Answer: To act as inoculum of useful microbes.
- A To increase the BOD of the effluent
- B To supply oxygen to the tank
- C To act as inoculum of useful microbes
- D To remove heavy metals chemically
Correct answer: C. To act as inoculum of useful microbes
Explanation: A small part of the activated sludge is pumped back as inoculum, because it is rich in the aerobic microbes needed to digest the organic matter of the fresh effluent.
Sewage passes through physical removal (primary), then aerobic biological treatment where microbes form flocs that consume organic matter (secondary); the settled activated sludge is then digested anaerobically to produce biogas - a deliberate switch from aerobic to anaerobic conditions between stages.
Concept context
Microorganisms in food, medicine, sewage treatment, biocontrol, and biofertilizers