Electrically Enhanced Membrane Fouling Resistance And Wastewater Treatment In Anaerobic Membrane Bioreactor

Recently,owing to the superior capacity on total suspended solids removal and small footprint,anaerobic membrane bioreactor?AnMBR?,integrates conventional anaerobic activated sludge processes with membrane separation technology,has been widely investigated.However,the serious problem of membrane fouling,the corresponding increase in costs,and the low conversion rate of energy-based gases restricted its practical application.With regard to the issues of severe membrane fouling and low methane yield,an electrically enhanced AnMBR combined with microbial electrochemical system was constructed this study.All-carbon nanotubes-based conductive hollow fiber membranes?CNT-HFM?were utilized to serve as dual functions of filtration and biocatalysis.Another reactor was operated as control in parallel under the same conditions but under open circuit mode.The membrane fouling and wastewater treatment efficiency were studied to evaluate the role of applied voltage on the domestic wastewater treatment performance of this system.The related results were shown as follows:During the continuous up-flow and constant flux operation process,there was an obvious relief on the increase of transmembrane pressure?TMP?under the applied potential of-1.0 V,and the growth rate of TMP is 0.0196 bar/d,which accounts for only half of those in control.On the other hand,the biofilm layer can be easily washed away by water with the assistant of electrical,where the electrostatic effect could not only inhibit the conglutination of pollutants on membrane surface,but also alleviate the block in membrane pore.Moreover,by analyzing the properties of the sludge,it was found that the average particle size of the sludge increased from 44.1 to 51.4?m under the assitance of the electric field,the contents of microbial metabolites were higher in the sludge around membrane but lower in sludge on membrane biofilm than that of control reactor.The zeta potential of the sludge around the membrane decreased from-15.2 to-19 mV.It was due to the change in the sludge properties induced by the electric field that enhance the interaction between contaminants and the membrane surface,and further alleviate the membrane fouling and operating energy consumption.The applied voltage also benefit for the removal of organic and production of biogas in the treatment of wastewater.Under the condition of influent chemical oxygen demand?COD?concentration of 500±50 mg/L,the effluent COD concentration of the reactor at hydraulic retention time?HRT?of 6-12 h was 36.1-58.8 mg/L,and the corresponding COD removal rate reached 87.8-93.1%,which was 3.1-3.3%higher than that of control.Although the discrepancy of COD removal rate is not obvious,the conversion of methane during anaerobic digestion process has a significant increase with applied voltage of-1.0 V.The final conversion rate of methane in the electro-assistant reactor reached 74.8 m L CH₄/g COD,which was approximately 1.3 times higher than that of the control?57.5 mL CH₄/g COD?.This result indicated that the applied voltage benefit for the recoveryof energy gas.After a integrity cycle of reaction,the sludge of membrane surface and reactor bottom were respectively taken to perform high-throughput sequencing of archaea and bacteria.The results showed that the amount of H₂-utlizing methanogens Methanobacterium on the surface of the cathodic membrane greatly increased under the assistance of electric field,which accounts for 82.4%of archaea gene sequences,and was 3.2 times higher than that of control.The existence of carbon nanotube film inhibited the attachment of filamentous bacteria on the membrane surface,especially under the electric field,thus alleviated membrane fouling.Moreover,the contents of acetoclastic methanogen Methanothrix in the bottom sludge also increased from 68.4%to 73.2%under the stimulation of the electric field.The co-existence of hydrogenotrophic methanogen and acetoclastic methanogen in the system promoted the organic matter degradation and methane production.The electroactive microorganisms Acinetobacter and Arcobacter,with the function of extracellular electron transport,were the dominant bacterial communities on the cathode,which account 20.9%and 15.4%of the total bacterial communities,and was 3.1 and2.5 times higher than those of the control,respectively.This result indicating that the presence of an electric field can promote the growth of these microorganisms,therefore improved the conversion efficiency of organic matter.