UNIVERSITY OF NAIROBI

DEPARTMENT OF CIVIL AND CONSTRUCTION ENGINEERING

SURVEY OF USE OF BIODIGESTERS IN KENYA

By Oduor Judy Adhiambo

F16/36173/2010

A Project submitted as a partial fulfillment for the requirement for

the award of the degree of Bachelor of Science in civil engineering

2016

SURVEY OF USE OF BIODIGESTERS IN KENYA

Abstract

On-site sanitation, also called decentralized sanitation, is a system where the treatment of excreta

or sewage takes place at the same location where it is generated. The bio-digester is a far more

environmentally friendly way of storing and treating effluent waste compared to the septic tank.

It works on a similar basis of a septic tank, however it does not need to emptied regularly

because the waste that comes out of the ‘Bio-digester’ has been treated so much so that it can be

released into the local environment. The system works by storing the untreated waste- allowing

the solid waste to fall to the bottom of the tank. Air is then used to agitate the sludge so that

aerobic digestion can occur.

The bio-digester occupies a small construction area. i.e. 1 square meter for domestic purposes

and only 2 square meters for commercial purposes hence leaving greater space for other

construction purposes.

The study is carried out through discussions and obtaining relevant information. The discussions

were conducted with the personnel involved in bio-digester construction. Information obtained

included the types and sizes of the bio-digesters and their cost. Site visit was conducted to

ascertain the works done.

On the basis of the findings in this study, the recommendations were made in order to promote

the use of bio-digesters.

SURVEY OF USE OF BIODIGESTERS IN KENYA

Dedication

I dedicate this research work to God, and to my family for their support throughout the process.

SURVEY OF USE OF BIODIGESTERS IN KENYA

Acknowledgement

First of all I would like to praise the Almighty God for his endless opportunity and help that

enabled me to continue my education and complete this research work successfully.

I am particularly grateful to my supervisor Dr. P.K. Ndiba for his constructive advice, guidance,

encouragement, willingness to supervise my research and their valuable comments from early

stage of proposing the research work to the final thesis research results write up.

Therefore, I would like to extend my deepest gratitude to him for his continuous technical

support and commitment during the whole course of this research work.

My appreciation also goes to the University of Nairobi, Department of Civil and Construction

Engineering for giving me the opportunity to partake my undergraduate degree at such a

prestigious institution of learning and excellence.

I would also like to thank Vision Drivers enterprises, Kenya Cast Products Limited and RIFLO

industries for providing me with the data for use in my research and allowing me to visit some of

their work in progress on site.

SURVEY OF USE OF BIODIGESTERS IN KENYA

TABLE OF CONTENT

Abstract ......................................................................................................................................................... 2

Dedication ..................................................................................................................................................... 3

Acknowledgement ........................................................................................................................................ 4

TABLES ....................................................................................................................................................... 7

TABLE OF FIGURES .................................................................................................................................. 8

CHAPTER ONE ........................................................................................................................................... 9

1.1 Background Information ..................................................................................................................... 9

1.2Problem Statement ............................................................................................................................... 9

1.3. Objectives ........................................................................................................................................ 10

1.4 Scope of the Study ............................................................................................................................ 10

1.5 Limitations of the Study .................................................................................................................... 10

CHAPTER TWO ........................................................................................................................................ 11

2.0 LITERATURE REVIEW ................................................................................................................. 11

2.1 Sanitation .......................................................................................................................................... 12

2.2 On-Site Sanitation ............................................................................................................................. 12

2.3 Septic tank ................................................................................................................................... 13

2.4 Bio-digester ................................................................................................................................. 14

2.4.1 The principle of waste water treatment in a bio-digester ........................................................... 16

2.4.2 Bio-digester tanks ...................................................................................................................... 16

2.5 Types of Bio-digesters ...................................................................................................................... 17

2.6 Accessories of bio-digesters.............................................................................................................. 18

2.6.1 Gulley traps ................................................................................................................................ 18

2.6.2 Grease trap ................................................................................................................................. 18

2.6.3 The recycling and irrigation system ........................................................................................... 19

2.6.4 Different Types of the Bio-digester Septic Tank based on size. ................................................ 19

2.7 Advantages of Bio-digesters ....................................................................................................... 20

CHAPTER THREE .................................................................................................................................... 22

3.0 METHODOLOGY ........................................................................................................................... 22

3.1 Introduction. ...................................................................................................................................... 22

3.2 Data collection methodology ............................................................................................................ 22

3.3 Data collected .................................................................................................................................... 22

SURVEY OF USE OF BIODIGESTERS IN KENYA

3.3.1 Primary data ................................................................................................................................... 22

3.3.2 Secondary data ............................................................................................................................... 22

CHAPTER FOUR ....................................................................................................................................... 23

4.0 RESULTS, DATA ANALYSIS AND DISCUSSION ..................................................................... 23

4.1 Bio-digester shapes and sizes ............................................................................................................ 23

4.2 Cost of the Bio-digesters ................................................................................................................... 27

4.3 Conformity of the Bio-digesters with NEMA regulations ................................................................ 27

CHAPTER FIVE ........................................................................................................................................ 29

5.0 Conclusion and Recommendation .................................................................................................... 29

5.1 Conclusion ........................................................................................................................................ 29

5.2 Recommendation .............................................................................................................................. 29

REFERENCES ........................................................................................................................................... 31

APPENDICES ............................................................................................................................................ 32

Appendix 1 .............................................................................................................................................. 32

Appendix 2 .............................................................................................................................................. 34

Bio-digester capacities ............................................................................................................................ 34

SURVEY OF USE OF BIODIGESTERS IN KENYA

TABLES

Table 1: Capacity of the bio-digesters .......................................................................................... 26

Table 2: Standards for Effluent Discharge into the Environment ................................................. 32

SURVEY OF USE OF BIODIGESTERS IN KENYA

TABLE OF FIGURES

Figure 2.1: Septic tank .................................................................................................................. 13

Figure 2.2: The System Layout ..................................................................................................... 15

Figure 2.3: Bio-digester Tank System .......................................................................................... 16

Figure 2.4: Jet Incorporated Bio-digester ..................................................................................... 17

Figure 2.5: A Gulley Trap ............................................................................................................. 18

Figure 2.6: Grease Trap ................................................................................................................ 19

Figure 4.1: The Cast ...................................................................................................................... 24

Figure 4.2: the Structures being molded ....................................................................................... 24

Figure 4.3: A Finished Bio-digester.............................................................................................. 25

Figure 4.4: The Complete Bio-digester with its French Drain ..................................................... 26

Figure 7.1: 1 cubic metre series .................................................................................................... 34

Figure 7.2: 2 cubic meter series .................................................................................................... 35

Figure 7.3: 2.25 cubic meter series ............................................................................................... 35

Figure 7.4: 3 cubic meter series .................................................................................................... 36

Figure 7.5: 4 cubic meter series .................................................................................................... 36

SURVEY OF USE OF BIODIGESTERS IN KENYA

CHAPTER ONE

1.1 Background Information

A bio-digester is an anaerobic space in which bacteria break down or “digest” organic material

fed into the system, which is decomposed by micro-organisms, i.e. bacteria in an anaerobic

environment to produce a renewable energy called biogas and other material that is mainly used

as fertilizer.

The bio-digester septic tank is a sewerage treatment system or an on-site sanitation system that

can be used both in residential and commercial properties. The bio-digester septic tank is used to

treat sewer water and the treated water can then be used for other functions like watering

gardens, irrigation flushing toilets and so on.

Bio-digester technology is becoming necessary Kenya. One of the main reasons is due to having

on-site sanitation systems rather than a sewer system in order to save on construction and

maintenance costs since bio-digesters never get filled up and therefore do not need exhauster

services.

A lot of people cannot afford a connection to a sewer or the sewer system maybe far from the

areas of resident. Therefore a bio-digester would be useful in the sewerage treatment. On-site

sanitation is also flexible with respect to population growth and temporary housing situations

such as slums and refugee camps. There is a growing concern about the crowding in some urban

estates and therefore there is a need for a clean environment and an improved method of waste

disposal.

1.2Problem Statement

Bio-digesters have some of their short comings. Small and middle-scale anaerobic technology

for the treatment of solid waste in middle- and low-income countries is still relatively new.

Experts are also required for the design and construction, depending on scale may also for

operation and maintenance. Reuse of produced energy such as transformation into, fire/light,

heat and power, needs to be established. There is also high sensitivity of methanogenic bacteria

SURVEY OF USE OF BIODIGESTERS IN KENYA

to a large number of chemical compounds. Sulphurous compounds emitted from the bio-digester

can lead to odor. Bio-digesters also functions poorly in colder climates unless external heating

provided. They also requires constant source of organic material and daily amount of work.

Therefore there is need for finding ways to use the bio-digester technology efficiently to improve

the onsite sanitation and enable the recycling of human waste.

1.3. Objectives

The overall objective of the study was to carry out a survey on the use of bio-digesters in Kenya.

The specific objective was to:

1. Identify the types of bio-digesters available.

2. To establish the size and cost of bio-digesters based on the number of users served.

1.4 Scope of the Study

A study involved research on the various places where the bio-digesters are used in Kenya

through the firms which construct them in order to determine the scope of their work and their

main clients.

1.5 Limitations of the Study

Because the concept of the use of bio-digesters is not that familiar to many Kenyans, there may

be limited places where the bio-digesters can be found. Educating the general public on its

importance may also be a challenge.

SURVEY OF USE OF BIODIGESTERS IN KENYA

CHAPTER TWO

2.0 LITERATURE REVIEW

Anaerobic digestion is a collection of processes by which microorganisms break down

biodegradable material in the absence of oxygen. The process is used for industrial or domestic

purposes to manage waste and/or to produce fuels. Much of the fermentation used industrially to

produce food and drink products, as well as home fermentation, uses anaerobic digestion.

Anaerobic digestion occurs naturally in some soils and in lake and oceanic basin sediments,

where it is usually referred to as "anaerobic activity”. The anaerobic digestion is the source of

marsh gas methane (Zehnder 1978)

The digestion process begins with bacterial hydrolysis of the input materials. Insoluble organic

polymers, such as carbohydrates, are broken down to soluble derivatives that become available

for other bacteria. Acidogenic bacteria then convert the sugars and amino acids into carbon

dioxide, hydrogen, ammonia, and organic acids. These bacteria convert these resulting organic

acids into acetic acid, along with additional ammonia, hydrogen, and carbon dioxide. Finally,

methanogens convert these products to methane and carbon dioxide. The methanogenic archaea

populations play an indispensable role in anaerobic wastewater treatments.

Anaerobic digestion is used as part of the process to treat biodegradable waste and sewage

sludge. As part of an integrated waste management system, anaerobic digestion reduces the

emission of landfill gas into the atmosphere. Anaerobic digesters can also be fed with purpose-

grown energy crops, such as maize. (www.clarke-energy.com ).

Anaerobic digestion is widely used as a source of renewable energy. The process produces a

biogas, consisting of methane, - carbon dioxide and traces of other ‘contaminant’ gases. This

biogas can be used directly as fuel, in combined heat and power gas engines or upgraded to

natural gas-quality biomethane. The nutrient-rich dig estate also produced can be used as

fertilizer.

With the re-use of waste as a resource and new technological approaches which have lowered

capital costs, anaerobic digestion has in recent years received increased attention among

SURVEY OF USE OF BIODIGESTERS IN KENYA

governments in a number of countries, among these the United Kingdom, Germany and

Denmark.

2.1 Sanitation

Sanitation is the hygienic means of promoting health through prevention of human contact with

the hazards of wastes as well as the treatment and proper disposal of sewage or wastewater.

Hazards can be physical, microbiological, biological or chemical agents of disease. Wastes that

can cause health problems include human and animal excreta, solid wastes, domestic wastewater

(sewage or greywater) industrial wastes and agricultural wastes. Hygienic means of prevention

can be by using engineering solutions such as sanitary sewers, sewage treatment, surface runoff

management, solid waste management, excreta management, and simple technologies for

example pit latrines, dry toilets, urine-diverting dry toilets, septic tanks), or even simply by

personal hygiene practices such as hand washing with soap and behavior change.

Providing sanitation to people requires a systems approach, rather than only focusing on the

toilet or wastewater treatment plant itself. The experience of the user, excreta and wastewater

collection methods, transportation or conveyance of waste, treatment, and reuse or disposal all

need to be thoroughly considered. The main objective of a sanitation system is to protect and

promote human health by providing a clean environment and breaking the cycle of disease.

2.2 On-Site Sanitation

On-site sanitation, also called decentralized sanitation, is a system where the treatment of excreta

or sewage takes place at the same location where it is generated. This is due to the high cost of

installation of a sewerage system for many low-income communities, particularly in developing

countries, hence the sewage is dealt with where it is generated, offering a hygienic and

affordable solution. Examples are pit latrines, septic tanks, and Imhoff tanks. A septic tank and

drainfield combination is the oldest and most common type of on-site sewage facility in the U.S.,

although newer aerobic and biofilter units exist which represent scaled down versions of

municipal sewage treatment plants. (https://en.wikipedia.org/wiki/Sanitation )

SURVEY OF USE OF BIODIGESTERS IN KENYA

2.3 Septic tank

A septic tank is a key component of the septic system, a small-scale sewage treatment system

common in areas that lack connection to main sewage pipes provided by local governments or

private corporations. Other components, generally controlled by local governments, may include

pumps, alarms, sand filters, and clarified liquid effluent disposal methods such as a septic drain

field, ponds, natural stone fiber filter plants or peat moss beds.

(https://en.wikipedia.org/wiki/Septic_tank )

The septic tank is the most conventional method for disposing of effluent waste- it is used by

most remote communities and leisure complexes. It provides an easy, cheap method of

temporarily storing and primarily treating waste. The waste, gets collected throughout the

building, just like any other building sewer system, however instead of entering the mains

sewage disposal system, the waste enters the septic tank. The tanks are usually stored

underground- in anaerobic conditions. This allows the sewage to go under primary treatment for

an extended period of time- this allows the decomposition of many of the large solids contained

within the waste and makes the waste a lot less toxic. (www.iwr.msu.edu)

Figure 2.1: Septic tank

The problem with a septic tank is that they need to be emptied on a regular basis- this can be an

inconvenience as well as an expensive endeavor, especially for a large building. Other problems

with the system are that, unless they are maintained properly they can become very unpleasant in

the way they smell. Also, unless they are concealed underground- which can become expensive

they can be a large eyesore.

SURVEY OF USE OF BIODIGESTERS IN KENYA

2.4 Bio-digester

The biological septic tanks apply two principles,

a) Bio-degration

The gases help to stir the sludge, scum and liquid layer which promotes digestion of

solids. Digestion takes place aerobically and an-aerobically due to the presence of both

aerobic and anaerobic bacteria that makes the process a success.

b) Displacement

The amount of water flashed into the tank displaces the same amount through the outlet

baffle into the French drain (soakage). The displacement process makes it impossible for

the tank to fill up and therefore does not require exhausting/emptying.

The bio-digester is a far more environmentally friendly way of storing and treating effluent waste

compared to the septic tank. It works on a similar basis of a septic tank, however it does not need

to emptied regularly because the waste that comes out of the ‘Bio-digester’ has been treated so

much so that it can be released into the local environment. The system works by storing the

untreated waste- allowing the solid waste to fall to the bottom of the tank. Air is then used to

agitate the sludge so that aerobic digestion can occur.

Bio-digesters for domestic waste water treatment enable 100% recycling of domestic waste

water. The bio-digester working mimics nature. The way water is treated is how the water would

be treated in nature anyway. The difference is that the bio-digester works faster and is compact.

For a domestic system, a tank of 1000 liters is sufficient to completely digest waste and treat the

waste water. In a home or office, waste water comes from toilets, bathrooms, kitchen and sinks.

The pollutants in this water are human waste, soaps and detergents, skin flakes, oils and fats and

solid particles.

SURVEY OF USE OF BIODIGESTERS IN KENYA

Figure 2.2: The System Layout

Human waste is largely organic. This can be degraded by bacteria thus reducing the mass of the

waste. The water can then be recycled. Bio-digesters treat black water. The grey water that

leaves the bathrooms, sinks and hand wash basins bypasses the bio-digester. However, solids,

soaps, oils and fats must be removed from this water before recycling.

SURVEY OF USE OF BIODIGESTERS IN KENYA

Figure 2.3: Bio-digester Tank System

It takes just about 2 weeks for the breakdown of matter to be complete, ensuring that only

water is discharged out of the tank.

2.4.1 The principle of waste water treatment in a bio-digester

Waste water is treated by aerobic or anaerobic means. With aerobic treatment, oxygen or air

must be present. Anaerobic decomposition however can take place without the presence of

oxygen. Components of a complete bio-digester with recycling include:

A bio-digester tank

A grease trap

A recycling tank

Pumps and irrigation systems

2.4.2 Bio-digester tanks

Bio-digester tanks are designed to be incubators to bacteria and to provide all the conditions

necessary for aerobic and anaerobic decomposition of organic waste. An enzyme is put into the

tank to catalyze the process. Once installed properly, they function very well and exhausting is

completely eliminated.

SURVEY OF USE OF BIODIGESTERS IN KENYA

2.5 Types of Bio-digesters

1. Jet Aeration Septic System

The aerobic treatment unit (ATU) is an "oxidizer" which uses extra oxygen dissolved in the

wastewater to support aerobic microorganisms which in turn decompose dissolved organic and

nitrogen compounds into simple CO₂ or into inorganic compounds. As microorganisms die off

they accumulate as sludge of biological material, some of which supports the development of

new cells or microorganisms to keep the system working. ATU's separate solid waste first in the

"trash tank" and later, additional solids are separated in the clarifier or settlement tank from

which they may be returned to the primary tank for more treatment.

Figure 2.4: Jet Incorporated Bio-digester

2. Enzyme producing bacteria bio-digester

This is an anaerobic process in which micro-organism break down biodegradable material.

Renewable organic feed stocks are used as the source of energy for the process. The nutrient-rich

solids resulting from the digestion can be used as a fertilizer subsequently. Almost any organic

material can be processed with dry fermentation. This includes biodegradable waste materials

such as waste paper, grass clippings, leftover food, sewage and animal waste.

SURVEY OF USE OF BIODIGESTERS IN KENYA

2.6 Accessories of bio-digesters

2.6.1 Gulley traps

Gulley traps are designed to capture solid particles in the waste water. This protects the bio-

digester from filling up.

Figure 2.5: A Gulley Trap

2.6.2 Grease trap

A grease trap uses the property of oil to float on the water and its viscosity to separate it

from the water. Oil should be removed from the waste water before treatment. This allows easy

aeration of water for bacterial action.

SURVEY OF USE OF BIODIGESTERS IN KENYA

Figure 2.6: Grease Trap

2.6.3 The recycling and irrigation system

The most effective way of recycling domestic waste water is to use it for lawn and garden

irrigation. For this to happen, the water has to be collected and pumped to drip, sprinkler, and

furrow or hosepipe irrigation. . (http://asepsis-kenya.com/total-waste-management/biodigesters-

waste-water-treatment.html )

2.6.4 Different Types of the Bio-digester Septic Tank based on size.

There are 3 different types of bio-digester septic tanks available, based on size.

The Standard Bio-digester

This is the smallest size and it can handle between 18-21 people (continuous users). This is

the best size for residential properties and small commercial establishments.

The Jumbo Bio-digester

The jumbo bio-digester can easily handle 100 people (continuous users) and is therefore

ideal for mid-size establishments, apartment blocks, hotels, farms and small gated

communities.

The Jumbo Deluxe Bio-digester

SURVEY OF USE OF BIODIGESTERS IN KENYA

This is the biggest size available and it can handle up to 400 continuous users. This is great

for much bigger establishments, estates, shopping malls, hotels, schools, hospitals and blocks

of flats.

Apart from these 3 standard sizes, different sizes can be created based on the need and the

size of the project. Custom designs can also be created for different clients.

(http://adroitarchitecture.com/green-architecture/sustainable-green-architecture-in-kenya-the-

biodigester-septic-tank/ )

2.7 Advantages of Bio-digesters

Bio digesters have their merits which make them a good substitute for the septic tank.

Their advantages are:

1. They eliminate environmental pollution which occurs during exhaustion of septic tanks

which may lead to infections.

2. Water from the system can be used in landscape hence cutting down on water bills or can

be directed to drainage systems outside the premises safely.

3. They require no exhausting unlike traditional septic tanks. This alone makes the bio-

digester the best option for dealing with sewer. Exhausting a septic tank is the process of

draining it when it is full. This process is undertaken after a number of years depending on the

size of the septic tank. The exhausting process is obviously an added expense, not to mention how

messy and potentially hazardous it can be.

4. They are approved by NEMA. The bio-digester has been fully approved and

recommended by both NEMA (National Environmental Management Authority) and the

Ministry of Water an Irrigation for dealing with commercial and domestic waste water in

Kenya. The bio-digester has been in use in Kenya for over 17 years without any major

issues

5. Cost Friendly Installation. The bio-digester septic tank is actually cheaper to install than

the cost of constructing a traditional septic tank and the accompanying soak pit. On the

site, one needs to excavate a hole that is 1.1 meters deep and some trenches. The

inspection chambers or manholes required are also few. The system occupies much less

space and can be used where space is an issue. Traditional septic tanks require a much

deeper hole and that comes with high costs of excavation. Excavation is also very tricky

SURVEY OF USE OF BIODIGESTERS IN KENYA

and expensive in areas that have a lot of rocks, swampy areas or areas with high water

tables as well as areas that have very loose soil.

6. Warranty. The on-site sewer system comes with a 5 year post installation warranty from

the manufacturer which covers manufacturer’s defects hence economical to the user.

SURVEY OF USE OF BIODIGESTERS IN KENYA

CHAPTER THREE

3.0 METHODOLOGY

3.1 Introduction.

This chapter presents the methods used to achieve the objectives of the study. Based on the

results obtained, a conclusion is derived.

The data collection included collection of data information from various agencies associated with

bio-digester construction and interviews various persons.

3.2 Data collection methodology

A research was conducted with the help of registered companies in Kenya that deal with

plumbing works and septic systems for all types of premises. One of the companies is Kenya

Cast Products Limited located in Kahawa Sukari off Thika Road. They offer their services all

over the country. This research helped in knowing the reception of consumers where they are

used, the types, cost, sizes, efficiency and other places that it can be adopted for use.

Discussions were also conducted with the manufacturers of the bio-digesters. The interviews

helped to clarify how the bio-digester plans are prepared, who’s in charge of construction and

operations and methods used for maintenance.

3.3 Data collected

Data collected was divided into two distinctive categories. Primary data which was any data

obtained from the enterprises or observed in the field. Second was secondary data, which was

any data published or collected by other parties other than the enterprises.

3.3.1 Primary data

Primary collection of data included conducting of interviews with bio-digester construction firm

managers and going to the field and observing the actual installation of a bio-digester based on

the type, cost and size in order to serve the required number of users.

3.3.2 Secondary data

Secondary data was obtained through literature, references such as books, journals, reports,

internet surfing.

SURVEY OF USE OF BIODIGESTERS IN KENYA

CHAPTER FOUR

4.0 RESULTS, DATA ANALYSIS AND DISCUSSION

The results obtained were from Kenya Cast products Limited. They include the different sizes of

the bio-digesters constructed, the shape and the costs incurred in construction.

4.1 Bio-digester shapes and sizes

Bio-digester tanks from Kenya Cast Products Limited are rectangular in shape. They are made of

highly vibrated reinforced concrete. They consist of the main body and inlet and outlet baffles.

The tanks are specifically designed to be completely gravity powered and are suitable in high

water table and inundating areas, they are structurally strong, water-tight, corrosion and

buoyancy resistant.

The septic tank occupies a small construction area, that is, 1 square meter for domestic purposes

and only 2 square meters for commercial purposes hence leaving greater space for other

construction purposes. The tank does not fill up as it applies the displacement principle, whereby

the amount of waste water that enters into the tank displaces the same volume of water from the

tank to the French drain (soakage). The tanks do not therefore leave the clients with the hard time

of exhausting the system time after time.

The bio-degradation process that takes place in the tank makes it easier for faster digestion of

waste. As a result it is not common to have bad odor when using the tanks as the digestion

process begins immediately the waste enters the tank. This makes it possible to install the tank

anywhere in the compound.

SURVEY OF USE OF BIODIGESTERS IN KENYA

Figure 4.1: The Cast

Figure 4.2: the Structures being molded

SURVEY OF USE OF BIODIGESTERS IN KENYA

Figure 4.3: A Finished Bio-digester

SURVEY OF USE OF BIODIGESTERS IN KENYA

Figure 4.4: The Complete Bio-digester with its French Drain

The bio-digesters come in different series:

Table 1: Capacity of the bio-digesters

SERIES (m³) CAPACITY(liters) TANK

MEASUREMENTS

NUMBER OF USERS

SERVED

1 1000 1M X 1M X 1M 40

2 2000 2M X 1M X 1M 100

2.25 2250 2¼M X 1M X 1M 150

3 3000 3M X 1M X 1M 220

4 4000 4M X 1M X 1M 400

The 1m³ series is ideal for individual domestic units, flats, office blocks or workshops. The

2m³series is ideal for residential and commercial flats, apartments, office blocks, school

SURVEY OF USE OF BIODIGESTERS IN KENYA

dormitories and farms. The 2.25m³ is ideal for residential and commercial flats, apartments,

office blocks, school dormitories and farms, hospitals and hotels. The 3m³ and 4m³ capacities is

also ideal for residential and commercial flats, apartments, office blocks, school dormitories and

farms, hospitals and hotels.

4.2 Cost of the Bio-digesters

The installation of the bio-digesters starts from the building’s last manhole, and the manufacturer

gives a quotation on the cost of construction and the dimensions needed in the construction. The

costs of the different capacities of the bio-digesters range between Ksh. 90,000 and Ksh. 100,000

depending on the size and the location of the client from the manufacturer. A larger capacity of a

bio-digester leads to increased cost of construction due to more construction material needed e.g.

concrete.

The costs exclude hole and soakage excavations in which their dimensions depend on the size of

the bio-digester to be constructed. The excavations can be done by the company or by the client

himself when given the dimensions by the company.

a) The prices also exclude:

b) VAT,

c) Filling the excavated area with hardcore,

d) Covering area with polythene paper,

e) Removal of excavated soil and transport of moulds and materials to the site,

f) Return of moulds back to office for any site outside Nairobi and environs.

70% of the installation cost is required before the work can commence, and the balance is paid

after the work is completed but before commissioning. A five year guarantee on manufacturer’s

faults or defects and a completion certificate is also issued on commissioning.

4.3 Conformity of the Bio-digesters with NEMA regulations

NEMA has various regulations that ensure that the environment is safeguarded at all times.

Among these regulations is the Environmental Management and Co-ordination (Water Quality)

Regulation of 2006. The main objective of these regulations is to protect human health and the

SURVEY OF USE OF BIODIGESTERS IN KENYA

environment by controlling discharge of waste water. This helps in the control of water borne

diseases.

The regulations provide standards for affluent discharge into the environment (Third Schedule).

All effluent or waste water therefore must meet the said standards before being discharged in to

the environment. A waste water analysis report undertaken by the Ministry of

Water and Irrigation is attached in appendix 1 to show the parameters of the pre-treated waste

from the biological septic tank before being discharged.

Many proponents undertaking various residential (flats) developments have also proposed to use

the system to contain their effluents during the Environmental Impact Assessment (EIA) process

and NEMA have issued them with EIA Licenses. Therefore the system is efficient and can

appropriately be used in the management of waste as per the requirements of the Water Quality

Regulations of 2006.

The standard values are daily/monthly average discharge values. Not detectable (nd) means that

the pollution status is below the detectable level by the measurement methods established by the

authority.

SURVEY OF USE OF BIODIGESTERS IN KENYA

CHAPTER FIVE

5.0 Conclusion and Recommendation

5.1 Conclusion

The importance of bio-digesters has been highlighted in the previous sections of the project.

From the study it was concluded that,

a) The bio-digester is a far more environmentally friendly way of storing and treating

effluent waste compared to the septic tank since works on a similar basis of a septic tank,

however it does not need to be emptied regularly because the waste that comes out has

been treated so much so that it can be released into the local environment.

b) The bio-digester occupies a small construction area. i.e. 1 square meter for domestic

purposes and only 2 square meters for commercial purposes hence leaving greater space

for other construction purposes hence can be used in residential and commercial areas.

c) The installation of the bio-digesters starts from the building’s last manhole and the cost

excludes excavation of the hole and the French drain.

d) The cost of the bio-digesters ranges between Ksh. 90,000 to 150,000 depending on the

size and purpose e.g. domestic or commercial purposes.

e) NEMA provides standards for affluent discharge into the environment from the bio-

digesters in order to protect human health and the environment. This also helps in the

control of water borne diseases.

f) Most of the manufacturers offer a five year guarantees on faults or defects hence

the client doesn’t have to spend much on maintenance.

5.2 Recommendation

The study came up with the following recommendations in regards to the survey of the use of

bio-digesters:

a) Bio-digesters should be adopted for usage since it leads to the degradation of all human

waste with no smell, occupies a small space, it is economical, requires no exhausting and

has a lifetime guarantee.

SURVEY OF USE OF BIODIGESTERS IN KENYA

b) More effort should be achieved in educating the general public on the importance of bio-

digesters.

SURVEY OF USE OF BIODIGESTERS IN KENYA

REFERENCES

http://adroitarchitecture.com/green-architecture/sustainable-green-architecture-in-kenya-the-

biodigester-septic-tank/

http://asepsis-kenya.com/total-waste-management/biodigesters-waste-water-treatment.html

https://en.wikipedia.org/wiki/Sanitation

https://en.wikipedia.org/wiki/Septic_tank

Kenya Cast Products Limited

Malina J.F. &Pohland F.G., Design of Anaerobic Process for the Treatment of Industrial and

Municipal Waste (TD755.D457)

RIFLO industries Kenya

Twinbro Ventures Kenya Limited

Vision Drivers enterprises Kenya

www.clarke-energy.com GE Jenbacher Biogas Engines

www.iwr.msu.edu

Zehnder, Alexander J. B. (1978). "Ecology of methane formation". In Mitchell, Ralph. Water

pollution microbiology

SURVEY OF USE OF BIODIGESTERS IN KENYA

APPENDICES

Appendix 1

Table 2: Standards for Effluent Discharge into the Environment by National

Environmental Management Authority (NEMA)

PARAMETER MAX. ALLOWABLE

(LIMIT)

1,1,1-trichloroethane (mg/l) 3

1,1,2-trichloethane (mg/l) 0.06

1,1-dichloroethylene 0.2

1,2-dichloroethane 0.04

1,3-dichloropropene(mg/l) 0.02

Alkyl Mercury Compounds Nd

Ammonia, ammonium compounds, NO₃ compounds and NO₂ compounds (Sum total of ammonia-N times 4 plus nitrate-N and

Nitrite-N (mg/l)

100

Arsenic (mg/l) 0.02

Arsenic and its compounds (mg/l) 0.1

Benzene (mg/l) 0.1

BOD 5 days at 20°C (mg/l) 30

Boron (mg/l) 1.0

Boron and its compounds-non marine (mg/l) 10

Boron and its compounds- marine (mg/l) 30

Cadmium (mg/l) 0.01

Cadmium and its compounds (mg/l) 0.1

Carbon tetrachloride 0.02

COD (mg/l) 50

Chromium VI (mg/l) 0.05

Chloride (mg/l) 250

Chlorine free residual 0.10

Chromium total 2

cis – 1,2 dichloro ethylene 0.4

Copper (mg/l) 1.0

Dichloromethane (mg/l) 0.2

Dissolved Iron 10

Dissolved Manganese 10

E.coli (Counts/100ml) Nil

Fluoride (mg/l) 1.5

Fluoride and its compounds (marine and non marine) (mg/l) 8

Lead (mg/l) 0.01

Lead and its compounds (mg/l) 0.1

n-Hexane extracts (animal and vegetable fats) (mg/l) 30

n-Hexane extracts (mineral oil) (mg/l) 5

Oil and grease Nil

SURVEY OF USE OF BIODIGESTERS IN KENYA

Organo-Phosphorus compounds (parathion, methyl parathion, methyl

demeton and Ethyl parantrophenyl phenylphosphorothroate EPN only

(mg/l)

1.0

Polychlorinated biphenyls, PCBs (mg/l) 0.003

pH (Hydrogen ion activity----marine) 5.0-9.0

pH (Hydrogen ion activity---non marine) 6.5-8.5

Phenols (mg/l) 0.001

Selenium (mg/l) 0.01

Selenium and its compounds (mg/l) 0.1

Hexavalent Chromium VI compounds (mg/l) 0.5

Sulphide (mg/l) 0.1

Simazine (mg/l) 0.03

Total suspended solids (mg/l) 30

Tetrachloroethylene (mg/l) 0.1

Thiobencarb (mg/l) 0.1

Temperature (°C) based on ambient temperature ±3

Thiram (mg/l) 0.06

Total coliforms (counts/100ml) 30

Total Cyanogen (mg/l) Nd

Total Nickel (mg/l) 0.3

Total dissolved solids (mg/l) 1200

Colour in Hazen Units (HU) 15

Detergents (mg/l) Nil

Total mercury (mg/l) 0.005

Trichloroethylene (mg/l) 0.3

Zinc (mg/l) 0.5

Whole effluent toxicity

Total phosphorus (mg/l) 2 Guideline value

Total nitrogen 2 Guideline value

SURVEY OF USE OF BIODIGESTERS IN KENYA

Appendix 2

Bio-digester capacities

1M3 it has a capacity of 1000 litres, it can serve up to 40 users.

Figure 7.1: 1 cubic metre series

SURVEY OF USE OF BIODIGESTERS IN KENYA

Figure 7.2: 2 cubic meter series

2M3 It has a capacity of 2000 litres; It can serve up to 100 users.

Figure 7.3: 2.25 cubic meter series

2.25M3 it has a capacity of 2250 liters, it can serve up to 150 users

SURVEY OF USE OF BIODIGESTERS IN KENYA

Figure 7.4: 3 cubic meter series

3M3 It has a capacity of 3000 liters; it can serve up to 220 users.

Figure 7.5: 4 cubic meter series

4M3 It has a capacity of 4000 liters; it can serve up to 400 users.