| Decreasing photoreactivation after wastewater UV disinfection can lead to considerable savings in capital and operating costs. Objectives of this study were to determine pre- and post-UV irradiation conditions able to decrease fecal coliform photoreactivation in a wastewater effluent from the Montreal Wastewater Treatment Plant.;Additional experiments showed that photoreactivation was significantly decreased when visible light (400-800 nm) was simultaneously applied prior and during UV irradiation. This was more obvious for winter samples, where photoreactivation was decreased by nearly 50%. Moreover, the effect of pre-illumination with visible light was maintained for at least 30 minutes. Finally, summer populations were more sensitive to inactivation and less able to photoreactivate than winter populations.;Results of the study indicated that delaying exposure to photoreactivating light for three hours suppressed photoreactivation at UV doses of 10 and 20 mJ/cm2. At least 440 lux of visible light was needed to initiate photoreactivation, and 700 lux or greater for maximum effect. |
