Patent Application
20210387874
Removal of pollutants from waters presents unique scientific, environmental and economic challenges. In the case of nitrate, currently, the US Environmental Protection Agency (EPA) lists ion-exchange resin (IX), reverse osmosis (RO) and electrodialysis (ED) as the state-of-the-art technologies for removal from waters. All the foregoing technologies produce highly concentrated brine residuals and are limited by expensive brine disposal and management requirements. Current options for brine disposal and management include evaporation in aeration ponds, deep well injection, direct release to sewers, and piping into oceans.
Brine disposal adds extra costs to the process of treating drinking water. For example, evaporation ponds for holding brines require substantially high maintenance costs and land usage. Injection wells can be a lower cost option, but their use raises environmental concerns. Moreover, environmental concerns are leading to tighter restrictions on surface and ocean releases of brine, and disposal costs are expected to rise accordingly.
Currently, IX and RO are the most common approaches for nitrate removal. However, for IX technologies, the possibility of competitive adsorption and the inefficient and energy-intensive regeneration processes have limited wide-spread adoption. For example, concentrated brine solutions used to regenerate spent resins are disposed after a single use, requiring ˜6 g of salt per gallon of water treated. Such salt use can represent more than 70% of the financial burden, and more than 83% of the environmental impact, of adsorption-based processes.
For RO, a major limitation is the freshwater recovery rate. Typically, the freshwater recovery rate is approximately 50%-65%. In other words, 35%-50% of the output is concentrated brine. ED, on the other hand, offers higher water recovery rates (>85%). However, ED processes are limited by high capital and energy costs.
All the foregoing technologies suffer from brine disposal issues. For inland areas in particular, where cost-effective concentrate management options are not available, safe disposal of large volumes of concentrated brines impacts operation costs significantly. Biological denitrification, on the other hand, avoids brine management issues. However, current biological denitrification processes are limited by long start-up times, long recovery times, required post-treatment processes to remove biological sludge, high relative temperature sensitivity, and high physical footprint requirements.
Accordingly, there remains an ongoing need for systems and methods capable of effectively removing unwanted pollutants, such as nitrate, from water while minimizing or avoiding brine management issues associated with the current state of the art.
Embodiments described herein include systems and processes for the removal of pollutants from water and their conversion to less harmful products. Certain embodiments are directed to systems configured to provide bi-functional operation in which (1) a first polarity provides an electrodialysis mode for removing one or more target pollutants from a feedwater stream, and (2) a second, reversed polarity provides an electrolysis mode for converting concentrated pollutant(s) to environmentally benign, less harmful, and/or value-added products. The electrodialysis and electrolysis modes are provided by the same system, thereby minimizing or negating the need for a separate, independent electrolysis system of other conversion system downstream of the electrodialysis system.
By reducing the need for separate, independent systems, the embodiments described herein beneficially provide increased operational and space efficiencies. Moreover, the electrodialysis mode functions to concentrate target pollutants at the active sites where effective conversion can occur during the subsequent electrolysis mode, thereby further increasing overall operational efficiencies.
In one embodiment, a system configured to provide both electrodialysis and electrolysis of a feedwater comprises a first electrode including a catalyst material associated therewith, a second electrode disposed opposite the first electrode, and one or more ion exchange membranes disposed between the first and second electrodes. The one or more ion exchange membranes are arranged to define: (i) a feedwater compartment through which a feedwater flows during operation of the system, and (ii) a first ion concentration compartment, the first ion concentration compartment being adjacent to the first electrode such that during operation of the system an ion-concentrated stream contacts the first electrode.
The one or more ion exchange membranes may comprise at least one anion exchange membrane and at least one cation exchange membrane. In such embodiments, the feedwater compartment is disposed between the anion exchange membrane and the cation exchange membrane, an anion concentration compartment is disposed between the anion exchange membrane and whichever electrode has a positive charge during electrodialysis mode, and a cation concentration compartment is disposed between the cation exchange membrane and whichever electrode has a negative charge during electrodialysis mode.
In the example of nitrate treatment, the ion exchange membranes are arranged so that the anion concentration compartment is adjacent the first electrode, and the first electrode is operated with a positive charge during electrodialysis mode to attract and concentrate nitrate ions into the anion concentration compartment. During electrolysis mode, the polarity of the electrodes is reversed so that the first electrode now carries a negative charge. The negative charge enables the catalyst material of the first electrode to catalyze the conversion of concentrated nitrate into environmentally benign, less harmful, and/or value-added products (such as nitrogen gas).
In some embodiments, the second electrode can also include an integrated catalyst material. In such embodiments, both cation and anion contaminants can be removed from the feedwater and then converted in the subsequent electrolysis mode.
A method for removing one or more contaminants from a feedwater via electrodialysis and converting the one or more contaminants via electrolysis comprises the steps of: providing an electrodialysis and electrolysis system such as described above; operating the system in an electrodialysis mode by providing a first polarity across the first and second electrodes while passing the feedwater through the feedwater channel to thereby generate an ion-concentrated stream in the first ion concentration compartment; and operating the system in an electrolysis mode by reversing the polarity across the first and second electrodes, wherein the catalyst material, under the reversed polarity, catalyzes conversion of one or more ions concentrated in the first ion concentration compartment.
In some embodiments, the feedwater comprises nitrate, and the nitrate is removed from the feedwater and concentrated in the first ion concentration compartment during the electrodialysis mode. Subsequently, at least a portion of the concentrated nitrate is reduced to nitrogen gas upon reversing polarity during the electrolysis mode. In this example, the first electrode is operated with a positive charge during the electrodialysis mode and with a negative charge during the electrolysis mode.
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an indication of the scope of the claimed subject matter.
Various objects, features, characteristics, and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings and the appended claims, all of which form a part of this specification. In the Drawings, like reference numerals may be utilized to designate corresponding or similar parts in the various Figures, and the various elements depicted are not necessarily drawn to scale, wherein:
Embodiments described herein include systems and processes for the removal of pollutants from water and their conversion to less harmful products. Certain embodiments are directed to systems configured to provide bi-functional operation in which (1) a first polarity provides an electrodialysis mode for removing one or more target pollutants from a feedwater stream, and (2) a second, reversed polarity provides an electrolysis mode for converting concentrated pollutant(s) to environmentally benign, less harmful, and/or value-added products. The electrodialysis and electrolysis modes are provided by the same system, thereby minimizing or negating the need for a separate, independent electrolysis system of other conversion system downstream of the electrodialysis system.
The ion exchange membranes 108 and 110 are spaced such that a feedwater compartment 116 in formed therebetween. The feedwater compartment 116 is configured to receive an inlet stream 112 (with high relative concentration of pollutant(s)) and to output an outlet stream 114 (with lowered concentration of pollutant(s)). The anion exchange membrane 108 and the first electrode 104 define an anion concentration compartment 118 formed therebetween. The cation exchange membrane 110 and the second electrode 106 define a cation concentration compartment 120 formed therebetween.
In electrodialysis mode operation (
After the system 100 has operated in the electrodialysis mode for a first time period, the polarities of the electrodes 104 and 106 are reversed and the system 100 transitions to the electrolysis mode.
As shown, the first electrode 104 includes a catalyst portion 102 connected and/or integrated thereto. The catalyst portion 102 incorporates one or more catalysts configured to provide conversion of the pollutant(s) that concentrate in the anion concentration compartment 118 to environmentally benign, less harmful, and/or value-added products. Continuing with the example of nitrate, nitrate concentrated in the anion concentration compartment 118 is reduced to less harmful nitrogen products such as nitrite, ammonia/ammonium, and/or (preferably) nitrogen gas. Corresponding oxidation reactions may occur at the second electrode 106 (e.g., water splitting).
A hybrid electrodialysis and electrolysis system such as illustrated beneficially combines the functions of pollutant removal and pollutant conversion into a single unit/system. This improves operational and space efficiencies as compared to using a dedicated electrodialysis system and a separate, downstream electrolysis system for denitrification. Moreover, because electrolytic energy efficiency and electrolytic rates are proportional to the localized concentration of the target pollutant, the pre-concentration of the pollutant in the direct vicinity of the catalyst portion 102 beneficially enables effective and efficient conversion within the same unit/system.
The following features can be incorporated individually or in combination with one or more of the other features into the hybrid electrodialysis and electrolysis systems described herein (including system 100 and/or system 200).
Various substrates may be utilized to form one or both electrodes of the hybrid electrodialysis and electrolysis system. Suitable electrode sub state materials include graphite, nickel, copper, iron, polytetrafluoroethylene (PTFE) membrane materials, carbon (e.g., activated carbon, carbon nanotubes), transparent conductive oxides, and combinations thereof. The form of the substrate is preferably configured to provide a high surface area. For example, the substrate may be configured as a mesh, felt, foamed structure, or other porous material. In systems where only one electrode includes a catalytic portion, the counter electrode may be formed from a simple conductive material such as stainless steel.
Where a porous substrate is utilized, the pores preferably have an average diameter of about 100 μm to about 1 mm, or more preferably about 200 μm to about 800 μm, or about 300 μm to about 700 μm, or about 350 μm to about 650 μm, or about 400 μm to about 600 μm, such as about 500 μm, or within a range having any two of the foregoing values as endpoints. A porous electrode substrate with an average pore diameter within the foregoing values was found to optimally balance sufficient charge transfer capabilities with high surface areas and ability to effectively integrate catalyst material therein.
Further, when a porous substrate is utilized, the substrate is preferably configured with a pore density of about 20 to about 200 pores per square inch (ppi), or more preferably about 25 ppi to about 150 ppi, or about 30 ppi to about 120 ppi, or about 35 ppi to about 100 ppi, or about 40 ppi to about 80 ppi, or about 50 ppi to about 70 ppi, such as about 60 ppi, or a pore density within a range defined by any two of the foregoing values. A substrate with a pore density within the foregoing values was found to provide sufficiently low charge transfer resistance while also providing sufficiently high electrochemically active surface area.
The catalyst associated with one or more of the electrodes to form the catalyst portion(s) may be provided as nanoparticles that are embedded or otherwise incorporated into the corresponding electrodes. For example, where the electrode substrate is formed as a porous material, catalyst nanoparticles may be distributed and embedded within the porous surfaces of the substrate to take advantage of the increased surface area provided by the porous structure.
Suitable catalyst materials for nitrate reduction (but which may be additionally or alternatively used for other pollutants) include Cu, Pd—Cu, Ni, Zn—Cu, Pt, Rh, Pt—Rh, Pd—Cu, Pt—Cu, Rh—Cu, Ir—Cu, Sn—Pt, Sn—Pd—Au, Pd—Sn, Pd—Cu, Pd—In, Fe—Ni, Pd, Ag, Au, Ru, Ir, metal oxides, metal hydroxides, and combinations thereof.
Exemplary electrode substrates and catalysts, and certain exemplary combinations of electrode substrates and catalysts that may be utilized together in a hybrid electrodialysis and electrolysis system, are provided below in Table 1:
Catalyst nanoparticles may be loaded onto the electrode substrate using a variety of integration or deposition methods known in the art. In some embodiments, electrodeposition is utilized to deposit the catalyst nanoparticles. In some embodiments where a multi-metallic catalyst is utilized, each metal may be electrodeposited using a co-electrodeposition technique. Alternatively, a galvanic displacement technique may be utilized wherein a base metal (having a relatively higher oxidation potential) is first deposited on the substrate, and subsequently a second metal (having a relatively lower oxidation potential) is introduced to galvanically displace the first metal. The mass loading of catalyst nanoparticles to the electrode substrate may range from about 0.05 mgcatalyst/cm2 to about 0.25 or up to about 0.5 mgcatalyst/cm2.
The size of the catalyst nanoparticles integrated with the electrode substrate may vary according to particular application needs. Catalyst nanoparticles may range in average size from about 2 nm to about 500 nm, more typically about 10 nm to about 300 nm, or about 15 nm to about 200 nm, or about 20 nm to about 100 nm, or may have an average size within a range with endpoints defined by any two of the foregoing values. Systems utilizing catalyst nanoparticles within the foregoing size ranges were found to provide effective surface area and catalytic activity while also balancing the ability to effectively integrate the nanoparticles into the pores of the electrode substrate.
The hybrid electrodialysis and electrolysis systems described herein may be utilized in a variety of water treatment applications. For nitrate removal and conversion applications, such systems can be installed as an edge-of-field installation for fields that are drained using tiles. The systems can then treat nitrate-laden waters prior to discharge from the field into surface waters. Systems can also be utilized to treat community water systems or to treat private water supplies (e.g., private groundwater wells). Presently, in the U.S., there are over 1,700 community drinking water systems with nitrate levels higher than 10 mg/L. Many private wells have nitrate levels above recommended health advisory levels, particularly in agricultural areas.
Although many of the examples described herein relate to nitrate removal and conversion, the components and principles described herein may also be utilized for the removal and conversion of a wide variety of other chemical and/or biological contaminants/pollutants. A non-exhaustive list of such chemical contaminants includes nitrogen, bleach, salts, pesticides, metals, toxins produced by bacteria, nitrate (NO3), chloride (Cl), chromium-6 (Cr-6), chromium-3 (Cr-6), copper (Cu), fluoride (F), iron (Fe), selenium (VI), boron, lithium (Li), sodium (Na), calcium (Ca), magnesium (Mg), zinc (Zn), arsenic (As), uranium (U), strontium (Sr), cadmium (Cd), cyanide (CN), nitrite (NO2), phosphate, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), 1,1-dichloroethane, acetochlor, methyl bromide (bromomethane), metolachlor, nitrobenzene, 1,4-Dioxane, 1,2,3-trichloropropane, and chloroamine.
A non-exhaustive list of medicinal pollutants that may be removed from feedwater and converted using the systems described herein includes aspirin, codeine, cyclophosphamide, galaxolide, pentoxifylline, tonalide, triclosan, etofibrate, etofyllinclofibrat, flurbiprofen, ketoprofen, nadolol, tolfenamic acid, carbamazepine, diazepam, ibuprofen, paracetamol, phenazone, bezafibrate, clofibrate, diclofenac, fenoprofen, fenofibrate, femfibrozil, indomethacine, iopromide, mefenamic acid, metoprolol, naproxen, propranolol, propyphenazone, roxithromycin, salbutamol, sulfamethoxazole, doxycycline, estrone, hydrochlorothiazide, iopamidol, metronidazole, ofloxacin, enalapril, furazolidone, ifosfamide, ketorolac, methicillin, nafcillin, erythromycin, furosemide, iomeprol, lincomycin, methotrexate, norfloxacin, oleandomycin, simvastatin, sotalol, omeprazole, oxacillin, oxytetracycline, penicillin, pindolol, piroxicam, ranitidine, ronidazole, spiramycin, sulfacetamide, sulfadiazine, sulfadiamethoxine, sulfadimidine, sulfafuanidine, sulfamethazine, sulfamethazine, sulfapyridine, sulfasalazine, sulfathiazine, tamoxifen, terbutaline, tetracycline, tilmicosin, trimethoprim, tylosin, virginiamycin, 17α-ethinylestradiol, 17β-estradiol, acetyl-sulfamethoxazole, amidotrizoic acid, aminopyridine, amoxycillin, anhydro-erythromycin, atenolol, bisoprolol, chloramphenicol, chlortetracycline, ciprofloxacin, clarithromycin, clenbuterol, cloxacillin, cyclophosphamide, dapsone, dimethyl diazepam, dextropropoxyphene, dicloxacillin, acetaminophen, and carbamazepine.
A non-exhaustive list of biological contaminants/pollutants that may be removed from feedwater and optionally destroyed using the systems described herein includes pathogenic microorganisms (viruses, bacteria, fungi, protozoa) and DNA and RNA contaminants. Common feedwater pathogens of concern include adenoviruses, caliciviruses, Campylobacter jejuni, enteroviruses, Escherichia coli, Helicobacter pylori, hepatitis A virus, Legionella pneumophila, Mycobacterium avium, Naegleria fowleri, and Salmonella enterica.
Table 2 provides a particular list of example contaminants that can be removed using the systems described herein, along with the present maximum contaminant level (MCL) as established by the U.S. Environmental Protection Agency (EPA), potential negative health effects associated with the contaminant, and common sources of the contaminant:
Various carbon supports (carbon foam, carbon cloth, carbon felt; available from vendor Fuel Cell Store), and their electroactivity (charge transfer resistance) was characterized using AC EIS. The EIS for these carbon supports was recorded in 0.1M H2SO4 at the open-circuit voltage in the frequency range of 1 MHz to 1 Hz with a 10-mV peak-to-peak sinusoidal potential perturbation. Saturated silver/silver chloride was used as the reference electrode and Pt wire as the counter electrode.
All carbon materials showed similar uncompensated series resistances (from 1.4 to 4.4-ohm cm2) as measured from the EIS, indicating the robustness of the measurement set-up (
A porous carbon electrode was also compared to a planar Pt electrode.
We developed various synthetic routes to deposit catalysts (Pd, Cu, and Pd—Cu bimetallic systems) on carbon substrates. Pd and Cu were selected as most likely to have high selectivity for nitrate reduction. Electrodeposition allows the synthesis of catalysts directly on the most accessible electroactive sites of the support substrate, thereby increasing catalyst utilization efficiency.
For bimetallic systems, two synthetic techniques were employed. The first technique utilized the co-electrodeposition of both metals in one single step. In the second technique, a base metal was first electrodeposited (Cu), which was then galvanically displaced by the second metal (Pd) having a lower oxidation potential than the displaced metal (Cu). While co-electrodeposition benefits from simplicity, electrodeposition followed by galvanic displacement enables good spatial for the deposition of the second metal. All synthesized catalysts were characterized for their morphology and elemental composition using SEM and energy dispersive spectroscopy (EDS).
Nitrate reduction studies were conducted in 30 mM NaNO3 in 0.1M NaOH electrolyte using a half-cell two-compartment electrochemical set-up. For control, electrochemical reduction studies were also carried out in 0.1M NaOH electrolyte and 0.1M NaOH with 30 mM NaNO2 electrolyte.
The catalytic activity of the Pd—Cu electrocatalyst for nitrate reduction was evaluated by linear sweep voltammetry measurements at 5 mV/s in N2-saturated 0.1M NaOH electrolyte with 30 mM NaNO3 electrolyte, and the data are compared in the absence of nitrate ion concentration. Nitrogen was purged to minimize currents originating from the reduction of dissolved oxygen. As seen in
The Pd—Cu catalyst was then integrated into a half-cell configuration and tested for its stability for nitrate conversion under accelerated testing conditions (1 kA/m2=100 mA/cm2). Testing was conducted in 0.1 M NaNO3 neutral electrolyte using an in-house half-cell two-compartment electrochemical set-up.
We assessed the performance of the electrode assembly described in the previous Examples in different feed water sources listed in Table 3. For each feedwater chemistry, nitrate removal in electrodialysis mode, nitrate-to-nitrogen conversion in electrolysis mode, and freshwater recovery were experimentally determined. The initial nitrate concentration was 1000 mg/L and the temperature was maintained at 26° C.
Table 3 shows that for all different feed water chemistries tested, we were able to achieve freshwater recovery of 85% and higher. We were also able to achieve nitrate-to-nitrogen conversion efficiencies >75% for all feed water chemistries, the only exception being feedwaters with chloride ion concentration equal to 5000 mg/L.
While certain embodiments of the present disclosure have been described in detail, with reference to specific configurations, parameters, components, elements, etcetera, the descriptions are illustrative and are not to be construed as limiting the scope of the claimed invention.
Furthermore, it should be understood that for any given element of component of a described embodiment, any of the possible alternatives listed for that element or component may generally be used individually or in combination with one another, unless implicitly or explicitly stated otherwise.
In addition, unless otherwise indicated, numbers expressing quantities, constituents, distances, or other measurements used in the specification and claims are to be understood as optionally being modified by the term “about” or its synonyms. When the terms “about,” “approximately,” “substantially,” or the like are used in conjunction with a stated amount, value, or condition, it may be taken to mean an amount, value or condition that deviates by less than 20%, less than 10%, less than 5%, less than 1%, less than 0.1%, or less than 0.01% of the stated amount, value, or condition. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
Any headings and subheadings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description or the claims.
It will also be noted that, as used in this specification and the appended claims, the singular forms “a,” “an” and “the” do not exclude plural referents unless the context clearly dictates otherwise. Thus, for example, an embodiment referencing a singular referent (e.g., “widget”) may also include two or more such referents.
It will also be appreciated that embodiments described herein may also include properties and/or features (e.g., ingredients, components, members, elements, parts, and/or portions) described in one or more separate embodiments and are not necessarily limited strictly to the features expressly described for that particular embodiment. Accordingly, the various features of a given embodiment can be combined with and/or incorporated into other embodiments of the present disclosure. Thus, disclosure of certain features relative to a specific embodiment of the present disclosure should not be construed as limiting application or inclusion of said features to the specific embodiment. Rather, it will be appreciated that other embodiments can also include such features.
This application claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 63/038,625, filed Jun. 12, 2020, the entirety of which is incorporated herein by this reference.
This invention was made with government support under grant no. 2019-33610-29769 awarded by the United States Department of Agriculture, National Institute of Food and Agriculture. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63038625 | Jun 2020 | US |
