Inland BWRO Concentrate Concentration by Electrodialysis

Reverse osmosis (RO) membrane desalination may be employed as a technically feasible treatment process for brackish water (BW) sources, but the product recovery ratio for inland BWRO applications is typically from 75-90%. The economic and environmental costs of concentrate disposal significantly limit the development of inland RO applications. Thus, the objective of this research is to investigate the efficacy and efficiency of electrodialysis as a treatment process for RO concentrate waste, especially for scenarios approaching zero liquid discharge. A laboratory experimental methodology was developed to test the performance of ED on RO concentrate wastes. An electrodialyzer with an active area of 64 cmý per membrane was used with mesh spacers of 0.5 mm thickness. A custom SCADA system was developed to continuously control and record the applied voltage and resulting current density, process stream flowrates, inlet and outlet pressures and stack headloss, as well as the pH, conductivity, and temperature of each process stream (diluate, concentrate, and electrode rinse). The ED system was used to treat synthetic waters modeling RO concentrate wastes (TDS ca. 7-18 g/L) in Arizona, Texas, and Florida, which contained supersaturated concentrations of sparingly soluble carbonate and sulfate salts. The experimental ED system successfully separated each of the three synthetic RO concentrates (without precipitation of the ED concentrate stream) with TDS removal ratios up to 99% and singlestage ED recovery ratios up to 75%, which corresponds to overall system recoveries up to 95%. This research indicates that ED can be used effectively to treat supersaturated RO concentrates.

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