Research On An MFC-MBR Integrated System For Wastewater Treatment And Membrane Fouling Mitigation

Membrane fouling is the bottleneck which restricts the widespread application of membrane bioreactor（MBR）.The low electric field generated by the microbial fuel cell（MFC）could be utilized to control the membrane fouling in MBR,if the MFC and MBR were effectively integrated.However,most of the reported MFC and MBR integrated systems used the cathodic flat membrane with low flux and complex structure,which restricted the pratical application of the MFC and MBR integtated system.In order to overcome the above shortages,in this research,an MFC was integrated with an MBR using hollow fiber membrane module,to construct a novel MFC-MBR integrated system with high effluent quality and mitigrated membrane fouling.This research evaluated the electrochemical performance,wastewater treatment,sludge reduction efficiency and membrane fouling condition of the MFCMBR integrated system.In addition,the effects of long-term low electric field on the sludge properties in the MFC-MBR system were investigated and the mechanisms of the membrane fouling control in MFC-MBR integrated system were also analyzed.During the long-term operation of MFC-MBR system,it was demonstrated that MFC-MBR could efficiently recover electricity from the wastewater,and form an internal electric field of 0.09V/cm between the anode and cathode.The sludge activity was improved by the stimulation of low electic field.The COD,NH₄⁺-N and TN removal efficiencies of MFC-MBR were 94.8%,97.5% and 50.8%,which were 20%,37.9% and 26.2% higher than those of C-MBR,respectively.Compared with the conventional activated sludge process,MFC-MBR achieve 54% of sludge reduction,and the sludge production of MFC-MBR was 28% lower than C-MBR.The TMP increasing rate of MFC-MBR was 57.28% lower than that of C-MBR.The pore blocking and cake layer fouling in the MFC-MBR were both markedly mitigated.The sludge properties of MFC-MBR were analyzed.Compared with C-MBR,MFC-MBR could reduce the concentrations of SMP and LB-EPS.The SMP and LBEPS concentrations in MFC-MBR were decreased by 37.4% and 0.6%,respectively.The SVI and CST of the sludge in MFC-MBR were decreased by 31.0% and 33.5%,indicating that the settleability and filterability of the sludge in MFC-MBR were improved.The EFLI/FAI value of the sludge in MFC-MBR was 52.9% lower than CMBR,inferring that growth of the filamentous bacteria in MFC-MBR was inhibited.The hydrophobicity and aggregation of the sludge in MFC-MBR were reduced,inducing the decrease of floc size.Additionally,in the MFC-MBR,the sludge was more homogeneous and spheroidized,and the structure of the sludge was more compact with lower compressibility.Mechanism of the membrane fouling mitigation in MFC-MBR was analyzed.Compared with C-MBR,the energy barrier between the membrane and SMP in MFCMBR was increased,while the secondary energy minimum was decreased,indic ating that the adhesion of the SMP in MFC-MBR on the membrane was weakened.The flux decline induced by the SMP in MFC-MBR was 8.2% lower than C-MBR.The membrane pore blocking and flux decline were mitigated.MFC-MBR decreased the hydrophobicity of LB-EPS,and reduced the free energy of adhesion between LB-EPS and membrane surface,which weakened the adsorption and accumulation of LB-EPS on the membrane surface.The porosity of the fouling layer formed by LB-EPS in MFC-MBR was improved,and the resistance of the fouling layer was decreased.The flux decline induced by the LB-EPS in MFC-MBR was 9.6% lower than C-MBR.In the MFC-MBR,the free energies between sludge floc and memrbane surface and cake layer were all decreased.When approaching the membrane surface and cake layer,the flocs in MFC-MBR need more energy to overcome the energy barrier.Moreover,the sludge cake layer on the membrane in MFC-MBR had higher porosity and lower content of foulants.This demonstrated that the adsorption of sludge floc on membrane and cake layer were mitigated in the MFC-MBR,and the cake layer formed in MFCMBR had higher filterability.Based on above analysis,the MFC-MBR can effectively mitigate the membrane fouling,and simultaneously improve the wastewater treatment e fficiency and sludge reduction,which provides an efficient and energy-saving approach for the membrane control in MBR.It has great significance on the widespread application of MBR.