The Department of Defense (DoD) has used perchlorate (ClO4-) as an oxidizer in ordnance items and rocket motors for over half a century. This water soluble and environmentally persistent compound now contaminates drinking water for tens of millions of people in the United States. On January 26, 2006, DoD issued a policy letter establishing 24 parts per billion (ppb) as the current level of concern for managing perchlorate. The cost for DoD to comply with cleanup and drinking water requirements has been estimated to be in the billions of dollars. It is important to reduce cleanup costs by identifying, demonstrating, and transitioning more efficient and economical perchlorate treatment technologies. The objective of this project was to evaluate and demonstrate a low-cost, regenerable ion exchange process for perchlorate.
The perchlorate ion exchange process developed by Applied Research Associates, Inc. (patent pending) uses weak base anion (WBA) resins that are regenerable as well as perchlorate-selective. The ion exchange process takes advantage of the pH dependant nature of WBA resins. At low pH, functional groups on these resins are ionized (R-NH3+) and capable of performing anion exchange. However, at high pH, the resin functional groups lose a proton and are uncharged (R-NH2), which permits rapid and complete regeneration with very high chemical efficiency. As a result, regeneration of perchlorate-selective WBA resin is up to 50 times more efficient than regeneration of strong base anion (SBA) resin, which typically generates more than 1% (volume) perchlorate-contaminated waste brine that requires disposal. The perchlorate-selective WBA resin D-4170, produced commercially by The Purolite Company, was used in this demonstration.
The WBA resin process successfully reduced perchlorate in groundwater at Redstone Arsenal in Huntsville, Alabama, from 2200 ppb to less than 4 ppb during a 15-week demonstration. Water treatment rates typical of SBA ion exchange processes (up to 3 gpm/ft3) were employed. Multiple regenerations demonstrated repeatable performance and minimization of spent regenerating solution to less than 0.05% of the treated water volume. Spent regenerating solution was treated by biodegradation and by a zero-discharge scavenging process. Both processes destroyed or removed perchlorate to below the method detection limit. The treatment cost using the WBA resin process was $90 to $95 per acre-foot of water treated.
Use of the WBA resin process for treating perchlorate is efficient and economical, resulting in a 75% savings over current regenerable resin technology such as the ISEP process and a 50% savings over single-use resin processes. Water quality parameters including alkalinity, hardness, perchlorate concentration, sulfate concentration, and treated water alkalinity can affect cost and performance. For treating the spent regenerating solution, it was determined that the zero-discharge scavenger resin process is best suited for applications with lower initial perchlorate concentrations (less than 100-500 ppb) and that biodegradation is best suited for applications with higher initial perchlorate concentrations (greater than 100-500 ppb). Other contaminants such as nitrate, selenate, arsenate, and/or chromate may be treated concurrently under certain circumstances. (Project Completed - 2006)