A method for modifying a stainless steel mesh cathode and application thereof in microbial electrolysis cell for phosphorus recovery from wastewater

Abstract

The application discloses a modification method of a stainless steel mesh cathode and application of the stainless steel mesh cathode in microbial electrolytic cell sewage phosphorus recovery, and belongs to the field of sewage phosphorus recovery. The modification method of the stainless steel mesh cathode comprises the following steps: taking a stainless steel mesh as a cathode, and adopting an electrodeposition method to prepare a Ni-Co-Sn modified stainless steel mesh cathode; and the electrolyte used in the electrodeposition method comprises sodium citrate, nickel sulfate, cobalt sulfate, stannous sulfate, boric acid and sodium chloride. The method selects a cheap and more beneficial to the attachment of struvite crystallization stainless steel mesh as a cathode, modifies the stainless steel mesh cathode by using nickel cobalt tin, enhances the phosphorus recovery rate by improving the hydrogen evolution performance, shortens the reaction time, and achieves the purpose of obtaining a high phosphorus recovery rate in a short time.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of sewage phosphorus recovery, and particularly relates to a modification method of a stainless steel mesh cathode and application of the modification method in sewage phosphorus recovery of a microbial electrolysis cell. BACKGROUND

[0002] Phosphorus (P) is an essential element for all living organisms and an irreplaceable element in fertilizer production, supporting the development of modern agriculture and being used in other industrial production. With the increasing demand for phosphorus year by year, the existing global phosphorus rock reserves may be depleted within 50-100 years in the future. Therefore, it is necessary to achieve sustainable utilization of phosphorus and develop alternative phosphorus sources. On the other hand, a large amount of phosphorus is discharged into natural water bodies through sewage or other means, disrupting the phosphorus cycle. Traditional phosphorus removal technologies, such as chemical precipitation and enhanced biological phosphorus removal, are only used to remove phosphorus from sewage to avoid discharge into water bodies, and the end products (chemical or biological sludge) are not safe and cannot be reused in agriculture, so more sustainable phosphorus utilization modes should be explored.

[0003] Microbial electrolysis cells (MECs) are a new and promising method for producing hydrogen (H2) from organic matter (including sewage and other renewable resources) and simultaneously recovering phosphorus. In MECs, electrochemically active bacteria utilize organic matter and produce carbon dioxide, electrons and protons, the bacteria transfer electrons to the anode, and protons are released into the solution, then the electrons reach the cathode through the wire and combine with free protons in the solution to produce hydrogen gas. The consumption of protons in the cathode chamber increases the pH of the solution, so phosphorus can be precipitated in the form of struvite, which can simultaneously recover nitrogen and phosphorus from sewage, and is a highly efficient slow-release phosphorus fertilizer that can avoid the phenomenon of plant "burning seedlings" caused by quick-acting phosphorus ammonium fertilizer. Using microbial electrolysis cells to recover phosphorus in the form of struvite does not require the addition of sodium hydroxide to provide alkaline conditions, which can achieve the purpose of simultaneously reducing chemical consumption and energy consumption, and efficiently recovering phosphorus resources.

[0004] CH3COO - +3H2O→8H + +8e - +HCO3 - +CO2↑

[0005] 8H2O+8e - →8OH - +4H2↑

[0006]

[0007] Improving hydrogen production by changing the MECs cathode is a hot research in recent years, and the enhancement of hydrogen production also significantly affects the phosphorus recovery performance of MECs. Similar to traditional electrolytic cells, MECs cathode needs catalyst to accelerate the slow kinetics of hydrogen evolution reaction. In MECs, improving the catalytic activity and stability of the electrode is an effective way to improve the phosphorus recovery rate in microbial electrolysis cells. SUMMARY

[0008] The purpose of the present application is to provide a modification method of stainless steel mesh cathode and its application in wastewater phosphorus recovery of microbial electrolysis cell. The modification method of stainless steel mesh cathode is simple and low cost. The prepared stainless steel mesh cathode has the advantages of fast hydrogen evolution and can recover phosphorus in a short time.

[0009] The present application first provides a modification method of stainless steel mesh cathode for wastewater phosphorus recovery of microbial electrolysis cell, which comprises the following steps:

[0010] The Ni-Co-Sn modified stainless steel mesh cathode is prepared by electrodeposition method using stainless steel mesh as cathode. The electrolyte used in the electrodeposition method comprises sodium citrate, nickel sulfate, cobalt sulfate, stannous sulfate, boric acid and sodium chloride.

[0011] In the above modification method, the concentration of sodium citrate in the electrolyte is 100-150 g / L; the concentration of nickel sulfate (NiSO4·6H2O) is 60-90 g / L; the concentration of cobalt sulfate (CoSO4·7H2O) is 30-45 g / L; the concentration of stannous sulfate is 5-20 g / L; the concentration of boric acid is 10-20 g / L; the concentration of sodium chloride is 15-18 g / L.

[0012] The pH value of the electrolyte is 4.5-7.

[0013] Specifically, the concentration of sodium citrate in the electrolyte is 129 g / L; the concentration of nickel sulfate (NiSO4·6H2O) is 78.8 g / L; the concentration of cobalt sulfate (CoSO4·7H2O) is 42 g / L; the concentration of stannous sulfate is 9.6 g / L; the concentration of boric acid is 18.5 g / L; the concentration of sodium chloride is 17.5 g / L.

[0014] In the above modification method, the material of the anode is nickel or graphite.

[0015] The temperature of electrodeposition is 20-65℃; preferably 20-50℃, more preferably 50℃.

[0016] The current density of electrodeposition is 0.2-0.35 A / dm 2 ; preferably 0.25-0.35 A / dm 2 , more preferably 0.30 A / dm2 ;

[0017] The time of the electrodeposition is 1200-2100s; specifically, 1500s or 1800s.

[0018] Secondly, the application further provides the Ni-Co-Sn modified stainless steel mesh cathode prepared by the modification method.

[0019] The application of the above-mentioned Ni-Co-Sn modified stainless steel mesh cathode in the phosphorus recovery of sewage in a microbial electrolytic cell also belongs to the protection scope of the application.

[0020] Finally, the application provides a phosphorus recovery method in sewage, which comprises the following steps:

[0021] In the anode chamber of the double-chamber microbial electrolytic cell, electrogenic bacteria are inoculated, and the sewage containing phosphorus to be treated is added into the cathode chamber; the above-mentioned Ni-Co-Sn modified stainless steel mesh cathode is used as the cathode of the electrolytic cell; and the double-chamber microbial electrolytic cell is operated to realize the recovery of phosphorus in the sewage.

[0022] In the above-mentioned recovery method, the cathode chamber and the anode chamber of the double-chamber microbial electrolytic cell are separated by a cation exchange membrane.

[0023] The electrogenic bacteria are Geobacter sulfurreducens PCA, and the preservation number thereof is ATCC51573.

[0024] The anode is a carbon fiber brush or carbon felt.

[0025] The anode solution in the anode chamber is composed of 0.2-0.5g / L ammonium chloride, 0.1-0.2g / L potassium chloride, 1.5-3.0g / L sodium bicarbonate, 0.5-0.7g / L NaH2PO4·H2O, 5-7mM sodium selenate, 5-25mM sodium acetate, 5-15mL / L trace element solution and 5-15mL / L vitamin solution.

[0026] Specifically, the anode solution in the anode chamber is composed of 0.25g / L ammonium chloride, 0.1g / L potassium chloride, 2.5g / L sodium bicarbonate, 0.6g / L NaH2PO4·H2O, 5mM sodium selenate, 10mM sodium acetate, 10mL / L trace element solution and 10mL / L vitamin solution, and the solvent is water.

[0027] The initial phosphorus concentration of the sewage containing phosphorus is 1-4mM, the molar ratio of magnesium to phosphorus is 1-1.5, and the molar ratio of nitrogen to phosphorus is 1-4.

[0028] In the above-mentioned recovery method, the operating temperature of the double-chamber microbial electrolytic cell is 20-35℃.

[0029] The applied voltage for running the double-chamber microbial electrolysis cell is 0.7-1.1V, and specifically 0.9V;

[0030] The double-chamber microbial electrolysis cell is run under anaerobic conditions.

[0031] The above-mentioned recovery method further comprises a step of starting the microbial electrolysis cell before running;

[0032] In the step of starting the microbial electrolysis cell, the anode solution is composed of 0.2-0.5g / L ammonium chloride, 0.1-0.2g / L potassium chloride, 1.5-3g / L sodium bicarbonate, 0.5-0.7g / L NaH2PO4·H2O, 5-7mM sodium selenate, 5-25mM sodium acetate, 5-15mL / L trace element solution and 5-15mL / L vitamin solution;

[0033] The anode solution and the electric-generating bacteria solution are mixed; the ratio of the volume of the electric-generating bacteria solution to the total volume of the anode solution and the electric-generating bacteria solution is 1:5-1:10, and specifically 1:10;

[0034] The OD 600 of the electric-generating bacteria solution is 0.5-0.6;

[0035] The electric-generating bacteria solution is taken from the electric-generating bacteria in the logarithmic growth phase;

[0036] The cathode solution is a phosphate buffer solution; specifically, the concentration of the phosphate buffer solution is 40-60mM.

[0037] In the above-mentioned recovery method, in the step of starting the microbial electrolysis cell, the double-chamber microbial electrolysis cell is run, the cathode chamber and anode chamber solutions are replaced when the voltage approaches zero, and when the electric-generating time and the maximum voltage of three cycles tend to be stable, it is considered that the starting is successful.

[0038] After the starting is successful, the current density of the double-chamber microbial electrolysis cell can reach 1.8-2.1A / m 2 .

[0039] The starting of the microbial electrolysis cell is run under anaerobic conditions.

[0040] The composition and concentration of the trace element solution are as follows: 0.5-2 g / L trisodium nitrilotriacetate (NTA), 2-4 g / L MgSO4·7H2O, 0.2-1 g / L MnSO4·H2O, 0.5-2 g / L NaCl, 0.1-0.2 g / L FeSO4·7H2O, 0.1-0.2 g / L CaCl2·2H2O, 0.1-0.2 g / L CoCl2·6H2O, 0.1-0.15 g / L ZnCl2, 0.01-0.02 g / L CuSO4·5H2O, 0.01-0.02 g / L AlK(SO4)2·12H2O, 0.01-0.02 g / L H3BO3, 0.025-0.03 g / L Na2MoO4·2H2O, 0.02-0.03 g / L NiCl2·6H2O, and 0.02-0.03 g / L Na2WO4·2H2O; and the solvent is water.

[0041] Specifically, the composition and concentration of the trace element solution are as follows: 1.5 g / L trisodium nitrilotriacetate (NTA), 3 g / L MgSO4·7H2O, 0.5 g / L MnSO4·H2O, 1 g / L NaCl, 0.1 g / L FeSO4·7H2O, 0.1 g / L CaCl2·2H2O, 0.1 g / L CoCl2·6H2O, 0.13 g / L ZnCl2, 0.01 g / L CuSO4·5H2O, 0.01 g / L AlK(SO4)2·12H2O, 0.01 g / L H3BO3, 0.025 g / L Na2MoO4·2H2O, 0.024 g / L NiCl2·6H2O, and 0.025 g / L Na2WO4·2H2O.

[0042] The composition and concentration of the vitamin solution are as follows:

[0043] 10-15 g / L pyridoxine hydrochloride, 0.1-0.3 g / L vitamin B12, 1-2 g / L biotin, 1-2 g / L folic acid, 3-5 g / L pantothenic acid, 3-5 g / L thiamine, 3-5 g / L riboflavin, 3-5 g / L nicotinic acid, 3-5 g / L p-aminobenzoic acid, and 3-5 g / L lipoic acid; and the solvent is water.

[0044] Specifically, the composition and concentration of the vitamin solution are as follows:

[0045] 10 g / L pyridoxine hydrochloride, 0.1 g / L vitamin B12, 2 g / L biotin, 2 g / L folic acid, 5 g / L pantothenic acid, 5 g / L thiamine, 5 g / L riboflavin, 5 g / L nicotinic acid, 5 g / L p-aminobenzoic acid, and 5 g / L lipoic acid.

[0046] The present application has the following advantages:

[0047] (1) The phosphorus recovery efficiency of the present application is high, and the phosphorus can be recovered in the form of struvite, and the phosphorus recovery rate reaches more than 90% in a short time;

[0048] (2) The reactor structure of the present application is simple, and the price of the cathode stainless steel mesh is low. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 It is a constant current deposition device of the present application, wherein 1 is a nickel plate anode, 2 is a stainless steel mesh, 3 is an Ag / AgCl reference electrode, and 4 is a rotor.

[0050] Figure 2 It is a polarization curve diagram of linear sweep voltammetry in Example 1 of the present application.

[0051] Figure 3 It is an electrochemical impedance diagram in Example 1 of the present application.

[0052] Figure 4 It is a device structure schematic diagram of a microbial electrolysis cell of the present application, wherein 5 is an anode chamber, 6 is a cathode chamber, 7 is a cation exchange membrane, 8 is a carbon fiber brush anode, 9 is a stainless steel mesh cathode, 10 is a platinum sheet electrode clamp, 11 is a two-way valve, 12 is a water inlet, 13 is a water outlet, 14 is a gas collection port 1, 15 is an electric lead wire, 16 is a resistor, 17 is a power supply, 18 is a gas collection port 2, and 19 is a sampling port.

[0053] Figure 5 It is a phosphorus recovery effect diagram in Example 1 of the present application.

[0054] Figure 6 It is a polarization curve diagram of linear sweep voltammetry in Example 2 of the present application.

[0055] Figure 7 It is an electrochemical impedance diagram in Example 2 of the present application.

[0056] Figure 8 It is a phosphorus recovery effect diagram in Example 2 of the present application.

[0057] Figure 9 It is an XRD diagram of a nickel-cobalt-tin modified stainless steel mesh and an original stainless steel mesh cathode in Example 2 of the present application.

[0058] Figure 10 It is an XPS spectrum diagram of nickel in a nickel-cobalt-tin modified stainless steel mesh cathode in Example 2 of the present application.

[0059] Figure 11 It is an XPS spectrum diagram of cobalt in a nickel-cobalt-tin modified stainless steel mesh cathode in Example 2 of the present application.

[0060] Figure 12XPS spectrum of tin in the nickel cobalt tin modified stainless steel mesh cathode in Example 2 of the present application.

[0061] Figure 13 XRD pattern of the product after the microbial electrolysis cell in Example 2 of the present application runs for a cycle.

[0062] Figure 14 Phosphorus recovery rate of four different cathodes of SSM, Ni-Co-SSM, Ni-Co-P-SSM and Ni-Co-Sn-SSM in Example 3 of the present application as a function of time. DETAILED DESCRIPTION

[0063] The present application is further described in detail below with specific reference to the embodiments. The examples given are only for the purpose of illustrating the present application and are not intended to limit the scope of the present application.

[0064] The experimental methods in the following examples are all conventional methods, unless otherwise specified.

[0065] In the quantitative test in the following examples, three repeated experiments are set up, and the average value is taken.

[0066] The materials and reagents used in the following examples can be obtained from commercial channels, unless otherwise specified.

[0067] The Geobacter sulfurreducens PCA used in the following examples is a common commercially available product, and is from the American Type Culture Collection, with the accession number ATCC51573.

[0068] Example 1, phosphorus recovery effect of microbial electrolysis cell of nickel cobalt tin stainless steel mesh cathode under different electrodeposition current density

[0069] Step 1, modification of cathode stainless steel mesh

[0070] The constant current deposition device is as follows Figure 1 : which includes a nickel plate anode 1, a stainless steel mesh 2, an Ag / AgCl reference electrode 3, and a rotor 4.

[0071] The cathode material is selected to be a 60x60 mesh 304 stainless steel mesh with a geometric area of 3x4 cm 2 , and the anode is selected to be a 4x4 cm 2 nickel plate, and the reference electrode is an Ag / AgCl electrode.

[0072] The electrolyte preparation method is as follows: First, dissolve 32.25g of sodium citrate in water, then add 19.7g of nickel sulfate hexahydrate (NiSO4·6H2O), 10.5g of cobalt sulfate heptahydrate (CoSO4·7H2O), 2.4g of stannous sulfate (SnSO4), 4.625g of boric acid and 4.375g of sodium chloride. Finally, adjust the pH to 4.5 with sodium hydroxide solution and bring the volume to 250mL.

[0073] Electrochemical workstation (Shanghai Chenhua CHI 660E) was used for chronopotential deposition using the potentiostatic method. A magnetic stirrer was used to maintain uniform deposition temperature and electrolyte concentration. The electrodeposition temperature and magnetic stirring speed were 20℃ and 400 rpm, respectively. The current density was 0.2–0.35 A / dm³. 2 Electrodeposition was performed for 1500 s under certain conditions, followed by rinsing with deionized water to prepare the cathode.

[0074] All electrochemical tests were performed using a three-electrode system on an electrochemical workstation (Shanghai Chenhua CHI 660E) in 50 mM phosphate buffer at pH 7. The electrodeposited samples were cut into 1×2 cm pieces. 2 The rectangular section served as the working electrode, the platinum mesh as the counter electrode, and Ag / AgCl as the reference electrode (filled with 3M KCl). The electrochemical testing temperature was maintained at 30℃ in a constant-temperature water bath. Nitrogen gas was bubbled into the phosphate buffer for 20 min before each test, followed by a 10 min incubation period. The buffer solution was changed after each sample electrochemical test. The experimental result was 0.3 A / dm³. 2 The stainless steel mesh electrode prepared below is used at a current density (j) of 10 mA / cm². 2 The cathode overpotential is the smallest at 1.36V. Figure 2 The charge transfer resistance is the lowest, at 60.12 ohms. Figure 3 ).

[0075] Step 2: Construction of the microbial electrolysis cell

[0076] The structure of a microbial electrolysis cell is as follows: Figure 4As shown, the system includes: an anode chamber 5, a cathode chamber 6, a cation exchange membrane 7, a carbon fiber brush anode 8, a stainless steel mesh cathode 9, a platinum electrode clamp 10, a resistor 16, and a power supply 17. The anode chamber 5 and cathode chamber 6 are separated by the cation exchange membrane 7, forming a dual-chamber microbial electrolysis cell. The carbon fiber brush anode 10 is fixed in the anode chamber 5, and the stainless steel mesh cathode 9 is clamped and fixed in the cathode chamber 6 by the platinum electrode clamp 10. The two chambers are fixed together by stainless steel screws. A sampling port 19 is provided above the anode chamber 5 and cathode chamber 6. A sampling needle is inserted into the sampling port 19, and the switch is controlled by a two-way valve 11. An inlet 12 and an outlet 13 are located on both sides of the anode chamber 5 and cathode chamber 6, with the inlet 12 above and the outlet 13 below. When not in use, they are sealed with rubber sleeves. Gas collecting ports 114 and 218 are provided above the anode chamber 5 and cathode chamber 6. Eighteen gas bags are connected to store the gas generated at the anode and cathode respectively; the anode and cathode are connected by copper wires 15, with a high-precision resistor 16 in between; the power supply 17 is connected in series in the circuit to supply power to the entire reactor system and is connected to a computer to record data in real time.

[0077] Step 3: Start-up of the microbial electrolysis cell

[0078] Geobacter sulfurreducens PCA strain was inoculated in the anode chamber of the microbial electrolysis cell. The ratio of the bacterial solution volume to the total volume of the anode solution and bacterial solution was 1:10 (total volume was 100 mL). A sterile anaerobic environment was required during inoculation. All solutions except vitamin solution were sterilized at high temperature. After inoculation, the cells were aerated for 20 min using an anaerobic workstation (N2:CO2 volume ratio 8:2). The total volume of the cathode solution was 100 mL.

[0079] Among them, the OD of Geobacter sulfurreducens PCA bacterial solution 600 It is 0.6;

[0080] The startup steps are as follows:

[0081] The reactor used in this experiment was started in MEC mode with an applied voltage of 0.7V during startup. The inoculum was *Geotrichum thioreductoids* in its logarithmic growth phase (24–48 h), and the substrate was sodium acetate (NaAc). Both the anode and cathode chambers had an effective volume of 118 mL. The anode was a carbon fiber brush, and the cathode was the stainless steel mesh prepared above (3 × 4 cm²). 2 The dual-chamber microbial electrolyzer was operated. When the voltage approached zero, the solutions in the cathode and anode chambers were replaced. Successful startup was achieved when the power generation time and maximum voltage stabilized after three cycles. After successful startup, the current density of the dual-chamber microbial electrolyzer in this study reached 1.9 A / m³. 2 about.

[0082] In the microbial electrolysis cell, the anode solution is composed of:

[0083] 0.25 g / L NH4Cl, 0.1 g / L KCl, 2.5 g / L NaHCO3, 0.6 g / L NaH2PO4·H2O, 5 mM Na2SeO4, 10 mM sodium acetate, 10 mL / L vitamin solution and 10 mL / L trace element solution, and the solvent is water.

[0084] The composition and concentration of the trace element solution are as follows: 1.5 g / L trisodium nitrilotriacetate (NTA), 3 g / L MgSO4·7H2O, 0.5 g / L MnSO4·H2O, 1 g / L NaCl, 0.1 g / L FeSO4·7H2O, 0.1 g / L CaCl2·2H2O, 0.1 g / L CoCl2·6H2O, 0.13 g / L ZnCl2, 0.01 g / L CuSO4·5H2O, 0.01 g / L AlK(SO4)2·12H2O, 0.01 g / L H3BO3, 0.025 g / L Na2MoO4·2H2O, 0.024 g / L NiCl2·6H2O, 0.025 g / L Na2WO4·2H2O; the solvent is water;

[0085] The composition and concentration of the vitamin solution are as follows:

[0086] 10 g / L pyridoxine hydrochloride, 0.1 g / L vitamin B12, 2 g / L biotin, 2 g / L folic acid, 5 g / L pantothenic acid, 5 g / L thiamine, 5 g / L riboflavin, 5 g / L nicotinic acid, 5 g / L p-aminobenzoic acid, 5 g / L lipoic acid; the solvent is water;

[0087] The composition of the cathode solution is as follows:

[0088] 6 mM NH4Cl, 2 mM KCl, 18 mM NaH2PO4·H2O and 3 mM Na2HPO4.

[0089] Step 4, Phosphorus recovery in a nickel-cobalt-tin stainless steel mesh cathode microbial electrolysis cell under different electrodeposition current densities

[0090] When the reactor started successfully, the anode solution and cathode solution were replaced to start the phosphorus recovery. No bacteria solution was added in each experiment, and the composition of the anode solution was the same as that in the start-up period. The simulated phosphorus-rich wastewater with 0.27 g / L of potassium dihydrogen phosphate, 0.43 g / L of ammonium chloride and 0.61 g / L of magnesium chloride was used as the cathode solution. The concentration of sodium acetate in the anode solution was 10 mM, the molar ratio of Mg / P in the cathode solution was 1.5, the molar ratio of N / P was 4.0, and the phosphorus concentration was 60 mg / L. A 10-Ω resistor was connected between the anode and the cathode, the temperature of the reactor was maintained at 30°C, and all operations still ensured the anaerobic conditions. The applied voltage of the experiment was adjusted to 0.9 V using a power supply, and the current was recorded every 30 seconds in each experiment. The phosphorus concentration was measured every 12 hours from the sampling port 19, and the reaction time was 48 hours. After the reaction was completed, the cathode was taken out, and the phosphorus recovery rate of the stainless steel mesh cathode with an electrodeposition current density of 0.3 A / dm 2 2 at 50°C was 94% in 48 hours, as shown in Figure 5 .

[0091] Example 2, Phosphorus recovery effect of microbial electrolysis cell with nickel-cobalt-tin modified stainless steel mesh cathode at different electrodeposition temperatures

[0092] The constant current deposition device was as shown in Figure 1 , and the modification method and conditions were the same as those in Example 1 except for the following indications; the electrodeposition temperature in the experiment was 20°C to 65°C, and the magnetic stirring speed was 400 rpm. The electrodeposition was carried out at a current density of 0.3 A / dm 2 2 and an electrodeposition time of 1800 s; then the prepared cathode was rinsed with deionized water. The overpotential of the electrode was the smallest at 50°C, which was 1.15 V Figure 6 , and the charge transfer resistance was the smallest, which was 34 ohm Figure 7 .

[0093] Steps 2 and 3 were the same as those in Example 1, and will not be repeated here.

[0094] Step 4, Phosphorus recovery of microbial electrolysis cell with nickel-cobalt-tin modified stainless steel mesh cathode at different electrodeposition temperatures

[0095] The experimental conditions were the same as those in Step 4 of Example 1. After the reaction was completed, the cathode was taken out, and the phosphorus recovery rate of the stainless steel mesh cathode at 50°C was 97.88% in 36 hours, as shown in Figure 8 .

[0096] Step 5, Characterization of nickel-cobalt-tin modified stainless steel mesh cathode and phosphorus recovery products of microbial electrolysis cell

[0097] The XRD characterization results of the original SSM and the Ni-Co-Sn-SSM at an electrodeposition temperature of 50°C are as shown inFigure 9 As shown, both exhibit characteristic peaks similar to those of austenite. The 2θ diffraction peaks at 43.8, 50.9, and 74.8° match the (111), (200), and (220) crystal planes of austenitic steel (PDF 33-0945), indicating that the main components of SSM are Ni, Fe, and Cr. In the XRD of Ni-Co-Sn-SSM, the diffraction angle of 33.9° corresponds to the (101) crystal plane of SnO2, and a characteristic peak of Sn appears at 30.65°, which is attributed to the (200) plane of tin. To further analyze the composition and valence state of the catalyst in the generated deposited layer, XPS analysis was performed on the Ni-Co-Sn-SSM cathode. Figure 10 XPS plot of Ni, Ni 2p 3 / 2 The peak at 855.3 eV represents partially charged Ni (Ni2) in the Ni-Sn compound. δ+ The characteristic peak at δ is likely close to 0, while the peak at 876.2 eV is the characteristic peak of Ni in nickel oxide. 2+ Characteristic peaks; the peaks at 859.88 eV and 883.43 eV are Ni 2p 3 / 2 and Ni 2p 1 / 2 The satellite peak. Figure 11 The XPS plot of Co shows two peaks at 782.5 eV and 797.2 eV originating from Co. δ+ and cobalt oxide (Co) 2+ / 3+ The peaks at 787.0 eV and 804.89 eV correspond to satellite peaks. From... Figure 12 The XPS spectrum of Sn showed two peaks, located at binding energies of 486.88 eV and 496.5 eV, respectively. 496.5 eV corresponds to Sn 3d... 3 / 2 Literature review shows that the two peaks correspond to Sn. 0 and Sn 4+ This indicates that Sn in the prepared Ni-Co-Sn-SSM electrode mainly exists as Sn metal and SnO2.

[0098] Figure 13 The image shows the XRD pattern of the cathode product in a Ni-Co-Sn-SSM microbial electrolysis cell at an electrodeposition temperature of 50℃. The experimentally generated product has a high degree of agreement with the struvite standard card, indicating that the generated product is mainly struvite crystals.

[0099] During one cycle (48h) of MEC operation, the anode and cathode solutions are not replaced. After the reactor operation is completed, the cathode products are collected, dried in a forced-air drying oven at 40℃ for 24h, and then characterized by XRD to analyze the crystal structure of the products.

[0100] Example 3: Phosphorus recovery effect of microbial electrolytic cells with different modified stainless steel mesh cathodes

[0101] Step 1, modification of cathode stainless steel mesh

[0102] Constant current deposition device such as Figure 1 , modification method and condition are the same as example 1 except the following indicated; in which, the electrolyte preparation method for Ni-Co-SSM stainless steel mesh cathode is as follows: first, dissolve 32.25 g of sodium citrate in water, then add 19.7 g of nickel sulfate hexahydrate (NiS04·6H20), 10.5 g of cobalt sulfate heptahydrate (CoS04·7H20), 4.625 g of boric acid and 4.375 g of sodium chloride, finally adjust the pH to 4.5 with sodium hydroxide solution and make up to 250 mL; the electrolyte preparation method for Ni-Co-P-SSM stainless steel mesh cathode is as follows: add 19.7 g of nickel sulfate hexahydrate (NiS04·6H20), 10.5 g of cobalt sulfate heptahydrate (CoS04·7H20), 2.4 g of potassium dihydrogen phosphate, 4.625 g of boric acid and 4.375 g of sodium chloride, finally adjust the pH to 4.5 with sodium hydroxide solution and make up to 250 mL;

[0103] The electrochemical workstation (Shanghai Chenhua CHI 660E) was selected to carry out constant current deposition by chronopotentiometry. A magnetic stirrer was used to keep the deposition temperature and electrolyte concentration uniform, and the deposition temperature was 50°C and the magnetic stirring speed was 400 rpm in the experiment. The current density was 0.3 A / dm 2 , and the deposition time was 1800 s to prepare Ni-Co-SSM and Ni-Co-P-SSM stainless steel mesh cathodes, respectively. Then the prepared cathodes were rinsed with deionized water.

[0104] Steps 2 and 3 are the same as example 1, which are not described here.

[0105] Step 4, phosphorus recovery of modified stainless steel mesh cathode microbial electrolysis cell

[0106] The experimental conditions are the same as those in step 4 of example 1. After the reaction, the cathode was taken out, and the phosphorus recovery rate of the original SSM and Ni-Co-SSM, Ni-Co-P-SSM, Ni-Co-Sn-SSM stainless steel mesh cathode MEC was compared with time, and the results are shown in Figure 14 From the figure, it can be seen that the phosphorus recovery rate of Ni-Co-Sn-SSM is the fastest, reaching about 90% in 12 hours of reaction, and the phosphorus recovery rates of Ni-Co-P-SSM and Ni-Co-SSM cathodes reach about 90% in 36 hours of reaction. The phosphorus recovery rate of Ni-Co-P-SSM is slightly faster than that of Ni-Co-SSM in the first 24 hours. The phosphorus recovery rate of the original SSM is the slowest and the lowest, only reaching about 50% in the first 24 hours.

Claims

1. Application of a Ni-Co-Sn modified stainless steel mesh cathode in microbial electrolysis cell for phosphorus recovery from wastewater; The preparation method of the Ni-Co-Sn modified stainless steel mesh cathode comprises the following steps: The Ni-Co-Sn modified stainless steel mesh cathode is prepared by using the stainless steel mesh as the cathode and adopting the electrodeposition method; the electrolyte used in the electrodeposition method comprises sodium citrate, nickel sulfate, cobalt sulfate, stannous sulfate, boric acid and sodium chloride; In the electrolyte, the concentration of sodium citrate is 100-150 g / L; the concentration of nickel sulfate is 60-90 g / L; the concentration of cobalt sulfate is 30-45 g / L; the concentration of stannous sulfate is 5-20 g / L; the concentration of boric acid is 10-20 g / L; and the concentration of sodium chloride is 15-18 g / L; The pH value of the electrolyte is 4.5-7; The temperature of electrodeposition is 20-65 ℃; The current density for the electrodeposition is 0.2 to 0.35 A / dm 2 ; The time of electrodeposition is 1200-2100 s.

2. Use according to claim 1, characterized in that: In the electrodeposition method, the material of the anode is nickel or graphite; The temperature of electrodeposition is 20-50 ℃; The current density for the electrodeposition is 0.30 A / dm 2 .

3. Use according to claim 2, characterized in that: The temperature of electrodeposition is 50 ℃.

4. A method for recovering phosphorus in wastewater, comprising the following steps: In the anode chamber of the double-chamber microbial electrolysis cell, electrogenic bacteria are inoculated, and the phosphorus-containing wastewater to be treated is added into the cathode chamber; the Ni-Co-Sn modified stainless steel mesh cathode is used as the cathode of the electrolysis cell; and the double-chamber microbial electrolysis cell is operated to realize the recovery of phosphorus in the wastewater; The preparation method of the Ni-Co-Sn modified stainless steel mesh cathode comprises the following steps: The Ni-Co-Sn modified stainless steel mesh cathode is prepared by using the stainless steel mesh as the cathode and adopting the electrodeposition method; the electrolyte used in the electrodeposition method comprises sodium citrate, nickel sulfate, cobalt sulfate, stannous sulfate, boric acid and sodium chloride; In the electrolyte, the concentration of sodium citrate is 100-150 g / L; the concentration of nickel sulfate is 60-90 g / L; the concentration of cobalt sulfate is 30-45 g / L; the concentration of stannous sulfate is 5-20 g / L; the concentration of boric acid is 10-20 g / L; and the concentration of sodium chloride is 15-18 g / L; The pH value of the electrolyte is 4.5-7; The temperature of electrodeposition is 20-65 ℃; The current density for the electrodeposition is 0.2 to 0.35 A / dm 2 ; The time of electrodeposition is 1200-2100 s.

5. The recycling method of claim 4, wherein: In the electrodeposition method, the material of the anode is nickel or graphite; The temperature of electrodeposition is 20-50 ℃; The current density for the electrodeposition is 0.30 A / dm 2 .

6. The recycling method of claim 5, wherein: The temperature of electrodeposition is 50 ℃.

7. The recycling method of claim 4, wherein: The cathode chamber and the anode chamber of the double-chamber microbial electrolysis cell are separated by a cation exchange membrane; The electrogenic bacteria is Geobacter sulfurreducens Geobacter sulfurreducens PCA, having the accession number ATCC 51573; The anode is a carbon fiber brush or carbon felt; The anode solution in the anode chamber comprises the following components: 0.2-0.5 g / L ammonium chloride, 0.1-0.2 g / L potassium chloride, 1.5-3.0 g / L sodium bicarbonate, 0.5-0.7 g / L NaH2PO4·H2O, 5-7 mM sodium selenate, 5-25 mM sodium acetate, 5-15 mL / L trace element solution and 5-15 mL / L vitamin solution; The composition and concentration of the trace element solution are as follows: 0.5-2 g / L trisodium amino triacetate, 2-4 g / L MgSO4·7H2O, 0.2-1 g / L MnSO4·H2O, 0.5-2 g / L NaCl, 0.1-0.2 g / L FeSO4·7H2O, 0.1-0.2 g / L CaCl2·2H2O, 0.1-0.2 g / L CoCl2·6H2O, 0.1-0.15 g / L ZnCl2, 0.01-0.02 g / L CuSO4·5H2O, 0.01-0.02 g / L AlK(SO4)2·12H2O, 0.01-0.02 g / L H3BO3, 0.025-0.03 g / L Na2MoO4·2H2O, 0.02-0.03 g / L NiCl2·6H2O, and 0.02-0.03 g / L Na2WO4·2H2O; and the solvent is water; The composition and concentration of the vitamin solution are as follows: 10-15 g / L pyridoxine hydrochloride, 0.1-0.3 g / L vitamin B12, 1-2 g / L biotin, 1-2 g / L folic acid, 3-5 g / L pantothenic acid, 3-5 g / L thiamine, 3-5 g / L riboflavin, 3-5 g / L nicotinic acid, 3-5 g / L p-aminobenzoic acid, and 3-5 g / L lipoic acid; and the solvent is water; The initial phosphorus concentration of the phosphorus-containing sewage is 1-4 mM, the molar ratio of magnesium to phosphorus is 1-1.5, and the molar ratio of nitrogen to phosphorus is 1-4.

8. The recycling method of claim 4, wherein: The operating temperature of the double-chamber microbial electrolysis cell is 20-35 ℃; The applied voltage for operating the double-chamber microbial electrolysis cell is 0.7-1.1 V; The double-chamber microbial electrolysis cell is operated under anaerobic conditions.

9. The recycling method of claim 4, wherein: The recovery method further comprises a step of starting the microbial electrolysis cell before operation; In the step of starting the microbial electrolysis cell, the composition of the anode solution is as follows: 0.2-0.5 g / L ammonium chloride, 0.1-0.2 g / L potassium chloride, 1.5-3 g / L sodium bicarbonate, 0.5-0.7 g / L NaH2PO4·H2O, 5-25 mM sodium selenate, 5-25 mM sodium acetate, 5-15 mL / L trace element solution, and 5-15 mL / L vitamin solution; The composition and concentration of the trace element solution are as follows: 0.5~2 g / L trisodium amino triacetate, 2~4 g / L MgSO4·7H2O, 0.2~1 g / L MnSO4·H2O, 0.5~2 g / L NaCl, 0.1~0.2 g / L FeSO4·7H2O, 0.1~0.2 g / L CaCl2·2H2O, 0.1~0.2 g / L CoCl2·6H2O, 0.1~0.15 g / L ZnCl2, 0.01~0.02 g / L CuSO4·5H2O, 0.01~0.02 g / L AlK(SO4)2·12H2O, 0.01~0.02 g / L H3BO3, 0.025~0.03 g / L Na2MoO4·2H2O, 0.02~0.03 g / L NiCl2·6H2O, 0.02~0.03 g / L Na2WO4·2H2O; the solvent is water; The composition and concentration of the vitamin solution are as follows: 10~15 g / L pyridoxine hydrochloride, 0.1~0.3 g / L vitamin B12, 1~2 g / L biotin, 1~2 g / L folic acid, 3~5 g / L pantothenic acid, 3~5 g / L thiamine, 3~5 g / L riboflavin, 3~5 g / L nicotinic acid, 3~5 g / L p-aminobenzoic acid, 3~5 g / L lipoic acid; the solvent is water; The anode solution and the electrogenic bacteria solution are mixed; the ratio of the volume of the electrogenic bacteria solution to the total volume of the anode solution and the electrogenic bacteria solution is 1:5~1:10; The OD of the electrogenic bacterial solution 600 It is 0.5~0.6; The cathode solution is a phosphate buffer solution; specifically, the concentration of the phosphate buffer solution is 40~60 mM.

10. The recycling method of claim 9, wherein: In the step of starting the microbial electrolysis cell, the double-chamber microbial electrolysis cell is operated, the solutions in the cathode chamber and the anode chamber are replaced when the voltage approaches zero, and the starting is completed when the power generation time and the maximum voltage of each cycle tend to be stable. The starting of the microbial electrolysis cell is operated under anaerobic conditions.

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