Molecular electrocatalytic systems and methods thereof

Abstract

Molecular electrocatalytic systems for ammonia production from wastewater nitrate are described. The electrocatalytic systems use ammonia-selective homogeneous molecular NOsRR catalysts in real wastewater.

Description

MOLECULAR ELECTROCATALYTIC SYSTEMS AND METHODS THEREOFCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The current application claims the benefit of and priority to U.S. Provisional Patent Application No. 63 / 519,533 entitled “Molecular Electrocatalytic Systems and Methods Thereof” filed August 14, 2023. The disclosure of U.S. Provisional Patent Application No. 63 / 519,533 is hereby incorporated by reference in its entirety for all purposes.STATEMENT OF FEDERALLY SPONSORED RESEARCH

[0002] This invention was made with government support under Grant No. 2132007, awarded by the National Science Foundation and under Grant No. 80NSSC22K1191 awarded by the National Aeronautics and Space Administration. The government has certain rights in the invention.FIELD OF THE INVENTION

[0003] The present invention generally relates to molecular electrocatalytic systems and methods thereof; and more particularly to molecular electrocatalytic systems for ammonia production and / or separation from wastwater nitrate.BACKGROUND OF THE INVENTION

[0004] Anthropogenic ammonia production has sustained exponential population growth but exacerbated wastewater nitrate pollution. Abundant nitrate could be refined to purified nitrogenous chemicals with the electrochemical nitrate reduction reaction (NO3RR). However, the dilute and impure composition of nitrate-bearing wastewaters presents barriers to practical electrocatalytic systems.

[0005] Circular wastewater refining processes can responsibly manage aqueous waste streams and sustainably produce chemical commodities, including nitrogencompounds. Conventionally, nitrogenous commodities are produced from ammonianitrogen made by the Haber-Bosch (HB) process; HB is energy-efficient but still contributes 1 -2% of global carbon dioxide emissions. The majority of HB-nitrogen is used as fertilizer, but 24-54% of HB-nitrogen is discharged from anthropogenic processes as aqueous nitrate (NO3) and ammonium (NH4). Excess reactive nitrogen species in surface waters cause algal blooms that damage aquatic ecosystems and exacerbate climate change. Refining these fugitive nitrogen emissions into a tunable, diverse portfolio of products could remediate harmful pollutants. The electrocatalytic NO3 reduction reaction (NO3RR) to ammonia can refine nitrate-rich wastewaters that contain 19-48 Tg NO3-N globally per year. Electrified NO3RR processes can integrate with renewable and decentralized energy sources, which could enable ammonia production at sites of wastewater generation. This circular NO3 refining paradigm can improve sanitation access, expand nitrogen commodity access, and offset costs and emissions of industrial ammonia production.

[0006] Despite the large overall flux of anthropogenic nitrogen discharges to the environment, most NO3 is contributed by dilute and impure wastewater sources. Both point sources (e.g., municipal wastewater) and nonpoint sources (e.g., agricultural runoff) generally contain less than 50 mg NO3 -N L-1(3.6 mM). Municipal and agricultural wastewaters are also impure; they contain co-constituents (e.g., organic / inorganic ions, organic carbon, suspended solids) that compete for catalyst active sites, degrade catalysts over time, passivate electrode surfaces, and alter solution pH outside of catalyst operating ranges. In contrast to real wastewaters, NO3RR electrocatalysts are mostly documented with NO3 concentrations above 100 mM (i.e., concentrated) in synthetic (i.e. , pure) electrolytes. NO3 refining methods need to overcome the difference in NO3 concentration and purity between catalysis investigations and real wastewaters to be relevant for wastewater treatment and chemical manufacturing.

[0007] Homogeneous molecular catalysts are promising for wastewater NO3 refining because their atomically precise reactivity could overcome both dilute and impure wastewater conditions. Homogeneous catalysts exist in the same phase (solid, liquid,and / or gas phase) as the reactants and products. Homogeneous catalysts (for example, organometallic complexes) can have high efficiency in terms of activity and selectivity, and can be active under mild reaction conditions, when compared to heterogeneous catalysts. However, additional separation processes are usually needed to recover the products and reuse the costly catalysts. It can be difficult to remove or separate homogeneous catalysts from products. This is particularly challenging in chemical production from aqueous feedstocks where contaminants in the impure reactant feed may deactivate the catalyst, and where treated water recovery is desirable. The ligand structures of molecular catalysts promote high reactant and product selectivity that could enhance NO3RR faradaic efficiency (FE) and reaction rates to total ammonia nitrogen (TAN; the sum of NH4-N(aq) and NH3-N(aq)) in dilute NO3solutions. The metal complex 2,3-dimethyl-1 ,4,8,11 -tetraazacyclotetradeca-1 ,3-diene (DIM) with a Co metal center, abbreviated Co(DIM), yields TAN as its major product and suppresses the competitive hydrogen evolution reaction (HER) in aqueous conditions from pH 3.5 to 10.1. Co(DIM) exemplifies benefits to employing molecular electrocatalysts for wastewater refining. The positively-charged metal center of Co(DIM) facilitates binding of negatively-charged NO3. Additionally, homogeneous electrocatalytic processes directly scale with volume (e.g., Fenton catalysts, porphyrins for PFAS remediation) and can use economical carbonaceous electrode materials. Rational design principles for molecular electrocatalyst design, operation, and separation in wastewater refining processes are currently ill-defined because few use-informed investigations of homogeneous catalysis in real wastewaters exist.

[0008] Rational design of wastewater refining unit processes is hampered by a dearth of electrochemical investigations that integrate reactions and separations, or reactive separations. Consequently, unit process performance (namely efficiencies, rates, and energy consumption) is difficult to benchmark against incumbent wastewater management processes. Reactive separations can overcome the challenges of dilute and impure wastewaters to enable NO3 extraction, NO3conversion to TAN, and purified TANrecovery. However, few investigations of reactive separations in real wastewater exist, and even fewer exist for dilute wastewaters.BRIEF SUMMARY OF THE INVENTION

[0009] Many embodiments are directed to molecular electrocatalytic systems for ammonia production from wastewater nitrate. Many embodiments implement ammoniaselective homogeneous molecular NO3RR catalysts in real wastewater and reactive separations architectures. Several embodiments provide electrocatalyst-in-a-box (ECaB) systems, NO3RR reactive separation systems that exhibit low energy consumption for purified wastewater-derived ammonia production (about 90.0 ± 2.7 kWh kg-N-1). Engineering ECaB’s subunit processes can enhance the rate of ammonia production by at least 20 times. Many embodiments provide a use-informed engineering approach that iterates between mechanistic insights and unit process-level performance of electrochemical wastewater refining systems in complex aqueous streams.

[0010] Some embodiments include an electrocatalytic system for nitrate reduction, comprising a first cell comprising: an input chamber configured to receive a liquid comprising nitrate; a first catholyte chamber, wherein an anion exchange membrane separates the input chamber and the first catholyte chamber, wherein the anion exchange membrane selectively transports nitrate from the input chamber to the first catholyte chamber; and a trap chamber, wherein a gas permeable membrane separates the first catholyte chamber and the trap chamber; a second cell comprising: a second catholyte chamber connecting a cathode and an anolyte chamber connecting an anode, wherein a membrane separates the second catholyte chamber and the anolyte chamber; wherein the first and the second catholyte chambers each comprise a catholyte and the chambers are in a fluidic connection; wherein the catholyte in the second catholyte chamber comprises a catalyst and the catalyst catalyzes a nitrate reduction reaction to generate ammonia; and wherein the nitrate and the generated ammonium are free flowing between the first and the second catholyte chambers such that the nitrate from the first catholyte chamber is transported to the second catholyte chamber and the generatedammonium from the second catholyte chamber is transported to the first catholyte chamber, wherein the gas permeable membrane transports the generated ammonia from the first catholyte chamber to the trap chamber.

[0011] In some embodiments, the liquid is selected from the group consisting of: nitrogen fixation reactor effluent, nitrate polluted groundwater, wastewater, agricultural wastewater, municipal wastewater, reverse osmosis brine, and ion exchange brine.

[0012] In some embodiments, the liquid has a pH from 5.5 to 7.5.

[0013] In some embodiments, the catalyst is a homogeneous catalyst, a heterogeneous catalyst, or a molecular catalyst.

[0014] In some embodiments, the catalyst is selected from the group consisting of: a metal complex 2,3-dimethyl-1 ,4,8, 11-tetraazacyclotetradeca-1 ,3-diene (DIM) with a Co metal center, a cobalt macrocycle complex [Co(CR)Br2]+, and a nitrate reductase.

[0015] In some embodiments, the anion exchange membrane is a monovalent anion exchange membrane, or an alkaline resistant anion exchange membrane.

[0016] In some embodiments, the gas permeable membrane is a hydrophobic gas permeable membrane.

[0017] In some embodiments, the membrane is a bipolar membrane or a cation exchange membrane.

[0018] In some embodiments, the trap chamber comprises an acid, and the acid protonates and recovers ammonia to ammonium.

[0019] In some embodiments, an effluent from the input chamber comprises a lower concentration of nitrate compared to the liquid.

[0020] In some embodiments, an effluent from the input chamber is recirculated as an input liquid to the input chamber.

[0021] Some embodiments include an electrocatalytic system comprising, a first cell comprising: an input chamber configured to receive a liquid; a first electrolyte chamber, wherein an anion exchange membrane separates the input chamber and the first electrolyte chamber; and a trap chamber, wherein a gas permeable membrane separates the first electrolyte chamber and the trap chamber; a second cell comprising: a secondelectrolyte chamber and a third electrolyte chamber, wherein a membrane separates the second and the third electrolyte chamber; wherein the first and the second electrolyte chambers each comprises an electrolyte and the chambers are in a fluidic connection; wherein the second electrolyte chamber comprises a catalyst, wherein the catalyst catalyzes a reaction that generates a gaseous compound; wherein the gaseous compound is free flowing between the first and the second electrolyte chambers; and wherein the gaseous compound transports through the gas permeable membrane into the trap chamber.

[0022] In some embodiments, the catalyst catalyzes a nitrate reduction reaction, a carbon dioxide reduction reaction, or an alcohol oxidation reaction.

[0023] In some embodiments, the liquid is selected from the group consisting of: nitrogen fixation reactor effluent, nitrate polluted groundwater, wastewater, agricultural wastewater, municipal wastewater, reverse osmosis brine, and ion exchange brine.

[0024] In some embodiments, the liquid comprises nitrate and the gaseous compound comprises ammonia.

[0025] In some embodiments, the catalyst is a homogeneous catalyst, a heterogeneous catalyst, or a molecular catalyst.

[0026] In some embodiments, the catalyst is selected from the group consisting of: a metal complex 2,3-dimethyl-1 ,4,8, 11-tetraazacyclotetradeca-1 ,3-diene (DIM) with a Co metal center, a cobalt macrocycle complex [Co(CR)Br2]+, and a nitrate reductase.

[0027] In some embodiments, the anion exchange membrane is a monovalent anion exchange membrane, or an alkaline resistant anion exchange membrane.

[0028] In some embodiments, the gas permeable membrane is a hydrophobic gas permeable membrane.

[0029] In some embodiments, the trap chamber comprises an acid.

[0030] In some embodiments, an effluent from the input chamber is recirculated as an input liquid to the input chamber.

[0031] In some embodiments, the membrane is selected from the group consisting of: a bipolar membrane, a cation exchange membrane, and an anion exchange membrane.

[0032] Some embodiments include an electrocatalytic system for nitrate reduction, comprising, a first cell comprising: an input chamber configured to receive an influent comprising nitrate; a first catholyte chamber, wherein an anion exchange membrane separates the input chamber and the first catholyte chamber, wherein the anion exchange membrane selectively transports nitrate from the input chamber to the first catholyte chamber; a second cell comprising: a second catholyte chamber comprising a cathode and an anolyte chamber comprising an anode, wherein a membrane separates the second catholyte chamber and the anolyte chamber; and a third cell comprising: a third catholyte chamber and a trap chamber, wherein a gas permeable membrane separates the third catholyte chamber and the trap chamber; wherein at least one of the first and the second catholyte chambers comprises a catholyte and a catalyst and the chambers are in a fluidic connection such that nitrate is transported from the first catholyte chamber to the second catholyte chamber; wherein the catalyst in the second catholyte chamber catalyzes a nitrate reduction reaction to generate ammonia; and wherein the second and the third catholyte chambers are in a fluidic connection; wherein the generated ammonia is transported from the second catholyte chamber to the third catholyte chamber, wherein the gas permeable membrane transports the generated ammonia from the third catholyte chamber to the trap chamber.

[0033] In some embodiments, the catalyst is a homogeneous catalyst, the first catholyte chamber, the second catholyte chamber, and the third catholyte chamber each comprise a catalyst.

[0034] In some embodiments, the catalyst is a heterogeneous catalyst and the second catholyte chamber comprises a catalyst.

[0035] In some embodiments, the first cell, the second cell, and the third cell are simultaneously in fluid connection with each other.

[0036] In some embodiments, the first cell is for Donnan dialysis, the second cell is for electrocatalysis, and the third cell is for ammonia stripping.

[0037] In some embodiments, the influent is selected from the group consisting of: nitrogen fixation reactor effluent, nitrate polluted groundwater, wastewater, agricultural wastewater, municipal wastewater, reverse osmosis brine, and ion exchange brine.

[0038] In some embodiments, the influent has a pH from 5.5 to 7.5.

[0039] In some embodiments, the catalyst is a homogeneous catalyst, a heterogeneous catalyst, or a molecular catalyst.

[0040] In some embodiments, the catalyst is selected from the group consisting of: a metal complex 2,3-dimethyl-1 ,4,8, 11-tetraazacyclotetradeca-1 ,3-diene (DIM) with a Co metal center, a cobalt macrocycle complex [Co(CR)Br2]+, and a nitrate reductase.

[0041] In some embodiments, the anion exchange membrane is a monovalent anion exchange membrane, or an alkaline resistant anion exchange membrane.

[0042] In some embodiments, the gas permeable membrane is a hydrophobic gas permeable membrane.

[0043] In some embodiments, the trap chamber comprises an acid, where the acid protonates and recovers ammonia to ammonium.

[0044] Some embodiments include an electrocatalytic system, comprising, a first cell comprising: an input chamber configured to receive an influent; a first catholyte chamber, wherein an anion exchange membrane separates the input chamber and the first catholyte chamber; a second cell comprising: a second catholyte chamber comprising a cathode and an anolyte chamber comprising an anode, wherein a membrane separates the second catholyte chamber and the anolyte chamber; and a third cell comprising: a third catholyte chamber and a trap chamber, wherein a gas permeable membrane separates the third catholyte chamber and the trap chamber; wherein at least one of the first and the second catholyte chambers comprises a catholyte and a catalyst and the chambers are in a fluidic connection; and wherein the second and the third catholyte chambers are in a fluidic connection.

[0045] In some embodiments, the catalyst is a homogeneous catalyst, the first catholyte chamber, the second catholyte chamber, and the third catholyte chamber each comprise a catalyst.

[0046] In some embodiments, the catalyst is a heterogeneous catalyst and the second catholyte chamber comprises a catalyst.

[0047] In some embodiments, the first cell, the second cell, and the third cell are simultaneously in fluid connection with each other.

[0048] In some embodiments, the first cell is for Donnan dialysis, the second cell is for electrocatalysis, and the third cell is for stripping.

[0049] In some embodiments, the influent is selected from the group consisting of: nitrogen fixation reactor effluent, nitrate polluted groundwater, wastewater, agricultural wastewater, municipal wastewater, reverse osmosis brine, and ion exchange brine.

[0050] In some embodiments, the influent has a pH from 5.5 to 7.5.

[0051] In some embodiments, the catalyst is a homogeneous catalyst, a heterogeneous catalyst, or a molecular catalyst.

[0052] In some embodiments, the catalyst is selected from the group consisting of: a metal complex 2,3-dimethyl-1 ,4,8, 11-tetraazacyclotetradeca-1 ,3-diene (DIM) with a Co metal center, a cobalt macrocycle complex [Co(CR)Br2]+, and a nitrate reductase.

[0053] In some embodiments, the anion exchange membrane is a monovalent anion exchange membrane, or an alkaline resistant anion exchange membrane.

[0054] In some embodiments, the gas permeable membrane is a hydrophobic gas permeable membrane.

[0055] Some embodiments include a method for nitrate reduction, comprises: extracting nitrate from a liquid via a dialysis process in a first cell of an electrocatalytic system; reducing the nitrate to a gaseous ammonia in an electrolyte; and recovering the gaseous ammonia in an acidic environment to generate ammonium.

[0056] In some embodiments, the dialysis process uses an anion exchange membrane.

[0057] In some embodiments, the anion exchange membrane is a monovalent anion exchange membrane, or an alkaline resistant anion exchange membrane.

[0058] In some embodiments, the dialysis process is a Donnan dialysis process.

[0059] In some embodiments, the liquid is selected from the group consisting of: nitrogen fixation reactor effluent, nitrate polluted groundwater, wastewater, agricultural wastewater, municipal wastewater, reverse osmosis brine, and ion exchange brine.

[0060] In some embodiments, the liquid has a pH from 5.5 to 7.5.

[0061] In some embodiments, the electrolyte comprises a catalyst that catalyzes a nitrate reduction reaction.

[0062] In some embodiments, the catalyst is a homogeneous catalyst, a heterogeneous catalyst, or a molecular catalyst.

[0063] In some embodiments, the catalyst is selected from the group consisting of: a metal complex 2,3-dimethyl-1 ,4,8, 11-tetraazacyclotetradeca-1 ,3-diene (DIM) with a Co metal center, a cobalt macrocycle complex [Co(CR)Br2]+, and a nitrate reductase.

[0064] In some embodiments, the recovering step uses a gas permeable membrane.

[0065] Additional embodiments and features are set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the specification or may be learned by the practice of the disclosure. A further understanding of the nature and advantages of the present disclosure may be realized by reference to the remaining portions of the specification and the drawings, which forms a part of this disclosure.BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The description will be more fully understood with reference to the following figures, which are presented as exemplary embodiments of the invention and should not be construed as a complete recitation of the scope of the invention, wherein:

[0067] Figure 1 illustrates a schematic of an electrocatalytic system in accordance with an embodiment.

[0068] Figure 2 illustrates a schematic of an electrocatalytic system for nitrate reduction in accordance with an embodiment.

[0069] Figure 3A illustrates cyclic voltammograms of various electrochemical tests in accordance with an embodiment.

[0070] Figure 3B illustrates peak current density of the second reduction peak NaCI with Co(DIM) in the presence and absence of NaNOs in accordance with an embodiment.

[0071] Figure 4 illustrates cyclic voltammograms of Co(DIM) in real secondary effluent wastewater and in simplified wastewater in accordance with an embodiment.

[0072] Figure 5A illustrates the mass balance of aqueous nitrogen species as a function of time during two-chamber controlled-potential electrolysis experiments in accordance with an embodiment.

[0073] Figure 5B illustrates cumulative TAN selectivity, TAN faradaic efficiency, and NO3 conversion for controlled-potential electrolysis experiments in accordance with an embodiment.

[0074] Figure 5C illustrates Mg 1s XPS spectra of the glassy carbon plate cathode after controlled-potential electrolysis experiments in accordance with an embodiment.

[0075] Figure 5D and Figure 5E illustrate SEM image and Mg EDS map respectively of glassy carbon plate cathode after a controlled-potential electrolysis experiment in real wastewater in accordance with an embodiment.

[0076] Figure 6 illustrates cation chromatograms of aqueous samples from controlled- potential electrolysis in modified simplified wastewater and in simplified wastewater in accordance with an embodiment.

[0077] Figure 7 illustrates charge decomposition into the first Co(DIM) reduction, second Co(DIM) reductions, and NO3RR in accordance with an embodiment.

[0078] Figure 8 illustrates pH trends of 2-chamber controlled-potential electrolysis as a function of time in accordance with an embodiment.

[0079] Figure 9 illustrates nitrogen mass balances for the rinse test in simplified wastewater in accordance with an embodiment.

[0080] Figure 10 illustrates N mass balances for the rinse test in real wastewater in accordance with an embodiment.

[0081] Figure 11A illustrates current density vs. time of rotating-disk electrode in controlled-potential electrolysis in accordance with an embodiment.

[0082] Figure 11 B illustrates Mg 1 s XPS of the glassy carbon rotating-disk electrode in accordance with an embodiment.

[0083] Figure 12A illustrates current density vs. time for controlled-potential electrolysis performed in a rotating-disk electrode setup with Co(DIM) in accordance with an embodiment.

[0084] Figure 12B illustrates steady-state currents of rotating-disk electrode in controlled-potential electrolysis from Figure 11 A plotted versus the square root of rotation rate in accordance with an embodiment.

[0085] Figure 13 illustrates chronoamperogram for longer Mg dose rotating-disk electrode in controlled-potential electrolysis experiment in accordance with an embodiment.

[0086] Figure 14A illustrates N mass balance for Ca2+dose two-chamber controlled- potential electrolysis experiment in accordance with an embodiment.

[0087] Figure 14B illustrates N mass balance for Mg2+dose two-chamber controlled- potential electrolysis experiment in accordance with an embodiment.

[0088] Figure 14C illustrates N mass balance for HCO3 dose two-chamber controlled- potential electrolysis experiment in accordance with an embodiment.

[0089] Figure 14D illustrates N mass balance for simultaneous Mg2+and HCO3 dose controlled-potential electrolysis experiment in accordance with an embodiment.

[0090] Figure 15 illustrates nitrate conversion for contaminant dose two-chamber controlled-potential electrolysis experiments in accordance with an embodiment.

[0091] Figure 16 illustrates Mg mass as a function of time for real wastewater controlled-potential electrolysis, simulated wastewater controlled-potential electrolysis, and Mg dose controlled-potential electrolysis in accordance with an embodiment.

[0092] Figures 17A and 17B illustrate NO3 and TAN concentrations and nitrogen mass balance respectively for electrocatalyst-in-a-box experiments in accordance with an embodiment.

[0093] Figure 18 illustrates pH trends of the 4 chambers in ECaB in accordance with an embodiment.

[0094] Figures 19A through 19C illustrate binding of TAN to Co(DIM) in accordance with an embodiment.

[0095] Figure 20 illustrates concentration of Co (59Co) in each chamber of ECaB at initial and final time points in accordance with an embodiment.

[0096] Figure 21A illustrates cumulative NO3 extraction efficiency, TAN yield, TAN recovery efficiency, and overall nitrogen recovery efficiency during ECaB experiments in accordance with an embodiment.

[0097] Figure 21 B illustrates cumulative FETAN as a function of cumulative controlled- potential electrolysis duration in accordance with an embodiment.

[0098] Figure 21 C illustrates pseudo-instantaneous NO3 conversion rate in accordance with an embodiment.

[0099] Figure 22 illustrates overall N recovery of ECaB calculated two ways in accordance with an embodiment.

[0100] Figure 23A illustrates the amount of nitrate and sulfate ions in wastewater chamber as a function of time for ECaB in accordance with an embodiment.

[0101] Figure 23B illustrates extraction flux of nitrate and sulfate ions as a function of time for ECaB in accordance with an embodiment.

[0102] Figure 23C illustrates extraction selectivity of nitrate ions over sulfate ions as a function of time for ECaB in accordance with an embodiment.

[0103] Figure 24 illustrates energy consumption of NO3 extraction, NO3 conversion, TAN production, and TAN recovery subunit processes for reports of reactive separations in NO3RR processes in accordance with an embodiment.

[0104] Figures 25A and 25B illustrate areal and volumetric nitrate extraction rates respectively in accordance with an embodiment.

[0105] Figures 25C and 25D illustrate areal and volumetric nitrate conversion rates respectively in accordance with an embodiment.

[0106] Figures 25E and 25F illustrate areal and volumetric TAN yield rates respectively in accordance with an embodiment.

[0107] Figures 25G and 25H illustrate areal and volumetric TAN recovery rates respectively in accordance with an embodiment.

[0108] Figure 26A illustrates subunit engineered ECaB configuration in accordance with an embodiment.

[0109] Figure 26B illustrates photos of the commercial electrolyzer and the electrocatalysis cell and recovery cell in operation in accordance with an embodiment.

[0110] Figures 27A and 27B illustrate nitrogen mass balance for subunit engineered ECaB Donnan dialysis nitrate extraction and Co(DIM)-mediated NO3RR in accordance with an embodiment.

[0111] Figures 28A and 28B illustrate rates of nitrate extraction and TAN production expressed as flux of nitrogen and partial current density in accordance with an embodiment.

[0112] Figure 28C illustrates nitrate extraction efficiency and TAN yield in accordance with an embodiment.

[0113] Figure 28D illustrates area-normalized volume of wastewater treated and farmland serviced with (NFk^SCU fertilizer in accordance with an embodiment.

[0114] Figures 29A through 29C illustrate rates, efficiencies, and energy consumption respectively of nitrate extraction, TAN production, and TAN recovery in ECaB and subunit engineered ECaB in accordance with an embodiment.

[0115] Figure 30A illustrates a flow diagram for simplified cost assessment of Co(DIM)-mediated NO3RR in ECaB in accordance with an embodiment.

[0116] Figure 30B illustrates TAN current density for experimental ECaB performance (Co(DIM)-ECaB) and for scenario-specific performance targets in accordance with an embodiment.

[0117] Figure 30C illustrates the cost contribution of OpEx and CapEx to the overall system in accordance with an embodiment.

[0118] Figures 31 A and 31 B illustrate nitrogen mass balance for ECaB with Co(DIM)- mediated NO2RR in accordance with an embodiment.

[0119] Figure 32 illustrates photos of electrocatalyst-in-a-box reactor in accordance with an embodiment.

[0120] Figure 33 illustrates a flow diagram of ECaB in accordance with an embodiment.DETAILED DESCRIPTION

[0121] Many embodiments implement electrocatalytic systems (also referred as electrocatalyst-in-a-box, ECaB) incorporating homogeneous and / or heterogeneous catalysts for various applications including reductions, carbonate commodity chemical production, wastewater refining, nitrate (NO3) reductions, nitrate conversion to purified ammonia, ammonia conversion to purified nitrate, sulfide conversion to purified sulfate, hydrogen production from water, carbon dioxide reductions, carbonate conversion to carbon monoxide or C2+ products such as (but not limited to) ethylene, and enzymatic reactions.

[0122] Traditional Haber-Bosch ammonia manufacturing needs large scales and operates at high temperatures and pressures, which can be carbon-intensive. Haber- Bosch ammonia synthesis may also require hydrogen production from steam-methane reforming, which emits greenhouse gases. The electrocatalytic systems in accordance with many embodiments can be operated at small scale and at atmospheric temperatures and pressures. Ammonia production with the electrocatalytic systems is energy efficient and can use renewable-powered electricity to reduce greenhouse gas emissions. The electrocatalytic systems in accordance with several embodiments can be used for sustainable, electrified ammonia production from aqueous nitrate feedstocks such as (but not limited to) nitrogen fixation reactor effluent, nitrate polluted groundwater, agricultural wastewaters, municipal wastewaters, reverse osmosis brines, ion exchange brines.

[0123] Various homogeneous catalysts are efficient and selective for their respective reactions but are seldom used because recovery of the products and the catalysts canbe cumbersome and may require that chemical production is run in batch operation. There is a need to enable semi-batch and continuous operation of homogeneous catalysts. In some embodiments, the electrocatalytic systems enable homogeneous catalysts reuse in semi-batch and / or continuous chemical production. The electrocatalytic systems can achieve simultaneous and complementary reactions and separations.

[0124] Plants uptake about 50% of the nutrients that are applied as fertilizers, and large amounts of nitrate are lost as groundwater or runoff. The lost nitrate could be recovered and resituated as purified fertilizer, cutting annual fertilizer costs for farmers. In certain embodiments, the electrocatalytic systems can be applied in decentralized fertilizer production.

[0125] Surface water nitrate pollution can threaten coastal ecosystems and groundwater nitrate pollution can cause medical complications if consumed by humans. There is a need for targeted nitrate treatment in a plethora of accessible water sources. In a number of embodiments, the electrocatalytic systems can be used for wastewater nitrate removal for purified water recovery. The electrocatalytic systems incorporating nitrate selective catalysts are selective for nitrate extraction and can up-concentrate nitrate before conversion to ammonia and make use of rapid catalytic reactions.

[0126] In several embodiments, the electrocatalytic systems include electrochemical reactor systems that enable reactant conversion, product recovery, and catalyst reuse by separating the catalysts from the reactant and product streams with ion-selective membranes and gas-permeable membranes. Certain embodiments implement the electrocatalytic systems for purified ammonia production from wastewater nitrate. Nitrate reduction can be important for re-balancing the global nitrogen cycle by sustainably producing ammonia from nitrate-bearing agricultural wastewaters that would otherwise contribute to aquatic ecosystem disruption. In several embodiments, electrocatalytic systems can selectively extract and up-concentrate nitrate from dilute wastewater using sodium chloride (seawater may be used as well) as a chemical input; require no electrical energy for nitrate extraction or ammonia recovery; enable homogeneous catalyst reuse over several cycles of operation; recover treated water with nitrate concentration belowthe drinking water limit and neutral pH; produce ammonia from nitrate with the low energy consumption. Electrocatalytic systems in accordance with some embodiments are compatible with homogeneous catalysts as well as heterogeneous catalysts. The compatibility of the system makes it a great candidate for scale-up toward different chemical manufacturing purposes.

[0127] Many embodiments investigate interfacial mechanisms that govern Co(DIM)- mediated NO3RR reactive separations performance in real wastewaters, and leverage these insights toward engineering molecular catalysis systems. Several embodiments develop and interrogate molecular catalysis systems capable of converting wastewater nitrate into high purity ammonia, which is enabled by several advances. First, investigating catalysis (via electrolysis, amperometry, and spectroscopy) in a systematic suite of simulated and real wastewater electrolytes elucidates the mechanistic influences of inorganic ions on reactor performance. Some embodiments investigate the role of bulk and interfacial ionic composition on activity and FE and find that magnesium ions play a deterministic role in electrode fouling. Second, these mechanistic insights enable rational design of a reactive separation unit process such as ECaB. The ECaB systems exhibit sustained activity, high FE, and low energy consumption for several cycles to treat a real, NOa-bearing wastewater: municipal secondary effluent. The ECaB systems enable longterm evaluation and benchmarking of the full unit process and its subunit processes against related NO3RR efforts and conventional nitrogen management (wastewater treatment and HB-ammonia production). The ECaB systems can also generate a high- purity TAN product with low energy consumption (about 90.0 ± 2.7 kWh kg-N-1) for various NO3RR reactive separation processes. Several embodiments leverage reactor design to improve subunit process rates toward scalable performance targets.

[0128] FIG. 1 illustrates a schematic of an electrocatalytic system in accordance with an embodiment. The electrocatalytic systems can include the processes such as (but not limited to) extraction, conversion, and recovery. The electrocatalytic systems can include reactors (such as, extraction / recovery cell and electrocatalysis cell), and recirculating electrolyte reservoirs (such as input fluid chambers, electrolyte chambers, and trapchambers). The electrocatalytic systems can operate under conditions including (but not limited to) open circuit potentials and / or a potential applied to an electrode (cathode or anode) against a reference electrode. In certain embodiments, reference electrodes may not be used. The extraction / recovery cell 101 can be a three-chamber cell where the input fluid chamber 102 can be separated from a first electrolyte chamber 103 by an ion exchange membrane (IEM) 104 and the first electrolyte chamber 103 can be separated from the trap chamber 105 by a hydrophobic gas permeable membrane (GPM) 106. The electrocatalysis cell 110 can be a two-chamber cell where a second electrolyte chamber 111 can be separated from a third electrolyte chamber 112 by a membrane 113. The membrane 113 can be a bipolar membrane (BPM), an ion exchange membrane (IEM), a cation exchange membrane (CEM), or an anion exchange membrane (AEM). The membrane 113 can be a BPM or a CEM for NO3RR. The electrolyte liquid can be circulated between the extraction / recovery cell and the electrocatalysis cell. The first, second, and third electrolyte chambers can include various electrolytes in a variety of solvents (such as, water, organic solvents). The first and the second electrolyte chambers can contain the same electrolyte, and the third electrolyte chamber can contain a different electrolyte. Electrodes 114 can be submerged in the electrolytes or contained within the electrolyte chambers. The electrodes 114 can be connected with each other. Electrical potentials can be applied through the electrodes.

[0129] Various lEMs, BPMs, and GPMs can be selected and used in the electrocatalytic system on the catalysts, reactants, and the electrolytes. lEMs can separate species based on their electrical charge and size because there are fixed charges and pores in the membrane. lEMs can include anion exchange membranes (AEMs) and / or cation exchange membranes (CEMs). AEMs have positively charged functional groups and thus can be selected for positively charged catalysts and negatively charged reactants for the electrocatalytic systems. For example, monovalent AEMs can be used for monovalent reactants. Alkaline resistant AEMs can be selected for solutions that are basic. CEMs have negatively charged functional groups and thus can be selectedfor negatively charged catalysts and positively charged reactants for the electrocatalytic systems. For example, monovalent CEMs can be used for monovalent reactants.

[0130] Various electrodes can be selected for the electrocatalytic systems. Cathodes, for catalytic reduction reactions, can connect with catholytes. Cathodes can comprise carbonaceous materials or metallic materials. Carbonaceous materials can be used as an inert conductor to conduct electrons to homogeneous catalyst. Examples of carbonaceous cathodes include (but are not limited to) glassy carbon, graphite, and carbon nanotubes. Metallic materials can be used as a heterogeneous co-catalyst to assist homogeneous catalyst with reaction steps. Examples of metallic cathodes include (but are not limited to) metal foils (e.g., Pt, Ti, Co, Au, Cu), and / or metal nanoparticles (e.g., Pt, Ti, Au, Cu). Anodes, for catalytic oxidation reactions, can connect with anolytes. Anodes can comprise boron doped diamond or metallic materials. Boron doped diamond can be used as an inert conductor to remove electrons from homogeneous catalysts. Metallic materials can be used as a heterogeneous co-catalyst to assist homogeneous catalyst with reaction steps. Examples of metallic anodes include (but are not limited to) mixed metal oxides (e.g. Ir-TaOx, CuNiOx), metals (e.g., Pt metal foil), and / or metal nanoparticles (e.g., Pt, lr).

[0131] Various catalysts can be incorporated in the electrocatalytic systems in accordance with many embodiments to perform the desired reactions. The lEMs and electrodes can be selected to accommodate the catalysts. The selected catalysts can be incorporated into the lEMs and electrodes to achieve the desired functions. For nitrate reduction (NO3RR) to ammonia, several embodiments use monovalent AEMs to transport nitrate, and glassy carbon cathode. Examples of catalysts for NO3RR reactions include (but are not limited to) metal complex 2,3-dimethyl-1 ,4,8,11-tetraazacyclotetradeca-1 ,3- diene (DIM) with a Co metal center (abbreviated Co(DIM)), cobalt macrocycle complex [Co(CR)Br2]+, and nitrate reductase (enzyme). For carbon dioxide reduction (CO2RR) to carbon monoxide, some embodiments implement AEMs to transport bicarbonate or carbonate and glassy carbon cathode. Examples of catalysts for CO2RR reactions include (but are not limited to) Fe porphyrins, and transition metal pincer complexes. For alcoholoxidation in presence of ammonia to make nitriles, some embodiments use CEMs to transport ammonium, and boron doped diamond anode. Examples of catalysts for alcohol oxidation reactions include (but are not limited to) Cu / TEMPO systems, and hydroxyimides. In various embodiments, the system can be used with heterogeneous catalyst(s) to facilitate reactions separate from the reaction matrix. Examples of heterogeneous catalysts for nitrate reduction include (but are not limited to) titanium foil or Co foil.

[0132] In various embodiments, homogeneous catalysts and molecular catalysts are used interchangeably; catalysts refer to homogeneous catalysts unless specified otherwise.

[0133] Several embodiments achieve nitrate reduction with electrocatalytic systems and homogeneous catalysts such as (but not limited to) Co(DIM) without additional separating processes. The electrocatalytic systems can include the processes such as (but not limited to) wastewater nitrate extraction, nitrate conversion to ammonia, and ammonia recovery. FIG. 2 illustrates a schematic of an electrocatalytic system for nitrate reduction in accordance with an embodiment. In various embodiments, the electrocatalytic systems can include reactors (such as, extraction / recovery cell 201 and electrocatalysis cell 202), and recirculating electrolyte reservoirs (such as reservoirs for wastewater, catholyte, anolyte, and trap). The electrocatalytic systems can operate under the applied potential conditions including (but not limited to) open circuit potential and a potential applied against a reference electrode (such as, -1.05 V vs. Ag / AgCI reference electrode). In certain embodiments, the references electrodes may not be used. The extraction / recovery cell 201 can be a three-chamber cell where the wastewater chamber 203 can be separated from the catholyte chamber 204 by an anion exchange membrane (AEM) 205. The catholyte chamber 204 can be separated from the trap chamber 206 by a hydrophobic gas permeable membrane (GPM) 207. The electrocatalysis cell 202 can be a two-chamber cell where the catholyte chamber 209 can be separated from the anolyte chamber 208 by a bipolar membrane (BPM) 210. The catholyte liquid can be circulated 211 between the extraction / recovery cell 201 and the electrocatalysis cell 202.A cathode 212 can be housed in the electrocatalysis cell catholyte chamber and an anode 213 can be housed in the electrocatalysis cell anolyte chamber.

[0134] Wastewater-NOa extraction 222 can be achieved by Donnan dialysis (DD) in the extraction / recovery cell 201 where NO3 ions exchange with Cl- ions due to an electrochemical potential gradient across the AEM 205. The catholyte recirculates between the extraction / recovery cell 201 and the BPM-separated electrocatalysis cell 202 where Co(DIM)-mediated NO3RR 224 converts NO3 to TAN. As the catholyte basifies under reducing conditions, the majority of TAN exists as NH3that is recovered 225 by diffusing across the GPM 207 into the acidic trap chamber 206.

[0135] Nitrate-rich wastewater 220 can be added to the wastewater chamber 203. Treated wastewater 221 after NO3 extraction process 222 (such as via Donnan dialysis) can be extracted from the wastewater chamber 203 for other uses. For nitrate reduction, certain embodiments use municipal secondary effluent as the wastewater 220, 1 M potassium chloride with 8 mM Co(DIM) as the catholyte, 0.1 M potassium perchlorate as the anolyte, 0.1 M sulfuric acid as the trap. At the beginning of operation, a Donnan dialysis process 222 facilitates wastewater nitrate extraction via ion exchange with catholyte chloride ions across the AEM 205 in the extraction / recovery cell. Due to the use of AEMs, the cations in the wastewater 220 cannot pass through the AEM 223. In order to increase the catholyte nitrate concentration, a higher volume of nitrate-rich municipal secondary effluent than the catholyte volume can be used. Meanwhile, the wastewater nitrate concentration decreases below the drinking water standard of about 10 mg-N / L. Donnan dialysis needs no electrochemical energy input to extract and up-concentrate nitrate in the catholyte, only the embedded energy needed to produce purified chloride salts like NaCI. Donnan dialysis paired with nitrate conversion in accordance with several embodiments can subvert the energy consumption-reaction rate tradeoff in electrochemical chemical production.

[0136] A potential of about -1 .05 V vs. Ag / AgCI can be applied to stimulate Co(DIM)- mediated electrocatalytic nitrate (NO3) conversion (nitrate reduction or NO3RR) 224, corresponding to a decrease in catholyte nitrate and an increase in catholyte ammonia.Under electrocatalytic conditions, the catholyte pH becomes basic and volatile ammonia (NH3) crosses the GPM and can be recovered (as NH4) in the acid trap during ammonia recovery process 225. In some embodiments, the wastewater remains a neutral pH (between about 5.5 to about 7.5) during the nitrate reduction processes. The treated wastewater 221 may be further treated for water reuse. In many embodiments, the combination of membrane-based Donnan dialysis 222 and membrane ammonia stripping 225 isolates the homogeneous Co(DIM) solution from the wastewater feed and the ammonia product, enabling treated wastewater recovery, product total ammonia nitrogen (TAN) recovery, and homogeneous catalyst reuse.

[0137] The electrocatalytic systems in accordance with many embodiments are selective for inorganic small molecules (such as nitrate and carbon dioxide) that are soluble in most solvents. The homogeneous catalysts can be dissolved in a solvent without the need of support materials. The AEM that separates the wastewater chamber and the catholyte chamber allows only anions to pass into the catholyte and react with the catalysts such that the electrocatalytic systems can minimize catalyst poisoning due to the presence of poisons present in the solvent. The GPM that separates the catholyte chamber and the trap chamber allows gaseous phase products to pass through such that the systems eliminate the need for separation of the products. In various embodiments, the electrocatalytic systems operate under a low voltage and are less energy intensive.

[0138] Systems and methods for molecular electrocatalytic systems in accordance with various embodiments of the invention are discussed in further detail below.Electrocatalytic Systems

[0139] The primary NOs -rich wastewaters are municipal secondary effluent and fertilizer runoff. Thus, NO3RR processes need to operate with feed compositions of dilute NO3 (<4 mM), low conductivity (<2 mS cm-1), and water hardness (i.e., presence of divalent metal cations). Many embodiments use secondary effluent containing 120 mg NO3- / L (28 mg NO3-N / L, 2.0 mM NO3) and a matrix of anions, alkaline earth metal cations, suspended solids, and organic and inorganic carbon. Table 1 lists thecompositions of the secondary effluent. Within this complex composition, several embodiments uncover the promoting or inhibiting effects of specific wastewater constituents on Co(DIM)-mediated NO3RR. Toward this goal, certain embodiments assess NO3RR performance as a function of electrolyte composition and provide generalizable interfacial mechanisms that influence Co(DIM)-mediated NO3RR behavior. These insights enable the reactive separations process ECaB. ECaB systems show robust performance with real wastewater. In some embodiments, ECaB systems show improved subunit process rates toward tractable performance targets.Table 1. Simplified, simulated, and real wastewater characterization.*Fluoride, nitrite, bromide, phosphate, and lithium are measured but not detected in the real wastewater by ion chromatography.

[0140] Several embodiments provide effects of bulk electrolyte composition on observed NO3RR performance. Cyclic voltammetry (CV) and controlled-potential electrolysis (CPE) elucidate Co(DIM)-mediated NO3RR catalytic activity and selectivity as a function of electrolyte composition. In Figure 3A, the GC working electrode without Co(DIM) in solution is inactive for NO3RR (NaCI and NaCI + NaNOs curves). In the presence of Co(DIM), two reversible redox peaks exist, the first at E1 / 2 = +0.24 V vs. Ag / AgCI (putatively CoIH / l1redox) and the second at E1 / 2 = -1 .00 V vs. Ag / AgCI (putatively CoH / lredox). With both Co(DIM) and NO3 in solution, catalysis is evidenced by an increased current density (i.e., catalytic current) of the second reductive wave and loss of reversibility on the reverse (anodic) scan. Catalytic current is caused by a local enrichment of [Co(DIM)] during heterogeneous activation and homogeneous NO3RR in the reaction-diffusion layer (RDL). With higher Co(DIM) concentration (i.e., lower excess factor), the second reduction peak current increases linearly both in the presence and absence of NO3. Prior work showed that the rate of homogeneous Co(DIM)-mediated NO3RR is independent of pH and is first order with respect to [Co(DIM)] (0.5-5 mM) and [NO3] (5-100 mM). Figure 3B shows that homogeneous NO3RR catalysis is first order with respect to [Co(DIM)] even at low excess factors (excess factor = [NO3] / [Co(DIM]) than tested previously (i.e., < 2), indicating catalysis outpaces bulk-phase catalyst diffusion. Additionally, the catalytic waveforms of 8 mM Co(DIM) are effectively identical in synthetic electrolyte (6.2 mM NaCI + 2 mM NaNOs) and in the real wastewater (Figure 4) at 100 mV s-1, implying intrinsic catalytic activity is unaffected by complex wastewater electrolyte. This conclusion is tested in two-chamber CPE experiments with three catholytes (Table 1 ). The sum of NO3-N and TAN mass (Figure 5A) remains near unity for all catholytes (97.7 ± 10.0% for simplified, 100.8 ± 4.7% for simulated, and 97.0 ± 4.8% for real wastewater). TAN selectivity (93.8 ± 7.3% for simplified, 106.5 ± 1.6% for simulated, and 79.5 ± 16.1 % for real wastewater) and FE (41.4 ± 2.4% for simplified, 41.2 ± 1 .6% for simulated, and 43.1 ± 7.0% for real wastewater) remains relatively unaffectedby electrolyte composition; neither the difference between simplified and simulated CPEs (p = 0.13 > 0.05 for selectivity, p = 0.17 > 0.05 for FE) nor the difference between simplified and real CPEs (p = 0.14 > 0.05 for selectivity, p = 0.62 > 0.05 for FE) are statistically significant (Figure 5B). Co(DIM) therefore enables selective NO3RR to TAN in dilute NO3 conditions. However, NO3 conversion is significantly lower in simulated (12.4 ± 1.0%, p = 0.029 < 0.05) and real (10.3 ± 3.1 %, p = 0.0083 <0.05) wastewaters compared to simplified wastewater (32.6 ± 6.1 %). Simulated wastewater is also a high- fidelity proxy of real wastewater, as demonstrated by the lack of significant difference in conversion between these two streams (p = 0.31 > 0.05). Therefore, inorganic ionic constituents in the wastewater matrix are most responsible for inhibiting catalyst activity.

[0141] Figure 3A illustrates cyclic voltammograms collected in 6.2 mM NaCI (background electrolyte matching the Cl- concentration in real wastewater), 6.2 mM NaCI with 2 mM NaNOs (background electrolyte with representative nitrate concentration), 6.2 mM NaCI with 8 mM Co(DIM) (background electrolyte with catalyst), and 6.2 mM NaCI with 2 mM NaNOs and 8 mM Co(DIM) (background electrolyte with catalyst and representative nitrate concentrations). Working electrode: 5 mm GC disk. Counter electrode: 6.4 mm graphite rod. Reference electrode: Ag / AgCI (4.0 M KCI). Scan rate: 100 mV s-1.

[0142] Figure 3B illustrates peak current density of the second reduction peak (~ -1.1 V vs. Ag / AgCI) of 6.2 mM NaCI with 8 mM Co(DIM) in the presence and absence of 2 mM NaNOs. The excess factor, defined as the concentration of substrate (NO3) divided by the concentration of catalyst (Co(DIM)), ranged from 2 to 200 previously. To address diluted real wastewaters, some embodiments minimize the excess factor with 8 mM Co(DIM) (the observed solubility limit at room temperature) to maximize NO3RR activity (excess factor = 0.25).

[0143] Figure 4 illustrates CVs of 8 mM Co(DIM) in real secondary effluent wastewater and in simplified wastewater (6.2 mM NaCI + 2 mM NaNOs) for comparison. Working electrode: 5 mm GC disk. Counter electrode: 6.6 mm graphite rod. Reference electrode: Ag / AgCI (4.0 M KCI).

[0144] Figure 5A illustrates mass balance of aqueous nitrogen species as a function of time during two-chamber controlled-potential electrolysis (CPE) experiments at -1.05 V vs. Ag / AgCI performed in three electrolytes: 8 mM Co(DIM) in simplified wastewater, 8 mM Co(DIM) in simulated wastewater, and 8 mM Co(DIM) in real wastewater. Error bars represent ± one standard deviation from triplicate experiments (n=3). For all three electrolytes, NO3-N and TAN closed the nitrogen mass balance within ± 3%. No TAN is detected after CPE without NO3 (Figure 6), confirming that measured TAN is the result of NO3RR. The closed mass balance and catalytic TAN formation support that NO3RR selectivity to TAN remained near 100% in all three electrolytes tested.

[0145] Figure 5B illustrates cumulative TAN selectivity, TAN faradaic efficiency, and NO3 conversion for 8-hour CPE experiments.

[0146] Figure 5C illustrates Mg 1s XPS spectra of the glassy carbon plate cathode after CPE experiments. After CPE the electrode is rinsed with nanopure water and blown dry with N2 before XPS and SEM-EDS analysis. Figure 5D and Figure 5E show SEM image and Mg EDS map respectively of glassy carbon plate cathode after a CPE experiment in real wastewater, showing dispersed deposits of Mg on the surface.

[0147] Figure 6 illustrates cation chromatograms of aqueous samples from CPEs in modified simplified wastewater (8 mM Co(DIM) + 6.2 mM NaCI) and in simplified wastewater (8 mM Co(DIM) + 6.2 mM NaCI + 2 mM NaNOs).

[0148] Figure 7 illustrates charge decomposition into the first Co(DIM) reduction, second Co(DIM) reductions, and NO3RR. -1 .05 V vs. Ag / AgCI applied for NO3RR (yellow; simplified wastewater: 8 mM Co(DIM) + 6.2 mM NaCI + 2 mM NaNOs) and 2ndCo(DIM) reduction (green; modified simplified wastewater: 8 mM Co(DIM) + 6.2 mM NaCI). -0.75V vs. Ag / AgCI (-0.99 V vs. first reduction, +0.25 V vs. second reduction) applied for 1stCo(DIM) reduction (purple; simplified wastewater: 8 mM Co(DIM) + 6.2 mM NaCI + 2 mM NaNOs). Error bars represent ± one standard deviation from triplicate experiments (n=3) for NO3RR experiments (yellow; simplified wastewater: 8 mM Co(DIM) + 6.2 mM NaCI + 2 mM NaNOs). The CPE experiments to quantify charge associated with non-catalytic 1stand 2ndreductions of Co(DIM) are only performed once because no conversion of nitrate and no production of TAN is observed.

[0149] Whereas NO3RR activity is strongly influenced by wastewater impurities, the relatively low FETAN is primarily influenced by NO3 concentration. Under purely kinetic conditions, Co(DIM)-mediated NO3RR is first order in [Co(DIM)] and [NO3], motivating the high catalyst concentrations employed in CVs and CPEs. However, purely kinetic conditions do not apply in the CPE experiments because the low excess factor imposed by the wastewater caused substrate consumption in the RDL, and consequently a significant amount of current is consumed by non-catalytic reductions of Co(DIM). Several control CPE experiments are performed to quantify non-catalytic charge allocation (i.e., FE). CPE at - 0.75VAg / Agci (-0.99 V vs. first reduction, +0.25 V vs. second reduction) in simplified wastewater (6.2 mM NaCI + 2 mM NaNOs) serve as a proxy for non-catalytic charge toward the first reduction of Co(DIM); CPE at -1 .05VAg / Agci in a modified simplified wastewater (6.2 mM NaCI + 0 mM NaNOs) serve as a proxy for non-catalytic charge toward the first and second reductions. The sum of charge associated with non-catalytic reductions of Co(DIM) accounts for 89.4% of charge passed in the simplified wastewater CPEs (Figure 6 and Figure 7), reasonably closing the balance of FE. Notably, the non- catalytic charge passed (49.3% FE) exceeds the catalytic charge passed (41.4 ± 2.4% FE). The excess factor therefore significantly influences the ratio of activated Co(DIM) molecules that successfully perform NO3RR in the homogeneous phase.

[0150] Because only NO3 conversion is significantly changed as a function of electrolyte composition, electrode fouling in simulated and real wastewater may reduce the observed NO3RR rate by impeding Co(DIM) activation at the heterogeneous electrode-electrolyte interface. Visible deposits are present on the electrode after 8 hours for all three electrolytes, prompting spectroscopic and electrochemical characterization of the GC surface. Based on simulated wastewater exhibiting electrode fouling, hardness (e.g., Mg2+, Ca2+) and HCOs / COf- ions can be precipitate components. XPS (Figure 5C) and SEM / EDS (Figures 5D and 5E) reveal magnesium on the GC surface for real and simulated wastewater. The pH required for precipitation of Mg(OH)2 from 1 .5 mM Mg2+is9.8. Table 2 lists possible precipitates from real secondary effluent wastewater. Because the bulk pH of all three catholytes remained below 9.8 (Figure 8), the interfacial pH in the RDL likely exceeds pH 9.8, which is common under reducing electrochemical conditions. No significant precipitation of Ca2+is observed by EDS after real wastewater CPE, implying that the interface remains below pH 12.8 required to precipitate Ca(OH)2 from 1.9 mM Ca2+. Some embodiments compare the catalytic activity and charge transfer resistance of the deposits formed on GC cathodes in simplified and real wastewaters. In rinse tests, both deposits are less active than homogeneous Co(DIM) and are not selective for TAN or NO2 (Figure 9 and Figure 10). Thus, the Mg-containing deposits may not be catalytic for NO3RR. The charge transfer resistance between the electrode surface and homogeneous Co(DIM) at the open circuit potential (OCP) is greater for the real deposit (Ret = 310 kQ) than for the simplified deposit (Ret - 189.4 kQ) and the pristine GC surface (Ret = 132.7 kQ) (Fig. S14). In conjunction with the insensitivity of TAN FE and selectivity to electrolyte composition (Figure 5B), greater charge transfer resistance suggests that catalysis is heterogeneously inhibited by Mg deposition and that the homogeneous Co(DIM)-mediated NO3RR mechanism is unaffected by real wastewater impurities.Table 2. Possible precipitates from real secondary effluent wastewater.*KsPshown for CaCCh corresponds to calcite, which has the lowest Kspamong possible precipitates.

[0151] Figure 8 illustrates pH trends of 2-chamber CPEs as a function of time. Error bars represent ± one standard deviation from triplicate experiments (n=3). Error bars not shown are smaller than the symbol.

[0152] Figure 9 illustrates nitrogen mass balances for the rinse test (in simplified wastewater) of the deposit formed in {8 mM Co(DIM) + simplified wastewater}. No TAN or NO2 is detected by ion chromatography. Detection limit for NO3 : 1.0 mg-NOa / L. Detection limit for NO2: 1.0 mg-NO^ / L. Detection limit for TAN: 0.25 mg NH4 / L.

[0153] Figure 10 illustrates N mass balances for the rinse test (in real wastewater) of the deposit formed in {8 mM Co(DIM) + real wastewater}. No TAN or NO2 is detected by ion chromatography. Detection limit for NO3: 1.0 mg-NOa / L. Detection limit for NO2: 1.0 mg-NO^ / L. Detection limit for TAN: 0.25 mg NH4 / L.

[0154] To identify specific inhibiting species, a small volume (28-38 pL, matching real wastewater concentrations, Table 1 ) of 1 M solutions (MgCh, CaCl2, and NaHCOs) is dosed into simplified wastewater electrolyte with 8 mM Co(DIM) (Figure 11A). Currentdensity remains unchanged for all dosed species during uninterrupted rotating-disk electrode (RDE) CPE experiments (green trace), contrary to the RDE CPE in real wastewater showing a distinct decay in current density (Figures 12A and 12B). However, introducing an open circuit potential (OCP; purple trace) period can cause a decay in current density for the Mg2+dose experiment, but not for Ca2+or HCO3. XPS detects Mg deposits on the GC surface with an OCP period but not for uninterrupted CPE (Figure 11 B), further highlighting Mg2+as the major foulant responsible for catalysis inhibition. If Mg2+is homogeneously dispersed throughout the electrolyte when CPE begins (the case for CPE after an OCP period), Mg2+can specifically adsorb to the GC cathode. When the pH conditions for precipitation are met in the RDL, adsorbed Mg2+ions form Mg deposits (most likely Mg(0H)2 based on the solubility product quotient, Qsp, versus the solubility product constant, Ksp; Table 2), passivating the electrode. Conversely, if the RDL is established prior to introducing Mg2+(the case for uninterrupted CPEs), positively- charged Co(DIM) in the RDL electrostatically and / or sterically impedes specific adsorption of Mg2+. Thus, even if the pH conditions for precipitation are met in the RDL, repulsive interactions between Co(DIM) and Mg2+may preclude precipitation and passivation for minutes to hours. To further confirm the role of Mg2+, prolonged passivation is tested in two ways. First, a longer CPE following Mg2+in RDE (Figure 13) shows no change in current density over 40 min but showed an immediate decay in current density after an OCP period. Second, two-chamber CPEs for 8 hours (same two-chamber CPE setup as in Figure 1 ; closed nitrogen mass balances in Figures 14A through 14D) with contaminant doses showed <6.3% change in NO3 conversion and TAN production (Figure 15). Thus activity, selectivity, and FE are unaffected by Mg2+, Ca2+, and HCO3 doses when Co(DIM) protects against passivation.

[0155] Magnesium precipitation during Co(DIM)-mediated electrocatalytic NO3RR is generalizable to reductive homogeneous electrocatalysis and to NO3RR (heterogeneous or homogeneous) in real wastewaters. Similar precipitation processes have been observed in homogeneous CO2 reduction electrocatalysis, and water hardness (i.e., Mg2+, Ca2+) has been shown to decrease heterogeneous NO3 removal. In the secondaryeffluent (1.5 mM Mg2+), a negligible proportion of Mg2+present is consumed to form a passivating cathode deposit (Figure 16). Other nitrate-rich wastewaters like polluted groundwaters, reverse osmosis brines, and ion exchange brines may contain higher Mg2+concentrations (up to 84 mM), increasing the likelihood of forming precipitates. Mg2+electrode fouling is likely a widespread barrier to implementation. A reactive separation system could conceivably perform uninhibited NO3RR directly in the native wastewater if divalent cations are repelled by near-surface confined Co(DIM) molecules. This insight motivates repulsive moieties at the electrode-electrolyte interface as a design principle for the microenvironment of homogeneous and heterogeneous catalyst systems. Electrode and catalyst design (e.g., heterogeneous molecular catalysts, single-atom catalysts, ionomer coatings) could protect the cathode from passivation, but would not address the low TAN FE induced by inherently low NO3 concentrations in real wastewaters. Some embodiments address cathode protection and FETAN with reactive separations that selectively extract and up-concentrate NO3 (and reject Mg2+) from wastewater before catalysis.

[0156] Figure 11A illustrates current density vs. time of RDE CPEs at -1.05 V g / Agci with suspected foulants manually dosed into the electrolyte at t = 10 min (no contaminant dose, 28 pL 1 M MgCl2, 30 pL 1 M NaHCOs, 38 pL 1 M CaCI?). Two experiment conditions are compared: the first experiment held -1 .05 VAg / Agci for the full 50 minutes (green trace), and the second experiment introduced a period of open circuit potential (OCP) from t = 20 min to t = 30 min. The counter electrode is a 6.4 mm graphite rod, and the reference electrode is a Ag / AgCI (4.0 M KCI) electrode. The RDE is operated at 25 rotations per minute (RPM) because both catalytic current (for simplified wastewater) and inhibition (for real wastewater) are observed at this rotation rate.

[0157] Figure 11 B illustrates Mg 1 s XPS of the glassy carbon RDE post Mg2+dose CPE for both the uninterrupted CPE and the CPE with OCP period.

[0158] Figure 12A illustrates current density vs. time for controlled-potential electrolysis (CPE) at -1.05 V vs. Ag / AgCI performed in a rotating-disk electrode (RDE) setup with 8 mM Co(DIM) as a function of rotations per minute (RPM) in three electrolyte:simplified wastewater (0 mM NO3 ), simplified wastewater (2 mM NO3 ), and real wastewater(2 mM NO3). The controlled rotation rate varies the delivery of NO3, Co(DIM), and wastewater constituents to the RDL while the current density was monitored as a proxy for the NO3RR activity. Rotation rates are kept below 400 RPM because faster rotation rates resulted in loss of catalytic current (i.e. , the same current density was observed for simplified wastewater (0 mM NO3) and simplified wastewater (2 mM NO3)).

[0159] Figure 12B illustrates steady-state currents of RDE CPEs from Figure 11A plotted versus the square root of rotation rate (a proxy for diffusion layer thickness). In the presence of nitrate and under sufficiently fast rotation rates, bulk catalyst delivery outpaces NO3RR, causing the green and blue points to be nonlinear.

[0160] Figure 13 illustrates a chronoamperogram for a longer Mg dose RDE CPE experiment. -1.05 VAg / Agci is applied from t = 0 to 50 minutes. 28 pL of 1 M MgCh is injected into the electrolyte at t = 10 min. Then a period of open circuit potential (OCP) is held from t = 50 min to 60 min. Finally, -1.05 VAg / Agci is applied from t = 60 to 110 minutes.

[0161] Figure 14A illustrates N mass balance for a Ca2+dose two-chamber CPE experiment. 95 pL 1 M CaCl2 was injected into the catholyte at t = 2 h. Figure 14B illustrates N mass balance for a Mg2+dose two-chamber CPE experiment. 70 pL 1 M MgCl2 was injected into the catholyte at t = 2 h. Figure 14C illustrates N mass balance for a HCO3 dose two-chamber CPE experiment. 75 pL 1 M NaHCOs was injected into the catholyte at t = 2 h. Figure 14D illustrates N mass balance for a simultaneous Mg2+and HCO3 dose CPE experiment. 75 pL 1 M NaHCOs and 70 pL 1 M MgCl2 were injected into the catholyte at t = 2 h.

[0162] Figure 15 illustrates nitrate conversion for contaminant dose two-chamber CPE experiments.

[0163] Figure 16 illustrates Mg mass as a function of time for real wastewater CPE, simulated wastewater CPE, and Mg dose CPE. Error bars represent ± one standard deviation from triplicate experiments (n=3). Note that Mg dose CPE data are from oneexperiment. Consumption of Mg in real wastewater CPE: 8.6 ± 1 .3%. Consumption of Mg in Simulated wastewater CPE: 15.3 ± 1.3%. Consumption of Mg in Mg dose CPE: 10.6%.

[0164] Several embodiments mitigate cathode passivation in NO3RR by pre-catalysis extraction of NO3 from wastewater via reactive separations. Extracting NO3 into a synthetic electrolyte for Co(DIM)-mediated NO3RR could be achieved by electrochemical separations such as electrodialysis, capacitive deionization, or electrosorption, but in low- conductivity NOs-rich wastewaters, electrochemical extraction can dominate the total process energy consumption. This observation motivates low-energy extraction methods like Donnan membrane dialysis. Because Donnan equilibrium conditions are governed by electrochemical potentials (not concentrations) across the membrane, NO3 ions can diffuse against their concentration gradient by exchanging with high-activity receiver solution anions (e.g., Cl-). If the receiver solution volume is less than the feed solution (wastewater) volume, NO3 in the receiver solution can be substantially up-concentrated relative to the feed concentration. The resulting receiver solution is an ideal electrolyte for NO3RR because of its high conductivity, high NO3 concentration, and absence of Mg2+. Donnan dialysis (DD) can also obviate challenges imposed by complex electrolyte compositions (e.g., high [Cl-], divalent ions, organics), like unselective ion extraction, high energy consumption, and high capital costs. Some embodiments provide a combined DD, NO3RR, and ammonia stripping system as shown in Figure 2.

[0165] The ECaB unit process performs three subunit processes - wastewater NO3 extraction 222, NO3 conversion to TAN 224, and TAN recovery 225 - in a configuration of four electrolyte reservoirs (wastewater, catholyte, anolyte, and trap) and two applied potential conditions (OCP and -1.05 VAg / Agci). First, DD facilitates wastewater NO3 extraction via ion exchange with catholyte CFions across an AEM 205. To up-concentrate the catholyte NO3, some embodiments use four times as much municipal secondary effluent volume (200 mL) as catholyte volume (50 mL). In ECaB experiments (Figure 17A), the catholyte NO3 is up-concentrated by 2.9 times from 27.8 ± 0.5 mg-N / L (2.0 ± 0.04 mM) to 80.8 ± 2.8 mg-N / L (5.8 ± 0.2 mM) over the first 24 h OCP period when only DD is active. Meanwhile, the wastewater NO3 concentration decreases to 5.0 ± 0.9 mg-N / L (0.36 ± 0.06 mM), below the drinking water standard of 10 mg-N / L, at a NO3 removal rate (7.8 ± 0.1 mg NO3-N L-1day-1) that exceeds conventional wastewater treatment (i.e., nitrification-denitrification; ~5 mg NO3 -N L-1day-1). DD requires no electrochemical energy input to extract and up-concentrate NO3 in the catholyte, only the embedded energy requirement to produce NaCI. DD paired with NO3RR therefore subverts the energy consumption-reaction rate tradeoff in NO3RR reactive separations. At 24 h, -1.05 VAg / Agci is applied to stimulate Co(DIM)-mediated NO3RR (24-34 h), corresponding to a decrease in catholyte NO3 and an increase in catholyte TAN. -1 .05 VAg / Agci is held for 10 h periods to keep Co(DIM) in its stable operating pH regime; operation for longer than 10 h in these experiments result in catholyte pH >11 and significant decrease in FETAN. After 6 h of CPE, the catholyte pH (Figure 18) is sufficiently alkaline for catholyte TAN to exist primarily as NH3 ( pKaNH+ / NH3= 9.25), which volatilizes, crosses the GPM, and is recovered in the acid trap (0.1 M H2SO4). ECaB is recirculated overnight (34-48 h) at open circuit as the remaining TAN migrated across the GPM. At 48 h, the catholyte is adjusted back to pH 6 with ~200 pL 10 wt% HCI to keep Co(DIM) in its stable operating pH regime before a second cycle of CPE (48-58 h) and OCP (58-72 h) begins. ECaB experiments are performed for three cycles for a total of 96 h (30 cumulative hours of CPE). The total measured N masses (Figure 17B) at 24 h, 48 h, 72 h, and 96 h accounted for 97.6 ± 1.4%, 88.7 ± 5.1 %, 84.1 ± 2.7%, and 84.9 ± 1.8% of the influent wastewater NO3-N. Binding of NH3 to Co(DIM) can be the largest contributor to unclosed mass balances because the largest changes occur during recirculation at OCP from 34-48 h and Co(DIM) in its Co(lll) oxidation has a high NH3 binding capacity (at least 1.6 mM TAN / mM Co(DIM); Figures 19A through 19C). Unlike many electrolysis approaches, the wastewater remains circumneutral for the duration of experiments (pH 7.07 ± 0.25 at t = 96 h, Figure 18), demonstrating potential for downstream water reuse. Combining membrane-based DD and ammonia stripping isolates the homogeneous Co(DIM) solution from the wastewater feed and the TAN product (Figure 20), enabling treated wastewater recovery, product TAN recovery, and homogeneous catalyst reuse. Thiscatalyst reuse is similar to catalyst-in-a-cup (in which thermal homogenous catalysts are separated from solvents, reactants, and products in chemical production).

[0166] Figures 17 A and 17B illustrate NO3 and TAN concentrations and nitrogen mass balance respectively for electrocatalyst-in-a-box experiments. Error bars represent ± one standard deviation from triplicate experiments (n=3). Detailed experimental parameters of ECaB tests can be found in the Examples section. Time periods where the electrochemical cell is held at open circuit (OCP; 0-24 h, 34-48 h, 58-72 h, 82-96 h) are indicated by a white background and time periods where the electrochemical cell is held at — 1 .05 Ag / Agci (24-34 h, 48-58 h, 72-82 h) are indicated by a green background. Applied potentials are held for 10 h at a time to keep Co(DIM) in its stable operating pH regime. The dashed line in Figure 17A indicates the drinking water limit of 10 mg NO3-N / L.

[0167] Figure 18 illustrates pH trends of the 4 chambers in ECaB. Error bars represent ± one standard deviation from triplicate experiments (n=3).

[0168] Figures 19A through 19C illustrate binding of TAN to Co(DIM). Experiments are carried out by adding 0, 1 , 2, 4, 8, 16, or 32 mM NH3 (as NH4OH) to vials of 1 M KCI + 8 mM Co(DIM), pH 10.5. Vials are shaken vigorously for 4 h, acidified with concentrated H2SO4, and then TAN is measured by cation IC. Figure 19A shows TAN concentration detected by cation IC as a function of NH3 concentration added. Deviation from the dotted line (y = x) indicates TAN adsorption by Co(DIM). Figure 19B shows the percentage of TAN detected as a function of NH3 added. More of the added nitrogen binds to Co(DIM) at low NH3 concentrations. Figure 19C shows observed TAN binding capacity of Co(DIM).

[0169] Figure 20 illustrates concentration of Co (59Co) in each chamber of ECaB at initial (0 h) and final (96 h) time points. Co concentration is below detection (0.85 pM) for the initial and final wastewater time points, and for the initial trap and anode time points. These data demonstrate that Co(DIM) remains in the cathode chamber of ECaB. Error bars represent ± one standard deviation from triplicate experiments (n=3).

[0170] By decomposing NO3 refining performance into subunit processes ( NO3 extraction, NO3 conversion, and TAN recovery), ECaB facilitates systematic comparisons of NO3 refining studies in terms of efficiencies, rates, and energy consumption (Tables 3-6). The overall nitrogen recovery efficiencyis theproduct of NO3 extraction efficiency, TAN yield, and TAN recovery efficiency Figure 22). For ECaB, 98.1 ± 0.3% of wastewater NO3 is extracted by the end of the 96 h experiments, with 81.3 ± 3.3% extracted in the first 24 hours (Figure 21 A). 60.8 ± 1.1 % of extracted NO3 is converted via Co(DIM)-mediated NO3RR and 91.0 ± 2.1% of produced TAN is recovered in the trap. Overall, 42.6 ± 1 .4% of influent wastewater NO3- N is recovered as TAN. ECaB can prevent cathode Mg fouling and enable sustained NO3 conversion via selective NO3 extraction (Figures 23A through 23C). Despite having a more complex composition, ECaB with real wastewater outperformed CPE in simplified wastewater in terms of FETAN (Figure 21 B) and NO3 conversion rate (Figure 21 C). Additionally, Mg2+is not detected in the catholyte nor on the GC surface by XPS or EDS, reinforcing that Co(DIM)-mediated NO3RR activity in ECaB is not inhibited by cathode passivation. ECaB exemplifies a reactive separation process for treating real wastewater, and outperforms a simplified (i.e. , ideal) system driven by insights of wastewater-induced inhibition.Table 3. Efficiency, rate, and energy of ECaB: Nitrate extractionTable 4. Efficiency, rate, and energy of ECaB: Nitrate conversion by NO3RRTable 5. Efficiency, rate, and energy of ECaB: TAN production by NO3RRTable 6. Efficiency, rate, and energy of ECaB: TAN recovery

[0171] Figure 21 A illustrates cumulative NO3 extraction efficiency (nN0-Extraction), TAN yield ( YTAN), TAN recovery efficiency ( nTAN Recovery), and overall nitrogen recovery efficiency ( nOvera|| N Recovery) during ECaB experiments. Error bars represent ± one standard deviation from triplicate experiments (n=3). Detailed experimental parameters of ECaB tests can be found in the Examples section. Time periods where the electrochemical cell is held at open circuit (OCP; 0-24 h, 34-48 h, 58-72 h, 82-96 h) are indicated by a white background and time periods where the electrochemical cell is held at -1 .05 VAg / Agci (24-34 h, 48-58 h, 72-82 h) are indicated by a green background.

[0172] Figure 21 B illustrates cumulative FETAN as a function of cumulative CPE duration.

[0173] Figure 21 C illustrates pseudo-instantaneous NO3 conversion rate (nitrate converted over one sample period divided by the preceding sample period nitrate concentration).

[0174] Figure 22 illustrates overall N recovery of ECaB calculated two ways. Black trace is calculated as the mass of TAN in the trap divided by the initial mass of nitratenitrogen in the wastewater. Blue is calculated by multiplying the nitrate extraction efficiency, the yield of TAN, and the TAN recovery efficiency. Error bars represent ± one standard deviation from triplicate experiments (n=3).

[0175] Figure 23A illustrates amount (in milliequivalents of charge) of nitrate and sulfate ions in wastewater chamber as a function of time for ECaB. Error bars represent ± one standard deviation from triplicate experiments (n=3).

[0176] Figure 23B illustrates extraction flux (normalized to concentration in milliequivalents of charge) of nitrate and sulfate ions as a function of time for ECaB. Error bars represent ± one standard deviation from triplicate experiments (n=3).

[0177] Figure 23C illustrates extraction selectivity (calculated as the fraction of nitrate flux divided by sulfate flux) of nitrate ions over sulfate ions as a function of time for ECaB. Error bars represent ± one standard deviation from triplicate experiments (n=3).

[0178] The ECaB system can recover a pure (NH4)2SO4 with low energy consumption (90.0 ± 2.7 kWh kg-N-1) for a NO3RR reactive separation process (Figure 24), due to the selectivity and FETAN of Co(DIM)-mediated NO3RR in relatively dilute NO3 (< 5.8 ± 0.2 mM for all time points). Energy consumption is a major driver of wastewater treatment technology feasibility and is therefore a crucial metric to compare to related systems and to incumbent processes. ECaB demonstrates that its subunits (NO3 extraction, NO3 conversion, and TAN recovery; Figure 24) consume a proportionate amount of energy in an integrated unit process format. The cumulative energy consumption is also achieved from real wastewater using reactive separations, demonstrating robust process capabilities (Figure 24). The cumulative energy consumption of ECaB is within 3.6-7.1 times that of conventional centralized nitrogen management (12.7-25.1 kWh kg-N-1), consisting of HB ammonia production (7.7-10.1 kWh kg-N-1) and nitrificationdenitrification (NDN) wastewater treatment (5-15 kWh kg-N-1). Additionally, the cost of producing ammonium sulfate in ECaB is $2.70 kg-N-1and competitive with the retail price ($2.89 kg-N-1) if electricity is considered the only operational expenditure. The low energy consumption and product cost in ECaB are promising, but the long operational timescale (96 h) is limited by the relatively slow NO3 conversion subunit rate (Figures 25A through 25H).

[0179] Figure 24 illustrates energy consumption of NO3 extraction, NO3 conversion, TAN production, and TAN recovery subunit processes for reports of reactive separations in NO3RR processes. Error bars for This Work represent ± one standard deviation from triplicate experiments (n=3). Error bars are included as-reported for references a, c, and e. Figure 24 shows ECaB energy consumption (kWh kg-N-1) where the numerator is thesame energy for all metrics and the denominator is the nitrogen mass associated with NO3 extraction, NO3 conversion, TAN production, and TAN recovery. Energy consumption values shown are therefore cumulative, such that a subunit process energy consumption is the sum of all preceding subunit processes (i. e. , TAN recovery will always be largest because it is the sum of all subunit processes). Equations used to calculate energy consumption are detailed in the Examples section. For ECaB, NO3 extraction and TAN recovery do not explicitly consume energy but are calculated as non-zero values here as the electrochemical energy consumed divided by the mass of nitrogen extracted or recovered, respectively. References for reported values from NO3RR studies in literature are as follows: a, (See, e.g., M. J. Liu, et al., Environ. Sci. Technol. Lett., 2023, 10, 458-463; the disclosure of which is incorporated by reference.) b, (See, e.g., K. Kim, et al., Nat Common, 2023, 14, 823; the disclosure of which is incorporated by reference.) c, (See, e.g., J. Gao, et al., Environ. Sci. Technol., 2022, 56, 11602-11613; the disclosure of which is incorporated by reference.) d, (See, e.g., J. Gao, et al., Environ. Sci. Technol., 2021 , 55, 10684-10694; the disclosure of which is incorporated by reference.) e, (See, e.g., P. Gayen, et al., Environ. Sci. Technol., 2018, 52, 9370-9379; the disclosure of which is incorporated by reference.) f, (See, e.g., J. Wang, et al., Journal of Environmental Management, 2020, 276, 111357; the disclosure of which is incorporated by reference.) g, (See, e.g., H. Cheng, et al., Chemical Engineering Journal, 2005, 108, 257-268; the disclosure of which is incorporated by reference.) h, (See, e.g., I. Katsounaros, et al., Journal of Hazardous Materials, 2009, 171 , 323-327; the disclosure of which is incorporated by reference.) i. (See, e.g., Y. Chen, et al., EES. Catal., 2023, 1 , 504-515; the disclosure of which is incorporated by reference.) Studies e, f, and g focus on removal of NO3 as N2. The dashed lines indicate the energy consumption of Haber- Bosch (HB), nitrification-denitrification (NDN), and the summed energy consumption of HB+NDN.

[0180] Figures 25A and 25B illustrate areal (normalized to AEM area) and volumetric (normalized to wastewater volume) nitrate extraction rates respectively. Figures 25C and 25D illustrate areal (normalized to GC area) and volumetric (normalized to catholytevolume) nitrate conversion rates respectively. Figures 25E and 25F illustrate areal (normalized to GC area) and volumetric (normalized to catholyte volume) TAN yield rates respectively. For nitrate conversion and TAN yield time is cumulative time of CPE. Figures 25G and 25H illustrate areal (normalized to GPM area) volumetric (normalized to catholyte volume) TAN recovery rates respectively. AEM, GC, and GPM have the same geometric surface area (5.4 cm2). Error bars represent ± one standard deviation from triplicate experiments (n=3) of ECaB.

[0181] Because ECaB subunit processes rely on preceding subunits, the rate-limiting NO3 conversion subunit can be improved by process engineering of the preceding NO3 extraction step. DD equilibrium calculations suggest that catholyte [NO3] up-concentration could exceed 100x from the 2 mM wastewater-NOs feed solution. In subunit engineered ECaB experiments, a commercial electrolyzer is used with a serpentine flow field to minimize solution-phase mass transport limitations (Figures 26A and 26B). This modification enables NO3 extraction in subunit engineered ECaB to treat 10x the volume of wastewater to below the drinking water [NO3] limit in the same 24 h period (67.5% of NO3 extracted; Figures 27A and 27B; Figure 28A through 28D). The corresponding subunit engineered NO3 extraction rate (151.6 pg-N cm-2IT1) is 14.6x that of the nonsubunit version (Table 7, Figures 29A through 29C). The resulting up-concentrated catholyte [NO3] is 54.4 mM, which improves the NO3 conversion subunit by Co(DIM)- mediated NOsRR’s first order dependence on [NO3]. Subunit engineered ECaB achieves a TAN partial current density QTAN) of 5.1 mA cm-2(319.6 pg-N cm-2h-1): 20.4x that nonsubunit version. Improved JTAN enables a TAN yield of 82.5% in only 8 h. Though no modifications are made to the TAN recovery subunit, TAN recovery rate is 7.6x that of non-subunit version due to an increased TAN concentration gradient from catholyte to trap. Mass transport enhancements can further improve the TAN recovery rate. Subunit engineered ECaB energy consumption for TAN production (67.2 kWh kg-N-1) is lower than the non-subunit version of ECaB (81 .9 ± 3.5 kWh kg-N-1, Figures 29A through 29C). ECaB rate limitations can be overcome by subunit process engineering while maintaining the low energy consumption and Mg fouling prevention benefits.Table 7. Summary of performance metrics for the ECaB and subunit engineered ECaB.

[0182] Figure 26A illustrates subunit engineered ECaB configuration used to demonstrate improved extraction and conversion rates. To improve extraction from ECaB, 2 L (increased from 200 mL) of wastewater is used (to increase up-concentration) and a commercial serpentine flow field electrolyzer (to reduce mass transport limitations). The resulting catholyte is used in the same commercial electrolyzer to perform Co(DIM)- mediated NO3RR. TAN recovery is performed in parallel with nitrate conversion using the same experimental setup as in non-subunit version of ECaB.

[0183] Figure 26B illustrates photos of the commercial electrolyzer (left) and the electrocatalysis cell and recovery cell in operation (right). Catholyte (C), anolyte (A), and trap (T) chambers and recirculation bottles are labeled.

[0184] Figures 27A and 27B illustrate nitrogen mass balance for subunit engineered ECaB (A) Donnan dialysis nitrate extraction and (B) Co(DIM)-mediated NO3RR (nitrate conversion and TAN production) of the resulting catholyte. The dashed horizontal line in Figure 27A describes the mass of nitrogen that needs to be removed from the wastewater to achieve an effluent concentration of 10 mg-N / L; subunit engineered ECaB is able to achieve this concentration in 24 h with 2 L of wastewater feed. 67.5% of nitrate is extracted in 24 h, and 80.8% of the extracted nitrate is converted to TAN in 8 h of CPE.

[0185] Figures 28A and 28B illustrate rates of nitrate extraction (orange) and TAN production (green) expressed as (A) flux of nitrogen and (B) partial current density. In Figure 28B, extraction partial current density is an effective ionic current density of nitrate crossing the AEM from wastewater to catholyte (balanced by an equal and opposite flux of chloride crossing the AEM from catholyte to wastewater); no external current is applied during extraction. Figure 28C illustrates Nitrate extraction efficiency and TAN yield. Figure 28D illustrates area-normalized volume of wastewater treated and farmland serviced with (NH4)2SO4 fertilizer. Farmland serviced is calculated by assuming a rate of 72 kg-N hectare-1year1.

[0186] Figures 29A through 29C illustrate rates, efficiencies, and energy consumption respectively of nitrate extraction, TAN production, and TAN recovery in ECaB (orange) and subunit engineered ECaB (purple). Error bars represent ± one standard deviation from triplicate experiments (n=3) for ECaB. Data points for subunit engineered ECaB do not have error bars because only one experiment is performed.

[0187] To quantify the performance gap between subunit engineered ECaB and operationally feasible systems, scenario-based JTAN targets are derived from a cost assessment of wastewater treatment coupled with fertilizer production. Cost is chosen as a basis for targets because it is the largest driver of wastewater treatment technology feasibility; JTAN is chosen as a representative performance target because it influencescost and facilitates comparisons across electrochemical systems. ECaB’s primary function (wastewater treatment) can be offset by its ability to recover chemical value, so target jTANvalues are determined that would allow Co(DIM) in the ECaB system to be a net-zero cost over a ten year lifetime treating wastewater NO3 from a large wastewater treatment plant (1 x106gal. . day-1) (Figure 30A). The assessment is conservative because it considers revenue from (NFk^SCU fertilizer but does not consider other financial incentives of ECaB in a wastewater treatment process, such as water recovery revenue, conventional nitrogen treatment costs, or avoided regulatory fines for environmental NO3 discharge. The calculated difference between target jTANand the experimental jTANdescribes the gap in reactor-level catalytic activity required for ECaB process feasibility. Using the same FETAN, HNO RP - andobserved in subunit engineered ECaB, the required jTANfor the unit process to be a net-zero cost is 619 mA cm-2(120x that of our experimental value; Figure 30B). While this gap is large, it can be overcome by engineering anode cost (Scenario B), thermodynamic performance (Scenarios C-E), electrolyte identity (Scenario F), and materials synthesis (Scenarios G- H). Anode cost plays a large role in reducing target jTANdue to the high cost of platinumgroup metals; nickel-based anodes are under active investigation as lower-cost oxygen evolution anode materials. FETAN plays a second largest role in reducing target jTANand could be addressed by unit process-level development (e.g., enhancing NO3 up- concentration to its thermodynamic limit). Seemingly innocuous changes have large contributions to reducing target JTAN (e.g., using seawater as a catholyte reduced target jTAN by 33.8%). In the limit where all Scenarios B-H are achieved and electricity is a free utility (i.e., Scenario J), the target jTANis 2.46x of the subunit engineered ECaB jTAN. The dominant cost contribution to jTANtargets in Scenarios A-H (Figure 30C) is operational expenditures (OpEx, specifically electricity for NO3RR). Only in Scenario I, when anode cost, FETAN, 0NO3RR , and qanode membraneare improved together, does capital expenditures (CapEx) outweigh OpEx. Meanwhile, Co(DIM) synthesis is a minority cost contributor inall scenarios, indicating that homogenous catalysts like Co(DIM) can be financially feasible and that efforts to reduce overall system cost should prioritize engineering reaction potentials and FEs. Practically, the cost analysis highlights that overcoming the limitations of reaction thermodynamics, electrolyte engineering, and materials synthesis can significantly reduce gaps between experimental and target JTAN of scalable systems.

[0188] In addition to converting wastewater NO3 to purified TAN at great energy efficiency, ECaB also provides a generalizable, modular platform for benchmarking electrocatalysis. For example, Co(DIM)-mediated nitrite reduction is performed in ECaB with a simplified wastewater feed containing NO2, achieving a TAN yield of 71.0% in 2 hours of CPE (Figures 31 A and 31 B). ECaB could similarly be used for CO2 reduction (homogeneous or heterogeneous) from HCO3 / CO3 feeds. The ECaB platform and the cost assessment could be adapted to other homogeneous and heterogeneous catalysts, electrodes, membranes, mass transport conditions, and operating parameters in specific wastewaters. Performing both extraction and recovery via membranes facilitates comparison of co-dependent reaction and separation rates and efficiencies (Tables 3-6). Volume reduction of NOs-containing electrolytes by low-energy separations processes like DD could help remediate the majority of NO3 emissions contributed by high volume, dilute NO3 sources. The combination of subunit processes in ECaB driven by only one electrochemical power source will integrate well with distributed renewable power generation and storage. ECaB is therefore a promising and practical platform to investigate modular and on-site reactive separations.

[0189] Figure 30A illustrates a flow diagram for simplified cost assessment of Co(DIM)-mediated NO3RR in ECaB. The flux of wastewater NO3 from a large wastewater treatment plant (1 *106galwastewaterday-1. 28 mg NO3-N L-1) influent treated to 10 mg NO3 -N L-1effluent = 64% removal efficiency is used as a basis for the operating expenditures (OpEx; chemical costs, NO3RR electricity costs, and pumping electricity costs), capital expenditure (CapEx), and revenue of a scaled-up ECaB system. The difference between the net present values of revenue and expenditures is set to zero todetermine the CapEx budget. The entire CapEx budget is spent on Co(DIM), anode material, membrane material, and cell hardware material, which defined the geometric surface area required. The total current is divided by the surface area to obtain )TAN.

[0190] Figure 30B illustrates TAN current density (jTAN; red) for experimental ECaB performance (Co(DIM)-ECaB) and for scenario-specific performance targets. In all scenarios, the cost of electricity was 03 kWh-1. For Co(DIM)-ECaB and Scenario A, FETAN is 62.9% and Eceii is 2.7 V (HN03RR 'S0.905 V and hanode rxnis 0.765, calculated from the pH-dependent equilibrium potentials of NO3RR and OER). With improvements to catalysis thermodynamic performance, electrolytes, and materials synthesis, the target current density for Co(DIM)-ECaB to be a net zero cost is decreased by 16.6 times (from 232.2 mA cm-2to 14.0 mA cm-2). If electricity becomes a free utility, this target can be further reduced to 9.2 mA cm-2.

[0191] Figure 30C illustrates the cost contribution of OpEx (chemical inputs, NO3RR electricity, and pumping electricity) and CapEx (Co(DIM), anodes, membranes, and cell hardware) to the overall system.

[0192] Figures 31 A and 31 B illustrate nitrogen mass balance for ECaB with Co(DIM)- mediated NO2RR. Figure 31 A shows nitrogen mass balance for Donnan dialysis extraction with 2 L of simulated nitrite-bearing wastewater (W; 6.2 mM NaCI, 2 mM NaNC ) and 50 mL of catholyte (C; 1 M KCI, 8 mM Co(DIM). The extraction cell configuration and operation are the same as for subunit engineered ECaB with real wastewater. Figure 31 B shows nitrogen mass balance for Co(DIM)-mediated nitrite conversion to TAN with concurrent TAN recovery. The conversion cell and trap cell configuration and operation are the same as for the subunit engineered ECaB with real wastewater, except that the constant potential -1.05 V vs. Ag / AgCI is applied for 15 minute increments instead of 1 h increments because Co(DIM)-mediated NO2RR is significantly faster than Co(DIM)-mediated NO3RR.

[0193] Many embodiments provide catalytically influential wastewater constituents (specifically Mg2+) and their effects on a homogeneous NO3RR catalyst’s (Co(DIM)) performance to rationally design a reactive separations process: electrocatalyst-in-a-box(ECaB). Iteratively investigating reactor-scale performance and microenvironment-scale interfacial phenomena provide design principles for a system resilient to wastewater impurities using simplified, simulated, and real wastewaters. The presence of Mg2+in real NO3 -bearing secondary effluent inhibits NO3RR activity but does not affect NO3RR selectivity or FE. Mg deposition on the cathode surface is shown to be a major passivation mechanism, aligned with recent heterogeneous NO3RR reports of water hardness passivating cathodes. Heterogeneous electron transfer between the cathode and homogeneous Co(DIM) is slowed by the passivated surface, but the homogeneous NO3RR reaction is not observably affected. Co(DIM) can protect the cathode from inhibition by preventing specific adsorption of Mg2+. Anion-selective separations via DD enable cathode protection along with homogeneous catalyst reuse and treated water recovery. Combining DD and NO3RR within the ECaB process demonstrate promising wastewater NO3 extraction, NO3 conversion to TAN, and TAN recovery as a purified product. ECaB can achieve 98.1 ± 0.3% NO3-N removal from a real municipal secondary effluent and recover a pure TAN product with a low energy consumption for an NO3RR system (90.0 ± 2.7 kWh kg-N-1). Subunit engineered ECaB enable a sustained jTANof 5.14 mA cm’gOmetricfor 8 h of Co(DIM)-mediated NO3RR with low energy consumption maintained (67.2 kWh kg-N-1for TAN production). A cost assessment show that subunit engineered ECaB jTANcan be improved by 120x to meet performance targets, but that tractable improvements to catalysts, electrolytes, and materials in ECaB systems can reduce targets to 2.46x the jTANin subunit engineered ECaB.

[0194] Many embodiments provide the use-informed selection of molecular catalysts and integrated unit process analysis for wastewater refining. The development of ECaB is informed by the composition of a generalizable NOs-rich wastewater, underscoring the imperative, insightful connections between systematic wastewater-based electrochemical research and the value propositions (i.e. , pollutant removal product generation). The developed ECaB architecture can also serve as a platform for comparative investigations of wastewaters, catalysts, and reactor operating conditions. Deployment feasibility forNOsRR reactive separations systems will be governed by analysis of efficiencies, rates, and energy consumption for extraction, conversion, and recovery unit processes. The study of integrated reactive separations that match the scale of wastewater- NO3 generation can accelerate use of wastewaters as feedstocks for electrified chemical production. Many embodiments provide incumbent centralized nitrogen management systems by producing commodities from impure, variable, and complex NO3 -rich wastewaters.EXEMPLARY EMBODIMENTS

[0195] Although specific embodiments of methods, systems and apparatuses are discussed in the following sections it will be understood that these embodiments are provided as exemplary and are not intended to be limiting.Example 1: Methods

[0196] Chemicals are purchased as reagent grade and used as received. Nanopure water (resistivity: 18.2 MQ cm) is used for all experiments and measurements unless stated otherwise. Before experiments, cation exchange membranes (CEM; CMI-7000, Membranes International Inc.) are stored in 0.1 M KCIO4; anion exchange membranes (AEM; ASVN, Selemion) are stored in nanopure water; and bipolar membranes (BPM; FBM, Fumasep) are stored in 1 M NaCI. Hydrophobic gas-permeable membranes (GPM; CLARCOR QP 952 (polytetrafluoroethylene), CLARCOR Industrial Air) are used as received.

[0197] Catalyst synthesis and characterization. The perchlorate salt of [Co(DIM)Br2] is prepared.CIO4~

[0198] 1H N MR spectra (Varian Inova 600 at 600 MHz) and LC-MS spectra of Co(D IM) confirm the anticipated structure, molecular weight, and axial ligation of the catalyst. Mass spectra for aqueous Co(DIM).Co(DIM) samples are prepared for HPLC-MS analysis by diluting 1 mg / mL aqueous solutions by a factor of 5 using a methanol / water mixture (50:50 v / v). Samples are analyzed via direct injection on an Agilent 1260 HPLC with an Agilent 6460 Triple Quadrupole MS. Samples are eluted using 98% aqueous mobile phase (0.1% formic acid) and 2% organic mobile phase (acetonitrile) at a flowrate of 0.6 mL / min. 10 pL of sample are injected during each run. Compounds are detected using positive electrospray ionization mode with a gas temperature of 300 °C, gas flowrate of 7 L / min, a nebulizer pressure of 45 psi, a sheath gas temperature of 250 °C, a sheath gas flowrate of 9 L / min, a capillary voltage of 3500 V, a nozzle voltage of 500 V, a fragmentor energy of 50 V, and a cell accelerator voltage of 7 V.

[0199] LC-MS fragment weights match reasonably well with the molecular weight of Co(DIM) bound to zero Br- ions (283.29), one Br- ion (363.19), and two Br- ions (443.09). Additionally,79Br and81Br exist in roughly equal parts naturally at standard temperature and pressure, causing the spectra to exhibit a triplet at 442.8 m / z, a doublet at 361 .9 m / z, and a singlet at 280.9 m / z.

[0200] Electrochemical methods. A BioLogic VMP-300 potentiostat is used to control the potential applied to the working electrode versus the reference electrode. Allelectrochemical experiments are recorded using 85% IR compensation based on the ohmic resistance obtained via potentiostatic electrochemical impedance spectroscopy.

[0201] Cyclic voltammetry (CV) and rotating-disk electrode (RDE) control led-potential electrolysis (CPE). All CV and RDE CPE experiments are conducted in a 5-port glass RDE cell. The working electrode is a 5 mm glassy carbon (GC) disk, the counter electrode is a 6.4 mm diameter graphite rod in a glass tube with a Teflon frit, and the reference electrode is a Ag / AgCI electrode (4.0 M KCI). The 5 mm GC electrode is polished with 1 pm alumina slurry (BASi) in a figure-eight motion on a microcloth polishing pad for one minute. After polishing, the GC electrode is sonicated in nanopure water for one minute and blown dry with N2. All CVs are collected at 100 mV / s and the first sweep of each CV is shown. All CVs begin at the open circuit potential (OCP) and are swept to the first switching potential of -1 .2 V vs. Ag / AgCI, then swept to the second switching potential of +0.6 V vs. Ag / AgCI, then sweep back to OCP. RDE CPEs are performed using an electrode rotator. During dosing experiments, 28 pL of 1 M MgCl2, 30 pL of 1 M NaHCOs, or 38 pL of 1 M CaCl2 are manually pipetted into 20 mL of electrolyte via a glass port in the cell. The injected volumes of 1 M salt solutions are such that each species (Mg2+, Ca2+, HCO3) concentration in the 20 mL of electrolyte match the concentration in the real wastewater.

[0202] Two-chamber controlled-potential electrolysis (CPE). Two-chamber CPE experiments are performed in a polycarbonate compression cell separated by a CEM and held together with stainless steel bolts. Each chamber has a volume of ~7 mL and a chamber cross-sectional area of 5.4 cm2. The working electrode (cathode) is a type II GC plate and is stored in 1 M H2SO4 when not in use to remove any trace metal impurities. Before CPE, the GC electrode is prepared in the same manner as described before. The counter electrode (anode) is a mixed metal oxide (MMO) iridium-tantalum mesh. The geometric cross-sectional area of the cathode, anode, and CEM are 5.4 cm2. The reference electrode is a leakless Ag / AgCI electrode (3.4 M KCI) calibrated against a master reference electrode (4.0 M KCI) and is inserted into the cathode chamber via a threaded port. Three catholytes are tested: simplified wastewater, simulated wastewater,and real wastewater (Table 1 ). The anolyte is 0.1 M KCIO4 in the experiments. 50 mL of each electrolyte are recirculated in batch at a volumetric flow rate of 3.5 mL min-1(linear flow rate in each chamber: 1.75 cm min-1). Buffers are not used in CPE because Co(DIM)- mediated NO3RR catalysis is inhibited by common inorganic (phosphate, carbonate / bicarbonate) buffers. Common “non-coordinating” buffers (TRIS, MOPS, borax) are tried, but no catalysis in CV or CPE.

[0203] The statistical significance of differences between observed CPE performance in the three catholytes is compared using paired t-tests for equal means, difference between CPE performance results from a normal distribution with mean equal to zero and unknown variance if p < 0.05.

[0204] Rinse tests are performed to assess the catalytic activity of deposits on GC cathodes. The cell is then reconstructed with the deposit-containing GC electrode. An eight-hour CPE is performed (identical operation to first CPE) with 50 mL simplified wastewater without dissolved Co(DIM) in the catholyte (i.e. , 0 mM Co(DIM), 6.2 mM NaCI, 2 mM NaNOs).

[0205] The ECaB reactor comprises of two compression cells: a two-chamber cell for electrocatalysis and a three-chamber cell for Donnan dialysis and ammonia gas stripping. Figure 32 illustrates photos of electrocatalyst-in-a-box (ECaB) reactor. The compression cell pieces are the same as used in two-chamber CPE experiments. Four electrolyte reservoirs (200 mL wastewater, 50 mL catholyte, 50 mL trap solution, and 50 mL anolyte) are recirculated in batch mode through the two cells. The only solution to recirculate between both cells is the catholyte to facilitate the three subunit processes of NO3- extraction by Donnan dialysis, NOs-conversion to TAN by Co(DIM)-mediated NO3RR, and TAN recovery by membrane stripping. In the Donnan dialysis and ammonia gas stripping cell, the wastewater and catholyte are separated by an AEM (to facilitate NO3 extraction) and the catholyte and trap solution are separated by a GPM (to facilitate TAN recovery). The electrocatalysis cell contains a GC plate cathode (to facilitate NO3 conversion to TAN), a MMO iridium-tantalum mesh anode, and a leakless reference electrode; the catholyte and anolyte are separated by a BPM. The flow rate is 3.5 mL / minfor the electrocatalysis cell, and the flow rate is 28 mL / min for the Donnan dialysis and ammonia gas stripping cell. During ECaB operation, the electrocatalytic cell is alternated between open circuit (0-24 h, 34-48 h, 58-72 h, 82-96 h) and -1.05 VAg / Agci (24-34 h, 48- 58 h, 72-82 h).

[0206] Subunit engineered ECaB systems. In subunit engineered ECaB systems, a commercial serpentine flow field electrolyzer (10 cm2) is used for both Donnan dialysis and electrocatalysis. Donnan dialysis is performed first in the electrolyzer; then the electrolyzer is disassembled and reassembled to perform electrocatalysis. In Donnan dialysis, an AEM is sandwiched between the two graphite flow field blocks. 2 L of municipal secondary effluent is used as the wastewater feed and 50 mL of 1 M KCI with 8 mM Co(DIM) is used as the receiving solution. The flow rate is 57 mL / min. In electrocatalysis, a CEM is sandwiched between the graphite flow field blocks and a pseudo reference electrode (a 250 pm Ag wire anodized in saturated KCI) is attached to the CEM. The graphite flow block is used as the cathode. The anode is a platinized Ti mesh in electrical contact with the anode graphite flow block. The catholyte is the resulting solution from Donnan dialysis and the anolyte is 50 mL of 0.1 M KCICU. The flow rate is 3.5 mL min-1in the electrolyzer. -1.05 V vs. Ag / AgCI is applied in 1 -hour increments. After each increment, the catholyte is adjusted back to pH 6 with ~200 pL 10 wt% HCI to keep Co(DIM) in its stable operating pH regime. A separate two-chamber 5.4 cm2compression cell is assembled to house the GPM for TAN recovery with 50 mL of 0.1 M H2SO4 as the trap solution; TAN recovery is run in parallel with electrocatalysis at a flow rate of 28 mL / min.

[0207] Aqueous characterization. Aqueous ion speciation is quantified with cation chromatography (Na+, NH4, K+, Ca2+, Mg2+) and anion chromatography (CT, NO2, NO3, SO4, PO4-). Both cation chromatography (4 mM tartaric acid / 2 mM oxalic acid eluent, SCS 1 column at 30 °C) and anion chromatography (4.5 mM carbonate / 0.8 mM bicarbonate eluent, AS23-4 pm column at 30 °C) are performed with a dual Dionex ICS- 6000 system. For ECaB, the high concentration of K+in the catholyte made quantification of TAN by cation chromatography difficult, so flow injection analysis (indophenol method)is conducted with a SEAL AA500 AutoAnalyzer. For both cation chromatography and flow injection analysis, aliquots above pH 7 are acidified to prevent ammonia volatilization and facilitate accurate quantification of measure total ammonia nitrogen (TAN: sum of aqueous ammonium, NH4 , and aqueous ammonia, NH3). Inductively coupled plasma mass spectrometry (ICP-MS) is used to quantify the concentration of59Co in each ECaB chamber at initial and final time points. ICP-MS is performed using a parallel flow nebulizer and a Peltier-cooled Scott-type double pass cyclonic spray chamber cooled to 2.7 °C.

[0208] Electrode characterization. X-ray photoelectron spectroscopy (XPS) is performed using a Phi Versaprobe 3 with monochromatized Al Ka (1486 eV) radiation. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) characterization is performed on a Thermo Fisher Scientific Apreo S LoVac (5 kV, 5.0 pA) with a Bruker Quantax EBSD 400i integrated system containing an XFIash 6|60 SDD EDS detector. Raw EDS data are processed and plotted with Broker’s ESPRIT software.Example 2: Controlled-Potential Electrolysis (CPE)

[0209] Equations used to evaluate CPEsnumber of electrons (8) required to produce one mole of TAN from NO3 , Qpassed= charge passed in CPE in units of C, and F = 96485 C mol-1(Equation 53.1.3)

[0210] To determine the interfacial pH required for precipitation of Mg(OH2), some embodiments set the solubility product quotient (Qsp) equal to the solubility product constant (Ksp).

[0211] Plugging in [Mg2+] = 1.5 mM and solving for [OH-] yields the pH necessary for precipitation of Mg(OH)2 in the RDL: PHRDL = 9.8. The same procedure is used to determine the necessary pH for precipitation of Ca(OH)2: PHRDL = 12.8.

[0212] Determining the interfacial pH required for precipitation of carbonates like MgCOs is only slightly more complex because of the HCOa / COg- acid / base pair, where magnesium and calcium bicarbonate are significantly more soluble than their carbonate analogues. Set Qspequal to Ksp. (Equation S3.3.2)

[0213] Plugging in [Mg2+] = 1 .5 mM and solving for [CO|’] yields the [COf ] necessary for precipitation of MgCOs in the RDL: 4.5 mM. This concentration is greater than the 1.4 mM bicarbonate in bulk solution, making precipitation of MgCCh unlikely. The same procedure is performed for CaCO3. (Equation S3.3.3)

[0214] Precipitation of CaCOs is possible because the [CO|‘] necessary is 1.8 pM.Because the bulk pH of the Real Wastewater is the majorityof inorganic carbon in bulk solution exists as bicarbonate. The concentration of carbonate is therefore dependent on the RDL pH assuming the acid / base pair is equilibrated by rapid proton transfer kinetics.

[0215] The unknown [HCO3]RDLcan be eliminated by a mass balance of bicarbonate and carbonate.

[0216] Plugging in1.8 pM, the RDL pH necessary for precipitation of CaCOs is 4.4 which is less than the pH of the bulk solution. Complex aqueous solutions like the real wastewater are nevertheless able to keep Ca2+and HCO3 solvated in bulk solution. Interfacial coulombic effects in Co(DIM)-mediated NO3RR can prevent CaCOs deposition and may explain why a strong signal for calcium in XPS or EDS for any GC cathode analyzed is not observed. One such effect could be Co(DIM) axially coordinating bicarbonate / carbonate, precluding deposition.

[0217] Finally, precipitation of magnesium as a sulfate is unlikely because the hydrate (MgSO4 • 7H2O) is soluble in mass fractions greater than 1 :1 with water. Precipitation of CaSO4 • 2H2O is also unlikely because the concentration of sulfate necessary (16.5 mM) exceeds the concentration in the real wastewater (1.1 mM), as shown by setting Qspequal to Ksp in Equation S3.3.8.3.14 x 10“5(Equation S3.3.8)Example 3: Transport and Contaminant Conditions for Catalysis Inhibition

[0218] Rotating disk electrode. To interrogate the sensitivity of inhibition to interfacial electrolyte composition, a rotating-disk electrode (RDE) is used to achieve well-defined transport conditions in the RDL. By varying the rotation rate, the delivery rate (and therefore steady-state concentrations) of NO3, Co(DIM), and wastewater constituents are modulated during CPE. Under stagnant conditions (0 rotations per minute (RPM)), the current density of Co(DIM)-mediated NO3RR in simplified wastewater (2 mM NO3) is greater than that of Co(DIM) in simplified wastewater (0 mM NO3), demonstrating steadystate catalytic current. Catalytic current in simplified wastewater is also observed with rotation rates of 9 and 25 RPM, indicating that homogeneous NO3RR outpaces bulk catalyst delivery to the electrode surface with modest forced convection. Conversely, catalytic current is lost in the range of 100 to 400 RPM, indicating that bulk catalyst delivery outpaces NO3RR. The rotation rates tested therefore span transport conditions for Co(DIM)-mediated NO3RR catalysis and for Co(DIM) activation with no catalysis. Inreal wastewater (2 mM NO3), the current density vs. time effectively overlays with the simplified wastewater (2 mM NO3) for the duration of the 5 min CPE, indicating no inhibition under stagnant conditions. Disturbing the RDL by forced convection causes a decay in current density in real wastewater, indicating inhibition. The coupled transport conditions and bulk solution composition for a fixed electrode potential therefore describe inhibition conditions.

[0219] Two-chamber CPE contaminant dosing experiments. In contaminant dosing experiments, the same two-chamber CPE setup is used as described above. After the 2 h sample aliquots are drawn from cathode and anode chambers, a small volume of 1 M salts is manually injected (70 pL 1 M MgCl2, 75 pL 1 M NaHCOa, 95 pL 1 M CaCla) into the catholyte recirculation bottle. The volume is chosen such that the catholyte concentration of the target contaminant matched the target contaminant concentration in real wastewater.Example 4: Electrocatalyst-in-a-box (ECaB)

[0220] Equations used to evaluate ECaB. Figure 33 illustrates a flow diagram of ECaB.Efficiencieswhere for ECaB, mol TANproduced(t) = mol TANcatholyte(t) + mol TANtrap(t) (Equation(Equation S5.1.6)**tlN recovery, overall f°rECaB is calculated by Equations S5 and S6. Data calculated by Equations S5 and S6 agree within experimental error for all time points. (Equation S5.1 .7)where n = number of electrons (8) required to produce one mole of TAN from NO3, Qpassed=charge passed in CPE in units of C, and F = 96485 C mol-1RatesEnergy consumptionEnergy consumed for NO?5extraction = (Equation S5.1 .17)Energy consumed for NO?6conversion = (Equation S5.1 .18)Energy consumed r for r TnAN production = (Equation S5.1 .19) r> j £ rr<Energy consumed for TAN recovery = — (Equation S5.1 .20)Electricity operational expenditureRecovered ( vNH4)2S04cost = (Equation S5.1 .21 ) *\ / Equation 5.1.21 is used to calculate the cost of producing purified ammonium sulfate when considering electricity as the only operational expenditure at a cost of 03 kWh-1.Example 5: Donnan Dialysis Equilibrium Calculations

[0221] In Donnan dialysis, an ion exchange membrane separates a wastewater (or feed solution) and a saline electrolyte (or receiving solution). Ion exchange between the two solutions is driven by an electrochemical potential gradient for each ion / in the system. More concretely, Donnan dialysis is employed using a concentrated CF electrolyte as the receiving solution and NOs-rich municipal secondary effluent as the feed solution. When separated by an AEM, feed NO3 ions spontaneously exchange with receiver CF ions in the synthetic electrolyte, while cation migration is precluded by the fixed positive charges in the membrane.

[0222] System of equations (ion mass balances, electroneutrality, and Donnan equilibrium). Some embodiments provide a system of equations used to model equilibrium conditions for a Donnan dialysis (DD) process. General equations which can be applied to any number of ions / in a system where there is a feed solution (FS) and receiving solution (RS) separation by an ion exchange membrane are shown. For the DD process, only CF and NO3 because the monovalent-selective anion exchangemembrane (AEM) used in ECaB experiments is selective against SO^- migration and rejected cation migration.Mass balance(Equation S6.1.1 )Electroneutrality(Equation S6.1 .2)(Equation S6.1 .3)Solution phase electrochemical potential equations for Donnan equilibrium (Equation S6.1.4)(Equation S6.1 .5)Rearranging Equation S6.1.5 yields an equality between the electrochemical potential difference arising from the activity of each ion / in feed and receiving streams, and the electrochemical potential difference arising from the electric potential difference across the membrane.(Equation S6.1 .6)Rearranging Equation S6.1.6 yields an equality between the electric potential difference across the ion exchange membrane and the solution phase electrochemical potential difference. (Equation S6.1.7)Making the approximation that the electric potential difference experienced by each ion i in the system is the same, the right-hand side of Equation S6.1.7 can be used to equate electrochemical potentials of dissimilar ions. The electrochemical potentials of CT and NO3 can be equated as in Equations S6.1.8 and S6.1.9.8) 9)The activities used in Donnan equilibrium equations are considered for both an ideal model and a Pitzer model based on the concentration of ions in the catholyte.Example 6: Simplified Cost Assessment

[0223] The cost assessment uses the flux of NO3 from a municipal wastewater treatment plant processing 106gal. day-1(the size of a large municipal wastewater treatment facility) with 28 mg-NOs-N L-1as the basis for electricity consumption (a total NO3RR current to convert all nitrate to TAN), chemical inputs (NaCI for nitrate extraction and H2SO4 for TAN recovery), and revenue ((NFU^SCU fertilizer sales). NO3RR overpotential (E|NO3RR) is calculated using the standard reduction potential of NO3RR to ammonia (+0.7 VRHE) and the Nernst equation assuming a steady state pH of 10 to facilitate TAN recovery by membrane stripping. Total charge required is calculated assuming a removal efficiency of 64.2% such that the effluent concentration was 10 mg-NOs-N L-1. OER overpotential (F|OER) is calculated using the standard reduction potential of OER (+1 .23 VRHE) and the Nernst equation assuming a steady state pH of 1.5 observed in subunit engineered ECaB experiment. Based on the FETAN, QNOSRR, and QOER, the required energy consumption is calculated. Multiplying this value by the electricity cost yielded the operational expenditure (OpEx) for electricity. The electricity costs associated with pumping is also calculated 1 )

[0224] In equation S7.2.1 , t is the duration of pumping wastewater through the extraction cell (24 hours), y is the specific weight of water (9.8 kN m-3), V is the flow rate (57 mL min-1), H* is the pump head determined by the length of the serpentine flow path in the extraction cell required to treat 107gal. . day-1(1.2 x 107m),is the pump efficiency (assumed 0.4), andis the motor efficiency (assumed 0.95). Subtracting this electricity OpEx value and chemical inputs OpEx value from the revenue of recovered (NH4)2SO4 fertilizer ($2.77 kg-N-1) to establish a yearly cash flow. To correct for inflation, the yearly cash flow is modified by Equation S7.2.2:Cash flow(year i) = (Revenue(year i) — Electricity costs(year i) —Chemical costs(year i) - CapEx(year i)) x 1.031(Equation S7.2.2)

[0225] The capital expenditure (CapEx) budget is calculated as the net present value of the cash flow over a ten-year reactor lifetime with a discount rate of 10%. The entire CapEx budget is spent (i.e., the unit process is a net zero cost) to establish a total surface area of reactor components. Dividing the CapEx budget by the sum of the area- normalized prices of Co(DIM), anode material, and cell hardware (graphite for flow field blocks) yields a total reactor geometric surface area. Dividing the product of total current and FETAN by the total reactor geometric surface area yielded a TAN partial current density target.

[0226] The costs of labor, the revenue from water recovery, or potential regulatory fines from environmental nitrate discharge are not considered. Table 8 outlines the parameters used for the cost assessment.Table 8. OpEx and CapEx used in simplified cost assessment of ECaB.DOCTRINE OF EQUIVALENTS

[0227] As can be inferred from the above discussion, the above-mentioned concepts can be implemented in a variety of arrangements in accordance with embodiments of the invention. Accordingly, although the present invention has been described in certain specific aspects, many additional modifications and variations would be apparent to those skilled in the art. It is therefore to be understood that the present invention may be practiced otherwise than specifically described. Thus, embodiments of the present invention should be considered in all respects as illustrative and not restrictive.

[0228] As used herein, the singular terms "a," "an," and "the" may include plural referents unless the context clearly dictates otherwise. Reference to an object in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more”.

[0229] As used herein, the terms “set” and “subset” refer to a collection of one or more objects. Thus, for example, a subset of features can include a single feature or multiple features.

[0230] As used herein, the term "about" is used to describe and account for small variations. When used in conjunction with an event or circumstance, the terms can refer to instances in which the event or circumstance occurs precisely as well as instances in which the event or circumstance occurs to a close approximation. When used in conjunction with a numerical value, the terms can refer to a range of variation of less than or equal to ± 10% of that numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1 %, less than or equal to ±0.5%, less than or equal to ±0.1 %, or less than or equal to ±0.05%.

[0231] Additionally, amounts, ratios, and other numerical values may sometimes be presented herein in a range format. It is to be understood that such range format is used for convenience and brevity and should be understood flexibly to include numerical values explicitly specified as limits of a range, but also to include all individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly specified. For example, a ratio in the range of about 1 to about 200 should be understood to include the explicitly recited limits of about 1 and about 200, but also to include individual ratios such as about 2, about 3, and about 4, and sub-ranges such as about 10 to about 50, about 20 to about 100, and so forth.

Claims

WHAT IS CLAIMED IS:1 . An electrocatalytic system for nitrate reduction, comprising, a first cell comprising: an input chamber configured to receive a liquid comprising nitrate; a first catholyte chamber, wherein an anion exchange membrane separates the input chamber and the first catholyte chamber, wherein the anion exchange membrane selectively transports nitrate from the input chamber to the first catholyte chamber; and a trap chamber, wherein a gas permeable membrane separates the first catholyte chamber and the trap chamber; a second cell comprising: a second catholyte chamber connecting a cathode and an anolyte chamber connecting an anode, wherein a membrane separates the second catholyte chamber and the anolyte chamber; wherein the first and the second catholyte chambers each comprise a catholyte and the chambers are in a fluidic connection; wherein the catholyte in the second catholyte chamber comprises a catalyst and the catalyst catalyzes a nitrate reduction reaction to generate ammonia; and wherein the nitrate and the generated ammonium are free flowing between the first and the second catholyte chambers such that the nitrate from the first catholyte chamber is transported to the second catholyte chamber and the generated ammonium from the second catholyte chamber is transported to the first catholyte chamber, wherein the gas permeable membrane transports the generated ammonia from the first catholyte chamber to the trap chamber.

2. The system of claim 1 , wherein the liquid is selected from the group consisting of: nitrogen fixation reactor effluent, nitrate polluted groundwater, wastewater, agricultural wastewater, municipal wastewater, reverse osmosis brine, and ion exchange brine.

3. The system of claim 1 , wherein the liquid has a pH from 5.5 to 7.5.

4. The system of claim 1 , wherein the catalyst is a homogeneous catalyst, a heterogeneous catalyst, or a molecular catalyst.

5. The system of claim 1 , wherein the catalyst is selected from the group consisting of: a metal complex 2,3-dimethyl-1 ,4,8,11-tetraazacyclotetradeca-1 ,3-diene (DIM) with a Co metal center, a cobalt macrocycle complex [Co(CR)Br2]+, and a nitrate reductase.

6. The system of claim 1 , wherein the anion exchange membrane is a monovalent anion exchange membrane, or an alkaline resistant anion exchange membrane.

7. The system of claim 1 , wherein the gas permeable membrane is a hydrophobic gas permeable membrane.

8. The system of claim 1 , wherein the membrane is a bipolar membrane or a cation exchange membrane.

9. The system of claim 1 , wherein the trap chamber comprises an acid, where the acid protonates and recovers ammonia to ammonium.

10. The system of claim 1 , wherein an effluent from the input chamber comprises a lower concentration of nitrate compared to the liquid.

11. The system of claim 1 , wherein an effluent from the input chamber is recirculated as an input liquid to the input chamber.

12. An electrocatalytic system comprising, a first cell comprising: an input chamber configured to receive a liquid; a first electrolyte chamber, wherein an anion exchange membrane separates the input chamber and the first electrolyte chamber; and a trap chamber, wherein a gas permeable membrane separates the first electrolyte chamber and the trap chamber; a second cell comprising: a second electrolyte chamber and a third electrolyte chamber, wherein a membrane separates the second and the third electrolyte chamber; wherein the first and the second electrolyte chambers each comprises an electrolyte and the chambers are in a fluidic connection; wherein the second electrolyte chamber comprises a catalyst, wherein the catalyst catalyzes a reaction that generates a gaseous compound; wherein the gaseous compound is free flowing between the first and the second electrolyte chambers; and wherein the gaseous compound transports through the gas permeable membrane into the trap chamber.

13. The system of claim 12, wherein the catalyst catalyzes a nitrate reduction reaction, a carbon dioxide reduction reaction, or an alcohol oxidation reaction.

14. The system of claim 12, wherein the liquid is selected from the group consisting of: nitrogen fixation reactor effluent, nitrate polluted groundwater, wastewater, agricultural wastewater, municipal wastewater, reverse osmosis brine, and ion exchange brine.

15. The system of claim 12, wherein the liquid comprises nitrate and the gaseous compound comprises ammonia.

16. The system of claim 12, wherein the catalyst is a homogeneous catalyst, a heterogeneous catalyst, or a molecular catalyst.

17. The system of claim 12, wherein the catalyst is selected from the group consisting of: a metal complex 2,3-dimethyl-1 ,4,8,11-tetraazacyclotetradeca-1 ,3-diene (DIM) with a Co metal center, a cobalt macrocycle complex [Co(CR)Br2]+, and a nitrate reductase.

18. The system of claim 12, wherein the anion exchange membrane is a monovalent anion exchange membrane, or an alkaline resistant anion exchange membrane.

19. The system of claim 12, wherein the gas permeable membrane is a hydrophobic gas permeable membrane.

20. The system of claim 12, wherein the trap chamber comprises an acid.

21. The system of claim 12, wherein an effluent from the input chamber is recirculated as an input liquid to the input chamber.

22. The system of claim 12, wherein the membrane is selected from the group consisting of: a bipolar membrane, a cation exchange membrane, and an anion exchange membrane.

23. An electrocatalytic system for nitrate reduction, comprising, a first cell comprising: an input chamber configured to receive an influent comprising nitrate; a first catholyte chamber, wherein an anion exchange membrane separates the input chamber and the first catholyte chamber, wherein the anion exchange membrane selectively transports nitrate from the input chamber to the first catholyte chamber; a second cell comprising:a second catholyte chamber comprising a cathode and an anolyte chamber comprising an anode, wherein a membrane separates the second catholyte chamber and the anolyte chamber; and a third cell comprising: a third catholyte chamber and a trap chamber, wherein a gas permeable membrane separates the third catholyte chamber and the trap chamber; wherein at least one of the first and the second catholyte chambers comprises a catholyte and a catalyst and the chambers are in a fluidic connection such that nitrate is transported from the first catholyte chamber to the second catholyte chamber; wherein the catalyst in the second catholyte chamber catalyzes a nitrate reduction reaction to generate ammonia; and wherein the second and the third catholyte chambers are in a fluidic connection; wherein the generated ammonia is transported from the second catholyte chamber to the third catholyte chamber, wherein the gas permeable membrane transports the generated ammonia from the third catholyte chamber to the trap chamber.

24. The system of claim 23, wherein the catalyst is a homogeneous catalyst, the first catholyte chamber, the second catholyte chamber, and the third catholyte chamber each comprise a catalyst.

25. The system of claim 23, wherein the catalyst is a heterogeneous catalyst and the second catholyte chamber comprises a catalyst.

26. The system of claim 23, wherein the first cell, the second cell, and the third cell are simultaneously in fluid connection with each other.

27. The system of claim 23, wherein the first cell is for Donnan dialysis, the second cell is for electrocatalysis, and the third cell is for ammonia stripping.

28. The system of claim 23, wherein the influent is selected from the group consisting of: nitrogen fixation reactor effluent, nitrate polluted groundwater, wastewater, agricultural wastewater, municipal wastewater, reverse osmosis brine, and ion exchange brine.

29. The system of claim 23, wherein the influent has a pH from 5.5 to 7.5.

30. The system of claim 23, wherein the catalyst is a homogeneous catalyst, a heterogeneous catalyst, or a molecular catalyst.

31. The system of claim 23, wherein the catalyst is selected from the group consisting of: a metal complex 2,3-dimethyl-1 ,4,8,11-tetraazacyclotetradeca-1 ,3-diene (DIM) with a Co metal center, a cobalt macrocycle complex [Co(CR)Br2]+, and a nitrate reductase.

32. The system of claim 23, wherein the anion exchange membrane is a monovalent anion exchange membrane, or an alkaline resistant anion exchange membrane.

33. The system of claim 23, wherein the gas permeable membrane is a hydrophobic gas permeable membrane.

34. The system of claim 23, wherein the trap chamber comprises an acid, where the acid protonates and recovers ammonia to ammonium.

35. An electrocatalytic system, comprising, a first cell comprising: an input chamber configured to receive an influent; a first catholyte chamber, wherein an anion exchange membrane separates the input chamber and the first catholyte chamber; a second cell comprising:a second catholyte chamber comprising a cathode and an anolyte chamber comprising an anode, wherein a membrane separates the second catholyte chamber and the anolyte chamber; and a third cell comprising: a third catholyte chamber and a trap chamber, wherein a gas permeable membrane separates the third catholyte chamber and the trap chamber; wherein at least one of the first and the second catholyte chambers comprises a catholyte and a catalyst and the chambers are in a fluidic connection; and wherein the second and the third catholyte chambers are in a fluidic connection.

36. The system of claim 35, wherein the catalyst is a homogeneous catalyst, the first catholyte chamber, the second catholyte chamber, and the third catholyte chamber each comprise a catalyst.

37. The system of claim 35, wherein the catalyst is a heterogeneous catalyst and the second catholyte chamber comprises a catalyst.

38. The system of claim 35, wherein the first cell, the second cell, and the third cell are simultaneously in fluid connection with each other.

39. The system of claim 35, wherein the first cell is for Donnan dialysis, the second cell is for electrocatalysis, and the third cell is for stripping.

40. The system of claim 35, wherein the influent is selected from the group consisting of: nitrogen fixation reactor effluent, nitrate polluted groundwater, wastewater, agricultural wastewater, municipal wastewater, reverse osmosis brine, and ion exchange brine.

41. The system of claim 35, wherein the influent has a pH from 5.5 to 7.5.

42. The system of claim 35, wherein the catalyst is a homogeneous catalyst, a heterogeneous catalyst, or a molecular catalyst.

43. The system of claim 35, wherein the catalyst is selected from the group consisting of: a metal complex 2,3-dimethyl-1 ,4,8,11-tetraazacyclotetradeca-1 ,3-diene (DIM) with a Co metal center, a cobalt macrocycle complex [Co(CR)Br2]+, and a nitrate reductase.

44. The system of claim 35, wherein the anion exchange membrane is a monovalent anion exchange membrane, or an alkaline resistant anion exchange membrane.

45. The system of claim 35, wherein the gas permeable membrane is a hydrophobic gas permeable membrane.

46. A method for nitrate reduction, comprises: extracting nitrate from a liquid via a dialysis process in a first cell of an electrocatalytic system; reducing the nitrate to a gaseous ammonia in an electrolyte; and recovering the gaseous ammonia in an acidic environment to generate ammonium.

47. The method of claim 46, wherein the dialysis process uses an anion exchange membrane.

48. The method of claim 47, wherein the anion exchange membrane is a monovalent anion exchange membrane, or an alkaline resistant anion exchange membrane.

49. The method of claim 46, wherein the dialysis process is a Donnan dialysis process.

50. The method of claim 46, wherein the liquid is selected from the group consisting of: nitrogen fixation reactor effluent, nitrate polluted groundwater, wastewater, agricultural wastewater, municipal wastewater, reverse osmosis brine, and ion exchange brine.

51. The method of claim 46, wherein the liquid has a pH from 5.5 to 7.5.

52. The method of claim 46, wherein the electrolyte comprises a catalyst that catalyzes a nitrate reduction reaction.

53. The method of claim 52, wherein the catalyst is a homogeneous catalyst, a heterogeneous catalyst, or a molecular catalyst.

54. The method of claim 52, wherein the catalyst is selected from the group consisting of: a metal complex 2,3-dimethyl-1 ,4,8,11-tetraazacyclotetradeca-1 ,3-diene (DIM) with a Co metal center, a cobalt macrocycle complex [Co(CR)Br2]+, and a nitrate reductase.

55. The method of claim 46, wherein the recovering step uses a gas permeable membrane.

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