| As typical refractory organic pollutants,halogenated phenols and volatile phenols are widely distributed in the environment,and are easy to enter and exist in groundwater for a long time.Traditional microbial remediation has some shortcomings,such as lack of electron donor and acceptor in groundwater,poor reaction controllability and so on.Therefore,it is necessary to develop a sustainable,controllable and environment-friendly remediation technology.With the intervention of weak current,the cathode and anode can act as electron donor/acceptor to provide electrons for microorganisms continuously and steadily,thereby promoting the enrichment of microorganisms and the improvement of degradation efficiency.At present,this method had achieved the degradation of various pollutants.In this study,an anaerobic biological reaction system with weak current intervention was constructed,and the biological cathode and biological anode were used as additional electron donors and acceptors to realize the enhanced decomposition and transformation of tribromophenol and m-cresol.The operating conditions of applied voltage,exogenous organic matter concentration and hydraulic retention time were optimized,and the long-term stability of the up-flow weak current intervention anaerobic biological reaction system was realized.The application advantages of the system in configuration are discussed through computational fluid dynamics(CFD)flow pattern simulation and application possibility analysis,which provides a theoretical basis for the scale-up application of this technology.The TBP reducing dehalogenated bacteria solution was successfully domesticated through continuous subculture and used as an inoculation source to construct an intermittent biocathode system to study the effect of applied voltage on the reduction of TBP by biocathode.It could be effectively degraded under three different applied voltages(0.2,0.5 and 0.8 V),open circuit control and non-biological cathode conditions.Its degradation intermediate products were DBP and 4-BP,and the degradation process conformed to first-order reaction kinetics.Compared with the open-circuit control and non-biological cathode,the weak current intervention significantly improved the TBP degradation efficiency.It was observed at 0.8 V that TBP was completely converted to 4-BP in 48 hours.At the same time,an intermittent bioanode system was constructed to study the effect of different initial concentrations on the degradation of Cresol by bioanodes.Cresol could be effectively degraded under various operating conditions,and the degradation process conformed to the first-order reaction kinetics.The initial concentration had a significant effect on the oxidative degradation of Cresol,and the degradation efficiency was up to 100% at a suitable initial concentration(15 mg/L).The initial concentration was too high(25 mg/L)to inhibit the microbial activity and affected the degradation efficiency.An continuous flow system was constructed to study the effect of this system on the simultaneous degradation of TBP and Cresol under different applied voltage(0.6,0.8,1.0,and 1.2 V),lactate concentration(10,7.5,5,2.5 and 0 m M)and HRT(12,24,36 and 48 h).The higher applied voltage increased the cathode and anode potentials and current,and significantly improved the degradation efficiency of TBP and Cresol.At 1.0 V,the removal rates of TBP and Cresol could reach 99.6% and 90.3%.At low concentration of sodium lactate,the degradation rate of TBP dropped to 70.1%.,and at 2.5 m M,the degradation efficiency of Cresol reached to 84.2%,and the lactate consumed 45.3%,which was the highest utilization rate.With the increase of HRT,the removal efficiency of all pollutants increased.The efficiency of HRT reached 88.03% and 85.6% at 36 h,and the conversion rates of DBP and 4-BP reached 4.26% and 79.25%,which was less than that at 48 h.After continuing to operate the system with optimized operating conditions,the removal efficiency of TBP and Cresol increased to 98.3% and 93.6%,and the conversion rate of DBP and 4-BP reduced to 1.8% and 87.6%.The flow pattern simulation and application possibility analysis of the continuous flow system are carried out.The system was reduced to a two-dimensional model,and ANSYS Fluent software was used to solve the pressure and flow changes in the system.The results showed that the introduction of the cathode increased the flow resistance of the fluid in the system and the flow rate was relatively uniform.The introduction of the anode strengthened the fluid disturbance and facilitates contact with the electrode.Compared with other systems,the configuration of the continuous flow system is simple,and the components can be modularized.The electrode material is cheap,and does not need diaphragm.The overall operation energy consumption is low.Taking into account the operating cost and treatment efficiency,the system provides a theoretical basis for the enhanced decomposition and transformation of refractory organic compounds represented by tribromophenol and m-cresol. |
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