Wastewater Chlorine Contact Calculator
Disinfection depends on dose and contact time. Enter average and peak flows, chlorine dose, and contact-basin volume to check feed rates and modal contact time at peak flow.
Chlorine Feed & Contact
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How the calculation works
Formulas
Chlorine feed (lb/day) = 8.34 × flow (MGD) × dose (mg/L)
Modal contact time (min) = contact volume (gal) ÷ flow (gpm)
Peak factor = peak flow ÷ average flow
“Modal” contact time is the theoretical detention time (volume ÷ flow). Real basins short-circuit, so tracer-tested T10 is lower — design guidance builds in that margin.
Chlorine feed (lb/day) = 8.34 × flow (MGD) × dose (mg/L)
Modal contact time (min) = contact volume (gal) ÷ flow (gpm)
Peak factor = peak flow ÷ average flow
“Modal” contact time is the theoretical detention time (volume ÷ flow). Real basins short-circuit, so tracer-tested T10 is lower — design guidance builds in that margin.
Notes & limitations
A 15–30 minute modal contact time at peak flow is common wastewater disinfection design guidance (Ten State Standards — Recommended Standards for Wastewater Facilities). It is guidance, not a universal permit condition: confirm the required contact time and residual with your state primacy agency.
- Feed equipment must cover the peak-flow dose: size chlorinators and chemical storage for the peak lb/day, not the average.
- Contact time here is theoretical (volume ÷ flow). Baffling factor and short-circuiting reduce the effective time — tracer studies give the real T10.
- Wastewater chlorine demand varies with effluent quality; dose to a target residual per your permit, and provide dechlorination where the permit requires it.
- This tool covers the contact basin only. Upstream demand (e.g., ammonia, organics) sets the dose needed to hold a residual.
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