In response to finding perchlorate at low levels in water private industry, in cooperation with the federal government, developed and is currently using sophisticated technologies for removing perchlorate from surface and groundwater supplies.
Aggressive efforts to prevent perchlorate from seeping into groundwater and other water sources include the ongoing use of underground barriers, extraction wells, pipes and associated water treatment facilities.
There currently are two major technologies used to treat large volumes of water that contain perchlorate: ion exchange and biological treatment. Other technologies are currently being developed and employed, including membrane filtration and electrodialysis.
Ion exchange technology uses a resin to absorb perchlorate and remove it from water. Contaminated water is pumped through a system of resin “beds,” which are up to six feet in diameter and up to six feet high. As negatively charged perchlorate is captured on the positively charged resin, it releases chloride, a component of table salt, in its place.
Biological treatment is a process that uses microorganisms to break down perchlorate into other components. Contaminated water and carbon sources such as alcohol or corn syrup are placed in a tank or underground, where microorganisms break down the perchlorate and carbon into three primary components; carbon dioxide, chloride, and nonhazardous biomass which naturally degrades.
Two technologies, reverse osmosis and nanofiltration, both involve forcing water through a semi porous polymer membrane. In reverse osmosis, artificial pressure is applied on one side of the membrane, forcing water to migrate through the membrane wall, leaving perchlorate and most other dissolved salts behind. Nanofiltration is a similar technique using membranes with slightly larger pores. Fouling membrane filters remains a concern for both reverse osmosis and nanofiltration technologies.
Currently under development, electrodialysis treatment passes water through different membranes while exposing it to an electric field. The electric field separates the perchlorate from the stream of treated water. The perchlorate-containing brine is then appropriately discarded.
Case Studies of how these removal technologies are being implemented
Rancho Cordova, California
An extensive system of wells and pipes has been drilled at the Aerojet site in Rancho Cordova, California, to prevent water migration off site, to isolate water in the underground plume, and to pump water out for treatment. Five treatment facilities are in operation.
As its primary cleanup technology, the company is using the biological treatment process that involves pumping water through biological treatment units that were originally seeded with nonpathogenic bacteria from a strawberry jam manufacturing company.
A significant amount of testing is also under way by Aerojet to use biological treatment to break down perchlorate in the groundwater as well as in the soil. All perchlorate cleanup technologies developed by Aerojet have been made publicly available.
American Pacific Corporation (AMPAC) operated a perchlorate chemicals manufacturing plant in Henderson, Nevada from 1958 to 1988. To address legacy deposits of perchlorate in groundwater at the site, beginning in 2005, AMPAC voluntarily installed an in situ bioremediation (ISB) treatment system comprised of multiple extraction wells, a water conditioning system a groundwater re-injection system, and approximately 20,000 ft. of water, electrical and control lines to move water through the remediation process. In 2012, AMPAC made significant investments to expand the treatment capacity at the site by implementing a different variation of a bioremediation technology. Between November 2012 and June 2014, more than 650,000 lbs. of perchlorate were removed from the groundwater in the area using this expanded system where aggregate concentrations of perchlorate have been in the 150-180 ppm range.
Instead of treating the groundwater in the aquifer, AMPAC’s expanded facility uses high capacity above ground Fluidized Bed Reactors (FBRs). The expanded groundwater treatment facility has a capacity to treat up to 1.15 million gallons per day (800 gpm). There are now 13 extraction wells in the system which is laid out over a roughly 10 square mile area. The process can treat groundwater with perchlorate concentrations in excess of 250 ppm.
Edwards Air Force Base, California
Edwards Air Force Base is using ion exchange to remove perchlorate from groundwater. It has field-tested a recently developed chemical regeneration process that may significantly reduce the cost of disposing of perchlorate waste.