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NATIONAL UNIVERSITY

FACULTY OF SCIENCE

DEPARTEMENT OF CHEMISTRY

ACADMIC YEAR 2013-2014

OPTION: Environmental

Chemistry

BACC 4

Presented by: HUMURA Emmanuel

UG:11111416

SUPERVISION: NKURANGA Jean Bosco

INTERNSHIP REPORT CARRIED OUT IN ENERGYWATER AND SANITATION AUTORITY AT GIHUMAWATER TREATMENT PLANT

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Done at HUYE on 30/10/2013

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ACKNOWLEDGEMENT

First of all I am very grateful to my only God for his continuous

help during my all studies from my birth up to now. But, all my

studies would not have been possible without the assistance of

numerous individuals and institutions. So, I honored and obliged

to extend my appreciation to the people and institutions

contributions to my education career in general and especially in

this internship.

I would like to thank a lot the lectures of chemistry department

in NUR who help me day by day for my studies development. I would

like to thanks also the Head of GIHUMA WATER TREATMENT PLANT for

his guidance, support, encouragements, and advices that help me

during my internalship.

I wish also to express my thanks to all employees of GIHUMA WATER

TREATMENT PLANT for their help during this period of

internalship.

I express my appreciation to my parents, brothers, sisters and

other students for their advices, and support .

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ABSTRACT

The EWSA and NUR have a good collaboration between them. So ,the

NUR send their students especially chemistry department ,to

develop their knowledge and do the practice on the field in

order to think well what they have learned in the class.

The report focuses primarily on the water treatment that is

realized in different steps .The purpose of this report is to

explain what we did, how we do it, materials and reagents used

and other possible reagents which can be used.

The report is also a requirement for the partial fulfillment of

NUR and the Department of chemistry. This training has the aim to

assess the water quality before and after water treatment that is

related to our field of Environmental Management and Water

Technology. The report comprises various numbers of comments,

manipulations, conclusion and recommendations on the attachment

work.

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TABLE OF CONTENTS

ACKNOWLEDGEMENT................................................i

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

TABLE OF CONTENTS............................................iii

LISTS OF FIGURES...............................................v

LISTS OF TABLES...............................................vi

GENERAL INTRODUCTION...........................................1

CHAPTER 1.GIHUMA WATER TREATMENT PLANT BACKGROUND..............2

1. GIHUMA WATER TREATMENT PLANT OVERVIEW......................2

1.1. LOCATION...............................................2

1.2. HISTORY................................................2

CHAPTER 2.WATER TREATMENT PROCESS..............................4

2.1. PRETEATMENT PROCESS......................................4

2.1.1. ROUGHING FILTERS.....................................4

2.1.3. OFF-STREAM STORAGE...................................5

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2.1.4 BANK INFILTRATION.....................................5

2.1.5.AERATION..............................................6

2.2. TREATMEN ROCESS..........................................8

2.2.1.COAGULATION AND FLOCULATION...........................8

2.2.2.TYPE OF COAGULANTS....................................9

2.2.3. FACTORS INFLUENCING COAGULATION.....................13

2.2.3. JAR TESTING.........................................14

2.3. SEDIMENTATION...........................................22

2.3.1. SEDIMENTATION BASIN.................................23

2.3.2.BASIN TYPES..........................................23

2.4 FILTRATION...............................................24

2.4.1. OPERATION...........................................24

.2.4.5. IMPORTANCE OF FILTER BACKWASH......................25

2.5.DISINFECTION.............................................25

2.6.WATER STORAGE AND WATER DISTRIBUTION.....................27

2.6.1. WATER QUALITY.......................................28

CHAP 3.PHYSICO-CHEMICAL ANALYSIS..............................29

3.1.pH.......................................................29

3.2 TURBIDITY................................................29

3.3 ALKALINITY...............................................29

3.4 TOTAL HARDNESS...........................................31

THE OBJECTIVE OF THE EXPERIENCE..............................31

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THE MATERIALS AND THE REAGENTS TO BE USED....................32

3.5. DETERMINATION OF ANIONS AND CATIONS PRESENT IN WATER....34

3.6. EXAMPLE OF SOME ELEMENT MEASURED USING SPECTROPHOTOMETER

.............................................................34

3.6.1 Free chlorine........................................34

3.6.2. Aluminium...........................................35

3.6.3.Cobalt...............................................35

3.7. RESULTS AND INTERPRETATION..............................36

CHAPTER.4.CONCLUSION AND RECOMMENDATION.......................37

REFERENCES....................................................38

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LISTS OF FIGURESFigure 1:Gihuma Water Treatment Plant................................3

Figure 2: Aeration tanks.............................................7

Figure 3: Coagulation and flocculations..............................8

Figure 4 :Floculation chamber........................................9

Figure 5: Stirring machine..........................................16

Figure 6: Formation of flocs........................................19

Figure 7 :Observation of flocs......................................19

Figure 8: Turbidimetre..............................................21

Figure 9: Sedimentation tank........................................23

Figure 10: Filtration tanks.........................................24

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LISTS OF TABLESTable 1: TABLE OF COAGULANT AID AND PRIMARY COAGALANT...............10

Table 2:TABLE OF DOSAGE FOR JAR TESTING.............................17

Table 3:TABLE OF RESULT OF JAR TEST.................................21

Table 4:TABLE OF RESULT OF PHYSICO-CHEMICAL ANALYSIS................36

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GENERAL INTRODUCTION

Water to be supplied for public use must be potable i.e.,

satisfactory for drinking purposes from the standpoint of its

chemical, physical and biological characteristics. Drinking water

should, preferably, be obtained from a source free from

pollution. The raw water normally available from surface water

sources is, however, not directly suitable for drinking purposes.

The objective of water treatment is to produce safe and potable

drinking water. The treatment processes may need pretreatment

like pre-chlorination and aeration prior to conventional

treatment. The type and degree of treatment are strongly

dependent upon the source and intended use of the water. Water

for domestic use must be thoroughly disinfected to eliminate

disease-causing microorganisms, but may contain appreciable

levels of dissolved calcium and magnesium (hardness). Water to be

used in boilers may contain bacteria but must be quite soft to

prevent scale formation. Wastewater being discharged into a large

river may require less rigorous treatment than water to be reused

in an arid region. As world demand for limited water resources

grows, more sophisticated and extensive means will have to be

employed to treat water.

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CHAPTER 1.GIHUMA WATER TREATMENT PLANT BACKGROUND

1. GIHUMA WATER TREATMENT PLANT OVERVIEW

1.1. LOCATION

GIHUMA Water Treatment Plant is located in the Southern Province;

District of MUHANGA in NYAMABUYE Sector and supplies potable

water to the people of MUHANGA city and its neighborhood. The

Plant has the related connection of pumping stations: Mbare,

Munyinya and Kimanama (Ruhango) which reinforce the water treated

at the plant allowing the water accessibility to the population

far from the town.

1.2. HISTORY

According to the history of this plant the activities of

construction started in 1984 and ended in 1988 and its capacity

in debit was small compared to that of today.

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Figure 1:Gihuma Water Treatment Plant

The capitation of raw water of this plant comes from MIGURAMO

River and MUHANGA dam. The plant is designed such that the

treatment will be easily and well performed. The installations

are constructed in chain according to the activities that are

carried out in each installation

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CHAPTER 2.WATER TREATMENT PROCESS

2.1. PRETEATMENT PROCESS

Pretreatment can broadly be defined as any process to modify

microbial water quality before, or at the entry to, the treatment

plant. Pretreatment of surface water includes processes such as

bank side filtration, presedimentation, off-river storage,

roughing filters, micro strainers, and aeration. Many

pretreatment processes are natural processes, enhanced by design

to improve water quality. Pretreatment options may be compatible

with a variety of water treatment processes ranging in complexity

from simple disinfection to membrane processes. Pretreatment is

used to reduce, and/or to stabilize variations in the microbial,

natural organic matter and particulate load.

2.1.1. ROUGHING FILTERS A roughing filter is a coarse media (typically rock or gravel)

filter used to reduce turbidity levels before processes such as

slow sand filtration, diatomaceous earth (DE) or membrane

filtration. The American Water Works Association Research

Foundation (AWWARF) has reviewed design variables Association

Research for roughing filters. Such filters typically have a

filter box divided into multiple sections containing gravel beds

of decreasing particle size, inlet and outlet structures, and

flow-control devices. Roughing filters have achieved peak

turbidity removals ranging from 60 to90%; generally, the more

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turbid the water initially, the greater the reduction that can be

achieved. These filters can achieve similar reductions of

coliform bacteria.

.2.1.2. MICROSTRAINERS

Microstrainers are fabric meshes woven of stainless steel or

polyester wires, with apertures ranging from 15 to 45 μm (usually

30–35 μm). Such meshes are useful for removing algal cells and

large protozoa , but have no significant impact on bacteria or

viruses. Microstrainers generally remove about 40–70% of algae

and, at the same time, about 5–20% of turbidity. The performance

of microstrainers for specific applications varies, depending on

the type of algae present. Although microstrainers can reduce the

amount of coagulant needed they do not remove smaller species or

reproductive forms of algae...

2.1.3. OFF-STREAM STORAGE

Off-stream storage refers to a storage reservoir that directly or

indirectly feeds a potable water intake. The effects of off-

stream storage are difficult to generalize because important

physical, biological and chemical processes are influenced by

hydrological and limnological characteristics of the reservoir.

For example, ‘round’ reservoirs and lowland impoundments

influenced by strong winds can be represented as homogeneous

biotypes because they are mixed effectively. On the other hand,

long reservoirs whose depth increases with length are best

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represented as a series of interconnected individual bas. The

characteristics of reservoirs created by construction of a dam

will differ from those of a natural or artificial lake.

2.1.4 BANK INFILTRATION

Bank infiltration refers to the process of surface water seeping

from the bank or bed of a river or lake to the production wells

of a water treatment plant. During the water’s passage through

the ground, its quality changes due to microbial, chemical and

physical processes, and due to mixing with groundwater. The

process can also be described as ‘induced infiltration,’ because

the well-field pumping lowers the water table, causing surface

water to flow into the aquifer under a hydraulic gradient. Bank

infiltration can be accomplished through natural seepage into

receiving ponds, shallow vertical or horizontal wells placed in

alluvial sand and gravel deposits adjacent to surface waters, and

infiltration galleries. Variations on the underground passage

concept include soil aquifer treatment, injection of surface

water for underground passage and aquifer recharge. The

efficiency of the process depends on a number of factors: the

quality of the surface water. (Turbidity, dissolved organic

matter, oxygen, ammonia and nutrients), the composition and

porosity of the soil, the residence time of the water in the soil

and. the temperature. This efficiency can vary over time,

depending on the difference in level between the source water

(e.g. river stage) and groundwater. This difference can influence

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the degree of groundwater mixing and the residence time of the

infiltrated surface water.

Advantages of bank infiltration

A natural pretreatment step requiring little chemical addition

Reduced turbidity and particles

Removal of biodegradable compounds

Reduction of natural organic matter and less formation of

disinfection by-products

Reduction of bacteria, viruses and protozoa

Equalization of concentration peaks (e.g. moderation of spills,

temperature, etc.)

Dilution with groundwater Adapted from Kuhn (1999)

2.1.5.AERATION

Aeration is a physical process aimed at:

• increasing the dissolved oxygen of the water; and/or

• decreasing the dissolved carbon dioxide or other gases.

The first objective is more common in wastewater treatment, where

oxygen is required for bacterial respiration. The second is more

common in drinking water. The aeration process removes the gas by

jostling it out of solution and sending it to the surface.

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Surface water such as stream or river water already has a high

dissolved oxygen and low dissolved carbon dioxide content.

However, this is not usually the case with groundwater.

When surface water goes underground, it often carries organic

material with it. This material decays over time, adding to the

carbon dioxide content. This is not toxic or even distasteful,

lemonade contains very high levels! The problem with carbon

dioxide is that it reacts with the water to form carbonic acid,

lowering the pH of the water. the following problems may occur

.

•The water will dissolve iron and manganese and, potentially,

other metals from the ground itself. These metals stay in

solution as long as the pH is low; higher pH levels will

normally see them precipitate out as unsightly red, brown or

black slimes or encrustations. This pH lift occurs at a tap

when the pressure is released and the carbon dioxide comes

out of solution

• Metallic fittings, particularly copper, zinc (in brass), and

iron will be corroded. This may affect people’s health,

especially in the case of copper, as well as causing bitter

tastes and staining of basins, baths and pans.

.

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Figure 2: Aeration tanks

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2.2. TREATMEN ROCESS

2.2.1.COAGULATION AND FLOCULATION

Coagulation/flocculation is a process used to remove turbidity,

color, and some bacteria from water.  In the flash mix chamber,

chemicals are added to the water and mixed violently for less

than a minute.  These coagulants consist of primary coagulants

and/or coagulant aids.  Then, in the flocculation basin, the

water is gently stirred for 30 to 45 minutes to give the

chemicals time to act and to promote floc formation.  The floc

then settles out in the sedimentation basin.

Coagulation removes colloids and suspended solids from the

water.  These particles have a negative charge, so the positively

charged coagulant chemicals neutralize them during coagulation. 

Then, during flocculation, the particles are drawn together by

van der Waal's forces, forming floc.  The

coagulation/flocculation process is affected by pH, salts,

alkalinity, turbidity, temperature, mixing, and coagulant

chemicals.

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.

Figure 3: Coagulation and flocculations

Figure 4 :Floculation chamber

2.2.2.TYPE OF COAGULANTS

Coagulant chemicals come in two main types - primary coagulants

and coagulant aids.  Primary coagulants neutralize the electrical

charges of particles in the water which causes the particles to

clump together.  Coagulant aids add density to slow-settling

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flocs and add toughness to the flocs so that they will not break

up during the mixing and settling processes. 

Primary coagulants are always used in the

coagulation/flocculation process.  Coagulant aids, in contrast,

are not always required and are generally used to reduce

flocculation time. 

Chemically, coagulant chemicals are either metallic salts (such

as alum) or polymers.  Polymers are man-made organic compounds

made up of a long chain of smaller molecules.  Polymers can be

either cationic (positively charged), anionic (negatively

charged), or nonionic (neutrally charged.)  The table below shows

many of the common coagulant chemicals and lists whether they are

used as primary coagulants or as coagulant aids.

Different sources of water need different coagulants, but the

most commonly used are alum and ferric sulfate.

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Chemical Name

Chemical

Formula

Primary

Coagulant

Coagulant

Aid

Aluminum sulfate

(Alum)

Al2(SO4)3 · 14

H2O

X

Ferrous sulfate FeSO4 · 7 H2O X

Ferric sulfate Fe2(SO4)3 · 9

H2O

X

Ferric chloride FeCl3 · 6 H2O X

Cationic polymer Various X X

Calcium hydroxide

(Lime)

Ca(OH)2 X* X

Calcium oxide

(Quicklime)

CaO X* X

Sodium aluminate Na2Al2O4 X* X

Bentonite Clay X

Calcium carbonate CaCO3 X

Sodium silicate Na2SiO3 X

Anionic polymer Various X

Nonionic polymer Various X

Table 1: TABLE OF COAGULANT AID AND PRIMARY COAGALANT

 

Alum

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There are a variety of primary coagulants which can be used in a

water treatment plant.  One of the earliest, and still the most

extensively used, is aluminum sulfate, also known as alum.  Alum

can be bought in liquid form with a concentration of 8.3%, or in

dry form with a concentration of 17%. When alum is added to

water, it reacts with the water and results in positively charged

ions. 

 

 

Coagulant Aids

Nearly all coagulant aids are very expensive, so care must be

taken to use the proper amount of these chemicals.  In many

cases, coagulant aids are not required during the normal

operation of the treatment plant, but are used during emergency

treatment of water which has not been adequately treated in the

flocculation and sedimentation basin.  A couple of coagulant aids

will be considered below. 

Lime is a coagulant aid used to increase the alkalinity of the

water.  The increase in alkalinity results in an increase in ions

(electrically charged particles) in the water, some of which are

positively charged.  These positively charged particles attract

the colloidal particles in the water, forming floc.

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Bentonite is a type of clay used as a weighting agent in water

high in color and low in turbidity and mineral content.  This

type of water usually would not form floc large enough to settle

out of the water.  The bentonite joins with the small floc,

making the floc heavier and thus making it settle more quickly

Coagulants and Polymers

The coagulation process includes using primary coagulants and may

include the addition of coagulant and/or filter aids. The

difference between these two categories is as follows:

1. Primary coagulants: Primary coagulants are used to cause

particles to become destabilized and begin to clump

together. Examples of primary coagulants are metallic salts,

such as aluminum sulfate (referred to as alum), ferric

sulfate, and ferric chloride. Cationic polymers may also be

used as primary coagulants.

 

2. Coagulant Aids and Enhanced Coagulants: Coagulant aids and

enhanced coagulants add density to slow-settling floc and

help maintain floc formation. Organic polymers, such as

polyaluminum hydroxychloride (PACl), are typically used to

enhance coagulation in combination with a primary coagulant.

The advantage of these organic polymers is that they have a

high positive charge and are much more effective at small

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dosages. Even though they may be more expensive, a smaller

amount may be needed, thereby saving money. Organic polymers

also typically produce less sludge.

 

Typical coagulants and aids are discussed in further detail

below:

Chemicals commonly used for primary coagulants include aluminum

or iron salts and organic polymers. The most common aluminum salt

used for coagulation is aluminum sulfate, or alum.

Alum may react in different ways to achieve coagulation. When

used at relatively low doses (<5 mg/L), charge neutralization

(destabilization) is believed to be the primary mechanism

involved.

At higher dosages, the primary coagulation mechanism tends to be

entrapment. In this case, aluminum hydroxide (Al(OH)2)

precipitates forming a “sweepfloc” that tends to capture

suspended solids as it settles out of suspension. The pH of the

water plays an important role when alum is used for coagulation

because the solubility of the aluminum species in water is pH

dependent. If the pH of the water is between 4 and 5, alum is

generally present in the form of positive ions (i.e., Al(OH)2+,

Al8(OH)4+, and Al3+). However, optimum coagulation occurs when

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negatively charged forms of alum predominate, which occurs when

the pH is between 6 and 8.

When alum is used and charge neutralization is the primary

coagulation mechanism, effective flash mixing is critical to the

success of the process. When the primary mechanism is entrapment,

effective flash mixing is less critical than flocculation.

Ferric chloride (FeCl3) is the most common iron salt used to

achieve coagulation. Its reactions in the coagulation process are

similar to those of alum, but its relative solubility and pH

range differ significantly from those of alum.

Both alum and ferric chloride can be used to generate inorganic

polymeric coagulants. These coagulants are typically generated by

partially neutralizing concentrated solutions of alum or ferric

chloride with a base such as sodium hydroxide prior to their use

in the coagulation process. The resulting inorganic polymers may

have some advantages over alum or ferric chloride for turbidity

removal in cold waters or in low-alkalinity waters.

Organic polymers tend to be large molecules composed of chains of

smaller “monomer” groups. Because of their large size and charge

characteristics, polymers can promote destabilization through

bridging, charge neutralization, or both. Polymers are often used

in conjunction with other coagulants such as alum or ferric

chloride to optimize solids removal.

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Cost may be a consideration when selecting chemicals. The system

should perform an economic analysis when comparing chemicals and

not just compare unit cost. For instance, a polymer may cost more

per unit than alum, but fewer polymers may be needed than alum.

Therefore, the total cost for polymer may not be much different

than the total cost for alum. The following issues may be

evaluated as options to consider for treatment process

enhancement.

 2.2.3. FACTORS INFLUENCING COAGULATION

In a well-run water treatment plant, adjustments are often

necessary in order to maximize the coagulation/flocculation

process.  These adjustments are a reaction to changes in the raw

water entering the plant.  Coagulation will be affected by

changes in the water's pH, alkalinity, temperature, time,

velocity and zeta potential.

The effectiveness of a coagulant is generally pH dependent. Water

with a color will coagulate better at low pH (4.4-6) with alum.

Alkalinity is needed to provide anions, such as (OH) for forming

insoluble compounds to precipitate them out. It could be

naturally present in the water or needed to be added as

hydroxides, carbonates, or bicarbonates. Generally 1 part alum

uses 0.5 parts alkalinity for proper coagulation.

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The higher the temperature, the faster the reaction, and the more

effective is the coagulation. Winter temperature will slow down

the reaction rate, which can be helped by an extended detention

time. Mostly, it is naturally provided due to lower water demand

in winter.

Time is an important factor as well. Proper mixing and detention

times are very important to coagulation.

The higher velocity causes the shearing or breaking of floc

particles, and lower velocity will let them settle in the

flocculation basins. Velocity around 1 ft/sec in the flocculation

basins should be maintained.

Zeta potential is the charge at the boundary of the colloidal

turbidity particle and the surrounding water. The higher the

charge the more is the repulsion between the turbidity particles,

less the coagulation, and vice versa. Higher zeta potential

requires the higher coagulant dose. An effective coagulation is

aimed at reducing zeta potential charge to almost 0.

2.2.3. JAR TESTING

Coagulation/flocculation is the process of binding small

particles in the water together into larger, heavier clumps which

settle out relatively quickly.  The larger particles are known as

floc.  Properly formed floc will settle out of water quickly in

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the sedimentation basin, removing the majority of the water's

turbidity. 

In many plants, changing water characteristics require the

operator to adjust coagulant dosages at intervals to achieve

optimal coagulation.  Different dosages of coagulants are tested

using a jar test, which mimics the conditions found in the

treatment plant.  The first step of the jar test involves adding

coagulant to the source water and mixing the water rapidly (as it

would be mixed in the flash mix chamber) to completely dissolves

the coagulant in the water. 

Then the water is mixed more slowly for a longer time period,

mimicking the flocculation basin conditions and allowing the

forming floc particles to cluster together.  Finally, the mixer

is stopped and the floc is allowed to settle out, as it would in

the sedimentation basin.

The type of source water will have a large impact on how often

jar tests are performed.  Plants which treat groundwater may have

very little turbidity to remove are unlikely to be affected by

weather-related changes in water conditions.  As a result,

groundwater plants may perform jar tests seldom, if at all,

although they can have problems with removing the more difficult

small suspended particles typically found in groundwater. 

Surface water plants, in contrast, tend to treat water with a

high turbidity which is susceptible to sudden changes in water

quality.  Operators at these plants will perform jar tests

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frequently, especially after rains, to adjust the coagulant

dosage and deal with the changing source water turbidity.

 

 

Materials

Volumetric flask (1,000 mL)

Analytical balance

Coagulants and coagulant aids

Magnetic stirrer (optional)

A stirring machine with six paddles capable of variable

speeds from 0 to 100 revolutions  per minute (RPM)

Beakers (1,000 mL)

Pipets (10 mL)

Watch or clock

Turbidometer and sample tubes

Figure 5: Stirring machine

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Procedure

1. Decide on six dosages of the chemical(s). You should use the

chemicals in use at the treatment plant you visit. These

chemicals may include coagulants, coagulant aids, and lime.

The dosages should be in a series with the lowest dosage

being lower than the dosage currently used in the plant and

the highest dosage being higher than the dosage currently

used in the plant. Insert the six dosages into your data

sheet.

If pre-lime has to be fed, it is usually best to hold the

amount of lime constant and vary the coagulant dosage.

 

2. Prepare a stock solution of the chemical(s). It is not

necessary to know the purity (strength) of the chemicals you

use since the strength will be the same for plant operation.

All results of the jar tests are in parts per million or

milligrams per liter. (1 ppm = 1 mg/L).

You will need to prepare a stock solution for each type of

chemical used. The strength of the stock solution will

depend on the chemical dosages which you decided to use in

step 1. The table below shows what strength stock solution

you should prepare in each circumstance.

 

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Approximate dosage

required, mg/L

Stock solution

concentration, mg/L

1 mL added to 1 L

sample equals

1-10 mg/L 1,000 mg/L 1 mg/L

10-50 mg/L 10,000 mg/L 10 mg/L

50-500 mg/L 100,000 mg/L 100 mg/L

 Table 2:TABLE OF DOSAGE FOR JAR TESTING

 

For example, if all of your dosages are between 1 and 10 mg/L,

then you should prepare a stock solution with a concentration of

1,000 mg/L.  This means that you could prepare the stock solution

by dissolving 1,000 mg of the chemical in 1 L of distilled

water.  However, this would produce a much larger quantity of

stock solution than you need and would waste chemicals.  You will

probably choose instead to dissolve 250 mg of the chemical in 250

mL of distilled water. 

Once you decide on the strength and volume of stock solution to

prepare, the procedure is as follows:

1. Weigh out the proper quantity of the chemical using the

analytical balance. Put an empty weigh boat on the

balance and tare it. Then add the chemical slowly to

the weigh boat until the desired weight has been

achieved. It is much easier to add chemical to the

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weigh boat than to remove it, add the chemical very

slowly and carefully.

 

2. Measure out the proper quantity of distilled water in

the volumetric flask.

 

3. Add the chemical to the distilled water.

 

4. Mix well. If lime is used, it is best to use a magnetic

stirrer since lime is not completely soluble in water.

In other cases, magnetic stirrers can still be useful.

5. Collect a two gallon sample of the water to be tested. This

should be the raw water.

6. Measure 1,000 mL of raw water and place in a beaker. Repeat

for the remaining beakers.

6. Place beakers in the stirring machine.

7. With a measuring pipet, add the correct dosage of lime

and then of coagulant solution to each beaker as

rapidly as possible. The third column of the table in

step 2 shows the amount of stock solution to add to

your beaker. Two examples have been explained below.

If you have prepared a 1,000 mg/L stock solution, then

1 mL of the stock solution added to your 1,000 mL

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beaker will result in a concentration of 1 mg/L. So, if

you wanted to have a chemical concentration in your

beaker of 4mg/L, you would add 4 mL of stock solution.

If you prepared a 100,000 mg/L stock solution and

wanted to achieve a chemical dosage of 150 mg/L, then

you would need to add 1.5 mL of stock solution to your

beaker.

 

8. With the stirring paddles lowered into the beakers,

start the stirring machine and operate it for one

minute at a speed of 80 RPM. While the stirrer

operates, record the appearance of the water in each

beaker. Note the presence or absence of floc, the

cloudy or clear appearance of water, and the color of

the water and floc. The stirring equipment should be

operated as closely as possible to the conditions in

the flash mix and/or flocculation facilities of the

plant. Mixing speed and time may vary at your plant

from the times and speeds listed in this and the

following step. Record any alterations on your data

sheet.

 

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Figure 6: Formation of flocs

 

 

9. Reduce the stirring speed to 20 RPM and continue

stirring for 30 minutes. Record a description of the

floc in each beaker 5, 10, 15, 20, 25, and 30 minutes

after addition of the chemicals.

10. Stop the stirring apparatus and allow the samples

in the beakers to settle for 30 minutes. Record a

description of the floc in each beaker after 15 minutes

of settling and again after 30 minutes of settling.

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Figure 7 :Observation of flocs

 

11. Determine which coagulant dosage has the best

flocculation time and the most floc settled out. This

is the optimal coagulant dosage. A hazy sample

indicates poor coagulation. Properly coagulated water

contains floc particles that are well-formed and dense,

with the liquid between the particles clear.

12. Test the turbidity of the water in each beaker

using a turbidometer. Pipet water out of the top of the

first beaker and place it in a sample tube, making sure

that no air bubbles are present in the sample. (Air

bubbles will rinse while turbidity will sink.)

Carefully wipe the outside of the sample tube clean.

Place the sample tube in a calibrated turbidometer and

read the turbidity. Repeat for the water from the other

beakers.

28

The least turbid sample should correspond to the

optimal coagulant dosage chosen in step 10.

13. If lime or a coagulant aid is fed at your plant in

addition to the primary coagulant, you should repeat

the jar test to determine the optimum dosage of lime or

coagulant aid. Use the concentration of coagulant

chosen in steps 10 and 11 and alter the dosage of lime

or coagulant aid.

14. Using the procedure outlined in step 11, measure

the turbidity of water at three locations in the

treatment plant - influent, top of filter, and filter

effluent..

 

  .

Figure 8: Turbidimetre

29

 TABLE1 RESULTS

REAGENT(ppm) 1 2 3 4 5 6

Al2SO4 20 25 30 35 40 45Ca(OH)2. 15 20 25 30 35 40Polymer. 0.1 0.1 0.1 0.1 0.1 0.1PH before

flocculation

6.5 6.5 6.5 6.5 6.5 6.5

PH after

flocculation.

7 7 6.5 6.5 6.5 6.5

Turbidity

before

flocculation.

29.6 29.6 29.6 29.6 29.6 29.6

Turbidity after

flocculation

8.9 6.27 5.71 4.64 3.04 1.42

Table 3:TABLE OF RESULT OF JAR TEST

RESULTS INTERPRETATION

The good result has been obtained on 6rd where 45ppm of Al2 (SO4)3

and 40 ppm of Ca (OH) 2 have been taken.

The obtained results are: .Turbidity: 1.42NTU

.PH:6.5

Then calculate the debut of reagents q= QT/ C

For Aluminium sulphate: q=9×10 7 ml/h×45 = 81000ml/h

50×1000

30

. For calcium hydroxide: q= 9×10 7 ml× 40=72000ml/h

50×1000

2.3. SEDIMENTATION

Sedimentation is thus defined as the removal of suspended

particle by gravity

Figure 9: Sedimentation tank.

2.3.1. SEDIMENTATION BASIN

The Basin can be divided into four zones.

Inlet zone

31

Settling zone

Sludge zone

Outlet zone

For more details a reference may be made to the Manual on “Water

Supply and Treatment”

published by Ministry of Urban Development. (1999 edition).

2.3.2.BASIN TYPES

The basins may be of the following types:

Rectangular basins.

Circular and square basins.

High Rate Settlers (Tube Settlers).

Solid Contact Units (Up-flow solid-contact clarification and up-

flow sludge blanket.

2.4 FILTRATION

The purpose of filtration is the removal of particulate

impurities and floc from the water being treated. In this regard,

the filtration process is the final step in the solids removal

process which usually includes the pretreatment processes of

coagulation, flocculation and sedimentation. The degree of

treatment applied prior to filtration depends on the quality of

water.

32

/

Figure 10: Filtration tanks

2.4.1. OPERATION

Filter Operation: A filter is usually operated until just before

clogging or breakthrough occurs or a specified time period has

passed (generally 24 hours).

Backwashing: After a filter clogs or breakthrough occurs or a

specified time has passed the filtration process is stopped and

the filter is taken out of service for cleaning or Backwashing.

Surface Wash: In order to produce optimum cleaning of the filter

media during backwashing and to prevent mud balls, surface wash

(supplemental scouring) is usually required. Surface. wash

systems provide additional scrubbing action to remove attached

floc and other suspended solids from the filter media.

33

.2.4.5. IMPORTANCE OF FILTER BACKWASH

When solids accumulate within a filter bed, they create a

resistance to flow. This resistance is measured as loss of head

(pressure increase) for the filter bed. The filter is backwashed,

usually with finished water, to remove the accumulated particles.

The need for backwashing may be determined using various criteria

— a terminal head loss, a fixed time interval, or a

Breakthrough of solids (measured as turbidity or particle

counts). Options for disposal of the spent filter backwash water

may include discharge to a sewer or a receiving stream. Because

backwash water may contain. Disinfectants and other chemicals

that may be harmful to the biological life of a stream, direct

discharge to streams may be restricted. Similarly, discharge to

sewers may be restricted, based on the constituents and total

quantity of the backwash water. For many water treatment plants,

particularly in arid or water-scarce areas with limited raw water

resources, it is often necessary to reuse backwash water. When

the water is recycled, accumulation of microbial and algal

contaminants is a concern. For example, algal toxins may be

released is a concern. For example, algal toxins may be released

from stored treatment sludges when the overlying water is

recycled. Because of the resistance of oocysts to conventional

disinfectants, Cryptosporidium has been a major concern for the

handling and operation of recycled process streams. The level of

treatment required for spent filter backwash water before recycle

will vary from site to site depending on the treatment process

34

and water-quality objectives. Equalization of the recycle flow

and sedimentation of the backwash solids, aided by the addition

of a polymer coagulant, is sufficient to reduce cyst

concentrations to raw water levels in most cases (Cornwell & Lee,

1993; Arora, Di Giovanni & LeChevallier, 1999; McTigue et al.,

2000).

2.5.DISINFECTION

Disinfection is carried out to kill harmful microorganisms that

may be present in the water supply and to prevent microorganisms

regrowing in the distribution systems.

Good public health owes a lot to the disinfection of water

supplies. Without disinfection, waterborne disease becomes a

problem causing high infant mortality rates and low life

expectancy.This remains the situation in some parts of the world.

Key factors considered by a water authority in selecting

disinfection system are:

.Effectivenes in killing a range of microorganisms

.Potential to form possibly harmful disinfection by products

.Ability of disinfection agent to remain effective in the

water throughout the distribution system.

.Safely and ease of handling chemicals and equipment.

.Cost effectiveness.

CHLORINE

35

Mode of action

Chlorine gas and water react to form HOCl and hydrochloric acid

(HCl). In turn, the HOCl dissociates into the hypochlorite ion

(OCl–) and the hydrogen ion(H+), according to the following

reactions:

1) Cl2+ H2O↔ HOCl+HCl

Inactivation (disinfection) process

2) HOCl↔ H+ + OCl-

The reactions are reversible and pH dependent:

• between pH 3.5 and 5.5, HOCl is the predominant species

• between about pH 5.5 and 9.5, both HOCl and OCl- species exist

in various proportions

• above pH 8, OCl- predominates. The OCl predominates. The OCl– and HOCl species are commonly referred to as free

chlorine, which extremely reactive with numerous components of

the bacterial cell. HOCl can produce oxidation, hydrolysis and

deamination reactions with a variety of emical substrates, and

produces physiological lesions that may affect several cellular

processes. Baker (1926) theorized that chlorine destroys mi

croorganisms by combining with proteins to form N-chloro

36

compounds. Chlorine was later found to have powerful effects on

sulfhydryl groups of proteins and to convert several -amino

acids by oxidation into a mixture of corresponding nitriles and

aldehydes. The exact product of e reaction depends on chlorine

concentration and pH . Cytochromes, iron-sulfur proteins and

nucleotides are highly vulnerable to oxidative degradation by

HOCl, suggesting that chlorine causes physiological damage

primarily to the bacterial cell membranes . Respiration, glucose

transport and adenosine triphosphate levels all decrease in

chlorine-treated bacteria .Electron microscopy of chlorinated

bacteria has demonstrated morphological changes in the cell

membrane. In addition, chlorination can kill microbes by

disrupting metabolism and protein synthesis or by modifying

purine and pyrimidine bases and thus causing genetic

defects .Nearly 100 years of chlorination for disinfection of

drinking-water has demonstrated the effectiveness of this process

for inactivation of microbial pathogens, with the notable

exception of Cryptosporidium

2.6.WATER STORAGE AND WATER DISTRIBUTION

After treatment drinking water is distributed via large trunk

main to water storage reservoir.From these reservoirs water is

reticulated to each houseld through a network of small water

mains.

In some urban water systems the water supply is obtained directly

from river or onother body of freshwater.In other, rivers are

37

dammed and the water supply is distributed from artificial

storage, such as reservoirs.

Dams are built across rivers and streams to reservoirs to

collect water from catchment to ensure sufficient supply will be

available when needed.Dams also have been built for a range of

purposes besides water supply.Such as agriculture and

hydroelectricity generation.

Water may also be released from a reservoir a an” environmental

flow’ to maintain the health of the ecosystem downstram of the

reservoir. It is estimated that significant reservoirs builts

around the world store five megalitres of water.

The water mains and pipes beneath the streets of a community are

described as the water supply distribution system or reticulation

system.A part of this system strategically located service

reservoirs are often large covered tanks in a elevated position.

Pumps and valves also form an important part of distribution

system.The end points of the system are the consumers taps.

After water has been treated to protected public health improve

aesthetics by removing colour and adour as required ,it is ready

to be delivered to consumers.The system of mains and pipes used

to deliver the water is known as the distribution,or reticulation

systems.

38

Treated water may be held at a treatment plant or immediately

discharged into the system of mains and pipes that will transport

it to consumers taps.on the way it may be held in short_ term

storage,which are located as close as possible to where the water

be used.

Sufficient water is required in local area to supply periods of

high demand,as on a hot summer day.

From a design perspective,the needs of fire service usually

determines the capacity of the system.

An important characteristic of a drinking water distribution

system is that is closed,to prevent contamination by birds,animal

or people.In contrast,irrigation water is usually delivered in

open channels or aqueducts.

A significant part of the water supply system lie buried

underground.Out of the public eye.Such infrastructure can be

overlooked.It is easy to forget how valuable and essential water

distribution systems are the community.In terms of money spent on

supplying water in Australia, most of it has been invested in

the mains and pipes buried under the streets of towns and suburbs

across the country.

Most distribution systems have developed and expanded as arban

areas have grown Map of water distribution system would show a

complex mixture of tree like and looped pipe networks,together

with valves and pumps.

Distribution systems require regular cleaning(flushing and

scouring)maintenance and a program to replace pipes and other

39

equipment as they near the end of their useful lives.Water mains

can be expected to have a usuful of 40 to 100 years.Many of the

pipes under the older parts of our cities may be towards the

upper end of this range.

2.6.1. WATER QUALITY

Water quality essential to human life and to the health of the

environment.As a valuable natural resourse, it comprise marine,

estuaire, freshwater (river and lakes) and grounder water

environenment,accros coostals and inland areas.Water has two

dimensions that are closely linked quality and quantity. Water

quality is commoly defined by its physical, chemical, biological

and aesthetic (appareance and smell) characteristics.A healthy

environment is one in which water quality support a rich and

varied community of organisms and protect public health.

Water quality in body of water influence the way in wich

communities use the water for activities such as drinking,

swimming or commercial purpose

CHAP 3.PHYSICO-CHEMICAL ANALYSIS

Physico-chemical parameters affecting the quality of water that

we analyse in the labalatory of Gihuma Treatment Plant

are:pH,TH(total hardness),Alkalnity including TA(alcalimetric

titration) , TAC (complete alcalimetric titration) ,and TCa

(calcic

40

titre ),turbiditity,nitrites(NO2),nitrates(NO3),chlorine(Cl-),man

ganese(Mn2+),fer,aluminium and other ions.

3.1.pH

The measures of pH is calculated with the pH-meters showing the

values of pH.The pH is the measure of acidity of water.The

naturally water have the pH between 6and 8.The lower value of

pH,the solution is called acide.The some aquatiques species such

as fish and others aquatiques organismes can not live in water of

high acidity.The atmospherique pollution and the acids rain are

sources of acidity in water.pH of water does not change because

water has tampon solution with the presence of the ions HCO3- and

CO3-.

3.2 TURBIDITY

Turbidity is the measure of suspended solids present in water

such as organic matter, Limons, algae and particulate load. The

turbidity is measured with the instrument called turbidimetre.

3.3 ALKALINITY

The capacity of water to accept H+ ions (protons) is called

alkalinity. Alkalinity is important in water treatment and in the

chemistry and biology of natural waters. Frequently, the

alkalinity of water must be known to calculate the quantities of

chemicals to be added in treating the water. Highly alkaline

water often has a high pH and generally contains elevated levels

of dissolved solids. These characteristics may be detrimental for

41

water to be used in boilers, food processing, and municipal water

systems. Alkalinity serves as a pH buffer and reservoir for

inorganic carbon, thus helping to determine the ability of water

to support algal growth and other aquatic life, so it can be used

as a measure of water fertility. Generally, the basic species

responsible for

Alkalinity in water is bicarbonate ion, carbonate ion, and

hydroxide ion.

HCO3- + H+→CO2+ H2O

CO3

2- + H+→HCO3-

OH-+ H+→H20

ALICALIMETRIC TITRATION (TA)

The alcalimetric titre is measured when the PH is greater

than8.2. The raison why we didn’t’ measure it, the PH is above

8.2 for raw water and for treated wate

COMPLETE ALCALIMETRIC TITRE (TAC)

T.A.C = OH- + CO32- +HCO3

-.

The measurement of water alkalinity is based on the

neutralization of the bases by using strong diluted acid which is

sulfuric acid (H2SO4) represented in the following reactions.

42

OH- + H3O+→ H2O

CO32− + H3O+ →HCO3

− + H2O

HCO3− + H3O+ →CO3

2− +2H2O

THE OBJECTIVE OF THE EXPERIMENT

The main objective of this experiment is to know the alkalinity

of water due to the presence of carbonates (CO32-), bicarbonates

(HCO3) that are weak base and we have also free base which is

strong base OH- of Ca, Mg and Na.

REAGENTS TO BE USED

. 100ml of sample

. 5 drops of methyl orange

. Sulfuric acid

MATERIALS TO BE USED

- Erlenmeyer flask

- Burette

- Dropper

PROCEDURE:

.Taking 100ml of sample in Erlenmeyer flask

.Adding 5drops of methyl orange as indicator, then we has to agitate

until the mixture will attain blue-green color.

.Filling the burette with sulfuric acid solution

43

.Titrate with sulfuric acid by pouring drop by drop in agitating to

homogenize the solution till the mixture will attain the persistent

pink.

.After all those process we have to read on the volume indicated

by the burette; normal our result is in ml that will be converted

in ppm by multiply by 10.

3.4 TOTAL HARDNESS

The presence of the cations Ca2+,Fe2+,Sr2+,Zn2+,Mn2+and Mg2+ are

responsible for total hardness,but,the ions Mg2+ and Ca2+ are the

only ions present in water with the significatif

concentration .The reason why total hardiness is considered as

sum of 2 cation (Ca2+ and Mg2+)

TOTAL HARDINESS=[Ca2+]+[Mg2+]

THE OBJECTIVE OF THE EXPERIENCE

The objective of

this experiment is to determine the hardness of water caused by calcium

and magnesium ions.

THE MATERIALS AND THE REAGENTS TO BE USED

Reagents:

.10ml of sample of raw water

.10ml of sample of treated water

.Buffer hardness solution

 

44

.EDTA

.Manver (indicator)

Materials:

-Erlenmeyer flask

-Burette

-Dropper

-Beaker

-Graduated cylinder

-spatula

PROCEDURE:

-Measuring 10ml of sample in graduated cylinder

-Pouring these in a flask of 250ml

-Adding 4drops of buffer hardness solution

-Adding 5ml of Manver with spatula

-Then filling the burette the titrant solution (EDTA)

-Starting the titration by pouring drop by drop of EDTA in

agitating until we reach to the equivalent point; the color

will change from red-violet.

-Then after all those we have to read the volume indicated to

the burette then multiply the result we have gotten by ten to

get accuracy result.

45

-After the experiment we have gotten 3.1ml multiply by 10

to get accuracy result which is equal to 31mg/l.

CALCIC TITRE (TCa)

OBJECTIVE OF THIS EXPERMENRT

The aim of this experiment is to determine the concentration of

calcium ions present in raw water and treated water.

Reagents:

.100ml of sample

.Sodium hydroxide

.EDTA 0.02N

.Murexide (indicator)

Materials:

-Erlenmeyer flask

-Burette

-Spatula

-Dropper

-Graduated cylinder

46

PROCEDURE:

-Measuring 10ml of sample in graduated cylinder

-Pouring these in a flask of 250ml

-Adding 2drops of sodium hydroxide

-Adding 5ml of Murexide with spatula

-Then filling the burette the titrant solution (EDTA)

-Starting the titration by pouring drop by drop of EDTA in

agitating until we reach to the equivalent point.

-Then after all those we have to read the volume indicated to the

burette then multiply

by 10 to get accuracy result in ppm.

Ca2+=TCa×0.4

3.5. DETERMINATION OF ANIONS AND CATIONS PRESENT IN WATER

Before treating water we have to know the quantity of anions and

cations present in raw water. Each cation and anion have its

specific reactif used for its determination and we may know the

quality of water treated according to the result obtained. The

instrument using for determining those parameters is called

SPECTROPHOTOMETER.

47

3.6. EXAMPLE OF SOME ELEMENT MEASURED USING SPECTROPHOTOMETER

3.6.1 Free chlorine

Take 10ml of sample,

- Add reagent for free chlorine DPD (N, N-diethyl-p-phenylene

diammine)

- Shack for 20 seconds to homogenize the solution, we can have

rose color in the presence free chlorine and then measure its

quantity.

Free chlorine is an oxidant agent which is hard and instable in

natural water. It reacts rapidly with many inorganic compounds

and oxidizes slowly those compounds.

Some factors that influence the presence of free chlorine in

water:

.concentration of reagent,Sun ,PH,Temperature and Salinity

Free chlorine is present in the sample as hypochlorite ion and

reacts immediately with indicator DPD to produce rose color

proportionally to the concentration of chlorine.

Total chlorine

Take 10ml of sample

- Add reagent for total chlorine DPD

- Shack for20 second to homogenize the solution

-Then wait for 3minutes of reaction

48

- Measure the quantity of total chlorine present.

Total chlorine is present in the form of monochlorammine,

dichlorammine, and nitrogen trichloride and halogen derivatives.

It oxidizes iodide of reagent in iodine. It reacts with indicator

DPD to produce red color proportionally to the concentration of

total chlorine.

3.6.2. Aluminium

-Take 10ml of sample

- Mixed with ascorbic acid reagent

- Return many times to homogenize

-Add reagent Alu ver.3, red-orange color can appear in the

presence of aluminium, then measure aluminum present.

The indicator alumino is combined with aluminium to form red-

orange color. The intensity of coloration is proportional to

concentration of aluminum. Ascorbic acid is added to avoid.

3.6.3.Cobalt

Take 10ml of sample,

-Add phthalate-phosphate

-Add 0.5ml of indicator PAN0.3%, return many times to homogenize

the solution

Wait for 3minutes of reaction, the color can vary from green to

red.

49

-Then add EDTA

- Shack to dissolve and measure the quantity of cobalt present.

After form a buffer with the sample and mask the iron (Fe3+) with

pyrophosphate the indicator 1-(2-pyridylazo)-2 naphtol is

added, form a complex with most metals present. After developing

the color EDTA is added to destroy metal complexes-PAN except

those of Nickel and Cobalt.

3.7. RESULTS AND INTERPRETATION

The water analysis was realized in laboratory two times in each

week. The table 1 gives the quantity/level of each element. This

resultants take from analyze physicochemistry

Date

05/08/20

13

05/08/20

13

19/08/20

13

22/08/20

13

Guidel

ine

Elem

ent

uni

ty

RW TW RW TW RW TW RW TW

pH 7 6.5 6.

5

6.5 6.7 6.5 6.5 6 6.5-

8.5TURB NTU 22.

3

5.3

4

31

.8

3.0

1

37.

1

3.7

7

37.

8

6.7

7

5

TMg Mg/

l

31 23 29 20 15 20 0.0 0.0

50

TAC Mg/

l

60 90 74 100 35 20 60 30

TH Mg/

l

45 43 53 25 50 100 40 150

TCa Mg/

l

14 20 24 25 35 80 35 60

Ca2+ Mg/

l

5.6 8 28 32 14 28 14 24

NO3+ Mg/

l

0.8 2.6 0.

1

0.2 0.2 1.2 1.0 1.6

Mn Mg/

l

0.2

53

0.2

49

-

0.

11

0.1

89

0.2

06

0.0

29

0.1

73

0.1

19

0.1

Co Mg/

l

0.0

5

0.0

1

0.

06

0.0

4

0.0

7

0.0

3

0.0

6

0.0

0

0.1

Al Mg/

l

-

0.0

8

-

0.3

3

-

0.

09

-

0.3

7

0.1

60

0.1

12

0.0

46

0.2

27

0.2

Fe Mg/

l

2.8 0.8

2

2.

67

0.1

6

3.1

0

0.3

2

- 1.8

Free

Cl2

Mg/

l

0.0

4

5.1

8

0.

03

0.0

7

0.0

2

1.9

1

0.0

9

0.9

5Tot.

Cl2

Mg/

l

0.0

4

40.

79

0.

02

0.5

7

0.0

2

2.7

9

0.1

1

1.2

5I2 Mg/

l

0.1

4

3.1

3

0.

50

0.0

9

0.0

8

9.9

2

0.3

7

4.3

4

5

Br2 Mg/ 0.0 13. 0. 0.1 0.0 5.5 0.2 2.8 5

51

l 7 93 27 0 9 6 4 6Table 4:TABLE OF RESULT OF PHYSICO-CHEMICAL ANALYSIS

From the table above the results show their level to be within

the permissible limit except for the elements, Turbidity,

Bromine, Iodine, Aluminium,Iron,Cobalt, Manganese and other

elements no analysed in laboratory,

CHAPTER.4.CONCLUSION AND RECOMMENDATION

Gihuma Water Treatment Plant produces a quantity of water and

supplied to the population in term of drinking and washing

water.The quantity of water produced at the plant has been

reinforced by pumping station for increasing the quantity and try

to satisfy the water demand users.

The water quantity consisted on raw water received for treatment,

water supplied, water treated and water used by the plant

itself.These quantities were depending in both stopping and

working time.However the works of maintanance,reparation of

some equipment, instability of raw water quantity and

availability of electrical energy have influenced on the working

time.

According to the raw water quality and the experience done in the

laboratory.Gihuma wate Treatment Plant can use the small quantity

of reactifs such as aluminium sulfate, polymer and hydroxide of

calcium.

52

REFERENCES

.Manahan, Stanley E."FRONTMATTER" Environmental Chemistry

Boca Raton: CRC Press LLC, 200

Alabama Department of Environmental Management.  1989. 

Water Works Operator Manual. 

Mark W Lechevalier and Kwok-Keung Au,Water treatment and

pathogen control,2004

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