Simulation Study On Membrane Fouling Mitigation Mechanism Of MFC-MBR System By Micro-electric Fields

The problem of membrane fouling limits the popularization and application of membrane bioreactor（MBR）.The coupling of microbial fuel cell（MFC）and MBR can effectively use the micro-electric field generated by MFC to control membrane fouling,and achieve the purpose of in-situ utilization of electric energy generated by microbial fuel cell.However,there is not a lot of research about the mechanism that the electric field mitigates membrane fouling in the MFC-MBR coupled system.in this thesis,aiming at the mechanism of electric field to mitigate membrane fouling,and considering the high energy consumption caused by aeration during the operation of the system,a new configuration of the annular electric field MFC-MBR system was used to study the effects of aeration intensity and electric field on the membrane.At the same time,a mathematical model was constructed to study the whole process of membrane fouling development.Through the research results of experiments and theoretical models,the mechanism of the MFC-MBR coupling system to reduce membrane fouling was explored.The results of the study are as follows:（1）In the absence of an external electric field,the aeration intensity of 2.5L/min prolong the system runtime best.Compared with the aeration intensity of 0.5L/min,the runtime is extended from 15 days to 21 days.The growth rate of TMP is the lowest.Within a certain range（0.5L/min-2.5L/min）,higher aeration intensity makes the system run better.In the MFC-MBR system,the aeration intensity of 1.5L/min makes the system run optimally.In the coupled system,the synergistic effect of electric field and aeration is more complicated.Under the aeration intensity of 2.5L/min,the electric field almost did not work,and the development of membrane fouling was completely dominated by aeration.The optimal aeration intensity in the MFC-MBR coupled system should be determined by experiments,and the method of setting the aeration intensity in stages may optimize the operating conditions and reduce energy consumption.（2）A new model for the MFC-MBR system is proposed with the modification of the classical filtration models to assess membrane fouling.In this model,the development of two-phase membrane fouling was observed,with intermediate blocking as the dominant mechanism,transitioning to a cake filtration mechanism over time.During the development of two-phase membrane fouling,the electric field in the first stage significantly mitigated the fouling,but it is difficult to observe in the second stage.The good fitting results show that the combined model can predict the membrane fouling of MFC-MBR in applications.（3）The whole process of membrane fouling is studied by using the constructed mathematical model.A study of filtration resistance found that the electric field slowed membrane fouling by slowing the rate of accumulation of membrane fouling,with no significant effect on the final accumulation of membrane fouling.The research on the available membrane area found that under the experimental conditions,the A/A₀value at the turning point was between 0.60-0.88.Combined with the model,it is possible to make predictions about range of time in which the turning point will occur.（4）Combined with theoretical model and experimental results,the mechanism of electric field slowing down the development of membrane fouling is proposed.It mainly acts on two aspects:electrostatic repulsion slows down the blockage of membrane fouling in the membrane pores,so that the available membrane area can maintain a good level for a longer time;it reduces the accumulation of cake layer on the membrane surface,thereby reducing the filtration resistance growth rate.The failure of the electric field force in the second stage is mainly due to the fact that the electric field force is not enough to contain the positive feedback effect of"flux rises-pumping action increases-available membrane area decreases-flux further rises".