Question

Polluted water can be purified by using
A.Micro organisms
B.Algae
C.Pesticides
D.Fishes

Answer 1

Sewage is the term used to denote the wastewater produced in day to day life. Major components of these are human excreta and other organic matters. We have developed several ways to purify the sewage water and to protect our water bodies from being polluted.

Complete answer: Water pollution is a major concern in industrial areas and cities. Sewage water contains several harmful components that are able to cause several communicable diseases. This has created severe health hazards in recent years. Mixing up the sewage with water bodies makes them polluted which leads to harmful effects on aquatic organisms. We can purify this wastewater created in day to day life with the help of microorganisms in sewage treatment plants.
We know that there are several microbes present in the wastewater. In sewage treatment, we make use of these microbes itself to purify the water before dumping it into water bodies.
Purifying wastewater involves several steps. The first step is called primary treatment which is completely physical treatment. It includes the removal of solid particles, floating debris, etc, and the supernatant is taken for secondary treatment after removing the sediment.
The secondary treatment is called a biological treatment or microbial treatment. The primary effluent is aerated and agitated leading to the formation of flocs that are masses of bacterias attached to fungal components. After this, the supernatant is allowed to be released to the water bodies, and the sediment is then converted to a substance called activated sludge.
Hence the correct option is A.

Note: In the secondary treatment in sewage plants, the flocs that are allowed to settle are converted into a substance called activated sludge. It is then taken into activated sludge digesters and during the process, methane gas is released along with carbon dioxide and hydrogen sulfide. Methane gas released here can be used as biogas.