Efficiency And Mechanism Of Azo Dyes Degradation By Persulfate Cathode Type Microbial Desalination Fuel Cells

Due to the rapid development of the textile industry,dyestuffs are used in large quantities,and with this comes the problem of wastewater discharge from the dye production industry,which not only affects the landscape of water bodies,but also endangers human health.Azo dyes are the most widely used synthetic dyes.Traditional water treatment methods are unable to remove azo dyes with high efficiency and low consumption,and the removal of azo dyes with high efficiency and low consumption has become the focus of research.In recent years,advanced sulfate oxidation technology based on sulfate radicals has been rapidly developed.In order to effectively degrade azo dyes in wastewater,this paper utilizes microbial desalination fuel cells（MDCs）to activate persulfate for the degradation of dye wastewater.The efficiency and mechanism of persulfate cathodic MDCs for degradation of two typical azo dyes were investigated using a bioelectric reactor with methylene blue（MB）and alizarin yellow（AYR）as the target pollutants instead of conventional power sources.The effects of initial p H,PDS concentration,common anions and organic matter in water on the removal efficiency of methylene blue（MB）and alizarin yellow R（AYR）were investigated,and the response surface method was used to find the optimal reaction conditions for the removal of two azo dyes by persulfate cathode MDCs.In the parameter optimization of the persulfate cathode MDCs,it was found that the cell parameters performed best at an initial COD concentration of 100 mg/L in the anode chamber and 15 g/L in the desalination chamber,with a COD removal rate of 70.46%in the anode,20.69%in the desalination chamber,and a maximum voltage of 1301 m V.The degradation of MB and AYR by persulfate cathode MDCs.The degradation of MB and AYR by persulfate cathode MDCs was consistent with the primary reaction kinetic model.Compared with the degradation of MB by MDCs alone and PDS alone,the coupled system of MDCs and PDS was able to remove MB efficiently with a maximum removal rate of 81.08%.The experimental results showed that the degradation rate constant(k_obs)of MB was the highest at p H=5.00±0.02.the k_obs of MB degradation by persulfate cathode MDCs showed a trend of promotion and then inhibition as the concentration of PDS increased.the removal of MB by co-existing Cl^-and Br^-in the system showed a trend of inhibition and then promotion.The presence of natural organic fulvic acid and bovine serum protein would inhibit the degradation of MB.The results of the degradation of AYR by persulfate cathode MDCs showed that the degradation rate of AYR reached the highest at p H 3±0.02 and PDS dosage of 1 m M.the degradation of AYR was inhibited by high concentration of coexisting anions,and the degree of inhibition was Br^->Cl^->NO₃^->CO₃^2-.the natural organic fulvic acid and bovine serum protein present in the reaction system showed an inhibitory effect on the degradation of AYR.The results showed that the model predicted the best treatment conditions for MB degradation by persulfate cathode MDCs:the initial p H value was 5.51,the PDS dosage was 1.28 m M,and the reaction time was 30.51 min,and the actual removal rate of MB could reach 83.92%,which was 1.91%different from the predicted value.In the experiment of AYR removal by persulfate cathodic MDCs,the optimized conditions were as follows:PDS concentration was 1.85 m M,initial p H was 3.49,and the reaction time was 109.47 min,and the actual removal rate of AYR was 85.58%,which was 0.45%different from the predicted value.Based on the results of LC-MS,the degradation MB of persulfate cathode MDCs was determined to have intermediate products with m/z of 305,270,228,224,149,and AYR with m/z of 287,257,303,272,153,108,138,193,168,177.The degradation pathways were basically through the breaking of azo bonds by·OH、SO₄^-·and ¹O₂.The main degradation mechanisms of MB include sulfur-chlorine bond breaking,carbon and nitrogen double bonding,demethylation and ring opening of thiazine ring.After 120 min of degradation reaction,the removal rate of TOC by AYR was still low at 21.56%,indicating that more intermediate products were produced in the oxidative degradation process of AYR.The main degradation mechanism of AYR includes multi-step reactions such as azo-bond breaking,decarboxylation,benzene ring breaking and denitrification.