| Microbial fuel cell（MFC）can use microorganisms as catalysts to convert chemical energy into electrical energy,and can also generate electricity while treating wastewater,but the treatment efficiency is low and the effluent quality is poor.Therefore,MFC combined with membrane bioreactor（MBR）is used for high-efficiency and high-quality water treatment.MBR is a promising technology combining membrane separation and bio-aerobic technology,which can effectively realize mud-water separation and ensure high pollutant removal efficiency,but membrane fouling still hinders its wide practical application.When the two systems are combined,the micro-electric field generated by the MFC can effectively remove pollutants and keep some degradation products and microorganisms away from the MBR membrane modules,effectively alleviating membrane fouling.However,the micro-electric field can alleviate the membrane fouling,but cannot completely eliminate the membrane fouling.At present,most studies have only demonstrated that the electric field can slow down the membrane fouling,but why the electric field can not completely solve the problem of MBR membrane fouling,and whether there are substances on the membrane surface that are not affected by the electric field are not very clear and need further exploration.In this study,the operation effect of the MFC-MBR coupling system in the treatment of phenol wastewater was evaluated,and the membrane fouling mechanism of the MFC-MBR coupling system in the process of degrading phenol wastewater was explored.Under open circuit and closed circuit conditions,the following aspects were investigated: the effect of different substrates on the electricity production capacity of the MFC-MBR coupled system,the ability of the MFC-MBR coupled system to degrade pollutants,the growth rate of transmembrane pressure（TMP）,the changes in contaminant morphology on membrane modules,and the differences between phenol degradation products and microorganisms in the cathode and on the membrane modules.The operation effect of MFC-MBR coupling system showed that the maximum voltage of the reactor can reach 0.60 V when phenol and glucose were used as the common carbon source for microbial growth,which was 0.12 V higher than that when glucose was used as the only carbon source.When the HRT was 36 h,the removal rates of chemical oxygen demand（COD）and ammonia nitrogen of the MFC-MBR coupling system were 94.3% and 55.9%under closed circuit conditions,which were 12.2% and 10.17% higher than those under open circuit conditions.Although almost all phenol can be removed in 36 h with or without electric field,the removal rate of phenol was close to 100% under closed circuit conditions for 30 h,while the removal rate of phenol under open circuit conditions was only 88.3%.The existence of the micro-electric field can effectively stimulate the sludge activity,made it better participate in the degradation of pollutants,and improved the ability of the MFC-MBR coupling system to degrade pollutants.The research on the membrane fouling mechanism of the MFC-MBR coupling system showed that: Under closed circuit conditions,TMP took 56 days to reach 30 k Pa,which was 8days longer than that under open circuit conditions.The pollutants attached to the surface of the membrane module were significantly reduced,the accumulation layer was thinned,the pollutants were dispersed,the blockage of the membrane pores and the surface deposition have been effectively alleviated.The existence of the micro-electric field reduced the types of degradation products on the membrane module,inhibited the generation of trimethylsilyl ethaneperoxoate,which was easy to approach the membrane module,and kept dodecamethylcyclohexasiloxane away from the membrane module.At the same time,the species diversity and species abundance of microorganisms on the membrane module were both reduced,indicating that the MFC-MBR coupling system can effectively slow down the adsorption and accumulation of degradation products and microorganisms,and improve the filtration performance of membrane modules.However,the micro-electric field cannot completely eliminate the membrane fouling.In both cases,the content of ethanethiol,a phenol degradation product,was as high as about 98%.In addition,Proteobacteria was as high as 58% in both cases,due to its outer wall was composed of bacterial ester polysaccharides,it was easy to adhere to the material and hardly affected by the electric field force.And Actinobacteria,as a filamentous fungus,actually increased under the stimulation of the electric field.In conclusion,the MFC-MBR coupling system can improve the removal efficiency of pollutants,and the existence of the micro-electric field can slow down the membrane fouling,which provided an efficient and energy-saving way for the control of MBR membrane fouling.However,the existence of micro-electric field cannot completely eliminate membrane fouling,some substances will still adhere to the membrane modules in the presence of electric field force,which provided theoretical guidance for the modification of MBR membrane modules. |
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