Study On The Efficiency Of Electro-Enhanced Anaerobic Membrane Bioreactor In Treating Municipal Sewage

Anaerobic membrane bioreactor is a technology that couples anaerobic biological treatment and membrane separation.Due to its low energy consumption and high methane recovery rate,this technology has attracted much attention.Therefore,researchers have applied it to the treatment of urban sewage.However,serious membrane pollution and low methane production greatly limit the development of anaerobic membrane bioreactors.There is a growing interest in applying an applied voltage to enhance the operational performance of anaerobic biofilm reactors and to mitigate the rate of membrane contamination.In this study,PVDF membranes were modified with conductive polymer monomers pyrrole and BVIMBF₄to improve the electrochemical performance of the membranes themselves.The experiments were conducted to investigate the effects of different applied voltages on the methane yield and pollutant removal rate of the reactor,to reveal the effects of voltage on enzyme activity,microbial activity and microbial community,and to elucidate the causes of membrane contamination mitigation under the effect of voltage.The main results are as follows:（1）In the constant flux continuous operation mode,the methane yield of the experimental group was increased by 0.062 LCH₄/g COD_rem,0.064 LCH₄/g COD_remand0.073 LCH₄/g COD_remrespectively compared to the control group by applying-1.2V,-1.0V and+1.0V electrical bias to the membrane surface;the average methane content of the control group was increased by 25.5%,28.5%and 34.3%respectively compared to the uncharged stage;the COD removal rate of the experimental group was 92.39%,93.0%and 93.62%respectively;the VFAs and p H values in the reaction system were in the normal range;the VFAs and p H values in the reaction system were in the normal range.The average methane content in the control group increased by 25.5%,28.5%and 34.3%respectively compared to the uncharged stage;the COD removal rates of the experimental groups were 92.39%,93.0%and 93.62%respectively;the VFA and p H values in the reaction system were in the normal range and the stable operation of the reactor was maintained.（2）The applied voltage was used to monitor the transmembrane pressure difference,membrane resistance distribution,metabolite changes,zeta point position and sludge particle size of the reactor,and to analyse the mitigation effect of the applied voltage on membrane contamination.The membrane resistance distribution was calculated from membrane resistance filtration tests,which showed that the electrochemical introduction slowed down the formation of sludge cake layer and reduced the total membrane resistance value.The concentration of dissolved microbial products（SMP）and extracellular polymers（EPS）)in the sludge was reduced by the decomposition of electroactive microorganisms,and the protein in SMP and EPS was significantly reduced compared to the non-applied voltage condition,with the protein concentration reduced by10.4 and 36.67 mg/L respectively;Zeta potential values and sludge particle size indicated the presence of an anodic biofilm formation process when the membrane module was used as an anode,improving the flocculation of the granular sludge.The control mechanism of membrane contamination is mainly due to the introduction of electrochemistry,which subjects the membrane module to electrochemical repulsion and electrochemical oxidation causing contaminants to move away from the membrane module or be consumed in large quantities,thus reducing the rate of membrane contamination.（3）The results of the 16Sr RNA high-throughput sequencing analysis and activity experiments showed that the percentage abundance of Methanobacterium hydrogen-depleting methanogens increased from less than 10%to 10.8%（with positive pressure applied）and 16.6%（with negative pressure applied）,and the relative abundance of Methanothrix acetate depleting methanogens in the total sequenced genes was 53.75%.The relative abundance of Methanothrix in the total sequenced genes was 53.75%and64.65%and 58.94%for the sludge samples after the application of positive and negative pressure,respectively.The two methanogenic mechanisms synergistically contribute to the organic matter degradation and methane gas production of the reaction system.Microbial activity experiments showed that the specific methanogenic activity of the reaction system increased significantly with the application of voltage.The acetic acid-loving SMA increased from 0.31 g COD-CH₄/g VS/d when no voltage was applied to0.45 g COD-CH₄/g VS/d when+1.0 V was applied;the hydrogen-loving SMA increased from 0.142 g COD-CH₄/g VS/d to 0.20 g COD-CH₄/g VS/d when-1.0 V was applied.In summary,the applied voltage enables the anaerobic membrane bioreactor to efficiently treat pollutants and control membrane contamination through electrochemical effects,for example,through electrochemical repulsion when negative pressure is applied,which inhibits pollutants from adhering to the membrane module to alleviate membrane contamination;or through electrochemical adsorption and oxidation to form a reticular biofilm when positive pressure is applied to inhibit membrane contamination.The applied voltage anaerobic membrane bioreactor is electrochemically promoted to improve microbial activity and methane production and optimise methane production for municipal wastewater,which supports the application of AnMBR technology.