Question
What processes are generally responsible for the deoxygenation of water?
Solution
Deoxygenation of water takes place through the following processes:
(i) Oxidation of organic matter: The dissolved oxygen in water is consumed rapidly by microorganisms to oxidise organic matter of sewage.
(ii) Bio-oxidation of the nitrogenous matter: Oxygen in water may be consumed by the bio-oxidation of the nitrogenous material. 
(iii) Oxidation of chemical reducing agent: The dissolved oxygen in water may be consumed by the chemical or biochemical oxidation of chemical reducing agents. 
