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i
DESIGN OF A KITCHEN WASTE BASED
MINI BIO-GAS UNIT FOR A SCHOOL:
“A Case Study of St. Henry’s College
Kitovu”
ORTEGA IAN
2015.
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KYAMBOGO UNIVERSITY
FACULTY OF ENGINEERING
DEPARTMENT OF MECHANICAL AND PRODUCTION ENGINEERING
DESIGN OF A KITCHEN WASTE BASED MINI BIO-
GAS UNIT FOR A SCHOOL: “A CASE STUDY OF ST. HENRY’S
COLLEGE KITOVU”
A Project Report Submitted to the Department of Mechanical and Production Engineering of
Kyambogo University as a Partial Fulfillment for the Award of Bachelor of Engineering in
Mechanical and Manufacturing Engineering.
By
ORTEGA IAN
(11/U/11049/EMD/PD)
Supervisor:
MR. SSEMPEBWA RONALD
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DECLARATION
I Ortega Ian declare to the best of my knowledge and belief that this Report is purely my original
project work under the supervision of Mr. Ssempebwa Ronald unless otherwise as stated in the
references. It has never been presented or submitted to any institute of higher learning for the
award of any academic qualification.
Signed……………………..
Date………………………..
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DEDICATION
This project proposal is dedicated with special appreciation to my two mothers, Florence
Ndagire, Elizabeth Birabwa and my late father, Kevin Aliro Ogen.
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ACKNOWLEDGMENTS
First and foremost, great thanks go to the Almighty God because without His mercy and Love,
that He has enabled me write this Report.
I would like to extend my appreciation to everyone who enabled me directly or indirectly to
successfully complete this Report.
I wish to express my sincere gratitude to my project supervisor, Mr.Ssempebwa Ronald, for his
great supervisory role during the preparation of this Report document especially for willingly
giving his time and attention without withholding anything from me.
I would also like to thank the following lecturers who have gave me assistance; Dr. Ssengonzi
Bagenda and Ms. Akello Lilian.
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ABSTRACT
Majority of Ugandan Schools use firewood for cooking (Oluka, 2014). The same schools also
have a good number of kitchen waste generated per day from the students. The researcher carried
out a study that designed a kitchen waste based bio-gas unit for a School that will see the school
better manage its kitchen and food waste and in return reduce the costs spend in procuring
firewood (Ainebyoona, 2014).
Firewood is very costly as a source of energy, both to the environment and to the school. Yet
coupled with this, is the lack of an efficient way for schools to dispose of their kitchen waste and
its proper management. The production of biogas from kitchen waste thus ensures an efficient
way of managing kitchen waste and also offsets some of the costs incurred from the procurement
of firewood for cooking (Fulford, 1988).
The objectives of the study were to study the different existing biogas digester technologies. The
study also determined the sizes of different components for the most efficient digester and
established the rational design specifications of the most efficient design. A financial evaluation
for the appropriate design for extracting biogas from Kitchen waste was carried out. The research
employed quantitative data analysis and was carried out for a period based on a planned work
schedule.
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TABLE OF CONTENTS
DECLARATION ............................................................................................................................. i
DEDICATION ................................................................................................................................ ii
ACKNOWLEDGMENTS ............................................................................................................. iii
ABSTRACT ................................................................................................................................... iv
TABLE OF FIGURES .................................................................................................................. vii
CHAPTER ONE: INTRODUCTION ............................................................................................. 1
1.1 Background ...................................................................................................................... 1
1.2 Historical Background of Biogas Technology In Uganda ............................................... 2
1.3 Problem Statement ........................................................................................................... 3
1.4 Objectives of the Study .................................................................................................... 4
1.4.1 General Objective ..................................................................................................... 4
1.4.2 Specific Objectives ................................................................................................... 4
1.5 Research Questions .......................................................................................................... 4
1.6 Scope of the Study............................................................................................................ 4
1.6.1 Geographical Scope .................................................................................................. 4
1.6.2 Subject Scope ............................................................................................................ 4
1.6.3 Time Scope ............................................................................................................... 4
1.7 Justification of the Study .................................................................................................. 4
1.8 Significance of the Study ................................................................................................. 5
CHAPTER TWO: LITERATURE REVIEW ................................................................................. 6
2.1 Introduction ...................................................................................................................... 6
2.2 Introduction To Biogas..................................................................................................... 6
Process of Biogas Production ...................................................................................................... 6
Hydrolysis ................................................................................................................................ 6
Acetogenisis............................................................................................................................. 6
Methanogenesis ....................................................................................................................... 7
Factors Affecting Biogas Generation .......................................................................................... 8
2.3 Bio Digester Models In Uganda ....................................................................................... 9
2.3.1 Floating Drum Digester ............................................................................................ 9
2.3.2 Fixed Dome Digester (CAMARTEC Design) .......................................................... 9
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2.3.3 Plastic Digester Designs ......................................................................................... 10
2.3.4 A Bio Digester Model Of Interest ........................................................................... 11
2.4 Design specifications In the Production of Bio Gas ...................................................... 13
CHAPTER THREE: METHODOLOGY ..................................................................................... 15
3.1 Overview ............................................................................................................................. 15
3.2 Research Design .................................................................................................................. 15
3.3 Data Source ......................................................................................................................... 15
3.3.1 Primary Sources ............................................................................................................ 15
3.3.2 Secondary Sources ........................................................................................................ 15
3.4 Data Collection Methods ..................................................................................................... 15
3.4.1 Use of Interviews .......................................................................................................... 15
3.4.2 Observation ................................................................................................................... 16
3.4.3 Library Research and Use of Internet ........................................................................... 16
3.4.4 Comparative Analysis Method ..................................................................................... 16
3.5 Design Parameters (James Kuria, 2008) ............................................................................. 16
3.8 Data Processing, Presentation and Analysis ....................................................................... 18
CHAPTER FOUR: PRESENTATION AND DISCUSSION OF FINDINGS ............................. 19
4.1 Overview ............................................................................................................................. 19
4.2 Digester Model For Consideration and Ranking................................................................. 19
4.3 Available Feedstock/Waste In The School ......................................................................... 21
4.3.1 Kitchen Waste ............................................................................................................... 21
4.3.2 Animal Waste ............................................................................................................... 23
4.3.3 Human Waste ............................................................................................................... 23
4.4 Energy Needs/ Requirements of The School ...................................................................... 23
4.5 Design of a Digester To Produce Biogas ............................................................................ 24
4.5.1 Two Cases Of Digesters For Consideration ................................................................. 26
4.5.2 Design Formulas: .......................................................................................................... 27
4.6 Final Design ........................................................................................................................ 28
4.7 Economic Analysis .............................................................................................................. 30
CHAPTER FIVE: ......................................................................................................................... 32
CONCLUSION AND RECOMMENDATIONS ......................................................................... 32
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5.0 Conclusions .................................................................................................................... 32
5.1 Recommendations .......................................................................................................... 32
REFERENCES ............................................................................................................................. 33
APPENDIX ................................................................................................................................... 35
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TABLE OF FIGURES
1 Uganda National Household Surveys (UNHS)............................................................................ 2
2 Composition of Biogas ................................................................................................................ 6
3 C/N Ratio of Some Organic Materials ......................................................................................... 7
4 Weighting Table......................................................................................................................... 20
5 School Menu .............................................................................................................................. 21
6 Foodwaste Generated Over 7 day period ................................................................................... 22
7 Energy Requirements of The School ......................................................................................... 24
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CHAPTER ONE: INTRODUCTION
1.1 Background
According to the ministry of Education, Uganda has at least 22,500 primary schools
(government-owned and private) and at least 2,000 secondary schools. If each of the schools
uses at least 12 trucks of firewood annually to feed its charges, then Uganda is effectively
losing a small forest to raise at least 294,000 trucks of firewood, assuming all the schools had
at least 700 leaners (Education, 2009).
Uganda has a forest cover of nearly three million hectares or 15.2 per cent of its total land
mass, according to recent statistics from the Food and Agriculture Organisation (FAO). It
should be more, if it was not for the fact that between 1990 and 2010, Uganda lost 37.1 per
cent of its forest cover, or about 1.8 million hectares (Mongabay, 2000) .
Currently, Uganda loses 2.2 per cent of its forest cover per year, with officials attributing the
losses mostly to encroachment on forest land for farming or settlement due to a high
population growth, as well as cutting of trees for fuel wood like firewood and charcoal.
Because most schools in Uganda really on firewood for their energy requirements as far as
cooking and heating of water are concerned, this poses a major problem for the environment
and the health risks involved in cooking using firewood. Thus, schools are playing an indirect
role in the depletion of forests, while at the same time posing a risk to those who cook and
those in the vicinity of the kitchens where firewood is the means of fuel.
Yet with all these problems, schools have a lot of Kitchen waste at the end of the day to
dispose. The increasing quantities of waste lead to increased threats to the environment as
already witnessed in town areas and cities.
Firewood and charcoal are still the most commonly-used sources of energy for cooking even
in Ugandan households. According to the Uganda National Household Survey Report
2009/2010, up to 95 per cent of the households still used wood fuels (GovUGA, 2012).
―Firewood was most commonly used by the rural household (86 per cent) while charcoal is
commonly used by urban households [70 per cent],‖ said the report. ―It is worth noting that
the proportions of households that used electricity for cooking was still very low which could
be due to the high tariffs charged per unit.‖ Biogas production from Kitchen waste presents
itself as a cheaper and safe alternative.
Household consumption of firewood and charcoal (Mill. Shs)
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Table 1 Uganda National Household Surveys (UNHS).
Item 1996/97 2002/03 2005/06 2009/10
Charcoal 4,076 6,936 9,345 98,699
Firewood 13,967 20,677 23,425 310,440
Total 18,043 27,613 32,770 409,139
Table shows the value of household expenditure on firewood and charcoal as estimated from
the Uganda National Household Surveys (UNHS). The total nominal value increased to
409.1 billion in 2009/10 from Shs. 32.8 billion in 2005/06. The value of charcoal and
firewood consumption went up by more than 10 times during the same period.
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 (Klinghoffer, 2013) (Young, 2010)
Thus, generating biogas from kitchen waste achieves many goals. First, the schools are able
to reduce on the costs spent on energy. Secondly, the threat on the environment caused by
deforestation is reduced. The other point is that the health risks imposed by cooking with
firewood are minimized and lastly, the byproducts after the production of biogas with kitchen
waste act as a good fertilizer thus increasing agricultural production. We also don’t forget,
thus in the end, it becomes easy for schools to utilize their kitchen waste in an efficient way
that saves them money. A recent study commissioned by the Global Village Energy
Partnership (GVEP) in (Uganda’s) Wakiso district shows that schools spend up to 400,000
UGX (US$158) per month on fuel for cooking meals and heating water, with urban schools
spending twice this amount. Thus an average secondary school spends at least Shs.4 million
per term for the cost of 4 trucks on firewood required to cook the school means (Afedraru,
2014). This puts significant strain on the school. Producing biogas from kitchen waste is one
important step towards the re-allocation of school funding for more productive uses.
1.2 Historical Background of Biogas Technology In Uganda
The first biogas plant in Uganda was built by the Church Missionary Society in Mbarara
district in the early 1950s and emphasis was on treatment of sewage (Odogola, Wilfred 1992,
p.2). In the 1960s, some missionaries built one demonstration plant in Kotido district
(Kikuuma, Andrew 2001, 2). However, the first documented study that was very extensive
was a PhD thesis by Boshoff (1969/70) then based at Makerere University. This digester
built at Kabanyolo Farm did generate gas but it didn’t go outside Kabanyolo (Simoga, Zap,
2000, 56). In 1974, Silverman made a baseline study of biogas in the central region of the
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country and recommended biogas as viable in Uganda (Odogola, Wilfred 1992, p.2).
Although Silverman made the recommendation, implementation was never reached due to
the unfavourable political climate at the time (Kikuuma, Andrew 2001, 2).
In 1985, the Chinese biogas team carried out a feasibility study and concluded that the
technology was most viable in small-scale private diary farms with easy access to feedstock
(Odogola, Wilfred 1992, p.3). In 1989, the government showed interest in the technology
and several demonstration farms were constructed in Karamoja district (Kikuuma, Andrew
2001, 2). FAO carried out another study sanctioned by the Ministry of Energy, which led to
the creation of the National Biogas programme in Uganda. They recommended a Chinese-
type design to be built at secondary schools as a bio-latrine using cow-dung but with
possibilities of incorporating human manure. A number of secondary schools consequently
received these plants and these include Budo, Namagunga, Mwiri and Tororo Girls.
In the early 90s, an estimated 120-170 biogas units were constructed in the country. Out of
these, probably 50%-60% are still operational (Odogola, Wilfred 1992, p.3).
Of all these studies in Uganda, none of the remarkable studies have been made regarding use
of kitchen waste. 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. However, none have been using the other organic wastes for this
purpose. 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 (Lama, 2013). When applied, it will
benefit the schools in Uganda 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 (Abbasi, 2011)
1.3 Problem Statement
Firewood is very costly as a source of energy, both to the environment and to the school. Yet
coupled with this, is the lack of an efficient way for schools to dispose of their kitchen waste and
its proper management. The production of biogas from kitchen waste thus ensures an efficient
way of managing kitchen waste and also offsets some of the costs incurred from the procurement
of firewood for cooking.
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1.4 Objectives of the Study
1.4.1 General Objective
To design a Kitchen-waste based mini-bio gas unit for St. Henry’s College Kitovu, a secondary
school in Masaka District of Uganda.
1.4.2 Specific Objectives
To study the different existing biogas digester technologies.
To determine the rational design specifications of the most efficient design
To do a financial evaluation for the appropriate design for extracting biogas from Kitchen
waste.
1.5 Research Questions
What forms of biogas digester models are being used at the moment?
What are the rational design specifications that will optimize the production of the
biogas?
How long will it take for a biogas unit for benefit the school as far as the investments are
concerned?
1.6 Scope of the Study
1.6.1 Geographical Scope
The project confined itself to St.Henry’s College Kitovu, a secondary school in Masaka
District.
1.6.2 Subject Scope
The main focus of the design of an appropriate kitchen-waste based bio-gas unit was
limited to the design concepts and calculations and the computer aided drawings of the
digester components.
1.6.3 Time Scope
The project was conducted with in a period of seven months that is from November to
May 2014/2015. From this time after approval of the design concepts and procedures, then the
preparations for fabricating the digester may be done.
1.7 Justification of the Study
1. There is lack of proper management of Kitchen Waste in Most Schools
2. The Cost of firewood impacts greatly on the school expenditure, yet alternative sources of
energy such as electricity from the main-grid are very expensive (G. Oelert, 1987).
3. Cooking with firewood results in indoor air pollution. Indoor air pollution is widely
recognized to be a ubiquitous problem linked with the burning of solid biomass fuels inside the
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kitchens. ―Use of inefficient fuel wood stoves promotes uncontrolled exposure to smoke leading
to a growing number of respiratory disorders.
1.8 Significance of the Study
Mitigation of forest depletion, biodiversity impact, CO2 emissions and global warming
all of which are associated with firewood as a source of energy. A single biogas unit is
estimated to directly help conserve 3 tons of fuel wood annually through fuel switching,
resulting in substitution of unsustainably harvested biomass and maintenance of forest
habitat, with associated biodiversity benefits and local benefits to soil stability and to the
dry season stream flows in the region (Khoiyangbam, 2011). Since fuel wood is generally
harvested unsustainably, this reduction translates into the prevented release of 5.5 tons of
carbon dioxide into the atmosphere annually from an average biogas digester, resulting in
environmental benefits from a reduced contribution to global warming and associated
impacts (Nijaguna, 2006).
Schools will be able to save on energy costs from firewood. The design can also be
adopted for homes as a substitute for charcoal, LPG, and electricity purchases for
cooking and lighting in urban and peri-urban areas (Sasse L, 1991).
Improved health from indoor environment in Kitchen because of substitution of wood
with biogas because of its smoke-free odour nature.
The spent waste material that emerges at the end of the biogas process, the slurry, is a
high nutrient organic fertilizer that surpasses raw manure, and can be applied either
directly or in conjunction with composted agricultural residue (Journal, 2011). If
composted properly, the slurry will give higher fertilizer yields and increase overall crop
yield and production, thereby augmenting income and restoring soil fertility in areas
where soil degradation is prevalent; simultaneously, as it replaces chemical fertilizers, the
slurry saves the money previously spent on chemical fertilizers (Discussion, 2012).
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CHAPTER TWO: LITERATURE REVIEW
2.1 Introduction
This chapter reviews the literature of the different biogas extraction mechanisms, process of
biogas production and the biogas potential of different feeds and appropriate conditions for peak
levels from these feeds.
2.2 Introduction To Biogas
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. (Rai, 2009)
2 Composition of Biogas (Ref: www.wikipedia.org)
Substances Symbol Percentage
Methane 50-70
Carbon dioxide 30-40
Hydrogen 5-10
Nitrogen 1-2
Water Vapor O 0.3
Hydrogen Sulphide Traces
Process of Biogas Production
There are three steps or the process involved in the production or the activity of the gas
(Mudhoo, 2012).
Hydrolysis
Acetogenisis
Methanogenesis
Hydrolysis
It is the first step involved in the process also known as the liquefaction. In this process the
fermentive bacteria converts’ insoluble complex organic into the soluble organic compound and
also complex polymer is converted into the simple monomer. (World, 2008) 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. (Mathur AN and Rathore, 1992)
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). (Mathur AN and Rathore, 1992)
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The reaction involve is
GlucoseEthanol + Carbon dioxide
Methanogenesis
Methane is produced by the action of the bacteria called methanogens bacteria. There are two
methods of the 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. (Mathur AN and Rathore, 1992)The reaction involve in this
process are:
Acetic ( ) Methane ( ) + Carbon dioxide ( )
Ethanol + Carbon dioxide Methane + Acetic acid
Carbon dioxide + Hydrogen Methane + Water
3 C/N Ratio of Some Organic Materials (Ref: www.norganics.com)
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
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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. (Mathur AN and
Rathore, 1992)
• 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. (Mathur AN and
Rathore, 1992)
• 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. (Mathur AN and Rathore, 1992)
• 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. (Mathur AN and Rathore, 1992)
• 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. (Mathur AN and Rathore, 1992)
• 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. (Mathur AN and
Rathore, 1992)
• 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. (Mathur AN and Rathore, 1992)
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• Pressure: It has been reported that better production of biogas takes place at
lower pressures. (Mathur AN and Rathore, 1992)
2.3 Bio Digester Models In Uganda
2.3.1 Floating Drum Digester
In this design, the digester chamber is made of brick
masonry in cement mortar. A mild steel drum is placed
on top of the digester to collect the biogas produced
from the digester (Walekhwa, 2009). Thus, there are
two separate structures for gas collection and
production. With the introduction of the fixed drum
plant, the floating drum plants have become obsolete in
the country due to a comparatively high investment
and maintenance costs, along with other design
constraints. (Bikash Pandey, 2007)
2.3.2 Fixed Dome Digester (CAMARTEC Design)
This is the most widely used in the country and is known as the CAMARTEC design named for
the government research institute in Arusha, Tanzania where it was first developed. It consists of
an underground brick masonry compartment (fermentation chamber) with a dome on top for gas
storage. Here the dome and the fermentation chamber are combined as one unit. This has
eliminated the costlier mild steel gas holder (floating drum type) which is susceptible to
corrosion (Bikash Pandey, 2007).
(Bikash Pandey, 2007) 2
(Bikash Pandey, 2007) 1
10
(Bikash Pandey, 2007) 3
2.3.3 Plastic Digester Designs
This design consists of a digester bag made of thick gauge polythene tube between
0.5 and 1.0 meter in diameter which is placed in a trench. The inlet and outlet are
typically made with 4 inch diameter PVC pipes tied at the end of the digester bag
with rubber bands from car tubes (Ilukor, 1986). Gas produced is collected in a
separate reservoir ―balloon‖ also made with a polythene tube. Gas is carried from the
digester first to the balloon then to the kitchen with half inch PVC plastic pipe. The
reservoir balloon is hung down from a beam and gas pressure is maintained by tying
brick weights to its end.
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One of the organizations that was actively promoting these designs was Integrated
Rural Development Initiative (IRDI). The designs were costing around Shs.340,000
including the cement channel constructed for the slurry to flow. These bio plants
turned out to be less popular than expected. Problems coupled with them included
low gas pressure, and correspondingly slow cooking times and insufficient brightness
of lights. Users also found that there was frequent clogging both at the inlet and outlet
pipes. However the biggest problem was the fragility of the polythene bags which
lasted no more than three years with some being damaged within six months. The
plastic membrane could easily be punctured by sticks or pointed stones and could also
be damaged by cows or other animals inadvertently stepping on them or easily
sabotaged by disgruntled neighbors (Bikash Pandey, 2007)
(Bikash Pandey, 2007) 5
2.3.4 A Bio Digester Model Of Interest
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). (Bikash Pandey, 2007)
Operation
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
12
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. (Bikash Pandey, 2007)
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. (Bikash Pandey, 2007)
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.
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• 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. (Bikash Pandey, 2007)
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.
• Since heat insulation is not considered, it cannot be used in region where weather
fluctuates more. (Bikash Pandey, 2007)
2.4 Design specifications In the Production of Bio Gas
Each of the following describes the factors that must be taken into consideration in generating
the final design of the bio-gas digester that’s appropriate for the purpose (Singh, 2008).
1. Physical Conditions
The performance of a biogas plant is dependent on the local conditions in terms of
climate, soil conditions, the substrate for digestion and building material availability. The
design must respond to these conditions. In areas with generally low temperatures,
insulation and heating devices may be important. If bedrock occurs frequently, the design
must avoid deep excavation work. The amount and type of substrate to be digested have a
bearing on size and design of the digester and the inlet and outlet construction. The
choice of design will also be based on the building materials which are available reliably
and at reasonable cost. (Bikash Pandey, 2007)
2. 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. (Bikash
Pandey, 2007)
3. Strength (pressure holding capacity): R.B.C and G.I. sheet has got high pressure
bearing capacity than polythene drum. (Bikash Pandey, 2007)
4. 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. (Bikash Pandey, 2007)
5. Durability: Durability of R.B.C is higher than polythene drum and G.I sheet.
6. 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.
14
7. 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. (Bikash Pandey, 2007)
8. Cost: R.B.C and G.I sheet fabrication cost is higher than Polythene drum.
15
CHAPTER THREE: METHODOLOGY
3.1 Overview
This chapter contains how the research was conducted and the major description of the methods
which was used to obtain data, tools and instruments used in the design of the kitchen-waste
based biogas unit.
3.2 Research Design
The research of this project was designed basing largely on the study of different biogas
production mechanisms with greater attention to the ―above-ground‖ designs, factors that affect
biogas production and digester design parameters and considerations to achieve efficient output.
3.3 Data Source
In this design, research was based on both the primary and secondary sources of information
3.3.1 Primary Sources
This was directly obtained from different players in the bio-gas energy industry in Uganda,
various designs already in use in different homesteads and in schools. This data is efficient in
that it offers adequate information as it centers on the live events from the field through
interviews.
3.3.2 Secondary Sources
This data type was obtained from mechanical engineering text books like mechanical
engineering design, related designs. Other sources to be included are the previous reports done
already by colleagues in the same field of engineering. The secondary sources were from text
books, reports, journals, articles from books of professional engineers and the use of internet.
The data in the literature review is intended to highlight on what other scholars had disposed in
relation to the research study.
3.4 Data Collection Methods
The researcher employed the use of interviews and the observation method, as instruments for
data collection.
3.4.1 Use of Interviews
The interviews were structured, for instance asking each informant (cooks, students and school
authorities) similar questions, all rotating around energy requirements and waste generated so as
to get the total capacity and select how much biogas can be generated per hour. The reliability of
information gathered will be of high essence since similar questions will be asked to many
different key players and this will give in-depth information about particular cases of interest to
me. However, am anticipating that the research may be limited by the responses given, because
the respondents might assume that they are under investigation hence being cautious.
16
On the other hand informal interviews were used where non structured questions will be
followed but a frame work of key points around which investigative discussions were built. It
was used to gather information from lecturers and design Engineers. This method was used to
gather information about the prices of the materials and some devices involved in the design
from which financial analysis of the design will be established. Some of the questions to students
included how much food waste every student gives out per day and how much firewood is used
per day and the equivalent of this as far as biogas requirements.
3.4.2 Observation
Through the on-site observation, the data in relation to the operation kitchen waste based biogas
design was collected. This helped me to know the quantity of kitchen waste generated per day
and hence formed a basis for the choice of the energy output and efficiency for this design.
3.4.3 Library Research and Use of Internet
This acted as a supplementary method of information gathering. It was used to crosscheck the
information and constants got using other techniques. Here, I dug deep to get more clear
information about the background of the study and the other design concepts. This kind of
research involved the use of technical reports, personal documents, project dissertation reports
and design journals and surfing from the internet.
3.4.4 Comparative Analysis Method
This method was used to compare the different oil extraction types used in industries and at
home based on their functional requirements and effects.
The sizes of the components for the biogas unit and the design specifications were determined by
the use of Calculations and formulas. These formulas about the design were got from text books
and design manuals.
They were used in establishing the financial analysis of the biogas unit design that were chosen
for example calculating the payback period.
Computer aided design programs like solid works and AutoCAD were used to develop the
drawings for the unit components.
3.5 Design Parameters (James Kuria, 2008)
Design Parameter Weighting Factor (1-5)
Physical Conditions 2
Availability 4
Capacity (Gas Production) 5
Strength (Pressure Holding Capacity) 5
Leakage 1
Durability 5
Fabricability 2
Cost 4
17
Maintenance and Servicing 3
Safety 5
Human Factors 4
From the Weighting Factor table shown above, it is evident that some design specifications
heavily outweigh and hold more importance than others. The design specifications that had a
weighting factor of five, therefore being of utmost important, are capacity, product cost, safety,
durability, human factors, health issues, and environmental conditions. As a result, those design
specification were be always considered when choosing a final design.
Objectives, Methods of data collection and their Description.
S/N Objective Method of data
collection
Description
1 To study the different existing
biogas digester models in Uganda.
Desk Research They was used to obtain data
concerning different literature
that exists when it comes to
digesters currently in use in
Uganda.
Observation This provided first-hand data on
the advantages and
disadvantages of the different
digesters.
Interviews This provided data about the
different digester models in
Uganda.
2 To determine the rational design
specifications of the most efficient
design
Desk Research
and Observation
Using internet and books, the
dimensions of the different
components of the digester were
determined
3 To do a financial evaluation for the
appropriate design for extracting
biogas from Kitchen waste.
Desk research
and Interviews
Using internet and books, the
payback period and the return on
investments were calculated.
18
3.7 Tools used for data collection
• Use of computer aided engineering design tools such as solid edge and solid works
software to develop engineering drawings , components and a model
During the process of data collection, the following tools were employed in attaining data that is
vital for the analysis of the design parameters of the various components of the biogas digester.
a) Trolley-type weighing scale (Scale with accuracy of up to 1000Kgs); this will be used
in the determination of the weight of the food waste generated per day.
b) Tape measure (Scale with accuracy of up to 15 Metres); this was vital in the
determination of the dimensions (lengths and breadths) of the gas holder and slurry tanks.
c) A Timer (accuracy of up to seconds); this was used to measure the time required to
cook food and heat water.
3.8 Data Processing, Presentation and Analysis
The data from respondents was collected, recorded and discussed for the better choice of the
design specifications.
The method applied in the analysis was quantitative in nature; interview responses and that got
through observation noted. After collecting of this data, it was analysed extracting meaningful
information hence easing the establishment of the financial analysis.
The process of data analysis mainly constituted of two major processes and they include; editing
and tabulation.
Editing involved crosschecking errors and omissions in the instruments in order to ensure
accuracy, uniformity and completeness. I ensured that each of the research instruments was clear,
logical and hence achievement of comprehensive responses.
Tabulation was the last stage of data processing where counting and adding of all answers to
particular questions about production capacities was done for the whole study. It involved
allocating individual answers of individual respondents to particular questions. Under tabulation,
computer packages were used like EXCEL to handle the quantitative data processing.
19
CHAPTER FOUR: PRESENTATION AND DISCUSSION OF FINDINGS
4.1 Overview
This chapter presents the findings on the different studies made, the various components
considered in the design of the kitchen-waste based biogas digester and the intended design
under study.
4.2 Digester Model For Consideration and Ranking
Weighting factors were evaluated for the different biogas digesters currently in use in Uganda.
These were based on the design parameters under consideration. These were the 11 design
parameters upon which each digester model was ranked;
Physical Conditions
Availability
Capacity (Gas Production)
Strength (Pressure Holding Capacity)
Leakage
Durability
Fabricability
Cost
Maintenance and Servicing
Safety
Human Factors
As stipulated from the methodology, each of these carried a specific weight from 1 to 5
according to how important it was in the design. Results from the tabulated analysis are shown
below for the four different biogas digester designs.
20
4 Weighting Table
Floating
Drum
Digester
Carmatec
(Fixed
Dome)
Plastic
Digester
Design
ARTI
Physical
Conditions
0 2 0 0
Availability
4 4 4 4
Capacity
(Gas
Production)
0 5 0 0
Leakage
0 0 1 1
Durability
0 5 0 5
Fabricability
2 2 2 2
Cost
4 4 4 4
Maintenance
and
Servicing
0 3 0 0
Safety
5 5 5 5
Human
Factors
0 4 0 4
Strength
(Pressure
Holding
Capactity)
0 5 0 5
TOTAL 15 39 16 30
Note: A 0 here means it fails to meet the required specifics, it doesn’t imply the absence of such
a quality, but simply implies that is scores low on that end.
According to the ranking system, CARMATEC which is a Floating Drum Digester design is the
best upon which to base our design scoring 39, ARTI comes it closely at 39 while the other two
designs score very low at 15 and 16 respectively thus ruling them out for design consideration.
CARMATEC is chosen as the final choice for the following reasons. It has a 24 hour biogas
output (maximum gas output daily) which is appropriate for the energy needs of the school. It
can sustain very high pressures. In addition, it has a service free maintenance for over 30 years.
21
4.3 Available Feedstock/Waste In The School
It was found out that the waste in the school was of three major types;
Kitchen Waste
Human Waste
Animal Waste
4.3.1 Kitchen Waste
Kitchen waste is made up of the following:
Food Waste/ food leftovers
Waste Water
Peelings (Matooke, Sweet potatoes etc)
This included the food leftovers from the servings of Breakfast, Lunch and Supper. Data here
was collected for a period of 7 days in order to get an accurate estimate of the average waste
generated per day.
The School Menu is as below
5 School Menu
Days Breakfast Lunch Evening Tea Supper
Monday Soya and Sugar
in porridge
accompanied
with a bun
Posho, fried
beans and
cabbages (fried)
Bla
ck T
ea
Posho and fried
beans
Tuesday Soya and Sugar
in porridge
accompanied
with a bun
Posho and fried
beans
Rice (pan oiled)
and fried beans
Wednesday Milk and Sugar
in porridge
accompanied
with a bun
Posho, fried
beans and friend
cabbages
Posho and fried
beans
Thursday Soya and Sugar
in porridge
accompanied
with a bun
Posho and fried
peas
Posho and friend
beans
Friday Milk and Sugar
in porridge
accompanied
with a bun
Posho and fried
beans
Rice (pan oiled)
and fried beans
Saturday Soya and Sugar Sweet Posho and fried
22
in porridge
accompanied
with a bun
potatoes/posho,
fried beans and
fried cabbages
beans
Sunday Milk and Sugar
in porridge
accompanied
with a bun
Matooke with
G.nuts or rice
with meat
Posho and fried
beans
After a 7 day survey, the following was noted;
6 Foodwaste Generated Over 7 day period
All In Kilograms TOTAL TOTAL
FOOD
WASTE
PER
DAY
Breakfast Lunch Supper
Monday
50 180 170 400 Cooked
3 15 10 28 143 Uneaten
40 40 35 115 Leftovers
Tuesday
49 180 290 519 Cooked
5 10 2 17 122 Uneaten
36 34 35 105 Leftovers
Wednesday
50 180 182 412 Cooked
5 12 15 32 153 Uneaten
40 41 40 121 Leftovers
Thursday
51 180 180 411 Cooked
4 13 15 32 149 Uneaten
40 35 42 117 Leftovers
Friday
50 180 290 520 Cooked
5 10 3 16 125 Uneaten
39 40 30 109 Leftovers
Saturday
49 160 160 369 Cooked
3 30 30 63 172 Uneaten
35 34 40 109 Leftovers
Sunday
50 290 185 525 Cooked
5 5 29 39 154 Uneaten
40 35 40 115 Leftovers
TOTAL
FOOD
WASTE IN
A WEEK
1018
23
AVERAGE
FOOD
WASTE
145.4
It is thus established that a total of 1018kg of food waste is generated per 7 days. This gives an
average of 145.4kg of food waste per day.
4.3.2 Animal Waste
The school has a farm that consists of pigs and cows.
COWS PIGS TOTAL animals
NUMBER 3 36 37
BIOGAS YIELD
*For Pig Slurry (0.25-
0.50 per kg)
*For Cattle Slurry
(0.20-0.30 per kg)
3*0.20=0.6cubic
metres of biogas per
day
36*0.25=9 cubic
metres of biogas per
day
TOTAL YIELD 0.6 + 0=9.6 cubic metres of biogas per day
4.3.3 Human Waste
The school is made up of 1100 students. According to the complete biogas handbook, the daily
biogas yield from a human being weighing 50kg is 0.028 of biogas per day taking the daily
amount of excrement to be 0.50kg and that of urine to be 1kg. Thus 1100 students can produce at
least 30.8 of biogas per day.
4.4 Energy Needs/ Requirements of The School
The energy needs are divided into three categories:
Cooking needs
1100 students require 0.3 *1100=330 of gas per day. Thus, to meet the cooking
requirements, the system must be designed to meet this capacity.
Heating
Lighting
One Lamp requires at least 0.1 /h of gas.
24
7 Energy Requirements of The School
Number Number Of Lights Biogas Requirement
Classrooms 25 4 lights (fluorescent
tube per
classroom)=4*25=100
lights
100*0.1 /h=10
Dormitories 11 6 lights 6*0.1 /h=0.6
Laboratories 4 4*4=16 lights 16*0.1 /h=1.6
Dining Hall 1 10 lights 10*0.1 /h=1
TOTAL GAS
REQUIRED 24
day
(10+0.6+1.6+1)=13.2
*24 hours=316.8
/h
Suitable digesting temperature 20 to 35 °C
Retention time 40 to 100 days
Biogas energy 6kWh/m3 = 0.61 L diesel fuel
Biogas generation 0.3 – 0.5 m3 gas/m
3 digester volume per
day
Human yields 0.02 m3/person per day
Cow yields 0.4 m3/Kg dung
Gas requirement for cooking 0.3 to 0.9 m3/person per day
Gas requirement for one lamp 0.1 to 0.15m3/h
Biogas guideline data. Adapted from WERN 1
4.5 Design of a Digester To Produce Biogas
The biogas digester design model has 8 basic components:
1. Mixing Pit or Inlet: This is where manure and water are measured and mixed before
feeding them into the digester. It is equipped with (a) sluice gate usually made of wood to
control or allow for the proper mixture of water and manure before the release of the
mixture into the digester, and (b) cover –which can be made of recycled corrugated G.I
sheet.
25
2. Inlet Pipe: This serves as a conveyor of the manure-water mixture or slurry from the
mixing pit to the digester. It is a straight slanting pipe, using prefabricated concrete
culvert 8 inches minimum inside diameter.
3. Digester/Gas Storage: This is where the slurry is allowed to ferment through bacterial
action and where gas is being stored. It is a water and air-tight structure , some features of
the digester are;
a) The flooring of the digester is concave or saucer-type where the inorganic solids and
parasite eggs settle and collect.
b) The wall is made of concrete hollowblocks with water-proofing plaster. The
inlet/outlet pipes fit midway the wall height.
c) Ring Beam, which acts as the ―foundation‖ of the dome. Made of reinforced plastic
concrete; it indicates correct slurry level when the digester is being filled initially.
The gas storage is fixed into the digester. It is that portion above the ringbeam or the space inside
the dome. The dome is made of reinforced concrete and is plastered twice and finally sealed with
paraffin or wax for complete proofing.
4. Outlet Chamber: It serves 2 important functions. (a) Where the effluent residue is taken
out; and (b) where the slurry is forced out when the gas pressure within digester/gas
storage exceeds atmospheric pressure.
The chamber consists of three parts:
(a) Outlet Pit---is circular in shape, made of concrete hollowblocks with plastering, and
having a volume to 1/3 of the volume of the digester/cylinder ( ).
(b) Outlet pipe—is prefabricated round concrete pipe with 8-inch inside diameter (same
as inlet pipe).
(c) Cover---to keep rain water, debris and children from falling into the pit. It can be
made recycled G.I. sheet.
5. Removable Manhole: It provides access to the digester for cleaning, inspection and
maintenance. It is made of concrete and is water-sealed. Asphalt material is used for
gasket seal.
6. Gas Outlet Pipe: It is located through the manhole sleeve. It is of 1-inch G.I. pipe.
7. Stirrer/Mixer: This is a mechanical device inside the digester used to stir the fermenting
slurry to stimulate gas production and to break the ―scum‖ layer forming at the surface of
the slurry. It is fabricated from G.I. pipes and flat bars. (The only component that requires
welding.)
8. Backfill: It serves to protect and insulate the concrete dome from the sun (dry and heat)
and provides rain water runoff. Soil and gravel with 70% and 30% proportion
respectively recommended.
26
4.5.1 Two Cases Of Digesters For Consideration
From available data collected; it is clear that to design a digester, there will be two cases to be
considered and upon which a choice can be made;
Case A: (Basing on Energy Requirements)
1. How much gas does the school need daily? (Overriding Consideration)
2. What digester volume is needed to produce this amount of gas?
3. How much daily volume of feedstock will be required?
4. What is the cost involved? (Feasibility/Viability Study)
In this case the biogas digester being designed must have a capacity of at least (330+316.8) m3/h
of biogas per day. Thus, to installed capacity had to be 646.8 m3 per day which is roughly
estimated to 650 m3 per day. Therefore, the researcher then set out to design a biogas digester of
the CARMATEC type with 650 m3 biogas per day.
Case B: (Basing on Available Feedstock)
27
1. How much raw materials and organic wastes are available? (Overriding Consideration)
2. What digester volume is needed to handle these materials?
3. What is the amount of gas expected?
4. How will this gas be utilized?
5. What is the cost involved? (Feasibility/Viability study)
Basing on available feedstock, the digester design must have an installed capacity of 20 cubic
metres. 9.6 coming from the livestock while the balance is met by the kitchen waste.
4.5.2 Design Formulas:
For structural stability and efficient performance, the design of a Chinese biogas model is
governed by certain mathematical formulas which are as follows:
1. h/d=1/3 That is, the diameter of the digester is three times its height.
2. /d=1/5 That is, the distance from the ringbeam to the manhole is one fifth the diameter.
3. That is, the distance from the bottom center to the wall bottom is one-tenth the
diameter.
4. =1/3 That is, the volume of the outlet chamber, is one third the slurry chamber
volume .
5. + That is, the slurry volume, Vs is equal to the volume of the digester
below the ringbeam.
6. Height of Inlet/Outlet pipes=1/2h That is, the inlet and outlet pipes are placed one-half
the height of the wall.
7. Vslurry=0.85Vt That is, the slurry volume is 85% the total digester volume, Vt.
Vdome=0.15Vt That is, the gas chamber volume (dome) is 15% of the total digester
volume, Vt. This volume relationship allows for gas pressure sufficient enough to force
the slurry to the outlet chamber.
8. Mixing pit volume should be slightly larger than the daily charge.
9. Manhole dimensions are standard for all volumes of digesters.
28
4.6 Final Design
To choose the final design, two approaches were compared (A and B). Case A would
base on the energy requirements while Case B would base on the available feedstock.
Thus, Case B was chosen as the final approach.
29
30
(Engineers, 2010)
The biogas plant size has a volume of 20cubic metres produced per day. Thus, the
components of the final design are as follows:
A. 264cm
B. 176cm
C. 233cm
D. 86cm
E. 203cm
F. 199cm
G. 293cm
H. 115cm
I. 137cm
J. 203cm
4.7 Economic Analysis
The techno-economic analysis for the project was used to evaluate the favourability and
profitability of the biogas investment project. The economic indicators considered were the
investment costs, the liquidation yield, the total operational costs, total income and revenues,
cost comparison, cost annuity comparison, profitability, static Pay Back Period (PBP), Net
Present Value (NPV) and Internal Rate of Return (IRR).
Procedure For Financial Evaluation
The procedure for financial evaluation is determined by Finck and Oelert (1985).
31
1985).
The cost of a Carmatec model in Uganda is estimated to be $1000 which is about Ugshs
3,002,000 at an exchange rate of IUSD=Ugshs3002.0.
*** The fixed dome design biogas plant has no moving or corroding parts and does not entail
significant repair and maintenance costs. Furthermore, all structures are made with masonry or
concrete and last for a very long time, unlike with tubular designs.
Payback Period=Cost of Project/Saving Per Month
Saving Per Month=Expenditure Before Installation of Biogas Plant-Expenditure After
Installation
Expenditure Per Term (3 Months):
The school uses 14 Lorries of firewood per term at a cost of Ugshs450, 000 per lorry.
This means an expenditure of Ugshs6, 300,000.
The school also uses 5000kg of briquettes which is a total of 125 bags at a cost of 4
million Uganda shillings per term.
Total expenditure on fuel per term is 6,300,000+4,000,000=Ugshs10, 300,000. A year has three
terms thus the school spends Ugshs30, 900,000 per year on fuel.
Savings Made Per Term
The school needs 330 of gas per day for cooking and heating purposes. The biogas generated
from the available feedstock is 20 per day. Percentage saved in form of gas is
⁄ *100=6.06% which is roughly estimated to 6%.
Thus 6% is saved by the school on fuel. Expressing this in a form of cash saved per term
6%* Ugshs10, 300,000=Ugshs 618,000 saved on fuel per term which comes to a saving of
Ugshs1, 854,000 per year.
Payback Period=10,300,000/1,854,000=5.55 years estimated to 6 years. Thus it will take 6
years to recover the money invested in the project.
32
CHAPTER FIVE:
CONCLUSION AND RECOMMENDATIONS
5.0 Conclusions
The project is feasible since it saves the school at least 6% on fuel expenses. And the payback
period is 6 years which implies that in 6 years the school will have recovered all the money
invested. The digester has a lifetime of 30 years thus; the excess years will be the profitable
periods assuming zero operation and maintenance costs.
• Different existing biogas digester technologies currently in use were studied. Carmatec
was found to be the most appropriate for our kitchen-waste design
• Rational design specifications and selection of the most efficient design was made.
• A financial evaluation for the appropriate design of extracting biogas from kitchen waste
was carried out. The project was found to be both feasible and viable basing on expected
rates of return and payback period of 6 years.
5.1 Recommendations
A study should be done on the biogas potentials of various kitchen and food wastes and
their combinations.
Food waste and biogas production for various digester models should be compared. This
will help in knowing which digester model really gives the best output when using food
waste.
Further study could then be carried out by adjusting suitable values of the factors like
C/N ratio, pH value and temperature by available methods.
33
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APPENDIX