Water Treatment

Water Treatment

The various methods used in sewage and industrial waste water treatment are as follows-

1. Preliminary treatment : The principle objectives of preliminary treatment are the removal of gross solid, i.e., large floating and suspended solid matters, girt, oil and grease if they present in considerable quantities.


2. Primary treatment: After removal of gross solids, gritty materials and excessive quantities of oil and grease, the next step is to remove the remaining suspended solids as much as possible. The step is aimed at reducing the strength of the waste water and also to facilate secondary treatment.

The methods used for primary treatment are-

a) Sedimentation
b) Sedimentation aids
c) Mechanical flocculation
d) Chemical coagulation
e) Coagulants acids
f) Equalization
g) Neutralization


3. Secondary treatment: In this treatment, the dissolved and colloidal organic matter present in waste waters is removed by biological process involving bacteria and other microorganisms. This treatment is of two types-
a) Aerobic process: In this process, bacteria and other microorganisms consume organic matters as food.
i. Activated sludge process
ii. Lagooning process

b) Anaerobic process: This is mainly used for the digestion of sludges.



4. Biochemical treatment :
i. Aerated lagoons
ii. Trickling filters
iii. Activated sludge process
iv. Oxidation ditch process
v. Oxidation pond
vi. Anaerobic digestion

5. Tertiary treatment: Tertiary treatment is the final treatment meant for polishing the effluents from the secondary treatment processes to improve its quality further. The major objectives of tertiary treatment are –
a) Removal of fine suspended solids
b) Removal of bacteria
c) Removal of dissolved inorganic solid
d) Removal of final traces of organic.