Answer: BOD reduction to acceptable levels.
- A Mainly pH levels measured before discharge
- B BOD reduction to acceptable levels
- C Chlorine concentration measured before discharge
- D Turbidity alone measured before discharge
Correct answer: B. BOD reduction to acceptable levels
Explanation: After secondary treatment, the effluent is released into water bodies only after its BOD has been sufficiently reduced to acceptable levels, ensuring minimal environmental impact.
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