Interrelated Resistance Mechanisms in Fouling Layers on Reverse Osmosis Membranes for Water Treatment

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Fouling is commonly regarded as the main cause for the permanent performance loss in membrane filtration by reverse osmosis (RO). Nevertheless, the extent and the effects of fouling are not identically pronounced for all filtration situations but are dependent on a number of different factors that determine the specific properties of the respective fouling layer. The individual composition and the spatial structure of the fouling layer, in turn determine the resistance mechanisms that are responsible for the fouling related performance loss of a filtration system. One of the major resistance mechanisms is the hydraulic permeation resistance raised by the formation of a more or less dense fouling layer on the membrane surface; another is the increased feed-side osmotic pressure induced by an intensification of the intrinsically existing polarization processes that occur at the membrane surface as a result of the separation. In classical Resistance-in-Series models hydraulic and polarization related effects are considered as separate processes. Recent studies, however, indicate that significant interactions exist between these mechanisms, which can either lead to a strengthening or weakening of the overall resistance of a fouling layer. The knowledge of these fundamental interactions could therefore be used to substantially reduce the resistance caused by fouling layers by controlling their composition and / or structure. It is, thus, the aim of the anticipated systematical studies to identify and investigate the interactions between different fouling related resistance mechanisms in dependence of the composition and structure of characteristic fouling layers and to quantify their effect on the overall resistance under filtration conditions of practical relevance. This is achieved by applying a combination of CFD-based model theory and defined laboratory experiments.