Analysis of model parameters for the prediction of mass transfer resistance for forward osmosis and pressure-retarded osmosis configurations

The relative magnitudes of mass transfer resistances in forward osmosis and pressure retarded osmosis can be assessed by comparing the solute profiles across the bulk of the feed and draw streams. Three models are used to compare the relative magnitudes of the mass transfer resistances and system performance by calculating the recovery ratio, membrane area, and power density. The first model (model I) includes only the resistance of the membrane active layer, while model II includes the resistance of the solute boundary layer in the draw stream and the resistance of the membrane active and support layers. The third model (model III) includes all five resistances. The solute profiles predicted by model III for either the complete mixing (CM) or the plug flow (PF) models indicate that the membrane active layer exhibits the largest mass transfer resistances, followed by the solute boundary layer in the draw stream. All three models provide similar trends for variations in the recovery ratio, membrane area, and power density as a function of operating parameters. Predictions of the recovery ratio and the power density by the (CM) of model III showed good agreement with literature data at low inlet concentrations of the draw stream. However, the use of the (PF) of model III is necessary at higher concentrations of the draw solution. In conclusion use of the (PF) of model III gives more accurate design and simulation data at large membrane areas and high concentrations for the draw solution. •Three models are studied to assess relative magnitude of mass transfer resistances in FO/PRO.•The major mass transfer resistance is found in the membrane active layer and the solute boundary layer on the draw side.•Trends obtained by the three models are similar, however, deviations between model III and model I can be as high as 50%.•The (PF) of model III provides more accurate design and simulation results than the (CM) approximation.