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Question

What are the various constituents of domestic sewage? Discuss the effects of sewage discharge on a river.


Solution

The various constituents of domestic sewage are 

(i)  dissolved salts such as nitrates, phosphates etc from detergents,

(ii) toxic metal lons from paints, varnishes, etc.

(iii) blodegradable organic matter from kitchen and tollet.

(iv) pathogenic microorganisms in the faecal matter.

Effects fo sewage waste discharge on river

(i) A sharp decline in dissolved oxygen, Low oxygen levels in the water causes death of fishes and other aquatic creatures.

(ii) Algal bloom which results from the presence of organic matter in water it causes

(a) deterioration of the water quality.

(b) fish mortality.

(c) toxicity to humans and animals.

(iii) Excessive growth of water hyacinth due to presence or organic matter in water causing an imbalance in the ecosystem dynamics of the water body.

(iv)  Biological magnification of a few toxic substances causing harmful effects in living species.

(v) Accelerated eutrophication (ageing of lakes and other water bodies).


Biology
NCERT Textbook
Standard XII

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