How much hydraulic detention time is required in the tank?

The correct choice indicates that a hydraulic detention time of 24 hours is required in the tank. This specific duration is crucial for the effective treatment of wastewater in septic systems.

Hydraulic detention time refers to the amount of time wastewater spends in the septic tank, allowing for proper separation of solids and liquids as well as the initial stages of biological treatment. A 24-hour period strikes an effective balance where sufficient time is given for solids to settle and for the natural processes to begin breaking down organic matter.

Shorter detention times could lead to insufficient treatment, as there wouldn't be enough time for effective sedimentation and digestion of materials. On the other hand, a too-long detention time could result in the accumulation of scum and could reduce the efficiency of the system if the liquid is stored for excessive periods. Therefore, 24 hours has been established as a standard to optimize the performance of septic systems while ensuring that solids are adequately treated before being discharged.