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Water Treatment• WATER TREATMENT : Water treatment plants can be classified as simple disinfection,

filtration, or softening plants. Plants using disinfection have high quality of water and

chlorinate to ensure that the water reaching customers must be safe from microorganisms.

Generally filtration plants can be used for surface water while Lime soda softening plants for

ground water treatment.

• Filtration unit are usually consists of screen devices, rapid mixing, coagulation, flocculation,

sedimentation, filtration and disinfection processes. The screens devices remove large

debris, chlorination and flocculation produce precipitate or flocs, which can be removed in

the sedimentation tank. The granular media filters remove most of the fine non settling flocs,

and disinfection kills pathogenic organisms, remove color, turbidity, taste and odor. After

disinfection process water is stored in clear well and is pumped to the distribution system by

pumping units. The clear well provide storage so that plant may operate at a constant rate

based on demand. The solids handling system for disposal of sludge from the clarifier

consists of filter press to dewater the sludge and be disposed of.

• Lime Soda softening consists of chemical precipitation, flocculation, sedimentation, re-

carbonation, filtration, and disinfection. The addition of slake lime {Ca (OH)2} and soda ash

(Na2CO3) precipitate the calcium and magnesium ions as calcium carbonate and magnesium

hydroxide. During flocculation, the precipitate or flocs formed is removed by settling basins.

Re-carbonation by CO2 lowers the pH to acceptable level. Disinfection kills the pathogenic

microorganisms. Lime-soda softening, along with removing hardness, produces coagulation

and settling of colloidal solids, although sometimes a coagulant is added to improve the

performance.

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Water Treatment Plants• Ground Water are usually of high quality and need only the treatment to remove gases like, co2 , H2S and others

when they are present in concentrated forms and disinfection to provide residual in the distribution system. The supply and treatment plant for such a water consists of well, a gas stripping unit, disinfection unit and a ground storage reservoir along with pumping unit. If ground water has sufficient hardness, softening will be required. Similarly, if ground water has sufficient iron or manganese contents, special treatment is required for their removal.

Rapid Mixing

R B S

sludgeco2

cwTo Distribution system

pump

screens

(Lime soda softening plant)

Raw River or Lake water

M F S GF Disinfection PUMP

M (Mixing); R B : Reaction Basin; F (flocculation); S (sedimentation tank) ; RC (Re carbonation); GF(Granular Filtration); c w (clear water

Filtration Plant

Ground water from well + Ca (OH)2 +Na2CO3

R C GF

Disinfection

CW

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sedimentationA solid-liquid separation used gravitational settling to remove suspended solids. It works on the

principle that when a liquid containing solids in suspension is placed in quiescent state, the solids

of higher specific gravity than liquid will tend to settle, while with lower specific gravity will tend to

rise. Thus the objective of treatment by sedimentation is to remove settle able particles and

reducing the suspended solids contents. Sedimentation may be either circular or rectangular in

shape. It consists of four zones Inlet, settling, out let and sludge storage. Inlet zone is to distribute

the flow and suspended particles across the cross section of the settling zone. As the flow is evenly

distributed, and the water velocity slowed down to the design velocity of the sedimentation zone.

At this point the inlet zone ends and settling zone begins. At settling zone particles started to settle

down in the settling zone.. The out let zone is designed to remove the water from the basin

without carrying away any flocculated particles. The velocity of flowing water is V = Q/A; where V is

water velocity in m/s; Q = water flow m3/sec and A = cross sectional area m2;