METHODS AND SYSTEMS FOR REMOVING TRICHLOROETHANE, TRICHLOROETHENE, AND 1,4-DIOXANE FROM CONTAMINATED WATER AND WASTEWATER

Abstract

The present invention is directed to systems and methods for removing trichloroethane (TCA), trichloroethene (TCE), and 1,4-dioxane (1,4-D) from contaminated water and wastewater. The system and methods relying on catalyst reduction of TCA and TCE, and the reduced products are degraded by microorganisms that are capable of biodegrading ethane and 1,4-D. In certain embodiments, a catalyst film comprises precious nanoparticles with diameters of 5-40 nm and a biofilm comprising microorganisms that are capable of degrading ethane and 1,4-D are used in a dual-reactor system to remove TCA, TCE, and 1,4-D from contaminated water and wastewater.

Claims

1. A system for removing trichloroethane (TCA), trichloroethene (TCE), and 1,4-dioxane (1,4-D) contaminants from a fluid, comprising: a first reactor and a second reactor, wherein: the first reactor and the second reactor are in fluid connection; the first reactor comprises: a catalyst film that reduces TCA and TCE, the catalyst film comprising precious metal nanoparticles with diameters of 5-40 nm; a first nonporous membrane comprising a gas-phase side and a liquid-phase side, wherein the catalyst film is deposed on the liquid-phase side of the first nonporous membrane; and a hydrogen (H.sub.2) gas source, wherein the H.sub.2 gas source delivers hydrogen to the gas-phase side of the first nonporous membrane and the precious metal nanoparticles and the H.sub.2 gas catalyze the reduction of TCA and TCE; and the second reactor comprises: a biofilm that oxidizes 1,4-D; a second nonporous membrane comprising gas-phase side and a liquid-phase side, wherein the biofilm is deposed on the liquid-phase of the second nonporous membrane; and an oxygen (O.sub.2) gas source, wherein the O.sub.2 gas source delivers oxygen to the gas-phase side of the second non-porous membrane.

2. The system of claim 1, wherein the catalyst film consists of precious metal nanoparticles with a mean diameter of less than 19 nm.

3. The system of claim 1, wherein the biofilm comprises microorganisms capable of degrading ethane and 1,4-D.

4. (canceled)

5. (canceled)

6. (canceled)

7. The system of claim 1, wherein fluid flows from the first reactor to the second reactor.

8. The system of claim 1, wherein the fluid flows at a hydraulic retention time (HRT) of no more than 24 hours.

9. The system of claim 1, wherein the precious metal is a platinum group metal or palladium.

10. A method of removing trichloroethane (TCA), trichloroethene (TCE), and 1,4-dioxane (1,4-D) contaminants from a fluid, the method comprising: contacting a fluid comprising TCA and TCE with a catalyst film to produce a fluid comprising 1,4-D, wherein the catalyst film comprises precious metal nanoparticles with diameters of 5-40 nm; and contacting the fluid comprising 1,4-D with a biofilm to produce a fluid comprising CO.sub.2, wherein the biofilm comprises microorganisms capable of degrading 1,4-D.

11. The method of claim 10, further comprising: providing a first nonporous membrane, wherein the first nonporous membrane comprises a gas-phase side and a liquid-phase side; contacting the liquid-phase side of the first nonporous membrane with a catalyst-precursor medium, the catalyst-precursor medium comprising a precious metal salt and a solvent; and contacting the gas-phase side of the first nonporous membrane with hydrogen (H.sub.2) gas at a sufficient partial pressure to convert at least 90% of the precious metal salt in the precious metal medium to elemental form, wherein the elemental form of the precious metal is in the form of a nanoparticles and is deposed on the liquid-phase side of the first nonporous membrane.

12. The method of claim 11, wherein the precious metal concentration in the catalyst-precursor medium is 0.01-100 mM.

13. The method of claim 11, wherein the pH of the catalyst-precursor medium is 6-8.

14. The method of claim 11, wherein the first nonporous membrane is in a first reactor.

15. The method of claim 10, further comprising: submerging a second nonporous membrane with a microorganism-enrichment medium comprising dissolved ethane and/or 1,4-D; contacting an inoculant with the second nonporous membrane, wherein the inoculant comprises microorganisms capable of degrading ethane and 1,4-D; and pressurizing the gas-phase side of the second nonporous membrane with oxygen (O.sub.2) gas at a desired partial pressure.

16. (canceled)

17. The method of claim 15, wherein the second nonporous membrane is in a second reactor.

18. The method of claim 10, wherein the fluid comprising TCA and TCE flows at a hydraulic retention time (HRT) of no more than 24 hours.

19. (canceled)

20. (canceled)

21. A method of establishing a catalyst film for reduction of trichloroethane (TCA) and trichloroethene (TCE), the method comprising: providing a nonporous membrane, wherein the nonporous membrane comprises a gas-phase side and a liquid-phase side; contacting the liquid-phase side of the nonporous membrane with a precious metal medium comprising a precious metal salt and a solven, wherein the concentration of the precious metal in the precious metal medium is 0.1-100 mM; and contacting the gas-phase side of the nonporous membrane with hydrogen (H.sub.2) gas at a sufficient partial pressure to convert at least 90% of the precious metal salt in the precious metal medium to elemental form; wherein the elemental form of the precious metal is in the form of nanoparticles with a diameter of 5-40 nm and the nanoparticles are deposed on the liquid-phase side of the nonporous membrane to form the catalyst film.

22. The method of claim 10, wherein the precious metal is a platinum group metal or palladium.

23. (canceled)

24. (canceled)

25. (canceled)

26. (canceled)

27. The system of claim 1, wherein the catalyst film consists of palladium nanoparticles.

28. The method of claim 11, wherein the precious metal salt consists of palladium salts.

29. The system of claim 1, wherein the biofilm comprises bacteria from: at least one family selected from the group consisting of Rhodocyclaceae, Pseudonocardiaceae, Brandyrhizobiaceae, and Chitinophagaceae, or at least one genus selected from the group consisting of: Methyloversatilis, Pseudonocardia, Bradyrhizobium.

30. The system of claim 1, wherein the biofilm comprises Methyloversatilis.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1A illustrates a schematic of a bench-scale form of the first reactor of the system in accordance with certain embodiments described herein. (1) Glass tube containing a fiber bundle; (2) recirculation pump; (3) liquid sampling port; (4) airtight bottle with headspace for gas sampling; and (5) palladium nanoparticles (PdNPs) coated on fiber surfaces.

[0024] FIG. 1B depicts, in accordance with certain embodiments, a scanning electron microscopic (SEM) image of PdNPs coated on fiber surfaces.

[0025] FIG. 1C depicts, in accordance with certain embodiments, the size distribution histogram of the PdNPs coated on fiber surfaces.

[0026] FIG. 1D depicts, in accordance with certain embodiments, the (energy-dispersive X-ray (EDX) spectrum of PdNPs coated on fiber surfaces.

[0027] FIG. 1E depicts, in accordance with certain embodiments, the X-ray diffraction (XRD) spectrum of PdNPs coated on fiber surfaces.

[0028] FIG. 2A depicts, in accordance with certain embodiments, TCA and TCE removal and selectivity to ethane at steady states during continuous treatment of TCE-contaminated and TCE-contaminated water in the Cata-reactor at various concentrations (mM) of influent TCA/TCE.

[0029] FIG. 2B depicts, in accordance with certain embodiments, TCA and TCE removal and selectivity to ethane at steady states during continuous treatment of TCE-contaminated and TCE-contaminated water in the Cata-reactor at various H.sub.2 supply pressures (psig).

[0030] FIG. 2C depicts, in accordance with certain embodiments, TCA and TCE removal and selectivity to ethane at steady states during continuous treatment of TCE-contaminated and TCE-contaminated water in the Cata-reactor at various pH values.

[0031] FIG. 2D depicts, in accordance with certain embodiments, TCA and TCE removal and selectivity to ethane at steady states during continuous treatment of TCE-contaminated and TCE-contaminated water in the Cata-reactor at various hydraulic retention times (HRT, hour).

[0032] FIG. 3A-1 depicts, in accordance with certain embodiments, 1,4-D degradability by Rhodococcus ruber 219 without an added carbon source and electron donor.

[0033] FIG. 3A-2 depicts, in accordance with certain embodiments, 1,4-D degradability by R. ruber 219 with acetate as the carbon source and electron donor.

[0034] FIG. 3A-3 depicts, in accordance with certain embodiments, 1,4-D degradability by R. ruber 219 with ethane as the carbon source and electron donor.

[0035] FIG. 3B-1 depicts, in accordance with certain embodiments, 1,4-D degradability by wastewater treatment plant (WWTP) activated sludge without an added carbon source and electron donor.

[0036] FIG. 3B-2 depicts, in accordance with certain embodiments, 1,4-D degradability by WWTP activated sludge with acetate as the carbon source and electron donor.

[0037] FIG. 3B-3 depicts, in accordance with certain embodiments, 1,4-D degradability by WWTP activated sludge with ethane as the carbon source and electron donor.

[0038] FIG. 3C-1 depicts, in accordance with certain embodiments, 1,4-D degradability by landfill leachate without an added carbon source and electron donor.

[0039] FIG. 3C-2 depicts, in accordance with certain embodiments, 1,4-D degradability by landfill leachate with acetate as the carbon source and electron donor.

[0040] FIG. 3C-3 depicts, in accordance with certain embodiments, 1,4-D degradability by landfill leachate with ethane as the carbon source and electron donor.

[0041] FIG. 3D-1 depicts, in accordance with certain embodiments, 1,4-D degradability by wetland sediment without an added carbon source and electron donor.

[0042] FIG. 3D-2 depicts, in accordance with certain embodiments, 1,4-D degradability by wetland sediment with acetate as the carbon source and electron donor.

[0043] FIG. 3D-3 depicts, in accordance with certain embodiments, 1,4-D degradability by wetland sediment with ethane as the carbon source and electron donor.

[0044] FIG. 4A depicts, in accordance with certain embodiments, the concentration profile of ethane during the initial 70 days of continuous operation at HRT of 15 hours after the bioreactor was inoculated with ethanotrophic biomass enriched from wetland sediments.

[0045] FIG. 4B depicts, in accordance with certain embodiments, the concentration profile of 1,4-D during the initial 70 days of continuous operation at HRT of 15 hours after the bioreactor was inoculated with ethanotrophic biomass enriched from wetland sediments.

[0046] FIG. 5 depicts, in accordance with certain embodiments, a schematic of the synergistic bioreactor system comprising a reactor with a catalyst film (Cata-reactor) and a reactor with an ethane-oxidizing biofilm (Bio-reactor).

[0047] FIG. 6 depicts, in accordance with certain embodiments, substrate concentrations in the synergistic system. The dashed horizontal lines represent the influent concentration of 1,4-dioxane, TCA, and TCE. The solid triangles represent the substrate concentration from Cata-reactor to Bio-reactor, including 1,4-dioxane, TCA, TCE, DCA, MCA and ethane. The dots represent the corresponding effluent concentration of different substrates.

[0048] FIGS. 7A and 7B depict, in accordance with certain embodiments, the composition of the inoculant and biofilm. FIG. 7A shows the bacterial community of the inoculum and biofilms of phases 0, III, and IV. Phylotypes are presented at the family level based on 16S rRNA gene amplicon sequencing. FIG. 7B shows the dominant phylotypes at the genus level in biofilm of phases 0, III, and IV.

DETAILED DESCRIPTION OF THE INVENTION

[0049] Detailed aspects and applications of the invention are described below in the drawings and detailed description of the invention. Unless specifically noted, it is intended that the words and phrases in the specification and the claims be given their plain, ordinary, and accustomed meaning to those of ordinary skill in the applicable arts.

[0050] In the following description, and for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the various aspects of the invention. It will be understood, however, by those skilled in the relevant arts, that the present invention may be practiced without these specific details. It should be noted that there are many different and alternative configurations, devices and technologies to which the disclosed inventions may be applied. The full scope of the inventions is not limited to the examples that are described below.

[0051] The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a step” includes reference to one or more of such steps.

[0052] The term “about” when used in the context of numeric values denotes an interval of accuracy that is familiar and acceptable to a person skilled in the art. The interval is ±10% of the given numeric value, ±5% of the given numeric value, or ±2% of the given numeric value.

[0053] As used herein, the term “precious metal” refers to gold (Au), silver (Ag), and platinum group metals (PGM). The members of PGM include platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), osmium (Os), and iridium (Ir).

[0054] As used herein, the terms “precious metal-film” and “catalyst film” refer to a film of precious metal nanocatalysts.

[0055] Currently, no physical-chemical treatment method or biological treatment method exist that can efficiently destroy trichloroethane (TCA), trichloroethene (TCE), and 1,4-dioxane (1,4-D). While TCA, TCE, and 1,4-dioxane often occur together in contaminated water and wastewater, these contaminants inhibit each other’s biodegradation. Described herein are methods and systems for removing TCA, TCE, and 1,4-D from contaminated water or wastewater by taking advantage of catalytic and biological processes for synergistic removal of TCA, TCE, and 1,4-D. Specifically, the described methods and systems address the current deficiencies in commercial application of removing TCA, TCE, and 1,4-D from contaminated water and wastewater by efficiently converting TCA and TCE into harmless ethane and Cl.sup.-. TCA and TCE is initially converted to 1,4-D via by catalysis in a first reactor (also referred to herein as a “Cata-reactor” or “H.sub.2-MCfR”), and then converting 1,4-D into harmless CO.sub.2 in a second reactor (also referred to herein as a “Bio-reactor” or “O.sub.2-MBfR”) by microbial biodegradation.

1. Synergistic System for Removal of TCA, TCE, and 1,4-D

[0056] In one embodiment, the system comprises a first reactor for H.sub.2-induced reduction of TCA and TCE and a second reactor for O.sub.2-induced oxidization of 1,4-D. The first reactor catalytically reduces TCA and TCE. The second reactor utilizes biological processes to oxidize 1,4-D. The first reactor is fluidly connected to the second reactor, wherein the effluent of the first reactor is the influent of the second reactor. In certain implementations, the influent of the concentration of TCA and TCE to the first reactor is less than 400 .Math.M total or the concentration of TCA is less 200 .Math.M and the concentration of TCE is less 200 .Math.M. In some embodiments, the first reactor is a reactor with catalysts (“Cata-reactor”), and a second reactor is reactor with microorganisms (“Bio-reactor”).

[0057] In certain nonlimiting embodiments, the system comprises at least one membrane, a hydrogen-gas source, and an oxygen-gas source. In some aspects, the first reactor comprises a membrane and a hydrogen (H.sub.2) gas source, while the second reactor comprises a membrane and an oxygen (O.sub.2) gas source. In certain implementations, the first reactor comprises a membrane, a catalyst film, and a H.sub.2 gas source, while the second reactor comprises a membrane, a biofilm, and an O.sub.2 gas source. The catalyst film and the biofilm are each anchored on the membrane of their respective reactor. Accordingly, the catalyst film is anchored on an H.sub.2-delivering membrane, while the biofilm is anchored on an O.sub.2-delivering membrane. In other words, the catalyst film is deposed on the liquid-phase side of the membrane of the first reaction, while the biofilm is deposed on the liquid-phase side of the membrane of the second reactor.

[0058] The catalyst film reduces TCA and TCE and comprises precious metal nanoparticles with a mean diameter of 15-20 nm. In some aspects, the diameters of the precious metal nanoparticles are between 5-40 nm. In some aspects, at least 80% of the precious metal nanoparticles have diameters of less than 25 nm. In particular embodiments, the mean diameter of the precious metal nanoparticles is about 19 nm. In some aspects, the catalyst film consists of the precious metal nanoparticles. In certain embodiments, the precious metal nanoparticles are monometallic palladium nanoparticles (PdNPs). Accordingly, in some aspects, the catalyst film is a Pd-film, which consist of monometallic palladium nanoparticles. To form the catalyst film, the H.sub.2 gas in the first reactor functions as the electron donor to drive reduction of the soluble precious metals (with an oxidation state of +2 or +3) to elemental precious metals (with an oxidation state of 0), which spontaneously deposit as catalysts on the liquid-phase side of a membrane. In some aspects, the catalyst film is deposed directly on the liquid-phase side of the membrane.

[0059] The biofilm biodegrades or oxidizes 1,4-D. In some aspects, the biofilm comprises ethane-oxidizing bacteria. In some embodiments, the biofilm comprises bacteria from at least one genus selected from the group consisting of: Methyloversatilis, Pseudonocardia, Bradyrhizobium and Rhodoccoccus. In some aspects, the biofilm comprises bacteria from at least one genus selected from the group consisting of: Methyloversatilis, Pseudonocardia, and Bradyrhizobium. The biofilm is also deposed on the liquid-phase side of a membrane. In some aspects, the biofilm is deposed directly on the liquid-phase side of the membrane.

[0060] In some implementations, for example, to establish a system for synergistic removal of TCA, TCE, and 1,4-D, the system further comprises a catalyst-precursor medium, a microorganism-enrichment medium, and an inoculant comprising a biofilm-forming population of microorganisms. For example, the first reactor comprises a catalyst-precursor medium, while the second reactor comprises a microorganism-enrichment medium and an inoculant comprising a biofilm-forming population of microorganisms.

[0061] Compared to other TCA/TCE-removing technologies, such as advanced oxidation, photocatalysis processes, and biological processes, the Cata-reactor is inexpensive to operate in that the only reagent that needs to be continuously supplied is H.sub.2 gas. H.sub.2 gas is nontoxic and can be generated on-site and on-demand. Furthermore, on-demand delivery of H.sub.2 gas in a bubble-free form enabled by the nonporous membrane is safe, efficient, controllable, and prevents stripping volatile TCA and TCE. Another improvement of the Cata-reactor over the current technologies for removing TCA and TCE is that the Cata-reactor requires no input of energy-consumables or environmentally unfriendly reagents, such as UV light, ozone, hydrogen peroxide, or peroxysulfates. Accordingly, the Cata-reactor results in substantial saving of energy and cost in catalyst synthesis compared to conventional abiotic synthesis approaches with high energy input yet low catalyst yield. Additionally, reducing TCA and TCE using the Cata-reactor does not encounter the problem in bioreduction of TCA and TCE, for which the TCA and TCE mutually inhibit their reductions. Furthermore, reducing TCE using the Cata-reactor does not produce toxic intermediates like vinyl chloride during bioreduction of TCE.

[0062] Compared to existing technologies for removing 1,4-D, the Bio-reactor does not require energy demand for aeration, which accounts for the greatest portion of operation costs of conventional aerobic treatment. The Bio-reactor also does not require the addition of organic carbon and therefore does not result in secondary contamination. Because O.sub.2 is provided on demand in the bioreactor, cost can also be controlled for optimal performance. Additionally, residual reductive dechlorination products from TCA and TCE are mineralized in the Bio-reactor. The combined use of the Cata-reactor with the Bio-reactor minimizes inhibition of chlorinated hydrocarbons (TCA and TCE and the undesired chlorinated intermediates) on 1,4-D biodegradation.

a. Membrane

[0063] The membrane used in the first reactor and the second reactor typically do not have pores in its wall (e.g., a nonporous membrane). The lack of pores in the membrane enables transferring gas (e.g., hydrogen or oxygen) in a bubble-free form at controllable rates. In some embodiments, the membrane is a hollow-fiber membrane. In such embodiments, gas is supplied to the lumen of the hollow-fiber membrane (the gas-phase side). Accordingly, catalyst film or biofilm would be anchored to the outer surface of the hollow-fiber membrane (the liquid-phase side). In other embodiments, the membrane is a flat- or curled-sheet membrane. In such embodiments, gas (for example, hydrogen for the first reactor and oxygen for the second reactor) is supplied to one side of the sheet membrane (the gas-phase side), while catalyst film or biofilm anchored to the other surface of the sheet membrane (the liquid-phase side).

[0064] The membrane may be made of a variety of polymeric materials, for example polypropylene, polyurethane, polysulfone, or composite forms. In certain embodiments, the thickness of the gas transfer membrane is may be 50-70 .Math.m, for example between 50-55 .Math.m.

[0065] In particular embodiments, the gas transfer membrane is a nonporous polypropylene hollow-fiber membrane (200 .Math.m OD, 100-110 .Math.m ID, wall thickness 50-55 .Math.m).

b. Catalyst-Precursor Medium

[0066] The catalyst-precursor medium provides the soluble precious metals (with an oxidation state of +2 or +3) for the production of the catalyst film. The catalyst-precursor medium comprises at least one precious metal precursor/salt, for example, gold (Au), silver (Ag), platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), osmium (Os), or iridium (Ir). In certain embodiments, the precious metal precursor is any chemical that rapidly dissolve in the solvent and release soluble precious metal ions (for example, Ru.sup.3+ released from ruthenium chloride (RuCl.sub.3)) or soluble precious metal complexes of various ligands (for example, (PdCl.sub.4).sup.2+ released from sodium tetrachloropalladate (Na.sub.2PdCl.sub.4)). The precious metal concentration is applied in a range of 0.01-100 mM. In certain embodiments, the precious metal concentration range in the catalyst-precursor medium is 0.1-5 mM, for example, about 0.1 mM, 0.1 ± 0.05 mM or 0.94 mM. In some embodiments, the catalyst-precursor medium comprises acids (for example, hydrochloric acid), bases (for example, sodium hydroxide), and/or pH buffers (for example, potassium phosphate species) to adjust the pH to a desired value in the range of 4-10. In particular embodiments, the pH range of the catalyst-precursor medium is 6-8.

[0067] In some aspects, the catalyst-precursor medium comprises a liquid solvent. The liquid solvent may be water, salt solution, hydrochloric acid, methanol, ethanol, acetonitrile, toluene, dichloromethane, chloroform, or tetrahydrofuran. In certain embodiments, the liquid solvent is deionized water.

c. Microorganism-Enrichment Medium

[0068] The microorganism-enrichment medium stimulates sufficient microbial growth to establish and/or maintain the biofilm. The microorganism-enrichment medium comprises dissolved ethane as the primary carbon source. In some embodiments, the medium comprises 1,4-D as the secondary electron donor and carbon source. In certain aspects, the microorganism-enrichment medium comprises salts of a full spectrum of macronutrients, such as calcium (Ca), magnesium (Mg), phosphorus (P), sodium (Na), potassium (K), and iron (Fe). In some aspects, the growth medium also comprises salts of micronutrients, for example, zinc (Zn), manganese (Mn), boron (B), cobalt (Co), copper (Cu), nickel (Ni), molybdenum (Mo), and selenium (Se). In other embodiments, the growth medium comprises mixed phosphate salts (for example, H.sub.3PO.sub.4, NaH.sub.2PO.sub.4, Na.sub.2HPO.sub.4, and Na.sub.3PO.sub.4) as pH buffers.

d. Inoculant

[0069] The inoculant comprises microorganisms capable of degrading ethane and 1,4-D. The microorganisms in the inoculant form a biofilm that is anchored to the membrane. In some embodiments, the inoculant is lake sediments, wetland sediments, or mixtures thereof. In other embodiments, the inoculant comprises at least one pure strain, activated sludge collected from aerobic zones of wastewater treatment plants, landfill leachate, or their mixtures.

[0070] In some aspects, the inoculant comprises bacteria from at least one family selected from the group consisting of Rhodocyclaceae, Pseudonocardiaceae, Brandyrhizobiaceae, and Chitinophagaceae. In certain embodiments, the inoculant comprises bacteria from at least one genus selected from the group consisting of: Methyloversatilis, Pseudonocardia, Bradyrhizobium and Rhodoccoccus. In particular embodiments, the inoculant comprises Methyloversatilis.

e. H.SUB.2.-gas source

[0071] The H.sub.2-gas source can be any reliable source of H.sub.2 gas for the first reactor, for examples, a gas storage tank having pressurized H.sub.2 gas, a H.sub.2 generator via water electrolysis, or a methane reformer. In some embodiments, the H.sub.2 purity is over 99%. In other embodiments, the H.sub.2-gas source include a built-in or external gas pressure regulator. The gas pressure regulator regulates the pressure of H.sub.2 gas from the gas storage tank to the gas-phase side of the membrane in the first reactor. In some aspects, the H.sub.2-gas source delivers H.sub.2 gas to the gas-phase side of the membrane in the first reactor at partial pressures of 1-10 psig, for example about 3 psig or 3 ± 0.25 psig for establishing the catalyst film and 3-5 psig for reduction of TCA and TCE.

f. O.SUB.2.-gas source

[0072] The O.sub.2-gas source can be any reliable source of O.sub.2 gas for the second reactor, for example, a gas storage tank having pressurized O.sub.2 gas or air, an air pump, or an O.sub.2-gas generator. In some embodiments, the O.sub.2 purity is over 99%. In other embodiments, the O.sub.2 source can be air (~21% O.sub.2). The O.sub.2-gas source includes a built-in or external gas pressure regulator. The gas pressure regulator regulates the pressure of O.sub.2 gas from the O.sub.2-gas source to the gas-phase side of the membrane in the second reactor. In some aspects, the O.sub.2-gas source delivers O.sub.2 gas to the gas-phase side of the membrane in the second reactor at partial pressures of 1-15 psig, for example about 10 psig for establishing the biofilm and around 3 psig for biodegradation of 1,4-D.

2. Methods for Removal of TCA, TCE, and 1,4-D

[0073] The method of removing TCA, TCE, and 1,4-D comprises reducing TCA and TCE in an H.sub.2-induced reaction catalyzed by precious metals and oxidizing 1,4-D in an O.sub.2-induced reaction mediated by microorganisms. The method be easily and accurately regulated to achieve minimal residues of TCA and TCE that inhibit subsequent 1,4-D biodegradation and maximize production of ethane that promote 1,4-D biodegradation. The regulations include adjusting the H.sub.2 gas provided to the Cata-reactor, the pH of fluid comprising TCA, TCE, and 1,4-D that is provided to the Cata-reactor, the concentration of TCA, TCE, and/or 1,4-D in the fluid provided to the system and thus the Cata-reactor, and the hydraulic retention time (HRT) of the fluid provided to the system and thus the Cata-reactor. In particular implementations, the pH of the fluid comprising TCA and TCE (the influent to the Cata-reactor) is about 7, and the mole ratio of ethane to 1,4-D in the effluent of the Cata-reactor (thus influent to the Bio-reactor) is 300. In certain implementations, the partial pressure of H.sub.2 gas provided to the Cata-reactor is 3-5 psig, for example, about 3 psig, 3 ± 0.3 psig, about 4 psig, 4 ± 0.4 psig, about 5 psig or 5 ± 0.5 psig. In certain implementations, the partial pressure of O.sub.2 gas provided to the Bio-reactor is 1-3 psig, for example, about 1 psig, 1 ± 0.2 psig, about 2 psig, 2 ± 0.2 psig, about 3 psig, or 3 ± 0.3 psig.

[0074] In some implementations, the method comprises establishing a catalyst film in a first reactor and establishing a biofilm in a second reactor, wherein the catalyst film reduces TCA and TCE and the biofilm causes the oxidation of 1,4-D. In some aspects, the precious metal catalysts are deposed on a nonporous Hz-delivery membrane as catalyst film, while the microorganisms are deposed on a nonporous O.sub.2-delivery membrane as biofilm.

[0075] The method of generating a catalyst film comprises providing an aqueous system comprising nonporous membrane; providing the system with catalyst-precursor medium to submerge the membrane into the solution of precious metal precursors; and pressurizing the gas-phase side of the membrane with H.sub.2 at desired partial pressure. In some aspects, the desired partial pressure of H.sub.2 gas to establish the catalyst film is 1-5 psig, for example, 2-4 psig, about 3 psig, 3 ± 0.3 psig, or 3 psig. The H.sub.2 gas donates electrons for the reduction of the soluble precious metals in the catalyst-precursor medium to elemental precious metals, which spontaneously deposit as catalysts on the membrane, particularly the liquid-phase side of the membrane. This coating of precious metal nanoparticles deposed on the membrane is the catalyst film, which is capable of reducing TCA and TCE. In certain embodiments, the loading density of the catalyst film is about 0.07 mmol/m.sup.2 or about 7.7 mg/m.sup.2.

[0076] In some aspects, the method of generating a catalyst film is a method of establishing the first reactor. In particular implementations, this method comprises contacting the liquid-phase side of the nonporous membrane with a catalyst-precursor medium. Meanwhile, the gas-phase side of the nonporous membrane is contacted with H.sub.2 gas at a sufficient partial pressure to convert at least 90% of the precious metal salt in the catalyst-precursor medium to elemental form with a mean diameter of 15-20 nm. In some aspects, at least 99% of the precious metal salt in the catalyst-precursor medium is converted to elemental form. In particular embodiments, the gas-phase side of the nonporous membrane is contacted with H.sub.2 gas at a sufficient partial pressure to convert the precious metal salt in the catalyst-precursor medium to elemental form nanoparticles with diameters of 5-40 nm. In some aspects, the desired partial pressure of H.sub.2 gas to establish the catalyst film is 1-5 psig, for example, 2-4 psig, about 3 psig, or 3 psig. In certain embodiments, the loading density of the catalyst film is about 0.07 mmol/m.sup.2 (about 7.7 mg/m.sup.2) or 0.07 ± 0.007 mmol/m.sup.2 (7.7 ± 0.08 mg/m.sup.2).

[0077] The method of generating a biofilm is a method of establishing the second reactor. This method comprises submerging a nonporous membrane with a microorganism-enrichment medium; contacting an inoculant with the nonporous membrane; and pressurizing the gas-phase side of the membrane with O.sub.2 at desired partial pressure. In some aspects, the desired partial pressure of O.sub.2 gas to establish the biofilm is 5-15 psig, 8-12 psig, 9-11 psig, or about 10 psig. The second reactor is continuously or repeatedly feed with the microorganism-enrichment medium. In some embodiments, the microorganism-enrichment medium is provided to the inoculated aqueous system at a HRT of 0.1-48 hours. In some embodiment, the HRT is between 4-20 hours. In other embodiments, the system is continuously fed with the microorganism-enrichment medium for 2-24 weeks.

ILLUSTRATIVE, NON-LIMITING EXAMPLES IN ACCORDANCE WITH CERTAIN EMBODIMENTS

[0078] The disclosure is further illustrated by the following examples that should not be construed as limiting. The contents of all references, patents, and published patent applications cited throughout this application, as well as the Figures, are incorporated herein by reference in their entirety for all purposes.

1. Formation of Pd-Film on Hz-Delivering Membrane in Cata-Reactor

[0079] The schematic in FIG. 1A shows the configuration of a bench-scale Cata-reactor. It had a total working volume of 80 mL (60 mL liquid phase and 20 mL headspace) and contained two bundles of 240 identical hollow-fiber membranes in two glass tubes (6 mm internal diameter and 27 cm length). Nonporous polypropylene fiber with 200 .Math.m OD, 100-110 .Math.m ID, and 50-55 .Math.m wall thickness (Teijin, Ltd., Japan) was used. H.sub.2 gas (>99.9%) was supplied to both ends of each fiber bundle at a pressure controlled by a pressure regulator. Solute concentrations inside the Cata-reactor were equal to its effluent concentrations due to mixing from a recirculation rate of 150 mL/min created by using a peristaltic pump (Masterflex, USA). A 30-mL serum bottle was set between two tubes to create gas-liquid interface; this enabled the volatile organic compounds (TCA, TCE, and their reduction products) to reach equilibrium of partitioning between the liquid phase and the headspace where gaseous samples were collected using a gas-tight syringe (Hamilton, USA).

[0080] A “fresh” coating of palladium nanoparticles (PdNPs) on the fibers was prepared right before testing TCA/TCE reduction in the Cata-reactor. The Cata-reactor was fed with a deoxygenated Na.sub.2PdCl.sub.4 solution containing ~10 mg/L of Pd(II) after purging the Cata-reactor with N.sub.2 gas for 15 minutes. After the Cata-reactor was filled with the Pd solution, H.sub.2 was provided and recirculation resumed, leaving the Cata-reactor in batch mode until most of the soluble Pd(II) was autocatalytically reduced to insoluble Pd.sup.0 and precipitated on the fiber surfaces. Thus, the Pd-film is spontaneously deposited on the liquid-phase side of the gas transfer membrane in the presence of H.sub.2 gas and the solution containing ~10 mg/L of Pd(II).

[0081] FIGS. 1B-1E present solid-state characteristics of 8 mg/m.sup.2 PdNPs autocatalytically synthesized and spontaneously coated on surfaces of the gas-transfer fiber membranes. An scanning electron microscopy (SEM) image of the fiber surface (FIG. 1B) shows that the PdNPs were well dispersed as a thin layer on the fiber surface. Over 80% of the particles were less than 25 nm in diameter (FIG. 1C), yielding to an average size of 19.0 nm. The energy dispersive X-ray analysis (EDX) spectrum (FIG. 1D) confirms the presence of Pd on the fiber surface. The X-ray diffraction (XRD) pattern (FIG. 1E) reveals major diffraction peaks at 40.0° (1 1 1), 46.5° (2 0 0), and 68.1° (2 2 0); this further confirms the predominant presence of the Pd.sup.0 crystal structure with dominant facets of {1 1 1}.

[0082] The Cata-reactor was continuously fed with TCA- and TCE-containing water at varied flow rates, influent substrate concentrations, pH, and H.sub.2 pressures for three months. The steady-state results summarized in FIGS. 2A-2D demonstrate that catalytic efficiency and selectivity of TCA and TCE reduction were sensitively affected by H.sub.2 pressure and surface loading (determined by flow rate or HRT at a certain influent concentration). For example, Higher TCA/TCE loading (e.g. higher influent concentration in FIG. 2A or shorter HRT in FIG. 2D) lowered selectivity to ethane, while heavier H.sub.2 supply (FIG. 2B) not only accelerated TCA removal but also enhanced selectivity to ethane.

2. Formation of Biofilm on O.SUB.2.-Delivering Membrane in Bio-R3eactor

[0083] Consortia capable of 1,4-dioxane biodegradation were screened from four different types of cultures: 1) pure strain of Rhodococcus ruber 219 purchased from Deutsche Sammlung von Mikroorganismen und Zellkulturen (DSMZ, Germany); 2) aerobic activated sludge collected from Mesa Northwest Wastewater Reclamation Plant (Mesa, AZ, USA); 3) landfill leachate collected from Salt River Landfill (Scottsdale, AZ, USA); and 4) wetland sediments collected from Tres Rios Flow-Regulating Wetlands (Tolleson, AZ, USA). The basic medium plus 1,4-D and acetate or ethane as the primary electron donor were distributed into 160-mL serum bottles, aerated with pure O.sub.2 gas, and inoculated with the cultures separately.

[0084] For the Bio-reactor configuration, setup, and inoculation, a bench-scale Bio-reactor was set up and inoculated with the enriched biomass capable of 1,4-D degradation. The configuration of the Bio-reactor was identical to the Cata-reactor except that the fiber material was composite polyethylene and polyurethane and the fiber lumens were pressurized with gaseous O.sub.2, not H.sub.2.

[0085] To test continuous 1,4-dioxane degradation in the Bio-reactor, the Bio-reactor was filled with the basic medium plus 0.5 mM 1,4-D and saturated with ethane (up to 58 mg/L or 1.9 mM soluble ethane after sparkling with pure ethane gas). The Bio-reactor was then inoculated with the ethanotrophic culture enriched from the wetland sediment. After leaving the reactor in batch overnight, the Bio-reactor was continuously fed with the medium (hydraulic retention time controlled at 15.0 ± 1.0 hours) to allow a biofilm to accumulate on the liquid-phase side of the gas transfer membrane.

[0086] Inoculum source and primary electron donor are important for the 1,4-D-degrading culture. FIGS. 3A-1 to 3D-3 shows the biodegradation of 1,4-D by four different inoculant sources in serum-bottles tests with no primary election donor or with acetate or ethane as the primary electron donor. The consortia from activated sludge and landfill leachate were not capable of degrading 1,4-D under any conditions during the initial 10 days (FIGS. 3B-1 to 3B-3 and 3C-1 to 3C-3) or even after months of incubation. The pure R. ruber 219 strain was able to degrade 1,4-D only when acetate was present as the primary electron donor, but it immediately lost the capacity of 1,4-D degradation once acetate was completely depleted after two days (FIG. 3A-2).

[0087] The consortium from the wetland sediment degraded on average 10% of the 1,4-D within 10 days when 1,4-D was introduced alone or with acetate (FIGS. 3D-1 and 3D-2, respectively). When ethane was present, this ethanotrophic consortium was able to degrade 1,4-D along with ethane, and over 50% of 1,4-D was depleted (FIG. 3D-3). Overall, using ethane as the primary substrate and wetland sediment as the inoculum are the most appropriate strategy for continuous stable 1,4-D degradation.

[0088] Continuous removal of 1,4-D and ethane occurred in the Bio-reactor inoculated with the ethanotrophic culture. FIG. 4 presents concentration profiles of ethane and 1,4-D during the continuous operation of the Bio-reactor. Upon inoculation, ethane was gradually consumed without noticeable delay. Substantial 1,4-D removal was not initiated until Day 25 when over 99.5% of the 1.9 mM ethane from the influent was depleted (i.e. effluent concentration <10 .Math.M). After then, 1,4-D began to be rapidly consumed. By Day 38, 1,4-D removal reached steady state at over 99.9% (i.e. effluent concentration below the detection limit of 0.6 .Math.M), and the removal remained almost over 99% for the following 32 days as the steady state.

[0089] Microbial community structures in the enriched biofilm. In the biofilm after the 70-day enrichment, the genera Methyloversatilis dominated the biofilm community with relative abundance of 77.0% and 48.7% before and after 1,4-D degradation, respectively. Methyloversatilis is typical methylotrophs that can utilize various single-carbon compounds as well as short chain alkanes (C2, C3, possibly C4-C5). This genus Methyloversatilis was ethanotrophs in the biofilm community. In addition, the relative abundance of the 1,4-D-oxidizing genus like Pseudonocardia and Bradyrhizobium were augmented (FIG. 7).

3. Synergistic Removal of TCA, TCE, and 1,4-D

[0090] The two reactors were connected by linking the effluent tube of the Cata-reactor (also referred to herein as H.sub.2-MCfR) to the influent tube of the Bio-reactor (also referred to herein as O.sub.2-MBfR) (FIG. 5). The hydraulic retention time for both reactors were controlled at 15.0 ± 1.0 hours. Operational parameter details of the bioreactor were listed in Table 1.

TABLE-US-00001 Cata-reactor parameters Value Unit 1 Value Unit 2 Catalyst synthesis Palladium Conc. 0.1 mmol/L 10.6 mg/L H.sub.2 pressure 3 psi 1.2 atm pH 10 Membranes type Polypropylene membrane Membranes area 0.0362 m.sup.2 360 cm.sup.2 Total Pd 0.007 mmol 0.74 mg Coated Pd 0.00686 mmol 0.73 mg Pd surface loading 0.19 mmol/m 20 mg/m.sup.2 Operation Flow rate 0.07 mL/min 96 mL/d H.sub.2 pressure 10 psig 1.7 atm TCE influent 100 .Math.mol/L 13 mg/L TCE loading 0.27 mmol/m.sup.2-d 35 mg/m.sup.2-d TCE Flux 0.83 mmol/m.sup.2-d 110 mg/m.sup.2-d TCA influent 100 .Math.mol/L 13 mg/L TCA loading 0.27 mmol/m.sup.2-d 36 mg/m-d TCA Flux 0.82 mmol/m.sup.2-d 110 mg/m-d Bio-reactor parameters Value Unit 1 Value Unit 2 Membrane Membranes type Composite membrane Membranes area 0.0143 m.sup.2 140 cm.sup.2 Operation Flow rate 0.07 mL/min 96 mL/d O.sub.2 pressure 10 psig 1.7 atm Dioxane influent 200 umol/L 17.6 mg/L Dioxane loading 1.35 mmol/m.sup.2-d 119 mg/m.sup.2-day Dioxane Flux 1.33 mmol/m.sup.2-d 117 mg/m.sup.2-day

[0091] A basic medium was prepared in 5-L medium bottles, sparged with C.sub.2H.sub.6 (only for separated operation of Bio-reactor) or N.sub.2 (for other operation conditions) for deoxygenation, and then transferred to 5-L Tedlar bags (CEL Scientific Corp., Santa Fe Springs, CA) in an anaerobic glove box. The components of the basic medium were 1 mM KH.sub.2PO.sub.4, 1 mM K.sub.2HPO.sub.4, 0.02 CaCl.sub.2.Math.2H.sub.2O, 0.018 mM MgCl.sub.2, 0.2 mM NH.sub.4Cl, 0.002 mM MgSO.sub.4.Math.7H.sub.2O, 0.002 mM FeCl.sub.2.Math.4H.sub.2O, and 4 mM NaHCO.sub.3, plus 1 mL/L trace metal stock solution. Pure liquid TCA+TCE and/or concentrated 1,4-D solution were then injected into the basic medium through the sampling septa of Tedlar bags.

[0092] After combining two reactors into a synergistic platform, the reactors were fed with 1 mM TCA, 1 mM TCE, and 0.5 mM 1,4-D, with an HRT of 15 hours as stage 1. The effluent concentration of TCA and TCE from the Cata-reactor were gradually stable at 80 .Math.M and 23 .Math.M, along with intermediates 41 .Math.M DCA and 35 .Math.M MCA (FIG. 6). The 1,4-D effluent concentration of the Bio-reactor greatly increased from <10 .Math.M to 420 .Math.M, which may have been caused by chlorinated solvent inhibition to 1,4-D biodegradation and the concentration decrease of the primary substrate ethane. Most of the remaining chlorinated solvents were removed in the Bio-reactor, by co-oxidation.

[0093] Because the chlorinated solvents strongly inhibit 1,4-D biodegradation, the influent concentration of TCA and TCE was reduced to 100 .Math.M and the concentration of 1,4-D to 200 .Math.M in stage II. Then, the effluent chlorinated solvents concentration from the Cata-reactor were well controlled to relatively lower level. The effluent 1,4-D concentration gradually decreased from over 100 .Math.M to < 1 .Math.M. The removal rate increase of 1,4-D reveal that the ethane produced from Cata-reactor was able to support the co-oxidation of 1,4-D. And the inhibition of chlorinated solvents could be minimized by pre-dechlorination in the Cata-reactor.

[0094] By increasing the influent concentration of TCA and TCE to 300 .Math.M, the 1,4-D biodegradation was inhibited again by the remaining chlorinated solvents. The mixture of 39 .Math.M TCA, 7.1 .Math.M TCE, 13.4 .Math.M DCA, and 44.6 .Math.M MCA from Cata-reactor was high enough to significantly inhibit the 1,4-D removal. To test the stability of the synergistic platform, the influent concentration of TCA and TCE was reduced back to 100 .Math.M. In an over one-month long-term operation of stage IV, stable simultaneous removal of TCA/TCE and 1,4-D was achieved, and all the substrates effluent concentration below the U.S. EPA MCLs.

[0095] Overall, the synergistic platform could use the Cata-reactor to reduce TCA/TCE concentration and produce ethane for subsequent co-oxidation of 1,4-D in the Bio-reactor. With proper surface loading control for TCA/TCE, the synergistic platform successfully achieved simultaneous removal of all three co-contaminants without extra organic carbon input and accumulation of toxic intermediates.