Pilot plant experiments have shown that UV irradiation is a qualified and non-polluting method for disinfection of the secondary effluent from wastewater treatment plant. It is possible to reduce the load of fecal indicator bacteria below the guide values and imperative limits of the Directive of 8 December 1975 concerning the quality of bathing water, enacted by the European Communities. The bacterial concentration was reduced to an average concentration of less than 10 counts per 100 ml for coliform bacteria and fecal streptococci. Photoreactivation was observed but the increase of the density (logarithmic scale) of coliform bacteria and standard plate count was not more than 1 after four hours of light exposure. Fecal streptococci did not show any photoreactivation.
