design of drinking water treatment plant

74
DESIGN OF DRINKING WATER TREATMENT PLANT FOR ARNI UNIVERSITY A PROJECT REPORT Submitted by SUKHSHAM SHARMA AACI0044A/09 VIPUL KERNI AACI0046A/09 AMAN SHARMA AACI0047A/09 AJAY VERMA AACI0048A/09 TARUN PURI AACI0050A/09 in partial fulfillment for the award of the degree of BACHELOR OF TECHNOLOGY in CIVIL ENGINEERING ARNI SCHOOL OF TECHNOLOGY ARNI UNIVERSITY:: KANGRA JUNE 2013

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Page 1: design of drinking water treatment plant

DESIGN OF DRINKING WATER TREATMENT

PLANT FOR ARNI UNIVERSITY

A PROJECT REPORT

Submitted by

SUKHSHAM SHARMA AACI0044A/09

VIPUL KERNI AACI0046A/09

AMAN SHARMA AACI0047A/09

AJAY VERMA AACI0048A/09

TARUN PURI AACI0050A/09

in partial fulfillment for the award of the degree

of

BACHELOR OF TECHNOLOGY

in

CIVIL ENGINEERING

ARNI SCHOOL OF TECHNOLOGY

ARNI UNIVERSITY:: KANGRA

JUNE 2013

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ARNI UNIVERSITY: KANGRA

BONAFIDE CERTIFICATE

Certified that this project report “DESIGN OF DRINKING WATER PLANT

FOR ARNI UNIVERSITY” is the bonafide work of “SUKHSHAM

SHARMA (AACI0044A/09), VIPUL KENRI (AACI0046A/09), AMAN

SHARMA (AACI0047A/09), AJAY VERMA (AACI0048A/09) and TARUN

PURI (AACI0050A/09)” who carried out the major project work under my

supervision.

SIGNATURE SIGNATURE

Mr. BHARANIDHARAN B Mr. DAVINDER SINGH

HEAD OF THE DEPARTMENT ASSOCIATE DEAN

EXTERNAL EXAMINER INTERNAL EXAMINER SUPERVISOR

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ABSTRACT

This project presents a review on design of drinking water treatment plant

including the design of for sedimentation, filtration, chlorination, aeration etc.

The main work of this project is to check the WHO standards for drinking

water, to check whether water is suitable for drinking purposes or not. If it is not

so then various treatment methods are used for maintaining the standards of

water. The application of modern water treatment processes had a major impact

on water-transmitted diseases, and these processes provide barriers or lines of

defense between the consumer and waterborne disease. This project provides an

overview of the drinking water treatment processes. The most common

treatment process train for surface water supplies is conventional treatment,

which consists of disinfection, coagulation, flocculation, sedimentation,

filtration, and disinfection. The safe drinking water requires a holistic approach

that considers the source of water and treatment processes. Depending on water

quality influent, each unit can be optimized to achieve the desired water quality

effluent, both in design and operation stages. A typical water treatment plant has

the combination of processes needed to treat the contaminants in the source

water treated by facility. The presence of unbeatable organic or mineral

substance causes some problems in obtaining drinking water. Understanding

these phenomena requires taking into account the physical and chemical natures

of the water to be treated.

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ACKNOWLEDGEMENT

We express our sincere and heartfelt thanks to the MANAGEMENT and the

CHANCELLOR and PRO CHANCELLOR for providing all the necessary

facilities and support required for carrying out this project successfully.

We thank our Vice Chancellor Dr. S.K. KAUSHAL for his care and

guidance which helped us in completing this project in time.

We express our sincere thanks to our Associate Dean Mr. DAVINDER

SINGH and Head of the Department Mr. B.BHARANIDHARAN for their

valuable suggestions and encouragement throughout this project.

We also express our sincere thanks to the TEACHING and NON-

TEACHING STAFF of our department, who had showed a keen interest at all

stages of our work and provided us with the required help.

We gratefully acknowledge the help rendered by our UNIVERSITY

LIBRARIAN and his Staff for providing us with the necessary books and

references.

Finally our unfailing gratitude is to our PARENTS and FRIENDS for

their love and affection, which kept us on wheels to do the work energetically

and successfully.

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TABLE OF CONTENTS

CHAPTER NO. TITLE PAGE NO.

ABSTRACT iii

LIST OF TABLES ix

LIST OF FIGURES x

LIST OF ABBREVATIONS xi

1. INTRODUCTION 1

1.1 GENERAL 1

1.2 WATER SOURCES 3

1.2.1 Hydrological cycle terms 3

1.3 SOURCES OF DRINKING WATER 4

1.4 WATER QUALITY 5

1.5 POTABLE WATER 7

1.6 REQUIREMENT FOR WATER 7

1.7 NEED FOR TREATMENT 8

1.7.1 Water borne diseases 8

2. LITRATURE REVIEW 10

2.1 OBJECTIVES OF PROJECT 18

3. WATER QUALITY ANALYSIS 19

3.1 CHARACTERISTICS OF WATER 19

3.2 PHYSICAL CHARACTERISTICS 20

3.2.1 Turbidity 20

3.2.2 Colour 21

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3.2.3 Taste and odour 21

3.2.4 Temperature 21

3.3 CHEMICAL CHARACTERISTICS 22

3.3.1 PH 22

3.3.2 Acidity 22

3.3.3 Alkalinity 22

3.3.4 Hardness 23

3.3.5 Chlorides 23

3.3.6 Sulphates 23

3.3.7 Iron 24

3.3.8 Solids 24

3.3.9 Nitrate 24

3.4 WATER TREATMENT METHODS 26

3.4.1 Aeration 27

3.4.2 Types of aerators 27

3.5 SETTLING 28

3.5.1 Purpose of settling 28

3.5.2 Principle of settling 29

3.5.3 Types of settling 29

3.5.4 Types of settling tanks 29

3.6 COAGULATION AND

FLOCCULATION

30

3.6.1 Flocculation 30

3.6.2 Mechanism of flocculation 31

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3.6.3 Coagulation in water treatment 31

3.7 FILTRATION 32

3.7.1 Filtration mechanism 32

3.7.2 Filter material 32

3.7.3 Types of filter 33

3.7.4 Principle of slow sand filter 34

3.7.5 Slow sand Vs rapid sand filter 35

3.8 DISINFECTION 36

3.8.1 Methods of disinfection 36

3.8.2 Forms of application of chlorine 37

4. EXPERIMENTAL PROCEDURE 39

4.1 TO DETRMINE TOTAL HARDNESS

OF WATER SAMPLE

39

4.2 TO DETERMINE ALKALINITY OF

WATER SAMPLE

40

4.3 TO DETRMINE PH VALUE OF

WATER SAMPLE

40

4.4 TO DETEMINE CHLORIDE CONTENT

IN WATER SAMPLE

41

4.5 TO DETRMINE THE TOTAL

DISSOLVED SOLIDS IN WATER

SAMPLE

42

4.6 TO DETERMINE DISSOLVED

OXYGEN IN WATER

43

5. RESULTS AND DISCUSSION 45

5.1 RESULTS OF CHEMICAL TEST 50

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5.2 DISCUSSION OF RESULTS 53

6. DESIGN OF DRINKING WATER

TREATMENT PLANT

54

6.1 WATER QUANTITY ESTIMATION 54

6.2 FLUCTUATIONS IN RATE OF

DEMAND

54

6.3 DESIGN PERIOD AND POPULATION

FORECAST

55

6.4 DESIGN DETAILS 56

6.5 DESIGN OF SEDIMENTATION TANK 58

6.6 DESIGN OF RAPID SAND FILTER 59

6.7 DESIGN FOR CHLORINATION 60

6.8 DESIGN OF COAGULATION TANK 60

7. CONCLUSION 62

REFERENCES 63

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LIST OF TABLES

TABLE NO. TITLE PAGE NO.

3.1 PHYSICAL STANDARADS OF DRINKING

WATER

25

3.2 CHEMICAL STANDARDS FOR

DRINKING WATER

25

3.3 FUNCTIONS OF WATER TREATMENT

UNIT

26

4.1 DETERMINATION OF PH 41

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LIST OF FIGURES

FIGURE NO. TITLE OF FIGURE PAGE NO.

1.1 HYDROLOGICAL CYCLE IN NATURE 4

3.1 CROSS SECTIONAL VIEW OF RAPID

SAND FILTER

34

3.2 OPERATION OF RAPID SAND FILTER 36

3.3 WATER TREATMENT STEPS 38

3.4 WATER TREATMENT PLANT 38

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LIST OF ABBREVATIONS

BCM Billion cubic meter

CPCB Central pollution control board

WHO World health organization

GIGO Garbage in garbage out

NTU Nephelometric turbidity unit

JTU Jackson turbidity unit

DBP Disinfection by product

ETSW Extended terminal sub fluidization wash filter

FPA Flavor profile analysis

TDS Total dissolved solids

EDTA Ethylene diamine tetra acetic acid

SSF Slow sand filter

EBT Erichrome black T

BOD Biological oxygen demand

DI Deionization

RO Reverse osmosis

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CHAPTER 1

INTRODUCTION

1.1 GENERAL

Water is a precious commodity. Most of the earth water is sea water. About

2.5% of the water is fresh water that does not contain significant levels of

dissolved minerals or salt and two third of that is frozen in ice caps and glaciers.

In total only 0.01% of the total water of the planet is accessible for

consumption. Clean drinking water is a basic human need. Unfortunately, more

than one in six people still lack reliable access to this precious resource in

developing world.

India accounts for 2.45% of land area and 4% of water resources of the world

but represents 16% of the world population. With the present population

growth-rate (1.9 per cent per year), the population is expected to cross the 1.5

billion mark by 2050. The Planning Commission, Government of India has

estimated the water demand increase from 710 BCM (Billion Cubic Meters) in

2010 to almost 1180 BCM in 2050 with domestic and industrial water

consumption expected to increase almost 2.5 times. The trend of urbanization in

India is exerting stress on civic authorities to provide basic requirement such as

safe drinking water, sanitation and infrastructure. The rapid growth of

population has exerted the portable water demand, which requires exploration of

raw water sources, developing treatment and distribution systems.

The raw water quality available in India varies significantly, resulting in

modifications to the conventional water treatment scheme consisting of

aeration, chemical coagulation, flocculation, sedimentation, filtration and

disinfection. The backwash water and sludge generation from water treatment

plants are of environment concern in terms of disposal. Therefore, optimization

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of chemical dosing and filter runs carries importance to reduce the rejects from

the water treatment plants. Also there is a need to study the water treatment

plants for their operational status and to explore the best feasible mechanism to

ensure proper drinking water production with least possible rejects and its

management. With this backdrop, the Central Pollution Control Board (CPCB),

studied water treatment plants located across the country, for prevailing raw

water quality, water treatment technologies, operational practices, chemical

consumption and rejects management.

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. Some of the

common treatment processes used in the past includes Plain sedimentation,

Slow Sand filtration, and Rapid Sand filtration with Coagulation-flocculation

units as essential pretreatment units. Pressure filters and diatomaceous filters

have been used though very rarely. Roughing filters are used, under certain

circumstances, as pretreatment units for the conventional filters. The treatment

processes may need pretreatment like pre-chlorination and aeration prior to

conventional treatment. The pretreatment processes comprising of Coagulation

and Flocculation have been discussed under the main title of Rapid Sand filters.

Detailed discussion on all such aspects as well a recommended unit operations,

is given in the Manual on Water Supply and Treatment (1999 Edition) Ministry

of Urban Development.

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1.2 WATER SOURCES

Before we discuss the types of treatment it is easier to first understand how the

source of water arrives.

1.2.1 HYDROLOGICAL CYCLE TERMS

Precipitation: The process by which atmospheric moisture falls on to the

land or water surface as rain, snow, hail or other forms of moisture.

Infiltration: The gradual flow or movement of water into and through

the pores of the soil.

Runoff: Water that drains from a saturated or impermeable surface into

stream channels or other surface water areas. Most lakes and rivers are

formed this way.

Evaporation: The process by which the water or other liquids become a

gas.

Transpiration: Moisture that will come from plants as a byproduct of

photosynthesis.

Condensation: The collection of the evaporated water in the atmosphere.

Once the precipitation begins water is no longer in its purest form. Water will

be collected as surface supplies or circulate to form in the ground. As it

becomes rain or snow it may be polluted with organisms, organic compounds,

and inorganic compounds. Because of this, we must treat the water for human

consumption.

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Fig 1.1 Hydrological cycle in nature

1.3 SOURCES OF DRINKING WATER

A clean, constant supply of drinking water is essential to every community.

People in large cities frequently drink water that comes from surface water

sources, such as lakes, rivers, and reservoirs. Sometimes these sources are close

to the community. Other times, drinking water suppliers get their water from

sources many miles away. In either case, when you think about where your

drinking water comes from, it's important to consider not just the part of the

river or lake that you can see, but the entire watershed. The watershed is the

land area over which water flows into the river, lake, or reservoir. In rural areas,

people are more likely to drink ground water that was pumped from a well.

These wells tap into aquifers--the natural reservoirs under the earth's surface

that may be only a few miles wide, or may span the borders of many states. As

with surface water, it is important to remember that activities many miles away

from you may affect the quality of ground water. Your annual drinking water

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quality report will tell you where your water supplier gets your water. Your

water will normally contain chlorine and varying amounts of dissolved minerals

including calcium, magnesium and sodium, chlorides, sulphates and

bicarbonates, depending on its source. It is also not uncommon to find traces of

iron, manganese, copper, aluminium, nitrates, insecticides and herbicides

although the maximum amounts of all these substances are strictly limited by

the regulations. These are usually referred to as 'contaminants'. Most of these

substances are of natural origin and are picked up as water passes round the

water cycle. Some are present due to the treatment processes which are used

make the water suitable for drinking and cooking. The water will also contain a

relatively low level of bacteria which is not generally a risk to health.

1.4 WATER QUALITY

Samples of raw and treated water will be taken at regular intervals for analysis.

In a large Waterworks with its own laboratory, sampling will almost certainly

be carried out daily, since the effluent analysis constitutes the only certain check

that the filter is operating satisfactorily and the raw water analysis provides

what is possibly the only indication of a change in quality that might adversely

affect the efficiency of treatment. In case of small plants with no laboratory

facilities, an attempt should be made to conduct sampling on regular basis. Field

testing equipment may be used to measure water quality.

Water is colorless, tasteless, and odorless. It is an excellent solvent that can

dissolve most minerals that come in contact with it. Therefore, in nature, water

always contains chemicals and biological impurities i.e. suspended and

dissolved inorganic and organic compounds and micro organisms. These

compounds may come from natural sources and leaching of waste deposits.

However, Municipal and Industrial wastes also contribute to a wide spectrum of

both organic and inorganic impurities. Inorganic compounds, in general,

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originate from weathering and leaching of rocks, soils, and sediments, which

principally are calcium, magnesium, sodium and potassium salts of bicarbonate,

chloride, sulfate, nitrate, and phosphate. Besides, lead, copper, arsenic, iron and

manganese may also be present in trace amounts. Organic compounds originate

from decaying plants and animal matters and from agricultural runoffs, which

constitute natural humic material to synthetic organics used as detergents,

pesticides, herbicides, and solvents. These constituents and their concentrations

influence the quality and use of the natural water resource. Primary water

quality criteria for designated best classes (for drinking water, outdoor bathing,

propagation of wildlife & fisheries, irrigation, industrial cooling) have been

developed by the Central Pollution Control Board. The presence of

contaminants and the characteristics of water are used to indicate the quality of

water. These water quality indicators can be categorized as:

Biological: bacteria, algae

Physical: temperature, turbidity and clarity, color, salinity, suspended

solids, dissolved solids

Chemical: pH, dissolved oxygen, biological oxygen demand, nutrients

(including nitrogen and phosphorus), organic and inorganic compounds

(including toxicants)

Aesthetic: odors, taints, color, floating matter

Radioactive: alpha, beta and gamma radiation emitters

Groundwater is often high in mineral content and can contain dissolved gases

such as methane and hydrogen sulphide. Surface water comes from two very

different sources: rivers, and lakes. Surface waters in their natural state are

potentially unsafe for human consumption because they are constantly exposed

to contamination from human, animal, industrial wastes, and from natural

sources such as soil, vegetation, and algae. Rivers can be a difficult source of

water to treat as the turbidity can change rapidly and dramatically. Lakes are

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less prone to changes in turbidity as suspended matter tends to settle to the

bottom, however, ice cover can cause degradation along with taste and odor

problems in water quality. All natural waters contain some turbidity and color.

Turbidity is caused by very finely divided particles held in suspension. This

gives the water a cloudy appearance. Color is caused by dissolved and colloidal

particles, a result of organic or inorganic material in the water.

1.5 DEFINITION OF POTABLE WATER

Potable or drinking water can be defined as the water delivered to the

consumers that can be safely used for drinking, cooking, and washing. A

certification by licensed professional engineer specialized in the field is no

longer sufficient. The public health aspects are of such importance and

complexity that the health authority having jurisdiction in the community now

reviews inspects, samples, monitors, and evaluates on continuing basis the

water supplied to the community using constantly updated drinking water

standards. Such public health control helps to guarantee a continuous supply of

water maintained within safe limits.

1.6 REQUIREMENTS OF WATER FOR DOMESTIC USE

It should be colourless and sparkling clear. It must be free from solid in

suspension and must not deposit a sediment on standing.

It should be of good taste, free from odour.

It should be reasonable soft

It should be plentiful and cheap.

It should be free from disease producing bacteria.

It should be free from objectionable dissolved gases, such as sulphuretted

hydrogen.

It should be free from harmful salts.

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It should be free from objectionable minerals such as iron, manganese,

lead, arsenic, and other poisonous material.

It should not lead to scale formation.

It should be free from radioactive substances such as radium, stronsium

etc.

1.7 NEED FOR WATER TREATMENT

Due to increased number of micro-organisms, pathogens and harmful bacterias,

There is a need of water treatment which includes many water treatment

methods for purification purposes. These harmful micro-organisms leads to

many water borne diseases.

1.7.1 WATER BORNE DISEASES

Water borne diseases are those diseases which are caused due to ingestion of

water contaminated by human or animal excrement, which contain pathogenic

microorganisms. Water borne diseases include cholera, typhoid, amoebic and

bacillary dysentery and other diarrheal diseases. In addition, water borne

diseases can be caused by the pollution of water with chemicals that have an

adverse effect on health.

The chemicals included are

Arsenic

Fluoride

Nitrates from fertilizers

Carcinogenic pesticides (DDT)

Lead (from pipes)

Heavy Metals

Various water borne diseases are listed below

Cholera

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Typhoid

Bacillary dysentery

Infectious hepatitis

Giardiasis

To make water free from these harmful bacteria and pathogens we need to treat

water for drinking purposes.

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CHAPTER 2

LITERATURE REVIEW

The main aim of water treatment and drinking water distribution is the

protection of health. Another important aim is to ensure access to the high-

quality drinking water. Epidemiological studies also suggest that drinking water

can be significant source of calcium. Calcium rich mineral water provides over

one-third of the recommended dietary of this mineral in adults. However

receiving calcium is important at all ages, but the need for Ca2+ is higher

during childhood, fetal growth, pregnancy and lactation (Azoulay et al., 2001).

Upwards of 99 % of total calcium is found in bones and teeth, where operate

like important structural component. Others calcium´s functions belong to

metabolic processes, where serve as signal for basic physiological processes, for

example vascular contraction. It influences on blood coagulation, because

cooperation in transformation fibrinogen on fibrin. Calcium ions influence

muscles contractions and nervous transmission. Calcium ions also are very

important on activation and elimination of various hormones secretion (e.g.

insulin), as well various enzymes (Melicherčík and Melicherčíková, 2010).

Based on the World Health Organization (WHO) findings, next to fluoride, for

calcium and magnesium are evident the strongest health benefits associated with

their presence in drinking-water (Cotruvo et al., 2009, Nordin 2010).

Japanese chemist Kobayashi described the relationship between water

hardness and the incidence of vascular diseases in 1957. His claims were based

on epidemiological analysis. Higher mortality rates from cerebrovascular

diseases in the areas of Japanese rivers with more acid (i.e. softer) water were

compared to those with more alkaline (i.e. harder) water used for drinking

purposes (Kožíšek, 2000).

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The contributions of drinking water to nutritional status also depend on water

consumption. It is highly variable depending on behavioural factors and

environmental conditions. Individuals with the greatest relative consumption of

water include infants, residents in hot climates, and individuals engaged in

strenuous physical activity. Consumption of moderately hard water containing

typical amounts of calcium and magnesium (1.6—2.2 mmol.l–1) provides an

important incremental percentage of their daily intake. Moreover, hard water

(>2.2 mmol.l–1) can reduce the losses of calcium, magnesium and other

essential minerals from food during cooking. If low mineralized (0—1.6

mmol.l–1) water is used for food and beverage production, reduced

concentrations of Ca and Mg, and other essential elements would also occur in

those products (Monarca et al., 2009, Poláček et al., 2010).

The reason of low mineral content in source water is that water is formed in the

poor soluble mineral geological structures. If the content of dissolved inorganic

salts in nature water is very low, it is necessary to supplement them in the

process of water treatment technology. Water treatment can affect the content of

minerals, and thus the total intake of calcium and magnesium. Recarbonization

process aims to increase water hardness (calcium and manesium content

increases) and is appropriate for very soft water treatment. Very soft water is

corrosive to plumbing resulting in the damage of the systems and potentially

increases content of metals such as copper and lead in drinking water.

Endurance of water facilities is determined by their resistance to corrosion. In

order to limit the corrosion of steel and concrete pipes, it is desirable to acid

neutralizing capacity must be reached 1.4 to 2.1 mmol.l–1. In this value is

applied inhibitory effect of calcium, bicarbonate and carbonate ions, which

means that the inner surface of the pipe begins to create protective carbonate

layer (Cotruvo et al., 2005; Yang et al., 2002; Olejko, 1999).

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The main aim of this contribution was to analyze raw surface source water

quality and prepared drinking water quality. The procedure of lab-scale

verification of recarbonization process using lime and carbon dioxide was

chosen. The lime reacts with CO2 to form calcium bicarbonate. Another aim

was to investigate the influence of recarbonization process on efficiency of

water treatment processes in lab-scale.

Rietveld et al. and Bookslooper et al. reported that although drinking water

treatment plants are already functioning for more than a century and in the last

decades the operation has become more complex. Because of more stringent

regulations, the plants efficient or effective use of” your water treatment plant

have to produce water of a better quality and, therefore different treatment

processes are placed in series to meet the guidelines. Because of frequent job

rotation and increased automation, experienced operators who are able to

interact with the processes are nowadays scared. Therefore, it is impossible to

compensate with the complexity of the operation.

Optimization of Conventional Drinking Water Treatment Plant: As a

“treatment train”, conventional drinking water Optimization of conventional

drinking water treatment plant compounds of many series stages and units

(coagulation-flocculation, sedimentation, filtration and disinfection), which on

each unit should be optimized on its design, process and operation.

Banff et al. defined optimization of conventional drinking water treatment plant

means “to attain the most efficient or effective use of” your water treatment

plant which consist of some principles, there are; achievement of consistently

high quality finished water on a continuous basis; and the importance to focus

on overall to interact with the process of plant performance, instead of focusing

too much on individual processes. Approaches to conventional drinking water

treatment plant optimization should be mostly common sensed, be organized

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and get into the facts first. Systematic gathering of information about plant

performance are need, such as: data trending and analysis, check plant design

criteria against actual track chemical dosing versus performance, field

measurements and visual observations. The data trending and analysis should

remind of the “GIGO” (Garbage In Garbage Out) principles and also correlate

to plant operating parameters trends against each other to look for valuable

information.

Rietveld et al. reported that in drinking water pumps, it is particular importance

to determine the water quality indicators for good operation. In the reported

research the objective was to focus on the instantaneous mixing and static

mixers which can lose target water quality parameters and direct indicators for

the performance. In the operational practice of drinking water treatment,

however, derived indicators are often used. In softening, for example, pH is

measured in the effluent as an indicator for performance, while the main

purpose of softening is to decrease the calcium concentration. Specific

questions and issues to be addressed by the model were linked to the different

interest group.

Optimization of Coagulation and Flocculation: Water is treated with

compounds that make small suspended particles stick together and settle out of

the water. Flocculation refers to water treatment processes that combine or

coagulate small particles into larger particles, which settle out of the water as

sediment.

Banff et al. also presented that optimization of coagulation and flocculation

should be have many considerations, such as: chemical dosing trends,

coagulation and flash mixing, colloid stability, selecting and evaluating

coagulant, operational and design factors affecting trends optimization

consist of; understand how chemical dosing impacts plant performance and

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look for over-or under-dosing, which it track to relation between; raw water

turbidity versus coagulant dose, raw and coagulated water pH and alkalinity

versus. Insufficient air loading is set 15 min total. Fourth, maximum coagulant

dose and clarified water turbidity versus coagulant dosage.

Franceschiet al. and Zularizam et al. reported that in some cases, the addition

of mineral salts or organic compounds causes the agglomeration of these

particles, allowing their elimination by decantation or filtration in most water

treatment plants, the minimal coagulant concentration and the residual turbidity

of the water are determined by the Jar-Test technique. In their paper a

systematic study of the influence of raw water quality and operating conditions

on the effectiveness of the coagulation-flocculation process using aluminum

sulphate is presented.

In the other research, Husseinet al. reported that the main possible applications

of ozone are preoxidation, intermediate oxidation and final oxidation.

Generally pre-ozonation decreases color, turbidity, tastes and odors. This

treatment is generally used to enhance the coagulation. Preozonation and

coagulation processes were optimized for total organic carbon removal and

bromate control.

Optimization of Sedimentation/Clarifier: Water is passed through a settling

basin or clarifier allowing time for mud, sand, metals and other sediment to

settle out. This particle conglomerate is removed from the water prior to

filtration.

Banff et al. presented that optimization of sedimentation/clarifier it should

be presented by many conditions, there are; consistently result less than 2 NTU,

stable when faced with rapidly changing water quality conditions, produces

sludge of consistent quality, sedimentation: 0.5-1% of Total Solid (TS).

Common causes for poor clarifier performance are: density currents due to

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temperature variation within basins, excessive operating loading rates, entrained

air-incidental flotation, poor hydraulics due to uneven inlet flow splitting.

Optimization of Filtration: Water is passed through a dual media (sand and

anthracite) filter, which removes many remaining pollutants. Many water

treatment facilities use filtration to remove all particles from the water.

Banff et al. presented that a “good” filter performance should be presented by

many conditions, such as; consistently less than 0.3 NTU, particle counts

less than 50 particles/mL, long and predictable filter runs (24+hours), minimal

premature particle breakthrough. Poor performance can be difficult to rectify,

but many issues can be resolved with simple fixes. He also presented that

“good” filter design should be presented by many conditions, most efficient

media design has largest media at the top and the finest at the bottom, however,

backwashing immediately re-classifies bed to place the finest grains at the

surface, therefore use multi-media to mimic this effect, with coarse grains in the

top layer to trap solid sand finer layer below for polishing.

In the other research James reported that the increased passage of particles and

microorganisms through granular media filters immediately following

backwashing is a common problem known to the water treatment community

as filter ‘‘ripening’’ or maturation. While several strategies have been

developed over the years to reduce the impact of this vulnerable period of the

filtration cycle on finished water quality, this research involves a recently

developed filter backwashing strategy called the Extended Terminal Sub

fluidization Wash Filter (ETSW). Their research concludes that optimality of

the coagulation process was also shown to influence magnitude of filter

ripening particle passage. Extended Wash, generally falling out of favour, but

common in Terminal Sub fluidization Wash on filtration is a method of

terminating the backwash cycle with a sub fluidization.

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Optimization of Disinfection: Chlorine is added to the water to kill and/or

inactivate any remaining pathogens. Fluoride is added to prevent tooth decay

and a rust inhibitor is added to preserve the pipes that deliver the water to

homes and businesses. Water is often disinfected before it enters the distribution

system to ensure that potentially dangerous microbes are killed.

Nikolaou et al. and Chaiket et al. reported that occurrence of disinfection by-

products (DBPs) in drinking water has been an issue of major concern due to

their adverse health effects. Application of disinfection processes during water

treatment leads to the formation of disinfection by-products. The development

and optimization of analytical methods for the determination of Disinfection by

Products in water are key points in order to estimate human exposure after water

treatment.

In the other research Huseyin et al. reported that much attention that the

purpose of intermediate oxidation is to degrade toxic micro pollutants and to

remove chlorinated by-product precursors.

Remarks for Optimization of Water Treatment Plant: Based on many

articles which discuss about optimization of particles of water treatment plant,

their researches have given us the basic scientific informations. From

Franceschi et al, we could conclude on flocculation-coagulation process that;

optimization of the residual turbidity needs to retain only a few parameters

as opposed to the optimization of minimally added Aluminium Sulfate

concentration.; there is an antagonistic influence of the different parameters

on the two studied responses turbidity and aluminium sulfate so it is impossible

to simultaneously optimize both of them. We also could conclude from Huseyin

et al. that after pre-ozonation, alum coagulation was applied and it was found

that pre-ozonation enhanced the efficiency of alum coagulation; however

Bromate removal was insignificant at the optimum alum concentration.

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James found that Extended Terminal Sub fluidization Wash (ETSW) on

filtration was shown to remove significantly greater quantities of backwash

remnant particles thereby reducing the magnitude of filter ripening turbidity and

particle count spikes. Optimum Extended Terminal Sub fluidization Wash flow

rates were determined for deep-bed anthracite and granular activated carbon

filters herein by monitoring filter effluent turbidities. Extended Terminal Sub

fluidization Wash was found to be equally effective for biological and

conventional deep-bed anthracite filters.

This paper discusses dissolved air flotation (DAF) applied to drinking water

treatment. It was first applied to drinking water treatment in the late 1960s in

Scandinavia and South Africa. The process is particularly efficient in removing

low density particles and flocs. DAF is a good clarification process for treating

supplies of low to moderate turbidity, and those containing algae and natural

color. It has found increasing favor over sedimentation processes for treating

these type supplies, and it is now widely used world-wide. The DAF reactor has

two functions, to provide collisions or contact opportunities between air bubbles

and flocs, and to provide removal of the floc-bubble aggregates. The paper

describes bubble properties, bubble suspension concentrations, and bubble

characteristics, and contact zone model. Model variables are discussed

beginning with the role of pretreatment coagulation chemistry and flocculation

for successful bubble attachment and collisions of flocs with bubbles. The

importance of bubble size and concentrations is addressed and the separation

zone modeling is also summarized. Rise velocities of floc-bubble aggregates are

compared to separation zone theory and hydraulics. Some applications are

presented on the removals of algae and protozoa pathogens by DAF, and on

recent trends of designing DAF plants with short flocculation times and high

hydraulic loadings.

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2.1 OBJECTIVES OF PROJECT

1. Water must be distributed in sufficient quantity and pressure at all times.

2. Storage capacity at the source as well as at intermediate points of the

distribution system, should maintain the water pressure and flow within

the conventional limits.

3. Maintenance of distribution system must be planned, implemented and

controlled at the same optimum level contemplated for the design,

construction and operation of the treatment facilities and the projection of

the water source.

4. Contaminants must be eliminated or reduced to safe level to minimize

menacing waterborne diseases and formation of long-term or chronic

injurious health effects.

5. Water quality cannot be monitored without adequate laboratories

facilities.

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of disease producing pathogenic bacteria. Pathogenic organisms cause water

borne diseases, and many non pathogenic bacteria such as E.Coli, a member

of coliform group, also live in the intestinal tract of human

beings. Coliform itself is not a harmful group but it has more resistance to

adverse condition than any other group. So, if it is ensured to minimize the

number of coliforms, the harmful species will be very less. So, coliform

group serves as indicator of contamination of water with sewage and

presence of pathogens.

The methods to estimate the bacterial quality of water are:

Standard Plate Count Test

Most Probable Number

Membrane Filter Technique

3.2 PHYSICAL CHARACTERISTICS OF WATER

Various physical properties of water are discussed below

3.2.1 Turbidity

If a large amount of suspended solids are present in water, it will appear turbid

in appearance. The turbidity depends upon fineness and concentration of

particles present in water. Originally turbidity was determined by measuring

the depth of column of liquid required to cause the image of a candle flame at

the bottom to diffuse into a uniform glow. This was measured by Jackson

candle turbidity meter. The calibration was done based on suspensions of silica

from Fuller's earth. The depth of sample in the tube was read against the part per

million (ppm) silica scales with one ppm of suspended silica called one Jackson

Turbidity unit (JTU). Because standards were prepared from materials found in

nature such as Fuller's earth, consistency in standard formulation was difficult to

achieve. These days turbidity is measured by applying Nephelometry, a

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technique to measure level of light scattered by the particles at right angles to

the incident light beam. The scattered light level is proportional to the particle

concentration in the sample. The unit of expression is Nephelometric Turbidity

Unit (NTU). The IS values for drinking water is 10 to 25 NTU.

3.2.2 Colour

Dissolved organic matter from decaying vegetation or some inorganic materials

may impart colour to the water. It can be measured by comparing the colour of

water sample with other standard glass tubes containing solutions of different

standard colour intensities. The standard unit of colour is that which is produced

by one milligram of platinum cobalt dissolved in one litre of distilled water. The

IS value for treated water is 5 to 25 cobalt units.

3.2.3 Taste and odour

Odour depends on the contact of a stimulating substance with the appropriate

human receptor cell. Most organic and some inorganic chemicals, originating

from municipal or industrial wastes, contribute taste and odour to the water.

Taste and odour can be expressed in terms of odour intensity or threshold

values.

A new method to estimate taste of water sample has been developed based on

flavour known as 'Flavour Profile Analysis' (FPA). The character and intensity

of taste and odour discloses the nature of pollution or the presence of

microorganisms.

3.2.4 Temperature

The increase in temperature decreases palatability, because at elevated

temperatures carbon dioxide and some other volatile gases are expelled. The

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ideal temperature of water for drinking purposes is 5 to 12 °C - above 25 °C,

water is not recommended for drinking.

3.3CHEMICAL CHARACTERISTICS OF WATER

Various chemical characteristics of water are discussed below

3.3.1 pH

pH value denotes the acidic or alkaline condition of water. It is expressed on a

scale ranging from 0 to 14, which is the common logarithm of the reciprocal of

the hydrogen ion concentration. The recommended pH range for treated

drinking waters is 6.5 to 8.5.

3.3.2 Acidity

The acidity of water is a measure of its capacity to neutralize bases. Acidity of

water may be caused by the presence of uncombined carbon dioxide, mineral

acids and salts of strong acids and weak bases. It is expressed as mg/L in terms

of calcium carbonate. Acidity is nothing but representation of carbon dioxide or

carbonic acids. Carbon dioxide causes corrosion in public water supply systems.

3.3.3 Alkalinity

The alkalinity of water is a measure of its capacity to neutralise acids. It is

expressed as mg/L in terms of calcium carbonate. The various forms of

alkalinity are (a) hydroxide alkalinity, (b) carbonate alkalinity, (c) hydroxide

plus carbonate alkalinity, (d) carbonate plus bicarbonate alkalinity, and (e)

bicarbonate alkalinity, which is useful mainly in water softening and boiler feed

water processes. Alkalinity is an important parameter in evaluating the optimum

coagulant dosage.

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3.3.4 Hardness

If water consumes excessive soap to produce lather, it is said to be hard.

Hardness is caused by divalent metallic cations. The principal hardness causing

cations are calcium, magnesium, strontium, ferrous and manganese ions. The

major anions associated with these cations are sulphates, carbonates,

bicarbonates, chlorides and nitrates. The total hardness of water is defined as the

sum of calcium and magnesium concentrations, both expressed as calcium

carbonate, in mg/L. Hardness are of two types, temporary or carbonate hardness

and permanent or non carbonate hardness. Temporary hardness is one in which

bicarbonate and carbonate ion can be precipitated by prolonged boiling. Non-

carbonate ions cannot be precipitated or removed by boiling, hence the term

permanent hardness. IS value for drinking water is 300 mg/L as CaCO3.

3.3.5 Chlorides

Chloride ion may be present in combination with one or more of the cations of

calcium, magnesium, iron and sodium. Chlorides of these minerals are present

in water because of their high solubility in water. Each human being consumes

about six to eight grams of sodium chloride per day, a part of which is

discharged through urine and night soil. Thus, excessive presence of chloride in

water indicates sewage pollution. IS value for drinking water is 250 to 1000

mg/L.

3.3.6 Sulphates

Sulphates occur in water due to leaching from sulphate mineral and oxidation of

sulphides. Sulphates are associated generally with calcium, magnesium and

sodium ions. Sulphate in drinking water causes a laxative effect and leads to

scale formation in boilers. It also causes odour and corrosion problems under

aerobic conditions. Sulphate should be less than 50 mg/L, for some industries.

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Desirable limit for drinking water is 150 mg/L. May be extended upto 400

mg/L.

3.3.7 Iron

Iron is found on earth mainly as insoluble ferric oxide. When it comes in

contact with water, it dissolves to form ferrous bicarbonate under favourable

conditions. This ferrous bicarbonate is oxidised into ferric hydroxide, which is a

precipitate. Under anaerobic conditions, ferric ion is reduced to soluble ferrous

ion. Iron can impart bad taste to the water, causes discolouration in clothes and

incrustations in water mains. IS value for drinking water is 0.3 to 1.0 mg/L.

3.3.8 Solids

The sum total of foreign matter present in water is termed as 'total solids'. Total

solids are the matter that remains as residue after evaporation of the sample and

its subsequent drying at a defined temperature (103 to 105 °C).Total solids

consist of volatile (organic) and non-volatile (inorganic or fixed) solids. Further,

solids are divided into suspended and dissolved solids. Solids that can settle by

gravity are settleable solids. The others are non-settleable solids. IS acceptable

limit for total solids is 500 mg/L and tolerable limit is 3000 mg/L of dissolved

limits.

3.3.9 Nitrates

Nitrates in surface waters occur by the leaching of fertilizers from soil during

surface run-off and also nitrification of organic matter. Presence of high

concentration of nitrates is an indication of pollution. Concentration of nitrates

above 45 mg/L causes a disease methemoglobinemia. IS value is 45 mg/L.

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Table 3.1 Physical Indian standards for drinking water

Parameter Desirable–tolerable

limits

If no alternative source

available, limits extends upto

Turbidity (NTU unit) <10 25

Colour (Hazen scale) <10 50

Taste and odour Un-objectionable Un-objectionable

Table 3.2 Chemical standards for drinking water

Parameter Desirable-

tolerable limit

If no alternative source

available, limits exceeds upto

Ph 7.0-8.5 6.5-9.2

Total dissolved solids (mg/l) 500-1500 3000

Total hardness(mg/l) as

CaCO3

200-300 600

Chlorides (mg/l) as Cl 200-250 1000

Sulphates (mg/l) as SO4 150-200 400

Fluorides (mg/l) as F 0.6-1.2 1.5

Nitrates (mg/l) as NO3 45 45

Calcium (mg/l) as Ca 75 200

Iron (mg/l) as Fe 0.1-0.3 1.0

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The typical functions of each unit operations are given in the following table

Table 3.3 Functions of water treatment unit

Unit treatment Function (removal)

Aeration, chemical use Colour, odour, taste

Screening Floating matter

Chemical methods Iron, manganese etc

Softening Hardness

Sedimentation Suspended matter

Coagulation Suspended matter, a part of colloidal matter

and bacteria

Filtration Remaining colloidal dissolved matter

Disinfection Pathogenic bacteria, organic matter,

reducing substance

3.4 WATER TREATMENT METHODS

There are various water treatment methods for the purification of water. Some

of these methods are discussed as below.

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3.4.1 AERATION

Aeration removes odour and tastes due to volatile gases like hydrogen

sulphide and due to algae and related organisms.

Aeration also oxidise iron and manganese, increases dissolved oxygen

content in water, removes CO2 and reduces corrosion and removes

methane and other flammable gases.

Principle of treatment underlines on the fact that volatile gases in water

escape into atmosphere from the air-water interface and atmospheric

oxygen takes their place in water, provided the water body can expose

itself over a vast surface to the atmosphere. This process continues until

an equilibrium is reached depending on the partial pressure of each

specific gas in the atmosphere.

It removes hydrogen sulphide, and hence odour due to this is also

removed.

It decreases the carbondioxide content of water and thereby reduces its

corrosiveness and raises it ph value.

It is also used for mixing chemicals with water, as in the aeromix process

and in the use of diffused compressed air.

3.4.2 TYPES OF AERATORS

Gravity aerators

Fountain aerators

Diffused aerators

Mechanical aerators

1. Gravity aerators

In gravity aerators, water is allowed to fall by gravity such that a large

area of water is exposed to atmosphere, sometimes aided by turbulence.

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2. Fountain aerators

These are also known as spray aerators with special nozzles to produce a

fine spray. Each nozzle is 2.5 to 4 cm diameter discharging about 18 to 36

l/h. Nozzle spacing should be such that each m3 of water has aerator area

of 0.03 to 0.09 m2 for one hour.

3. Diffused aerators

It consists of a tank with perforated pipes, tubes or diffuser plates, fixed

at the bottom to release fine air bubbles from compressor unit. The tank

depth is kept as 3 to 4 m and tank width is within 1.5 times its depth. If

depth is more, the diffusers must be placed at 3 to 4 m depth below water

surface. Time of aeration is 10 to 30 min and 0.2 to 0.4 litres of air is

required for 1 litre of water.

4. Mechanical aerators

Mixing paddles as in flocculation are used. Paddles may be either

submerged or at the surface.

3.5 SETTLING

Solid liquid separation process in which a suspension is separated into two

phases

Clarified supernatant leaving the top of the sedimentation tank

(overflow).

Concentrated sludge leaving the bottom of the sedimentation tank

(underflow).

3.5.1 PURPOSE OF SETTLING

To remove coarse dispersed phase.

To remove coagulated and flocculated impurities.

To remove precipitated impurities after chemical treatment.

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To settle the sludge (biomass) after activated sludge process / tricking

filters.

3.5.2 PRINCIPLE OF SETTLING

Suspended solids present in water having specific gravity greater than

that of water tend to settle down by gravity as soon as the turbulence is

retarded by offering storage.

Basin in which the flow is retarded is called settling tank.

Theoretical average time for which the water is detained in the settling

tank is called the detention period.

3.5.3 TYPES OF SETTLING

Type I: Discrete particle settling - Particles settle individually without

interaction with neighboring particles.

Type II: Flocculent Particles – Flocculation causes the particles to

increase in mass and settle at a faster rate.

Type III: Hindered or Zone settling –The mass of particles tends to settle

as a unit with individual particles remaining in fixed positions with

respect to each other.

Type IV: Compression – The concentration of particles is so high that

sedimentation can only occur through compaction of the structure.

3.5.4 TYPES OF SETTLING TANKS

Sedimentation tanks may function either intermittently or continuously.

The intermittent tanks also called quiescent type tanks are those which

store water for a certain period and keep it in complete rest. In a

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continuous flow type tank, the flow velocity is only reduced and the

water is not brought to complete rest as is done in an intermittent type.

Settling basins may be either long rectangular or circular in plan. Long

narrow rectangular tanks with horizontal flow are generally preferred to

the circular tanks with radial or spiral flow.

3.6 COAGULATION AND FLOCCULATION

Colloidal particles are difficult to separate from water because they do

not settle by gravity and are so small that they pass through the pores of

filtration media.

To be removed, the individual colloids must aggregate and grow in size.

The aggregation of colloidal particles can be considered as involving two

separate and distinct steps:

i. Particle transport to effect interparticle collision.

ii. Particle destabilization to permit attachment when contact

occurs.

Transport step is known as flocculation whereas coagulationis the overall

process involving destabilization and transport.

3.6.1 FLOCCULATION

Flocculation is stimulation by mechanical means to agglomerate destabilised

particles into compact, fast settleable particles (or flocs). Flocculation or gentle

agitation results from velocity differences or gradients in the coagulated water,

which causes the fine moving, destabilized particles to come into contact and

become large, readily settle able flocs. It is a common practice to provide an

initial rapid (or) flash mix for the dispersal of the coagulant or other chemicals

into the water. Slow mixing is then done, during which the growth of the floc

takes place.

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Rapid or flash: mixing is the process by which a coagulant is rapidly and

uniformly dispersed through the mass of water. This process usually

occurs in a small basin immediately preceding or at the head of the

coagulation basin. Generally, the detention period is 30 to 60 seconds and

the head loss is 20 to 60 cms of water. Here colloids are destabilised and

the nucleus for the floc is formed.

Slow mixing: brings the contacts between the finely divided destabilized

matter formed during rapid mixing.

3.6.2 MECHANISM OF FLOCCULATION

Gravitational flocculation: Baffle type mixing basins are examples of

gravitational flocculation. Water flows by gravity and baffles are

provided in the basins which induce the required velocity gradients for

achieving floc formation.

Mechanical flocculation: Mechanical flocculators consists of revolving

paddles with horizontal or vertical shafts or paddles suspended from

horizontal oscillating beams, moving up and down.

3.6.3 COAGULATION IN WATER TREATMENT

Salts of Al(III) and Fe(III) are commonly used as coagulants in water and

wastewater treatment.

When a salt of Al(III) and Fe(III) is added to water, it dissociates to yield

trivalent ions, which hydrate to form aquometal complexes

Al(H2O)63+ and Fe(H2O)6

3+. These complexes then pass through a series

of hydrolytic reactions in which H2O molecules in the hydration shell are

replaced by OH- ions to form a variety of soluble species such as

Al(OH)2+ and Al(OH)2+. These products are quite effective as coagulants

as they adsorb very strongly onto the surface of most negative colloids.

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Commonly used coagulants are aluminum sulphate or alum, chlorinated

copperas, ferrous sulphate and lime, magnesium carbonate, sodium

aluminate.

3.7 FILTERATION

The resultant water after sedimentation will not be pure, and may contain some

very fine suspended particles and bacteria in it. To remove or to reduce the

remaining impurities still further, the water is filtered through the beds of fine

granular material, such as sand, etc. The process of passing the water through

the beds of such granular materials is known as Filtration.

3.7.1 FILTERATION MECHANISM

There are four basic mechanism

Sedimentation:The mechanism of sedimentation is due to force of

gravity and the associate settling velocity of the particle, which causes it

to cross the streamlines and reach the collector.

Interception: Interception of particles is common for large particles. If

a large enough particle follows the streamline that lies very close to the

media surface it will hit the media grain and be captured.

Brownian diffusion: Diffusion towards media granules occurs for very

small particles, such as viruses. Particles move randomly about within

the fluid, due to thermal gradients. This mechanism is only important for

particles with diameters < 1 micron.

Inertia: Attachment by inertia occurs when larger particles move fast

enough to travel off their streamlines and bump into media grains.

3.7.2 FILTER MATERIALS

Sand: Sand, either fine or coarse, is generally used as filter media. The

size of the sand is measured and expressed by the term called effective

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size. The effective size, i.e. D10 may be defined as the size of the sieve in

mm through which ten percent of the sample of sand by weight will pass.

The uniformity in size or degree of variations in sizes of particles is

measured and expressed by the term called uniformity coefficient. The

uniformity coefficient, i.e. (D60/D10) may be defined as the ratio of the

sieve size in mm through which 60 percent of the sample of sand will

pass, to the effective size of the sand.

Gravel: The layers of sand may be supported on gravel, which permits

the filtered water to move freely to the under drains, and allows the wash

water to move uniformly upwards.

Other materials: Instead of using sand, sometimes, anthrafilt is used as

filter media. Anthrafilt is made from anthracite, which is a type of coal-

stone that burns without smoke or flames. It is cheaper and has been able

to give a high rate of filtration.

3.7.3 TYPES OF FILTER

Slow sand filter: They consist of fine sand, supported by gravel. They

capture particles near the surface of the bed and are usually cleaned by

scraping away the top layer of sand that contains the particles.

Rapid-sand filter: They consist of larger sand grains supported by

gravel and capture particles throughout the bed. They are cleaned by

backwashing water through the bed to 'lift out' the particles.

Multimedia filters: They consist of two or more layers of different

granular materials, with different densities. Usually, anthracite coal,

sand, and gravel are used. The different layers combined may provide

more versatile collection than a single sand layer. Because of the

differences in densities, the layers stay neatly separated, even after

backwashing.

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Fig 3.1 Cross sectional view of rapid filter

3.7.4 PRINCIPLE OF SLOW SAND FILTER

In a slow sand filter impurities in the water are removed by a combination

of processes: sedimentation, straining, adsorption, and chemical and

bacteriological action.

During the first few days, water is purified mainly by mechanical and

physical-chemical processes. The resulting accumulation of sediment and

organic matter forms a thin layer on the sand surface, which remains

permeable and retains particles even smaller than the spaces between the

sand grains.

As this layer develops, it becomes living quarters of vast numbers of

micro-organisms which break down organic material retained from the

water, converting it into water, carbon dioxide and other oxides.

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Most impurities, including bacteria and viruses, are removed from the

raw water as it passes through the filter skin and the layer of filter bed

sand just below. The purification mechanisms extend from the filter skin

to approx. 0.3-0.4 m below the surface of the filter bed, gradually

decreasing in activity at lower levels as the water becomes purified and

contains less organic material.

When the micro-organisms become well established, the filter will work

efficiently and produce high quality effluent which is virtually free of

disease carrying organisms and biodegradable organic matter. They are

suitable for treating waters with low colors, low turbidities and low

bacterial contents.

3.7.5 SLOW SAND FILTER VS RAPID SAND FILTER

Base material: In SSF it varies from 3 to 65 mm in size and 30 to 75 cm

in depth while in RSF it varies from 3 to 40 mm in size and its depth is

slightly more, i.e. about 60 to 90 cm.

Filter sand: In SSF the effective size ranges between 0.2 to 0.4 mm and

uniformity coefficient between 1.8 to 2.5 or 3.0. In RSF the effective size

ranges between 0.35 to 0.55 and uniformity coefficient between 1.2 to

1.8.

Rate of filtration: In SSF it is small, such as 100 to 200 L/h/sq.m of

filter area while in RSF it is large, such as 3000 to 6000 L/h/sq.m of filter

area.

Flexibility: SSF are not flexible for meeting variation in demand whereas

RSF are quite flexible for meeting reasonable variations in demand.

Post treatment required: Almost pure water is obtained from SSF.

However, water may be disinfected slightly to make it completely safe.

Disinfection is a must after RSF.

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Method of cleaning: Scrapping and removing of the top 1.5 to 3 cm

thick layer is done to clean SSF. To clean RSF, sand is agitated and

backwashed with or without compressed air.

Loss of head: In case of SSF approx. 10 cm is the initial loss, and 0.8 to

1.2m is the final limit when cleaning is required. For RSF 0.3m is the

initial loss, and 2.5 to 3.5m is the final limit when cleaning is required.

Fig 3.2 Operation of rapid sand filter

3.8 DISINFECTION

The filtered water may normally contain some harmful disease producing

bacteria in it. These bacteria must be killed in order to make the water safe for

drinking. The process of killing these bacteria is known as Disinfection or

Sterilization.

3.8.1 METHODS OF DISINFECTION

Boiling: The bacteria present in water can be destroyed by boiling it for a

long time. However it is not practically possible to boil huge amounts of

water. Moreover it cannot take care of future possible contaminations.

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Treatment with Excess Lime: Lime is used in water treatment plant for

softening. But if excess lime is added to the water, it can in addition, kill

the bacteria also. Lime when added raises the pH value of water making it

extremely alkaline. This extreme alkalinity has been found detrimental to

the survival of bacteria. This method needs the removal of excess lime

from the water before it can be supplied to the general public. Treatment

like recarbonation for lime removal should be used after disinfection.

Treatment with Ozone: Ozone readily breaks down into normal oxygen,

and releases nascent oxygen. The nascent oxygen is a powerful oxidising

agent and removes the organic matter as well as the bacteria from the

water.

Chlorination: The germicidal action of chlorine is explained by the

recent theory of enzymatic hypothesis, according to which the chlorine

enters the cell walls of bacteria and kill the enzymes which are essential

for the metabolic processes of living organisms.

3.8.2 FORMS OF APPLICATION OF CHLORINE

Chlorine may be applied to water in one of the following forms

As bleaching powder or hypochlorite

As chloramines

As free chlorine gas

As chlorine dioxide

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Fig 3.3 Water treatment steps

Fig 3.4 Water treatment plant

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CHAPTER 4

EXPERIMENTAL PROCEDURE

4.1 TO DETERMINE TOTAL HARDNESS OF GIVEN WATER

SAMPLE

The apparatus required and procedure for the determination of hardness of water

is discussed below.

4.1.1 Apparatus required

Conical flask

Burette

Pipette

Beaker measuring flask

0.01 M EDTA solution

Buffer solution of pH 10 ± 0.1

Erichrome black T

Given water sample

4.1.2 Procedure

Take 25 ml of unknown hard water in a conical flask.

Add 5 ml of buffer solution and 5 drops of Erichrome black-t

indicator.

Continue until colour of solution turns wine red.

Titrate the solution against EDTA so that the colour changes from

wine red to blue.

Repeat the titration for two concordant readings.

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4.2 TO DETERMINE ALKALINITY OF THE GIVEN WATER SAMPLE

The apparatus required and procedure for the determination of alkalinity of

water is discussed below.

4.2.1 Apparatus required

0.2 N HCL solution

Phenolphthalein solution

Methyl orange solution

Burette

Pipette

Conical flask

Sodium carbonate

4.2.2 Procedure

Take 25 ml of the sample solution in titration flask.

Add 2-3 drops of phenolphthalein indicator.

Titrate this sample against HCL solution until the pink colour

caused by phenolphthalein just disappears.

Note down this reading as phenolphthalein shows the end point.

Now add 2-3 drops of methyl orange indicator in the same

solution.

Continue the titration until the yellow colour changes into orange.

4.3 TO DETERMINE THE pH VALUE OF GIVEN WATER SAMPLE

When measuring pH with pH paper, dip the end of a strip of pH paper intoeach

mixture you want to test. After about two seconds, remove the paper, and

immediately compare the color at the wet end of the paper with the color chart

provided with that pH indicator. When measuring pH with pH meter, dip the

end of electrode of pH meter into each mixture you want to test. Write down the

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pH value and color. Always use a clean, unused strip of pH paper for each

mixture that you test.

TABLE 4.1 Determination of pH

Indicator Acid (color

change)

Base (color change) pH range

Methyl orange Red Yellow 3.1-4.4

Methyl red Red Yellow 4.2-6.3

Bromothymol Blue Yellow Blue 6.0-7.8

Phenol red Yellow Red 6.4-8.0

Phenolphthalein Colorless Pink 8.0-9.8

Thymol Blue Red Yellow 1.2-2.8

Alizarin Yellow Yellow Red 10.1-12.0

4.4 TO DETERMINE THE CHLORIDE CONTENT IN GIVEN WATER

SAMPLE

The apparatus required and procedure to determine chloride content in water is

discussed below.

4.4.1 Apparatus required

Burette

Pipette

Conical flask

Standard silver nitrate(𝑁

50) solution

Potassium chromate(K2CrO4) indicator

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4.4.2 Procedure

Take 25 ml of distilled water in a conical flask and add at least 5

drops of potassium chromate indicator. Slowly add standard

solution of AgNO3 from the burette and the volume of the

solution is noted down as end point. When yellow colour starts

changing to red. Repeate this titration for concordant readings.

Take 25 ml of water sample in a conical flask. Add 5 drops of

freshly prepared K2CrO4 solution. Titrate it against AgNO3

solution until the light yellow colour starts changing to red and

the red colour persists. Repeate this titration till two concordant

readings are obtained.

4.5 TO DETERMINE THE TOTAL DISSOLVED SOLIDS IN WATER

SAMPLE

The apparatus required and procedure for determination of dissolved solids in

water is discussed below.

4.5.1 Apparatus required

Silica and porcelain crucibles

Beakers

Measuring cylinders

Filter papers

Weighing balance

4.5.2 Procedure

Take 50 or 100 ml of water sample in a weighed crucible or

beaker.

Place the sample in an oven and evaporate to dryness at 980 C.

Then dry the evaporated sample for at least one hour at1030 –

1050C.

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Cool the crucible in desiccators and weight it.

4.6 TO DETERMINE THE DISSOLVED OXYGEN PRESENT IN

WATER SAMPLE

The apparatus required and procedure for the determination of dissolved oxygen

present in water is discussed below.

4.6.1 Apparatus required

Measuring cylinder

Pipette with elongated tip

Conical flask

BOD bottle

Funnel

Burette stand

4.6.2 Chemicals required

Alkaline iodide azide

Starch indicator distilled water

Manganous sulphate

Sulphuric acid

Sodium thiosulphate (0.025N)

4.6.3 Procedure

Take two 300mL stoppered BOD bottle and fill it with sample to

be tested. Avoid any kind of bubbling and trapping of air bubbles.

Take the sample collected from the field. It should be collected in

BOD bottle filled up to the rim.

Add 2mL of manganese sulphate to the BOD bottle by inserting

the calibrated pipette just below the surface of the liquid.

Add 2mL of alkali-iodide-azide reagent in the same manner.

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Squeeze the pipette slowly so no bubbles are introduced via the

pipette.

If oxygen is present, a brownish-orange cloud of precipitate or

floc will appear.

Allow it to settle for sufficient time in order to react completely

with oxygen.

Add 2mL of concentrated Sulphuric acid via a pipette held just

above the surface of the sample.

Carefully stopper and invert several times to dissolve the floc.

At this point, the sample is fixed and can be stored for up to 8

hours if kept in a cool, dark place.

Rinse th burette with sodium thiosulphate and fill it with sodium

thiosulphate. Fix the burette to the stand.

Measure out 50mL of the solution from the bottle and transfer to

an conical flask.

Titration needs to be started immediately after the transfer of the

contents to the conical flask.

Titrate it against sodium thiosulphate using starch indicator. (Add

3-4 drops of starch indicator solution).

End point of the titration is first disappearance of the blue colour

to colourless.

Note down the volume of sodium thiosulphate solution added

which gives the dissolved oxygen in ml.

Repeat the titration for concordant values.

In these ways we performed chemical test on water sample, to check whether

water is suitable for drinking purpose or not. The discussion about the results

obtained by performing these experiments is done in next chapter.

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CHAPTER 5

RESULTS AND DISCUSSION

5.1 RESULTS OF CHEMICAL TEST OF WATER SAMPLE USED

Hardness of water sample = 400 mg/l

Total dissolved solids = 700 mg/l

pH value of water sample = 6.5

Chlorides in water = 300 mg/l

Alkalinity of water sample = 105 mg/l

Dissolved oxygen in water = 21.88 mg/l

5.2 DISCUSSION OF RESULTS

The results obtained from the laboratory experiments on water sample are

discussed below.

5.2.1 pH

The pH value of a water source is a measure of its acidity or alkalinity. The pH

level is a measurement of the activity of the hydrogen atom, because the

hydrogen activity is a good representation of the acidity or alkalinity of the

water. The pH scale, as shown below, ranges from 0 to 14, with 7.0 being

neutral. Water with a low pH is said to be acidic, and water with a high pH is

basic, or alkaline. Pure water would have a pH of 7.0, but water sources and

precipitation tends to be slightly acidic, due to contaminants that are in the

water. The pH scale is logarithmic, which means that each step on the pH scale

represents a ten-fold change in acidity. For example, a water body with a pH of

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5.0 is ten times more acidic than water with a pH of 6.0. And water with a pH of

4.0 is 100 times more acidic than water with a pH of 6.0.

5.2.2 pH ADJUSTMENT

There are several methods that can increase the pH of water, before disinfection.

The pH is commonly increased using sodium carbonate and sodium hydroxide,

but a better way of dealing with low pH is to use calcium and magnesium

carbonate, which not only will increase pH levels, but will also make the water

less corrosive and both calcium and magnesium are of health benefits as

opposed to sodium.

5.3 TOTAL DISSOLVED SOLIDS (TDS)

TDS stands for total dissolved solids, and represents the total concentration of

dissolved substances in water. TDS is made up of inorganic salts, as well as a

small amount of organic matter. Common inorganic salts that can be found in

water include calcium, magnesium, potassium and sodium, which are all

cations, and carbonates, nitrates, bicarbonates, chlorides and sulfates, which are

all anions. Cations are positively charged ions and anions are negatively

charged ions.

5.3.1 TDS TREATMENT

Water treatment facilities can use reverse osmosis to remove the dissolved

solids in the water that are responsible for elevated TDS levels. Reverse

osmosis removes virtually all dissolved substances, including many harmful

minerals, such as salt and lead. It also removes healthy minerals, such as

calcium and magnesium, and ideally such water should be filtered through a

magnesium and calcium mineral bed to add the minerals to the water. The

mineral bed also increases the pH and decreases the corrosive potential of the

water. With TDS, the treatment process must deal with a number of different

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mineral compounds or “salts.” The available treatment processes for TDS while

effective, are relatively more expensive than treatment for other water quality

problems, such as iron removal. Of the available treatment processes for TDS,

reverse osmosis (RO) and deionization (DI) units are the only ones capable of

treating the entire household supply. Because deionized water is also corrosive,

DI units are not recommended for whole-house use. Where only the taste of the

water is of concern, point of- use devices are another means for treating TDS.

These are small treatment units which use distillation, deionization, reverse

osmosis, or ultra filtration to treat only enough water for use in drinking and

cooking. They are limited to a production of from 10 to 15 gallons of water per

day.

1. Reverse Osmosis (RO): RO units remove TDS by forcing the water, under

pressure, through a synthetic membrane. The membrane contains microscopic

pores which will allow only molecules of a certain size to pass through. Since

the molecules of dissolved mineral salts are large compared to the water

molecules, the water will squeeze through the membrane leaving the mineral

salts behind.

A properly operated RO unit is capable of removing 90 percent of the dissolved

mineral salts from a water supply. A pre-filter is usually required to protect the

membrane from abrasion. The membrane cartridges require periodic

replacement.

2. Distillation: Distillation units are better known as “stills.” They are

manufactured from heat-resistant glass or stainless steel. Stills work by heating

small amounts (less than 2 gallons) of water to produce steam. The steam is

then collected and condensed back into water. The dissolved mineral salts will

not vaporize and are left behind in the heating chamber. Stills require frequent,

rigorous cleaning to remove the baked-on mineral salts. The “flat” taste from

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boiling the water can be reduced by pouring the water back and forth between

two containers to aerate it.

3. Deionization (DI): Deionization units are available as small, wall-mounted

cartridges containing ion exchange resins. When water passes through the

cartridge, the dissolved minerals salts are retained in the resin, producing

mineral-free water. The DI cartridges have a limited life. They will usually

show a color change in the resin to indicate when they should be replaced.

4. Combination Point-of-Use Devices: These are multi step treatment systems

designed to fit under the kitchen sink. They use a pre-filter, RO membrane or DI

cartridge, and a carbon polishing filter top produce up to 15 gallons of water per

day. The treated water is stored in a small pressure tank and piped to a special

faucet on the sink. Each of the treatment steps is in a cartridge form.

5.4 CHLORIDES

Chlorides, not to be confused with chlorine, are in nearly all water supplies.

They are usually associated with the salt content and the amount of dissolved

minerals in water. The recommended limit for chlorides is 250 milligrams per

liter (mg/1). This is the concentration in water where most people will notice a

salty taste.

5.4.1 CAUSES

Chlorides are soluble mineral compounds that are dissolved by the water as it

filters through the earth. The amount of chlorides in water is determined by the

type of rock sand soils it has contacted. In coastal areas, the leaking of sea water

into a well can also because of increased chlorides. Water supplies having high

concentrations of total dissolved solids (TDS) may also contain elevated

chloride levels as part of the TDS. As much as 50 percent of the TDS may be

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due to chlorides. Human and animal wastes contain a high concentration of

chlorides. If a sudden, large increase in the chloride content is noticed, or if the

well water begins to taste salty, then samples should be taken to see if the well

has been contaminated.

5.4.2 EFFECTS

The presence of chlorides in drinking water is generally not considered to be

harmful to humans or animals. The most noticeable effect of high chlorides is a

salty taste. If a water softener is being used, the taste will be even more

pronounced. In mineralized waters (high TDS), chlorides contribute to the

corrosion of household appliances and domestic plumbing by preventing the

formation of protective oxide film son exposed surfaces. The average life of

water heaters has been estimated to shorten by one year for every 100 mg/l

chloride over the first 100 mg/I.

5.4.3 TREATMENT

Chlorides cannot be easily removed from drinking water. Of the available

treatment processes, reverse osmosis (RO) and deionization (DI) are capable of

effectively treating the entire household supply. However, both are relatively

expensive. Because deionized water can also be corrosive, DI units are not

recommended for whole-house use. If the taste of the water is the only concern,

the treatment methods described below are available as point of-use devices. A

point-of-use device is a small treatment unit that will produce between 10 and

15 gallons of water per day for drinking and cooking. The device is usually

located near the kitchen sink.

1. Reverse osmosis (RO): RO units remove dissolved minerals by forcing the

water, under pressure, through a synthetic membrane. The membrane contains

microscopic pores that will allow only molecules of a certain size to pass

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through. Since the molecules of dissolved mineral salts are large compared to

the water molecules, the water will squeeze through the membrane leaving the

mineral salts behind. A properly operated RO unit is capable of removing 90

percent of the dissolved mineral salts from a water supply. A pre-filter is usually

required to protect the membrane from abrasion. The membrane cartridges

require periodic replacement.

2. Distillation: Distillation units are better known as “stills.” They are

manufactured from heat-resistant glass or stainless steel. Stills work by heating

small amounts (less than 2 gallons) of water to produce steam. The steam is

then collected and condensed back into water. The dissolved minerals will not

vaporize and are left behind in the heating chamber. Stills require frequent,

rigorous cleaning to remove the baked-on mineral salts. The “flat” taste from

boiling the water can be reduced by pouring the water back and forth between

two containers to aerate it.

3. Deionization (DI): Deionization units are available as small, wall-mounted

cartridges containing ion exchange resins. When water passes through the

cartridge the dissolved mineral salts are retained in the resin, producing mineral-

free water.

The DI cartridges have a limited life. They will usually show a color change in

the resin to indicate when they should be replaced.

4. Combination Point-of-Use Devices: These are multistep treatment systems

designed to fit under the kitchen sink. They use a pre-filter, RO membrane or DI

cartridge, and a carbon polishing filter top and produce up to 15 gallons of

water per day. The treated water is stored in a small pressure tank and piped to a

special faucet on the sink. Each of the treatment steps is in a cartridge form.

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5.5 HARDNESS

Hard water is one of the most common water quality problems in the United

States. In the past, hardness was measured by the amount of soap that had to be

added to water to produce lather. It is now measured as the concentration of

dissolved calcium and magnesium compounds (expressed as calcium

carbonate). There is no firm dividing line between hard and soft water.

However, for most household uses, a hardness of between 50 and 150

milligrams per liter (mg/1) is acceptable. Hardness may sometimes be expressed

as grains per gallon (gpg) instead of mg/l. 1gpg are equal to 17.1 mg/l.

5.5.1 CAUSE

The amount of naturally occurring calcium and magnesium compounds

dissolved by the water as it filters through the earth will determine its hardness.

Hardness varies with location and the types of minerals and rocks in the earth.

5.5.2 EFFECTS

Despite all of the problems it causes, hard water is not considered to be a health

hazard. Moderate amounts of hardness are desirable because of the protective

coating it produces on exposed metal surfaces. Excessively hard water,

however, will cause a hard, chalky scale (boiler scale) to form when the water is

heated. Water heaters are especially affected by hardness. The boiler scale will

accumulate on the heating elements, reducing their heating capacity, and

eventually causing them to burn-out. Hard water will form a white, powdery

residue on plumbing fixtures, and will cause spots on dishes. Because calcium

and magnesium compounds are not very soluble in coldwater, ice made from

hard water may contain white particles. Vegetables cooked in hard water may

be tough. More soap must be added to a hard water to produce lather. With very

hard water, soap will form a sticky “curd,” which is difficult to remove from

fabrics and containers.

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Laundry washed in hard water will be stiff and dingy. Hair becomes dull and

limp when washed in hard water.

5.5.3 TREATMENT

The minerals that cause water hardness can be removed by a water softener.

Water softeners use an ion exchange process to replace the calcium and

magnesium that cause hardness with an equivalent amount of sodium, which

does not contribute to water hardness. With use, all of the sodium in a softener

will eventually be replaced by calcium and magnesium. When this occurs, the

softener must be regenerated to maintain its softening ability. In regeneration,

the softener is filled with a concentrated salt solution. The sodium in the salt

solution replaces the calcium and magnesium in the softener, restoring it to its

original condition. Most manufacturers offer either a manual or an automatic

regeneration cycle in their softeners. Ion exchange softeners produce water with

near zero hardness. Because a moderate amount of hardness is desirable, some

individuals choose to soften a portion of the water and blend it with unsoftened

water to produce a final hardness of 50 to 100 mg/1.

In cases where the water hardness exceeds 200 mg/1 or where elevated levels of

chlorides are present, softening may produce a salty taste in the water. In these

instances, a by-pass line can be installed from before the softener to a kitchen

faucet; or a point-of use treatment device can be used (see below).If excessive

iron and manganese are present, it may be necessary to remove these metals

prior to softening. While water softeners will remove small amounts of iron and

manganese, excessive amounts will foul the water softener. As a rule of thumb,

the total amount of iron and manganese should not exceed 1.0 mg/l for every

140 mg 1 (8 gpg) of hardness.

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1. Point-of-Use Devices: Where the taste of the water or the increased amount

of sodium due to softening is a concern, a point-of-use device may be used to

produce a limited amount of water per day for drinking and cooking. These

devices are small, multi-step treatment system designed to fit under the kitchen

sink. They produce up to 15 gallons per day of treated water. The treated water

is stored in a small pressure tank, piped to a special faucet on the sink. Each of

the treatment steps is in a cartridge form and requires periodic replacement.

2. Laundry Water Softening: Water for laundry may be softened in the

washing machine by using a group of chemicals known as non-precipitating

water softeners. This group includes borax, washing soda, trisodium phosphate,

and ammonia. Always follow the manufacturer’s instructions in using these

chemicals. Under no circumstances should these chemicals be used for

softening drinking water.

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CHAPTER 6

DESIGN OF DRINKING WATER TREATMENT PLANT

6.1 WATER QUANTITY ESTIMATION

The quantity of water required for municipal uses for which the water supply

scheme has to be designed requires following data:

1. Water consumption rate (Per Capita Demand in liters per day per head)

2. Population to be served.

𝑄𝑢𝑎𝑛𝑡𝑖𝑡𝑦 = 𝑝𝑒𝑟𝑐𝑎𝑝𝑖𝑡𝑎𝑑𝑒𝑚𝑎𝑛𝑑 × 𝑃𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛

6.2 FLUCTUATIONS IN RATE OF DEMAND

Average Daily per Capita Demand

= Quantity Required in 12 Months/ (365 × Population)

If this average demand is supplied at all the times, it will not be sufficient to

meet the fluctuations.

Seasonal variation: The demand peaks during summer. Firebreak outs

are generally more in summer, increasing demand. So, there is seasonal

variation.

Daily variation depends on the activity. People draw out more water on

Sundays and Festival days, thus increasing demand on these days.

Hourly variations are very important as they have a wide range. During

active household working hours i.e. from six to ten in the morning and

four to eight in the evening, the bulk of the daily requirement is taken.

During other hours the requirement is negligible. Moreover, if a fire

breaks out, a huge quantity of water is required to be supplied during

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short duration, necessitating the need for a maximum rate of hourly

supply.

So, an adequate quantity of water must be available to meet the peak demand.

To meet all the fluctuations, the supply pipes, service reservoirs and distribution

pipes must be properly proportioned. The water is supplied by pumping directly

and the pumps and distribution system must be designed to meet the peak

demand. The effect of monthly variation influences the design of storage

reservoirs and the hourly variations influences the design of pumps and service

reservoirs. As the population decreases, the fluctuation rate increases.

Maximum daily demand = 1.8 x average daily demand

Maximum hourly demand of maximum day i.e. Peak demand

= 1.5 × average hourly demand

= 1.5 × Maximum daily demand/24

= 1.5 × (1.8 × average daily demand)/24

= 2.7 × average daily demand/24

= 2.7 × annual average hourly demand

6.3 DESIGN PERIODS & POPULATION FORECAST

This quantity should be worked out with due provision for the estimated

requirements of the future. The future period for which a provision is made in

the water supply scheme is known as the design period

Design period is estimated based on the following:

Useful lives of the component, considering obsolescence, wear, tear, etc.

Expandability aspect.

Anticipated rate of growth of population, including industrial,

commercial developments & migration-immigration.

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Available resources.

Performance of the system during initial period.

6.3.1 POPULATION FORECASTING METHODS

The various methods adopted for estimating future populations are given below.

The particular method to be adopted for a particular case or for a particular city

depends largely on the factors discussed in the methods, and the selection is left

to the discretions and intelligence of the designer.

1. Arithmetic Increase Method

2. Geometric Increase Method

3. Incremental Increase Method

4. Decreasing Rate of Growth Method

5. Simple Graphical Method

6. Comparative Graphical Method

7. Ratio Method

8. Logistic Curve Method

6.4 DESIGN DETAILS

1. Detention period: for plain sedimentation: 3 to 4 h, and for coagulated

sedimentation: 2 to 2.5 h.

2. Velocity of flow: Not greater than 30 cm/min (horizontal flow).

3. Tank dimensions: L: B = 3 to 5:1. Generally L= 30 m (common)

maximum 100 m. Breadth= 6 m to 10 m. Circular: Diameter not greater

than 60 m. generally 20 to 40 m.

4. Depth 2.5to 5.0 m (3 m).

5. Surface Overflow Rate: For plain sedimentation 12000 to 18000

L/d/m2tank area; for thoroughly flocculated water 24000 to 30000 L/d/m2

tank area.

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6. Slopes: Rectangular 1% towards inlet and circular 8%.

Standard design practice of Rapid Sand filter:

1. Maximum length of lateral should not less than 60 times its diameter.

2. Spacing of holes = 6 mm holes at 7.5 cm c/c or 13 at 15 c/c.

3. C.S area of lateral should not less than 2 times area of perforations.

4. C.S area of manifold is equal to2 times total area of laterals.

5. Maximum loss of head is equal to 2 to 5 m.

6. Spacing of laterals is equal to 15 to 30 cm c/c.

7. Pressure of wash water at perforations should not greater than 1.05

kg/cm2.

8. Velocity of flow in lateral is equal to 2 m/s.

9. Velocity of flow in manifold is equal to 2.25 m/s.

10. Velocity of flow in manifold for wash water is equal to 1.8 to 2.5 m/s.

11. Velocity of rising wash wateris equal to 0.5 to 1.0 m/min.

12. Amount of wash water is equal to 0.2 to 0.4% of total filtered water.

13. Time of backwashing is equal to10 to 15 min.

14. Head of water over the filter = 1.5 to 2.5 m.

15. Free board = 60 cm. Bottom slope = 1 to 60 towards manifold.

Note: Q = (1.71 × b ×h3/2) where Q is in m3/s, b is in m, h is in m. L:B = 1.25 to

1.33:1

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6.5 DESIGN OF SEDIMENTATION TANK

6.5.1 NECESSARY DATA REQUIRED FOR SEDIMENTATION TANK

DESIGN

1. Quantity of water to be treated per day = 1.5 million liters

2. Detention period = 2 hours

Raw water flow per day = 1.5 million liters

Detention period = 2 hours

Volume of tank = flow × detention period

= 1.5 ×103 × (2÷24)

= 125 m3

Assume depth of tank = 3m

Surface area of tank = (125÷3)

= 41.66 m2

L/B = 2 (assumed)

L = 2B

2B2 = 41.66

B = 4.5m

L = 2B

L = 9.0 m

Hence surface overloading (flow rate) = 1.5×10

41.66

6

= 36005.76 l/d/m2

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6.6 DESIGN OF RAPID SAND FILTER

6.6.1 NECESSARY DATA REQUIRED FOR DESIGN

1. Population = 100,000

2. Average rate of demand = 120 litres per head per day

Maximum daily demand = 100,000 × 120 × 1.5 = 108000 liters

Let us assume an average filtration rate of 2500 liters per hour per m2 of filter

area.

Therefore, area of filters = 100000

2500 ×24 = 1.8 m2

Let the size of each filter unit be 3 m × 2 m

No. of units required = 1.8

3 ×2 =0.3

Design of filters units

Let us assume that 3% of filtered water is used for washing of filter every day

Filter water requirement per day = 1.03 × 1.5 = 1.545 Mld

Again, let us assume that 30 minutes are lost every day in washing the filter.

The quantity of filtered water required per hour = 1.545

(24−0.5) = 0.0657 Ml/hour

Again let us assume that an average filtration rate of 3000 liters/h/m2 of filter

area

Therefore filter area A = 0.0657 × 100000

3000 = 2.191 m2

Let L= 4

3 B and let there is 2 filter units, two being the minimum number to be

provided

Then 2(𝐵 ×4

3𝐵) = 2.191

From which B = .289 m

Keep B = 3 m and L= 4 m for each filter unit giving total area

A = 2 × 3 × 4 = 24 m2

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6.7 DESIGNS FOR CHLORINATION

6.7.1 NECESSARY DATA REQUIRED FOR DESIGN

1. Population=100000

2. Average rate of demand = 120 litres per head per day

3. Chlorine consumed per day = .09 kg/day

4. Residual chlorine after 10 minutes = 0.2 mg/l.

Water treated per day = 120 × 100000 × 1.5 = 108000 litres

Chlorine consumed per day = .09 kg = .09 × 1000000 mg/day

Therefore, chlorine used per litre of water = .09×1000000

108000 =0.83 mg/l

Also, residual chlorine = 0.2 mg/l

Therefore, chlorine demand = 0.83-0.2 = 0.63 mg/l

6.8 DESIGN OF COAGULATION CUM SEDIMENTATION TANK:

6.8.1 NECESSARY DATA REQUIRED FOR DESIGN

1. Population = 100,000

2. Average rate of demand = 120 litres per head per day

Maximum daily demand = 100,000 × 120 × 1.5 = 108000 liters

Assume detention period = 2 hours

Therefore, quantity of water to be treated during an assumed detention period of

4 hours = 108000

24× 2 = 9000 cu-m.

Hence, capacity of tank required = 9000 cu-m.

Assuming an overflow rate of 1000 litres/hr/m2 of plan area, we get

q

b.l =1000

Where q = 108000

2 = 54000 lires/hr.

Plan area =b.l

= 𝑞

1000= (54000÷1000) = 54 m2.

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Using the width of tank as 6 m, we get

Length of the tank = 54

6 = 9 m.

Hence, use a tank of 9 m × 6 m × 2 m.

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CHAPTER 7

CONCLUSION

From the results of chemical analysis performed with the samples of drinking

water follows that produced water can be characterized as a very soft. Hence it

could be summarized that potable water should meet physical, chemical,

bacteriological, and radionuclide parameters when supplied by an approved

source, delivered to a treatment and disinfection facility of proper design,

construction and operation and in turn delivered to the consumers through a

protected distribution system in sufficient quantity and pressure. Water

purification is the removal of contaminants from untreated water to produce

drinking water that is pure enough for the most critical of its intended uses,

usually for human consumption. Substances that are removed during the process

of drinking water treatment include solids, bacteria, algae, viruses, fungi,

minerals such as iron, manganese and sulphur, and other chemical pollutants

such as fertilizers. Measures taken to ensure water quality not only relate to the

treatment of the water, but to its conveyance and distribution after treatment as

well. It is therefore common practice to have residual disinfectants in the treated

water in order to kill any bacteriological contamination during distribution.

World Health Organisation (WHO) guidelines are generally followed

throughout the world for drinking water quality requirements. In addition to the

WHO guidelines, each country or territory or water supply body can have their

own guidelines in order for consumers to have access to safe drinking water.

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REFERENCES

1. Rietveld, A.W.C. van der Helm, K.M. van Schagen and L.T.J. van der

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