effluent has a high COD due to vegetable fats and oils. 
Acetogenic reaction was allowed to take place in the first reactor and when the 
VFA level came to around 12000 mg/1 it was fed to the methanogenic reactor. 
Without an initial seeding of microbial population and a growing media the trial 
was not successful. So a filter bed was introduced to the second reactor with a 20 
liters of methanogenic bacterial sludge from a running reactor. Research trials 
indicate that the two-phase system works successfully with proper controlling. It 
also gave out biogas with 84% methane, which is very rich in methane. From 
these pilot trials, it was able to find out design process parameters for a suitable 
large-scale two-phase system where the biogas can be generated in large scale 
with the same waste effluent. These findings help industries to generate energy 
from their organic waste, hence reducing the dependency on fossil fuels as well as 
reducing w&ste disposal problem. 
in 
0 
TABLE OF CONTENT 
Page no. 
f > Abstract •» 
Table of contents «V 
List of figures 
List of Tables xiv 
Acknowledgement xvi 
Chapter 
1.0 Introduction 1 
1.1 Problem Statement 3 
1.2 Objectives 4 
1.3 Scope 4 
2.0 Industrial waste management in Sri Lanka 6 
2.1 Nature of waste 9 
* 2.2 Current methods of Industrial waste disposal 23 
2.3 Waste to energy option 29 
2.3.1 Incineration 30 
2.3.2 Landfill 31 
2.3.3 Biomethanation 33 
4 
Page no. 
2.4 Process of Biomethanation 34 
2.4.1 Low rate Biomethanation systems 36 
^ 2.4.2 High rate Biomethanation systems 38 
3.0 High rate Biomethanation 48 
3.1 Evolution of High rate Biomethanation 49 
technology - a brief history 
3.2 Process fundamentals 51 
3.2.1 Microbiology of Biomethanation digester system 53 
^ 3.2.2 Why high rate Biomethanation is efficient 58 
3.3 Technological aspects 60 
3.3.1 Energy and the Biomethanation 64 
3.4 Characteristic of Feedstock 66 
3.4.1 Total Solids (TS) 69 
3.4.2 Volatile solids (VS) 70 
^ 3.4.3 Chemical oxygen demand (COD) 71 
3.4.4 Carbon to Nitrogen ratio 71 
3.4.5 Toxic effect 72 
3.4.6 Sulfides 75 
3.4.7 Heavy Metals 76 
Page no. 
vi 
3.5 Industrial Potential for high rate Biomethanation 77 
3.5.1 Yield Estimation 79 
3.5.2 Industrial Potential 79 
4.0 Process Control of high rate systems 86 
4.1 Physical parameters 86 
4.1.1 Temperature 86 
4.1.2 Mixing effects 89 
4.1.3 Start-up 92 
4.2 Chemical parameters 92 
4.2.1 Redox potential 92 
4.2.2 pH 94 
4.2.3 Nutrient balance 95 
4.2.4 Alkalinity 96 
4.3 Other Factors 98 
4.3.1 Toxicity 98 
4.3.2 Sulfides 98 
4.3.3 Heavy Metals 99 
4.3.4 Loading 100 
4.3.5 Biological Parameters 101 
Page no. 
5.0 Development of high rate biogas technology 105 
5.1 Introduction 105 
5.2 High rate digestion studies - Pilot scale digester 106 
5.3.1 Overview 106 
5.3 Design of appropriate reactor configuration 107 
5.4 Material of Construction 110 
6.0 Industrial Effluent for high rate biomethanation 114 
6.1 Biscuits Industry in Sri Lanka 114 
6.2 Wafer biscuit manufacturing process 116 
6.2.1 Formulation of wafer batter 116 
6.2.2 Mixing of wafer batter 118 
6.2.3 Process description 119 
6.3 Analysis of Chocolate waste effluent for feed preparation 120 
6.3.1 Nitrogen supplement requirement 120 
6.3.2 Phosphorous supplement requirement 122 
6.4 Feed preparation 123 
6.5 Theoretical calculation of energy production from 124 
wafer biscuit effluent 
VII 
Page no. 
* 
viii 
7.0 Experimental studies using wafer biscuit waste effluent 126 
7.1 Process kinetics 139 
7.1.1 Models 139 
7.1.2 Process Monitoring Parameters 141 
7.1.3 Process Control systems 149 
7.2 Fundamental design consideration 157 
7.2.1 Digester volume and retention time 159 
7.2.2 COD loading on reactor 160 
7.2.3 Biogas production 161 
7.2.4 Sludge production 162 
8.0 Conclusions & Recommendations 164 
8.1 Conclusions 164 
8.2 Recommendations 166 
References 169 
Appendix 1 173 
List of figures 
Figure Page no. 
2.1a Solid waste from industries flashy untreated into the 8 
urban environment 
2.1b Liquid waste from industries flashy untreated into the 8 
urban environment 
2.2 Solid Waste Generation 10 
2.3 Solid Waste Disposal 10 
2.4 Solid Waste Disposal Details 11 
2.5 Wastewater generating industries 14 
2.6 Hazardous waste generation 20 
2.7 Industrial areas and proposed future areas for industrialization 25 
2.8 Wastewater treatment availability - sector wise 27 
2.9 Wastewater treatment non-availability-sector wise 28 
2.10 Projection of extractable landfill gas quantities. 3 2 
2.11 Biogas collecting network of a landfill -CETEM, Belgium. 33 
2.12 Process of Biomethanation 34 
2.13 Various types of methanogenic bacteria. 3 5 
2.14 The gas production rate in low rate Biomethanation 37 
2.15 Diagramatic representation of a high rate digester 39 
2.16 A schematic diagram of an anaerobic contact digestion 40 
IX 
Figure Page no. 
x 
2.17 Anaerobic filter 41 
2.18 Upflow Anaerobic Sludge Bed Reactor 42 
2.19. Granules developed in a UASB reactor. 42 
2.20 Anaerobic fluidized or expanded bed 43 
2.21 Down flow stationery fixed film reactor 44 
2.22 Packing of an anerobic contact process 45 
2.23 Schematic diagram of two-stage digestion consisting of 46 
high rate digestion in the first stage and conventional unmixed 
digestion in the second stage. 
2.24 A schematic diagram of two-phase digestion involving two 47 
high rate digesters in series. 
3.1 The three stage anaerobic fermentation of biomass 52 
3.2. Mainly Methanosarcina sp.from the stationary bed reactor 57 
described in "Ney, U.,A.J.L.Macario,Aaivasidis, S.M.Schoberth, 
andH.Sahm. 1990. Appl. Environ. Microbiol. 56:2389-2398" 
3.3 Methanogenic Communities 57 
3.4 Engine running on biogas, Denmark 60 
3.5 Typical systems for the anaerobic digestion 61 
3.6 An overview of the anaerobic digestion process 64 
3.7 Biogas requirement for various purposes. 67 
Figure Page no. 
xi 
3.8 Waste types used for Biomethanation 68 
3.9 Industrial wastewater (chemical) treatment plant, 77 
Tuntex, Taiwan-UASB digester 
3.10 Dairy factory in France. Fixed film stationery 78 
bed digester developed by Proserpol SA, France. 
3.11 Sewage sludge treatment plant, Bottrop, Germany. 78 
The largest in the world Egg shaped digesters -
volume 4* 15000 m 3 - capacity 3000 m 3 sludge/day 
4.1. (a) Internal heating, (b) External hearing 87 
4.2 Performance of the process according to temperature 88 
4.3. Advantages of mixing 89 
4.4 (a) Hydraulic mixing 90 
4.4 (b) Submerged motor with rotor stirring 90 
4.4. ©Mechanical paddle rotor 91 
4.4 (d) Shaft-driven rotor 91 
4.4 (e) Mixing through injection of biogas 91 
4.5 Variation of redox potential with time 93 
4.6 Methane formation at different pH in an anaerobic 95 
filter (Methane generation from wastes) 
4.7 MCRT vs. Methane production 97 
Figure Page no. 
4.8 The estimated relation between the imposed sludge 
loading rate, the sludge retention time, the total 
granule yield and the composition 
5.1 Arrangement of four tanks; holding tank, acedogenic 
tank, buffer tank and methanogenic tank 
5.2 Two-phase digester system -pilot scale 
5.3 Gas valves, developed by Organics Ltd, United Kingdom 
6.1 Waste water treatment plant at wafer manufacturing plant 
6.2 Basic flow diagram of the process and the wastewater treatment plant. 
7.1 Variation of pH with residence time for sucrose solution 
7.2. COD variation with Residence time for the Sucrose solution 
7.3 COD reduction with retention time 
7.4 Variation of pH with residence Time for the wafer 
waste effluent in acedogenic reactor 
7.5 Variation of COD with residence Time for the wafer 
waste effluent in acedogenic reactor 
7.6 Variation of VFA with time for the acedogenic reactor. 
7.7 Change in COD, VFA and Methane production with time. 
7.8 Biogas combustion in a modified gas cooker 
101 
108 
109 
113 
115 
121 
128 
128 
129 
130 
130 
133 
135 
138 
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Figure Page no. 
xm 
7.9 Variation of COD, VFA, and Methane produced with 13 8 
retention time for wafer biscuit effluent of methanogenic Reactor 
7.9 Combustion of biogas 139 
7.10 Variation of methane production rate with temperature 143 
7.11 Effect of pH, on rates of methane and total gas production 147 
from formic acid. 
7.12 Methane Production at 5 5°C as a function of wastewater from 149 
distillery at RT=18.2 days. 
7.13 An improved digester control system 151 
7.14 High rate systems incorporate detailed process control 154 
system ensuring process stability (Chemical Engineer, 1975). 
7.15 Rotameter 156 
7.16 SO/S vs retention time 158 
VS 
7.17 Plot of Rvs — ° - 162 
g 
10.1 Modified two-phase Biomethanation system 170 
List of Tables 
Table Page No. 
2.1 Number of Industries Registered with the Ministry 7 
of Industrial Development 
2.2 Waste collection in Colombo and surrounding urban areas. 12 
2.3 General quality standard for the discharge of effluent 14 
2.4 Industrial wastewater characteristics 15 
2.5 Profile of Industrial sector (ERM report, February 1994) 23 
2.6 Central Wastewater Treatment Plant in Industrial Estates 28 
3.1 Substrates converted to CFL) by various methanogenes 56 
3.2 Characteristics of methanogenic bacteria 56 
3.3 Possible conversion of manure to biogas 63 
3.4 Industrial Feedstock 70 
3.5 Carbon and Nitrogen content of feedstock 72 
3.6 Stimulatory and Inhibitory Concentration of Light Metal cations 75 
3.7 Concentration of Soluble Heavy Metals Exhibiting 50% 76 
Inhibition of Anaerobic Digesters (Biological waste treatment, Vol.12) 
3.8 Waste effluent characteristics of various Industries 80 
3.9 Biogas production from various industries 81 
3.10 Characteristics of industrial wastes in Sri Lanka (CEA reports) 81 
3.11 Summary of Table 3.10 84 
4.1 Stimulatory and Inhibitory Concentration of Light Metal cations 100 
xiv 
Table Page no. 
4.2 Concentration of Soluble Heavy Metals Exhibiting 50% 102 
Inhibition of Anaerobic Digesters 
6.1 Basic recipe of wafer. 117 
6.2 Wafer batter composition 119 
6.3 Feed characteristics 123 
7.1 Parameters that were monitored 127 
7.2 Feed characteristic of the effluent 131 
7.3 pH and COD variation 132 
7.4 Change in volatile fatty acid 133 
7.5 Monitored Results observed 134 
7.6 pH, COD and methane generated with time 135 
7.7 pH, COD ,VFA and methane generated with time 136 
7.8 pH, COD and methane generated in volume % with time 137 
7.9 Several kinetic models have been developed 139 
7.10 Concentration of VFA, which correspond to the 50% inhibition 146 
of methanogenic activity 
7.11 Variation of COD and Fraction of COD with time 15 8 
7.12 Calculated k values for various other products 159 
7.13 Summary of process design parameters for the anaerobic 165 
digestion of wafer batter washing effluent. 
Acknowledgements 
I wish to express my sincere gratitude to Dr Ajith De Alwis for supervising my research 
project and the invaluable assistance, guidance, advice and encouragement, given to me 
during the course of this research study. 
Further more, let me sincerely thank Dr Rohan Thittagala, the Head of the Mechanical 
Engineering department of the University of Moratuwa and the staff, Dr Rahula Attalage, 
Dr Thusitha Sugathapala and Dr Kapila Perera for their valuable assistance in numerous 
ways in completing the research. 1 am also grateful to Eng. S.A.S Perera, Head of the 
Chemical & Process Engineering department and his staff for the never-ending support. 
I would like to thank Mr. Sarath De Silva, Factory Manager, Mr. Rohan and Mr. Indika 
Abeyrathna all at Ceylon Biscuits (Pvt.) Ltd. Homagama for making arrangements to get 
down waste water samples throughout this research work providing process data. 
Financial assistance from the University Research Fund for the research and the funds 
from Intermediate Technology Development Group (1TDG) for the purchase of the 
Methane Analyzer is gratefully acknowledged. 
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xv» 
I also like to thank Mr. Upul, Mr. Sanadanayaka, Mr. Somasiri and Miss Kuraari staff of 
the Department of Mechanical Engineering for giving their support in various ways. 
Another valuable thank should go to Mr. Somarathna & Mr. Jayanthalal for fixing the 
necessary pipe fittings. I should also appreciate the help given to me by Mr. Somasiri, 
(Technical officer), Mr. Dharsana (System Analysis) of Mechanical Engineering 
Department of university of Moratuwa when using workshop facilities and computers 
respectively. 
Mr. D.C.A. Neville, the owner of the Nawajeewana Industries at Katubedda, Moratuwa 
gave his fullest support when fabricating the pilot plant unit. So I like to thank him too. 
I would like to include the following personnel in my word of appreciation, Mrs. Dineshi 
Martino, Mr. P.A.S Peris, Mr. U.G.Athula Fernando, Mr. Saraneris, Mr. N.L.Chandrasiri, 
Mr. W.L.Dayasiri Fernando, Mr. T.Masekorala, and Mr. Jayaweera of the Technical staff 
of Chemical Engineering Department of university of Moratuwa. Finally I like to thank 
Mr. Buddhika De Silva (Research Assistant) for his fullest support during the research. 
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