| The three-dimensional electrode technology is developed based the traditional two-dimensional electrode technology,and has the advantages of large specific surface area,low energy consumption,and high current efficiency.The advantage of the three-dimensional electrode technology is due to the addition of the particle electrodes.These particle electrodes are repolarized to form many microelectrodes,which provide more active sites for the reaction.In this study,granular activated carbon(GAC)was used as the particle electrodes in the three-dimensional electrolysis system for wastewater treatment,and novel particle electrodes of GAC supported metal were also prepared.Three electrolysis systems,namely system with GAC as bipolar particle electrodes,system with GAC supported metal as bipolar particle electrodes,and system with GAC supported metal as monopolar particle electrodes,were investigated in terms of the treatment of dye wastewater.Compared with the two-dimensional electrode technology,the three-dimensional electrode system with GAC as the particle electrodes achieved a higher removal efficiency for methyl orange(MO).The operating conditions had great impacts on the performance of the three-dimensional electrode reactor in the MO degradation:The current density was in the range of 0-10 mA·cm-2,the MO removal increased with the increase of current density,but the increase rate was gradually reduced.The electrolyte concentration in the range of 2000-4000mg·L-1,the MO removal increased first and then decreased with the increase of the electrolyte concentration.The electrode spacing was in the range of 2.5-6.5 cm,when the electrode spacing was reduced,the MO removal was increased.Therefore,the optimum operating conditions for the three-dimensional electrode reactor with GAC as the particle electrodes were:aeration to supply O2,electrolysis current 7 mAcm-2,Na2SO4 concentration 3000 mg·L-1 electrode spacing 2.5 cm,initial concentration 100 mg·L-1.Under the optimum condition,the MO removal at 4 h was 98.5%.Three kinds of catalytic particle electrodes of Mn-GAC,Ce-GAC and Mn/Ce-GAC were prepared by the impregnation calcination method,and then used in the three-dimensional electrode system for dye removal.The experimental results showed that the catalytic activity of different particle electrodes followed the order of:Mn-GAC>Ce-GAC>Mn/Ce-GAC>GAC.For Mn-GAC,the effects of metal,metal loading,calcination time,and calcination temperature on the catalytic activity of the GAC supported metal particle electrodes were investigated.The MO removal first increased and then decreased with the increase of the metal loading,and the optimal loading was 6%.With the increase of the calcination temperature,the MO removal also increased first and then decreased.The MO removal was the highest at 600?.The calcination time has no significant effect on the catalytic activity.The MO degradation using the GAC supported Mn in the repolarized three-dimensional electrode reactor followed the first-order kinetic model.The removals of methyl orange,methylene blue,and rhodamine B were consistently good during the 5 times of reuse of Mn-GAC,the concentration and chromaticity removal was stable at 90%,and the TOC removal was stable at 80%.The concentration of Mn in the effluent<5 mg·L-1 was in line with China's comprehensive wastewater discharge standard(GB 9878-1996).In the monopolar three-dimensional electrode system with GAC supported metal,the particle electrodes with the highest catalytic activity was Mn-GAC with the Mn loading of 6%.The MO removal was better when the particle electrodes were filled in the anode zone,and the degradation kinetics were consistent with the first-order kinetic model.When the particle electrode was filled in the anode,the removal of the organic matters in the solution mainly depended on the oxidation via·OH;however,when the particle electrode was filled in the cathode,the removal of the organic matter in the solution mainly depended on the oxidation via·O2-. |
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