In-situ Chemical
Oxidation—Permanganate and Fenton's Reagent
Description
In-Situ
Chemical Oxidation (ISCO) involves injecting chemical oxidants into the vadose zone and/or groundwater to oxidize organic contaminants. The common oxidants are hydrogen
peroxide-based Fenton's reagent, and potassium manganate (KMnO4), better known as
permanganate. Ozone can also oxidize organic contaminants in situ, but it has been used
less frequently. Complete mineralization to carbon dioxide and water is the
desired endpoint of an ISCO process.
Fenton's reagent is produced on site by adding
an iron catalyst to a hydrogen peroxide solution. A 50% solution of peroxide is
common for this application. A pH adjustment may be needed, as Fenton's reagent
is more effective at acidic pH. For permanganate application, a 1% to 5%
solution is prepared on site from potassium permanganate crystals that are delivered
in bulk to the site. The most common oxidant delivery method involves the
injection of oxidants. Where a significant hydraulic gradient exists, the
targeted delivery of oxidants to the contaminant zones may require both
injection and extraction wells. ISCO delivering KMnO4 through recirculation
wells has been successful at some demonstrations. A patented process is used to
inject the Fenton's reagent.
Limitations and Concerns
Subsurface heterogeneity can cause the uneven
distribution of oxidants. There is no control of the subsequent movement of the
oxidant after its release. Hence, recirculation is sometimes the preferable
delivery system.
The number and pattern of injection and
extraction wells and monitoring wells must be designed to ensure maximum coverage
of the treatment zone. Because cost is related to the depth and quantity of dense non-aqueous phase liquids (DNAPL), the
number and spacing of the wells becomes critical. A system for handling
precipitated solids may need to be incorporated when high concentrations of
oxidants are recirculated. Injection and extraction wells may eventually become
clogged from entrained silt, biological growth, mineral precipitates, or other
factors.
Porosity of the subsurface may be reduced due to
the formation of metal oxide precipitates. ISCO often requires more than one
application of oxidant to address rebound effects.
Native organic matter exerts a demand for
oxidants, thus increasing costs for chemicals. An Underground Injection Permit
may be required. For example, Florida, New Jersey, South Carolina, and
Tennessee regulators have stated that they would require such a permit.
With ISCO systems using KMnO4, the pH of the system
must be between 3 and 10, and the rate of the reaction increases with higher
oxidant-to-contaminant loading rates. With ISCO systems using Fenton's Reagent,
reduction of pH to levels between 3 and 6 is needed. Naturally occurring
buffering agents, such as carbonates, may prevent pH from being reduced to this
level.
Hydrogen peroxide in Fenton's reagent decomposes
rapidly before it travels far from the well. Anaerobic bioremediation will be impeded if oxygen from
the hydrogen peroxide is introduced in the treatment zone. In addition,
Fenton's reagent is toxic to microbial populations.
ISCO requires strict health and safety
procedures for high-pressure injection. For Fenton's reagent, care should be
given for exothermic reactions (i.e., release of heat) and handling hydrogen
peroxide. For example, the application of Fenton's Regent at Cherry Point Naval
Air Station in NC resulted in an explosion. Fenton's Reagent is typically not
applicable at sites where more than six inches of contaminant free-product is
present.
Natural oxidant demand within a treatment area,
as it relates to oxidant-dosing requirements, needs to be better understood.
There is no screening procedure for evaluating site-specific geochemical
factors for compatibility with ISCO.
At this time, problems exist in differentiating
between dissolved contaminant displacement and treatment, as well as dilution
and treatment.
ISCO may mobilize other contaminants, such as
metals.
It has been reported that ISCO using KMnO4 is messy and has odors
that are a nuisance.
Applicability
ISCO using permanganate for soil and groundwater
treatment has been demonstrated at a number of sites on the following organics:
chlorinated solvents (such as trichloroethylene [TCE]), naphthalene, and
pyrene. Fenton's Reagent can be used to treat a wide range of organic
contaminants in soil and groundwater, including chlorinated solvents, petroleum
hydrocarbons, semi-volatile organic compounds (SVOCs), and pesticides. ISCO has also been used to
remediate polyaromatic hydrocarbons (PAHs), petroleum products, and ordnance
compounds.
Technology Development Status
ISCO is a mature technology for the treatment of
hazardous waste. H.J.H. Fenton developed
Fenton's Reagent in the 1890's. This chemical is widely used by the wastewater
industry for the treatment of organic waste.
Web Links
http://www.frtr.gov/matrix2/section4/4_4.html
http://www.itrcweb.org/Documents/ISCO-2.pdf
http://clu-in.org/download/citizens/oxidation.pdf
http://clu-in.org/download/techfocus/chemox/4_brown.pdf
http://www.ert2.org/isco/tool.aspx
Other Resources and Demonstrations
See http://www.itrcweb.org/Documents/ISCO-1.pdf
Technical and Regulatory Guidance for in Situ Chemical Oxidation of
Contaminated Soil and Groundwater (ISCO-1) 2001 and http://www.itrcweb.org/Documents/ISCO-2.pdf
Technical and Regulatory Guidance
for In Situ Chemical Oxidation of Contaminated Soil and Groundwater, Second
Edition (January 2005). ISCO refers to a general group of specific
technologies, with each technology representing specific combinations of
oxidants and delivery techniques. Specific primary oxidants addressed in this
document are hydrogen peroxide, potassium and sodium permanganate, and ozone
See http://toxics.usgs.gov/highlights/dnapl_removal.html
for description of demonstrations of ISCO at Old Camden County Landfill, Naval
Submarine Base (NSB) Kings Bay.
A full-scale demonstration of in-situ destruction of DNAPL by
Fenton's Reagent was successfully completed at the Savannah River Site in
April, 1997. Six hundred pounds of DNAPL was oxidized at this four-day
demonstration. Groundwater chemistry showed that there are lingering effects
from the demonstration. The effects of the relatively vigorous reaction on the
mineralogy, chemistry, and microbiology of the aquifer are detailed in the
second publication below.
See Jerome, K.M., B. Riha, and B.B. Looney, Final
Report for Demonstration of In Situ Oxidation of DNAPL Using the Geo-Cleanse
Technology,
Westinghouse Savannah River Company, Aiken, SC and Denham et al, Effects of
Fenton's Reagent on Aquifer Geochemistry and Microbiology at the A/M Area, Savannah River Site,
Westinghouse Savannah River Company, Aiken, SC.
See
http://www.serdp-estcp.org/content/download/5130/72907/file/ER-0623_Summary_Proceedings.pdf
for 2008 proceedings on ISCO.