Question

Explain the process of secondary treatment given to the primary effluent up to the point it shows significant change in the level of biological oxygen demand (BOD) it.

Answer 1

The effluent from the primary treatment is passed to aeration tanks where air is pumped into it. The useful aerobic microbes grow into flocs (masses of bacteria associated with fungal filaments) and consume the major part of the organic matter in the effluent which reduces BOD of the effluent. The effluent is then passed into a settling tank where bacterial flocs are allowed to sediment. This sediment is called activated sludge.