Question

How is activated sludge process carried out for the treatment of waste water? Explain with flow sheet diagram.

Answer 1

Sewage is the liquid which includes human and household waste water, industrial waste,
ground waste and street and storm water. Hence due to the toxicity the sewage have to be
treated because of the reasons like:

1. To prevent pollution of water into which the sewage is left off
2. To prevent offensive odour in the water, and the destruction of fish and other aquatic life.

SEWAGE TREATMENT BY ACTIVATED SLUDGE PROCESS.

1. Preliminary Treatment.
The principal objective of preliminary treatment is the removal of gross solids i.e., large floating and suspended solid matter, grit, oil, and greases if present in considerable quantities. For removing inorganic matter, sewage is allowed to pass through bar screen and mesh screen.

2.Primarv Treatment.
For removing suspended matter efficiently and economically, sedimentation process is carried out .Sewage is treated with certain chemicals (e.g., alum, hydrated lime etc.) which form a floe that absorbs and entraps the suspended and colloidal particles presen.

3. Secondarv or Biological Treatment.
It is an essential an aerobic chemical oxidation which includes filtration and activated sludge process. Sewage water is filtered through specially designed sprinkling filters to maintain aerobic conditions. Carbon of the organic matter is converted into co₂ ; and nitrogen into NH₃ and finally into nitrates and nitrites. Trickling filters are used for biological oxidation of sewage. Trickled sewage starts percolating downwards an the aerobic bacteria bring about the biological oxidation of organic matter of sewage.

Hence the sludge formed is known as Activated Sludge. The further process includes mixing of sedimental sewage with proper quantity of activated sludge and mixture is then agitated for 4-5 hrs by blowing air. Suspended and dissolved organic matter is oxidised by aerobic bacteria . after all these process a part of sludge deposited is used for next oxidation batch and the remainder is either spread on land as fertile matter or used for biogas or dumped in.