A novel water disinfection method based on dual-wavelength UV radiation of KrCl (222 nm) and XeBr (282 nm) excilamps

Abstract

Dual-wavelength ultraviolet (DWUV) radiation has emerged as an advanced tool for water disinfection in view of potential synergistic effect. In the present study, E. coli and E. faecalis in synthetic water at pH 6.4–7.0 were inactivated under simultaneous exposure to DWUV radiation of KrCl (222 nm) and XeBr (282 nm) excilamps (UV222/UV282) at different irradiances. A time-based synergistic effect in terms of 5-log (complete) inactivation was found in all dual-wavelength combinations with synergistic coefficients ranging from 1.3 to 3.8. No dose-based synergistic effect was observed due to comparable dose requirements for single-UV and DWUV disinfection. The DWUV doses for 5-log inactivation were low in all cases and varied in the range of 2.3–5.4 mJ/cm2. Inactivation by advanced oxidation process using hydrogen peroxide (UV222/UV282/H2O2) also showed a time-based synergy and required low doses. The synergistic inactivation at 222 and 282 nm was proposed to be caused by simultaneous action of two key mechanisms: 1) the proteins destruction with subsequent DNA photo- and dark-repair suppression, 2) direct and indirect DNA damage. Photo- and dark-repair experiments supported this concept and showed no cell reactivation after DWUV exposure. High inactivation efficiency, low dose requirements, absence of oxidant’s excess and environmental safety make the UV222/UV282 method more advantageous compared to single-UV and H2O2-assisted method, and applicable to fast and energy-efficient disinfection of low turbid waters.