Monovalent selective electrodialysis : optimizing energetics for desalination and mineral recovery

Abstract

Monovalent selective electrodialysis (MSED) is a variant of conventional electrodialysis (ED) that employs selective ion exchange membranes to induce preferential removal of monovalent ions relative to divalent ions. This process can be beneficial when the divalent rich stream has potential applications. In agriculture, for example, a stream rich in calcium and magnesium is deemed beneficial for crops and can decrease dependence on fertilizers that would otherwise need to be re-introduced to the source water prior to irrigation. MSED has been used previously for salt production, brine concentration, and irrigation. An experimentally validated computational model to predict its performance, however, is not available in the literature. The proposed work uses concepts from conventional ED modelling to build a high-resolution predictive performance model for MSED. The model was validated with over 35 experiments at different operating conditions and observed to fit the data to within 6% and 8% for two different sets of membranes, respectively. The model was then used to predict selectivity, specific energy consumption, and second law efficiencies for different system conditions. An optimization study was also carried out to determine the optimal operating parameters for the MSED system. The optimized system led to a decrease in specific energy consumption and an improvement in second law efficiency of 30% relative to the bench-scale system used in the lab.