Previous Year Question

Biodegradable Pollutants are pollutants that can be broken down into relatively simpler substances by microorganisms through natural processes.

Sewage contains a large amount of biodegradable organic matter. Bacteria and other microorganisms can break down this organic matter through decomposition.

The same principle is used in Biological or Secondary Sewage Treatment, where microorganisms degrade biodegradable organic material present in sewage.

However, the fact that sewage is biodegradable does not mean that it is harmless. If a large quantity of untreated sewage enters a water body, microorganisms consume large amounts of dissolved Oxygen while decomposing it.

This can increase Biochemical Oxygen Demand (BOD) and reduce Dissolved Oxygen (DO) in water, adversely affecting fishes and other aquatic organisms.

On the other hand—

Mercury is a heavy metal and is not biologically degraded.

Plastic generally degrades very slowly and is not considered a conventional biodegradable pollutant.

Asbestos consists of mineral fibres and is not biodegraded by microorganisms.