The Research On Characteristics And Mechanisms Of Membrane Fouling In The AnMBR+FOMBR Combined System

Anaerobic membrane bioreactor(An MBR) + Forward osmosis membrane bioreactor(FOMBR) combines the advantages of An MBR low energy consumption, recycling energy and FOMBR low fouling rate and high potential treatment efficiency of nitrogen and phosphorus, which is a new way to solve the key problem of high concentration of nitrogen and phosphorus in effluent of An MBR. It should be noted that the membrane fouling of An MBR and FOMBR is the main problem which restricts its application. The research on the characteristics and mechanism of membrane fouling in An MBR and FOMBR can provide a basis for its application.In this study, the treatment efficiency and membrane fouling characteristics of the combined An MBR + FOMBR system under different operating condition were managed. PCR and Illumina-Mi Seq techniques were used for analyzing the microbial population change rules of combined system; GPC and FTIR techniques were used for analyzing the composition and characters of EPS in the combined process; sequencing batch filtration experiments and XAD resin fractionation technology were used for studying the EPS fouling characteristics in An MBR; EEM technology was used for analyzing the internal fouling and external fouling of FOMBR.Contrasting the treatment efficiency and membrane fouling characteristics of the combined system, it is showed that the treatment efficiency of 25 ℃ An MBR was lower than that of 35 ℃ An MBR, and the fouling rate of 25 ℃ An MBR was higher than that of 35 ℃ An MBR. It is found that FOMBR can improve the removal rate of nitrogen and phosphorus in An MBR, the higher concentration of pollutants in the influent of FOMBR can be better maintaining the microbial growth, decreasing the contents of the fine fouling in FOMBR and thus reducing the flux decline rate of FOMBR.Comparing the activated sludge properties and microbial population structure of activated sludge in combined system, it was found that the dominant microbial populations in 35 ℃ An MBR was differed from that of 25 ℃ An MBR, the abundances of Bacteroidetes in cake layer of 25 ℃ An MBR were higher than that in 35 ℃ An MBR, the population of Sphingobacteriia and Bacteroidia were the major classes caused anaerobic membrane fouling. It was found that Bacteroidetes and Proteobacteria were the dominant species in FOMBR, Cytophagia was the mainly class in cake layer of FOMBR, and Chryseolinea was the mainly bacteria in Cytophagia class.Comparing the membrane fouling characteristics in 35 ℃ An MBR and 25 ℃ An MBR, it was found that the concentration of S-EPS was reduced with decreasing HRT, the concentrations of tryptophan and aromatic protein in 35 ℃ An MBR were higher than that of 25 ℃ An MBR. The concentration of bound EPS was increased with decreasing HRT, the concentrations of LB-EPS and TB-EPS in 25 ℃ An MBR were significantly higher than that in 35 ℃ An MBR under every HRT operation, the higher concentration of LB-EPS and TB-EPS in 25 ℃ An MBR was the main reason for the serious membrane fouling.The fouling potentials of each EPS in bulk sludge and cake layer in An MBR were compared. It was found that the rejection rate of LB-EPS in bulk sludge was 77.6%, and the rejection rate of S-EPS in cake layer was 89.5%. It is showed that the membrane fouling was mainly caused by LB-EPS in bulk sludge and S-EPS in cake layer. The lower poriness of fouled membrane meant the higher fouling potential of each EPS. It was found that the neutral hydrophobic organic compounds(HPO-N) influenced the fouling, so reducing the amount of HPO-N can mitigate membrane fouling of An MBR.Comparing the membrane fouling characteristics in FOMBRs, it was found that the different influents of FOMBR resulted in the different characteristics of S-EPS and B-EPS in FOMBRs, the nano particle size of B-EPS in M-FOMBR was lower than that of P-FOMBR, and the large size of B-EPS has larger pore in cake layer in P-FOMBR, the micro size of S-EPS was easily deposited or adsorbed on the membrane pores in M-FOMBR, which may cause severe internal fouling, and thus different fouling rates.