title: Reduction of photoreactivation with the combined UV/peracetic acid process or by delayed exposure to visible light.
abstract: Photoreactivation of microorganisms following UV inactivation is a well-known, but complex, phenomenon. It is affected by several factors, including UV fluence, wavelength, light intensity, and exposure time to photoreactivating light. The effect on photoreactivation of a combined peracetic acid (PAA)/UV process has not been investigated. Accordingly, this study compared the degree of photoreactivation, under both sunlight and artificial lights, following UV and combined PAA/UV inactivation of fecal coliforms. Effluent samples from the Montreal Wastewater Treatment Plant (MWTP) (Quebec, Canada) were exposed, for 3 hours, to both low- and high-intensity artificial lights and sunlight. All resulted in similar photoreactivation levels. However, average photoreactivation for UV-treated wastewater samples was 1.2 logs, compared with 0.1 log for the combined PAA/UV treatment. Hence, the use of PAA in combination with UV can significantly reduce the potential for photoreactivation. To simulate the photoreactivation conditions of the MWTP effluent (which passes through a 4-km outfall tunnel with approximately 3 hours detention time), UV-treated samples were kept in the dark for 3 hours before photoreactivating light exposure. After this period, photoreactivation levels were close to zero. Hence, the effects of photoreactivation may be diminished by use of a combined disinfection scheme and/or by delaying exposure of the disinfected wastewater to light.
authors.affiliation: SNC-Lavalin, Montreal, Quebec, Canada.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Martin
authors.forename: Ronald
authors.initials: R
authors.lastname: Gehr
mesh_terms: D002170:Canada; D004202:Disinfectants / Q000494:pharmacology; D004755:Enterobacteriaceae / Q000302:isolation & purification; D005243:Feces / Q000382:microbiology; D017909:Levivirus; D008027:Light; D010083:Oxidants, Photochemical / Q000494:pharmacology; D010084:Oxidation-Reduction; D010463:Peracetic Acid / Q000494:pharmacology*; D010777:Photochemistry; D011792:Quebec; D013997:Time Factors; D014466:Ultraviolet Rays; D014865:Waste Disposal, Fluid / Q000379:methods*; D014871:Water Microbiology; D018508:Water Purification / Q000379:methods*
chemical_list: D004202:Disinfectants; D010083:Oxidants, Photochemical; D010463:Peracetic Acid