Experimental techniques for quantifying the cake mass, the cake and membrane resistances and the specific cake resistance during crossflow filtration of microbial suspensions

Simple techniques are reported for (i) measuring the cake mass formed during crossflow filtration of microbial cells, (ii) recovering and measuring the cake mass after crossflow filtration, and (iii) measuring the specific cake resistance during crossflow filtration. The first technique is based on measuring the decline in cell concentration in the feed reservoir during total recycle operation. Cell concentrations are measured on a dry basis and converted to wet weight concentrations using the previously measured wet-to-dry weight ratio of the cells. The second technique involves a series of flushing steps at zero transmembrane pressure followed by wet weight analysis of the suspension formed by the recovered cake. In the third technique, two types of specific cake resistance are defined; an apparent value, αapp, and the true value, αtrue. These are related by the expression αapp=αtrue+(Rm−Rm0)/m where Rm−Rm0 is the flow resistance due to membrane fouling (as distinct from cake formation), and m is the cake mass per unit area. A methodology for decoupling the effects of cake formation and membrane fouling during crossflow filtration is presented, thus, providing a way of monitoring the time evolution of αtrue.