It involves three types of treatments- (i) Primary, (ii) secondary and (iii) Tertiary
treatment.

(i) Primary treatment-It includes physical processes ike separation of large debris
and sedimentation etc.

(ii) Secondary treatment-It consists of use of microorganisms in oxidation ponds
or activated sludge process. Oxidation pond is a shallow water reservoir where
human faucal matter is collected. It is rich in organic substances and thus
stimulates growth of algae and bacteria.

Bacteria decompose the organic matter and release carbon dioxide, which is used by algae, in photosynthesis. Oxygen released during photosynthesis reduces water pollution. In this way in oxidation ponds algae and bacteria show symbiosis. The processes Occurring in oxidation ponds kill infectious bacteria leaving nonpathogenic bacteria and harmless organic matter.

(iii) Tertiary treatment-It involves physic-chemical processes that remove turbidity in the waste water (due to nitrogen and phosphorus etc.). This treatment involves the oxidation of waste-water by strong oxidizing agents (like chlorine, perchlorate salts, 0zone gas and UV radiations). After tertiary treatment, the water can De discharged into natural water and can be used for irrigation purpose.

Tags: Treatment of Waste Water