Using a yeast cell layer as a secondary membrane in microfiltration

Microfiltration of yeast suspensions (Sacch. cerevisiae) was carried out to investigate the impact of a secondary membrane, composed of deposited yeast cells, on the filtration performance. Cross-flow filtration experiments with yeast–water suspensions in a rectangular channel showed the deposition of cells of different sizes, depending on the hydrodynamic parameters of the experiments. In dead-end filtration experiments with yeast–wort suspensions, the presence of the yeast layer provided, for constant filtrate flux, a slower increase in transmembrane pressure and for constant transmembrane pressure a slower decrease of filtrate flux. The positive effect of the yeast presence, which was observed, strongly depends on the yeast concentration. In cross-flow filtration experiments at a given filtrate flux the lower cross-flow velocity enables the formation of the yeast cell layer, which acts as secondary membrane and protects the primary membrane from the fouling agents of the wort, such as proteins and polysaccharides. At higher cross-flow velocity, there is no yeast layer formation, which results in blocking of the membrane through the fouling agents and the transmembrane pressure rises dramatically.