Multiple Biological Toxicity Assessment And Water Quality Evaluation During Typical Municipal Wastewater Treatment Process

In order to accurately assess the comprehensive ecotoxicity of domestic wastewater and the reduction of toxicities by different treatment processes,simultaneously to make up for the inadequacy of traditional physical and chemical indicators for water quality,in this paper,three bio-toxicity tests were used including the acute toxicity test performed on luminescent bacteria,the genotoxicity by SOS/umu,and the estrogenicity focused on yeast estrogen screen(YES).At the same time,the fate of the concentrations of estradiol(E2)was detected by enzyme-linked immunosorbent assay(ELISA)and the modulations of endrocrine disrupting effects of the wastewater and reclaim water on aquatic organisms were analyzed by zebrafish.Finally,the safety evaluation of biological toxicity test results was carried out by the toxicity unit grading method,the potential ecotoxic effects probe(PEEP)method,and the water quality safety grading method,thus an effective water biological safety assessment system was established to detect and control the impact of pollutants on the aquatic environment.The results showed that the acute toxicity,genotoxicity,estrogenic activity and the level of E2 were significantly high in the influents of the wastewater treatment plants.After the secondary biological treatment stage—A2O and oxidized ditch processes,the acute toxicity,estrogenic activity and E2 concentration were obviously decreased by85.33%~91.67%,72.39%~73.33% and 75.88%~77.84%,respectively.Whereas theremoval efficiency of genotoxicity during A2 O and oxidized ditch processes was only34.56% and 29.0%,respectively.In addition,the concentration of the estradiol equivalent(EEQ)and E2 adsorbed by sludge was 1.73~1.90 ng·g-1 and 11.70~12.84ng·g-1,respectively.Although the estrogenic effect of wastewater was decreased by the adsorption,the estrogenic activity in the effluent of wastewater treatment plants,which still has potential hazard to the aquatic organisms in the receiving water.Meanwhile,the experimental results showed that the three kinds of biological toxicities and E2 concentrations increased inordinately after chlorination disinfection.The exposure of2.5 times concentrated wastewater samples resulted in a significant increase in the expression levels of the vitellogenin gene(vtg1)and the estrogen receptor gene(esr1)in the male zebrafish liver.It was concluded that the effluent could regulate the biological endocrine activity by interfering with the expression of the target gene;In addition,the inhibition of esr1 gene expression in the gonad of male zebrafish indicated that the sewage might have anti-estrogenic effect.Therefore,the analysis of biological toxicity should be conducted from multiple organizations or organs in order to obtain comprehensive information.Finally,it was found that the enzyme-linked immunoassay method had a good agreement with the YES assay,which provided a new method for the rapid screening and evaluation of estrogen in water environment.The safety evaluation of biological toxicity test results was carried out by the toxicity unit grading method,the potential ecotoxic effects probe(PEEP)method,and the water quality safety grading method.The consequence showed that high toxicities in the influents were obtained through toxicity unit grading method,while after the treatment of oxidation ditch and A2 O process,the toxicities of the effluents were moderate.For PEEP index method,the influents were also highly toxic,although after oxidation ditch and A2 O process,the wastewaters were highly toxic,as well as the effluents.Finally,the water quality safety classification showed that the influents were C grade,and after biological treatments –both oxidation ditch and A2 O process,the effluents were both B grade.Although the different water quality assessment methods of consideration and focus is slightly different,but the PEEP method specifically considers the effect of the flow factor,and it can be concluded that the method is better to evaluate the water quality safety of the sewage treatment plant.The experimentalresults showed that the typical urban sewage treatment process had a certain removal effect on the toxicity of the sewage,especially in the secondary biological treatment stage,but it was not enough to completely remove the toxicities of the sewage,the ecological safety risk of the effluent quality needed attention.