116
VOCs are toxic and their presence in drinking water may be very harmful. Vinyl
chlorine is most toxic and are generally used in polyvinyl chloride resins.
Triochloroethelene (TCE) is a solvent that was commonly used for cleaning
electronic parts, as a medium of heat transfer and in the production of chlorofluro
carbons. Carbon tetrachloride, used for household cleaning and is very toxic if
ingested, only a few millimeter can cause death.
Water Treatment Systems for Drinking Water
Water treatment system for drinking water will depend upon the source of
water. Surface water treatment system seldom needs softening of hard water
whereas ground water invariably require softening, since the hardness level is
often more than 1000 mg/l. A simple surface water treatment system consists
of the following :
1.
Screening : to remove large floating and suspended solids.
2.
Mixing : The water with some chemicals so that small particles may
coagulate the suspended solids which may settle.
3.
Flocculation : is the process when water mixes gently with the floculant.
4.
Sedimentation : When the velocity of flow is reduced, the flocs settles
down as sediment.
5.
Sludge processing is the process whereby the settled solids and liquids
are dewatered and disposed of.
6.
Disinfection of the liquid is then effected to make water free of harmful
objects for drinking.
7.
Softening process is used when the source is ground water to remove
hardness of water.
Fig.7.1 : Schematic flow of a typical water treatment plant for surface water
(After Gilbert, 1955)
