Answer:
(i) Municipal waste water containing human excreta is called sewage.
(ii) (a) Sewage contains large amount of biodegradable organic matter. When such organic wastes are decomposed by naturally occurring 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, fishes, etc.
Such waters become unfit for human consumption.
(b) Sewage also contains many types of pathogenic micro-organisms which are responsible for diseases like cholera, typhoid, dysentry, hepatitis, etc.
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