Repair of wastewater microorganisms after ultraviolet disinfection under seminatural conditions
Abstract:Repair of wastewater microorganisms after ultraviolet (UV) disinfection was studied by incubating secondary effluent previously irradiated to UV doses of 40 to 60 mW·s/cm2 in diffusion chambers for 2 to 24 hours. For somatic coliphage repair estimations, the effluent was incubated in flasks for 2 hours. There was only slight repair of fecal streptococci, and it did not depend on the UV irradiation dose. Repair of the thermotolerant coliforms was a function of the UV dose. Repair corresponded to a maximum increase of 1 log unit after irradiation to 40 mW·s/cm2, and to smaller increases after 50 or 60 mW·s/cm2. No relationship was observed between repair and suspended solids content of the effluent in the range of 4 to 12 mg/L. For the Salmonella, no repair was observed after a 60-mW·s/cm2 irradiation and a 24-hour incubation. No repair was observed for the viruses in nine in-flask incubations, with coliforms showing increases between 1 and 2 log units in the same flasks. Compared with the coliforms, this absence of repair of microorganisms that cause the greatest health risk in bathing and shellfish-breeding zones brings interesting perspectives in the debate of post-UV-irradiation repair.
Document Type: Research Article
Publication date: July 1, 1997
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