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://t2.serdp-estcp.org/t2template.html#tool=Perchlorate&page=Intro1
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.
http://www.waterworld.com/articles/2011/05/groundwater-remediation-project-in-nevada.html
https://ert2.navfac.navy.mil/printfriendly.aspx?tool=energeticconstituents
for sampling of energetic constituents.