| Under the background of resource and energy crisis and carbon neutrality,the traditional aerobic sewage treatment process of energy consumption for water quality is facing severe challenges,and the anaerobic treatment process has been increasingly valued and respected in recent years due to its characteristics of low energy consumption,low-carbon emission and energy recovery.As a new anaerobic treatment process,anaerobic membrane bioreactor（AnMBR）can decouple the hydraulic residence time（HRT）and sludge residence time（SRT）in the reactor through membrane interception,which has significant advantages in increasing the total amount of anaerobic microorganisms and improving energy recovery.However,due to the limitations of the anaerobic treatment process,the further removal of nitrogen and phosphorus nutrients has become a hot spot for effluent discharge and reuse of anaerobic membrane bioreactors.The anaerobic electric membrane bioreactor（AnEMBR）was constructed by combining anodic electrochemistry with AnMBR,which could strengthen membrane fouling control by electric field.On the other hand,anode active metal can release high-valence metal ions,and the removal and recovery of phosphorus by chemical methods is an important direction for the upgrading of AnMBR technology.（1）The performance and mechanism of AnEMBR in enhancing organic matter removal and methane production were studied.Compared with the addition of iron salt and the control group AnMBR,the average COD removal rate of AnEMBR increased by 1.3%and 2.1%,reaching 96.5±0.39%,and the average effluent COD concentration decreased to 17.1±2.40mg/L.More than 76%of the COD was converted to methane through anaerobic digestion,with a methane yield of 0.224 LCH4/g CODremoved.The results of sludge electron transfer system activity showed that the electric field and the released iron ions stimulated the respiration,decomposition,and metabolism of anaerobic microorganisms,accelerated the extracellular electron transfer of microorganisms,thereby improving the efficiency of organic matter removal and methane production performance.（2）The phosphorus forms in AnEMBR were analyzed,and the mechanism of phosphorus removal through anodic iron release was clarified.The highest removal rate of TP in the AnMBR system was achieved at 33.2%after adding iron salts,while the AnEMBR achieved nearly 100%TP removal steadily.After the addition of iron salts,iron-bound phosphorus（23.1%）,carbonate adsorption phosphorus（55.3%）,and water-soluble phosphorus（14.9%）were the main forms of phosphorus in AnMBR,while iron-bound phosphorus increased to 72.9%,and carbonate adsorption phosphorus and water-soluble phosphorus decreased significantly in AnEMBR.The element and phase composition of the AnEMBR sludge crystal precipitation were analyzed by scanning electron microscopy,X-ray energy dispersive spectroscopy,and X-ray diffraction.The results further confirmed that the generated vivianite[Fe3（PO4）2·8H2O]was the main pathway for iron removal in AnEMBR.（3）The membrane fouling characteristics of AnEMBR were revealed,and an efficient operation strategy for AnEMBR was proposed.The analysis of mixed liquor characteristics showed that the concentration of soluble microbial metabolites in AnEMBR decreased significantly,the surface charge of sludge flocs decreased,the particle size increased,and the filtration resistance was significantly reduced（more than 60%compared with the control group）,which is conducive to improving membrane filtration performance.However,the concentration of iron ions related to the iron ion release rate directly affects the membrane fouling process,and a high concentration of iron ions can lead to the accumulation of iron-rich inorganic pollutants on the membrane surface.Therefore,the key to the efficient operation of AnEMBR is to adjust the voltage/current to maintain an appropriate iron concentration. |
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