Disinfection Time for Low-Pressure High-Intensity UV

UV disinfection performance is determined by UV dose (Dose = UV intensity × exposure time), not fixed exposure duration. For swimming pool flow-through UV systems, the hydraulic retention time inside the reactor is typically 1–6 seconds, and the rated design dose is 40 mJ/cm² (NSF/ANSI 50 standard).

Microorganism UV dose for 3-log inactivation Retention time in reactor

E. coli 4~6 mJ/cm² 0.4~0.8 s

Legionella pneumophila 7~8 mJ/cm² 0.7~1.2 s

Pseudomonas aeruginosa 8~10 mJ/cm² 0.8~1.5 s

Staphylococcus aureus 10~14 mJ/cm² 1.0~2.0 s

Salmonella 6~8 mJ/cm² 0.6~1.0 s

Mycobacterium 18~22 mJ/cm² 2.0~3.0 s

Key notes:

Bacterial spores require much higher UV dose (40–80 mJ/cm², 4–8 s exposure), low-pressure high-intensity UV cannot easily inactivate spores.

Water turbidity, iron content and quartz sleeve fouling reduce UV transmittance and effective UV dose.

Retention time refers to hydraulic residence time inside the UV chamber. Higher flow rate shortens exposure time and reduces disinfection efficiency.

Swimming pool UV design standard: 40 mJ/cm², which achieves 99.9% inactivation for most common pool pathogens