Bioremediation - Perchlorate
Perchlorate (ClO4) is the soluble anion associated with the solid salts of ammonium, potassium, and sodium perchlorate. Ammonium perchlorate is used as an energetic booster or oxidant in solid propellant for rockets and missiles. Approximately 90 percent of the ammonium perchlorate produced in the U.S. is used as a solid rocket fuel oxidizer. The handling of perchlorate by its manufacturers and the rocket propellant industry has led to widespread contamination of surface water and groundwater. The high solubility of ammonium perchlorate coupled with its chemical stability in water has led to expansive plumes.
Of the technologies being evaluated to treat perchlorate, ex-situ and in-situ bioremediation are the most prevalent, in part because they destroy perchlorate rather than transferring perchlorate to another waste stream. For example, ion exchange processes, reverse osmosis, and nanofiltration generate perchlorate-rich waste brines that may be difficult to dispose. Further treatment of the brine may be needed to reduce its volume or toxicity before disposal.
Limitations and Concerns
The treatment of perchlorate contamination in water is complicated because the perchlorate anion does not respond to typical water treatment techniques, due to its fundamental physical and chemical nature. The perchlorate molecule is structured such that the four oxygen atoms surround the central chlorine atom, effectively blocking reducing agents from directly attacking the chlorine. Perchlorate is soluble and very mobile in aqueous systems. It can persist in the environment for many decades under typical groundwater and surface water conditions because of its resistance to reaction with other available constituents.
The optimum treatment technology for perchlorate depends on several site-specific factors, including perchlorate concentration, the presence and concentration of co-contaminants, other water quality parameters (e.g., pH, total dissolved solids, metals, etc.), and geochemical parameters (e.g., nitrate, sulfate, chloride, dissolved oxygen, redox potential, etc.). The presence of indigenous perchlorate-reducing microbes (PRM) and substances inhibitory to PRM activity will greatly influence perchlorate treatment technology effectiveness.
Establishment of a cleanup standard for perchlorate is of concern. Cleanup standards have been proposed in several states, ranging from 1 part per billion (ppb) to 18 ppb. Perchlorate interferes with iodide uptake into the thyroid gland. Because iodide is an essential component of thyroid hormones, perchlorate disrupts how the thyroid functions. In adults and children, the thyroid helps to regulate metabolism. In children, the thyroid also plays a major role in proper development. The impairment of thyroid function in expectant mothers may impact the fetus and newborn and result in effects such as behavioral changes, delayed development, and decreased learning capability. Changes in thyroid hormone levels may also result in thyroid gland tumors.
This technology is designed to treat perchlorate in groundwater.
Technology Development Status
None of the mechanisms for the biological reduction of perchlorate are well understood. Ongoing experiments will provide a fundamental understanding of the factors promoting perchlorate degradation in subsurface environments. This technology is in the early stages of development.
Other Resources and Demonstrations
See http://www.epa.gov/fedfac/documents/perchlorate_site_summaries.htm, http://www.clu-in.org/download/remed/542-r-05-015.pdf and http://www.clu-in.org/contaminantfocus/default.focus/sec/perchlorate/cat/Overview/ for basic information regarding perchlorate and remediation. Also see http://www.itrcweb.org/Documents/PERC-2.pdf (2008) for full description of perchlorate remediation options.
https://ert2.navfac.navy.mil/printfriendly.aspx?tool=energeticconstituents for sampling of energetic constituents.