Work out uv dose for disinfection instantly with clear inputs, formula shown and shareable results.
UV dose is intensity times exposure time, in millijoules per square centimetre. Water absorbs UV, so transmittance at 254 nm scales the delivered dose. Regulatory targets are typically 40 mJ/cm2 for 4-log virus inactivation in drinking water and 30 mJ/cm2 for wastewater reuse.
UV dose
Dose (mJ/cm2) = intensity (mW/cm2) x time (s) x UV transmittance
UV disinfection systems used for potable water must be validated to a recognised protocol and monitored continuously for intensity, flow and transmittance.
Dissolved organics, iron and colour absorb UV, reducing the dose reaching organisms in the far part of the reactor. A drop from 90% to 70% transmittance can halve the effective dose.
Quartz sleeve fouling and lamp output decline over life both reduce delivered dose. Validated reactors apply a lamp ageing and fouling factor, and intensity sensors monitor performance continuously.