Ultraviolet disinfection for wastewater reclamation and reuse subject to restrictive standards

Abstract

ABSTRACT: An ultraviolet (UV) disinfection system was operated under field conditions using both unfiltered and filtered secondary wastewater effluents to assess the feasibility of using UV light to meet the stringent criterion specified in the California Wastewater Reclamation Criteria (CWRC). In the unfiltered wastewater the CWRC criterion that the 7‐day median not exceed 23 total coliform/100 mL was met consistently in effluent exposed to an average UV dose of 60 mW · s/cm2 or greater. In the filtered wastewater, the CWRC criterion that the 7‐day median not exceed 23 total coliform/ 100 mL was met consistently in effluent exposed to an average UV dose of 48 mW · s/cm2 or greater. The most stringent criteria, that the 7‐day median not exceed 2.2 total coliform/ 100 mL and that the total coliform not exceed 23/100 mL in more than one sample in a 30‐day period, was met consistently in filtered effluent exposed to an average UV dose of at least 97 mW · s/cm2. Filtration of the secondary effluent clearly enhanced the performance of the UV disinfection. Filtration was effective in removing significant amounts of suspended solids, in altering the particle size distribution of the secondary effluent, and in providing a consistently high quality effluent (turbidity < 2 NTU).