Question

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

Answer 1

Domestic sewage is the waste originating from the kitchen, toilet, laundry, and other sources. It contains impurities such as suspended solid (sand, salt, clay), colloidal material (fecal matter, bacteria, plastic and cloth fiber), dissolved materials (nitrate, phosphate, calcium, sodium, ammonia), and disease-causing microbes. When organic wastes from the sewage enter the water bodies, it serves as a food source for micro-organisms such as algae and bacteria. As a result, the population of these micro-organisms in the water body increases. Here, they utilize most of the dissolved oxygen for their metabolism. This results in an increase in the levels of Biological oxygen demand (BOD) in river water and results in the death of aquatic organisms. Also, the nutrients in the water lead to the growth of planktonic algal, causing algal bloom. This causes deterioration of water quality and fish mortality.

Answer 2

Domestic sewage contains four kind of impurities:

(i)Suspended solids: They are soil particles such as sand and silt.

(ii)Colloidal particles: They are inorganic and organic materials such as faecal matter, bacteria, paper and cloth.

(iii)Dissolved solids : They are nitrates, phosphates, ammonia, sodium, calcium and other nutrients

(iv)Pathogens : Domestic sewage has pathogens of various diseases such as typhoid, cholera, dysentery, diarrhoea, etc. Effect of sewage discharge on river are:

(i)Eutrophication.

(ii)Growth of pathogenic bacteria.

(iii)Ageing of river where slit and decaying matters start accumulating and filling river.

(iv)Increase in BOD.

(v)Destruction of flora and fauna of that river.