Driving force shapes the biocake characteristics in membrane-based bioreactors

The operation of membrane-based reactors is inevitably challenged by fouling. The driving force in these reactors is not only critical for water passage through membranes but also significantly influences fouling, such as biocake formation. This study investigated the differences between biocakes formed under transmembrane pressure (TMP) and forward osmosis (FO) conditions, specifically focusing on their components, spatial structures, and microbial communities. The findings reveal that the MF-biocake, formed under TMP conditions, contained a greater diversity of foulants, microbes, and metabolic products compared to the FO-biocake. Clustering and correlation analyses indicated that MF-biocake formation was predominantly influenced by dead cells, extracellular polymeric substances, and physicochemical parameters, whereas FO-biocake formation was mainly affected by live cells and adhesion forces. Particle image velocimetry tests further highlighted nonselective foulant adsorption in MF-biocake formation versus selective adhesion in FO-biocake formation. These insights enhance our understanding of the distinct characteristics of biocakes formed under TMP- and FO-driven conditions, aiding in the development of more targeted strategies to control biocake formation based on the driving forces.