Question

Treatment of sewage is done by the ________________ naturally present in it.

• A. algae
• B. heterotrophic microbes
• C. autotrophic microbes
• D. autotrophic and heterotrophic microbes

Answer 1

The correct option is B heterotrophic microbes

The large quantities of waste water that is generated every day in cities and towns is known as sewage. It contains human excreta, large amounts of organic matter (food waste) and pathogenic microbes. It is treated in sewage treatment plants (STPs) before it is discharged into natural water bodies. The treatment involves digestion of the organic matter present in the sewage by heterotrophic microorganisms such as bacteria and fungi that are naturally present in sewage. The amount of organic matter in sewage is proportional to its polluting potential. The heterotrophic microbes utilise the organic matter as a source of nutrition and thereby reduce the pollution potential of sewage before it is disposed into water bodies.

Algae and autotrophic microbes are capable of manufacturing their own food and do not make use of organic matter from external sources for their nutrition. Therefore, they cannot be used to digest the organic matter present in the sewage.