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

Explanation

Domestic sewage includes biodegradable pollutants such as animals and human excreta , dissolved organic compounds , nitrate and phosphates , sodium , potassium, c alcium and chloride ions . Usually these pollutants undergo rapid decomposition , but some time they accumulate in larger quantities in the field and cause problems .
The sewage may also percolate through the soil and reach the water table and contaminate the drinking water. Besides, the sewage kills the living fish and other aquatic animals and reduces the oxygen content of the water and causes excessive growth of microorganisms (algal bloom) ad aquatic vegetation . This process is know as eutrophication . Under such conditions , oxygen content is very low and the river water becomes foul smelling due to putrifaction and the river becomes degraded.
Due to high growth of micro-organisms, the biological oxygen demand (BOD) of the water increases. BOD is a test of the amount of oxygen needed for bacteria to break down the organic matter in a water sample a period of fice days.