Biogas in Tanzania
Slaughterhouse Waste Treatment Facility
Location:
Vingunguti Slaughterhouse, Ilala Municipal Council, Dar es Salaam, Tanzania
Partner:
Sapporo Mobi-Vet and Ilala Municipal Council, Agriculture and Livestock Department
Group Members:
Dr. Assenga Severine
Edward Silva
Matt Kallerud
Scott Moskowitz
sevaassenga@gmail.com
ejsilva@ucdavis.edu
mckallerud@ucdavis.edu
samoskowitz@ucdavis.edu
Spring 2012
Table of Contents
Introduction
3
Project Definition
3
Project Background and Literature Review
3
Expected Environmental and Socioeconomic Benefits
8
Project Methodology
10
Stakeholders Analysis
11
Results
12
Anaerobic Digester Design
14
Cost Benefit Analysis
17
Recommendations
19
References
21
Appendices
23
2
Introduction
The Ilala Municipal Council (IMC) is one of the local authorities in Dar es Salaam, Tanzania.
The council is involved in a variety of community development and income generating activities
and among these is a public slaughterhouse facility. The slaughterhouse facility faces energy and
waste management problems and accordingly the IMC has sought to create a waste treatment
facility which will manage the slaughterhouse waste while producing useful byproducts biogas
and bio-fertilizer. The biogas will be used to provide electricity to the slaughterhouse facility,
boil water. The bio-fertilizer will be used to grow vegetables and the surplus sold to farmers.
This project will greatly benefit the IMC in generating more income, creating jobs, improving
the living stands of the people in the surrounding communities, and most importantly improving
the environmental health and sanitation of the area.
Problem Definition
The goal of this report is to conduct a feasibility study that discusses, designs, and analyzes the
most economically and environmentally viable way of eliminating solid and liquid waste from
the Vingunguti slaughterhouse in Dar es Salaam, Tanzania. The suggested alternative from the
client is an anaerobic digester used to manage waste and produce biogas to be used as a source of
electricity and solid waste to be used as fertilizer. The intention of this feasibility study is not to
produce a set of definitive plans, but rather an outline, basic schematic and output data of biogas
and biofertilizer that the system will produce. Finally, this study will include a cost/benefit
analysis of the project to quantify economic feasibility and payback time to aid the policy makers
in Dar es Salaam. This study will use all available and provided data, including current
operations descriptions, waste streams, and energy and water requirements.
This project must work with respect to social, environmental, financial, and technological
aspects. The scope of this project entails the design, construction, and use of a biogas digester on
the property of the slaughterhouse. Further, the management of the biogas will be studied,
including both storage and method of power generation. Also, distribution of the digested waste
as fertilizer will be discussed. Not included in the scope of this project is the construction of a
new slaughterhouse or the management of the slaughterhouse.
Project Background and Literature Review
Tanzania Background
Tanzania is an East African country with a population of 42,746,620 (Tanzania national website)
and with a total land area of 947,300 km2. The main natural resources in Tanzania are
hydropower, tin, phosphates, iron ore, coal, diamonds, gemstones, gold, natural gas, nickel and a
high range of forests and game reserves. Its economy relies heavily on agriculture (43.3%),
fisheries (3%), industries (17.7%), and services (36%), which traditionally are featured by the
processing of agricultural, trade, tourism, agrarian, fisheries and farming products and light
3
consumer and manufactured goods. The Tanzanian GDP is estimated to be US$ 22.7 billion with
a growth rate of 6.5% and GDP per capita of US$ 548.30.
Figure 1: Map of Tanzania
Figure 2: Map of Dar es Salaam
Tanzania Energy Capacity
The Tanzanian commercial energy generation system consists mainly of hydro, thermal and coal
based generation. Hydro contributes the largest share (73% of total power generated) while gas
and thermal contribute the remaining amount. The hydro-plants are interconnected with the
national grid system which produces a total of 561 MW. Within the energy sector, the electricity
sub-sector contributes approximately 0.6% of the total energy consumption. The energy situation
in Tanzania indicates that less than 15% of the country has energy access, but in rural areas,
energy access is about 2%. Also, rural energy consumption makes up to 85% of the national
biomass energy consumption. Per capita electricity consumption is 100 KWh (versus 500 KWh
required for quality of life), but the country has abundant energy sources (largely untapped
renewable energy resources) which could be harnessed for power generation and access
expansion (Olotu, 2010). The potential solutions that are currently being developed and
implemented are the national solar and wind power programs which are developed by effort and
cooperation between governments, the private sector and NGOs which promote wider use of
renewable energy sources. The government is currently working to encourage investment in the
electricity sub-sector in order to expand its generating capacity and distribution systems while
also working to develop the local energy sources, including wind energy, solar energy, coal and
biogas.
4
Figure 3: Tanzania energy consumption
Biomass fuel can be derived from waste or byproducts from industrial or agricultural industries
such as wood waste from forestry or furniture industries; straw remains from wheat crops;
chicken litter; sewage; manure and used vegetable oil. Biomass can be converted into energy
through various methods include burning, pyrolysis (chemical decomposition through high
temperature heating in the absence of air), gasification (conversion of solids into gaseous fuel),
and anaerobic digestion (also in the absence of air, this is involves using bacteria for
decomposition and fermentation). In anaerobic digestion, sewage or manure is used to generate
biogas after feeding slurry into a digester (conversion can take from 10 days to several weeks);
this method is well established in many parts of the country with livestock (Marree et al, 2007).
The energy sector in Dar es Salaam is dominated by the public utility Tanzania Electric Supply
Company (TANESCO), and their participation will determine the viability of this project. The
on-grid energy sector in Tanzania relies heavily on hydropower, but as the energy sector of
Tanzania is dominated by the use of biomass and non-grid fuel sources, the electric corporations
are considered a sub-sector of the Tanzanian energy sector (Ahlborg et al., 2011). However, with
the Tanzanian Electricity Act of 2008, alternative public and private corporations are encouraged
and incentivized to cooperate with TANESCO for usage of transmission lines and the charging
of tariffs.
Why Biogas in Tanzania
With a GDP (PPP) of US$ 1300 per capita and 37% of the population living below the poverty
line, Tanzania belongs to the poorest countries worldwide. This is reflected in the low share of
commercial energy use; 94% of the country’s energy requirement is met by biomass, primarily
wood fuel and over 80% of the total energy consumption is used in rural areas. The high
consumption of wood fuel contributes to deforestation and soil degradation. Nearly 80% of the
national energy consumption is applied for domestic energy (cooking and lighting). Poor
households spend a considerably higher share (up to 35%) of their income on domestic energy.
5
The biogas development program in Tanzania joins well with the development intentions of the
Government of Tanzania (Kellner, 1992). Notably, a national biogas program will support
realization of government policies in the fields of energy, poverty reduction, livestock
development, rural development and SME development.
The Benefits of Biogas
The benefits of domestic biogas in energy supply, agriculture, health, sanitation, gender and
environment are well documented. Domestic biogas contributes to sustainable development and
reaching the UN Millennium Development Goals. Various aspects of well-functioning biogas
systems have multiple benefits.
Health and Sanitation Benefits
Animal dung and ruminal contents from the slaughterhouse are collected regularly and fed into
the biogas digester; this reduces pollution, leading to a cleaner slaughterhouse environment. It
also reduces human and animal disease by improving sanitary conditions related to bad
sanitation and polluted surface water and soil and reduces greenhouse gas emissions from
traditional waste handling (dump trucks, etc.)
Gender Equality and Environmental Benefits
The generated gas from biogas is a substitute for conventional fuels and therefore reduces
deforestation by reducing the demand for firewood and reduces indoor air pollution associated
with the incomplete combustion of conventional biomass fuels (which result in a reduction of
eye and respiratory illnesses, particularly of those most heavily exposed to smoke, namely
women and children). It’s also reduces workload, especially in regards to fetching firewood,
maintaining the fire and cleaning cooking pots. The use of biogas can reduce workload by 2 to 3
hours per day, particularly the workload of women and children. It reduces fuel expenses,
traditional domestic fuels are increasingly becoming part of the formal economy and provides
income generation opportunities by providing an energy source for different economic activities
such as generating electricity, pumping of water, running of machines and other farm activities
(incubators, kilns, lanterns) as a new or more efficient resource. Biogas also increases benefits of
better lighting and boiling hot water through the use of appliances such as gas lamps and water
heaters;
Agricultural Benefits
The residue of the biogas process bio-slurry is a potent organic fertilizer when used in the farms
provide a superior organic fertilizer in terms of available nutrients and soil texture, increasing
agricultural yields by 10-40% and provide a catalyst for composting other agricultural waste in
the farm and by applying this practice increases the amount and quality of organic fertilizer
(FAO, 1996). Raw waste material contains infectious pathogens, but by passing through biodigester many of these pathogens are killed. It also reduces chemical fertilizer costs of farmers
by reducing the amount of synthetic fertilizer used, encouraging organic crop production. It
6
enables farmers to participate in animal husbandry in areas in which discharge regulations would
otherwise have been prohibitive, especially by reducing odor and environmental load that result
from livestock holding.
Wastewater Treatment in Tanzania
A primary goal of this study is to determine a way to eliminate the slaughterhouse waste stream
in an environmentally viable way. Physiochemical and biological treatment is not highly
prevalent in Tanzania due to the high cost of treatment, however this anaerobic digestion system
is proposed for not only the treatment of water, but the production of biogas to subsidize the cost
of the treatment. Most wastewater treatment in Tanzania occurs in the form of constructed
wetlands, where areas are constructed to manipulate plant life and bacterial growth in such a way
that they provide a sufficient level of wastewater treatment without harm to the environment
(Mahudi et al, 2001). However as this type of treatment is area intensive and does not produce
biogas in a containable manner, it is not recommended for the slaughterhouse.
Biogas Project in Ilala Municipal Council
Ilala Municipal Council is one of the 128 Local Authorities in Tanzania and it's among three
Municipalities of grand Dar es Salaam City Council. Ilala Municipal Council (together with
citywide Authority and other two Municipalities) was officially established on 1st day of
February 2001. During that time the Ilala Municipality was given authority to own, coordinate
and develop the Vingunguti abattoir house. In 2001 the slaughterhouse was handed to the Ilala
Municipal Council, and was given the following activities: frequent rehabilitation of the abattoir,
collection of fees and revenue, ensure expert staff are available in the areas, coordinate safety
and cleanliness, and also communicate with the ministry in case of any zoonotic diseases.
Figure 4: Map of Ilala Municipal Council
with a star on Vingunguti Ward
Figure 5: Aerial view of Vingunguti
Slaughterhouse (Google Maps)
Project Background
7
The Ilala Municipal Council is intending to construct a new modern slaughterhouse in the old
Vingunguti abattoir center. At present the existing old slaughterhouse is apathetic to the
treatment of solid and liquid waste material. Ilala Municipal council intends to improve its
services to those that buy meat from outside the country. The project will be located in
Vingunguti old abattoir center in Vingunguti ward. The project site has a total area of about five
acres.
The study conducted in the areas revealed that building a new solid and liquid waste treatment
plant will tremendously improve the cleanliness of the abattoir and prevent pollution to the
surrounding environment, including nearby Msimbazi River and nearby neighborhoods. The
project will be a good source of income to the Ilala Municipal Council. The slaughter house
currently collects an income of US$ 241,250 and with a total capacity of 86,500 liters of a
mixture of solid and liquid wastes for daily slaughter of 300 cattle and 350 sheep and goats with
consumption of about 40,000 liters of clean water daily.
This project is targeting to serve Dar es Salaam City dwellers, who always claimed that the meat
produced by this slaughterhouse is not clean and that the number of cattle and goats slaughtered
per day are not enough to meet their demand. Therefore, constructing a solid and liquid
treatment plant and later building a new modern slaughterhouse will satisfy the consumer
demands and eventually will increase the revenue of the municipality. The lease rate charged to
each slaughter is US $2 for cattle and US $0.50 for goat/sheep per head.
Consequences of Inaction
In the absence of the project, the slaughterhouse waste would be left to decay at the disposal sites
anaerobically, emitting methane to the atmosphere. This process would continue due to the fact
that the slaughtering of animals would continue for the whole year and cost to maintain would be
higher and environmental pollution would continue. As far as electricity generation is concerned,
the absence of the project activity would mean a continuation of using fossil fuels from the grid
which is not reliable due to allocation caused by low supply and result in continued emissions of
CO2 to the atmosphere.
Figures 6, 7, and 8: Current method of waste disposal
Expected Environmental and Socioeconomic Benefits
Local benefits
8
The proposed project will create employment to the local residents, especially during the
construction and operation of the biogas plants. Moreover, many jobs will be created for the
youth during the construction and in providing slaughter services. This will make them busy and
keep them from indulging in crime and irresponsible sexual behavior, which may lead to the
spread of AIDS and unwanted pregnancies. It will also supply organic fertilizer to the farmers
from the slurry produced by the biogas plant at an affordable cost. This will positively impact
agricultural production and ensure food security. This will lead to more income generation to the
municipal council and also a relief to the farmers since the bio-fertilizer will be cheap compared
to artificial fertilizers. By reducing the accumulation of slaughter house waste at the disposal
sites and avoid its mixing with local water resources, the project will protect the environment and
reduce hazardous impact of slaughterhouse waste to the local people.
Global benefits
Globally, the project will contribute in preventing the anthropogenic GHG emissions by reducing
emissions of CH4 from the slaughterhouse waste disposal sites, and reducing CO2 emissions from
pile up manure and waste removal.
Socio-economic aspects
The proposed project and that of constructing new slaughterhouse are expected to increase the
income from US$ 241,250 to US$ 468,750 per year after completion and also will improve the
image of Vingunguti ward. This project will greatly benefit the Municipal council in generating
more income, creating jobs, improving the lives of the people and most importantly improving
environmental health and sanitation in the slaughterhouse area. An increase in overall income of
the municipal council will result from revenue collection as well as carbon credit trading CERs,
sale of electricity to the grid/neighbors, and avoiding purchase of electricity from the grid. This
will lead to increase in employee’s salaries and other fringe benefits. The project will necessitate
operators and municipal officers to acquire relevant skills, especially in biogas technology. These
skills would not have been acquired in the absence of this biogas project and will enable
adoption of similar technologies and processes by other slaughterhouses in the country. As the
environmental strategy/priorities of the country, Tanzania prioritizes environmental protection
and its well-being. The sustainable use of slaughterhouses waste to produce biogas will lead to a
sustainable environmental and eventually help in achieving the sustainable development in
Tanzania.
Wastewater Treatment in Tanzania
A primary goal of this study is to determine a way to eliminate the slaughterhouse waste stream
in an environmentally viable way. Physiochemical and biological treatment is not highly
prevalent in Tanzania due to the high cost of treatment, however this anaerobic digestion system
is proposed for not only the treatment of water, but the production of biogas to subsidize the cost
of the treatment. Most wastewater treatment in Tanzania occurs in the form of constructed
wetlands, where areas are constructed to manipulate plant life and bacterial growth in such a way
9
that they provide a sufficient level of wastewater treatment without harm to the environment
(Mahudi et al, 2001). However as this type of treatment is area intensive and does not produce
biogas in a containable manner, it is not recommended for the slaughterhouse.
Agriculture in Tanzania
As eight percent of the Tanzanian workforce are involved in the agricultural sector, a sector
accounting for twenty-five percent of GDP (FAO, 2012), there is considerable incentive to
provide cheap fertilizer. Along with biogas, the other primary byproduct of anaerobic digestion
is nutrient rich solid sludge commonly regarded as biofertilizer. With progress, farmers who
would be able to make more money would ideally be able to pay for some of the externalities
that their animal waste is creating for the slaughterhouse, such as unavoidable environmental
degradation of the local rivers and water sources, transportation cost of the manure, and potential
for disease spread with the proximity of wastes to raw meat processing.
Design of Anaerobic Digestion Systems
Anaerobic digestion is a process by which organic material is broken down into inorganic
material in the absence of oxygen. The end products are a reduced amount of high-nutrient
biomass as well as biogas and of course water. It is commonly used for waste stabilization in
industrial wastewater treatment plants (Tchobanoglous, Burton, & Stensel, 2003).
Three types of anaerobic digestion systems are prevalent in developing countries in Africa.
These are the floating drum reactor, the fixed dome reactor, and the plastic tubular reactor.
Floating dome reactors are designed with the top of the reactor as unfixed; it moves up and down
depending on the amount of biogas in the reactor. Fixed dome reactors are similar but the top of
the dome is fixed, and these reactors are typically built underground. Plastic tubular reactors are
similar except they are made from plastic. They are compared in Table 2.
Table 1 - Anaerobic Digestion System Comparison (Kenya, 2009)
Project Methodology
10
The methodology of completing this study was implemented in three sections. The first steps
were to create a project statement and to define the scope of what this study was to entail. This
beginning component of the project was done with the primary goal of understanding the needs
and goals of the clients. Speaking with the clients, it was understood that the primary goal of the
project was the elimination of slaughterhouse wastes and that the suggested alternative to the
current disposal method was an anaerobic digester.
The literature reviews were conducted to understand the techniques and methods of other similar
projects and to see what factors caused them to succeed or to fail. Experts from the University of
California, Davis were interviewed and relied upon to contribute practical knowledge and
scholarly advice. These contacts were exceedingly important and including student Michael
Cunningham, a D-Lab alum and student with extensive experience designing and working with
anaerobic digesters and wastewater treatment. Dr. Frank Loge of the Environmental Engineering
Department contributed his years of experience with wastewater treatment systems to discuss the
possibilities and necessities of a treatment train which would adequately serve the
slaughterhouse. The knowledge gained in this component of the project allowed the team to
define the scope of the project and what was to be delivered.
Moving forward, the team goal was to complete the deliverables that are analyzed in this report.
This involved the calculations pertaining to the suggested treatment train and gas and electricity
output. Peer reviewed literature values and current industry textbooks were utilized to estimate
the specifications of the proposed process. These outputs were then used to create a cost-benefit
analysis.
With these deliverables completed, the team was able to summarize the results of the study in
order to provide recommendations to the clients.
Stakeholders Analysis
In order to identify and assess the importance of key parties involved in the development of solid
and liquid waste treatment project option in Vingunguti slaughter house we conducted a
stakeholder’s analysis. Within this process, stakeholders were organized according to their
impact and influence levels as displayed in Table 2. “Impact” measures the degree of change
they will experience in response to the project, and “influence” measures their degree of support
for the project’s objectives.
High Impact



Low impact




Neighborhood community
Business community at
slaughter house
Political
parties
and
politicians
Transporter
Building contractors
Traders
Meat buyers






Financial institutions
Ilala municipal council
D-Lab at UC Davis
Power utility company
(TANESCO)
Staff
working
with
Municipality
Ministries related to the
sector
11

Food venders
Low influence
High influence
Table 2: Stakeholders Analysis
Stakeholders who will be highly impacted by the project and have had high influence on project
development are critical to this initiative, as they will be the primary decision makers in the
process, and thus their opinions matter most. Those stakeholders are the financial institutions and
Ilala municipal council who will be responsible to decide and provide funds for construction of
the project also D-Lab whose goal is to both design and disseminate low-cost, clean and efficient
intervention technologies in developing countries will decide on the option to be undertaken to
remove the waste from the slaughter house also the power utility company TANESCO is
responsible to purchase the excess electricity produced and to ensure grid infrastructures are
available for transmission of the electricity.
Stakeholders with high influence on the project but who receive little direct benefit are staff
working with Municipality and Ministries related to the sector like livestock, agriculture,
environment, energy and water will benefit from the project because it’s one of the key
responsible activity and should be kept informed of project developments. Those that are highly
impacted by project outcomes but have low influence, are the neighborhood community,
business community at slaughter house and political parties and politicians who suffer from odor
and environmental contamination caused by pile-up of the waste and politicians who provide
support to municipality by sensitize community to accept the project. Transporter, building
contractors, traders, meat buyers and food venders are in large numbers but have low impact, and
their influence is relatively low since their aim is to get or supply service to others, they don’t
mind about the situation existing in the slaughter house.
Essentially, the stakeholders consist of individuals, groups, and institutions as both beneficiaries
and funders. While the slaughter house customers will be impacted the most by this project, their
influence is low in the development of the biogas project, but IMC as the recipient of this
technology chosen by D-Lab as a consultancy it has a big role on the analysis and decision of the
project. Notable however, is that their decision as to whether or not to invest in the biogas project
or other alternative ultimately exposes them to the most risk, and perhaps more costs to clean the
slaughter house and therefore effort should be made to increase their involvement in this process
to analyze the feasibility of the project.
Results
The proposed treatment for treating the slaughterhouse’s waste is shown in Figures 9 and 10. The
system is a complete treatment plant for a wastewater stream. All slaughterhouse waste
materials, including wastewater blood and ruminal fluid, will be input into the anaerobic
digester.
12
As it has been assured that the waste materials have sufficiently small sized particles (less than
12 mm), no grinding or pre-processing is expected to be needed. The recommended anaerobic
digester is a low-rate anaerobic digester, meaning that heating and mixing are not required. Lowrate systems generally have residence times of 30 to 50 days compared to a high-rate system
requiring 12 to 20 days. This means a low rate system will have a higher volume, but as the
primary reason anaerobic digesters fail is due to poor maintenance and operation, the simpler
low-rate system is what is designed in this scenario.
The anaerobic digester will produce two products, biogas and digested sludge. The biogas is
collected from the digester and the sludge moves on to further treatment. Once digested, in order
to use the solids as bio-fertilizer, the effluent must go through a dewatering process. There are
several ways to do this, and it is suggested that this be explored if this project moves on into the
design phase. Currently existing technologies include centrifuges and belt presses. However,
open drying beds are also common. This method is currently done with the untreated waste on
site at the slaughterhouse, but as this waste would be more inert and lower in volatile content
after digestion as well as lower in volume, odor from hydrogen sulfide and space would not be
an issue so much as it is currently. However it is suggested that the drying pit be lined with
concrete to prevent the leaching of ammonium into the ground which nitrifies in the soil to
nitrate and contaminates aquifers and rivers.
If mechanical dewatering is utilized or a settling tank clarifier, the removed water must be treated
before it is disposed of to the river or reused as grey-water as the effluent water would be high in
both ammonium and biological oxygen demand (BOD). There are many ways of doing this but
the system generally regarded as simplest is a trickling filter. A system of two filters would be
necessary. The first filter would be utilized aerobically to nitrify the ammonium to ammonia and
then to nitrate as well as lower BOD. A second trickling filter would then be utilized anoxically
to denitrify the remaining nitrate into harmless nitrogen gas. The resulting effluent would then be
able to be discharged harmlessly to the river or used for agriculture or municipally as grey water.
From the digester the gas may be passes through the disulphuric tower where H2S is removed,
and then into a gas storage tank where the gas is stored or fed into the generator for electricity
production (Knoef, and Stassen, 1999). The excess gas can be used for boiling water or flared
using a safety flare. The residues left from the process can be dried and used as organic fertilizer
and the liquid part can be treated and used for irrigation of gardens. The biogas produced will be
used for electricity generation and powering abattoir equipment. Weerasinghe and Silva (1999)
describe two main types of electricity generation equipment to be considered for biogas power
generation:
Microturbines are small gas turbines that burn methane, mixed with compressed air. As
they burn, the hot pressurized gases are forced out of the combustion chamber and
through a turbine wheel, causing it to spin and turn the generator, thus making the
electricity (Monteiro et al, 2011).
Reciprocating gas engines that have been modified from natural gas engines but which
can handle the larger quantities of carbon dioxide and contaminants that are found in
13
biogas. They work on a much larger scale, burn efficiently, and deliver between 1MW
and 2 MW of electrical power (Ottinger, 2005).
Figure 9: Treatment Train Schematic
Figure 10: Anaerobic Digester Schematic
Anaerobic Digestion Design
Influent Waste Stream
The daily waste stream produced by the slaughterhouse includes the rumen, stomach, and
intestinal content of 300 cows and 300 sheep/goats. Several parts of the animals that are not
traditionally used are utilized, including the hides and the blood. Additionally, 40,000 liters of
water are used by the slaughterhouse daily that also enter the waste stream. The mass of solid
waste can be calculated based on known values for cattle and sheep/goats. On average, solid
waste from the slaughter of a cattle averages 83 kg and for that of a sheep/goat 2.5 kg (CED
India, 2011). Because the microorganisms in the digester only process volatile solids, this mass
14
is used in design. Slaughterhouse waste consists of approximately 30% solids, 85% of which are
volatile solids (CED India, 2011). Using these numbers, the mass of volatile solids can be
calculated.
83 𝑘𝑔 300 𝑐𝑎𝑡𝑡𝑙𝑒 2.5 𝑘𝑔 300 𝑠ℎ/𝑔𝑜
𝑘𝑔 𝑉𝑆
(
+
) ∗ 0.30 ∗ 0.85 = 6540
𝑐𝑎𝑡𝑡𝑙𝑒
𝑑𝑎𝑦
𝑠ℎ/𝑔𝑜
𝑑𝑎𝑦
𝑑𝑎𝑦
Biogas Production
The mass of volatile solids is used to estimate biogas production. Low rate systems are simpler
but more inefficient that high rate systems and have a have a relatively low biogas production
rate. Biogas production is stoichiometrically related to the mass of volatile solids destroyed. A
typical value for a low rate system is 40% volatile solids destruction. Biogas production ranges
depending on operating conditions but a typical value is 0.85 m3/kg VSdestroyed (Tchobanoglous,
Burton, & Stensel, 2003). Therefore, the biogas production can be estimated.
6540
𝑘𝑔 𝑉𝑆
𝑚3 𝑏𝑖𝑜𝑔𝑎𝑠
𝑚3 𝑏𝑖𝑜𝑔𝑎𝑠
∗ 40% ∗ 0.85
= 2,223
𝑑𝑎𝑦
𝑘𝑔 𝑉𝑆𝑑𝑒𝑠𝑡
𝑑𝑎𝑦
Biogas can be burned in a generator to produce 1.7 kWh / m3 biogas (Government of Alberta,
2008). This represents approximately 28% conversion efficiency based on a heating value of 6
kWh / m3 of biogas. The electricity generation per year can be then estimated.
2,223
𝑚3 𝑏𝑖𝑜𝑔𝑎𝑠 365 𝑑𝑎𝑦𝑠
𝑘𝑊ℎ
𝑘𝑊ℎ
∗
∗ 1.7 3
= 1,350,500
𝑑𝑎𝑦
𝑦𝑒𝑎𝑟
𝑚 𝑏𝑖𝑜𝑔𝑎𝑠
𝑦𝑒𝑎𝑟
Cost of Project
Though difficult to accurately estimate, installed capital costs are operation costs can be
estimated. One estimation for a biogas electricity generating plant is based on power production.
At 1,350,500 kWh/year operating continuously, divide by 365 and 24 to obtain power production
of approximately 150 kW. Capital costs can be estimated at $7,000/kW for the entire power
production system (digester, generator, etc) (Government of Alberta, 2008). This results in
approximately $1,000,000 installed capital costs. The same source suggests an estimation of
$0.02/kWh (year) for operation and maintenance costs. At 1,350,500 kWh/year, this results in
$27,000/ year.
An alternative cost estimation for a biogas production system is offered by Electrigaz biogas
engineering firm (http://www.electrigaz.com/). Based on waste stream inputs, they provided a
capital estimate of $1,200,000. These estimates are in line with a survey of capital costs of
biogas digesters in California (Chen, Overholt, Rutledge, & Tomic, 2010).
Neither of these costs account for the secondary treatment trickling filters recommended for
complete treatment of digester effluent. Costs can be estimated based on flow rate. This flow
rate (86,000 L/day or ~0.025 MGD) results in trickling filters that cost approximately $20,000
15
and operation and maintenance costs of $1500 per year (USEPA, 2000). This is a small price
relative to the digester and generator.
The price of $1,200,000 was multiplied by 1.5 to account for the small price of the trickling
filters, unforeseen costs, and a general cost safety factor to obtain $1,800,000. Operation and
maintenance estimates were increased to $50,000 per year for the same reasons.
Factors to consider when building a successful biogas digester
Technical
To ensure sufficient raw feedstock must be available on a long-term basis and over the whole
year, or supplies will be inconsistent and people will lose confidence in the technology. In this
case the feedstock from the slaughter house is enough to run the project for the whole year. The
temperature has to be high enough (25oC – 37oC) to cause the digestion process to work or
additional building work/source of temperature must be employed to create a warm environment
for microbes to work. The quality of the building materials must be high as the biogas is held
under pressure and skills and know-how are needed both to build and to maintain biogas plants.
Many units built in the past have been abandoned for lack of servicing skills.
Social
The project will succeed if there is a market for the fertilizer end product. This supply chain
should be part of the planning stage of biogas introduction. Even if the set-up costs are
subsidized, those who will use the gas should have some financial stake in the construction or
they may not have a sufficient sense of ownership to maintain the plant. Promotion and
dissemination of the benefits of biogas will be needed to the stakeholders if it is to be accepted
by community around the project area.
Financial / political
Government promotion and involvement in the project can assist in dissemination. This can be a
win-win solution as it provides clean energy and reduces problems associated with waste and
private sector investment will support long-term sustainability.
Four Lenses of Viability
Within the scope of this project, we develop four lenses of vitality, which state that if this project
is undertaken, there will be four key areas where potential prosperity and vitality can occur.
Socially, developing and implementing this project will primarily allow for better aesthetics for
the slaughterhouse, surrounding neighborhood, and hopefully become a trend for
slaughterhouses in Tanzania. Greater aesthetics includes less pungent smells, which are a main
complaint of the locals. Also, greater aesthetics makes any further investment in the
slaughterhouse seem more appealing. It also has potential to increase the real estate value of the
16
area, which can have tremendous affects. Socially, implementing this project can also lead to
more employment, as the slaughterhouse will need personnel to run/manage the digester, teach
the local farmers how to use the new fertilizer form, and oversee the input of solid waste into the
digester. Also, the benefits of this digester can have a trickling effect down to the local farmers,
who in will have access to a better source of fertilizer, and at least in theory, potential for greater
output in their crops. Finally, with better management and processing of the animal waste, there
is a much lesser chance that any backtracked-contamination can occur with the meat, therefore
preventing a market scare among the public meat consumers, which ultimately serves to protect
the job sector and health of the people.
Environmentally, there are many benefits that can be derived from the implementation and
development of this bio-digester. Firstly, by developing this digester we can help to prevent what
could become an environmental catastrophe for the Dar-es-Salaam area. With a local water
source so close to the stockpile of waste, the neighborhood houses so near the gases and fumes,
and the ground water dangerously exposed, it is only time before this waste triggers irreversible
consequences on the local environment, and the people. Also, developing this bio-digester can
help to transfer the use of other conventional energies to more sustainable ones, and in turn
reduce potential green house gases. Also, the fertilizer developed from this process is much more
efficient in delivering nutrients in amount compared to the pre-treated waste. This greater
efficiency can lead to less transportation needed to distribute this fertilizer, and overall a lesser
toll on the land and the air.
From a technical perspective, there is obviously the great technological introduction of the biodigester into the slaughterhouse. Yet, there are many other opportunities that the technological
perspective of viability can bring. With this digester, there exists the technical capacity to
develop an adjourning water treatment facility, create a more resourceful, efficient animal
process, and provide technical capacity building to locals and farmers. Also, there is large
potential for many different uses of the bio-gas produced, such as for boiling water and blood,
for emergency lighting, pumping water, cooking, and even heating the building.
From a financial standpoint, there are several aspects that can potentially make this project very
viable if it can find proper funding. Eventually this project can develop into a larger income for
the municipality by allowing them to save money on electricity, waste transportation costs, and
even earn profit through selling the excess energy. Altogether, this perspective is one of the most
important, and rightfully so, but it must be noted that many times the ability to find funding, and
the limitations on that money, can often blur the potential for a productive financial vision.
Cost-Benefit Analysis
In developing the cost benefit analysis, we of course are not necessarily placing a greater
importance on the financial lenses of this project, but rather acknowledging the well-known
understanding that the financials of any project of this magnitude are often the determining factor
in it being implemented. In developing this cost/benefit analysis, we developed a few
assumptions to ensure that the scope of our feasibility study was established:
Project Assumptions:
17





Feasibility study ends analysis at the development of useful biogas.
The supply of waste is constant, and energy is produced 365 days a year.
Power can be sold back to the municipality at $.07 per kWh.
The interest rate, as stated by the CIA Factbook, is 18% minimum.
Operating and management costs of the digester are $50,000 per year.
Now that the assumptions are understood, it is important to understand the parameters of our
data. The cost of the project is estimated as 1.8 million dollars, which is $600,000 more than our
original estimate so that we may account for fluctuations in cost. In order to understand if this
project is feasible, we must see how long it would take to pay back this investment, and if it is
worth it ultimately.
Technical research we were able to derive the following cost train:
Slaughterhouse yearly cost - 1 less waste
$99,439 - $11,102 - $9600= $78,737
removal – Slaughterhouse energy
Slaughterhouse (SH) yearly profit – Cost
$142,000 - $78,737= $53,263
Net SH profit
$53263
Projected kWh produced per day from
3700 kWh x 365= 1,350,500
biogas x days of the year
Yearly energy production x price can sell
1,350,500 x $.07 = $94535
each kWh
Bio-gas profit per year – Operating and
$94,535 – $50,000= $44535
management cost per year
It can be seen that from this model and thought process, we are taking a very simple, yet
effective approach by splitting up the slaughterhouse and the actual digester, and then looking at
them together. This becomes important for understanding the potential of the digester along with
conducting the cost-benefit analysis much better. And as one can see below, the cost-benefit
analysis was developed by look at payback periods of the large investment, keeping the 4 lenses
of vitality in mind, and deciding if this project is still worth it.
In the first chart below, we looked at solely the profit and cost of the digester, and wanted to
analyze whether that would be a project that, stand alone of the slaughterhouse, could have a
financial return. As one can see, with only looking at 7 years, the cumulative cash flow is still
increasingly decreasing, which there is an increased debt that one would undergo if the $1.8
million was acquired by a bank which stuck to the national average lending rate of 18%.
Project payback period of digester only, assuming free constant waste input
Cash Flow
Cumulative
Period (Solely digester)
Interest (18%)
Cash flow
0
-1800000
0
-1800000
1
44535
-324000
-2079465
18
2
3
4
5
6
7
44535
44535
44535
44535
44535
44535
-374303.7
-433662.066
-503704.9379
-586355.5267
-683883.2215
-798965.9014
-2409233.7
-2798360.766
-3257530.704
-3799351.231
-4438699.452
-5193130.353
Now assuming that the slaughterhouse and the digester are one entity, as shown below, we
compile costs to find out if the extra profit from the slaughterhouse would make this project
viable. It seems to be the same case that in fact, as the 7 year trend clearly shows, there is no sign
of the cumulative cash flow increasing, meaning that this project, in its current state, is not
necessarily feasible to conduct and undergo simply based off of financial data.
Project cumulative cash flow assuming slaughterhouse and digester are joined
Cash Flow
Period
(Total
Cumulative
Facility)
Interest (18%)
Cash Flow
0
-1800000
0
-1800000
1
97798
-324000
-2026202
2
97798
-364716.36
-2293120.36
3
97798
-412761.6648
-2608084.025
4
97798
-469455.1245
-2979741.149
5
97798
-536353.4069
-3418296.556
6
97798
-615293.3801
-3935791.936
7
97798
-708442.5485
-4546436.485
There are however several potential possibilities that could allow this project to develop and
grow into a viable project, thereby creating a digester with a payback period within a reasonable
time. Some possibilities include:




Government reduction of the 18% interest rate
Cheaper than expected local costs
Grant funding from non-profit, humanitarian efforts
Increased cost to slaughter animal
We believe these potentials are possible, and very likely to occur under the circumstances told to
us by our Tanzanian contact. With that said, we still believe it is worth the opportunity to
proceed with this project, and at the very least, a more in-depth cost-benefit analysis aligning
true costs in the very local context. Further recommendations will be listed below.
Recommendations
It is recommended for the council to move forward with the design and implementation of the
anaerobic digester. The environmental benefits of the treatment system are clear and prevalent,
19
minimizing odor, eliminating direct emissions of methane, and protecting the water and
surrounding area from contamination.
There are many design aspects left incomplete by this feasibility study, and it is understood that
the financial implications of this project will drive the decision making of the IPC. A further
detailed cost-benefit analysis delivered by a contractor pricing the treatment system would be
required prior to the beginning of constructing such a system. Pilot testing would also be needed
in order to characterize the waste stream and determine the appropriate residence time, the
biogas output per unit of input, as well as the quality of the sludge leaving the digester.
Of incredible importance to this project is the electrical output of the biogas and the ability to
generate and distribute the energy from the biogas. A working relationship with TENESCO is
imperative to understanding the technical and financial implications of such project. The
municipality must work with the power company to survey the infrastructure surrounding the
slaughterhouse and developing a cost structure for the selling and purchasing of electricity.
In regards to the digester system and the accompanying treatment train. Discussions with the
contractor in regards to the type of system used will be necessary. A high rate system that
requires heating and mechanical mixing may be more cost effective as the digester size is
minimized. However heating and mixing have costs and require more skilled operation to
prevent upsets. It is recommended that this be explored further.
Financially, the numbers as of right now do not leave us with a digester that has a feasible
payback period, however with all the positive externalities, and variables that can change the
affordability and feasibility of this project, we are undergoing the recommendation regardless.
This recommendation looks into the massive impact an investment in such a project can have on
the community, and the possible trend it can start with regards to research and implementation in
Tanzania and at other slaughterhouses.
Overall this is an excellent project and if this type of project with many details to be discussed
and worked out, however a project of this type that becomes successful would prove a useful
model for dissemination of slaughterhouse waste treatment. A system that improves the
environmental viability of the plant, the social implications to the community, is technically
sound, and economically feasible and possibility profitable would be a unique opportunity to
improve communities and better their circumstances.
20
References
CED India. (2011, March). Solids Waste Management in Slaughter House. Retrieved from
http://www.cedindia.org/wp-content/uploads/2011/03/slaughter-house-wastemanagment.pdf
Chen, P., Overholt, A., Rutledge, B., & Tomic, J. (2010). Economic Assessment of Biogas and
Biomethane Production form Manure. Pasadena, CA: CALSTART.
Government of Alberta. (2008, June). Economic Feasibility of Anaerobic Digesters. Retrieved
from Agriculture and Rural Development:
http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex12280
USEPA. (2000). Wastewater Technology Fact Sheet - Trickling Filters. Washington, D.C.:
Office of Water.
Ahlborg, H. and Hammar, L. (2011). “Drivers and barriers to rural electrification in Tanzania
and Mozambique – grid extension, off-grid and renewable energy sources.” World
Renewable Energy Conference. Linkoping, Sweden May 2011. Accessed March 2012. <
http://www.ep.liu.se/ecp/057/vol10/028/ecp57vol10_028.pdf>
Bensah, E.C. and Brew-Hammond, A. (2008). “Biogas Effluent and Food Production in Ghana”.
Faculty of Mechanical and Agricultural Engineering, Kwame Nkrumah University of
Science and Technology, Kumasi, Ghana.
<http://pdf.usaid.gov/pdf_docs/PNADO940.pdf.>.
Davis, M. L. (2010). Water and Wastewater Engineering. New York: McGraw-Hill.
"FAO." Tanzania, United Rep of. Food and Agricultural Organization of the U.N., 17 Feb. 2012.
Web. 17 Feb. 2012. <http://www.fao.org/countries/55528/en/tza/>.
“Kenya” Group, M. S.-H. (2009). Slaughterhouse Waste Treatment Facility. Huruma, NairobiKenya: The World Student Community for Sustainable Development.
Mahudi, A.S., Mashauri, D.A., Mayo, A.W., and Mbwette, T.S.A. (2001). “Constructed wetlands
for wastewater treatment in Tanzania.” University of Dar es Salaam.
<http://www.usdm.ac.tz/faculty/foe/wetlands/>.
Tchobanoglous, G., Burton, F. L., & Stensel, H. D. (2003). Wastewater Engineering Treatment
and Reuse. New York, New York, United States of America: McGraw-Hill.
Ananda Dissanayake "Review of Biogas Project of Intermediate Technology - Sri Lanka" 1999
Energy Conservation Fund, Sri Lanka "Sri Lanka Energy Balance 1998 (1st draft copy)"
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Integrating Energy and Environmental Management through Biogas - A country Review
1996 Practical Action.
FAO (1996), Training Manual on Biogas Technology for Nepal, Session Four –Utilization of
Slurry as Feed and Fertilizer.
Kellner C. (1991), Biogas Dissemination - The Tanzanian Experience, Biogas Forum, No. 47.
Tanzania Domestic Biogas Programme (TDBP) http://www.biogas-tanzania.org/
Knoef, H., Stassen, H.E. and Quaak, P., Energy from biomass: a review of combustion and
gasification technologies. World Bank technical paper no. 422, Energy Series 1999.
Marree F., Nijboer M., and Kellner C. (2007), Report on the Feasibility Study for a Biogas
Support Programme in the Northern Zones of Tanzania, SNV publication
Monteiro, E.; Mantha, V.; Rouboa, A. 2011. Prospective application of farm cattle manure for
bioenergy production in Portugal. Journal of Renewable energy, 36: 627–631.
Olotu Jones “Experience in terms of policies (subsidizing/ financing programs) implemented by
Rural Energy Agency (REA) to improve access to sustainable/renewable energies in rural
areas”. “UN Expert Meeting on Renewable Technologies as Energy Solutions for Rural
Development -9 to 11 February 2010”
Ottinger, R. L., 2005. Experience with promotion of renewable energy. Journal of Renewable
energy, 30: 425–460.
Tanzania national website- Tanzania Gross Domestic Product (GDP)
http://www.tanzania.go.tz/economy.html
Weerasinghe, K.D.N., Dharshanie de Silva L.A.Y. (University of Ruhuna, Sri Lanka)
"Assessment of gas liberation of Sri Lankan & Chinese type biogas generators and their
by-product utility" 1999
22
Utilized Tools
Loan Calculater to reassure cost-benefit analysis numbers
http://www.bankrate.com/calculators/mortgages/loan-calculator.aspx
Biogas web calculator
http://www.electrigaz.com/kefir/index.php
Appendices
Initial Project Definition
Problem Statement:
Describe and design a process in which the Vingunguti abattoir in Dar es salaam, Tanzania can
manage and utilize solid and liquid waste with an anaerobic digester. The goal of this digester is
to both manage waste and produce biogas to be used as a source of electricity and solid waste to
be used as fertilizer. This document discusses the feasibility of this project.
Scope:
The scope of this project entails the design, construction, and use of a biogas digester on the
property of the slaughterhouse. Further, the management of the biogas will be studied, including
both storage and method of power generation. Also, distribution of the digested waste as
fertilizer will be discussed. Not included in the scope of this project is the construction of a new
slaughterhouse or the management of the slaughterhouse.
23
Revised Project Definition
Problem Statement:
The goal of this project is to create a feasibility study that discusses, designs, and analyzes the
most economically and environmentally viable way of eliminating solid and liquid waste from
the Vingunguti slaughterhouse in Dar es Salaam, Tanzania. The suggested alternative from the
client is an anaerobic digester used to manage waste and produce biogas to be used as both a
source of electricity and solid waste to be used as fertilizer. The intention of this feasibility study
is not to produce a set of definitive plans, but rather an outline, basic schematic and output data
of biogas and biofertilizer that the system will produce. Finally, this study will include a
cost/benefit analysis of the project to quantify economic feasibility and payback time to aid the
policy makers in Dar es Salaam. This study will use all available and provided data, including
current operations descriptions, waste streams, and energy and water requirements.
This project must work in respect to social, environmental, financial, and technological aspects.
See other group project. Answer, why have other projects worked/more importantly not worked?
The scope of this project entails the design, construction, and use of a biogas digester on the
property of the slaughterhouse. Further, the management of the biogas will be studied, including
both storage and method of power generation. Also, distribution of the digested waste as
fertilizer will be discussed. Not included in the scope of this project is the construction of a new
slaughterhouse or the management of the slaughterhouse.
Questions to be answered














What is the slaughterhouse's primary need, waste removal or electricity?
What electricity source is currently used by the slaughterhouse?
Is the current generator adaptable for use with biogas? (Is a specific generator required?)
Will biogas need further refining/compression/treatment after collection? What treatment
and to what extent?
How will biogas be stored/collected/used?
How much biogas can be expected to be created from the given waste stream?
How much electricity can this biogas be expected to produce?
How will solid bio-fertilizer waste be removed/collected/sold from the slaughterhouse
after being digested?
What type of fertilizer forms are needed from locals?
Where would consumers get their fertilizer if the slaughterhouse did not exist?
Is there an opportunity to charge those who slaughter their animals for the waste the
slaughterhouse has to remove?
How will the solids leaving the reactor be dewatered?
How much water is required in the system?
How is outgoing water quality effected? Will there be need for further treatment? (high
ammonia)
24




What is the existing ducting/piping of the slaughterhouse? What is required for the biogas
reactor?
What process does the slaughterhouse currently have for moving solids out of the
slaughterhouse to where waste is stored?
Could there be a way that those who bring animals take away with them as much waste
as animals brought
What characteristics of waste stream must we understand to design the biogas digester?
o Percent solids?
o Carbon to nitrogen ratio?
o Volatile to inert solids ratio?
25