Answer: Removal of suspended solids by settling and screening.
- A Biological degradation of organic matter using activated sludge
- B Removal of suspended solids by settling and screening
- C Chlorination of treated water before final discharge
- D Addition of coagulant chemicals to settle out solids
Correct answer: B. Removal of suspended solids by settling and screening
Explanation: Primary treatment of sewage involves physical removal of suspended solids through screening and sedimentation.
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