Electrodialysis and Electrodialysis Reversal
|Publication Date:||1 January 1995|
Electrodialysis (ED) is an electrically driven membrane process used to demineralize brackish water. Brackish waters lie under approximately two thirds of the United States, and inland rivers, such as the Rio Grande and the lower reaches of the Colorado, also contain high levels of salinity. Water is classified as brackish when mineral content ranges between that of fresh drinking water and that of seawater. Brackish water contains more than 500 mg/L of total dissolved solids (TDS) and seawater more than 30,000 mg/L TDS.
ED and electrodialysis reversal (EDR) reduce TDS in brackish source water by electrically removing contaminants that exceed acceptable levels for drinking and process water. An overview of membrane process applications based on the molecular weights of contaminants appears in Figure 1-1. The ED and EDR processes are competitive with reverse osmosis (ROI in treating brackish waters. Typical ED systems include chemical feed systems for antiscalant and perhaps acid addition, a cartridge filter for prefiltration, the ED unit, and equipment for aeration, disinfection, and stabilization. EDR systems can often operate without fouling and scaling chemical feed, and they can treat high-fouling sources more efficiently than RO. However, it is important to remember that the types of membranes used in ED and EDR systems do not provide a barrier to remove microorganisms as do RO, nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF) membranes.