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A numerical model is presented for a two-stage seawater reverse osmosis (SWRO) desalination unit with spiral-wound modules. The model, which is based on the mass and momentum transport equations, takes into consideration the longitudinal variation of the velocity, the pressure, and the salt concentration in the membrane modules. This model was calibrated with the field data of a 600 m 3 /day SWRO unit of the desalination plant of Porto Santo Island (Portugal) and was used to optimize the module configuration and the operating conditions of a medium-sized SWRO with spiral-wound modules. For a typical reverse osmosis (RO) plant with a capacity of 1000 m 3 /day, with a single stage and four membrane modules (FilmTec SW30HR-380) per pressure vessel, operating at a feed pressure of 6.0 MPa and with an inlet feed velocity of 0.12 m/s, the water recovery rate is 33%, the energy consumption is 4.28 kWh/ m 3 , and the specific water cost is 81.4 eurocent/m 3 . The water cost can be reduced to 66.7 eurocent/ m 3 , for a two-stage SWRO unit operating at a 56.7% water recovery rate, with seven membrane modules per pressure vessel, operating at transmembrane pressures of 7.2 and 8.0 MPa and inlet feed velocities of 0.23 and 0.20 m/s, in the first and second stages, respectively.

Implementation of reverse electrodialysis (RED) is economically limited by the relatively high ion-exchange membranes price. Additionally, the shadow effect of non-conductive spacers reduces the membrane area available for counter-ion transport and increases the stack electric resistance. A promising alternative could be utilization of profiled membranes, since the reliefs formed on their surface keeps the membranes separated and provides channels for solutions flow. Herein, we have simulated, through computational fluid dynamics (CFD) tools, fluid behavior in channels formed by various profiled membranes. The highest net power density values were obtained for corrugations shape and arrangement in a form of chevrons due to the increase of the available membrane area and an excellent balance between enhancement of mass transfer and the increase of the pressure drop in the channel. When properly designed, corrugated membranes may offer a better performance even compared to the case of conductive spacers. The proposed membrane corrugation design in not limited to the RED application, and could be also extended to other electromembrane processes, such as electrodialysis and Donnan dialysis, in which high ionic mass transport rates are desirable at as low as possible energy costs.

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