The Minute Electric Field And Conductive Membrane For Membrane Fouling Mitigation In Electric-MBR

The membrane bioreactor (MBR) has been investigated and applied widely because of its compact structure, good effluent property and high degree of automation. But the membrane fouling has been the main limitation on its further development and application. The systematic research had been carried out to identify the effect of external and internal minute electric field on membrane fouling mitigation, which based on integrated membrane-cathode membrane module to construct a series of Bio-Electrochemical Membrane Reactors (E-MBR) with external electric field infliction or electricity generation. The research included:(1) The copper wires were setted inside the flat sheet membrane module working as cathode, the stainless steel mesh and terylene filter cloth were adopted as anode and membrane, respectively, to construct integrated membrane-cathode membrane module. When the external0.073V cm-1electric field was applied, the final flux of test group was1.8times higher than that of control group after4cycles and6hour of filtration. In long term filtration, there was only one time of chemical cleaning in17days of operation, but there were3times in control test.(2) The filter cloth was modified by liquid phase polymerization of polypyrrole. The resistance rate of the filter cloth was reduced to1.84±0.98kQ cm-1～2.11±1.4kΩcm-1after modification with2mL L-1pyrrole solution and adoption with1g L-1～2g L-1sodium dodecyl benzene sulfonate (SDBS). The conductivity and hydrophily of the membrane were enhanced further when the polypyrrole was adopted by SDBS. The conductive filter cloth could work as membrane and cathode at the same time, which simplified the membrane module structure. The flux reduction and membrane resistance increase were mitigated in short and long term filtration tests, respectively, when0.2V cm-1electric field was applied. The vapor phase pyrrole was used for membrane modification to enhance the conductivity and stability of polypyrrole, because of its loose structure and weak intensity after liquid phase polymerization. The polypyrrole on fiber surface from vapor phase polymerization was tight and uniform, which improved the membrane properties and increased the utilization efficiency of pyrrole. The optimal oxidant concentration was20%FeCl3-6H2O (w/v). The final membrane flux of test group was2times higher than tant of control test after3cycles and12hours of filtration when0.2V cm-1electric field was applied.(3) The stainless steel meshes were replaced by iron sacrificial anode to construct the E-MBR with the electric flocculation/coagulation. No extra cathode was necessary because the membrane module was worked as cathode at the same time. And the filtration property of active sludge could be improved by the flocculating agent from anode. In the reactor with1mA electric current, the specific filtration resistance of active sludge was reduced by about38%, the polysaccharide in extracellular polymeric substance was reduced by40%, and the average filtration time of each cycle reached24days, which was2times longer than control test. The removal rate of total organic carbon and total phosphate was enhanced because of the electric field and flocculating agent.(4) The external power source was replaced by the external resistance to construct the galvanic cell in E-MBR, which would avoid the extra energy input for membrane fouling mitigation in this E-MBR with electricity generation. The specific filtration resistance of active sludge was reduced by about17.5%because of the flocculating agent from anode. The amount of filter cake was recuded by about37.3%because of the electrostatic repulsion from internal electric field. In comparison with control test, the filtration time in E-MBR lasted3more days at the first cycle of the first stage and it was3times of the control test at the second cycle, which was extended to24days after the sludge retention time was reduced to30days. There was about0.2V output voltage from the reactor during the operation.(5) The MBR was separated into one anaerobic anode chamber and two aerobic cathode chamber to construct the E-MBR including microbial fuel cell (MFC). The stainless steel meshes were adopted as cathode and membrane, the active carbon granules were used as anode. The output voltage of the integrated reactor was about0.2V with100Ω resistance. The filtration time of membrane modules was increased from13-15days to21-27days when the external circuit was closed, because there was about2.5x10"14N electrostatic force on membrane foulants as the result of internal electric field. The turbidity, ammonia nitrogen and total phosphate were removed effectively when the artificial wastewater was treated by the sequential anaerobic-aerobic treatment process, which remedied the limitation of MFC effluent properties.(6) The total current and cell potential output, coulombic efficiency and energy output were increased in integrated E-MBR including MFC after cathode system division, which indicated the efficiency of the electricity generation was enhanced. The2,4,6-tribromophenol (TBP) was removed effectively in the integrated reactor, the mineralization rate was50%-62%, the circumstance temperature was the limiting factor of debromination. The LC-MS test result indicated the main intermediates in decomposition of TBP included bromophenol,1,5-dibromophenol acetate, bromophenol acetate,2,6-dibromo-4-methylphenol,2-bromo-4-methylphenol,1-bromo-2-methoxy-5-methylbenzene, acetophenone and benzaldehyde.Those researches indicated that the filter cloth and stainless steel membrane fouling could be mitigated effectively by the external and internal minute electric field in E-MBR. The filter cloth could work as cathode after liquid and vapor phase polymerization polypyrrolc modification, which simplified the structure of membrane module obviously. No extra energy was necessary to mitigate the membrane fouling when the MBR was integrated with galvanic cell or MFC. The persistent organic pollutants TBP could be decomposed during the sequential anaerobic-aerobic treatment process, which revealed high potential in practical application.