Correct Option
The correct option is (c) 1 and 3 only.
Explanation
Wastewater treatment involves physical, chemical, and biological processes to remove contaminants. The secondary treatment stage primarily utilizes biological processes, such as the Activated Sludge Process, to decompose organic matter. Aeration is a fundamental component of this stage.
Statement-wise Analysis
- Statement 1 is Correct: An aerator is a mechanical device used to mix air with wastewater. Mechanical surface aerators or submerged diffusers vigorously agitate the water to dissolve oxygen and keep the biological solids (sludge) in suspension, ensuring effective contact between bacteria and organic matter.
- Statement 2 is Incorrect: The purpose of an aerator is to supply oxygen to the wastewater, not remove it. This oxygen is essential for the survival and growth of aerobic bacteria, which break down organic pollutants. Anaerobic bacteria, conversely, require an environment devoid of oxygen.
- Statement 3 is Correct: In a typical wastewater treatment flow, the aeration tank is positioned after primary treatment and before the secondary clarifier (settling tank). After the biological degradation occurs in the aeration tank, the mixture flows into the secondary clarifier, where the biological mass (sludge) settles out from the treated water.
Key Takeaway
Aerators are critical in secondary wastewater treatment to introduce oxygen for aerobic decomposition and are operational prior to the secondary clarification stage.