techno-economic assessment of w2e conversion: anaerobic digestion for solid waste managemenet in kmc
TRANSCRIPT
TRIBHUVAN UNIVERSITY
INSTITUTE OF ENGINEERING
PULCHOWK CAMPUS
Techno-economic Assessment of Waste-to-Energy Conversion:
Anaerobic Digestion for Solid Waste Management
in Kathmandu Metropolitan City (KMC)
By
Anirudh Prasad Sah (064 MSREE 502)
A THESIS
SUBMITTED TO THE DEPARTMENT OF MECHANICAL ENGINEERING
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF MASTER OF SCIENCE IN RENEWAL ENERGY ENGINEERING
DEPARTMENT OF MECHANICAL ENGINEERING
LALITPUR, NEPAL
MARCH, 2010
COPYRIGHT
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Pulchowk Campus, Institute of Engineering may make this thesis freely available for
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project work recorded herein or, in their absence, by the Head of the Department
wherein the thesis was done. It is understood that due recognition will be given to the
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Campus, Institute of Engineering in any use of the material of this thesis. Copying or
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and author’s written permission is prohibited.
Request for permission to copy or to make any other use of the material in this report
in whole or in part should be addressed to:
The Head
Department of Mechanical Engineering
Pulchowk Campus, Institute of Engineering
Lalitpur, Kathmandu
Nepal
TRIBHUVAN UNIVERSITY
INSTITUTE OF ENGINEERING
PULCHOWK CAMPUS
DEPARTMENT OF MECHANICAL ENGINEERING
The undersigned certify that they have read, and recommended to the Institute of
Engineering for acceptance, a thesis report entitled " Techno-economic Assessment of
Waste-to-Energy Conversion: Anaerobic Digestion for Solid Waste Management in
Kathmandu Metropolitan City (KMC) " submitted by Anirudh Prasad Sah in partial
fulfillment of the requirements for the degree of Master of Science in Renewable
Energy Engineering.
_____________________________________________ Supervisor, Dr. Tri Ratna Bajracharya Associate Professor Institute of Engineering, Pulchowk Campus
_____________________________________________
Supervisor, Mr. Ram Chandra Sapkota Associate Professor Institute of Engineering, Pulchowk Campus
_____________________________________________
External Examiner, Mr. Surendra Bhakta MathemaExecutive Director PowerTech Pvt. Ltd. Lalitpur
_____________________________________________
Committee Chairperson, Dr. Rajendra Shrestha Head of Department
Department of Mechanical Engineering, Pulchowk Campus
_________________Date
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ABSTRACT
Growing climate, energy, and environmental concerns, coupled with technological
developments and regulatory changes, have ignited new interest in municipal solid
waste (MSW) as an energy source with the potential to provide renewable energy
while reducing greenhouse gas emissions and the need for landfill space. Moreover,
the utilization of MSW as electricity generation source provides the better waste
management solution than the traditional. Hence, this thesis has envisaged performing
a techno-economic assessment of anaerobic digestion technologies. Kathmandu
Metropolitan City (KMC) generates 112,566 ton per year comprising 70% of the
organic components (80,000 tons/year). The lab experiments shows that organic
fraction of wastes has 65,663,500 kWh per year energy content with the lower
calorific value of 3MJ/kg at 69% moisture content and has a potential of extracting
16.41GWh per year energy thermally. However, the high moisture content (62%-
82%) and very low calorific values make thermal conversion infeasible and
Anaerobic Digestion feasible technically. This thesis thus studied two AD based
technologies: Valorga and Kompogas. Based on these technologies, the mass and
energy balance for the KMC plant were estimated and hence analyzed technically and
economically. The results shows that though both the technologies are feasible
technically, the KMC plant would not be economically feasible without the levy from
KMC and this plant based on Kompogas technology was found to be more
economical in comparison to Valorga technology each having 20 years of project life
when internal rate of return and net present value for each technology was analysed
under different scenarios.
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ACKNOWLEDGEMENT
I would like to express my sincere gratitude and appreciation to my thesis supervisors
Asso. Prof. Dr. Tri Ratna Bajracharya, Director of Center for Energy Studies and
Asso. Prof. Ram Chandra Sapkota, MSREE Co-ordinator, whose ideas, knowledge,
and efforts are very much embedded into this thesis. Similarly I would like to express
my sincere gratitude to Prof. Dr. Bhakta Bahadur Ale, whose suggestions during the
thesis helped me to analyse the technologies and Prof. Amrit Man Nakarmi, whose
remarkable suggestions helped me to carry out the economical analysis based on real
scenario.
I would like to express my deep gratitude to Department of Mechanical Engineering,
Pulchowk campus and am very much thankful to Dr. Rajendra Shrestha, Head of
Department of Mechanical Engineering, for his support and encouragement, Mr.
Nawraj Bhattarai, Deputy Head of Department of Mechanical Engineering, for his
suggestions and all the faculty members for their concerns and encouragements.
I would also acknowledge to Center for Energy Studies (CES) for providing all the
facilities needed, PowerTech Pvt. Ltd for providing encourageable support, Energy
for Development-Nepal (EDEN) for supporting financially, Teku Transter Station for
assisting to collect samples needed, my colleagues Mr. Mukesh Ghimire, Mr. Alok
Dhungana, Mr. Nirajan Thapaliya, Mr. Shubhrajeet Bhattacharya, Mr. Babu Raja
Maharjan for providing different journals, documents and assistance whenever
needed, BE students Amir Tiwari, Anil Prajapati, Anil Kumar Gupta, Ashok Poudel
for assisting while carrying out experiments to for this thesis and Senior Divisional
Engineer Hare Ram Acharya for his suggestions and co-operations. Their
encouragement, advice and their bright thoughts helped me to shape up my ideas.
At last but not least I would also acknowledge to Deputy Administrative Head, Mr.
Ganesh Shrestha and the staffs Mr. Manish Shrestha, Mr. Ram Hari Puri, Mr. Saroj
Maharjan and my family for their cooperation in making this complete.
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TABLE OF CONTENTSCOPYRIGHT 1
TRIBHUVAN UNIVERSITY 2
ABSTRACT 3
ACKNOWLEDGEMENT 4
TABLE OF CONTENTS………………………………………………………………5
LIST OF TABLES 7
LIST OF FIGURES 8
LIST OF ACRONYMS AND ABBREVIATIONS……………………………….......9
CHAPTER ONE: INTRODUCTION11
1.1 Background....................................................................................................11
1.2 Problem statement.........................................................................................15
1.3 Literature review............................................................................................16
1.4 Hypothesis.....................................................................................................26
1.5 Research objective.........................................................................................26
CHAPTER TWO: RESEARCH METHODOLOGY 28
2.1 Research methods..........................................................................................28
2.2 Research tools................................................................................................28
2.3 Assumptions and limitations..........................................................................30
CHAPTER THREE: RESULTS AND DISCUSSIONS 31
3.1 Site Visit (Teku Transfer Station in KMC)...................................................31
3.2 Waste Quantities and Characteristics............................................................31
3.3 Calorific Value of the MSW..........................................................................33
3.4 Theoretical Energy Calculations derived from MSW...................................34
3.5 Budget Allocation for SWM of KMC...........................................................35
3.6 Preliminary Survey for Cost of Fertilizers (Compost)..................................35
6
CHAPTER FOUR: CASE STUDIES OF AD BASED TECHNOLOGY 36
4.1 Valorga Technology......................................................................................40
4.2 Kompogas Technology..................................................................................44
CHAPTER FIVE: TECHNOLOGICAL ASSESSMENT FOR KMC PLANT 50
5.1 Based on Valorga Technology.......................................................................50
5.2 Based on Kompogas Technology..................................................................52
CHAPTER SIX: ECONOMICAL ANALYSIS OF KMC PLANT 56
6.1 Based on Kompogas Technology..................................................................56
6.2 Based on Valorga Technology.......................................................................60
CHAPTER SEVEN: RISK ANALYSIS....................................................................62
CHAPTER EIGHT: CONCLUSION AND RECOMMENDATIONS 65
8.1 Conclusions...................................................................................................65
8.2 Recommendations..........................................................................................66
REFERENCES 67
APPENDIX A: AD KEY PARAMETERS 71
APPENDIX B: ECONOMIC ANALYSIS SHEETS 78
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LIST OF TABLES
Table 3.1 Total amount of Waste Generated in Kathmandu Metropolitan City..........30
Table 3.2: Overall Waste Compositions and the total amount of generated
composition wise in KMC in 2004.............................................................31
Table 3.3: Moisture Content and Calorific Value of the Waste Samples....................32
Table 3.4: Moisture Content and the Raw Calorific Value of MSW components.......33
Table 3.5: Electricity generation from and thermal plant capacity needed for waste of
KMC...........................................................................................................33
Table 3.6: Budget allocated for Environment management of KMC during different
fiscal years..................................................................................................34
Table 3.7: Fertilizer cost survey in a village of Sarlahi District in 2010.....................35
Table 3.8: Fertilizer cost survey in Hetuada in 2010...................................................35
Table 4.1: Possible unit processes, products and quality standards involved in an
anaerobic digestion plant for organics solids.............................................38
Table 4.2: Characteristics of acceptable feedstock (mix).............................................45
Table 4.3: Mass Balance Estimate by Kompogas........................................................47
Table 4.4: Energy balance estimated by Kompogas....................................................48
Table 6.1: Summary of Net Present Worth and Internal Rate of Return under different
scenarios for KMC plant based on Kompogas Technology.......................59
Table 6.2: Summary of Net Present Worth and Internal Rate of Return under different
scenarios for KMC plant based on Kompogas Technology.......................60
Table 7.1: The parameters considered and assumptions defined for performing risk
analysis using Crystal Ball…………………………………………………...62
LIST OF FIGURES8
Figure 1.1: A scheme of anaerobic digestion pathways...............................................17
Figure 4.1: Examples of unit processes commonly used in conjunction with anaerobic
digesters of solid wastes.............................................................................38
Figure 4.2: The Flow diagram of Valorga Process......................................................40
Figure 4.3: Kompogas Flow Sheet...............................................................................45
Figure 5.1: An estimated mass balance for the KMC Plant based on the Valorga
Technology.................................................................................................51
Figure 5.2: An estimated production and consumption of energy based on the Valorga
Technology.................................................................................................52
Figure 5.3: An estimated mass balance for KMC plant based on the Kompogas
Technology...............................................................................................53
Figure 5.4: An estimated energy balance based on the Kompogas Technology..........54
Figure 7.1: Frequency distribution chart under real scenario for Valorga based KMC Plant.
………………………..…………………………………………….......63
Figure 7.2: Frequency distribution chart when KMC provides levy to the Valorga based
KMC plant…………………………………………………………….………64
Figure 7.3: Frequency distribution chart under real scenario for Kompogas based KMC
Plant…………………………………………………………………………...65
Figure 7.4: Frequency distribution chart when KMC provides levy to the Kompogas based
KMC plant…………………………………………………………….………64
LIST OF ACRONYMS AND ABBREVIATIONS
9
AD Anaerobic Digestion
ASTM American Standard for Test and Measurement
BAT Best Available Technology
BT Biomethanation Technology
CDRI Central Drug Research Institute
CADDET Center for Analysis and Dissemination of Demonstrated Energy Technologies
CES Center for Energy Studies
CHP Combined Heat pOWER
CKV Clean Kathmandu Valley
CV Calorific Value
CVgross Gross Calorific Value (Higher Heating Value)
CVraw Raw Calorific Value (Lower Heating Value)
EIA Environment Impact Assessment
ENVICO Environmental and Resources Corporation
EPA Environmental Protection Agency
g gram
g/t gram per ton
VGF Garden and Fruit w\Waste
GTZ German Technical Cooperation Agency
HHV Higher Heating Value
HRT Hydraulic Retention Time
IOE Institute of Engineering
IUCN International Union for Conversion of Nature
kWh/t kilowatt-hours per ton
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KMC Kathmandu Metropolitan City
KV Kathmandu Valley
kW kilowatt
kWh/d kilowatt-hours per day
kWh/y kilowatt-hours per year
LFS Landfill Site
MBI Mass Burn Incinerator
MC Moisture Content
MJ/kg Mega Joule per kilogram
MSW Municipal Solid Waste
MW Mega Watt
MWh MegaWatt-hour
SWMRMC Solid Waste Management and Resource Mobilization
Committee
ST/ LFS Short Term- Landfill Site
TS Total Solid
U.S. EPA United States, Environment Protection Agency
UGR Unit Generation Rate
UNEP United Nations Environment Program
VFA Volatile Fatty Acids
WB Weight Basis
WTE Waste-to-energy
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CHAPTER ONE
INTRODUCTION
This chapter deals with the background, problem statement, literature review, and
hypothesis and research objectives for this thesis.
1.1 Background
This sub chapter mainly deals with the origin of ideas, need for this thesis and its
scope and issues left that have to be addressed or find studied.
1.1.1 The origin of ideas
Economy, energy and ecology are interrelated and must go hand in hand to ensure a
sustainable prosperity of human beings. Technological innovations are continuously
improving the quality of human life, which necessarily demand additional energy
inputs at every stage of improvement. This ever-increasing energy demand is mostly
met through consumption of non-renewable commercial fuels resulting in irreversible
adverse impacts on the environment coupled with depletion of natural reserves of
commercial fuels. The Nepalese economy mostly relies on expensive imports of
commercial fuels for industrial and urban needs, and forestry biomass for rural
communities. This necessitates development of innovative technologies for
exploitation of renewable energy sources to compensate the energy balance. A
number of attempts are being made to harness the renewable sources of energy such
as solar, wind, biomass etcs.
At the same time the situation of solid waste management of Kathmandu Metropolitan
City (KMC), the study area for this thesis, has been pathetic and unmanaged due to
different seen and unseen problems and in principle due to understanding of the waste
as unproductive and uneconomic resources. Hence to turn the solid waste of KMC
into liability, it is very important that the waste generated here has the potential of
generating positive energy and is economical as well as technically feasible.
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Anaerobic Digestion (AD) also called as Biomethanation technology (BT) has been
perceived as a potential alternative as it not only provides renewable source of energy
but also utilizes recycling potential of degradable organic portion of solid waste
generated by a numerous activities sorting out the management problem faced by
KMC. This study hence has envisaged making a techno-economic assessment of
commercial AD technologies available.
1.1.2 Attempts so far made by others to address the issues
Solid waste was not such a big problem in the old days in the Kathmandu Valley.
People in the Kathmandu Valley had their own method to get rid of their household
waste, including a kind of circulation of organic waste between city and rural areas
nearby. In line with increasing population in the Valley and changing life style and
consumption habits, SWM (Solid Waste Management) has been increasingly
recognized as one of the major environmental issues in the Valley as a result of the
increasing amount of waste generated and the change of waste compositions.
According to the report “The study on the solid waste management for the
Kathmandu valley” (prepared by Nippon Co. Ltd and Yachiyo Engineering Co. Ltd in
September 2005), the concept of landfill site (LFS) started from 1976. Regarding final
disposal in the Kathmandu Valley, Gokarna located a distance of 13 km from
Kathmandu city core area was selected as a landfill site in 1976. After GTZ’s studies,
Gokarna LFS commenced its service in 1986 and was being supervised by
SWMRMC and KMC together. The LFS was the only official sanitary LFS at that
time, and KMC and LSMC dumped almost all of their waste there. However, after the
closure of Gokarna LFS in 2000 due to the opposition of the surrounding local people,
final disposal could not be other than river side dumping as a temporary solution since
there were no options in the form of LFSs. Following Dhobi Khola River dumping
which was discontinued due its contributing bird strike problem at Tribhuvan
International Airport, Bagmati River dumping by KMC and LSMC began and has
been continuing for almost five years so far and also whenever there is restriction and
strong oppositions from the locals. Looking ahead to the necessity of a new LFS
before the closure of Gokarna LFS, SWMRMC has conducted various studies from
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early 1990s to develop a new LFS within the Kathmandu Valley. However, the sites
identified by the studies could not be developed due to strong public opposition as
well as due to technical reasons in some cases. Because of the low availability of
LFSs in the Valley, the central government and IUCN jointly conducted preliminary
alternative analysis as per the request of KMC, and Okharpauwa (Banchare Danda) as
a long-term LFS. Then the related infrastructure development including access road
construction started based on the announcement by the local government for
Okharpauwa development. After closure of Gokarna LFS in 2000, the necessity of a
new short-term (S/T) LFS was recognized for receiving the waste from KMC and
LSMC instead of Bagmati River dumping. Due to the expected difficulty of LFS
development within the Valley, Sisdol in Okharpauwa was identified by the central
government as the short-term (S/T) LFS to have an immediate solution against the
Bagmati River dumping. SWMRMC after conducting the necessary site preparation
for Sisdol S/T-LFS, including EIA and land acquisition, on June 5, 2005, KMC and
LSMC commenced disposal of part of their waste at Sisdol short-term Landfill (S/T-
LF).
With respect to Waste-to-energy conversion technologies, no proper study or
evidence has been observed till now. So, these are the new concepts in case of KMC
as well as Nepal as an option for waste management and energy extraction in the
municipalities.
1.1.3 Issues left
As the waste characterization and quantification has been done in general, the eligible
components for AD (Anaerobic Digestion) have not been analyzed till now. How
much of energy can be exploited from this conversion technologies and whether this
technology is feasible technically and economically has still been a question? For
estimating the preliminary amount of energy, it is very important that the calorific
value of the wastes is determined. Moreover, proximate and ultimate analysis need to
be done to know the carbon, hydrogen, moisture content, ash content for approximate
energy assessment and to find the theoretical energy that can be obtained and hence
the technology that can be used for conversion.
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Neither detailed assessment and availability of AD technology nor its economics in
context of KMC has been studied. The environmental impact, social impact and
regarding the abatement of greenhouse gas emission are few issues that has not also
been observed or studied.
1.1.4 Scope of the work
Study area within KMC,
Characterization and quantification of solid waste of KMC,
Determination of the Calorific Value and moisture content of waste,
Two case studies of best available commercial technology based on Anaerobic
Digestion Systems,
Technical and technological analysis based mainly on the results of laboratory
values and mass and energy balance and its feasibility in KMC and
The economical analysis based on the available and current parameters.
1.1.5 Rationale in brief
The techno-economic assessment would provide an understanding of the viability of
AD technology which in turn would provide a waste management option diverting
wastes from landfill and at the same time it would save a significant amount of
greenhouse gas emissions, since these recovers energy from waste which usually
replaces an equivalent amount of energy generated from fossil fuels. Moreover,
insignificant, uneconomic and unproductive waste, the earlier perception of the
stakeholders and the public about the waste will be changed to as a valuable source
for economic generation and energy. If implemented successfully, these renewable
energy technologies would help to manage the current problem of waste disposal at
KMC which in turn improve environment of city and also enhance power supply.
When the country has been suffering from a chronic shortage of electricity load
shedding and power outage are common phenomena experienced by the electricity
consumers of KMC as well as rest of the country which has been the detriment of
economic activities and growth, the outcomes of the study would encourage the
stakeholders to adopt these technologies for MSW management and generation of
15
electricity. The improved municipal management and environment as a result can
accelerate economic growth in view of the expanding role of the urban sector of the
economy.
This study is justified on the following grounds:
The lack of study about the waste as a resource for the electricity and hence
economic generation would not motivate stakeholders and investors for its
utilization.
Lack of study on technical and economical study will never motivate the
stakeholders to adopt new technology.
1.2 Problem statement
Rapid urbanization of municipalities has resulted into increased urban wastes and they
are also making water polluted, which could be a major problem in near future which
has been considered trifling problem till now though. Moreover waste management is
the most problematic and expensive responsibility of Municipality. Though large
chunks of KMC budget i.e. 18% of the total (according to the Rabin Man Shrestha,
Chief Environment Management Department Kathmandu Metropolitan City Office,
Nepal) are expended on SWM, sustainable management is not achieved yet.
The major cause behind all these problems is due to lack of understanding of waste at
principle. At the current situation, intense competition over natural resources has
rendered waste as one of the economic resource for electricity generation. A choice of
appropriate technology for generating electric energy from MSW of KMC should
have to be based on examination of all available and relevant technologies on the
field. Many WTE conversion options such as landfill, composting, anaerobic
digestion, mass burn incinerator, fluidized bed incinerator, gasifier, plasma gasifier
which are seen technically and economically feasible (Yang and Li, 2002). Except
landfill, composting, and anaerobic digestion all the others are thermal conversion
technologies. In that case, it is important to know whether these technologies are
suitable for processing the waste generated in KMC. After KMC’s problematic
landfill use and unsuccessful composting tried at Teku Transfer Station, Kathmandu,
16
can the anaerobic digestion technology be technically and economically feasible. For
that it becomes necessary to know the physical properties and the energy content of
the generated waste, suitability of anaerobic digestion technology, land availability for
installation and economical viability of this technology.
1.3 Literature review
This topic mainly deals with the literature surveyed while conducting this study.
1.3.1 Waste as a Source of Energy
In the traditional sense, renewable sources of energy are those that nature can regrow,
such as wood, crops, or other plants (biomass), that are available through the Earth’s
unique physical set-up, such as wind, water, and solar radiation. However, the term
biomass often includes one manmade good that is the byproduct of industrialization:
waste. The U.S. EPA repeatedly called MSW renewable. Although it is desirable to
minimize the amount of waste during production and distribution of goods, it is
almost certain that a minimum quantity of waste will be generated. Because it is
believed that the global community will continue to produce industrial products, there
will be a continuous stream of new waste, which therefore could be considered to
replenish the previously generated garbage.
1.3.2 Anaerobic digestion
Anaerobic digestion is the breakdown of organic material by micro-organisms in the
absence of oxygen. Although this takes place naturally within a landfill, the term
normally describes an artificially accelerated operation in closed vessels, resulting in a
relatively stable solid residue. Biogas is generated during anaerobic digestion (AD) -
mostly methane and carbon dioxide - this gas can be used as a chemical feedstock or
as a fuel. Anaerobic digestion can treat many biodegradable wastes, including wastes
that are unsuitable for composting, such as meat and cooked food.
1.3.3 Reactions of Anaerobic Digestion
AD is a collection of many biological reactions occurring in the absence of oxygen. In
reality, the biological pathways of the process depend on the concentration and nature
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of the substrate, bacteria and surrounding conditions. As shown schematically in
Figure 1.1, AD takes place in three stages: hydrolysis, acidogenesis/acetogenesis and
methanogenesis (Baldwin, Lau, and Wang, 2009). During the hydrolysis stage,
complex organic polymers are broken down into their monomer intermediates: sugars,
amino acids and volatile fatty acids (VFA). During acetogenesis, these intermediates
are converted into acetate (acetic acid) with CO2 and hydrogen as by-products. Finally
in the methanogenesis stage, hydrogen and acetate are converted into CH4 and CO2.
Table 1.1 is a brief summary of the main reactants and products during each phase. In
general, the microorganisms involved in hydrolysis and acetogenesis grow more
rapidly than the microorganisms involved in methanogenesis. As a result,
methanogenesis tends to be the rate-limiting step. However, for some materials, such
as grasses and newsprint, which contain more recalcitrant celluloses, hydrolysis may
be very slow and become rate-limiting (Baldwin, Lau and Wang, 2009).
Figure 1.4: A scheme of anaerobic digestion pathways
Source: Development of a Calculator for the Techno-economic Assessment of Anaerobic Digestion Systems
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Table 1.1: Reactants and products involved in the three phases of anaerobic digestion
Phase Reactants ProductsHydrolysis Organic materials Sugars, amino acids, volatile fatty acids (VFAs)Acetogenesis
Sugars, amino acids,
VFAs
CH3COOH (acetic acid), alcohols, CO2, H2
CO2, H2 CH3COOHMethanogenesis
CH3COOH CH4, CO2
CO2, H2 CH4
Source: Development of a Calculator for the Techno-economic Assessment of Anaerobic Digestion Systems
1.3.4 Digesters
Digesters can be categorised by dry or wet systems – below 15 percent dry solids is
termed wet. Also digesters can operate within two temperature ranges, either at 350C
(mesophilic) or 550C (thermophilic). Some are loaded in batches while others have
continuous feed. On completion of the process digesters are emptied leaving 10-15
percent behind as a seed culture for the next batch. Various AD processes have been
developed, operating at different temperatures, moisture levels and speeds. The purity
of material fed into the AD process determines the quality of the end product. Some
plants are designed to remove as many other materials as possible (for example,
ferrous metals) before digestion. Others are designed to optimise gas collection for
energy production and a soil conditioner may not be their main objective. Others
might optimise the horticultural product, regarding energy of secondary importance.
All of the processes share a common approach where shredded materials and water
are held in a reactor for 6-25 days at a constant temperature between 35 and 550C.
Wet continuous digestion
Waste is slurried with a large proportion of water to give a feedstock of 10 percent dry
solids. Glass and stones must be removed to prevent them accumulating in the bottom
of the reactor. This method can be used for co-digestion of biodegradable waste with
sewage sludge.
Multi-stage wet digestion
There are a range of multi-stage wet digestion processes which take municipal solid
waste and add to recycled liquor. The mixture is fermented by micro-organisms to
19
release volatile fatty acids. These are then converted to gas in a specialised high-rate
industrial digester.
Dry batch digestion
Waste is fed into the reactor with digested material from another reactor and then the
digester is sealed. Leachate is collected from the bottom and is re-circulated to
distribute nutrients and micro organisms and maintain even moisture levels.
Leach-bed process
Similar to the dry batch method, but once the third stage of methanogenesis is reached
the reactor is connected to a fresh batch of waste in a second reactor.
Dry continuous digestion
Waste is fed continuously into a digestion reactor with 20-40 percent dry matter. The
process of anaerobic digestion in a digester takes about 35 days, which compares
favourably with a landfill site which may remain active for 35 years producing
methane and leachates which can harm the environment.
1.3.5 Digestate use
Digestate is the residual fibrous material left at the end of processing. End-use ranges
from landfill cover, landspread for agriculture or the production of a high quality soil
conditioner after an additional maturation process. The quality of the original input
biowaste determines the quality of the digestate at the end of the process. The
efficiency of the source-separation systems is important as the contamination of the
biowaste with potentially toxic chemicals and too many non-biodegradable inclusions
will be apparent in the final product. The presence of heavy metals severely limits its
eventual use.
The digestate produced by most operational plants is destined for use as a soil
conditioner and most have a useful level of nutrients resulting in less demand for
inorganic fertilisers. There is also evidence that using digestate on land has the benefit
of suppressing normal pathogen and parasite levels.
20
Depending on the quality of the original feedstock, digester residue can be used for
landfill cover or further matured into a compost product.
1.3.6 Biogas
During the process of anaerobic digestion the organic wastes produce biogas. This is
composed largely of methane (55-70%) and carbon dioxide (30-45%). Methane is a
greenhouse gas thirty times more damaging than the equivalent amount of carbon
dioxide. The quality of the biogas produced from AD affects its final usefulness. The
main concern in this context is the presence of hydrogen sulphide which occurs as a
metabolic bi-product of sulphur-reducing bacteria in the digester. Hydrogen sulphide
can rapidly corrode the gas-handling and electricity generating equipment in the plant.
Table 1.2: Typical Biogas composition
Methane 55-70 % by volumeCarbon dioxide 30-45 % by volumeHydrogen sulphide 200-4000 ppm by volumeEnergy content of AD gas product 20-25 MJ/m3
Energy content of CH4 per ton MSW 167-373MJ/ton MSWSource: Reference: Regional Information Service Centre for South East Asia on
Appropriate Technology (RISE-AT) (Nov 1998), Review of current status of Anaerobic Digestion Technology for treatment of MSW.
If one tonne of putrescible food waste consists of 77 percent water and 23 percent
solids, the digester will convert approximately 75 percent of the solids to biogas. The
maximum possible yield of biogas in is 400m3, but in practice is nearer to 100m3.
This has an energy value of around 21-28 MJ/m3. Between 20 - 50 percent of the
energy produced will be used to run the plant.
Biogas may be used directly or as a replacement fuel for kilns, boilers and furnaces
located close to the AD site. If the gas is used in power generation gas clean-up is
required to remove corrosive trace gases, moisture and vapours.
21
1.3.7 Process liquor
There has been a focus on the digestate and biogas production from AD but the
process liquor is often overlooked. There are however environmental considerations
and costs to be considered with the generation of contaminated water. Some process
liquor is used to re-wet incoming biowaste as it contains useful bacterial populations.
This method can produce a faster reaction then the original start-up. If all the liquor
was recycled in this way however, the concentration of contaminants would become
too high. Excess liquor can be disposed of in three ways: discharge, landfill or
landspreading. Discharge is the simplest but it may be expensive to achieve
environmental standards required by regulators.
Limits on certain chemical components are likely to be in place. Discharge into the
sewerage system is more likely to be permitted than to a water course. AD process
liquors can be very polluting and treatments may include aeration de-nitrification and
reverse osmosis techniques.
A major area of concern is the heavy metal content particularly when considering
application to land, and also nitrogen and phosphorous content. Haulage charges for
transporting contaminated water to disposal may be a third of the total transport and
disposal fee.
1.3.8 Biogas Yields and Power Generation
The biogas yield primarily depends on the type of feed. Most commonly used feeds
for AD are animal manures from cattle, hog and poultry, crop residues as well as corn
and grass silage. Organic wastes from food processing, restaurants, fish processing,
slaughterhouse, sewage sludge (biosolids) and the organic fraction of municipal waste
may also be used as feeds for AD. Table 3 shows the biogas generation potential of
substrates, as compiled from Preusser (2006) and Electrigaz (2007), which are similar
to the information provided in the Wisconsin Agricultural Biogas Casebook (Baldwin,
Lau and Wang, 2009). According to Birse (1999), these values should only be used as
indicative values. The biogas yields of food and yard wastes can be considerably
higher than the biogas yields of animal wastes (Baldwin, Lau and Wang, 2009).
22
Table 1.3: Biogas yields (lab-scale and pilot-scale AD studies)
Source: Source: Development of a Calculator for the Techno-economic Assessment of Anaerobic Digestion Systems
A large number of papers have been published in the past several decades dealing
with the performance of different reactor configurations digesting and co-digesting
organic solid wastes. According to Jerger and Tsao (1987), the theoretical CH4 yields
(about 60% of biogas yields) due to the action of most microbial species are similar,
with a value of about 0.5 m3 CH4/kg VS added. Biogas yield data based on actual
observations or monitoring records have been compiled and shown in Table 1.3 for
lab-scale and pilot-scale studies and in Table 1.4 for full-scale systems. This
information is not meant to be exhaustive, though these may be considered as
representative values. Kelleher (2007) cited results obtained from studies by various
23
researchers on the biodegradation of MSW components in lab-scale landfills; kitchen
waste (TS 30%) and yard waste (TS 40%) have biogas yield of 113 m3/ton and 34
m3/ton, respectively. Ward et al. (2008) conducted a review of the AD of agricultural
resources and compiled the CH4 producing potential of a wide range of substrates.
Regardless of the scale of study, it is quite clear that animal manures provide lower
yields while food processing wastes, especially fats oil and grease, provide higher
yields.
Table 1.4: Biogas yield full-scale AD studies
Source: Development of a Calculator for the Techno-economic Assessment of
Anaerobic Digestion Systems
Gregerson et al. (1999) reported that at the time in Denmark, approximately 75% of
the biomass resource was manure mostly in the form of slurry, whereas the remaining
24
biomass was waste that mainly originated from food processing industries. In these
biogas plants, manure and organic waste were mixed and digested in AD tanks for a
hydraulic retention time (HRT) of 12 - 25 days. The biogas produced was cleaned and
normally utilized in CHP plants. The biogas yields from some of the 20 systems
installed between 1984 and 1998 are shown in Table 1.4. The biogas yield ranged
from 23 to 92 m3/ton biomass (wet mass basis).
1.3.9 Energy use
Whereas composting is an energy-consuming process, requiring 50-75 kilowatt-hours
per tonne (kWh/t) MSW input, AD is a net energy-producing process (75-150 kWh/t
MSW).
The amount of energy required to run a digester is directly related to the moisture
content of the feedstock. High-moisture systems use more heat but require less
electricity to circulate the fluid digestate. Anaerobic digestion requires an additional
15kWh/ton of energy in comparison to aerobic composting plants.
1.3.10 Odour
Several aerobic plants have been closed or put under constant review due to odour
complaints. In anaerobic systems most volatile components are broken down by
bacteria in the digester. A study has shown that whereas 588g/t of volatile organics
were produced in aerobic composting, only 3g/t were produced in an anaerobic
system.
1.3.11 Economics of AD
The capital investment required for a modern AD plant are less than those of an
energy from waste plant but similar to those of a materials reclamation facility
(MRF). Experience in Europe suggests that a plant which can handle up to 15-20,000
tpa is the smallest scale which will be financially viable. High costs are imposed by
the superior technical requirements to provide adequate gas seals to prevent air
ingress, safe gas handling and internal environmental controls and monitoring
techniques, such as the detection of very low levels of concentrations of hydrogen (an
25
intermediate product). When the digestion process is complete the digester is emptied
and 10 – 15 percent may be left behind as a starter for the next batch.
1.3.12 Problems
Anaerobic digestion is relatively expensive and requires a major capital investment.
Waste water from the process may contain a high concentration of metals, nitrogen
and organic materials.
Because of the complex association of different types of bacteria, digesters have a
higher risk of breakdown and may be difficult to control. The variable nature of the
waste may be a problem for AD plants. In summer households produce more organic
kitchen wastes and grass clippings, while in autumn prunings and woody materials
predominate.
1.3.13 Approaches to determine Calorific Value
There are several experimental and empirical approaches available for determining
the calorifc value (CV) of materials such as MSW. Calorimetric measurement is the
common method for determining the energy content of MSW. One method of
determining the CV of a given material is by means of an open calorimeter in which
pressure is maintained at 1 atmosphere. Under constant pressure conditions, the heat
released is equal to the enthalpy change for the reaction. Another type of calorimeter
is the bomb calorimeter in which combustion is conducted under conditions of
constant volume.
Regarding the empirical approaches, there are three types of models that are used to
predict CV values based on the following analyses:
Physical composition
Ultimate analysis
Proximate analysis
The physical composition analysis is based on the levels of different components of
the solid waste matrix, such as plastics, paper and garbage. The ultimate analysis of
26
waste typically involves determination of the carbon, oxygen, nitrogen and sulfur
contents, while the proximate analysis includes an assessment of the levels of
moisture, volatile combustible matter, fixed carbon and ash. Because MSW is a
heterogeneous material and its production rate and physical composition vary from
place to place as they are a function of socio-economic level and climatic conditions
(Abu-Qadis, et al), the energy content of one country will be different from that of
another.
1.4 Hypothesis
There are two municipal solid waste-to-energy schemes that could be adopted in
Nepal depending upon the initial literature review of the waste characteristics:
incineration with electricity recovery and anaerobic digestion in which electricity and
fertilizer are produced. To be promoted as effective methods of solid waste
management in terms of environmental soundness and energy saving, a techno-
economic assessment needs to be performed. But according to “The study on the solid
waste management for the Kathmandu valley” (prepared by Nippon Co. Ltd and
Yachiyo Engineering Co. Ltd in September 2005) the moisture content is in the high
range of 60-75% and the SWMRMC Act, 1987 prohibits the use of incinerator except
the incineration of hazardous waste. Hence, of the two technologies, AD which has
been successful in a smaller scale for Nepal could be an option for energy recovery
and hence waste management. This thesis hypothesizes with the available commercial
AD technologies; the waste-to-energy (WTE) conversion using this technology will
be technically and economically feasible.
1.5 Research objective
This topic deals with the objectives has been set for the study after the literature
survey and the need for this thesis.
1.5.1 Main Objective:
To perform a techno-economic assessment of Anaerobic Digestion Technology
27
1.5.2 Specific Objectives:
To quantify and characterize the eligible components of the Municipal Solid
Waste of Kathmandu Metropolitan City.
To determine calorific value and moisture content of the MSW
To estimate the amount of green energy from MSW
To perform two case studies of AD based technologies.
To estimate mass and energy balance for KMC plant based on the case studies
and hence technical feasibility of it.
To do economic analysis of KMC plant based on AD technology that would
be implemented in Kathmandu.
28
CHAPTERE TWO
RESEARCH METHODOLOGY
This chapter deals with the methodology used, research tools needed and assumptions
and limitations considered while carrying out this research.
1.6 Research methods
This thesis is mainly based on quantitative and partly experimental analysis.
Quantitative method is used to carry out waste characterization, quantification, energy
recovery, mass and energy balance, and economic analysis whereas experimental
method is used to determine the calorific value, ash percentage and moisture content
in the lab.
1.7 Research tools
This study is conducted by using research tools: literature survey, experiments, and
statistical techniques using Microsoft excel 2007 and Crystal Ball.
1.7.1 Literature Survey
The secondary data is used for the estimation of the volume of waste and
characterization by literature survey and also the relevant Journals and other available
documents have been reviewed and assessed for Anaerobic Digestion technologies.
1.7.2 Quantification and Characterization of Wastes of KMC
The study is carried out for Kathmandu Metropolitan City. The data relevant to this
study for characterization and quantification of eligible components of MSW was
collected from different sources such as Kathmandu Municipal Corporation (KMC),
and Solid Waste Management and Resource Mobilization Committee (SWMRMC).
Mainly “The study on the solid waste management for the Kathmandu valley”
(prepared by Nippon Co. Ltd and Yachiyo Engineering Co. Ltd in September 2005)
has been followed throughout the study for this purpose.
29
1.7.3 Sampling for Determination of Calorific Value and Moisture
Content of MSW
Analysis done during this study based on the report “The study on the solid waste
management for the Kathmandu valley” depicts that the major portion of the waste
constitutes organic and other constituents are minimal with respect to the organic
portion. Hence, Judgment Sampling, based on ASTM D487-95-2006, was used to
collect samples for determining the calorific value and moisture content of the MSW.
In total five commingle samples of organic portion of MSW were obtained from the
Teku Transfer Station.
1.7.4 Proximate analysis
Proximate analysis is mainly used for determining moisture content in the samples.
Five samples collected were brought immediately with proper care to the lab where
these were used to obtain moisture content in accordance with the procedures of
ASTM 949.
1.7.5 Determination of Calorific value
Same samples were ground using electrical mixer separately. The ground samples
were then used in Parr Oxygen Bomb Calorimeter to determine the calorific value of
each sample. All the samples were mixed to get one more sample which was also used
to determine the CV of the mixed samples. ASTM D468-02-2007 procedures were
used for determining the CV of MSW. CV determined from this calorimeter was
gross or upper value embedded in it. The raw or lower CV was obtained using the
following empirical formula
Where,
CV = calorific value (“raw” is real “as delivered” value, “gross” is value for dried
material) in MJ/kg
MC = % moisture content (by weight)
H = % Hydrogen content (Shaine, Martin and Eric et al).
30
The calorific value of each samples found in the sampled waste was obtained with the
help of Oxygen Bomb Calorimeter in accordance with the ASTM D 468-02-2007.
1.7.6 Techno-economic Assessment
The technologies for Anaerobic Digestion are assessed. These technologies are
assessed on the basis of different parameters: availability of technology, financial
analysis, revenue generation, effective waste to energy conversion, social impact
analysis.
1.8 Assumptions and limitations
The study will be conducted within Kathmandu Metropolitan City. The study on the
solid waste management for the Kathmandu valley conducted by “The study on the
solid waste management for the Kathmandu valley” (prepared by Nippon Co. Ltd and
Yachiyo Engineering Co. Ltd in September 2005) team will be the basis for the
quantification and characterization of the wastes of KMC. The samples have been
taken at Teku transfer station. Technical and economical analyses are based on the
two case studies. The thesis assumes that whatever wastes gets generated is used by
the KMC plant.
31
CHAPTER THREE
RESULTS AND DISCUSSIONS
This chapter deals with all the results obtained during this study and the discussions
on the results.
1.9 Site Visit (Teku Transfer Station in KMC)
Katmandu Metropolitan City (KMC), the capital of Nepal, covers about 53 sq. km
area and politically divided into 35 wards. The 2001 National Census has estimated
the population of the KMC to be 741,008 (CBS, 2002) with the annual average
growth rate of 4.67%.The KMC is responsible to collect the waste from the street and
containers and transfer to the Teku Transfer Station (TTS) before transferring to the
final dumping site.
The Teku Transfer Station covers an area of 150mx100m and receives 308 tons of
waste per day. Two loaders, four guards, and two administrative officers are
employed at this location.
1.10 Waste Quantities and Characteristics
A prerequisite for the successful implementation of any solid waste management plan
is the availability of information on the composition and quantities of solid waste
generated.
Table 3.2 Total amount of Waste Generated in Kathmandu Metropolitan City
Municipalities Population Average generated quantity (tons/day)Year 2004 2015 2004 2015KMC 741,008 1,055,591 308.4 547.9LSMC 180,397 260,790 75.1 135.4BKM 80,476 117,380 25.5 46.2MTM 53,853 83,696 14.3 27.8KRM 43,424 54,400 11.6 18.1
Total 5 municipalities 1,099,158 1,571,857 434.9 775.4Source: Nippon Koei Co. Ltd and Yachiyo Engineering Co. Ltd, 2005
32
Waste generation trends are driven by several factors, such as economic activity,
demographic changes, technological innovations, life-style and patterns of production
and consumption (Oliga and Katica, 2008). Municipal unit generation rate has been
taken as the product of household unit generation rate and additional index. The unit
generation rate of solid waste is estimated at 0.416 kg/day-capita in KMC. Increase in
the household increases the population of the city and hence waste generation.
Without measures for source reduction, the annual increase in unit waste generation is
2.6% (Nippon Koei Co. Ltd and Yachiyo Engineering Co. Ltd, 2005). The total
amount of waste quantity generated in KMC is as shown in Table 3.1.
In 2004, the total amount of waste generated in five municipalities is 434.9 tons/day
of which KMC is the dominant waste generator with approximately 71% i.e. 308.4
tons/day of the total waste generated. If the waste is generated in future with an
annual increasing rate higher than 2%, say as much as 5%, the total daily generation
quantity from KMC is estimated to be more than 700 tons in 2015. The annual waste
generation rate of KMC is estimated to be 112,566 tons.
Table 3.3: Overall Waste Compositions and the total amount of generated
composition wise in KMC in 2004.
Waste Components KMC % by weight Waste Generated (tons/day)Organic 70 216Paper 9 27.8Plastic 9 27.8Glass 3 9.25Metals 1 3.08Textile 3 9.25
Rubber/leather 1 3.08Others 4 12.3Total 100 308
Source: Nippon Koei Co. Ltd and Yachiyo Engineering Co. Ltd, 2005
Table 3.2 shows the physical composition and the typical percentage distribution of
MSW components in KMC. It can be noted that the major fraction of the solid waste
generated is organic, paper and plastics. Organic wastes (70% of the total waste
generated in KMC) include all kitchen waste, garbage, commercial etc. The other 33
significant constituents are plastic and paper with equal percentage of 9%. The
amount of organic component constituted the majority with generation of 216 kg/day
in year 2004.
1.11 Calorific Value of the MSW
The upper calorific value is the gross energy content including the energy that is
necessary to evaporate the moist content. In practice, this value is relatively
uninteresting for incineration, gasification or pyrolysis. The lower heating value is
important, because this is the energy content, which can be utilized for the production
of thermal and electrical power.
Table 3.4: Moisture Content and Calorific Value of the Waste Samples.
Sample Moisture content (% WB) CVgross (MJ/kg) CVraw (MJ/kg)1 82.14 13.26 0.132 69.41 17.02 3.113 66.22 18.48 4.184 61.71 11.40 2.365 76.97 16.89 1.71
6(mixed) 71.29 13.16 1.66Average 71.29 15.04 2.19
Source: Lab Results,2009
The Table 3.3 shows MC and CV of the samples of the waste. The maximum and
minimum moisture content is estimated to be 82.14% and 61.71% by wet basis but in
average it is estimated to be around 71.29%. These conditions are typical in many
developing countries (Savage et al., 1998). The relatively high moisture content of the
MSW may lead to a reduction in the calorific value of the MSW (Abu-Qudais and
Abu Qdais, 2000). The CVgross of the samples ranges from 11.40 to 18.48 MJ/kg (dry
basis) whereas the CVraw ranges from 0.13 to 4.18 MJ/kg. In average, the moisture
content is found to be 71.29% and CVgross and CVraw to be 15.04 MJ/kg (dry basis) and
2.19 MJ/kg respectively.
Similarly, Table 3.4 shows the components of MSW and their corresponding CV
which can be utilized for the generation of energy in the thermal facility. As the major
34
portion of MSW is organic, the CV obtained from the lab also represents for the same.
The estimated CVraw of the organic portion at 68% MC is found to be 3MJ/kg. The
CVs of the other components of MSW being similar have been taken from the
literatures.
Table 3.5: Moisture Content and the Raw Calorific Value of MSW components.
Waste components Moisture content (%WB) CVraw, MJ/kg Remarks for CV
Organic 68 3 EstimatedPaper 7 14.9
Literature*
Plastic 10 32.8Glass NA 0Metals NA 0Textile 26.8 10.6
Rubber/leather <1 41Others NA NA NA
Source: Integrated Solid Waste Management Plan, volume-1’ published by United Nation Environment Programme.
1.12 Theoretical Energy Calculations derived from MSW
These calculations are based on the assumption that 112566 tons of MSW per annum
(308.4 t/d) are generated from KMC which is sorted and utilized in a thermal
treatment facility. The calculation doesn’t include plastic, metal, glass, others.
Table 3.6: Electricity generation from and thermal plant capacity needed for waste of
KMC.
Waste
components
Energy Content,
kWh/y
Electricity generation,
kWh/y
Plant Capacity,
kW
Organic 65663500 16415875 1874Paper 41930835 10482709 1197
Textile 12663675 3165919 361Rubber/leather 12820017 3205004 366
Total 133078027 33269507 3798Source: Author's calculation based on lab results.
The study has not taken into consideration the non combustible parts of MSW like
glass, plastic and metal. As shown in Table 3.5 organic and the paper are the main
35
two waste combustible parts from which 65,663,500 and 41,930,835 kWh per year of
energy can be extracted respectively of which 16,415,875 kWh per year 10,482,709
kWh per year respectively. In total 33,269,507 kWh per day of thermal energy is
available and from it in total 33,269,507 kWh per year electricity can be production
assuming the overall efficiency to be 25%. As the table shows, the plant capacity of
3798 kW will be needed for exploiting the generated municipal solid waste.
1.13 Budget Allocation for SWM of KMC
The budget allocation for all types of waste and environment management comes
under the heading of Environment Management. According to the KMC annual
report, 2009 most of the budget allocated under this heading is expended for solid
waste management. So, in a sense the budget has been allocated for SWM. The
increment in EM budget shows the stakeholders concerns over the waste management
issue. Table 3.6 provides summary of budget allocated during different fiscal year for
EM. The increment in budget during fiscal year 08/09 and 09/10 is similar whereas
between fiscal year 06/07 and 07/08, there has been an increment by almost 13%.
Hence, the average budget increment has been estimated to be 12.63%.
Table 3.7: Budget allocated for Environment management of KMC during different fiscal years
KMC Budget for Environment ManagementFiscal year Expenditure, Rs (in crores) Increment percentages Average2006/2007 19.70 -
12.63%2007/2008 20.48 3.98%2008/2009 24.61 16.79%2009/2010 29.69 17.11%
Source: http://www.kathmandu.gov.np/uploads/bud-66-67.pdf, 2010
1.14 Preliminary Survey for Cost of Fertilizers (Compost)
The selling price of compost, according to the presentation by Mr. Rabin Man Singh
in 2009, Chief Environment Management Department, Kathmandu Metropolitan City
Office, has been Rs 10 per kg since 2003. However, any documented evidence
couldn’t be found regarding its selling price. The slaughter house composting unit at
Marutol in Kathmandu situated at the bank of Bishnumati despite producing compost
36
since long time (date couldn’t be figured out due to unavailability of authorized
person) hasn’t sold any amount of compost.
While in the survey done in different places indicate that the compost can be sold in
better price if it is well proved. The current selling price of fertilizer as shown in
Table 3.1 and 3.2 in Sarlahi district and Hetauda are approximately Rs 2 and Rs 4.
However according to the sellers at Hetuada, the demand of proven compost or such
fertilizer is higher and can be sold in better price than estimated.
Table 3.8: Fertilizer cost survey in a village of Sarlahi District in 2010
Type of compostCost for a bullock
cart of Gowa (Compost)
Weight of Gowa per bullock cart, kg
cost per kg, Rs
Gothe Mal called Gowa locally
Rs 1000 500 2
Source: Based on author Survey, 2010
Table 3.9: Fertilizer cost survey in Hetuada in 2010
Types of compost
Cost of a Bora (Sack) in Rs
Approximate weight of compost in a bora (Sack), kg
Average weight, kg
Rs/kg (average)
Gothe mal Compost
120-140 25-40 32.5 4
Source: Based on author Survey, 2010
37
CHAPTER FOUR
CASE STUDIES OF AD BASED TECHNOLOGY
The literature on anaerobic digestion of MSW appears confusing and difficult to
summarize. The reason is that it is hard to find papers with similar experimental set-
ups. In fact, it is precisely the appropriateness of a given reactor design for the
treatment of particular organic wastes which forms the focus of most research papers.
The comparison of research data and drawing of conclusions is difficult because the
reactor designs differ largely on variability of waste composition and choice of
operational parameters (retention time, solids content, mixing, recirculation,
inoculation, number of stages, temperature, etc) (details in Appendix A). And hence
there exists only empirical knowhow for the optimal reactor design to treat municipal
solids and it is also due to the complexity of biochemical pathways, the novelty and
varieties in the technologies.
For designing the reactor (digester) for AD, the feedstock should be mainly organic
fraction of municipal solid wastes (OFMSW) sorted mechanically in central plants or
organics separated at the source, referred to here as the organic components in MSW
of KMC. Hence while designing the reactor; the need for specific pre- or post-
treatment unit processes becomes very important. Necessary pre-treatment steps may
include magnetic separation, comminution in a rotating drum or shredder, screening,
pulping, gravity separation or pasteurization. As post-treatment steps, the typical
sequence involves mechanical dewatering, aerobic maturation, and water treatment
but possible alternatives exist such as biological dewatering or wet mechanical
separation schemes wherein various products may be recovered as shown in Figure
4.1.
A plant treating municipal solids anaerobically is therefore best seen as a complex
train of unit processes whereby wastes are transformed into a dozen products.
Appropriate rating of given reactor designs should therefore also address the quantity
and quality of these products (Table 10) as well as the need for additional pre- and
38
post-treatments. These considerations are often decisive factors for the election of a
technology for an actual project.
Figure 4.5: Examples of unit processes commonly used in conjunction with anaerobic digesters of solid wastes.
Source: Biomethanization of OFMSW
39
Table 4.10: Possible unit processes, products and quality standards involved in an anaerobic digestion
plant for organics solids.
Unit Processes Reusable Products Standards or Criteria
PRETREATMENT
- Magnetic separation
- Size reduction (drum or
shredder)
- Pulping withngravity
separation
- Drum screening
- Pasteurization
- Ferrous metals
- Heavy inerts reused as
construction material
- Coarse fraction, plastics
- Organic impurities
- Comminution of paper,
cardboard and bags
- Organic impurities
- Calorific value
- Germs kill off
DIGESTION
- Hydrolysis
- Methanogenesis
- Biogas valorization
- Biogas
- Electricity Heat (steam)
- Norms nitrogen, sulfur
- 150 - 300 kWhe/ton
250 - 500 kWhheat/tonPOST-TREATMENT
- Mechanical dewatering
- Aerobic stabilization or
Biological dewatering
- Water treatment
- Biological dewatering
- Wet separation
- Compost
- Water
- Compost
- Sand, Fibres (peat)
Sludge
- Load on water treatment
- Norm s soil amendments
- Disposal norms
- Norm s soil amendments
- Organic impurities
Norms potting media
Calorific value
Source: Biomethanization of OFMSW
About 90 % of the full-scale plants currently in use in Europe for anaerobic digestion
of OFMSW and biowastes rely on one-stage systems and these are approximately
evenly split between 'wet' and 'dry' operating conditions (De Baere, 1999). But this
industrial trend has not been followed by the scientific literature, which reports as
many investigations on two-, multi-stage or batch systems as on one-stage systems. A
likely reason for this difference is that two- and multi-stage systems afford more
possibilities to the researcher to control and investigate the intermediate steps of the 40
digestion process. Industrialists, on the other hand, prefer one-stage systems because
simpler designs suffer less frequent technical failures and have smaller investment
costs. Biological performance of one-stage systems is, for most organic wastes, as
high as that of two-stage systems, provided the reactor is well designed and operating
conditions carefully chosen (Weiland, 1992).
This thesis therefore has performed two case studies but focussed mainly on the
commercial based KOMPOGAS AD technology available in the market. Using this
study, the techno-economic assessment of Hypothetical KMC plant has been
performed.
1.15 Valorga Technology
Figure 4.6: The Flow diagram of Valorga Process
Source: The Anaerobic Digestion and the Valorga Process, Jan 1999, Literature and
brochures of the company.
The processes used in Valorga technology (VT), a German company, was initially
designed to treat organic MSW and was later adapted to the treatment of mixed
MSW, biowaste (source separated household waste), and grey waste (organic residual
fraction after biowaste collection).
41
Water Treatment
Anaerobic Digestion Biogas Utilization
Compost Curing
Air Treatment
Waste Reception & Pre-treatment
The basic Valorga process plant (Figure 4.2) consists of essentially six units: waste
reception, preparation unit, AD, compost curing, biogas utilization, air treatment, and
an optional water treatment unit (when effluent is not treated in municipal wastewater
treatment plant). The reception unit has a scale for weighing the trucks bringing in the
organic materials. The waste is unloaded in a closed pit equipped with a foul air
collection system. The feed material passes through an electromechanical system,
designed according to the waste to be treated, that includes plastic bag opening and
size reduction equipment. The waste is then conveyed and fed continuously to the AD
unit.
In the AD unit, the waste is mixed with re-circulated leachate into a thick sludge of
about 20-35% solids content, depending on the type of waste. Therefore, the water
requirement is minimal. The digester operates either in the mesophilic range or the
thermophilic range. The Valorga digesters are concrete vertical cylinders of about 20
meters height and 10 meters internal diameter. They are designed so as to maintain
plug flow through the reactor. They are equipped with a vertical partition in the center
that extends over 2/3 of the diameter and over the full height of the reactor. This inner
partition minimizes shortcircuiting of the sludge and ensures plug flow through the
entire volume of the reactor. The orifices for introducing feed and removing digestate
are located on either side of the inner wall. Mixing of the fermenting material is
provided by a pneumatic system i.e. biogas at high pressure is injected through
orifices at the bottom of the reactor and the energy of the rising bubbles serves to mix
the sludge.
There are no mechanical parts and maintenance consists of periodic cleaning of the
nozzles at the bottom of the digester. The digested material exiting the reactor goes
through a filter press that separates the compost material from the leachate solution.
The leachate is reused for diluting incoming waste and any excess is transferred to the
water treatment unit or the municipal sewage network. The filter cake is transferred to
composting piles where it is subjected to curing in a closed building for about two
42
weeks. Stones and other inert materials are removed. The compost product is
considered to be of high quality and is sold as soil conditioner.
The biogas produced is used to generate electricity and steam or is fed to the city gas
network. The biofilters and the water treatment facilities ensure that the Valorga
plants control all air and water emissions and meet local regulations.
1.15.1 The Valorga plant at Tilburg, Netherlands
The Tilburg plant began its operation in 1994 and treats primarily vegetable, garden
and fruit waste (VGF). The plant capacity is rated at 52000 tons/year of VGF, or
40000 tons VGF plus 6000 tons of non-reusable paper and cardboard. A central refuse
treatment company collects and separates municipal waste from the participating 20
municipalities. The feed consists of 75% kitchen and garden waste and 25% paper,
cardboard. The annual rate of MSW generation in the Netherlands is nearly 450 kg
per capita. Thus, the estimated amount of VGF generated by the Tiburg population of
380,000 is 64,000 tons of VGF per year.
The plant consists of two digesters, each of 3300m3 capacity, and produces 2.8
million m3 of methane per year (70m3/ton). The waste is sheared to less than 10cm
particles before being fed to digestion unit. The retention time in this plant is 20 days
at a mesophilic temperature of 380C. The biogas production can be up to 106 m3 per
ton of waste, some of which is pressurized and pumped back into the reactor to
improve mixing. The biogas product is piped to an upgrading plant, where it is refined
to natural gas quality and then supplied to the municipal network. The biogas contains
56% CH4 and has a calorific value of about 20 MJ/m3 while the refined gas contains
31.7 MJ/m3 (Verma, 2002). Gas refining consists of compressing, cooling, scrubbing,
and drying. The methane gas after undergoing refining is fed to the municipal grid.
The Tilburg facility highlights the technical and economic feasibility of using energy
from waste in the form of biogas to generate electricity. The compost product
amounts to 28000 tons/year and is reported to be of high quality for agricultural use.
A technical report produced by the Center for Analysis and Dissemination of
43
Demonstrated Energy Technologies (CADDET) analyzed the economic and
environmental performance of the Tilburg facility between 1994 and 1999. CADDET
reported that the natural gas yield was about 50m3/ton. The net yield of natural gas,
i.e. after providing for heating and electrical energy for the plant, was 1,360,000 m3 of
methane per year, i.e. about 34 m3 of methane per ton of organic material processed.
The economic analysis by CADDET reported that the capital investment for the
Tilburg plant was equivalent to $17,500,000. This corresponds to $440 per yearly ton
processed currently or $146,000 per daily ton of capacity. For comparison, the capital
cost of a large size Waste-to-Energy plant (combustion of MSW) amounts to about
$120,000 per daily ton of MSW processed (Verma, 2002).
The main sources of revenue of this plant are the “tipping” fees paid by the
municipalities for waste treatment and the sale of natural gas. Between 1994 and1999,
the average fee for waste treatment was $90/ton resulting in the average annual
revenue of $3,600,000 per year. Assuming an average gas price of $0.06/m3
(CADDET, 1998), the gas revenues were $81,600 per year.
Assuming administrative and operating personnel of twenty and an average wage and
benefits cost of $40,000 per person, the labor cost is estimated at $800,000. Assuming
an equal amount for all other costs (maintenance, supplies and materials, etc.), adds
another $800,000. For an assumed 20-year life of the plant and at 10% required return
on investment, the annual capital charge for repayment of the $17.5 million principal
is calculated to be $920,000. Subtracting these three cost items from the annual
revenues of $3.68 million, results in a net annual income of $1.16 million. It can be
seen that under the above assumptions the Tilburg operation is profitable.
The environmental performance of the Tilburg indicates that 1.36 million m3 of
methane per year are recovered and used for electricity generation. This corresponds
to 728 tons of carbon in the form of CH4. Considering that one ton of C as methane is
equivalent to 21 tons of C as carbon dioxide the Tilburg operation avoids landfill
emissions of about 15,000 tons of carbon equivalent.
44
1.16 Kompogas Technology
In the late eighties, the KOMPOGAS technology was developed in Switzerland for
the conversion of organic waste materials such as garden and kitchen wastes into
electricity and compost. Since then, Kompogas has established over 25 plants in
different parts of the world.
The technology is an example of an anaerobic digester facility for processing of
source separated organic materials. Key features of the Facility include:
Modular capacity from 10,000 t/yr to over 100,000 t/yr;
A nominal capacity of 20,000 t/yr has been assumed for this report;
20 year operating contract life; and
Waste processing and resource recovery via three unit processes:
Conditioning: Includes receival, screening, nuisance separation, intermediate
storage and moisture adjustment.
Fermentation: Intensive fermentation with gas production and energy
generation;
Maturation: Prepares compost products suitable for beneficial use.
The proposed process is shown in Figure 4.3.
1.16.1 Product Output The technology has been designed to yield a range of products, including:
Electricity
Compost; and
Liquid fertiliser.
45
Figure 4.7: Kompogas Flow Sheet.
1.16.2 Waste Characterisation
The Kompogas technology developed for the processing of source separated organic
waste now can also process mixed (residual) waste using mechanical-biological
treatment (MBT) facilities. The types of organic waste materials suitable for
kompogas process are : garden waste, parks and garden waste, kitchen waste
commercial food wastes, biosolids, other organics such as Grease trap wastes, algae
where as Street sweepings, textiles, mineral oil, mixed wastes, glass, stones, metals,
rubber, plastics are not suitable for it.
The actual performance of the plant in terms of compost and electricity generation
depends on the final composition of the feedstock which may vary for individual
projects. However, key feedstock characteristics and bandwidths are given in Table
11.
46
Table 4.11: Characteristics of acceptable feedstock (mix).
Vegetable matter (% solids) < 30%Food waste (% solids) > 30%Proportion of non-processables <2mm < 3%Average particle size 40mmLongest particles <200mmC/N ratio 15-25
Source: Independent review of Kompogas Technology, 2005
These characteristics are relevant for the fermentation operation and hence accepted
feedstock outside these specifications are consequently conditioned (by shredding,
screening, mixing) to achieve the parameters indicated above.
1.16.3 Anaerobic Digestion (Fermentation)
From the mixer, the substrate is pumped by a reciprocating pump though the heat
exchangers into the horizontal fermenter. The heat exchangers use off heat from the
generator sets to pre-heat the substrate. The process in the fermenter is an anaerobic
thermophilic ‘dry’ fermentation process that takes place at a temperature of
approximately 550C. The retention time in the fermenter is between 15 and 20 days.
The fermenter is fully enclosed and heated. The constant high temperature sterilises
undesirable plant seeds, rootlets and pathogenic organisms.
The substrate moves through the fermenter in a ‘plug flow’. This happens
predominantly though the high pressure pumps between the mixer and the fermenter
and is assisted through a central, low speed agitator. The agitator is in continuous
operation and enables optimal degassing and temperature distribution.
The fermentation residues are discharged from the fermenter by a reciprocating pump
and transferred to the dewatering section. Dewatering of the residues takes place in
screw presses (straining screws).
47
Depending on expected detailed feedstock characteristics, water prices and markets
for liquid fertiliser, more solids can be removed from the press water through a
decanter (centrifuge).
Some of the process water is then recirculated to the feeder/mixer to reach the optimal
substrate moisture prior to entering the fermenter. Remaining process water contains
nutrients and is commonly used as liquid fertiliser. As the feedstock consists of
‘clean’ source separated organics, the process water and the liquid fertiliser do not
contain any toxic substances.
Gas from the fermenter is directed firstly to a gas cleaning device and then to a
generator set (combustion engine) for electricity generation. Additionally, the system
features a gas flare for combustion of any excess gas, particularly during ramp up and
later for generator maintenance and emergencies. Several brands can be used as
generators however, Kompogas favours the GE Jenbacher engines which are being
used worldwide for such plants as well as for landfill gas-to-energy operations.
Efficiency of these cogeneration units has reached an impressive 40-42% for
electricity and up to 45% for heat. Unless there are any close users for the generated
heat it is usually taken to the aeration system to assist in the speedy composting of the
fermenter residues.
1.16.4 Composting and Refining
After passing through the dewatering unit(s), the spent organics from the fermenter
need to be treated aerobically to eliminate any remaining odour generating potential.
Depending on the market situation, this process is usually conducted over two to three
weeks during which the fermenter residues are turned into ‘compost’.
This composting (‘maturing’) takes place in an enclosed composting hall where the
material is piled up to three meters high on a slotted floor to enable forced aeration.
The piles are turned once a week. Although several enclosed composting systems are
available, for a plant with a capacity of 20,000 t/y this is usually done by a front end
loader.
48
An area of approximately 450 m2 is required for the aerated compost piles. Including
space for the discharge of the fermenter residues and room to operate the front end
loader, Kompogas recommends the compost hall be a minimum of 750m2.
After three weeks, the compost is mature and can be stored outdoors without causing
any odour problems. Prior to sale, the compost is usually refined. Refining is done
though screening to produce higher value fine compost, and lower value coarse
compost. The coarse fraction can also be used as a bulking agent to provide additional
structure to the feedstock if needed. Occasionally, the refining step also includes a
windsifter (air classifier) to remove any plastic film that may not have been
eliminated at the front end of the facility.
1.16.5 Mass Balance
For a plant with the capacity of fermenter input 20,000 ton/year, a set of technical
data sheets provided by Kompogas form the basis for the mass balance estimate given
in Table 4.3. As with all other calculations, these are estimates which may change
slightly depending on the actual feedstock composition.
Table 4.12: Mass Balance Estimate by Kompogas.
Ferment Input, t/yr 20,000Ferment Input per day, t/d 54.7Facility input per day (5d/week), t/d 80Fresh compost (45% DS), t/yr 9,000Mature compost (65% DS), t/yr 7,200Liquid Fertiliser, t/yr 9,000
Source: Technical Data sheet provided by Kompogas,2009
1.16.6 Energy Balance
For an assumed ‘average’ feedstock comprising mainly ‘biowaste’ (i.e. mix of garden
and food waste from residential premises) KOMPOGAS calculates a gas production
of 2.1M Nm3/year with an average energy value of 5.5 kWh/m3.
49
Table 4.13: Energy balance estimated by Kompogas.
Biogas production, Nm3/yr 2100000Total energy content of biogas, MWh/yr 11,550Electricity generation, MWh/yr 4,700Internal electricity consumption, MWh/yr 370Heat generation, MWh/yr 5,000Internal heat consumption, MWh/yr 1,900Net electricity export, MWh/yr 4,330Capacity of generator set (gas engine), MWh 0.54
Source: Technical Data sheet provided by Kompogas,2009
50
CHAPTER FIVE
TECHNOLOGICAL ASSESSMENT FOR KMC PLANT
Based on above case studies, this section tries to perform a techno-economic
assessment of a Hypothetical KMC plant that would process all the waste generated
throughout the year. All the estimations have been done on the basis of the
specifications provided by the companies.
1.17 Based on Valorga Technology
The organic content as stated earlier constitutes about 70% of 308 tons of waste
generated per day in KMC and is estimated to be 216 tons per day and 78,840 tons per
year (Table 3.2). The organic content includes garbage, kitchen waste, yard waste and
miscellaneous organics. If the paper also a degradable component is mixed with the
organic fraction of the MSW, the total waste to be treated amounts to 244 tons per day
and 89,000 tons per year.
Of 90,000 tons it is assumed that only 80,000 tons will be available for waste
treatment annually. Hence to treat 80,000 tons of waste per year, KMC can implement
a facility based on the Valorga process described earlier, that consists of two reactors
with digester volume 2*3300 m3 of the type used at Tilburg (Netherlands) treating
40,000 tons of mixed MSW per year and producing 2.8 million m3.
On the basis of the data from the Tilburg plant, the hypothetical KMC plant for
80,000 tons per year of organic input would require four digesters each of volume
3300m3 and the generation of methane from this plant would amount to 5,600,000 m3
per year (70m3 yearly per ton of feed). The feedstock should be sheared to less than
10cm particles and withhold in reactor for at least 20 days at a mesophilic temperature
of 38oC. The other processes in this plant would be similar to the Tilburg plant as
stated earlier.
51
1.17.1 Mass Balance of the processes based on Valorga Technology
Figure 5.1 shows an estimated mass balance for 80,000 tons per year of waste to be
processed in the hypothetical KMC plant based on the Valorga Technology. Of 100%,
approximately 5.91% of waste would be recycled and the rest 94.09% would be
processed to get approximately 6871 tons of biogas (density of biogas has been taken
as 1.227 kg/m3) and 56,000 tons of compost annually.
Figure 5.8: An estimated mass balance for the KMC Plant based on the Valorga Technology
Source: Author calculation based on the Valorga technology specifications
52
Mechanical Pretreatment(Including Hand picking)
Mixer
Valorga's Dry AD
Organic Fraction of MSW(100%, 80,000 tons/year)
Biogas to Gas Engines(8.59%, 6871 tons/year)
Rejects/Recyclables(5.91%, 4,729 tons/year)
Waste Water (some recirculated as process water)
(14%, 11,200 tons/year)
Tunnel Composting
Steam(1.5%, 1200 tons/year)
Fertilzer (compost)(70%, 56,000 tons/year)
Digestate Dewatering
KMC Plant Process based on Valorga's Technology
Pretreatment(Including Hand picking)
Net Energy Output(7000 MWh/y)
Energy needed for Processes (3000MWh/y)
1.17.2 Energy Balance of the KMC Plant based on Valorga Technology
As stated earlier per ton of waste processed will produce 70 m3 of methane (54%) and
the calorific value of methane is 20 MJ/m3. The total energy content of biogas
produced from this plant would amount to 31,000 MWh/y. Assuming overall
efficiency of 35% of a gas genset, the amount of electricity that would be generated is
estimated to be 10,000 MWh/y out of which 3000 MWh/y will be the internal
consumption for the processes. Then the net amount of electricity available annually
will be 7000 MWh/y as shown in Table 5.
Figure 5.9: An estimated production and consumption of energy based on the Valorga Technology
Source: Author calculation based on the Valorga technology specifications
1.18 Based on Kompogas Technology
As the AD of Kompogas Technology uses only organic portion of the total wastes
generated, this technology as stated earlier uses mechanical treatment processes which
sorts out the organic portion of the waste. In context on KMC, out of 308 tons
generated per day, 216 tons is organic portion which is 78,840 tons per year. For
simplicity, the amount of waste that will be processed in fermenter has been taken
80,000 tons per year and all the estimations are based on the technical sheets provided
by the Kompogas Technology and few literatures.
53
Mechanical Treatment
Liquid Fertilizer (45%, 36,000 tons/year)
Composting System
Compost(36%, 28,800 tons/year)
Mixer
Kompogas Fermenter
Total Waste Generated112,566 t/y
Biogas to Gas Engines(13%, 10,080 t/y)
Rejects/Recyclables(32,566 t/y)
OFMSW (100%, 80,000 t/y)
Dewatering System
Some waste water is recirculated
Hence to process organic wastes (OFMSW) of 80,000 tons per year, four fermenters
each of capacity 20,000 tons per year are selected. With each of the 20,000 tons per
year capacity fermenter producing 2,100,000 m3 of biogas, the total biogas coming
out of the plant will be amounted to 8,400,000 m3 per year (assuming the a ton of
organic wastes produces 105 m3).
1.18.1 Mass Balance of the processes based on Kompogas Technology
54
Figure 5.10: An estimated mass balance for KMC plant based on the Kompogas Technology.
Source: Author’s calculation based on technical sheets provided by Kompogas.
Figure 5.3 shows an estimated mass balance for 80,000 tons per year of only organic
fraction of solid waste (OFMSW) waste to be processed in the hypothetical KMC
plant based on the Kompogas Technology. Of 112,566 tons per year, 32,566 of
inorganic wastes will be sorted out by mechanical treatment which is approximately
30% and will be recycled and the rest 70%, assuming now this 70% of the waste as
100% input to the fermenter, will be processed to get approximately 10,080 tons of
biogas, 36,000 tons of liquid fertilizer and 28,800 tons of compost annually. The input
to the fermenters according to the technical specifications provided by the Kompogas
Technology for the KMC plant will be 208.8 tons per day.
1.18.2 Energy Balance of the KMC Plant based on the Kompogas
Technology
55
KMC Plant Process based on the
Kompogas Technology
Heat losses(12,400 MWh/y)
Internal Heat Consumption
(7,600 MWh/y)
Electricity Generation
(18,800 MWh/y)
Heat Generation(20,000 MWh/y)
Net Electricity Output
(17,320 MWh/y)
Internal Electricity Consumption
(1,480 MWh/y)
Figure 5.11: An estimated energy balance based on the Kompogas Technology
Source: Author’s calculation based on technical sheets provided by Kompogas.
The estimated electricity generation provided by Kompogas is based on an average
gas production rate of 105 m3/t of input with energy content of 5.5 kWh/Nm3. The
actual generation rates though will depend on the final composition of the feedstock.
The internal power consumption is estimated to be 18.5 kWh/t of input. However, the
consumption may increase if the mechanical treatment plant becomes complex.
Similarly as shown in figure the heat generated during the processes much higher and
no use in context of KMC except for the purpose of internal consumption.
1.18.3 Requirement of space
The space required for this plant is 12,000 m2 for installing full facilitated plant. The
space available at Teku Transfer Station as stated earlier (15,000m2) is sufficient
enough to establish this plant.
56
CHAPTER SIX
ECONOMICAL ANALYSIS OF KMC PLANT
An economical analysis is usually undertaken in order to evaluate whether the project
that need to be implemented will be economically feasible i.e. the cost and benefit
brought about by a project to a person or the stakeholders. The benefits are given by
the revenue receipts from the sale of the project outputs and the inputs are given by
the costs (expenditures) of production. On the basis of cash flow generated during this
analysis for the hypothetical waste processing plant in KMC, some financial
parameters and their variability are computed. The economic analysis has been done
for both Volrago and Kompogas technologies so as to select the more feasible one
considering the project life of 20 years from installment. All the details related to the
economic analysis are in Appendix B.
57
1.19 Based on Kompogas Technology
All the costs and expenditures for installing the Kompogas technology based KMC
plant has been taken from the technical sheets provided by Kompogas whereas the
other costs such as operating and maintenance costs and values such as inflation rate,
depreciation rate, income tax etc have been taken from the different current literatures
and documents available for economical evaluation of this plant.
1.19.1 Quantum of Investment
According to the technical sheet of the Kompogas, the initial investment of 20,000 t/y
capacity plant is scaled up for 80,000 t/y KMC plant which is estimated to be 373.16
crores rupees (3.73 billion rupees) for all the infrastructure needed for the plant (from
machine purchase to installation and commissioning) except land lease cost. As the
investment is huge the KMC plant has to be public limited and hence of the total
initial investment, the ratio of debt and equity will be 70% and 30% respectively.
1.19.2 Quantum of Expenses
Expenses for the KMC plant will be operation and maintenance cost (O&M), debt
interest and depreciation. Considering O&M cost at 5% (http://www.anaerobic-
digestion.com/html/ad_plant_cost_estimates.php) with annual inflation of 7%
(http://red.nrb.org.np/publica.php?tp=special_publication&&vw=15), debt interest at
13% (Standard Chartered Bank) quarterly compounding and one year payment period
and depreciation at 20% (http://www.fncci.org/text/trade_industry_tax.pdf) the total
expenses has been estimated which varies as the inflation gets varied. Except debt
interest all the other expenses are subjected to variation.
1.19.3 Quantum of Revenue Generation
The revenue source for the KMC plant is from the sale of electricity generated,
compost, liquid fertilizer and annual tipping fees collected from the households.
58
1.19.3.1 Electricity
According to the NEA steering committee (meeting number 427, 2061 BS), for
biomass the power purchase agreement (PPA) will be done at Rs 3.80 per unit of
electricity supplied and with the rate will be escalated at 6% per year for five years
and will be constant afterwards.
1.19.3.2 Mature Compost and Liquid Fertilizer
The selling price of liquid fertilizer, an important product of this technology, couldn’t
be made estimated as there is no any commercial or small scale production of this
product in the country. But according to Prof. Amrit Man Nakarmi, IOE, Pulchowk,
before the use of chemical fertilizer in Bhaktapur for farmig, the locales used to sell
the liquid sludge in ‘Kharpan’. The tipping fee per household for collecting wastes
from the source has been determined on the basis of survey.
1.19.3.3 Tipping Fees
In case of tipping fees, the non-government solid waste management organizations
(NGSWMOs) in KMC collect service charges from their customers for solid waste
related services. Every organization has its own rate. The service charges levied by
the organizations range from 20 NRs to 500 NRs per month per household (HH). For
some prominent waste generators, such as large hotels, the service charge can reach
up to 20000 NRs per month (Alam, R et all, 2007). But the survey done by author
shows that the current service charges are Rs 100, Rs 150 and Rs 200 per HH
depending upon the sizes of houses in an average Rs 150 per HH (by triangular
calculation method). For the calculation of the revenues, Rs 150 per HH i.e. Rs 2694
per ton has been considered.
1.19.4 Return on Investment and Net Present Value in Different
Scenarios
Income statement which includes revenues, expenses and income tax at 20%
(http://www.fncci.org/text/trade_industry_tax.pdf) produced net income/loss per year
for 20 years of project life. Similarly, using operating, investment and financing
activities, cash flow was prepared producing net cash flow. This net cash flow was
59
then analyzed to get internal rate of return and net present value using minimum
attractive rate of return (MARR) of 15.6% which was calculated using weighted
average cost of capital (WACC). WACC was calculated using the following
equations:
Where,
Ce = amount of equity capital (in crore),
Cd = amount of debt capital (in crore),
C = Ce + Cd = total amount of capital or investment (in crores),
i = cost of debt (13%) and
ke = cost of equity (%) which was calculated using the following equation:
Where,
Rf = risk free rate of return (6.5%) (Nepal Rastra Bank, 2010) and
β = beta value (considered 2 as the renewable energy project is riskier than the
other energy project)
WACC or MARR is the rate at which the common shareholder should get the return
on the equity and hence the internal rate of return (IRR) must be greater than MARR.
The economic analysis has been done based on this parameter using different scenario
and variables for this project. The analysis has been summerised as below:
Case I: Current Scenario
When selling price of electricity per kWh, mature compost per kg and liquid fertilizer
per kg are Rs 3.80, Rs 10 and Rs, 1 respectively and tipping fee is Rs 150, the net
present value at discount rate of 15.6% and IRR are estimated to be -89.26 and 1%
respectively. If the economic analysis is done using compost selling price of Rs 3/kg,
60
NPV comes out to be Rs -189.12 crores indicating huge loss in the project. This
indicates that the project cannot be profitable at all and has IRR much lesser proving
the KMC plant not feasible economically under current scenario.
Case II: Under current scenario KMC provides 100 % EM budget as levy
without increment in annual budget
Using the same selling price of the output entities used during case I, if KMC spends
its all EM budget for paying levy to KMC plant, NPV and IRR comes out to be Rs
49.93 crores and 25% respectively when compost selling price considered Rs 10/kg.
IRR then is greater than MARR and hence under this condition the project seems
feasible economically. But for Rs 3/kg of compost selling price, NPV is negative
indicating losses and hence under this condition the project will not be feasible
economically.
Case III: Under current scenario KMC provides 75 % EM budget as levy
without increment in budget
Using the same selling price of the output entities used during case I, if KMC spends
its only 75% EM budget, without any increment in annual budget, for paying levy to
KMC plant, NPV and IRR comes out to be Rs 14.94 crores and 18% respectively.
IRR in this case also is greater than MARR and hence under this condition also the
project seems feasible economically. But again for Rs 3/kg of compost selling price,
NPV is negative indicating losses and hence under this condition the project will not
be feasible economically.
Case IV: Under current scenario KMC provides 100% EM budget as levy with
12% increment in annual budget
If it is done so, NPV and IRR come out to be Rs 192.97 crores and 40% respectively.
IRR in this case is almost triple of MARR and hence under this condition the project
will be feasible economically.
The table below depicts the summary of above scenarios
61
Table 6.14: Summary of Net Present Worth and Internal Rate of Return under different scenarios for KMC plant based on Kompogas Technology
Cases ScenarioNet Present Value at Discount
Rate of 15.6%, Rs, CroresInternal Rate of Return (IRR)
ICurrent Scenario (without levy from KMC)
-89.26*-189.12**
1%*-
II
Under current scenario KMC provides 100 % EM budget as levy without increment in budget
49.93*-44.42**
25%*8%**
III
Under current scenario KMC provides 75 % EM budget as levy without increment in budget
14.94*-77.45**
18%*3%**
IV
Under current scenario KMC provides 100 % EM budget as levy with 12% increment in budget
192.67*102.54**
40%*25%**
*Compost SP: Rs 10/kg**Compost SP: Rs 3/kg
Source: Author estimation
1.20 Based on Valorga Technology
The economical assessment of KMC plant based on Valorga Technology was done
considering the same parameters as for KMC plant based on Kompogas. According to
Verma (2002), the total amount of investment needed for 80,000 t/y capacities will be
Rs 435.86 crores and the revenues will be generated by sale of electricity and
compost. The summary of economic assessment under different scenario is as in
Table 6.2 which depicts that the economic feasibility of this plant is totally dependent
upon the selling price of the fertilizers. Only in case IV the plant based on Valorga
Technology is economically feasible.
Table 6.15: Summary of Net Present Worth and Internal Rate of Return under different scenarios for KMC plant based on Kompogas Technology
Cases ScenarioNet Present Value at Discount
Rate of 15.6%, Rs, CroresInternal Rate of Return (IRR)
ICurrent Scenario (without levy from KMC)
-33.49*-223.07**
11%*-
62
II
Under current scenario KMC provides 100 % EM budget as levy without increment in budget
110.09*-79.49**
31%*3%**
III
Under current scenario KMC provides 75 % EM budget as levy without increment in budget
14.94*-116.60**
18%*-
IV
Under current scenario KMC provides 100 % EM budget as levy with 12% increment in budget
255.02*68.28**
50%*21%**
*Compost SP: Rs 10/kg**Compost SP: Rs 3/kg
Source: Author estimation
CHAPTER SEVEN
RISK ANALYSIS
Considering the various parameters shown in Table 7.1, risk analysis is performed
using Crystal Ball 7.3.1 software for 1,000 trials. The various results are described
below.
63
Table 7.16: The parameters considered and assumptions defined for performing risk analysis using Crystal Ball
Parameters Min Max Assumptions Defined
Levy 50% and 112% of EM Budget
crores
14.8 33.25
Triangulation distribution
OM cost @ 2.5% and 10%, crores 9.33 37.31
Debt @10% and 15%, crores 26.12 39.18
Compost, Rs/ton 1000 15000
Fertilizer, Rs/ton 1000 15000
Tipping Fees, Rs/HH-month 50.00 200.00
Electricity Price, Rs/unit 3.8 10 Log normal distribution
Figure 7.12: Frequency distribution chart under real scenario for Valorga based KMC Plant.
The results of risk analysis using software for Valorga based KMC plant shows that
this plant will not be economically viable as the certainty of getting the net present
value (NPV) zero are 13.07 and 42.25% during real scenario and when the levy is
provided by KMC to the plant as shown in Figure 7.1 and 7.2 respectively.
64
Figure 7.13: Frequency distribution chart when KMC provides levy to the Valorga
based KMC plant
The results of risk analysis using software for Kompogas based KMC plant shows
that this plant will not be economically viable under the real scenario as the certainty
of getting the net present value (NPV) zero is only 24.92 % as shown in Figure 7.3
whereas if the levy is provided by KMC to the plant, the plant becomes feasible
economically with 75.12% certainty of getting the net present value zero as shown in
Figure 7.4.
65
Figure 7.14: Frequency distribution chart under real scenario for Kompogas based KMC Plant.
Figure 7.15: Frequency distribution chart when KMC provides levy to the Kompogas based KMC plant.
66
CHAPTER EIGHT
CONCLUSION AND RECOMMENDATIONS
1.21 Conclusions
With the growing technology there are many companies that provide technology for
anaerobic digestion of the municipal solid waste among them Valorga and Kompogas
are the two. Based on these technologies, the studies shows that the KMC plant can be
installed using these technologies and is technically feasible. However the economic
analysis shows that both of the technologies under current scenario is infeasible
economically as their NPV are negative and IRR are much lesser than expected
MARR. The KMC plant based on these technologies will only be economically
feasible when KMC pays its budget under Environmental Management heading as
levy. Among the two technologies, study shows that technically and economically, the
Kompogas based KMC plant is superior however both of the technologies needs huge
investment making difficult to install such plant in a developing countries like Nepal.
The following key conclusions drawn from this study are:
The major components of wastes generated from KMC is organic comprises
70% and 70% of which is kitchen waste.
Moisture content is high ranging from 62-82%.
The lower calorific value (Balance Energy) at 69% moisture content is
estimated to be 3 MJ/kg.
The electricity that can be generated from the energy content in the wastes
thermally at overall efficiency of 25% is estimated to be 33.26 GWh per year.
The technical parameters show the technical viability of Anaerobic Digestion
systems while thermal conversion technologies unviable.
The electricity that can be generated from Kompogas based KMC Plant is 18.8
GWh per year which will also produce high quality 28,800 tons of compost
and 36,000 tons of liquid fertilizer per year.
The electricity that can be generated from Valorga based KMC Plant is 7
GWh per year which will also produce high quality 56,000 tons of compost
per year.
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Economically Kompogas based KMC plant is evaluated as more feasible than
the Valorga based KMC Plant though both are technically feasible.
The Valorga based KMC Plant is riskier than the Kompogas based KMC
plant.
1.22 Recommendations
This thesis presents the following recommendations:
A thorough and new study should be done to know the characteristics of the
solid wastes as KMC has urbanized rapidly with increment in population.
A lab based study should be done to determine the key parameters that
enhance and suppress the biogas reaction.
After determining the key parameters affecting the biogas generation from
waste, a lab scale experiment should be done to know the effect of these
parameters which can be helpful for a pilot scale plant.
As Socio-economic Analysis has totally been left during this study and hence
need an assessment to know the aspects of society and how they can benefit
with the launch of this project in the project area.
Market Survey of the compost and liquid fertilizer are must to make this kind
of project economically viable.
The private and social organizations that have been involved for the solid
waste management should be taken into considerations to make this project
viable.
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68
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http://www.mrec.org/biogas/adgpg.pdf.
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APPENDIX A: AD KEY PARAMETERS
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The following summarizes the information collected during the course of this study
on the technical details of Anaerobic Digestion of MSW.
Digester Material
Anaerobic digestion occurs naturally wherever high concentrations of wet organic
matter accumulate in the absence of dissolved oxygen. Only waste of organic origin
can be processed in an anaerobic digester. As this makes up 30-60% of household
waste there is a considerable benefit in diverting this waste from landfill. Municipal
solid waste is composed of:-
1) Digestible Organic Fraction – Readily biodegradable organic matter, e.g.
kitchen scraps, food residue, grass cuttings etc.
2) Combustible Fraction – Slowly digestible organic matter such as coarser
wood, paper, cardboard. These are lignocellulosic materials which do not
readily degrade under anaerobic conditions and are better suited to aerobic
digestion, i.e. composting. (Opinions vary over the digestibility of paper,
which depends on the lignin content, some forms of paper are much more
digestible than others – generally only paper that is too contaminated with
organic waste to be recycled, is considered for digestion). The combustible
fraction also consists of indigestible and
3) Inert Fraction – Stones, glass, sand, metal, etc. Some of these products are
suitable for recycling, the remainder can be landfilled.
Joint treatment of municipal solid waste with animal manure/sewage slurry is
apopular method in existi plants; the process tends to be simpler and is economically
more viable than an MSW only treatment system.
Separation
Source Separation: Recyclable materials separated from organic waste at the source.
Mechanical Separation: This can be used to separate an organic fraction of the
wasteif source separation is not available. The fraction obtained is more contaminated
which will affect the heavy metal and plastic content of the final digestate composting
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product. In many countries compost derived from mechanical separation will not meet
standards required for a soil conditioner product.
Pre-treatment
Having separated any recyclable or unwanted materials from the waste, t organic
material must be chopped or shredded before it is fed into the digester.
The organic matter is also diluted with a liquid, ranging from sewage slurry, to
recycled water from the digestate, to clean water.
In some system ms an aerobic pre-treatment allows organic matter to be partly
decomposed under aerobic conditions before undergoing anaerobic digestion.
C/N Ratio: The relationship between the amount of carbon and nitrogen present in
organic materials is expressed in terms of the Carbon/Nitrogen ratio. A C/N ratio of
20 3 is considered to be optimum for an anaerobic digester.
If C/N ratio is very high, the nitrogen will be consumed rapidly by the methanogens to
meet their protein requirement and will no longer react on the left over carbon content
in the material. As a result the gas production will be low.
If the C/N ratio is very low, nitrogen will be liberated and accumulate in the form of
ammonia. This will increase the pH value of the material. A pH value higher than 8.5
will start to show a toxic effect on the methanogenic bacterial population. Animal
waste, such as cow dung, which has been used successfully in biogas systems for
many years, has an average C/N ratio of 24. Plant materials contain a high percentage
of carbon and so the C/N ratio is high, (rice straw = 70, sawdust >200). Human
excreta has a C/N ratio of about 8. To maintain the C/N level of the digester material
at acceptable levels, materials with high C/N ratio can be mixed with those with a low
C/N ratio, i.e. organic solid waste can be mixed with sewage or animal manure.
Dilution: Water or slurry can be added to the raw material to maintain the required
consistency. If material is too diluted, the solid particles will settle down in the
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digester and if it is too thick the particles will impede the flow of gas to the upper part
of the digester. Different systems can handle different percentages of solid to liquid,
average ratios are 10-25%, but some systems can cope with solids up to 30% .
pH Value: Optimum biogas production is achieved when the pH value of the input
mixture is between 6 and 7. The pH value will be affected by mixture retention time
in the digester. In the initial period of fermentation, large amounts of organic acids are
produced and the pH value of the mixture can decrease to below 5. This will inhibit,
or even stop, the digestion and fermentation process. The methanogenic bacteria are
very sensitive to pH value and will not thrive below a value of 6.5. As digestion
continues and the concentration of ammonia increases, due to the digestion of
nitrogen, the pH value can increase to above 8. When the methane gas production has
stabilised, the pH will remain between 7.2 and 8.2.
When plant material is fermented in a batch system, the acetogenesis/fermentation
stage is rapid, producing organic acids which reduce the pH and inhibits further
digestion. Reduction in pH can usually be controlled by the addition of lime.
Loading Rate: This is an important process control parameter in continuous systems.
Many plants have reported system failures due to overloading. This is often caused by
inadequate mixing of the waste with slurry. If there is a significant rise in volatile
fatty acids this normally requires that the feedrate to the system be reduced.
Retention Time: Wastes remain in a digester that is operating in the mesophilic range
for a varying period of 10 – 40 days, the duration being dictated by differing
technologies, temperature fluctuations and waste composition.
Toxicity: Mineral ions, heavy metals and detergents are some of the toxic materials
that inhibit the normal growth of bacteria in the digester. Small quantities of minerals,
(sodium, potassium, calcium, magnesium, ammonium and sulphur), also stimulate the
bacterial growth, but heavy concentrations will have a toxic effect.
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Heavy metals such as copper, nickel, chromium, zinc, lead are essential for bacterial
growth in small quantities, but higher quantities will also have a toxic effect.
Detergents such as soap, antibiotics,organic solvents also inhibit the bacteria.
Recovery of digesters following toxic substances inhibiting the system can only be
achieved by cessation of feeding and diluting the contents to below the toxic level.
Mixing/Agitation: Results from existing systems tend to show that a level of mixing
is required to maintain the process stability within the digester. The objectives of
mixing are to combine the fresh material with the bacteria, to stop the formation of
scum and to avoid pronounced temperature gradients within the digester.
Over frequent mixing can disrupt the bacterial community and it is generally
considered that slow mixing is better than rapid mixing. The amount of mixing
required is also dependent on the content of the digestion mixture.
Health Issues: Bacteria and viruses present in municipal solid waste can be a risk to
the workers handling the waste. For a combination of sewage sludge and household
waste, which are regarded as having a higher infectivity risk than animal manure, pre-
treatment processing at 700C for at least one hour is recommended by the Danish
Energy Authority.
Solid residue/Slurry: After the biological degradation is complete the solid residue or
digestate is removed and can be cured aerobically and screened for any unwanted
items, (like glass shards, plastic pieces etc), before being used on the land. The purity
of the material fed into the system will dictate the quality of the slurry produced. This
is used as a product to condition and improve soil.
Problems specific to MSW anaerobic digestion:
1) Nature of organic waste may vary according to location and time of year. In
wet season horticultural plant cutting levels may be higher than in the dry
season. This may lead to a variation in the C/N ratio and affect the rate of gas
production.
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2) Inadequate mixing of refuse and sewage can affect efficiency of system.
3) Blockage of pipes can be caused if large pieces of waste enter the system; this
causes problems, particularly in continuous systems.
Advantages of MSW anaerobic digestion:
1) Makes landfills easier to manage by removing problematic organic waste
material which is responsible for gaseous and liquid emissions.
2) Enclosed system allows all of the biogas to be collected, unlike on landfills
where recovery only yields 30-40% of gas generated. Methane is a greenhouse
gas with twenty times the impact of carbon dioxide.
3) An end product that can be used as a soil conditioner is produced. Mixing the
refuse with animal dung improves the system efficiency and allows for a more
simple process design, improving the economic viability of the system. This is
due to the improved nitrogen content that is achieved by mixing with dung.
Important points to be considered when designing a mixed MSW/animal dung or
sewage Biogas system.
1) Health Issues: Bacteria and viruses present in municipal solid waste and
human sewage can be harmful to those handling the waste and can remain in
the slurry following the digestion process. Treatment of waste at 700C for 1
hour is recommended, either before digestion or on slurry prior to use as a soil
conditioner.
2) Sampling: It is useful to design into the digester system the ability to take
samples of the digester material so that a check on the content can be
maintained.
This allows adjustments to be made to the content of the mixture if gas
production reduces.
3) Gas Storage: Many existing animal dung biogas systems store the gas in a
hemispherical concrete and brick structure, which forms the top of the digester
unit. In some cases leakage from cracks in the concrete has been found.
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Attention should be paid to the construction of the concrete vessel or
alternatively a steel vessel could be used for gas storage.
4) Agitation: Digestion rate is improved if a method of stirring is incorporated
into the digester design.
5) Waste Content: The waste must be sorted so that all inorganic products are
removed from the refuse prior to entry into the digester. Ideally the refuse
should be sorted at source, if not; it could be sorted by hand on delivery to the
site. However, at this stage recyclable materials are more likely to be
contaminated with organic material and this is not desired for recycling.
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APPENDIX B:
ECONOMIC ANALYIS SHEETS
80