Optimum recovery of saline gradient power using reversal electrodialysis: influence of the stack components

Abstract

Salinity gradient power (SGP), has gained attention in last years, due to its numerous advantages as renewable and continuous source of energy. Furthermore, the possibility of deploying this new source of green energy in coastal wastewater treatment plants (WWTPs) offers an attractive alternative to advance the energy sustainability in these installations while contributing to increase the prospects for water reclamation. As part of a global project that integrates the recovery of SGP through reverse electrodialysis within a water reclamation process, we report the analysis of the influence of the main components of a reversal electrodialysis (RED) stack, membranes, and spacers, on the recovery of energy. Additionally, the optimal number of cell pairs and velocity of the water streams is determined to maximize the gross power density. The study is carried out with model waters with a sodium chloride concentration of 0.5 M (seawater) and 0.02 M (close to WWTP effluents) as high and low concentration solutions respectively, in a RED stack with 3 to 20 ion exchange membrane pairs. The results reveal that membrane thickness exerts a more decisive influence than the spacers thickness. Power density values as high as 1.59 W·m−2 and 1.77 W·m−2 have been obtained using membranes of 50 μm thickness and spacers of 270 and 155 μm thickness, respectively. The information here reported helps in the decision-making for the proper design of the membrane stack, making a step forward to facilitate the integration of SGP recovery within water reclamation processes, reducing fossil fuel dependence in WWTPs.