Chemical, microbial and toxicological assessment of wastewater treatment plant effluents during disinfection by ozonation

Municipal wastewater treatment plants (WWTP) effluents are primary sources of pathogenic microorganisms and contaminants of emerging concern (CECs) released into the aquatic environment. Main concerns regarding these pollutants include transmission of waterborne diseases to humans and toxic and endocrine disrupting effects on aquatic organisms. In the coming years, WWTPs are expected to invest billions of dollars in upgrades to meet new regulatory requirements for wastewater from Environment Canada. For this reason, we investigated the performance of ozone when the technology is used for disinfection to overcome multiple risk factors such as disinfection, CEC removal, endocrine activity and toxicity for real effluents collected from three WWTPs. Two secondary effluents required mean specific ozone doses for disinfection of 0.25 and 1.04 gO(3)/gDOC whereas the advanced primary effluent required 1.52 gO(3)/gDOC to achieve a total coliform target disinfection criteria of 1000 MPN/100 ml (equivalent to 200 MPN/100 ml E. coli). At ozone doses for disinfection, CECs with high reactivity with ozone were removed at levels greater than the target CEC removal of 80% for all WWTP effluents. For the secondary effluents, ozone doses above 2.6 +/- 0.6 gO(3)/gDOC were required to satisfy the target removal for the recalcitrant CECs. Within the disinfection ozone dose range, estrogenic activity was reduced by more than 98% and androgenic activity was removed by more than 68%, while the anti-estrogenic activity remained unchanged. Lastly, based on the luminescence inhibition of V. fischeri, ozone doses for disinfection produced secondary effluents exhibiting less than 20% inhibition, thus falling under the hazard classification no acute/chronic toxicity.