| As the country raises the requirements for industrial wastewater treatment,pollutant discharge standards have become stricter,and"zero discharge"has gradually become a major trend in wastewater treatment.Coking wastewater,as a typical industrial wastewater that is difficult to biodegrade,has the characteristics of high organic load,high salinity and high toxicity.After the conventional secondary biochemical treatment,the effluent still contains a large number of toxic,harmful,and difficult-to-degrade organic pollutants,and the suspended solids,chroma,and salt content are still high.Advanced treatment is required to reduce the concentration of pollutants in wastewater.Advanced oxidation processes are a kind of feasible method.Among them,electrocatalytic oxidation does not require an additional oxidant,and can make full use of the high-salt components in the electrolyte,and only uses electric energy to degrade organic matter in wastewater through direct and indirect oxidation.This kind of green environmental protection advanced oxidation process attracts attention.This topic first used electrocatalytic oxidation-activated carbon adsorption to deeply treat high-salt bio-treated coking wastewater,and explored the rule of the combined process to remove refractory organics;then used ultraviolet light to induce high salt to produce chlorine free radicals to enhance the electrocatalytic performance,finally compared the advantages and disadvantages of before and after strengthening from both technical and economic aspects.The main content and results were as follows:Study on the performance and mechanism of electrocatalytic oxidation-activated carbon adsorption to treat bio-treated coking wastewater.The anode used the commercially used Ti/Ir O2-Ru O2 electrode,and the cathode used the Ti plate.The effects of current density,the number of polar plates,electrode interval and the kind of activated carbon on the treatment efficiency were investigated when the raw wastewater COD was 137mg/L and TOC was 57mg/L.The results indicated that the COD and TOC removal rate of electrocatalytic effluent reached 99.7%and 47.9%respectively under the condition of polar plates of two pairs,electrode interval of 1.8cm,current density of 20m A/cm2 and reaction time was 6 hours.The coal-based charcoal with larger specific surface area had better adsorption performance than coconut shell charcoal.When the dosage of coal-based charcoal was 20g/L,and reaction time was 120 minutes,the effluent TOC was 18.2mg/L,and the total TOC removal rate reached 67.9%.The adsorption of organic pollutants in wastewater by coal-based carbon was a complex process and was dominated by chemical adsorption.The results of three-dimensional fluorescence spectra showed that electrocatalytic oxidation could decompose some humic acid-like compounds in wastewater,and activated carbon adsorption might further remove residual humic acid-like compounds.In order to improve the treatment efficiency and reduce the energy consumption,the ultraviolet chlorine enhanced electrocatalytic oxidation method was used to treat bio-treated coking wastewater.The anode used Ti/Ir O2-Ru O2 electrode,and the cathode used Ti plate.The effects of current density and electrode interval on the treatment efficiency through ultraviolet light enhanced electrocatalytic oxidation were investigated when the raw wastewater COD was 170mg/L and TOC was 65mg/L,and chromaticity was 717 times.The results indicated that the removal rates of COD,TOC and chromaticity could reach 95.8%,77.2%and 94.0%respectively under the condition of current density of 10m A/cm2 and electrode interval of 6cm,and reaction time was 3hours.And the degradation rate constants of COD and TOC were 1.85×10-2min-1 and1.16×10-2min-1 respectively.The results of mechanism research and energy consumption analysis showed that the HCl O produced by electrochemical oxidation formed chlorine free radicals under the action of ultraviolet light,and the indirect oxidation of chlorine free radicals with high oxidation activity played a major role in the degradation of organic pollutants;Compared with a single electrolysis process,the ultraviolet chlorine enhanced electrocatalytic process could generate active chlorine free radicals with high oxidizing property,together with the active oxygen free radicals of electrochemical oxidation,it could more effectively oxidize and remove the humic acid-like substances in wastewater;Compared with electrocatalysis,the rate constants of ultraviolet chlorine enhanced electrocatalytic degradation of TOC was increased by3.1 times.The treatment efficiency of ultraviolet chlorine enhanced electrocatalytic oxidation was higher than that of electrocatalytic oxidation,and the treatment energy consumption of this method was 41.56k W·h/m3 and 0.83k W·h/g TOC,which was lower than the energy consumption of most salt-containing wastewater treatment processes,which proved its economic feasibility as a kind of coking wastewater advanced treatment process.In order to verify the universal applicability of DSA in the application of ultraviolet chlorine enhanced electrocatalytic treatment of high-salt bio-treated coking wastewater,DSA—Ti/Ir O2 and DSA—Ti/Ir O2-Ta2O5 were selected as anodes,and the ultraviolet chlorine enhanced DSA electrocatalytic oxidation method was used to treat bio-treated coking wastewater.Under the conditions that the raw wastewater COD was 175mg/L,TOC was 83mg/L,and chromaticity was 1120 times.The current density was 5m A/cm2,the electrode interval was 9cm,and reaction time was 3 hours.The removal rates of COD,TOC and chromaticity of the ultraviolet chlorine enhanced Ti/Ir O2 anode electrocatalysis could reach 97.8%,86.2%and 94.8%respectively,and the degradation rate constants of COD and TOC were 2.1×10-2min-1 and 1.09×10-2min-1 respectively;The current density was 20m A/cm2,the electrode interval was 6cm,and reaction time was 3 hours.The removal rates of COD,TOC and chromaticity of the ultraviolet chlorine enhanced Ti/Ir O2-Ta2O5 anode electrocatalysis were as high as 99.2%,87.2%and 96.4%respectively,and the degradation rate constants of COD and TOC were2.64×10-2min-1 and 1.15×10-2min-1 respectively.Performance research and energy consumption analysis results showed that compared with DSA electrocatalysis,the high efficiency of the ultraviolet chlorine enhanced DSA electrocatalytic oxidation method was verified.The energy consumption of the ultraviolet chlorine enhanced DSA electrocatalytic oxidation method was lower than that of most salt-containing wastewater treatment processes,which verified the economic feasibility and low energy consumption of the ultraviolet chlorine enhanced DSA electrocatalytic oxidation as a kind of advanced treatment process for coking wastewater. |
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