Photoreactivation of UV-Irradiated Coliforms in Wastewater Effluent

Ultraviolet (uv) radiation of wastewater is currently being considered as an alternative to chlorination. However, the problem of the extent of photoreactivation (PR); and under what conditions it would occur most severely has not yet been defined. The parameters of optimal exposure time, sunlight intensity, nutrient content, temperature, and uv dose were examined. These same parameters were also studied under laboratory conditions, using an artificial PR light source. During strong summer sunlight, 60 minutes of exposure gave the maximum amount of repair at temperatures near 25°C. At higher (36°C) or lower (17°C) temperatures, the level of PR declined. Nutrient attenuation, achieved by diluting the sample 1:10 or 1:40 in receiving water did not decrease PR, however a very large decrease in nutrients did negatively affect the level of survival after PR. Under optimal conditions, the effective level of disinfection at a given uv dose was decreased by approximately 67-75%.Master of Science in Public Healt