What is the most nearly sewage detention time in an aeration tank using modified aeration?

In the context of sewage treatment using modified aeration, the detention time in an aeration tank is crucial for effective biological treatment of wastewater. Detention time refers to the duration that sewage remains in the aeration tank, allowing microorganisms to break down organic matter.

Typically, modified aeration systems are designed for shorter detention times compared to conventional systems, which optimize the biological processes while maintaining sufficient contact between the microorganisms and the sewage. The most effective range for detention time in a modified aeration system is typically around 2 to 4 hours.

When considering the provided answer of 2 hours, this option aligns well with common design parameters and operational practices for modified aeration systems, where rapid treatment and stabilization of sewage can occur efficiently in this time frame. A detention time of 2 hours allows adequate contact for the microorganisms to metabolize the organic matter effectively while preventing excessive growth that could lead to operational challenges.

Therefore, the choice reflecting a sewage detention time of about 2 hours is rational given the operational efficiencies sought in modified aeration processes.