Evaluation Of Detoxification Efficiencies Of Typical Wastewater Secondary Treatment And The Following Advanced Treatment Process For Industrial Wastewater

In recent years,approximately hundreds million tons of industrial wastewater are produced each year as a result of the rapid development of industrial production in China.The industrial wastewater is characterized as containing a complicated composition,recalcitrant substances and strong toxicity,which is harmful to ecological environment and human health.At present,the evaluation of wastewater quality is mainly based on physico-chemical parameters such as COD,NH4+-N,TOC and TN.However,the quality control of wastewater based on physico-chemical parameters is not sufficient to assess the toxicity of wastewater due to the joint toxic effects of the complex pollutants.Biotoxicity assays can not only reveal the presence of a mixture of toxic substances in wastewater,but also establish the dose-effect relationship.The present study focuses on evaluating the effectiveness of the tyical wastewater secondary treatment and the following advanced treatment process in operational industrial wastewater treatment plants?WWTPs?with respect to the removal of biotoxicity.The aim is to provide scientific basis for safe discharge of wastewater and perfecting the biological indexes in water quality assessment.The main research contents are shown as follows:?1?The detoxification efficiencies of aIaerobic-anoxic-oxic treatment process?A2O?for dying wastewater and pigment wastewater were evaluated by zebrafish acute toxicity test and comet assay.The raw influents COD from these two WWTPs were 569 mg/L and 342 mg/L,respectively.The TUs to zebrafish of raw influents were 4.06 and 2.50,respectively.The raw influents showed obviously genotoxic activity in terms of the TMs were 5.32 ?m and 2.05 ?m at 5%dilution,respectively,which were significantly higher than those of NC?p<0.01?.After passing through the A₂O process,COD were reduced to 64.7 mg/L and 76.4 mg/L,at a removal rate of 88.6%and 77.7%,respectively.The A₂O effluents COD did not meet the wastewater discharge standard GB18918-2002 in China?COD ? 50 mg/L?.The TUs were reduced to 1.46 and 2.00,at a removal rate of 64%and 20%,respectively.The A₂O effluents still exhibited moderately acute toxicity to zebrafish.The TMs at 5%dilution were reduced to 5.25 ?m and 9.88 ?m,respectively,which had no significant difference with those of raw influent?p>0.05?.The A2O process was not capable of removing genotoxicity significantly?p<0.05?.?2?The detoxification efficiencies of combined A2O-ozonation and combined A₂O-Fenton oxidation process in two coking WWTPs were evaluated.For the raw coking wastewaters,TUs to daphnia were 70.3 and 50.2,and TUs to zebrafish were 52.5 and 34.2,respectively.TUs of Zebrafish embryo SI were 41.0 and 35.2,respectively.Furthermore,the raw influents displayed teratogenic effects on larvae at 1.5%dilution,and caused a significant body length decrease at 2.1%and 3.0%dilution?p<0.05?,respectively.And the raw influents showed obviously genotoxic activity at 1.55%dilution?TMs were 8.91 ?m and 7.40?m,respectively,which were significant higher than those of NC?p<0.01??.A2O effluent displayed no obviously toxicity to daphnia,zebrafish and zebrafish embryo SI.However,bone malformation was observed after exposure to A2O effluents at 80%dilution.A2O process unit was not capable of removing the genotoxicity significantly?p<0.05?.A2O effluents still displayed obviously genotoxic activity at 1.55%dilution?TMs were 6.60 ?m and 7.82 ?m,respectively,which were significant higher than those of NC?p<0.01??.In adition,the A2O effluents COD and NH4+-N did not meet the wastewater discharge standard.After going through the AOPs,the effluents COD and NH4+-N met the wastewater discharge standard.The effluents had no obviously teratogenic effect on larvae.And the ramoval rate of genotoxcity were signifiantly increased?p<0.05?.However,the final effluents still had potential genotoxicity at 6.25%dilution?TMs were 4.05 ?m and 4.96 ?m,respectively,which were signigicant higher than that of NC?p<0.01??.?3?The detoxification ability of a combined A/O-ABFT process to ACN wastewater was evaluated and the potential toxicants of the ACN wastewaters were identified by GC-MS.The raw influent TUs to daphnia,zebrafish and zebrafish embryo SI were 125,29.6 and 14.3.respecively.In addition,the raw influent displayed teratogenic and growth inhibition effects?p<0.01?on larvae at 4%dilution.And the raw influent displayed genotoxicity in terms of the TM was 4.54 ?m at 1%dilution,which was significant higher than that of NC?p<0.01?.The main toxicants detected in raw influent were 3-cyanopyridine and succinonitrile,and a series of nitriles?such as fumaronitrile and 3-anilinopropionitrile?.After flowing through A/O process unit,the removal rates of daphnia acute toxicity,zebrafish acute toxicity and zebrafish embryo SI were 98%,81%and 20.3%,respectively.And significant malformation and body length decrease?p<0.01?were observed after exposure to A/O effluent at 7%dilution.In addition,A/O process unit couldn't remove the genotoxicity significantly?p<0.05?.The A/O effluent still displayed genotoxicity in terms of the TM was 4.50 ?m at 1%dilution,which was significant higher than that of NC?p<0.01?.The main toxicants in A/O effluent were the undegraded fumaronitrile and imidazole,and some byproducts?phenol,3-methyhexanenitrile and 4-cumylphenol?.After flowing through ABFT process unit,the effluent had no obvious toxicity to daphnia,zebrafish and zebrafish embryo SI.The final effluent also displayed no teratogenic effects on larvae.However,a significant decrease in body length was observed after exposure to the final effluent at 32%dilution?p<0.01?.In addition,the removal rate of genotoxcity was significantly increased?p<0.05?.However,the TM of final effluent at 14%dilution was 14.7 ?m,which was significant higher than that of NC?p<0.01?,indicating the final effluent still had obvious genotoxicity.The final effluent still contained some fumaronitrile,4-Methyl-1,3-diazine and biphenyl.The industrial wastewaters in this study all displayed strong biotoxicity.The traditional A/O and A₂O peocesses could remove 20%?100%of acute toxicity and 20.3%?100%of zebrafish embryo SI from wastewaters.However,they were not capable of removing genotoxicity significantly?p>0.05?.The AOPs and ABFT proess units could further remove the acute and embryo toxicity.Furthermore,they significantly improved the removal rate of genotoxicity?p<0.05?.However,the final effluents still had obvious genotoxicity in range from 5%to 14%dilution?p<0.05?,which probably posed potential risks to human health and environment.