Linking dynamics in morphology, components, and microbial communities of biocakes to fouling evolution: A comparative study of anaerobic and aerobic membrane bioreactors

Abstract

Biocake governs membrane fouling in anaerobic membrane bioreactors (AnMBRs) and thorough understandings of its dynamics could aid in better fouling control. However, little is known about biocake dynamics in the AnMBRs, especially compared with the well-studied aerobic membrane bioreactors (AeMBRs). Hence, a comprehensive investigation on biocake dynamics of an AnMBR was conducted, simultaneously operating an AeMBR with identical conditions for comparisons. Observed by the scanning electron microscopy (SEM) and confocal laser scanning microscope (CLSM) in 3D-mode, the biocakes of the AnMBR possessed smoother morphology and denser structure than those of the AeMBR regardless of fouling stages. Fluorescence staining of extracellular polymeric substances (EPS) matrix of biocakes integrated with quantitative and chemical analyses illustrated that the dynamics of the biocake components in the AnMBR featured as a steady and progressive process but drastic in the AeMBR. The sequencing data similar to the SEM and CLSM observations showed that filamentous bacteria (i.e., the f_Anaerolineaceae) dominated in the AnMBR biocakes. In the AeMBR, the f_Microscillaceae prevailed in the biocakes and increased markedly from 24.38% to 36.67% after TMP jump. According to network analysis, microbial interactions were more positive but less intensive in the AnMBR compared with the AeMBR, which might mutually impact with the biocake dynamics. As the keystone taxa, the f_Anaerolineaceae and f_Microscillaceae had strong positive correlations with the variation of organic foulants in the biocakes of AnMBR and AeMBR, respectively, indicating their significant roles in the fouling evolution. Overall, this study provides new insights into the biocake dynamics in AnMBRs and facilitates to gain better understandings of differences in fouling evolutions between AnMBRs and AeMBRs.