High-recovery electrodialysis reversal for the desalination of inland brackish waters

Abstract

Since the inland disposal of large volumes of desalination concentrate is environmentally and financially impractical, a high-recovery desalination design is required to reduce concentrate volume. In practical applications, recovery is limited by scale formation from minimally soluble salts, which acids and antiscalant compounds can inhibit only temporarily. Therefore, the risk of scale formation, which is governed by the system’s electrochemical behavior, determines the high-recovery potential of desalination technologies. In this research, high recovery was investigated using a pilot-scale electrodialysis reversal (EDR) system and natural feedwaters from a deep aquifer at the Brackish Groundwater National Desalination Research Facility in Alamogordo, NM. Experiments were performed to identify the maximum permissible CaSO4 saturation levels during long-term, continuous operation with antiscalant dosing. The results indicated that EDR has enormous potential for treating CaSO4-rich inland brackish waters and that EDR may not be severely limited by the risk of scale formation in the hydrodynamic/concentration boundary layer. Long-term operation saturation indices were achieved, which were significantly greater than previously published values, and the system’s eventual failure point provides insight into the hypothesized operating conditions. Therefore, the obtained results for high-recovery inland brackish water EDR determined the highest permissible CaSO4 saturation index during long-term, continuous system operation.