Answer: Methane, CO2, and H2S.
- A Methane and oxygen
- B Methane, CO2, and H2S
- C Hydrogen and nitrogen
- D Carbon monoxide and methane
Correct answer: B. Methane, CO2, and H2S
Explanation: Biogas produced by anaerobic digestion of sewage sludge contains methane (CH4), carbon dioxide (CO2), and hydrogen sulfide (H2S).
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