Investigation On The Effect Of Activated Carbon Addition On Methane Fermentation And Membrane Fouling Of Anaerobic Membrane Bioreactor

Anaerobic membrane bioreactor?AnMBR?couples anaerobic bioprocesses with membrane technology to retain slow-growing functional microorganisms through solid-liquid separation of membranes.AnMBR has currently attracted attention due to its efficient organic degradation and the potential of energy recovery from wastewater.However,the methanogenesis process is the main rate-limiting step for anaerobic fermentation.Promoting methane fermentation potential is beneficial to improve energy recovery efficiency.In addition,membrane fouling is the major obstacle in the practical application of AnMBR,which can reduce membrane flux,shorten membrane life and increase operating costs.The methane fermentation and membrane fouling can be effectively controlled by adding activated carbon,but few studies compared the effects of powdered activated carbon?PAC?and granular activated carbon?GAC?on the methane fermentation and membrane fouling control of AnMBR.In order to improve the methane fermentation and membrane pollution control effect,three 2L-AnMBRs of C-AnMBR?Control?,P-AnMBR?adding PAC?and G-AnMBR?adding GAC?were treated synthetic municipal wastewater.Based on investigating the effect of activated carbon on the methane potential,the methanogenic capacity of continuous operated AnMBR added activated carbon was further analyzed.The effect of activated carbon on membrane fouling and membrane filtration test were carried out to analyze the different mechanisms of PAC and GAC for membrane fouling control.The main work and conclusions are as follows:?1?Batch tests under different loads showed that adding PAC and GAC can increase cumulative methane production,PAC can effectively increase the maximum methane production rate(R_max)and shorten the lag period?t₀?.While GAC can increase R_max,but has no effect on t₀,indicating that the PAC is better than the GAC in improving the methanation potential.In addition,PAC and GAC can alleviate the accumulation of volatile fatty acids and improve the system load.?2?The average COD removal efficiency of C-AnMBR,P-AnMBR and G-AnMBR was 95.0%,95.6%and 95.7%,respectively.At HRT 6 h,the methane production rates of C-AnMBR,P-AnMBR and G-AnMBR was 0.637,0.632 and 0.633 L/L-reactor/d and the methane conversion rates were 81.6%,80.8%and 80.9%,respectively.The microbiological analysis results showed that the dominat archaea of the three AnMBRs was Methanothrix,indicating that the methanogenesis pathway in the reactor was mainly by acetate degradation.The main bacteria phylum are Chloroflexi,Firmicutes,Proteobacteria,Bacteroidetes and Synergistete.?3?Trans-membrane pressure?TMP?kept rising during the operation of the reactor.When hydraulic retention time?HRT?was longer than 12 h,PAC and GAC could effectively alleviate membrane fouling compared with no activated carbon,and PAC was more obvious than GAC.When HRT was shorter than 12 h,GAC could slow down the membrane fouling rate and prolong the membrane life cycle,which was batter than PAC.?4?Through the analysis of the morphology and elemental composition of the sludge on the membrane surface,it could be found that there were large sludge particles on the membrane surface of the C-AnMBR,which was the main pollutant.While there were more inorganic elements on the membrane surface of the P-AnMBR,which were related to the gel layer,indicating that a gel layer was formed on the surface of the P-AnMBR.There were more organic pollutants on the membrane surface of G-AnMBR.?5?The ex-situ filtration test of the polluted membrane showed that when HRT was longer than 12 h,adding PAC had a significant alleviation effect on membrane fouling,mainly due to alleviate the formation of cake layer by physical scouring.When the HRT was shorter than 12 h,the adsorption of PAC to the membrane surface was enhanced,and the gel layer was formed on the membrane surface,which increased the resistance of cake layer?Rc?and made P-AnMBR worse than G-AnMBR.From the perspective of long-term operation,the membrane fouling formed by the cake layer was the main one in the three AnMBRs.The Rc of C-AnMBR and P-AnMBR?95%?was larger than that of G-AnMBR?76.5%?,due to that GAC reduced the accumulation of proteins and polysaccharides on the membrane surface,which made GAC have a better mitigation effect on membrane fouling and prolong the membrane life.