Question

Describe secondary treatment of sewage till can be discharged into a natural water body.

Answer 1

• Secondary treatment of wastewater is done to achieve a certain degree of effluent quality.
• During this, a physical phase separation is used to remove settleable solids and a biological process to remove dissolved and suspended organic compounds.

1) The water at this stage is put into large rectangular tanks called aeration lanes.

2) Air is pumped into the water to initiate the aerobic bacteria to break down the organic matter present within the wastewater.

3) The treated wastewater is then passed through a settlement tank where more sludge is formed at the bottom of the tank by the settling of the bacterial action

4) This sludge is collected for treatment, the water at this stage is almost free from harmful substances and chemicals.

5) Later this water is allowed to flow over a bed of sand to remove any additional particles and is filtered.

6) The filtered water is then released into the river.