In-situ Chemical Oxidation—Permanganate and Fenton's Reagent
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.
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.
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.
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.