Experiment and modeling for performance of a spiral-wound pressure-retarded osmosis membrane module

Pressure-retarded osmosis (PRO) process utilizes the transport of water through a semipermeable membrane to generate electricity from salinity gradient resources. Recent PRO research has shown the feasibility of PRO technologies in laboratory-scale experiments, but there is currently a lack of experimental pilot-scale investigations to ensure the success of PRO technology. This study was conducted to predict the power density of a PRO module using PRO membrane transport properties such as water permeability, salt permeability, and membrane structure parameter. The performance of an 8040 spiral-wound PRO module was experimentally investigated, and the results were compared with the simulated prediction. The maximum power density of the investigated PRO module was 1.8 W m⁻² at 10.4 bar using 35 g L⁻¹ of NaCl as a draw solution. At the outlet of the module, the concentration changes of the draw and feed solutions were observed, suggesting a gradual decrease of membrane power density inside the PRO module. The simulation model, which considered concentration changes of draw and feed solutions, reverse salt flux, and mass transport coefficient inside the module, closely estimated the performance of the PRO module. However, the model overestimated the power density at high hydraulic pressure difference. It was concluded that severe increase of reverse salt flux at a high hydraulic pressure difference negatively contributed to the performance of the PRO module.