Dr. DharmendraAssistant Professor

Department of Civil Engineering Office Location: Environmental Laboratory

Civil Department (Ground Floor)

Course No.: CED-223Course title: Environmental Engineering –I (Water Supply and treatment)

L T P 3 1 0

Introduction: Scope and importance of Environmental Engineering and Management. Introduction to Environmental

pollution, Impact on human health, Significant water quality parameters for Municipal Water Supplies. Standards and guidelines for Water Quality Parameter.

Demand and sources of water: Water demand Population forecast; Water quality requirements

Sources and its yield for water requirements; Intake structures; Water quality parameters and their significance in domestic use.

Water treatment: Design of treatment units such as aeration, sedimentation, coagulation and flocculation, filtration,

Disinfection, water softening; Advanced water treatment methods. Water distribution systems: Pumps and pumping system Pipes; Pipe appurtenances testing of water main Distribution

reservoirs, Distribution methods, Pipe network analysis, Planning of water supply project; Plumbing and fittings for water supply House water connection, Design consideration for water piping system and storage of water in building.

Rural water supply and treatment:

Water demand and treatment techniques for rural area, water problems and remedial measures. Technical tour & report: within semester visit to water treatment plant and prepare report.

National Institute of Technology, Hamirpur, H.P. – 177005, IndiaDepartment of Civil Engineering

Course No.: CED-223Course title: Environmental Engineering –I (Water Supply and treatment)

Credits Description:

Course Type CorePrerequisites CE 101, Environmental Science & Disaster Management

CE 212, Fluid MechanicsCourse Coordinator Dr.DharmendraGrading End Semester Exam (60%), Mid Sem Exam (20 %),

Class Test (10%), Others (10%) [Quizzes, assignments, etc..]Class Timings Lectures Mon [9:25-10:20], Thur. [9:25-10:20], Fri [8:30-9:25],

Tutorials Mon [8:30-9:25], Mid Term Exam March 02 – 08, 2015Text Book 1.S.K.Garg, Water Supply Engineering, Khanna Publishers, New Delhi. 20032.B. C. Punmia, Ashok Jain, Arun Jain, Water Supply Engineering, Laxmi Pub., New Delhi. 2003.3.Davis and Cornwell, Elements of Water Supply and Waste water Disposal, John Wiley & Sons, New York. 1998.4.Ronald L. Droste, Theory and Practice of Water and Wastewater Treatment, John Wiley & Sons, New York, 1997.5.McGhee, T.J., Water Supply & Sewerage, McGraw Hill International Edition, 1991.

Reference Book

•Ministry of Urban Development, Manual on Water Supply and Treatment 3rd Ed. Central Public Health & Environmental. Engg. Organization, Govt. of India, New Delhi, 1991.•Warren Viessman Jr, Mark J. Hammer & Elizabeth Perez, Water Supply & Pollution Control, PHI • Mark J. Hammer & Mark J. Hammer Jr., Water & Wastewater Technology, PHI • Syed R. Qasim, Edward M. Motley, Guang Zhu, Water Works Engineering, PHICourse Outcomes

L T P Credits3 1 0 4

Topics Objectives Target POs

Duration(Hours)

Readings

IntroductionScope and importance of Environmental Engineering and Management - Introduction to Environmental pollution - Impact on human health -, Significant water quality parameters for Municipal Water Supplies. Standards and guidelines for Water Quality Parameter.

Introduction to Environment and its components.

Understand the necessity of environmental engineering.

Know the basic of water quality & the concept of implementing standards.

PO 1, PO 4, PO 6, PO 7, PO 12.

6 T(1, 8)R3(1)R4(1)

Demand and Sources of Water Water demand - Population forecast - Water quality requirements - Sources and its yield for water requirements- Intake structures – Water quality parameters and their significance in domestic use.

How to forecast future population of an area.

Understand & analyze various requirements of water.

Understand & analyze various sources of water.

Analyze the importance of water quality.

Analyze and design the intake structures.

PO 1, PO 2, PO 3, PO 4, PO 5, PO 6, PO 7, PO 12.

14 T(2, 3, 4, 5, 8)R1(3, 4, 5, 8)R2(5, 8)R3(2, 3, 4, 6)R4(1, 2, 3, 4, 5 , 6)

Water Treatment Design of treatment units such as aeration, sedimentation, coagulation and flocculation, filtration, Disinfection, water softening- Advanced water treatment methods.

Understand the basic components & concept of water treatment.

Analyze in detail every component of a water treatment plant.

Design of a water treatment plant.

PO 1, PO 2, PO 3, PO 4, PO 5, PO 6, PO 7, PO 12.

16 T(9)R1(9, 10, 11)R2(7)R3(3, 4, 6, 8, 9, 10, 11, 12)R4(7, 8, 9, 10, 11, 12, 13)

Water Distribution Systems Pumps and pumping system – Pipes - Pipe appurtenances - Testing of water main – Distribution reservoirs - Distribution methods - Pipe network analysis - Planning of water supply project

Analyze the concepts of pumps & pipelines in water supply

Understand the concepts & requirements of water distribution system.

Analysis of water distribution system.

How to plan a water supply project.

PO 1, PO 2, PO 3, PO 4, PO 5, PO 6, PO 7, PO 10, PO 11, PO 12.

12 T(1, 6, 7, 10, 13)R1(6)R2(8)R3(3, 7, 13)R4(14, 15, 16)

Topics Objectives Target POs

Duration(Hours)

Readings

Plumbing and Fittings For Water Supply House water connection, Design consideration for water piping system and storage of water in building.

How to supply water to your house.

Understand all the requirements for house supply

PO 1, PO 3, PO 4, PO 5, PO 6, PO 7, PO 11,PO 12.

3 T(11)R1(7)R2(8)R4(17)

Rural Water Supply and TreatmentWater demand and treatment techniques for rural area, water problems and remedial measures.

How to supply water in rural area, understand and analyse all the concepts of water supply required for a rural area.

PO 1, PO 2, PO 3, PO 4, PO 5, PO 6, PO 7, PO 10, PO 11, PO 12.

3 T(12)

Topics Objectives Target POs

Duration(Hours)

Readings

Introduction

• Importance of water & Global Distribution of Water• Sources of Water for Development & Pollution• Surface water Development & Pollution• Groundwater Development & Pollution• Water Supply Planning• Water Quality Management• Water Law• Integrated Water Resources Management (IWRM)

Global Distribution of Water

Source Volume PercentOcean 97.2000Glaciers and other ice 2.1500Ground Water 0.6100Lakes

fresh 0.0090saline 0.0080

Soil Moisture 0.0050Atmosphere 0.0010Rivers 0.0001

Distribution of water stored on the earth

1. 97% of all water on earth is in oceans.

2. ~ 2% of the earth's water in ice caps & glaciers

3. About 0.6% of earth's water is groundwater

4. Water in rivers, lakes, and the atmosphere amounts to less than 0.02% of earth's water

Sources of Water for Development

• Water is considered one of the major resources for development in any nation. Its supply in sufficient quantity, adequate quality at the right time is critical to all aspect of civilization.

• Early civilizations flourished along river valleys where there was abundant supply of water to support life.

• The ultimate sources of water on earth are indicated in the Hydrological cycle, this is the cyclic exchange of water between the land, sea and Air systems on earth. The figure below explains the cycle better

Hydrologic Cycle

Evaporation

Precipitation

Runoff

Precipitation

Infiltration

Evaporation

Water sources

• Atmospheric water – Rainfall, Dew, Snow etc.

• Surface water – Rivers, Sea, Oceans, Streams, • Lakes, Springs etc.

• Groundwater – Aquifers

Water Supply Planning • The development and utilization of available water resources require

adequate planning and design. • In order to select a suitable water supply source, the demand that will be

placed on it must be known. • The elements of water demand include the average daily water use and

the peak rate of demand.• In the planning process, the ability of the water In the planning process,

the ability of the water source to meet demands during critical periods (when surface flows and groundwater tables are low) must be determined.

• The “peak demand rate” must be estimated in order to determine plumbing and pipe sizing, pressure losses and storage requirements necessary to supply enough water during periods of peak water demand.

Water Quality Management • The quality of water is determined by its physical, chemical and biological

properties. • Naturally existing water contains impurities which need to be removed by

treatment. • Natural waters contains suspended solids as well as dissolved substances, these

must be either removed or kept at within certain limits to make the water potable.• The tolerable limit of impurities in water depends • The tolerable limit of impurities in water depends on the purpose for which it is to

be used for, water that is completely free from suspended or dissolved matter eg. Distilled water is unpalatable.

• Water for domestic purposes must not contain disease-causing organisms (Pathogens)

• water for washing in a laundry or textile factory should be free of suspended matter.

Water Quality Management Contd

• Substances found in surface water depend on the catchment where it was generated, impurities like clay, organic and inorganic mineral matter, algae, bacteria and protozoa may be found in suspended or colloidal form.

• Dissolved gasses like oxygen, nitrogen, carbon dioxide and hydrogen sulphide may also be present.

• Organic matters found in water may include ammonia, organic acids, chlorides, nitrites and nitrates; they may be found in dissolved state.

• Pollution of surface water may also occur as a result of the following activities of Man Discharge of effluents from industries Discharge of domestic wastes from homes, abattoirs etc. Leaching and discharge of contaminants from agricultural lands eg. Fertilizers,

herbicides, pesticides etc Acid rains due to heavy air pollution from industrial estates or parks

• Water Law• In regions where the available water is inadequate to meet

the needs of potential users, a system of laws has been developed to determine who has the right to water when shortages occur.

• Water law plays a major role in the economic aspects of water development since limitations on who may develop water often control how it is developed and utilized.

• Riparian Rights• The doctrine of riparian rights evolved from Europe and has

been adopted world wide with little or no modification. • The doctrine holds that the owner of the land adjacent to a

stream is entitled to receive the full natural flow of the stream without change in quantity and quality.

• Prior Appropriation• This doctrine evolved as a result of the failure of the riparian

doctrine to meet modern challenges of allocating water equitably. • This gives room of access to water for land owners who are not

located in close proximity to the stream. • Water is appropriated based on the principle of “first in time, first

in right”• Groundwater Law• Under the common law, rights to groundwater are inherent in the

overlying property; the owner of this property is free to abstract the water.

• This can only hold if the groundwater resource is vast, but if the water is inadequate to meet all needs problems will emerge and this often lead to court cases which brought about decisions that tends towards the doctrine of reasonable use.

• National water policy• The nation’s water sources are under serious threat from inadequate catchment

management and widespread pollution, including the indiscriminate disposal of hazardous substances.

• The National Water Resources Policy aims at providing a framework for addressing these challenges in order to achieve the following:

Clear and coherent regulation.

Clear definitions of the functions and relationship of sector

institutions. institutions.

Coordination Finds solution to the problem of dwindling funds.

Reliable and adequate data for planning and project ions.

Decentralization in order to boost efficiency, performance and sustainability.

Autonomy of water supply agencies.

Regard water as an economic good.

Create public awareness about water conservation and management.

Integrated Water Resources Management (IWRM)

• At its simplest, integrated water resources management is a logical and appealing concept.

• Its basis is that the many different uses of water resources are interdependent.

• High irrigation demands and polluted drainage flows from agriculture mean less freshwater for drinking or industrial use; contaminated municipal and industrial wastewater pollutes rivers and threatens ecosystems; if water has to be left in a river to protect fisheries and ecosystems, less can be diverted to grow crops.

• There are plenty more examples of the basic theme that unregulated use of scarce water resources is wasteful and inherently unsustainable.

(IWRM) contd..• Integrated water resources management is therefore a systematic

process for the sustainable development, allocation and monitoring of water resource use in the context of social, economic and environmental objectives .

• A meeting in Dublin in 1992 gave rise to four principles that have been the basis for much of the subsequent water sector reform: Fresh water is a finite and vulnerable resource, essential to sustain life,

development and the environment. Water development and management should be based on a participatory

approach, involving users, planners and pol icy makers at all levels. Women play a central part in the provision, management and safeguarding of

water. Water has an economic value in all its competing uses and should be recognized as an economic good as well as a social good.

Water pollution & Impact on health

• Source of pollution:– Natural

• Precipitation• Atmosphere• Soil erosion• Surface runoff

– Anthropogenic• Domestic & Industrial

wastewater• Solid Waste &

• Water-borne Diseases

• Surface water Pollution– Point source– Non Point source or

Diffused source• Ground water Pollution

– Depleting water table– Metal & metalloid leach– Shallow irrigation

Diseases Related to Water

Water-borne Diseases

Water-washed Diseases

Water-based Diseases

Water-related Diseases

Water-borne Diseases • Diseases caused by ingestion of water contaminated by

human or animal excrement, which contain pathogenic microorganisms

or• Transmission occurs by drinking contaminated water,

particularly contamination by pathogens transmitted from human excreta.

• These include most of the enteric and diarrheal diseases caused by bacteria and viruses worldwide.

• Include cholera, typhoid, amoebic and bacillary dysentery and other diarrheal diseases

LIST OF INFECTIOUS AGENTS POTENTIALLY PRESENT IN DRINKING WATER CONTAMINATED

BY SEWAGEORGANISM DISEASE REMARKS/Symptoms

Bacteria

Escherichia coli (enteropathogenic)

Gastroenteritis Diarrhea

Legionella pneumophila Legionellosis Acute respiratory illness

Leptospira (150 spp.) Leptospirosis Jaundice, fever

Salmonella typhi Typhoid fever High fever, diarrhoea

Salmonella (~1700 spp.) Salmonellosis Food poisoning

Shigella (4 spp.) Shigellosis Bacillary dysentery

Vibrio cholerae Cholera Extremely heavy diarrhoea, dehydration

Yersinia enterocolitica Yersinosis Diarrhoea

LIST OF INFECTIOUS AGENTS POTENTIALLY PRESENT IN DRINKING WATER CONTAMINATED

BY SEWAGEORGANISM DISEASE REMARKS/Symptoms

Protozoa

Balantidium coli Balantidiasis Diarrhoea, dysentery

Cryptosporidium Cryptosporidiosis Diarrhoea

Entamoeba histolytica Amoebic dysentery Prolonged diarrhoea with bleeding

Giardia lamblia Giardiasis Mild to severe diarrhoea, nausea

Viruses

Enteroviruses (67 types, e.g., polio, echo, and Coxsackie viruses)

Gastroenteritis, heart anomalies, meningitis Not available

Hepatitis A Infectious hepatitis Jaundice, fever

Norwalk agent Gastroenteritis Vomiting

In addition, water-borne disease can be caused by the pollution of water with chemicals that have an adverse effect on health

• The major contaminants of concern, in potable water supplies are: a) Suspended solids;b) Biodegradable organics (proteins, carbohydrates and fats);c) Pathogens;d) Nutrients (Nitrogen, phosphorus and carbon);e) Priority pollutants (highly toxic chemicals);f) Refractory organics (pesticides, phenols, surfactants);g) Heavy metals;h) Dissolved inorganic (nuisance chemicals).

Suspended solids

• The presence of suspended solids in water gives rise

to turbidity.

• Suspended solids may consist of clay, silt, airborne

particulates, colloidal organic particles, plankton and

other microscopic organisms.

Biodegradable organics• Composed principally of proteins, carbohydrates, and

fats, biodegradable organics are measured most commonly in terms of BOD (Biological Oxygen Demand).

• BOD is the quantity of oxygen required for the oxidation of organic matter by bacterial action in the presence of oxygen.

• The higher the demand for oxygen (the more organic the pollution) the less is the oxygen left to support life.

• Urban sewage commonly has a BOD of 300-500 mg/litre.

• Arsenic• Flouride• Nitrates from fertilizers• Carcinogenic pesticides (DDT)• Lead (from pipes)• Heavy Metals

HEALTH EFFECTS Arsenic

Over a prolonged contact exposure the resulting symptoms can be very dangerous and can cause focal hyperemia, which means it decreases to blood flow to your arteries and veins and vesicular eruptions.

IMPACT OF SKELETAL FLOUROSIS ON HUMAN HEALTH

Water-washed Diseases

• Diseases caused by poor personal hygiene and skin

and eye contact with contaminated water

• These include scabies, trachoma, typhus, and other

flea, lice and tick-borne diseases.

Water-based Diseases

• Diseases caused by parasites found in intermediate organisms living in contaminated water

• Schistosomiasis is the second most important • parasitic infection after malaria (public health and

economic impact).• Caused by :Schistosoma haematobium, S.

japonicum,• Dracunculiasis, also called guinea worm disease

(GWD)

Free-swimming larvae penetrate human skin. The larvae develop in fresh-water snails

Water-related Diseases

• Water-related diseases are caused by insect vectors, especially mosquitoes, that breed or feed near contaminated water.

• Include dengue, filariasis, malaria, onchocerciasis, trypanosomiasis and yellow fever

• Note: They are not typically associated with lack of access to clean drinking water or sanitation services

Other Water-borne diseases

• Bathing• Swimming• Other recreational activities that have

water contact• Agriculture• Aquaculture

The Problem

• ~80% of infectious diseases • > 5 million people die each year • > 2 million die from water-related diarrhea

alone • Most of those dying are small children

Other Consequences

• Lost work days• Missed educational opportunities• Official and unofficial healthcare costs• Draining of family resources

Control & Prevention

Global

Governments

Communities

Individuals

Education Issues

• Hygiene education• Good nutrition• Improvements in habitation and general

sanitation• Higher education training in water-related

issues

Global Surveillance

• Public health infrastucture• Standardized surveillance of water-borne

disease outbreaks• Guidelines must be established for

investigating and reporting water-borne diseases

Communication and the Media

• Impacts at all levels

• Very powerful, when others fail

General Guidelines

• Avoid contacting soil that may be contaminated with human feces.

• Do not defecate outdoors. • Dispose of diapers properly. • Wash hands with soap and water before handling food. • When traveling to countries where sanitation and

hygiene are poor, avoid water or food that may be contaminated.

• Wash, peel or cook all raw vegetables and fruits before eating.

A Simple Rule of Thumb

"Boil it, cook it, peel it, or forget it"

More Challenges

• Developed countries and chlorine-resistant microbes

• Climate Changes• Economic barriers for developing countries

to sanitize large amounts of water

The Answer

• Unmet human needs for water• Education• Commitment to the elimination of specific

diseases• Research

Demand and

source of water

Municipal Water Supply: Sources and Quality

Raw Water Source :The various sources of water can be classified into two categories:

• Surface sources, such as – Ponds and lakes; – Streams and rivers; – Storage reservoirs; and – Oceans, generally not used for water supplies, at present Technology

available. • Sub-surface sources or underground sources, such as

– Springs; – Infiltration wells ; and – Wells and Tube-wells.

Water Quality Physical Characteristics:

TurbidityColourTaste and Odour Temperature

• Chemical Characteristics:pHAcidityAlkalinity HardnessChloridesSulphatesIron SolidsNitrates

• Bacteriological Characteristics:MPN Plate count

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. • Earlier 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 scale

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 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.

Based on Principle of Beer-Lambert Law • The unit of expression is Nephelometric Turbidity Unit (NTU). • The IS values for drinking water is 1 to 5 NTU. • Beyond this limit it becomes unpleasant.

Spectroscopic Methods of Analysis• Substances can absorb radiation in

specific wavelengths of the visible range of the electromagnetic spectrum

• This is practical for obtaining quantitative chemical information through the use of a spectrophotometer or a colorimeter

• This ratio of incident radiation (I) to outputted radiation (Io) is called transmittance (T)T = Io/I

• Absorbance, A, is related to transmission by the equation

A = – log 10 T

LIMITATIONS OF THE BEER-LAMBERT LAW

• Deviations in absorptive coefficients at high concentrations (>0.01M) due to electrostatic interactions between molecules in close proximity

• Scattering of light due to particulates in the sample • Shifts in chemical equilibrium as a function of

concentration • Fluorescence or phosphorescence of the sample• stray light

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.• Beyond this limit taste becomes unpleasant.

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 expessed 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.

Temperature

• The increase in temperature decreases palatability, because at elevated temperatures carbon dioxide and some other volatile gases are expelled.

• The ideal temperature of water for drinking purposes is 5 to 12 °C - above 25 °C, water is not recommended for drinking.

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.

• Effect: Beyond this range the water will effect the mucous membrane and / or water supply system

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.

Alkalinity

• The alkalinity of water is a measure of its capacity to neutralize 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.

• Desirable 200 mg/L CaCO3 Permissible limit 600 mg/L CaCO3 • Beyond this limit taste becomes unpleasant.

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.• Desirable 300 mg/L as CaCO3 Permissible limit 600 mg/L as CaCO3.• Encrustation in water supply structure and adverse effects on domestic use.

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.

• Desirable 250 mg/L Permissible limit 1000 mg/L .• Beyond this limit tast, corrosion and palatability are effected

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. Desirable

limit for drinking water is 150 mg/L. May be extended upto 400 mg/L.• Beyond this causes gastrointestinal irritation when magnesium or

sodium are present

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 favorable 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. • Desirable limit for drinking water is 0.3 mg/L. May be

extended upto 1.0mg/L.

Solids• The sum total of foreign matter present in water is termed as 'total

solids'. • Total solids is 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. • Desirable limit for drinking water is 500 mg/L. May be extended

upto 3000 mg/L of dissolved limits.

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 cause a disease methemoglobinemia (Blue baby disease).

• Desirable limit for drinking water is 45 mg/L. May be extended upto 100 mg/L Nitrates as NO3.

Bacteriological Characteristics:• Bacterial examination of water is very important, since it indicates the

degree of pollution. • Water polluted by sewage contain one or more species 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 that coliform group serves as indicator of contamination.• In drinking water number of bacteria should be nil.

Most Probable Number • Most probable number is a number which represents the bacterial density

which is most likely to be present.• E.Coli is used as indicator of pollution. • E.Coli ferment lactose with gas formation with 48 hours incubation at 35°C.

Based on this E.Coli density in a sample is estimated by multiple tube fermentation procedure, which consists of identification of E.Coli in different dilution combination.

• MPN value is calculated as follows:• Five 10 ml (five dilution combination) tubes of a sample is tested for E.Coli. If

out of five only one gives positive test for E.Coli and all others negative. • From the tables, MPN value for one positive and four negative results is read

which is 2.2 in present case. • The MPN value is expressed as 2.2 per 100 ml. These numbers are given by

Maccardy based on the laws of statistics.

Standard Plate Count Test

• In this test, the bacteria are made to grow as colonies, by innoculating a known volume of sample into a solidifiable nutrient medium (Nutrient Agar), which is poured in a petridish.

• After incubating (35°C) for a specified period (24 hours), the colonies of bacteria (as spots) are counted.

• The bacterial density is expressed as number of colonies per 100 ml of sample.

Membrane Filter Technique • In this test a known volume of water sample is filtered

through a membrane with opening less than 0.5 microns. • The bacteria present in the sample will be retained upon the

filter paper. • The filter paper is put in contact of a suitable nutrient

medium and kept in an incubator for 24 hours at 35°C.• The bacteria will grow upon the nutrient medium and visible

colonies are counted. Each colony represents one bacterium of the original sample.

• The bacterial count is expressed as number of colonies per 100 ml of sample.

Demand & population forecasting

• Purpose and Scope:• How much potable water is used today, and in what locations? • From which sources does the potable water originate, and

once used, where does it go for wastewater treatment? • Following treatment, how much of the water is reused, and

where is the balance disposed of? • Are there future imbalances in water supply, wastewater

disposal or reclaimed water usage, and if so, in which planning areas?

• Are there planning areas with adequate capacity to address imbalances?

Water Quantity Estimation• The quantity of water required for municipal uses for which the

water supply scheme has to be designed requires following data: Water consumption rate (Per Capita Demand in litres per day per head)

• Quantity= Per capita demand x Population Average Daily Per Capita Demand

= Quantity Required in 12 Months/ (365 x Population) • Maximum daily demand = 1.8 x average daily demand• Maximum hourly demand of maximum day i.e. Peak demand

= 1.5 x average hourly demand = 1.5 x Maximum daily demand/24 = 1.5 x (1.8 x average daily demand)/24

Water Consumption Rate

Water Consumption for Various Purposes:  Si.no. Types of Consumption Normal Range

(lit/capita/day) Average %

1 Domestic Consumption 65-300 160 35 2 Industrial and Commercial Demand 45-450 135 30 3 Public Uses including Fire Demand 20-90 45 10 4 Losses and Waste 45-150 62 25

It is very difficult to precisely assess the quantity of water demanded by the public, since there are many variable factors affecting water consumption.

The various types of water demands, which a city may have, may be broken into following classes:

Trend & Facts of Domestic Water Uses in Different Nation

The demand of water• Domestic water requirement for urban population:• According to National Water Policy (2002), domestic water

supplies for urban areas under various conditions are given below.

• The units mentioned “lpcd” stands for Liters per Capita per Day”. 1. 40 lpcd where only spot sources are available 2. 70 lpcd where piped water supply is available but no sewerage

system 3. 125 lpcd where piped water supply and sewerage system are both

available. 4. 150 lpcd may be allowed for metro cities

Domestic and livestock water requirement for rural population

• This may be done through individual effort of the users by tapping a local available source or through co-operative efforts, like Panchayats or Block Development Authorities.

• The accepted norms for rural water supply according to National Water Policy (2002) under various conditions are given below. 40 lpcd or one hand pump for 250 persons within a walking

distance of 1.6 km or elevation difference of 100 m in hills. 30 lpcd additional for cattle in Desert Development

Programme (DDP) areas.

Factors affecting per capita demand

1. Size of the city2. Presence of industries. 3. Climatic conditions. 4. Habits of people and their economic status.5. Quality of water: If water is aesthetically & medically safe, the

consumption will increase as people will not resort to private wells, etc. 6. Pressure in the distribution system. 7. Efficiency of water works administration8. Cost of water. 9. Policy of metering and charging method: Water tax is charged in two

different ways: on the basis of meter reading and on the basis of certain fixed monthly rate.

Fluctuations in Rate of Demand

• 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 During active household working hours i.e. from six to ten in the morning and four to eight in the evening.

Design Periods• 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 life of the component, considering obsolescence, wear, tear, etc. Expandability aspect. Anticipated rate of growth of population, including industrial,

commercial developments & migration-immigration. Available resources. Performance of the system during initial period.

Design period of different project component

S.no. Item Design period in years

1 Storage by dams 50

2 Infiltration works 30

3 Pumping

3.I Pump house 30

3.II Electric motors and pumps 15

4 Water treatment units 15

5 Pipe connection to the several treatment unit and other small appurtenances

30

6 Raw water and clear water conveying mains 30

7 Clear water reservoirs at the head works, balancing tanks and service reservoirs ( overhead or ground level)

15

8 Distribution system 30

Population Forecasting Methods

• Arithmetic Increase Method • Geometric Increase Method • Incremental Increase Method • Decreasing Rate of Growth Method • Simple Graphical Method • Comparative Graphical Method • Ratio Method • Logistic Curve Method

Population Forecasting Methods Cont…

• Arithmetic Increase Method :• This method is based on the assumption that the population

increases at a constant rate; i.e. dP/dt=constant=k; Pt= P0+kt. • This method is most applicable to large and established cities.• Geometric Increase Method:• This method is based on the assumption that percentage

growth rate is constant i.e. dP/dt=kP; lnP= lnP0+kt. • This method must be used with caution, for when applied it

may produce too large results for rapidly grown cities in comparatively short time.

• This would apply to cities with unlimited scope of expansion.

Population Forecasting Methods Cont…

• Incremental Increase Method : Used on the basis of the Average of the incremental increases in the past population of city is positive or negative.

• The population for a future decade is worked out by adding the mean arithmetic increase to the last known population as in the arithmetic increase method, and to this is added the average of incremental increases, once for first decade, twice for second and so on

• Decreasing Rate of Growth Method : In this method, the average decrease in the percentage increase is worked out, and is then subtracted from the latest percentage increase to get the percentage increase of next decade.

Population Forecasting Methods Cont…

• Simple Graphical Method: In this method, a graph is plotted from the available data, between time and population.

• The curve is then smoothly extended upto the desired year. • This method gives very approximate results and should be

used along with other forecasting methods.• Comparative Graphical Method:In this method, the cities

having conditions and characteristics similar to the city whose future population is to be estimated are selected.

• It is then assumed that the city under consideration will develop, as the selected similar cities have developed in the past.

Population Forecasting Methods Cont…

• Ratio Method:In this method, the local population and the country's population for the last four to five decades is obtained from the census records.

• The ratios of the local population to national population are then worked out for these decades.

• A graph is then plotted between time and these ratios, and extended upto the design period to extrapolate the ratio corresponding to future design year.

• This ratio is then multiplied by the expected national population at the end of the design period, so as to obtain the required city's future population.Drawbacks:

• Depends on accuracy of national population estimate. • Does not consider the abnormal or special conditions which can lead to

population shifts from one city to another.

Population Forecasting Methods Cont…

• Logistic Curve Method • The three factors responsible for changes in population are :

(i) Births, (ii) Deaths and (iii) Migrations.• Logistic curve method is based on the hypothesis that when

these varying influences do not produce extraordinary changes,

• The population would probably follow the growth curve characteristics of living things within limited space and with limited economic opportunity.

• The curve is S-shaped and is known as logistic curve.

Problem

• Predict the population for the years 1981, 1991, 1994, and 2001 from the following census figures of a town by different methods.

Year 1901 1911 1921 1931 1941 1951 1961 1971

Population: (thousands)

60 65 63 72 79 89 97 120

SolutionYear Population:

(thousands) Increment per

Decade Incremental

Increase Percentage Increment per

Decade

1901 60 - - -

1911 65 +5 - (5/60) x100=+8.33

1921 63 -2 -7 (2/65) x100=-3.07

1931 72 +9 +11 (9/63) x100=+14.28

1941 79 +7 -2 (7/72) x100=+9.72

1951 89 +10 +3 (10/79) x100=+12.66

1961 97 +8 -2 (8/89) x100=8.98

1971 120 +23 +15 (23/97) x100=+23.71

Net values 1 +60 +18 +74.61

Averages - 8.57 3.0 10.66

+ = Increase - = Decrease

Arithmetical Progression Method: Arithmetic Expression Pn = P + ni • Average increases per decade = i = 8.57 • Population for the years, • 1981= population 1971 + ni, here n=1 decade • = 120 + 8.57 = 128.57 • 1991= population 1971 + ni, here n=2 decade • = 120 + 2 x 8.57 = 137.14 • 2001= population 1971 + ni, here n=3 decade • = 120 + 3 x 8.57 = 145.71 • 1994= population 1991 + (population 2001 - 1991) x 3/10 • = 137.14 + (8.57) x 3/10 = 139.71

Incremental Increase Method

• Population for the years, • 1981= population 1971 + average increase per

decade + average incremental increase • = 120 + 8.57 + 3.0 = 131.57 • 1991= population 1981 + 11.57 • = 131.57 + 11.57 = 143.14 • 2001= population 1991 + 11.57 • = 143.14 + 11.57 = 154.71 • 1994= population 1991 + 11.57 x 3/10 • = 143.14 + 3.47 = 146.61

Geometric Progression Method: • Average percentage increase per decade = 10.66 • P n = P (1+i/100) n

• Population for 1981 = Population 1971 x (1+i/100) n

• = 120 x (1+10.66/100), i = 10.66, n = 1 • = 120 x 110.66/100 = 132.8 • Population for 1991 = Population 1971 x (1+i/100) n

• = 120 x (1+10.66/100) 2 , i = 10.66, n = 2 • = 120 x 1.2245 = 146.95 • Population for 2001 = Population 1971 x (1+i/100) n

• = 120 x (1+10.66/100) 3 , i = 10.66, n = 3 • = 120 x 1.355 = 162.60 • Population for 1994 = 146.95 + (15.84 x 3/10) = 151.70

Intake Structure• The basic function of the

intake structure is to help in safely withdrawing water from the source over predetermined pool levels.

• From pool this water discharge to water treatment Plant through conduit (normally called intake conduit).

The following are the various types of intake structures used are,

• Simple Submerged Intakes • Intake Towers

– Wet Intake Towers – Dry Intake Tower

• Medium Sized River Intake Structure– Twin well type of Intake Structure – Single well type of intake structures

• Canal Intake Structures • Intakes for Sluice-Ways of Dams

Simple submerged intake:– It is starting end of withdrawal pipe with a simple support

of concrete block or rock fill timber crib.– A sump well at shore is connected with withdrawal pipe

from where water is lifted by pump.– The intake opening is covered by screen so as to prevent

entry of debris, ice etc specially in river.– intake opening is generally kept at about 2 to 2.5 m above

the bottom of the lake and thus to avoid entry of silt and sediment.

– It is used for small water supply project drawing water from streams or lakes where little change in water surface elevation.

– It is not used in bigger project on rivers or reservoirs

Intake towers• It is generally used for large project on rivers and reservoirs

where surface water elevation fluctuating.• quantity and quality of water withdraw controlled by making

of gate arrangement .• The gate should be high enough above the reservoir bed so

that sediment is not withdraw.• Generally intake tower used in reservoir.• When large amount of water withdraw form river then intake

tower may be classified as:– Single well or twin well type intake structure

Types of intake towers

1 Wet intake tower:1. It consists a concrete circular

shell filled with water up to reservoir level.

2. Water withdraw generally through gravity, may be lifted by pumps in case of river.

3. There are no buoyant force, hence no heavier construction required

2 Dry intake tower• Water is directly drawn into the

withdrawal conduit through entry ports.

• Due to direct exposure additional buoyant force exert on the structure, hence heavier construction required.

• Advantage of this structure is water can be withdraw from any selected level of the reservoir by opening the port at that level.

Intake tower are huge structure so that at the time of design must consider worst possible combination of various forces, such as hydrostatic pressures, wind and earth quake forces, force cause by waves, ice debris etc.

Dry Intake Towers Wet Intake Towers

Single well• It is generally used in

alluvial river.• Water is ponded up by

constructing a weir across the river or by diversion head works.

Twin well• It is used for all kind of river

but specially constructed in the non-alluvial river.

Both types of river intake structure consists of:(i) Inlet well(ii) Inlet pipe(iii) Jack wellDesign Considerations:• Sufficient factor of safety against external forces such as heavy currents, floating materials, submerged bodies, ice pressure, etc. • Should have sufficient self weight so that it does not float by up thrust of water.

Canal Intake Structures• In this the intake well is generally located in the bank of the canal, and

water enters the chamber through an inlet pipe, covered with a fine screen.

• the top of which is generally provided at minimum water level in the canal, and bottom is about 0.15 m above the canal bed to avoid entry of bed load.

• This inlet end is of bell mouth shape with perforations of fine screen on its surface.

• An outlet valve, operating from the top, is provided to control the entry of water into the outlet pipe.

• The flow velocity through the outlet conduit is generally kept at about 1.5 m/sec, and this helps in determining the area and diameter at the withdrawal conduit.

Canal Intake Structures

Inlet well or collector well

• It`s shape in a circular or oblong well.

• Water enters into the well through the port.

• Ports fitted with vertical iron bars of 20 mm dia.@ 30 to 50mm center to center.

• Flow velocity range between 15 to 20 cm/s.

• Ports provides at 2 to 3 levels.• Inlet should be above the 1 to 3

metre above the bed of river.

Intake pipe

• The intake well connected to sump or jack well by intake pipe.

• None pressure pipe used as an intake pipe.

• Slope should be gentle 1 in 200 or so.

• Dia. Of pipe not less than 45cm.

• Flow velocity does not exceed @ 1.2m/s

Jack well

• Generally jack well constructed on high ground but try to locate close to river, always higher than HFL.

• Jack well should construct on the ground which bearing capacity should not less than 450 kN/m2. If not available R.C.C. raft may be laid at the bottom.

• Diameter of jack well @ 4 to 5 metre.

Factors Governing Location of Intake

• As far as possible, the site should be near the treatment plant so that the cost of conveying water to the city is less.

• The intake must be located in the purer zone of the source to draw best quality water from the source, thereby reducing load on the treatment plant.

• The intake must never be located at the downstream or in the vicinity of the point of disposal of wastewater.

• The site should be such as to permit greater withdrawal of water, if required at a future date.

• The intake must be located at a place from where it can draw water even during the driest period of the year.

• The intake site should remain easily accessible during floods and should not get flooded. Moreover, the flood waters should not be concentrated in the vicinity of the intake.

Pumping• A pump is a device which converts mechanical energy into

hydraulic energy. • It lifts water from a lower to a higher level and delivers it at

high pressure. • Pumps are employed in water supply projects at various

stages for following purposes:– To lift raw water from wells. – To deliver treated water to the consumer at desired pressure. – To supply pressured water for fire hydrants. – To boost up pressure in water mains. – To fill elevated overhead water tanks. – To back-wash filters. – To pump chemical solutions, needed for water treatment.

Classification of Pumps

• Based on principle of operation, pumps may be classified as follows:

• Displacement pumps (reciprocating, rotary) • Velocity pumps (centrifugal, turbine and jet

pumps) • Buoyancy pumps (air lift pumps) • Impulse pumps (hydraulic rams)

Capacity of Pumps• Work done by the pump,• H.P.=rQH/75• where, r= specific weight of water kg/m3, Q= discharge of

pump, m3/s; and H= total head against which pump has to work.

• H= Hs + Hd + Hf + (losses due to exit, entrance, bends, valves, and so on)

• where, Hs=suction head,

• Hd = delivery head, and

• Hf = friction loss.

Conveyance• There are two stages in the transportation of water:• Conveyance of water from the source to the treatment plant. • Conveyance of treated water from treatment plant to the

distribution system. • In the first stage water is transported by gravity or by pumping

or by the combined action of both, depending upon the relative elevations of the treatment plant and the source of supply.

• In the second stage water transmission may be either by pumping into an overhead tank and then supplying by gravity or by pumping directly into the water-main for distribution.

Free Flow System

• In this system, the surface of water in the conveying section flows freely due to gravity.

• In such a conduit the hydraulic gradient line coincide with the water surface and is parallel to the bed of the conduit. It is often necessary to construct very long conveying sections, to suit the slope of the existing ground.

• The sections used for free-flow are: Canals, flumes, grade aqueducts and grade tunnels.

Pressure System• In pressure conduits, which are closed conduits, the water

flows under pressure above the atmospheric pressure. • The bed or invert of the conduit in pressure flows is thus

independent of the grade of the hydraulic gradient line and can, therefore, follow the natural available ground surface thus requiring lesser length of conduit.

• The pressure aqueducts may be in the form of closed pipes or closed aqueducts and tunnels called pressure aqueducts or pressure tunnels.

• Due to their circular shapes, every pressure conduit is generally termed as a pressure pipe.

Pressure System Cont…

• When a pressure pipe drops beneath a valley, stream, or some other depression, it is called a depressed pipe or an inverted siphon.

• Depending upon the construction material, the pressure pipes are of following types: Cast iron, steel, R.C.C, hume steel, vitrified clay, asbestos cement, wrought iron, copper, brass and lead, plastic, and glass reinforced plastic pipes.

Hydraulic Design• The design of water supply conduits depends on the

resistance to flow, available pressure or head, and allowable velocities of flow.

• Generally, Hazen-William's formula for pressure conduits and Manning's formula for freeflow conduits are used.

• Hazen-William's formula U=0.85 C rH0.63S0.54

• Manning's formula U=1/n rH2/3S1/2

• where, U= velocity, m/s; rH= hydraulic radius,m; S= slope, C= Hazen-William's coefficient, and n = Manning's coefficient.

Water Treatment

Disinfection Filtration

Coagulation/ Flocculation

Raw Water ScreeningPST

Distribution

Flow Diagram of Water Treatment Plant

SST

Unit operations in water treatment

1. Storage2. Pre-Chlorination 3. Aeration4. Rapid mixing5. Flocculation (Slow

mixing)6. Sedimentation7. Slow sand filtration

8. Rapid sand filtration

9. Softening10. Post-Chlorination

11. Demineralization

The types of treatment required for different sources

Source Treatment required 1. Ground water and spring water fairly free from contamination

No treatment or Chlorination

2. Ground water with chemicals, minerals and gases

Aeration, coagulation (if necessary), filtration and disinfection

3. Lakes, surface water reservoirs with less amount of pollution

Disinfection

4. Other surface waters such as rivers, canals and impounded reservoirs with a considerable amount of pollution

Complete treatment

The types of treatment required for different sourcesand Characteristics of raw water

Source/ Characteristics Treatment required 1 Ground waters has Turbidity below 10 NTU and free from odor and color

No treatment or plain disinfection

2. Surface waters has Turbidity below 10 NTU and free from odor and color

Storage and plain disinfection

3. Ground water contains excessive iron, dissolved carbon dioxide and odorous gases

Aeration followed by flocculation (rapid and slow mixing), sedimentation, rapid gravity or pressure filtration and disinfection

10G.W

1S.W 10

G.W 3 8 1054 6

The types of treatment required for different sourcesand Characteristics of raw water

Source/ Characteristics Treatment required 4 Surface water with turbidities not exceeding 50 NTU and where sufficient area available

Plain sedimentation followed by slow sand filtration and disinfection practiced

5. Highly polluted surface waters laden with algae or other micro organisms

Pre-Chlorination , aeration, rapid mixing, flocculation , sedimentation, rapid sand filtration and post-chlorination

6 Surface water with low turbidity 10-15 NTU & TSS 50mg/L

Rapid sand filtration followed by Flocculation with alum addition by slow mixing (10 min)

10S.W

2S.W 8

S.W

3

7

1054

6

6

4 5 108

Functions of Water Treatment Units

Unit treatment Function (removal)

Aeration, chemicals 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, bacteria

Disinfection Pathogenic bacteria, Organic matter and Reducing substances

Aeration • Aeration removes odor 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.

• This process continues until an equilibrium is reached depending on the partial pressure of each specific gas in the atmosphere.

• Types of Aerators 1 Gravity aerators 2.Fountain aerators 3.Diffused aerators 4.Mechanical aerators.

Types of Aerators • Gravity Aerators (Cascades): 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.

• 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.

Types of Aerators Cont…

• Injection or 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.

• Mechanical Aerators : Mixing paddles as in flocculation are used. Paddles may be either submerged or at the surface.

• SettlingSolid 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).

• Purpose of Settling• To remove coarse dispersed

phase.• To remove coagulated and

flocculated impurities.• To remove precipitated

impurities after chemical treatment.

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

Sedimentation

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.

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.

Type I Settling• Size, shape and specific gravity of the particles do not change with

time. • Settling velocity remains constant. • If a particle is suspended in water, it initially has two forces acting

upon it:(1) force of gravity: Fg=ρpgVp (2) the buoyant force quantified by Archimedes as: Fb= ρ gVp

If the density of the particle differs from that of the water, a net force is exerted and the particle is accelerated in the direction of the force: Fnet = (ρp- ρ)gVp

• This net force becomes the driving force.• Where: ρp is the particle density; ρ is the fluid density Vp the

particle volume and g the acceleration of gravity

Type I Settling Cont…

• Once the motion has been initiated, a third force is created due to viscous friction.

• This force, called the drag force, is quantified by:Fd=CDAp ρ v2/2CD= drag coefficient.Ap = projected area of the particle. v = Linear settling velocity

• Because the drag force acts in the opposite direction to the driving force and increases as the square of the velocity, acceleration occurs at a decreasing rate until a steady velocity is reached at a point where the drag force equals the driving force: (ρp- ρ)gVp = CDAp ρ v2/2For spherical particles,Vp= π d3/6 and Ap=πd2/4 Thus, v2= 4g(ρp-ρ)d 3 CD ρ

Type I Settling Cont…

• Expressions for CD change with characteristics of different flow regimes. For laminar, transition, and turbulent flow, the values of CD are:CD = 24 (laminar) Re CD= 24 + 3 +0.34 (transition) Re Re

1/2

CD= 0.4 (turbulent)where Re is the Reynolds number:

• Re= ρvd μ Reynolds number less than 1.0 indicate laminar flow, while values greater than 10 indicate turbulent flow. Intermediate values indicate transitional flow.

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 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.

Long Rectangular Settling Basin

• Long rectangular basins are hydraulically more stable, and flow control for large volumes is easier with this configuration.

• A typical long rectangular tank have length ranging from 2 to 4 times their width.

• The bottom is slightly sloped to facilitate sludge scraping.

• A slow moving mechanical sludge scraper continuously pulls the settled material into a sludge hopper from where it is pumped out periodically.

A long rectangular settling tank can be divided into four different functional zones:

1. Inlet zone: Region in which the flow is uniformly distributed over the cross section such that the flow through settling zone follows horizontal path.2. Settling zone: Settling occurs under quiescent conditions.3. Outlet zone: Clarified effluent is collected and discharge through outlet weir.4. Sludge zone: For collection of sludge below settling zone.

Long Rectangular Settling Basin

Inlet and Outlet Arrangement

• Inlet devices: Inlets shall be designed to distribute the water equally and at uniform velocities.

• A baffle should be constructed across the basin close to the inlet and should project several feet below the water surface to dissipate inlet velocities and provide uniform flow.

• Outlet Devices: Outlet weirs or submerged orifices shall be designed to maintain velocities suitable for settling in the basin and to minimize short-circuiting.

Circular Basins• Circular settling basins have the same functional zones

as the long rectangular basin, but the flow regime is different.

• When the flow enters at the center and is baffled to flow radially towards the perimeter, the horizontal velocity of the water is continuously decreasing as the distance from the center increases.

• Thus, the particle path in a circular basin is a parabola as opposed to the straight line path in the long rectangular tank.

• Sludge removal mechanisms in circular tanks are simpler and require less maintenance.

Design Details• Detention period: for plain sedimentation: 3 to 4 h, and for

coagulated sedimentation: 2 to 2.5 h. • Velocity of flow: Not greater than 30 cm/min (horizontal

flow). • 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.

• Depth 2.5 to 5.0 m (3 m). • Surface Overflow Rate: For plain sedimentation 12000 to

18000 L/d/m2 tank area; for thoroughly flocculated water 24000 to 30000 L/d/m2 tank area.

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

Sedimentation Tank Design• Problem: Design a rectangular sedimentation tank to treat 2.4 million

litres of raw water per day. The detention period may be assumed to be 3 hours.

• Solution: Raw water flow per day is 2.4 x 106 l. Detention period is 3h.• Volume of tank = Flow x Detention period = 2.4 x 103 x 3/24 = 300 m3

• Assume depth of tank = 3.0 m.• Surface area = 300/3 = 100 m2

• L/B = 3 (assumed). L = 3B.• 3B2 = 100 m2 i.e. B = 5.8 m • L = 3B = 5.8 X 3 = 17.4 m• Hence surface loading (Overflow rate) = 2.4 x 106 = 24,000 l/d/m2

10018000 L/d/m2 < 24,000 l/d/m2 < 30,000 L/d/m2

Coagulation - Flocculation Theory• General Properties of Colloids• Colloidal particles are so small that their surface area in

relation to mass is very large.• Electrical properties: All colloidal particles are electrically

charged. • If electrodes from a D.C. source are placed in a colloidal

dispersion, the particles migrate towards the pole of opposite charge.

• Colloidal particles are in constant motion because of bombardment by molecules of dispersion medium. This motion is called Brownian motion (named after Robert Brown who first noticed it).

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: – Particle transport to effect interaparticle collision.– Particle destabilization to permit attachment when contact

occurs.Transport step is known as flocculation whereas coagulation is the overall process involving destabilization and transport.

Flocculation• Flocculation is stimulation by mechanical means to

agglomerate destabilized particles into compact, fast settleable particles (or flocks).

• 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 settleable flocks.

• 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 flock takes place.

Types 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.

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 aqua metal complexes Al(H2O)6

3+ and Fe(H2O)63+.

• 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 Fe(OH)2+.

• These products are quite effective as coagulants as they adsorb very strongly onto the surface of most negative colloids.

Destabilization using Al(III) and Fe(III) Salts

• Al2(SO4)3.14H2O + 6 HCO3- 2 Al(OH)3(s) + 6CO2 +14 H2O + 3 SO4

2-

• FeCl3 + 3 HCO3- Fe(OH)3(S) +3 CO2 + 3 Cl-

Jar Test

• The jar test is a common laboratory procedure used to determine the optimum operating conditions for water or wastewater treatment.

• This method allows adjustments in pH, variations in coagulant or polymer dose, alternating mixing speeds, or testing of different coagulant or polymer types, on a small scale in order to predict the functioning of a large scale treatment operation.

Jar Testing Apparatus

Jar Test Procedure• Fill the jar testing apparatus containers with sample water.• Add the coagulant to each container and stir at approximately 100 rpm for

1 minute. • The rapid mix stage helps to disperse the coagulant throughout each

container. • Turn off the mixers and allow the containers to settle for 30 to 45 minutes.

Then measure the final turbidity in each container. • Reduce the stirring speed to 25 to 35 rpm and continue mixing for 15 to

20 minutes. • This slower mixing speed helps promote floc formation by enhancing

particle collisions which lead to larger flocs. • Residual turbidity vs. coagulant dose is then plotted and optimal

conditions are determined. • The values that are obtained through the experiment are correlated and

adjusted in order to account for the actual treatment system

Filtration

• 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.

Filtration Mechanisms

• There are four basic filtration mechanisms: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.

Filtration Mechanisms

• 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.

Particle followed path with different mechanism

Final position

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 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.

Filter Materials

• 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.

• Advanced material (New Research)

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.

Isometric View of Rapid Gravity filter

Cross section of Rapid-sand filter

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.

Principles of Slow Sand Filtration

• 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.

Principles of Slow Sand Filtration• As this layer (referred to as “Schmutzdecke”) 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.

• 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 to 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.

Principles of Slow Sand Filtration

• 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.

Slow Sand Filters vs. Rapid Sand Filters

• 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.

Slow Sand Filters vs. Rapid Sand Filters Cont..

• 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.

• 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.

When is Backwashing Needed• The filter should be backwashed

when the following conditions have been met:

• The head loss is so high that the filter no longer produces water at the desired rate; and/or

• Floc starts to break through the filter and the turbidity in the filter effluent increases; and/or

• A filter run reaches a given hour of operation.

Operational Troubles in Rapid Gravity Filters

• Air Binding : The negative pressure so developed, tends to release the dissolved air and other gases present in water. The formation of bubbles takes place which stick to the sand grains. This phenomenon is known as Air Binding as the air binds the filter and stops its functioning.

• Initially, the loss of head of water percolating through the filter is generally very small. However, the loss of head goes on increasing as more and more impurities get trapped into it.

• A stage is finally reached when the frictional resistance offered by the filter media exceeds the static head of water above the and bed.( Most of this resistance is offered by the top 10 to 15 cm sand layer. The bottom sand acts like a vacuum, and water is sucked through the filter media rather than getting filtered through it).

• To avoid such troubles, the filters are cleaned as soon as the head loss exceeds the optimum allowable value.

Troubles Cont..

• Formation of Mud Balls :– The mud from the atmosphere usually accumulates on the sand

surface to form a dense mat. – During inadequate washing this mud may sink down into the

sand bed and stick to the sand grains and other arrested impurities, thereby forming mud balls.

• Cracking of Filters :– The fine sand contained in the top layers of the filter bed shrinks

and causes the development of shrinkage cracks in the sand bed.

– With the use of filter, the loss of head and, therefore, pressure on the sand bed goes on increasing, which further goes on widening these cracks

Remedial Measures to Prevent Cracking of Filters and Formation of Mud Balls

• Breaking the top fine mud layer with rakes and washing off the particles.

• Washing the filter with a solution of caustic soda.

• Removing, cleaning and replacing the damaged filter sand.

Standard design practice of Rapid Sand filter:

• Maximum length of lateral = not less than 60 times its diameter.

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

• C.S area of lateral = not less than 2 times area of perforations.

• C.S area of manifold = 2 times total area of laterals. Maximum loss of head = 2 to 5 m.

• Spacing of laterals = 15 to 30 cm c/c.

Standard design Cont..

• Pressure of wash water at perforations = not greater than 1.05 kg/cm2.

• Velocity of flow in lateral = 2 m/s. • Velocity of flow in manifold = 2.25 m/s. • Velocity of flow in manifold for wash water=

1.8 to 2.5 m/s. • Velocity of rising wash water= 0.5 to 1.0

m/min.

Standard design Cont..

• Amount of wash water = 0.2 to 0.4% of total filtered water.

• Time of backwashing = 10 to 15 min. • Head of water over the filter = 1.5 to 2.5 m.

Free board = 60 cm. • Bottom slope = 1 to 60 towards manifold. Q = (1.71 x b x h3/2) • where Q is in m3/s, b is in m, h is in m. • L:B = 1.25 to 1.33:1 .

Disinfection• Def.n :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.

• Disinfection Kinetics– When a single unit of microorganisms is exposed to a single unit of

disinfectant, the reduction in microorganisms follows a first-order reaction.

dN/dt=-kN ; N=N0e-kt

• This equation is known as Chick’s Law:- N = number of microorganism

N0 = Initial number of microorganism k = disinfection constant t = contact time

Methods of Disinfection• Boiling: The bacteria present in water can be destroyed by boiling it for a

long time• 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. • When Lime is added it rais 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.

• Drawback: Treatment like recarbonation for lime removal should be used after disinfection.

Methods of Disinfection Cont..

• Treament 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.

Chlorine Chemistry

• Chlorine is added to the water supply in two ways. It is most often added as a gas, Cl2(g). However, it also can be added as a salt, such as sodium hypochlorite (NaOCl) or bleach. Chlorine gas dissolves in water following Henry's Law. Cl2(g) Cl2(aq)

Once dissolved, the following reaction occurs forming hypochlorous acid (HOCl): Cl2(aq)+H2O HOCl + H+ + Cl-

Chlorine Chemistry• Hypochlorous acid is a weak acid that dissociates to form

hypochlorite ion (OCl-). HOCl OCl- + H+ • All forms of chlorine are measured as mg/L of Cl2 (MW = 2 x

35.45 = 70.9 g/mol)• Hypochlorous acid and hypochlorite ion compose what is

called the free chlorine residual. • These free chlorine compounds can react with many organic

and inorganic compounds to form chlorinated compounds. • If the products of these reactions posses oxidizing potential,

they are considered the combined chlorine residual.

Chlorine Chemistry

• A common compound in drinking water systems that reacts with chlorine to form combined residual is ammonia.

• Reactions between ammonia and chlorine form chloramines, which is mainly monochloramine (NH2Cl), dichloramine (NHCl2) and trichloramine (NCl3) .

• Many drinking water utilities use monochloramine as a disinfectant.

• If excess free chlorine exits then once all ammonia nitrogen has been converted to monochloramine so that chloramine species will oxidized such reaction is known as breakpoint reactions.

Chlorine Chemistry

• The overall reactions of free chlorine and nitrogen can be represented by two simplified reactions as follows:

• Monochloramine Formation Reaction. This reaction occurs rapidly when ammonia nitrogen is combined with free chlorine up to a molar ratio of 1:1.

HOCl +NH3 NH2Cl + H2O

Chlorine Chemistry

• Breakpoint Reaction: When excess free chlorine is added beyond the 1:1 initial molar ratio, monochloramine is removed as follows: 2NH2Cl + HOCl N2(g)+ 3H++ 3Cl-+ H2O

Types of chlorination

1. Plain chlorination2. Pre-chlorination3. Post-chlorination4. Double-chlorination5. Break point chlorination6. Super chlorination7. Dechlorination

Principle of Plant Layout

• The selection of site for treatment plant based on features as character, topography, and shoreline.

• The following principles are important to consider:• A site on a side-hill can facilitate gravity flow that will reduce

pumping requirements and locate normal sequence of units without excessive excavation or fill.

• When landscaping is utilized it should reflect the character of the surrounding area.

• Site development should alter existing naturally stabilized site contours and drainage as little as possible.

• The developed site should be compatible with the existing land uses and the comprehensive development plan.

Water Distribution Systems

• Requirements of Good Distribution System• Water quality should not get deteriorated in

the distribution pipes. • It should be capable of supplying water at all

the intended places with sufficient pressure head.

• It should be capable of supplying the requisite amount of water during fire fighting.

Requirements of Good Distribution System Cont..

• The layout should be such that no consumer would be without water supply, during the repair of any section of the system.

• All the distribution pipes should be preferably laid one metre away or above the sewer lines.

• It should be fairly water-tight as to keep losses due to leakage to the minimum.

• There are no chance of any contamination.

Layouts of Distribution Network

• The distribution pipes are generally laid below the road pavements, and as such their layouts generally follow the layouts of roads.

• We can also develop permanent duct along the road.

• There are, in general, four different types of pipe networks are:

Dead End System• It is suitable for old towns and

cities having no definite pattern of roads.

• Advantages:– Relatively cheap. – Determination of discharges

and pressure easier due to less number of valves.

• Disadvantages– Due to many dead ends,

stagnation of water occurs in pipes.

Grid Iron System• It is suitable for cities with rectangular

layout, where the water mains and branches are laid in rectangles.

• Advantages:– Water is kept in good circulation

due to the absence of dead ends. – In the cases of a breakdown in

some section, water is available from some other direction.

• Disadvantages– Exact calculation of sizes of pipes

is not possible due to provision of valves on all branches.

Ring System• The supply main is laid all along

the peripheral roads and submains branch out from the mains.

• Thus, this system also followsthe grid iron system with the flow pattern similar in characterto that of dead end system.

• So, determination of the size of pipes is easy.

• Advantages:• Water can be supplied to any

point from at least twodirections.

Radial System• The area is divided into

different zones. • The water is pumped into

the distribution reservoir kept in the middle of each zone and the supply pipes are laid radially ending towards the periphery.

Advantages:• It gives quick service. • Calculation of pipe sizes is

easy

Pipe Network Analysis• In any pipe network, the following two conditions

must be satisfied:• The algebraic sum of pressure drops around a

closed loop must be zero, i.e. there can be no discontinuity in pressure.

• The flow entering a junction must be equal to the flow leaving that junction; i.e. the law of continuity must be satisfied.

• The widely used method of pipe network analysis is the Hardy-Cross method