Study On The Process And Mechanism Of Electro-assisted Microbial Reduction And Degradation Of Azo Dyes

As a result of azo dyes being widely used in dyeing and printing,paper and other industrial production,the dyeing wastewater of the world is mostly azo dye wastewater.And the wastewater with high toxicity,high chroma,complicated component is greatly harmful to the environment and become recognized as a difficult wastewater to deal with.According to relevant research,we found that a simple physical,chemical or biological method could bring a certain degradation for azo dyes,but using any kind of treatment methods are not very ideal.In this paper,we use electric auxiliary microbial system combining the electro-chemical and microbial system to reduce pollutants.Previous studies have found that electric auxiliary microbial system has good removal effect for chlorinated phenolic compounds,but whether the dual azo dyes can also achieve a better removal and the degradation process and mechanism there are few researches at present and need in-depth study.The article selects azo dye reactive brilliant red X-3B as treatment object.At first,the degradation rate of azo dye reactive brilliant red X-3B in electro-assisted microbial system(EAMS)was studied compared with that in electro-chemical system(ECS)and in microbial system(MS).Secondly,in the EAMS the influence of key factors including the voltage,temperature,sulfate and nitrate on the degradation of reactive brilliant red X-3B was studied,and the best voltage and reaction activation energy were determined.Thirdly,through the ultraviolet-visible spectrophotometer and GC-MS analysis of the degradation products,the degradation mechanism of reactive brilliant red X-3B in EAMS was speculated.Finally,redox mediators anthraquinone-2-sulfonate(AQS)was added into EAMS to study strengthening effect of AQS for degradation of azo dye and changes of current in reaction system.And its reinforcement mechanism was analyzed.The results indicated that there was a obvious synergetic effect between the electrochemical catalytic degradation and microbial degradation technology for degradation of azo dye in EAMS,which greatly improve the rate of the degradation of reactive brilliant red X-3B,Compared with the ECS and MS.The degradation of dyes under different voltage accorded with first-order kinetics characteristics,and dye degradation was fastest under 0.4V voltage.In a certain temperature range,temperature is helpful to the degradation of dye.The measured activation energy values for the degradation of reactive brilliant red X-3B in EAMS was 60.526kJ/mol by Arrhenius equation,which indicated that dye degradation mainly rely on microbial oxidation reduction rather than biological adsorption.Sulfate radical has slightly influence for dye degradation,only when the concentration is as high as 600 mg/L,dye degradation rate slightly decreased.Sulfate radical has a greater influence on the dye degradation.Adding any concentration of Sulfate radical,dye degradation rate decreased.The main reason is that the capability of denitrifying bacteria for take electronic,reduction of nitrate is preferred.In EAMS,azo bonds rupture of reactive brilliant red X-3B was firstly occurred,triazine and naphthalene ring structure can also be degraded.A part of benzene ring was degraded some alkanes,and another part of benzene was transformed to a new aromatic hydrocarbon substance.Through GC-MS analysis for product of reactive brilliant red X-3B in EAMS and in MS,we found that the main product is non-toxic alkane substances in EAMS,but in MS main product is toxic benzene class materials.When c(AQS)was 0.050mmol/L,the azo dye degraded fastest.The first order kinetics constants was 1.962 h-1,which was 7.42-fold that without AQS(0.2644 h-1).The current of system rose after adding AQS,which demonstrated that AQS promoted the speed of electrons transferring in the degradation process.The long-range electron transfer processes of multiphase interface between electrode,microorganism away from electrode and pollutants were implemented after adding AQS.The process make microorganism of the whole system could work quickly,which strengthened the degradation of azo dyes.