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

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 cm 2 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