The photocatalytic disinfection of urban waste waters

In this paper we present the results of the photocatalytic disinfection of urban waste water. Two microbial groups, total coliforms and Streproccocus faecalis, have been used as indexes to test disinfection efficiencies. Diff erent experimental parameters have been checked, such as the effect of TiO2 , solar or UV-lamp light and pH. Disinfection of water samples has been ach ieved employing both W-lamp and solar light in agreement with data shown by other authors. The higher disinfection rates obtained employing an UV-lamp may be explained by the stronger incident light intensity. Nevertheless no consistent differences have been found between TiO2-photocatalysis and dir ect solar or W-lamp light irradiation at natural sample pH (7.8). At pH 5 t he presence of TiO2 increases the relative inactivation rate compared with the absence of the catalyst. After the photocatalytic bacterial inactivatio n, the later bacterial reappearance was checked for total coliforms at natu ral pH and pH 5, with and without TiO2. Two h after the photocatalytic trea tment, CFU increment was almost nill. But 24 and 48 h later an important ba cterial CFU increment was observed. This CFU increment is slower after irra diation with TiO2 at pH 5 in non-air-purged samples. (C) 2000 Elsevier Scie nce Ltd. All rights reserved.