The effect of permeation flux on the specific resistance of polysaccharide fouling layers developing during dead-end ultrafiltration

Abstract

Development of polysaccharide fouling layers during dead-end membrane ultrafiltration is an inherent problem in water treatment and similar separation processes. Despite its practical significance, ultrafiltration membrane fouling under constant permeate flux J has received inadequate attention. Therefore, constant-flux experiments, with typical alginate model-solutions covering the flux range of practical interest (i.e. 10–100L/m2h), are employed to obtain new insights into fouling layer characteristics. The specific resistance α, as the most representative fouling-layer property, is used for data interpretation. The behavior of resistance α, with increasing permeate volume, confirms that these gel-type layers are strongly affected by flux J and generally compressible. Layer compressibility is evident beyond an initial phase of membrane coverage by alginates. The initial resistance αi, corresponding to thin developing layers and relatively small pressure-drop across the layer/“cake” ΔPc, is independent of ΔPc, approximately linearly increasing with J. For all data-sets, variation of resistance α with ΔPc is well correlated by a generalized expression involving (in addition to αi) two parameters, n and Pa, considered to represent layer/cake compressibility index and reference pressure, respectively; these parameters also increase (and are fairly well correlated) with J. The usefulness of these data is demonstrated in elucidating issues such as "critical flux" for this filtration mode.