Special features of microbial cake under high pressure conditions in microfiltration

Abstract

Here, cell separation from microbial suspensions (gram-negative bacterium Escherichia coli, gram-positive bacterium Lactococcus lactis, and yeast Saccharomyces cerevisiae) was performed by dead-end microfiltration. From the results of three types of experiments, namely constant-rate and constant-pressure filtration, and constant-pressure consolidation, it was revealed that the microfiltration behaviors of microbial suspensions can be described on the basis of the pressure dependences of the average void ratio and specific resistance of the microbial cake. However, under high-pressure conditions, we found that the cake structure of Escherichia coli was changed, and the calculations were inconsistent with constant-rate filtration data. The data, such as constant-rate filtration behaviors, spectra of filtrate, electron micrographs of filter cake, and constant-pressure consolidation behaviors, indicated the possibility of cellular destruction of Escherichia coli under pressures above 700 kPa. In contrast, this phenomenon was not observed at pressures of up to 1000 kPa in yeast with different cell envelope compositions. Cellular destruction affected the filtration performance, and since intracellular water was discharged, the dehydration characteristics of the cake changed significantly. The findings on the properties of microbial cakes under high pressure obtained in this study are useful for improving the efficiency of filtration operations for microbial suspensions and dehydration operations for biological sludge.