Comparison of E. coli inactivation by UV₂₂₂-ADPs and UV₂₅₄-ADPs in water

Abstract

Pathogenic microorganisms pose a significant threat to water safety. Emerging disinfection processes that combine far-ultraviolet radiation with oxidants offer promising strategies for controlling these pathogens. This study investigated advanced disinfection processes (ADPs) that use 222 and 254 nm far-ultraviolet radiation in conjunction with hydrogen peroxide (H₂O₂), sodium percarbonate (SPC), and persulfate (PDS) to inactivate E. coli in water. The inactivation efficiencies of E. coli were measured as 6.50-log for UV₂₂₂ alone and 2.50-log for UV₂₅₄ alone at 0.0014 Einstein/L. When using UV₂₂₂-ADPs, the inactivation ranged from 5.20-log to 6.50-log, while UV₂₅₄-ADPs achieved inactivation levels of 2.55-log to 2.95-log. The inactivation occurred in the order of UV₂₂₂ ≥ UV₂₂₂-ADPs > UV₂₅₄-ADPs > UV₂₅₄, which was related to photon competition between E. coli and the oxidants, superiority of UV₂₂₂ radiation compared with UV₂₅₄ radiation, and the yields of radicals. When UV₂₂₂ was combined with H₂O₂, SPC and PDS, the absorption fractions of 222 nm photons by E. coli reduced from 13.7% to 13.1%, 12.4%, and 12.2%, respectively, and the actual inactivation also decreased. This reduction was attributed to the light shielding effect of the oxidants. In addition, intracellular organic matter released from ruptured bacterial cell membranes during UV₂₂₂-ADPs could be further damaged by UV₂₂₂ photons and radicals. The effectiveness of UV₂₂₂-ADPs was also demonstrated in real water samples. Moreover, it was shown that UV₂₂₂-ADPs are less susceptible to dissolved organic matter (DOM) than UV₂₂₂ alone. This study provides novel insights into disinfection by UV₂₂₂-ADPs in water.

Graphical abstract

Keywords

Disinfection / UV ₂₂₂ / Advanced disinfection processes / Lake water / DOM

Highlight

	● The inactivation of E. coli ranks as: UV222 ≥ UV222-ADPs > UV254-ADPs > UV254.
	● In UV222-ADPs, the direct photolysis of UV222 photons is predominant.
	● UV254/H2O2 has an advantage over UV222/H2O2 in generating HO• during disinfection.

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