Bench-scale experiments were conducted with low- and medium-pressure ultraviolet (UV) lamps
to inactivate pathogenic and nonpathogenic strains of Escherichia coli and mixtures of naturally
occurring heterotrophic bacteria suspended in granular-media filtered water. Prior to UV
exposure, E. coli life cycle characteristics were measured to understand the effects of cell
dormancy (a characteristic that may be similar to E. coli present in the environment) on
inactivation kinetics. Following UV exposure, bacteria were incubated at 20oC in lighted and
dark environments to simulate subsequent treated water storage in open-air and enclosed
reservoirs, respectively. Approximately 9 mJ/cm2 of UV light provided 2-log inactivation of
heterotrophic bacteria. However, suspensions of heterotrophic bacteria treated with 140 mJ/cm2
were able to regrow to pre-treatment levels during light or dark incubation. Incubation of UV-
treated bacteria with a 2.5 mg/L chloramine residual prevented regrowth. For E. coli, resistance
to UV varied significantly. To provide 2-log inactivation of all the strains studied, a dose
between 0.2 and 7 mJ/cm2 was required. E. coli resistance to UV was observed to increase when
DNA replication was dormant. UV-inactivated, light-incubated E. coli were able to repair within
2 hours of treatment. To provide a more complete barrier to pathogens and sustain public health
protection, UV treatment should be followed with a residual disinfectant (e.g., chloramines).
Includes 15 references, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 330 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 10 |
| Published : | 11/01/2002 |
