Low-irradiance inactivation kinetics of Escherichia coli during prolonged exposure to ultraviolet-C radiation

Abstract

There is growing interest in using continuous, low-irradiance germicidal ultraviolet (UV) radiation to prevent bacterial attachment, growth, and biofilm formation on surfaces through water distribution pipes, appliances, and point-of-use plumbing. This study explored the low irradiance dose response of surface-bound Escherichia coli (E. coli). A linear model was used to calculate the pseudo-first-order inactivation rate constant (k′), and a minimum irradiance (μW cm⁻²) was established to achieve inactivation of surface-bound organisms in a nutrient-rich environment. The k′ for irradiance above 0.21 μW cm⁻² was calculated to be 1.06 ± 0.05 cm² mJ⁻¹. The kinetic model reveals that UV irradiance above 0.21 μW cm⁻² can result in up to 6 log inactivation at a dose of <6.0 mJ cm⁻². The minimum UV irradiance required for complete inactivation of surface-bound E. coli during prolonged exposure was averaged to be 0.38 ± 0.11 μW cm⁻² and 0.18 ± 0.02 μW cm⁻² for 265 nm and 280 nm wavelength, respectively. This study provides new knowledge and guidance to design technologies for disinfecting surfaces and a control strategy for biofilm prevention with very low UV irradiance (μW cm⁻²).