Question

Why is aerobic degradation more important than anaerobic degradation for the treatment of large volumes of waste waters rich in organic matter? Discuss.

Answer 1

Secondary treatment:

Aerobic degradation is used in the secondary treatment of sewage. The secondary treatment involves the usage of the following:-

● Aeration tank: The waste water is aerated constantly so that flocs can develop. The flocs are masses of aerobic bacteria meshed in with fungal filaments. Aerobic degradation of organic matter takes place here.

● Settling tank: Here, the flocs are allowed to settle down.

● Anaerobic digester: Most of the sedimented floc is pumped into these digesters where these are digested anaerobically to release biogas.

Aerobic degradation:

The flocs formed in the aeration tank contain heterotrophs that actively use organic matter for metabolism. This significantly reduces the organic content of the sewage, ensuring a reduction of BOD (Biochemical Oxygen Demand), making the waste water suitable for discharge into water bodies. This is because lower BOD signifies less polluting potential of water. Additionally, this process is fast and cost-effective.

Anaerobic digestion:

Anaerobic degradation happens in the anaerobic digester and is not considered for large volumes because the process is slow and therefore will not be efficient in a sewage treatment plant that receives a lot of waste water every day. Also, it is not the primary method of reduction of organic matter in sewage.