Lagoons · How a Facultative Lagoon Works
What Is Hydraulic Detention Time in a Lagoon?
Hydraulic detention time is the average time water stays in a treatment unit, in theory. For a lagoon, measure usable volume in million gallons (MG) and average flow in million gallons per day (MGD). EPA and operator-training references compare usable volume with average flow to find detention time in days.
The math box shows the formula and a worked example. This math assumes ideal flow. Sludge buildup, short-circuiting, uneven flow, and dead areas can all cut the real treatment time.
Use checked volume and flow data that represent normal conditions. Remember that usable volume shrinks as sludge builds up.
A calculated detention time does not prove the lagoon is working well. Compare it with field observations, test results, design information, and permit requirements.
Key point: Detention time is a useful estimate, but real lagoon flow is never perfectly ideal.
Keep learning
Lagoons and Small Wastewater Plants
This page comes from the course. It covers facultative and aerated lagoons, monitoring, lagoon problems, berms and liners, package plants, permits and safe work, one step at a time, with short knowledge checks and a certificate of completion.
Take the course