Detoxification Of Municipal Wastewater By Secondary Treatment And Advanced Treatment Process In Reclaimed Water Plant

Reclaimed water can benifit efficient recycling of urban water resources,but the Residual microorganic pollutants and by-products in reclaimed water during the reuse process will pose potentially negative effects on aquatic ecosystem and human health.At present,the water quality standards of reclaimed water at home and abroad mainly adopt conventional physical,chemical and microbial indicators,but the presence of multiple pollutants in reclaimed water will cause combined pollution and joint toxicity.Thus,general physic-chemical index can not accurately reflect the actual harmful effects of chemical wastewater.Therefore,multi-level,multi-species and multi-target biological testing methods are used to evaluate the comprehensive toxicity of reclaimed water,and to provide supporting data for optimizingwastewater treatment process.we tested general toxicity,endocrine disruption,oxidative damage and genotoxicity during treatment in four municipal wastewater treatment plants?WWTPs?employing secondary treatment and one reclaimed water plant?RWTP?employing tertiary treatment in Dalian,Shenyang,Harbin and Tianjin by using bacteria?Photobacterium phosphoreum?,phytoplankton?Scenedesmus obliquus?,human estrogen receptor recombinant yeast assay and fish?Gobiocypris rarus?.The toxicity reduction efficiency of key treatment processes were evaluated by integrated biomarker response?IBR?.Different kinds of aquatic organisms at 3 nutrient levels were applied to evaluate the general toxicity,including bacteria?Photobacterium phosphoreum?,phytoplankton?Scenedesmus obliquus?and fish?Gobiocypris rarus?.No significant adverse effects wereobserved on the growth of Scenedesmus obliquus,lumination of Photobacteriumphosphoreum and survival of Gobiocypris rarus,with inhibition/lethality lower than 50%exposed to the highest dilution water sample,indicating that acute toxicity was not a sensitive toxicity index of reclaimed water.The estrogen equivalent?EEQ?of the effluents from four WWTPs employing activated sludge and UV disinfection ranged from 0.5 to1.5 ng?L^-1.After tertiary treatment process in the reclaimed water plant,estrogen activity of the effluent was below the method detection limit(0.02 ng?L^-1).The effluents of WWTPs and RWTPs exposure increased VTG content of male Rare minnow by 1.82-2.28 times and decreased T content of male Rare minnow by26-45%.Meanwhile,vtg,ear,ea?and cyp19a were up-regulated.The endocrine disruption effect of effluent from RWTP is not significantly lower than WWTPs,which indicates that the current tertiary treatment technology have low efficiency in removing endocrine disruption effect.The results of in vivo and in vitro analysis showed that the reclaimed water had estrogenic and anti-androgenic effects.The effluents of WWTPs exposure inhibited or induced the contents of MDA,GSH,SOD and CAT oxidative stress markers in gill and liver tissues of Rare minnow,and it also significantly induced the tail distance of comets and the incidence of micronuclei in blood cells.The effluents of RWTP exposure also significantly affected the content of oxidative stress markers and resulted DNA damage,but did not induced the incidence of micronuclei in blood cells.The effluent of WWTPs also significantly affected the DNA repair and growth arrest related genes,including atm,gadd45a,xrcc6 and rad51.The effluent of RWTP only increased the fold change of atm and gadd45a.It also showed that the genotoxicity of effluent of RWTP was lower than the genotoxicity of effluent of four WWTPs.,which were consistent with the results of comet test and micronucleus test.Detoxification Efficiencies of coagulation process and reverse osmosis process is higher,with IBR removal of 67%-71%and 90%respectively.There was a significant positive correlation between COD and IBR?r²=0.83?in the effluent.To a certain extent,the results of biological testing can supplement physical and chemical indicators to evaluate Detoxification Efficiencies of wastewater treatment processes and the safety of reclaimed water.