Question

Explain the stages involved in secondary treatment of water.

Answer 1

Water treated by primary treatment is not fit for drinking. Therefore, it undergoes the process of secondary treatment. Secondary treatment has the following two steps:
(i) Softening: The hard water has actions of calcium and magnesium. To soften water lime and soda ashore-added to the water to precipitate calcium and magnesium ions as carbonates. The precipitate is then filtered out. The water so treated goes through porous actions exchanger in which water becomes action free.
(ii) Aeration: In order to make the water fit for drinking some amount of oxygen is forced into it. Aeration of water is carried out by forcing air through water in the form of air bubbles. This process adds oxygen and other gases and reduces the content of carbon gases and reduces the content of carbon dioxide and hydrogen sulphide in the water.