Transport through composite membranes, part 2: Impacts of roughness on permeability and fouling

Transport through composite membranes is influenced by the permeability and selectivity of the coating film and also by the skin layer pore morphology of the underlying porous support; however, the previous published research considered coating films with uniform thickness. Herein, we employed a numerical model to probe the impacts of coating film morphology on: (1) coating film permeability, (2) composite permeability, and (3) local permeate flux distribution. For the geometries modeled, coating film roughness can result in higher permeability provided that the mass of coating film is redistributed to produce both thinner and thicker cross-sections. On the other hand, permeability decreases when rough features are placed over a constant base film thickness. Further, rough coating films can exacerbate or dampen permeate flux ‘hot spots’ that appear over support membrane pores, depending on their relative orientation; however, dampening morphologies exhibit lower overall permeability even when the support membrane ‘solid phase’ is highly water-permeable. The presented theoretical results offer further insights into the fundamental challenges in designing high flux, fouling resistant RO membranes.