Brian omondi odhiambo

U N I V E R S I T Y O F N A I R O B I
S C H O O L O F E N G I N E E R I N G
DEPARTMENT OF ENVIRONMENTAL AND BIOSYSTEMS ENGINEERING
PROJECT REPORT
PROJECT TITLE: DESIGN OF A COST EFFECTIVE WATER PURIFICATION SYSTEM
USING REVERSE OSMOSIS (A CASE STUDY OF TATU CITY- KIAMBU COUNTY)
CANDIDATE’S NAME: BRIAN OMONDI ODHIAMBO
CANDIDATE NO : F21/2246/2014
SUPERVISOR’S NAME: PROF ELIJAH .K. BIAMAH
SUBMITTED TO: ENG DANIEL AMEDI MUTULI
A Report Submitted in Partial Fulfillment for the Requirements of the Degree of Bachelor of Science
in Biosystems Engineering, of the University Of Nairobi.
FEB 540: ENGINEERING DESIGN PROJECT
2014/2015 ACADEMIC YEAR

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DECLARATION
I declare that this is my original project work and has not been submitted in any other University.
Brian Omondi Odhiambo Signature………………………
(F21/2246/2014) Date …………………………..
This project work is acceptable and has my approval as a university supervisor.
Prof Elijah .K. Biamah Signature…………………..
Supervisor Date……………………….

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DEDICATION
This design project is dedicated to my father Mr. Benson Apuoyo for his resolve to make a difference in
my life through education and parental support. To my late mother Ercah, though you went back to be
with your maker in 2000, the spirit of your faint voice urging me to put up my best and invisible support
have seen me this far. To my mother Monicah and my siblings Lavender, Collins, Vierri, Jeff and Agnes
thank you all for the personal sacrifices you made in one way or the other for me to pursue my
education. To you all I say, “Learning is a Lifetime Gift!”

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ACKNOWLEDGEMENT
I thank God for enabling me to come this far and walking this journey with me. This work has been a
long journey involving the guidance and assistance of a lot of people without whom the progress of this
work would have been hardly possible. I am deeply indebted to my supervisor Prof Elijah .K. Biamah
for his constant guidance, advice and financial support throughout my entire project work. I would also
like to acknowledge all the lectures in the EBE Department, their constant flow of knowledge and
consultations was an enabler to this design project. Finally, I would like to give special thanks to our lab
technologists at the department whose insightful assistance helped to piece together this design project.

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LIST OF ABBREVIATIONS
RO Reverse Osmosis
SWRO Sea Water Reverse Osmosis
BWRO Brackish Water Reverse Osmosis
WHO World Health Organisation
TDS Total Dissolved Solids
TSS Total Suspended Solids
TFC Thin Film Composite
CA Cellulose Acetate
UV Ultra Violet
EDR Electro Dialysis Reversal

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LIST OF FIGURES
Fig 1: Kenyan map showing the location of Kiambu County.
Fig 2: Administrative map of Kiambu County.
Fig 3: Ruiru constituency map.
Fig 4: Tatu City map.
Fig 5: Site Image of Tatu City borehole location.
Fig 6: Illustration of pump mechanism in RO
Fig 7: Illustration of Osmosis and Reverse Osmosis
Fig 8: ROSA software user interface.

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LIST OF TABLES
Table 1: Classiffication of water into soft or hard.
Table 2: Pretreatment water parameters for evaluation.
Table 3: Common causes of fouling and their pre-treatment
Table 4: Membrane area correction factors for different temperature.
Table 5: Properties of CA and TFC membrane.
Table 6: Domestic water demand.
Table 7: ROSA results and permeate water.
Table 8: Permeate storage tank details.
Table 9: EMCA and WHO standard comparisons with permeate water.

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Contents
DECLARATION..............................................................................................................................................................i
DEDICATION................................................................................................................................................................ii
ACKNOWLEDGEMENT ...............................................................................................................................................iii
LIST OF ABBREVIATIONS............................................................................................................................................iv
LIST OF FIGURES .........................................................................................................................................................v
LIST OF TABLES ..........................................................................................................................................................vi
ABSTRACT ..................................................................................................................................................................ix
1.0 INTRODUCTION ................................................................................................................................................... 1
1.1 PROBLEM STATEMENT .................................................................................................................................... 4
1.2 JUSTIFICATION OF THE SOLUTION ........................................................................................................ 5
1.3 SITE ANALYSIS AND INVENTORY.......................................................................................................... 6
1.3.1 LOCATION.............................................................................................................................................. 6
1.3.2CLIMATE AND BIODERVISITY........................................................................................................... 9
1.3.3 INFRASTRUCTURE......................................................................................................................... 10
2.0 PROJECT OBJECTIVES......................................................................................................................................... 12
2.1 OVERALL OBJECTIVES .................................................................................................................................... 12
2.2 SPECIFIC OBJECTIVES..................................................................................................................................... 12
3.0 SCOPE OF STUDY ............................................................................................................................................... 12
4.0 LITERATURE REVIEW.......................................................................................................................................... 12
4.1 Physical Characteristics Of Borehole Water ................................................................................................. 15
4.2 Chemical Characteristics............................................................................................................................... 17
4.3 Biological Characteristics.............................................................................................................................. 17
4.4 PRE-TREATMENT ...................................................................................................................................... 18
4.5 REVERSE OSMOSIS................................................................................................................................... 21
4.6 REVERSE OSMOSIS MEMBRANES.................................................................................................................. 24
4.7 ADVANTAGES OF A REVERSE OSMOSIS SYSTEM........................................................................................... 26
4.8 DISADVANTAGES OF A REVERSE OSMOSIS SYSTEM...................................................................................... 27

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4.9 ENVIRONMENTAL IMPACTS OF REVERSE OSMOSIS ....................................................................... 29
4.9.1 POST- TREATMENT ..................................................................................................................................... 29
4.9.2 BASIC REQUIREMENTS FOR SOURCES OF DOMESTIC WATER .................................................. 30
4.9.3 ROSA ......................................................................................................................................................... 30
THEORETICAL FRAMEWORK.................................................................................................................................... 31
5.0 GENERATION OF CONCEPT DESIGN .................................................................................................................. 33
5.1 MATERIALS .................................................................................................................................................... 33
5.2 METHODOLOGY............................................................................................................................................. 33
5.3 The Reverse Osmosis System Design Process.............................................................................................. 34
6.0 DATA ANALYSIS.................................................................................................................................................. 36
7.0 RESULTS OF THE DESIGN PROCESS.................................................................................................................... 40
8.0 DESIGN DRAWINGS...................................................................................................................................... 44
9.0 DISCUSSIONS OF THE RESULTS ................................................................................................................ 46
10.0 CONCLUSIONS ................................................................................................................................................. 48
11.0 RECOMMENDATIONS...................................................................................................................................... 50
12.0 REFERENCES.................................................................................................................................................... 52
13.0 APPENDICES..................................................................................................................................................... 54
Appendix 1 .......................................................................................................................................................... 54
Appendix 2 .......................................................................................................................................................... 55
Appendix 3 .......................................................................................................................................................... 56
Appendix 4 .......................................................................................................................................................... 58
Appendix 5........................................................................................................................................................... 59
Appendix 6........................................................................................................................................................... 60
Appendix 7 .......................................................................................................................................................... 61
Appendix 8 .......................................................................................................................................................... 61
Appendix 9 .......................................................................................................................................................... 62
Appendix 10......................................................................................................................................................... 72
14.0 BILL OF QUANTITIES ........................................................................................................................................ 73

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ABSTRACT
The Tatu City developers through Tianjin Sino Hydro Company have already sunk a borehole which
will act as a supplement source of water to the Tatu City residents. The borehole is expected to supply
1000M3
of water daily to the residents and industrial establishments around. The developers have
estimated an average water demand of 10000M3
/day however, the water supply in the area cannot meet
this demands, as the pipeline network in the area is very poor and also the county water source does not
have this capacity. The developers of this city are thus faced with a water scarcity problem.
Alternative solutions to this problem were assessed, including rain water harvesting, groundwater and
county water supply. However all three options had their own advantages and disadvantage, and the
most optimum solution to this problem was sourcing water from the borehole. The borehole water
however is hard water hence the need arises for its purification to make it suitable for domestic
consumption.
Various methods can be used to purify hard water, but taking into considerations various factors
including the economical and technical feasibility of these methods, RO is the most appropriate.
Using the required permeate flow rate and the known raw groundwater characteristics, the types and
number of membrane elements to be used were calculated step by step using known reverse osmosis
system design guidelines. This data was then fed into a software, the Reverse Osmosis System Analysis
(ROSA) software for processing of the system design.
The average amount of water that can be supplied by the system is 280.84m3
/day, as compared to the
300m3
/day that is the average daily water demand of the area. Tatu City is still under construction hence
the water demands of the area cannot be fully determined yet.

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This design project was able to asses that reverse osmosis is an important method for water purification.
Especially for areas hit with the hard groundwater problem. If its adopted with appropriate
considerations it is an economical method for purifying hard water.

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1.0 INTRODUCTION
Adequate clean water supply and sanitation facilities is one of the key amenities to economic
development and public health in any functional society. In Kenya, as a basic need, this has not yet been
realised. Our country is experiencing a number of challenges with water supply. The natural recourses
that we have aren’t enough to provide an equitable delivery of water to the various regions of the
country and the country's water basins do not reach an equitable area of the country. This leaves most of
the population without any fresh water. In the urban areas, the major problem is that rapid urbanization
has pushed poor urban dwellers to the slums, where there is no water or sanitation. They are
overcrowded which worsens the already hazardous health conditions. Most rural areas and urban slums
have no proper connection to a water supply system, and even those in the urban areas experience
intermittent and unreliable water supply. This is mainly due to fluctuations in the reservoir levels,
mismanagement issues and illegal connections. The water authorities lack the funds to run pumping
stations and existing piping systems are often pirated and in disrepair. In order to alleviate the prevailing
difficulties, the country should adopt use of alternative sources of water that can efficiently meet the
demands.
It is not only our country that faces problems with water supply and sanitation. Generally, in the world
all over, increasing demand for allocated freshwater resources, declining freshwater quality, drought,
and the need for a diverse reliable water supply portfolio are among the many reasons that many
countries are looking to for other sources as potential water supply areas. However, the high cost of
water purification projects hinder this from being achieved.
In recent years, our country has experienced a shift in real estate trends where development agencies
have been constructing large gated communities for homes and related amenities such as shopping

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centres, schools and entertainment facilities. An example of such mixed use gated development is Tatu
City.
Tatu city is a 5,000 acre mixed development area that encompasses homes, schools, offices, a shopping
area, medical clinics, nature parks, a sport and entertainment complex and an industrial park. It is
expected to host more than 15,000 residents and thousands of day visitors.
The Tatu City developers through Sinohydro Tianjin Engineering Company have come up with a water
supply system for the Tatu City. The main source of water will be a borehole which has already been
dug, this will be supplemented by the Kiambu county municipal water.
Water is a necessity for survival of humans. Tatu City being a mixed use development adequate water
supply is of essence. Also the quality of water will be of huge importance to the residents. Most city
residents have access to water, but in contrast with accessibility to pure water always lays the big
question of water purity.
Hence, the management of water resources and supply will be of huge significance to the development
and growth of Tatu City. Sustainable water use and the provision of quality water to the growing
population of Tatu city will truly define the success story of the project.
Water purity is often a very complex term to define clearly. There are very many parameters used to
study the purity of water. In some studies it might be defined according to the level of pollution while in
others the contamination levels are considered.
Water is a compound made of hydrogen and oxygen, hence pure water is only supposed to contain this
two compounds. However, in natural conditions this is not possible but in a controlled environment of a
laboratory pure water can exist. From a drinking water standpoint, most references to "pure water" are in
relation to bacteria content and not the chemical contaminant concentrations.

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Consumers can achieve healthy water by identifying the unhealthy contaminants in their water and then
taking action to remove them. In general, the public discussion about water can and will switch from the
notion of ‘pure’ to ‘healthy’. Healthy water is attainable, whereas pure water is not.
Healthy water usually have a PH value of 7.2 to 7.6. Water contaminants such as dissolved minerals,
harmful chemicals and metals can be identified and removed by appropriate purification processes.

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1.1 PROBLEM STATEMENT
Our country Kenya is classified as a chronically water scarce country meaning that it is a country with
less than 1000m3 of fresh water available per person per year. In a country whereby the issue of water
rights is heating up rapidly, we still face a number of challenges relating to supply of pure water for
domestic consumption. Despite Kenya relying economically on water resources it is still a water scarce
country. Some of the major problems related to supply of clean domestic water are:
i. Lack of financial and administrative capacities in the water sector
ii. Low social acceptance among communities of water purification interventions.
iii. High concentration of unnecessary boreholes in urban areas.
iv. Conflicts and general lack of political goodwill in improving the water sector.
Looking at a case study of Tatu city, the developers have dug a borehole which will be the main source
of water supply to the gated community. They hope to achieve sufficient water supply to their residents
by supplementing this with the Kiambu County Municipal Water and small-scale water harvesting.
The borehole water which is the main source of water supply to the city is mainly hard water. Hence this
makes it largely unsuitable for domestic consumption to some extent. With this problem in mind and
lack of an elaborate water purification system for the city, as a future Engineer I have decided to come
up with a solution that will help in the purification of the hard water.
Water purification is a process by which undesired chemical compounds, organic and inorganic
materials and biological contaminants are extracted from water.
There are various methods of water purification, the most common are:
• Chemical Purification: In this method water is purified by addition of chemical
substances such as chlorine and Sodium Dichloroisocyanurate (NaDCC). It is

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mainly used in purification of water infested with bacterial micro-organisms that can
cause diseases.
• Boiling: It is one of the most effective methods of water purification in small scale.
It involves heating of water till its reaches its boiling point which is usually at
100˚C.
• Filtration: It is a technique which is normally used whereby water flows through a
filter to remove suspended particles in it.
• Reverse Osmosis: This method involves the use of a semi-permeable membrane in
the purification process.
This project work will mainly focus on purification by Reverse Osmosis. Reverse Osmosis is a water
purification technology that uses a semipermeable membrane to remove ions, molecules and larger
particles from water. It is a process that can remove many types of dissolved and suspended species
from water, including bacteria.
1.2 JUSTIFICATION OF THE SOLUTION
This proposed design project is a feasible solution to the problem of water purification for domestic
consumption in Tatu City. Taking into considerations proper sizing of the RO membranes and carefully
worked out designs, this project will offer a reliable and affordable solution of pure domestic water to
the residents.
This design project is highly justifiable on the grounds that it will be an economical method for large
scale water purification for domestic consumption for the residents of the city.

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1.3 SITE ANALYSIS AND INVENTORY
1.3.1 LOCATION
The project site for the Reverse Osmosis System will be at Tatu City, the outskirts of Ruiru town, in
Kiambu County. Ruiru Town is mainly an agricultural centre famed for large scale coffee and tea
farming.
Tatu city borders Nairobi county to the east. Accessing the site can either be via the Thika superhighway
or the Southern bypass. It is located approximately 22.7 Km from Nairobi CBD.
Tatu city is approximately 8.6 km from Ruiru town and can be accessed via Kamiti road.
Fig 1; Kenyan Map showing Location of Kiambu County.

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Fig 2: Administrative Map Of Kiambu County
Tatu city will be a mixed use development that will occupy an area of around 5000 acre in Ruiru
Constituency. The piece of land was acquired by Rendeavour Africa who are the major shareholders in
the development from Kofinaf LTD and from small scale farmers in Ruiru.

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Fig 3: Ruiru Constituency Map
The borehole location is within the Kofinaf coffee plantation within Tatu city.
Fig 4: Tatu City Map

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Fig 5: A Site Image of Tatu City borehole Water Tower
1.3.2CLIMATE AND BIODERVISITY
Ruiru’s climate is generally mildly cold and temperate. The temperature here averages 19.5 °C. The
rainfall here averages 797 mm. Rainfall is lowest in July, with an average of 13 mm. In April, the
rainfall reaches its peak, with an average of 170 mm. At an average temperature of 21.0 °C, March is the
hottest month of the year. At 17.2 °C on average, July is the coldest month of the year.

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Graph 1: A graph showing the weather pattern of Ruiru
1.3.3 INFRASTRUCTURE
Infrastructure at the project site can be characterized by elements such as;
• Roads – for transport, the site is easily accessible via the Thika Super Highway, or
through Ruiru Kamiti Road and a murram road that leads directly to the site.
• Energy – energy for construction of the project and lighting will come from electrical
power, connections are available from the national grid within Tatu City. Power lines are
already set up.

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• Water - water lines are being built up in the city. The main source will be the sites
borehole. This will be supplemented by Kiambu county water supply system.
• Waste Management – all waste coming from the project will be managed and handled by
a private company that will be hired by the developers of the city.

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2.0 PROJECT OBJECTIVES
2.1 OVERALL OBJECTIVES
• The design of a cost effective reverse osmosis plant for the purification of borehole water at
Tatu City.
2.2 SPECIFIC OBJECTIVES
• To analyse the cost of production of every m3
of the purified water from the Reverse osmosis
system.
• To establish the TDS and PH composition of the raw borehole water.
3.0 SCOPE OF STUDY
This project will ideally come up with workable design drawings that can be used in the design of a
water purification system by Reverse Osmosis for Tatu City. I will particularly focus on the borehole
water and how to come up with clean water that meets the WHOs standards of pure water and WRA
standards of clean domestic water. The purified water will only be supplied for drinking and small scale
domestic use. It will have a separate supply line from the normal water supplied to the homes. Its usage
will be highly regulated depending on the area covered by a house and its household numbers. This
design project will focus on a target purification of 300 m3
of borehole water daily.
4.0 LITERATURE REVIEW
Hard Water is water that contains high mineral content.

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According USGS Water science school, they define water hardness as; the amount of dissolved calcium
and magnesium in the water.The minerals contained in hard water are usually calcium and magnesium.
Hard water can also contain chlorides , sulphates and ferrous ion. Water hardness that is caused by
calcium bicarbonate is known as temporary, because boiling converts the bicarbonate to the insoluble
carbonate; hardness from the other salts is called permanent and cannot be removed by boiling.
Permanent hardness can also be softened. Water usually collects these minerals from the ground as it
flows.
The most common way of identifying water hardness is by looking at lather formation with soap(Mehdi
Metaiche et al.,1994). When there is less lather formation when the soap is used with water then the
water is considered to be hard water. Another way in which water manifests its hardness is scaling i.e.
forming deposits through calcification that clog plumbing. These scales are usually white because
calcium and magnesium are the most common sources of hardness in water. In swimming pools, a
cloudy or milky appearance characterizes hard water.
Water hardness however cannot be described accurately in a scale since it varies according to a number
of factors (P. Belfast 1974:294) such as:
• Minerals in the water
• PH of the water
• Temperature of the water
The following table can be used as a bench mark for water classification into soft and hard water.
Table 1 ; Classification of Water into Soft or Hard Water

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Though hard water does not have an adverse effect on human health, studies have shown that it can
cause eczema in children(Erin .D. Mackay2002). This is attributed to the fact that the minerals can dry
the skin and hair. Hair washed in hard water tend to be sticky and dull.
Hard water can also cause hair treatment such as dyes to fade away faster and can also cause hair
breakage.
Hard water is not considered to be dangerous to one's health, and it is perfectly healthy to drink.
However, the minerals found in hard water can be detected in the taste, and so some people may find
that it is slightly bitter, whereas soft water is very pure, although occasionally it might have a slightly
salty taste.
The salt in hard water is also attributed to the discolouration of teeth among users of hard water.
Other effects of hard water are:
• Clogging of pipes
• Spots and films on dishes and bathtubs
• Scaling of water taps
With these issues in mind, it is therefore advisable to come up with a water purification system for the
borehole to make it suitable for domestic consumption.

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In every system, it is crucial to have regulations that control the quantity and quality of products for the
protection of people, animals, and the whole environment. Such regulations in Kenya, for the control of
the quality standards for the sources of domestic water are stipulated in the first schedule of the
environmental management and co-ordination (water quality) regulations of 2006.
The borehole water in Tatu City must hence be tested to ensure that it meets the chemical and physical
characteristics of safe water as specified by the act.
Also the characteristic features of the borehole water have to be considered in the design and operation
of the pretreatment and the reverse osmosis process.
4.1 Physical Characteristics Of Borehole Water
Borehole water can be classified as groundwater source.
Often the designation of groundwater refers to water in the saturated zone( Biamah et al 2015). However
water combined with minerals or hold in small, closed pores of tight rocks is often not strictly
considered groundwater.
Physical parameters of the Borehole water that may affect a reverse osmosis system include;
i. Total solids (dissolved and suspended)
ii. Turbidity
iii. Color (apparent and true)
iv. Taste & odor (organic compounds in ground water; dissolved gases in ground water)
v. Temperature

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Temperature surveys are very important in identifying interbedded clay soil in ground water,(
Stanley E. Norris and A.M. Spieker 1966, Groundwater resources of the Dayton area, Ohio,
USGS Water-Supply Paper 1808).
Temperature monitoring can also be useful in the detection of lateral changes in permeability by
monitoring grids of thermistors. This can be used to show that changes in soil temperature can be
used to detect shallow ground water systems(K. Cartwright 1968, Temperature prospecting for
shallow glacial and alluvial aquifers in Illinois, Illinois Geological Survey Circular 433; 1974,
Tracing shallow groundwater, systems by soil temperatures, Water Resources Research 10, no.
4)
• Temperature of the ground water directly affects its density. Cold water is denser
than warm water. In respect to membrane performance, temperature has the
following effects;
i. Feed pump pressure requirements. For every 10-degree Fahrenheit decrease in feed
temperature increases the feed pump pressure requirement by 15 %.
ii. Permeate flux – increase in water temperature causes the elements located in the
front end of the system produce more permeate which results in reduced permeate
flow by the elements located at the rear of the system. Permeate flux is improved
under cooler temperatures.
iii. Permeate quality – increase of temperature causes decreased permeate quality as salt
passage increases due to the increased mobility of the ions through the membrane
• Specific heat/unit volume – the specific heat/unit volume of water is 4000 times
greater than that of air. This affects the system’s performance in that more energy is
required to raise the temperature of each unit volume of the water.

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• Pressure – an increase in the pressure of water causes an increase in the quantity
of permeate water, and its quality up to certain limits.
4.2 Chemical Characteristics
The performance of the reverse osmosis system will be affected by the chemical components of the
ground water which includes the composition of different elements in the ground water. Such
characteristics includes;
i. pH
ii. Anions & cations(dissolved solids)
iii. Alkalinity (HCO3-, CO32+,OH- system)
iv. Hardness (Ca2+, Mg2+)
v. Dissolved gases (O2, CO2, H2S, NH3, N2,CH4…)
vi. Priority pollutants (organic and inorganic)
4.3 Biological Characteristics
Biological characteristics of groundwater include the biological organisms that are contained in the
water. Biological impurities in the groundwater have to be cleaned from the water before being fed into
the system so as to prevent biofouling of the membranes. They include;
i. Bacteria – Salmonella, typhus, cholera, shigella
ii. Viruses – Polio, hepatitis A, meningitis, encephalitis
iii. Protozoa – Amoeba, cryptosporidium, giardia, algae
iv. Coliform bacteria (indicate human waste)
v. Helminths – Guinea worm, hookworm, roundworm
vi. Fungi, algae

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The World Health Organization, created a list of the guidelines of the composition requirements for
drinking-water quality which are the international reference point for standards setting and drinking-
water safety. The latest guidelines drew up by the WHO are those agreed to in Geneva, 1993. Not all
elements were taken into account as there have not been sufficient studies about the effects of the
substance on the organism, and therefore it is not possible to define a guideline limit. In other cases, the
reason for a non-existing guideline is the impossibility of that substance to reach a dangerous
concentration in water, due to its insolubility or its scarcity.
With such guidelines and act in place this project design will focus on water purification of the Tatu City
borehole using them as reference points to mainly meet our project objective.
4.4 PRE-TREATMENT
All parameters in a RO system usually operate most efficiently on filtered water with a pH of less than
6.5 and a SDI of 3 or below. Given that Tatu city water emanates from the borehole which provides hard
water, the pH is thus high hence other forms of pre-treatment is necessary.
Pre-treatment in RO can be described as the process whereby various physical and chemical water
treatment processes occur upstream the reverse osmosis plant. Pre-treatment before running the water
through the reverse osmosis membranes is a necessary stage so as to protect the membranes and pipes
from damage and extend their service life. The water coming from the intake system to the holding tanks
may contain many suspended materials, including rust, scale and silt, and may cause fouling of the
membrane. These materials if let to go through the membranes will clog the pores and reduce the
efficiency of the system. Pre-filtration also allows the membranes to be able to tackle the smaller
contaminants.

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Hence a water analysis prior to start up of the RO system is necessary. This will ensure continued
longevity of the membrane life.
At a minimum, the following parameters shown in Table must be evaluated.
Table 2 :Pre-treatment Water Parameters for Evaluation
Iron in ppm or mg/lt Calcium Hardness in ppm as CaCO3
Manganese in ppm or mg/lt Magnesium Hardness in ppm as CaCO
Magnesium Total Hardness in ppm as CaCO3
Silica Feed Water Temperature in ℃
Calcium in ppm or mg/lt Feed Water TDS in ppm as CaCO3
Fluoride Total Suspended Solids( TSS)
Chloride Turbidity in NTU
Aluminium Silt Density Index
Feed Water pH
Pre-treatment can be achieved by the following filtration methods:
• Carbon Filtration
An activated carbon filter is a filter whose media consists of activated carbon. The raw water contains
traces of chlorine which is hazardous to the membranes. The activated carbon is thus used to absorb the

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chlorine, to protect the membrane material to absorb chlorine, as the chlorine is capable of damaging the
membranes.
• Fine filtration
A 5-micron cartridge filter is required as the last step before the RO membranes to prevent any debris,
sand particles or piping material to damage the membranes. It used to in the event that the under drains
of the sand and carbon filter fail. This will prevent the media in the sand and carbon filters from
damaging downstream pumps and fouling the RO system.
For Borehole water RO, in addition to physical treatment, chemical treatment is included in anticipation
of scaling and corrosion or biological fouling. This involves chlorination and use of an anti-scalant. A
very cost-effective way to avoid biological fouling chlorination. Unfortunately, chlorine oxidizes the
membrane material, therefore only 1000 ppm can be tolerated.
The anti-scalant solution should be dosed before the reverse osmosis membranes to disperse calcium
carbonate and sulfates precipitates in order to avoid scaling.
Table 3: A table illustrating the common causes of fouling and their appropriate pre-treatment
options, (http://www.lenntech.com/ro/ro-pretreatment.htm#ixzz3WuJKEPCZ)
Fouling Cause Appropriate Pre-treatment
Biological fouling Bacteria, microorganisms, viruses, protozoan Chlorination
Particle fouling Sand, clay (turbidity, suspended solids) Filtration

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Colloidal fouling Organic and inorganic complexes, colloidal
particles, micro-algae
Coagulation + Filtration
Optional: Flocculation /
sedimentation
Organic fouling Natural Organic Matter (NOM) : humic and fulvic
acids, biopolymers
Coagulation + Filtration +
Activated carbon adsorption
Coagulation+ Ultrafiltration
Mineral fouling Calcium, Magnesium Barium or Strontium
sulfites and carbonates
Antiscalant dosing
Acidification
Oxidant fouling Chlorine, Ozone, KMnO4 Oxidant scavenger dosing:
Sodium (meta)bilsulfite
Granulated Activated Carbon
4.5 REVERSE OSMOSIS
Reverse Osmosis, commonly referred to as RO, is a process where you demineralize or deionize water
by pushing it under pressure through a semi-permeable Reverse Osmosis Membrane,(
https://puretecwater.com/reverse-osmosis/what-is-reverse-osmosis).
Reverse Osmosis operates by the application of high pressure pumps to increase the pressure on the salt
side of the RO and force movement of water across the semi-permeable RO membrane, leaving almost
all of dissolved salts behind in the reject stream. The pure water that flows across the membrane is
known as the permeate water. The TDS accumulating on the other side of the membrane are flushed by
the concentrated solution that isn’t able to cross the membrane. This is known as the reject water.
The amount of pressure applied is directly proportional to the salt concentration of the feed water. The
more concentrated it is, the more pressure it will require to overcome the osmotic pressure.

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Fig 6; Illustrating the pumping mechanism in RO
Fig 7: An illustration of Osmosis and Reverse Osmosis Process
Osmotic pressure is the minimum pressure that is required to be applied to a solution to prevent the
inward flow of water across the semi-permeable membrane. It is the measure of the tendency of a
solution to take up water by osmosis. The osmotic pressure of solutions of electrolytes is be determined
by the following equation:
𝜋 = ∅𝑣
𝑛
𝑉
𝑅𝑇
Where;
• π = osmotic pressure

23
• φ = osmotic coefficient
• ν = number of ions formed from one molecule of electrolyte
• n = number of moles of electrolyte
• V = volume of solvent
• R = universal gas constant
• T = absolute temperature
If the external pressure is equal to the osmotic pressure is applied, equilibrium of the two streams will
occur. The reject stream has a much higher chemical potential than the permeate stream. The main
design parameter of the system is the permeate flux.
𝑄 = (𝐴)(𝑆)(𝛥𝑃 – 𝛥𝜋)
Where
• Q = water flux (gal/day or l/day)
• A = mass transfer coefficient (gal/d-ft2-psi or l/d-m2-kPa)
• ∆p = pressure difference between feed and product water (psi or kPa)
• ∆ π = osmotic pressure difference between feed and product water (psi or kPa)
The membrane flux value furnished by manufacturer is usually for 25°C. Temperature variations causes
the flux to vary, thus membrane area correction factor should be applied;
𝐴 =
𝐴 𝑇
𝐴25

24
Table 4: Membrane area correction factors for different temperatures,
(http://faculty.kfupm.edu.sa/CE/abukhari/Courses/CE370/Lectures/Membrane%20Processes_par
t%202.pdf)
Temp.(°C) Correction Factor
10 1.58
15 1.34
20 1.15
25 1.00
30 0.84
4.6 REVERSE OSMOSIS MEMBRANES
Membrane elements are the key to reverse osmosis. Interleaved layers of semipermeable membrane,
spacer and permeate carrier spiralled around a central permeate tubes make up the element. They are
usually the operational centre of the system in that it attracts water molecules, and repels dissolved
solids. These are the solids that are too small to be removed by the filters. Membranes are usually very
tough in order to overcome the pressures needed for maximum contaminant removal efficiency and have
a long life span of averagely two or three years before replacement. Artificial ones could be made from
cellulose acetate (CA), thin film composite, (TFC). Generally, TFC membranes have a longer life than
CA membranes because of the CA membrane’s tendency to compact.
Some important properties of these membranes are as in the table below;

25
Table 5: A table showing properties of CA and TFC Membranes
Feature CA Membranes TFC Membranes
Filtration of organic
compounds
Low High
Water Flux Medium High
pH tolerance 4-8 2-11
Temperature Stability Max 35°C Max 45°C
Oxidant Tolerance High Low
Compaction Tendency High Low
Cost Low High
Reverse osmosis (RO) membrane elements use a strong pressure gradient to drive water through a semi-
permeable membrane, while leaving salts and other larger molecules behind.
The ideal characteristics of RO Membranes include
i. High water flux (low capital cost)
ii. High solute rejection (high water purity)
iii. Long-term stability of water flux and rejection (Membrane fouling)
iv. Mechanical, chemical and thermal stability
v. Minimum pre-treatment (back flushing and chemical treatment)

26
vi. Can be processed into large-scale membranes and modules
vii. Inexpensive
However, the problems associated with current membranes in the market are;
i. Poor long-term stability of water flux (Membrane Fouling)
ii. Back-flushing and chemical treatment
iii. High membrane replacement cost
iv. Poor resistance to chlorine
v. Membrane system size
4.7 ADVANTAGES OF A REVERSE OSMOSIS SYSTEM
1. Systems Use a Low Amount of Energy- The energy usage of reverse osmosis systems is
relatively low compared to other similar systems. This productivity causes these systems to be
ideal for those that need to use as little energy as possible.
2. It removes dissolved salts, dissolved organic substances and micro fine particles such as germs,
and thereby it purifies water for cleaning, drinking and other wide range of applications for pure
water. It is also suitable for use in the industrial sector, to minimize scaling, fouling and rust of
equipment parts.
3. The equipment used in reverse osmosis is compact and uses the least amount space.
4. Reverse osmosis is a simple process, its operation and control are uncomplicated, while
maintenance is easy and free from trouble.

27
5. It has provided a solution to the water issues that have become a global threat. Climate change
has caused unforeseen environmental impacts including torrential flooding, droughts, rising and
falling sea levels. Also due to overpopulation, water shortages and pollution are on the rise.
Reverse Osmosis can be used to purify flood water or desalinate ocean water to provide an
alternative source of clean water.
4.8 DISADVANTAGES OF A REVERSE OSMOSIS SYSTEM
1. High amounts of water are wasted in the process; Household reverse osmosis units in
particular use a lot of water because they have low back pressure. RO generally wastes two
times the permeate water that is produced. Large-scale industrial/municipal systems have a
higher efficiency because they can generate the high pressure needed for more efficient RO
filtration.
2. The applied pressure must exceed the osmotic pressure to obtain product flow and to separate
the solute from the solvent. The maximum feed pressure for seawater devices varies from
800 - 1000 psig, while the limit for brackish water varies from 400 - 600 psig. Due to the
high pressure requirement (about 200 psig or more above the osmotic pressure) RO is usually
not applicable for concentrated solutions.
3. R.O water is also not the best option for a continuous source of drinking water. This is owing
to the fact water that has been purified by a reverse osmosis system contains virtually no
trace minerals that our body requires for good health. It removes minerals and ions that
provide taste to the water and electrolytes important for human health. The long term effects
of drinking this water may be damaging to our bodies. Elements such as magnesium, calcium
and other nutrients in potable water can help to protect against nutritional deficiency or they
need to be supplemented from other sources. Reverse osmosis water doesn’t have fluoride
which provides protection against dental cavities. The World Health Organization (WHO)

28
guide (4, 7, and 8) on pure water list the following possible adverse consequences of low
mineral content water consumption:
i. Direct effects on the intestinal mucous membrane, metabolism and mineral
homeostasis or other body functions.
ii. Increased diuresis and serum sodium concentrations, decreased serum potassium
concentration, and increased the elimination of sodium, potassium, chloride, calcium
and magnesium ions from the body.
iii. Loss of calcium, magnesium and other essential elements in prepared food.
iv. Possible increased dietary intake of toxic metals.
v. The guide further states that water with a total dissolved solids (TDS) level of less
than 100 mg/L disturbs the water-salt balance in the body and results in the leaching
of individual salts such as sodium, potassium and chloride, as well as some calcium
from the person who drinks it.
4. This water is also slightly acidic, which isn’t advisable for being a continuous source of
drinking water for our bodies. A solution to this, according to US Water, would be to use a
calcite mineral tank, so as to raise the pH of the water. The acidic water may also cause
leaching of some metals from pipes, dependent upon placement of the filtration system in the
plumbing
5. RO feed streams must be compatible with the membrane and other materials of construction
used in the devices. If the feed stream contains incompatible compounds, these must be
removed in pretreatment, or another compatible device and/or membrane must be considered.

29
6. Because all RO membranes and devices are susceptible to fouling, the RO process usually
cannot be applied without pretreatment.
4.9 ENVIRONMENTAL IMPACTS OF REVERSE OSMOSIS
The Reverse Osmosis plant will be based at Tatu City since the borehole site is next to a coffee
plantation then the region is generally an environmentally sensitive area. These area require public
participation in acceptance of the project, however, regulatory approval can be difficult and costly. RO
plants may impact the environment in the following ways;
• Aesthetics
• Disturbance to local ecosystems (wetlands or other local flora and fauna)
• Impacts upon existing land use
• Impacts to local water users
• Influences on local freshwater aquifers
• Contamination from the construction process
4.9.1 POST- TREATMENT
Post treatment is a control mechanism to increase the alkalinity and the mineral content of the product,
usually through the addition of dosed quantities of mineral carbonates or mineral hydroxides due to the
fact that;
• RO water is slightly acidic and thus could be potentially corrosive.
• The permeate is very low in mineral content and isn’t suitable for drinking

30
The post-treatment of the product water as it leaves the reverse osmosis process is usually designed to
meet the compliance specifications for the end-use application. The most common method is
disinfection. This may be done through; chlorination, use of a UV filter, decarbonation and
electrodialysis reversal.
4.9.2 BASIC REQUIREMENTS FOR SOURCES OF DOMESTIC WATER
In every system, it is crucial to have regulations that control the quantity and quality of products for the
protection of people, animals, and the whole environment. Such regulations in Kenya, for the control of
the quality standards for the sources of domestic water are stipulated in the first schedule of the
environmental management and co-ordination (water quality) regulations of 2006. The borehole water in
Tatu City must be tested to ensure it meets the below physical/chemical characteristics.
Also the basic domestic water demand has to be met. Some of the water consumption rates based on
intended uses are:
Location Litres/day/head M3
/year/head
Rural 10-90 4-33
Urban 30-300 10-110
Table 6: Domestic Water Demand
4.9.3 ROSA
ROSA is the Reverse Osmosis System Analysis program that was developed by the Dow Water And
Process Solutions Company for analysis of the parameters of a reverse osmosis system. Analysis
through it is very helpful compared to manual calculations and analysis due to;
• Manual calculations are tedious and time consuming, the program eliminates the need for
long tedious calculations and saves time.

31
• It has high levels of accuracy thus improving results for the system.
Fig 8; ROSA SOFTWARE USER INTERFACE SCREENSHOT
THEORETICAL FRAMEWORK
Most of the equations used in reverse osmosis are already incorporated in ROSA, as stated in the
literature review, under design equations. The equations as used in the data analysis are;
2. No of elements per vessel = (no. of elements required)/ (standard no. of elements per pressure
vessel)
1. No. of elements required in an RO system, 𝑁𝐸 =
𝑄 𝑃
𝑓∗𝑆 𝐸
Where
• Qp is the permeate flow rate (l/hr)
• F is the design flux (l/h.m)
• Se is the active surface area of the membrane (m2
)

32
3. Design of permeate water tank;
V= A* h
• Where V = volume (m3
)
• A = cross-sectional area (m2
)
• h = height (m)

33
5.0 GENERATION OF CONCEPT DESIGN
5.1 MATERIALS
The materials that were used in this design project include:
• GPS for determination of the coordinates of the site.
• Water collection bottles for collecting water samples from the borehole for testing.
• Water testing kits for analysis of the water samples.
• Thermometer to note down the onsite temperature of the water.
• Documentation for recording the data on date and time of collection of the water
samples.
5.2 METHODOLOGY
The preliminary desk study in this project involved;
• Review of existing files and documents on reverse osmosis. This involved studying existing
projects that had already been done on reverse osmosis systems in the documentation center,
upper kabete, University of Nairobi. Reading these past projects enhanced my idea of what
was expected to be done.
• Study of an existing and working reverse osmosis system. This involved visiting a site,
Cocacola Industries, Nairobi, Kenya. Observing their installed working reverse osmosis
system to know the parameters that are required for proper working and maintenance.
• Study of documents from books and the internet, to get knowledge on all the details of
working of a reverse osmosis system.

34
This project design involved the collection of the following set of data:
• Borehole water characteristics. The borehole water was used as the feed water into the
system, and to access the concentration of different elements in the water for proper
treatment. This increases the life cycle of the reverse osmosis system by getting rid of the
elements that may cause scaling and fouling of the membranes, or even corrosion of the
equipment parts.
• Operating parameters of the specifications of items that are to be used in the design of the
Reverse Osmosis system from the manufacturer.
• The temperature range of the site area since a reverse osmosis system is always affected by
temperature.
• The feed pressure of the borehole water.
5.3 The Reverse Osmosis System Design Process
i) System Design Information and Feed Water
The RO membrane system highly depends on the available feed water. The feed water was analysed and
determined if it was suitable for treatment. The system design information includes required product
flow rate, expected recovery rate, annual water temperature, water source, application, pre-treatment,
required product water quality, operating pressure limit. These parameters were studied and considered
in selection of the RO system design.
ii) Selection of Element Type and Average Permeate Flux

35
Considering the feed water source, pre-treatment and feed water hardness, the type of RO membrane
element was selected from (appendix 6). The recommended value of the average permeate flux was then
selected from (appendix 4).
iii) Calculation of Number of Total RO Elements
The number of total elements was calculated from the equation relating it to the product flow rate and
the average permeate flux. The calculated number of RO elements may be a slightly changed based on
the decision of element arrangement, that is, the number of pressure vessels and RO elements per
pressure vessel.
iv) Decision of Recovery Rate
The recovery rate of the system was then computed, and the relationship with the concentration factor
was picked from (appendix 7).
v) Decision of Number of Stages
The number of RO stages defines how many pressure vessels are in series in the RO membrane system.
Every stage consists of a certain number of pressure vessels in parallel. The number of stages is a
function of the system recovery rate, the number of elements per vessel, and the feed water quality. The
no, of stages was then picked from (appendix 9).
vi) Decision of Number of RO Elements per Pressure Vessel
Decisions regarding the number of RO elements per pressure vessel, plant size is usually considered
first. In a large-scale plant (> 40 m3/h), 6-8 elements per pressure vessel are usually adopted, and in a
smaller plant, 35 elements per pressure vessel. The space required to install or remove the RO elements
have to be considered in the plant design. This was calculated.

36
vii) Decision of Element Arrangement
For the decision of element arrangement, the system design parameters should be consistent with the
design flux guideline.
viii) ROSA
The parameters were then run on the ROSA software and the results that were acquired were compared
from the results of the actual calculations.
ix) Preparation of the design drawings
From the results and parameters acquired, the design drawings were prepared using AutoCAD and Solid
Works.
6.0 DATA ANALYSIS
1. Consideration of the feed source, quality, flow and the required output quality:
Selection of the borehole water type based on the lab analysis. The intake should be open.
From the design guidelines, (appendix 4), the silt density index is <3 and from (appendix 5),
the flow factor for hard water is 0.75.
2. Anti-scalant dosing: from design guidelines (lenntech water treatment guidelines) dosing=
3mg/l
3. Selection of the flow configuration and the number of passes: The standard flow
configuration for hard water purification is plug flow, where the feed volume is passed once
through the system. But since it was ground water a double pass system was selected.

37
4. Selection of membrane element type: Elements are selected according to feed water
salinity, feed water fouling tendency, required rejection and energy requirements. from
design guidelines (appendix 6), standard element size for systems greater than 2.3m3
/hr is 8”
diameter, 40” length.
5. Selection of the average membrane flux: The design flux, f, (gfd or l/m2
-h) was
selected. This was based on the pilot data, customer experience and the typical design fluxes
according to the feed source: from the design guidelines, (appendix 4) flux for well water
open intake = 30l/h/m
6. Calculation of the number of elements needed:
The design permeate flow rate QP is divided by the design flux f and by the membrane
surface area of the selected element SE (ft2
or m2
) to obtain the number of elements NE.
In one day water will be pumped for 15 hours; thus for 300m3
/day
=
300
15
= 20m3
/hr=20000l/h
SE= 35m2
NE=
20000
30×35
= 19.05 Elements
= 20 Elements
7. Calculation of the number of pressure vessels needed:
The number of elements NE will be divided by the number of elements per pressure
vessel, NEpV, to obtain the number of pressure vessels, NV , rounding up to the nearest
integer. For large systems, 6-element vessels are standard, but vessels with up to 8 elements

38
are available. For smaller and/or compact systems, shorter vessels may be selected.
Ref. design guidelines (appendix 6) standard no. is 6
Nv =
20
6
= 3.33
= 4 Pressure Vessels
8. Selection of the number of stages: The number of stages defines how many pressure
vessels in series the feed will pass through until it exits the system and is discharged as
concentrate. Every stage consists of a certain number of pressure vessels in parallel. The
number of stages is a function of the planned system recovery, the number of elements per
vessel, and the feed water quality.
We selected a double stage system.
9. The acquired data was then run on ROSA software.
10. Pressure requirement;
• High pressure pump for feed water:
Required pressure 68.5 bar
Pump pressure ratings may be approximated at a maximum of 80 bar, (1200psi)
Select Grundfos pump model BMH with power rating of 60V, 5.5 kW and flow of
20m3
/hr
• High pressure pump for permeate water to storage tank:
Pump pressure ratings may be approximated at a maximum of 80 bar, (1200psi)
Select Grundfos pump model CRN with power rating of 50V, 4 kW and flow of
17m3
/hr
11. Balancing of the permeate flow rate

39
The goal of a good design is to balance the flow rate of elements in the different positions.
This can be achieved by the following means:
• Boosting the feed pressure between stages: preferred for efficient energy use
• Apply a permeate backpressure.
12. Piping Requirements
From design guidelines (lenntech water treatment guidelines)
• Feed water pipes – 5”
• Permeate water pipes – 4”
• Concentrate water pipes – 4”
13. Skid Mounting
From design guidelines (lenntech water treatment guidelines)
Select stainless steel 304 skid.
14. Permeate Water Storage Tank Requirements
• Hourly permeate production is 16.0m3
/hr
Design steel tank of capacity 100m3
. Say height of 2m
V= A*h
100 = 2*πr2
R =1.78m
15. Analysis and optimisation of the membrane system: The system should be analysed and
thorough testing carried out on the designs to determine their suitability.

40
7.0 RESULTS OF THE DESIGN PROCESS
1. The TDS and pH of the raw water were tested at the Chemistry Department lab at
Chiromo campus and found to be;
TDS 2730.43mg/l
pH 7.6
2. The results as run on ROSA show that the plant estimates to have a flow of 280.84m3
/
day. If this is run per hour, the flow estimates to 11.70 m3
/hr. however this is the design
value and it’s when the plant is operating at maximum design capacity. The results of the
design are as attached on the ROSA datasheet.
3. The permeate water has the following concentrations based on the ROSA run;
Pass
Streams
(mg/l as
Ion)
Name Feed Adjusted Feed
Concentrat
e Permeate
Stage 1 Stage 1 Total
NH4+ + NH3 0.00 0.00 0.00 0.00 0.00
K 0.00 0.00 0.00 0.00 0.00
Na
109.6
7
109.6
7
123.2
7 32.65 32.65
Mg 16.50 16.50
18.8
4 3.23 3.23

41
Ca 0.00 0.00 0.00 0.00 0.00
Sr 0.00 0.00 0.00 0.00 0.00
Ba 0.00 0.00 0.00 0.00 0.00
CO
3 0.02 0.02 0.03 0.00 0.00
HC
O3 32.21 32.21
35.7
1 12.41 12.41
NO
3 0.00 0.00 0.00 0.00 0.00
Cl
198.5
0
198.5
0
224.2
7 52.56 52.56
F 0.00 0.00 0.00 0.00 0.00
SO4 0.00 0.00 0.00 0.00 0.00
SiO
2 0.00 0.00 0.00 0.00 0.00
Boro
n 0.00 0.00 0.00 0.00 0.00
CO
2 4.54 4.54 4.55 4.53 4.53
TDS
356.9
1
356.9
1
402.1
1 100.85 100.85
pH 6.98 6.98 7.02 6.61 6.61
Table 7: ROSA results on Permeate Water.
4. A cost of production of every m3
of the system is as calculated below;
• From ROSA specific energy consumption is 8.07kWh/m3
• Amount of permeate produced = 11.70 m3
/hr
•
𝟖.𝟎𝟕
𝟏𝟏.𝟕𝟎
= 0.6897kwh

42
• Kenya power tariff for small commercial systems is 15.60Ksh/ kwh
• 0.6897×15.60 = 10.76Ksh/m3
of water
• At design capacity, 280.84m3
/day is produced.
• Thus at design capacity cost of water production = 10.76×280.84 = 3021.83Ksh/day
• Overhead costs, (say approximately equal to cost of production) = 3021.83Ksh/day
• Total cost of water production by RO/day = 3021.83×2 = 6043.66Ksh/day
• Cost of water from main water pipeline supply = 40Ksh/m3
• If we were to supply the same amount from the mains therefore, = 40 × 280.84=
11233.6Ksh/day
5. Difference between receiving water from the mains and RO plant = 11233.6-6043.66 =
5189.94Ksh
6. The details of the pumps, pipe and permeate storage tanks are as shown
Permeate Storage Tank Details
Material to be used; steel tank
Volume 100m3
Height 3m
Diameter 6.5m
Pump Details
Feed water pump BMH with power rating of 60V, 5.5 kW
and flow of 20m3
/hr

43
Permeate to storage CRN with power rating of 50V, 4 kW
and flow of 17m3
/hr
Pipe Details
Concentrate water pipes 4”
Feed water pipes 5”
Permeate water pipes 4”
Table 8 :Permeate Storage Tank Details
7. The ROSA Analysis provided the results as shown in appendix 9

46
9.0 DISCUSSIONS OF THE RESULTS
1. The TDS of the raw borehole water was found to be 2730.43mg/l. Standard borehole water TDS
is usually 2200mg/l, thus the results found from this analysis was close to the standard values.
The pH was 7.6, which is also close to standard values of approximately 7.4. This analysis was
done at the Department of Chemistry lab at Chiromo campus.
2. From the design analysed by the ROSA software, the amount of permeate that can be supplied
by the system is 280.84m3
as compared to the required amount of 300m3
. Any further increase of
feed flow or pressure to the system so as to increase the permeate flows would have exceeded the
element recoveries of 15% and thus would have exposed the system to risk of fouling, decreasing
its capacity life. However this value represents the design capacity and is a maximum value that
the plant doesn’t run on, on a daily basis.
3. The levels of TDS that were found in the permeate water were 100.85mg/l, sodium ions were
32.65mg/l , chloride ions were 52.56mg/l, carbonate ions were 12.41mg/l and magnesium ions
were 3.23mg/l. These values are lower than the maximum permissible limits by EMCA and
WHO as shown below.
Table 9: EMCA and WHO standards comparison with permeate water
Element Permeate EMCA WHO
Na 32.65mg/l No guideline No guideline
Cl 52.56mg/l No guideline 250mg/l
HCO3 12.41mg/l No guideline No guideline
Mg 3.23mg/l No guideline No guideline
TDS 100.85mg/l 1200mg/l 500mg/l

47
4. The cost of energy of the production of the water was calculated using tarrifs from the Kenya
Power and Lighting Company, and the Water Services Board. The cost of water production from
an RO plant was found to be 6043.66Ksh/day while that of supplying from the main water
pipeline was found to be 11233.60Ksh/day
5. The size of the pipes, pumps and permeate storage tank were as shown in the results.

48
10.0 CONCLUSIONS
➢ The Overall objective of this design project was met. The cost of production from the RO
Plant was found to be 6043.66Ksh/day while that of supplying from the Kiambu County
Water and Sewerage company was 11233.6Ksh/day. Hence the design was a cost effective
method for purification of borehole water to recommended standards for drinking and
domestic use.
➢ The second objective was achieved in that we were able to calculate the cost of production of
a M3
water to be 10.76ksh.
➢ The third objective was met in that we were able to determine the TDS of the raw borehole
water to be 2730.43Mg/L and the pH to be 7.6
➢ The fourth objective was met. The elements that were analysed in the water by the ROSA
program, ie the TDS had a value of 100.85 mg/l as compared to the max allowable 1200mg/l
by EMCA, and 500mg/l by W.H.O. The levels of sodium ions were 32.65mg/l , chloride ions
were 52.56mg/l, magnesium ions were 3.23mg/l, and carbonates were 12.41mg/l. This
value is way below the maximum allowable and thus is suitable. However, by following data
results from other working reverse osmosis cases and considering the recovery of this
project, the other elements are also most possibly way below the maximum allowable limits
of EMCA.
It can thus be concluded that a reverse osmosis plant is important to water scarcity problems, however
it is a costly option. On the overall, the procurement of the reverse osmosis plant, installation and
testing and commissioning have no significant negative impacts on the natural resource and neither do
they pose any danger to the front ecosystem. A key positive impact however is the introduction of the
modern water purification technology and knowledge transfer to our local engineers and technicians
as the supplier will train our local people to operate and maintain the reverse osmosis plant. In addition,

49
once the reverse osmosis plant has been set up and in operation, it will create employment
opportunities for the local engineers/technicians from Kiambu County and Kenya at large.

50
11.0 RECOMMENDATIONS
• The plant design capacity is 280.84m3
. Water demand will vary over time and seasons, the estate
residents will rarely require this amount of water. With the estate being under construction, the
homes are sold in phases, meaning that the demand will progress slowly with time, before it can
get close to the design capacity. It may be pumped for a period of a few hours in the morning, and
a few hours in the evening. This should be done according to the demand, even as the population
grows over the years. A projection of the population growth in the development should be
estimated to account for water demand at the present time and over the next few years. To change
this flow, throttling must be done at the inlet valve to the high pressure pump to cater for the
demand at that certain time. The no. of hours for pumping may also be changed according to the
demand. Over the years, as the population grows, so does the water demand grow. If the demand
surpasses the 300m3
demand, procurement of another RO system should be considered.
• In terms of energy efficiency of the project, an alternative means of water supplement such as
rainwater harvesting potential of the area should be incorporated to the system to increase water
supply during the peak demand, so as to reduce the energy cost. A connection to the main pipeline
in the area should also be considered to provide supplemental amounts of water to the residents,
rather than wholly relying on the reverse osmosis plant.
• Water fortification should be incorporated to the design to provide the necessary nutrients required
in the human body. A storage tank for potable water should be included in the design, where the
permeate water that is in this tank, will exclusively be used for human consumption, may be
fortified with the right amounts on nutrients, so as to achieve the specific objective of the water
meeting the W.H.O guidelines.

51
• Use of microfiltration should be considered as opposed to use of reverse osmosis membranes. This
is due to the fact that microfiltration is less costly & consumes less energy as compared to RO, and
it doesn’t strip the water of all its necessary nutrients. This would make the water suitable for
drinking in the long term without need for fortification

52
12.0 REFERENCES
The following references are technical papers. They are unpublished e-sources.
Berge Djebedjian, Helmy Gad, Ibrahim Khaled and Magdy Abou Rayan (2008) Optimization of
Reverse Osmosis Desalination System Using Genetic Algorithms Technique.
Chaoyi B.A (2010) Design of Advanced Reverse Osmosis and Nanofiltration Membranes for
Water Purification.
Guidelines for Drinking-water Quality FIRST ADDENDUM TO THIRD EDITION Volume 1
Recommendations.
Julia E. Nemeth, Tomas F. Seacord. (2000) Cost Effective RO and NF Systems: Importance of
O&M Considerations in Design, Procurement and Manufacturing.
Mark Wilf Ph. D. And Craig Bartels (2004) Optimization of seawater RO systems design
Mehdi Metaiche And John Palmeri (2009) Optimization of Reverse Osmosis (RO) and
Nanofiltration (NF) Desalination Systems
Michael Pilutti and Julia E. Nemeth Technical and cost review of commercially available mf/uf
membrane products.
Prof. Elijah K. Biamah, Catherine Wanja Njeru Water Systems Engineering Lecture
Notes(2015)
The Environmental Management and Co-Ordination (Water Quality) Regulations, (2006).
Water Association Desalination Committee (2011) Overview of Plant Desalination Activities
World Health Organization. Guidelines for drinking-water quality [electronic resource]:
incorporating ﬁrst addendum.Vol.1, Recommendations. – 3rd Ed. (2006)

53
Internet Sources
1. (http://www.lenntech.com/applications/drinking/standards/who-s-drinking-water-
standards.htm#ixzz3WuFzCs9o)
2. http://www.dowwaterandprocess.com/en/resources/steps_to_design_an_ro_nf_membrane_sy
stem#/accordion/CEEEFB7A-1A4E-46D8-AF59-DF3
3. www.engineeringtoolbox.com/pumps-discharge-reulation
4. www.membranetreatmentguide.com/membrane-foulant-identification

54
13.0 APPENDICES
Appendix 1
Categorization of permeate post-treatment depending on source water type, (American Membrane
Technology Association, (2010)

55
Appendix 2
“All sources of water for domestic uses shall comply with the standards set out in First Schedule of these
Regulations.”
Parameter Guide Value (max allowable)
pH 6.5 – 8.5
Suspended solids 30 (mg/L)
Nitrate-NO3 10 (mg/L)
Ammonia –NH3 0.5 (mg/L)
Nitrite –NO2 3 (mg/L)
Total Dissolved Solids 1200 (mg/L)
Scientific name (E.coli) Nil/100 ml
Fluoride 1.5 (mg/L)
Phenols Nil (mg/L)
Arsenic 0.01 (mg/L)
Cadmium 0.01 (mg/L)
Lead 0.05 (mg/L)
Selenium 0.01 (mg/L)
Copper 0.05 (mg/L)
Zinc 1.5 (mg/L)
Alkyl benzyl sulphonates 0.5 (mg/L)
Permanganate value (PV) 1.0 (mg/L)
Nil means less than limit of detection using prescribed sampling and analytical methods and
equipment as determined by the Authority.
• And any other parameters as may be prescribed by the Authority from time to time

56
Appendix 3
Inorganic Compounds
Element/
substance
Symbol/
formula
Normally found in fresh
water/surface
water/ground water
Health based guideline
by the WHO
Aluminium Al 0,2 mg/l
Ammonia NH4 < 0,2 mg/l (up to 0,3 mg/l in
anaerobic waters)
No guideline
Antimony Sb < 4 μg/l 0.005 mg/l
Arsenic As 0,01 mg/l
Asbestos No guideline
Barium Ba 0,3 mg/l
Berillium Be < 1 μg/l No guideline
Boron B < 1 mg/l 0,3 mg/l
Cadmium Cd < 1 μg/l 0,003 mg/l
Chloride Cl 250 mg/l
Chromium Cr+3
,
Cr+6
< 2 μg/l 0,05 mg/l
Colour Not mentioned
Copper Cu 2 mg/l
Cyanide CN-
0,07 mg/l
Dissolved
oxygen
O2 No guideline
Fluoride F < 1,5 mg/l (up to 10) 1,5 mg/l
Hardness mg/l
CaCO3
No guideline
Hydrogen
sulphide
H2S No guideline

57
Iron Fe 0,5 - 50 mg/l No guideline
Lead Pb 0,01 mg/l
Manganese Mn 0,5 mg/l
Mercury Hg < 0,5 μg/l 0,001 mg/l
Molybdenum Mb < 0,01 mg/l 0,07 mg/l
Nickel Ni < 0,02 mg/l 0,02 mg/l
Nitrate and
nitrite
NO3,
NO2
50 mg/l total nitrogen
Turbidity Not mentioned
pH No guideline
Selenium Se < < 0,01 mg/l 0,01 mg/l
Silver Ag 5 – 50 μg/l No guideline
Sodium Na < 20 mg/l 200 mg/l
Sulfate SO4 500 mg/l
Inorganic tin Sn No guideline
TDS No guideline
Uranium U 1,4 mg/l
Zinc Zn 3 mg/l

61
Appendix 7
Recovery Rate Concentration Factor
50% 2
75% 4
80% 5
90% 10
Appendix 8
1 stage system: < 50%
Usual recovery SWRO (< 50%)
2 stage system: < 75-80%
Usual recovery BWRO (< 80%)
High recovery SWRO (< 60%)
High recovery 2nd pass (< 90%)
3 stage system: < 85-90%
High recovery BWRO (< 90%)
High recovery 2nd pass (< 95%)
(special case)
SWRO: seawater desalination, BWRO:
Brackish water desalination

62
Appendix 9
ROSA Detailed Report Page 1 of 7
Reverse Osmosis System Analysis for FILMTEC™ Membranes ROSA ROSA_Desalitech ConfigDB u399339_356
Project: MyProject Case: 1
Brian Odhiambo, University Of Nairobi 17/03/2019
Project Information:
Case-specific:
System Details -- Pass 1
Feed Flow to Stage 1 20 m³/h Pass 1 Permeate Flow 16 m³/h Osmotic Pressure:
Raw Water Flow to System 20 m³/h Pass 1 Recovery 15.00 % Feed 2.44 bar
Feed Pressure 3.02 bar Feed Temperature 25.0 C Concentrate 2.81 bar
Flow Factor 0.85 Feed TDS 2730.43 mg/l Average 2.62 bar
Chem. Dose (100% H2SO4) 0.00 mg/l Number of Elements 1 Average NDP 0.32 bar
Total Active Area 37.16 M² Average Pass 1 Flux 1.22 lmh Power 8.07 kW
Water Classification: Well Water SDI < 3 Specific Energy 0.70 kWh/m³
System Recovery 2.25 % Conc. Flow from Pass 2 0.00 m³/h
Feed Feed Recirc Conc Conc Perm Avg Perm Boost Perm
Stage Element #PV #Ele Flow Press Flow Flow Press Flow Flux Press Press TDS
(m³/h) (bar) (m³/h) (m³/h) (bar) (m³/h) (lmh) (bar) (bar) (mg/l)
1 ECO PRO 400 1 1 20 2.67 0.00 16.26 2.67 0.05 1.22 0.00 0.00 356.91
Pass Streams
(mg/l as Ion)
Name Feed Adjusted Feed Concentrate Permeate

63
NH4+ + NH3 0.00 0.00 0.00 0.00 0.00
K 0.00 0.00 0.00 0.00 0.00
Na 913.61 913.61 1055.46 109.67 109.67
Mg 221.43 221.43 257.59 16.50 16.50
Ca 0.00 0.00 0.00 0.00 0.00
Sr 0.00 0.00 0.00 0.00 0.00
Ba 0.00 0.00 0.00 0.00 0.00
CO3 1.14 1.14 1.56 0.02 0.02
HCO3 185.36 185.36 211.92 32.21 32.21
NO3 0.00 0.00 0.00 0.00 0.00
Cl 1408.89 1945.62 2253.89 198.50 198.50
F 0.00 0.00 0.00 0.00 0.00
SO4 0.00 0.00 0.00 0.00 0.00
SiO2 0.00 0.00 0.00 0.00 0.00
Boron 0.00 0.00 0.00 0.00 0.00
CO2 4.71 4.61 4.91 4.54 4.54
TDS 2730.43 3267.17 3780.42 356.91 356.91
pH 7.60 7.60 7.62 6.98 6.98
*Permeate Flux reported by ROSA is calculated based on ACTIVE membrane area. DISCLAIMER: NO WARRANTY, EXPRESSED OR
IMPLIED, AND NO WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, IS GIVEN. Neither FilmTec
Corporation nor The Dow Chemical Company assume any obligation or liability for results obtained or damages incurred from the application of
this information. Because use conditions and applicable laws may differ from one location to another and may change with time, customer is
responsible for determining whether products are appropriate for customer’s use. ROSA projections do not guarantee performance nor are such
projections meant to be a warranty for the system or its design. If you choose to design your systems based on the ROSA projections, you will take
full responsibility for such design and for the system. You acknowledge that Dow gives a system warranty only in limited circumstances and only
under certain specific terms and conditions. Should you decide to buy Membranes, to the extent Dow gives its standard Membrane warranty,
which is the standard FilmTec 3-year prorated element warranty, Dow will provide such a limited warranty. You acknowledge that a system
warranty is not typical and is not an entitlement. You agree to use best engineering practices and process judgment in product selection and system
design FilmTec Corporation and The Dow Chemical Company assume no liability, if, as a
file:///C:/Users/Apuoyo/Documents/ROSA/MyProject01Detail.html 17/03/201

64
result of customer's use of the ROSA membrane design software, the customer should be sued for alleged infringement of any patent not owned or
controlled by the FilmTec Corporation nor The Dow Chemical Company.

65
Design Warnings -- Pass 1
CAUTION: The concentrate flow rate is less than the recommended minimum flow. Please change your system design to increase
concentrate flow rates. (Product: ECO PRO 400, Limit: 26.95m³/h)
Solubility Warnings -- Pass 1
-None-
Stage Details -- Pass 1
Stage 1 Element Recovery
Perm Flow Perm TDS Feed Flow Feed TDS Feed Press
(m³/h) (mg/l) (m³/h) (mg/l) (bar)
1 0.15 16.05 356.91 20.30 2730.17 2.67
under certain specific terms and conditions. Should you decide to buy Membranes, to the extent Dow gives its standard Membrane warranty, which
is the standard FilmTec 3-year prorated element warranty, Dow will provide such a limited warranty. You acknowledge that a system warranty is
not typical and is not an entitlement. You agree to use best engineering practices and process judgment in product selection and system design
FilmTec Corporation and The Dow Chemical Company assume no liability, if, as a result of customer's use of the ROSA membrane design
software, the customer should be sued for alleged infringement of any patent not owned or controlled by the FilmTec Corporation nor The Dow
Chemical Company.

66
Project Information:
Case-specific:
System Details -- Pass 2
Feed Flow to Stage 1 20 m³/h Pass 2 Permeate Flow 16.11 m³/h Osmotic Pressure:
Raw Water Flow to System 20.0 m³/h Pass 2 Recovery 15.00 % Feed 0.28 bar
Feed Pressure 0.59 bar Feed Temperature 25.0 C Concentrate 0.31 bar
Flow Factor 0.85 Feed TDS 356.91 mg/l Average 0.30 bar
Chem. Dose None Number of Elements 1 Average NDP 0.03 bar
Total Active Area 37.16 M² Average Pass 2 Flux 0.18 lmh Power 0.00 kW
Water Classification: RO Permeate SDI < 1 Specific Energy 0.14 kWh/m³
System Recovery 2.25 %
Feed Feed Recirc Conc Conc Perm Avg Perm Boost Perm
Stage Element #PV #Ele Flow Press Flow Flow Press Flow Flux Press Press TDS
(m³/h) (bar) (m³/h) (m³/h) (bar) (m³/h) (lmh) (bar) (bar) (mg/l)
1 ECO PRO 400 1 1 20 0.25 0.00 0.04 0.25 16.11 0.18 0.00 0.00 100.85
Pass Streams
(mg/l as Ion)
Name Feed Adjusted Feed
Concentrate Permeate

67
NH4+ + NH3 0.00 0.00 0.00 0.00 0.00
K 0.00 0.00 0.00 0.00 0.00
Na 109.67 109.67 123.27 32.65 32.65
Mg 16.50 16.50 18.84 3.23 3.23
Ca 0.00 0.00 0.00 0.00 0.00
Sr 0.00 0.00 0.00 0.00 0.00
Ba 0.00 0.00 0.00 0.00 0.00
CO3 0.02 0.02 0.03 0.00 0.00
HCO3 32.21 32.21 35.71 12.41 12.41
NO3 0.00 0.00 0.00 0.00 0.00
Cl 198.50 198.50 224.27 52.56 52.56
F 0.00 0.00 0.00 0.00 0.00
SO4 0.00 0.00 0.00 0.00 0.00
SiO2 0.00 0.00 0.00 0.00 0.00
Boron 0.00 0.00 0.00 0.00 0.00
CO2 4.54 4.54 4.55 4.53 4.53
TDS 356.91 356.91 402.11 100.85 100.85
pH 6.98 6.98 7.02 6.61 6.61
under certain specific terms and conditions. Should you decide to buy Membranes, to the extent Dow gives its standard Membrane warranty,
which is the standard FilmTec 3-year prorated element warranty, Dow will provide such a limited warranty. You acknowledge that a system
warranty is not typical and is not an entitlement. You agree to use best engineering practices and process judgment in product selection and system
design FilmTec Corporation and The Dow Chemical Company assume no liability, if, as a

68
result of customer's use of the ROSA membrane design software, the customer should be sued for alleged infringement of any patent not owned or
controlled by the FilmTec Corporation nor The Dow Chemical Company.

69
Design Warnings -- Pass 2
CAUTION: The concentrate flow rate is less than the recommended minimum flow. Please change your system design to increase
concentrate flow rates. (Product: ECO PRO 400, Limit: 26.95m³/h)
Solubility Warnings -- Pass 2
-None-
Stage Details -- Pass 2
Stage 1 Element Recovery
Perm Flow Perm TDS Feed Flow Feed TDS Feed Press
(m³/h) (mg/l) (m³/h) (mg/l) (bar)
1 0.15 16.1 100.85 20.05 356.91 0.25
under certain specific terms and conditions. Should you decide to buy Membranes, to the extent Dow gives its standard Membrane warranty, which
is the standard FilmTec 3-year prorated element warranty, Dow will provide such a limited warranty. You acknowledge that a system warranty is
not typical and is not an entitlement. You agree to use best engineering practices and process judgment in product selection and system design
FilmTec Corporation and The Dow Chemical Company assume no liability, if, as a result of customer's use of the ROSA membrane design
software, the customer should be sued for alleged infringement of any patent not owned or controlled by the FilmTec Corporation nor The Dow
Chemical Company

70

71
Scaling Calculations
Raw Water Pass 1 Adjusted Feed Pass 1 Concentrate Pass 2 Concentrate
pH 7.60 7.60 7.62 7.02
Langelier Saturation Index -8.78 -8.78 -8.64 -9.99
Stiff & Davis Stability Index -8.81 -8.81 -8.78 -10.36
Ionic Strength (Molal) 0.06 0.07 0.08 0.01
TDS (mg/l) 2730.43 3267.17 3780.42 402.11
HCO3 185.36 185.36 211.92 35.71
CO2 4.71 4.71 4.90 4.54
CO3 1.14 1.14 1.56 0.03
CaSO4 (% Saturation) 0.00 0.00 0.00 0.00
BaSO4 (% Saturation) 0.00 0.00 0.00 0.00
SrSO4 (% Saturation) 0.00 0.00 0.00 0.00
CaF2 (% Saturation) 0.00 0.00 0.00 0.00
SiO2 (% Saturation) 0.00 0.00 0.00 0.00
Mg(OH)2 (% Saturation) 0.01 0.01 0.02 0.00
To balance: 536.74 mg/l Cl added to feed

72
Appendix 10
Student working on Daesign Drawings.

73
14.0 BILL OF QUANTITIES
NO. MATERIAL SI
UNIT
QTY UNIT
COST
(ksh)
TOTAL
COST
(ksh)
1 FEED STEEL TANK 8’ * 4’ ft 7 7000 49000
2 4 * 4 WOODEN PLATE m3
1 3000 3000
3 FEED PVC 5” Inches 8 120 960
4 PERMEATE &
CONCENTRATE PVC 4”
Inches 16 100 1600
6 90° ELBOW 5” SECTION Inches 3 2500 7500
7 90° ELBOW 4” SECTION Inches 6 720 4320
8 90° TEE 5” SECTION Inches 5 2500 12500
9 90° TEE 4” SECTION Inches 10 920 9200
10 MAIN R.O PLANT (including
20 membrane elements, 4
pressure vessels, 1 steel skid, 2
flow meters, 2 dosing pumps, 3
pressure meters)
This can be acquired from
Davis and Shirtliff RO Plants(
DRO)
2,500,000
12 50L DOSING PLASTIC TANK litres 1 4500 4500
13 PERMEATE TANK 4’*8’ ft 34 2500 85000
TOTAL 2,677,580
LABOUR (10% 0F TOTAL COST) 267,758
NET TOTAL COST 2,945,338

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