Water treatment plants can be classified based on the processes used, which include disinfection, filtration, or softening. Filtration plants typically treat surface water and use screens, mixing, coagulation, flocculation, sedimentation, filtration and disinfection to remove debris, flocs, pathogens, and improve water quality. Lime soda softening plants treat groundwater, using lime, soda ash, and similar processes to precipitate calcium, magnesium, and remove hardness. Sedimentation separates solids from water using gravitational settling according to particle density and size.

1. 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.
1

2. 2
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
sludge
R C GF
co2
Disinfection
To Distribution cw
system
pump
Ground water from well +
Ca (OH)2 +Na2CO3
screens
(Lime soda softening
plant)
Raw River
or Lake
water
M F S GF Disinfection PUMP
Filtration Plant
CW
M (Mixing); R B : Reaction Basin; F (flocculation); S (sedimentation tank) ; RC (Re carbonation);
GF(Granular Filtration); c w (clear water

3. 3
sedimentation
A 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;