Toward improvement of methods for predicting fouling of desalination membranes — The effect of permeate flux on specific fouling resistance

•The specific resistance is recommended as most representative fouling layer property.•The specific cake resistance α depends on permeate flux to a power greater than one.•An impact assessment of main process variables on membrane fouling is performed.•Narrow ranges of α and index I are identified as criteria of fluid fouling propensity.

Progress is reported toward development of a realistic and theoretically sound approach, enabling reliable predictions of membrane fouling in desalination processes. A significant amount of recent data obtained with typical organic foulants, in constant-flux and constant-pressure desalination, is revisited focusing on the dependence of specific fouling resistance α on permeate-flux J. Although clarifying quantitatively this dependence requires more work, these data suggest that, for the initial phase of fouling, α depends on J to a power greater than one. Furthermore, it is argued that α is the most appropriate fouling layer (intrinsic) property to both develop constitutive-type expressions relating fouling resistances to system variables (for predicting fouling evolution throughout membrane modules), and serve as a reliable indicator of feed-fluid fouling propensity. The advantages of resistance α for both applications are discussed; for the latter case, a simple parametric analysis of main process variables (flux, foulant concentration, membrane resistance Rm) shows that there is no single-value indicator (α or other) that can represent the fouling propensity of feed-fluids under all conditions (e.g. for both high-pressure and low-pressure desalination). Moreover, specific narrow ranges of resistance α values can be identified as criteria to assess membrane fouling for various desalination conditions.