| In recent years,with the development of industrialization and urbanization,water pollution has become more and more serious.The toxic and harmful components of sewage are becoming more and more complicated,and there are long-term potential risks to human health and ecological environment.Therefore,how to conduct a comprehensive and systematic assessment for the quality of sewage is particularly important.In this study,luminescent bacteria toxicity test,algal growth inhibition test,zebrafish larva mortality test and SOS/umu test were conducted to investigate the variation of ecotoxicity during the A2O-MBR wastewater treatment and reclaimed water reuse processes.At the same time,the safety assessment method that based on the four bioassays was established and applied to evaluate the safety of the water from reclaimed water reuse processes.For the established safety assessment method,the predicted no effect concentrations(PNECs)of the four positive controls used in four bioassays were derived from the species sensitivity distribution curves.The score of each bioassays was set according to its PNEC and the ecological safety of water was classified as four different levels according to its score.The results showed that A~2O biological treatment exhibited desirable capability on decrease the toxicity of wastewater to luminescent bacteria,alga and zebrafishlarvae,which achieved ? 94% of toxicity reduction.In contrast,only 50.92% of genotoxicity reduction was obtained during this process.The four ecotoxicity of MBR effluent increased with different amplitude due to the disinfection processes.When the reclaimed water was reused to an artificial lake system,the four ecotoxicity of water was reduced notably,especially for the genotoxicity of reclaimed water,which reduced by 89.21%.Based on the established safety assessment method,it could be obtained that the water quality of wastewater was enhanced from C-level to A-level after A~2O biological treatment.Then,the water quality of reclaimed water was enhanced from B-level to A-level after reusing as landscape water.It indicates that the A~2O secondary biological treatment processes and the artificial lake can effectively decrease the toxicity of wastewater and reclaimed water,but the disinfection process resulted in toxicity increase.Interestingly,an open semi-natural system could further remove the residual toxic substances from the wastewater treatment processes,especially genotoxic substances,and improve the water quality.The traditional secondary treatment can reduce the concentration of bacteria and virus greatly,but there is still some potential harm if the secondary effluent were reused,so the traditional secondary treatment process has been not to meet the requirements of wastewater treatment and reuse,it needs further deep processing.This study is about on the effect of ozone oxidation treatment,ultrafiltration and nanofiltration membrane treatment and activated carbon treatment for the A~2O secondary effluent,and provide the theoretical basis for the optimization of wastewater reuse technology.The results showed that several deep treatments had certain removal effect on acute toxicity and genotoxicity.When the ozone exposure time was 15 min,that the actual ozone consumption was about 65.62mg/L,the effect of ozone oxidation on the acute toxicity and genotoxicity of A~2O secondary effluent was the best.The effect of nanofiltration and ultrafiltration on the acute toxicity and genotoxicity of A~2O secondary effluent was obvious.The removal efficiency of nanofiltration was superior to ultrafiltration.After the adsorption of activated carbon,the acute toxicity and genotoxicity of A~2O secondary effluent were decreased significantly,and the removalrate of acute toxicity and genotoxicity reached 77% and 96% respectively.The optimum dose of activated carbon was 20~30g/L.In addition to the simple depth of the treatment method,we can use a variety of deep processing technology that play their own advantages to achieve better treatment results. |
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