METHODS AND SYSTEMS FOR REDUCTION OF HALOGENATED COMPOUNDS

Abstract

Methods and systems for dehalogenating organohalides are disclosed. In one respect, the systems can generate hydrogen in an electrolysis cell and supply the hydrogen to anaerobic dehalogenating bacteria to decontaminate organohalides at a contamination site.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the reduction of halogenated compounds using anaerobic dehalogenating bacteria.

2. Description of Related Art

Halogenated organic compounds (e.g., chloroethenes, brominated flame retardants, fluorinated flame retardants) are often released accidentally into the soil and groundwater. These anthropogenic compounds are dangerous to humans because they are likely carcinogenic and frequently decompose into even more toxic compounds. Current technologies use microbiological anaerobic dehalogenation, but are unable to efficiently provide the hydrogen (H₂) necessary for anaerobic dehalogenating bacteria to completely or efficiently dehalogenate the halogenated compounds. Accordingly, a significant need exists for the technique described and claimed in this disclosure, which involves various improvements to the current techniques of the art.

SUMMARY OF THE INVENTION

The present disclosure provides methods and systems for dehalogenating organohalides present at a contamination site. Dehalogenation of harmful contaminants can be achieved by generating hydrogen providing the hydrogen to anaerobic dehalogenating bacteria. In some embodiments, the hydrogen is generated at a first location and provided to the dehalogenating bacteria at a second location.

Dehalogenation of harmful contaminants can be achieved by detecting the presence of anaerobic dehalogenating bacteria at a contamination site, generating hydrogen from wastewater, and supplying the hydrogen to the anaerobic dehalogenating bacteria at the contamination site. In some embodiments, organic-containing wastewater is used to generate hydrogen molecules in an electrolysis cell. In other embodiments, hydrogen is generated using anode-respiring bacteria (ARB), an exogenous electron donor, an anode, and a cathode coupled to a power source. The hydrogen is then supplied to the anaerobic dehalogenating bacteria present at the site of the contamination, hydrogen being the preferred electron donor for reduction of organohalides to ethene. The bacteria reductively dehalogenate the halogenated solvents to harmless compounds. This efficient, inexpensive, renewable, and carbon-neutral implementation enables in situ dehalogenation of contaminated water and soil.

The present disclosure provides methods and systems to dehalogenate organohalides present in groundwater and soils. In one embodiment, anaerobic dehalogenating bacteria may be provided to a contamination site. In other embodiments, anaerobic dehalogenating bacteria may already be present at a contamination site. A microbial electrolysis cell (MEC) may use organic-containing wastewater as an exogenous electron donor to generate hydrogen molecules. In other embodiments, a MEC may use organic chemicals, food-industry byproducts, beverage-industry byproducts, or agricultural byproducts. The hydrogen molecules may be provided to the anaerobic dehalogenating bacteria, which then reductively dehalogenate the organohalides present at the contamination site into harmless compounds. The organic-containing wastewater used in the MEC may be provided from a pipe connected to a wastewater treatment plant, and the MEC-treated water can be returned to the wastewater treatment plant by another pipe. Thus, the MEC may provide hydrogen to drive the reductive dehalogenation of organohalides present in groundwater and soils without causing a secondary contamination in the groundwater or subsurface.

In one respect, a method is provided. The method may comprise generating hydrogen at a first location, and providing the hydrogen gas to anaerobic dehalogenating bacteria at a second location.

In another respect, a method is provided. Organic-containing wastewater may be provided to the anode-respiring bacteria (ARB), which may be coupled to an anode. Electrons are transferred from organic-containing wastewater to the anode by the ARB. The electrons are transported through a circuit to a cathode. Hydrogen molecules are generated at the cathode and are provided to anaerobic dehalogenating bacteria that are present at a contamination site. The contamination site may be contaminated with halogenated organohalides. Using the hydrogen as an electron donor, the anaerobic dehalogenating bacteria may dehalogenate the halogenated organohalides and reduce the organohalides to harmless compounds.

In another respect, a system is provided. The system may comprise a microbial electrolysis cell (MEC). The MEC may comprise a power supply, an anode chamber coupled to the power supply, a cathode chamber coupled to the power supply, and an ion exchange membrane coupled to the anode chamber and cathode chamber. Anode-respiring bacteria may be coupled to the anode chamber using, by non-limiting example, an ARB biofilm. The MEC may be configured to generate hydrogen gas. Anaerobic dehalogenating bacteria may be provided to a contamination site. The hydrogen gas may be distributed to the anaerobic dehalogenating bacteria using, by way non-limiting example, a gas diffusion membrane, a pump, or a manifold.

In another respect, a system is provided. The system may comprise a contamination site. The contamination site may further comprise a first subsurface zone, where the first subsurface zone is saturated with groundwater, and a second subsurface zone, where the second subsurface zone is not saturated with groundwater. The system may further comprise a power supply, a cathode chamber coupled to the power supply, an anode chamber coupled to the power supply, and anode-respiring bacteria coupled to the anode chamber. The anode chamber may be configured for placement in the unsaturated subsurface zone. The cathode chamber may be configured for placement in the saturated subsurface zone and configured to generate hydrogen gas. The anode chamber may be configured for placement near the cathode compartment. In some embodiments, the cathode compartment may be in the saturated subsurface zone, while in other embodiments the cathode compartment may be in the unsaturated subsurface zone.

In another respect, a system is provided. The system may comprise a pump configured to pump water that has been contaminated with a chlorinated solvent. The system may further comprise a power supply, a cathode chamber comprising a cathode, the cathode being coupled to the power supply, and an anode chamber comprising an anode. The cathode chamber may comprise anaerobic dehalogenating bacteria. The cathode chamber may be configured to receive contaminated water.

The term “organic-containing wastewater” includes water that contains any amount of organic material whether the identity of the particular organic constituents is known or not.

The terms “hydrogen,” “hydrogen molecule,” or “hydrogen molecules” include “hydrogen gas,” “dihydrogen,” and “H₂”.

The term “coupled” is defined as connected, although not necessarily directly, and not necessarily mechanically.

The terms “a” and “an” are defined as one or more unless this disclosure explicitly requires otherwise.

The term “substantially,” “about,” “approximation” and its variations are defined as being largely but not necessarily wholly what is specified as understood by one of ordinary skill in the art, and in one non-limiting embodiment these terms refer to ranges within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5% of what is specified.

The terms “comprise” (and any form of comprise, such as “comprises” and “comprising” and “comprised of”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”) and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, a method or device that “comprises,” “has,” “includes” or “contains” one or more steps or elements possesses those one or more steps or elements, but is not limited to possessing only those one or more elements. Likewise, a step of a method or an element of a device that “comprises,” “has,” “includes” or “contains” one or more features possesses those one or more features, but is not limited to possessing only those one or more features. Furthermore, a device or structure that is configured in a certain way is configured in at least that way, but may also be configured in ways that are not listed.

Other features and associated advantages will become apparent with reference to the following detailed description of specific embodiments in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present disclosure. The figures are examples only. They do not limit the scope of the disclosure.

FIG. 1 illustrates one embodiment of a system for delivering hydrogen gas from a microbial electrolysis cell to a contamination site;

FIG. 2 illustrates one embodiment of a microbial electrolysis cell;

FIG. 3 illustrates one embodiment of a system where the cathode is placed in a contamination site;

FIG. 4 illustrates one embodiment of a system for dehalogenating contaminated groundwater with a microbial electrolysis cell;

FIG. 5 illustrates one embodiment of a method for dehalogenating contaminated soils and water using a microbial electrolysis cell;

FIG. 6 illustrates an MEC used in a working example demonstrating dehalogenation of TCE to ethene;

FIG. 7 illustrates the generation of an electrical current as a function of time in a dual-chamber MEC being fed with acetate;

FIG. 8 illustrates concentrations of TCE, cis-DCE, VC, and ethene as a function of time at with 5 mM NaHCO₃ buffer;

FIG. 9 illustrates concentrations of of TCE, cis-DCE, VC with 5 mM NaHCO₃ and 5 mM HEPES.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The disclosure and its various features and advantageous details are explained more fully with reference to the nonlimiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known starting materials, processing techniques, components, and equipment are omitted so as not to unnecessarily obscure the invention in detail. It should be understood, however, that the detailed description and the specific examples, while indicating embodiments of the invention, are given by way of illustration only and not by way of limitation. Various substitutions, modifications, additions, and/or rearrangements within the spirit and/or scope of the underlying inventive concept will become apparent to those of ordinary skill in the art from this disclosure.

Overview

The present disclosure provides methods and systems for dehalogenating organohalides present at a contamination site. Dehalogenation of contaminants can be achieved by providing hydrogen to anaerobic dehalogenating bacteria at the contamination site. These bacteria may be present naturally, or, if not present, the bacteria may be provided to the contamination site. These bacteria prefer hydrogen as the electron donor for the reduction of organohalides, such as chlorinated solvents. Using the process of electrolysis, hydrogen is generated from a carbon source and an organic electron donor in water. In some embodiments, organic-containing wastewater is the electron donor. In other embodiments, the electron donor may be organic chemicals, food-industry byproducts, beverage-industry byproducts, or agricultural byproducts. In some embodiments, hydrogen is generated in an electrolysis cell. In other embodiments, hydrogen is generated using an anode and a cathode coupled to a power source. This efficient, inexpensive, renewable, and carbon-neutral implementation enables in situ dechlorination of contaminated water and soil.

The system may be adapted to suit the conditions at a particular site. In some embodiments, hydrogen gas is generated in a microbial electrolysis cell (MEC) and transported to a contaminated site using a gas diffusion membrane. In other embodiments, a cathode is placed underground in a groundwater-saturated zone and an anode is placed underground close to the cathode in a saturated zone or an unsaturated zone. In still other embodiments, water that has been contaminated with organohalides is pumped through the cathode chamber. Both hydrogen generation and dehalogenation occur in the cathode chamber.

The dehalogenation of organohalides contained in water and soil helps eliminate chemicals that are thought to be carcinogenic in humans and hazardous to the natural environment. For example, chlorinated solvents are a byproduct of manufacturing processes and are often released inadvertently into soil and groundwater. Trichloroethene (TCE) is an example of a common chlorinated solvent frequently found in groundwater. It is estimated that 9%-34% of drinking water resources are contaminated with TCE. The Environmental Protection Agency has set the maximum contamination level of TCE at 5 parts per billion (ppb) in drinking water because of the danger TCE poses to humans.

Microbiological anaerobic dehalogenation of organohalides is known in the art. Dehalogenation of organohalides under anaerobic conditions requires an electron donor, a carbon source, the absence of more favorable electron acceptors, and most importantly, an appropriate microbial consortium that can reduce organohalides. Because many organohalides do not readily dissolve in water, they may form zones of dense non-aqueous phase liquid (DNAPL) and continue to contaminate the groundwater for many years through slow but continuous dissolution.

Non-limiting examples of anaerobic dehalogenating bacteria include members of genera Dehalobacter, Dehalococcoides, Desulfitobacterium, Geobacter, and Sulfurospirillum. A common feature of these dehalogenating bacteria is their preference for using hydrogen molecules as the electron donor for the reduction of chlorinated solvents to ethene. For example, Dehalococcoides require hydrogen molecules as the electron donor in order to complete dehalogenation of TCE to ethene. Complete anaerobic dehalogenation using Dehalococcoides is possible only when hydrogen molecules are delivered to TCE-contaminated water and soil.

Existing techniques for dechlorinating chlorinated solvents deliver hydrogen molecules to the site of the TCE contamination using fermentable organic substrates such as lactate. Long-term treatment of TCE in groundwater and soil requires a continuous supply of these fermentable organic substrates, which are difficult to store and deliver. Additionally, fermentable organic substrates can stimulate the growth of other anaerobic bacteria that can outcompete dechlorinators or scavenge small amounts of hydrogen molecules produced by fermentation. Thus, TCE dechlorination can be incomplete, resulting in accumulation of toxic intermediate compounds such as dichloroethene (DCE) or vinyl chloride (VC).

Embodiments of the invention disclose a more effective technique for dehalogenating organohalides than those currently employed. In some embodiments of the invention, hydrogen is generated away from the site of the contamination and then provided directly to the site. In other embodiments, hydrogen is generated at the site of the contamination. In still other embodiments, contaminated groundwater is pumped to a cathode chamber, and hydrogen production and reductive dechlorination occur in the cathode chamber.

In some embodiments, organic-containing wastewater is supplied to an MEC. Organic-containing wastewater is a readily available source of the electrons necessary to complete the process of reductive dechlorination. Using this wastewater, the MEC generates hydrogen molecules to be used for dehalogenating organohalides. The organic-containing wastewater used in the MEC can be pumped back into the wastewater pipeline and on to a wastewater treatment plant. In other embodiments, non-limiting examples of an organic electron donor include organic chemicals, food-industry byproducts, beverage-industry byproducts, or agricultural byproducts. Because the MEC delivers only hydrogen to the contamination site, there is no secondary contamination in the groundwater and the soil. Industries benefitting from an improved technique for dehalogenating organohalides include the bioremediation, water treatment, and bioenergy industries.

Exemplary Embodiments

A first embodiment of a system 100 for dehalogenating organohalides is depicted in FIG. 1. In this embodiment, organohalides are present underground at a contamination site 110. Contamination site 110 may consist of a zone that is unsaturated with groundwater 120 and a zone that is saturated with groundwater 121. Anaerobic dehalogenating bacteria are present at contamination site 110. Non-limiting examples of anaerobic dehalogenating bacteria include members of genera Dehalobacter, Dehalococcoides, Desulfitobacterium, Geobacter, and Sulfurospirillum. In some embodiments, anaerobic dehalogenating bacteria are naturally present at the contamination site. In other embodiments, it may be necessary to provide the bacteria to the site.

Organic-containing wastewater 130 is supplied to an electrolysis cell 140, where hydrogen gas is generated. In one embodiment, electrolysis cell 140 is a microbial electrolysis cell (MEC). In other embodiments, electrolysis cell 140 may be a biological electrolysis cell. Organic-containing wastewater 130 is then returned to a wastewater pipeline 150, where it may continue on to a wastewater treatment plant 151. In one embodiment, the hydrogen molecules generated by the MEC are delivered to the contamination site using a gas diffusion membrane 160. In other embodiments, hydrogen may be delivered with a pump, a manifold, or a pipe, or other such mechanisms known in the art. Using the hydrogen as an electron donor to drive reductive dechlorination, the anaerobic dehalogenating bacteria present at contamination site 110 degrade the chlorinated solvents into ethene.

An embodiment of a microbial electrolysis cell 200 is depicted in FIG. 2. The MEC comprises a power source 210, an anode 220, an anode chamber 222, a cathode 230, a cathode chamber 231, an ion-exchange membrane 240, and a circuit 260. In one embodiment, anode 220 is a bundle of carbon fiber and cathode 230 is a graphite rod. Other material known to persons skilled in the art may be used for anode 220 and cathode 230. Anode 220 and cathode 230 are coupled to power source 210 and are coupled to circuit 260. Ion-exchange membrane 240 is located between anode chamber 222 and cathode chamber 231. In one embodiment, ion-exchange membrane 240 is a cation-exchange membrane that allows positively charged ions to pass from the anode chamber to the cathode chamber. In other embodiments, ion-exchange membrane 240 may be an anion-exchange membrane or a non-ion-specific membrane. Any non-conductive material may be used for the ion-exchange membrane 240. In still other embodiments, no ion-exchange membrane may be used. A biofilm comprising anode-respiring bacteria 221 is coupled to anode 220.

In this embodiment, the MEC generates hydrogen molecules as follows. First, wastewater containing organic material is introduced into anode chamber 222 through a wastewater inlet 250. Then, biofilm comprising anode-respiring bacteria 221 oxidizes the organic material and transfers electrons to anode 220. The transfer of electrons from the organic-containing wastewater yields hydrogen ions and carbon dioxide. The wastewater exits anode chamber 222 through wastewater outlet 251. The electrons from the wastewater move through circuit 260 to cathode 230. In one embodiment, hydrogen ions pass from anode chamber 222 through cation-exchange membrane 240 to cathode chamber 231. The hydrogen ions in cathode chamber 231 bond with the electrons from cathode 230 and become hydrogen molecules. The hydrogen molecules are then directly supplied to the anaerobic dehalogenating bacteria present at the contamination site.

Another embodiment of a system 300 for reducing halogenated compounds is depicted in FIG. 3. This embodiment is similar to previously discussed embodiments except that instead of generating hydrogen using an electrolysis cell, the anode 330 and the cathode 331 are placed into the ground at the contamination site 310. In some embodiments, anaerobic dehalogenating bacteria are present at contamination site 310. In other embodiments, anaerobic dehalogenating bacteria are provided to contamination site 310. Cathode 331 is placed underground at the contamination site in a zone that has been saturated with groundwater 321. In some embodiments, an anode chamber 332 comprising anode 330 is placed underground in an unsaturated zone 320. In other embodiments, anode 330 is placed in saturated zone 321.

Anode 330 and cathode 331 are coupled to a power source 350. Organic-containing wastewater 340 is provided to anode chamber 332, and anode-respiring bacteria transfer electrons from organic-containing wastewater 340 to the anode 330. Organic-containing wastewater 340 is then returned to a wastewater pipeline 360, where it may continue on to a wastewater treatment plant 361. Hydrogen molecules generated at cathode 331 are delivered to the anaerobic dehalogenating bacteria at contamination site 310. In some embodiments, a gas diffusion membrane may be used at cathode 331 to increase the effectiveness of hydrogen delivery.

Another embodiment of a system 400 for dehalogenating organohalides is depicted in FIG. 4. This embodiment is similar to the embodiment depicted in FIG. 1. However, instead of delivering hydrogen from the MEC to the contaminated groundwater, the contaminated groundwater is pumped directly into a cathode chamber 441. In one embodiment, an anode chamber 431 and cathode chamber 441 are located on the surface, but in other embodiments anode chamber 431, cathode chamber 441, or both may be located underground. In one embodiment, both hydrogen generation and dehalogenation occur in cathode chamber 441. This embodiment comprises an anode 430, anode chamber 431, a biofilm comprising anode-respiring bacteria 432, a cathode 440, cathode chamber 441, a power source 450, a source of organic-containing wastewater 420, a source of groundwater that has been contaminated with an organohalide 461, and a pump 460.

Organic-containing wastewater 420 is provided to anode chamber 431 containing anode 430. A biofilm comprising anode-respiring bacteria 432 is coupled to anode 430. The anode-respiring bacteria present in biofilm comprising anode-respiring bacteria 432 transfer electrons from organic-containing wastewater 420 to anode 430. The transfer of electrons from organic-containing wastewater 420 yields hydrogen ions. The electrons from organic-containing wastewater 420 move through a circuit 451 to cathode 440, which is located in cathode chamber 441. Organic-containing wastewater 420 is then returned to a wastewater pipeline 470 and continues on to a wastewater treatment plant 471.

Using pump 460, groundwater 461 that has been contaminated with an organohalide is pumped from a saturated region 480 into cathode chamber 441. Anaerobic dehalogenating bacteria 442 are provided in cathode chamber 441. Anaerobic dehalogenating bacteria 442 dehalogenate groundwater 461 using hydrogen molecules produced at cathode 440 as electron donors. The dechlorinated groundwater from cathode 440 may be returned to the subsurface or used as a clean water resource.

An embodiment of a method 500 of dehalogenating halogenated solvents is depicted in FIG. 5. In this embodiment, organic-containing wastewater is provided to anode-respiring bacteria coupled to an anode 510. Electrons are then generated in the anode 520. The electrons are transported to a cathode 530. Hydrogen molecules are then generated 540. The presence of anaerobic dehalogenating bacteria is detected at a contamination site 550. Hydrogen molecules are provided from the cathode to the anaerobic dehalogenating bacteria 560. The anaerobic dehalogenating bacteria then dehalogenate the contamination site 570.

In other embodiments, the method may comprise an additional step. If anaerobic dehalogenating bacteria are not detected at a contamination site, they may be provided to the contamination site.

A WORKING EXAMPLE

One skilled in the art may conduct TCE reduction tests with H₂ produced from a dual-chamber MEC having an anion exchange membrane, as shown in FIG. 6. Working volumes of each chamber may be 300 mL. One bundle of carbon fibers (24K Carbon Tow, FibreGlast, Ohio) may be used as the anode and a graphite rod (Mcmaster-carr, LA; diameter: 0.79 cm, and 7 cm long) may be used as the cathode. One bundle of the carbon fibers may consist of 24,000 fibers, having a geometric surface area per bundle of 530 cm². The specific surface area of the bundle may be 286,000 m²/m³. The carbon fibers may be cleaned with nitric acid, acetone, and ethanol for 3 days; 1 N nitric acid for 1 d, 1 N acetone for 1 d, and 1 N ethanol for 1 d in series.

Before being used in the MEC, the fibers may be cleansed with 18 MΩ deionized water. Acetate having a concentration of 25 mM may be used to model a source of organic-containing wastewater. The composition of the mineral medium may be, in units of milligrams per L of deionized water: KH₂PO₄ 3,200 mg/L, Na₂HPO₄ 12,400 mg/L, NaCl 1,600 mg/L, NH₄Cl 380 mg/L, 5 mg EDTA, 30 mg/L MgSO4.7H₂O, 5 mg/L MnSO4.H₂O, 10 mg/L NaCl, 1 mg/L CO(NO₃)₂, 1 mg/L CaCl₂, 0.001 mg/L ZnSO_4.7H₂O, 0.001 mg/L ZnSO_4.7H₂O, 0.1 mg/L CuSO_4.5H₂O, 0.1 mg/L AlK(SO₄)₂, 0.1 mg/L H₃BO₃, 0.1 mg/L Na₂MoO₄.2H₂O, 0.1 mg/L Na₂SeO₃, 0.1 mg/L Na₂WO₄.2H₂O, 0.2 mg/L NiCl₂.6H₂O and 1 mg/L FeSO₄.7H₂O.

The initial pH in the anode chamber may be 7.6±0.1. Deionized water having phosphate buffer of 100 mM at pH 7.6 may be used as a catholyte. The inoculum of the dual MEC may be the effluent from a mother MEC. A peristaltic pump (Masterflex L/S®, Cole-Parmer) may be used to transfer 50 mL of effluent to the dual MEC. Hydraulic retention time may be two hours.

An Ag/AgCl reference electrode (MF-2052, Bioanalytical Systems, Inc.) may be placed less than 1 cm distant from the anode bundle in the anode compartment. The anode potential may be fixed at −0.13 V vs a standard hydrogen electrode with a potentiostat (VMP3, Applied Princeton Research, TN) that provides the applied voltage for the MEC.

Using EC lab software, current, anode potential, cathode potential, and applied voltage values may be recorded every 120 seconds. Gas may be released from the top of a cathode compartment of the MEC, and its volume may be measured with a Milligas counter (Calibrated Instruments, Inc., NY).

The gas percentages of H₂ and CO₂ in off-gases may be measured with a gas-tight syringe (SGE 500 μL, Switzerland) using a gas chromatography (GC 2010, Shimadzu) equipped with a thermal conductivity detector. A packed column (ShinCarbon ST 100/120 mesh, Resteck Corporation) may be used for separating sample gases. Nitrogen may be used as the carrier gas, and the nitrogen may be fed at a constant pressure of 5.4 atm and a constant flow rate of 10 mL/min. The temperature conditions for injection, column, and detector may be 110° C., 140° C., and 160° C., respectively. Analytical grade H₂ and CO₂ may be used for standard calibration curves. Gas analyses may be carried out in duplicate.

The acetate concentration may be measured with high performance liquid chromatography (HPLC; Model LC-20AT, Shimadzu). An Aminex HPX-87H (Bio-Rad) column may be used for separating the simple acids and solvents. Sulfuric acid at 2.5 mM may be used as eluent, and fed at a flow rate of 0.5 mL/min. Chromatographic peaks may be detected using a photodiode-array (210 nm) and refractive index detectors. The total elution time may be 60 min, and the oven temperature may be held constant at 50° C. A new calibration curve may be established with standard solutions for all the compounds for every set of analyses. Assays may be performed in duplicate, and data may be reported as average concentrations.

In a first TCE test, H₂ gas produced from the MEC may be collected in a 160-mL serum bottle. The bottle may be connected for at least 1 day to ensure that air is pushed out and H₂ fills the bottle. The bottle may be moved into an anaerobic glove box (5% H₂ and 95% N₂). Ten mL of dechlorinating culture DehaloR̂2 and 90 mL of growth medium may be provided to the bottle.

One liter of medium may contain 10 mL of 100-fold concentrated salts stock solution, 1 mL trace elements solution A, and 1 mL trace elements solution B. 100-fold concentrated salts stock solution contains per liter: 100 g NaCl, 50 g MgCl2.6H2O, 20 g KH2PO4, 30 g NH4Cl, 30 g KCl, and 1.5 g CaCl2.2H2O. Trace element solution A contains per liter: 10 mL HCl (25% solution, w/w), 1.5 g FeCl2.4H2O, 0.19 g CoCl2.6H2O, 0.1 g MnCl2.4H2O, 70 mg ZnCl2, 6 mg H3BO3, 36 mg Na2MoO4.2H2O, 24 mg NiCl2.6H2O, and 2 mg CuCl2.2H2O. Trace element solution B contains per liter: 6 mg Na2SeO3.5H2O, 8 mg Na2WO4.2H2O, and 0.5 g NaOH.

Additionally, the medium is supplemented with 0.25 mL of 0.1% resazurin solution, 5 mM NaHCO₃, 0.2 mM L-cysteine, 0.2 mM Na₂S, 10 mL ATCC vitamin supplement for bacteriological culture media, and 5 mL of 20 mg/L vitamin B₁₂ solution, and 2 mM sodium acetate. The pH of the medium may be adjusted to 7-7.5 with 20% CO₂ and N₂ gas mix. Five μL neat TCE may be added. The bottle may be incubated in the dark at 30° C.

Using a gas chromatograph with a flame ionization detector (GC-FID), TCE, cis-DCE, 1,1-DCE, trans-DCE, VC, and ethene may be measured. A Shimadzu GC-2010 (Columbia, Md.) with an RtTM-QSPLOT capillary column (30 m×0.32 mm×10 μm, Restek, Bellefonte, Pa.) and a flame ionization detector (FID) may be used to analyze 200-μL headspace samples withdrawn from the serum bottle with a 500-μL gas-tight syringe (Hamilton Company, Reno, Nev.).

The initial oven temperature of 110° C. may be held for 5 minutes. The oven temperature may be raised at a gradient of 10° C./min to 150° C., then raised at a gradient of 20° C./min to 200° C., and then raised at a gradient of 5° C./min to 220° C. Then the oven temperature may be held at 220° C. for 5 min. The temperature of the FID and injector may be 240° C. The carrier gas may be ultra-high-purity helium. Ultra-high-purity hydrogen and zero-grade air may be used for the FID. The calibration curves for chlorinated compounds may be generated based on known masses of TCE, 1,1-DCE, cis-DCE, and trans-DCE. The calibration curves for VC and ethene may be established by directly injecting different volumes of 100-ppm and 1000-ppm gases into the GC with the gas-tight syringe.

FIG. 7 shows current generation at steady state in the MEC after 3 weeks. As a result of acetate oxidation by ARB that were well-developed on the anode fibers, the average current was 108±4 mA, which corresponds to 50±2 mL H₂/h. The effluent acetate concentration was from 16 to 18 mM. The H₂ composition of the off-gas ranged from 88%-90% without any CO₂ detected. Measured H₂ production rates accounted for 95-97% of the computed H₂ production rates. This confirms that the MEC produces H₂ gas without significant losses.

FIG. 8 shows the first batch run of TCE dechlorination to ethene using the DehaloR̂2 inoculum and H₂ from the MEC. Twenty mL H₂ from the MEC was injected into the serum bottle on day 0 and day 16. TCE disappeared completely in less than four days. cis-DCE was further reduced to VC by day 6. During the experiment, 1,1-DCE and trans-DCE were not detected at concentrations above 1.5 μmoles per 100 mL. VC accumulated by day 7, but by day 19, VC was completely converted to ethene, the only compound still detected in the headspace.

The pH of the medium decreased from 7.5 to 6.8 after complete dechlorination of the TCE. The first batch test shows that coupling dechlorination with H₂ production from MEC may result in successful detoxification of TCE into the harmless compound ethene.

In a second batch test, medium may be supplemented with 5 mM HEPES buffer to maintain the pH within an optimal range for dechlorination. The second bottle may be inoculated with 10 mL of DehaloR̂2 culture. FIG. 9 shows full reduction of TCE to ethene in 17 days with a final pH value of 7.13.

These proof-of concept experiments clearly show that an MEC can provide hydrogen for dechlorinating bacteria to reduce TCE to ethene. Thus, an electrolysis cell may be used to provide renewable hydrogen as donor for reductively dechlorinating DNAPL contaminants and other oxidized contaminants including, by way of non-limiting example, nitrate, nitrite, selenate, chromate, trichloroethane, chloroform, carbon tetrachloride, and bromate.

With the benefit of the present disclosure, those having skill in the art will comprehend that techniques claimed herein may be modified and applied to a number of additional, different applications, achieving the same or a similar result. The claims cover all such modifications that fall within the scope and spirit of this disclosure.

REFERENCES

Each of the following references is hereby incorporated by reference in its entirety:

61/074,852	Bicarbonate and Carbonate	Hyung-Sool Lee	Jun. 23, 2008
	as Hydroxide Carriers in the	Bruce Rittmann
	biological Fuel Cell	Cesar Torres
PCT/US2009/048274	Bicarbonate and Carbonate	Hyung-Sool Lee	Jun. 23, 2009
	as Hydroxide Carriers in a	Bruce Rittmann
	Biological Fuel Cell	Cesar Torres
61/106,225	Microbial Electrolytic Cell	Hyung-Sool Lee	Oct. 17, 2008
		Bruce Rittmann
		Cesar Torres
PCT/US09/59697	Microbial Electrolytic Cell	Hyung-Sool Lee	Oct. 06, 2009
		Bruce Rittmann
		Cesar Torres
61/167,394	Microbial Electrolytic Cell	Hyung-Sool Lee	Apr. 07, 2009
		Bruce Rittmann
		Cesar Torres
61/228,059	Microbial Cultures and	Rosa Krajmalnik-Brown	Jul. 23, 2009
	Methods For Anaerobic	Rolf Halden
	Bioremediation

Claims

1. (canceled)

2. A method of dehalogenating organohalides, comprising:

providing organic-containing wastewater to anode-respiring bacteria coupled to an anode;

generating electrons in the anode;

transporting electrons to a cathode;

providing electrons to hydrogen ions at the cathode;

generating hydrogen molecules;

providing hydrogen molecules to anaerobic dehalogenating bacteria at a contamination site, where the contamination site is contaminated with organohalides; and

dehalogenating the organohalides.

3. The method of claim 2, further comprising detecting anaerobic dehalogenating bacteria at the contamination site.

4. The method of claim 2, further comprising providing anaerobic dehalogenating bacteria to the contamination site.

5-8. (canceled)

9. A system for dehalogenating organohalides, comprising:

an electrolysis cell, the electrolysis cell being configured to generate hydrogen; a contamination site, where the contamination site is contaminated with chlorinated solvents:

anaerobic dehalogenating bacteria;

a distribution mechanism configured to distribute the hydrogen to the anaerobic dehalogenating bacteria;

where the electrolysis cell comprises:

a power supply;

an anode chamber containing an anode, the anode being coupled to the power supply;

anode-respiring bacteria coupled to the anode; and

a cathode chamber containing a cathode, the cathode being coupled to the power supply.

10. The system of claim 9 further comprising an ion-exchange membrane adjacent to the anode chamber and the cathode chamber;

11. The system of claim 9 where the electrolysis cell is a microbial electrolysis cell.

12. The system of claim 9 where the electrolysis cell is a biological electrolysis cell.

13. The system of claim 9 where the distribution mechanism comprises a gas-diffusion membrane.

14. The system of claim 9 where the distribution mechanism comprises a pump.

15. The system of claim 14 where the distribution mechanism is a manifold coupled to the pump.

16. The system of claim 9 where the anode comprises carbon fibers.

17. The system of claim 9 where the cathode comprises a graphite rod.

18. A system for dehalogenating organohalides, comprising:

a contamination site, where the contamination site is contaminated with organohalides, the contamination site comprising:

a first subsurface zone, where the first subsurface zone is saturated with groundwater;

and a second subsurface zone, where the second subsurface zone is not saturated with groundwater;

anaerobic dehalogenating bacteria;

a power supply;

a cathode, the cathode being coupled to the power supply, where the cathode is configured for placement in the first subsurface zone; and

an anode chamber configured to receive organic-containing wastewater, the anode chamber comprising:

an anode, the anode being coupled to the power supply; and

anode-respiring bacteria coupled to the anode.

19. The system of claim 18, where the anode chamber is configured for placement in the first subsurface zone.

20. The system of claim 18, where the anode chamber is configured for placement in the second subsurface zone.

21. The system of claim 18, where the first subsurface zone is a dense non-aqueous phase liquid zone.

22. The system of claim 18 where the anode comprises carbon fibers.

23. The system of claim 18 where the cathode comprises a graphite rod.

24. A system for dehalogenating organohalides, comprising:

a pump configured to pump water, the water being contaminated with organohalides; a power supply;

a cathode chamber, comprising:

anaerobic dehalogenating bacteria; and

a cathode coupled to the power supply;

where the cathode chamber is configured to receive water, the water being contaminated with organohalides, and where the cathode chamber is configured to generate hydrogen gas; and

an anode chamber configured to receive organic-containing wastewater, comprising: an anode coupled to the power supply; and

anode-respiring bacteria coupled to the anode.

25. The system of claim 24 where the anode comprises carbon fibers.

26. The system of claim 24 where the cathode comprises a graphite rod.