Effect of water-swollen organic materials on crossflow filtration performance

Studies have demonstrated that cakes formed on filter media when filtering microorganisms behave differently from cakes of inorganic particles. It has been suggested that this is due to the water-swollen layer of extracellular polymeric substances on the cell walls of the microorganisms. This idea was tested by preparing simple core–shell particles with a hard polystyrene core and a water-swollen polyacrylic acid shell. The same filtration phenomena were observed when crossflow filtering core–shell particles as reported for microorganisms, i.e., a compressible cake was formed, the compression was reversible, and a linear dependency between resistance and pressure was observed. Thus, the water-swollen layer greatly affected the filtration. From the slope obtained by plotting resistance vs. pressure, the pressure required to double the initial resistance was calculated. This pressure was used as a measure of cake compressibility and determined to be 0.35 bar, in the same range as reported for the microorganisms.