\[HRT=\frac{V}{Q}\]
Variables
HRThydraulic retention time (time)
Vreactor or tank volume (m³)
Qflow rate (m³/time)
Description
What is this formula?
Hydraulic Retention Time (HRT) represents the average time that water or wastewater remains inside a treatment unit.
When to use it
Use it when designing or evaluating treatment tanks, clarifiers, equalization basins, digesters, lagoons, and biological reactors.
Example
Data:
V = 1500 m³
Q = 500 m³/day
Formula:
HRT = V / Q
Substitution:
HRT = 1500 / 500
Result:
HRT = 3 days
Applications
Wastewater treatment design, drinking water treatment, anaerobic digesters, activated sludge systems, lagoons, reactors, and process optimization.
Note
Although the formula is exact, actual retention times may differ from theoretical values due to short-circuiting, dead zones, mixing conditions, and hydraulic inefficiencies within the treatment unit.