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DEVELOPMENT OF AN EXPERT SYSTEM 
FOR BETTER MANAGEMENT OF 
SOLID WASTE COMPOSTING 
BY PRADESHIYA SABHAS 
IN SRI LANKA 
A thesis submitted in partial fulfillment of the requirement for the Degree of 
By 
H . M . L . C . J a y a w a r d h a n a 
Master of Science 
in 
Environmental Engineering 
Research work supervised 
074620 
U n i v e r s i t y o f M o r a t u w a 
1 \ \ 
Department O f Civil Engineering 
University of M o r a t u w a 
M o r a t u w a 
SRI LANKA 
Apri l 2002 
A B S T R A C T 
The increasing population and the ever-changing life style of the public have begun to 
add to the growing solid waste problem in Sri Lanka. 
As a solution to the growing solid waste management problem in Sri Lanka, Local 
Authorities, NGOs, researchers and environmentalists have implemented several 
composting projects. As waste characteristics of municipal solid waste in Sri Lanka 
show a very high proportion of organic matter (60-85%), high moisture content (60-
75%) and low calorific value (1000-1200kcal/kg). 
Most of these projects are currently abandoned or operating under poor conditions due to 
social, economic and technical problems encountered and none of options have solved 
the solid waste management problem itself. A key issue that is highlighted is the lack of 
qualified personnel (experts) to advise and assist Local Authorities to adopt the best 
solid waste management practices. 
Decision Support Systems and Expert Systems are favourable tool to overcome these 
problems. Therefore by capturing past mistakes, weak points and considering past 
experience, a user friendly Expert System called BESTCOMP was developed for better 
management of solid waste composting by Pradeshiya Sabhas in Sri Lanka. This 
research mainly focused on the behaviour of the physical, chemical and biological 
process in composting. The model is geared towards decision making as well as 
providing required expertise to solid waste composting hierarchy. 
BESTCOMP consists of many decision models such as compost process and control, 
pictorial database, site selection, technology selection, waste analysis reports, expertise 
information, Government laws and regulation on solid waste management, information 
desk for researchers and training tool, such that the user can identify problems faster, 
examine various alternatives and make prudent choices. It performs all the functions of a 
decision support system. 
The developed system will guide the Local Authorities of Sri Lanka to find the most 
suitable composting solution to solve solid waste management problem with the available 
resources in their area and aid their decision making process on solid waste composting. 
It also helps in determining resource deficiencies when the user utilizes the data provided 
in an instructive manner. 
ii 
Acknowledgements 
I have been privileged to work with four dedicated and unique supervisors, Prof. Malik 
Ranasinghe, Dr. Ajith de Alwis , Dr. Sumith Pilapitiya and Dr. Indrika Abeygunawardena. 
My deepest gratitude to all o f them who readily gave me their wisdom, strength and 
encouragement. 
First, I give my sincerest gratitude and deepest appreciation to Dr. Ajith de Alwis for his 
many contributions to research project. He helped me to discover new ocean, by giving 
all courage for me to leave shore. He has been a source of both as a unique supervisor and 
an excellent guider at every stage of this research work. He provided many resources such 
as software, books, journals, newspaper articles, pictures etc to make this research a pool 
o f knowledge. He has been created many links among several institutions in locally as 
well as internationally. Without his great assistance and unflagging encouragement, this 
research would not have been gone this far succeeding. For all reasons and giving the 
strongest foundation for this research , he will have my loyalty and sincere gratitude 
forever. 
My deepest gratitude goes to Dr. Sumith Pilapitiya for his unflagging encouragement and 
being always there to share all difficulties with me as an adviser and as an expertise in all 
phases o f this research. In addition to his guidance in the topic of this research, he has 
also been unfailing in helping me get the resources and information I needed to complete 
both research and thesis. Both Dr. Ajith De Alwis and Dr. Sumith Pilapitiya have been a 
source o f main inspiration and driving force behind me being able to accept all 
challenges. 
In appreciation of the time, effort and patience extended to me in the pursuit o f this thesis, 
I would like to gratitude our research team leader, Prof. Malik Ranasinghe. His attitude of 
persistence toward work and achievement continue to inspire me to do all I can. M y 
special thanks to go to him for providing me with all necessary resources and comfortable 
environment to make this research successful. M y admiration for his masterful editing 
and always encouraging me to write, re-write and re-write. My gratitude to Dr. Ajith de 
Alwis , Dr. Sumith Pilapitiya and Prof. Malik Ransinghe who made it possible for me to 
pursue these studies to be by arranging all financial assistance from several sources. 
I am honoured to have Dr. (Mrs.) Indrika Abeygunawardena as one of my supervisors. 
She made valuable contributions as an adviser and a reviewer for all phases of the project. 
M y deepest gratitude for her encouragements and support through out this research. She 
also provided with me the basics in understanding biological aspects being a teacher and 
further in imparting knowledge on experimental techniques. 
M y sincere thanks to my research colleague Mr. Aruna Manipura for sharing all 
difficulties with me during this research projects . My gratitude for him for his 
in 
unwavering support, consistent empathy and unending kindness through out two years 
friendship. 
The funding provided by the University of Moratuwa, National Research Council and 
Environmental Action One Project ( E A 1 P ) for this research, continuing support and 
facilities provided by the University o f Moratuwa to carry out this research are gratefully 
acknowledged. 
M y great appreciation and gratitude to National Library and National Science Foundation 
that gave me an excellent beginning for my literature review. I would like gratefully thank 
to E M P A (Switzerland), SIDA, SI, A F R , Chalmers University (Sweden), G T Z (German), 
USEPA, W H O , UNDP, all universities, Institutions, Scientists and all individuals around 
the world who sent me thousand of published articles, magazines, books, Audio Video, 
CDs and best compliments. Without their willing co-operation, this research could not 
have gone ahead successfully. 
M y admiration and gratitude go to Dr. Ben Basnayake (University o f Peradeniya), Prof. 
C. Vishvanathan (AIT-Thailand), Dr. Per Eo Berg and Prof. William Hogland (Sweden) 
with their wide experience and indefatigable activities, have gratefully helped in several 
steps of the research. 
Thanks are also due to Mr. Sanjeev Bhardwaj (India) and Mr. Sahika Peiris for helping 
me in writing codes and helping me to be an expertise in Visual Basic. M y deepest 
appreciation goes to both of them for devoting their precious time into making this 
research successful. 
I owe special thanks to Dr. Gamini Kodikara, Dr. Niranjan Gunawardena , Dr. Ashok 
Perera and Prof. Priyan Dias in the Department of Civil Engineering for their great 
support and encouragements during this research work. 
I truly thankful that Department of Civil Engineering and Department of Chemical & 
Process Engineering having made me feel so welcome during this period of research. 
My deepest gratitude to my parents who impressed upon me since my childhood, having 
impressed on me to ' I f I am going to do some thing, I must be sure to do it right'. I could 
do anything I wanted, if I worked hard enough. 
I would like to thank my friends and colleagues for their great love and unflagging 
encouragement and being with me whenever 1 needed them. 
Finally, I also thank the following individuals who assisted me in many ways, Champika 
Jayawardene, Sanjaya Sooriyabandara, and all staff members both in office and computer 
division in the Department Civil Engineering. 
iv 
Contents 
Abstract 1 1 
Acknowledgements 1 1 1 
1.0 Introduction 1 
* 1.1 Background 1 
1.2 Waste Characteristics and Composition 2 
1.3 Treatment Methods 3 
1.3.1 Landfilling 3 
1.3.2 Biological Treatments 5 
1.4 Sri Lankan experience in Composting 7 
1.5 Research problem 8 
1.6 Research objectives 9 
1.7 Structure of Thesis 9 
2.0 Literature Review 11 
2.1 General 11 
2.2 Composting 11 
2.2.1 Pre-processing 11 
2.2.2. Processing 13 
2.2.3. Role of Microorganisms 15 
2.2.4. Factors influencing the composting process 18 
2.2.5. Odour 20 
2.2.6. Compost Maturity 21 
* 2.2.7 Post-processing 22 
2.2.8. Benefits of using compost 25 
2.3 Expert Systems 27 
2.3.1 General 27 
2.3.2 Rule-based Expert Systems 30 
V 
V 
2.3.3 Expert Systems and Decision Support Tools in General 31 
2.4 Summary 38 
3.0 Methodology 40 
3.1 General 40 
3.2 S W M Problem Identification and Analysis 41 
> 3.3 System Specification & Development Tool Selection 44 
3.4 Construction of the Knowledge base 45 
3.5 Testing and Validation 46 
4.0 B E S T C O M P Expert System 47 
4.1 General 47 
4.2 User Interface 48 
4.3 Knowledge-based system 48 
4.4 Inference Engine 51 
4.5 Database 51 
4.6 Knowledge base development of the BESTCOMP Expert System 52 
4.7 Reports 57 
4.8 Sub Modules of BESTCOMP Expert System 57 
4.8.1 Overview 57 
4.8.2 Literature Module 59 
4.8.3 Expertise Module 59 
4.8.4 Photo Gallery Module 60 
4.8.5 Training Tool Module 60 
5.0.1 Info Desk Module 61 
* 5.0.2 Legislations Module 61 
4.8.8 Reports Module 62 
4.9 BESTCOMP Main Features 63 
5.0 Validation of B E S T C O M P 64 
5.1 General 64 
5.2 Empirical Validation 64 
5.2.1 General 64 
5.2.2 Raw Material 67 
5.2.3 Compost Process 67 
5.3 Summary 71 
6.0 Conclusion and Recommendations 
6.1 Conclusions 72 
6.2 Recommendations for Future Works 73 
References 75 
Bibliography 81 
vii 
Declaration 
This thesis is a report o f research work carried out in the Department of Civil 
Engineering, University of Moratuwa, Sri Lanka? between December 2000 and April 
2002. The work included in the thesis in part or whole, has not been submitted for any 
other academic qualification at any institution. 
H . M . L . C . Jayawardhana 
Department o f Civil Engineering 
University of Moratuwa 
Prof. Malik Ranasinghe 
Supervisor 
University o f Moratuwa 
To My Darling Dad, Mum and Dr. Ajith De Alwis 
For their great assistance and unflagging encouragement