EVALUATION OF UV DISINFECTION FOR WASTEWATER RECYCLING AT WEST BASIN, CALIFORNIA: TECHNICAL AND SANITARY ASPECTS

Tests were carried out at the laboratory- and pilot-scale to determine the suitability of UV irradiation for the disinfection of recycled wastewater in the State of California. At the laboratory-scale, UV dose-response curves were generated to compare the susceptibility of laboratory-propagated MS2 to that of vaccine strain poliovirus. With a UV-resistance 3 times higher than poliovirus, MS2 was found a safe and easy-to-use biodosimeter for UV equipment qualification tests. Using practical dosages for wastewater reclamation in the State of California, the inactivation of the viral indicator was found much larger with UV than with chlorine.On-site automatic sampling over a 3-month period showed that the coagulation-filtration tertiary effluent and the MF-RO effluent were eligible for reliable UV disinfection. No serious alteration of UV transmittance occurred, and worse-case UV transmittance and turbidity did not occur concurrently. The RO effluent was found particularly suitable for UV disinfection, with almost no particles and a UV transmittance larger than 93% in 95% of samples.Pilot tests demonstrated that the California requirement of 4 log MS2 bacteriophage inactivation could be met by both low-pressure high output and medium-pressure UV systems with a calculated dose of 140 mJ/cm2 in the filtered effluent. Loss of plug flow behavior occurred at low flows. This supported the approach that no extrapolation should be made to effluent velocities other than tested. The MF-RO effluent was found an excellent candidate for UV disinfection, with detention times for 4 log MS2 bacteriophage inactivation in the range of 1 second and subsequent footprint reduction.