WO2014004691A1

WO2014004691A1 - In situ remediation

Info

Publication number: WO2014004691A1
Application number: PCT/US2013/047929
Authority: WO
Inventors: Robert Steffan; Charles SCHAEFER, Jr.; Richard SCHOWENGERDT; Guy SEWELL
Original assignee: Robert Steffan; Schaefer Charles Jr; Schowengerdt Richard; Sewell Guy
Priority date: 2012-06-26
Filing date: 2013-06-26
Publication date: 2014-01-03

Abstract

A method of in situ remediation comprising inserting electrodes into soil and/or a aquifer and applying a voltage direct current which results in generation of hydrogen both on the cathode and on the soil surfaces located between the electrodes, resulting in remediation of contaminants including, but not limited to: chlorinated solvents, metals, nitroaromatic and/or nitramine explosives, nitrates, perchlorates, and chlorates. Such electrode configurations and low voltage proton reduction systems of this variety may be powered by low cost and sustainable photovoltaic systems.

Description

TITLE: IN SITU REMEDIATION

Cross Reference to Related Applications

[0001] This application claims priority to a provisional application, U.S.

Application No. 61/664,364, which was filed on June 26, 2012.

Statement Regarding Federally Sponsored Research or Development

[0002] This invention was made with Government support under Contract

Award Number W912HQ-10-C-0021 awarded by the Department of the Army.

Reference to a "Sequence Listing," a Table, or a Computer Program

[0003] Not Applicable. Technical Field

[0004] The technical field relates generally to an in situ bioremediation of compounds in soil, including but not limited to, chlorinated organic solvents, heavy metals, and other contaminants.

Background

[0005] The contamination of soil can become a problem at any industrial site where chemicals are present. Additionally, soil contamination may also be an issue for residential property where chemicals are present. Current methods for treating contaminated soil include ex situ remediation and in situ remediation. In ex situ remediation the soil containing the contaminants is removed from the site and usually brought to a different location for treatment. This ex situ remediation is usually accompanied with the replacement of the removed soil with non- contaminated soil, usually obtained from a separate location. Additionally, for some ex situ remediation, groundwater containing contaminants is removed from the ground, usually by the installation and operation of pumps, and either treated on site or brought to a separate facility for treatment. Current methods of in situ remediation of contaminated soil tend to rely upon groundwater flow to distribute additives, which are added to the contaminated soil. The additives are added "up stream" and rely on the movement of groundwater for the distribution of the additives in the soil.

Disclosure

[0006] The method described herein comprises inserting electrodes into contaminated soil. The electrodes may be inserted into an aquifer or into soils which contain at least a minimal amount of water, but are not saturated with water. A voltage direct current is then applied to the electrodes. This results in hydrogen (H₂) being generated on both the cathode and on the surface of the soil particles located between the electrodes. Accordingly, the method of in situ bioremediation described herein does not rely on the flow of groundwater for remediation and can be used on even low-permeability soils and soils with at least a minimal concentration of water. Therefore, the method described herein overcomes the problems encountered in the currently used methods of in situ remediation which rely on groundwater movement. Additionally, the embodiments described herein do not rely on the extraction of groundwater or soil for ex situ treatment.

[0007] The method of in situ bioremediation may be used to remediate various contaminants, including, but not limited to: chlorinated organic solvents, metals, nitro- and/or nitramine- containing explosives, anionic pollutants, nitrites, nitrates, perchlorates, chlorates, halogenated organic contaminants, 2,4,6- trinitrotoluene (TNT), 2,4-dinitrotolulene (DNT), l ,3,5-trinitroperhydro-l,3,5- triazine ( DX, octahydro-l,3,5,7-tetranitro-l,3,5,7-tetrazocine (HMX), [3- nitrooxy-2,2-bis(nitrooxymethyl)propyl] nitrate (PETN), NO₃ ^", NO₂ ^", ClO₄ ^", ClO₃ ^", heavy metals, selenium, chromium, arsenic, manganese, or any other contaminant which is susceptible to reduction through the application of the method described herein. Further, the method of in situ bioremediation may be used for bioremediation of contaminated sites that have low permeability soils, soils with at least a minimal concentration of water, fractured rock systems, high concentration contaminant areas, dense non-aqueous phase liquids (DNAPL), and/or large, dilute plumes.

[0008] In one embodiment, the soil being treated contains clay. In another embodiment, the soil being treated does not contain clay. In one embodiment, the soil being treated is located in a vadose zone. In another embodiment, the soil being treated is located in an aquifer. In a prophetic embodiment, the area treated is a low permeability layer below the water table. In one embodiment, the contaminants treated are chlorinated volatile organic compounds. In another embodiment, the in situ bioremediation occurs in soil having a permeability that makes emulsified oil substrate treatment impractical.

[0009] In another embodiment, the voltage is supplied by a system which is solar powered. In yet another embodiment, the method of bioremediation includes utilizing a system comprising batteries which store energy generated by a photovoltaic system, which comprises at least one solar panel. In yet another embodiment, the electrodes are capable of switching polarity. In still another embodiment, at least four electrodes are inserted into the contaminated soil. The electrodes are positioned such that there is a flow of electrical current across the cathode and anode. The electrodes may be positioned in any conceivable array. In one embodiment, the electrodes are spaced in two rows, with each cathode being located directly across from its corresponding anode. In another embodiment, the electrodes are spaced in two rows, one row comprising cathodes and the second row comprising anodes, with each cathode being offset from its corresponding anode, similar to a zig-zag pattern. In another embodiment, the electrodes are placed in two rows and those rows are perpendicular to the direction of the groundwater flow. In yet another embodiment, the electrodes are positioned in a circular pattern where there is at least one circle of cathodes borders the area to be treated and at least one anode located within the perimeter of the circle. In still another embodiment, the electrodes are positioned in a circular pattern where there is at least one circle of cathodes located within the area to be treated and at least one anode located within the perimeter of the circle. In another embodiment, the pattern of electrodes comprises concentric circles. In another embodiment, the electrodes are placed in groundwater wells. In yet another embodiment, the electrodes are placed directly into the ground, without using wells, either with or without the use of a conductive material that improves the flow of electrical current between the electrode and the soil.

[0010] In one embodiment, the voltage applied is a voltage which is sufficient to achieve the generation of a sufficient amount of hydrogen (H₂) to reduce the concentration of a contaminant in the soil. In another embodiment the voltage applied is a voltage which is sufficient to achieve a current of between approximately 1 and approximately 1000 mA between the electrodes. In one embodiment, the voltage applied is between approximately 1 and approximately 100 volts direct current. In another embodiment, the voltage applied is between approximately 1 and approximately 30 volts direct current. In yet another embodiment, the voltage applied is less than approximately 5 volts direct current. In another embodiment, the system transforms an AC power source into a DC power source. [0011] The electrodes used can be comprised of any conductive material, including, but not limited to, titanium mesh, NiTi wires, titanium filings, copper wire, mixed metal oxide-coated titanium mesh, steel rods, iron filings, or iron particles. In one embodiment, the electrodes comprise mixed oxide-coated titanium mesh.

[0012] In another embodiment, the method of in situ bioremediation comprises electrodes, a power source, a control panel, and sensors. The electrodes, power source, and sensors are either directly or indirectly connected to the control panel. The sensors monitor the voltage and/or the current produced by the system. The control panel comprises electronics capable of controlling the voltage and/or the current based off of the information received from the sensors. In another embodiment, the control panel comprises electronics and other devices capable of switching the polarity of the electrodes. In yet another embodiment, the control panel comprises electronics and other devices capable of converting AC to DC. In another embodiment, the control panel comprises timers. The timers can be used in monitoring and controlling the voltage and/or current. In another embodiment, the timers are used to determine when to switch the polarity.

[0013] In another embodiment, a parcel of contaminated land, comprising soil and at least one contaminant, is treated by acquiring at least one soil sample from the contaminated parcel of land. The soil sample is evaluated to determine at least one of the following: the initial concentration of contaminant; the permeability of the soil; and the susceptibility of the soil to treatment by in situ bioremediation by determining whether the soil sample generates hydrogen when subjected to a voltage or results in a lower concentration of a contaminant when subjected to a voltage. After evaluation of the soil sample, at least two electrodes are inserted into the contaminated land within the area of contamination and then a voltage is applied across the electrodes. In another embodiment, a parcel of contaminated land, comprising soil and at least one contaminant, is treated by inserting at least two electrodes into the soil adjacent to the area of contamination. In another embodiment, a parcel of contaminated land, comprising soil and at least one contaminant, is treated by inserting at least one electrode into the soil adjacent to the area of contamination and by inserting at least one electrode into the parcel of contaminated land.

Description of the Drawings

[0014] The drawings constitute a part of this specification and include exemplary embodiments of in situ remediation, which may be embodied in various forms. It is to be understood that in some instances, various aspects may be shown exaggerated or enlarged to facilitate the understanding of certain aspects of the in situ remediation. Therefore the drawings may not be to scale.

[0015] Figure 1 is a diagram of one embodiment of a soil testing system.

[0016] Figure 2 is a diagram of one embodiment of a solar powered in situ treatment system.

[0017] Figure 3 is a graph of the ppmv hydrogen generated in the first test soil, over time, as a result of applied current.

[0018] Figure 4 is a graph of the μg/L hydrogen generated in the first test soil, over time, as a result of applied current.

[0019] Figure 5 is a graph of the μΜ hydrogen generated in the first test soil, over time, as a result of an applied current.

[0020] Figure 6 is a graph of the ppmv hydrogen generated in the second test soil, over time, as a result of current.

[0021] Figure 7 is a graph of the μg/L hydrogen generated in the second test soil, over time, as a result of applied current.

[0022] Figure 8 is a graph of the μΜ hydrogen generated in the second test soil, over time, as a result of an applied current. [0023] Figure 9 is a graph of the ppmv hydrogen generated in the third test soil, over time, as a result of current.

[0024] Figure 10 is a graph of the μg/L hydrogen generated in the third test soil, over time, as a result of an applied current.

[0025] Figure 1 1 is a graph of the μΜ hydrogen generated in the third test soil, over time, as a result of an applied current.

[0026] Figure 12 is a diagram of one embodiment of an in situ remediation system.

Modes for Carrying Out the Invention

[0027] The subject matter of the present invention is described with specificity to meet statutory requirements. However, the description itself is not intended to necessarily limit the scope of claims. Rather, the claimed subject matter might be embodied in other ways to include different steps or combinations of steps similar to the ones described in this document, in conjunction with other present or future technologies. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0028] For the purpose of understanding the in situ remediation, references are made in the text to exemplary embodiments, only some of which are described herein. It should be understood that no limitations on the scope of the invention are intended by describing these exemplary embodiments. One of ordinary skill in the art will readily appreciate that alternate but functionally equivalent components, materials, designs, and equipment may be used. The inclusion of additional elements may be deemed readily apparent and obvious to one of ordinary skill in the art. Specific elements disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one of ordinary skill in the art to employ the present invention. [0029] Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized should be or are in any single embodiment. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment. Thus, discussion of the features and advantages, and similar language, throughout this specification may, but does not necessarily, refer to the same embodiment.

[0030] Furthermore, the described features, advantages, and characteristics may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize that in situ remediation may be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments.

[0031] References throughout this specification to "one embodiment," "an embodiment," or similar language mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases "in one embodiment," "in an embodiment," and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment. Moreover, the terms "substantially" or "approximately" as used herein may be applied to modify any quantitative representation that could permissibly vary without resulting in a change to the basic function to which it is related.

[0032] In situ proton reduction produces hydrogen gas (H₂), which is important to the bioremediation of many compounds, including but not limited to, chlorinated organic solvents and heavy metals. Embodiments described herein have the ability to remediate soil containing chlorinated organic solvents and other contaminants. Embodiments described herein have a lessened reliance on groundwater flow, which is greatly reduced in low permeability soils. Embodiments described herein overcome problems encountered in bioremediation including the efficient distribution of additives, including biological stimulants and oxidants. The embodiments described herein do not rely on the extraction of groundwater for ex situ treatment.

[0033] H₂ can be produced in water by electrolysis and the reduction of hydrogen ions (a.k.a., protons) through the introduction of an electrical current. Embodiments described herein utilize proton reduction in which electrodes are inserted into contaminated soil. The electrodes may be inserted into an aquifer or into soils which contain at least a minimal amount of water, but are not saturated with water. A voltage direct current is utilized to generate hydrogen (H₂) on soil surfaces, as opposed to exclusively at the electrodes. Protons are reduced to hydrogen on the cathode surface at a potential of approximately 0.5V. Hydrogen is generated on both the inserted cathode and on the surface of soil particles located between electrodes. The generated hydrogen can support in situ bioremediation of various contaminants in soils. The molecular hydrogen (H₂) can be used as an electron donor for dehalogenating or metal reducing bacteria.

[0034] The contaminants that can be remediated using the in situ bioremediation include, but not limited to, chlorinated organic solvents, metals, nitro- and/or nitramine- containing explosives, anionic pollutants, nitrites, nitrates, perchlorates, and/or chlorates. In one embodiment, the electrode configurations and a low voltage proton reduction system may be powered by low cost and sustainable photovoltaic systems.

[0035] In one embodiment, the voltage applied is a voltage which is sufficient to achieve the generation of a sufficient amount of hydrogen to reduce the concentration of a contaminant. In another embodiment, the voltage applied is a voltage which is sufficient to achieve a current of between approximately 1 and approximately 1000 mA between the electrodes. In yet another embodiment, the voltage applied is between approximately 1 and approximately 100 volts direct current. In another embodiment, the voltage applied is between approximately 1 and approximately 30 volts direct current. In yet another embodiment, the voltage applied is less than approximately 5 volts direct current. In another embodiment, the system transforms an AC power source into a DC power source.

[0036] The electrodes can be comprised of any conductive material, including, but not limited to, titanium mesh, NiTi wires, titanium filings, copper wire, mixed metal oxide-coated titanium mesh, steel rods, iron filings, or iron particles. In one embodiment, the electrodes comprise mixed oxide-coated titanium mesh.

[0037] The techniques described herein may be utilized for the remediation of contaminated sites that have low permeability soils, soils with at least a minimal concentration of water, fractured rock systems, high concentration contaminant areas, especially those with dense non-aqueous phase liquids (DNAPL), and/or large dilute plumes.

[0038] Embodiments described herein produce hydrogen in soil, including but not limited to low permeable soils, and between the electrodes, rather than merely on the electrode surface. Accordingly, hydrogen, which is an electron donor, is produced near the degradative bacteria, that are already present in the soil, thereby reducing the amount of groundwater transport required for distribution of the hydrogen.

[0039] Generally, soil with higher clay contents have lower resistance, resulting in increased current flow through the soil. Not wishing to be bound by theory, reductive clay surfaces may have the ability to directly reduce chlorinated solvents in addition to the ability to reduce protons. Thus, clay-associated proton reduction and potentially other electrochemical processes, have the potential to treat contaminants in low permeable soils. In one embodiment, the soil being treated contains clay. In another embodiment, the soil being treated does not contain clay. In one embodiment, the soil being treated is located in a vadose zone. In another embodiment, the soil being treated is located in an aquifer. In a prophetic embodiment, the area treated is a low permeability layer below the water table. In one embodiment, the contaminants treated are chlorinated volatile organic compounds. In another embodiment the in situ bioremediation occurs in soil having a permeability that makes emulsified oil substrate treatment impractical.

[0040] In one embodiment, a parcel of contaminated land, comprising soil and at least one contaminant, is treated by inserting at least two electrodes into the contaminated parcel of land within the area of contamination. A voltage is applied across the at least two electrodes, creating hydrogen gas in situ in soil located between the at least two electrodes. The generation of hydrogen gas created in situ results in a reduction of the amount of the contaminant contained within the soil located between the two electrodes. Without wishing to be bound by theory, it is believed that the generated hydrogen is utilized by bacteria in the soil, resulting in the bacteria degrading/reducing the contaminant(s). In another embodiment, a parcel of contaminated land, comprising soil and at least one contaminant, is treated by inserting at least two electrodes into the soil adjacent to the area of contamination. In another embodiment, a parcel of contaminated land, comprising soil and at least one contaminant, is treated by inserting at least one electrode into the soil adjacent to the area of contamination and by inserting at least one electrode into the parcel of contaminated land.

[0041] In a further embodiment, the voltage is supplied by a system which is solar powered. In yet a further embodiment, the system comprises batteries which store energy generated by a photovoltaic system. In this embodiment, the solar panel charges the batteries which supply power to the in situ bioremediation system. In one embodiment, the solar system is capable of supplying approximately 10mA of current to the at least two electrodes. In a further embodiment, the solar system is a 160 W system. In another embodiment, the batteries are 12 V batteries. [0042] In another embodiment, the electrodes are capable of switching polarity. Typically, the polarity can be switched to distribute hydrogen throughout the treatment area and/or to prevent pH swings. In yet another embodiment, at least four electrodes are inserted into the soil. The electrodes are positioned such that there is a flow of electrical current across the cathode and anode. The electrodes may be positioned in any conceivable array. In one embodiment, the electrodes are placed in two parallel rows with each cathode being located directly opposite from its anode. In another embodiment, the electrodes are placed in at least two parallel rows, one row comprising cathodes and the second row comprising anodes, with each cathode offset from its anode, creating a zig-zag pattern. In another embodiment, the electrodes are spaced in two rows perpendicular to groundwater flow. In yet another embodiment, the electrodes are positioned in a circular pattern wherein cathodes are positioned in a circle around and/or in the area to be treated, and at least one anode is located within the perimeter of the circle. In another embodiment, the pattern of electrodes comprises concentric circles.

[0043] In one embodiment the electrodes are placed in existing groundwater wells. In yet another embodiment, the electrodes are placed directly into the ground, without using wells, either with or without the use of a conductive material that improves the flow of electrical current between the electrodes and the soil. In another embodiment the electrodes can be moved from one location in the parcel of contaminated land to different location in the parcel of contaminated land.

[0044] In one embodiment, a parcel of contaminated land is treated by acquiring at least one soil sample from the contaminated parcel of land. The at least one soil sample is evaluated to determine the initial concentration of a contaminant. The at least one soil sample is also evaluated to determine the permeability of the at least one soil sample. The at least one soil sample is also evaluated to determine the susceptibility of the at least one soil sample to treatment by in situ bioremediation as described herein. In one embodiment, the determination of susceptibility to treatment by in situ hydrogen production comprises determining whether the at least one soil sample generates hydrogen when subjected to a voltage. This test may also be used to determine the optimal distance between the electrodes when placing the electrodes into the parcel of contaminated land. In another embodiment, the determination of susceptibility to treatment by in situ bioremediation comprises determining whether exposure of the at least one soil sample to hydrogen results in a lower concentration of the contaminant within the at least one soil sample than the initial concentration of the contaminant in the at least one soil sample. After the at least one soil sample is tested, at least two electrodes are inserted into the contaminated parcel of land within the area of contamination. In one embodiment, at least two electrodes are inserted into soil adjacent to the area of contamination. In another embodiment, a parcel of contaminated land, comprising soil and at least one contaminant, is treated by inserting at least one electrode into the soil adjacent to the area of contamination and by inserting at least one electrode into the parcel of contaminated land. A second voltage is applied across the at least two electrodes, creating hydrogen gas in situ in soil located between the at least two electrodes. The hydrogen gas created in situ results in a reduction of the amount of the contaminant contained within the soil located between the at least two electrodes.

[0045] In a further embodiment, the contaminant treated is a heavy metal, including, but not limited to selenium, chromium, arsenic, manganese or other elements classified as heavy metals. In yet another embodiment, the contaminant treated is an explosive, including but not limited to 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), l,3,5-trinitroperhydro-l,3,5-triazine ( DX), octahydro- l,3,5,7-tetranitro-l,3,5,7-tetrazocine (HMX), or [3-nitrooxy-2,2- bis(nitrooxymethyl)propyl] nitrate (PETN). In another embodiment, the contaminant treated is an explosive which is susceptible to reduction by bacteria upon exposure to an electron donor source, such as H₂. In another embodiment, the contaminant treated is an anion, including but not limited to, NO₃ ^~, NO₂ ^", ClO₄ ^" , ClO₃ ^", or any other anion which may be present in a contaminated soil. In a further embodiment, the contaminant treated is an anionic pollutant, including but not limited to, perchlorate, chlorate, nitrate, or nitrite. In still another embodiment, the contaminant treated is an anionic pollutant which is susceptible to reduction by bacteria upon exposure to an electron source, such as H₂.

[0046] In another embodiment, the method of in situ bioremediation comprises electrodes, a power source, a control panel, and sensors. The electrodes, power source, and sensors are either directly or indirectly connected to the control panel. The sensors monitor the voltage and/or the current produced by the system. The control panel comprises electronics capable of controlling the voltage and/or the current based off of the information received from the sensors. In another embodiment, the control panel comprises electronics and other devices capable of switching the polarity of the electrodes. In yet another embodiment, the control panel comprises electronics and other devices capable of converting AC to DC. In another embodiment, the control panel comprises timers. The timers can be used in monitoring and controlling the voltage and/or current. In another embodiment, the timers are used to determine when to switch the polarity.

EXAMPLES

Example 1

[0047] Bench scale tests were performed on three soil samples obtained from two different chlorinated solvent-contaminated sites. The first test soil was gray in color and consisted mainly of fine sand and silt with some clays. The first test soil was contaminated with trichloroethene (TCE) and c^-l,2-dichloroethene (cDCE) at a concentration of 6800 μg/L and 3000 μg/L, respectively. The second test soil consisted of nearly equal parts gravel and stones (19%), very coarse sand (17%), fine sand (23%), and silt and clay (17%), yielding an almost equal mixture of coarse and fine particles. The second test soil was contaminated with TCE and cDCE at a concentration of 15 mg/L and 40 mg/L, respectively. The third test soil was obtained from a site near the source of the second test soil and consisted mainly of gravel and stones (37%), fine sand (17%), silt and clay (16%), and very coarse sand (15%). The coarse particles in the third test soil accounted for 52% of the soil composition, and the finest particle types accounted for 33% of the composition of the soil. The third test soil was contaminated with TCE and cDCE at a concentration of 15 mg/L and 40 mg/L, respectively. The testing of those samples was conducted on laboratory equipment configured as displayed in Figure 1 of the drawings. Referring now to Figure 1 of the drawings, soil chamber 45 was filled with either the first test soil or the second test soil. Open cathode vessel 25 was filled to cathode liquid level 30 and open anode vessel 65 was filled to anode liquid level 70 such that open cathode vessel 25 was in fluid communication with open anode vessel 65 through the soil in soil chamber 45. Cathode wire 20 connected titanium mesh cathode 40 to a DC power supply which supplied a constant voltage across titanium mesh cathode 40 and titanium mesh anode 75. Titanium mesh anode 75 was connected to the opposite terminal of the power supply by anode wire 60. Both titanium mesh cathode 40 and titanium mesh anode 75 were constructed of mixed metal oxide-coated titanium mesh material used for commercial electrodes. Open cathode vessel 25 and open anode vessel 65 were of open construction such that hydrogen produced at titanium mesh cathode 40 and oxygen produced at titanium mesh anode 75 freely vented and were unlikely to significantly contribute to the gases present in soil chamber 45. H₂ capture chamber 50 was configured such that vapors produced in soil chamber 45 would preferentially enter H₂ capture chamber 50. Sample port 55 was configured at the upper end of H₂ capture chamber 50 such that the gases produced in the soil that entered H₂ capture chamber 50 could be extracted from H₂ capture chamber 50, measured, and quantified.

[0048] Soil chamber 45 was a cylinder constructed from ½-inch diameter plastic tubing and a T-fitting. A small length of ½-inch diameter polyvinyl chloride pipe and a Teflon fitting were added on top of the T-fitting to form H₂ capture chamber 50. The ½-inch diameter PVC pipe created a chamber with a calculated volume of 2.4 cm³ which made up H₂ capture chamber 50. The tubing holding the soil had a calculated volume of 30 cm³. For calculating the amount of water contained in the soil-filled tubing, a pore volume of 35% was assumed for each soil. Thus, the soil-filled tubing could contain 7.3 milliliters (mL) of groundwater. Control experiments not described herein were performed confirming that hydrogen measured in H₂ capture chamber 50 did not originate in the cathode chamber.

[0049] The potential maintained on the electrodes throughout the tests was

25 V. 25 V is higher than the potential expected in similar field applications (i.e., 1 to 2 V). The higher voltage was used because that voltage was needed to supply sufficient current in through the soil chamber 45 in the laboratory systems. Not wishing to be bound by theory, the differences may be attributable to differences in soil packing. Electrical current in the system was measured by using a multi meter and a set of high ohm resistors that allowed measurement of current in the sub-milliamp (niA) range. Low voltage field-scale systems typically generate 10 to 100 mA, so the current produced in the lab system (10^~4 to 10^"5 A range) was significantly less than equivalent embodiments in the field.

[0050] For calculating the amount of hydrogen produced in the soil, a gaseous sample was collected from the H₂ capture chamber 50 and it was injected into a gas chromatograph fitted with a pulse discharge ionization detector (PDID). The dimensionless Henry's Law coefficient for hydrogen was then used to calculate the expected amount of H₂ that would have had to be present in the 7.32 mL of groundwater (within the soil-filled tubing) to yield the amount of H₂ found in the gas sample collected from the chamber. H₂ estimates were conservative in that those estimates were based on an assumption that all H₂ produced throughout the column collected in the capture chamber. Based on experiments performed to evaluate diffusion of high concentrations of H₂ from the cathode chamber to the collection chamber, diffusion of H₂ through the saturated soil was very slow relative to the time frame of these experiments. As a result, most of the hydrogen collected was likely produced very near the capture chamber in the soil column. Likewise, because of the many fittings and tubing connections employed in the system, and the use of plastic that is somewhat permeable to H₂, it is likely that some H₂ was lost from the system, again making estimates of hydrogen production conservative.

[0051] Results of H₂ production experiments using the first test soil are presented in Figures 3-5. The results demonstrate that H₂ was produced in the site soils under an applied electrical current. H₂ calculated concentrations for the soil pore water indicated that H₂ concentration in the pore water could reach more than 500 nM. These levels are sufficient to support complete biological reductive dechlorination of TCE.

[0052] Results of H₂ production experiments using the second test soil and the third test soil indicate that H₂ was produced in these soils under an applied electrical current. Extremely conservative calculations for H₂ concentrations in the soil pore water indicated that H₂ concentration could reach more than 150 nM. Again, these levels also are sufficient to support biological reductive dechlorination of TCE. Results from the second test soil suggest that the H₂ produced in the cells also was eventually consumed or lost. Although the soil was autoclaved to kill soil microbes, soil microbes are notoriously difficult to kill and it is likely that some organisms survived autoclaving and ultimately grew and consumed some the produced H₂.

[0053] Test conducted with the configuration described in Example 1 were used to test the first test soil. Data from the testing of the first test soil is depicted in Figures 3-5. The tests associated with Figures 3-5 were conducted at 25 V DC 15xl0^"4 Amp. Figure 3 shows the hydrogen production from the first test soil in parts per million by volume (ppmV) as measured in H₂ capture chamber 50. Figures 4 and 5 show calculated values for H₂ concentration in the groundwater in micrograms per liter ^g/L) and micromolar (uM) respectively assuming 35% soil porosity and that all hydrogen volatilized reached H₂ capture chamber 50. As indicated in Figures 3, after 400 hours, approximately 17.0 ppmv of hydrogen was recovered from sample port 55. Figure 4 indicates that after 400 hours approximately 950 μg/L of hydrogen was present in the pore water/groundwater of the soil contained in soil chamber 45. Finally, Figure 5 indicates that after 400 hours, approximately 0.50 μΜ hydrogen was present the pore water/groundwater of the soil contained in soil chamber 45.

[0054] Data from the testing of the second test soil is depicted in Figures 6- 8. The tests associated with Figures 6-8 were conducted at 25 V. Figure 6 shows the hydrogen production from the second test soil in parts per million by volume (ppmV) as measured in H₂ capture chamber 50. Figures 7 and 8 show calculated values for H₂ concentration in the groundwater in micrograms per liter ^g/L) and micromolar (uM) respectively assuming 35% soil porosity and that all hydrogen volatilized reached H₂ capture chamber 50. As indicated in Figures 6, at approximately 100 hours, approximately 5.4 ppmv of hydrogen was recovered from sample port 55. Figure 7 indicates that at approximately 100 hours approximately 0.31 μg/L of hydrogen was present in the pore water/groundwater of the soil contained in soil chamber 45. Finally, Figure 8 indicates that at approximately 100 hours, approximately 0.16 μΜ hydrogen was present in the pore water/groundwater of the soil contained in soil chamber 45.

[0055] Data from the testing of the third test soil is depicted in Figures 9-1 1. The tests associated with Figures 9-1 1 were conducted at 25 V. Figure 9 shows the hydrogen production from the third test soil in parts per million by volume (ppmV) as measured in H₂ capture chamber 50. Figures 10 and 1 1 show calculated values for H₂ concentration in the groundwater in micrograms per liter ^g/L) and micromolar (μΜ) respectively assuming 35% soil porosity and that all hydrogen volatilized reached H₂ capture chamber 50. As indicated in Figures 9, after 150 hours, approximately 3.3 ppmv of hydrogen was recovered from sample port 55. Figure 10 indicates that after 150 hours approximately 0.19 μg/L of hydrogen was present in the pore water/groundwater of the soil contained in soil chamber. Finally, Figure 1 1 indicates that after 150 hours, approximately 0.095 μΜ hydrogen was present in the pore water/groundwater of the soil contained in soil chamber 45.

Example 2

[0056] In a prophetic embodiment, soil having low permeability that is contaminated with cis- 1 ,2-dichloroethene (cDCE) is treated, using methods in situ bioremediation through Hydrogen generation described herein, to produce H₂ in situ such that the con_centration of H₂ is greater than 2 nM but less than 100 nM. In this e_mbodiment the native level of methanogenesis is not substantially impacted. In a related embodiment dehalogenating bacteria consume H₂ at a rate greater than the native _untreated rate while methanogenesis occurs at a rate that is substantially equivalent to the pretreatment rate.

[0057] Referring now to Figure 2 of the drawings, hydrogen is produced at cathode 100 and at intermediate soil location 1 15 below Ground level 1 10. Solar panel 120 provides the voltage required for hydrogen production between cathode 100 and anode 105 by way of anode wire 125.

[0058] In a prophetic embodiment, the electrodes are arranged in contaminated soil, containing dehalogenating bacteria, and an electrical potential is applied to the soil such that a current of approximately 10 mA flows between two electrodes situated in the soil. In a related prophetic embodiment, the current is less than 400 mA and greater than 0.01 mA. In a further related embodiment the current is less than 400 mA and greater than 1 mA. [0059] Not wishing to be bound by theory, the mechanism of in situ hydrogen release may be related to constituents of the soil acting as micro- capacitors or the action could be related to the release of bound organic material liberated by the electrical current coupled with the fermentation of that material to H₂ by indigenous organisms.

Example 3

[0060] In a prophetic example, a soil treatment method, utilizing techniques described herein, may comprise identification of a low permeability aquifer contaminated by chlorinated solvents, characterization of the aquifer properties, testing of soil samples to evaluate the susceptibility of the soil to the in situ production of hydrogen, setting up an array of electrodes, and producing hydrogen at locations between those electrodes such that dehalogenating bacteria are stimulated in a way that decreases the concentration of the chlorinated solvents in the aquifer.

Example 4

[0061] In a prophetic embodiment related to the previous example, after the selection of a suitable site, additional site characterization may be performed in the area selected for the remediation. The site characterization may include soil core collection to better characterize the low permeability soils and to determine the chlorinated volatile organic compound(s) (cVOC) concentrations or concentrations of other contaminants and distribution of the cVOCs or other contaminants in the soils. In addition to logging the soils in the field, soil cores may be collected and transported to a laboratory for characterization and treatability testing. Such treatability testing may take the form of testing conducted in Example 1. A grain size analysis may be performed so that electrical current during the demonstration can be correlated to grain size. Contaminant concentrations and distribution within the cores may be determined. Treatability testing may involve a bottle assay test to confirm that bacteria in the site soils can completely dehalogenate target cVOCs or other contaminats, and that complete dechlorination or decontamination can be supported by the addition of H₂ alone. Additional testing would involve measuring abiotic H₂ generation in the soils by using a H₂ production test cell similar to the cell depicted in Figure 1. Based on the results of the treatability testing a decision would be made regarding whether to implement a full scale in situ remediation system.

[0062] Upon successful test results, an in situ remediation system would be constructed. The exact configuration of the remediation system would be determined after site characterization work, but an example design may include at least four electrodes (2 cathodes and 2 anodes), and at least 5 monitoring wells. One of the monitoring wells may be located up gradient of the test cell, three monitoring wells may be located within the test cell to measure degradation between the electrodes, and a fifth monitoring well may be located down gradient. The electrodes would be powered by a solar system capable of continuously delivering approximately 10 mA of current to the electrode pairs. The expected voltage required would be approximately 1 V, but the actual voltage would be dependent on the soil resistivity. It is anticipated that this power could be supplied by a 160 W system with two 12 V batteries for energy storage. The electrodes could be spaced in two rows perpendicular to groundwater flow and on approximately 10 to 15-foot centers.

[0063] Referring now to Figure 12 of the drawings, an example remediation configuration includes a first set of electrodes 210 arranged in a row, a second set of electrodes 220 arranged in a row parallel to the row of the first set of electrodes 210 and a set of test wells 230. In Figure 12, arrow 255 indicates the direction of groundwater flow, upgradient test well 250 measures untreated groundwater, and downgradient well 200 measures treated water that has left Treatment area 215. In Figure 12, the first set of electrodes comprises cathodes and the second set of electrodes comprises anodes. [0064] Measuring changes in contaminant concentration in low permeability soils is challenging because of either low bulk groundwater velocity through the soils, or because of high groundwater velocities through fractured flow paths. It is uncertain which condition would be encountered at any given site. Another problem associated with sampling for H₂ is the relatively high Henry's Law coefficient of H₂ causes it to partition into the headspace of monitoring wells, thereby making measurements of low concentrations difficult. In the present example one of several sampling techniques may be used to allow monitoring over extended periods, and allow indirect evaluations of performance. The first, indirect approach is to use biotraps (un-baited) that allow capture and enumeration of Dehalococcoides sp. dechlorinating bacteria. Because these dechlorinating bacteria require both cVOCs and H₂ for growth, their growth on the biotrap beads should be correlated with H₂ production. An alternate approach is to use passive samplers and well packers that would allow collection of equilibrated groundwater without well purging. The well packers may be installed under the water table level so that there is no headspace in the well. Passive sampling devices can be installed in monitoring wells and left for extended periods so that the water in the sampler equilibrates with the surrounding water in the formation. The samplers are then withdrawn from the wells without the need to purge the wells. Techniques used for the sampling of cVOCs may be adapted for measurements of H₂. The use of these samplers should allow for the measurement and documentation of even small changes in cVOC concentrations and possibly low concentrations of H_2. Because these samplers would be placed into monitoring wells that have an open headspace, however, there is a chance that dissolved H₂ would be lost by volatilization into the well headspace. To minimize this risk, inexpensive well packers may be used to seal off the section of the monitoring well containing the passive samplers and the biotraps.

[0065] In an alternate example, the sampling techniques described above may be substituted with a more extensive network of small diameter sampling points. By increasing the density of the sampling wells, the ability to measure changes in contaminant and H₂ concentrations throughout the test plot area should be increased as well. Once the remediation system is installed, groundwater monitoring would be performed for a sufficient time to ensure that the generated analytical results represent reactions and processes occurring within the low permeability soils.

Example 5

[0066] In one embodiment, a site needing remediation is selected. In many cases the site will be a site that has limited susceptibility to conventional treatment for halogenated organic contaminants. Known information about the site is evaluated to determine whether the site is a good candidate for in situ hydrogen production remediation. Characteristics of the site soil, including characterization of the contamination and treatability of the soil, are measured. Based on the information gleaned from the testing, a system is designed and installed with electrodes arranged and configured such that in situ production of hydrogen is likely. The system is operated by applying an electrical potential between electrodes placed in the soil to produce hydrogen in situ. Hydrogen production and contaminant concentration are measured during the operation and evaluations of performance are made on a continuing basis.

Example 6

[0067] The present example presents a combination of prophetic and measured characteristics that reflect circumstances in which the treatments described herein may be employed. Some embodiments, but not all embodiments, described herein have electrode configurations with characteristics described in Table 1.

Table 1 : Ranges: Always between: Rarely outside of: Typically

between:

Voltage 0.5V - 25V IV - 5V IV - 5V

Current 10^"4A - 0.5A 0.05A - 0.2A 0.01A - 0.2A

Spacing between 2ft - 30ft 5ft - 15 ft electrodes

[0068] Some embodiments, but not all embodiments, described herein have soil that has the following characteristics described in Table 2, prior to implementation of the treatment.

Table 2:

In one embodiment, the soil being treated has a coefficient of permeability

6 7

between 1 x 10^" cm/s to 1 x 10^" cm/s. In a related embodiment, the soil being treated has a coefficient of permeability between 1 x 10^"5 cm/s to 1 x 10^"6 cm/s.

[0069] Determinations as to whether samples generate hydrogen when subjected to a voltage may be made by directly measuring hydrogen either absorbed or evolved, or by measuring biological or chemical markers that are indicative of the production of hydrogen.

[0070] There are, of course, other alternate embodiments which are obvious from the foregoing descriptions, which are intended to be included within the scope of the in situ remediation method disclosed herein, as defined by the following claims.

Claims

1. A method of treating a contaminated parcel of land comprising:

a. inserting at least two electrodes into a contaminated parcel of land, said contaminated land comprising soil and at least one contaminant; b. applying a first voltage across the at least two electrodes;

c. creating a first quantity of hydrogen gas in situ in the soil located between the at least two electrodes; and

d. lowering the concentration of said at least one contaminant

contained within the soil located between the at least two electrodes.

2. The method of claim 1 , wherein the contaminant is a heavy metal

3. The method of claim 1, wherein the contaminant is an explosive.

4. The method of claim 1, wherein the contaminant is an anion.

5. The method of claim 1, wherein the contaminant is a chlorinated organic compound.

6. The method of claim 1 , wherein the contaminant is a halogenated organic compound.

7. The method of claim 1 , wherein the power supply is a photovoltaic system.

8. A method of treating contaminated land comprising:

a. acquiring at least one soil sample originating from a contaminated parcel of land, said contaminated parcel of land comprising soil and at least one contaminant;

b. evaluating an initial concentration of said contaminant from the at least one soil sample;

c. evaluating a permeability of the at least one soil sample;

d. evaluating a susceptibility of the at least one soil sample to treatment by in situ hydrogen production by conducting an evaluation selected from (i) determining whether the at least one soil sample generates hydrogen when subjected to a first voltage and (ii) determining whether exposure of the at least one soil sample to hydrogen creates a second concentration of the halogenated organic contaminant within the at least one soil sample that is lower than the initial concentration of the halogenated organic contaminant in the at least one soil sample;

e. inserting at least two electrodes into the contaminated parcel of land; f. applying a second voltage across the at least two electrodes; g. creating a second quantity of hydrogen gas in situ in a quantity of soil between the at least two electrodes; and

h. lowering the concentration of the contaminant contained within the quantity of soil between the at least two electrodes.

9. The method of claim 8, wherein the contaminant is a heavy metal

10. The method of claim 8, wherein the contaminant is an explosive.

1 1. The method of claim 8, wherein the contaminant is an anion.

12. The method of claim 8, wherein the contaminant is a chlorinated organic compound.

13. The method of claim 8, wherein the contaminant is a halogenated organic compound.

14. The method of claim 8, wherein the power supply is a photovoltaic system.