Answer: It is used as excellent manure.
- A It can be refermented to make more gas
- B It is used as excellent manure
- C It is a source of drinking water
- D It is rich in methane gas
Correct answer: B. It is used as excellent manure
Explanation: The spent slurry removed through the outlet is used as fertiliser, as it is rich in nutrients and serves as good manure.
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