Question

Polluted‌ ‌water‌ ‌can‌ ‌be‌ ‌purified‌ ‌by‌ ‌using‌ ‌
(a)‌ ‌Microorganisms‌ ‌
(b)‌ ‌Algae‌ ‌
(c)‌ ‌Pesticides‌ ‌
(d)‌ ‌Fishes

Answer 1

Hint: Polluted water contains harmful organic wastes that can be decomposed into simple non-toxic substances.

Complete answer:
Microorganisms are used for several purposes like biogas production, fermentation, curd formation, production of antibiotics, etc. In recent years microbes have been integrated with the sewage treatment system and polluted water can be treated with the help of these microorganisms.

Additional Information:
Sewage treatment is a three-step process:
1. Primary Treatment of Sewage: The primary treatment involves the mechanical and physical removal of large and small-sized particles by the process of filtration and sedimentation. It is done in stages, the first stage involves the removal of floating debris by sequential filtration. The second stage involves the removal of grit, pebbles, and soil particles by sedimentation. All of the solids settle at the bottom of primary settling tanks and form the primary sludge. The effluent is formed by the supernatant.
2. Secondary or Biological Treatment of Sewage: The effluent from primary treatment is moved into large aeration tanks. Fresh air is pumped into the aeration tanks and the effluent is mechanically agitated constantly. This promotes the growth of aerobic bacteria which get associated with fungal filaments to form flocs. These microbes consume the majority of the organic part of sewage and this results in the reduction of BOD of the effluent. After the reduction of BOD, the flocs are allowed to sediment, this forms activated sludge/secondary sludge. A small part of It is used as inoculum or starter in the aeration tanks. The rest of it is transferred to anaerobic sludge digester tanks, where anaerobic bacteria digest the aerobic bacteria and fungi in flocs.
3. Tertiary Treatment: After secondary treatment, the water undergoes chlorination or ozonation to free it of remaining germs and impurities. After which it is ready to be discharged as a source of pure water.

So, the correct answer is, “polluted water can be purified by using microorganisms.”

Note: It should be noted that both aerobic and anaerobic bacteria play a major role in sewage treatment. Flocs are formed by the association of bacterial colonies with the fungal filament.