Read the paragraph below and answer the given question:
Ganga Action Plan Phase I (GAP I) was the first attempt of Government to clean the river Ganga. The plan was formulated on the basis of a comprehensive survey of the Ganga basin carried out by the CPCB in 1984. According to the CPCB survey, the total sewage generated from 25 Class I towns in 1985 was estimated as 1340 million litres per day (mld). Out of this, due to resource crunch, pollution abatement works corresponding to 882 mld only (65% at that time) were taken up under GAP Phase I. To accomplish this task, a total of 261 projects of pollution abatement covering these 25 towns in three States were sanctioned at a cost of 462 crore. Of these, 259 projects have been completed and the remaining two projects of sewage treatment plants in Bihar (STPs at Patna & Munger) are in the final stage of completion. These projects have been delayed due to litigation and the State Government has been asked to complete the same at the earliest. The GAP I was declared closed in 31st March, 2000. The completion cost of GAP Phase I including the cost of these two works is ₹452 crore out of which an expenditure of ₹433 crores has been incurred by the State Governments. Under this plan, a sewage treatment capacity of 865 mld has been created.
The major component of domestic sewage is:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Human excreta and bacteria
Domestic sewage comes from homes. Apart from water, its main content is human excreta and the bacteria in it; this organic matter is what sewage treatment removes.
Option (1) Chemical pollutants — Incorrect. Chemical pollutants such as heavy metals come mainly from industrial waste water. Sewage from homes carries mostly organic matter from human excreta, so chemicals are not its major part.
Option (2) Paper and fiber — Incorrect. Paper and fibre may be present, but only in small amounts. Domestic sewage is mostly water carrying organic matter from human excreta, together with bacteria.
Option (3) Human excreta and bacteria — Correct. Domestic sewage is mostly water, but its main harmful content is human excreta, full of organic matter and bacteria, many of them pathogenic. That is why it must be treated before it is let into rivers.
Option (4) Grit — Incorrect. Grit is removed in primary treatment but is a small part.