NDUNG’U CHRIS KIMANGA UNIVERSITY OF...

F16/36480/2010 NDUNG’U CHRIS KIMANGA

i FCE 590: QUALITY OF GREY WATER

UNIVERSITY OF NAIROBI

QUALITY OF GREY WATER

By NDUNGÚ CHRIS KIMANGA

F16/36480/2010

A project report submitted as a partial fulfillment of the requirement for

the award of the degree of

BACHELOR OF SCIENCE IN CIVIL ENGINEERING

2015


ii FCE 590: QUALITY OF GREY WATER

ABSTRACT

Numerous settlement areas around urban and rural areas are plagued by lack of a

public sewer system. Hence, septic tanks are installed in which the wastewater is

discharged.

When the septic tank gets full, vacuum trucks are hired to empty it. However, this

becomes expensive if done frequently.

A good solution to avoid high maintenance costs for septic tanks, would be to separate

grey water from black water. The black water can be led into the septic tank.

The grey water can undergo primary treatment systems such as filtration and settling

tanks, disinfection and constructed wetlands. From here, this water can be re-used or

discharged into the environment through soak pits depending on the effluent quality.

Waste water from households include black water (discharge from toilets) and grey

water (discharge from kitchens and bathrooms). Grey water however constitutes the

greater proportion of total wastewater. Grey water makes up about 50-80% of total

wastewater.

Samples were collected from a block of flats in Ongata Rongai and the quality of the

grey water would then determine the manner in which the effluent would be handled.

The study begins with the introduction and objectives and the literature review

together with the theoretical frame work highlighted. The methodology, data

collected, results and analysis are discussed within. Finally, the conclusions and

relevant recommendations are made.

The findings of the project are compiled in this report.


iii FCE 590: QUALITY OF GREY WATER

DEDICATION

This project is dedicated to my parents. Your support is incomparable.


iv FCE 590: QUALITY OF GREY WATER

ACKNOWLEDGEMENTS

This project completion has been made possible with the assistance of a number of people to

whom I would like to express my sincere gratitude.

I am indebted to my supervisors Eng. J N. Gitonga for his continued guidance, suggestions,

comments and encouragement throughout the period and completion of this study.

I would also like to express my gratitude to the Public Health Engineering Laboratory staff

for the assistance they gave me during the study.

Finally, I owe special thanks to my family for their encouragement and moral support.

Thank you all for your prayers.

MAY GOD BLESS YOU ALL


v FCE 590: QUALITY OF GREY WATER

1 CONTENTS

ABSTRACT ................................................................................................................................................ ii

DEDICATION ........................................................................................................................................... iii

ACKNOWLEDGEMENTS .......................................................................................................................... iv

LIST OF TABLES ...................................................................................................................................... vii

LIST OF MAPS ....................................................................................................................................... viii

LIST OF PLATES ....................................................................................................................................... ix

1 INTRODUCTION ............................................................................................................................... 1

1.1 BACKGROUND INFORMATION ................................................................................................ 1

1.2 PROBLEM STATEMENT ............................................................................................................ 1

1.3 STUDY OBJECTIVES .................................................................................................................. 2

1.4 SCOPE OF STUDY ..................................................................................................................... 2

2. LITERATURE REVIEW ....................................................................................................................... 3

2.1 INTRODUCTION TO GREY WATER ........................................................................................... 3

2.2 GREY WATER CHARACTERISTICS ............................................................................................. 3

2.3 GREY WATER REUSE ................................................................................................................ 5

2.3.1 BENEFITS OF GREY WATER REUSE .................................................................................. 5

2.3.2 USES OF RECYCLED GREY WATER ................................................................................... 6

2.3.3 UNTREATED GREY WATER .............................................................................................. 6

2.4 GREY WATER TREATMENT ...................................................................................................... 7

2.4.1 TREATING GREY WATER .................................................................................................. 7

2.4.2 GREY WATER TREATMENT SYSTEMS .............................................................................. 7

2.5 WATER QUALITY .................................................................................................................... 10

2.5.1 CHARACTERISTICS OF WATER ....................................................................................... 10

2.5.2 BACTERIOLOGICAL QUALITY OF WATER ....................................................................... 22

2.5.3 INDICATOR ORGANISMS ............................................................................................... 22

2.5.4 THERMOTOLERANT COLIFORM BACTERIA ................................................................... 23

2.6 BACTERIOLOGICAL QUALITY METHODOLOGIES ................................................................... 25

2.7 PUBLIC HEALTH CONSIDERATIONS ....................................................................................... 26

2.8 ENVIRONMENTAL CONSIDERATIONS.................................................................................... 28

3 METHODOLOGY ............................................................................................................................ 32

3.1 INTRODUCTION ..................................................................................................................... 32

3.2 BACKGROUND KNOWLEDGE OF THE STUDY AREA ............................................................... 32

.............................................................................................................................................................. 32


vi FCE 590: QUALITY OF GREY WATER

3.2.1 LOCATION .................................................................................................................. 33

3.2.2 PLANNING AND URBAN DEVELOPMENT ........................................................... 33

3.2.3 GEOGRAPHY AND ECONOMY ............................................................................... 34

3.2.4 INFRASTRUCTURE ................................................................................................... 34

3.3 METHOD OF STUDY ............................................................................................................... 35

3.3.1 SAMPLING ..................................................................................................................... 35

3.3.2 LABORATORY TESTS. ..................................................................................................... 40

4 RESULTS AND ANALYSIS ................................................................................................................ 50

4.1 1st SAMPLE (FROM MANHOLE) ............................................................................................. 50

4.1.1 LAB RESULTS.................................................................................................................. 50

4.2 2nd SAMPLE (FROM PIPE) ...................................................................................................... 53

4.2.1 LAB RESULTS.................................................................................................................. 53

5 DISCUSSIONS ................................................................................................................................. 58

5.1 LAB RESULTS ......................................................................................................................... 58

5.1.1 SAMPLE 1 (FROM MANHOLE) ....................................................................................... 58

5.1.2 SAMPLE 2 (FROM PIPE) ................................................................................................. 58

5.2 POLLUTION LEVELS OF SAMPLES .......................................................................................... 59

5.3 REMARKS ON POLLUTION LEVELS ......................................................................................... 59

5.3.1 SAMPLE 1 ...................................................................................................................... 59

5.3.2 SAMPLE 2 ...................................................................................................................... 60

5.4 HOW TO HANDLE GREY WATER ............................................................................................ 60

5.4.1 DIVERT TO SEPTIC TANK ................................................................................................ 60

5.4.2 FILTRATION AND SETTLING SYSTEM ............................................................................. 61

5.4.3 USE OF SOAK PIT ........................................................................................................... 61

5.4.4 USE OF WETLANDS ........................................................................................................ 62

5.4.5 DISINFECTION ................................................................................................................ 62

6 CONCLUSION ................................................................................................................................. 64

7 RECOMMENDATIONS.................................................................................................................... 65

8 APPENDIX ...................................................................................................................................... 66

8.1 PHOTO GALLERY .................................................................................................................... 67


vii FCE 590: QUALITY OF GREY WATER

LIST OF TABLES

Table 2.1: Various Sources Of Odour And Taste In Water 13

Table 2.2: Bacterial Waterborne Diseases 20

Table 2.3: Protozoa Waterborne Diseases. 20

Table 2.4: Standards For Effluent Discharge Into The Environment 29

Table 4.1: General Coliforms Lab Results (Sample 1) 49

Table 4.2: E. Coli Lab Results (Sample 1) 49

Table 4.3: COD Lab Results (Sample 1) 49

Table 4.4: BOD0 (Sample 1) 50


Table 4.6: Calculation of BOD (Sample 1) 51

Table 4.7: General Coliforms Lab Results (Sample 2) 53

Table 4.8: E. Coli Lab Results (Sample 2) 53

Table 4.9: COD Lab Results (Sample 2) 54



Table 4.12: Calculation of BOD (Sample 2) 55

Table 5.1: Lab Results 58

Table 5.3: Comparison of Sample Pollution Levels Against WQ Regulations 59


viii FCE 590: QUALITY OF GREY WATER

LIST OF MAPS

MAP 1: THE SATELLITE IMAGE OF THE AREA OF STUDY 30


ix FCE 590: QUALITY OF GREY WATER

LIST OF PLATES

Plate 3-1: Sampling Point: Block Of Apartments 31

Plate 3-2: Access Manhole, Sampling Point 1. 34

Plate 3-3: Obtaining the Sample 1 A) 35

Plate 3-4: Obtaining the Sample 1 B) 35

Plate 3-5: The Sample 1 Collected. 36

Plate 3-6: Pipe, Sampling Point 2. 37

Plate 3-7: The Sample 2 Collected. 37

Plate 3-8: PHE Laboratory. 38

Plate 4-1: Sample 1:300 Fully Depleted Of Dissolved Oxygen 51

Plate 8-1: Presumptive Test Reagents 66

Plate 8-2: BOD Test Bottles 66

Plate 8-3: Positive Presumptive Test Results 67

Plate 8-4: PH Meter 67


1 FCE 590: QUALITY OF GREY WATER

1 INTRODUCTION

1.1 BACKGROUND INFORMATION

Grey water is composed of variable quantities of components of wastewater which may come

from the shower, bath tub, spa bath, hand basin, laundry tub, clothes washing machine,

kitchen sink and dishwasher.

Grey water therefore does not come from a toilet or urinal. Grey water contains impurities

and micro-organisms derived from household and personal cleaning activities. Because of the

high potential of grey water to contain pathogenic micro-organisms and other materials, it is

considered by health authorities to be a potentially infectious and polluting liquid waste

material which people normally want to eliminate from their homes. It is an accepted practice

and community expectation in sewered areas that grey water is drained to a sewer to promote

sanitation and hygiene in the home.

However, in non-sewered areas various on-site waste disposal systems need to be employed.

1.2 PROBLEM STATEMENT

In areas where there is no public sewer, people have installed septic tanks in which they

discharge their wastewater. When the septic tanks get filled up, residents acquire services

from private firms who empty the faecal sludge into vacuum trucks. Acquiring these services

are is costly.

So as to reduce the frequency of emptying these septic tanks, people opt to channel their grey

water and black water separately. In doing this, black water is channelled into the septic tanks

and grey water is channelled into a soak pit where the water seeps into the ground.

This reduces the cost significantly as proportion of grey water to the total waste water

produced from households is estimated to be about 60%. This practise saves money and

resources whereby only highly polluted wastewater is treated.



However, in order to discharge wastewater into the environment, some parameters have to be

met to ensure this wastewater does not pollute the environment. This grey water has to be

analysed to ensure its quality is safe for discharge into the environment.

If the quality of the grey water is within the set parameters for discharge into the

environment, this practise can be encouraged amongst residents in areas which lack a pubic

sewer.

1.3 STUDY OBJECTIVES

The study was carried out through the following objectives.

- Determine the quality of grey water.

- Hence, determine a suitable on-site waste disposal system for areas with no public

sewers.

- Recommending solutions to improve on site disposal systems.

1.4 SCOPE OF STUDY

The study will focus on a block of apartments in Ongata Rongai and will involve.

Collecting grey water samples from the area of study

Conducting laboratory tests on the grey water samples

Tabulating and analysing the laboratory results.

Compare grey water quality against set effluent standards.

Suggest appropriate recommendations



2. LITERATURE REVIEW

2.1 INTRODUCTION TO GREY WATER

Good quality drinking water in many areas is becoming a scarce commodity. Additional

demands is placed on limited water supplies as populations increase and there may be little

scope to expand available water sources, particularly for large cities e.g. Nairobi.

Grey water is defined as waste water generated from wash hand basins, showers and baths.

Grey water often includes discharge from laundry, dishwashers, kitchen sinks and other

domestic purposes.

This is unlike the discharge from toilets which is sewage or black water. It is called so (black

water) because it contains human waste.

The main difference therefore between grey water and sewage (black water) is, sewage has a

much larger organic loading as compared to grey water.

Grey water makes up the largest proportion of the total wastewater flow from households in

terms of volume.

Typically, 50-80% of the household wastewater is grey water. If a composting toilet is also

used, then 100% of the household wastewater is grey water. [(WHO). 2006. Guidelines for

the Safe Use of Wastewater.]

2.2 GREY WATER CHARACTERISTICS

Grey water characteristics vary according to:

1 The source: Be it a domestic household or office block.

2 Lifestyle characteristics of occupants

3 Water usage patterns.

The above are expounded further.



2 The Source

The grey water that will be produced highly depends on the source.

Office block: Grey water would contain detergents for washing the floors and utensils. It will

contain less food particles concentration as compared to a domestic household where there is

relatively more cooking.

Domestic households: Grey water would contain relatively more solid particles from food,

dirt and lint as a result of cooking, cleaning and laundry activities respectively.

Factories: Grey water from factories might contain heavy metals or toxic chemicals which

will necessitate treatment of grey water before reuse. In addition, grey water from factories

may be very hot especially if used for cooling purposes. This hot water if discharged directly

into water bodies may will cause an imbalance of the aquatic environment hence putting the

aquatic organisms at risk of death.

Hospitals: Grey water from hospitals may contain a lot of chemicals and disease causing

micro-organisms. Hence, the reuse of grey water produced by hospitals is highly discouraged

as it will lead to illness and infections to anyone who comes into contact with this water.

For example, clothes worn by patients with highly contagious diseases are washed but the

grey water produced cannot be reused due to the risk of contracting the highly contagious

disease.

3 Lifestyle characteristics of occupants

Living standards: Occupants of an area with relatively higher income are more likely to use

more water hence will produce more grey water, other factors held constant. Occupants who

have relatively less income are more likely to conserve a lot of water where possible hence

their grey water discharge will be lower.

Single occupancies and Family occupancies: Single occupants are more likely to cook and

wash less hence the grey water composition will be different from family occupancies which

are more likely to cook and wash more.



4 Water usage patterns

Grey water characteristics are dependent on the water usage patterns. This can be explained

as below

Early Mornings: A lot of people at this time will be taking a shower hence grey water

discharged in the morning have a large loading of hair, soaps and oils from bath tubs and

wash sinks.

Mid Mornings - Late Afternoon: At this time, a lot of people will do their laundry, house

cleaning and washing of kitchen utensils. The grey water produced will have a large loading

of lint, soil and food particles.

Early Evenings: Few people will take an evening shower hence grey water contains soaps,

oils and hair. A lot of food preparation goes on at this time hence food particles may be found

in the grey water.

2.3 GREY WATER REUSE

Most grey water is easier to recycle than black water, because of lower levels of

contaminants.

2.3.1 BENEFITS OF GREY WATER REUSE Grey water recycling has a lot of potential ecological benefits.

Lower fresh water extraction from rivers and aquifers: Reduced strain on the

natural resources brings about a more sustainable hydrological cycle.

Reduce strain on septic system or treatment plant - Grey water makes up the

majority of the household wastewater stream, so diverting it from the septic system

extends the life and capacity of the system. For municipal systems, decreased input

translates to more effective treatment at lower operational costs.

Groundwater Recharge - Grey water recycling for irrigation replenishes

groundwater.

Increased plant growth - Grey water used for irrigation can support plant growth in

areas that might otherwise not have enough water.

Reclamation of nutrients - The nutrients in the grey water are broken down by

bacteria in the soil and made available to plants hence improving soil fertility.



Enhance water quality - Greater quality of surface and ground water when preserved

by the natural purification in the top layers of soil than generated water treatment

processes.

2.3.2 USES OF RECYCLED GREY WATER Grey water can be recycled for the following uses

1 Car washing

2 Irrigation

3 Toilet flushing

4 Construction

5 Fire fighting

Grey water contains solid particles (hair, lint, soil, food particles) which may however cause

land application systems to block.

Land applications system such as irrigation should have some type of coarse screens

installed. These systems will however require frequent maintenance and cleaning to ensure

no blockages occur.

2.3.3 UNTREATED GREY WATER

Untreated grey water should not be stored. This is because, untreated grey water when

stored will turn septic hence giving rise to bad odour and an environment for micro-

organisms to thrive.

However untreated grey water could still be put to good use.

However, the following precautions should be considered when using untreated grey

water



a) Grey water containing sodium or bleaching agents can damage plants. For this reason,

such water should not be used for irrigation.

b) Grey water generated from kitchen sinks as a result of cleaning utensils may contain

grease, fats and oils and hence will be unsuitable for re-use.

2.4 GREY WATER TREATMENT

2.4.1 TREATING GREY WATER

This involves the improvement of the quality of grey water depending on the method of grey

water utilisation. Treatment systems consist of processes like settling of solids, floatation of

lighter materials, anaerobic digestion in a septic tank, aeration, clarification and finally

disinfection.

Treatment processes only reduce the gross primary pollutant nature of wastewater. Secondary

pollution may still occur because chemical components such as nitrates, phosphates and

sodium may not be reduced by treatment processes.

2.4.2 GREY WATER TREATMENT SYSTEMS

Some treatment processes include;

2.4.2.1 TANKS

Use of a settling tank enables solids and large particles to settle to the bottom, while grease,

oils and small particles will float. The remaining liquid will be reused. A settling tank also

allows for hot water to cool before reuse.

Such tanks should be large enough to hold twice the expected dally flow plus 40 % to allow

for sludge accumulation and surge loading. One widely-used type of settling tank well-suited

for grey water treatment is a septic tank.



A septic tank is specifically designed to allow settling. The use of a septic tank to treat grey

water should never be confused with the conventional use of a septic tank. Grey water

intended for reuse should never be mixed with toilet wastes.

Grey water coming out of a septic tank contains very little or no oxygen. Grey water from an

aerobic tank will contain more oxygen, which is better for irrigation purposes. An electrical

pump or aerator could be added to a septic tank to create an aerobic environment. Aerobic

conditions allow more decomposition of wastes in the tank thus may help to minimize sludge

build-up and blockages in the system.

Both aerobic and septic tanks will need to be emptied from time to time depending on the

quantity of grey water generated into the tank. An interval of 5 years of emptying will suffice

to avoid backflow or leakages due to overflow.

2.4.2.2 DISINFECTION

The most common chemical used to disinfect water is chlorine. This is because it is cheap,

readily available, and stable and will, with time, vaporize from the water after disinfection.

Organic matter in grey water may combine with chlorine hence reducing the amount

available for the disinfection process. Because of this reason, a settling tank or filter before

this stage is highly recommended.

Iodine could also be used since it is less affected by organic material, persists longer and may

be more effective at high pH of grey water. However, it is not widely used as compared to

chlorine particularly in Kenya.

2.4.2.3 FILTERS

The type of filter required for a grey water system depends on the amount of grey water to be

filtered and the type of contaminants present. A drain filter is an easy and cheap way to filter

out lint, hair and food particles. A cloth bag can be tied at the end of a garden hose and this

will filter grey water during irrigation.



Commercial water filters could also be used. Most households use an activated charcoal,

cellulose or ceramic cartridge that must be clean or replaced regularly. Slow sand filters may

also be used and these are built by the homeowner.

Slow sand filters require regular cleaning and replacement of the top layer of media.

Directing grey water to a settling tank before filtering reduces contaminant load and hence

lengthen the efficiency and life of the filtering media.

2.4.2.4 CONSTRUCTED WETLANDS

Physical, chemical, and biological processes are combined in wetlands to remove

contaminants from wastewater. Grey water treatment is achieved by soil filtration in reed-bed

systems which reduces the organic load of the grey water considerably

In addition, constructed wetlands decrease the concentration of faecal bacteria. If designed

properly, these systems would produce a clear and odourless effluent.

Constructed wetlands tend to be simple, cheap to maintain and environmentally friendly. On

top of that, they provide food for aquatic organisms and increase the aesthetic value in an

area by improving the appearance of the landscape.

2.4.2.5 ROTATING BIOLOGICAL CONTACTORS (RBC)

This is a biological treatment process used in the treatment of wastewater following primary

treatment. Primary treatment process removes the grit and other solids through a screening

process followed by a period of settlement.

The RBC process involves allowing the wastewater to come in contact with a biological

medium in order to remove contaminants in the grey water before discharge of the treated

grey water to the environment.



It consists of a series of closely spaced, parallel discs mounted on a rotating shaft, whereby

microorganisms grow on the surface of the discs where the biological process of breaking

down the wastewater takes place.

2.4.2.6 MEMBRANE BIOREACTORS (MBR)

The membrane bioreactor is basically a suspended growth activated sludge system that

utilises micro-porous membranes for liquid separation. The system consists of a pre-treatment

settling tank, an aerated settling tank which also stores the intermittently produced grey water

and the aerated activated sludge tank.

The generated grey water is held back by the submerged membrane filter module installed in

the aeration tank. The purified grey water passes through the membrane yielding a bacteria-

free effluent.

2.5 WATER QUALITY

Water quality refers to the chemical, physical, biological and radiological characteristics of

water. The specific treatment process used in any specific case depends on the nature and

quality of the raw water and the desired water quality.

There are various references which can be used to assess the sufficiency of water treatment

but the International Standards for Drinking Water (WHO) in its revised forms and the

Kenyan adaptations of the same are probably the most suited in this country.

2.5.1 CHARACTERISTICS OF WATER

Water characteristics are divided into physical, chemical and biological characteristics.

2.5.1.1 PHYSICAL CHARACTERISTICS OF WATER



a) Colour

Presence of colour in water is due to substances in solution or in colloidal suspension, which

can be unacceptable especially in high levels. Colour could also be due to extraction of

colouring materials from humus or any other organic matter.

Experience shows that consumers may turn to alternative, perhaps unsafe sources when their

water displays aesthetically displeasing levels of colour.

The guideline value is 15 True Colour Units (TCU). This is the WHO guideline. Most people

can detect levels of colour above 15 TCU in a glass of water. (Tebbutt, 1983)

b) Temperature

Temperature change impacts chemical and biological characteristic of surface water.

Temperature also affects the dissolved oxygen (DO) levels in water, photosynthesis of

aquatic plants and metabolic rates of aquatic organisms.

Thermal pollution occurs when relatively warmer water is introduced into a water body.

Sources of warm water mostly include industries where water is used for cooling purposes.

c) Turbidity

Turbidity is defined as the dispersion and interference of light passage due to the presence of

suspended particles.

Some of the causes of turbidity include, surface runoff, algae growth and discharge from

waste. Surface water is more prone to experiencing turbidity especially during the rainy

seasons.

Suspended particles in turbid water absorb heat from sunlight, making it warmer hence

reducing concentration of DO in the water. This poses a risk to survival of some aquatic

organisms.

The main impact of turbidity lies in its aesthetic value in that highly turbid water is an

indicator of the bad quality of the water. Turbidity is measured in NTU Nephelometric

Turbidity Units, measured by a turbidimeter or nephelometer. WHO standards state that

maximum allowable turbidity in drinking water should not be more than 5NTU.

Turbidity in excess of 5NTU may be noticeable and consequently objectionable to

consumers.



d) Solids

Solids in water are categorised into 2 main classes

- Total dissolved solids (TDS)

- Total Suspended solids (TSS)

Total dissolved solids are a measure of all inorganic and organic substances contained in a

liquid in molecular, ionized or micro-granular suspended form.

Total suspended solids include all particles in water which will not pass through a filter.

Settleable solids are those that can settle out in a graduated hope cone and can be measured

volumetrically.

e) Electrical conductivity

Electrical conductivity is the ability of a substance to conduct an electrical current, measured

in microsiemens per centimetre (mS/cm). Electrical conductivity of water depends on the

quantity of dissolved salts present and for a dilute solution, it is proportional to total dissolved

solids content (TDS).

Hence, conductivity is often used to estimate the amount of total dissolved solids (TDS)

rather than measuring each constituent separately.

The relationship between conductivity and TDS can hence be expressed using the following

equation

Conductivity = K. TDS

K = constant

f) Taste and Odour

Water for domestic use should have no taste or odour. Tastes and odours may be due to the

presence of organic substances for example algae growth and decomposing matter. In

addition, domestic, industrial and agricultural activities may also cause tastes and odours.

Changes in normal taste of a public water supply may signal changes in the quality of the

water source of poor treatment practices.

Generally, the taste buds in the oral cavity detect the inorganic compounds of metals such as

magnesium, calcium, sodium, copper, iron and zinc. (WHO



Table 2.1: VARIOUS SOURCES OF ODOUR AND TASTE IN WATER.

TASTE OR ODOR SOURCE

Musty MIB, isopropylmethoxypyrazine

(IPMP), isobutylmethoxypyrazine

(IBMP)

Turpentine, oily Methyl tertiary butyl ether (MTBE)

Fishy/rancid 2,4-heptadienal,octanal

Chlorinous Chlorine

Medicinal Chlorophenols, iodoform

Oily, gas-like, paint Hydrocarbons, volatile organic compounds

(VOCs)

Metallic Iron, copper, zinc, manganese

Grassy Green algae

Earthy Geosmin

Source: (Trojan technologies, 2005)

2.5.1.2 CHEMICAL CHARACTERISTICS OF WATER

Chemical properties of surface water depends on the characteristics of the catchments or

source.



These chemical properties include:

a) PH

PH is a measure of the intensity of acidity or alkalinity of water. Measurement is carried out

on a pH scale from 0 to 14 with 7 as the neutral. When the pH value is less than 7, it is acidic

and when the value is above 7, it is alkaline.

Water in its natural state is ionized to hydroxyl and hydrogen ions as shown below.

H2O ⇌ H+ + OH-

PH is given by

PH= -log10 = log10 (1/ [H+])

Many chemical reactions are controlled by pH and biological activity is usually restricted to a

fairly narrow pH range of 5 to 8. Highly acidic or alkaline water is undesirable because of

corrosion hazards and possible difficulties in treatment.

b) Dissolved oxygen

Dissolved oxygen is an important element in water quality control. Dissolved oxygen

concentration is determined by the physical (temperature and pressure), chemical (presence

of reducing and organic substances) and biochemical (microorganisms and biodegradable

substances) activities prevailing in the water body.

Presence of dissolved oxygen in water is essential to sustain the higher forms of biological

life and the oxygen balance of the system largely determines the effect of wastewater

discharge into a river.

Adequate dissolved oxygen is necessary for good water quality

As dissolved oxygen levels in water drop below 5.0mg/l, aquatic life is put under stress. The

lower the concentration the greater the stress. (KY Water watch, 2013)



c) 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. The

BOD test is an empirical bioassay-type procedure which measures the dissolved oxygen

consumed by bacteria (and other microbial life) while the organic substances present in the

solution.

The BOD standard test conditions are incubation at 20℃ in the dark for a specified period

time, mostly five days. The reduction in dissolved oxygen concentration during this

incubation period is a measure of the biochemical oxygen demand and is expressed in mg/l

oxygen or mg/l BOD.

The BOD test is widely used to determine the “pollutional strength” of domestic and

industrial wastes in terms of the oxygen that they will require after being discharged into

natural waters systems.

A high BOD value hence means that the wastewater will require a large quantity of oxygen

from the surrounding natural waste system. Hence, a very high BOD value is detrimental to

aquatic life as it will lead to depletion levels in oxygen levels.

d) Chemical Oxygen Demand

The chemical oxygen demand (COD) test is a measure of the quantity of oxygen required to

oxidise the organic matter in a waste water sample, under specific conditions of oxidising

agent, temperature and time.

During the 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 oxidised completely.

As a result, COD values should be greater than BOD values and may be much greater when

significant amounts of biologically resistant organic matter is present.

COD values are used extensively in the analysis of industrial wastes. In conjunction with the

BOD test, the COD test is helpful in indicating toxic conditions and the presence of



biologically resistant organic substances. The test is widely used in the operation of treatment

facilities because of the speed with which results can be obtained.

e) Chloride

Excess chloride of about 250 mg/litre in water leaves a bad taste in water. In addition, excess

chloride ions (Cl-) ions in water may result to water hardness.

Chloride concentrations exist in natural waters as observed in sea water. Wastewater also

contains large amounts of chloride, as do some industrial effluents. Chlorides are widely

distributed in nature as salts of sodium (NaCl), potassium (KCl) and calcium (CaCl2).

Chlorides are leached from various rocks into water by weathering. The chloride ion is highly

mobile and is transported to closed basins or oceans.

Chlorides also increases the electrical conductivity of water and thus increases its corrosivity.

f) Carbon (IV) oxide

Carbon (IV) oxide in water exists in form of carbonates, or as free carbon (IV) oxide. When

carbon (IV) oxide dissolves in water, it forms carbonic acid which is corrosive hence will

destroy steel pipes in the distribution system. High levels of carbonates tend to cause lime

scale deposits which with time reduces the useful cross-sectional area of pipes.

g) Hardness

Water hardness is a characteristic that prevents lather formation from soap. Hardness is a

measure of water to consume soap without the formation of lather. It is mainly caused by the

cations, calcium and magnesium in combination with anions, carbonate, chloride and

sulphate.

Hard drinking water is generally not harmful to one’s health, but can pose serious problems

in industrial settings, where water hardness is monitored to avoid costly breakdowns in

boilers, cooling towers and other equipment that handle water.



Other problems associated with hard water include grey staining of washed clothes, scum on

wash basins following use of soap and reduced water flow in hot water distribution pipes due

to scale build-up.

The most common method of removing hardness from drinking water is the installation of

water softener. A water softener replaces the calcium and magnesium molecules with sodium

molecules. However, high levels of sodium in drinking water will have an adverse effect on

the health of the consumer. Persons on a sodium restricted diet or suffering from high blood

pressure are not allowed to drink water with more than 20mg/l of sodium (Vermont

Department of Health, 2013)

h) Alkalinity

Alkalinity is the measure of the ability of water to absorb hydrogen ions which are almost

entirely due to hydroxide, bicarbonate and carbonate ions in the reaction.

OH- + H

+⟷H2O

CO32-

+ H+ ⟷

HCO3-

HCO3- + H

+⟷ H2CO3

Most of the alkalinity in raw water is due to the presence of bicarbonate ions produced by the

action of ground water on limestone or chalk.

Alkalinity has no health significance but is very important for the water treatment processes

particularly coagulation/flocculation and chlorination. In addition, Alkalinity is useful in

water in the sense that it provides buttering to resist the changes in PH.



i) Acidity

Acidity arises from the presence of weak or strong acids and/or certain inorganic salts. The

presence of dissolved carbon (IV) oxide is usually the main acidity factor in unpolluted

surface waters. Carbon (IV) oxide dissolves in water to form weak carbonic acid (H2CO3).

Acidity has no health and sanitary implications apart from palatability considerations in

excessively acid waters.

High acidity in water causes corrosion in distribution pipes.

j) Iron and Manganese

Iron makes up at least 5% of the earth’s crust. Rainwater infiltrates the soil and underlying

geological formations dissolving iron as it seeps into aquifers that serve as sources of ground

water for wells.

Presence of large iron concentration in public water supplies causes staining in plumbing

fixtures and washed clothes. Iron can cause water hardness though to a lesser extent as

compared to magnesium and calcium ions.

WHO water quality standards for public water supplies state the maximum allowable Iron

concentration to be 0.3 mg/l.

Manganese behaves so much like iron that it is sometimes difficult to distinguish the two.

This s in that, excess quantities of manganese leads to staining of washed clothes and small

quantities affect water colour.

WHO water quality standards for public water supplies state the maximum allowable

manganese concentration to be 0.1 mg/l.

2.5.1.3 BIOLOGICAL CHARACTERISTICS OF WATER

Disease carrying microorganisms can be carried in water and their presence in drinking water

is a serious hazard to human health. Such microorganisms that cause disease by transmission

through contaminated water are called waterborne pathogens.

a) Microbiology



Microbiology is the study of microorganisms, of small living things. Microorganisms of

interest to the water quality include the following:

- Bacteria

- Protozoa

- Viruses

- Algae

- Fungi

Bacteria

These are primitive, single-celled organisms with a variety of shapes. Bacteria range in size

from 0.5 to 2 microns in diameter and about 1 to 10 microns in length. Bacteria are

categorised into 3 general groups based on the physical shape.

Rod-shaped bacteria are called bacilli

Spherical shape bacteria are called cocci

Spiral-shaped bacteria

Bacteria are responsible for a number of diseases. The bacterial pathogen responsible for

these diseases enter potential drinking water supplies through faecal contamination. The table

below shows a number of bacterial waterborne diseases.

Table 2.2: BACTERIAL WATERBORNE DISEASES.

Bacteria Disease

Salmonella typhi Typhoid fever

Shigella spp. Gastroenteritis

Vibrio cholera Cholera

Campylobacter spp. Gastroenteritis

Enteropathogenic E. coli Gastroenteritis

Leptospira spp. Leptospirosis



Protozoa

Protozoa are one-celled animal like organisms with a fairly complex cellular structure. The

protozoa are the giants of the microbial world. They are many times larger than bacteria and

range in size from 4 to 500 microns.

They are categorized into the following groups based on their method of locomotion.

• Amoebas: move about by a gliding action. Have changing shape as they glide from

place to place.

• Ciliates: covered with short hair-like projections called cilia, which beat rapidly and

propel the ciliates through the water.

• Flagellates: have one or more long whip-like projections, called flagella, which propel

the free-swimming organisms.

• Suctoria: these are attached organisms, similar to attached ciliates, but have tentacles

rather than cilia.

• Sporozoa: they are non-mobile and are simply swept along with the current of the

water.

Protozoa are responsible for the following waterborne diseases.

Table 2.3: PROTOZOA WATERBORNE DISEASES.

Protozoa Disease

Entamoeba histolytica Amoebic dysentery

Glardia lamblia Glardiasis

Cryptosporidia Cryptosporidosis

Viruses

They are many times smaller than the bacteria. Range in size from 0.02 to 0.25 microns in

diameter. Viruses are intra-cellular parasites that must have a host cell in which to multiply.



They are extremely simple life forms. They contain no mechanisms by which to obtain

energy or reproduce some of their own.

Waterborne diseases caused by bacteria include

- Hepatitis

- Viral gastroenteritis

- Poliomyelitis

Algae

Algae are a form of aquatic plants. Although in mass, they are easily seen by the naked eye,

many of them are microscopic as single cells. They exist as single-celled forms and also as

huge, multicellular forms, such as marine kelp. They occur in fresh and polluted water, as

well as in salt water.

They are able to use energy from the sun though photosynthesis. They usually grow near the

surface of the water because light cannot penetrate very deep through the water.

Algae are categorised in the following groups based on their colour:

• Green algae: contain green chlorophyll and are found mostly in fresh water. This form

is the green roadside ditch algae, and the type that grows on clarifier and basin walls.

• Eugleniods: single-celled, green pigmented algae that resemble protozoa. They have

flagella, but are considered algae because they carry out photosynthesis.

• Diatoms: are golden-brown, single celled forms that have a hard silica shell. The

shells of millions of dead diatoms are mined commercially and known as

diatomaceous earth.

• Blue-green algae: is bluish-green in colour and undergoes photosynthesis.

Although algae are not considered waterborne pathogens, they do cause some problems with

water operations. They grow easily on walls of basins and troughs, and heavy growth may

cause plugging of screens and intakes. Algae also releases chemicals that can cause taste and

odour problems in drinking water.

Control of algae in raw water supplies is done with chlorine and potassium permanganate.



Fungi

Fungi are non-photosynthetic organisms that grow as multicellular, filamentous, mould-like

forms or as single-celled, yeast-like organisms. Fungi must have organic material as a food

source.

2.5.2 BACTERIOLOGICAL QUALITY OF WATER

The principal risk associated with water in community supplies is that of infectious diseases

related to faecal contamination.

The microbiological examination of drinking water emphasizes assessment of the hygienic

quality of the supply. This requires the isolation and enumeration of organisms that indicate

the presence of faecal contamination

In certain circumstances, the same indicator organisms may also be used to assess the

efficiency of drinking water treatment plants, which is an important element of quality

control. Other microbiological indicators, not necessarily associated with faecal pollution,

may also be used for this purpose.

2.5.3 INDICATOR ORGANISMS

The US Environmental Protection Agency (EPA) lists the following criteria for an

organism to be an ideal indicator of faecal contamination

1. The organism should be present whenever pathogens are present.

2. The organism should be useful for all types of water.

3. The organism should have a longer survival time than the hardiest pathogen.

4. The organism should be found in warm-blooded animals’ intestines.

Examples of indicator organisms include:



2.5.4 THERMOTOLERANT COLIFORM BACTERIA

These are the coliform organisms that are able to ferment lactose at a temperature of 44 –

45℃.This group includes the genus Escherichia and some species of Klebsiella, Enterobacter

and Citrobacter.

Regrowth of the bacteria in the distribution system is unlikely unless sufficient bacterial

nutrients are present, unsuitable materials are in contact with the water or the water is above

13℃, and there is no free residual chlorine.

Mostly, presence of thermotolerant coliform is directly related to that of E. coli. Its use for

assessing water quality is hence acceptable for routine purposes. Thermotolerant coliform

organisms are readily detected, therefore play an important secondary role as indicators of the

presence of faecal bacteria in water.

Thus, thermotolerant coliform organisms may be used in assessing degree of treatment

necessary for waters of different quality and for defining performance targets for removal of

bacteria.

2.5.4.1 COLIFORM ORGANISMS (TOTAL COLIFORMS)

Coliform organisms have been widely used as a suitable microbial indicator of water quality,

largely because they are easy to detect in water. The term “coliform organisms” refers to

Gram-negative, rod-shaped bacteria capable of growth in the presence of bile salts or other

surface-active agents with similar growth-inhibiting properties and able to ferment lactose at

35–37°C with the production of acid, gas, and aldehyde within 24–48 hours.

Presence of coliform organisms however do not always directly relate to the presence of

faecal contamination or pathogen in water, however, this test is useful for monitoring the

microbial quality of water.



2.5.4.2 FAECAL STREPTOCOCCI

This is streptococci generally present in human and animal faeces. Faecal streptococci rarely

multiply in polluted water, and they are more persistent than E. coli and coliform bacteria.

They are therefore valuable as indicators of water quality.

In addition, faecal streptococci are highly resistant to drying and therefore will be valuable

for routine checks on distribution systems or for detecting pollution of ground waters or

surface waters by surface run-off.

2.5.4.3 ESCHERICHIA COLI (E. COLI)

Escherichia coli is a member of the family Enterobacteriaceae. Escherichia coli is abundant

in human beings and animal faeces. E. coli is a species of faecal coliform bacteria that is

specific to faecal material from humans and other warm-blooded animals. EPA recommends

E. coli as the best indicator of health risk as it is used as an indicator to monitor the possible

presence of other more harmful microbes.

It is found in sewage, treated effluents and natural waters and soils which have been subject

to faecal contamination, whether from humans, wild animals, or agricultural activity.

Presence of E. coli cannot be ignored because it brings to the conclusion that the water has

been faecally contaminated and hence the presence of pathogen in the water is possible.

Possible sources of faecal contamination include:

- Agricultural runoff

- Wildlife that uses the water as their natural habitat

- Runoff from areas contaminated with pet manure

- Wastewater treatment plants

- On-site septic systems



2.6 BACTERIOLOGICAL QUALITY METHODOLOGIES

Plate Count Method: It is a relatively simple method used to find the concentration

of coliform in a sample of water. It involves the fixing single invincible cells in

position and creating favourable conditions. I.e. nutrients, temperature, pH and many

more to enable the cells to grow into colonies of millions of cells clustered together at

the spot where the cells are fixed so that one can count them. Knowing the volume of

water taken, one can then work out the density of the cells.

For best results the colonies should neither be overcrowded or too few. Hence dilution

may need to be applied. Coliforms are used to assess the effectiveness of disinfection.

Multiple tube: In this method, a measured sub-sample (perhaps 10ml) is diluted with

100 ml of sterile growth medium and an aliquot of 10 ml is then decanted into each of

ten tube is then decanted into each of ten tubes The remaining 10 ml is then diluted

again and the process repeated. At the end of 5 dilutions this produces 50 tubes

covering the dilution range of 1:10 through to 1:10000.

The tubes are then incubated at a pre-set temperature for a specified time and at the

end of the process the number of tubes with growth in is counted for each dilution.

Statistical tables are then used to derive the concentration of organisms in the original

sample. This method can be enhanced by using indicator medium which changes

colour when acid forming species are present and by including a tiny inverted tube

called a Durham tube in each sample tube. The Durham inverted tube catches any gas

produced. The production of gas at 37 degrees Celsius is a strong indication of the

presence of Escherichia coli.

Filter membrane: This is a refinement of total plate count in which serial dilutions of

the sample are vacuum filtered through purpose made membrane filters and these

filters are themselves laid on nutrient medium within sealed plates. This method is

otherwise similar to conventional total plate counts. Membranes have a printed



millimetre grid printed on and can be reliably used to count the number of colonies

under a binocular microscope.

2.7 PUBLIC HEALTH CONSIDERATIONS

Grey water is contaminated with human and animal excretions from bathing, food

preparation and from washing clothes. All forms of grey water are therefore capable of

transmitting disease.

Disease transmission is principally through the faecal-oral route where the grey water may be

directly ingested through contaminated hands, or indirectly ingested through contact with

contaminated items such as grass, soil, toys, garden implements, and diversion or treatment

devices while they are being serviced.

Transmission may also occur through inhalation of irrigated spray, by penetration through

broken skin, by insect vectors such as flies and cockroaches and vermin vectors such as rats

and mice.

Even household pets may transmit disease by tracking and carrying grey water into the home

or when petted by children.

Ground water contamination and pollution may also lead to disease transmission.

Contaminated drinking water aquifers may facilitate ingestion of pathogens when the water is

used for drinking and other domestic purposes.

People vary in their susceptibility to disease while some people may pass pathogenic micro-

organisms without showing any symptoms of the disease. As the number of persons in a

community served by a centralised wastewater management facility increases so does the risk

of transmission. This is because the diversity (number of the types) of pathogenic micro-

organism load increases with the population.

The same applies to a community increasingly served by on-site wastewater management

systems such as grey water treatment devices. Such a risk to health should be recognised as a

cumulative impact of installation or development.



Therefore, to reduce the risk of transmission, all reused grey water must be totally contained

within the boundaries of the premises. Care must be taken to ensure that there is no cross

connection between the grey water reuse system and the water supply so that drinking water

is not inadvertently contaminated. This has the greatest chance of occurring when grey water

is used for toilet flushing and a cross connection accidentally is made to the water supply.

Grey water reuse plumbing if used for toilet flushing should be coloured purple and labelled

“Treated wastewater – not fit for human consumption.” A backflow prevention device should

also be fitted to the water supply.

Where grey water reuse is practiced the sewer must still be available for reconnection or used

as an overflow during wet weather or when excess grey water cannot be utilised. During wet

weather untreated grey water may be brought to the surface as the water table rises and

therefore provide a source of contamination.

Caution must be exercised with the reuse of grey water to ensure that the potential to transmit

disease has been minimised. This is achieved by:

- Minimising human contact with untreated grey water i.e. subsurface utilisation

- Placing barriers between the grey water and people (and their pets) to minimise

exposure to grey water by containing grey water in vessels or tanks as it is utilised.

- Disinfection to an even higher standard for utilisation in toilet and urinal flushing or

laundry use.

- Sign posting the land application system to advise that grey water is being reused and

that contact must be avoided.

- No irrigation using grey water during periods of wet weather.

- Distinguishing plumbing which contains recycled grey water and to prevent cross

connection to the potable water supply.

- Maintaining a connection to the sewer so as to enable isolation of the land application

system.

- Installing a backflow prevention device on the potable water supply when grey water

is used for toilet flushing.

- Not irrigating raw or treated grey water on edible plants which are consumed raw.

- Using a dedicated land application system not used for recreation such as a children’s

play area or BBQ area.

- Not storing grey water except for surge attenuation, unless treated and disinfected;



- Preventing surface ponding or surface run-off of grey water and confining grey water

within the disposal area.

2.8 ENVIRONMENTAL CONSIDERATIONS

To manage wastewater effectively it is essential that water conservation is practiced.

Wastewater generation should be minimised for three important reasons

- To conserve drinking water as a precious natural resource;

- To ensure that wastewater does not overload the installed grey water management

system, which may then cause a public health risk, as discussed in the preceding

chapter.

- To minimise land requirements for a grey water reuse system.

However, if mishandled, grey water could cause harm to the environment as discussed

below.

• By exceeding the hydraulic loading, the land application system with water

causing run off of polluted water to storm-water drains, rivers, streams and other

people’s property.

• By raising the water table which may affect foundations of houses causing

instability in structures.

• By causing the soil to become permanently saturated, it may prevent plants from

growing and cause odour.

• By altering the soil salinity.

• Altering the soil permeability.

• Changing the soil pH.

• Altering the soil electrical conductivity.

• By degrading the soil with chemical impurities which affect the properties of the

soil to assimilate nutrients or water.

Because grey water contains many impurities, including the nutrients of nitrogen and

phosphorus, which may harm the environment and the soil in particular, great care must be

exercised when designing land application areas to ensure that they are sustainable. There are



some chemicals which are not capable of being treated or degraded in the soil. Therefore, the

soil ecosystem must be capable of adsorbing, absorbing, assimilating or treating the chemical

impurities and nutrients without medium term and long term degradation of the soil, or the

environment.

Domestic grey water treatment systems are designed primarily to treat organic matter and are

not normally designed to remove many chemical salts, such as sodium, nitrates and

phosphates, which may be found in grey water.

2.9 LEGISLATION

2.9.1 WATER QUALITY REGULATIONS

The Minister for Environment and Natural Resources in consultation with relevant lead

agencies made regulations. These regulations are known as the Environmental Management

and Coordination, (Water Quality) Regulations 2006.

The authority with the mandate to enforce these regulations is known as the National

Environment Management Authority established under section 7 of the Environmental

Management and Co-ordination Act No.8 of 1999.

NEMA ensures that effluent discharged into the environment like in our case (grey water into

soak pits) meets the following standards.

Table 2.4: STANDARDS FOR EFFLUENT DISCHARGE INTO THE

ENVIRONMENT

Parameter Max

Allowable(Limits)

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

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

1,1-dichloroethylene 0.2

1,2-dichloroethane 0.04

1,3-dichloropropene (mg/l) 0.02

Alkyl Mercury compounds Nd

Ammonia, ammonium compounds, NO3 compounds

and NO2 compounds (Sum total of ammonia-N

times 4 plus nitrate-N and Nitrite-N) (mg/l)

100

Arsenic (mg/l) 0.02



Arsenic and its compounds (mg/l) 0.1

Benzene (mg/l) 0.1

Biochemical Oxygen Demand (BOD 5days at 20 oC) (mg/l) 30

Boron (mg/l) 1.0

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

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

Cadmium (mg/l) 0.01

Cadmium and its compounds (mg/l) 0.1

Carbon tetrachloride 0.02

Chemical Oxygen Demand (COD (mg/l) 50

Chromium VI (mg/l) 0.05

Chloride (mg/l) 250

Chlorine free residue 0.10

Chromium total 2

cis –1,2- dichloro ethylene 0.4

Copper (mg/l) 1.0

Dichloromethane (mg/l) 0.2

Dissolved iron (mg/l) 10

Dissolved Manganese(mg/l) 10

E.coli (Counts / 100 ml) Nil

Fluoride (mg/l) 1.5

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

Lead (mg/l) 0.01

Lead and its compounds (mg/l) 0.1

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

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

Oil and grease Nil

Organo-Phosphorus compounds (parathion,methyl parathion,methyl

demeton and Ethyl parantrophenyl phenylphosphorothroate, EPN only)

(mg/l)

1.0

Polychlorinated biphenyls, PCBs (mg/l) 0.003

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

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

Phenols (mg/l) 0.001

Selenium (mg/l) 0.01

Selenium and its compounds (mg/l) 0.1

Hexavalent Chromium VI compounds (mg/l) 0.5

Sulphide (mg/l) 0.1

Simazine (mg/l) 0.03

Total Suspended Solids, (mg/l) 30

Tetrachloroethylene (mg/l) 0.1

Thiobencarb (mg/l) 0.1



Temperature (in degrees celious) based on ambient temperature ± 3

Thiram (mg/l) 0.06

Total coliforms ( counts /100 ml) 30

Total Cyanogen (mg/l) Nd

Total Nickel (mg/l) 0.3

Total Dissolved solids (mg/l) 1200

Colour in Hazen Units (H.U) 15

Detergents (mg/l) Nil

Total mercury (mg/l) 0.005

Trichloroethylene (mg/l) 0.3

Zinc (mg/l) 0.5

Whole effluent toxicity

Total Phosphorus (mg/l) 2 Guideline value

Total Nitrogen 2 Guideline value

And any other parameters as may be prescribed by the Authority from time to time

Remarks

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

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

the Authority.

2.9.2 OFFENCES

Contravening the above regulations constitutes an offence.

As outlined in PART VI MISCELLANEOUS PROVISIONS of the NEMA WATER

QUALITY REGULATIONS

Offences 27. (1) Any person who contravenes any of these Regulations commits

an offence and shall be liable on conviction to a fine not exceeding five

hundred thousand shillings.

(2) In addition to the above, the court may give such other orders as

provided for by the Act.



3 METHODOLOGY

3.1 INTRODUCTION

The aim of this study was to determine the quality of grey water and the application of

internal waste treatment systems. In remote areas, we find that there is mostly a lack of an

operational sewer system. Therefore, households have to establish on-site waste management

methods. Such methods include, septic tanks, soil percolation systems and pit latrines.

3.2 BACKGROUND KNOWLEDGE OF THE STUDY AREA

Samples were collected from a block of residential flats in Ongata Rongai.

MAP 1: THE SATELLITE IMAGE OF THE AREA OF STUDY

Plate 3.1 Sampling point: Block of apartments



3.2.1 LOCATION

Ongata-Rongai is a fast developing residential urban aggregation within Kajiado County;

situated at Kajiado’s border Nairobi at latitude (0° -53' 60 S), and longitude (36° 25' 60E).

Located 50 Kilometres from Kajiado District Headquarters (the core to which it is

subordinate), and 20 Kilometres from Nairobi City Centre on the Langata-Magadi Road,

several reasons explain the growth of this area which started in the late 1950's as a stone

mining township in present day Kware (quarry) area of Rongai.

3.2.2 PLANNING AND URBAN DEVELOPMENT

As a local satellite urban centre, it owes its existence to proximity to Nairobi (locational

advantage). Secondly, Ongata Rongai grew out of a small settlement put up by casual

labourers who provided labour to neighbouring affluent Karen.

Ongata Rongai functions as Nairobi’s dormitory. Physical development in the area has not

occurred under planning control, with haphazard developments first coming along Magadi



road and then spreading into the interior. Present too, is unchecked animal keeping and

settlements polluting Mbagathi River.

Dominated by economic motive and in total disregard of social, aesthetic and environmental

long-term impacts on the areas’ inhabitants; private developers dictate pace of physical

developments. This has resulted in high densities, overcrowded housing, unsanitary

conditions, diminishing open spaces, and haphazard peripheral development.

This is precipitated by increasing demand for shelter, physical and social infrastructure,

ineffective physical planning systems, informal investment finance and speculative land

costs.

3.2.3 GEOGRAPHY AND ECONOMY

Ongata Rongai with two administrative wards; Ongata-Rongai and Nkaimurunya, has mixed

population except for lacking upper class in socio-economic terms.

Ongata Rongai spatially consists of four areas namely Rongai shopping centre, a commercial

area to the north, Nkoroi, an upper class area to the south, Kandisi, a semi-rural area to the

east and Kware, a slum to the west. Though predominantly residential, formal and informal

commercial developments have come up in an unplanned fashion, and functionally zoning

the area along Magadi road.

3.2.4 INFRASTRUCTURE

Though characterised by proliferation of road links to Nairobi, Ngong and Kiserian to enable

commuter travel, Rongai lacks infrastructure and social amenities commensurate to its

population. An example is the acute shortage of public schools. Rongai’s single bitumen

standard Magadi road serves its entire population, while local access roads are narrow and

un-tarmacked.

Ongata Rongai lacks a trunk sewer. 53 per cent of residents rely on septic/ conservancy tanks

whereas 43 per cent use pit latrines. Oloolaier Water and Sewage Company operated a



sewage exhauster which has since been grounded. Residents contract private solid waste

disposal companies.

The main challenges for water and sewerage provision are:

1. Narrow roads in private land leaving no room for laying of water and sewer pipes.

2. Lack of land for sewerage treatment.

3. Limited financing for water and sewage connections.

3.2.5 SAMPLING POINT

The sampling point was 2 blocks of residential flats namely “Gits” and “Josally” that lead its

wastewater to a similar central point.

Collectively, these two blocks of flats had a population of approximately 74 residents.

3.3 METHOD OF STUDY

3.3.1 SAMPLING

As in the case of wastewater, the value of wastewater analyses depends largely upon the

accuracy of sampling. Thus it was necessary to observe strict precautions in the selection of

sampling points and methods of sampling to ensure the collection of representative samples

at all times.

At the block of flats, grey water is separated from black water. Black water is led to an

underground septic tank within the compound of the block of flats. Grey water on the other

hand, is led to an access manhole which further leads the wastewater to a soil percolation

system where the grey water percolates into the soil.

3.3.1.1 OBTAINING SAMPLE 1



This was obtained directly from the manhole.

Plate 3-2: Access Manhole, sampling point 1.

From the PHE Laboratory at Hyslop building, 2 sampling bottles were obtained.

One 500ml plastic bottle and a 250ml glass bottle. Using these bottles, the samples of grey

water were obtained by simply submerging the bottles into the access manhole until they

were completely full.



Plate 3-3: Obtaining the sample 1 a)

Plate 3-4: Obtaining the sample 1 b)



Plate 3-5: The sample 1 collected.

3.3.1.2 OBTAINING SAMPLE 2

This was obtained directly from the pipe.

From the PHE Laboratory at Hyslop building, 2 sampling bottles were obtained.

One 500ml plastic bottle and a 250ml glass bottle. Using these bottles, the samples of grey

water were obtained by filling the bottles with grey water flowing from the pipe until they

were completely full



Plate 3-6: Pipe, sampling point 2.

Plate 3-7: The sample 2 collected.



Care was taken not to disturb the contents by creating currents at the sampling point.

Examination of the samples should ideally be made as soon as possible after collection.

3.3.2 LABORATORY TESTS.

Laboratory tests were conducted after sampling in the Public Health Engineering Laboratory

at the University of Nairobi.

The tests performed were:

• Faecal bacteria

• General coliform

• pH

• BOD (Biochemical Oxygen Demand)

• COD (Chemical Oxygen Demand)

• Dissolved oxygen

• Chloride

• Solids: Suspended

• Sulphates.

Plate 3-8: PHE Laboratory.



3.3.2.1 LAB PROCEDURES.

a) pH

Method (pH meter)

About 75ml of the sample was placed in a 100 ml beaker. The electrodes were carefully

raised out of the beaker and rinsed with distilled water. Drops of water from the electrodes

were wiped. The electrodes were then immersed in the beaker containing the sample.

The selector switch was turned to ‘pH’. The pH was read directly from the meter and

recorded. The selector switch was then turned to “CHECK”.

Carefully, the electrodes were raised and rinsed with distilled water. They were then replaced

into the beaker of distilled water.

b) Chloride

Method

To 100 ml of the sample, 1 ml of potassium chromate solution was added in a conical flask.

The mixture was then titrated against standard silver nitrate solution with constant stirring

until a slight red precipitate appears.

The volume if titrant used is recorded and concentration of chloride calculated.

c) Dissolved Oxygen (DO)

Reagents

- Manganous Sulphate solution

- Concentrated Sulphuric acid

- Starch indicator solution

- Alkali-azide-iodide reagent

- Standard Sodium Thiosulphate Solution, 0.025N



Method

The sample was poured into a DO bottle until full. The volume of the DO bottle was 280ml.

The stopper was replaced carefully so as not to trap any air bubble in the bottle. The stopper

was then removed and in quick succession, 2ml of Manganous Sulphate Solution and Alkali-

azide-iodide reagent were added with the tip of the pipette well below the water level in the

bottle.

The sample did not turn yellow on adding the reagents hence concluded that the DO in the

sample is too little. (Below 1.0mg/l).

d) General Coliform

Presumptive Test

Reagents and Apparatus

- Durham tubes

- MacConkey broth media

- Incubator

- Fermentation tubes

Method

Untreated water from raw water sources (as was my case) were examined using different

inoculation volumes in tenfold dilution steps. The following inoculations were prepared.

10ml of sample to each of three tubes containing 10 ml of double-strength medium;

1.0 ml of sample to each of three tubes containing 10 ml of single-strength medium;

1.0 ml of a 1: 10 dilution of sample (i.e. 0.1 ml of sample) to each of three tubes

containing 10 ml of single-strength medium.

In each fermentation tube, there was an inverted Durham tube. This tube was to be filled with

the sample. The purpose of these tubes were to catch any gas produced. This method was

enhanced by using indicator medium which changes colour when acid forming species are

present. In my case, colour change was from purple to cloudy yellow for the first

presumptive test.



After gently shaking the tubes to mix the contents, the tubes were incubated at a temperature

of 37℃ for 48 hours. However, observations were made after 24 hours to check for positive

indications of coliform. Incubation began at 1: 55 pm.

After 24 hours, the samples from presumptive tests were observed for the presence of gas.

Using a loop wire, broth was transferred from the passed presumptive test fermentation tube

into a corresponding confirmative test fermentation tube.

For the tubes from the presumptive test that had negative results i.e. no presence of gas in the

Durham tube, they were re-incubated for a further 24 hours at the same temperature of 37℃.

After 48 hours, the presumptive test samples that had not passed were observed to check the

presence of gas in the inverted Durham tubes. The samples that were positive i.e. presence of

gas in the inverted Durham tubes, were transferred using a wire loop into the corresponding

confirmatory test fermentation tube.

The presumptive test sample that was negative after 48 hours was discarded.

Confirmatory Test


- Durham tubes

- Incubator


- Brilliant green lactose (bile) broth.

Method

Similar to the presumptive test, the following media were prepared;

Three tubes containing 10 ml of double-strength medium;

Three tubes containing 10 ml of single-strength medium;

Three tubes containing 10 ml of single-strength medium.

The confirmative test fermentation tubes also had inverted Durham tubes which were filled

with the sample.

Only samples that passed the presumptive test were used in the confirmatory test.



They were then incubated at 37℃ for 48 hours.

After 24 hours, observations were made to check for the presence of gas in the inverted

Durham tubes and the results recorded.

The samples that were negative i.e. no presence of gas in the inverted Durham tubes were re-

incubated for an additional 24 hours at the same temperature of 37℃.

After 48 hours, the remaining confirmatory test samples were observed for the presence of

gas in the inverted Durham tubes.

Statistical tables were then used to derive the concentration of general coliforms in the

sample.

e) Faecal Bacteria (E. coli)


- Durham tubes

- Incubator


- Brilliant green lactose (bile) broth.

Method

Similar to the confirmatory test, the following media were prepared;

Three tubes containing 10 ml of double-strength medium;

Three tubes containing 10 ml of single-strength medium;

Three tubes containing 10 ml of single-strength medium.

The E. coli test fermentation tubes had inverted Durham tubes.

Samples from the confirmatory that were positive for general coliform were used in this test.

Using a wire loop, samples from positive confirmatory sample, were transferred into

corresponding the E. coli fermentation tubes.



The Durham tubes were filled with the sample. The samples were then incubated at 44℃ for

48 hours.

After the full 48 hours, the samples were observed and those that were positive were recorded

whereas the negative ones were discarded.

Statistical tables were then used to derive the concentration of faecal coliforms (E. coli) in the

sample.

f) Chemical Oxygen Demand (COD)


- Distilled water

- Standard Potassium dichromate solution (0.025N)

- Concentrated Sulphuric acid containing silver sulphate

- Standard ferrous ammonium sulphate (0.1N)

- Powdered mercuric sulphate

- Phenanthroline ferrous sulphate (ferroin indicator solution)

- Reflux apparatus with ground glass joint

- 250ml Erlenmeyer flask with ground glass joint

- Glass beads

- Pipettes

Method

To a 250ml Erlenmeyer flask, the following was added;

0.4 g solid mercuric sulphate

0.5 ml of the sample

10.0 ml of 0.25 N potassium dichromate

A few glass beads

The above was repeated but with 20.0 ml of distilled water instead of the sample to act as

blank. The flask was fitted to the condenser system, making sure the ground glass joint was

snug. The flow of cooling water was started through the condensers.



Very slowly, 30 ml of silver sulphate-concentrated sulphuric acid solution was added to the

flask through the open end of the condenser. The contents of the flask were mixed by

swirling while adding the acid.

The heaters were switched on and the flasks refluxed for two hours. The heaters were then

switched off. The condensers were rinsed with distilled water and the flask removed from the

heater after disconnecting the condenser, carefully after they cooled.

The contents of each flask were then diluted with distilled water to about 150 ml, mixing the

contents while adding the distilled water.

2-3 drops of Ferroin indicator were added to each flask. The contents of the flask were

titrated with standard ferrous ammonium sulphate solution of 0.1 N strength.

The end point of the experiment was a colour change from blue-green to reddish brown. The

volume of the titrant used was observed and recorded.

COD of the sample was then determined through the following formula

(Mg/l) COD = (𝑎−𝑏 ) ×𝑁 ×8000

𝑚𝑙 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒

Where a = ml of titrant used for the blank

b = ml of titrant used for the sample

N = normality of the sample (0.1N)

g) Biochemical Oxygen Demand


Reagents for Dilution water: 1. Phosphate Buffer solution

2. Ferric Chloride solution

3. Magnesium sulphate solution

4. Calcium chloride solution

5. Manganous sulphate solution



6. Concentrated Sulphuric Acid

7. Starch indicator solution

8. Standard sodium Thiosulphate solution 0.025N

Apparatus

- Burettes

- Pipettes

- BOD bottles

Method

6 litres of dilution water was prepared by adding

- 6 ml of phosphate buffer solution

- 6 ml of ferric chloride solution

- 6 ml of magnesium sulphate solution

- And 6 ml of calcium chloride solution,

To 6 litres of distilled water kept aerated in the aspirator bottle. They were mixed well and

aeration continued. The BOD bottles to be used had a capacity of 300 ml each. The volume

of sample to be taken in each bottle was calculated which when filled with dilution water will

result in dilutions of 1:300, 1:560, 1:750, 1:1000 and 1: 1500.

The five sets of BOD bottles each set containing two bottles were arranged. The bottles were

then labelled with the dilution factors mentioned above. The calculated amounts of sample

was transferred to each bottle as appropriate.

The bottles were then filled with dilution water without overflowing and the stopper replaced

without trapping any air bubble. Another set of two bottles was taken. They were identified

as dilution water BLANK and they were filled with dilution water without any sample.

The dissolved oxygen concentration in one bottle was determined from each of the six sets of

bottles as follows.

The stopper was removed and in quick succession, 2 ml each of manganous sulphate solution

and alkali azide-iodide reagent with the tip of the pipette well below the water level in the

bottle was added. The stopper was replaced again taking care not to trap any air bubbles.



The contents of the bottle were mixed by inverting the bottle several times and letting the

precipitate settle half-way down the bottle. The contents were mixed again and the precipitate

let to settle again as before

2 ml of concentrated sulphuric acid was added to the contents of the bottle using a bulb, with

the tip of the pipette just below the water level. The stopper was replaced and the contents

mixed again, till all the precipitate dissolved.

203 ml was measured from the bottle and transferred to an erlenmeyer flask. This was then

titrated against standard sodium thiosulphate solution till all the colour changed to pale

yellow. 1 ml of starch indicator solution was added and titration continued until all the blue

colour disappeared. Reappearance of the blue colour after the first disappearance was

disregarded.

The remaining bottle in each of the six sets were incubated at 20℃ for 5 days in the incubator

cabinet.

Once 5 days were over, the DO was determined for each dilution as stated above. Volume of

titrant used was observed and recorded. The DO was then determined using the following

formula.

DO, mg/l = ml of titrant used under above conditions

h) Suspended solids

Apparatus

- Filter paper

- Desiccator

- Drying oven

- Suction pump

Procedure

The weight of a new filter paper was determined using an analytical balance (W1). The filter

paper was then mounted onto the suction pump. The sample was shaken vigorously and 20

ml transferred rapidly to the funnel of the suction pump by means of a 100ml volumetric

cylinder.



The suction pump was then turned on and was left to run until all the sample had passed

through the filter paper. The filter paper was then removed carefully and dried in the oven to

constant weight i.e. overnight.

The filter paper and contents were then weighed (W2).

TSS in mg/l = 𝑊2−𝑊1

𝑚𝑙 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒 𝑓𝑖𝑙𝑡𝑒𝑟𝑒𝑑

TSS = Total Suspended Solids



4 RESULTS AND ANALYSIS

4.1 1ST SAMPLE (FROM MANHOLE)

4.1.1 LAB RESULTS

a. PH

PH meter reading: 6.59

b. Chloride

Initial reading: 0.0 ml

Final reading: 38.4 ml

Volume used: 38.4 ml

Chloride concentration = 38.4 × 10

Chloride concentration = 384 mg/l

c. Dissolved Oxygen

D.O below than 1.0 mg/l

D.O concentration = <1.0mg/l

d. General Coliforms

Final result.

Positive result: Presence of air bubble in the inverted Durham tube after incubation at 37℃

for 48 hours.



Table 4.1: GENERAL COLIFORMS LAB RESULTS

Double strength

(10ml sample)

Single strength

(1ml of sample)

Single strength

(0.1 ml of sample)

3 3 2

Therefore, 1100 coliforms per 100ml of sample.

From table 908.11 Standard Methods for Examination of Waste and Wastewater 14th

Edition

1975

e. Faecal Bacteria (E. coli)

Final result.


for 48 hours.

Table 4.2: E. COLI LAB RESULTS

Double strength

(10ml sample)

Single strength

(1ml of sample)

Single strength

(0.1 ml of sample)

2 0 2

Therefore: 14 E. coli in 100 ml of sample


Edition

1975

f. COD

0.5 ml of sample was used in this test.

Table 4.3: COD LAB RESULTS

Reagent Initial Final Volume of titrant

Blank 0.0 24.0 24.0

Sample 0.0 20.1 20.1



(Mg/l) COD = (24.0−20.1 ) ×0.1 ×8000

0.5

COD = 6560 mg/l

g. BOD

This sample was quite polluted, hence 6 sets of BOD bottles were prepared in the

following ratios. BOD bottles used had a volume of 300ml.

1:560 (0.5ml)

1:750 (0.4ml)

1:1000 (0.3ml)

1:1500 (0.2ml)

1:300 (1ml)

Blank

Table 4.4: BOD0

Ratio Initial Reading Final Reading Volume of Titrant

1: 1500 7.0 14.4 7.4

1:1000 14.4 21.8 7.4

1:750 21.8 29.1 7.3

1:560 29.1 36.3 7.2

1:300 0.0 7.0 7.0

Blank 36.3 43.9 7.6

Table 4.5: BOD5


1: 1500 10.9 14.9 4.7

1:1000 7.6 10.9 3.3

1:750 2.4 4.0 2.0

1:560 1.0 2.4 0.5

1:300* NO OXYGEN

Blank 0.0 7.6 7.6



1:300 sample did not have any dissolved oxygen remaining. This was because, on addition of

2 ml each of manganous sulphate solution and alkali azide-iodide reagent, the sample turned

white signifying no oxygen remaining. The test ended there for that particular sample.

Table 4.6: CALCULATION OF BOD

Ratio BOD0-Vol (V1) BOD5-Vol (V2) V1 – V2 BOD 5

1: 1500 7.4 4.7 2.7 3.4*1500 = 4050

1:1000 7.4 3.3 4.1 4.1*1000 = 4100

1:750 7.3 2.0 5.3 5.3*750 = 3975

1:560 7.2 0.5 6.7 6.7*560=3752

1:300* 7.0 NO OXYGEN -

Average BOD5 values

BOD5 = 4050+4100+3975+3752

4

BOD5 = 3969.3 mg/l

Plate 4-1: Sample 1:300 fully depleted of Dissolved Oxygen

4.2 2ND SAMPLE (FROM PIPE)

4.2.1 LAB RESULTS

a. PH



PH meter reading: 7.56

b. Chloride



Volume used: 22.6 ml

Chloride mg/l = 22.6 × 10

Chloride = 226 mg/l

c. Dissolved Oxygen



Volume used: 0.5 ml

DO concentration = 0.5 mg/l

d. Sulphates

Sample turbidity: 100

Sulphates concentration = Above 500 mg/l

e. Suspended solids

20 ml of sample.

Weight of filter paper: 0.168g

Filter paper and suspended solids: 0.179g

TSS in mg/l: 0.179 – 0.168

20 = 0.00055 mg/l

Suspended solids = 0.00055 mg/l

f. General Coliforms



Final result.


for 48 hours.

Table 4.7: GENERAL COLIFORMS LAB RESULTS

Double strength

(10ml sample)

Single strength

(1ml of sample)

Single strength

(0.1 ml of sample)

3 3 1

Therefore, 460 coliforms per 100ml of sample.


Edition

1975

g. Faecal Bacteria (E. coli)

Final result.

Negative result: No air bubble in the inverted Durham tube after incubation at 44℃ for 48

hours.

Table 4.8: E. COLI LAB RESULTS

Double strength

(10ml sample)

Single strength

(1ml of sample)

Single strength

(0.1 ml of sample)

0 0 0

Therefore: No E. coli




Edition

1975

h. COD

2 samples were used in this test

5 ml sample

2 ml sample

Table 4.9: COD LAB RESULTS

Reagent Initial Final Volume of titrant

Blank 0.0 24.7 24.7

5 ml Sample 23.5 45.2 21.7

2 ml sample 0.0 23.5 23.5

Calculation

5ml: COD

(24.7 – 21.7) × 8000 × 0.1

5 = 480 mg/l

2ml: COD

(24.7 – 23.5) × 8000 × 0.1

2 = 480 mg/l

Average COD values

480 + 480

2 = 480

COD = 480 mg/l

i. BOD

This sample was not as polluted, hence 4 sets of BOD bottles were prepared in the following

ratios. BOD bottles used had a volume of 280ml.



1:50 (5.6ml)

1:100 (2.8ml)

1:200 (1.4ml)

Blank

Table 4.10: BOD0


1: 50 7.3 14.5 7.2

1:100 14.5 21.7 7.2

1:200 22.3 29.6 7.3

Blank 0.0 7.3 7.3

Table 4.11: BOD5


1: 50 6.8 8.0 1.2

1:100 8.0 12.4 4.4

1:200 12.4 18.1 5.7

Blank 0.0 6.8 6.8

Table 4.12: CALCULATION OF BOD

Ratio BOD0-Vol (V1) BOD5-Vol (V2) V1 – V2 BOD 5

1: 50 7.2 1.2 6.0 6.0*50 = 300

1:100 7.2 4.4 2.8 2.8*100 = 280

1:200 7.3 5.7 1.6 1.6*200 = 320

Average BOD values

300 + 280 + 320

3 = 300

BOD5 = 300 mg/l



5 DISCUSSIONS

5.1 LAB RESULTS

Table 5.1: LAB RESULTS

Parameter Sample 1 Sample 2

Total Suspended Solids 2100 550

Sulphates >500 500

Chloride 384 226

BOD 3969.3 300

COD 6560 480

pH 6.59 7.56

Faecal bacteria (E. coli) 14 Nil

Total coliforms 1100 460

5.1.1 SAMPLE 1 (FROM MANHOLE)

This sample was highly polluted. Most surprisingly, it contained E. coli which does not

reflect the fact that grey water originates from kitchens and bathrooms hence ideally, should

not contain E. coli.

In addition, the COD and BOD values were far too large. This was because, the sampling

point contained grey water that had been stagnant for an unknown period.

Stagnant grey water is susceptible to contamination and will in time become septic. This

explains the highly polluted sample.

5.1.2 SAMPLE 2 (FROM PIPE)

This sample was obtained from the water flowing from the pipe into the access manhole. It

had a better representation of the study objectives as observed from the laboratory test results.

The results obtained were acceptable and much lower than the results from the initial

manhole sample.

Errors encountered were small and acceptable. Such experimental errors may have risen from



- Contamination of sampling equipment when obtaining the sample.

- Contamination of the sampling point from external factors.

- Parallax error in reading volumes of reagents in the laboratory.

5.2 POLLUTION LEVELS OF SAMPLES

Results of the samples tested versus the set standards can be tabulated as shown below

Table 5.2: COMPARISON OF SAMPLE POLLUTION LEVELS AGAINST WQ

REGULATIONS

Parameter Sample 1 Sample 2 WQ standard

Total Suspended Solids 2100 550 30

Sulphates >500 500 -

Chloride 384 226 250

BOD 3969.3 300 30

COD 6560 480 250

pH 6.59 7.56 6.5 – 8.5

Faecal bacteria (E. coli) 14 Nil Nil

Total coliforms 1100 460 30

5.3 REMARKS ON POLLUTION LEVELS

5.3.1 SAMPLE 1

As earlier indicated, Sample 1 was much polluted and as seen from Table 5.2. The only

parameter that conformed to the WQ regulations was pH. The other parameters exceeded the

WQ regulations by much.

The high levels of pollution can be attributed to the fact that this water was stagnant hence

turning septic.



5.3.2 SAMPLE 2

Parameters that conformed to the WQ regulations include:

- Chloride

- Faecal bacteria

- pH

This as compared to Sample 1 proved to be less polluted. However, some important

parameters such as BOD and COD were too far exceeded.

Of significance was that, Sample 2 did not have faecal bacteria meaning that there was no

cross-contamination with black water. Presence of E. coli in grey water will indicate cross-

contamination with black water (waste water from toilets) and hence the piping system will

need repair.

5.4 HOW TO HANDLE GREY WATER

5.4.1 DIVERT TO SEPTIC TANK

Conventional practise has been to direct all wastewater to a septic tank which is then emptied

from time to time of sludge using a tanker with a suction pump.

This practise has some shortcomings as listed below;

- For homeowners, more waste water volumes being directed to the septic translates to

added running and maintenance costs for the septic tanks.

- Directing grey water to septic tanks greatly increases the load carried by the septic

system leach field, hence reducing the system’s life expectancy and effectiveness.

- Grey water is laden with phosphates from soaps and detergents such that when

directed to the septic, it ends up disrupting the digestive function of the septic tank.

As observed above, this measure is not as effective.



5.4.2 FILTRATION AND SETTLING SYSTEM

5.4.2.1 SCREEN

Screen can be a mesh with less than 10 mm size to remove coarse particles. The screens can

be placed at the inlet to the piping system of sources such as bathroom, sinks etc. to remove

large particles and prevent an overload of particles at the outlet.

The screens can be cleaned manually and solids disposed along with solid waste.

5.4.2.2 USE OF SETTLING TANK

Use of a settling tank enables solids and large particles to settle to the bottom, while grease,

oils and small particles will float.

Such tanks should be large enough to hold twice the expected dally flow plus 40 % to allow

for sludge accumulation and surge loading. One widely-used type of settling tank well-suited

for grey water treatment is a septic tank.

A septic tank is specifically designed to allow settling. The use of a septic tank to treat grey

water should never be confused with the conventional use of a septic tank. Grey water

intended for reuse should never be mixed with toilet wastes.

An electrical pump or aerator could be added to a septic tank to create an aerobic

environment. Using a settling tank prior to discharging waste into the environment will

reduce the pollution loading of the grey water.

Grey water quality will improving by reducing quantity of TSS and with the installation of an

aerator, BOD and COD will also decrease.

5.4.3 USE OF SOAK PIT

This is a covered, porous walled chamber that allows water to slowly soak into the ground.

The grey water is discharged, either raw or from primary treatment, into the underground

chamber from where it infiltrates into the surrounding soil.

As the grey water percolates through the soil from the soak pit, small particles are filtered out

by the soil matrix and organics are digested by microorganisms.



Soak pits are however very effective for soil with good absorptive properties: clay, hard

packed or rocky soil is not appropriate. Soils with very fast soil percolation rates (i.e., less

than one (1) minute per inch) are not suitable for soak pits. Soils with very fast percolation

rate do not provide adequate treatment of wastewater because the effluent moves too quickly

through the soil and may reach ground water before being fully treated.

Soak pits should not be constructed directly over visible bedrock, cracks, crevices,

depressions, sinkholes or other susceptible geologic formations to protect the underlying

aquifer.

Soak pits should be located a safe distance from a drinking water source especially if the

drinking water is sourced from a shallow well.

Water tables are not static, and may rise above the bottom of the seepage pit, flooding it and

allowing direct contact of pathogens and nitrogen species with ground water.

Soak pits would be most effective if the effluent has undergone some primary treatment.

5.4.4 USE OF WETLANDS

Physical, chemical, and biological processes are combined in wetlands to remove

contaminants from wastewater. Grey water treatment is achieved by soil filtration in reed-bed

systems which reduces the organic load of the grey water considerably

In addition, constructed wetlands decrease the concentration of faecal bacteria. If designed

properly, these systems would produce a clear and odourless effluent.

Constructed wetlands tend to be simple, cheap to maintain and environmentally friendly.

However, construction of wetlands require large amount of space that is not available at the

block of apartments.

5.4.5 DISINFECTION

A little disinfection before discharging effluent into the environment helps to reduce the

pollution levels.



An appropriate chemical to be used to disinfect water is chlorine. This is because it is cheap,

readily available, and stable and will, with time, vaporize from the water after disinfection.

Organic matter in grey water may combine with chlorine hence reducing the amount

available for the disinfection process. Because of this reason, a settling tank or filter before

this stage is highly recommended.



6 CONCLUSION

From the findings, it is clear that the grey water effluent exceeds the WQ regulations for effluent

discharged into the environment. Hence therefore, this effluent should undergo primary treatment

before discharge into the environment.

The other option should thus be discharge into the septic tank for non-sewered areas or discharge

into the public sewer for sewered areas.



7 RECOMMENDATIONS

- Residents in rural areas should partner with the county government to set up a public

sewer system to avoid rampant effluent discharge which may be hard for enforcing

bodies like NEMA to monitor.

- For residents with enough space, wetlands are effective, cheap and easy to install for

treating grey water. Effective wetlands can even produce water that can be reused for

irrigation and other commercial purposes. This water cannot be used for drinking.

- Well designed soak pits are effective but disinfection and settling tanks systems prior

to this ensures that soak pits are effective.

- Enforcing bodies like NEMA should carry out regular quality assessment of effluent

discharged into the environment to ensure that the set standards are not exceeded.

This project can be used and modified so as to provide a solution to grey water treatment and

discharge in non-sewered areas.



8 REFERENCES

A-Boal, D. Christov, Lechte, P. and Shipton, R. 1995. Installation and Evaluation of

Domestic grey water reuse Systems: Executive Summary. Department of Civil and Building

Engineering, Victoria University of Technology, Victoria, Australia: Victoria University of

technology, 1995. Technical Memorandum

Environmental Management and Coordination, (Water Quality) Regulations 2006:

Environmental Management and Coordination Act, (1999), the Minister for Environment and

Natural Resources

Guidelines for drinking-water quality. 2nd

Edition: Volume 3 Surveillance and control of

community supplies. World Health Organization, Geneva 1997.

Little, V. 2000: Residential grey water reuse: The Good, The Bad, The healthy. Tucson, AZ:

The Water Conservation Alliance of southern Arizona (Water CASA), 2009

Mullegger E, Langergrabber G. Jung H. Starkl M. and Laber J. 2003: Potential for Grey

water treatment and reuse in rural areas, 2nd

International Symposium on ecological sanitation

Peter L.M. Veneman and Bonnie Stewart 2002: Grey water characterization And

Treatment Efficiency; Final Report for The Massachusetts Department of Environmental

Protection, Bureau of Resource Protection, December 2002

Public Health Engineering Laboratory Manual: Department of Civil Engineering,

University of Nairobi.



APPENDIX

PHOTO GALLERY

Plate 8-1: Presumptive Test Reagents

Plate 8-2: BOD Test Bottles



Plate 8-3: Positive Presumptive Test Results

Plate 8-4: PH Meter

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