THE EFFECT OF COLLOID STABILITY ON MEMBRANE FOULING

An experimental study is presented of UF and RO membrane fouling by co lloidal particles. Membrane flux and rejection are monitored in a labo ratory scale, cross-flow, narrow channel unit employing flat sheet mem branes, which are challenged by suspensions of mono-disperse colloidal particles. Apart from the influence of basic parameters, such as part icle size, concentration, cross-flow velocity aid cans-membrane pressu re, the effect of colloid stability is systematically investigated by regulating the suspension ionic strength. Ln parallel, colloid stabili ty is assessed by Brownian aggregation measurements employing light sc attering techniques. Finally, the fouling tendency of the model suspen sions is assessed by performing standard batch filtration tests for fo uling index determination. It is found that stable colloidal suspensio ns cause relatively less fouling, whereas, when colloid stability is d ecreased, significant deposits form on the membranes. Furthermore, it appears that the commonly used fouling indices may give opposite trend s from those observed in cross-flow filtration tests. Finally, the exp erimental results are compared with existing colloidal fouling models and it is demonstrated that these models are not adequate to predict m embrane performance.