Question

Identify the correct statements from the given set of statements.
i) In primary treatment first, floating debris of waste is removed by sequence filters
ii) The soil and small pebbles are removed by sedimentation in settling tanks.
iii) The sediment is called primary sludge and supernatant is effluent.
iv) The sludge is taken for secondary treatment
v) Lower the B.O.D., higher the pollution.
vi) When DDT enters the food chain then they reach water and are easily degradable.
vii) Discharge of sewage in the river will decrease its B.O.D.
viii) Chlorine is added to disinfect drinking water
A. (i), (ii), (iii), (iv)
B. (i), (ii), (iii), (vii)
C. (i), (ii), (iv), (v)
D. (i), (iv), (v), (viii)

Answer 1

During the treatment of water the wastage which is released into the water bodies generally has a lower BOD and chlorine is not good for the health of a normal human being as it is harmful for the body.

Complete answer:
We all know that the water which needs to be treated again should be free of all types of hard sediments like wood logs, plastics. To achieve this the water is filtered in the primary treatment to remove the impurities visible to naked eyes. Then after this process the filtered water is collected into a tank called the settling tank whose main function is to accumulate the soil particles and the other small impurities which get deposited in the bottom and the impurities so collected are called the primary sludge and the clean water is called the effluent. Now it is the effluent which is taken for the secondary treatment where it is treated with the chemicals to remove other chemical impurities from the effluent. The biological oxygen demand of the chemically treated water is increased so as to remove the organic impurities by the action of microorganisms which will undergo aerobic respiration to get rid of the organic matter. This indicates that higher the OD, higher will be the impurities into the water. DDT is a harmful pesticide which is mixed with the crops to protect them from the insects. When the crops are consumed this DDT is removed via faeces and gets mixed into the water and thereby polluting them. DDT is known to be a non-bio-degradable element.
If the sewage water is directly introduced into the rivers, then the organic impurities inside the river will increase and therefore as a result the BOD will also increase so as to get rid of the organic impurities. Chlorine is added to water of the swimming pools to protect it from giving stagnant water like smell and therefore leading to non-pollution of water.

So according to our discussion we found that among all the 8 statements only 4 are correct which are 1, 2, 3, and 7.

Note: If chlorine is consumed via the drinking water then it may cause health related issues to the person and also the DDT is now not suggested to be added to the crops because of its non-biodegradability.