Research On The Effect Of Electrode Performance Degradation On System Performance In Bioelectrochemical Systems

Bio-electrochemical systems(BES)has a promising future in the field of water treatment.However,the interface behavior of the electrode is the decisive factor affecting the BES performance.Since the bioelectricity is affected by complex factors and leads to performance attenuation,it is necessary to analyze the theoretical internal factors affecting the performance decay of the BES system,so as to find a reasonable solution to further improve the operating efficiency of the BES system.In this study,single chamber air cathode microbial fuel cells(MFCs)were used as the subject to analyze the influence of ions concentration(Ca²⁺and Mg²⁺)in the feed solution on the attenuation performance of the MFCs.Through electrochemical testing,including LSV,CV,and EIS,the impact of ions concentration on the cathode,anode and overall performance of MFCs were mainly discussed.Meanwhile,the COD and ammonia nitrogen of the inlet and solution of the system were monitored.The formation of biofilm and the deposition of ions on the cathode surface were monitored by in-situ ultrasonic monitoring technology for 150 days.Moreover,the MFCs performance recovery were studied by applying electric field reversal.The results showed as follows:(1)According to the MFCs performance changes of during operation,it could be divided into three stages,and ions concentration showed differentiated influence characteristics in each stage.When the ion concentration was higher,it played a certain role in the growth stage and combined growth stage of the biofilm,but the performance attenuation in the growth inhibition stage was also more obvious,so controlling reasonable material and liquid ions had important impact on the system operation efficiency;(2)Based on the ultrasonic monitoring method,the MFCs electrode interface changes were monitored throughout the period.Through continuous monitoring and calculation of the electrode surface density and thickness characteristics,the research results showed that the biofilm was first formed on the MFCs cathode surface with a density of about 0.6 g/cm³,then the scale accumulates on the electrode surface and diffuses to the main body of the biofilm gradually,the density of the mixed layer was about 0.9 g/m³;(3)Based on SEM and EDS analysis of the electrode samples at each stage,the results showed that the electrode interface deposition layer at each stage presented regular changed in characteristics:firstly,biofilm was formed on the cathode surface,and then Ca²⁺and Mg²⁺formed deposition on cathode due to the concentration accumulation gradually,electric field induction and the related effect of biofilm.The related effects of biofilms gradually formed deposits in biofilms.Ion deposition first occurred on the electrode surface,then invaded the inside of the biofilm slowly;(4)The performance recovery experiment was carried out by applying a reverse electric field to MFCs,and the results showed that the reverse electric field method could restore the performance of the electrode to a certain extent.For the system without ion deposition layer,the peak performance could be restored to 74.07%;for the MFCs containing ion deposition layer,the electrochemical performance could be recovered to 84.72% of the peak value.