At what rate is air applied in a conventional activated sludge treatment plant?

In a conventional activated sludge treatment plant, the rate of air applied is crucial for maintaining the appropriate conditions for the aerobic microorganisms that break down organic material present in sewage. The correct range of air application, identified in the answer, is 1 to 1 1/2 cubic feet per gallon of sewage. This rate effectively provides enough oxygen to support the biological processes necessary for effective treatment.

Applying air at this rate helps to optimize the metabolic activity of the microorganisms, facilitating the biodegradation of organic pollutants. Ensuring that the oxygen levels are within this range is essential to enhance the growth of bacteria while preventing conditions that could lead to the development of anaerobic pockets, thereby maintaining a healthy and efficient treatment process.

The other options present higher air application rates than what is typically necessary for effective treatment. Higher air application could lead to operational inefficiencies and unnecessary energy consumption without providing any additional benefits to the treatment process. Therefore, the identified range of 1 to 1 1/2 cubic feet per gallon strikes a balance between biological efficiency and operational sustainability.