Bioremediation - Perchlorate
Description
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.
Applicability
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.
Web
Links
http://www.dtsc.ca.gov/TechnologyDevelopment/upload/TD_REP_Perchlorate-Alternatives.pdf
http://www.clu-in.org/download/contaminantfocus/perchlorate/LHAAPfinalSchnoor.pdf
http://www.ert2.org/perchlorate/tool.aspx
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.