Which statement best defines detention time in a wastewater treatment unit?

• A. The time wastewater spends in the entire plant from influent to final effluent.
• B. The hydraulic retention time; the average time wastewater spends in the unit; used to estimate treatment effectiveness and design.
• C. The duration required to flush the unit during maintenance.
• D. The time solids spend in the final clarifier only.

Answer: (B)