What are the mesh-like structures formed by masses of bacteria held together by fungal filaments called in the biological treatment of sewage?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Flocs
In secondary (biological) treatment of sewage, the primary effluent is passed into large aeration tanks. It is stirred and air is pumped in. Useful aerobic microbes grow fast and form flocs: masses of bacteria joined with fungal filaments into mesh-like structures. The flocs eat up most of the organic matter, which lowers the BOD. Later the flocs settle in a tank as activated sludge.
NCERT Extract:
Microbes in Sewage Treatment – “… Secondary treatment or Biological treatment : The primary effluent is passed into large aeration tanks (Figure 8.6) where it is constantly agitated mechanically and air is pumped into it. This allows vigorous growth of useful aerobic microbes into flocs (masses of bacteria associated with fungal filaments to form mesh like structures). While growing, these microbes consume the major part of the organic matter in the effluent. This significantly reduces the BOD (biochemical oxygen demand) of the effluent.”