Location of Biological Foulants Within a Wet Membrane Structure

During beverage clarification, proteins, polysaccharides, and polyphenols foul microfiltration membranes (MF) despite their small size relative to the membrane pore size. To develop fouling mitigation strategies for such systems, it is important to understand fouling mechanisms. The objective of this study is to use confocal laser scanning microscopy (CLSM) to determine the location and extent of fouling by individual components within a wet membrane structure, to visualize depth profiles of foulants at different stages of fouling, and to examine how interactions among foulants impact these profiles. In this contribution, work is presented on direct-flow filtration of a protein solution, with conditions emulating those of beer, using an asymmetric polyethersulfone membrane. Measurements of permeate flux versus permeate volume were taken to determine the rate and degree of flux decline associated with membrane fouling. After filtering different volumes of the protein solution, membrane samples were analyzed by CLSM using a cross-sectional imaging CLSM protocol that was developed by our research group. Using this protocol, we were able to visualize the location of protein fouling throughout the full thickness of the membrane in a way that has not been done before. Image analysis was done to generate profiles of foulant concentration versus depth. Much of the protein was deposited near the feed surface of the membrane; however, significant amounts of protein are found throughout the entire membrane thickness. Analyses of membranes at different stages of flux decline elucidate how the foulant depth profiles develop with increasing volume processed.