Answer: The liquid that passes out after primary and secondary treatment.
- A The raw, untreated sewage entering the treatment plant initially
- B The liquid that passes out after primary and secondary treatment
- C The settled sludge collected from the bottom of the settling tanks
- D Biogas collected from the anaerobic sludge digesters
Correct answer: B. The liquid that passes out after primary and secondary treatment
Explanation: Effluent refers to the treated liquid waste (supernatant) that is discharged from sewage treatment plants after primary and secondary treatment processes.
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