Answer: Pumped into anaerobic sludge digesters to produce biogas.
- A Directly applied as fertilizer without any further treatment steps
- B Pumped into anaerobic sludge digesters to produce biogas
- C Discharged directly into nearby rivers and streams
- D Used to make biochar through pyrolysis treatment
Correct answer: B. Pumped into anaerobic sludge digesters to produce biogas
Explanation: Activated sludge (settled biomass) from secondary treatment tanks is pumped into anaerobic sludge digesters where microorganisms produce biogas.
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