Electrolysis: processes – compositions used therein – and methods – Electrolytic material treatment – Organic
Reexamination Certificate
2002-01-29
2004-03-23
Phasge, Arun S. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic material treatment
Organic
C205S688000, C205S758000, C205S760000, C205S761000, C204S275100
Reexamination Certificate
active
06709567
ABSTRACT:
TECHNICAL FIELD
The present invention is directed toward the treatment of contaminated water, and more particularly toward an electrolytic system promoting oxidation and reduction of ground water contaminants.
BACKGROUND ART
After decades of active research, cost effective mitigation of ground water contamination remains a major technical challenge. In general, most in situ treatment processes have proven both expensive and ineffective. Many of the more promising advances in the last few years have centered on natural or engineered in situ oxidation-reduction (REDOX) reactions. Through these reactions, toxic compounds are transformed in situ to non-toxic products. Examples include biological oxidation of benzene to carbon dioxide and water and abiotic reductive de-halogenation of trichloroethene to chloride and ethylene. Other examples of similar REDOX reactions are described by Weidemeier, Technical Protocol for Evaluating Natural Attenuation of Solvents in Ground Water, Air Force Center for Environmental Excellence, Brooks Air Force Base, San Antonio, Tex., November 1996. While the potential advantages of mitigation of ground water contamination through REDOX reactions has been recognized, effective engineering systems for driving such reactions have proven inadequate. Problems with existing technologies include excessive energy consumption and cost.
Several existing technologies use reduction reactions to degrade contaminants in water. Gillham, U.S. Pat. No. 5,266,213, describes the reductive de-chlorination of chlorinated contaminants in ground water using particulate metal. Gillham, U.S. Pat. No. 5,868,941, describes the use of an electrolytic system for the treatment of halogenated hydrocarbons that passes a plume of contaminated water through a bed of granular iron. An electric circuit is promoted for providing electrons for reducing the contaminant in the vicinity of the granular iron bed. By inducing a voltage in the current in the vicinity of the iron bed, Gillham contends his invention increases the rate at which halogenated hydrocarbons are broken down by reduction and deposition of iron and other precipitants is inhibited. However, known prior art systems fail to provide a suitable anode for promoting oxidation reactions which can be useful both in degrading intermediaries produced in the reductive de-halogenation of certain halogenated hydrocarbons and in degrading other contaminants by oxidation.
The present invention is directed to overcoming one or more of the problems discussed above.
SUMMARY OF THE INVENTION
An apparatus for treating a flow of water containing contaminants includes first and second permeable electrodes. In one embodiment, as illustrated in
FIG. 1
, a power supply is coupled to each of the first and second permeable electrodes to create an electrical potential therebetween. The first and second permeable electrodes are disposed within the flow of water containing contaminants with the first permeable electrode upstream from the second permeable electrode and the water containing contaminants flowing through and between the permeable electrodes. The permeable electrodes are spaced a select distance to promote an electric current in the water containing contaminants between the electrodes sufficient to sustain oxidation or reduction of the contaminants either at and/or near the electrodes. Laboratory data indicates treatment of target contaminants at a distance of ½ m up and downstream of the electrodes. Treatment of contaminants at larger distance is anticipated in field application.
The electrodes are preferably substantially planar plates disposed in parallel and substantially normal to the direction of water flow. The distance between the plates is between about 0.001 and 1 meter. A non-conductive spacer can be placed between the electrodes to maintain the select distance. In another embodiment, illustrated in
FIGS. 8 and 9
, the electrodes may also be closely spaced rods that approximate planar plates. The distance between the rods is approximately between 1 and 5 feet. Preferably the rods are disposed in rows which are laterally offset so that rods of adjacent rows lie laterally between each other forming a tortuous path for water traveling perpendicular to the rows. The electrodes and rods are made of a conductive material selected from the group including, but not limited to carbon black, vitreous carbon, graphite, stainless steel, platinized titanium, mixed metal oxides, aluminum, copper, gold and gold plated stainless steel. The electrodes are preferably in the form selected from the group including perforated plates, sintered metal, expanded metal, screens, wool (e.g., copper wool), felt and weave. The rods are preferably titanium or a titanium mixed metal oxide. When necessary or desired, the invention further contemplates more than one pair of first and second permeable electrodes disposed in series. Each of the first and second permeable electrodes is coupled to the power supply to create an electrical potential therebetween. The power supply may be a DC power supply having a positive terminal coupled to one of the first and second permeable electrodes and a negative terminal coupled to the other of the first and second permeable electrodes. Where multiple pairs of electrodes are provided in series, different voltages can be applied to the electrode pairs as may be necessary or desired to promote a given oxidation or reduction reaction. Additionally, the power supply may be applied continuously or may be pulsed on and off at a frequency sufficient to sustain the desired treatment, typically in the range of seconds to minutes.
Another aspect of the present invention is a method of treating water containing contaminants. In one embodiment, the method includes providing a pair of first and second permeable electrodes and flowing the water containing contaminants through and between the electrodes. A voltage is applied between each of the permeable electrodes of the pair sufficient to promote oxidation of the contaminants either at and/or near one electrode and reduction of the contaminants either at and/or near the other electrode. The contaminants treated must be subject to degradation through oxidation or reduction, such as halogenated hydrocarbons or the contaminants must be subject to a change in mobility due to a change in oxidation state of either the contaminant itself, such as a metal, or the change in oxidation state of some other compound that causes the contaminant to coprecipitate with that compound. The electrodes used in the method are preferably substantially planar plates disposed in parallel substantially normal to the direction of flow of water containing contaminants. The electrodes may also be offset rows of closely spaced rods that approximate planar plates. The method may further include periodically alternating the polarity of the electrodes to minimize formation of precipitants in the vicinity of the electrodes and to remove solid phase precipitates that may have formed on the electrode surface. More than one pair of first and second permeable electrodes may be provided. If so, a voltage applied to at least one pair of the permeable electrodes may be different from the voltage applied to another pair of permeable electrodes. The power supply may be applied continuously or may be pulsed on and off at a frequency sufficient to sustain the desired treatment.
The invention uses electrolytic technology to effect either the oxidation or reduction of ground water contaminant(s) to non-hazardous product(s). Treatable contaminants include, but are not limited to those subject to REDOX degradation, including, but not limited to compounds such as halogenated hydrocarbons, fuel hydrocarbons, nitrates, ammonium perchlorate, trinitrotoluene (TNT), Royal Demo Explosives (RDX) or methyl tertiary-butyl ether (MTBE). Illustrative is the reductive de-halogenation of perchloroethene (PCE). At the cathode, PCE is reduced to methane gas through the following reactions:
At the anode the products will be oxidized through t
Gilbert David Mark
Sale Thomas Clay
Phasge Arun S,.
Swanson & Bratschun LLC
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