FOULING OF A MICROFILTRATION MEMBRANE BY 2 GRAM-NEGATIVE BACTERIA

In this study a method is described to assess fouling of microfiltration membranes based on aggregation and redispersion of bacteria from filter cakes. Fouling by the hydrophobic Gram-negative marine bacterium SW8, grown in continuous culture under conditions of carbon- and nitrogen-limitation was compared to fouling by the hydrophilic, batch grown Escherichia coli. Effects of ionic strength and dissolved protein on cake stability were investigated. Cake redispersion was found to depend on the solution ionic strength and on the presence of dissolved proteins. Redispersion was also found to depend on bacterial physiology. However, it was not possible to discriminate between carbon- and nitrogen-limited bacteria based on measurements of surface charge and cell surface hydrophobicity. This work shows that studies which rely on bacterial surface charge and cell surface hydrophobicity to describe membrane surface fouling overlook bacterial surface interactions which control cake stability.