ASSESSMENT OF TERTIARY-TREATMENT TECHNOLOGY FOR WATER RECLAMATION IN SAN-FRANCISCO, CALIFORNIA

Tertiary treatment processes were tested to demonstrate their ability to produce effluents that meet the most stringent standards in the Cal ifornia Wastewater Reclamation Criteria. The processes studied were in -line, granular media filtration and microfiltration for particulate r emoval, and chlorination and UV light for disinfection. In-line filtra tion met CWRC turbidity requirements, although filter performance was dependent on feed water turbidity, and alum and polymer doses. Microfi ltration produced an effluent virtually free of suspended solids and c oliforms, and a 1.9-log removal of MS2 phage. This decreased the level of microorganism inactivation required of the UV system. MS2 phage se nsitivity to UV light was not constant, which may question its suitabi lity as an indicator organism to assess virus inactivation. Minimum ch lorine Ct value of 340 mg.min/l, and UV dose of 800 J/m(2) were identi fied for in-line filtration effluent, while a dose of 450 J/m(2) was s ufficient for microfiltration effluent. In-line filtration followed by UV disinfection is less costly for water reclamation than any other c ombination of treatment units tested, and, therefore, these processes were selected for a 53.000 m(3)/d water reclamation plant in San Franc isco. Copyright (C) 1996 IAWQ.