Architecture and unit design of a capital cost optimized, household electrodialysis desalination device with continuous flow

Abstract

Improved solutions for water desalination are necessary in the urban Indian setting. Currently, a majority of point-of-use (POU) purifiers use reverse osmosis (RO) to desalinate household water. However, RO purifiers waste up to 70% of the feed water when used in the domestic context. Electrodialysis (ED) is a water-efficient alternative means of desalination that preserves >80% of the feed as product water. Though it has been proposed previously and is used in industrial processes, ED has not been successfully implemented for domestic POU desalination in India or globally. This work aims to understand how ED systems can be modified to the POU scale and, critically, how they can be made cost competitive to RO systems. We do this by proposing and then validating a new, direct-flow continuous ED architecture with differential flow rates (and pressures) between the diluate and concentrate channels. This architecture is made possible by a small ED stack, which can withstand a flow channel pressure imbalance. Using numerical system models, a system design was optimized for minimum capital cost, informed by design requirements for a characteristic Indian usage context. A prototype of this system was capable of a 37±6% reduction in feed water salinity from (1500±20 to 940±140 mg/L) at !90% water recovery and incorporated electrodialysis reversal and acid dosing as mechanisms to enhance reliability and prevent mineral scaling. If realized as a commercial POU product, ED has the potential within the Indian market to conserve >200 million liters of water per day if adopted in place of low-recovery RO purifiers among even a small fraction of high-income Indian households.