water & waste water engineering - water treatment process & units
TRANSCRIPT
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
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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
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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
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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