Ecotoxicological effects of disinfection of treated wastewater

Treated wastewater may provide an effective alternative for meeting agriculture's demands and increase freshwater resources for other needs. Disinfection of treated wastewater protects the receivers; nevertheless, hazards of handling disinfectants, and the fact that some of them do not remove certain pathogenic and opportunistic organisms, are two main reasons for undertaking research in this field. Ecotoxicity of effluent from a full-scale wastewater treatment plant, subjected to disinfection by chlorination, ozonation and UV irradiation, was investigated under laboratory conditions. The efficiency of bacterial inactivation was examined: microorganisms were sensi-tive to chlorine and UV disinfection, however, they were more resistant to ozonation. Ecotoxicity was evaluated on samples before disinfection and on disinfected samples in which the bacterial inactivation level was similar. Immobilization, growth and enzymatic ecotoxicological tests were performed using consumers, producers and decomposers, respectively. UV irradiation had the least negative impact on the tested bioindicators. Although some studies have shown opposite trends, it has been proved that ozonation and chlorination increase the toxicity of treated wastewater. This study suggests that the wide application of disinfectants to wastewater should be reviewed because, under the experimental conditions tested, they were able to cause harmful effects on one or more of the species tested and they could adversely affect biodiversity in the environment.

Automated summary

Treated wastewater can be a useful alternative for meeting agriculture demands and increasing freshwater resources. Disinfection methods vary in their effectiveness against microorganisms, with chlorine and UV being more efficient than ozonation. UV irradiation has the least negative impact on tested bioindicators, while studies show that ozonation and chlorination can increase toxicity of treated wastewater.