The correct option is (b).
Explanation
Aerobic bacteria are microorganisms that require oxygen for respiration and metabolic processes. In the context of wastewater treatment, they are utilized in the secondary (biological) treatment stage to decompose organic impurities.
Statement-wise Analysis:
- Statement 1 is Incorrect. By definition, aerobic bacteria require the presence of oxygen to survive and function effectively. Bacteria that function in the absence of oxygen are classified as anaerobic bacteria.
- Statement 2 is Correct. During the biological treatment phase (specifically in aeration tanks), air is pumped into the water to support the growth of aerobic bacteria. These bacteria consume organic contaminants, including human waste, food waste, soaps, and other biodegradable matter remaining in the clarified water.
- Statement 3 is Incorrect. These bacteria do not remain permanently suspended. After they have consumed the organic matter, the water is transferred to a settling tank. Here, the bacterial flocs (masses of bacteria) settle at the bottom to form activated sludge, allowing the treated water to be separated from the top.
Key Takeaway:
Aerobic bacteria require oxygen to decompose biodegradable organic matter during the secondary stage of wastewater treatment and subsequently settle as activated sludge.