Hello dear
I was looking for a reference for HRT in the equalization tanks for domestic wastewater treatment. Better with the AWWA or WHO references.
With best regard

The hydraulic residence time in the equalization tank is a function of minimum and maximum flow rates, and any periods of no flow, and finally the overall volume of wastewater arising over "cycle" such as a day or a week or a season. So it's not really possible to select a specific time period and simply design on that basis. A review of the inflow volumes and flow rates is necessary at the design stage.