Correct Option
The correct option is (c).
Explanation
Wastewater treatment involves physical, chemical, and biological processes to remove contaminants. The biological phase, known as Secondary Treatment, relies heavily on microbial activity to degrade organic pollutants and reduce the Biochemical Oxygen Demand (BOD).
Statement-wise Analysis
- Statement 1 is Correct: After the activated sludge settles, a significant portion is pumped into large tanks known as anaerobic sludge digesters. Here, anaerobic bacteria digest the bacteria and fungi present in the sludge. This process produces a mixture of gases such as methane, hydrogen sulphide, and carbon dioxide, which form biogas used as a fuel source.
- Statement 2 is Incorrect: In the secondary treatment stage, the effluent is passed into large aeration tanks. Air is mechanically pumped into these tanks specifically to facilitate the vigorous growth of useful aerobic bacteria into flocs (masses of bacteria associated with fungal filaments). These bacteria require oxygen to function; therefore, they are actively introduced and supported, not prevented.
- Statement 3 is Correct: The primary function of the microbes (bacteria and fungi) in the treatment process is to consume the major portion of the organic matter in the effluent. By consuming these organic impurities, the microbes significantly reduce the BOD of the wastewater, making it less polluting before discharge.
Key Takeaway:
Wastewater treatment utilizes aerobic bacteria in aeration tanks to consume organic matter (reducing BOD) and anaerobic bacteria in sludge digesters to decompose sludge and generate biogas.