title: Inactivation of indigenous coliform bacteria in unfiltered surface water by ultraviolet light.
abstract: This study examined the potential for naturally occurring particles to protect indigenous coliform from ultraviolet (UV) disinfection in four surface waters. Tailing in the UV dose-response curve of the bacteria was observed in 3 of the 4 water samples after 1.3-2.6-log of log-linear inactivation, implying particle-related protection. The impact of particles was confirmed by comparing coliform UV inactivation data for parallel filtered (11 microm pore-size nylon filters) and unfiltered surface water. In samples from the Grand River (UVT: 65%/cm; 5.4 nephelometric turbidity units (NTU)) and the Rideau Canal (UVT: 60%/cm; 0.84 NTU), a limit of approximately 2.5 log inactivation was achieved in the unfiltered samples for a UV dose of 20 mJ/cm2 while both the filtered samples exhibited >3.4-log inactivation of indigenous coliform bacteria. The results suggest that particles as small as 11 microm, naturally found in surface water with low turbidity (<3NTU), are able to harbor indigenous coliform bacteria and offer protection from low-pressure UV light.
authors.affiliation: Department of Civil Engineering, University of Toronto, 35 St. George Street, Toronto, Ontario, Canada M5S 1A4.
authors.forename: Raymond E
authors.initials: RE
authors.lastname: Cantwell
authors.forename: Ron
authors.initials: R
authors.lastname: Hofmann
mesh_terms: D004307:Dose-Response Relationship, Radiation; D004755:Enterobacteriaceae / Q000528:radiation effects*; D005374:Filtration; D007700:Kinetics; D015203:Reproducibility of Results; D014466:Ultraviolet Rays; D014871:Water Microbiology