What is sewage? In which way can sewage be harmful to us?

Explanation

Municipal waste water containing human excreta is called sewage.
(ii) (a) Sewage caontais large amount of biodegradable organic matter. When such organic wastes are decomposed by naturally occuring microbes in the presence of oxygen, then there is sharp decline in dissolved oxygen (DO). This causes suffocation of large number of aquatic animals like prawns, fihes, etc. Such waters become. unift for human consumption.
(b) Sewage also contains many types of pathogenic micro-organisms which are responsible for diseases ike cholera,typhoid, dysentery, hepatitis etc.