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TRIBHUVAN UNIVERSITY
INSTITUTE OF ENGINEERING
PULCHOWK CAMPUS
Design and Fabrication of a Kitchen Waste Based Biogas Plant and Testing With
Different Feed Materials
by
Ambish Kaji Shakya
Kundan Lal Das
Ravi Shah
A PROJECT REPORT
SUBMITTED TO THE DEPARTMENT OF MECHANICAL ENGINEERING
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF BACHELOR OF ENGINEERING
DEPARTMENT OF MECHANICAL ENGINEERING
LALITPUR, NEPAL
MARCH, 2009
2
COPYRIGHT
The authors have agreed that the library, Department of Mechanical Engineering,
Pulchowk Campus, Institute of Engineering may make this report freely available for
inspection. Moreover, the authors have agreed that permission for extensive copying
of this project report for scholarly purpose may be granted by the professor(s) who
supervised the project work recorded herein or, in their absence, by the Head of the
Department wherein the project report was done. It is understood that the recognition
will be given to the authors of this project and to the Department of Mechanical
Engineering, Pulchowk Campus, Institute of Engineering in any use of the material of
this report. Copying or publication or the other use of this report for financial gain
without approval of the Department of Mechanical Engineering, Pulchowk Campus,
Institute of Engineering 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:
Head
Department of Mechanical Engineering
Pulchowk Campus, Institute of Engineering
Lalitpur, Kathmandu
Nepal
3
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 project report entitled " Design and fabrication of a
kitchen waste based biogas plant and testing with different feed materials" submitted
by Ambish Kaji Shakya, Kundan Lal Das and Ravi Shah, in partial fulfillment of the
requirements for the degree of Bachelor Engineering.
________________________________________
Supervisor, Dr. Rajendra Shrestha
Department of Mechanical Engineering
_____________________________________________
External Examiner, Mr. Prakash Lamichhane
Manager (Chief – Research and Development)
Biogas Sector Partnership – Nepal
___________________________________________________
Committee Chairperson Dr. Rajendra Shrestha
Department of Mechanical Engineering
_____________________
Date:
4
ABSTRACT
The report deals with the test carried with different kitchen wastes produced majorly
in kitchens of particularly Kathmandu valley. The feasibility study of generation of
biogas from these kitchen wastes was done. The amount of kitchen wastes generated
per head per day is 0.468 kg. 20 L jar biogas plant was used for the experiments.
Different wastes like cabbage leaves, potato, rice, and banana peels were tested. Half
a kg of cow-dung as an activator was used in the plant to generate biogas. The total of
about 14 L feed was fed to each different digester. The measurement of the biogas
production was done. Methane content by volume was found to be low. Low gas
productions due to small jar make it feasible only for testing purpose. The low
temperatures, high temperature fluctuation, over acidification were some of the
problems observed during testing. However, the methane content was found
increasing gradually. This report is expected to provide future reference to biogas
testing with potential kitchen wastes.
5
ACKNOWLEDGEMENTS
We would like to express our sincere gratitude and appreciation to Dr. Rajendra
Shrestha for supervising our project work
We remain indebted to Prof. Jagan Nath Shrestha and Center for Energy Studies
family for immense help in providing all the equipment without which our project
was impossible. We would like to thank Mr. Mahaboob siddiki sir of BSP for his
valuable time giving knowledge on biogas concepts.
We would like to thank Prof Dr. Bhakta Bahadur Ale for his valuable suggestions.
Also we would like to thank Associate Prof. Ram Chandra Sapkota for giving
valuable suggestions in project work.
We would like to thank Mr Prakash Lamichhane for helping us by making corrections
in report and giving suggestions. Also we would like to thank BSP-Nepal for helping
in providing information and instrument related to biogas.
We are indebted to Mr. Nilesh Pradhan, Mr. Pradeep Man Shrestha and Mr. Harka
Man Limbu for providing full co-operation in the project work. Without them our
project work was very difficult to accomplish. Also we would like to thank Mr. Jatin
Man Amatya for his help.
We would like to thank Mr. Ram Krishna Karki from Kathmandu Municipality for
providing required information on the condition of kitchen wastes in Kathmandu
Municipality.
6
TABLE OF CONTENTS
Copyright ....................................................................................................................... 2
Approval Page ................................................................................................................ 3
Abstract .......................................................................................................................... 4
Acknowledgements ........................................................................................................ 5
Table of Contents ........................................................................................................... 6
List of Tables ............................................................................................................... 10
List of Figures .............................................................................................................. 11
List of Symbols ............................................................................................................ 12
List of Acronyms and Abbreviations ........................................................................... 13
CHAPTER ONE: INTRODUCTION ......................................................................... 14
1.1 Problem/Background ............................................................................................ 14
1.2 Historical Background of Biogas Technology in Nepal ....................................... 16
1.3 Objective ................................................................................................................ 17
1.4 Methodology .......................................................................................................... 18
1.5 Limitations ............................................................................................................. 18
CHAPTER TWO: LITERATURE REVIEW ............................................................. 19
2.1Introduction ............................................................................................................ 19
2.2Process of the Biogas Production .......................................................................... 19
2.2.1 Hydrolysis ....................................................................................................... 20
2.2.2 Acetogenisis .................................................................................................... 20
2.2.3 Methanogenesis................................................................................................ 20
2.3 Biogas Plant System ............................................................................................. 21
2.4 Factors Affecting Biogas Generation .................................................................... 22
7
2.5 Types of Biogas Plant ........................................................................................... 23
2.5.1 On the Basis of the Construction of Plant ....................................................... 24
2.5.1.1 Floating Drum Digester ................................................................................ 24
2.5.1.2 Fixed Dome Digester ................................................................................... 25
2.5.2 On the Basis of Types of Feeding ..................................................................... 27
2.5.2.1 Batch Digester .............................................................................................. 28
2.5.2.2 Continuous Digester ..................................................................................... 28
2.6 Currently Existing Other Biogas Plant ................................................................. 29
2.6.1 Puxin Biogas Plant .......................................................................................... 29
2.6.2 Agri / Kitchen Waste Based Biogas Plant ...................................................... 30
2.6.3 ARTI Biogas Plant .......................................................................................... 32
2.6.4Experimental Model Biogas Plant by Ajay Karki ........................................... 34
CHAPTER THREE: CONSTRUCTION AND FABRICATION .............................. 36
3.1 Idea Generation ..................................................................................................... 36
3.2 Idea Screening ....................................................................................................... 38
3.3 Selection ................................................................................................................ 39
3.4 Detail List of Selected Parts .................................................................................. 40
3.5 Description of Fabrication .................................................................................... 41
3.6 Alternative Design ................................................................................................ 42
3.6.1 List of Parts .................................................................................................. 43
3.6.2 Fabrication Method for Alternative Batch Type .......................................... 43
3.7 Insulation and Heating System ....................................................................... 44
CHAPTER FOUR : MATERIAL AND METHODS ................................................. 45
4.1 Basis of Material Selection .................................................................................... 45
4.1.1 Volume ........................................................................................................... 45
8
4.1.2 Kinds of Wastes ........................................................................................... 45
4.1.2.2Rice ............................................................................................................. 46
4.1.2.3Potato .......................................................................................................... 47
4.1.2.4Banana......................................................................................................... 47
4.2 Charging of Plants ................................................................................................. 47
4.2.1 Continuous Digester ..................................................................................... 47
4.2.2 Batch Digester .............................................................................................. 48
4.3 Measuring Methods .............................................................................................. 49
CHAPTER FIVE : KITCHEN WASTE SURVEY .................................................... 52
5.1 Introduction ................................................................................................ 52
5.2 Factors Influencing Kitchen Waste Generation ........................................ 52
5.3 Limitation .................................................................................................. 52
5.4 Research Methodology .............................................................................. 52
5.5 Result of the Study ..................................................................................... 53
CHAPTER SIX : GAS PRODUCTION AND ANALYSIS ....................................... 54
6.1 Experiment in 200L Drum ........................................................................ 54
6.2 Experiment in 20 L Jars ............................................................................ 56
6.2.1 From Banana Peels (Plant I) ....................................................... 56
6.2.2 From Cabbage Leaves (Plant II) ................................................. 57
6.2.3 From Rice (Plant III) ................................................................... 58
6.2.4 From Potato (Plant IV) ................................................................ 60
6.2.5 From Banana Peels (Plant V) ...................................................... 61
9
CHAPTER SEVEN: FINANCIAL ANALYSIS ......................................................... 63
CHAPTER EIGHT: LIMITATIONS .......................................................................... 70
CHAPTER NINE: RECOMMENDATIONS AND CONCLUSION.......................... 71
REFERENCES ..................................................................................................... 73
APPENDIX A: Photos .......................................................................................... 75
APPENDIX B: Construction Procedure of 20L Jar Biogas Plant ........................ 76
APPENDIX C: Physiological Properties of Constituent Gases of Biogas ........... 77
APPENDIX D: Biogas Plant-GGC 2047 Model and Dimensions of Different
Components of Various Sized .............................................................................. 78
APPENDIX E: Gas Collection through Downward Displacement of Water ....... 79
APPENDIX F: Survey Formats and Reports ........................................................ 81
APPENDIX G: Gas Production, Temperature and pH Data for Different Plants 85
APPENDIX H: Cost Details ................................................................................. 89
APPENDIX I: Financial Analysis for the Substitution of Firewood and Kerosene90
APPENDIX J: Drawing of Continuous Fixed Dome Biogas Plant ...................... 92
APPENDIX K: Drawing of Batch Type Biogas Plant ........................................... 93
10
LIST OF TABLES
Table 2.1: Composition of Biogas .............................................................................. 19
Table 2.2: C/N Ratio of Some Organic Materials ....................................................... 21
Table 3.1: Factor Rating Table .................................................................................... 39
Table 4.1: Parameters of Different Feed Materials ..................................................... 46
Table 4.2: Quantity of Different Constituents of the Plants ........................................ 49
11
LIST OF FIGURES
Figure 1.1: Energy Consumption Pattern in the World (2003 Data) ........................... 15
Figure 1.2: Energy Consumption Pattern in Nepal ...................................................... 16
Figure 2.1: A Typical Biogas System Configuration................................................... 22
Figure 2.2: Floating Drum Type ................................................................................. 24
Figure 2.3: Sketch of KVIC Floating Gas Holder System .......................................... 25
Figure 2.4: GGC Concrete Model Gas Plant .............................................................. 26
Figure 2.5: Fixed Dome Type Biogas Plant ................................................................ 27
Figure 2.6: Puxin Biogas Model ................................................................................. 29
Figure 2.7: NISARG-RUNA Plant ............................................................................. 31
Figure 2.8: ARTI Model ............................................................................................. 33
Figure 2.9: 200 L Capacity Demonstrations Model Biogas Plant ............................... 34
Figure 3.1: Rough Sketch of Design ............................................................................ 37
Figure 3.2: Sketch of the Continuous Feed Plant ....................................................... 42
Figure 3.3: Drawing of the Alternative Plant (Batch Digester) ................................... 43
Figure 6.1: Temperature Profile for 200L Drum (Ombahal) ....................................... 55
Figure 6.2: Temperature Profile for 200L Drum (CES) .............................................. 55
Figure 6.3: Temperature and PH Profile for Plant I..................................................... 56
Figure 6.4: Temperature and pH Profile for Plant II ................................................... 57
Figure 6.5: Temperature and pH Profile for Plant III .................................................. 58
Figure 6.6: Volume Profile for Plant III ..................................................................... 59
Figure 6.7: Temperature and pH Profile for Plant IV .................................................. 60
Figure 6.8: Volume Profile for Plant IV ...................................................................... 60
Figure 6.9: Temperature and pH Profile for Plant V ................................................... 61
Figure 6.10: Volume Profile for Plant V ..................................................................... 62
12
LIST OF SYMBOLS
CH4 Methane
CH3COOH Acetic acid
CH3CH2COOH Propionic acid
C2H5OH Ethanol
C6H12O6 Glucose
CO Carbon monoxide
CO2 Carbon dioxide
H2 Hydrogen gas
H2O Water vapour
H2S Hydrogen sulphide
N2 Nitrogen gas
13
LIST OF ACRONYMS AND ABBREVIATIONS ADB Asian Development Bank
ARTI Appropriate Rural Technology Institute
ATC Agricultural Technology Center
AFPRO Action for Food Production
BSP Biogas Support Program
BSP-N Biogas Sector Partnership - Nepal
C/N Carbon to nitrogen
CES Center for Energy Studies
g gram
GGC Gobar Gas and Agricultural Equipment Development Company
GHG Green House Gases
IOE Institute of Engineering
IRR Internal Rate of Return
kg kilogram
KVIC Khadi Village Industries Commission
L Liter
LPG Liquefied Petroleum Gas
m meter
MARR Minimum Attractive Rate of Return
MJ Mega Joule
MJ/m3 Mega Joule per cubic meter
MJ/kg Mega Joule per kilogram
Rs. Rupees (Nepalese)
NPW Present Worth
RBC Reinforced Brick Concrete
14
CHAPTER 1
INTRODUCTION
1.1 Problem/Background
The unavailability of LPG and kerosene is increasing day by day. The price of these fuels
has increased and will keep on increasing. This has created a negative impact on the
economy of Nepali people. Even when people are willing to pay the price, fuel is not
available in required quantity or at times not available at all. The scarcity of fuel is
worldwide but for countries like ours it is turning out to be one of the major issues of the
country.
Most of the energy consumed in Nepal comes from traditional sources such as fuel wood,
the use of which contributes to deforestation. Tremendous potential exists for
hydroelectric power development, but growth is inhibited by terrain, lack of
infrastructure and insufficient capital investment. Nepal has harnessed only a fraction of
its potential hydropower; however, a major hydroelectric facility was under construction
on the Kali Gandaki River in western Nepal in the early 2000s. The country is heavily
reliant on India for imported and nonrenewable sources of power such as oil and
kerosene. (Reference: Microsoft ® Encarta ® 2008. © 1993-2007 Microsoft
Corporation)
Many reasons are there for the shortage of fuel but the major reason is that the fuel is
depleting worldwide. The natural sources of the fossil fuels are being consumed in an
alarming rate and these resources are coming to an end. Since these fuels are non
renewable and cannot be produced by methods known to man, these fuels won’t last for
very long. In other words the fossil fuel era is coming to an end. In this condition Nepal
will be one of the country having the highest energy crisis if alternate fuel sources aren’t
utilized. Thus the crisis of energy and price the people have to pay for the energy will
continue to increase if necessary steps for surviving the crisis are not implemented as
soon as possible.
15
The increasing industrialization, urbanization and changes in the pattern of life, which
accompany the process of economic growth, give rise to generation of increasing
quantities of wastes leading to increased threats to the environment. The disposal of
kitchen waste has created many problems in large cities like Kathmandu, Lailitpur,
Biratnagar and Pokhara.
Kitchen wastes are organic materials which are easily bio-degradable. They are a
potential raw material for biogas production. Generally Kitchen waste is treated as waste
and thrown which acts as the key factor for the pollution. The pollution leads to number
of diseases which affect human health. Energy production from waste is becoming more
popular these days. It has mainly two direct advantages. One, the disposal waste is
reduced as it is utilized. Another, energy is generated.
Traditional biogas plant such as fixed dome or floating drum made of concrete or other
materials are generally below the ground. The scarcity of land in urban areas like
Kathmandu has made it nearly impossible for the local people to install the biogas plant.
Further, cattle dung is not available in these areas. Use of biogas plant (above ground)
using kitchen wastes seem to decrease the problem arising from scarcity of LPG.
Energy Trend in the World
Figure 1.1: Energy Consumption Pattern in the World (2003 Data) (Reference: Encarta Encyclopedia, Microsoft Corporation 2008)
16
Energy Trend in Nepal (1992/93 Data)
Figure 1.2 : Energy Consumption Pattern in Nepal (Reference: Bajracharya T.R., 1989, “Course Manual on Energy resources and
combustion processes” IOE)
1.2 Historical Background of Biogas Technology in Nepal
The first biogas plant in Nepal was introduced in 1955. The initiation started as an
experiment of late Father B.R. Saubolle in St. Xavier’s School, Godavari, and
Kathmandu. The first biogas plant was made up of an old oil drum of 200 liter capacity.
HMG, Nepal introduced official biogas program in 1975 aiming controlling deforestation
and prevention burning of cow-dung which otherwise could be utilized as valuable
fertilizer. In 1992, Biogas Support Programme (BSP) was established aiming to develop
and disseminate biogas technology as a commercially viable and market oriented
industry. Biogas plants installation and quality was increased rapidly after the
establishment of BSP (Bajgain, 2003). The number of plants installed rose to 86,400 by
May 2002, covering 65 districts of the country, especially villages in rural areas of Nepal.
According to Biogas Sector Partnership – Nepal, 189,698 biogas plants have been
established in 69 districts till the end of December, 2008.
17
Some studies have been made for the biogas plants having cow dung as input. But none
of the remarkable studies have been made regarding use of kitchen waste in Nepal.
Literature regarding use of kitchen waste only or vegetable wastes only as input for
biogas generation is difficult to find. All of the plants installed use cattle dung as
feedstock and about 80 percent of them have also been connected with toilet to add the
human excreta as feedstock (Dhakal, 2002). However, none have been using the other
organic wastes for this purpose. There are so many farmers in rural and sub-urban areas
who want to install a biogas plant but have insufficient number of cattle and/or people to
produce sufficient amount of feed stocks to run the biogas plant. If use of organic wastes
and plant residue is encouraged they will be greatly benefited (Dhakal, Patrabansh, Karki,
Sharma and Adhikari, 2003).
Therefore, the use of organic wastes, of which the Vegetable and Kitchen Waste (VKW)
comprises the main part, for the production of biogas is an environment-friendly
technology both in the urban as well as rural areas. When applied, it will benefit the
marginal farmers in rural and suburban areas and at the same time it will initiate at source
management of municipal solid waste in urban areas. It will decrease firewood, fossil fuel
as well as chemical fertilizer demand thus saving the foreign currency of the country and
discouraging deforestation (Dhakal, 2002).
1.3 Objective
The main objective is:
• To generate and evaluate biogas from kitchen waste in “above ground fixed dome
biogas plant” and to find the potential of biogas generation from major kitchen wastes
The project targets the various problems such as shortage of the cooking gas, problem of
management of kitchen waste etc.
The specific objectives of this project are:
• To generate biogas in kitchen waste Biogas plant from kitchen wastes, using cow
dung as an activator
18
• To conduct test of biogas obtained from different feeds(kitchen wastes)
• To determine the energy production pattern on the plant
• To do financial evaluation of the biogas plant for substituting wood and kerosene
Hence, the target of the project is to design a biogas plant which can be installed in the
urban areas where there is very limited space which can address the problem of the
shortage of cooking gas seen in the urban areas. The other objective of the project is the
management of the kitchen waste.
1.4 Methodology
1. The extensive and sufficient literature review has been carried out and will be
updated in the course of the continuing project. The literature review has been done
from different media.
2. The preliminary designs were sketched.
3. The design was finalized by the discussion among the group members.
4. Cost of the plant was estimated.
5. The materials required for the construction or fabrication of the plant was collected.
6. Plant was fabricated.
7. The plant was tested with different feed materials.
8. Financial evaluation of the plant was performed.
9. The final project conclusion was drawn.
10. Submission of project report
1.5 Limitations
1. All kitchen wastes couldn’t be tested.
2. The proposed biogas plant was basically for testing purpose.
3. There occurred over-acidification due to over feeding of plant as the plant was of
little capacity and the diameter to height ratio was low.
19
CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
Biogas is the inflammable gas produced from the anaerobic fermentation of the bio
degradable substance due to the activity of the methanogenic bacteria. This gas is mainly
composed of the methane (CH4), carbon dioxide (CO2), water vapor etc.
Table 2.1: Composition of Biogas
Substances Symbol percentage
Methane CH4 50-70
Carbon dioxide CO2 30-40
Hydrogen H2 5-10
Nitrogen N2 1-2
Water vapor H2O 0.3
Hydrogen sulphide H2S Traces
(Ref: http://en.wikipedia.org)
2.2 Process of the Biogas Production
There are three steps or the process involved in the production or the activity of the gas.
Process is
2.2.1 Hydrolysis
2.2.2 Acetogenisis
2.2.3 Methanogenesis
20
2.2.1 Hydrolysis
It is the first step involved in the process also known as the liquefaction. In this process
the fermantive bacteria converts insoluble complex organic into the soluble organic
compound and also complex polymer is converted into the simple monomer. Examples
are cellulose is converted into the sugar, amino acid and fatty acid.
This is being the important step, is also the rate limiting step. Industrially this problem is
overcome by use of the chemical reagent
2.2.2 Acetogenisis
In this process the product from the first process is converted into the simple organic
acid, carbon dioxide and hydrogen. Major acids which are produced during this process
are Acetic acid (CH3COOH), propionic acid (CH3CH2COOH), (CH3CH2CH2COOH),
and ethanol (C2H5OH).
The reaction involve is
C6H12O6 → 2C2H5OH + 2CO2
(Glucose) (Ethanol) (Carbon dioxide)
2.2.3 Methanogenesis
Methane is produced by the action of the bacteria called methanogens bacteria. There are
two methods of he production of the methane, first is by the cleavage of acetic acid to
generate the carbon dioxide and methane.
Second process is the reduction of carbon dioxide with the hydrogen.
Methane production is higher from the second process, but it is limited by the amount of
the hydrogen in the digester. The reaction involve in this process are:
CH3COOH → CH4 + CO2
(Acetic acid) (Methane) (Carbon dioxide)
2C2H5OH + CO2 → CH4 + 2CH3COOH
(Ethanol) (Carbon dioxide) (Methane) (Acetic acid)
21
CO2 + 4H2 → CH4 + 2H2O
(Carbon dioxide) (Hydrogen) (Methane) (Water)
Table 2.2: C/N Ratio of Some Organic Materials
S.N. Raw materials C/N Ratio
1 Duck dung 8
2 Human excreta 8
3 Chicken dung 10
4 Goat dung 12
5 Pig dung 18
6 Sheep dung 19
7 Cow dung/ buffalo dung 24
8 Water hyacinth 25
9 Elephant dung 43
10 Straw (maize) 60
11 Straw (rice) 70
12 Straw (wheat) 90
13 Saw dust Above 200
(Ref: www.norganics.com)
2.3 Biogas Plant System
The feed material is mixed with water in the influent collecting tank. The fermentation
slurry flows through the inlet into the digester. The bacteria from the fermentation slurry
are intended to produce biogas in the digester. For this purpose, they need time to
multiply and to spread throughout the slurry. The digester must be designed in a way that
only fully digested slurry can leave it. The bacteria are distributed in the slurry by stirring
(with a stick or stirring facilities). The fully digested slurry leaves the digester through
the outlet into the slurry storage.
22
The biogas is collected and stored until the time of consumption in the gasholder. The gas
pipe carries the biogas to the place where it is consumed by gas appliances like stove,
lamp and generator. Condensation collecting in the gas pipe is removed by a water trap.
Figure 2.1: A Typical Biogas System Configuration
2.4 Factors Affecting Biogas Generation
• Carbon to Nitrogen (C/N) ratio: Carbon (as carbohydrates) and nitrogen (as protein,
ammonium nitrates etc.) are the main food of anaerobic bacteria. If the C/N ratio is
very high, nitrogen will be consumed rapidly and the rate of reaction will be
decreased. On the other hand if the C/N ratio is very low, nitrogen will be liberated
and accumulated in the form of ammonia. The ammonia can kill or inhibit the growth
of bacteria specially methane producers. In general a ratio of in range of 20-30:1 is
considered the best for anaerobic digestion.
• pH value: Both over acidic and over alkaline than certain limits are harmful to
Methanogenesis organisms. The optimum biogas production is achieved when the pH
value of the input mixture to the digester is between 6 and 7.
23
• Temperature: Enzymatic activity of bacteria largely depends upon temperature,
which is critical factor for methane production. The bacteria work best at a
temperature of 35°C to 38°C.
• Loading Rate: The digester load is primarily dependent upon four factors- substrate,
temperature, volumetric burden and type of plant. The correct rate of loading is
important for efficient gas production.
• Retention Time: It depends on the type of feedstock and the temperature. The
retention time is calculated by dividing total capacity of the digester by the rate at
which organic matter is fed into it.
• Total Solid Content: For proper solubility of organic materials, the ratio between
solid and water should be 1:1 on unit volume basis when the domestic wastes are
used. If the slurry mixture is too diluted, the solid particles can precipitate at the
bottom of digester and if it is too thick, the flow of gas can be impeded. In both cases
gas production will be less than optimum production.
• Toxicity: Mineral ions, heavy metals and the detergents are some of the toxic
materials that inhibit the normal growth of the pathogens in the digester. Small
quantity of mineral ions like sodium, potassium, calcium, magnesium and sulphur
stimulates the growth of bacteria while very heavy concentration of these ions will
have toxic effect.
• Pressure: It has been reported that better production of biogas takes place at lower
pressures.
2.5 Types of The Biogas Plant
Bio gas plant can be classified with accordance to the different criteria
2.5.1 On the basis of the construction of plant
2.5.2 On the basis of types of feeding
24
2.5.1 On the Basis of the Construction
In this type of the classification of the plant there are two types of plants.
2.5.1.1 Floating Drum Digester
This type of plant basically comprises of an underground brick masonry digester
connected with an inlet and outlet and covered by a floating steel gas holder for gas
collection. It is divided into two parts. One side has the inlet, from where slurry is fed to
the tank. The tank has a cylindrical dome made of stainless steel that floats on the slurry
and collects the gas generated. Hence the name given to this type of plant is floating gas
holder type of bio gas plant. The slurry is made to ferment for about 50 days. As more
gas is made by the bacterial fermentation, the pressure inside dome increases. The
decomposed matter expands and overflows into the next chamber in tank T. This is then
removed by the outlet pipe to the overflow tank and is used as manure for cultivation
purposes. Gas holder moves up and down guided by a central guide pipe depending upon
accumulation and discharge of gas. The floating gas holder at the top of the digester helps
to keep the pressure constant. The gas holder rises when the pressure is increased due to
production of gas and allows the generated gas to let out through the gas supply pipe. It
lowers when the pressure is decreased to stop the supply of biogas. In 1956 Jasu Bhai J.
Patel developed design of floating drum biogas plant is popularly known as Gobar Gas
Plant. In 1962, the Khadi Village Industries Commission (KVIC) of India approved
Patel’s design and this model soon gained popularity in India as well as the sub-
continent. This design is also known as KVIC design.
Figure 2.2: Floating Drum Type
25
Advantages
Since the floating drum is made of steel, therefore it is less favorable for corrosion.
Disadvantages
• The plants have become obsolete.
• It needs large investment and maintenance cost.
• Design weaknesses are present in the model. viz. mild steel drum corrodes and needs
to be replaced within 5-10 years.
• The drum has to be anchored to prevent it from overtopping due to high gas pressure.
2.5.1.2 Fixed Dome Digester
In fixed dome digester, the gas holder and the digester are combined. Gas is stored in the
upper part of the digester. Upper portion of the digester pit itself acts as a gas holder.
Displaced level of slurry provides requisite pressure for release of gas for its subsequent
use. The pressure inside the digester varies as the gas is collected. Fixed dome digester
varies as the gas is collected. Fixed dome digesters are usually built below the ground
level. Based on the principles of fixed dome Chinese model, various countries have put
forth modified designs to suit their local conditions. For example, Gobar Gas and
Figure 2.3: Sketch of KVIC Floating Gas Holder System
26
Agricultural Equipment Development Company (GGC) of Nepal have developed a
design commonly known as the GGC model. Compared to the Chinese fixed dome
model, the GGC model is easier to construct as this structure has less curved profiles. In
an effort to lower the investment cost of the fixed dome plant, the Deenbandhu model
was put forth in 1984 by the Action for Food Production (AFPRO), New Delhi. In India
this model proved 30 percent cheaper than the Chinese fixed dome model of comparative
size. However, in Nepal preliminary studies carried out by BSP did not find any
significant difference between the investment cost of GGC and the Deenbandhu design of
comparative size (Karki, Shrestha and Bajgain, 2005).
Figure 2.4: GGC Concrete Model Gas Plant
27
Figure 2.5: Fixed Dome Type Biogas Plant Advantages
• It can be built with local materials.
• Its construction costs are low.
• The life of fixed dome plant is longer (20 to 50 years) compared to KVIC plant, as
there are no moving parts and both concrete and cement masonry is relatively less
susceptible to corrosion.
Disadvantages
The volume of this model is fixed. So if the gas pressure increases inside, it may cause
damage to the concrete dome.
2.5.2 On the Basis of Types of Feeding
Depending on type of feeding they can be classified into (Ostrem, 2004)
28
2.5.2.1 Batch Digester
In the batch process, the substrate is put in the reactor at the beginning of the degradation
period and sealed for the complete retention time, after which it is opened and the
effluent is removed. The reaction stages occur more or less consecutively and the
production of the biogas follows a bell curve with time. When waste is first loaded,
hydrolysis takes place and gas production is low, forming only carbon dioxide. Methane
production increases during the acid forming stages and is maximum halfway through the
degradation period when methanogenesis dominates the processes. Towards the end of
the degradation period, only the least easily digestible material remains, and gas
production drops. The sludge in a batch reactor is normally not mixed, allowing the
content of the digester to stratify into layers of gas, scum, supernatant, an active layer,
and stabilized solids at the bottom. Influent and effluent valves reside in the supernatant
layer and solids must be removed near the bottom. Retention times range from 30-60
days with an organic loading rate between 0.48 and 1.6 kg TVS/m3 reactor volume/day.
The disadvantage of this type of system is the large tank volume required due to the long
retention time, the low organic loading rate and the formation of a scum layer. Only
about 1/3 of the tank volume is used for active digestion, making this a poor option in
crowded urban settings.
2.5.2.2 Continuous Digester
In the continuous process, fresh material continuously enters the tank and an equal
amount of digested material is removed in an ongoing process. There are distinct stages
of digestion throughout the batch process whereas equilibrium is achieved in the
continuous process. When consistent feedstock input is used, all reactions occur at a
fairly steady rate resulting in approximately constant biogas production. The structure for
a continuous process can be identical to a batch process, a cylindrical tank with influent
and effluent valves. Because there is constant movement, however, material inside the
tank is mixed and does not become stratified. This allows for more optimal use of the
tank volume. The disadvantage of the continuous process is the removed effluent is a
29
combination of completely digested and partially digested material. To minimize the
removal of partially digested material, some designs dictate the path of the digestion
inside the chamber, for example through the use of interior walls. The reported residence
time for a continuous process is an average across the substrate.
2.6 Currently Existing Other Biogas Plant
2.6.1 Puxin Biogas Plant
The Puxin biogas digester is a kind of hydraulic pressure biogas digester, and is
composed of a fermentation tank built with concrete, and a gas cover made with glass
fiber reinforced plastic. The fermentation tank has a capacity of 6 cubic meters, and is
constituted by a tank stomach, a tank neck, an entrance pipe and an exit pipe. The gas
cover is installed in the tank neck, fixed by a component and sealed up with water. The
Puxin biogas gasholder is 1.6 m in diameter and 0.6 m in height. The gas cover has the
capacity of 1 m3 and has weight of 60 kg. The biogas cover is 100% airtight comparing to
the traditional Hydraulic Biogas Digester.
Figure 2.6: Puxin Biogas Model
Advantages
• It is easy to build.
Inlet Gas PipeOutlet
30
• It is highly industrialized and hence is fit for cosmically and fleetly spread.
• It is convenient to replace fermentation material and fit to use straw and other solid
organic material for fermentation.
• It is easy to maintain and has a long operation life.
• It has airtight function and has high rate of biogas production.
Disadvantages
• There is water loss due to seepage in the joints due to the movement of the pipe in
pressure.
• The steel moulds are heavy and difficult to transport to remote areas.
• The cost of the plant is quite high.
2.6.2 Agri / Kitchen Waste Based Biogas Plant
This technology has been developed by "Nuclear Agriculture and Biotechnology
Division" of BARC. NISARG-RUNA plant can process almost any biodegradable waste
including kitchen waste, paper, grass, night soil, dry leaves etc. There is a good potential
for energy generation in this biphasic biomethanation plant. The manure is weed free and
does not have any offensive smell.
The plant produces biogas from kitchen waste by using thermophilic microorganisms that
flourish in extreme environment. The biogas plant has following components: A
mixer/pulper (5 HP motor) for crushing the solid waste, Premix tanks, Predigested tank,
Solar heater for water heating, Main digestion tank (35 m3), Manure pits, Gas lamps for
utilization of the biogas generated in the plant.
The waste is converted into slurry by mixing water (1:1) in this mixture. The other
modification is use of thermophilic microbes for faster degradation of the waste. The
growth of thermophiles in the predigestor tank is assured by mixing the waste with hot
water and maintaining the temperature in the range of 55-60°C. The hot water supply is
from a solar heater.
31
From the predigestor tank, the slurry enters the main tank where it undergoes mainly
anaerobic degradation by a consortium of archaebacteria belonging to Methanococcus
group. They produce mainly methane from the cellulosic materials in the slurry.
The undigested lignocellulosic and hemicellulosic materials then are passed on to the
settling tank. After about a month, high quality manure is dug out from the settling tanks.
The organic contents are high and this can improve the quality of humus in soil.
Advantages
• Generation of fairly good amount of fuel gas.
• Generation of high quality manure, which would be weedless and an excellent soil
conditioner.
• The gas generated in this plant can also be used as a source of natural gas. The
composition of biogas is - Methane (CH4): 70-75% - Carbon Dioxide (CO2): 10-15%
- Water vapors: 5-10%.
Disadvantages
• This model of biogas plant requires large space.
Figure 2.7: NISARG-RUNA plant
32
• It makes the use of motor and solar heater which makes it unfavorable for the rural
areas where no electricity is present.
2.6.3 ARTI Biogas Plant: A Compact Digester for Producing Biogas from Food
Waste
Introduction
ARTI has developed a compact biogas plant which uses waste food rather than
dung/manure as feedstock, to supply biogas for cooking. The plant is sufficiently
compact to be used by urban households, and about 2000 are currently in use – both in
urban and rural households in Maharashtra. A few have been installed in other parts of
India and even elsewhere in the world.
Dr. Anand Karve (President of ARTI) developed a compact biogas system that uses
starchy or sugary feedstock (waste grain flour, spoilt grain, overripe or misshapen fruit,
no edible seeds, fruits and rhizomes, green leaves, kitchen waste, leftover food, etc).
Working
The smaller tank is the gas holder and is inverted over the larger one which holds the
mixture of decomposing feedstock and water (slurry). At inlet feeding matter should be
ground or pulped and mix with 2 to 3 bucket full of water. So, an inlet is provided with
much smaller amount of solid matter than the residue from a manure-based plant, and
ARTI recommend that the liquid is mixed with the fedstock and recycled into the plant.
A pipe takes the biogas to the kitchen, where it is used with a biogas stove. Such stoves
are widely available in India which has a long tradition of using manure-based biogas
plants.
The gas holder gradually rises as gas is produced, and sinks down again as the gas is used
for cooking. Weights can be placed on the top of the gas holder to increase the gas
pressure.
33
Advantages
• The immediate benefit from owning a compact biogas system is the savings in cost.
• It is an environmentally friendly cooking system.
• The size and cost of this system is relatively lower.
• It is an extremely user friendly system, because it requires daily only a couple of kg
feedstock, and the disposal of daily just 5 liters of effluent slurry.
• A single plant produces sufficient biogas to at least halve the use of LPG or kerosene
for cooking in a household, as well as a small amount of solid residue which can be
used as fertilizer.
Disadvantages
• The biogas plant can become acidic and fail if it is over-fed, and this is a particular
challenge with a plant using highly digestible organic materials.
• Plant’s heat insulation is not considered.
Figure 2.8: ARTI Model
34
• Since heat insulation is not considered, it can not be used in region where weather
fluctuates more.
2.6.4 Experimental Model Biogas Plant by Ajay Karki
A 200L volume biogas plant as shown in the figure 12 was designed by Ajay Karki and
manufactured at the workshop of equipment maintenance centre (EMC), Kathmandu,
Nepal. The design is partially based on fixed dome Chinese model plant but fabricated
out of mild steel sheet. Gas storage space is provided at the upper dome which is fixed
and input is fed from the inlet as shown in the figure. However, unlike the conventional
fixed dome model where the digested effluent is poured out automatically by the gas
pressure built inside the digester ( and the dome), in this demonstration plant the effluent
has to be manually removed by opening the bulb valve at the outlet.
The raw material (input) used for demonstration model consists of potato peels, banana
peels, vegetable stem as well as cooked food and uncooked vegetable waste. 150L has
been allotted for the fermenting material (slurry) inside the digester and around 50L have
been left for gas storage and was increased by the material with digested slurry from an
operating biogas plant which is about 10% to 20%. The chopped vegetable waste with
equal volume of water is mixed to enhance the pre-fermentation process.
Figure 2.9: 200L Capacity Demonstration Model Biogas Plant
35
This bio reactor has been designed to operate both as continuous and batch feeding
system. If each day for a given input, an equal volume of digested output is removed, it
would be a continuous system. Conversely, if the plant is fed fully and, once gas
production diminishes drastically or even ceases it is completely emptied; it would be a
batch fed system. The design allows the plant to operate under both systems since unlike
conventional biogas plants where the pressure governs the slurry outflow; a valve is used
to remove the digested slurry. In his study, the plant is being used as semi-continuous or
semi-batch system (Bajagain, 2005).
36
CHAPTER 3
CONSTRUCTION AND FABRICATION
The design process was carried out in the following stages:
3.1 Idea Generation
During idea generation phase, different model, design and type of bio gas plant were
studied.
The most common type of design studied was:
a) Floating drum Type
b) Fixed dome type
Floating Drum Type
Floating Drum is mostly popular in India and some part of South East Asia. In India, It is
popularly known as ARTI (Appropriate Rural Technology Institute) model. So ARTI is
well known institute for floating drum Biogas plant in India. Detail of this type is already
discussed in literature review part. So it has got both advantages and disadvantages.
Floating drum is normally made from two drum where one drum is floating gas holder
drum which should be polythene drum, but the Digester tank may be either R.B.C or
G.I.sheet or polythene drum.
Fixed Dome Type
Fixed dome type is popular all over Asia and it is popularly known as Gobar gas plant in
south East Asia. It was introduced from china. It has only one fixed dome where the drum
half part acts as gas holder and half for fermentation. But it has also got both advantages
and disadvantages. It can also be made of either Re-inforced Brick Concrete, or G.I.sheet
or polythene drum.
37
The common existing model and design are:
a. Fixed Dome Type
i. GGC concrete Model Biogas plant
ii. Chinese model fixed dome biogas plant
iii. Deenbanhdu Biogas plant.
iv. PVC bag Digester etc.
b. Floating Drum Type
i. KVIC floating gas holder system
ii. ARTI floating drum gas holder system. Etc
After studying all above types, model and design, fixed dome plant was chosen for our
testing purpose to avoid moveable part and wear-ability. So, for this 200L drum was
decided as our digester tank. So, for this either it was needed to be fabricated by G.I.
sheet or by R.B.C or by already existing polythene drum (such as Hilltake drum, sprit
drum, paint drum etc.). The rough sketch of the design is shown below.
Figure 3.1: Rough sketch of design
38
The above fixed dome was specially targeted for continuous feed type because for this
less initial feed was required and less quantity of particular kitchen waste like rice was
easily available for a day. So, that testing becomes effective and efficient.
The alternative design for the testing was Batch type digester which include 20L water jar
that is easily available in market. But for this, it required large quantity of feeding
material and pre-fermentation only once at first.
Incase the initial design failed or, it becomes difficult to carry out the experiment, so
second plan had been thought off.
Hence at first 200L drum (fixed type) was decided as digester for testing purpose.
3.2 Idea Screening
The material that can be used for fabricating the digester tank may be either G.I. sheet or
R.B.C or readymade 200L polythene drum like: Hilltake, spirit drum, or paint drum.etc
Factor considered for Idea screening are as follows:
a. Availability: G.I. sheet, R.B.C and polythene drum, all are easily available in the
market. But Polythene drum are easily available in the form of drum in the market.
b.Strength (pressure holding capacity): R.B.C and G.I. sheet has got high pressure
bearing capacity than polythene drum.
c. Leakage: Concrete may have major leakage problem if fabrication is done in poor
management way. So ratio of cement water should be well maintained. G.I sheet may
have leakage problem through joint like rivet joint. But there is less leakage chance for
polythene if adhesive are properly stocked on the joints.
d.Durability: Durability of R.B.C is higher then polythene drum and G.I sheet.
39
e. Fabricability: Polythene drum plant fabrication is easier than R.B.C and G.I sheet due
to less labor cost and less machining parts respectively.
f. Solid Waste Reuse: Polythene drum such as sprit drum and paint drum are reused
material. R.B.C can also be reuse but G.I sheet need to fabricate.
g.Cost: R.B.C and G.I sheet fabrication cost is higher than Polythene drum.
(Reference for cost: according to 2004-2005 cost of steel plant was NRs.4000/-, -Ajay
Karki, Biogas As Renewable source of energy in Nepal theory and development. Editor:
Dr. A.B. Karki, Prof. Jagan N. Shrestha, Mr. Sundar Bajgain).
Above factors are rated on the scale 1 to 5 which forms the basis of selection.
3.3 Selection
Fixed dome type was already selected in screening phase. So, here, the selection meant
the selection of material that was to be used during fabrication of digester. The following
are for selection of fabricating material by scale rating method from 1to 5.
So, with the help of table below, material with higher mark scoring was selected.
Table 3.1: Factor Rating Table
S.N
Mat
eria
l
*Mar
ket
Ava
ilabi
lity
**St
reng
th
**D
urab
ility
***L
eaka
ge
*Reu
se
*Fab
ricat
ion
***C
ost
Tota
l
1. R.B.C 4 4 4 2 3 4 2 23
2. M.S sheet 3 4 3 3 2 3 3 21
3. Polythene
drum
4 3 4 4 4 4 4 27
where,
40
* Availability, Reuse, Fabrication
1 for Very difficult
2 for difficult
3 for moderate
4 for easy
5 for very easy
** Strength, Durability
1 for very low
2 for low
3 for moderate
4 high
5 very high
***Cost, leakage
1 for very high
2 for high
3 for moderate
4 for low
5 for very low
So from above discussion and table, it became clear that polythene drum was used as
digester. But through market study, it becomes ineffective to use Hilltake drum as fixed
drum because it has got big mouth opening which makes the fabrication difficult. So
lastly we decided to use spirit drum as digester drum because it had got small threaded
mouth cap with sealing and becomes easy fabrication.
Note: Strength is on the basis of 4 inch wall, 2mm steel sheet and 8mm thick poly drum.
Also from above discussion, for alternative batch type plant, water jar became well suited
batch digester.
3.4 Detail List of Selected Plant
Part Name:
a. 200L poly drum,
b. PVC pipes of 2.5” and 4”,
c. Gas cock,
d. 0.5 inch sucket and elbow,
e. 4 inch door bent,
f. 15L bucket,
g. M-sheal, and PVC seal,
41
h. 2.5inch and 4inch barrel,
i. Gas collecting pipe,
j. Thermometer,
k. Bundle of straw,
l. Sheet of polythene plastic.
3.5 Description of Fabrication
Step 1
First the 200L sprit drum was taken and cleaned properly from inside by water.
Step 2
4 inch dia. Circle was drawn at one side of the drum at 80cm depth. Then 4” barrel was
heated for 5 minute and was placed on that mark to make 4” hole for outlet pipe. Also 4”
hole is made to bottom of 15L bucket by same barrel.
Step 3
Second marking of 2.5” dia. Circle was drawn at the top of the drum 20 cm from the
center of drum. Then 2.5” barrel was head for 5min. and was placed at the mark to make
second hole for inlet pipe
Step 4
0.5” barrel was heated for 5 min and threaded at the top most surface center for
placement of gas cork setup.
Step 5
4” PVC pipe of 20cm long was inserted to 4” hole and joined section was sealed by M-
seal.4” doors bent was joined to this pipe and sealed by PVC seal. Next 4” pipe of 33cm
long was placed vertically to other end of door bent and was sealed by PVC seal. So the
bucket is placed vertically at the top of this pipe and sealed by PVC seal.
Step 6
Next 2.5” pipe of 78cm long was also inserted completely from the top leaving 10% of
total length at the top end. The joint was sealed by M-seal.
42
Step 7
Elbow and socket were fixed at the top centre. Gas cock was then fixed on the elbow.
Step 8
Slurry mixture was poured to the tank from inlet to 1/3 level of drum. Then the gas cock
was closed and air leakage from joint was checked by placing soap water.
Insulation Step
Straw was packed in a polythene bag to make polythene blanket. This blanket was rapped
all over the cylindrical drum for insulation.
The sketch of plant is shown below. The picture of the same is provided in annex J.
Figure 3.2: Sketch of the Continuous Feed Plant (Dimension in cm)
3.6 Alternative Design
Common water jar of 20L capacity was chosen and it was fabricated as explained in
fabrication method below.
43
Figure 3.3: Drawing of the Alternative Plant (Batch Digester) (Dimension in cm)
3.6.1 List of Parts
a. 20L jar
b. rubber cork
c. delivery tube 7.5 mm in diameter
d. Plastic pipe of 7.5mm diameter
e. Aluminum tube of 8mm diameter
f. clips
g. thermometer
h. straw and foam
3.6.2 Fabrication method for alternative batch type:
Step1
The top of the cork was marked with 7.5mm diameter and 8mm diameter circle at 20mm
distance. Then it was drilled by 7.5mm diameter drill and 8mm diameter drill to insert
8cm long delivery tube and 35 cm long aluminum tube.
44
Step 2
Then the calculated feeding mixture was poured onto the jar.
Step 3
So the cork with the tubes were inserted on the jar mouth and hammered with mallet
hammer.
Step 4
Gas pipe was joined to the delivery tube by little preheating.
Step 5
The gas pipe was clipped to make air tight.
Step 6
Mouth of aluminum tube was joined by small piece of gas pipe which was also closed by
clipping. Aluminum tube was used for inserting thermometer.
The picture of the plant is provided in annex K.
3.7 Insulation and heating system:
• At first the insulation was done by placing the jar in foam box and jar was
covered with straw by compacting it. Also 1200W halogen heater was used for
external heating.
• In a plant, aquarium water heater was also used to heat the pool of water
surrounding the jar.
• Later insulation was done by rapping the jar with polystyrene foam (thermo-
cot).The pictures is provided in annex A.
45
CHAPTER 4
MATERIALS AND METHODS
Since all the wastes generated from the kitchen cannot be tested in the plant which is also
one of the limitations of our project, therefore some of the materials are selected which
can meet the objective of the project and cover every aspect of the kitchen wastes.
4.1 Basis of Material Selection
There are two bases that are selected for the selection of kitchen wastes. The bases are as
explained below.
4.1.1 Volume
The volume of kitchen waste generated has been considered as the prime basis for the
selection of geed material for testing in the plant. There are different kinds of wastes
generated from the kitchens in the households. Among them the kitchen wastes that are
produced in abundant quantity which have potential for the biogas production is selected
as the feeding materials for the biogas. e.g. Rice is present in the abundant quantity in the
kitchen waste. Hence rice is used as feed material. Also among fruits, banana is quite
common and hence banana peels can be considered as potential feed for the biogas plant.
4.1.2 Kinds of wastes
Since the attempt has been made to cover all the types of kitchen wastes, therefore a
kitchen waste from each category (crops, vegetables, fruits) has been selected as feeding
materials.
Among crops, rice is quite common food in Nepalese society. So, rice is considered as
the feed materials.
Among vegetables potato is the most common vegetable and potato can be mixed with
almost all kinds’ of vegetables. So, potato is also considered as the feed material for on of
the plants. Also cabbage is widely consumed in the Nepalese society. So, cabbage has
also made its way as a testing feed material for the plant.
46
Among fruits, banana is quite common fruit. Also, banana is available throughout the
year . Hence, banana peels are also considered for the testing purpose in the plant.
Table 4.1: Parameters of Different Feed Materials
S.N. Material Kind Initial
pH
Moisture(%) Total
Solid(T.S.)(%)
Carbon-
nitrogen
ratio(C:N)
1. Rice Crop 6 80.05 19.95 25.1
2. Cabbage Vegetable 7 91.06 8.94 12
3. Potato Vegetable 7 81.46 18.54 25
4. Banana Fruits 7 91.5 8.5 23.64
(Reference for C:N value www.norganics.com and
moisture contentfrom Mr. Harka man limbu)
Since we are making a test using these materials, therefore it is quite important to know
these materials quite better. Thus, the information regarding these wastes is provided in
the following parts:
4.1.2.1. Cabbage
The cabbage is a leafy garden plant of the Family Brassicaceae (or Cruciferae), used as a
vegetable. It is a herbaceous, biennial, dicotyledonous flowering plant distinguished by a
short stem upon which is crowded a mass of leaves, usually green but in some varieties
red or purplish, forming a characteristic compact, globular cluster (cabbagehead). Only
green cabbage has been used during the study.
4.1.2.2. Rice
Rice is a staple food for a large part of the world's human population, Southeast Asia,
making it the second-most consumed cereal grain, after maize. Rice is also one of the
major or most common kitchen wastes.
47
4.1.2.3. Potato
The potato is a starchy, tuberous crop from the perennial Solanum tuberosum of the
Solanaceae family. The word potato may refer to the plant itself as well. In the region of
the Andes, there are some other closely related cultivated potato species. Potatoes are the
world's fourth largest food crop, following rice, wheat, and corn.
4.1.2.4. Banana
Banana is the common name for a fruit and also the herbaceous plants of the genus Musa
which produce this commonly eaten fruit. They are cultivated throughout the tropics.
Each individual fruit (known as a banana or 'finger') has a protective outer layer (a peel or
skin) with a fleshy edible inner portion. Both skin and inner part can be eaten raw or
cooked. Bananas are grown in at least 107 countries. The bananas from a group of
cultivars with firmer, starchier fruit are called plantains. Bananas may also be cut and
dried and eaten as a type of chip. Dried bananas are also ground into banana flour.
Bananas are classified either as dessert bananas (meaning they are yellow and fully ripe
when eaten) or as green cooking bananas. Almost all export bananas are of the dessert
types; however, only about 10-15% of all production is for export.
4.2 Charging of plants
The charging of the different plants fabricated is different regarding their types. The
methods for charging are described in the following parts.
4.2.1 Continuous digester
Volume of the digester = 200 L
Volume required for the gas collection = one-third of volume of digester
= (200/3)L
= 66.66 L
Volume available for feed = (200-66.66) L
=133.33 L
48
By approximation, 140 L of volume was allocated for the feeding of material with water
to the plant.
Date of charging
First continuous digester-October 27, 2008
Second continuous digester-November27, 2008
For better result, 90% of moisture is desired. So to make up the proportion, 65 l of water
was added with 65kg of cow dung and 10kg of inoculums from the existing floating drum
biogas plant designed by Harka Man Limbu was added.
Then no feed was supplied for 40 days. After initial loading by above procedure the
moisture was allowed to ferment. But due to rapid fluctuation of temperature, the
methane content was not in satisfactory proportion. Thus, the plant was not started to feed
by the kitchen wastes and was discarded as the plant had turned to acidic nature.
Thus we operated for 20L jar batch digester plant and continued our project on testing in
small batch digester.
4.2.2 Batch digester
The feeding of the batch digester was done by the following methods:
Capacity of the jar=20L
Volume required for the gas collection=one-third of volume of digester
= (20/3)
=6L(approx)
Volume available for feed = (20-6)
=14L
By approximation, 14L of volume was allocated for the feeding of material with water to
the plant.
49
Different batch digester contains different amount of particular feed which are described
in the following parts.
a) Banana Plant(Plant I)
Volume of water fed=7L
Weight of banana peel fed=6 kg
Weight of cow dung=1 kg
Total volume of feed=14L
b) Cabbage Plant(Plant II)
Volume of water fed=7L
Weight of cabbage fed=6 kg
Weight of cow dung=1 kg
Total volume of feed=14L
c) Rice Plant (Plant III)
Volume of water fed= 4.5L
Weight of rice fed= 3.5 kg
Weight of cow dung= 0.5 kg
Total volume of feed=8.5L
d) Potato Plant (Plant IV)
Volume of water fed=6.5L
Weight of potato fed= 5 kg
Weight of cow dung= 1.5 kg
Total volume of feed=13L
e) Banana Plant (Plant V)
Volume of water fed=6.5L
Weight of banana peel fed=6 kg
Weight of cow dung=1 kg
Volume of cow urine=0.5L
Total volume of feed=14L
Table 4.2: Quantity of Different Constituents of the Plants
Plant I Plant II Plant III Plant IV Plant V
Volume of water 7L 7 L 4.5 L 6.5 L 6.5 L
Weight of feed 6 kg 6 kg 3.5 kg 5 kg 6 kg
Weight of cow dung 1 kg 1 kg 0.5 kg 1.5 kg 1 kg
Total volume 14L 14 L 8.5L 13L 14 L
Note: 0.5 L urine was added in plant V
4.3 Measuring Methods
The following three techniques were used to measure different parameters such as pH,
proportion of gases, temperature, volume of the gas produced, etc.
50
a. pH
The pH of the slurry of different stages and different states of reaction is an important
parameter for the biogas production. The pH of the slurry was measured by making the
use of pH paper. The paper had the range from 1 to 10 on the basis of color coding. The
procedures followed are listed below:
i. The pH paper leaf was taken out of the stack of pH paper.
ii. The paper was dipped in the slurry.
iii. The color of the paper was changed.
iv. The changed color or the new color of the slurry was compared to the color code
on the stack of the pH paper cover.
v. The corresponding reading of the color was noted and marked on the data sheet.
b. Volume
The measurement of volume of the gas produced is and important part of this project. The
measurement of the volume has been carried out by the process of downward
displacement of water of pH 5. As the biogas is lighter than water; the volume of water
gets collected at the top of the water in the measuring cylinder. The process is explained
as below:
i. Apparatus Setup
The trough was filled with water. The measuring cylinder after filling with water was
mounted on the beehive shelf inside the water. The gas outlet pipe from the digester was
joined to the beehive shelf.
ii. Measuring Procedure
The procedures followed for measuring of the volume are as follows:
a. The valve of at the gas outlet pipe was opened.
b. The gas was allowed to pass into the measuring cylinder through beehive shelf.
c. The gas displaced the water downward and occupied the space at the top.
d. The volume displaced was noted from the scale of the measuring cylinder.
51
e. If the gas coming out was found to exceed the capacity of the measuring cylinder
scale, the valve was closed at the appropriate position up to where the gas volume
could be recorded.
f. The gas collected inside measuring cylinder was allowed to escape.
g. The water was again filled in measuring cylinder and mounted on the beehive shelf.
h. The volume of the gas was measured by following the steps from i to iv and the cycle
was repeated until the gas was evolved.
c. Proportion
Gas board was used to measure the proportion of the different gases in the biogas.
Since the gas board was able to show the proportion of carbon-dioxide (CO2) and
methane (CH4), therefore only two gases was analyzed in the study. The process followed
to measure the proportion of methane and carbon dioxide.
i. The setup was made by connecting one end of rubber tube to gas board inlet and
other end to gas filter.
ii. The analyzer power was switched on.
iii. It took 30 seconds to remove residual gas
iv. The indicator shows 0% of methane and carbon dioxide.
v. The longer tip of gas filter was connected to the gas collecting pipe of gas jar.
vi. If the pressure of the gas is higher, the gas circulates freely and indicator starts to
show the percentage of methane and carbon dioxide.
vii. If the gas pressure is low, then suction switch is pressed and analyzer starts to
vibrate and indicator shows the percentage of methane and carbon dioxide.
d. Temperature:
The temperature of the slurry was measured with the simple mercury thermometer of
ranges 0°C to 100°C. The temperature was always checked after gas was extracted by
dipping thermometer through aluminum tube which is fixed in the cork. But the
aluminum tube was close by clipping all the time.
52
CHAPTER 5
KITCHEN WASTE SURVEY
5.1 Introduction
The kitchen waste generation was surveyed in various families. The survey was
basically done to find out the per head generation of kitchen waste. It also covers the
per head consumption of food.
5.2 Factors Influencing Kitchen Waste Generation
Following factors were found to be affecting the kitchen waste generation:
a. No. of members in the family
The kitchen waste was found to be increased as the no. of members in the family
increased.
b. Family background (or status)
The culture and financial status affected the kitchen waste generation.
c. Eating habit and local food availability
People with different eating habit produced different wastes. Also the food
availability in the local market differs the waste generation.
5.3 Limitation
a. The weight of the food consumed could not be weighted properly.
b. Less no. of samples was taken.
5.4 Research Methodology
a. Sampling
Sampling was done so that the survey covered the people of different caste.
Mostly, Newar, Chhetri, and Brahmin were included.
53
b. Instrumentation
One page questionnaire set was developed as survey instrument to measure the
per head kitchen waste generation. This questionnaire set is provided in appendix
F.
c. Data Collection Process
Data were collected with the help of questionnaire. The data were collected in
written or oral form.
d. Data Analysis
Data analysis was done with the help of weighted arithmetic mean. The tables of
consumption and production are provided in the appendix F.
5.5 Result of the Study
The max amounts of kitchen waste produced are rice, cabbage, mustard waste and
banana. The production of kitchen waste per head from calculation was found to be 0.468
kg per head per day but it can only be at tentative data as lesser number of samples was
taken.
54
CHAPTER 6
GAS PRODUCTION AND ANALYSIS
6.1 Experiment in 200L Drum
Two drums of 200 L capacity each were fabricated as explained in ‘Construction of
biogas plant’ in October 3rd and October 10 of 2008 respectively. The set-ups were
established as explained in chapter ‘Material and Methods’. Insulation was done with the
help of straw webbed in black plastic. The first plant was kept in Ombahal, Kathmandu at
open space of top floor of a house, second plant was kept at top floor of CES (Centre for
Energy Studies) building.
Cow dung mixed with water was left for biogas production in both the drums. In first
plant first production of gas was observed in 24th day after installation. Flame test was
carried, but it showed negative result. The gas flow took place only for 10 seconds.
On 27th day, again for 10 seconds gas was observed but this time too, the gas
extinguished the flame giving clear indication of CO2 gas abundance. Again in 33rd day
for 6 seconds gas was observed but this time too non-ignitable. Finally on 58th day, the
plant was discarded.
Same was with the case of 2nd biogas plant kept at CES. On 20th day check, for 6 seconds
gas was produced. Similarly for 15 seconds gas was observed in 30th day, 16 seconds in
41st day. This plant was also discarded on 51st day.
The major reason behind discarding the plants was not being able to control temperature
even with insulation. The differences in temperatures at night and day times vary greatly.
By consulting Mr. Harka Man Limbu (who is conducting thesis and experiment on
similar biogas plant using kitchen waste), it was known that if methanogens are active by
summer, then only there is a little chance of production of biogas from the plant.
55
The temperature patterns in two plants were almost same. The maximum and minimum
temperatures are shown in graph below.
Figure 6.1: Temperature Profile for 200L Drum (Ombahal)
Figure 6.2: Temperature Profile for 200L Drum (CES)
Thus, the temperature couldn’t be controlled. So, 20 L jar plant was opted in room
condition.
56
6.2 Experiment in 20 L Jars
Plants each consisting of different feed materials viz; banana peels, cabbage leaves, rice
and potato were set up. The production of biogas was performed using a 20L volume jar
single stage digester. The experiments were carried at different times and first banana
peels were tried. In all the experiments, focus was given to following parameters.
a) Total volume of gas generated
Note: The gas before pH rise wasn’t considered.
b) Methane content in the gas
c) pH fluctuation pattern
6.2.1 From Banana Peels (Plant I)
The moisture content, C/N ratio and pH values are already mentioned in previous chapter
‘Material and Methods’.
The experiment was carried out in a room with insulation by using straw. As it was
winter condition, the temperature further reduced. Later to maintain temperature, 1200W
heater was used. Due to various circumstances at the time, temperature couldn’t be
maintained. Also pH went on falling. The whole experiment was carried out in
physophillic range. The following graphs shows the temperature and pH fluctuations.
Figure 6.3: Temperature and pH Profile for Plant I
57
On fifth week, about 750 gm of chalk powder was used. Also 1 liter of water was added.
But pH didn’t improve. So, the plant was discarded.
6.2.2 From Cabbage Leaves (Plant II)
Experiment on biogas plant consisting cabbage leaves was carried out just one week after
the plant for banana peels was constructed. Similar as plant for banana peels¸ the
experiment was carried out in a room with insulation by using straw. As it was winter
condition, the temperature further reduced. Later to maintain temperature, 1200W heater
was used. Due to various circumstances at the time, temperature couldn’t be maintained.
Also pH went on falling. The following graphs shows the temperature and pH
fluctuations.
Figure 6.4: Temperature and pH Profile for Plant II
There is a lapse in reading between 11th day and 29th day due to the circumstances in
college. On the 30th day, 420 gm chalk powder was added and 2L water was also added
but pH didn’t improve till 36th day to pH 5. On 47th day 100 gm CaO was added to
increase pH to 6. But on 65th day, pH reduced to 5 again. The plant was discarded on 69th
day.
58
6.2.3 From Rice (Plant III)
In above two experiments, pre-fermentation wasn’t done. The rice was pre-fermented two
days. Also it was determined to carry out experiment in mesophilic range.
The temperature was tried to control through the use of 65 watts heaters using water pool
as stated in previous chapter ‘Construction of biogas plant’ for rice.
The temperature was difficult to control due to irregular electrical supply & the
temperature varied some days largely thus hampering the methanogens’ activities.
Following chart shows the fluctuation of temperature and pH.
Figure 6.5: Temperature Profile for Plant III
Large fluctuations were observed until about week third. The room temperature by then
has reached about 19 °C so; it was decided to keep it in room temperature by covering
with straw again. Also, the pH showed no sign of increment so, by titration and hit and
trial method, 100 gm lime (CaO) was added to increase pH to 5.
pH was raised to 5 from 4 by adding 100gm of CaO, the gas was generated. The gas
generated before this was not taken in consideration. Following the increment in pH, the
pressure increased in the plant due to gas production. Before the pressure reached above
59
12 KPa, volume of gas was analyzed with gas analyzer and collected through downward
displacement of water. Again in about 30th day, the ph raised to 6.
The volume of gas generated was collected 18 times in different time. The total
cumulative volume was about 67.61 liters up to the 71st day.
Figure 6.6: Volume Profile for Plant III
Initially, the methane content was very low as shown in above chart. Probable reasons for
low methane content may be as follows.
i. Initial temperature fluctuation couldn’t be controlled.
ii. Initial steep pH drop couldn’t be controlled. It may be due to not enough pre-
fermentation.
But from 41st day, the methane content gradually increased and reached up to 44.8% by
volume in 72th day.
60
6.2.4 From Potato (Plant IV)
This plant was installed in February 15, 2009. It was insulated by polystyrene thermo-cot.
Four days were allowed for pre-fermentation. The following graph represents pH and
temperature variation.
Figure 6.7: Temperature and pH Profile for Plant IV
The pH fell considerably in 2 weeks and so on 15th day, pH was increased to 6 by adding
lime (CaO) about 180gm by hit and trial method. In 31st day, it increased to 7.
0
1
2
3
4
5
6
7
0102030405060708090
100
21 22 26 2829 30 31 32 33 34 36 38 39 40 41 42 43 44 45
volume in %
Days
Volume
Volume in litre
CO2 %
CH4 %
litre
Figure 6.8: Volume Profile for Plant IV
61
0
1
2
3
4
5
6
7
8
1213141516171819202122232425
1 3 5 7 9 11131517192123252729313335373941
Temperature( °C)
Days
Temperature and pH profile
Min temperature
Max. temperature
pH
pH
The methane content in biogas gradually increased up to 38.5% in 38th day by volume
and carbon dioxide content gradually decreased. A total of 47.04 L of gas was collected
up to 44th day. The temperature was maintained around 20°C. The pattern of obtained
volume of gas was reminiscence to normal distribution. The complete collection of gas
couldn’t be done due to time limitation.
6.2.5 From banana peels (Plant V)
6 kg banana peels were grinded to pieces and left for pre-fermentation for 22 days. 1 kg
of cow dung along with six and half liter of water and half a liter of cow urine were
mixed. In this case also, polystyrene was used for insulation and it was kept in warm
room. The pH chart showed following result up to the thirty-first day after installation.
The maximum temperature was 22°C and minimum was 19°C during the experiment.
Figure 6.9: Temperature and pH Profile for Plant V
In first week, in total 110 gm of CaO was added two times. During first 15 days, gas was
collected and analyzed twice; first time in seventh day, and second time in thirteenth day.
Total 110 gm of CaO was added two times in the first week so that sharp fall of pH could
be reduced.
62
8.118.2
24 28 28 29.4 29.8 30.2 29.6
76.2
63.5 59.855
49.5 48.2 47.5 44.2 45.2
0102030405060708090
0
0.5
1
1.5
2
2.5
7th 13th 20th 26th 30th 34th 36th 38th 41st
Volume in litres
Day
Volume
Gas collected in LMethane %
%
Following chart shows the gas collected.
Figure 6.10: Volume Profile for Plant V
The methane content was found high and carbon dioxide content low than previous feeds.
The methane content has gradually increased and carbon dioxide content has gradually
decreased. The volume of gas obtained was rather fluctuating in pattern. In total, nine
times the gas was collected. A total of 15.91 L was obtained till 41st day. The maximum
methane content was observed 30.2 % in 38th day. The complete collection of gas
couldn’t be done due to time limitation.
63
CHAPTER SIX
FINANCIAL ANALYSIS
6.1 Introduction
The general approach for carrying out the economic and financial analysis follows the
conventional practice where benefits and cost streams are first estimated on a common
basis. For a project to be feasible and viable, the benefits should be more than the costs.
Financial analysis is the most commonly used tool that helps to decide whether a benefits
by installing a biogas plant and if so, by how much. The basic underlying assumption for
financial analysis is people will adopt a new technology only if they expect it to have a
positive impact in their financial situation.
In financial analysis, all costs and benefits are valued from the point of view of the user
for whom this is being done. Since, this analysis is undertaken before making a decision
to install the plant, it is important to ensure that all costs and benefits are estimated as
they are most likely to be realized by the user after the plant installation. (FAO, 1996)
6.2 Major Parameters for the Financial Analysis
The major parameters that need to be considered for the financial viability of biogas
plants are discussed below. The parameters are evaluated only for the batch digester
considering 60 days life for a batch which means six batches a year. The volume of gas
per batch is considered to be 18 litres per batch of useful gas.
6.2.1 Project Life and Salvage Value
According to American-Eurasian Network for Scientific Information, the life of the
continuous kitchen waste based Biogas Gas Holder is over 10 years and that of the batch
digester is above 5 years. However, the economic life of the batch plant is assumed 5
years mainly because any cost or benefits accrued after 5 years will have insignificant
value when discounted to the present worth.
64
The salvage value of biogas plant is not generally included in the benefit stream of
financial analysis because after 5 years of operation, the plant or its parts will not be
resalable.
6.2.2 Benefits or Inflows
The benefits of biogas technology are as follows:
6.2.2.1 Fuel Saving
Benefit of a biogas plant is realized by the family in terms of the cost avoided in
purchasing firewood and/or kerosene. It is generally estimated that if the biogas plant is
not constructed, a wood fuel cooking stove in rural areas or kerosene stove in semi urban
or urban areas will be constructed to meet the coking energy demand of the household.
So the saving on these fuels is considered as benefit due to biogas plant construction.
6.2.2.2 Emission Benefits
In addition, these cooking stoves emit gases, which contribute to the green house gas
(GHG) effects, where as biogas plant is considered as a clean source of energy in terms
of air pollution and GHG emissions. An added benefit is thus attributed to biogas plant by
allocating a benefit equal to the equivalent amount of greenhouse gases that would be
emitted by an equivalent thermal plant considering the quantity of GHG emissions and
proxies for the environmental cost of those emissions. Although the bio-slurry produced
from the biogas plant reduces the CH4 and N2O emission for replacing cooking fuels and
the household consumption of chemical fertilizers, these emissions are not counted for
benefits in the project.
a. Emission Reduction from Biogas Plant
The constructed biogas plant is mostly used for cooking. The major contribution for the
GHG emission reduction is through the switching of wood fuel in rural area and kerosene
in semi urban or urban area. Study conducted on the GHG emission reduction potential
shows that, in an average each biogas plant helps to reduce seven tones CO2 equivalent
65
per year (BSP-N). The GHG emission and emission factors due to the combustion of
various fuels are shown on table 6.1.
Table 6.1 Emission Sources and Emission Factors for Various Fuels
Emission
Sources GHG/Process
Emission
Factor CO2 eq Sources
Kerosene CO2 from burning 2.41 kg/l 2.41 kg/l IPCC,
1996.
Fuel wood
CO2 from burning 1.83 kg/kg 1.83 kg/kg IPCC,
1996.
CH4 from burning 3.9 g/kg 0.0819 kg/kg
Smith
et.al.,
2000.
b. Benefits Estimation
Benefits of the biogas plant are estimated by the saving on alternate fuel used for cooking
purpose and emission reduction benefits are considered. Wood fuel and kerosene are
considered for the replacement of biogas.
• Alternate fuel saving benefits
Cost of alternative fuel = Caf
Annual saving of alternative fuel = Maf
Annual fuel saving benefit = Caf x Maf
• Emission Benefits
CO2 emission from fuel wood
Emission factor = 1.83 kg CO2/kg of fuel wood.
CH4 emission from fuel wood
66
Emission factor = 3.9 g CH4/kg of fuel wood
GWP of CH4 = 21 tCO2eq/tCH4.
CO2 emission from kerosene
Emission factor = 2.41 kg CO2/l kerosene
Overall emission factor per each fuel= CO2 emission from alternate fuel
saving in tCO2eq + CH4 emission
from alternate fuel saving
Transaction cost of CO2 = $ 7/tonCO2eq
Emission benefit = $ (Annual CO2 emission reduction (tons) x 7)
6.2.2.3 Valuation of Slurry
Slurry from a biogas plant is known to have better influence on soil and its productivity
compared to the use of fresh or composted dung. During the process of anaerobic
digestion, some enzymes and vitamins are produced. Also, bio-chemical composition of
some of the nutrients such as nitrogen is changed and becomes more readily available for
plants.
The money value of such benefits depends on whether the slurry is actually used and the
benefits realized by the particular user for whom the financial analysis is done. The value
of slurry cannot be included in the financial analysis as the potential increase in crop
yield is not actually realized by the use of slurry. However, it should be noted that slurry
has a potential to increase the income or saving of a farmer and needs to be considered
whenever it is very likely that the actions will be taken to realize such benefits. Such
possible benefits should not be included in the financial analysis until there is a strong
reason to believe that such opportunity will actually be realized by the user in a definite
time frame in the future. So, valuation of slurry is not taken for benefits.
67
6.2.3 Costs or Outflows
There are various costs which should be considered for the valuation purposes. Since
only batch digester is considered for the financial analysis, therefore only cost accrued for
the batch digester is taken into account.
6.2.3.1 Investment cost
The investment cost is initial cost to construct the whole biogas plant. It includes
• Cost of materials
• Cost on pipes and appliances
The cost of construction of the biogas plant of 0.2m3 is detailed in APPENDIX B. The
total plant cost is N.Rs.3,026 for the continuous plant and N.Rs.520 for the batch
digester. However, transport cost of material, pipes and appliances are excluded.
6.2.3.2 Operation and Maintenance (O and M) Cost
The Operation and Maintenance cost includes the labor, time and use of resources like
kitchen waste, feeding it in digester, and collect necessary water. In addition to the time
spent on O and M, additional cost may accrue in changing gas valves and pipes and
procuring technical support services from biogas companies. This cost is estimated as
N.Rs. 20.
The operation and maintenance costs for the batch digester includes the time required to
prepare slurry for charging, recharge the digester, and make arrangement for the supply
of the gas produced to the burner.
6.2.4 Cash Flow Analysis
The basic procedure of a cash flow analysis is to enter all the year-by-year income to be
received over the estimated life of the project as inflows. Similarly, yearly expenditures
are entered in the analysis as outflow. Finally, for each year, expenditure is deducted
from the income. The result thus arrived at is the net cash flow or net benefit. Generally,
in the initial period of the project, the net cash flow tends to be negative, because of the
expenditures incurred to meet the establishment costs.
68
6.2.5 Net Present Worth (NPW) Criterion
As the costs and benefits of a project are spread over the useful years of project life, they
need to be discounted so that all values could be compared to the value of a single year.
The discounted net cash flow will provide a widely used criterion for measuring the
profitability of a project. For this purpose, all purpose, all future values are discounted to
make them equivalent to the present value and is expressed as Net Present Worth (NPW)
or Net Present Value (NPV) which determines whether or not the project is an acceptable
investment.
The basic procedures for applying the present worth criterion to a typical investment
project are (Park, 2002)
• Determine the interest rate that the firm wishes to earn in its investments. This
interest rate is called as Minimum Attractive Rate of Return (MARR).
• Estimate the service life of the project.
• Estimate the cash inflow for each period over the service life,
• Estimate the cash outflow over each service period.
• Determine the net cash flows
• Find the present worth of each net cash flow at the MARR. Add up these present
worth figures, their sum is defined as the project’s NPW.
PW(i)= ∑An/(1+i)n
Where PW(i)= NPW calculated at i
An= Net cash flow at the end of period n
i=MARR
n= Project life
• A positive NPW means that the equivalent worth of the inflow is greater than the
equivalent worth of the outflows. This means the project makes a profit.
If PW(i)>0, accept the investment.
69
If PW(i)=0, remain indifferent
If PW(i)<0, reject the investment.
6.2.6 Internal Rate of Return (IRR)
Internal Rate of Return (IRR) is defined as the discount rate which makes the NPW of the
project equal to zero. In other words, IRR is that discount rate which makes the
discounted benefits of the project equal to its discounted costs. The decision rule for the
simple project is as follows:
If IRR>MARR, accept the project.
If IRR=MARR, remain indifferent
If IRR<MARR, reject the project
6.3 Result of Financial Analysis
The detail calculations of financial analysis for the substitution of firewood and Kerosene
are shown in APPENDIX I. In this calculation NPV, IRR and Payback period are used as
financial indicators.
Table 6.2 Financial Evaluation of the Biogas Plant for Kitchen Wastes
The result of financial analysis indicates that the batch type biogas plant feeding kitchen
wastes is not feasible for both firewood and kerosene because the NPW is negative and
the IRR is far less than the opportunity cost in the capital market which is about 10 %.
And, also the NPW for the kerosene is less negative than the NPW for firewood.
Name of substituted fuels
NPV,
N.Rs.
IRR,
%
Payback periods,
yrs:month
Firewood -606.43 - -
Kerosene -601.59 - -
70
CHAPTER 8
LIMITATIONS
1. The temperature fluctuation was the major parameter for the biogas plant. It
couldn’t be controlled properly although various insulations were applied.
2. The temperature was fairly low when the project was initiated. It hampered the
biogas formation process. The suitable temperature is considered as 35°C (Rai,
1996). In the months; November, December, January and February; the ambient
temperature ranged from below 5°C to 29°C. The room temperature was about
15°C and less.
3. The pH analysis was made with pH paper. So, the intermediate data couldn’t be
generated.
4. The biogas was collected through downward displacement of water of pH 5. The
pressure was fairly high. The report hasn’t accounted for the carbon dioxide
mixing with water and has considered it as negligible.
5. The comparative analysis of biogas production from different feeds couldn’t be
done as similar set of circumstances couldn’t be maintained in those plants.
6. The survey couldn’t be carried with greater sample population.
7. During financial analysis, the financial benefits of wastes like slurry and others
couldn’t be quantified. The 200 L biogas plant couldn’t be financially analyzed.
71
CHAPTER 9
RECOMMENDATIONS AND CONCLUSION
9.1 Recommendations for the 200L Plant Design
a. There was water loss due to seepage in the joints of outlet pipe. This is due to the
movement of the pipe in pressure. So, the outlet pipe should be connected with
screw thread system.
b. Better insulation and heating system could be provided with techniques like
trombe wall or solar hut.
9.2 Recommendations for the High Biogas Generation from Kitchen Wastes
a. Further study could be carried out by adjusting suitable values of the factors like
C/N ratio, pH value and temperature by available methods.
b. The banana peels, potato peels, and rice could be used for better production of
biogas.
c. Enough pre-fermentation time; preferably 15 to 20 days will lead to better yield.
d. The use of hydrolytic enzymes can be used to accelerate the biogas production.
9.3 Recommendations for the Further Study
a. Feasibility study of other bio-degradable wastes from kitchen wastes can be done. In
this project work the results show that there is production of biogas using kitchen
wastes like rice, banana and potato wastes. Other degradable wastes may also have
sufficient gas production potential. The mixed kitchen wastes also can be tried.
b. Comparison of bio-slurry produced from vegetable wastes and that produced from
other composting methods like aerobic composting, vermi-composting for use as a
fertilizer can be done.
c. The pH level at low temperature was found difficult to control. The constant heat
providing mechanism during winter time using other wastes at considerable price can
be studied for.
72
9.4 Conclusion
Average daily production of the Kitchen wastes from homes of middle class and lower
middle class per head of Kathmandu valley is 0.468 kg per head per day.
The 20 L water jar was used for the study of biogas generation from some of the kitchen
wastes. Batch digestion was used and 0.5 to 1 kg of cow dung was used in different
plants. Existing slurry was tried, not to be used to find the real potential of each
individual feeds.
The methane content by volume in the biogas was observed low whereas the carbon
dioxide content was fairly high. This can be justified with fluctuating temperature, low
ratio of base diameter to depth of the jar, and not enough pre-fermentation. However in
the plant V, the pre-fermentation time was more, temperature fluctuation was less; which
in the end yielded higher percentage of methane content.
The pH at first was observed to be decreased and then increased after some days. The
acetogenesis followed by methanogenesis can be accounted for this. The generation of
biogas increased, reached maximum value and gradually decreased with time. This is due
to decreasing availability of feed for the methanogens, as the feed was provided in a
single batch only.
However the rice, potato (cooked), and banana peels produced higher volume of biogas.
The cabbage fairly lacked the potential than these three. The Maximum methane (CH4)
percentage of Potato was 38.5%, Rice was 44.8% and that of banana was 30.2%.
Gas was burned freely and gently with blue flame when methane concentration of gas
was greater than 32%.
It can be concluded that use of rice, potato, and banana peels help to yield greater volume
of biogas.
The financial analysis of the 20L biogas plant using kitchen wastes was not found
feasible. This was due to insufficient production of gas from small batch. The experiment
showed that the practical implementation of producing biogas is somewhat difficult.
73
REFERENCES
• Karki, Dr. A.B., Shrestha, Prof. J.N., and Bajgain, S., 2005, Biogas as Renewable
Source of Energy in Nepal Theory and Development, Biogas Support Program
(BSP), Nepal.
• Rao, C. S., 2000, Environmental Pollution Control Engineering, New Age
International, India.
• Park, C.S., 2002, Contemporary Engineering Economics, 3rd Edition, Prentice Hall of India Pvt. Ltd., New Delhi, India ISBN: 81-203-2143-X.
• Aryal, S., 2006, “Study of generation of biogas from cattle dung and grasses”, M.Sc. Thesis in Renewable Energy Engineering, Department of Mechanical Engineering, Tribhuvan University, Nepal.
• Bajgain, S., 2003, "Biogas in Nepal- Development, Opportunities and Challenges", Processing of International Conference on Renewable Energy Technology for Rural Development, 12-14 October2003, Kathmandu, Nepal.
• Dhakal, N. R., 2002, “Microbial Digestion of Vegetable and Kitchen Wastes for Biogas Production”, M.Sc. Thesis, Central Department of Microbiology, Tribhuvan University, Nepal.
• Tiwari, G. N. and Ghosal, M. K., 2005, Renewable Energy Resources Basic principles and Opportunities, Narosa Publication, India.
• Dhakal, N. R., Patrabansh, S., Karki, A. B., Sharma, A. P. and Adhikari, S., 2003, "Use of Vegetable and Kitchen Wastes as Alternative Feedstocks for Biogas Production", Processing of International Conference on Renewable Energy Technology for Rural Development, 12-14 October2003, Kathmandu, Nepal.
• Tamrakar, P.M., Palikhel D.R., Maharjan D., 2006,Project report on Puxin biogas
• Movie-Appropriate Rural Technology Institute (ARTI)
• http://www.biogasworks.com - Microbes in AD.
• http://www.engineeringtoolbox.com/fuels-higher-calorific-values-d_169.html
• http://www.lpgforyou.com/physical.htm
• http://www.nepalnews.com/weather.htm
• http://www.topsaving.com
74
• www.artiindia.com (Appropriate Rural Technology Institute- India )
• www.barc.com (“Nuclear Agriculture and Biotechnology Division" of BARC)
• www.wikipedia.com
• www.hedon.com
• www.cst.net
• www.webhop.org
• www.methanetomarkets.org
• www.kriegfisher.com
• www.library.witpress.com
• www.bt.com
• www.pcret.gov.pk
75
APPENDIX- A
Photos
Continuous Feed Digester Plant
Alternative Design (20 L Jar- Batch Type)
Insulated System (Heater)
Insulation by Styrene Foam and Hot Water Pool
Pressure Gauge to Check Gas Pressure inside
Plant
Gas Analyzer
Cork
Gas outlet pipe
InletOutlet
Digester
76
APPENDIX B
Construction Procedure of 20L Jar Biogas Plant
1. Inserting glass and aluminum tubes
2. Placing it in the mouth of the jar
3. Placing thermometer inside aluminum
tube dipped inside slurry
4. Attaching plastic tube with glass tube
77
APPENDIX C
Physiological Properties of Constituent Gases of Biogas
Gas Specific Gravity1
Odor Color Min %
Max %
MIO2 (ppm)
MAC3 (ppm)
Concentration4 (ppm)
Exposure5 Period (min)
Physiological6 Effects
NH3 0.6 sharp pungent
none 16 - 53 100 - Irritant 400 - Irritation of
throat 700 - Irritation of
eyes 1,700 - Coughing and
frothing 3,000 30 Asphyxiating.
Could be fatal.
CO2 1.5 None None - - - 5,500 Asphyxiant 20,000 Safe 30,000 Increased
Breathing 40,000 Drowsiness,
headache. 60,000 30 Heavy,
asphyxiating breathing
300,000 30 Could be fatal.
H2S 1.2 Rotten Smell
none 4 46 0.7 20 Poisonous. 100 60 200 60 500 30 1000 -
CH4 0.5 none none 5 15 - - 500,000 - Asphyxiate Headache, nontoxic
Note:
1. Specific gravity is the ratio of the weight of pure gas to standard atmospheric air. If number is less than one, the gas is lighter than air other wise it is heavier.
2. MIO in expanded form is the Minimum Identifiable Odor which is threshold odor, i.e. the lowest concentration (highest dilution) level that enables detection.
3. MAC in expanded form is the Maximum Allowable Concentration which is the concentration prescribed by the health authorities at the maximum allowable in atmosphere in which people can work during 8-10 hour period. These levels need be lower in confinement units as animals stay in such environment continuously for 24 hours.
4. Concentration in parts of the pure gas in million parts of atmospheric air. For changing the concentration to percent by volume, the listed number is to be divided by 10,000.
5. Exposure period is the time during which effects of noxious gas are felt by an adult human being or an animal (especially pig) of about 150 lb weight.
6. Physiological effects are those that occur in adult human beings; similar effects would be felt by animal weighing 150 lb, lighter animals will be affected sooner and at lower levels, heavier animals at later times and higher concentrations.
Source: Hills, D.J., Firbank, W.C., Methane Generation from Agricultural Wastes, A Report, Department of Agricultural Engineering, University of California, Davis, Jan, 1979.
78
APPENDIX D
Biogas plant-GGC 2047 Model and Dimensions of Different Components of Various Sized Bio-Gas Plants
79
APPENDIX E
Gas Collection through Downward Displacement of Water
1. Filling the known volume of measuring cylinder
2. Not letting the water of cylinder to escape
3. Placing the cylinder vertical
4. Adding water in trough
5. Letting gas pipe in the cylinder
80
6. Opening the cork and letting the gas inside measuring cylinder
7. Continuing the gas flow
8. Towards the end- checking the volume occupied by gas
81
APPENDIX F
Survey Formats and Reports
No. of house where survey carried out: 13 1. Format of questionnaire Kitchen waste survey: Date (ldlt): Name (gfd): No. of Family members (kl®jf®sf ;b:øfx¿sf] ;+Vøff): Address (7]ufgf): CONSUMPTION (daily): (b}lgs vkt) in kg
i. Rice(eft): ii Vegetables (t®sf®Lx¿ ):
a. b. c. d. e. f.
iii. Fruits (kmnk'mnx¿) a. b. c. d. e.
iv. Others( cGøf):
Per Day Quantity of waste (Ps lbgdf lg:sg] efG5fsf] kmf]xf]®x¿) S.N Name Kg I II III IV V VI VII
82
2. An example of filled questionnaire
Kitchen waste survey: Date (ldlt): 15 March 2009 Name (gfd): Bidya Devi shakya No. of Family members (kl®jf®sf ;b:øfx¿sf] ;+Vøff): 7 Address (7]ufgf): Ombahal, kathmandu CONSUMPTION (daily): (b}lgs vkt) in kg
ii. Rice(eft): 1 ii Vegetables (t®sf®Lx¿ ):
a. Potato 0.3 b. Cabbage 0.3 c. Mustard 0.4 d. Cauliflower 0.3 e. Reddish 0.2
iii. Fruits (kmnk'mnx¿) a. Banana 1 b. Apple 0.5 c. Papaya 1 d. Carrot 1
v. Others( cGøf):
Per Day Quantity of waste (Ps lbgdf lg:sg] efG5fsf] kmf]xf]®x¿) S.N Name Kg I Rice 0.2 II potato 0.02 III cabbage 0.03 IV Mustard waste 0.2 V VI
83
3. Table: Consumption of Food
S.N
Family
No. of family members (ni)
Consumption(in Kg)
Food(in Kg) Fruits(in Kg)
rice
potato
Pumpkin
Cabbage
mustard
spinach
Radish
banana
orange
apple
carrot
papaya
grapes
1 1 4 1.5 0.2 1.0 0.5 0.5 0.5 0.5 0.3 0.4 0.5 0.3 0.5 0.2 2 2 7 `2 0.5 1.0 0.5 0.4 - 0.5 - 1 0.5 1 - 3 3 9 2 0.5 - 1.0 0.5 0.5 - 1 - 1 1 1 - 4 4 17 4 2 - 2.0 0.6 0.6 1.5 1.0 1.0 1 0.5 - 0.5 5 5 4 1.5 0.25 - 0.25 - 0.3 - 0.3 0.3 0.3 - - - 6 6 4 0.5 0.2 0.2 0.2 - 0.5 0.2 0.3 - 0.5 - - 0.2 7 7 3 0.5 0.25 - 0.1 0.25 - 0.25 0.3 - 0.5 0.5 - - 8 8 3 0.5 0.5 - 0.25 0.5 0.3 0.2 0.2 9 9 6 2 0.5 - 0.5 - 0.5 0.5 0.5 0.5 1 0.5 - 0.5 10 10 6 1.6
6 0.4 0.5 0.5 1 0.4 0.5 - - 0.3
11 11 4 1 0.2 0.25 0.5 - 0.5 - 0.5 0.4 - - - 0.5 12 12 3 0.6 0.15 0.3 0.5 0.3 0.5 13 13 7 2 - - 0.3 0.5 0.3 - 1 0.3 0.2 ∑
ni=77
Note: The blank spaces or hyphen (-) represents nil consumption.
84
4. Table: Production of Waste
S.N Family Production (in Kg) Total Waste(Xi)
(ni*xi)
Food (in Kg) Fruits (in Kg)
Rice Potato peel
Mustard roots
Cabbage cover
Tea waste
Banana cover
Apple waste
Papaya cover
1 1 0.1 0.01 0.1 0.02 0.01 0.1 0.01 0.1 0.45 1.8
2 2 0.05 0.01 0.1 0.05 0.01 0.2 0.02 0.1 0.54 3.78
3 3 0.02 0.01 0.15 0.05 0.02 0.3 0.02 0.1 0.67 6.03
4 4 0.05 0.02 0.1 0.05 0.01 0.2 0.015 - 0.445 7.565
5 5 - 0.025 - 0.05 - 0.1 0.01 - 0.185 0.74
6 6 0.01 0.02 0.1 0.05 - 0.1 0.01 - 0.29 1.16
7 7 0.1 0.01 0.1 0.05 - 0.1 0.01 - 0.37 1.11
8 8 0.1 0.01 - 0.05 0.01 0.1 0.005 - 0.275 0.825
9 9 0.1 0.01 0.15 0.05 0.05 0.2 0.02 - 0.58 3.48
10 10 0.1 0.01 - 0.05 - 0.15 0.01 - 0.32 1.92
11 11 0.05 0.01 - 0.04 0.02 0.2 - 0.32 1.28
12 12 0.02 0.03 0.03 0.05 -
-
0.2 -
0.33 0.99
13 12 0.3 0.1 0.05 0.3 0.01 - 0.76 5.32
∑=1.00 ∑=0.175 ∑=0.93 ∑=0.61 ∑=0.13 ∑=2.25 ∑=0.14 0.3 ∑ni*xi 36
Weighted mean method: X=∑(xi ni)/∑ ni Where, xi = weight of waste ni = no. of family X = 36/77 = 0.468 kg waste per day Therefore, per head waste = 0.468 kg per day
85
APPENDIX G
Gas Production, Temperature and pH Data for Different Plants 1. Plant I (Banana) Days temperature pH
1 18 6 2 16 6 3 15 5 4 15 5 5 15 4 6 15 4 7 15 4 8 15 4 9 15 4
10 15 4 11 15 4 12 15 4 13 15 4 14 15 4 15 15 4 16 15 4 17 15 4 18 15 4 19 15 4 20 15 4 21 16 4 22 19 3 42 12 3 43 11 3
2. Plant II (Cabbage) Days temperature pH
1 18 6 2 18 5 3 18 4 4 17 4 5 15 4 6 15 4 7 15 4 8 16 4 9 18 4
10 18 4 11 15 4
29 12 4 30 11 4 31 12 4 32 13 4 33 12 4 34 14 4 35 15 4 36 14 5 37 14 5 38 14 5 39 14 5 40 14 5 41 16 5 42 14 5 43 14 5 44 14 5 45 14 5 46 14 5 47 14 6 48 14 6 49 14 6 50 14 6 51 14 6 52 14 6 53 14 6 54 14 6 55 16 6 56 25 6 57 25 6 58 25 6 59 25 6 60 28 6 61 28 6 62 28 6 63 20 6 64 25 6 65 27 5 66 24 5 67 29 5 68 19 5 69 19 5
86
3. Plant III (Rice) Days Temperature pH
1 19 6 2 20 5 3 22 4 4 25 4 5 30 4 6 23 4 7 24 4 8 25 4 9 24 4
10 20 4 11 28 4 12 25 4 13 24 4 14 23 4 15 28 4 16 25 4 17 17 4 18 25 4 19 25 4 20 25 4 21 30 5 22 31 5 23 19 5 24 18 5
25 19 5 26 19 5 27 18 6 28 18 6 29 18 6 30 19 6 31 17 6 32 18 6 33 18 6 34 18 6 35 19 6 36 18 6 37 18 6 38 18 6 39 18 6 40 18 6 41 18 6 42 18 6 43 19 6 44 19 6 45 20 6 46 19 6 47 21 6 48 21 6 49 20 6
50 20 6 51 20 6 52 20 6 53 21 6 54 20 6 55 19 6 56 19 6 57 18 6 58 19 6 59 20 6 60 20 6 61 20 6 62 21 6 63 20 6 64 20 6 65 20 6 66 20 6 67 21 6 68 21 6 69 20 6 70 20 6 71 20 6 72 21 6
Days
Volume in litre
CO2 %
CH4 %
23 1.35 85.3 0.2 24 2.23 78 0.1 25 5.04 90.1 0.6 27 7.9 89.2 0.5 28 6.16 87 0.2 29 7.03 83.5 0.1 48 2.73 86.2 4.3 49 3.06 83.4 6.8 51 2.23 87.5 8.1
53 1.74 85.2 9.5 54 1.25 86.2 10.8 55 1.7 83.5 11.2 56 1.51 81.7 14.3 57 1.41 80.2 15.2 58 2.56 78.6 18.1 59 1.82 74.4 22.3 60 2.05 72.2 24.2 61 3.85 65.5 34.2 62 1.78 63.1 35.4 63 2 62.8 36.2
64 1.32 59.4 37.5 65 1.9 53.2 38.9 66 1.22 46.4 36.4 67 0.6 36.3 37.8 68 1.18 36.2 38.6 69 0.52 40.4 36.8 70 0.92 38.6 37.2 71 0.65 34.2 37.6 72 0.9 35.5 44.8
87
4. Plant IV (Potato)
Days Max. temperature
Min temperature
pH
1 20 20 6
2 20 19 5
3 20 18 4
4 20 19 4
5 20 19 4
6 19 18 4
7 19 18 4
8 19 19 4
9 19 18 4
10 19 18 4
11 19 18 4
12 18 18 4
13 18 18 4
14 18 17 4
15 18 17 3
16 18 17 3
17 20 19 4
18 21 21 4
19 22 21 4
20 22 21 5
21 22 22 5
22 22 21 5
23 21 20 5
24 21 20 5
25 22 21 5
26 23 22 5
27 23 22 6
28 22 22 6
29 22 22 6
30 22 22 6
31 23 22 7
32 22 21 7
33 22 21 7
34 21 20 7
35 21 20 7
36 21 20 7
37 21 20 7
38 21 21 7
39 21 21 7
40 21 21 7
41 21 20 7
42 21 21 7
43 21 21 7
44 21 21 7
45 21 20 7
Days Volume in litre CO2 % CH4 %
21 5.49 91.3 5.1
22 1.6 85.4 6.8
26 1.36 86.2 6.9
28 2.42 89.8 7.1
29 1.73 90.9 7.9
30 1.93 89.5 8.1
31 5.1 78.6 16.1
32 5.45 74.6 23.4
33 5.65 59.9 25.6
34 5.82 54.5 26.4
36 5.67 52.8 34.8
38 1.65 52.4 38.5
39 0.85 54.9 34.5
40 0.83 53.4 32.8
41 0.36 51.3 33.4
42 0.38 49.6 22.4
43 0.4 50.4 24.6
44 0.35 50.2 23.1
45 0.53 65.6 28.2
88
5. Plant V (Banana) Days Min temperature Max. temperature pH
1 20 20 6 2 20 20 5 3 20 20 5 4 20 20 5 5 20 19 4 6 19 20 6 7 19 19 6 8 19 20 6 9 19 20 6
10 19 20 6 11 19 20 6 12 18 20 6 13 18 20 7 14 18 20 7 15 18 20 7 16 19 21 7 17 20 21 7 18 21 21 7 19 21 22 7 20 21 22 7
21 21 22 7 22 21 22 7 23 21 22 7 24 21 22 7 25 21 22 7 26 21 22 7 27 21 22 7 28 21 22 7 29 21 22 7 30 21 22 7 31 21 22 7 32 21 22 7 33 20 21 7 34 20 21 7 35 20 21 7 36 20 21 7 37 20 21 7 38 20 21 7 39 20 21 7 40 20 21 7 41 20 21 7
Day Gas collected in L Methane % CO2 %7th 0.95 8.1 76.2 13th 1.63 18.2 63.5 20th 2.05 24 59.8 26th 1.85 28 55 30th 1.93 28 49.5 34th 2.2 29.4 48.2 36th 1.4 29.8 47.5 38th 1.8 30.2 44.2 41st 2.1 29.6 45.2
89
APPENDIX H
Cost Details
1. Details of the cost of Continuous plant
(200L Drum)
2. Details of the cost of 20 l JAR batch
digester plant.
S.N. Components Cost in Rupees
1. Jar 300
2. Rubber cork 30
3. Delivery tube 20
4. Aluminium tube 25
5. Level pipe 15
6. Lime(CaO) 20
7. Thermometer 90
8. pH paper 20
Total cost
Rs. 520
S.N. Components Cost in Rupees
1. Drum 1600
2. Door bent 344
3. Elbow 54
4. Nipple 60
5. PVC pipe 235
6. M-seal 40
7. PVC seal 140
8 Covering plastic 125
9. Gas cork 128
10. Pressure gauge 150
11. Ph paper 110
12. Straw 20
13. Teflon tape 20
Total cost
Rs. 3026
90
APPENDIX I
Financial analysis for the substitution of firewood and kerosene
1. Financial analysis for the substitution of firewood
Investment cost of biogas plant (excluding instruments for testing) (N.Rs.) 395 Discount rate (%) 10% Efficiency of biogas stove measured at CES lab (%) 62.01% Cost of wood(N.Rs./kg) 6 Calorific value of wood (K. Cals. /Kg.) (www.lpgforyou.com/physical.htm) 4300 Efficiency of wood stove 13.5% Calorific value of biogas (MJ/m3) 18.855 Cumulative Energy for one year (MJ) 2.064 Service life (yrs) 5 Minimum attractive rate of return of investment (MARR, %) 10 Carbon dioxide emission (kg CO2/kg of fuel wood) 1.83 Methane emission ( g CH4/kg of fuel wood) 3.9 GWP of methane (t CO2 eq/tCH4) 21 Transaction cost of CO2 (N.Rs./tCO2 eq-yr) $7
Rupees /$ as on 15th march 2009 81.16
Annual CO2 Reduction Due to Biogas Plant = (CO2 emission from fuel wood saving + CH4 emissions from fuel wood saving) in tCO2eq
Year
Cash outflows Cash inflows Net Cash Flow
Ending Balance
Investment Interest O and M Net Cash Fuel Saving Carbon Trading Net Cash Cost Amount Cost Outflow Benefit Benefit Inflow
0 395 0 0 395 0 0 0 -395 -395 1 39.5 20 59.5 3.15 0.57 3.72 -55.78 -450.78 2 39.5 20 59.5 3.15 0.57 3.72 -55.78 -506.56 3 39.5 20 59.5 3.15 0.57 3.72 -55.78 -562.34 4 39.5 20 59.5 3.15 0.57 3.72 -55.78 -618.12 5 39.5 20 59.5 3.15 0.57 3.72 -55.78 -673.9
NPV(N.Rs.) = -606.43
91
2. Financial analysis for the substitution of kerosene
Investment cost of Biogas Plant.(excluding instruments for testing) (N.Rs.) 395
Discount rate (%) 10
Efficiency of biogas stove measured at CES lab (%) 62.01 Cost of kerosene(N.Rs./l) (NOC's ex-depot prices, 2006 March) 50 Calorific value of kerosene (kJ/l) (www.engineeringtoolbox.com) 35,000 Efficiency of Kerosene Stove 38.0%
Calorific value of biogas (MJ/m3) 18.855 Cumulative Energy for 1 Year 2.064
Service life (yrs) 5
Minimum attractive rate of return of investment (MARR, %) 10
Carbondioxide emission (kg CO2/l of kerosene) 2.41
Transaction cost of CO2 (N.Rs./tCO2 eq-yr) $7
Annual CO2 Reduction Due to Biogas Plant = CO2 emission from kerosene saving in tCO2eq
Years Cash outflow Cash inflow
Net Cash Ending Investment Interest O and M Net Cash Fuel Saving Carbon Trading Net Cash Cost Amount Cost Outflow Benefit Benefit Inflow Flow Balance
0 395 0 0 395 0 0 0 -395 -395 1 39.5 20 59.5 4.866 0.132 4.998 -54.502 -449.502 2 39.5 20 59.5 4.866 0.132 4.998 -54.502 -504.004 3 39.5 20 59.5 4.866 0.132 4.998 -54.502 -558.506 4 39.5 20 59.5 4.866 0.132 4.998 -54.502 -613.008 5 39.5 20 59.5 4.866 0.132 4.998 -54.502 -667.510
NPV(N.Rs.) = -601.59
