Hydraulic and earth engineering – Soil remediation – In situ contaminant removal or stabilization
Reexamination Certificate
2000-10-24
2001-11-13
Bagnell, David (Department: 3673)
Hydraulic and earth engineering
Soil remediation
In situ contaminant removal or stabilization
C405S128700
Reexamination Certificate
active
06315494
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable.
STATEMENT REGARDING FEDERAL RESEARCH AND DEVELOPMENT
Not Applicable.
BACKGROUND—Field of Invention
A method for remediation of contaminants in soil and/or ground water by permanganate oxidation that achieves post-treatment secondary drinking water standards for dissolved manganese in ground water as established by the United States Environmental Protection Agency (USEPA).
BACKGROUND—Description of Prior Art
An October 1989 Public Health Statement from the Agency for Toxic Substances and Disease Registry Recent suggested that up to 34 percent of U.S. water sources are contaminated with chlorinated alkenes such as perchloroethylene (PCE), trichloroethylene (TCE), dichloroethylene (DCE) and vinyl chloride (VC). Recent news reports and investigations also suggest that oxygenated fuel supplements like methyl-tert-butyl ether (MTBE) have adversely affected our ground water supplies. These chemicals are classified as recalcitrant compounds because they are difficult to treat with conventional remediation technologies. However, testing has demonstrated that chemical oxidation processes may work well for the treatment of these contaminants.
The process of chemical oxidation for remediation purposes involves the injection of oxidizing chemicals into the soil and/or ground water to destroy or oxidize contaminants in place. Although chemical oxidation processes have been studied and publicized for decades in the field of organic chemistry, the use of chemical oxidation for remediation applications is limited to the past decade. The most common chemicals used for in-situ chemical oxidation are hydrogen peroxide and Fenton's reagent. Fenton's reagent is a mixture of hydrogen peroxide and ferrous iron, usually prepared under low pH conditions. However, recent attention has focused on the potential use of permanganate salts as an oxidant for remediation purposes.
Permanganate salts are well-known oxidizing agents as they are commonly used in many water treatment applications at low concentrations. Over 30 percent of the surface water treatment plants in the United States and 20 percent of the ground water treatment plants use potassium permanganate for water treatment. The reaction mechanisms for permanganate oxidation have been published in several technical writing, including books by Stewart in 1964 and Lee in 1980.
As an oxidizer, permanganate has a unique affinity for destroying organic compounds that contain carbon-carbon double bonds. The permanganate ion is strongly attracted to the negative charge associated with electrons in the pi-cloud of carbon-carbon double bonds of chlorinated alkenes such as PCE, TCE, DCE and VC. The permanganate ion borrows electron density from the pi-bond, which disturbs the carbon-carbon double bond, thus forming a bridged oxygen compound known as the hypomanganate diester. This intermediate product is unstable and further reacts by a number of mechanisms including hydroxylation, hydrolysis or cleavage. The final oxidation product is carbon dioxide, chloride salt and manganese dioxide. Other contaminants like MTBE may be oxidized by free radical oxidation.
Although the reaction of the permanganate ion with contaminants is well understood, these reactions have not been commonly used for in-situ remediation due to complications that result from manganese dioxide which is formed as a precipitate of the reaction. Plugging of the soil matrix with manganese dioxide has been observed when permanganate salts are injected into the soils through injection wells or points. This plugging results in poor contact of the oxidizing agent with the contaminants of concern, resulting in inefficient treatment due to channeling of the oxidant in the subsurface. Injuries to workers have occurred from the pressure build-up caused by injection techniques. Injection techniques have also been found to be ineffective in some cases where globules of contamination exist in the subsurface because the globules become encrusted with manganese dioxide precipitate, thus preventing further oxidant contact. Finally, the manganese dioxide precipitates that form from the reaction are unstable as they are readily reduced by chemical or biological in-situ processes to form soluble divalent manganese ions.
Dissolved manganese adversely affects the taste and color of ground water at elevated concentrations. The United States Environmental Protection Agency (EPA) has established a secondary drinking water standard of 50 ug/l for dissolved manganese. However, post-treatment analyses have shown that manganese concentrations in the ground water may exceed the USEPA secondary drinking water standards by more than 100-fold after permanganate remediation is completed. Manganese dioxide plugging, dangerous injection pressures, inadequate chemical contact, chemical channeling and elevated dissolved manganese concentrations have all limited the use and regulatory acceptance of permanganate oxidation as a remediation tool.
Review of Existing Patents
Several patents for in-situ chemical oxidation remediation have been issued during the past decade. Examples include Chem-Ox (Mantech) U.S. Pat. Nos. 5,520,483 and 5,286,141, Method and system for remediation of groundwater contamination, February 1994 and May 1996; Geo-Cleanse U.S. Pat. Nos. 5,525,008 and 5,61,642, Remediation apparatus and method for organic contamination in soil and groundwater, June 1996 and March 1997; Terra Vac U.S. Pat. No. 5,615,974, Process for Soil Decontamination by Oxidation and Vacuum Extraction, April 1997; Richard Watts, U.S. Pat. No. 5,741,427, Soil and/or groundwater remediation process, April 1998.; Kent Cooper, U.S. Pat. No. 5,967,230, In situ water and soil remediation method and system, October 1999; Hoag, et al, U.S. Pat. No. 6,019,548, Chemical oxidation of volatile organic compounds, February 2000 and Siegrist, et al, U.S. Pat. No. 6,102,621, Oxidative particle mixtures for groundwater treatment, August 2000.
The majority of these patents refer to free-radical oxidation methods that use hydrogen peroxide as the oxidizing agent for contaminant destruction. The CleanOX U.S. Pat. No. 5,286,141 primarily covers the injection of hydrogen peroxide into “mutually spaced wells” for the in situ remediation of hydrocarbon compounds. The patent includes various dependant claims to cover a variety of injection volumes, pressures and injection ratios. The CleanOX 5,520,483 patent is a continuation-in-part of the U.S. Pat. No. 5,286,141 which addresses Fenton's oxidation (i.e. the injection of acid and ferrous iron into the groundwater prior to the injection of hydrogen peroxide). Both of these patents differ from the present invention because they involve the injection of hydrogen peroxide as the oxidizing agent to induce free-radical oxidation. The GeoCleanse, Richard Watts and Kent Cooper patents also involve the injection of a hydrogen peroxide into the subsurface for remediation purposes, with various enhancements to the liquid injection process and application techniques. The patents do not pertain to permanganate oxidation, nor do they address a method of treatment that achieves USEPA secondary drinking water standards for dissolved manganese.
The Terra Vac patent (U.S. Pat. No. 5,615,974) covers the injection of oxidizing agents into the subsurface for in situ oxidation of contaminants when used in combination with vacuum extraction wells. Potassium permanganate is listed as a potential oxidant in the patent specifications. However, the patent differs from the current invention because it focuses on oxidation to reduce contaminants into smaller, volatile compounds that are recoverable by the use of vapor extraction wells. The Terra Vac patent involves liquid injection techniques that could result in potentially unsafe injection pressures and inefficient chemical channeling in the subsurface. Finally, the Terra Vac patent does not incorporate an alkaline earth metal base to prevent elevated post-treatment concentrations of dissolved manganese in the ground wa
Bagnell David
Kreck John
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