Question

The release of municipal wastewater and industrial waste into our natural water bodies is causing disastrous effect to the aquatic life. Explain the biological treatment that should be given to it before releasing into the natural water bodies. [3 marks]

Answer 1

The biological treatment is done in the following steps:
The primary effluent is passed into large aeration tanks where it is constantly agitated mechanically and air is pumped into it. This allows vigorous growth of useful aerobic microbes. While growing, these microbes consume the major part of the organic matter in the effluent which significantly reduces the BOD. The effluent is then passed into a settling tank where the bacterial flocs are allowed to sediment. This is the activated sludge. A small part of the activated sludge is pumped back into the aeration tank to serve as the inoculum. The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters where other kinds microbes are grown anaerobically. Finally, the effluent from the secondary treatment plant is generally released into natural water bodies. [3 marks]