Role of permeability coefficients in salinity gradient energy generation by PRO systems with spiral wound membrane modules

Processes that can transform a salinity gradient into electrical energy have gained attention in recent years. One such process, which uses semipermeable membranes to generate electrical energy through a turbine, is pressure retarded osmosis (PRO). As a potential renewable energy technology, this process could also be integrated in desalination plants to reduce the energy consumption. However, principally because of certain drawbacks concerning membrane and module characteristics, PRO technology has not yet been fully exploited at commercial scale. This study aims to assess the impact of membrane permeability coefficients on the energy generated by full-scale single-stage PRO systems. This allow an evaluation of the performance of PRO modules in series considering variation of the permeability coefficients that may be due to the impact of fouling. An evaluation was made of the HTI OsMem™ 2521 spiral wound membrane module considering a diameter of 8 inches (high up-scaled active area) and different permeability coefficient ranges. The results showed that a 50% water permeability coefficient decrease would produce an approximately 25% decrease in the amount of energy that could be generated, while a 50% increase in the solute permeability coefficient would have virtually no effect when considering optimal operating points. Variation of the water permeability coefficient had more impact on the potential amount of generated energy than variation of the solute permeability coefficient.