Bioenergy Production Enhancement And Membrane Fouling Mitigation Mechanism Of Anaerobic Membrane Bioreactor (AnMBR) System Under Biological Electric Field

The membrane fouling in anaerobic membrane bioreactor（AnMBR）system greatly restricts the further application of AnMBR in wastewater treatment.Herein,we constructed a new single chamber air cathode microbial fuel cell coupled with anaerobic membrane bioreactor（ScMFC-AnMBR）system.In addition,the performance enhancement and membrane fouling mitigation mechanism of AnMBR system in bioelectric field environment were explored.The main conclusions are given as follows:（1）The ScMFC-AnMBR integrated system was successfully constructed and operated.Under the external resistance of 1000Ω,the integrated system operated stably.The output voltage was maintained at 95±4 mV,and the electric field intensity reached225.63 mW·m^-2.The organic matter removal and methane production performance of the coupling system and the traditional AnMBR（named C-AnMBR）under the same operating conditions were compared and analyzed.Results indicated that the start-up speed of ScMFC-AnMBR integrated system was accelerated（16d）,the time was shortened to half of the start-up time of C-AnMBR.The COD removal efficiency of the integrated system reached up to 99.81%.At the end of operation,the methane yield of the integrated system was 85.92 ml·g COD^-1,which was 1.2 times that of the control group C-AnMBR under the same conditions.Moreover,the volatile fatty acids（VFAs）content(626.35 mg·L^-1)in C-AnMBR was 2.6 times higher than that in ScMFC-AnMBR integrated system.Therefore,the introduction of bioelectric field effectively enhanced the organic matter removal,methanogenic performance and acid resistance of AnMBR system.（2）The membrane fouling characteristics of ScMFC-AnMBR integrated system and C-AnMBR were compared.Results indicated that the transmembrane pressure（TMP）of C-AnMBR exceeded 35 kPa on days 38,56 and 73 of the whole operation cycle.Despite twice chemical cleaning,the TMP increase rate in the C-AnMBR system was still large(2.75 kPa·d^-1),and it was difficult to maintain long-term stable operation by cleaning alone.However,the TMP of ScMFC-AnMBR integrated system was always in a state of slow growth,with a low value of only 18.513 kPa in the later stage of experimental operation.Meanwhile,compared with C-AnMBR,the contents of SMP and EPS in the integrated system decreased by 30.01 mg·L^-1 and 84.17 mg·L^-1respectively.Thus,bioelectric field not only strengthened the electrostatic repulsion between microorganisms,but also significantly reduced the membrane surface fouling rate.The aggravating trend of membrane fouling in the integrated system slowed down.In addition,due to the changes of particle size,charge number,SMP and EPS content and microbial community structure caused by the existence of bioelectric field,the synergistic effect of multiple factors had jointly alleviated membrane fouling in the system.（3）The microbial community structure of ScMFC-AnMBR integrated system and C-AnMBR were analyzed.Results indicated that the ScMFC-AnMBR integrated system significantly inhibited the reproductive growth of Megasphaera（relative abundance was only 0.002%）in a stable micro bioelectric field environment（95±4mV）.Because Megasphaera were considered to be a bio-foulant that was easy to adhere under acidic conditions,it showed that the bioelectric field environment can alleviate membrane fouling by inhibiting the growth of bio-foulant.The relative abundance of aceticlastic methanogens（Methanosaeta,6.83%）,syntrophic bacteria of methanogens（Syntrophobacter（0.46%）,Smithella（1.37%）and Syner-01（1.22%））and exoelectrogens（Desulfovibrio,6.81%）in the integrated system increased significantly.The synergy between methanogens and exoelectrogens led to the removal of organic matter,the enhancement of methanogenic performance and the mitigation of membrane fouling in the integrated system.Desulfovibrio（6.81%）,Methanosaeta（6.83%）and Methanosarcina（1.5%）were the most important functional bacteria in the two groups.In conclusion,the ScMFC-AnMBR system greatly improved the methanogenic performance,effectively alleviated membrane fouling and prolonged the operation cycle of the system.It presents a good application prospect in wastewater treatment and resource recovery.