Electrified Membrane Flow-Cell Reactor For Concurrent Nitrate Reduction And Ammonia Production From Wastewater

Abstract

Disclosed is an electrified membrane flow-cell reactor system and method for nitrogen wastewater treatment and upcycling towards ammonia nitrogen without external acid/base consumption. This electrified membrane flow-cell reactor includes a cathodic membrane module having a gas-permeable or gas-exchange membrane and a cathodic catalytic layer, an anode, and a semi-permeable membrane between the cathodic and anodic chamber. Three chambers in the flow-cell reactor include (i) a cathode chamber for nitrate reduction and upcycling towards NH.sub.3, (ii) a trap chamber for NH.sub.3 capture and storage, and (iii) an anode chamber for H.sup.+ production and protonation of gaseous NH.sub.3 to NH.sub.4.sup.+. The cathodic membrane and anode are connected to an electric power source to provide a stable cathodic potential and enable electrode reactions. This method will continuously treat nitrate-containing wastewater and achieve simultaneous electrochemical nitrate reduction from the wastewater and ammonia recovery as ammonium salts in the trap chamber.

Claims

1. A method of wastewater treatment, comprises: using an electrified membrane flow-cell reactor including a cathode chamber, an anode chamber, and a trap chamber for nitrate upcycling towards ammonia; conducting a nitrogen containing wastewater treatment and upcycling towards ammonia (NH.sub.3) in the cathode chamber with a special three-phase interface membrane module design and fabrication; wherein a catalytic layer and a hydrophobic gas-permeable membrane are located in the cathodic membrane module; conducting an ammonia (NH.sub.3) transport across the hydrophobic gas-permeable membrane and a subsequent capture of the ammonia in the trap chamber; and conducting a hydrogen ion (H.sup.+) production and protonation of gaseous ammonia (NH.sub.3) to ammonium (NH.sub.4.sup.+) in the trap chamber or the anode chamber; wherein wastewater is treated by removing nitrogen and upcycling towards ammonia nitrogen fertilizer without using an external acid or having base consumption.

2. The method of claim 1, further includes utilizing the anodic chamber to produce acids to absorb ammonia into ammonium salts without the use of an external acid.

3. The method of claim 1, further includes redirecting the fluid containing NH.sub.3 and hydrogen gas (H.sub.2) from the cathode chamber into the anodic chamber to shift water oxidation to hydrogen gas (H.sub.2) oxidation and harvest the chemical energy from the hydrogen gases to decrease the total cell voltage and energy consumption of the electrified membrane flow-cell system.

4. The method of claim 3, further includes connecting the cathodic membrane module and the anode membrane module to at least one of a power source to enable a cathodic potential and an electrode reaction, a potentiostat, an electrochemical working station, or any combination thereof.

5. The method of claim 1, wherein the catalytic layer in the cathodic membrane module has materials selected from a group of metals, metal alloys, composite materials, nanocomposite materials, nanoparticles, and combinations thereof.

6. The method of claim 1, wherein the catalyst layer is formed by surface coating, doping or mechanical attachment of catalysts onto the gas exchange hydrophobic membranes.

7. The method of claim 6, wherein the surface coating and doping methods include physical coating techniques and chemical coating techniques.

8. The method of claim 7, wherein the physical coating techniques include at least one selected from the group physical vapor deposition, dip coating, spin coating, casting, filtration-evaporation, lay-by-layer assembly, and any combination thereof.

9. The method of claim 7, wherein the chemical coating techniques include at least one selected from the group coupling agents, sol-gel method, chemical vapor deposition, surface grafting, in situ growth, and any combination thereof.

10. The method of claim 1, further includes providing a mechanical attachment to the electrified membrane flow-cell reactor module by clipping different forms of a catalyst-containing platform onto the gas-permeable hydrophobic membrane.

11. The method of claim 10, wherein the catalyst-containing platform is selected from the group a sheet, a mesh, a foam, a hollow fiber, a porous membrane, a lamellar membrane, and any combination thereof.

12. A system for wastewater treatment, comprising an electrified membrane flow-cell reactor, the electrified membrane flow-cell reactor comprises: a cathode chamber, an anode chamber, and a trap chamber for optimal nitrate upcycling towards ammonia as compared to not using the electrified membrane flow-cell reactor.

13. The system of claim 12, wherein the cathode chamber further includes a gas exchange membrane and materials of the gas exchange membrane in the cathodic chamber is selected from a group of polytetrafluoroethylene (PTFE), polypropylene (PP), polyvinylidene fluoride (PVDF), polydimethylsiloxane (PDMS), and any combinations thereof.

14. The system of claim 13, wherein materials of the gas exchange membrane in cathodic membrane has a structural configuration selected from the group of flat, tubular, hollow fibers, porous, and any combination thereof.

15. The system of claim 12, further comprises a semi-permeable or a selective membrane integrated to separate the cathode chamber and the anode chamber.

16. The system of claim 15, wherein the semi-permeable or the selective membrane is selected from the group of a proton exchange membrane (PEM), a cation exchange membrane, an anion exchange membrane, and any combinations thereof.

17. The system of claim 12, wherein the anode chamber has an anode and the anode is selected from the group of metals, metal alloys, composite materials, nanocomposite materials, nanoparticles, and any combinations thereof.

18. A system for wastewater treatment, comprising an electrified membrane flow-cell reactor, the electrified membrane flow-cell reactor comprises: a cathodic membrane chamber having a gas-permeable or a gas-exchange membrane and a cathodic catalytic layer, wherein the cathode chamber is for nitrate reduction and upcycling towards NH.sub.3; an anode chamber for H.sup.+ production and protonation of gaseous NH.sub.3 to NH.sub.4.sup.+; a semi-permeable membrane or a gas-permeable hydrophobic membrane disposed between the cathodic membrane chamber and anode chamber; and a trap chamber for NH.sub.3 capture and storage.

19. The system of claim 18 further comprises a mechanical attachment for holding the cathodic membrane chamber, the anode chamber, and the trap chamber together, the mechanical attachment is a catalyst-containing platform clipped onto the gas-permeable hydrophobic membrane, and wherein the catalyst-containing platform is selected from the group of a sheet, a mesh, a foam, hollow fibers, a porous membrane, a lamellar membrane, and any combination thereof.

20. The system of claim 18 further comprises an electric power source connected to the cathodic membrane chamber and anode chamber to provide a stable cathodic potential and an electrode reaction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] So that those having ordinary skill in the art will have a better understanding of how to make and use the disclosed composition and methods, reference is made to the accompanying figures wherein:

[0038] FIG. 1 is a schematic diagram of a design of an electrified membrane flow-cell reactor system;

[0039] FIG. 2 is a schematic diagram of the detailed structure of the electrified membrane flow-cell reactor shown in FIG. 1;

[0040] FIG. 3 is an illustration of the working diagram and major electrode reactions of the electrified membrane flow-cell in FIG. 1; and

[0041] FIGS. 4A, 4B and 4C are the pictures of the assembled parts of membrane modules and illustrates of operation principles using CuO as cathodic catalyst as example in FIG. 1.

DETAILED DESCRIPTION

[0042] The present disclosure is directed to an apparatus, system, and methods comprising a novel electrified membrane flow-cell reactor that enables electrochemical conversion of nitrate/nitrite in wastewater into ammonium salts using in situ base/acid production without external chemical addition.

[0043] Adverting to the figures, FIG. 1 is a schematic diagram of a typical design of this electrified membrane flow-cell reaction system comprising a three-chamber flow cell 1, two influent ports 2-1 and 3-2, two effluent ports 2-2 and 3-2, and a DC electric power source 4. During the operation process of the invention, the feed nitrate wastewater in tank 5 is pumped into the influent port 2-1 by the circulating pump 6 to pass through cathodic chamber for nitrate reduction reactions and then recycled back to the nitrate wastewater tank 5. The catalytic layer or cathodic catalysts such as copper (Cu) are coated or immobilized on a gas-permeate hydrophobic membrane that separates the trap chamber and the cathodic chamber. Under a cathodic potential applied to the cathodic membrane, nitrate is electrochemically reduced to NH.sub.3 that could immediately transfer across the cathodic membrane.

[0044] The remaining NH.sub.3 in the alkalized solution will be circulated back to the anodic chamber and is further stripped into the trap tank filled with an acidified electrolyte solution produced from the anodic chamber. On the other hand, the electrolyte solution in the trap tank 7 is pumped into the influent port 3-1 by the circulating pump 8 to absorb the transferred NH.sub.3, which is immediately converted to ammonium salts (e.g., NH.sub.4SO.sub.4 if Na.sub.2SO.sub.4 is used as the electrolyte) and accumulates inside the trap tank. The effluent port 3-3 circulates the electrolyte fluid into the anodic chamber for acidification due to the anodic reactions (e.g., water and/or H.sub.2 oxidation). The acidified fluid comes outs of the effluent port 3-2 and enters the trap tank again for further use in the ammonia capture in the cathodic chamber. The electrified membrane flow-cell 1 will be described in detail in FIG. 2.

[0045] FIG. 2 is a detailed illustration of the electrified membrane flow cell structure. According to one embodiment of the invention, a proton exchange membrane (PEM) 9 with an effective reactive area of approximately 4 cm.sup.2 is integrated to separate the cathode and anode chambers, preventing chlorine ions (Cl.sup.-) from translocating from the cathodic chamber to the anodic chamber that could result in the formation of active chlorine (HOCl or OCl.sup.-). These active chlorine species could oxidize NH.sub.4.sup.+/NH.sub.3 to N.sub.2 and reduce the ammonia recovery. A cathodic membrane 10 consists of a catalytic layer and a gas exchange membrane for nitrogen pollution reduction to NH.sub.3 and NH.sub.3 gas transfer, respectively. Moreover, the cathodic membrane 10 is also used to separate the fluids in trap chamber and the cathodic chamber. Platinum mesh is used as the anode 11 and anchored onto an end plate (plexiglass or other insulating materials) 15 to produce H.sup.+ ion from water or H.sub.2 oxidation. As said above, the produced acid in anodic chamber 14 will be used to capture the migrated NH.sub.3 and convert to (NH.sub.4).sub.2SO.sub.4 or other ammonium salts.

[0046] FIG. 3 illustrates the major concepts or principles of different reactions and functions achieved in different chambers or compartments.

[0047] The following examples utilize the principles set forth in this disclosure. The examples are merely given to demonstrate the principles of the present invention and do not in any way limit the scope of the invention.

EXAMPLES

[0048] EXAMPLE 1. FIGS. 4A-4C illustrate a benchtop electrified membrane flow-cell reactor system utilizing the principles of the invention. FIG. 4A is a photograph showing a potentio-stat, a trap tank, a wastewater tank, an air pump, and other devices utilized in the system. A potentiostat is used to provide constant electrode potentials for anode and cathode. The saturated calomel electrode is connected to the CHI 1100C multichannel potentiostat (CH Instrument, USA) to measure and control the cathodic potential. FIGS. 4B-4C further illustrate the overlay of the CuO catalyst-coated foam and the gas-permeable membrane. The conductive plate (stainless steel sheet ) is used to connect the catalyst foam to the power supply.

[0049] To prepare the CuO catalyst-coated foam, a copper (Cu) foam with purity > 99.99%, a pore density of 130 ppi (pores per linear inch), and a thickness of 0.7 mm is immersed in a 3-M HCl acid for 10 min to remove the oxide layer. The Cu(OH).sub.2 precursor on the Cu foam (3 by 3 cm) is immersed in 25 mL 3 M NaOH solutions with another Cu foam as the counter electrode (placed about 5 cm away from each other) and applied at around 3 mA cm.sup.-2 for 30 min. After the anodic oxidation, the form will be annealed at 300° C. for 2 h at a heating rate of 1° C..Math.min.sup.-1 under the O.sub.2 atmosphere to obtain the CuO layer.

[0050] Subsequently, the CuO-coated foam is clipped to a flat sheet membrane (the nominal pore size: 0.45 .Math.m) composed of the PTFE hydrophobic surface layer and a polypropylene (PP) substrate to construct a CuO composite cathode membrane assembly. As illustrated in FIGS. 4B–4C, the PP substrate and the CuO coating layer face the trap and cathode chambers, respectively.

[0051] EXAMPLE 2. The applicants assessed the performance of nitrogen wastewater treatment and nitrogen fertilizer production using the device in FIG. 4A. The fluid was recirculated between the three chambers and the trap or feed tanks by two peristaltic pumps at 50 mL.Math.min.sup.-1. An electrolyte solution (0.5 M Na.sub.2SO.sub.4, pH 7) was recirculated between the trap and anode chambers, while a synthetic wastewater (150 mM NO.sub.3.sup.-, 10 mM Cl.sup.-, 0.5 M Na.sub.2SO.sub.4, pH 7) was recirculated between the cathode chamber and the feed tank. The inlet temperatures at the feed were constantly maintained at 20 ± 0.5° C. throughout the entire experiment. The electrified membrane flow-cell was operated at a constant cathodic potential of -2 V vs. SCE without the control of anodic potential or the total cell potential. Finally, the nitrogen fertilizer was produced/enriched in trap chamber. The average NO.sub.3.sup.- removal rate and nitrogen fertilizer production rate were measured to be 1258±39 g-N.Math.m.sup.-2.Math.d.sup.-1 and 3100±91 g-(NH.sub.4).sub.2SO.sub.4.Math.m.sup.-2.Math.d.sup.-1, with a nitrate removal efficiency of 99.9% after operation time of 5 h.

[0052] EXAMPLE 3. The applicants assessed the performance of real nitrogen wastewater treatment and nitrogen fertilizer production. The real nitrate containing wastewater is made of NO.sub.3.sup.--N (436±15 mg.Math.L.sup.-1), Br.sup.- (80±3 mg.Math.L.sup.-1), Cl.sup.- (214±9 mg.Math.L.sup.-1), SO.sub.4.sup.2- (106728±918 mg.Math.L.sup.-1), Na.sup.+ (19100±523 mg.Math.L.sup.-1), K.sup.+ (2447±68 mg.Math.L.sup.-1), and chemical oxygen demand COD (140±4 mg.Math.L.sup.-1) with a solution pH 2.1±0.5. The NO.sub.3.sup.- removal rate and nitrogen fertilizer production rate were measured to be 436±18 g-N.Math.m.sup.-2.Math.d.sup.-1 and 1037±31 g-(NH.sub.4).sub.2SO.sub.4.Math.m.sup.-2.Math.d.sup.-1, with a nitrate removal efficiency of 99.4% after operation time of 5 h.

[0053] Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.