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 over the subsequent movement
of the oxidant after its release. There is a concern that contaminants will be
distributed into previously uncontaminated portions of the aquifer. While
a recirculation network may mitigate this potential problem, it raises the
possibility that contaminated water will be re-injected. Therefore, any
ISCO system should be comprehensively monitored during implementation and
after completion.
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.
Hexavalent chromium may be generated or introduced
using permanganate.
Potassium permanganate is in solid form and is
usually mixed with water in the field before application. However, KMnO4
dust can be a health hazard and requires dust control measures.
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
https://ert2.navfac.navy.mil/printfriendly.aspx?tool=ISCO
http://clu-in.org/download/techfocus/chemox/ISCO-tm-navfac-exwc-ev-1302.pdf
http://t2.serdp-estcp.org/t2template.html#tool=ISCO&page=b1
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.
See http://www.clu-in.org/characterization/technologies/exp.cfm for a technical
description of explosives in different media and the use of some analytical
techniques.
In Europe, catalyzed hydrogen peroxide (CHP) has
been successfully demonstrated at a drycleaner site, reducing chlorinated VOCs
by 95 to 99 percent in groundwater, and eliminated the target DNAPL area.
A full-scale system is being implemented. Vent wells were installed to
ensure that off-gases did not build within the subsurface and compromise nearby
structures.
In
New York, a mixture of surfactant combined with sodium persulfate
and sodium hydroxide was used to reduce 90 percent of coal-tar
related contaminants at a former manufactured gas plant (MGP). Soil and
groundwater were contaminated with benzene, toluene, ethylbenzene,
and xylene (BTEX), naphthalene, and polycyclic aromatic hydrocarbons (PAHs).
The majority of contamination was present as non-aqueous phase liquid (NAPL)
held within the pore spaces of the predominately sandy and silty
soil. A pressure-pulsing method was used to create subsurface pressure
waves that open soil pore spaces. This enhances the uniformity of chemical
dispersion and the treatment's radius of influence. See http://www.epa.gov/superfund/remedytech/tsp/download/2009_november_meeting/tuesday/2_harrington.pdf.
See http://kahlassociates.com/a-practical-primer-on-in-situ-chemical-oxidation/for
an ISCO primer.