Effects of filtration modes on fouling characteristic and microbial community of bio-cake in a membrane bioreactor

This study investigated the effects of filtration modes, i.e., constant transmembrane pressure (TMP) and constant flux mode, on nutrient removal, fouling characteristic and microbial community in a membrane bioreactor. The results showed that filtration mode had minor effects on membrane rejection of COD and nutrients. Membrane fouling rate was higher in constant flux mode than in constant TMP mode. Significantly higher polysaccharide and protein concentrations were found for membrane bio-cake operated under constant flux mode. Fourier transform infrared spectroscopy revealed a significant difference in chemical compositions of SMP and EPS in bio-cake between two filtration modes. Furthermore, constant flux mode had higher portion of α-helix (70.35%) and β-sheet (67.53%), which is related to aggregation and biofilm formation of bacterial cells, in amide I band than those of constant TMP mode (45.67% and 43.44%, respectively). This was corroborated by the fact that thicker bio-cake layer was formed on membrane surface operated under constant flux mode. In addition, excitation-emission matrix fluorescence spectroscopy showed that the fluorescence intensity related to protein-like and humic acid-like substances in constant flux mode were higher than that in constant TMP mode, suggesting their important roles in accelerating membrane fouling. Finally, the microbial communities of bio-cake in constant TMP mode differed significantly from those in constant flux mode. Overall, the results indicated that different contents, characteristics and microbial communities of membrane foulants led to distinct fouling rates between filtration modes.