Rapid Inactivation of Fungal Spores in Drinking Water by Far-UVC Photolysis of Free Chlorine

Effective and affordable disinfection technology is one key to achieving Sustainable Development Goal 6. In this work, we develop a process by integrating Far-UVC irradiation at 222 nm with free chlorine (UV₂₂₂/chlorine) for rapid inactivation of the chlorine-resistant and opportunistic Aspergillus niger spores in drinking water. The UV₂₂₂/chlorine process achieves a 5.0-log inactivation of the A. niger spores at a chlorine dosage of 3.0 mg L^-1 and a UV fluence of 30 mJ cm^-2 in deionized water, tap water, and surface water. The inactivation rate constant of the spores by the UV₂₂₂/chlorine process is 0.55 min^-1, which is 4.6-fold, 5.5-fold, and 1.8-fold, respectively, higher than those of the UV₂₂₂ alone, chlorination alone, and the conventional UV₂₅₄/chlorine process under comparable conditions. The more efficient inactivation by the UV₂₂₂/chlorine process is mainly attributed to the enhanced generation of reactive chlorine species (e.g., 6.7 × 10^-15 M of Cl^•) instead of hydroxyl radicals from UV₂₂₂ photolysis of chlorine, which is verified through both experiments and a kinetic model. We further demonstrate that UV₂₂₂ photolysis damages the membrane integrity and benefits the penetration of chlorine and radicals into cells for inactivation. The merits of the UV₂₂₂/chlorine process over the UV₂₅₄/chlorine process also include the more effective inhibition of the photoreactivation of the spores after disinfection and the lower formation of chlorinated disinfection byproducts and toxicity.