Katarzyna Anna Affek , Adam Muszyński , Monika Załęska-Radziwiłł , Nina Doskocz , Aleksandra Ziętkowska , Marcin Widomski
Treated wastewater may be a valuable source of water and/or nutrients for crop production and fish farming. Disinfection of treated wastewater should be performed to protect water resources against pathogenic and opportunistic microorganisms, as well as micropollutants contained in effluents. However, in the case of ozonation of treated wastewater, a large portion of contaminants do not undergo complete mineralization and can be transformed into by-products of unknown toxicity. The research performed in this study by culture-dependent and independent methods showed that the inactivation of bacteria in treated wastewater by ozonation does not take place effectively and may depend on the presence of other contaminants that may first react with the disinfectant. Some bacterial cells proved to be damaged by a disinfectant to the extent that they were unable to grow on nutrient media, but they were still viable and potentially posing a sanitary threat. Possible reasons for the disinfection failure were investigated and discussed. Ecotoxicity tests with algae Desmodesmus quadricauda, crustacean Daphnia magna, and bacteria Aliivibrio fischeri showed that by-products may be formed during ozonation of treated wastewater which is toxic to aquatic organisms. The toxicity class of treated wastewater may change from the completely non-toxic to very high hazard category, and there is a clear relationship between the time of ozonation and the increase in ecotoxicity.