Abstract
A more comprehensive investigation into fouling properties of cake and bulk sludge played an essential role in better understanding membrane fouling caused by the bio-cake formation in an anammox membrane bioreactor (MBR). In this work, the cake and bulk sludge from a stable anammox MBR were analyzed with the composition, interfacial thermodynamics and microbial community. Physicochemical analysis indicated that cake sludge agglomerated into larger flocs with a denser structure and a higher protein/polysaccharide (PN/PS) ratio as compared with bulk sludge. It also revealed that cake sludge was found to have looser protein secondary structures and more hydrophobic components than those of bulk sludge, which means the differences in surface hydrophobicity between two sludges might play a key role in revealing anammox sludge aggregation and further cake layer formation process. The dominant role of hydrophobic attraction energies between cake sludge and membrane surface at a shorter separation distance (< 2 nm), after the analysis of the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) method, confirmed cake layer formation process related with surface hydrophobicity. Furthermore, biological analysis demonstrated that the relative microbial abundances of Candidatus_Brocadia and Candidatus_Kuenenia in cake sludge were much greater than those of bulk sludge, implying a higher biofouling potential for them. Overall, this study fills the gap in understanding the mechanism between anammox sludge properties and cake formation, which provides basic knowledge for membrane fouling control in anammox MBR.
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