university of...

UNIVERSITY OF NAIROBI

DEPARTMENT OF CIVIL AND CONSTRUCTION ENGINEERING

FINAL YEAR PROJECT

NAIROBI DAM POLLUTION PROFILE

SUPERVISOR: PROFESSOR P. ODIRA

BY

ALLAN ANUSU KAMALIKI

REG NO. F16/2343/2009

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UNIVERSITY OF NAIROBI

DEPARTMENT OF CIVIL AND CONSTRUCTION

ENGINEERING

NAIROBI DAM POLLUTION PROFILE

BY ALLAN ANUSU KAMALIKI

F16/2343/2009

A project submitted as partial fulfillment for the requirement for the award of the degree of

BACHELOR OF SCIENCE IN CIVIL ENGINEERING

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DEDICATION

Dedicated to TONY ADEMBESA – My late brother who died just when I was about to start working on

this project. Rest In Peace.

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ACKNOWLEDGEMENT

I express my gratitude to my supervisor PROFESSOR P. ODIRA from the Department of Civil and

Construction Engineering, University of Nairobi for his guidance and supervision of this project. I also

thank Miss Wambui, Miss Cathrine and Mr. Kaunda, the lab technicians who assisted me during the lab

sessions and the Undugu Group Management in Kibera who assisted me in getting the samples and gave

me one of their worker to take me around during the field sessions. Thanks Denis Oyunge for

accompanying me during the field studies and special thanks to my mum Nancy Kamaliki for supporting

me all through.

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ABSTRACT

The project involves investigation of the pollution profile of Nairobi Dam and Reservoir. Investigation was

carried out by determining the physical, chemical and bacteriological properties of the water flowing into

and out of the reservoir. The sample stations were thus selected at the mouths of the inlets flowing into the

reservoir and at the outlet of the reservoir. The samples were then analyzed based on the standard analysis

methods in the laboratory.

The reservoir is situated in a quite unsafe area so a reconnaissance was conducted before the actual

fieldwork. I was lucky enough to find a resident guide thanks to the management of one Undugu Group

that run a waste management project at the shores of the reservoir. From the actual field study it was

realized that the dam was extremely polluted and released an awful odour. Most of the reservoir was either

filled up or covered in water hyacinth. The laboratory results didn’t make things any better either, the water

was found to contain very high concentrations of pollutants. After the research, some recommendations

were made towards restoration of the dam to its former glory. They included: -

Strict implementation of wastewater regulations to the residents of the area surrounding the

reservoir.

Slum upgrading of the Kibera Informal Settlement and installation of proper sewerage system.

Regulation of farming activities in Ngong.

Banning of settlement too close to the reservoir and its inlets.

Improving on garbage collection and disposal in Kibera slums.

Dredging the reservoir to restore it’s initial volume.

Structural repair of the dam.

Removal of water hyacinth from the reservoir.

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Table of Contents CHAPTER ONE.............................................................................................................................................. 1

1.0 INTRODUCTION ............................................................................................................................ 1

1.1 General .......................................................................................................................................... 1

1.3 Dam Morphometry and Size ......................................................................................................... 2

1.3 Environmental Issue ...................................................................................................................... 3

1.4 Objectives...................................................................................................................................... 3

1.5 Methodology ................................................................................................................................ 4

1.6 Test Parameter............................................................................................................................... 4

CHAPTER TWO ............................................................................................................................................. 6

2.0 LITERATURE REVIEW ................................................................................................................. 6

2.1 Water Pollution ............................................................................................................................. 6

2.2 Types of Water Pollutants ............................................................................................................... 7

2.3 Water Quality Parameters ............................................................................................................ 12

2.4 Major Causes of Water Pollution .................................................................................................. 15

CHAPTER THREE ....................................................................................................................................... 32

3.0 FIELD STUDIES ............................................................................................................................... 32

3.1 Methodology ................................................................................................................................. 32

3.2 Visual Analysis.............................................................................................................................. 32

3.3 Interviewing Residents .................................................................................................................. 38

3.4 Selection of Parameters for Sampling ............................................................................................. 40

3.5 Collecting Samples .......................................................................................................................... 41

CHAPTER FOUR ......................................................................................................................................... 42

4.0 RESULTS .......................................................................................................................................... 42

4.1 Sampling Stations .......................................................................................................................... 42

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4.2 Selection of Test Parameters and Testing. ..................................................................................... 44

CHAPTER FIVE ........................................................................................................................................... 54

5.0 DISCUSSION .................................................................................................................................... 54

5.1 Biochemical Oxygen Demand....................................................................................................... 54

5.2 Chemical Oxygen Demand ........................................................................................................... 54

5.3 Dissolved Oxygen ......................................................................................................................... 54

5.4 Feacal Coliform Count .................................................................................................................. 55

5.5 Suspended Solids ........................................................................................................................... 55

5.6 pH .................................................................................................................................................. 55

5.7 Nitrates Concentration ................................................................................................................... 55

5.8 Colour ............................................................................................................................................ 56

5.9 Conductivity .................................................................................................................................. 56

CHAPTER SIX ............................................................................................................................................. 58

6.0 CONCLUSIONS AND RECOMMENDATIONS ............................................................................ 58

6.1 Conclusion ..................................................................................................................................... 58

6.2 Recommendations ......................................................................................................................... 58

REFERENCES .............................................................................................................................................. 60

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LIST OF FIGURES

Figure 1.1: Location of Nairobi Dam in Nairobi County………………………………………………..…..2

Figure 2.1: Contour ploughing ……………………………………………………………………..………29

Figure 2.2: Strip Cropping in Iowa, USA……………………………………………………………..……30

Figure 2.3: Terraced Farmlands in Guanxi Province, China………………….………………………...…..30

Figure 2.4: Agroforestry in Kenya……………………………….………………………………..………..31

Figure 3.1: A general view of the dam…………………………………………………………………...…33

Figure 3.2: A different View of the reservoir……………………………………………………………….34

Figure 3.3: A view of Lang’ata Estate viewed from Soweto………………………………………………34

Figure 3.4: Nice apartments Constructed dangerously at close to the Dam outlet…………………………35

Figure 3.5: A view of the spillway of the Dam……………………………………………………………..35

Figure 3.6: More of the spillway…………………………………………………………………………....36

Figure 3.7: This is the section where water enters the spillway…………………………………………….36

Figure 3.8: The spillway overlooking Highrise Housing Estate…………………………………………....37

Figure 3.9: Plastics dumped in one of the inlet streams…………………………………………………….37

Figure 3.10: More plastics dumped in one of the inlet streams…………………………………………….38

Figure 3.11: A Greenhouse project by Undugu Self Help Group on a filled part of the reservoir…………39

Figure 3.12: A Toilet initiative of the Pee Poo project……………………………………………………..39

Figure 3.13: Part of the structures built by the slum-upgrading program…………………………………..42

Figure 4.1: Location of the Sampling stations on the reservoir map………………………………………43

Figure 4.2: Satelitte image of the reservoir…………………………………………………………………44

LIST OF TABLES

Table 4.1: Description of Sampling Stations……………………………………………………………..…44

Table 4.2: BOD5 Variation with stations…………………………………………………………………...45

Table 4.3: COD Variation with stations…………………………………………………………………….46

Table 4.4: Feacal Coliform Count Variation with station………………………………………………….47

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Table 4.5: pH Levels Variation with stations……………………………………………………………….48

Table 4.6: Conductivity Variation with stations…………………………………………………………....49

Table 4.7: Nitrate Concentration Variation with stations…………………………………………………...50

Table 4.8: Colour Variation with stations………………………………………………………………….51

Table 4.9: Total Suspended Solids Variation with stations………………………………………………...52

Table 4.10: Dissolved Oxygen Variation with stations……………………………………………………..53

LIST OF CHARTS

Chart 4.1: BOD5 Variation with stations…………………………………………………………………...45

Chart 4.2: COD Variation with stations…………………………………………………………………….46

Chart 4.3: Feacal Coliform Count Variation with station………………………………………………….47

Chart 4.4: pH Levels Variation with stations……………………………………………………………….48

Chart 4.5: Conductivity Variation with stations…………………………………………………………....49

Chart 4.6: Nitrate Concentration Variation with stations…………………………………………………...50

Chart 4.7: Colour Variation with stations………………………………………………………………….51

Chart 4.8: Total Suspended Solids Variation with stations………………………………………………...52

Chart 4.9: Dissolved Oxygen Variation with stations…………………………………….………………..53

LIST OF ABBREVIATIONS AND SYMBOLS

NCC - Nairobi City County

BOD5 - Biochemical Oxygen Demand (5days at 200C)

COD - Chemical Oxygen Demand

pH - Potential Hydrogen

TSS - Total Suspended Solids

D.O - Dissolved Oxygen

Mg/l - Milligrams per Litre

x

J/kg - Joules per kilogram

PHE - Public Health Engineering

NEMA - National Environment Management Authority

KAR - Kenya African Rifles

DNA - Deoxyribonucleic Acid

UNEP - United Nations Environmental Programme

EEP - European Economic Community

NGO - Non Govenmental Organization

SDHEC - South Carolina Department of Health and Control

TCU - True Colour Unit

Nairobi Dam Pollution Profile

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CHAPTER ONE

1.0 INTRODUCTION

1.1 General

Nairobi city is the largest city in east Africa in terms of population, built up area and infrastructural

development. It is a rather young city; it began in 1899 as a supply depot of the Uganda railway.

Initially it was a swamp and a watering point for the Maasai pastoralists who called it Enkare Nairobi

meaning, ‘the place of cool waters’. The railway builders chose it as their supply depot due to the

availability of the cool waters for them.

As the city grew bigger, there was need for alternative sources of water. The first piped water was from

Kikuyu springs and Kabete treatment plant developed in 1906. In 1936 the Ruiru dam was built then the

Sasumua Dam followed in 1945, both located in the Aberdare Range north of Nairobi (NCC website).

Deep wells were also dug to supplement the water sources of the constantly growing city that was now

the capital of the British East Africa Protectorate. Amidst fears of acute water shortages in the mid 20th

century, the British Colonial Government was under pressure to provide emergency water for the city

and thus the Nairobi Dam project was born. The Department of Public works in conjunction with

Uganda Railway and Harbour Services then came up with the design in 1946.

Initially the dam was a great success as it didn’t just serve the purpose of providing emergency water for

the city but also became a hot spot for recreational activities pulling things like sport fishing, diving,

picnics and boating. The then licensed users were the Nairobi City Council and the Nairobi sailing and

sub aqua club for water abstraction and sports respectively.

With time, heavy pollution has befallen the dam leading to encroachment of invasive plant species like

the water hyacinth and parrot’s feather since 1998 hence rendering it impossible for the recreational

activities that used to take place in it. The springing up of the nearby Kibera slum has completely altered

the aquatic ecology and flow regime of it’s associated rivers.

According to studies by the Nairobi River Basin Project 2002, organic pollution was the most acute

problem of the Nairobi Dam especially during the dry weather. The Nairobi Dam receives most of the

human waste from the Kibera slum. Nearly 131 tons of solid waste per day is generated from Kibera and

neighboring slums exerting a lot of BOD5 (Krhoda 2002). The dam presently acts as a waste treatment

plant with poor efficiency due to oxygen depletion and sunlight reduction due to presence of heavy plant

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growth. The effects of organic pollution reduce the oxygen levels in the Nairobi Dam reservoir and the

inflowing River Motoine/Ngong and promote anoxic conditions. The result is a dark colored, foul

smelling river with floating scum due to the anaerobic conditions. Although both the river and the

reservoir can realize self-purification, it may only be possible if there is less or no more organic matter

introduction into the water source. The reservoir, like all other reservoirs, does not have high turbulence

that is required for faster exchange of oxygen from the air to the water. Figure 1.1 a map of the location

of the Nairobi Dam in Nairobi County. (Formerly Nairobi Province)

Figure 1.1: Location of Nairobi Dam in Nairobi County

1.3 Dam Morphometry and Size

The initial capacity of the dam reservoir was about 98422 m3 although with periods of siltation the

capacity is now smaller than that. No excavation was undertaken in the construction of the reservoir so it

remains relatively shallow with an average depth of just 2.76m. The principal inlet into the dam is the

Motoine River whose catchment area is largely the Ngong forest.


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1.3 Environmental Issue

The Nairobi dam started as great success before it started lapsing into a national shame majorly due to

pollution. In early 1900s, when the Nubian Soldiers returned from service with Kenya African Rifles

(KAR), they were offered plots in the region around the location of the reservoir. The region was an

enclave of the Europeans residential land and there were efforts by some people in the colonial

government to relocate it but since the British Colonial Government felt indebted to the former soldiers,

they allowed them to stay. As the economy developed, there was more rural to urban migrations and

other people moved in to rent land from the Nubian landlords hence resulting in sprawling informal

settlements around the site of the reservoir.

The informal settlements have since then led to an increase in waste dumping into the poor dam causing

pollution that has eventually rendered it useless for its initial use. Concentration of toxic chemicals has

increase in the dam mixed with surfactants as observed in May 2004 when some mysterious foam

formed over the reservoir after a heavy downpour. (Sunday Standard 2004)

Organic wastes from the slums seem to have taken a heavy toll on the dam too judging from the pungent

smell of the water from the reservoir. The water is also mixed with a lot of plant nutrients judging from

the eutrophication characteristics of its ecosystem. Aquatic plants such as water hyacinth (Eichhornia

crassipes) have heavily infested the dam making it impossible to sail in the reservoir. The water

hyacinth has been a major issue since it was first introduced into the dam back in 1998 coming with

effects such as:

Reduced penetration of the sunlight

Reduced levels of dissolved oxygen

Provision of suitable habitats for biological vectors of human diseases

Impeding fishing and recreational activities

Causes increased sedimentation

Causes damage to dams, bridges and hydroelectric plants.

1.4 Objectives

The main objective of this project is to collect data on the status and impact of pollution on the Nairobi

dam. It will involve data collection and analysis in order to determine the trends of major pollutants as

well as main pollution points on the dam site.

It is aimed at understanding the levels and source of pollution so that the changes and interventions

necessary to restore the dam to its former glory can be determined and effected. The main vision of the

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project is, ‘a sustainable healthy and beautiful river ecosystem that is both aesthetically pleasing and

serving its economic purpose’.

The success of the project is crucial to the communities living around the dam, the Nairobi City Council,

the Government of Kenya and the whole Nairobi community at large, as they are all beneficiaries.

1.5 Methodology

The first fieldwork task of the project will commence with one on one interviews with the natives of the

area around the dam. This will be majorly to find out: -

The ‘other’ causes of pollution that we are not aware of that only the natives might be aware of.

The effects of pollution of the dam to the community

Extent to which Nairobi residents could be engaged to develop partnerships in support of

environmental initiatives.

Fieldwork will also be undertaken to determine the location of the four sampling stations. The stations

will be chosen on the basis of: -

Ease of accessibility

The premise of determining pollution strength of organic and inorganic wastes into and out of

the dam.

Samples for laboratory measurement will be collected in the dry and wet seasons.

The laboratory examinations will be divided into three: -

Physical tests that involve measurement and recording of properties detectable by exteroceptive

senses (the smell and colour of the water)

Chemical analysis that involves determination of concentration of minerals and organic matter

present in water.

Bacteriological examinations that indicate the presence and concentration of bacterial

characteristics of pollution

1.6 Test Parameter

The parameters of the water that will be tested include

1. Dissolved oxygen – Oxygen influences the fauna, microbial activity and composition shifting of

chemical species.

2. Nitrates - These are the major nutrients contributing to eutrophication.

3. Phosphorous – Major nutrients contributing to eutrophication


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4. Total suspended solids – reflects the sediment drain into the dam reducing dam capacity

5. pH – Influences mobility of chemical species and gives indication of biological activity

particularly respiration and photosynthesis.

6. Appearance, taste and odor – Affects recreation activity on the dam.

7. Color – Influences depth to which sunrays can penetrate in water.

8. Fecal coliform counts – Establish quality and quantity of disease causing coliforms.

9. Chemical Oxygen Demand (COD) – Indicates toxic conditions and the presence of biologically

resistant organic substance.

10. Biochemical Oxygen Demand (BOD) – to determine the oxygen that bacteria would require to

breakdown organic material.

The results of the project will be analyzed, conclusions made and recommendations made may restore

and rehabilitate the once useful and beautiful Nairobi dam hence helping realize the initial vision of the

project - ‘a sustainable healthy and beautiful river ecosystem that is both aesthetically pleasing and

serving its economic purpose’.

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CHAPTER TWO

2.0 LITERATURE REVIEW

The state of Nairobi Dam and reservoir currently is a result of water pollution, which is a result of

activities mostly arising from negligence, improper planning and improper land use. Before doing the

research on the state of pollution of Nairobi Dam and reservoir, it is important to understand what

pollution is, the sources of pollution at large and particularly the possible sources of pollution of Nairobi

dam and reservoir. Furthermore, understanding some of the measures that could be put up to control this

kind of pollution is also very necessary. In this literature review, water pollution and sources pollution

that could be the possible sources for the pollution of Nairobi dam reservoir, effects of pollution and

some of the measures that could be put in place to reduce pollution in Nairobi Dam reservoir will be

discussed.

2.1 Water Pollution

Pollution can be caused by nature itself like when water flows through soils with high acidities hence

becoming too acidic but the bulk of pollution is done by human activities. Sources of pollution may be

Point sources or Non point sources depending on the nature of how the pollutant is delivered into the

water source. Point sources include wastewater treatment facilities, factories and septic systems. It

basically includes all sources that are clearly discharging pollutants into water sources. Non point

sources are difficult to identify and trace back to a particular location. They include runoff including

fertilizer, sediment, chemicals and farm wastes, fields, mines and construction sites.

2.1.1 Sources of Water Pollution

2.1.1.1 Point Sources of Water Pollution

Domestic Sewage

Domestic waste includes human waste and a variety of waste materials that arise from household

products such as foods, soaps, paints, oils and grease. These wastes contains microorganisms, metals,

plastics, decomposable organic chemicals and xenobiotic chemicals (Xenobiotic chemicals are

chemicals found in organisms but which are not normally produced or expected to be present in it. This

encompasses substances that are in much higher concentrations than usual. Examples of xenobiotic

chemicals include drugs like antibiotics in human bodies since human bodies do not produce them

naturally nor are they part of a normal diet) (Pepper, Gerba and Brusseau 1996) The word xenobiotic is

coined from the two words, xeno – meaning foreign and biotic – meaning biologically active to

represent the foreign and biologically active nature of these chemicals. Being in the middle of very high


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density settlements (Kibera, Highrise, Langata), Nairobi dam reservoir probably receives a lot of

domestic wastes from these settlements - especially Kibera Slum which is an informal settlement with

no proper sewerage system.

Municipal Domestic Sewage

This includes wastewater from industries, schools, hospitals, airports and other institutions connected to

the municipalities sewer system. This includes chemical wastes from industries and institutions and hot

water used as a coolant in the industries. Hot water increases the temperature in water bodies making it

unsuitable for plant and animal use. Being in the middle of a big city, Nairobi dam is susceptible to

being polluted by municipal wastes.

Solid Waste

This is discarded solid material from municipal, industrial and agricultural activities. Solid wastes are

mostly discarded at the same point on a regular basis. (Henry & Heinke 1996) In informal settlements

like Kibera, solid wastes (especially plastics nd plastic bags) are discarded everywhere and might find

themselves in any water body around the area. Solid wastes are a major cause of filling up of reservoirs

and may act as breeding a breeding ground for disease vectors e.g rats.

2.1.1.2 Non-Point Sources of Water Pollution

Storm Water and Surface Runoff

Storm water and runoff contains dust and other particles from roads, leaves from trees, grass cuttings

from lawns and parks, fallout from air pollution, excess fertilizers and herbicides from agricultural

lands, sediments from improperly managed construction sites, debris from eroded river banks etc. River

Motoine that is a tributary runs from Ngong where people practice some farming through Karen,

Jamhuri into Nairobi Dam reservoir. Heavy rainfall within the city could lead to numerous wastes being

carried into the river from the slums while upstream in the farm fields, fertilizers and other agricultural

chemicals may also find their way into the river.

2.2 Types of Water Pollutants

Water pollution occurs when the discharge of wastes into water bodies impairs water quality or disturbs

the natural ecological balance. It takes just a small amount of contaminant to pollute a water body

intended for drinking water supply but the same water might not be considered polluted if it were to be

used for instance for agriculture.(Pepper, Gerba and Brusseau 1996) Different factors contribute to

pollution including physical factors such as those that causes an increase in temperature or a change in

colour of the water. Water pollutants are classified into the following categories.

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Oxygen Demanding Wastes

Oil

Suspended Matter

Inorganic Chemicals and Minerals

Synthetic organic compounds

Plant Nutrients

Thermal Discharges

Radioactive Substances

Pathogens

2.2.1 Oxygen Demanding Wastes

A water body system both produces and consumes oxygen through various processes. Through these

processes a balance of oxygen concentration is maintained in water below which water becomes too

contaminated for its intended use. If more oxygen is consumed than produced then aquatic life may

migrate or die. (Khopkar, 2007) The following processes influence amount of dissolved oxygen in

water: -

Re-aeration

Photosynthesis

Respiration

Oxidation of wastes

From the list, re-aeration and photosynthesis are the processes that increase the dissolved oxygen (D.O)

in the water while respiration and oxidation of wastes depletes the dissolved oxygen. Respiration

however is a natural process by organisms living in the water bodies and can easily be restored by

photosynthesis and re-aeration through the self-purification action of the water body. Meanwhile

oxidation of wastes is a process brought about by pollution and may render the water unsuitable for use.

(Pepper, Gerba and Brusseau 1996)

Bacteria and other microorganism living in water decompose biodegradable organic compounds. Some

organics are mineralized into carbon dioxide and oxides of nitrogen while others are synthesized into

more microbial mass most of which is decomposed as well. All these processes consume dissolved

oxygen. The kind of waste that requires oxygen to be decomposed into simpler compounds is thus

known as oxygen demanding waste. This type of waste is mostly organic matter. The potential oxygen

demand of organics in water is measured by two parameters know as Biochemical Oxygen Demand

(BOD) and Chemical Oxygen Demand (COD).


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Biochemical Oxygen Demand

Biochemical oxygen demand (BOD) is defined as the amount of oxygen required by bacteria while

breaking down decomposable organic matter under aerobic conditions. (Khopkar 2007) The BOD test is

a procedure which measures the dissolved oxygen consumed by bacteria (and other microbial life) while

breaking down the organic substances present in the solution. Basically, a high BOD in water means the

water is highly polluted with biodegradable organic matter. The human wastes from Kibera slums could

increase the BOD of Nairobi Dam. From my reconnaissance visit, the reservoir already looks so much

polluted with organic matter and its BOD is likely to be very high.

Chemical Oxygen Demand

The chemical oxygen demand (also known as COD) test is basically a measure of the quantity of

oxygen required to oxidize organic matter in a polluted water sample under specific conditions of

oxidizing agent, temperature and time. During determination of COD, organic matter is converted to

carbon dioxide and water, amino nitrogen to ammonia nitrogen and organic nitrogen in higher oxidation

states to nitrates regardless of the biological degradability of the substances. For example glucose

(biologically degradable) and lignin (biologically resistant) are both oxidized completely. As a result

COD values are normally greater than BOD values and may be much greater when significant amounts

of biologically resistant organic matter is present. (PHE laboratory)

2.2.2 Oil

Oil is lighter than water and insoluble in water too. When discharged in water, oil forms a thin film on

the surface of the water and spreads out all over the surface. The lighter molecules of oil, which are

mostly toxic to living organisms, soon evaporate from the surface but at a very slow rate. The thin film

of oil on the surface of the water prevents re-aeration of the water hence leads to reduced D.O levels.

Within Kibera, Lang’ata and Jamhuri, there are several garages, which release oil that is washed down

into the dam via runoff. (Wikipedia)

2.2.3 Suspended Matter

These are suspended solids in water. Suspended matter causes water quality deterioration leading to

aesthetic issues, higher costs of water treatment and a decline in fisheries resource. Pathogens are

carried on the surface of suspended solids hence rendering the water unfit for drinking. Suspended solids

cause turbidity in water that reduces the amount of sunlight penetration in water leading to reduction in

photosynthesis hence death of aquatic plant life and increase in the amount of organic matter (BOD) in

water. This leads to a reduction in dissolved oxygen amounts in the water. (Sincero and Sincero, 1996)

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2.2.4 Inorganic Chemicals and Minerals

Low concentrations of acids, caustics, cyanides, arsenic and other heavy metals and numerous chemicals

are toxic to living organisms and microbial populations utilized in wastewater treatment processes.

Several harmful metals are biologically accumulative hence even the tiniest concentrations of them

matter. (Sincero and Sincero 1996) Acids originate from acid rainfall, which is caused by emissions of

sulphur dioxide and nitrogen dioxide into the atmosphere. Acids cause corrosion to water pipes and fatal

to fish. Chemicals from industries can also increase salinity of water. This may cause scale formation in

in pipes and boiler tubes and also become harmful to some species of plant and animal life. Being a

large city with a lot of industries, Nairobi might as well be the place that receives the highest amount of

acid rain in Kenya. Thus high pH levels in the water in the Nairobi Dam reservoir shouldn’t come as a

surprise.

2.2.5 Synthetic Organic Compounds

These include pesticides, herbicides, fungicides, detergents and synthetic organic chemicals. These

compounds are not biodegradable and may persist for a long time. They are also accumulative.

Pesticides, herbicides and fungicides from farms up in Ngong hills can be a source of pollution to the

waters of the two main inlets into Nairobi dam reservoir – River Motoine and Ngong River. However

this type of pollution is not of very big significance in this case since the two rivers are quite clean

further upstream.

2.2.5.1 Pesticides, Herbicides and Fungicides

Pesticides, herbicides and fungicides are all ‘toxins’ – they kill or adversely affect their target organism.

These chemicals are not very harmful when used properly. Even the most dangerous chemical is not a

pollutant until it shows up where it is not wanted. However due to extensive use of these chemicals and

their ability to persist (not biodegradable) allows them to accumulate to high levels which are harmful to

several forms of life. (Pepper, Gerba and Brusseau 1996)

2.2.5.2 Detergents

Detergents are surfactants – i.e lowers surface tension of water and allows dirt particles to become

linked to water. Surfactants cause production of foam (Diminished surface tension allows air bubbles to

persist at the water’s surface) and gives drinking water an off – taste. They also reduce the rate of

oxygen absorption into the water. Detergents also contain phosphates, which are important plant

nutrients that lead to eutrophic conditions - the condition where a body of water experiences excessive

growth of algae and phytoplankton. It occurs when a water body acquires a high concentration of

nutrients.)


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2.2.6 Plant Nutrients

Municipal wastewater and runoff from farms may contain nitrates and phosphates. These are inorganic

nutrients that promote plant and algal growth. Amounts as low as 0.01mg/l of phosphorous and 0.1mg/l

of nitrogen are sufficient to trigger eutrophication when other elements are in excess. In some cases,

algal blooms may be established. As the algae die and decompose, high levels of organic matter and

decomposing organisms deplete water of dissolved oxygen causing death of other organisms such as

fish whose carcasses add more to the already decomposing organic matter. (Pepper, Gerba and

Brusseau 1996)

In addition to having a detrimental aesthetic effect on lakes (odor, appearance), algae can be toxic to

animals that come to drink, spoil the taste of the water, plug filtration units and increase chemical

requirements in water treatment. Judging from the heavy water hyacinth and algae growth in the

reservoir, Nairobi Dam reservoir is certainly very much polluted with plant nutrients.

2.2.7 Thermal Discharges

Water used for cooling machines in industries may be disposed off into water sources. This water will

have temperatures way higher than the average temperature of the water sources. This leads to heating

up of water sources. An increase in the temperature of the water source lowers the saturation level of

dissolved oxygen and accelerates lowering of dissolved oxygen levels because the hot warmer forms a

layer over the cooler water and prevents replacement of oxygen in the cooler water below. Falling

dissolved oxygen levels may lead to anaerobic conditions. (Sincero and Sincero 1996) Extreme

temperatures may also kill plant and animal life. Thermal discharges into Nairobi dam might not be such

a big problem since there are no heavy industries around but sometimes domestic wastewater than is

usually dumped into the reservoir is of higher temperatures hence causing this type of pollution.

2.2.8 Radioactive Substances

Wastes from radioactive substances such as uranium and thorium can find their way into water sources.

Wastes from nuclear power plants are also radioactive. Radioactive substances have adverse effects on

human and other lives. Exposure to large amounts of radioactivity can cause nausea, vomiting, hair loss,

diarrhea, haemorrhage, destruction of the central nervous system and death. It also causes DNA damage

and raises the risk of cancer particularly in young children and feotuses. (Pepper, Gerba and Brusseau

2006)

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2.2.9 Pathogens

Pathogens are microorganisms that can cause diseases. The pathogens of particular concern include

bacteria, protozoa and viruses.

Pathogenic bacteria can occur in surface water in large numbers, either being excreted in feaces

or occurring naturally in the environment. They typically range in size between 0.5 and 2

micrometres. The disease causing bacteria that can be transmitted in water include Vibrio

cholera, Salmonella species, Campylobacter species, Shigella species and Staphylococcus

aureus. (Henry & Heinke 1996)

Viruses vary widely in size and shape but are the smallest of all pathogens. They typically range

in size from 0.03 to 0.1 micrometres. More than 100 known types of human and animal enteric

viruses, which may be transmissible through water, are known to humans currently. Viral

diseases that can be transmitted by water include rotavirus, enterovirus, norovirus and hepatitis

A among others. (Henry & Heinke 1996)

Protozoa are single celled eukaryotes. They include a number of groups of protozoans that are

waterborne pathogens including amoebae Naeglaria fowleri and Giardia and Entamoeba

hystolitica. There is a greater range of size among the protozoa. (Henry & Heinke 1996)

2.3 Water Quality Parameters

There are several measures of water quality. Good quality water is that that is healthy and suitable for its

intended use without creating harm to anything else. Water quality parameters are the testable

parameters used to determine the quality of water in the laboratory. These parameters will have to be

tested to find the level of pollution in Nairobi Dam. Below are some actions that lead to a reduction in

water quality.

2.3.1 Loss of Dissolved Oxygen

Oxygen is important in all forms of higher life (Living organisms that respire). Aerobic bacteria require

oxygen to decompose organic matter. Depressed dissolved oxygen concentrations are inimical to life

forms living in water. For example, some fish can survive at concentrations near 1mg/l but most are

adversely affected at D.O concentrations below 4mg/l. (Peppe, Gerba and Brusseau 1996) The

maximum amount of oxygen a pure water can hold is a function of salinity and temperature. Freshwater

contains 8 – 15 mg/l of dissolved oxygen over a temperature of 0 – 300 while seawater will contain 6 –

11 mg/l over the same range.


13

The BOD is a measure of oxygen consuming property of water due to organic matter contained in it.

BOD5 is a waste strength that represents the amount of oxygen that will be consumed in 5 days at a

given temperature.

2.3.2 Extreme pH

Most freshwater lakes, streams and ponds have a natural pH in the range of 6 – 8. Very low pH or very

high pH has adverse effects on aquatic systems. Here are some of the effects of low pH (increased

acidity) in fresh water sources.

Low pH below 6 causes some species of plankton and mosses to invade while

populations of some fish species begin to disappear. (Twort,1974)

Below pH 5, fish populations begin to disappear, the bottom is covered with undecayed

material and mosses may dominate nearshore areas. (Twort,1974)

Below pH 4.5 the water will practically become devoid of fish. (Twort,1974)

Aluminium ions (Al3+

) attached to minerals in nearby soil can be released into lakes

killing fish by stimulating excessive mucus formation. (Twort,1974)

High pH interferes with fish reproductive cycle by lowering calcium levels in female

fish, which hinders egg production. (Twort,1974)

Very high pH may kill fish, cause damage to outer surfaces like gills and eyes and cause inability to

dispose metabolic wastes. It also increases toxicity of other substances such as ammonia.

2.3.2 Pathogenic Contamination

Pathogens are disease-causing microorganisms. Water contaminated with pathogens is unsuitable for

drinking and other uses. The various pathogens found in water include: -

Viruses – Tiny organisms that consist solely of nucleic acid surrounded by a protective protein

cast called capsid. They cannot grow outside of the host organism but are capable of surviving

for long periods in the environment. (Peppe, Gerba and Brusseau 1996.)

Bacteria – Prokaryotic single celled organisms surrounded by a membrane and a cell wall.

(Peppe, Gerba and Brusseau 1996.)

Protozoa – Single celled organisms that cause various diseases including amoebic dysentery.

(Peppe, Gerba and Brusseau 1996.)

Helminths – These are literally worms. They are multicellular animals that parasitize humans.

They include roundworms, hookworms and tapeworms. (Peppe, Gerba and Brusseau 1996.)

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Blue-green algae – Prokaryotic organisms that do not contain an organized nucleus – unlike the

green algae. Some species produce toxins that may kill animals that come to drink or cause

illness to humans. (Peppe, Gerba and Brusseau 1996.)

2.3.3 Presence of Nutrient Salts

Nutrient salts such as nitrates and phosphates create a condition called Eutrophication.

Eutrophication in water is the enrichment of the water source with nutrients that results in excessive

growth of aquatic plant life favouring simple algae and plankton over more complicated plants. Some of

the sources of these nutrients include untreated sewage effluent and agricultural run-off carrying

fertilizers.

The phosphates feed algae, which assimilate other necessary nutrients needed for aquatic plants. When

algae die, they all sink to the bottom where they are decomposed and nutrients contained in organic

matter are converted into inorganic form by bacteria. The process uses a lot of oxygen thus reducing the

dissolved oxygen level of the entire water source. (Peppe, Gerba and Brusseau 1996) Enhanced growth

of aquatic vegetation and algae (algae blooms) disrupts normal functioning of the ecosystem causing

problems like lack of enough oxygen for fish to survive. The water becomes cloudy reducing the

amount of sunlight penetration. Eutrophication also reduces the value of water bodies for recreation and

aesthetic enjoyment.

2.3.4 Turbidity

Turbidity is a measure of the extent to which suspended matter in water either absorbs or scatters radiant

light. It practically is a measure of water clarity. High turbidity means less clear water. Turbid water is

polluted water. Turbidity is caused by soil particles and organic solids from domestic sewage.

Suspended particles in turbid water absorb sunlight making the water to be warmer hence reducing its

oxygen carrying capacity. It also decreases the photosynthetic activity of aquatic plants which requires

light leading to a further decrease in dissolved oxygen levels. It also reduces the aesthetic value of the

water body by making it look dirty. (Sincero and Sincero, 1996) Suspended particles in water form an

attachment surface for toxic substances and pathogens in water.

2.3.5 Aesthetic Degradation

Water is considered polluted if it has bad odours and is visibly unattractive. Nairobi Dam and reservoir

is very much degraded aesthetically for instance. Aesthetic degradation renders a water source useless

for its initial recreation point status. Nairobi Dam used to have a Yatch Club, a sport fishing club and a


15

swimming point to the public before aesthetic degradation rendered it useless for those activities. (NCC

Website) Aesthetic degradation is a result of all sorts of pollution and neglect.

2.4 Major Causes of Water Pollution

Environmental pollution is a potential health risk to all forms of life. In water, most of the pollution

occurs due to the carelessness of man encompassing uncontrolled disposal of water, improper land use

and accidents (e.g oil spills). Pollution occurs when pollutants are channeled into the receiving water.

For a proper analysis of the level of pollution in Nairobi dam, the possible causes of pollution and their

effects to the receiving water must be understood.

2.4.1 Sewage

Sewage is the remains of water mixed wastes to a point where it is considered useless for further use.

Usually this sewage is disposed off into water bodies. Such disposable water is also called wastewater.

Wastes that may be disposed off include: -

Domestic wastewater

Industrial wastewater

Storm water from precipitation runoff

Domestic wastewater contains majorly organic wastes from the kitchen, toilets and food remains. The

pollutants usually associated with industrial effluents are organic matter, inorganic dissolved solids,

fertilizing materials; thermal constituents in form of heat, suspended solids, microorganisms and

pathogens. Organic pollutants decrease the limit of dissolved oxygen and imparts bad odour and colour

while inorganic are toxic and harmful to life and also increase the salinity of water. Being bordered by

several informal settlements without proper sewerage systems makes the Nairobi Dam and reservoir

susceptible to sewage discharges.

2.4.1.1 General Characteristics of Wastewater

Due to the harmful nature of sewage, world bodies concerned with environment and development like

United Nations Environmental Program (UNEP), Organization for Economic Co-operation and

Development and European Economic Community (EEC) have standards for maximum amount of

pollutants allowed in wastewater prior dumping into water bodies. There is thus a need to treat sewage

to meet the required standards before dumping it into water sources. The characteristics of wastewater

can be physical, chemical or biological.

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Physical Characteristics

Includes total solids, colour, odour and temperature. Wastewater transmits its undesirable physical

characteristics to the receiving water polluting it.

Total Solids

These are the residues after the liquid portion has been evaporated. It includes both dissolved and non-

dissolved solids. About 40% of the solids are suspended. Suspended solids and volatile suspended solids

are used as an indicator of organic content of raw water and can provide a measure of active microbial

population and biological processes.

Colour

Colour is a qualitative characteristic used to assess the general condition of wastewater. A light to

medium grey colour is characteristic of wastewater that has undergone some decomposition. Dark grey

or black colour indicates that the wastewater is typically septic. Blackening of the wastewater is after

due formation of various sulphides particularly ferrous sulphides. (Rao, 2007)

Odour

Odour is the pungent smell of water. It is present due to volatile organic matter and biological materials

such as algae. Odour depends on temperature hence all measurements should be done at a fixed

temperature. Odour is a big issue when effluent emerges from food processing industries. (Rao, 2007)

Temperature

Wastewater from heavy industries is very likely to be of high temperature. Depending on the size of the

water source, high temp water will increase the temperature of the water source.

Chemical Characteristics

These include the BOD, COD, free ammonia, organic nitrogen, nitrites, nitrates, organic and inorganic

phosphorous etc. Wastewater with chemical pollutants is usually coloured and with strong offensive

odour. Acid containing waste is hazardous and needs special treatment. Chemicals that are also plant

nutrients will cause eutrophication.


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Biological Characteristics

These include the amount of pathogens and other microorganisms in the wastewater. Pathogens cause

illness while some microorganisms help in biological decomposition of organic wastes.

2.4.1.2 Phosphorous Removal

Phosphorous, a pollutant that originates from wastewater from agricultural farms can be removed from

wastewater to reduce its effect on the receiving water. Phosphorous is mainly removed from wastewater

by chemical precipitation although some biological methods have been suggested. The chemicals used

include lime, iron salts and aluminium salts. Lime precipitation can be carried out after secondary

treatment where high pH of 10.5 to 11.5 is required.

Some bacteria have the ability to take phosphorous in excess of their immediate nutritional

requirements and store it in bacteria cell in form of polyphosphates. The polyphosphates can then be

removed from the system. More biological methods are being investigated.

2.4.1.3 Nitrogen Removal

Nitrogen too can be removed from wastewater to reduce its effects on the receiving water body. All

forms of nitrogen in wastewater effluents are potentially harmful. There are two popular methods of

removing nitrogen from wastewater.

1. Ammonia stripping

2. Biological nitrification and denitrification

2.4.1.4 Ammonia Stripping

The main concept is converting ammonium ion to ammonia gas. The reaction that governs the

conversion is: -

NH4+

+ OH- ↔

NH4OH

↔ NH3 + H20

Increase in pH (the OH- concentration) shifts the reaction to the right to create more free ammonia,

which escapes.

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Nitrification and Denitrification

The water is treated in aeration chamber where NH4+ is converted by bacteria to nitrate ions.

Nitrosomanas and nitrobacter bacteria converts ammonium ions to nitrates.

NH4+

→

NO2-

NO2-

→

NO3-

The NO2- and NO3

- forms are then removed from the system by the process of denitrification.

2.4.2 Solid Wastes

Solid wastes are wasted material in solid form. Solid waste is synonymous with the word refuse though

refuse might also be used liquid and gaseous waste. (Sincero and Sincero 1996) Solid wastes are one

major reason why a large part of the Nairobi Dam reservoir is filled up. Residents of neighbouring

settlements dump lots of solids waste into the reservoir everyday. Proper collection, transportation and

disposal of solid waste is necessary for a clean environment and unpolluted water

resources.Classification of solid waste is by virtue of its content but solid waste might also be classified

based on moisture content and heating value as below.

Garbage/food waste - This is animal and plant residue produced as a result of handling, preparing

and eating food. Garbage has an average moisture content of 70% and a heating value of around 6 x

10^6 J/kg.

Rubbish - This is the combustible and non-combustible portion of solid waste excluding food waste. It

has a moisture content of 25% and heating value of about 15 x 10^6 J/kg. The combustible part of

rubbish is also known as trash. (Sincero and Sincero, 1996)

Pathological Waste - This is dead animal waste. It has a moisture content of 85% and has a 5% non-

combustible solids. It has a heating value of 2.5 x 10^6 J/kg.


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Agricultural Waste - This includes plant residues and manure. It generates a lot of oxygen demands

in water bodies.

2.4.2.1 Sources of Solid Wastes

Household Wastes - These are wastes generated in homes. It includes all solid wastes originating on

the property including garden waste. It may also be called Domestic Waste. It is further divided into

two: -

Collected Household Waste – This is household waste collected from the property by waste

collectors.

Delivered Household Waste – This is household waste delivered to a collection point by the

householder. It includes bulky items like recyclable old clothes and kitchenware, spoilt

refrigerators and TVs etc.

Commercial Waste - Produced by commercial properties like shops, offices, restaurants etc.

Institutional Waste - This is waste generated in schools, leisure facilities, hospitals etc.

Industrial Wastes - This is waste produced in industries as industrial residue (e.g bagasse) or

defective industrial products that don’t meet the required standards hence have to be disposed

off.

2.4.2.2 Public Health Aspects of Solid Wastes

Solid wastes causes damage to the environment when not handled well. The main risks to human health

that arise from improper handling of solid wastes are: -

They are breeding grounds for disease vectors such as flies and rats. (Sincero and Sincero, 1996)

Water collects in some of the plastic solid waste and creates breeding ground for mosquitos that

transmit malaria. (Sincero and Sincero, 1996)

Refuse dumps are also a source of food for rats and other rodents that quickly proliferate to other

areas. (Sincero and Sincero, 1996)

Handling and transportation of solid waste poses a threat to the person handling it. Disease may occur

direct contact with the waste, through an infection of open sores or through vectors. The waste might

also be injurious e.g broken glass may cut into the body of the handler. Solid waste causes aesthetic

harm to the environment by making it look dirty and unsightly. Uncontrolled dumping of urban waste

has destroyed the beauty of Nairobi Dam. Leachate from a refuse dump might enter surface water or

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ground water resources and contaminate it. For effective disposal of solid waste, it is necessary that the

collection be carried out efficiently.

2.4.2.3 Modes of Refuse Collection

Refuse collection lies at the very hub of integrated waste management system. The way waste material

is collected (and subsequently disposed) determines which waste management options can be

subsequently used. The method of collection will influence the quality of recycled material and the

compost or fuel that can be produced from the refuse. Waste collection is also the contact point between

waste generators and waste management system. Methods of collection include: -

Block Collection – Householders bring waste in containers to a waiting vehicle where the crew

of the waiting vehicle takes over and transports the waste to the point of disposal.

Kerbside Collection – householders bring waste to a roadside place prior the collection time.

Communal Storage Point – There is a large communal storage bin where households dispose

their wastes. A transportation crew empties the bin regularly.

2.4.2.4 Transportation of Solid Waste

The waste has to be transported to the point of disposal. Where a single transportation facility serves a

small population over a short distance, handcarts are used. Similarly handcarts may be used to transport

waste from narrow and congested places and deliver it to larger trucks that transport to disposal sites.

Otherwise trucks will collect refuse directly from the collection point to disposal point. Note that poor

solid waste transportation methods could also lead to pollution as the waste spills over the ground.

2.4.2.5 Disposal Methods

There are four main disposal methods of solid waste used: -

Open Dumping

Incineration

Landfilling

Composting

Open Dumping

This is the cheapest and simplest method of disposal of solid waste. Open dumps pose public Health

problems as they may cause accidents especially to little children and are breeding grounds for disease

vectors.


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Incineration

Incineration involves burning up wastes to a less harmful residue before disposing it safely (probably by

burying it). Materials that cannot be incinerated (like metals) are removed by use of large magnets. The

process of incineration destroys highly toxic and hazardous organic waste. In general, low temperature

(up to 8500) and high temperature (1200

0) incinerations use energy to oxidize Carbon and water to CO2

and H2O vapour.(Pepper, Gerba and Brusseu, 1996)

Advantages of Incineration

It can also be used as a source of energy – the heat produced can be used to generate electricity

or for cooking.

It has high efficiency; it destroys 99.99% of organic compounds.

Requires small space for ultimate disposal.

Disadvantages of Incineration

It is expensive to put up, run and maintain.

It cannot be used with waste that has high concentrations of water and non-combustible solids

and radioactive material.

Does not completely eliminate problems of metal contamination as it produces low volumes of

highly toxic metal ash.

Landfills

Waste is usually disposed off in the soil. It is the best method in disposing of hazardous waste. A large

pit is dug in the ground and lined with highly compacted soils of low permeability to prevent penetration

of hazardous leachate into the soil. Pipes are connected to the deepest point of the pit to collect the

leachate for treatment. The waste is then dumped into the pit, which is then covered with a layer of soil.

(Henry & Heinke 1996)

Advantages

Less hazardous than open dump.

Can be used to dispose off hazardous waste.

No air pollution from burning.

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Disadvantages

Danger of ground water pollution from leachate.

Composting

This is an aerobic method of decomposing solid waste. It uses micro-organisms (bacteria, fungi etc.)

present in waste to decompose and stabilize it. It can however only be used on organic wastes.

The microorganisms oxidize the organic matter to CO2 and less harmful substances liberating some heat

in the process. The compost must be aerated well. This is realized by churning the waste regularly.

Other Methods of Disposal

Recovering of Solid Wastes

Although it might be considered waste, some useful things might still be present in the waste.

Salvaging the waste might lead to recovery of some things that could be in quite good condition and

restore them back to use. The process involves recycling and reclaiming of various wastes. E.g

Reclaiming of Paper

This is done through the following processes: -

1. Bailing System

2. Containerized System (Rao, 2007)

Bailing involves shredding the paper then compressing the material and tying it into bales that are

transported to factories for recycling. Containerized systems compact and contain waste in large steel

containers which are transported to recycling points.

Reclaiming Scrap Metal

The scrap metal is removed from the refuse by use of strong magnets. The scrap metal is smelted and

reformed into usable material.

2.4.3 Agricultural activities

Agricultural activities that are not well controlled are some of the worst water polluting activities. The

inlet rivers into Nairobi Dam reservoir originate from farming areas up in the Ngong hills hence could


23

be carrying pollutants that result from agricultural activities. Agricultural activities as water polluting

activities can be classified into the following: -

Agricultural Fertilizers

Animal Wastes

Pesticides

2.4.3.1 Agricultural Fertilizers

For plants to complete their life cycles, they need an array of chemical elements. These elements include

C, H, N, P, K, Ca, Mg, Zn,Cu, Mo, B and Cl. Plants obtain these nutrient from the soil solution via

mineral weathering, atmospheric inputs, inputs from stream deposition and nutrient recycling.

Harvesting of crops leads to removal of these nutrients from the soil leading to a concomitant decline in

production after long periods of crop production. Fertilizers are materials that contain these essential

elements. They are soluble inorganic compounds that dissolve to give ionic nutrient forms in the soil.

These elements might be leached and find their way into water sources.

Nitrogen

Nitrogen is supplied into the soil in form of ammonium and nitrate compounds in fertilizers. It is mostly

applied prior to planting but may also be applied to growing crops. Nitrates may pollute both

groundwater and surface water. Groundwater pollution involves risks associated with consumption of

high nitrate water such as methemoglobinemia (blue baby syndrome). (Public health website). Surface

water pollution by nitrates leads to eutrophication and its associated effects. Neutral pH conditions (6-8)

and porous soils promote nitrate leaching while saturated soil conditions promote denitrification of soil

nitrates leading to a need to use nitrate fertilizers.

Phosphorous

Phosphorous is applied to the soil as triple superphosphate (Ca(H2PO4)2) or as various ammonium

phosphate compounds. It is taken from soil solution as H2P04- or H2P04

2-. . Phosphorous leaching is high

in areas with a high water table. Phosphorous fertilizers carried by runoff threaten surface water bodies.

Too much phosphorous in surface water bodies will cause eutrophication. (Pepper, Gerba and Brusseau

2006)

2.4.3.2 Animal Wastes

Animal wastes are pollutants of increasing concern to public health. In the past, animals were

concentrated only intermittently for short periods followed by a return to pasture as such management

24

activities as milking or shearing took place. Today animal production is done in concentrated animal

facilities that may be located far away from any crop production facility. The animal wastes that initially

were beneficially used as manure for crop production have now become a nuisance especially with

increased use of inorganic fertilizers. Thus the traditional reincorporation of animal wastes back into the

soil no longer happens. (Rao 2007) It might sound unbelievable but many domestic animals are kept

around Nairobi dam and all their waste is dumbed into the reservoir.

Animal Waste Pollutants

Nitrate – Nitrogen – Nitrogen is formed from the ammonification of organic nitrogen contained

in plant materials that animals consume. This ammonia is released through animal urine as urea

then nitrified to nitrates by bacteria, which is subject to leaching in the soil and getting into water

bodies.

Phosphorous – Phosphorous is found in animal feaces as phosphate (PO43-

). Phosphorous

causes eutrophication to surface water.

Feacal coliform bacteria and pathogens – Feacal coliform bacteria are not directly harmful to

humans. They however are an indicator of the amount of pathogens in the feaces of animals. Gut

pathogens from animals may find there way into sources of water and pollute it to an extent that

it becomes unsuitable for drinking.

Biochemical Oxygen Demand (BOD) – Animal wastes have high levels of BOD and will

increase BOD of water bodies they pollute.

2.4.3.4 Pesticides

Pesticides are categorized into

Insecticides – Formulated to control insects.

Herbicides – Formulated to control weeds.

Fungicicides – Formulated to control fungi.

Contact pesticides enter the target pest upon application while systematic pesticides must pass through

a host organism hosting the targeted pest. (Henry & Heinke 1996) The two most important properties of

a chemical that determine whether a pesticide poses a threat to groundwater are persistence and mobility

in the soil. Pesticides with low persistence and mobility are not considered a threat to groundwater

quality. Pesticides are toxic to all forms of life.


25

2.4.4 Surface Run-off

Surface run-off is a major concern in most storm water management problems. Knowledge of the peak

rate of run-off is sufficient for the analysis and design of simple storm water management systems.

Surface runoff is a major discharger of toxic chemicals and solid waste into Nairobi dam.

2.4.4.1 Run-off Processes

The processes that control the generation and transportation of surface run-off must be understood

correctly in order to predict the runoff flow at any point. Run-off is generated when rainfall intensity

exceeds the rate of infiltration of rainwater into the soil. This causes accumulation of water on the

ground surface, which will flow due to gravity in the form of run-off.

Vegetation and other objects may intercept raindrops and allow water to trickle down to the soil surface

at a slower rate that is less likely to exceed the rate of infiltration or exceed it by a smaller margin

reducing the total amount of run-off generated. This process, known as interception, is very important as

it reduces the amount of run-off and its effects. Infiltration rate is normally higher at the beginning of

the storm and reduces as the soil becomes more saturated with water. More run-off is thus generated at

the end of a storm than at the beginning. Storm water run-off generation can be divided into three

processes: -

Hortonian Overland Flow – This process occurs when the rainfall rate exceeds the soil’s

capacity to absorb water and is most common in arid and semi arid areas where hydraulic

conductivity of the soil is low. It is most common in areas with less vegetation and low

interception. (Sincero and Sincero 1996)

Saturation Overland Flow – This process occurs when the water table rises close to the ground

surface and prevents infiltration of water of rainwater into the ground. It is thus more common in

areas with very high rainfall and high sub surface bedrock. It is also common in low-lying areas

where the water table is more likely to be closer to the ground. (Sincero and Sincero 1996)

Sub surface Storm Flow – It involves rainwater flowing just below the ground surface. This

type of flow occurs everywhere but is most common in areas with very high hydraulic

conductivities. The process is not very significant as its volume is very low. (Sincero and

Sincero 1996)

2.4.4.2 The Rational Formula

This is the most common method of estimation of surface run-off. The equation used is

Q = CIA

26

Where C = run-off coefficient

I = Rainfall intensity (cm/hour)

A= Rainfall basin area (ha)

Q = Peak rate of runoff (m3/s)

2.4.4.3 Pollution by Surface Run-off

Surface run-off is a non – point source of water pollution because it is generated and transported as part

of the hydrologic cycle. Unlike point sources that are easier to monitor, non-point sources are harder to

control since they are not concentrated in a small area. They are much more diffuse and are driven by

random intermittent precipitation events. (Pepper, Gerba and Brusseau 1996) The flow rate and quality

of water varies over several orders of magnitude. Surface run-off generates pollutants in the following

ways: -

Accumulation of pollutants occurring on impervious layers is washed off by surface run-off into

water sources.

Erosion loads are transported into water sources bringing in suspended solids and filling up of

reservoirs.

Run-off carries over plant nutrients such as fertilizers from farmlands into water sources causing

eutrophication.

Run-off carries toxic agricultural chemicals from farms into sources of water making it

unsuitable for drinking and also killing aquatic life.

Run-off carries animal wastes from farmlands into water sources. These wastes include plant

nutrients that cause eutrophication and pathogens.

From towns and cities, run-off carries greases from petrol stations and vehicle repair plants into

water sources.

2.4.5 Soil Erosion

Soil erosion is the process by which soil and weathered rock particles are washed off from the surface of

the earth and transported and deposited to other locations. The major negative effect of soil erosion on

water bodies is siltation. Nairobi Dam reservoir looks half filled and soil erosion certainly caused a big

proportion of the filling. The agents that facilitate soil erosion include: -


27

Wind

Water

Animals

Gravity

Glaciers

Water

Water is the biggest cause of soil erosion. The primary cause of water erosion is rainfall. Water erosion

can further be divided into four: -

Splash Erosion

Rill Erosion

Gully Erosion

Sheet Erosion

Splash Erosion is where the impact of a raindrop creates a small crater in the ground ejecting soil

particles. It is the least serious of the types of water erosion.

Rill Erosion involves the development of small concentrated flow paths, which function as both

sediment source and sediment delivery systems for erosion on hill slopes.

Gully erosion occurs when runoff water accumulates and rapidly flows in narrow channels during or

immediately after heavy rains or melting snow, removing soil to a considerable depth.

Sheet Erosion – Soil particles are transported downhill in a uniform sheet over bare ground.

Wind - Wind erosion is common in arid and semi arid areas. It is also a major source of land

degradation, evaporation, desertification, harmful airborne dust, and crop damage. Wind erosion comes

in two forms:

Deflation where the wind picks up and carries away loose particles.

Abrasion where surfaces are worn down as they are struck by airborne particles carried by wind.

Animals - Erosion caused by animals occurs when soil particles stick to animal’s hooves and paws and

are transported to different destinations. This type of erosion is of negligible significance.

28

Gravity - This type of erosion occurs due to mass movement of earth in what is commonly referred to

as Landslides. It can also happen at the banks of rivers and dams with earth material falling into the

water body and filling it.

Glaciers - This is a very serious form of erosion that occurs in very cold areas with snow and glaciers.

Glaciers cut and transport thick layers of rock and earth with them as they move over land. Of course

glaciers as an agent of soil erosion is of no significance in Kenya.

2.4.5.1 Water Pollution Effects of Soil Erosion

Erosion may cause the following types of pollution to water bodies.

Chemical

Biological

Physical

Biological Contaminants are bacteria, viruses and other harmful organisms that are washed into water

sources due to erosion. These organisms may be found living in soil or washed down from septic

systems and solid waste landfills when the soil layer covering them is eroded.

Chemical Contaminants from chemicals embedded in contaminated soils may find their way into

water sources. Landfills and sewer systems whose soil cover layer is washed off by erosion subject

water sources to risks of chemical contamination.

Physical Contamination by soil erosion is basically the contamination caused by the actual soil that’s

deposited in water sources. Suspended solids make water dirty and unusable while plant and animal

residues increased the BOD of the water. Soil deposition into reservoirs fills the reservoir and reduces

its volume capacity.

2.4.5.2 Soil Erosion Control

Soil erosion is a controllable phenomenon. Proper land use and application of the right measures could

reduce soil erosion and reduce its effects to reservoirs and other water bodies. Nairobi dam gets it’s

water from inlets that run from agriculture practicing areas, lack of proper erosion control in these areas

could see Nairobi dam getting polluted due to the effects of soil erosion. The following are practices that

help control soil erosion.


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Contour Ploughing.

Figure 2.1: Contour ploughing

This is a type of farming where crops are planted across a slope along it’s contour lines as shown in the

diagram above. The contours create a water break that reduces velocity of runoff water and prevents

formation of rills and gullies. This type of ploughing reduces soil erosion caused by ploughing of land

which exposes loosely held soil particles to running water. (Wikipedia) Figure 2.1 above is a piece of

land with contour ploughing being practiced on it.

Strip Cropping

This is a type of farming where the farmer alternates rows of crops, which hold soil particles loosely

with those that hold it more firmly to prevent erosion. It can also involve alternating newly sown crops

on loose ground with existing crops that already hold the soil firmly. Figure 2.2 below illustrates strip

cropping a farmland.

30

Figure 2.2: Strip Cropping in Iowa, USA

Terracing

Figure 2.3: Terraced Farmlands in Guanxi Province, China.


31

Terracing is the practice of cutting farmlands on a slope into a series of receding platforms resembling

steps. Sometimes channels may be dug between the terraces. Terraces decrease the velocity of runoff

hence decreasing its power to erode the soil. Figure 2.3 illustrates terracing being practiced in China.

Tree Planting (Agroforestry)

Trees hold soil particles firmly together and help control erosion. Vegetation cover is the most effective

way of controlling erosion in farmlands. The integrated approach of using the interactive benefits from

combining trees and shrubs with crops is called Agroforestry. This practice helps control erosion at the

same time bringing in the commercial benefit of trees. Figure 2.4 below is an illustration of

Agroforestry in Kenya.

Figure 2.4: Agroforestry in Kenya.

32

CHAPTER THREE

3.0 FIELD STUDIES

3.1 Methodology

My approach towards getting the necessary data involved: -

Visual Analysis.

Interviewing the residents.

Selection of Parameters for Sampling.

Collecting Samples.

Selection of test parameters and Testing

Result

3.2 Visual Analysis

The dam (and reservoir) lies between two very different neighborhoods; the middleclass Lang’ata

neighborhood on the west bank and Kibera, the sprawling shanty on the East bank. Most of the pollution

comes from, of course, the Kibera side.

The first impression to a first visitor to the Dam site is always ‘there is no dam here’. From any side, it

looks like a swampy field (that’s if we ignore the stench). The surface of the dam is completely covered

with water hyacinths. Natives have converted more than half of the initial reservoir area to farming

lands. (Kibera residents plant cabbage arrow root, Napier grass and Corn). Some of the inlet streams to

the dam are no different from sewers – it would be hard to convince anyone that it is actually a stream.

Different NGOs have set up on the banks of the dam but they are more concerned on helping some of

the residents earn a living and not exactly restoration of the dam. The area around the dam is stinky and

very unhygienic.

Different structures, both formal and informal, have been constructed dangerously too close to the

reservoir with some even being constructed on filled up areas that were initially covered by the

reservoir. One structure that is quite visible and almost completely is a nice high-rise residential

building constructed just beside the outlet of the dam. Such kind of constructions will obviously course

some trouble to the restoration of the reservoir.

There is garbage thrown everywhere. Plastic and plastic bags have been dumped in heaps into the

reservoir or close to the reservoir. From what the residents said, past excavations show that most of the

filled areas of the reservoir are composed of plastics.


33

One very disheartening observation is the deposition of human feaces into the reservoir and we actually

saw in it happening while on the ground. All this is due to lack of toilet facilities in Kibera slums. The

area is generally in a mess and needs a thorough revival. Figure 3.1, 3,2, 3.3 and 3.4 illustrates general

views of the reservoir and its surroundings from Kibera.

Figure 3.1: A general view of the dam; In the foreground are some arrowroot plantations, the green

fields further behind is the water hyacinth covered surface of the dam and the background is

Lang’ata Estate.

34

Figure 3.2: A different View of the reservoir showing arrowroot plantations, Water hyacinth and nice

apartments constructed too close to the banks.

Figure 3.3: A view of Lang’ata Estate viewed from Soweto across the reservoir.


35

Figure 3.4: Apartments Constructed dangerously at close to the Dam outlet.

The Dam’s spillway is pretty old and dilapidated despite attempts to repair it. Figures 3.5, 3.6, 3.7 and

3.8 shows some parts of the dilapidated spillway.

Figure 3.5: A view of the spillway of the Dam

36

Figure 3.6: More of the spillway

Figure 3.7: This is the section where water enters the spillway.


37

Figure 3.8: The spillway overlooking Highrise Housing Estate.

Figure 3.9: Plastics dumped in one of the inlet streams

38

Figure 3.10: More plastics dumped in one of the inlet streams

3.3 Interviewing Residents

An NGO at Undugu Primary school runs a project called Pee Poo where people collect their feaces in

paper bags and instead of dumping it into the dam, give it out where it is taken to be transformed into

manure for farming. The NGO has also introduced greenhouses for farming to help the slum dwellers

earn a living. The natives are quite excited with the slum-upgrading project though some are skeptical

that the buildings might be rented to people who were not residents initially. Some residents have taken

action through construction of gabions which reduces the amount of sedimentation occurring in the

reservoir.Figures 3.11, 3.12 and 3.13 illustrates efforts by the society to reduce the amount of pollutants

dumped into the reservoir.


39

Figure 3.11: A Greenhouse project by Undugu Self Help Group on a filled part of the reservoir.

Figure 3.12: A Toilet initiative of the Pee Poo project – the human waste is collected from the bottom

chambers and transported for conversion into manure.

40

Figure 3.13: Part of the structures built by the slum-upgrading program. If successful, this project

would greatly improve the sanitation of the area and reduce the amount of garbage dumped into the

dam.

3.4 Selection of Parameters for Sampling

Selection of points of collecting samples was based on: -

Points of sources of pollution

Inlet points to the Reservoir.

Outlet Points from the Reservoir.

Using this it will be possible to determine which inlet pollutes the reservoir most and the quality of

water getting into and out of the reservoir. The sampling was done in a dry season so it reflects the worst

quality of water discharged into the dam though it will have the least sediments in it.

Owing to the bad security record of the area, I had to do a reconnaissance first accompanied by a friend

and then got a resident to take me around on the actual sample collection day. The samples were

collected in washed, rinsed and dried plastic soda bottles and marked


41

3.5 Collecting Samples

Sampling was done during the day. It was a dry season so the samples were quite concentrated. I

intended to collect samples twice, in the dry and wet season but unfortunately the project time did not

overlap both seasons. Cleaned and rinsed and dried plastic bottles were used to collect the samples and

transport them to the laboratory.

42

CHAPTER FOUR

4.0 RESULTS

4.1 Sampling Stations

4.1.1 Location

The Nairobi dam is located in the South West of Nairobi County (former Nairobi Province). It’s

reservoir covers the area between Lang’ata Estate and Kibera slums. It’s main inlets are Motoine River

and it also has smaller streams, Ngong Stream and Soweto stream emptying into the reservoir.

The sampling stations were selected such that they brought about a summarized analysis of the whole

reservoir. The stations were strategic so as to determine the quality of water getting into the dam and the

quality getting out. The stations were thus basically located at the major inlets of the reservoir and

another one at the outlet (spillway) of the dam. The following stations were chosen: -

Station 1 = Dam outlet

Station 2 = Soweto Stream inlet

Station 3 = Motoine River inlet (main inlet)

Station 4 = Ngong Stream inlet

Figure 4.1 illustrates the locations of the sampling stations on the Nairobi dam map.

Figure 4.1: Location of the Sampling stations on the reservoir map.


43

On the satellite image shown below, you can see that most of the reservoir is either filled upor covered

with water hyacinth. A closer view of the satellite image of the dam showing a very small section that is

neither filled nor covered with water hyacinth.

Key

Water hyacinth and other vegetation covering the reservoir.

Visible water.

Figure 4.2: Satelitte image of the reservoir.

Note from Google maps the main inlet to the reservoir is known as Nairobi River but that’s actually the

Motoine River. Nairobi River runs from the North west into the city close to the CBD towards the East.

44

Table 4.1: Description of Sampling Stations

Station Name Description

1 Motoine River - Main Inlet Strong smell. Water turbid and grey in colour;

Some garbage dumped in the stream.

2 Soweto Stream

Inlet

Extreme pollution; the stream is practically a

sewer, water black in colour; excessive dumping

of garbage in the stream; strong awful smell

3 Ngong River - Inlet Dirty turbid water with a few plastics dumped in

the stream. The stream was the cleanest of the

three though – we were told that people even

bathed in this stream.

4 Spillway

Dam Outlet

Black fast running water with an awful smell.

4.2 Selection of Test Parameters and Testing.

The parameters of testing were chosen such that they describe all dimensions of pollution of the water

and also help identify the sources of pollution.

The reasons for doing the testing were: -

To identify the palatability of the water

To identify the kind and source of pollution of the water

To check the clarity of the water

To identify the bacteriological quality of the water

To check the type of chemicals present in the water.

Standard procedures were used in conducting of the laboratory tests.s

4.2.1 Biochemical Oxygen Demand

The Biological Oxygen Demand (BOD) ranged from93mg/l to 260mg/l. Table 4.2 and Chart 4.1 below

shows the variations of BOD5 levels with stations as recorded in the laboratory: -


45

Table 4.2: BOD5 Variation with stations

Station BOD5 (mg/l)

1. Dam Outlet 100

2. Soweto Stream 260

3. Motoine River 195

4. Ngong Stream 93

Chart 4.1: Variation of BOD5 by station

4.2.2 Chemical Oxygen Demand

The COD was determined by use of standard tests. The COD values varied from 128mg/l to 352mg/l.

Table 4.3 and Chart 4.2 illustriates how the COD varied with the stations.

0

50

100

150

200

250

300

1 2 3 4

BO

D i

n m

g/

l

Sampling Stations

BOD (5 days, 20 degrees)

BOD (5 days, 20 degrees)

46

Sample COD (mg/l)

1. Dam Outlet 144



4. Ngong Stream 128

Table 4.3: COD Variation with stations

Chart 4.2: Variation of COD by station

4.2.3 Feacal Coliform Count

From the standard test that was employed, the feacal coliforms varied from 94 counts/ml to 299

counts/ml. The table 4,4 and Chart 4.3 illustriate how the feacal coliform counts varied with the station.

0

50

100

150

200

250

300

350

400

1 2 3 4

CO

D i

n m

g/

l

Sampling Stations

COD

COD


47

Table 4.4: Feacal Coliform Count Variation with station

Station Counts/ml

1. Dam Outlet 165



4. Ngong Stream 94

Chart 4.3: Variation of Feacal Coliform Count with station

4.2.4 pH Levels

Good quality water has an almost neutral pH. pH levels in these samples were found not vary so much

from the neutral with the highest pH recorded being 7.5 while the lowest was 7.14. Table 4.5 and Chart

4.4 below illustrate how the pH varied with the stations.

0

50

100

150

200

250

300

350

1 2 3 4

Co

lifo

rm C

ou

nts

/m

l

Sampling Station

Counts/ml

Counts/ml

48

Table 4.5: pH Levels Variation with stations

Station pH

1. Dam Outlet 7.25

2. Soweto Stream 7.14

3. Motoine River 7.50

4. Ngong Stream 7.44

Chart 4.4:Variation pH levels with station

4.2.5 Conductivity

Conductivity of water measures the amount of ions in the water. Conductivity of these samples was

quite high with the lowest conductive sample registering a conductivty of 491 µS against a highest of

1642 µS as shown below in Table 4.6 and Chart 4.5.

6.9

7

7.1

7.2

7.3

7.4

7.5

7.6

1 2 3 4

pH

Sampling Station

pH Level

pH Level


49

Table 4.6: Conductivity Variation with stations

Station Conductivity (µS)

1. Dam Outlet 780



4. Ngong River 491

Chart 4.5: Variation Conductivity with station

4.2.6 Nitrates

Nitrogen is present in water majorly in the form of nitrates. The samples contained some Nitrates with

the most concentrated sample having 7mg/l of Nitrates while the least concentrated had 6.6mg/l as

shown in Table 4.7 and Chart 4.6.

0

200

400

600

800

1000

1200

1400

1600

1800

1 2 3 4

Co

nd

uct

ivit

y i

n µ

S

Sampling Station

µS

µS

50

Table 4.7: Nitrate Concentration Variation with stations

Station Nitrates (mg/l)

1. Dam Outlet 7.0



4. Ngong Stream 6.5

Chart 4.6: Variation of Nitrate Concentration with station

4.2.7 Colour

The colour of water is merely a physical visual aspect of the water that can be detected by mere

observation. However due to different individual perspectives, the colour tests were done in the lab too.

The colour ranged from 1400 Hazen to 560

0 Hazen. Table 4.8 and Chart 4.7 show how colour varied in

the sampled stations.

6.2

6.3

6.4

6.5

6.6

6.7

6.8

6.9

7

7.1

1 2 3 4

Nit

rate

s in

mg

/l

Sampling Station

Nitrates (mg/l)

Nitrates (mg/l)


51

Table 4.8: Colour Variation with stations

Station 0 Hazen

1. Dam Outlet 1400

2. Sowero Stream 5600


4. Ngong Stream 6300

Chart 4.7: Variation Colour Concentration with station

4.2.8 Suspended Solids

Station 2 had the highest conventration of suspended solids at 200mg/l while station 4 had the lowest

concentration at 50mg/l. Table 4.9 and Chart 4.8 give a clearer presentation of how the concentration of

suspended solids varied with the stations.

0

100

200

300

400

500

600

700

1 2 3 4

De

gre

es

Ha

zen

Sampling Station

Degrees Hazen

Degrees Hazen

52

Table 4.9: Total Suspended Solids Variation with stations

Station TSS (mg/l)

1. Dam Outlet 120



4. Ngong Stream 50

Chart 4.8: Variation Total Suspended Solids with station

4.2.9 Dissolved Oxygen

Station 1 at 3.5 mg/l had the highest concentration of dissolved Oxygen while station 2 had the lowest at

2.8 mg/l. Table 4.10 and Chart 4.9 give a clearer view.

0

50

100

150

200

250

1 2 3 4

To

tal

Su

spe

nd

ed

So

lid

s (m

g/

l)

Sampling Stations

TSS(mg/l)

TSS(mg/l)


53

Table 4.10: Dissolved Oxygen Variation with stations

Station D.O mg/l

1. Dam Outlet 3.5



4. Ngong Stream 4.5

Chart 4.9: Variation Dissolved Oxygen with station

Appearance Taste and Odour

This was determined on site - of course we couldn’t taste the water because it was extremely polluted

beyond human palatability. The water was generally dirty and had a foul smell.

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

1 2 3 4

Dis

solv

ed

Ox

yg

en

(m

g/

l)

Sampling Stations

D.O

D.O

54

CHAPTER FIVE

5.0 DISCUSSION

5.1 Biochemical Oxygen Demand

From the results, Station 2 (Soweto stream) had the highest BOD levels at BOD5 of 260mg/l. Station 4

had the least BOD at BOD5 of 93mg/l. The average BOD5 of raw sewage is about 260mg/l so station 2

is practically a sewage channel discharging into the dam if its BOD is to go by. The BOD at the outlet

was lower than the total incoming BOD. This is an indication some waste was being impounded within

the dam and that the water takes quite some time to move from the inlets to the outlet giving it time to

break down some of the BOD.

The presence of water hyacinth in the reservoir also meant more oxygen produced by photosynthesis

and more carbon dioxide consumed too. The produced Oxygen was used by bacteria to break down

some of the organic matter hence considerably reducing the BOD of the water at the outlet. Very high

BOD levels were recorded from the inlet streams due to lack of proper sanitation in the slum areas and

lack of a proper sewerage system that leads to residents dumping human wastes into the river.

The average BOD of unpolluted water is about 2mg/l (Chapman 1992). Looking at the results above, the

state of the water is a far cry from good quality water and is in fact best described as polluted.

5.2 Chemical Oxygen Demand

The COD, just like the BOD were very high and varied in a similar pattern as the BOD from station to

station. The maximum COD was at station 2 with a COD of 352mg/l while the minimum COD was at

station 4 with a COD of 124mg/l. Generally in unpolluted water, the COD should be less than

20mg/l(Chapman 1992), in this particular case, the lowest COD was 124mg/l.

5.3 Dissolved Oxygen

In streams the average daily dissolved oxygen to be no less than 5.0 mg/l and individual readings should

never be less than 4.0 mg/l. When DO standards are not met due to natural conditions, a DO deficit of

0.1 mg/l below the natural concentration which is caused by anthropogenic activities will be allowed

(SCDHEC 1998). D.O the reservoir water varied between 2.8mg/l to 4.5mg/l. These levels are too low

for the survival of fish in the reservoir rendering sport fishing impossibe in the reservoir. ( According to

the South Carolina Department of Health and Control, most fish cannot survive in water with D.O

concentrations of less than 5.0mg/l)

http://www.nerrs.noaa.gov/doc/siteprofile/acebasin/html/glossary/glintro.htm#anthropogenic


55

5.4 Feacal Coliform Count

Fecal coliform concentrations for river waters are required to remain below a geometric mean of 200 per

100 ml, based on five separate samples during a 30-day period, and no more than 10 percent of all

samples may exceed 400 per 100 ml. This is according to the American river standards. In Nairobi Dam,

the feacal coliform count hit an extreme too with the station with the lowest count, station 4, having 94

counts/ml (9400counts/100ml) while the worst station, station too had 299 counts/ml (29900

counts/100ml). Fromthe field study, visible disposal of human waste into the reservoir are the major

cause of this very high feacal coliform counts. NEMA standards for recreation waters does not give any

allowance for feacal coliforms in the water. (see Tenth Schedule: Quality Standards for Recreation

Waters attached)

5.5 Suspended Solids

From the results, the least polluted sample had 50mg/l of suspended solids (samples 4) while the least

polluted sample had 200mg/l of suspended solids (sample 2). The net suspended solids getting into the

reservoir is a bit higher than the net leaving the reservoir (The main inlet has 150mg/l SS, the second

largest inlet has 200mg/l SS while the outlet has 120mg/l SS). This is an indication that there is some

siltation happening in the reservoir thus causing the filling up of the reservoir.

5.6 pH

NEMA allows a pH of 6 - 9 in recreational water. (see Tenth Schedule: Quality Standards for Recreation

Waters attached) In its initial state, Nairobi Dam was used for recreation and restoring it to its former

self includes restoring its recreational aspect too. The pH of water from Nairobi dam reservoir was

found to be slightly above neutral but almost uniform over the four stations under consideration. The

station with the highest pH, station 3, had a pH of 7.50 while the station with the lowest pH had 7.14.

The slight basic characteristics of the water are probably due to the numerous water plants (like water

hyacinth) and algae, which utilize carbon dioxide during photosynthesis hence increasing the pH value.

Despite this, the pH levels of the water fell well in the allowed range of 6.5 – 8.5. The pH of the water

lies within the required range as set by NEMA. (See Tenth Schedule; Quality Standards for Recreational

Waters)

5.7 Nitrates Concentration

The four stations from the Nairobi Dam reservoir had nitrate concentrations of between 6.5mg/l to 7.0

mg/l. The presence of the nitrates is probably because the inlet rivers run from farmlands up in Ngong

hence bring down the fertilizer residues from the farms with them. Nitrates, alongside phosphorous and

other plant nutrients, cause the algal bloom and growth of water hyacinth in the dam.

56

5.8 Colour

The water was heavily coloured. The dark colour is due to deposition of domestic wastewater into the

dam and algal blooms. Deposition of soil and farm waste products arising from the farming activities on

the shores of the reservoir is also another factor causing this deep colour. NEMA quality standards for

recreational water allows a maximum of 100 TCU (True Colour Unit) for recreation water (See Tenth

Schedule; Quality Standards for Recreational Waters attached at the end of the chapter), in this case, the

water had TCUs ranging from 140 – 630 TCU. (1 TCU approximately 10 hazen after filtration)

5.9 Conductivity

The water had high conductivity. This is probably due to a high mineral content that comes from small

Jua Kali industries from Kibera slum judging from the fact that station 2, which is situated at the mouth

of the Soweto stream inlet that flows directly from Kibera slum had an exceptionally high conductivity

(1642 µs) in comparison to the other stations.

N/B

Contrary to what international media has been quoting over the years as Kibera population, the

population is not that big. From the 2009 Population Census, Kibera’s population was only about

170,000 people and shrinking contrary to figures quoted as high as 2,000,000 people. (The most popular

figures thrown around are 500 000, 800 000 and 1 000 000 people) (Kenya National Bureau of

Statistics). The figure is perhaps exaggerated by fund seeking NGOs that operate within the slum in the

name of bettering the slum dwellers lives so as to convince donors.

The average water consumption per day per head in slum areas in Kenya is about 50 litres per head per

day. Total wastewater production is equal to about 80% of total water consumption.

Total water consumption = 170,000 x 50/1000 = 8500m3 of water per day

Total wastewater production = 8500 x 0.8 = 6800m3

of wastewater per day

Much of this wastewater is dumped in Nairobi dam causing pollution in it.


57

58

CHAPTER SIX

6.0 CONCLUSIONS AND RECOMMENDATIONS

6.1 Conclusion

Nairobi Dam reservoir is heavily polluted. It has characteristics of sewage. Without being told, a

new visitor to Nairobi Dam will see negligence as the biggest problem affecting the dam. The

aesthetic value of the dam is pathetic. Most natives don’t even know that it is a dam; they think it

is a dumpsite. The following are the main sources of pollution in Nairobi dam: -

1. Dumping of organic wastes into the reservoir increasing the BOD and the COD of the water in

the reservoir. Another cause of this is the death and decay of aquatic plants such as water

hyacinth hence releasing organic matter into the water.

2. The lack of a sewerage system in Kibera slums resulting in domestic wastewater being deposited

directly into the dam

3. Farming activities around the reservoir by ignorant residents cause high feacal coliform counts

since the animal excreta ends up in the reservoir hence polluting it with pathogenic

microorganisms that live in the intestines of warm blooded animals.

4. Deposition of Nitrates and phosphates from the farming activities up in the Ngong hills.

5. Metal ions from Jua Kali industries in Kibera slums end up in the reservoir via runoff or via

domestic wastewater resulting in the high conductivity of the water in the reservoir.

6. Illegal farming activities. Illegal farmers till land and fill the reservoir with soil causing water to

be polluted by the soil and turn its colour to black/brown.

The major points of pollution in the reservoir are the inlet streams. Most of the wastewater is deposited

into the inlet streams before flowing ino the reservoir.

6.2 Recommendations

Nairobi Dam a national gem, a source of income to Nairobi City Council, a recreation and an

aesthetically appealing point within the city of Nairobi. Currently the dam is practically the exact

opposite of all these. The following recommendations have been proposed to reduce the impact of

pollution in the dam and help restore it to its former glory: -

1. Deploying employees of the NCC to the area to help in implementation of the waste

management regulations. Deploying enforces in the region will ensure no one dumps plastic

waste and other forms of waste directly into the reservoir.


59

2. Slum upgrading and installation of a good sewer system in the slums is a key step in stopping

release of pollutants into the dam.

3. Prosecute relocated slum dwellers who rent off their allocated high-rise apartments to non

Kibera residents at a higher rent rate only to end up building other shacks for themselves.

4. Design a new sewage system for the slum and better structures put up.

5. Regulation of farming activities in the Ngong hills to avoid deposition of farming chemicals into

the reservoir. The improved farming techniques discussed in literature review (agroforestry, strip

farming, contour ploughing etc) should be employed.

6. Implement laws to prevent settlement and agricultural activities too close to the reservoir and it’s

inlets.

7. Plant trees on the banks of the inlets where possible.

8. Leave a reasonable space left between the reservoir and settlements to prevent direct deposition

of pollutants into the water and a nice vegetation cover helps control deposition of pollutants by

surface runoff.

9. Improve garbage collection in Kibera and deploy garbage collection trucks probably at a lower

cost than normal putting into consideration the low-income levels of the residents of Kibera..

10. Employ Dredging in the reservoir to increase the volume of the reservoir, remove pollutants

from the reservoir making it suitable for storage of clean water and restore the reservoir for

leisure activities.

11. Structural repair of the Dam – Repair the spillway. After dredging, some riprap should be lined

on the banks of the reservoir where necessary to avoid falling in of the banks too.

12. Removal of Water Hyacinth from the reservoir surface.

Implementation of these recommendations could restore the lost glory of the Nairobi Dam and become a

key step in the implementation of the Vision 2030 flagship projects.

…………………END………………..

60

REFERENCES

1. Allan C Twort, (1974) – Water Supply, American Elsevier Pub. Co.

2. Arcadio Pacquiao Sincero and Gregoria Alivio Sincero (1996) – Environmental

Engineering, Prentice Hall of India.

3. C.S Rao, (2007) – Environmental Pollution, New Age International Pvt Ltd Publishers,

New Delhi, India.

4. EPA (United States Environmental Protection Agency.

5. Google maps 2014.

6. Ian L. Pepper, Charles P. Gerba and Mark L. Brusseau (1996) – Pollution Science,

Academic Press, Waltham Massachusets, USA.

7. Ian L. Pepper, Charles P. Gerba and Mark L. Brusseau (2006) – Environmental and

Pollution Science, Academic Press, Waltham Massachusets, USA.

8. J Glynn Henry and Gary W Heinke (1996) – Environmental Science and Engineering,

Prentice Hall International, London UK.

9. Krhoda G. (2002) – Nairobi River Basin Project Phase 11.

10. Nairobi City County Website

11. Ndede H. (2002) – The Nairobi River Basin Project Phase 11.

12. NEMA Website - Quality Standards for Recreational Waters

13. R.O Preston (1947) – The Genesis of Kenya Colony, Colonial Print Works.

14. S.M Khopkar, (2007) – Environmental Pollution Monitoring and Control, New Age

International Pvt Ltd Publishers, New Delhi, India.

15. Sunday Standard May 2, 2004, The Standard Media Group publishers

16. SCDHEC (South carolina Department of Health and Control) website

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