ivan report

8/7/2019 Ivan Report

1/70

MAKERERE UNIVERSITY

FACULTY OF TECHNOLOGYDEPARTMENT OF CIVIL ENGINEERING

PERFORMANCE OF BIOSAND FILTERS WITHPRETREATMENT IN IMPROVING THE QUALITY OF RAW

WATER FOR DRINKING PURPOSES

A final year project report submitted in partial fulfilment of the

requirement for the award of the Degree of B.Sc. CivilEngineering

Main Supervisor: MRS KULABAKO ROBINAH

Signature:

Co Supervisor: ENG. Dr. RUGUMAYO ALBERT

Signature:

Student: MASUBA IVAN

Reg. No: 03/U/314

Signature:


2/70

DEDICATION

This work is dedicated to my family and relatives.

i


3/70

ACKNOWLEDGEMENT

First and foremost, I would like to express my sincere gratitude to the Village Health

Project of the University of Wisconsin-Madison, USA for the financial support that hasgreatly facilitated this research. To Mr Kimera without him, it would have not been

possible to conduct this research.

Limitless thanks go to my faculty supervisors Mrs. Robinah Kulabako and Eng. Dr.

Rugumayo for their tireless contribution to this research project.

My sincere thanks go to Rita, Moses and Budigi for their technical support offered during

the laboratory sessions of this study.

I also wish to extend my gratitude to my fellow colleagues more especially Charles

Kalinaki who was a partner in this research.

Finally, my special appreciations go to my family and relatives for their continued

support and above all to the Almighty God without whom, I would not be.

ii


4/70

ABSTRACTThis study was conducted to assess the performance of biosand filters with cloth pre-

filtration in improving the quality of drinking water from different domestic sources in

Kampala (Kawempe division). It involved the construction, installation and the

commissioning of three biosand filter units.

Field visits were undertaken to identify and locate the domestic water supply sources and

collect water samples from these sources; a spring, a shallow well and a concrete

rainwater tank supplied by an iron roof catchment. Laboratory experiments were then

undertaken to determine the quality of raw water from these sources, cloth filtered water

and treated biosand filtered water.

Results showed that the raw water sources were contaminated with the worst

bacteriological contamination in the shallow well (upto 10300 TTCs cfu/100ml). The

cloth filtration prior to the BSF improved the quality of the raw water particularly the

microbiological quality and turbidity by over 30 to 50% and therefore the BSFs with

prior cloth filtration performed better than those without with respect to these parameters.

The filters flow rates were between 1.25 1.67 L/min through out the test period and

hence due to the limited duration of the research study the filter runs were not

ascertained. From this, it is recommended that the filters should be tested for a longer

period preferably at least one year to cover the impact of seasonal variations and to

determine filter runs. Since the BSFs did not completely remove the faecal bacteria

coliforms, further treatment of the filtered water is recommended for example with

chlorine disinfection to kill off the remaining pathogens.

iii


5/70

TABLE OF CONTENTS............................................................................................................................ 1

DEDICATION ......................................................................................................................iACKNOWLEDGEMENT ...................................................................................................ii

ABSTRACT .......................................................................................................................iii

LIST OF FIGURES ............................................................................................................. vLIST OF TABLES ............................................................................................................... v

CHAPTER 1- INTRODUCTION ........................................................................................ 1

1.1 BACKGROUND AND JUSTIFICATION OF STUDY ........................................... 11.2 STATEMENT OF THE PROBLEM .........................................................................2

1.3 STUDY AREA .......................................................................................................... 2

1.4 OBJECTIVES ............................................................................................................31.5 SCOPE ....................................................................................................................... 3

1.6 REPORT LAYOUT ................................................................................................... 3

CHAPTER 2 - LITERATURE REVIEW ............................................................................ 5

2.1 INTRODUCTION ..................................................................................................... 5

2.2 WATER QUALITY ...................................................................................................52.2.1 Bacteriological Quality Aspects ......................................................................... 5

2.2.2 Physical Quality Aspects .................................................................................... 52.2.3 Chemical parameters ...........................................................................................7

2.2.4 Water Quality Standards ..................................................................................... 8

2.3 SOURCES OF DRINKING WATER ...................................................................... 92.3.1 Shallow groundwater .......................................................................................... 9

2.3.2 Rainwater harvesting ....................................................................................... 10

2.4 WATER TREATMENT PROCESSES ..................................................................10

2.5 BIOSAND FILTER TECHNOLOGY ..................................................................... 112.5.1 Theory of Biosand Filtration .............................................................................12

2.5.2 Pre-Treatment of Raw Water Prior to BSF .......................................................132.5.3 Benefits of Biosand Filtration ........................................................................... 162.5.4 Performance and Considerations of Biosand Filtration ................................... 16

CHAPTER 3 - MATERIALS AND METHODS ..............................................................18

3.1 INTRODUCTION ...................................................................................................183.2 ACTIVITIES ............................................................................................................18

3.2.1 Construction of Biosand Filters ........................................................................ 18

3.2.2 Installation and Commissioning ....................................................................... 203.2.3 Source Identification and Water Sample Collection .........................................21

3.2.4 Experimental set-up ..........................................................................................22

3.3 METHODS .............................................................................................................. 23

3.3.1 Water Quality Analysis .....................................................................................233.3.2 Filter Run .......................................................................................................... 25

3.4 DATA ANALYSIS ..................................................................................................25

CHAPTER 4 RESULTS AND DISCUSSION ...............................................................264.1 INTRODUCTION ...................................................................................................26

4.2 WATER QUALITY .................................................................................................26

4.2.1 pH ......................................................................................................................264.2.2 Temperature ...................................................................................................... 29

iv


6/70

4.2.3 Turbidity ...........................................................................................................31

4.2.4 Apparent Colour ...............................................................................................35

4.2.5 Dissolved Oxygen, DO ..................................................................................... 384.2.6 Electrical conductivity, EC ............................................................................... 39

4.2.7 Iron and Manganese ..........................................................................................44

4.3 FLOW RATES ........................................................................................................52CHAPTER 6 CONCLUSIONS AND RECOMMENDATIONS ................................... 54

5.1 INTRODUCTION ...................................................................................................54

5.2 CONCLUSIONS ......................................................................................................545.3 RECOMMENDATIONS ......................................................................................... 55

REFERENCES ..................................................................................................................56

APPENDIX ........................................................................................................................58

A.1: Table of Results .....................................................................................................58A.2: BSF Construction Photos ....................................................................................... 62

LIST OF FIGURES

LIST OF TABLESFigure 1. 1: Map of Kampala showing the study areas in Kawempe division (The

positions of the water sources are approximate)..................................................................4

Table 2. 1: Classification of raw waters according to bacterial numbers as given by theWHO European standards (Source: Twort et al., 1985)......................................................8

Table 2. 2: Drinking Water Standards (Source: DWD, 2005).............................................9

Table 2. 3: Water treatment processes (Source: CRC, 2005)............................................11

Figure 2. 1: Cross section of a typical biosand filter (Source: Manz, 2006).....................12Table 2. 4: The different forms of pre-treatment methods (Source: Herman et al., 1996)

............................................................................................................................................14

Table 2. 5: Performance of Biosand Filter (Source: Manz, 2006)....................................17

Figure 3. 1: A spring in Makerere Kikoni..........................................................................21Figure 3. 2: A shallow well in Mukere, Kawempe I..........................................................22

Figure 3. 3: A concrete rainwater tank at Dr. Musaazi Residence in Makerere University............................................................................................................................................22

Figure 3. 4: Shows the stages of raw water treatment.......................................................22

Figure 4. 1: pH variation of the raw, pretreated water and BSF effluents with time.........29

Figure 4. 2: Temperature variation of raw, pretreated water and BSF effluents with time.............................................................................................................................................30

v


7/70

Figure 4. 3: Turbidity Variation of raw, pretreated water and BSF effluent with time.....34

Figure 4. 4: Turbidity comparison of BSF with or without cloth filtration.......................35

Figure 4. 5: Colour variation with time of raw, pretreated water and BSF effluents........38Figure 4. 6: DO variation of raw, pretreated water and BSF effluent with time...............41

Figure 4. 7: EC variation of raw water, pretreated water and BSF effluent with time......44

Figure 4. 8: Iron variation of raw, pretreated water and BSF effluent with time..............47Figure 4. 9: Manganese variation of the raw, pretreated water and BSF effluent with time.

............................................................................................................................................48

Figure 4. 10: TTCs and E. coli variation of raw, pretreated water and BSF effluent withtime....................................................................................................................................51

Figure 4. 11: TTCs comparison in the BSF effluent with or without pre-filtration...........52

vi


8/70

CHAPTER 1- INTRODUCTION

1.1 BACKGROUND AND JUSTIFICATION OF STUDY

The demand for water is rapidly increasing at a rate three times faster than the worldspopulation growth. It was highlighted at the 3 rd World Water Forum that about 1.2 billion

people in the world are lacking safe water supplies. This Forum and many more in the

past have consistently emphasized the need for local communities, governments, and

non-government organizations to build on sustainable development and technologies to

improve water supply and sanitation needs in developing countries (Yung, 2003).

Currently 2.3 billion people suffer from diseases related to unclean water conditions,

resulting in 5 million deaths each year which is ten times the number of people killed in

wars (Kelly et al., 2004). To address this need, low cost and appropriate water treatment

technologies have been developed and implemented world wide. Examples of these

include: the traditional slow sand filters, the rapid sand filters, biosand filters, purifier of

water (PuR), fabric filters, use of coagulants and flocculants, sedimentation, and many

more. However of interest to this study is the use of biosand filter technology to address

the above issues. It is an innovation on traditional slow sand water filters, having been

specifically designed for intermittent use because of its adaptability and sustainability in

developing communities. It can achieve excellent removals of waterborne pathogens, is

cheap to construct, requires little maintenance, and operates under gravity flow

conditions (ie. no pumping required during treatment). The technology has the ability to

improve community health. Overall, it is an attractive technology for local governments

on a limited budget, as well as hospitals, humanitarian NGOs, disaster relief camps and

individual households (Cleary et al., 2004).

Recent studies show that there are 20,000 household size concrete BioSand Filters (BSF)

in over 30 developing countries. The BSF is a simple and robust design and is made from

readily available materials such as concrete, sand, and piping. However, in the case of

almost all projects, the BSF continues to require more research and address issues such as

1


9/70

the appropriateness of the design when applied to a developing country, cost, and the

technical problems that the BSF encounters under different environments (Yung, 2003).

In Uganda, increased urbanization and industrialization in the recent years, especially in

the capital city, Kampala has led to an increase in the citys population and development

of informal settlements. The informal low-cost settlements in peri-urban areas lack or

have inadequate clean water supply (Kulabako, 2005). Therefore this project was

designed to assess the performance of biosand filters with pretreatment in improving the

quality of raw water from different domestic supply sources for drinking purposes in

Kampala, Uganda.

1.2 STATEMENT OF THE PROBLEMIt has been observed that the poor environmental sanitation in peri-urban settlements in

Kampala has consequently led to contamination of the shallow groundwater aquifers, a

source that is heavily relied on by these communities (Howard et al., 2003). In 2004 for

example cholera hit Kawempe and parts of central division of Kampala claiming over 12

lives. According to the Ministry of Health statistics, the cholera epidemic claimed 119

lives in Uganda in 2002. A recent out break of cholera in Kawempe and Makindye

divisions which saw 147 patients admitted and ten dead in Kampala (Mwanje, 2006).

This therefore calls for a need to develop suitable and less costly technologies that will

safely treat contaminated waters to make them suitable for drinking as given by the WHO

and National guidelines for drinking water quality.

This study assessed the performance of BSF technology with regard to drinking water

treatment. Like all other slow sand filters, the BSFs can only treat relatively clear water,

pretreatment was included to cater for high turbid waters as well as improve on the

bacteriological quality of water.

1.3 STUDY AREA

The selected study areas were located in Kawempe division of Kampala (Fig 1.1) and

included: a spring situated in Makerere Kikoni which lies on the western side of

Makerere University campus and is about 3 km northwest of Kampala city centre; a

2


10/70

shallow well located in Mukere, Kawempe about 5 km from Kampala centre; and a

concrete rain water tank situated at Dr Musaazi residence in Makerere University. These

areas with the exception of Makerere University are informal low-lying settlements with

a high population density. They have inadequate infrastructure and poor services

including water supply. The water table in these areas is high and prone to anthropogenic

pollution.

1.4 OBJECTIVES

The aim of this project was to assess the performance of a biosand filter with

pretreatment in improving the quality of raw water from different sources for drinking

purposes.

The specific objectives were to:

i) construct three full scale models of the biosand filters

ii) identify the different domestic water supply sources and collect samples from

these sources.

iii) determine the raw water quality from the selected water sources prior to treatment

and also to determine the quality of influent (pretreated water) and effluent from

the BSF.

iv) compare the performance of BSF with or without pretreatment so as to justify or

otherwise the essence of the pretreatment stage.

v) determine the filter run and hence make recommendations on the filter with or

without pretreatment.

1.5 SCOPE

The study was limited to water sources in Kampala, specifically a spring, shallow well

and collected rainwater from an iron roof house. Drinking water treatment was limited to

the BSF with cloth filtration. Water quality tests were limited to pH, temperature, DO,

EC, turbidity, colour, iron, manganese, thermotolerant coliforms and E. coli.

1.6 REPORT LAYOUT

This project research report is organized into five chapters. Chapter one provides

background information to the study. Chapter two covers the literature on water quality

standards, the drinking water sources, water treatment processes and the BSF

3


11/70

technologies including pretreatment methods. Chapter three illustrates the methodology

used to achieve the objectives of the study. Chapter four presents results and discussions.

Chapter five gives conclusions and recommendations based on the outcome of the study.

Figure 1. 1: Map of Kampala showing the study areas in Kawempe division (The positions of the water

sources are approximate)

MAKEREREUNIVERSITY

Shallow well in Mukere Kawempe I

Spring in Makerere Kikoni

Rain concrete tank in Makerere University

Makindye

Nakawa

Rubaga

Central

Kawempe

N

4


12/70

CHAPTER 2 - LITERATURE REVIEW

2.1 INTRODUCTION

In many developing countries adequate sanitation facilities are scarce to non-existent

especially in the rural areas as well as in informal settlements in the peri-urban areas of

the cities. Sanitation issues increase when rural or urban areas become densely populated

without appropriate water treatment services and sewage is left untreated in the

communitys drinking water supply (Yung, 2003). This chapter covers the literature on

water quality standards, the drinking water sources, water treatment processes and the

BSF technologies including pre-treatment methods.

2.2 WATER QUALITYThis section covers aspects of bacteriological quality, physical quality, chemical quality

and the water quality standards.

2.2.1 Bacteriological Quality Aspects

The main purpose of bacteriological examination is the detection of the recent faecal

contamination and pollution in drinking water sources. Ideally, drinking water should not

contain any microorganisms known to be pathogenic. It should also be free from bacteria-

indicative of excremental pollution. Water samples should be examined regularly for

indicators of faecal pollution (Hutton, 1990). The primary bacterial indicator for this

purpose is the coliform group of organisms, in particular the E. coli and thermotolerant

coliforms found in the faeces of man and other warm blooded animals. The verification

of the microbial quality of drinking-water includes testing forEscherichia coli as an

indicator of faecal pollution. E. coli provides conclusive evidence of recent faecal

pollution and should not be present in drinking-water. In practice, testing for

thermotolerant coliform bacteria can be an acceptable alternative in many circumstances

(WHO, 2006).

2.2.2 Physical Quality Aspects

Turbidity

Turbidity is a measure of the cloudiness of water- the cloudier the water, the greater the

turbidity. Turbidity in water is caused by suspended matter such as clay, silt, and organic

5


13/70

matter and by plankton and other microscopic organisms that interfere with the passage

of light through the water. Turbidity is closely related to total suspended solids (TSS), but

also includes plankton and other organisms. The turbidity measurement of drinking water

is important for the following reasons: aesthetic reasons, filterability because the filtration

of turbid waters can impede the flow significantly in filters and lastly where disinfection

is applied prior to filtration, it would reduce the contact between the agent and the

pathogens thus making it less effective (Twort et al., 1985).

Colour

The colour of drinking water may be due to the presence of organic matter (primarily

humic and fulvic acids) associated with the humus fraction of the soil. Colour is strongly

influenced by the presence of iron and other metals, either as natural impurities or ascorrosion products. Coloured water is not only undesirable because of consumers

objection to its appearance, but may discolour clothing (WHO,2006).

pH

pH represents the effective concentration (activity) of hydrogen ions (H+) in water. The

activity of hydrogen ions can be expressed most conveniently in logarithmic units. pH is

defined as the negative logarithm of the activity of H+ ions: pH = -log [H+]

Although pH usually has no direct impact on drinking water consumers, careful attention

to pH is necessary to ensure satisfactory water clarification and disinfection because its

important in the control of a number of water treatment and waste treatment processes

and in control of corrosion (Steel et al., 1979).

Temperature

The temperature of water is important because it affects the concentration of dissolved

oxygen and can influence the activity of bacteria and toxic chemicals in water (Hutton,

1990).

Electrical conductivity, EC

A rapid method of estimating the dissolved salts in a water sample is by measurement of

its electrical conductivity. The conductivity is related to the total concentration of ions in

solution, their valency (charge), mobility and to the temperature. Conductivity increases

6


14/70

with increasing amount and mobility of ions. These ions, which come from the

breakdown of compounds, conduct electricity because they are negatively or positively

charged when dissolved in water. Therefore, SC is an indirect measure of the presence of

dissolved solids such as chloride, nitrate, sulfate, phosphate, sodium, magnesium,

calcium, and iron, and can be used as an indicator of water pollution (Hutton, 1990).

2.2.3 Chemical parameters

Iron

Iron can exist in water either in dissolved aqueous form, or in solid form as a brown,

suspended Iron (III) compound. Iron is objectionable in domestic water supplies where it

imparts an undesirable taste and colour to the water, and stains laundry and plumbing.

High quantities of iron normally occur in groundwater usually as a result of weathering of

iron minerals by acid water (Twort et al., 1985).

Manganese

Manganese occurs in water less commonly than iron and generally in smaller amounts. If

the manganese concentration exceeds 0.05 mg/l, manganese is oxidized into sediment,

which clogs pipes, discolours fabrics, and stimulates organic growths. The colour of the

deposits and stains ranges from dark brown, if there is a mixture of iron, to black if only

manganese oxide is present (Steel et al., 1979).

Dissolved Oxygen, DO

The concentration of dissolved oxygen in water varies greatly and is dependant on

several physical, chemical, biological and microbiological processes. Water in contact

with air will contain a quantity of oxygen depending on: the atmospheric pressure, the

temperature of water and the salinity or TDS. In groundwater the dissolved oxygen

content ranges from zero to 100% saturation. The lower values at depth may be due to

oxidation of organic material depleting the oxygen as the water percolates downwards ormay be related to oxidation of iron and manganese. In surface waters the dissolved

oxygen content is influenced by the degree of biological and biochemical activity

(Hutton, 1990).

7


15/70

2.2.4 Water Quality Standards

The primary purpose of the Guidelines for Drinking-water Quality is the protection of

public health. Water is essential to sustain life and a satisfactory (adequate, safe and

accessible) supply must be available to all. Improving access to safe drinking-water can

result in tangible benefits to health. Every effort should be made to achieve a drinking-

water quality as safe as practicable (WHO, 2006).

a) Raw Water Quality Standards

The classification of raw waters can sometimes be useful in indicating under what

conditions a water source could be used or whether its inadvisable to use it at all for

public supply purposes. In any such classification, bacteriological quality of water plays a

dominant part (Twort et al., 1985). Table 2.1 classifies raw water according to their

degree of bacterial contamination.

Table 2. 1: Classification of raw waters according to bacterial numbers as given by the WHO

European standards (Source: Twort et al., 1985)

Classification Total coliforms per

100ml

Faecal coliforms per

100ml

Bacterial quality applicable to disinfection treatment

only

0 50 0 20

Bacterial quality requiring g conventional methods of

treatment (coagulation, filtration, disinfection

50 5000 20 2000

Heavy pollution requiring extensive types of treatment 5000 50000 2000 20000

Very heavy pollution, un acceptable unless special

treatment designed for such water are used, source to be

used only when avoidable

Greater than 50000 Greater than 20000

b) Drinking Water StandardsThe quality of drinking-water may be controlled through a combination

of protection of water sources, control of treatment processes and

management of the distribution and handling of the water. Guidelines

must be appropriate for national, regional and local circumstances,

which require adaptation to environmental, social, economic and

cultural circumstances and priority setting (WHO, 2006). For this

reason National and DWD guidelines for drinking water quality are

summarized in the table 2.2.

8


16/70

Table 2. 2: Drinking Water Standards (Source: DWD, 2005)

Parameter Units WHO, 2006

Guidelines

National

Guidelines, 1996

Remark

Turbidity NTU 5 10 Appearance

Temperature oC - -Iron mg/l 0.3 1 Taste, Colour, Staining of

laundry, plumbing and

food

Manganese mg/l 0.4 1 Taste and staining of

laundry

TDS mg/l 1000 1000 Taste and corrosion/

encrustation

Conductivity S/cm - Taste

Colour PtCo 5 Appearance

pH ----- 6.5 - 8.5 5.5 - 8.5 High: taste, soapy feel

Low: corrosion

DO ----- - -

E. Coli/FC cfu/100ml 0 0 Health

2.3 SOURCES OF DRINKING WATER

There are various sources of drinking water however this study will be limited to the

shallow groundwater sources and rainwater harvesting in Kampala.

2.3.1 Shallow groundwaterThe major source of groundwater supply within Kampala is springs within the shallow

aquifer. Shallow wells, dug in alluvial clayey sediments are limited in yield due to low

soil percolation and therefore, their occurrence is fairly low. Springs supply about 50% of

Kampalas population with the majority of these occurring in high-density settlement

areas mainly in the peri-urban. In these areas, they are susceptible to pollution related to

anthropogenic activities even when notionally protected. The previous studies

undertaken on the protected springs in Kampala point to widespread faecal contamination

and the findings demonstrate microbiological contamination to be most severe during the

rainy (recharge) season. The sources of contamination of these shallow groundwaters are

noted to result from solid waste dumps, low coverage of excreta disposal facilities (pit

latrines), resulting in indiscriminate disposal of faecal matter into the environment. Most

of the shallow groundwater sources particularly the springs have acceptable physico-

9


17/70

chemical quality (electrical conductivity, turbidity and total hardness). However, the pH

is below 5.5 (acidic range) for most of these sources (Kulabako, 2005).

2.3.2 Rainwater harvesting

For domestic rainwater harvesting the most common surface for collection is the roof ofthe dwelling. The style, construction and material of the roof affect its suitability as a

collection surface for water. Typical materials for roofing include corrugated iron sheet,

asbestos sheet; tiles (a wide variety is found), slate, and thatch (from a variety of organic

materials). The rapid move towards the use of corrugated iron sheets in many developing

countries favours the promotion of rainwater harvesting. Debris, dirt, dust and droppings

will collect on the roof of a building or other collection area. When the first rains arrive,

this unwanted matter will be washed into the tank. This will cause contamination of the

water and the quality will be reduced. Many rainwater harvesting systems therefore

incorporate a system for diverting this 'first flush' water so that it does not enter the tank.

Rainwater is often used for drinking and cooking and so it is vital that the highest

possible standards are met. Rainwater, unfortunately, often does not meet the World

Health Organisation (WHO) water quality guidelines. This does not mean that the water

is unsafe to drink provided the rainwater is clear, has little taste or smell, and is from a

well-maintained system. Generally the chemical quality of rainwater will fall within the

WHO guidelines and rarely presents problems. There are two main issues when looking

at the quality and health aspects of drinking rainwater harvesting: Firstly, there is the

issue of bacteriological water quality. Rainwater can become contaminated by faeces

entering the tank from the catchment area. It is advised that the catchment surface always

be kept clean. Rainwater tanks should be designed to protect the water from

contamination by leaves, dust, insects, and vermin. Tanks should be sited away from

trees, with good fitting lids and kept in good condition. Incoming water should be filtered

or screened, or allowed to settle to take out foreign matter (Petersen et al., 1999; Lee etal., 1992).

2.4 WATER TREATMENT PROCESSES

The processes and technologies used to remove contaminants from water and to improve

and protect water quality are similar all around the world. The choice of which treatment

10
http://en.wikipedia.org/wiki/Rainwater_harvestinghttp://en.wikipedia.org/wiki/Rainwater_harvesting


18/70

to use from the great variety of available processes depends on the characteristics of the

water, the types of water quality problems likely to be present, nature of catchment and

the costs. The most widely applied water treatment technology includes; a combination of

some or all of coagulation, flocculation and sedimentation, and filtration which has been

used routinely for water treatment since the early part of the twentieth century with a

tertiary treatment of disinfection (Cooperative Research Centre, 2005). Table 2.3

summarizes the roles and limitation of water treatment processes.

Table 2. 3: Water treatment processes (Source: CRC, 2005)

Treatment processes Role Limitation

Sedimentation Settlement of particles fromstanding water.

Its a slow process.Requires a temporary storage tank

or basin

Coagulation and Flocculation Chemicals (coagulants), such as

alum, are added to the water.

These react with the unwantedparticles to form larger particles,

called flocs, which settle out of

water.

The chemicals such as alums are

costly

Filtration Removes fine suspended solid

matter as well as some other

particles, such as larger

microorganisms.

Nature and type of filter medium

Ion Exchange Remove inorganic contaminants

if they cannot be removed

adequately by filtration or

sedimentation.

Expensive.

Work in very narrow range of

effective doses.

Water stabilization by lime or

carbon dioxide.

Neutralize the pH to prevent

corrosion of the pipings.

Addition of lime increases Ca2+

ions thus hardnessDisinfection using chlorine or

ozone or irradiation by ultra-

violet rays.

Kill any pathogens that may be

present in the water supply and to

prevent them from re-growing in

the distribution systems.

Expensive.

Most of the water treatment processes in Table 2.3 are applied on a large scale like Gaba

I and II treatment plants in Uganda but they are not appropriate for household treatment

because of the high costs and technical expertise involved. For this purpose, this study

seeks to assess the performance of the BSF as an appropriate drinking water treatment

facility.

2.5 BIOSAND FILTER TECHNOLOGY

The BSF (Fig. 2) is a water filtering technology that was modified from the traditional

large-scale community slow sand filter to a small-scale filter for household use. The BSF

was developed in 1988 by Dr. David Manz of the University of Calgary, Canada, in

11


19/70

response to various issues that were brought to attention from previous water treatment

projects. The issues the BSF had to face were higher flow rates than the traditional slow

sand filter, effective pathogen removal, improve the taste and appearance of the water,

allow for intermittent flow, and still provide an appropriate technology for the developing

world. The filter can be produced locally anywhere in the world because it is built using

materials that are readily available. It is simply a concrete container, enclosing layers of

sand and gravel whose purpose is to eliminate sediments, pathogens and other impurities

from the water. Water is poured into the top of the filter as needed, where a diffuser plate

placed above the sand bed dissipates the initial force of the water. Traveling slowly

through the sand bed, the water then passes through several layers of gravel and collects

in a pipe at the base of the filter. At this point, the water is propelled through plastic

piping encased in the concrete exterior, and out of the filter, for the user to collect (Yung,

2003).

Figure 2. 1: Cross section of a typical biosand filter (Source: Manz, 2006)

2.5.1 Theory of Biosand FiltrationAs with all slow sand filters, the removal of pathogens occurs in the BSF due to a

combination of biological and mechanical processes. When water is poured into the top

of the filter, the organic material it is carrying is trapped at the surface of the fine sand,

forming a biological layer (biofilm) orschmutzdecke. Over a period of two to three

weeks, micro-organisms colonize the schmutzdecke, where organic food and oxygen

12


20/70

derived from the water abounds. The biofilm involves a set of biological mechanisms in

which it is not easy to pinpoint a specific mechanism that attributes to the removal, as the

system operates in multiple biological and physical mechanisms. The biological

mechanisms include:

Predation: where micro-organisms within the Schmutzdecke consume bacteria and

other pathogens found in the water (i.e. bacteria grazing by protozoa)

Scavenging: detritus are scavenged by organisms such as, aquatic worms that are

found in the lower layers of the sand beds.

Natural death/inactivation: most organisms will die in a relatively hostile

environment due to increased competition. For example, it was found that E. Coli

numbers decrease as soon as they are introduced into the filter supernatant water.

Metabolic breakdown: is a step that accounts for partial reduction of the organic

carbon.

The physical mechanisms include:

Straining: particle capture mechanism where particles are too large to pass

through the media grains.

Adsorption: even though a physical process, it still accounts for organic matter

removals that were traditionally attributed to purely biological effects (Yung,

2003).

2.5.2 Pre-Treatment of Raw Water Prior to BSF

The sand within the BSF requires periodic cleaning because typically the Schmutzdecke

layer (biofilm) in the BSF continues to accumulate and grow until the pressure and flow

loss due to the top layer becomes excessive. The Schmutzdecke layer in the BSF is

cleaned every one to three months depending on the average level of turbidity. However,

during wet seasons, the turbidity is so high that the sand requires cleaning every two

weeks or even as frequent as daily cleaning. The amount of cleaning depends on

available head, sand particle distribution, the quality of influent, and the temperature of

the water. As the filter becomes more clogged and the flow rate decreases, the initial head

(5cm above the sand) in the outflow pipe decreases causing the overall head loss to

increase. As the media pore sizes decreases, the amount of particle capture increases.

13


21/70

Without cleaning the biofilm, build-up of particles will become excessive. An important

note is that the majority of the water turbidity could be eliminated in pre-treatment

processes preceding the BSF, whereby lowering the amount of suspended solids would

reduce the amount of cleaning of the biosand layer (Yung, 2003).

There are many forms of pre-treatment methods that are implemented world wide

however studies must be made on the appropriateness of these methods when

implemented in a developing country. Table 2.4 gives the different forms of pre-

treatment methods with their respective advantages and disadvantages. In this study, the

pre-treatment preferred was a cotton cloth filter. Water collected after cloth filtration has

a greatly reduced pathogen count - though it is not necessarily perfectly safe, it is an

improvement for poor people with limited options. Cotton cloth is preferred because

repeated washing reduces the space between the fibres. The cloth is effective because

most pathogens are attached to particles and plankton, particularly a type of zooplankton

calledcopepods, within the water. By passing the water through an effective filter, most

cholera bacteria and other pathogens are removed. It was demonstrated by Dr. Rita

Colwell, 2003 to greatly reduce cholera infections in poor villages where disinfectants

and fuel for boiling are difficult to get. A cotton cloth folded four to eight times, creates a

smaller effective mesh size (approximately 20-m). This should be small enough to

remove a large proportion of the cholera in the water. The cloth filter provides less than

ideal purification on its own - usually filtering is an initial step, to be followed by further

treatment methods e.g. disinfection. However, where there are no other options, water

professionals may consider that it is "of course, better than nothing" (Colwell, 2003).

Table 2. 4: The different forms of pre-treatment methods (Source: Herman et al., 1996)

Forms of Pre-treatment Description/ Function Advantage Disadvantages

Physical forms of pre-treatment methods

Roughing filter In this method, the water

passes through one or two

roughing filters in series.This allows most of the

solids to be filtered out.

Effectively removes

large particles and

excess iron andmanganese

It would increase the

initial cost

substantially due toincreased filter

materials.

14
http://en.wikipedia.org/wiki/Pathogenhttp://en.wikipedia.org/wiki/Pathogenhttp://en.wikipedia.org/wiki/Copepodhttp://en.wikipedia.org/wiki/Copepodhttp://en.wikipedia.org/wiki/Cholerahttp://en.wikipedia.org/wiki/Cholerahttp://en.wikipedia.org/wiki/Pathogenhttp://en.wikipedia.org/wiki/Copepodhttp://en.wikipedia.org/wiki/Cholera


22/70

Fiber/cloth filter Fiber filters contain spun

cellulose or rayon or cloth.

They remove suspended

sediment (or turbidity).

Its cheap.

Its less larbour

intensive.

Requires less training.

It effectively removes

large particles.

Easily contaminated

and needs cleaning

after every use.

Carbon filtering Charcoal, a form of carbonwith a high surface area,

absorbs many compounds

including some toxic

compounds.

Its cheap.Absorbs toxic

compounds.

Slightly changes thecolour of water and

taste

Reverse Osmosis It includes a pre-filter to

remove sediment, anactivated carbon filter to

remove odors and taste, a

semi-permeable membrane

through which water flows

under pressure

Effective at removing

pathogens and largeand small particles in

water.

Removes odors and

taste.

Its expensive.

Unless membranes arewell-maintained, algae

and other life forms

can colonise the

membranes.

Ultrafiltration membranes They use polymer film with

chemically formed

microscopic pores that can

be used in place of granular

media to filter water

effectively without

coagulants.

Effective at removing

large particles and

microorganism

(pathogens)

Needs pressure to

drive the water

through the

membrane.

Its expensive.

pH Adjustment

Softeners (lime/Soda ash) If the water is acidic, lime

orsoda ash is added to raise

the pH.

Removes hardness-

calcium and

magnesium.

Expensive.

Coagulation and flocculation methods

Alum (Aluminium Sulphate) Alum removes dissolved

salts by forming flocs of

aluminium hydroxide.

Very effective in

removing dissolved

particles

Expensive.

High concentrations of

alum are toxic to

humans.

Iron Sulphate or Chloride This acts similarly to Alum

by forming Iron (III)

coagulant

Work over a large pH

range compared to

AlumIts a needed trace

mineral in humans

Leave brownish stains

in water.

Impart slight changesin taste of water.

Not as effective asAlum

Cationic and Other Polymers These act in conjunctionwith inorganic compounds

to remove arsenics in water.

Produce less settledwaste.

Dont need water to be

alkaline.

Expensive.Block sand filter.

Work in very narrow

range of effective

doses.

15
http://en.wikipedia.org/wiki/Charcoalhttp://en.wikipedia.org/wiki/Lime_(mineral)http://en.wikipedia.org/wiki/Soda_ashhttp://en.wikipedia.org/wiki/Charcoalhttp://en.wikipedia.org/wiki/Lime_(mineral)http://en.wikipedia.org/wiki/Soda_ash


23/70

Moringa Coagulant In this method, particles aredestabilized through

electrostatic means by the

addition of a Moringa

coagulant, thereby leading

to the formation of largerflocs.

Cheaper than thechemical coagulants.

Its independent of raw

water pH, and it does

not affect the pH of the

treated water.

Limited to onlyMoringa growing

areas.

Sedimentation

Sedimentation in tank or

basin

This is the quiescent settling

of suspended particles with

specific weight heavier than

water.

Its a self cleansing

action.

Its a slow process

Requires a temporary

storage tank or basin

2.5.3 Benefits of Biosand Filtration

Some of the main benefits of the BSF include:

i) Allows for intermittent flow and can be used only during the times when

treatment is required without any decrease in performance.

ii) Pre-treatment methods or other treatment process can be used before or after the

BSF.

iii) BSF has a faster flow rate of 0.6 m/h (30L/hr), whereas the traditional slow sand

filtration rates are 0.1m/hr.

iv) There is no surface scraping, media disposal or replacement, and very little

wastewater. The means of cleaning the Schmutzdecke is through a method calledfilter harrowing. The sand within the filter does not need replacement and filter

harrowing does not produce a lot of sludge, therefore waste levels are kept at a

minimum (Yung, 2003).

2.5.4 Performance and Considerations of Biosand Filtration

Taking into account that the BSF is versatile, and that biological treatment of the raw

water is very successful (Table 2.5), there are two major drawbacks of the current BSF

technology. These drawbacks include:i) The BSFs inability to handle high turbidity during wet seasons, where the high

amount of rain and runoff greatly increase the turbidity. The high turbidity leads

to increased particle deposition and decreased pore size. As a result, frequent

clogging of mainly the top layer of the sand occurs, reducing the flow rate of the

BSF greatly.

16


24/70

ii) The initial cost of the BSF is also relatively high in most developing countries,

depending on the availability of the materials (Yung, 2003).

In view of the above, despite the relatively high initial cost of the BSF, its a one-time

cost and the maintenance is free. To address the issues of high turbidity clogging the

BSF, a cloth filter pre-treatment method was considered in this study (section 2.5.2).

Table 2. 5: Performance of Biosand Filter (Source: Manz, 2006)

Water Quality Parameters Purification Effect

Faecal coliform More than 90% reduction

Protozoa and helminthes 100% removal

Organic and inorganic toxicants 50-90% removal

Iron and Manganese < 67% reduction

Arsenic


25/70

CHAPTER 3 - MATERIALS AND METHODS

3.1 INTRODUCTION

This chapter covers the activities and techniques that were undertaken, details of whichare presented in the subsequent sections.

3.2 ACTIVITIES

The activities that were carried out included; the construction of the BSFs, source

identification, collection of the water samples and the experimental set up.

3.2.1 Construction of Biosand Filters

Three BSFs were constructed in view of the different selected water sources. The

construction and installation of the BSFs was done according to the concrete biosand

water filter construction manual provided by Manz (2006). The activities included:

Construction of the concrete filter body

Tools and materials used included: rubber hammer, two spanners, claw hammer, spade,

wheelbarrow, a file, trowel, hack saw and spare blades, PVC primer and cement, a piece

of wood (wedge), tape measure, steel mould, steel rod, hand wrench, sand, gravel and

Portland cement.

Construction photos are shown in the appendix - A.2.

Procedure

The mould surfaces were oiled with the Mukwano vegetable oil which, were to be

in contact with the concrete and then the mould was set up.

The PVC pipe was measured, marked and cut into 585mm, 75mm and 60mm

pieces. After the three pipe pieces (standpipe components) ends were smoothened

with a file.

The connections of the standpipe components were primed with PVC cement and

joined with elbows to form the standpipe.

The bolts on the front, back and one side of the steel mould were loosened and the

stand pipe was held in place with the pin.

18


26/70

The standpipe was positioned over the nose plate on the front panel and the

nose plate was clamped.

The second side panel was located, the bolts were hand tightened and further

tightened firmly with a wrench.

The wood spacer was used to position the standpipe intake and the interior mould

was covered with a small piece of plastic paper from the cement bag.

Field concrete mixing and placing

The sand was measured and spread on the clean surface.

An equal volume of gravel to sand was measured and spread on the gravel.

The cement of the same volume was measured and the dry ingredients were

mixed thoroughly. The ratio of sand to gravel to cement was 1:1:1. A depression

was made in the centre of the pile.

Water was added into the depression and the mixture mixed thoroughly well.

The concrete was added to the mould and a steel rod was used to make sure that

the concrete was properly distributed throughout the mould. A rubber hammer

was used to make sure that the concrete was in contact with the mould.

After about 3 hours the wood spacer block was removed and extra concrete was

added to the top of the mould to allow for settling. After the concrete had started

to harden, the base was levelled and smoothened to remove the excess concrete.

Removing the filter from the mould

After 24 hours, the filter was removed from the mould, first by removing the pin

and loosening the locating bolts.

The nose plate was removed and the mould was turned on its side. The bolts

from the base were then loosened and removed.

The puller was located and inserted into the base. After which the puller bolts

were tightened. The nut was then also tightened until the interior mould was

released. The mould was lifted until it entirely was released and carefully

removed.

The remaining bolts were removed. After which the side and back panels were

then removed.

19


27/70

The concrete mould was then tilted to seat on its base and a thin strip of wood was

placed beneath the bottom edge then the front panel was finally removed.

Repairing and cleaning the mould

Cement and sand was mixed to repair any damaged areas on the filter especially

the nose.

The mould surfaces and panels were cleaned.

After, all the steel mould surfaces were oiled immediately after cleaning.

Diffusers and Lids

A well fitting bucket was used as a diffuser. The grid of 1X1 was drawn on the

bottom of the bucket and a hot iron wire of about 1/8 in diameter was used to

make the holes. A small wooden lid was constructed to be placed on the filter top.

Sieve set and Filter media

Sieve set

The materials included three sieve screens of inch (12mm opening), inch (6mm

opening) and mosquito netting and sieve frame of 24 (60cm) by 18 (45cm)

The sieve frame was constructed and the screens were added to the frame and

were held by bent nails to the frame.Filter media

Material Crushed inert rock

The crushed inert rock was sieved first through the mosquito netting to obtain the

fines, then the residue was sieved through the inch to obtain the sand and lastly

the residue was sieved through the inch to obtain the gravels/coarse.

These were then washed until clean and placed in three clean bags.

3.2.2 Installation and Commissioning

After the construction of the filters concrete body, they were placed at the Makerere

appropriate technology centre for installation because it was a safe location (protected

from direct sunlight, wind, and rain) and its proximity to the PH and EE laboratory.

20


28/70

Procedure

Gravel was added to the filter up to a depth of 2 and then well leveled.

After the support media was added to a depth of 2 and water was added to cover

the support media. Finally the filter media was added.

The diffuser basin was inserted and water poured through the filter until it was

clean.

Sanitation of Filter

A sanitation pipe was attached to the outlet of the standpipe and 2 litres of

sanitizing solution (Sodium Hypochlorite) was carefully poured into it. The filter

was then flushed with 20 litres of clean water.

3.2.3 Source Identification and Water Sample Collection

The selected study areas in Kawempe division were visited for source identification. The

three sources identified included a shallow well (Fig 3.2) located in Mukere, a spring (Fig

3.1) in Makerere Kikoni, and a rain water concrete tank (Fig 3.3) located at Dr Musaazi

residence in Makerere University. Water samples were collected once a week in sterilized

plastic bottles and analyzed taking into consideration the seasonal variations. These

samples were analyzed for pH, DO, EC, turbidity, temperature, apparent colour,

thermotolerant coliforms and E. coli in the Public Health and Environment Engineering

Laboratory, and for iron and manganese in the Chemistry Laboratory, Makerere

University.

Figure 3. 1: A spring in Makerere Kikoni

21


29/70

Figure 3. 2: A shallow well in Mukere, Kawempe I

Figure 3. 3: A concrete rainwater tank at Dr. Musaazi Residence in Makerere University

3.2.4 Experimental set-up

The experiment set up involved a pre-treatment stage with the cloth filter and the final

treatment stage with the BSF as shown in the Fig 3.4.

Raw water Pretreated Effluent

Water

Figure 3. 4: Shows the stages of raw water treatment

Cloth Filter BSF

22


30/70

The procedure involved placing the cloth (folded about 8 times) on an empty clean

bucket. Raw water was then filtered through the cloth to remove suspended particles.

After filtering, the cloth was rinsed in clean water and then dried in sunlight. The

pretreated water from the cloth filter was then subjected to the BSF from which the

effluent was collected.

3.3 METHODS

This section covers the analytical techniques used in the testing of the collected water

samples.

3.3.1 Water Quality Analysis

Samples of raw water, filtered water from the cloth filter and the effluent from the BSFs

were analyzed once a week for physical, chemical and bacteriological parameters as

described in the subsequent sections.

3.3.1.1 Physical parameters

Turbidity

The turbidity of water samples was determined by the HACH DR 4000

spectrophotometer in Formazin Turbidity Units (FAU) using the Attenuated Radiation

Method (HACH, 1999).

Colour

The apparent colour tests were determined by the HACH DR 4000 spectrophotometer in

Platinum Copper Units (PtCo) using Attenuated Radiation Method (HACH, 1999).

pH and temperature

Measurement of pH and temperature was by using a HANNA HI 991003 pH/temperature

meter according to the electrode method following the instrument operation manual. This

involved lowering the probe of the pH meter into the water and taking the stable readings

of pH and temperature.

Dissolved Oxygen, DO

DO was determined using a CAMBLAB handylab OX1 meter according to the electrode

method following the instrument operation manual. The probe was lowered in the water

and stable readings taken of DO on the meter in mg/l.

23


31/70

Electrical conductivity, EC

EC was determined using a WTW LF 197 conductivity meter according to the electrode

method following the instrument operation manual. The probe was lowered into water

and the EC was recorded in S/cm.

3.3.1.2 Chemical parameters

Iron

Total iron was determined using the FerroVer method according to HACH DR 4000

spectrophotometer Handbook (1999).

Manganese

The pan method was used to determine manganese in the water samples using the HACH

DR 4000 spectrophotometer (HACH DR 4000 spectrophotometer Handbook, 1999).

3.3.1.3 Bacteriological Analysis

Thermotolerant coliforms analysis

This involved the analysis of thermotolerant coliforms using the Membrane Filtration

Technique according to Standard Methods for Examination of Water and Wastewater

(APHA/AWWF/WEF, 1998). The method gives a direct count of thermotolerant

coliforms present in a given sample of water. A measured volume of water is filtered,under vacuum, through a cellulose acetate membrane of uniform pore diameter 0.45m.

Bacteria are retained on the surface of membrane which is placed on a suitable selective

medium in sterile container and incubated at 44oC. If thermotolerant coliforms are present

in the water, characteristic yellow colonies form that can be counted directly and

expressed as number of colonies per 100ml of sample (APHA/AWWF/WEF,1998).

E. coli analysis

E. coli was analyzed using the Petrifilm plate method which involved point source testing

for E. coli in 1ml of water, which was then incubated at 35 oC for 24 48 hours. The

details of this method are given in the Petrifilm interpretation Guide (2001).

24


32/70

3.3.2 Filter Run

The filter run is the period between two successive filter cleanings. This was determined

by assessing the flow rates of the filter until they were very low necessitating filter

cleaning. The filter flow rate was determined by measuring the time it would take to fill a

known volume of the container and was calculated from the formula:

containerfilltotakenTime

containerofVolumeRateFlow =

3.4 DATA ANALYSIS

Ms Excel software package was used for the development of graphical plots for the

analysis of water quality variations from different water sources. From these graphical

plots, the trends of water parameters were compared with each other and with the WHO(2006) and National drinking water standards.

25


33/70

CHAPTER 4 RESULTS AND DISCUSSION

4.1 INTRODUCTION

This chapter presents the results obtained from the laboratory experiments that were

carried out over a period of 14 weeks from January to March 2007 and their subsequent

discussions. The details of these are presented in the next sections.

4.2 WATER QUALITY

This section covers the discussion of results on the water parameters that were analyzed

in Laboratory. Water from the three sources that is shallow well, spring and rain were fed

into filters 1, 2 and 3 respectively. The table of results on the water quality parameters is

presented in Appendix A.1.

4.2.1 pH

pH results are presented in Fig 4.1, from which it can be seen that the pH values of the

rain raw water were higher than those in the shallow groundwater sources. This suggests

that probably the storage in the concrete tank, the nature of the iron roof considering its

old age (Fig 3.3) and the materials that were on the roof (dust, decomposing organic

matter i.e leaves) must have been the contributing factors to these pH values of stored

rainwater (section 2.3.2). There was very little difference between the pH values of raw

water from the spring and shallow well. Most of their pH values were lying between 4.40

and 6.91, which implied that these two water sources were acidic. This agrees with the

results of previous studies on shallow groundwaters in Kampala, which showed that they

were acidic (Rukia et al., 2005; Kulabako, 2005). It can also be seen in Fig 4.1 that the

pH values of the raw water and the filtered water through the cloth (pretreated) were

nearly the same for all the three filters suggesting that cloth material composition had no

effect on the pH.

Generally all the three BSFs raised the pH irrespective of the water sources implying that

filter medium had residual bases (alkali ions) that were constantly dissolving into the

water and thus raising the pH (Manz, 2006). This may explain why the trend of BSF

performance with respect to pH resembles that of electrical conductivity (Fig 4.7) since

26


34/70

both parameters have to do with dissolved solids. Generally the pH values of water

collected from the three BSFs were above the WHO (2006) and National pH set range of

6.5-8.5 (Table 2.1). pH does not have a direct health impact on consumers but high

values above 8.5 as was the case of the BSFs effluents, affect the taste of drinking water

(WHO, 2006).

27


35/70

Filter 1 - Shallow well

0

5

10

15

1 2 3 8 10 11 12 13 14

Time (Weeks)

pH

Filter 2 - Spring

0

5

10

15

1 2 3 8 10 11 12 13 14

Time (Weeks)

pH

Raw water Pretreated water BSF-Effluent

Raw water Pretreated water BSF Effluent

28


36/70

Figure 4. 1: pH variation of the raw, pretreated water and BSF effluents with time.

4.2.2 Temperature

The results of temperature measurement are presented in Fig 4.2. From this figure, it canbe seen that there was no significant temperature difference that was noted between raw

water, the filtered water from the cloth and the BSF effluent from the three water sources.

This is attributed to the fact the analysis was done a few hours after sampling implying

that the samples had adequate time to adjust to the room temperature. From the WHO,

2006 drinking water guideline values there is no impact of temperature on the human

health although it affects the other water quality parameters like the total dissolved solids

(WHO, 2006).

Filter 3 - Rain water

0

5

10

15

1 2 3 8 10 11 13

Time (Weeks)

pH


29


37/70

Figure 4. 2: Temperature variation of raw, pretreated water and BSF effluents with time.


22

23

2425

26

1 2 3 8 10 11 12 13 14

Temp

(oC)

Raw water Preteated water BSF Effluent

Filter 2 - Spring

22

23

24

25

26

1 2 3 8 10 11 12 13 14

Time (Weeks)

Raw water Pretreated water BSF-Effluent

Temp

(oC)


21

22

23

2425

26

1 2 3 8 10 11 13

Time (Weeks)


Temp

(oC)

Time (Weeks)

30


38/70


39/70

than those without. This was attributed to the initial cloth removal of suspensions (solid

particles) that were present in the raw water prior to the BSF filtration (section 2.5.2).

It was noted that the turbidity of the BSFs effluents were within the WHO (2006) and the

National guideline for drinking water ( 5 FAU), which implied that the water collected

from the BSFs were aesthetically acceptable (Table 2.2).

32


40/70


0

5

10

1520

25

1 3 5 7 9 11 13 15

Time (Weeks)

Turbid

ity

(FAU)

BSF Effluent Raw water Pretreated water

Filter 2 - Spring

05

10

15

20

25

1 3 5 7 9 11 13 15

Time (Weeks)


Turbid

ity

(FAU)

33


41/70

Figure 4. 3: Turbidity Variation of raw, pretreated water and BSF effluent with time.


0

5

10

15

20

25

1 3 5 7 9 11 13 15

Time (Weeks)


Turb

id

ity

(FAU

)

34


42/70


43/70

From which it can be observed that rain raw water registered the highest colour of the

three water sources followed by the shallow well and then the spring. It was observed

during sampling that the colour of the rain raw water was brown which was attributed to

probably the presence of precipitated Iron III oxides and suspended matter (section

2.2.2). The colour difference of the raw water from the shallow well and the spring may

be attributed to fact that the shallow well (Fig 3.2), allows freely the unfiltered run off to

end up in it. As earlier mentioned the trend of Fig 4.5 resembles that of Fig 4.3 showing

that there is a close relationship between colour and turbidity since both are indicative of

suspended matter (Twort et al., 1985). This may explain why where there high colour

values, there are high turbidity values for any given source. This is very noticeable in the

case of the rainwater source.

It also can be seen in Fig 4.5 that the cloth slightly removed the apparent colour of the

raw water irrespective of the water source. This may be attributed to the fact that most of

the suspensions in the raw water were smaller than the pore size of the cloth. However on

further treatment through the BSFs it can be noted that the colour removal was by 53%

for filter 1, 45% for filter 2 and 62% for filter 3. This implies that the colour removal

efficiencies of the BSFs were directly related to the colour of the raw water source. The

BSFs performance with respect to colour removal was not affected by the break between

week 3 and 8 because the units were fed daily.

Although it was observed during experimentation that the water treated by the BSF was

aesthetically attractive, the apparent colour of all BSFs effluents were between 9 and 59

PtCo, implying that there was still a considerable number of suspended matter (Steel et

al., 1985) and dissolved materials (Fig 4.7) in the effluent. According to WHO, 2006 and

the National guidelines for drinking water there is no health-based effect of water colour

but its recommended for drinking water to have values 15 PtCo (Table 2.2).

36


44/70


0

50

100150

200

1 3 5 7 9 11 13 15

Time (Weeks)

Colou

r (PtCo

)


Filter 2 - Spring

0

50

100

150

200

1 3 5 7 9 11 13 15

Time (Weeks)

Colou

r (PtCo)

Pretreated water Raw water BSF Effluent

37


45/70

Figure 4. 5: Colour variation with time of raw, pretreated water and BSF effluents.

4.2.5 Dissolved Oxygen, DO

The results of dissolved oxygen are presented in Fig 4.6, from which it can be seen that

the values of the DO of the raw water and filtered water through the cloth were nearly the

same for any one given source. However the DO values varied from one source to

another with the shallow well registering the highest values up to 2.2 mg/l, followed by

the spring and then the rainwater. This may be explained from the fact that since the

shallow well is open to the atmosphere (Fig 3.2) its well replenished with atmospheric

oxygen compared to the other two sources (spring and the rain water concrete tank). The

rain raw water had the least DO values of the three water sources which may be attributed

to depletion processes by the oxidation of organic matter and soluble ions (like Fe 2+)

(WHO, 2006). The following subsequent weeks after week 3, there was a general

decrease in the water DO irrespective of the sources. This decrease in DO values may be

attributed to the fact that there was no (recharge) fresh replenishment of the sources

during this dry period.

Generally all the three BSFs reduced DO values of water. The decrease in dissolved

oxygen by the BSF was due to microbial reduction within the BSF (Manz, 2006). No

health-based guideline values were recommended for DO (WHO, 2006) but basing on the

DO levels in the raw water, pretreated water and BSF treated water of all the three

sources (Fig 4.5) show that the waters had enough oxygen because there were low

quantities of iron and manganese (Fig 4.8 and 4.9) and there was no odour problems

usually associated with low DO after oxidation of organic matter (section 2.2.3).


0

50

100

150

200

1 3 5 7 9 11 13 15

Time (Weeks)

Colour

(PtCo)


38


46/70

4.2.6 Electrical conductivity, EC

Electrical conductivity results are presented in Fig 4.7 with the highest values of EC

recorded in the shallow well raw water followed by the spring and the lowest EC values

were recorded in the rain raw water. This may be explained from the fact that water from

the groundwater sources (shallow well and the spring) interact with soil material thus

increasing the number of dissolved solids in water (section 2.3.1). The rain water lacks

the above interaction except with the roof and the concrete tank (storage). It was also

noticed that the EC values of raw water for the spring dropped after it had rained the

previous day before sampling was done (week 10 and 13). This decrease may be

attributed to the dilution due to the recharge (section 2.3.1). It can also be observed in the

same figure that the cloth filtration prior to the BSF had no impact on the EC of the raw

water implying that physical straining by the cloth has no impact on EC.It was also observed in Fig 4.7 that there was a general increase in the electrical

conductivity of the BSFs effluents for all the three filters irrespective of the raw water

quality. This increase may have been the result of the total dissolved solids from the filter

medium, which suggest that the medium may have probably contained considerable

amounts of dissolved solids (section 2.2.2). The trend of EC of BSFs effluents resembles

that of pH (Fig 4.1), which is in agreement with the findings of WHO (2006) since both

are indicative of dissolved solids. And according to WHO and National guidelines values,

EC have no known health consequences but the high values of EC would suggest a

considerable number of dissolved solids were present in the BSFs effluents (Table 2.2).

39


47/70


0

1

2

3

1 2 3 8 10 11 12 13 14

Time (Weeks)

DO

(mg/l)


Filter 2 - Spring

0

1

2

3

1 2 3 8 10 11 12 13 14

Time (Weeks)

DO

(mg/l)



0

1

2

3

1 2 3 8 10 11 13

Time (Weeks)

DO

(mg/l)


40


48/70

Figure 4. 6: DO variation of raw, pretreated water and BSF effluent with time.

41


49/70

42


50/70


0

100

200

300

400

1 2 3 8 10 11 12 13 14

Time (Weeks)

EC

(S/c

m)


Filter 2 - Spring

0

100

200

300

400

1 2 3 8 10 11 12 13 14

Time (Weeks)

EC

(S/c

m)


43


51/70

Figure 4. 7: EC variation of raw water, pretreated water and BSF effluent with time.

4.2.7 Iron and Manganese

The results of iron and manganese are presented in the Fig 4.8 and Fig 4.9 respectively.Sample tests of these two parameters began on week 8 because of lack of financial

logistics. The rain raw water registered the highest values of iron and manganese of the

three sources and the lowest were recorded in the shallow well. The slightly higher values

of iron in the rain raw water compared to the other two sources may be attributed to the

rusty condition of the iron roof which was evidenced by the observed brown color of the

water suggesting the presence iron as earlier discussed in section 4.2.4. Manganese

presence in the rainwater may be attributed to the concrete tank material and dust

particles on the roof (section 2.3.2). The spring contained slightly higher values of iron

and manganese than the shallow well which may be attributed to the weathering of Iron

and manganese rock minerals in earth by water (acidic) to form soluble compounds

(section 2.2.3). It can also be observed in the same figures that the values of iron and

manganese in the spring and shallow well raw waters in weeks 10 and 13 (samples were

collected after it had rained) were lower than the other weeks. This may be explained

from the fact that the recharge from the runoff and the infiltration for the shallow well

and spring respectively increased the water oxygen, which precipitated the iron and

manganese out of solution (section 4.2.5). This too explains why the DO values of the

raw water for the spring and shallow well in week 10 and 13 remained the same as the

other weeks despite the recharge (Fig 4.6), may be because part of the oxygen was being

used up by the iron and manganese to form insoluble oxides (section 2.2.3).


0

100

200

300

400

1 2 3 8 10 11 13

Time (Weeks)

EC

(S/c

m)


44


52/70

It can be seen in Fig 4.8 and 4.9 that there was generally a slight decrease in the amounts

of iron and manganese present in pretreated water (after raw water was filtered through

the cloth). This may be explained from the fact that as water was filtered through the

cloth, aeration (increased DO) of the raw water took place, which precipitated some of

iron and manganese ions out of solution (section 2.2.2).

The BSFs reduced further the remaining amounts of iron and manganese that were still

present in water. The effluent from filter 1 had lowest values iron and manganese of the

three filters while filter 3 effluents had the highest values of iron and manganese. This

implies that the performance of the BSF with respect to the iron and manganese removal

was directly related to the quantities in the raw water sources (that is the higher the

quantities in the raw water, the higher is quantities in the BSF effluent as was the case of

the rain raw water with filter 3). It is worth noting, that the levels of iron and manganese

in raw water, pretreated water and BSF treated water were all within the National and

WHO (2006) guideline values of less than 0.3 mg/l and 0.4 mg/l respectively (Table 2.2).

This implies that these two parameters had little to do with taste and colour of water.

45


53/70


0

0.05

0.1

0.150.2

0.25

8 10 11 12 13 14

Time (Weeks)

Iron

(mg/l)


Filter 2 - Spring

0

0.05

0.1

0.15

0.2

0.25

8 10 11 12 13 14

Time (Weeks)

Iron

(mg/l)


46


54/70

Figure 4. 8: Iron variation of raw, pretreated water and BSF effluent with time.


0

0.05

0.1

0.15

0.2

0.25

8 10 11 13

Time (Weeks)

Iron

(mg/l)


47


55/70

Figure 4. 9: Manganese variation of the raw, pretreated water and BSF effluent with time.

4.2.8 Bacteriological Quality

The results of thermotolerant (faecal) coliforms (TTCs) and E. coli of the raw water,

cloth filtered water (pretreated water) and BSF treated water are presented in Fig 4.10.

From this figure it can be observed that zero counts of coliforms were recorded in the

first BSFs effluents (week 1). This is because the filters had earlier been disinfected


0

0.05

0.10.15

0.2

0.25

8 10 11 12 13 14

Time (Weeks)

Mn

(mg/l

)


Filter 2 - Spring

0

0.05

0.1

0.15

0.2

0.25

8 10 11 12 13 14

Time (Weeks)


Mn

(mg/l

)


0

0.05

0.1

0.15

0.2

0.25

8 10 11 13

Time (Weeks)


Mn

(mg/l

)

48


56/70

using sodium hypochlorite (section 3.2.2). It was also observed in the same figure that the

worst contaminated of the three water sources was the shallow well, with values up to

10300 TTCs (cfu/100 ml) and 2200 E. Coli (cfu/100ml). This may be explained by Fig

3.2, which shows that the area surrounding the well was uncovered and was therefore

vulnerable to pollution as a result of contaminated run off. The rainwater source was the

least contaminated of the three sources however its contamination may be attributed to

the birds (marabou-storks) droppings, which would eventually be washed into the

concrete tank after raining (section 2.2.1). The spring raw water registered an

intermediate number of thermotolerant (faecal) coliforms and E. coli of the three sources.

The spring bacteriological contamination was attributed to low coverage of excreta

disposal facilities (pit latrines) and sewage contamination (Kulabako, 2005; Rukia et al.,

2005). Coliform counts were high in weeks 10 and 13 due to the flesh replenishment of

the sources (it had rained the day before samples were collected).

It was observed that the cloth removed up to 30%-50% of the coliform bacteria from the

raw water irrespective of the water source. This removal performance of the cloth was

attributed to the fact that the cloth was folded eight times, which reduced its pore spacing

(Colwell, 2003). Fig 11 shows TTCs and E. coli results in the treated BSF water with or

without cloth pre-filtration. The coliforms numbers were lower in the BSFs effluents

with cloth pre-filtration than without.

For all the three filters the removal efficiencies with respect to the coliforms varied from

90% to 100% with filter 3 exhibiting the highest removal up to 100% followed by filter 2

which was also followed by filter 1. From this it can be said that the performance of the

BSFs was dependant on the level of contamination of the raw water sources. It can also

be seen that the trend of E. coli resembles that of TTCs implying that, in the absence of

E. coli test, TTC test can be an acceptable alternative for feacal contamination (WHO,

2006). The raw water and the pretreated water did not meet the National and WHO

drinking water standards (Table 2.2). The water from the BSF was not completely safe or

clean for drinking even in those effluents that had zero coliform counts in 100ml because

other pathogens like viruses were not tested for.

49


57/70


0

500

1000

1500

2000

2500

1 3 5 7 9 11 13 15

Time (Weeks)

TTCs x 10 in Raw water Pretreated water BSF Effluent

E. coli in Raw water Pretreated water BSF Effluent

cfu

/10

0m

l

Filter 2 - Spring

0

100

200

300

400

500

600

700

1 3 5 7 9 11 13 15

Time (Weeks)

cfu/

100

ml

TTCs x 10 in Raw water Pretreated water BSF effluent

E. coli in Raw water Pretreated water BSF effluent

50


58/70

Figure 4. 10: TTCs and E. coli variation of raw, pretreated water and BSF effluent with time.


0

100

200

300

400

1 3 5 7 9 11 13 15

Time (Weeks)

cfu/

100

ml

TTCs in Raw water Pretreated water BSF effluent

E. coli in Raw water Pretreated water BSF effluent

51


59/70

Figure 4. 11: TTCs comparison in the BSF effluent with or without pre-filtration

4.3 FLOW RATES

From the appendix A.1, the flow rate of filters 1, 2 and 3 were between 1.36 1.5L/min,

1.5 1.67L/min and 1.25 1.36L/ min respectively. Of the three filters, filter 3 which

treated the rain water had the lowest flow rate. This may be attributed to the high


0

200

400

600

1 3 5 7 9 11 13 15

Time (Weeks)

TTCs

(cfu/10

0ml)

With Pre-filtration Without Pre-filtration

Filter 2 - Spring

0

50

100

150

1 3 5 7 9 11 13 15

Time (Weeks)

TTCs

(cfu/1

00ml)

With Pre-filtration Without Pre-filtration

Filter 3 - Rainwater

0

5

15

25

1 3 5 7 9 11 13 15

Time (Weeks)

TTCs

(cfu/

100ml)

With Prefiltration Without Prefiltration

52


60/70

turbidity (Fig 4.3) of rain raw water as compared to the other raw water sources. Filter 2

which treated spring water with the least turbidity (Fig 4.3), had the highest flow rates of

the three filters. This implied that the BSF flow rate was higher with less turbid waters

and lower with higher turbid waters. This is in agreement with Yung (2003) findings on

the effect on turbidity on the BSF flow rates.

53


61/70

CHAPTER 6 CONCLUSIONS AND

RECOMMENDATIONS

5.1 INTRODUCTION

This chapter highlights the conclusions and recommendations drawn from the study.

5.2 CONCLUSIONS

The selected raw water sources did not conform to the WHO (2006) and National

drinking water standards with high thermotolerant coliforms and E. Coli counts in

the shallow well (up to 10300 cfu/100ml) and the spring (up to 3600 cfu/100ml).

In the rain raw water, the coliform numbers were 360 cfu/100ml. Turbidity of

the sources were between 5 and 20 FAU and hence outside the National and

WHO guideline values (


62/70

The quality of treated water by the BSFs particularly the microbiological quality,

pH and EC did not completely conform to the National and WHO drinking water

guidelines.

The performance of the BSF with cloth pre-filtration was higher than that without

in terms of turbidity, and coliform (TT

ivan report

Documents