Bhagwan Mahavir College of

Engineering and Technology

PRESENTATION ON

Prepared by : Ankit Gangani 140060106055

OUTLINE

Introduction

Objectives of water treatment

Conventional water treatment plant layout

Various Methods of purification of waterScreening

Plain Sedimentation

Sedimentation aided with coagulation

Filtration

Disinfection

Aeration

Softening

Introduction

Water treatment is the process of making water suitable oracceptable for an end-use.

It removes existing water contaminants and so reduces theirconcentration that the water becomes fit for its desiredapplication.

The amount & type of treatment process (Treatment Train )depends upon quality of raw water and various standards requiredafter treatment.

Objectives of water treatment

The objectives of water treatment are to produce:

Water that is safe for human consumption

Water that is appealing aesthetically to the consumer

Water at a reasonable cost

Indian Standards for drinking water

Screening

Coagulation

Flocculation

Sedimentation

Filtration

Disinfection

Storage

Distribution

Raw water

Alum Cl2

sludge

sludge

sludge

7

Functions of Water Treatment Units

Selection of treatment process-Train

The types of treatment required for different sources are given in the following table:

Removes large solids

logs

branches

rags

fish

Simple process

may incorporate a mechanized trash removal system

Protects pumps and pipes in Water Treatment Plants

Plain Sedimentation

Sedimentation is the removal of suspended particles by gravitational settling.

Types of Sedimentation Tanks

1) Fill And Draw Type2) Continuous Flow type

Shape of sedimentation tank

1. Rectangular tank with horizontal flow.

2. Circular tank with radial or spiral flow.

3. Hopper bottom tank with vertical flow.

SEDIMENTATION

13

Water flows to a tank called asedimentation basin

Gravity causes the flocs to settle to thebottom

It would take a very long time for allparticles to settle out and that wouldmean we would need a very largesedimentation basin.

Sedimentation aided with coagulation

Addition of measured quantity of chemicals calledcoagulants to water and their through mixing ( rapidmixing ).

Formation of precipitate which coagulates and forms aflow ( flocculation )

Sedimentation

Sedimentation added with comprises of three step

Coagulants

Aluminum Sulfate Al2(SO4)3

Ferrous Sulfate FeSO4

Ferric Sulfate Fe2(SO4)3

Ferric Chloride FeCl3

Lime Ca(OH)2

Aluminum salts are cheaper butiron salts are more effective over

wider pH range

15

Aeration Unit Work : Diffusion of Air

Removes odour and tastes

Oxidizes iron and manganese, increases dissolved oxygen content in

water, removes CO2 and reduces corrosion and removes methane and

other flammable gases.

Types of Aerators

1. Gravity aerators

2. Fountain aerators

3. Diffused aerators

4. Mechanical aerators.

Gravity Aerators (Cascades): In gravity aerators,water is allowed to fall by gravity such that a large areaof water is exposed to atmosphere, sometimes aided byturbulence.

Aeration Unit

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. Time

of aeration is 10 to 30 min and 0.2 to

0.4 litres of air is required for 1 litre

of water.

Aeration Unit

Fountain Aerators : These are also known as sprayaerators with special nozzles to produce a fine spray. Eachnozzle is 2.5 to 4 cm diameter discharging about 18 to 36l/h. Nozzle spacing should be such that each m3 of waterhas aerator area of 0.03 to 0.09 m2 for one hour.

Aeration Unit

Mechanical Aerators : Mixing paddles as inflocculation are used. Paddles may be eithersubmerged or at the surface.

Aeration Unit

Types of Mixing Devices

Mixings basins with baffle walls

`

Mixing Basins Equipped with Mechanical devicies

Flocculation

Flocculation is a slow mixing or agitating process in whichthe destablished colloidal particles are brought intointimate contact in order to promote the floc formation .

Rate of flocculation depends upon

Types and amount of turbidity

Types of coagulant

Dosages of coagulant

Mean velocity gradient in basin

Clariflocculator

Clarifier and flocculator are provided in single unitcalled clariflocculator.

The flocculating chamber is provided in the centreand clarifier component is formed by the peripheralspace.

Velocity of flow of water around 0.3 m/min.

Mechanical scrapper provided to remove sludge.

Filtration The process of passing the water through the beds of

such granular material is known as filteraton

Types of Filtration

Slow sand gravity filter

Rapid sand gravity filter

1. Rapid sand gravity filter

2. Pressure filter

Method of disinfection Physical method

By heat

By U.V. rays

Chemical method

Oxidizing chemicals

Metal ions

Alkalis and acids

Minor method

Boiling of water

Treatment with excess lime

Treatment with ozone

Treatment with iodine and bromine

Treatment with ultra-violet rays

Treatment with potassium permanganate

Water softening Water is said to be hard when it contains relatively large

amounts of bicarbonates, carbonates, sulphates andchlorides of calcium and magnesium dissolved in it.

Types of Hardness

Temporary hardness Permanent hardness

Types of Hardness

Temporary Hardness- caused by dissolved

bicarbonates of Ca and Mg.

-AKA ‘alkaline or carbonate hardness’

Permanent Hardness – caused by dissolved

chlorides and sulphates of Ca, Mg, Fe and Al etc.

Removal of Hardness

Removal of temporary hardness

1. Boiling

2. By adding lime

Removal of temporary hardness

1. Lime-soda process

2. Zeolite process

3. Demineralization or De-ionization process

Disinfection The filtered water may

normally contain someharmful disease producingbacteria in it.

These bacteria must bekilled in order to make thewater safe for drinking.

The process of killing thesebacteria is known asDisinfection orSterilization.

Methods of Disinfection

Boiling: The bacteria present in water can be destroyed by boiling it for a longtime. However it is not.

Treatment with Excess Lime: Lime is used in water treatment plant forsoftening. But if excess lime is added to the water, it can in addition, kill thebacteria also. Treatment like recarbonation for lime removal should be usedafter disinfection.

Treatment with Ozone: Ozone readily breaks down into normal oxygen, andreleases nascent oxygen. The nascent oxygen is a powerful oxidizing agent andremoves the organic matter as well as the bacteria from the water.

Chlorination : The germicidal action of chlorine is explained by the recenttheory of Enzymatic hypothesis, according to which the chlorine enters the cellwalls of bacteria and kill the enzymes which are essential for the metabolicprocesses of living organisms.

Reference

Water & waste water Engineering -4th edition ByMahajan Publishing House

http://web.iitd.ac.in/~arunku/files/CVL100/L8.pdf

http://nptel.ac.in/courses/105104102/Lecture%2020.htm

http://www.sswm.info/sites/default/files/reference_attachments/SCHUTTE%202007%20Handbook%20for%20the%20Operation%20of%20Water%20Treatment%20Works.pdf