A study was undertaken to evaluate the efficiency of ultraviolet radiation in disinfecting secondary and tertiary effluents using wastewater from two full scale treatment plants located in the greater Athens area, the one receiving municipal sewage and the other receiving municipal sewage and septage. The effective UV dose for coliform removal, the effects of feedwater characteristics on UV disinfection and the lamp fouling potential were examined. For secondary effluent samples the required UV dose to achieve effluent fecal concentrations of less than 2,000 FC/100 ml varied from 30 to 60 mW-sec/cm2, depending on the water quality characteristics of the feedwater. High effluent suspended solids significantly increased the UV dose required to achieve adequate disinfection. For tertiary effluent the required UV dose to meet the 2000 FC/100 ml criterion was only 10 mW-sec/cm2, where as a dose of 40-50 mW-sec/cm2 was sufficient to achieve effluent coliform concentrations of less than 10 FC/100 ml. The inactivation of coliforms followed first order kinetics for relative low UV doses, with inactivation rates in the 0,107–0,303 cm2/mW-sec range for secondary effluent and 0,325 cm2/mW-sec for tertiary effluent. The lamp fouling potential was relatively high and the required lamp cleaning frequency was approximately twice per month.

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