ULTRAVIOLET DISINFECTION FOR WASTE-WATER RECLAMATION AND REUSE SUBJECT TO RESTRICTIVE STANDARDS

An ultraviolet (UV) disinfection system was operated under field condi tions using both unfiltered and filtered secondary wastewater effluent s to assess the feasibility of using UV light to meet the stringent cr iterion specified in the California Wastewater Reclamation Criteria (C WRC). In the unfiltered wastewater, the CWRC criterion that the 7-day median not exceed 23 total coliform/100 mL was met consistently in eff luent exposed to an average UV dose of 60 mW . s/cm2 or greater. In th e filtered wastewater, the CWRC criterion that the 7-day median not ex ceed 23 total coliform/ 100 mL was met consistently in effluent expose d to an average UV dose of 48 mW . s/cm2 or greater. The most stringen t 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 sa mple in a 30-day period, was met consistently in filtered effluent exp osed to an average UV dose of at least 97 mW . s/cm2. Filtration of th e secondary effluent clearly enhanced the performance of the UV disinf ection. Filtration was effective in removing significant amounts of su spended solids, in altering the particle size distribution of the seco ndary effluent, and in providing a consistently high quality effluent (turbidity < 2 NTU).