Purification of Water Supplies

Method of treatment employed depends on the nature of raw water constituents and the desired standard of water quality.

The unit operations in water treatment includes Screening, Aeration, Flocculation, Filtration, Disinfection, Softening, Deferrization, Defluoridation.  

The choice of a particular sequence of treatment unit will depend on quality of raw water and treated water desired.

In case of ground water and surface water with storage having turbidity less than 10 NTU and free from colour. odour. Plan disinfection is sufficient for drinking purposes.

For ground water containing excessive Iron: dissolved carbon dioxide and odourous gass, the treatment process will be: Aeration -> Flocculation and Sedimentation -> Rapid gravity filter -> Disinfection -> Supply 

If ground water contains only CO. and odourous gases. Aeration and disinfection is sufficient.

Surface water with turbidity less than 50 NTU and where sufficient land is available, the treatment will be: Sedimentation -> Slow sand filter -> Disinfetion

Highly polluted surface water -- laden with algae and other microorganisms the sequence of treatment will be: Prechlorination -> Aeration -> Flocculation and Sedimentation -> Rapid gravity filter -> Disinfection(post chlorination) -> Supply 

(a) Screening
(b) Aeration
(c) Flocculation
(d) Filtration 
(e) Disinfection 
(f) Softening 
(g) Deferrization 
(h) Defluoridation