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REPORT OF THE

STUDENTS’ INDUSTRIAL WORK EXPERIENCE SCHEME (SIWES)
UNDERTAKEN AT

REID CROWTHER NIGERIA LIMITED,

19B Adeola Odeku Street, Victoria Island, Lagos.
FROM MARCH 2002 TO AUGUST 2002.
BY

OBASEMO, OLUMIDE MOSES KAYODE

(CVE/1998/059)


SUBMITTED TO

THE SIWES COORDINATOR,

DEPARTMENT OF CIVIL ENGINEERING,

OBAFEMI AWOLOWO UNIVERSITY (OAU),

ILE-IFE, NIGERIA.
OCTOBER 2002.
Department of Civil Engineering,

Obafemi Awolowo University,

Ile-Ife, Nigeria.

31st October 2002.

The SIWES Coordinator,

Department of Civil Engineering,

Obafemi Awolowo University,

Ile-Ife, Nigeria.

Dear Sir,

Letter of Transmittal

In partial fulfilment of the requirements for the award of B.Sc (Civil Engineering), I hereby submit, for grading, the report of the SIWES undertaken at Reid Crowther Nigeria Limited, Victoria Island, Lagos from March 2002 to August 2002.

Yours faithfully,

OBASEMO, O. M. K.


EXECUTIVE SUMMARY

Students Industrial Work Experience Scheme (SIWES) is an effective instrument for exposing students to the realities of the work environment in Nigeria especially, and the world in general, in their chosen professions so as to achieve the much needed technological advancement for the nation. To give an account of the activities carried out during the scheme, the trainee submits a technical report stating, in details, all the knowledge and experience gained.

This report gives a detailed explanation of all the activities carried out by the trainee. Before giving details of these activities, general background knowledge, as studied from relevant engineering texts available, is briefly explained. Then followed by the details of these activities, with each project been involved in outlined under each chapter. Thereafter, comes the chapter that explains the various problems encountered in executing the afore-mentioned projects and the solutions proffered to solve those problems. In order not to distract the line of thought while reading this report and to further elucidate on what has been written in the body of the report, the appendix section is provided to show calculations made in the course of carrying out these activities.

At the end of it all, conclusions are drawn, and recommendations made on how these activities carried out have trained the mind of the trainee in the engineering profession and have given some of necessary experience needed to face the challenges of this profession as well.



DEDICATION

This is report is dedicated to the Only True God – who was, is, and is to come. The Author of life – that made the heavens and the earth out of nothing; that led His people, with a pillar of cloud during the day and a pillar of fire at night, out of the land of bondage into the Promised land; that gave His only begotten Son to be led as a lamb to the slaughter just for my redemption; that destroyed the powers of hell and death by raising Christ Jesus from the dead, so as to call me out of the darkness into His marvellous light and make me a son for His own possession.




ACKNOWLEDGEMENT

I know the plans I have for you, Olumide. They are plans of good and not for disaster to give you a future and a hope…for I knew you before I formed you in your mother’s womb. Before you were born, I set you apart and appointed you as my one of my spokesmen to the world.” With these words, you commissioned my life and sent me into OAU to be trained as a civil engineer. I stand in awe before you – my God and Lord – to thank you for the special grace, favour, love through Christ Jesus upon my life throughout the 6-month industrial training and always. To that, I respond with the lyrics of one of my favourite hymns as composed by Rev. H. Collins in C. H. 369 (verses 3 and 4):



JESU, what didst Thou find in me,

That Thou hast dealt so lovingly?

How great the joy that Thou hast brought,

So far exceeding hope or thought!

Chorus: JESU, my Lord, I thee adore;

O make me love Thee more and more.
JESU, of Thee shall be my song,

To Thee my heart and soul belong;

All that I am or have is Thine;

And Thou, Blest SAVIOUR, Thou art mine.

Chorus: JESU, my Lord, I thee adore;

O make me love Thee more and more.
Also, I acknowledge the rare privilege granted to me by the entire staff of Reid Crowther Nigeria Limited to learn the knowledge outlined in this report as well as other skills, which are outside the scope of this report. In particular, I cannot but mention the blank cheque for knowledge-acquisition that Messrs John Rowe, Mike Whiting, Greg Trevor and Aaron Rowe gave me during my training with them. This allowed me to learn many skills and ideas in the field of civil engineering. I am grateful to you all.

Thirdly, I acknowledge the company of co-trainees – Isemede ’Egbe, Beyioku Jumoke, Atika Enitan, Sobanjo Bunmi, Ojomu Teslim, Ogunrewo Olakunle, Oghotuama Paul and Adenuga Kehinde – from which important issues emanated to give shape to this report; as well as the guidance counselling offered by Iwakun Olumide and Ayeni Paul. You all have a place in my heart, and play a role in my challenging journey unto divinely ordained greatness.

Furthermore, I appreciate the labour of love of all my immensely erudite lecturers, at OAU, in guiding me aright in this chosen career of mine. I affirm that this report will not be anything if they did not offer their expertise to it. In particular, I am grateful for the discipline, encouragement, and love of Prof. M. O. Ogedengbe, Mr I. K. Adewumi, Engr. K. T. Oladepo, and Mr. A. B. Fajobi. They truly demonstrate that “great men are those who make others feel great”.

Importantly acknowledged, also, are the human pillars of my life – Mr Gabriel O. Obasemo and Mrs. Margaret Musa-Obasemo. Their indomitable will make them go through life’s thick and thin to give me education for a bright future. Thank you, Dad and Mum.

Moreover, I acknowledge the moral, financial, professional support of families, friends, classmates, roommates, neighbours, etc. You are wonderful, and have taught me: “only a life lived for others is worthwhile”. In particular, I thank Isemede Idiegbeyenoise for providing the indissoluble bonds of friendship – out of which I have gained more – even in her difficult time. Just trust in the Lord and be courageous. He is able to build you an enviable edifice out of the rubbles of the past, and He will.

Lastly, I acknowledge those great minds that have taught me to believe that “within me is a hidden store of energy—energy needed to complete in the marathon of life; within me is a hidden store of courage—courage to give me the strength needed to face any challenge of life; within me is a hidden store of determination—determination to keep me in the race, when all seems lost.” You may be dead, but your God-given ideas gave us today’s comfort of life.


TABLE OF CONTENTS

Title Page…………………………………………………………………………………

Letter of Transmittal………………………………………………………………………

Executive Summary………………………………………………………………………..

Dedication………………………………………………………………………………….

Acknowledgement…………………………………………………………………………

Table of Contents………………………………………………………………………….

List of Figures………………………………………………………………………………

List of Tables……………………………………………………………………………….

CHAPTER ONE: INTRODUCTION……………………………………………………


    1. SIWES ……………………………………………………………….

    2. The Company……………………………………………………………………..

    3. Objective and Scope of the report…………………………………………………

CHAPTER TWO: LITERATURE STUDY……………………………………………

2.1 Water Supply and Design Processes ………………………………………………



      1. Water Supply Processes…………………………………………………….

2.1.2 Flow Process Design……………………………………………………

2.2 Reinforced Concrete Design…………………..…………………………



      1. Introduction……………………………………………………………

      2. Design Objectives……………………………………………………..

      3. Design Methods………………………………………………………..

      4. Reinforced Concrete Members…………………………………………

      5. Design Process……………………………………………………………

    1. Geographic Information System...….…………………………………………

      1. Introduction…………………………………………………………..

      2. Definition of GIS……………..………………………………….

      3. Fundamental of GIS…………..……………………………….

      4. GIS Process……………………………………………………….
      5. Application of GIS…………………………………………………


CHAPTER THREE: VILLAGES’ WATER SUPPLY SCHEMES…………….……

    1. Project Background………………………………………………………………

    2. Work Carried Out and Experience Gained…………………………………………

CHAPTER FOUR: PROPERTY IDENTIFICATION EXERCISE FOR LAGOS

STATE……………..……………………………………………….

    1. Project Background…………………………………………………………………

    2. Work Carried Out and Experience Gained…………………………………………

CHAPTER FIVE: ISSUES ON CIVIL ENGINEERING PRACTICE……………….

    1. Construction Site Experience…………………………………………………..

    2. Developments in Civil Engineering Practice……………………………………..

    3. Principles of Project Management……………………………………………..

5.3.1 Introduction……………………………………………………………

5.3.2 Application of Partnering to implement Reid Crowther’s Projects……...



CHAPTER SIX: PROBLEMS ENCOUNTERED AND SOLUTIONS

PROFFERED………………………………………………………

    1. Concerning Villages’ Water Supply Scheme…………………………………..

    2. Concerning the PIE for Lagos State……………………………………………

    3. Concerning Construction Site Experience………………………………………….

CHAPTER SEVEN: CONCLUSION AND RECOMMENDATIONS………………
    1. Conclusion……………………………………………………………………….


    2. Recommendations…………………………………………………………………

REFERENCES…………………………………………………………………………..

APPENDIX A: Weights Of Constructional Materials……………………………

APPENDIX B: Design Process for the Drainage Channel……………………….

APPENDIX C: Design Process for the Cantilever Retaining Wall…………….

LIST OF FIGURES

Figure 2.1 Components of GIS…………………………………………………….

Figure 2.2 Map showing the coastal areas of Lagos State, Nigeria……………….

Figure 2.3 Diagram showing typical layers of Data in a GIS……………………

Figure 3.1 Revised Flow Process Design for a typical Village……………………..

Figure 3.2 The Davnor ‘Biosand’ Filter Treatment Unit…………………………….

Figure B1 Typical Cross-section of Drainage Channel……………………………….

Figure B2 Typical Load Distribution on Drainage Channel…………………………

Figure B3 Resultant End Moments on Drainage Channel’s Cross-section…………

Figure B4 Detailing for a typical Drainage Channel………………………………

Figure C1 Outline of the Retaining Wall Site…………………………………….

Figure C2 Cross-sectional Load Diagram of the Cantilever Retaining Wall……

Figure C3 Detailing of the Cross-section of the Cantilever Retaining Wall………

LIST OF TABLES

Table 2.1 Load Combination and their Values of Partial Factor of Safety

for the ULS……………………………………………………………….

Table 2.2 Nominal Cover to all Reinforcement (including links) to meet

Durability Requirements….………………………………………….

Table B1 Bar Bending Schedule of Reinforcement for the Drainage Channel………

Table B2 Bar Bending Schedule of Reinforcement for the Cantilever Retaining Wall……………………………………………………………………….



CHAPTER ONE

INTRODUCTION


    1. SIWES

The SIWES was established as a result of the realization by the Federal Government, in 1971, of the need to introduce a new dimension to the quality and standard of education obtained in the country in order to achieve the much needed technological advancement; because it has been shown that a correlation exists between a country’s level of economic and technological development, and its level of investment in manpower development (Oniyide, 2000). Some of the objectives of SIWES are:

  • To provide, for the students, opportunities to be involved in the practical aspect of their respective disciplines; thus, bridging the gap between the theoretical aspect taught in the class and the real world situations.

  • To expose students to latest developments and technological innovations in their chosen professions.

  • To prepare students for industrial working environments they are likely to meet after graduation.

    1. The Company

Reid Crowther Nigeria Limited is an employee-owned Canadian company that has being offering comprehensive engineering services for over 10 years, with the mission to provide Quality Engineering and Project Management Services using creative and innovative solutions that are responsive to client and public needs by applying the art of engineering to solve everyday problems.

The areas of specialisation of the company can be grouped into five main areas, namely: Environmental, Municipal, Transportation, Building and Industrial engineering. Specifically, these include Water Supply and Distribution, Wastewater Collection and Treatment, Solid Waste Management, Marine and Road Transportation, Harbour works, Drainage, Flood Protection, Environmental Impact Assessments, Geographical Information System (GIS).

The company started operations in Nigeria in 1986 with its office in Lagos alone, but various jobs, through which it has demonstrated its expertise, had created offices in other parts of the country such as Warri, Abuja, Ondo and Ekiti states. The company’s staff strength is about 200, made up of expatriates and indigenes.

The company has demonstrated its expertise in a number of major projects such as the Redesigning and Supervision of Lagos State Water Distribution System, Consultancy service for Otamiri River Water Supply Project, Mapping for Rapid Transit System in Lagos, Upgrading of Sewage Treatment Plant and Disposal of Treated Effluent and Stormwater for Chevron’s estate at Satellite Town, Front-End Engineering and Master Plan Design for Potable Water at Chevron Nigeria Limited (CNL) Escravos Terminal, Design Modification of Sewage Collection and Treatment Plant at Chevron Nigeria Limited (CNL) Escravos Terminal, Water Supply System Rehabilitation in Federal Capital Territory, Ondo and Ekiti states for the Federal Government, and so on.

Reid Crowther has the vision of constantly demonstrating its high degree of competence as an international consultant in all engineering projects, and is committed to impart the Nigerian environment as well.



    1. Objective and Scope of the Report

The objective of this report is to present, in details, the various activities carried out by the trainee at Reid Crowther Nigeria Limited from March 2002 to August 2002 as well as provide the general background knowledge about the aspects of Civil Engineering applied while undergoing the SIWES programme.

For the reasons stated above, the report covers only the extent of work, in brief, that has been done before the trainee was involved in the various projects; as well as background engineering knowledge applied in these projects, except in cases where other engineering knowledge not applied cannot but be mentioned, because they are intertwined with the knowledge applied in these projects, and in such cases they are very brief. Consequently, no mention is made of any further activities carried out in these projects after the trainee’s completion of training.



CHAPTER TWO

LITERATURE STUDY

This chapter is to serve as a preparatory background of knowledge for the practical training that the trainee went through. It provides elementary knowledge of supply and the design processes of water schemes; design processes of reinforced concrete structural units; application of geographical information studies.



    1. Water Supply and Design Processes

2.1.1 Water Supply Processes

Water is essential to life, it also serves as a reference liquid in science, as the medium for countless chemical reactions and as the conveyor of the vital substances, which it needs-- mineral salts, organic molecules (Laing, 1973). This makes issues about water to be such important to man’s life that it cannot be pushed aside. These issues are briefly explained in the following sections.


  1. How much water is needed?

Hammer and Hammer, Jr. (1996) states that the amount of water needed by a community depends on industrial use, climate, economic, social as well as locality conditions.

It is convenient to divide water consumption, according to Twort et al (1985), into the following categories:



  • Domestic: In-house uses such as drinking, cooking, sanitation, house cleaning, car and clothes washing, garden watering, etc.

  • Economic: Industrial usage in factories, power stations, etc; commercial usage in shops, offices, restaurants, etc; institutional usage in schools, hospitals, government offices, etc.

  • Agricultural: Use of water for crops, livestock, horticulture, dairies etc.

  • Public: Usage of water in public parks, for sewer flushing, fire fighting, etc.

  • Losses: Consumer wastages (leakages and wastages from consumers’ premises, misuse or unnecessarily wasteful use of water by consumers); distribution losses (leakages and overflows from service reservoir, leakages from mains, service connections, valves and washouts); metering and other losses.

Since all these categories of water consumption do not apply to all design situations, Twort et al (op. cit.) further explained that it is expedient that a consumption survey (or, its trend be determined) be carried out to investigate likely losses from a system, consumers’ lifestyle, forecast future demand based on population, and come up with an average daily demand (ADD) per capita.

Thereafter, a maximum daily demand (MDD) is computed. It is usually expressed as either a percentage of the ADD or, simply, a multiplying factor of ADD. This factor ranges from 110 to 200%.

Also, the peak hourly flowrate is calculated, depending on the size of area to be served and the nature of demand. This applies flow factors, as well, to the ADD—it ranges from 2.0 to 4.0. This is to cater for peak demand during peak flow period, usually in the morning (5.30 a.m-9a.m) and the evening (6p.m.-9p.m.). Peaking factors, as they are called, are not just chosen on the basis of water demand, it must relate to other factors in consideration such as future upgrading.

Upon an accurate estimation of daily demand, the design process moves to the next stage of locating water source(s) that will guarantee that demand and proximity to the location of the consumers.


  1. Sourcing for water

In assessing the water resources, the modern approach is to consider all the possible means of development, and to examine, comprehensively, the hydrology of the catchment involved. Twort et al (op. cit.) listed the full range of possible developments as follows:

    1. Surface water

  • River intake,

  • Reservoir for direct supply,

  • Reservoir for indirect gravity or pumped inflow, and

  • Tanks fed by collected rainfall.

    1. Groundwater

  • Springs, and

  • Wells and boreholes.

    1. Water Reclamation

  • Reuse of treated sewage effluent.

The evaluation of a source involves an inventory of all water available including rainfall, losses, catchment areas etc. To do this, a hydrological survey, if necessary, must be conducted in which all flows into and out of the catchment are quantified and balanced, so ensuring that all have been accounted for. The parameters to be measured for a particular catchment will be as follows:

  1. Inflows (or Gains)—These include precipitation, surface runoff into the area, groundwater movement into the area, etc.

  2. Outflows (or Losses)—These include evaporation and transpiration, surface runoff out of the area, groundwater movement out of the area, irrigation abstractions, etc.

  3. Storage—This includes soil moisture changes, change in contents of impounding reservoir and aquifer storage changes.

In summary, a water evaluation survey provides a means of understanding water use in catchment area, checking that catchment are adequate and accurate, and quantifying average resources. In choosing between sources of supply, the main factors, according to Laing (op. cit.), to be considered are quality of the available water, quantity of the water required, regularity of flow, and cost of finding, transporting, treating, and distributing water.

(c) Estimation of yield

No source, according to Twort et al (op. cit.), can be said to have a fixed yield because catchment conditions and consumer requirements change with time. It is essential that a water engineer be able to appraise the net yield—water remaining for supply after any compensation water or residual flow has been left for other riparian interests—of a catchment prior to planning any new development. The basic requirement of a catchment to be chosen as a source is that its net yield must be able to meet the MDD in excess, other factors being constant.

In estimating the yield of a source, the nature and type of the source plays an important role. In estimating the yield of a surface yield, it necessary to obtain and study the record of rainfall data, analyse results of runoff measurements at location concerned (Adewumi, 2000). Furthermore, hydrographs are to be studied in order to forecast a future critical event, as well as preparing contingency plans for an existing source; and to provide a convenient tool for the rapid and consistent testing of a variety of schemes to find their likely critical drawdown period and associated yield. If all these do not guarantee the design requirements in terms of demand, especially during dry periods, Twort et al (op. cit.) advised that the option of excess water storage in high flow period should be considered, such as damming the site.

For underground source, there are two distinct ways in which well or borehole yields can be estimated (Twort et al, op.cit.). The first concentrates on well hydraulics and installed pumping plant; while the second attempts to predict yield from the hydrogeology of the borehole site and the contributing catchment. The aim of these methods is to attain the ideal yield, whereby the source output is safely maximised with no more than is necessary in the way of pumps. Whatever technique is employed, water quality information of source must be obtained to indicate whether saline water has been struck or some other characteristics have been observed which makes the yield, however large, useless for the designed purpose(s). Care must therefore be taken when estimating groundwater yield that the result does not imply a steady encroachment of coastal seawater into the aquifer or that a poor quality water zone of the aquifer will be drawn upon.

For the borehole yield to be established as being suitable for the design conditions, a pumping test needs to be carried out with the following objectives:


  • To find the abstraction limit of the hole and the rate at which the water level falls with time;

  • To define the discharge-pumping level relationship in order to choose an efficient permanent pump;

  • To monitor the effect of the use of source on the local environment;

  • To determine the aquifer’s permeability and storage characteristics.

Where the aquifer is confined under pressure by an impermeable layer above it, steadier rates will prevail; so, also, in riverbank aquifers. For unconfined aquifers, a test sequence for investigation is recommended (Twort et al, op. cit.). Once it is guaranteed that the borehole discharge estimate will satisfactorily meet the MDD, over a period of years, a borehole is sunk, and developed by pumping.

On a general note, whichever source chosen, the basic requirement is that it must be able to meet the MDD, as well as allow a cost-effective treatment option guaranteed to produce water that meets the Drinking Water Quality Standards/Guidelines.



  1. Analysis of Raw Water

Depending on many circumstances, the presence of various substances in raw water and their significances vary. A thorough consideration of raw water quality, and sampling frequency in conditions of limited resources is important and a prelude to choosing a treatment process of raw water to be supplied to a community. The likely substances, or conditions, according to Twort et al (op. cit.), that may be present in raw water, and needs consideration, are:

  • Acidity

  • Alkalinity

  • Aluminium

  • Ammoniacal compounds

  • Arsenic

  • Biochemical Oxygen Demand (BOD)

  • Calcium

  • Carbon dioxide

  • Chloride salts

  • Chlorine
  • Colour


  • Copper

  • Corrosive Quality

  • Cyanide

  • Fluoride

  • Hardness

  • Iron

  • Lead

  • Magnesium

  • Manganese

  • Nitrite and Nitrate

  • Organic matter

  • pH value

  • Sodium

  • Sulphates

  • Suspended Solids (SS)

  • Taste and Odour

  • Turbidity

  • Zinc

(e) Drinking Water Quality Standards/Guidelines

It is a generally accepted fact that life is dependent on water and that water exists in nature in many forms—clouds, rain, snow, ice, and fog; however, strictly speaking, chemically pure water does not exist for any appreciable length of time in nature. Even while falling as rain, water picks up small amount of gases, ions, dust, and particulate matter from the atmosphere. Then as it flows over or through the surface layers of the earth, it dissolves and carries with it some of almost everything it touches, including that which is dumped into it by man.

All these impurities, Twort et al (op. cit.) stated, may give water a bad taste, colour, odour, or cloudy appearance (turbidity), and cause hardness, corrosiveness, etc. They may transmit disease. Many of these impurities are removed or rendered harmless, however, in municipal drinking water treatment plants in order to provide ‘pure’ water to consumers.

‘Pure’ water means different things to different people. One way of establishing, and assuring the purity and safety of water, which is generally acceptable to all and sundry, is to set a standard—a definite rule, principle, or measurement that is established by governmental authority—for various contaminants. Thus, we have the 1993 Guidelines for Drinking Water Quality by World Health Organisation (WHO), 1986 Drinking Water Regulations by United States Environmental Protection Agency (US EPA), 1989 Water Quality Regulations by United Kingdom, 1999 National Guidelines and Standards for Water Quality in Nigeria by Federal Environmental Protection Agency (FEPA), etc. There is no international standard for drinking water quality, according to WHO (1993a), in order to allow the use of a risk-benefit approach, which would allow nations to establish their own standards and regulations that takes into consideration peculiar local conditions; all with the primary aim of ensuring the protection of public health.

WHO (op. cit.) further stated that water is evaluated for quality in terms of its:

(1) Physical Properties:


  • Turbidity—suspended particles

  • Taste

  • Odour

  • Colour

(2) Chemical Properties: Inorganic and organic compounds dissolved in water that are harmful.

  1. Microbiological Properties: Pathogens, especially coliform bacteria.

There are two categories of standards, namely:

    1. Primary Standards—based on health criteria; and

    2. Secondary Standards—based on aesthetic and non-aesthetic conditions.

For all standards, there are guide limits/levels for various water qualities. These are defined as follows:

      • Maximum Contaminant Levels (MCL)—The highest level of a contaminant that is allowed in drinking water. MCLs are enforceable standards.

      • Maximum Contaminant Level Goal (MCLG)—The level of a contaminant in drinking water below which there is no known or expected risk of health. MCLGs allow for a margin of safety and are non-enforceable public health goals; rather they are intended as guidelines. They are also known as Secondary Maximum Contaminant Level (SMCL).

      • Maximum Residual Disinfectant Level (MRDL)—The highest level of a disinfectant allowed in drinking water. There is convincing evidence that addition of a disinfectant is necessary for control of microbial contaminants.

(f) Water Treatment Methods

According to American Water Works Association (AWWA) (1984), the main function of water treatment is to provide a continuous supply of safe, good-tasting, and cold drinking water that is free of contaminants that can cause disease or be toxic to a consumer. The water must also be free of unpleasant things such as colour, turbidity and odour.


Therefore, the water treatment processes used in any specific instance must take into account the quality and nature of the raw water supply source. The intensity of treatment must depend on the degree of contamination of the source water (WHO, 1993b). This implies that, according to Lo (1999), the fundamental purpose of water treatment is to protect the consumer from pathogens and impurities in the water that may be offensive or injurious to human health; and to bring raw water up to drinking water quality standards.

Since there are three categories of contaminants in raw water, there are, correspondingly, three categories of treatment to bring raw water to the required condition, safe for human consumption and use (Twort et al, op. cit.). These are:


      1. Physical Treatment Processes: These processes entail the use of physical means to treat water in terms of its physical/aesthetic properties, which are mostly visible to the naked eyes. They include Screening, Aeration, Sedimentation, Filtration, and Distillation.

      2. Chemical Treatment Processes: These processes involve the addition of chemicals to neutralize the effects of harmful organic and inorganic compounds dissolved in the raw water. It involves Chlorine, Coagulation and Flocculation, Ozonation, Fluoridation, etc.

      3. Biological Treatment Processes: These involve the use of biological means to remove pathogens and other microbial organisms that cannot be removed by the two processes above. They use impermeable membranes, basically, to achieve this. They include Reverse Osmosis, Micro-filters, etc, according to Turner (1998).

It is quite possible for any of the treatment process to perform more than one category mentioned above. For instance, filtration is basically a physical treatment process; it can also allow the purification of water contaminated by pathogenic bacteria (Twort et al, op. cit.).

The basic processes of the water treatment are briefly explained below.



Screening: This is to remove relatively large floating and suspended solids/debris. This is done through the use of screens which may be coarse (above 25mm perforations) for removing sticks and other solids which cannot pass through it; and/or fine (below 25mm) to remove fine particles that pass through the coarse screens, but should not go through the plant (Reynolds, 1991).

Aeration: Twort et al (op. cit.) explained that aeration is basically used to:

  • To increase the dissolved oxygen (DO) content of the water.
  • To reduce taste and odour caused by dissolved gases in the water, such as hydrogen sulphide, and also to oxidise and remove organic matter.


  • To decrease the carbon dioxide content of a water and thereby reduce its corrosiveness and raise its pH value.

  • To convert iron and manganese from their soluble states to their insoluble states, and thereby cause them to precipitate so that they may be removed by infiltration.

To achieve this goals, four main types of aerators commonly used are free-fall, spray, injection and, surface aerators.

Plain Sedimentation: Basically, sedimentation tanks are designed to reduce the velocity of flow of water so as to permit suspended solids to settle out of the water by gravity. Plain sedimentation is to allow raw water settle in tanks for a period of 6-8 hours so that large and settleable SS will be removed by gravity alone—without the use of chemicals (Lo, op. cit.). Twort et al (op. cit.) explained that they are designed for continuous supply and the velocity of flow through the tank being sufficiently low to permit gravitational settlement of the SS to occur, say maximum velocity of 10cm/s for particle’s diameter not greater than 1mm.

Chemical Coagulation and Flocculation: Lo (op. cit.) explained that chemical coagulation is the addition of chemicals (coagulants) into water in a mixing tank so as to encourage the non-settleable solids to coagulate into large particles (chemical flocs) that will more easily settle; while flocculation is a gently mixing process that induces particle collision and allow the formation of large particles of floc. This takes about 15 – 20 minutes to complete. Twort et al (op. cit.) further explained that these floc particles could thereafter be removed either by sedimentation and/or filtration. The commonest coagulant is Aluminium Sulphate, usually referred to as ‘alum’; others include Sodium Aluminate, Ferrous Sulphate, etc.

Chemically assisted Sedimentation: This, according to Reynolds (op. cit.), is the last stage of the process called clarification—the first two stages (coagulation and flocculation) having been explained above. Sedimentation takes place in a sedimentation, or settling, tank in which the produced chemical flocs settle out by gravity. This implies that the primary function of a sedimentation tank is to provide settled water with the lowest possible turbidity level, thereby decrease the loading on subsequent treatment processes.


Reynolds (op. cit.) further stressed that efficient sedimentation tanks must be designed to have a sludge collection system. This is necessary, because as the water move slowly through the tank with low velocity and turbulence, the solid flocs settle to the bottom of the tank and the accumulation of these solids on the floor of the tank forms what is called sludge. It is now the function of the sludge collection system to remove the sludge periodically so that the tank can continue to supply low-load water to subsequent treatment processes.

Filtration: Reynolds (op. cit.) explains that the primary purpose of the filtration process is to remove suspended materials (measured in turbidity) from water. This suspended material can be floc that hadn’t settled out in the sedimentation tank, microorganisms, and any chemical precipitates such as iron and manganese. These suspended materials are removed when the water from the sedimentation tanks passes through the filter media—usually beds of granular and fine materials, such as anthracite coal, sand, gravel, etc.

The filtration process has two types, Twort et al (op. cit.) explained. These are Rapid Sand filtration and the Slow Sand filtration. It is established (Lo, op. cit.; Twort et al, op. cit.) that the purpose of rapid sand filtration is to filter out, quickly, chemical flocs that fail to settle in the previous sedimentation tank. The filtered water is normally free of particles and turbidity; and the removal of the particles is largely by physical action. Though, Twort et al (op. cit.) mentioned that with some contaminated waters, the oxidation of ammonia to nitrate could occur when the water passes through rapid sand filters.

Slow sand filter, on the other hand, passes water slowly through a bed of sands (Twort et al, op. cit.). It is an effective method devised for the purification of bulk waters contaminated by pathogenic bacteria. Pathogens and turbidity are removed by natural die-off, biological action, and filtering. The incoming water is led gently on to the filter bed and percolates downwards, then the water is expected to maintain the design rate of flow through the bed. However, as suspended material in the raw water is deposited on to the surface of the bed, organic and inorganic materials build up on the surface of the sand and increase the friction loss through the bed, thereby reducing the efficiency of the filter. To maintain the efficiency, there is need for periodic cleaning of the bed through scraping, backwashing etc.

The slow sand filter does not act by a simple straining process. Twort et al (op. cit.) explained that it works by a combination of both straining and microbiological action of which the latter is more important. Van de Vlaed (1955) gave a clear account of the details of the purification process. It distinguishes three zones of purification in the bird—the surface coatings, the ‘autotrophic’ zone existing a few millimetres below the surface coating, and the ‘heterotrophic’ zone that is extended some 300mm into the bed.

As the incoming water into the filter bed passes through it, during the first few weeks, the upper layers of sand grains become coated with a reddish-brown sticky deposit of partly decomposed organic matter together with iron, manganese, aluminium and silica. This coating tends to absorb organic matter existing in colloidal state. After some weeks, there exists in the uppermost layer of the sand a film of algae, bacteria, and protozoa, to which are added the finely divided suspended material, and other organic matter deposited by the incoming water. This film acts as an extremely fine, meshed straining mat.

A few millimetres below this film is the autotrophic zone, where the growing plant breaks down organic matter and uses up available nitrogen, phosphates, and carbon dioxide, providing oxygen in their place. The filtrate thus becomes oxidised at this stage.

Below this again, a still more important action takes place in the heterotrophic zone, which extends some 300mm into the bed. Here the bacteria multiply to very large numbers so that the breakdown of organic matter is completed, resulting in the presence of only simple inorganic substances and unobjectionable salts. The bacteria act not only to break down organic matter but also to destroy each other and so tend to maintain a balance of life native to the filter so that the resulting filtrate is uniform.

The advantages of slow sand filters, according to Twort et al (op. cit.), provided that the water they treat, either directly, following storage, or following rapid gravity filters, has relatively good physical and chemical characteristics, then they will produce excellent-quality water. It is efficient in the removal of viruses from contaminated reservoir waters. It allows for easier and cheaper disposal of chemical sludge from coagulation plants.

The limitation of slow sand filter is that it does not materially reduce the ‘true colour’ of water (The term ‘true colour’ may be taken as the colour of the filtrate after removing colloidal clay). Thus, they are only suitable for dealing with waters of relatively low colour. Also, slow sand filter cannot be expected to be effective in removing any high concentration of manganese in solution. They are also not very suitable for dealing with any substantial amount of finely divided inorganic suspended matter.


Disinfection: This is a means of disinfecting the filtered water so that all pathogenic bacteria will become killed, literally. In the true sense, disinfection means the reduction of organisms in water to such low levels that no infection of disease results when the water is used for domestic purposes (Twort et al. op. cit.).

The efficacy of any disinfection process depends upon the water being treated beforehand having a high degree of purity, as disinfectants will be neutralised to a greater or lesser extent by organic matter and readily oxidisable compounds in water. Micro-organisms that are aggregated or are adsorbed to particulate matter will also be partly protected from disinfection, and there are many instances of disinfection failing to destroy waterborne pathogens and faecal bacteria when the turbidity was greater than 5 NTU1. It is therefore essential that the treatment processes preceding terminal disinfection be always operated to produce water with a mean turbidity not exceeding 1 NTU and maximum of 5 NTU in any water sample. Normal conditions of chlorination (i.e. a free residual chlorine of 0.5 mg/l, at least 30 minutes contact time, pH less than 8.0, and water turbidity of less than 1 NTU) can bring about 99% reduction of E. coli and certain viruses, but not the cysts of parasitic protozoa (WHO, 1993b).

Twort et al (op. cit.) stated that the commonly used disinfectants are:



  • Chlorine,

  • Chloramine,

  • Sodium Hypochlorite,

  • Ozone,

  • Ultraviolet radiation, and

  • Iodine.

Reynolds (op. cit.) explained that when chlorine is added to water, it forms hypochlorous acid, one of the two forms of free chlorine. Chlorine combines with impurities in the water and enough chlorine must be added to react with these impurities to the point where the addition of chlorine results in free chlorine, meaning it has react with everything it is going to react with. The free chlorine indicates enough chlorine is available to disinfect the water. It is important to note that the effectiveness of chlorination depends on five factors—concentration, contact time, temperature, pH and substances in the water. The destruction of organisms is directly related to the concentration and contact time.

(g) Miscellaneous Water Treatment methods:


  1. Fluoridation—This is the addition of fluoride into water, when they are found to be in short supply of fluoride. This is necessary to strengthen the dental care of baby infants and reduce the incidence of dental caries (Lo, op. cit.; Twort et al, op. cit.).

  2. Softening—This is a means of removing/reducing the hardness of water, caused by high concentration of metallic ions, such as Ca, Mg, etc (Lo, op. cit.).

  3. Use of Package plants—The type mentioned here is the Davnor BioSand Filter System. It is based on a unique intermittently operated slow sand filtration process where the flow through the filter does not need to be continuous to achieve the objectives. It can remove pathogenic organisms as well as taste, odour, turbidity etc (Manz, 2001).

  4. Reverse Osmosis—Osmosis is a natural phenomenon in which a liquid (water, in this case) passes through a semi-permeable membrane from a relatively dilute solution towards a more concentrated solution. This flow produces a membrane pressure called the osmotic pressure. If pressure is applied on the more concentrated solution, and if that pressure extends the osmotic pressure, water flows through the membrane from the more concentrated solution to the more dilute solution. This reversed process of osmosis is called Reverse Osmosis, which removes up to 98% of dissolved minerals. To perform this reversed process, a pump is used to pressurise the feedwater flow through the membrane.

(h) Storage System

Twort et al (op. cit.) explained that the storage system is an important part of any water treatment and supply system. It has two main functions:



  • To balance the fluctuating demand from the distribution system against the output from the source.
  • To act as a safeguard for the continuance of the supply, should there be any breakdown at the source or on the main trunk pipelines.


  • To provide adequate contact time for the chlorine added to do its job of disinfection before the treated water is distributed to the consumers.

If the service storage system is to be of maximum value, as a safeguard to the undertaking against breakdown, then it should be positioned as near as possible to the area of demand. From the service storage tanks, the distribution system should spread directly, with such ramification of mains that no single breakage could cause a severe interruption to the continuity of the supply. There should be sufficient interconnection between the distribution mains that, should a breakdown of any one of the mains occur, a supply may still be maintained by rerouting the water.

Hammer and Hammer Jr. (op. cit.) explained that storage system may be provided by the use of elevated tanks, underground basins, or covered reservoirs. The advantage of elevated tank is the pressure derived from holding water higher than the surrounding terrain. The elevation at which it is desirable to position a service reservoir depends upon the distance of the reservoir from the distribution area, the elevation of the highest building to be supplied, and the influence of corresponding pump selected.

The factors influencing depth for a given storage, according to Twort et al (op. cit.), are:


  1. Depth at which suitable foundation conditions are encountered,

  2. Depth at which outlet mains must be laid,

  3. Topography of site,

  4. Volume of storage.

In designing a storage system, the following are the salient features to be taken care of, where applicable, are depth and shape of storage tanks, roofing of the tanks, walls, access manholes, etc.

Generally, storage systems are made from any of these materials—metals, plastic, and concrete. Whatever the material from which it is produced, storage systems must be watertight, i.e. no leakage, in order to be able to adequately supply the needed demand.

(i) Distribution Network

WHO (1993b) explained that the distribution network transports water from the place of treatment to the consumers. Its design and size will be governed by the topography, location and size of the community. The aim of any distribution network should always be to ensure that consumers receive a sufficient and uninterrupted supply, and that contamination is not introduced in transit.

Distribution network, according to Hammer and Hammer Jr. (op. cit.), includes a network of mains with storage reservoirs, booster, pumping stations (if needed), fire hydrants, service connections as well as fittings.

Twort et al (op. cit.) stated that pipes, for the mains, are made of different materials. These include:


  • Copper pipes—They are expensive, but are strong, durable, resistant to corrosion, easily jointed, and capable of withstanding high internal pressures.

  • Steel pipes—They are widely used because they are one of the cheapest forms of pipes and can sustain high pressure.

  • uPVC pipes—This means unplasticized polyvinyl chloride pipes. It is used mostly for cold water service piping, because it is not wholly suitable for working environment with temperatures above 200C. They are corrosion-resistant, light to handle, and easy to join.

  • Polyethylene pipes—Polyethylene is a thermoplastic material, which softens with heat. Polyethylene pipes are light in weight and flexible, resistant to abrasion and corrosion, and have a better impact resistance at low temperature than uPVC pipes do. Three types of this pipe are available for water supply purposes: low density polyethylene (LDPE), medium density polyethylene (MDPE), and high density polyethylene (HDPE).

  • Concrete pipes—As the name implies, they are pipes made from concrete. They are types of it, as well: Prestressed concrete pipes-noted for its higher pressure resistance; Reinforced concrete pipes-similar to Prestressed pipes, advantageous for relatively high head mains, resistance to abrasion, etc.

The choice of pipe to be used for a main, according to Twort et al (op. cit.), depends on the locality conditions, capacity of mains, cost, length of mains needed, appropriate resistance coefficients, etc.

Fittings of a water distribution network, according to Twort et al (op. cit.), are all the necessary accessories needed to ensure that the distribution network meets its objectives. They include:



  • Adaptors
  • Bends—used to change the direction of flow in a main. They are usually 900, 450, 22.50, 11.250.


  • Valves—are installed throughout the water distribution network, as well as in the treatment plant and the storage system. This is to control the magnitude and direction of water flow. The various types, according to functions, are Gate valves, Check valves, etc (Hammer and Hammer Jr., op. cit.).

  • Fire hydrants—They provide access to underground water mains for the purpose of extinguishing fires, flushing out the water mains (Hammer and Hammer Jr., op. cit.).

  • Pumps—They are used for a variety of functions in water. Low-lift pumps are used to elevate water from a source to treatment plant, usually. High-lift pumps are used to discharge water to various outlets of the distribution network; depending on other factors such as size of community, length, height of discharge, etc.

  • The power output of a pump is the work done per unit time in lifting water to a higher elevation. The efficiency of a pump is the ratio of the power output to the power input. Mathematically, (Hammer and Hammer Jr., op. cit.).

  • ep == Po / Pi (2.1)

where: ep = efficiency of pump, dimensionless;

Po = power output, horsepower (or kilowatts);

Pi = power input, horsepower (or kilowatts).


  • Service Connection—Hammer and Hammer Jr. (op. cit.) explained that the service connections into a property includes a corporation stop tapped into the water main, a service to a gate valve at the curb, as well as a water metre and the metre box, which houses the metre.

      1. Flow Process Design

This is the aspect that applies the basic principles of hydraulics in determining the unknown design parameters of water supply process—such as mains’ sizes, pipe types, flowrate, power of pumps, size of storage sizes, etc.—from the known design parameters—such as population of consumer, distances, per capita consumption, etc.

This process, according to Reid Crowther (2001), can be subdivided into four main parts:


  • Design of mains,

  • Design of pumps,

  • Design of storage facilities, and

  • Design of treatment plant.

In hydraulics, there are both empirical formulae and fundamental equations to solve various problems. These empirical formulae work well for the practical situations for which they were intended; however, there are occasions where the incorrect use of an empirical formula may lead to gross error in calculations (Twort et al, op. cit.).

Design of Mains

This entails the determination of the diameters of the pipes, given the flowrate, Q, and limiting velocity, V. This is done by using the relationship among the flowrate of fluid, velocity, and the cross-sectional area of flow, given by equation 2.2:

Q = A x V (2.2)

where Q = quantity of water flowing per unit time (cubic metres per seconds, m3/s)

V = velocity of flow (metres per second, m/s)

A = cross-sectional area of flow (square metres, m2)

This formula is known as the continuity equation. It states that “for an incompressible fluid”, such as water, “if the cross-sectional area decreases, the velocity of flow must increase; conversely, if the area increases, the velocity must decrease” (Hammer and Hammer Jr., op. cit.)

Having determined the values of Q and V, A is calculated. From the value of A, the diameter, d, of the pipe is determined from geometrical formula:



D =√ (4 x A)/ ∏ (2.3)

Design of Pumps

The design of pumps involves determining the working conditions for which the pumps will operate. These include calculating, for any given flowrate,



  1. The total head, H;

  2. The power of the pump.


Total Head, H: This is the sum of the elevation head, pressure head, velocity head, and the head losses in flow. The total head is also known as the total energy of a flow.

For an ideal, incompressible fluid flow, the total head (with metres as unit) is calculated from the Bernoulli equation, according to Featherstone and Nalluri (1982),

Z + (P/ρg) + (V2/2g) = C (2.4)

where C = constant

Z = elevation above datum

P = pressure

V = velocity of flow

g = acceleration due to gravity

ρ = density of fluid

That is, the total energy, at all points, along a steady continuous streamline of an ideal incompressible fluid flow is constant. Simply stated, it is the sum of the elevation head, pressure head, and velocity head; thus the constant C can be replaced with E—total energy. Twort et al (op. cit.) however cautioned that the limitations of this equation must be carefully noted. It applies only to steady flow, and to flow where no energy is lost through friction.

For a real fluid flow, Featherstone and Nalluri (op. cit.), stated that the Bernoulli equation can be modified by (i) introducing a loss term in the equation 2.4, which would take into account the energy expended in overcoming other resistances due to changes in section, fittings, etc; and (ii) by correcting the velocity energy term for true velocity distribution. The frictional losses depend upon the type of flow, the roughness of the interior surface of the pipe.

Therefore, the modified Bernoulli’s equation for real incompressible fluid flow, for two points, is

Z1 + (P1/ρg) + (α1V12/2g) = Z2 + (P2/ρg) + (α2V22/2g) + hf (2.5)

where hf = total head losses (significantly, frictional losses of the pipe)

α = velocity correction factor.

Therefore, total head, H is determined from

H = Z + (P/ρg) + (αV2/2g) (2.6)

In computing the value of hf, for a given pipeline, there are generally two types of formulae, namely: the dimensionally correct, and the empirical. Twort et al (op. cit.) stated.



The dimensionally correct one is the Darcy’s equation:

hf = (f x l x V2) (2 x g x d) (2.7)

where: hf = head loss (m head of water)

f = Darcy’s coefficient of friction

l = length of the pipeline in metres

V = velocity of flow (m/s)

d = diameter of pipe (m)

The value of f is related to the relative roughness of the pipe material and the fluid flow characteristics (Hammer and Hammer, op. cit.).

The empirical formulae are Hazen-Williams formula and the Manning’s equation, however, the former is more popular, Twort et al (op. cit.) stated. Hazen-Williams formula is

hf = (6.78 x l x (V/C)1.85) / (d1.165) (2.8)

where: C = coefficient of pipe

l = length of pipe

d = diameter of pipe

It can also be written, conveniently, according to Bouthillier (1981), as

hf = R x L x Q1.85 (2.9)

where: R = resistance coefficient for a particular diameter,

L = length in kilometres,

Q = flowrate, or discharge in Litres/minute

The actual power of the pump is calculated from, according to Al-Layla (1977),

Pa = Pt / ep (2.10)

But, Pt = ρ x g x Q x H (2.11)

where: Pt = theoretical power of pump, or power output (kW)

ρ = density (kg/m3)

g = acceleration due to gravity (m/s2)

Q = flowrate (m3/s)

H = total head (m)

Pa= actual power of pump, or power input (kW)

ep= efficiency of pump.


Design of Storage System

The basic thing to be done here is determining the total volume of water to be supplied to the community per day, and getting an appropriate tank size that can supply the same volume. Madu (2001) explained that this has to do with the discretion of the designer, in collaboration with list of standard tank sizes from manufacturers.



Design of the Treatment Process Facility

Madu (op. cit.) explained that, having carried out the quality analysis of the raw water, the treatment process, on the one hand, is designed to take the raw water through the step-by-step treatment methods that will remove the contaminants, or supply sufficient substances as the case may be, to ensure that the treated water meets the drinking water quality standards.

On the other hand, the treatment plant structures/facility needed to be designed as well. This involves the structural analysis of various units of the treatment plant such as aeration tank walls and beds, filtration walls and beds, etc. All these come after the capacity and treatment rate of plant has been calculated, in order to get the volume required and the corresponding forces that will act.



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