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 (UV 222 /chlorine) for rapid inactivation of the chlorine-resistant and opportunistic Aspergillus niger spores in drinking water. The UV 222 /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 UV 222 /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 UV 222 alone, chlorination alone, and the conventional UV 254 /chlorine process under comparable conditions. The more efficient inactivation by the UV 222 /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 UV 222 photolysis of chlorine, which is verified through both experiments and a kinetic model. We further demonstrate that UV 222 photolysis damages the membrane integrity and benefits the penetration of chlorine and radicals into cells for inactivation. The merits of the UV 222 /chlorine process over the UV 254 /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.