The disinfection of wastewater by ultraviolet light

The aim of this study, carried out over four months at a pilot wastewater treatment facility, was to evaluate ultraviolet treatment of final effluent discharged into bathing waters in coastal zones. Minimum disinfection values were fixed with a target limit of 10³cfu/100mL for faecal coliforms (FC) in line with the present and proposed European Directive on bathing water quality. Disinfection performance with different sources of water was studied and the disinfectant capacity with other indicator microorganisms was also checked. The target limit was reached using doses around 30mW.s/cm². Results of this study suggest that the applied UV dose is influenced by transmittance and the microbiological load. The most sensitive indicators were faecal coliforms, the specific F-RNA bacteriophages being the most resistant. From the results obtained in these experiments, UV treated water is suitable for being discharged into bathing zones, being an alternative to submarine discharges, avoiding high investment and maintenance costs.