Abstract:
An apparatus and method for remediating an underground and/or aqueous contaminant. The method and apparatus utilize at least one electrically conductive surface to attract aqueous hydrogen ions. At the surface, the hydrogen ions interact with excess electrons to form dissolved hydrogen molecules. Dissolved hydrogen molecules provide a proton source for bioreactive material, either provided to or naturally occurring in the environment. The bioreactive material assists in the reduction of the contaminant into a less environmentally harmful compound.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is directed to the field of contaminant removal from a water source. 
       SUMMARY OF THE INVENTION 
       [0002]    The invention is directed to a method for producing dissolved hydrogen molecules for bioremediation of water. The method comprises providing an electrically conductive surface, providing a continuous negative electric potential to the surface to attract hydrogen ions, and converting aqueous hydrogen ions to dissolved hydrogen molecules. The hydrogen ions are converted using the electron source provided by the negative electric potential. 
         [0003]    Another embodiment of the invention is directed to a method for bioremediation of a contaminant plume in water. The method comprises producing dissolved hydrogen. The step of producing dissolved hydrogen comprises the steps of providing an electrically conductive surface, providing a continuous negative electric potential to the electrically conductive surface, and attracting aqueous hydrogen ions to the electrically conductive surface. Dissolved hydrogen molecules are then formed proximate the surface from the aqueous hydrogen ions, and a bioreactive material is provided proximate the conductive surface to facilitate bioremediation of the contaminant plume. 
         [0004]    Another embodiment of the invention is directed to a method for reducing a halogenated organic compound in an aqueous plume. The method comprises providing a plurality of underground electrically conductive surfaces. A continuous negative electric potential is then produced at the conductive surface, such that the negative electric potential increases a concentration of aqueous hydrogen proximate at least one of the plurality of surfaces. Aqueous hydrogen ions are caused to form dissolved hydrogen molecules proximate the at least one surface, and a bioreactive material is provided proximate the at least one surface to reduce the halogenated organic compound. 
         [0005]    Yet another embodiment of the invention is directed to a barrier for treating an aqueous contaminant plume by providing a location for hydrogen ions to form dissolved hydrogen molecules. The barrier comprises a plurality of electrically conductive surfaces and a means for generating a low voltage negative electrical charge at a selected plurality of conductive surfaces. 
         [0006]    Another embodiment of the invention is directed to a barrier for treating an aqueous contaminant plume. The barrier comprises a low-voltage electric source and a plurality of electrically conductive surfaces. The plurality of conductive surfaces are adapted to receive a low-voltage negative charge from the source. The plurality of surfaces provide electrons to aqueous hydrogen ions proximate the surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0007]      FIG. 1  is a representative diagram of an apparatus for remediation of a contaminant plume in water, as shown in an embodiment for remediation of ground water. 
           [0008]      FIG. 2  is an alternative embodiment of the apparatus of claim  1  adapted for remediation of surface water. 
           [0009]      FIG. 3  is a demonstrative diagram of a microscopic process taking place at a charged surface located proximate hydrogen ions in solution. 
           [0010]      FIG. 4  is a representation of a step-wise reduction of tricholoroethane to ethane and ethene. 
       
    
    
     DETAILED DESCRIPTION  
       [0011]    Contamination of water, both in aquifers and surface water, such as a stream or lake, may have significant consequences for both the users of that water and the environment as a whole. While natural attenuation of many contaminants will occur given enough time and soil or sediment in which the water may be remediated, the time required may not be feasible for the use of the water contemplated, either for the public or wildlife. 
         [0012]    Chlorinated solvents were used and released to the environment in massive quantities during the mid 1900s. These contaminants have migrated through the subsurface and impacted ground water at thousands of sites. Their widespread use and unique properties have resulted in the chloroethenes being the most commonly detected class of organic contaminants in ground water. Chloroethenes can become human health hazards when processed in the liver, or via reductive dehalogenation in the environment. 
         [0013]    Many remediation methods have developed to either treat the affected contamination or contain the contamination to prevent the damage it causes from spreading. Until recently, cleanup options have been limited because once these dense non-aqueous phase liquids have penetrated the water table and traveled downward, removal is extremely difficult. Existing methods have significant disadvantages which the present invention overcomes. 
         [0014]    For example, the affected water may be pumped away from the site, treated, and returned without the contaminant present. This method requires external construction, such as a pipeline, and high pumping costs. One alternative is in situ chemical or biological treatment, where treatment chemicals are introduced into the water source. This method may require expensive installation and transportation of the chemicals to the site. Further, the method may require a secondary treatment procedure to remove the introduced chemicals from the water. Finally, it may be possible to dredge or excavate a contaminated area to remove contaminated water and soil/sediment for ex situ treatment or disposal. This method is effective at extracting the contaminant plume, but has a significant environmental impact due to the amount of material that must be removed. 
         [0015]    Research suggests that molecular hydrogen (H 2 ) is a metabolic reductant in a process of microbial reduction of a contaminant such as a halogenated solvent. Therefore, a process that could directly provide molecular hydrogen in situ would be important for supporting remediation. Unfortunately, the most common method for creating molecular hydrogen in situ is through the electrolysis of water. While electrolysis produces large amounts of hydrogen, the hydrogen is created in gaseous form, which is not readily usable in the remediation process. Further, the process requires a large supply of energy to cause the reaction to begin. Finally, the introduction of large amounts of gaseous molecular hydrogen and oxygen into the environment is potentially dangerous, as both gasses are flammable. Use of electrolysis underground is particular dangerous, as gasses may collect until ignited. The present invention discloses a method for providing molecular hydrogen in a dissolved form for remediation forces, utilizing only low amounts of electrical current. Further, the present invention avoids having to inject hydrogen gas in situ, which does not provide dissolved hydrogen gas and requires further operating cost for the purchase and transportation of the hydrogen gas. 
         [0016]    Turning now to the figures in general and  FIG. 1  in particular, shown therein is a barrier  10  for remediation of a contaminant  12  in sediment and soil, in the presence of water. The contaminant  12  comprises a source area  14  and a dissolved plume  16 . For exemplary purposes, the barrier  10  is shown remediating both the source area  12  and the plume  14 . The contaminant  12  may be an organic or inorganic compound, such as a halogenated organic compound, a perchlorate, or a reducible inorganic compound. The barrier  10  comprises an electric source  18  and a plurality of electrically conductive surfaces  20 . As shown, the plurality of electrically conductive surfaces  20  comprises a plurality of pylons. The electrically conductive surfaces  20  may also comprise alternative structures, such as a lattice, wires, or a similar means depending on the needs of the particular application. For instance, in a groundwater contamination scenario as the one shown in  FIG. 1 , pylons  20  may be more appropriate. If surface water is in need of remediation, wires or a lattice grid may be more appropriate as shown in  FIG. 2 . The conductive surfaces  20  may be composed of iron or any conductive material capable of supporting a stable negative potential suitable for this application. 
         [0017]    With continued reference to  FIG. 1 , the plurality of pylons  20  is placed in an arrangement around the source area  14  such that migration of the contaminant  12  from the source area to a previously uncontaminated area is prevented. Pylons  20  are further placed along the path of migration  22 , along which the contaminant plume  16  would extend. These pylons  20  may be placed in a substantially co-planar arrangement, effectively providing a barrier to continued contaminant migration. Further, wood chips (not shown) or other absorbent material may be used in conjunction with the barrier  10  to slow the spread of the contaminant  12 . 
         [0018]    The source  18  may comprise a generator adapted to provide a continuous low-voltage negative electric potential at each of the plurality of electrically conductive surfaces  20 . Alternatively, the source  18  may be a solar cell or battery, or may use a combination of metals to produce the low-voltage electric charge. One such method of generating a charge which is common to those in the art is the use of a sacrificial anode  24 , which provides a low-voltage electrical potential to a cathode surface  20  as described in U.S. Pat. No. 2,645,612. 
         [0019]    With reference now to  FIG. 2 , the barrier  10  is shown as would be utilized in surface water  26  and/or sediment  28 . In  FIG. 2 , the plurality of electrically conductive surfaces  20  comprises a plurality of wires  30 . As shown, the barrier further comprises a bioreactive material port  32 , through which bioreactive material beneficial to remediation may be provided. 
         [0020]    Biological compounds, such as a sulfate-reducing bacteria (SRBs) or other bioreactive materials, may be provided in situ at one or more of the bioreactive material ports  32 . As shown in  FIG. 2 , this port  32  may comprise a tube  34 . The bioreactive material port  32 , as shown, may provide bioreactive material in situ through gravitational force, pressure differential or external force provided by a pump  36  or other similar means. It should be noted that many SRBs, and other bioreactive materials, may be preexisting in situ in quantities which make reduction of contaminants  12  possible. Thus, use of the bioreactive port  32  particularly, or use of added biological material in general, may be determined by the conditions in the area to be treated. 
         [0021]    Turning now to  FIG. 3 , the electrically conductive surfaces  20  provide a location for the formation of dissolved hydrogen molecules in water. A low negative electric charge is provided at the electrically conductive surface  20 , attracting positively charged aqueous hydrogen ions  100  which exist naturally in equilibrium with hydroxide ions  102  and water molecules  104 . Two hydrogen ions  102 , in proximity to the negatively charged surface, may bond utilizing donated electrons  105  from the surface to form a hydrogen molecule  106 . Low concentrations of hydrogen molecules  106  are soluble in water, thus the hydrogen molecules formed will be dissolved in surrounding water. 
         [0022]    The dissolved hydrogen  106  is formed by creating a mono-layer  108  intermediate at the cathode surface  20 . Hydrogen molecules  106  are then removed to solution. The removal may take place as a result of equilibrium-driven dissolution and/or action of microbes existing in solution. Some removal may also take place due to formation of bubbles. Some species of anaerobic microorganisms, notably sulfate-reducing bacteria (SRBs)  110  contain hydrogenases which allow the organisms to remove the hydrogen film  108  and utilize hydrogen  106  as an energy source. These organisms then transfer hydrogen ions  100  and electrons  105  to a reducible species. 
         [0023]    The presence of dissolved hydrogen molecules  106  has been shown to attract naturally-occurring or introduced biological compounds and induce the reduction of contaminants by the compounds into a more inert form. Turning now to  FIG. 4 , one such reduction reaction is shown in written form. Dissolved hydrogen  106  can be reduced to hydrogen ions  100  and electrons  105  by the hydrogenase properties of the biological material. As shown, the ions  100  and electrons  105  are then utilized to convert trichloroethene  112  to ethene and ethane. The trichloroethene  112 , in the presence of hydrogen ions  100  and excess electrons  105 , is converted to cis- and trans-dichloroethene  114 . The continued presence of hydrogen ions  105  in a negatively charged solution reduces the dichloroethene  114  to vinyl chloride  116  and finally ethene  118 . Ethene  118  may be further reduced to ethane  120  in the presence of excess hydrogen ions  100 . 
         [0024]    While trichloroethane  112  is utilized in  FIG. 4  for exemplary purposes, any number of reducible species may be remediated through this process. For example, other halogenated hydrocarbons such as PCP or chloromethanes may accept electrons  105 , as will reducible compound such as nitrates, chromium, uranium, perchlorates, and MTBE. 
         [0025]    Various modifications can be made in the design and operation of the present invention without departing from the spirit thereof. Thus, while the principal preferred construction and modes of operation of the invention have been explained in what is now considered to represent its best embodiments, which have been illustrated and described, it should be understood that the invention may be practiced otherwise than as specifically illustrated and described.