- 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.
Concept context
Microorganisms in food, medicine, sewage treatment, biocontrol, and biofertilizers