Simultaneous atrazine degradation and E. coli inactivation by UV/S2O82-/Fe2+ process under KrCl excilamp (222 nm) irradiation

Abstract

This study is the first to reveal that the iron-catalyzed photo-activation of persulfate (UV/PS/Fe²⁺system) under mercury-free KrCl excilamp irradiation (222 nm) is capable of simultaneous degradation of an organic pollutant and inactivation of a microorganism in aqueous media using the herbicide atrazine (ATZ) and E. coli as model contaminants, respectively. Deionized water, natural water and wastewater effluents, contaminated with 4 mg/L ATZ and/or 10⁵ CFU/mL E. coli, were sequentially treated by direct UV, UV/PS and UV/PS/Fe²⁺ processes. Lowering the pH to 3.5 accelerated both the degradation and inactivation during the UV/PS/Fe²⁺ treatment of natural water. Comparison of the apparent UV dose-based pseudo first-order rate constants showed the negative effect of E. coli on ATZ degradation by decreasing rates in all of the examined water matrices. This can be due to the competitive effect between ATZ and bacterial cells for reactive oxygen species (ROS). By contrast, E. coli in the presence of ATZ was inactivated faster in natural water and wastewater (but not in deionized water), as compared to the case without ATZ. A scheme of possible synergistic inactivation under ROS exposure in water, containing ATZ, natural organic matter and chloride ions as primary constituents, was proposed. Radical scavenging experiments showed a major contribution of SO₄•^- to ATZ degradation by UV/PS/Fe²⁺ treatment of deionized water and natural water. The UV doses, required for 90% removal of ATZ from natural water and wastewater, achieve 160 mJ/cm² (pH 5.5) and concurrently provide 99.99% E. coli inactivation. These results make the UV/PS/Fe²⁺ system with narrow band UV light sources promising for simultaneous water treatment and disinfection.

Keywords: Inactivation; Persulfate; Simultaneous degradation; Ultraviolet excilamp.