AMMONIA AND NUTRIENT ION RECOVERY FROM MANURE WASTEWATER AND ELECTROSYNTHESIS OF VALUE-ADDED CHEMICALS USING ION SELECTIVE REDOX MATERIAL
20250059070 ยท 2025-02-20
Inventors
Cpc classification
C02F2201/46115
CHEMISTRY; METALLURGY
C02F2305/00
CHEMISTRY; METALLURGY
International classification
Abstract
A method for recovering NH.sub.4.sup.+ or K.sup.+ ions from manure wastewater is disclosed. The method includes contacting manure wastewater having organic matter and salts with an ion-selective redox material with ionic channels. The manure wastewater reduces the ion-selective redox material which spontaneously takes up NH.sub.4.sup.+ or K.sup.+ ions from the manure wastewater. NH.sub.4.sup.+-or K.sup.+ may be released electrochemically and paired with the simultaneous electrosynthesis of value-added chemicals.
Claims
1. A method for recovering NH.sub.4.sup.+ or K.sup.+ ions from manure wastewater, the method comprising: contacting a manure wastewater comprising organic matter and salts with an ion-selective redox material comprising ionic channels, wherein contacting the manure wastewater with the ion-selective redox material reduces the ion-selective redox material to form a reduced material, and wherein the reduced material spontaneously takes up NH.sub.4.sup.+ or K.sup.+ ions from the manure wastewater to form an ion-loaded material.
2. The method of claim 1, wherein the reduced material takes up NH.sub.4.sup.+ and K.sup.+ preferentially over Na.sup.+.
3. The method of claim 1, wherein the ion-selective redox material is a Prussian Blue analog.
4. The method of claim 3, wherein the ion-selective redox material is one of potassium nickel hexacyanoferrate or copper hexacyanoferrate.
5. The method of claim 1, further comprising the steps of: applying a current to the ion-loaded material, wherein applying the current to the ion-loaded material oxidizes the ion-loaded material to release the NH.sub.4.sup.+ or K.sup.+ ions from the ion-loaded material.
6. A method for utilizing NH.sub.4.sup.+ or K.sup.+ ions, the method comprising: applying a current to an ion-loaded material, wherein applying the current to the ion-loaded material oxidizes the ion-loaded material to release NH.sub.4.sup.+ or K.sup.+ ions from the ion-loaded material.
7. The method of claim 6, wherein the oxidation of the ion-loaded material is coupled to a cathodic reaction.
8. The method of claim 7, wherein the cathodic reaction is a hydrogen evolution reaction.
9. The method of claim 7, wherein the cathodic reaction is a two-electron oxygen reduction reaction producing H.sub.2O.sub.2 and optionally wherein the cathodic reaction is separated from the anodic reaction by a separator.
10. A system for treatment of manure wastewater, the system comprising: a manure waste supply having manure wastewater therein, a cell comprising at least one inlet and at least one outlet, and a wastewater treatment chamber, wherein the cell has an ion-selective redox material disposed therein, wherein the inlet is fluidly coupled to the manure wastewater supply, wherein the outlet is fluidly coupled to the wastewater treatment chamber, wherein the manure wastewater flows from the manure waste supply into the cell through the inlet, contacts the ion-selective redox material, and exits the cell through the outlet to the wastewater treatment chamber, and wherein the manure wastewater comprises organic material and salts.
11. The system of claim 10, wherein the organic material reduces the ion-selective redox material upon contact to form a reduced material, and wherein the reduced material spontaneously takes up NH.sub.4.sup.+ ions or K.sup.+ from the manure wastewater to form an ion-loaded material.
12. The system of claim 10, wherein the ion-selective redox material is a Prussian Blue analogue.
13. The system of claim 12, where the ion-selective redox material is one of potassium nickel hexacyanoferrate or copper hexacyanoferrate.
14. The system of claim 10 wherein the ion-selective redox material is incorporated into an electrode having an electrical connection outside the cell.
15. The system of claim 14 wherein a current applied to the electrode through the electrical connection oxidizes the ion-loaded material and releases the NH.sub.4.sup.+ or K.sup.+ ions.
16. The system of claim 15, wherein the oxidation of the ion-loaded material is coupled to a cathodic reaction.
17. The system of claim 16, wherein the cathodic reaction is a hydrogen evolution reaction.
18. The system of claim 16, wherein the cathodic reaction is a two-electron oxygen reduction reaction producing H.sub.2O.sub.2.
19. The system of claim 18, wherein the cathodic reaction is separated from the anodic reaction by a separator.
20. The system of claim 18, wherein the H.sub.2O.sub.2 is directed to the wastewater treatment chamber.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention.
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DETAILED DESCRIPTION
[0055] Pressure to protect the environment from the effects of greenhouse gas emissions and water contamination generated by livestock manure motivates the development of new approaches to reduce the environmental impact of livestock and improve sustainability. Effective approaches to recover nutrients, especially ammonium (NH.sub.4.sup.+) and potassium (K.sup.+) ions, from manure wastewater to produce fertilizer are needed.
[0056] Disclosed herein is an electrochemical strategy to achieve ammonium (NH.sub.4.sup.+) and/or potassium (K.sup.+) ion recovery and electrochemical synthesis using open framework materials as ion-selective redox materials to mediate the process. In this new approach, ammonium and potassium ions can be recovered from manure wastewater and utilized to generate H.sub.2 or H.sub.2O.sub.2 (
[0057] Manure having high nitrogen, phosphorous, and potassium content is prized as a fertilizer. A method is disclosed herein for recovering nutrient ions from manure wastewater. Additionally, and alternatively, the method may be used to recover K.sup.+ ions from manure wastewater. The manure wastewater can be a heterogeneous mixture. The manure wastewater can be a combination of feces and urine obtained from farm animals (e.g., cows, horses, pigs, goats, sheep, poultry) or from human waste sources. The manure wastewater can also be a digestate from any of the various digestion processes commonly used in the general treatment of manure. The manure wastewater may include additional water that is combined with the manure waste. As a byproduct of living organisms, the manure wastewater may include organic matter comprising organic carbon. For example, the manure wastewater may include bacterial biomass, protein or other nitrogenous matter, carbohydrates (e.g., cellulose) and undigested plant matter, fats and other lipophilic matter as well as other organic matter. A variety of cations and anions may be found within the manure wastewater. The cations may include for example. NH.sub.4.sup.+ , Na.sup.+, K.sup.+, Mg.sup.2+, and Ca.sup.2+. The anions may include for example, Cl.sup., OH.sup., NO.sub.3.sub.
[0058] The method for recovering nutrient ions from manure wastewater can include contacting the manure wastewater with an ion-selective redox material. In one embodiment, the open framework materials can be a three-dimensional array of metal ions bridged by non-metal ions. In one example, the ammonium-ion selective redox material can be a Prussian Blue analog, or a metal hexacyanoferrate. The chemical structure of the Prussian Blue analog is characterized by the general structural formula: A.sub.xM.sub.y[Fe(CN).sub.6].Math.nH.sub.2O, with the specific x, y, z and n parameters and the type of monovalent cation (A=K.sup.+, Na.sup.+, NH.sub.4.sup.+), and a bivalent transition metal cation (M=Fe.sup.2+, Ni.sup.2+, Co.sup.2+, Mn.sup.2+, Cu.sup.2+, Zn.sup.2+, etc.). In one specific example, the ammonium-ion and potassium-ion selective redox material can be potassium nickel hexacyanoferrate. In another specific example, the ammonium-ion selective redox material can be copper hexacyanoferrate.
[0059] The ammonium-ion and potassium-ion selective redox material can have a three-dimensional structure with ionic channels, where the ionic channels are interconnected cavities or pores within the three-dimensional structure. The ionic channels can have an effective diameter, or pore size, ranging between 0.3 nm to 2 nm. The ionic channels can be occupied by hydrated ions. The hydrated ions may be bound in the ionic channels by electrostatic attraction. For example, cations may be bound within an ionic channel having a negatively charged component. In another example, anions may be bound within an ionic channel having a positively charged component. The ionic channels can be large enough for the hydrated ions to exchange and move freely through the channels when the ammonium-ion and potassium-ion selective redox material is in contact with a liquid solution.
[0060] Contacting the manure wastewater with the ion-selective redox material can reduce the ion-selective redox material by electron transfer to form a reduced material. In an aspect, the manure wastewater is capable of reducing the ammonium-ion selective redox material by transferring one or more electrons to the ammonium-ion selective redox material upon contact. For example, organic material (e.g., organic carbon components) in the manure wastewater can supply electrons to reduce the ion-selective redox material. Additionally, and alternatively, an electrode can be used to supply electrons to reduce the ion-selective redox material. Other reducing agents that can be added can include formic acid, glucose, or glycine.
[0061] The reduced material can have ionic channels similar in shape and structure to those found in the ion-selective redox material. However, the reduced material may have ionic channels with electrostatic properties that are different from those of the ion-selective redox material due to the addition of electrons. For example, the reduction of the ion-selective redox material can add negative charges to the atoms along the sides of the ionic channels. The ionic channels of the reduced material may have pore sizes that are different from the ion-selective redox material.
[0062] The reduced material can spontaneously take up nutrient ions from the manure wastewater to form an ion-loaded material. In one example, the reduced material spontaneously can take up select ions into the ionic channels. In other words, the pore size and/or electrostatic potential of the ionic channels in the reduced material can be configured to preferentially host specific ions over other ions. In one example, the reduced material can take up NH.sub.4.sup.+ or K.sup.+ ions preferentially over other ions (e.g., Na.sup.+). By preferentially taking up NH.sub.4.sup.+ or K.sup.+ ions into the ionic channels, the reduced material can effectively separate NH.sub.4.sup.+ or K.sup.+ ions from a mixture and store the ions until they can be released at a specified time and place, where the NH.sub.4.sup.+ or K.sup.+ ions can be collected and utilized.
[0063] The method for recovering ions from manure wastewater can include applying a current to the ion-loaded material. In an aspect, applying current to the ion-loaded material can reduce the ion-loaded material. In another aspect, applying current to the ion-loaded material can oxidize the ion-loaded material. Oxidation or reduction of the ion-loaded material changes the oxidation state of the ionic channels and thus changes the capacity of the ion-loaded material to host ions. For example, upon oxidation, the ion-loaded material can release any cations that are loosely bound in the ionic channels upon oxidation. In one specific example, applying the current to the ion-loaded material oxidizes the ion-loaded material and releases NH.sub.4.sup.+ ions from the ion-loaded material. In another example, the ion-loaded material can release K.sup.+ ions upon oxidation. Releasing the ions from the ion-loaded material allows the ions to be utilized.
[0064] The method for recovering ions from manure wastewater can include coupling the oxidation of the ion-loaded material to a cathodic reaction. In other words, electrons released from the ion-loaded material upon oxidation can be consumed by a cathodic reaction occurring at the same time. In one example, the cathodic reaction is the hydrogen evolution reaction, where electrons and protons combine to form H.sub.2. In another example, the cathodic reaction can be a two-electron oxygen reduction reaction producing H.sub.2O.sub.2 from O.sub.2 and 2H.sup.+.
[0065] A system for treatment of manure wastewater is shown in
[0066] The ion-selective redox material can be disposed within the internal volume of the cell. The ion-selective redox material can be fixed within the cell. Additionally, and alternatively, the ion-selective redox material can be removably disposed within the cell. The manure wastewater contacts the ion-selective redox material in the cell. For example, the ion-selective redox material can be submerged in manure wastewater within the cell. Upon contact with the manure wastewater, the ion-selective redox material can be reduced by organic carbon in the manure wastewater, whereupon it becomes the reduced material. As discussed above, the reduced material takes up NH.sub.4.sup.+ or K.sup.+ ions from the manure wastewater to generate the ion-loaded material.
[0067] The cell can include at least one outlet that is fluidly coupled to the wastewater treatment chamber. The manure wastewater flows from the manure waste supply into the cell through the at least one inlet, contacts the ammonium-ion selective redox material to generate the ion-loaded material, and exits the cell through the outlet to the wastewater treatment chamber. The manure wastewater in the wastewater treatment chamber can be contacted with disinfectants or other additives. In one example, the wastewater treatment chamber can be fluidly coupled with the wastewater supply such that the manure wastewater can be recirculated through cell.
[0068] The ion-selective redox material can be incorporated into an electrode having an electrical connection outside the cell. In one example, the ion-loaded material in the cell can be incorporated into an electrode having an electrical connection outside the cell. The ion-loaded material can be an electrode coupled to the electrochemical controller as an anode. A cathode can be disposed in the cell. The anode and cathode are electrically coupled to the electrochemical controller, where the electrochemical controller is capable of applying a current to the anode and cathode, or applying a potential to the anode and to the cathode. Additionally, and alternatively, the ion-loaded material can be transferred to a second cell having a cathode disposed therein, where the ion-loaded material is electrically coupled to the electrochemical controller as an anode, and where the anode and cathode are both electrically coupled to the electrochemical controller. The electrochemical controller can apply a current such that the anode is oxidized. As the anode is the ion-loaded material, the NH.sub.4.sup.+ ions can be released when the anode is oxidized.
[0069] In one example, the second cell can contain an aqueous solution of H.sup.+ ions. As the anode is oxidized, the electrons can be supplied to a cathodic reaction. In one example, the cathodic reaction is the reduction of H.sup.+ ions to H.sub.2.
[0070] The second cell can include a separator extending across the interior volume of the second cell to form two compartments within the second cell. The separator can be a glass frit or other suitable material. The separator allows ions to pass through but prevents the mixing of the solutions inside the two compartments. In this example, the anode is disposed in one compartment while the cathode is disposed in the second compartment. The solution can include ions to maintain charge balance. As the electronic controller drives the oxidation at the anode, NH.sub.4.sup.+ and/or K.sup.+ ions can be released from the ion-loaded material, and simultaneously oxygen can be reduced at the cathode, producing H.sub.2O.sub.2.
[0071] The NH.sub.4.sup.+ ions and other cations, such as K.sup.+ ions, released from the ion-loaded material can be collected by drying the remaining solution. In on example, the NH.sub.4.sup.+ ions and K.sup.+ ions can be used to supplement fertilizer.
[0072] The second cell can include an outlet. In one example, the outlet can be a gas outlet for directing gases out of the cell. The gas outlet can be fluidly coupled to a device that can utilize H.sub.2 as a source of energy. In another example, the gas outlet can be fluidly coupled to a storage unit for storing H.sub.2. In another example, the outlet can be fluidly coupled to the wastewater treatment chamber. In this example, the H.sub.2O.sub.2 generated by the reduction of oxygen at the cathode can be directed to the wastewater treatment chamber to act as a disinfectant to kill bacteria and pathogens.
[0073] Additionally, and alternatively, H.sub.2O.sub.2 can be converted to hydroxyl radicals using an advanced oxidation process such as an electro-Fenton process, to enable wastewater treatment.
Miscellaneous
[0074] Unless otherwise specified or indicated by context, the terms a, an, and the mean one or more. For example, a molecule should be interpreted to mean one or more molecules.
[0075] As used herein, about, approximately, substantially, and significantly will be understood by persons of ordinary skill in the art and will vary to some extent on the context in which they are used. If there are uses of the term which are not clear to persons of ordinary skill in the art given the context in which it is used, about and approximately will mean plus or minus 10% of the particular term and substantially and significantly will mean plus or minus >10% of the particular term.
[0076] As used herein, the terms include and including have the same meaning as the terms comprise and comprising. The terms comprise and comprising should be interpreted as being open transitional terms that permit the inclusion of additional components further to those components recited in the claims. The terms consist and consisting of should be interpreted as being closed transitional terms that do not permit the inclusion additional components other than the components recited in the claims. The term consisting essentially of should be interpreted to be partially closed and allowing the inclusion only of additional components that do not fundamentally alter the nature of the claimed subject matter.
[0077] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., such as) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
[0078] All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
[0079] Preferred aspects of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred aspects may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect a person having ordinary skill in the art to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
EXAMPLES
Example 1: Ammonium Recovery From Manure Wastewater and Electrochemical Synthesis
[0080] The present Example demonstrates ammonium recovery from manure wastewater and electrochemical synthesis of H.sub.2 or H.sub.2O.sub.2 using an ion-selective redox material (
Results
Design of the Ammonium Recovery and Electrochemical Synthesis System
[0081] The integrated system for ammonia recovery and electrosynthesis includes the NH.sub.4.sup.+ uptake, fertilizer production, electrochemical synthesis, and wastewater treatment processes (
[0082] As illustrated in
[0083] The manure wastewater prepared from cow feces and urine is a weakly alkaline suspension with a pH value of 9 and contains different inorganic ions (NH.sub.4.sup.+, Na.sup.+, K.sup.+, etc.), organic species, and solid particles (see cation and anion analysis details in
TABLE-US-00001 TABLE 1 Chemical compostions of the manure wastewater. Real manure waterwater pH 9.0~9.2 NH.sub.4.sup.+ (mM).sup.[a] 497 23 Na.sup.+ (mM).sup.[a] 148 4.2 K.sup.+ (mM).sup.[a] 183 8.8 Cl.sup. (mM).sup.[a] 47 4.5 Sulfate (mM).sup.[a] 11 0.88 Total phosphate (ppm).sup.[b] 1602 28 Acetate (mM).sup.[a] <164 Total nitrogen (mM).sup.[b] 558 30 Nitrate (mM).sup.[a] 0 Nitrite (mM).sup.[a] 0 Total inorganic carbon (ppm).sup.[c] 3700 13 Total organic carbon (ppm).sup.[c] 6400 54 Chemical oxygen demand (g O.sub.2 L.sup.1) 24.04 0.4 .sup.[a]The concentractions of cations and anions were analyzed using IC. .sup.[b]Total phosphates and nitrogen were analyzed using the corresponding reagent sets from Hach. .sup.[c]The concentractions of the carbon sepecies were analyzed using a total organic carbon analyzer
Synthesis and Electrochemical Performance of NH.sub.4.sup.+-Selective Redox Reservoirs
[0084] Because the Stokes radius and desolvation energy barrier of NH.sub.4.sup.+ are smaller than those of common metal ions (e.g., Na.sup.+, K.sup.+, Ca.sup.2+, Mg.sup.2+), the (de) intercalation of NH.sub.4.sup.+ should be intrinsically faster than other cations. Furthermore, recent progress suggests that redox materials with large ionic channels that can form non-ionic H-bonding with charge carriers may selectively accelerate the NH.sub.4.sup.+ migration over other metallic cations. Following such general guidelines, we choose Ni and Cu-based Prussian Blue analogs (PBAs) with open-framework structures (
[0085] We used co-precipitation methods to synthesize various PBAs with different morphologies (see Methods), including KNiHCF nanoparticles (
[0086] The element compositions were analyzed using inductively coupled plasma optical emission spectroscopy (ICP-OES, Table 2). The exact chemical formulas of the KNiHCF, NaNiHCF, and CuHCF samples were determined to be K.sub.0.1Ni.sub.1.5[Fe(CN).sub.6].Math.6.7 H.sub.2O, Na.sub.2.1Ni[Fe(CN).sub.6].Math.2.1 H.sub.2O, and K.sub.0.06Cu.sub.1.5[Fe(CN).sub.6].Math.5.5 H.sub.2O, respectively.
TABLE-US-00002 TABLE 2 Weight percentages of metal elements and water content in various PBA samples. RR Na or K, Ni or Cu, H.sub.2O, materials.sup.[a] wt % wt % Fe, wt % wt % Chemical formula KNiHCF 0.9 20.7 13.1 28.6 K.sub.0.1Ni.sub.1.5[Fe(CN).sub.6] .Math. 6.7 H.sub.2O NaNiHCF 13.6 16.6 15.8 10.4 Na.sub.2.1Ni[Fe(CN).sub.6] .Math. 2.1 H.sub.2O CuHCF 0.6 23.6 13.6 24.3 K.sub.0.06Cu.sub.1.5[Fe(CN).sub.6] .Math. 5.5 H.sub.2O .sup.[a]For metal elemental analysis, PBA samples were annealled in air at 600 C. for 1 h and dissolved in 5% HNO.sub.3 at 80 C. overnight. The dissolved samples were diluted for the ICP-OES measurements.
[0087] Cycling stability of these PBA electrodes was evaluated in manure wastewater. The CuHCF electrode showed near zero capacity in the first few cycles from cyclic voltammograms (CV) measurements (
[0088] NaNiHCF and KNiHCF electrodes were measured. The NaNiHCF electrode with pre-intercalated cations showed obvious capacity decay at 2 C rate in weakly alkaline solutions (
TABLE-US-00003 TABLE 3 Cycling stability of the various PBA electrodes in various solutions. Capacity Stability Material Solution (mAh g.sup.1) .sup.[a] (decay per cycle) KNiHCF 1M NaCl 61.0 0.01% 1M KCl 59.4 0.006% 1M NH.sub.4 Cl 56.3 0.03% Synthetic wastewater 51.8 0.06% Manure, pH~7.sup.[b] 52.8 0.19% Manure, pH~9.sup.[c] 52.3 0.60% 0.5M KHCO.sub.3 58.8 0.11% NaNiHCF 0.5M KHCO.sub.3 56.5 1.49% Diluted manure 48.6 2.51% wastewater (1:4 dilution) CuHCF 0.5M KHCO.sub.3 24.1 12.5% Manure, pH~7 54.8 0.10% Manure, pH~9 0.31 .sup.[d] .sup.[a] The listed capacities of PBA electrodes were measured in different solutions at 2 C rate. .sup.[b]Manure wastewater with a pH of ~7 was prepared by acidifying manure wastewater (pH~9) using 3M H.sub.2SO.sub.4 solution. .sup.[c]Manure wastewater without further modification. .sup.[d]The capacity of the CuHCF electrode decayed to ~0 after the first GCD cycle.
[0089] Based on these results, KNiHCF was chosen as the model RR material and systematically studied its cation intercalation properties. CV profiles of the KNiHCF electrode in 1 M NaCl, 1 M
[0090] KCl, and 1 M NH.sub.4Cl solutions at 1 mV s.sup.1 (
TABLE-US-00004 TABLE 4 Concentrations of common cations in manure waster, urine, and various types of municipal wastewater. NH.sub.4.sup.+, Na.sup.+, K.sup.+, Wastewater pH mM mM mM NH.sub.4/Na NH.sub.4/K Ref Our manure wastewater 9.0 497.0 146.0 183.0 3.4 2.7 This work Pretreated human urine 9.0 188.9 69.6 35.8 2.7 5.3 .sup.2 Real urine 9.0 272.9 70.4 37.6 3.9 7.3 .sup.3 Human urine 9.2 392.1 107.4 58.6 3.7 6.7 .sup.4 Human urine 8.9 289.3 80.4 38.1 3.6 7.6 .sup.5 Real livestock wastewater 4.2 158.3 28.3 40.4 5.6 3.9 .sup.6 Centrate from wastewater 8.4 47.1 18.5 5.8 2.5 8.1 .sup.7 treatment plant (WWTP) Centrate from WWTP 7.6 84.9 12.0 2.6 7.1 32.9 .sup.8 Treated wastewater from 6.8 0.1 1.8 0.3 0.05 0.3 .sup.9 WWTP Landfill leachate 7.9 324.3 145.3 33.2 2.2 9.8 .sup.10
NH.sub.4.sup.+ Recovery From Synthetic Manure Wastewater
[0091] NH.sub.4.sup.+ recovery was studied from a simpler synthetic wastewater solution (sww, 0.50 M NH.sub.4.sup.+, 0.183 M K.sup.+, and 0.146 M Na.sup.+) using an integrated electrochemical system that includes an anodic cell for NH.sub.4.sup.+ uptake from 25 mL synthetic wastewater (Cell.sub.anodic), a cathodic cell for NH.sub.4.sup.+ release in 25 mL 0.1 M Li.sub.2SO.sub.4 solution with a pH of 1.3 (Cell.sub.cathodic), and a KNiHCF RR electrode with a specific capacity (charge) of 186 C g.sup.1 (
[0092] To investigate the relationship between nutrient selectivity and NH.sub.4.sup.+ removal, five cycles of the recovery process were conducted, where the full recovery process cycle (
[0093] A three-cycle recovery process was performed in synthetic wastewater to further confirm the ion selectivity. Experiment demonstrates 10% NH.sub.4.sup.+ loss and no loss of Na.sup.+ and K.sup.+ through the process (
NH.sub.4.sup.+ Recovery From Manure Wastewater
[0094] NH.sub.4.sup.+ recovery from manure wastewater was investigated using a two-step recovery process (
[0095] The Experiment studied how NH.sub.4.sup.+ recovery in manure wastewater was influenced by the capacity of the RR electrode (
[0096] (
[0097] Furthermore, we performed the NH.sub.4.sup.+ uptake and release process for 50 runs (
Simultaneous NH.sub.4.sup.+ Recovery and Electrochemical Production of H.sub.2 and H.sub.2O.sub.2
[0098] NH.sub.4.sup.+ recovery and electrochemical H.sub.2 production was demonstrated using similar two-step processes. After the spontaneous NH.sub.4.sup.+ uptake in 10 mL manure wastewater, the oxidation of the KNiHCF electrode (with a specific capacity of 186 C g.sup.1) that have been intercalated with NH.sub.4.sup.+ ions released the NH.sub.4.sup.+ into 25 mL 0.1 M (NH.sub.4.sup.+).sub.2SO.sub.4 solution with a pH of 1.3. Moreover, this reaction was paired with the production of hydrogen gas on the Pt cathode at 0.30 V versus SHE (
[0099] NH.sub.4.sup.+ recovery could also be paired with the electrochemical two-electron oxygen reduction reaction (2e.sup.ORR) to produce H.sub.2O.sub.2 (
TABLE-US-00005 TABLE 5 Chemical stability of H.sub.2O.sub.2 mixed with NH.sub.4.sup.+ ions. Solution pH H.sub.2O.sub.2 (ppm) .sup.[a] H.sub.2O ~7 1249 60 mM NH.sub.4Cl ~7 1250 1M NH.sub.4Cl ~7 1245 60 mM NH.sub.4Cl + 60 mM KCl ~9.2 1248
[a] 0.5 mL 3 wt % H.sub.2O.sub.2 solution was added to different solutions (nanopure water, 60 mM NH.sub.4Cl, 1 M NH.sub.4Cl, and 60 mM NH.sub.4Cl+60 mM KCl) with a volume of 15 mL. The concentration of H.sub.2O.sub.2 was analyzed using the UV-Vis method after mixing for 2 hours.
[0100] NH.sub.4.sup.+ recovery and electrochemical H.sub.2O.sub.2 production was demonstrated in a two-compartment H-cell separated by a microporous glass frit (
[0101] To further improve NH.sub.4.sup.+ recovery from manure wastewater, we conducted two cycles of NH.sub.4.sup.+ recovery and H.sub.2O.sub.2 production to achieve a more complete NH.sub.4.sup.+ removal of 84% and COD removal of 56% (
[0102] This integrated system for ammonia and/or potassium recovery and chemical production could produce fertilizers at a lower energy consumption and cost. Because the chemical feedstocks mainly come from the manure wastewater or can be recycled in this integrated process, the most significant operational cost for this process include electricity, electrolytes, and ion-selective redox materials. Furthermore, the co-produced H.sub.2O.sub.2 has substantial commercial value and can be useful locally for disinfection and other environmental applications.
Conclusions
[0103] In summary, an electrochemical process for ammonia and nutrient recovery and electrochemical synthesis was developed by integrating spontaneous NH.sub.4.sup.+ and/or K.sup.+ uptake from manure wastewater, fertilizer production, and electrochemical production of H.sub.2 or H.sub.2O.sub.2, using an ion-selective redox material. The developed electrode with a high NH.sub.4.sup.+ and/or K.sup.+ selectivity, a suitable redox potential, and good chemical and electrochemical stability enables the spontaneous ion-selective intercalation into the open framework redox material driven by the oxidation of organic matter in manure wastewater. Model NH.sub.4.sup.+ recovery processes in synthetic wastewater reveal near 100% nutrient selectivity of the ammonium-ion selective redox material. In addition, recovery processes from manure wastewater exhibit spontaneous uptake of NH.sub.4.sup.+ and K.sup.- ions with excellent ion selectivity and little NH.sub.4.sup.+ loss, as well as the reduction of organic matter content. Furthermore, the developed electrochemical system achieves the co-production of NH.sub.4.sup.+ and K.sup.+-rich fertilizer and hydrogen gas as a green fuel or H.sub.2O.sub.2 as a disinfectant for wastewater treatment and could allow the recycling of K.sup.+-rich salts as electrolytes or fertilizers. The disclosed technology provides for electrochemical nutrient recovery from wastewater and on-demand distributed electrochemical manufacturing with high recovery efficiency and low energy cost.
Methods
Chemicals.
[0104] All chemicals were used as purchased without further purification. Sodium citrate dihydrate (ACS reagent grade) was purchased from ICN Biomedicals Inc. Carbon black (Super P Conductive, 99.0+%) and carbon black (acetylene, 99.9+%) were purchased from Alfa Aesar.
[0105] TUBALL BATT NMP 0.4% (a mixture of single-wall carbon nanotubes, 0.4 wt %; polyvinylidene fluoride, 2 wt %; N-methyl-2-pyrrolidone, >96.7 wt %) was purchased from OCSiAl. Other chemicals were purchased from Sigma Aldrich. Titanium mesh (150 mesh, with a thickness of 230 um) was purchased from HeBei ChaoChuang Metal Mesh Co., Ltd., available through Alibaba.com. Deionized nanopure water (18.2 M.Math.cm) from ThermoScientific Barnstead water purification systems was used for all experiments.
Synthesis of KNiHCF.
[0106] Potassium nickel hexacyanoferrate (KNiHCF) was synthesized using a modified co-precipitation method (Wessells CD, Peddada SV, Huggins RA, Cui Y. Nickel Hexacyanoferrate Nanoparticle Electrodes For Aqueous Sodium and Potassium Ion Batteries. Nano Lett 11, 5421-5425, 2011). Typically, 80 mL of 40 mM Ni(NO.sub.3).sub.2 solution and 80 mL of 20 mM K.sub.3Fe(CN).sub.6 solution were added dropwise into 40 mL H.sub.2O under vigorous stirring. The solution was stirred for 6 h at 70 C. to yield a dark-orange precipitate. Then the precipitate was centrifuged, rinsed with deionized water multiple times, and dried in a vacuum oven at 60 C. overnight. ps Synthesis of NaNiHCF.
[0107] Sodium nickel hexacyanoferrate (NaNiHCF) was synthesized using a co-precipitation method (Wang F, et al. Modular Electrochemical Synthesis Using a Redox Reservoir Paired with Independent Half-Reactions. Joule 5, 149-165, 2021). Typically, 100 mL of 0.1 M NiCl.sub.2 and 1 M sodium citrate dihydrate solution and 100 mL of 0.1 M Na.sup.+Fe(CN).sub.6 solution were added dropwise to 100 mL H.sub.2O under vigorous stirring. The molar ratio between Ni.sup.2+ and citrate was 1:10. The solution was then stirred for 24 h at 80 C. to yield a light-green precipitate. This precipitate was centrifuged, rinsed with deionized water multiple times, and dried in a vacuum oven at 60 C. overnight.
Synthesis of CuHCF.
[0108] Copper hexacyanoferrate (CuHCF) was synthesized using a modified co-precipitation method (Wu X, et al. Diffusion-free Grotthuss topochemistry for high-rate and long-life proton batteries. Nat Energy 4, 123-130, 2019). Typically, 40 mL of 0.2 M CuSO.sub.4 solution was added dropwise into 40 mL of 0.1 M K.sub.3Fe(CN).sub.6 solution under vigorous stirring at room temperature. After 6 h of reaction, the olive-green precipitate was centrifuged, rinsed with deionized water multiple times, and dried in a vacuum oven at 60 C. overnight.
Synthesis of Fe-CNT Catalyst.
[0109] The synthesis of Fe-CNT catalyst followed a reported impregnation and reduction method (Wang R, Sheng H, Wang F, Li W, Roberts DS, Jin S. Sustainable Coproduction of Two Disinfectants via Hydroxide-Balanced Modular Electrochemical Synthesis Using a Redox Reservoir. ACS Cent Sci 7, 2083-2091, 2021). In a typical synthesis, a 7.5 mM iron nitrate solution was first prepared by dissolving 30.3 mg Fe(NO.sub.3).sub.3.9H.sub.2O into 10 mL nanopure water. Next, the carbon nanotube (CNT) suspension was prepared by mixing 50 mg MWCNT (724769, >95% carbon from Sigma Aldrich) with 20 mL of ethanol via sonication for 1 h until a well-dispersed suspension was achieved. Then 200 L of 7.5 mM Fe.sup.3 solution was added dropwise into the CNT suspension under sonication for 30 min. Then the solvent was removed using a rotary evaporator, and the as-prepared material was dried in a vacuum oven at 60 C. for 20 min to evaporate the residual solvent further. Finally, the dried Fe(NO.sub.3).sub.3/CNT powder was heated in a tube furnace to 600 C. within 20 min under a gas flow of 100 sccm Ar (UHP, Airgas) and a pressure of 1 Torr and kept at the same temperature for another 40 min before cooling down to room temperature.
Materials Characterizations.
[0110] Powder X-ray diffraction (PXRD) patterns of the KNiHCF, NaNiHCF, and CuHCF samples were collected using a Bruker D8 Advance X-ray diffractometer equipped with Cu-K radiation. The size and morphology of the samples were characterized using a scanning electron microscope (SEM, Zeiss SUPRA 55VP) equipped with an energy-dispersive X-ray spectroscopy (EDS) detector. An inductively coupled plasma-optical emission spectrometer (ICP-OES, Agilent 5110) was utilized to determine the compositions of K, Na, Cu, Ni, and Fe elements. Thermogravimetric analysis (TGA, TA Q500) was used to determine the water content in various samples.
Fabrication and Electrochemical Tests of the RR Electrodes.
[0111] The RR electrodes were prepared via a conventional slurry-casting method using TUBALL BATT NMP 0.4% (0.4 wt % SWCNT, 2 wt % polyvinylidene fluoride, >96.7 wt % N-Methyl-2-pyrrolidone), super P conductive carbon, and the active materials. Typically, 70 wt % active materials and 18 wt % Super P carbon black were grounded for 30 min using a high-energy ball mill (Mixer/Mill 8000M, Horiba). Then the mixtures were added into TUBALL BATT NMP 0.4% that provided 2 wt % SWCNT and 10 wt % polyvinylidene fluoride for the electrode slurry (SWCNT and PVDF both from TUBALL BATT NMP 0.4%). The slurry was stirred at 700 r.p.m. overnight at room temperature and then cast onto titanium mesh current collectors (150 mesh, with a thickness of 230 m). The titanium mesh was held in place by two PTFE (polytetrafluoroethylene) plates on both sides of the mesh and a clamp to secure the plates. The slurry was cast onto one side of the Ti mesh and subsequently onto the other side using stainless steel spatulas. The prepared electrodes were dried in a vacuum oven at 60 C. for 12 h to remove the residual solvent. The areal mass loading ranged from 5 to 24 mg cm.sup.2.
[0112] The electrochemical performance of the RR electrode was characterized in a three-electrode cell, with a Pt wire counter electrode and a saturated calomel electrode (SCE) as the reference electrode in various solutions (1 M NH.sub.4Cl, 1 M KCl, 1 M NaCl, synthetic wastewater, and manure wastewater). Synthetic wastewater (0.50 M NH.sub.4Cl+0.183 M KHCO.sub.3+0.146 M NaHCO.sub.3) was prepared based on the chemical compositions of manure wastewater (Table 1). Manure wastewater with a pH of 7 was prepared by acidifying manure wastewater (pH9) using 3 M H.sub.2SO.sub.4. Cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) tests of the RR electrodes were recorded on a Bio-Logic VMP-3 multichannel potentiostat. The galvanostatic cycling was performed at 2 C rate for stability characterization and the rates of 1 C to 1000 C for the kinetics characterization, where 1 C is defined as 65 mA g.sup.1 based on the theoretical capacity of as-synthesized materials. For studying the self-reduction behaviors, two KNiHCF RR electrodes with similar mass loading (80 mg) were oxidized to 0.9 V vs. SCE in synthetic wastewater and transferred to two beaker-type cells containing 80 mL of either manure or synthetic wastewater. The potentials of the RR electrodes were monitored using a Bio-Logic SP-200 potentiostat.
Preparation of Manure Wastewater.
[0113] Cow feces and urine were collected from the campus dairy cattle center at UW-Madison and stored in the cold room at 4 C. before use. To prepare manure wastewater, the feces and urine were mixed with a mass ratio of 1:9 with trace carbon black under stirring (e.g., 20 g feces, 180 g urine, and 10 mg carbon black for a typical preparation). Since this solid-liquid mixture could not pass the filter membrane with a pore size smaller than 10 m even when a vacuum system was used, centrifugation would be the proper method to separate the solids with large particle sizes. Here, trace carbon black was added to the mixture of cow urine and feces to achieve solid-liquid separation because it could work as the coagulation reagent and be easily separated from manure wastewater after centrifugation. After centrifugation at 9000 r.p.m for 15 min at 4 C. (50 g of the mixture in each centrifuge tube), the brownish supernatant with some suspended particles was used as manure wastewater without further filtration throughout this study. The precipitate with a brownish-yellow color was formed gradually during the storage of manure wastewater, but the precipitate was not used in the study.
Chemical Characterization of Manure Wastewater and Recovered Solutions.
[0114] Manure wastewater was used without further treatment, and its pH value was determined to be 9.0-9.2 using the Orion 810 BNUWP ROSS Ultra pH meter. The concentrations of various cations ([NH.sub.4.sup.+], [K.sup.+], and [Na.sup.+]) and anions in the manure wastewater and recovered samples were analyzed using ICS-1100 (cations) and Dionex ICS-2100 (anions) ion chromatography (IC) systems equipped with conductivity detectors, respectively. Typically, cation analysis was performed using a Dionex IonPac CS12A IC column with 7.5 mM methanesulfonic acid (MSA) solution as the mobile phase at 1.5 mL min.sup.1. The current of the suppressor was 33 mA. Antion analysis was performed using a Dionex IonPac AG/AS-14 column with 3.5 mM Na.sub.2CO.sub.3 and 1.0 mM NaHCO.sub.3 solution as the mobile phase at 1.2 mL min.sup.1. The current of the suppressor was 24 mA. The standard cation solutions were prepared by dissolving NaCl, LiCl, KCl, and NH.sub.4Cl in nanopure water. The standard anion solutions were prepared by dissolving NaF, NaBr, NaCl, NaNO.sub.2, NaNO.sub.3, NaH.sub.2PO.sub.4, and Na.sub.2SO.sub.4. The standard acetate solution was prepared by dissolving only sodium acetate without other salts in nanopure water because of F.sup.and acetate coelution. All samples were diluted and filtrated using 0.45 m syringe filters before analysis.
[0115] Total nitrogen (TN) in manure wastewater was analyzed using the total nitrogen reagent set from Hach (Total Nitrogen Reagent Set, HR, TNT, product #2714100). Total phosphate in manure wastewater was analyzed using the total phosphate reagent set from Hach (High Range Total Phosphate Reagent Set, product #2767245). Total carbon, organic carbon, and inorganic carbon in manure wastewater were analyzed using a Sievers M5310C total organic carbon analyzer after proper dilution and filtration. Chemical oxygen demand (COD) of manure wastewater was analyzed using the COD reagent set from Hach [TNTplus Vial Test, HR (20-1,500 mg/L COD), product #2415925].
NH.sub.4.sup.+ recovery From Synthetic Wastewater.
[0116] Two electrochemical cells, the NH.sub.4.sup.+-uptake cell (Cell.sub.anodic) containing 25 mL synthetic wastewater and the NH.sub.4.sup.+-release cell (Cell.sub.cathodic) with 25 mL 0.1 M Li.sub.2SO.sub.4 solution (PH 1.3), were used to recover NH.sub.4.sup.+ from synthetic wastewater. The KNiHCF RR electrodes with the size of 44 cm.sup.2 and a total capacity of 294 C were prepared as described above and used as the working electrode in both cells. In Cell.sub.anodic, a Pt wire electrode and a SCE were used as the counter electrode and reference electrode. In addition, about 1 g CaCO.sub.3 was added to the electrochemical cell to stabilize the pH. The NH.sub.4.sup.+-uptake process was conducted under a current of 45 mA. In Cell.sub.cathodic, a Pt wire electrode and a SCE were used as the counter electrode and reference electrode. The NH.sub.4.sup.+-release process using KNiHCF RR electrodes was measured under a constant current of 30 mA.
[0117] Typically, one NH.sub.4.sup.+ recovery cycle included the NH.sub.4.sup.+ uptake from wastewater and the NH.sub.4.sup.+ release in Li.sub.2SO.sub.4 solution. For the five-cycle recovery process, the cations in the same 25 mL synthetic wastewater were recovered five times, and the recovered ions were collected in a new 0.1 M Li.sub.2SO.sub.4 solution for each cycle. The RR electrodes were oxidized to 0.9 V vs. SCE (RR.sup.OX) in synthetic wastewater to de-intercalate cations before the NH.sub.4.sup.+ recovery processes. In Cell.sub.anodic, the reduction of RR.sup.OX to RR.sup.red is accompanied by cation intercalation, which was paired with OER at the Pt anode. After the NH.sub.4.sup.+ uptake, the RR electrode was washed with nanopure water and 0.1 M Li.sub.2SO.sub.4 solution to remove the residual electrolyte, then moved to Cell.sub.cathodic. In Cell.sub.cathodic, the oxidation of RR released intercalated cations until 0.9 V vs. SCE, which was paired with HER at the Pt cathode. During these recovery processes, the capacity of the RR electrode was controlled by the potential and capacity restrictions to ensure the RR electrode was operated within the desired potential windows. For the three-cycle NH.sub.4.sup.+ recovery process, Cell.sub.anodic contained 16 mL synthetic wastewater and Cell.sub.cathodic contained 18 mL 0.1 M Li.sub.2SO.sub.4 solution (PH 1.3). Other electrochemical configurations and operations were the same as those for the five-cycle recovery process.
[0118] The concentrations of cations in synthetic wastewater and recovered solutions after each recovery cycle were measured by IC following the above procedures. Based on the concentrations of cations, the ion selectivity between different cations, nutrient (NH.sub.4.sup.+ +K.sup.+) selectivity, and Faradaic efficiency (FE) were calculated according to the following equations:
where the [M].sub.recovered and [N] .sub.recovered were the concentrations of M and N cations in the recovered solutions, the [M].sub.initial and [N].sub.initial were the concentrations of M and N cations in synthetic wastewater, [NH.sub.4.sup.+].sub.recovered +[K.sup.+].sub.recovered +.sub.recovered [Na.sup.+].sub.recovered were the concentrations of NH.sub.4.sup.+, K.sup.+, and Na.sup.+ in the recovered solutions, and Q.sub.RR was the charge passing through the RR electrode in the recovery processes.
Detection of Active Chlorine (AC).
[0119] The concentration of the produced AC at the anode was detected by iodometric titration. Specifically, the following steps were taken: 1) 1.000 g KI (>99%, Sigma-Aldrich) was first dissolved in 10 mL acetate buffer with a pH of 3.7. 10 mL sample solution containing CIO was added into the above solution, and the color of the solution changed to yellow. 2) The sample solution was then titrated using 1.00 mM standard Na.sub.2S.sub.2O.sub.3 solution until the yellow solution became colorless. 3) Add 1.0 mL 0.5 wt % starch solution as the indicator (the color of the sample solution became brownish red), then continuously titrate with 5.00 mM standard Na.sub.2S.sub.2O.sub.3 solution until the color disappeared. Finally, the concentration of the produced NaCIO was calculated with the volume of the 5.00 mM Na.sub.2S.sub.2O.sub.3 solution consumed using the following equations:
ClO.sup.+2I.sup.+2H.sup.+.fwdarw.Cl.sup.+I2+H.sub.2O (4)
I.sub.2+2S.sub.2O.sub.3.sup.2.fwdarw.2I.sup.+S.sub.4O.sub.6.sup.2(5)
The FE of NaCIO production reaction was calculated using the following equation:
where V, [ClO.sup.], and Q.sub.input are the volume of the solution, the concentration of produced NaClO, and the input charge during the electrolysis, respectively.
NH.sub.4.sup.+ Recovery From Manure Wastewater Using RR Electrodes.
[0120] The NH.sub.4.sup.+-uptake cell (Cell.sub.N-uptake) containing 2 mL manure wastewater and the NH.sub.4.sup.+-release cell (Cell.sub.N-release) with 10 mL 0.1 M Li.sub.2SO.sub.4 solution (PH 2) were used to recover NH.sub.4.sup.+ from manure wastewater. The KNiHCF RR electrodes with a size of 22 cm.sup.2 and a total active material loading of 1200 mg were used in both cells. In Cell.sub.N-uptake, a SCE electrode was used as the reference electrode to monitor the potential of the RR electrode. In Cell.sub.N-release, a Pt wire electrode and a SCE were used as the counter electrode and reference electrode. The NH.sub.4.sup.+-release process using KNiHCF RR electrodes was measured under a constant current of 10 mA. COD removal was calculated according to the following equation to describe the consumption of organic matter over the NH.sub.4.sup.+ recovery process:
where [COD].sub.initial and [COD].sub.final are the amounts of COD in manure wastewater before and after recovery.
[0121] Three parallel recovery experiments were conducted, denoted as Run 1, Run 2, and Run 3. Typically, one NH.sub.4.sup.+ recovery run included the NH.sub.4.sup.+ uptake from manure wastewater and NH.sub.4.sup.+ release in Li.sub.2SO.sub.4 solution. Cations in 2 mL manure wastewater were recovered only once, and the recovered ions were collected in 0.1 M Li.sub.2SO.sub.4 solution for each run. The RR electrodes were oxidized to 0.9 V vs. SCE before use. For each run, in Cell.sub.N-uptake, the reduction of RR and NH.sub.4.sup.+ uptake occurred spontaneously. After a 24-h reduction process, the RR electrodes were washed with nanopure water and 0.1 M Li.sub.2SO.sub.4 solution to remove the residual electrolyte, then moved to Cell.sub.N-release. In Cell.sub.N-release, the oxidation of RR released intercalated cations until 0.9 V vs. SCE, which was paired with HER at the Pt cathode. During these recovery processes, the capacity of the RR electrode was controlled by the potential and capacity restrictions to ensure the RR electrode was operated within the desired potential windows. The concentrations of cations in manure wastewater and recovered solutions were measured by IC and the ion selectivity, nutrient selectivity, and FE were calculated based on the above equations. For the 50 recovery runs, each run included a 10-hour NH.sub.4.sup.+ uptake in manure wastewater and nearly 2-hour electrochemical NH.sub.4.sup.+ release. The COD removal and nutrient selectivity were analyzed every 5 runs.
NH.sub.4.sup.+ Recovery From Manure Wastewater and H.sub.2 Production.
[0122] NH.sub.4.sup.+ recovery and H.sub.2 production were demonstrated in two cells, the NH.sub.4.sup.+-uptake cell (Cell.sub.N-uptake) containing 10 mL manure wastewater and the H.sub.2 cell (Cell.sub.H.sub.
Electrochemical Characterization of the Electrocatalytic H.sub.2O.sub.2 Production.
[0123] All electrocatalytic characterizations were performed using a Bio-Logic SP-200 potentiostat or a Bio-Logic VMP-3 multichannel potentiostat at room temperature.
Preparation of Fe-CNT Electrodes.
[0124] 10 mg of as-prepared Fe-CNT catalyst was typically mixed with 1 mL of ethanol and 100 L of Nafion 117 solution (5%) and then sonicated for 2 h to get a well-dispersed catalyst ink. Next, a fixed volume of catalyst ink was drop-cast onto the Toray carbon paper (TGP-H-060, Fuel Cell Store) and then dried under ambient conditions. The mass loading of each electrode was around 1 mg with 100 L catalyst ink.
H.sub.2O.sub.2 Production and Detection.
[0125] The H.sub.2O.sub.2 production reaction was performed in an H-cell separated with a glass frit (89057-758, ACE glass Incorporated, USA), using a Fe-CNT electrode as the working electrode, a Pt wire as the counter electrode, and a SCE reference electrode in 1 M NH.sub.4Cl, 1 M NH.sub.4Cl+1 M KCl, and 1 M KCl solutions. Prior to the measurements, the electrolyte solution was purged with O.sub.2 gas for at least 15 min. Then, the electrocatalytic performance of the Fe-CNT electrode was investigated in the above solutions with continuous O.sub.2 gas bubbling via CV and linear scan voltammetry (LSV) at 50 mV s.sup.1, and chronoamperometry (CA) at different potentials (0.454, 0.554, 0.654 V vs. SCE). All potentials measured against SCE were converted to the reversible hydrogen electrode (RHE) scale using E.sub.RHE=E.sub.SCE+0.241 V+0.059pH, where the pH values of solutions were determined to be 6.66.8 using an Orion 810 BNUWP ROSS Ultra PH meter.
[0126] The concentration of the H.sub.2O.sub.2 generated from CA was quantified by the colorimetric titration with ceric sulfate. The sample solution containing H.sub.2O.sub.2 with a proper volume was added into 5.0 mL 0.4 mM Ce(SO.sub.4).sub.2 solution and measured by UV-Vis spectroscopy at 319 nm. The concentration of H.sub.2O.sub.2 could be determined by the following equations:
where V.sub.1, V, [Ce.sup.4 +] and [Ce.sup.4 +, detected] are the original volume of 0.4 mM Ce.sup.4 + standard solution, the volume of added H.sub.2O.sub.2 sample solution, the concentration of standard Ce.sup.4 + solution, and the detected concentration of Ce.sup.4 + solution after adding H.sub.2O.sub.2 sample, respectively. In this experiment, V.sub.1 was 5.0 mL and [Ce.sup.4 +] was 0.4 mM.
[0127] The FE of H.sub.2O.sub.2 production reaction was then calculated based on the concentration of detected H.sub.2O.sub.2 and input charge using the following equation:
where V, [H.sub.2O.sub.2], and Q.sub.input are the volume of the solution, the concentration of produced H.sub.2O.sub.2 and the input charge during the electrosynthesis, respectively.
NH.sub.4.sup.+ Recovery From Manure Wastewater and H.sub.2O.sub.2 Production.
[0128] NH.sub.4.sup.+ recovery and H.sub.2O.sub.2 production using the NH.sub.4.sup.+ -selective RR electrodes were demonstrated in two cells, the NH.sub.4.sup.+-uptake cell (Cell.sub.N-uptake) containing 10 mL manure wastewater and the H-cell (Cell.sub.H.sub.
[0129] The operations were the same as those in NH.sub.4.sup.+ recovery from manure wastewater, except the H.sub.2O.sub.2 production occurred on the Fe-CNT electrode in this configuration. For the 2-cycle recovery process with H.sub.2O.sub.2 production, cations in 10 mL manure wastewater were recovered twice, and the recovered ions were collected in a new 14 mL 0.5 M K.sub.2SO.sub.4 solution for each cycle. The same KNiHCF RR electrodes in these 1-cycle recovery processes were used. The concentrations of cations in manure wastewater and recovered solutions, ion selectivity, nutrient selectivity, and FE were analyzed and calculated based on the above procedure and equations. The recovered solution in the RR chamber was dried to get solid product powder, and the PXRD pattern of the sample was collected.
[0130] The concentration of the produced H.sub.2O.sub.2 was measured following the procedures described above. Based on the product concentrations, the Faradaic efficiencies were calculated according to the following equations:
where V, [H.sub.2O.sub.2], and the Q.sub.passing,RR are the volume of the solution, the concentration of produced H.sub.2O.sub.2, and the charge passing through the RR electrode, respectively.
Example 2: Calculated Difference of Intercalation Potential Between NH.SUB.4..SUP.+ and M.SUP.+ (Cations With 1+ Charge) at Difference Molar Ratios of NH.SUB.4..SUP.+ to M+
[0131] The intercalation potentials of different cations, E.sup.O, were estimated based on E.sub.1/2 from cyclic voltammograms of the KNiHCF electrode in various solutions at 1 mV s.sup.1 (
E.sup.O.sub.NH.sub.
E.sub.NH.sub.
When E.sub.NH.sub.
Example 3: Coulombic Efficiency During the Ammonium Recovery Process in Manure Wastewater
[0132] The Coulombic efficiency, defined as the ratio of the charges passing through the RR (C.sub.RR) to the charges needed for COD removal (C.sub.COD),
[0133] is used to evaluate the efficiency of organic-to-electricity over the recovery processes. C.sub.COD could be calculated based on the measured COD removal in manure wastewater and Faraday's constant. For example, the initial COD is 24.04 g L.sup.1, the COD removal is 30%, and the volume of manure wastewater is 2 mL. The COD removal is 0.0144 g O.sub.2, equal to 4.51104 mol O.sub.2. Then the charge based on COD removal was n(O.sub.2)F4=174 C. Here the C of RR is the charge passing through the RR electrode during the electrochemical NH.sub.4.sup.+ release process, which is measured by the potentiostat. When C.sub.RR is 60 C, the CE will be 34.5%.