PUBLIC
WATER TREATMENT SYSTEMS
The
water supplied to big cities is derived from surface water sources like
lakes, rivers, dams, reservoirs etc. The water from these sources will
be naturally turbid and will have high bacterial contamination. The
turbidity is removed by coagulation with alum. This is done in a mechanical
unit called clariflocculator. The water is then filtered through filter
beds; it is disinfected using chlorine or bleaching powder and supplied
to the public.
Simple
treatment for water containing turbidity and iron
Water
containing iron will be turbid and brownish. On standing, the turbidity
settles within 2 to 12 hrs. depending on the form in which iron is present
(inorganic or organic iron). The water after settling can be filtered
and directly used. Addition of bleaching powder and alum (at a dosage
level of 5-10 g and 30-50 g respectively per 1000 liters) can quicken
the settling of iron and the water can become clear within 1 to 2 hrs.
