| Dyeing wastewater has many problems,such as high chroma,complex components and difficult degradation.The iron-carbon micro-electrolysis process was used to treat dyeing wastewater for the improvement of biodegradability and removal efficiency of pollutants.The effect of initial pH,iron dosage,iron/carbon mass ratio and reaction time on the treatment efficiency of dyeing wastewater was investigated.The results showed that under the initial pH 4,the iron dosage of 80 g/L,the iron-carbon molar ratio of 0.8 and the reaction time of 90 min,the removal efficiencies of chemical oxygen demand(COD),turbidity,chroma,ammonia nitrogen and total organic carbon(TOC)were 75.48%,87.88%,75.34%,92.01%and 81.09%,respectively.In order to improve the efficiency of the actual dyeing wastewater treatment by the iron-carbon micro-electrolysis process,the method of response.surface was used to optimize the process conditions.A response surface model was constructed and the significance of the model was analyzed when removal efficiency of COD was used as response value and initial pH,iron dosage,iron-carbon mass ratio and reaction time were used as experimental factors.The results showed that when the initial pH was 3.53,the iron dosage was 83.92 g/L,the iron-carbon mass ratio was 0.82 and the reaction time was 78.48 min,the predicted COD removal efficiency was 75.25%.Its deviation was 0.23%(<2%)compared with the measured value.The model could be used to predict the changes of COD removal efficiency.The biotoxicity of the influent and effluent in the iron-carbon microelectrolysis process was tested by E.coli.The morphology,antioxidant enzymes and biomarker of E.coli were analyzed,and the changes of biotoxicity were studied before and after the dyeing wastewater was treated by iron-carbon microelectrolysis process.The results showed that E.coli cells were broken in the influent and most of E.coli cells were in normal shape in the effluent.Compared with the influent group,the release of lactate dehydrogenase(LDH)in the effluent group decreased from 2.13 times to 1.64 times in the control group,while the production of reactive oxygen species(ROS)decreased from 19.26 times to 4.81 times in the control group.The cell death rate decreased from 98.1%to 61.5%,and the growth phase was extended from 5 h to 9 h,and the BOD5/COD rose from 0.151 to 0.416.Compared with the influent,antioxidant enzyme,malondialdehyde(MDA),glutathione(GSH),superoxide dismutase(SOD),catalase(CAT),and total antioxidant ability(T-AOC)in the effluent group decreased by 80.85%,53.73%,67.74%,44.90%and 43.38%,respectively.After the dyeing wastewater was treated by the iron-carbon microelectrolysis process,its toxicity was reduced and the antioxidant system of E.coli was nearly in normal level.The glucose consumption inhibition rates of the influent and effluent were 85%and 47%,respectively.Compared with the influent group,calorific value increased by 21.95%,endogenous fluorescent protein increased by 112.96%,and nucleic acid content decreased by 44.04%in effluent wastewater,respectively.Therefore,the iron-carbon microelectrolysis process has the effect of reducing the biological toxicity of dyeing wastewater.Scanning electron microscopy(SEM),X-ray energy dispersive spectroscopy(EDS)and X-ray diffractometry(XRD)were used to analyze the changes in the compositions of iron and carbon before and after the treatment of dyeing wastewater.IR and UV-Vis spectra were used to compare the changes 'of organic matter before and after wastewater treatment,and the degradation mechanism of dyeing wastewater was explored.The results showed that before the treatment of dyeing wastewater,the composition of the iron-carbon reactor was mainly composed of iron and carbon,and the pore structure of the activated carbon was developed.After the reaction,the surface of the iron carbon adhered to other metal substances such as Al,K and the hydrox-ide flocs of iron.The iron-carbon micro-electrolysis process could degrade esters,alcohols and organic substances,decompose macromolecular substances and improve the biodegradability of wastewater.According to the Zeta potential analysis of the wastewater before and after the iron-carbon micro-electrolysis process,it could be seen that iron hydroxide flocs were generated during the reaction of the iron-carbon micro-electrolysis process,which had a strong adsorption flocculation effect.Through spectrum analysis and gas-mass spectrometry analysis,it could be seen that the iron-carbon micro-electrolysis process could efficiently decompose pollutants such as esters and alcohols,and converted them into small-molecule organic pollutants that were easy to biochemically treat. |
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