| At present, the wastewater quality are often evaluated by conventional indexes, such as biochemical oxygen demand (BOD), chemical oxygen demand (COD) and so on. These conventional indexes can be used to quantify the refractory componds in wastewater. which cannot monitor the ecotoxicity of wastewater. This limitation of convertional evaluation standards can be compensated by biological toxicity determination, which can completely assess the ecological risk of wastewater and provide precausions for degradation of environmental quality. In addition, more refractory organic pollutants have been discharged into the water, which are difficult to be mineralized by traditional treatment processes. Therefore, it is meaningful to evaluate the toxicity of the wastewater before its discharge into the environment and develop new detoxification technologies for environmental safety.This research focuses on evaluating the ability of A/O and A2/O processes to reduce the acute toxicity and genotxocity of municipal wastewater using zebrafish (Danio rerio). Furthermore, typical advanced oxidation processes were employed to reduce the acute toxicity and genotxocity of dye wastewater. The objectives of this research are to provide theoretical bases for perfecting the indexes of biological toxicity in water quality assessment and designing wastewater treatment processes to reduce biological toxicity. Correspondingly, the main works and results are as follows:(1) The acute toxicity and genotoxicity of municipal wastewater from three different municipal wastewater treatment plants (A, B, C) employed anoxic-oxic (A/O) process were evaluated. The hydraulic retention time of anoxic and aerobic periods in the three plants were all about2.5h and5h, respectively. The COD of raw wastewater were104-147mg/L. After the treatement of A/O process, the COD were reduced to23.0-49.8mg/L, which met the first grade of discharge standard of pollutants for municipal wastewater treatment plant in China. Then for acute toxicity assessment, the mortality rate of zebrafish exposed to raw wastewater from plant A, B and C for96h were50%,0and25%, respectively. After the treatment of A/O process, they were all reduced to0, indicating the A/O process can effectively remove the acute toxicity from municipal wastewater. The genotoxicity results showed before and after the treatment by A/O process from plant A, the MN frequency of municipal wastewater at25%dilution were2.7%and5.3%, the tail moment were13.6and13.5, respectively. For plant B, the MN frequency of municipal wastewater at25%dilution were1.5‰and3‰, the tail moment were7.8and7.2, respectively. For plant C, the MN frequency of municipal wastewater at25%dilution were2.0%o and3.0‰, the tail moment were6.9and6.1, respectively. These results demonstrated the A/O process cannot reduce the genotoxicity. The eliminated effluent may pose genotoxic threaten although its COD level has met the sewage discharge standard.(2) One wastewater treatment plant employed anaerobic-anoxic-oxic (A2/O) process was evaluated its ability to remove96h acute toxicity and genotoxicity of municipal wastewater on zebrafish, in which hydraulic retention time of anaerobic, anoxic and aerobic periods were1h,1h and5h, respectively. The COD of wastewater was reduced from177mg/L to18.8mg/L after the treatement of A2/O process, which met the first grade of discharge standard of pollutants for municipal wastewater treatment plant in China. The toxicity assessment results indicated, the mortality rate of zebrafish exposed to wastewater for96h was reduced from55%to0after A2/O process, and the MN frequency and tail moment were changed from6.0‰and14.4to5.3‰and13.3, respectively. There is no significant differences between raw wastewater and effluent. The results indicated the A2/O process cannot reduce the genotoxicity effectively.(3) Fenton-coagulation process was carried out for COD removal, acute toxicity and genotoxicity reduction of dye wastewater. The dye wastewater was collected from an industrial wastewater treatment plant of a textile factory, which exhibited COD of96.1mg/L and zebrafish mortality rate of17%. The results indicated that at Fe2+concentration of0.36mM, Fenton reagent ratio of12:1and pH3, the COD of effluent was reduced to33.6mg/L after4h of treatment by Fenton-coagulation process. Meanwhile, the mortality rate of zebrafish exposed to wastewater for96h was reduced to0, the acute toxicity removal was100%. The MN frequency and tail moment of dye wastewater at75%dilution were reduced from4.5‰and7.4to1.8‰and2.0, and the effluent exhibited no significant genotoxicity to zebrafish. The results illustrated the Fenton-coagulation process can effectively reduced the acute toxicity and genotoxicity of dye wastewater.(4) The catalyst MCM-Mn was synthesized using MCM-41(Mobil Composition of Matter No.41) as support and Mn as active component by dip-coating method, and applied in catalytic ozonation of dye wastewater to investigate the ability of mineralization as well as detoxification efficiency. The catalyst MCM-Mn can improve the treatment efficiency of dye wastewater by ozonation. The results indicated the COD and TOC were respectively reduced from82.4mg/L and37.3mg/L to23.4mg/L and17.3mg/L treated by catalytic ozonation for2h at ozone dose of300mg/h·L and catalyst dose of1g/L. Furthermore, the bioassays revealed the mortality rate of zebrafish exposed to it for96h was77%and the inhibition of luminous bacteria was21.9%. After the treatment of catalytic ozonation, the inhibition of luminous bacteria was reduced to12.6%, and the mortality rate of zebrafish was reduced to0. The MN frequency and tail moment of dye wastewater at75%dilution were reduced from6.3‰and14.4to3.3%o and7.3, respectively. And the genotoxicity reduction was47.6%and 49.3%detected by MN and comet assays, respectively. The results illuminated the catalytic ozonation can effectively reduce acute toxicity as well as genotoxicity. |
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