Modification method of stainless steel mesh cathode and application of stainless steel mesh cathode in sewage phosphorus recovery of microbial electrolysis cell

Abstract

The invention discloses a modification method of a stainless steel mesh cathode and application of the stainless steel mesh cathode in sewage phosphorus recovery of a microbial electrolysis cell, and belongs to the field of sewage phosphorus recovery. The modification method of the stainless steel mesh cathode comprises the following steps: preparing a Ni-Co-Sn modified stainless steel mesh cathode by taking a stainless steel mesh as a cathode and adopting an electro-deposition method; electrolyte used in the electrodeposition method comprises sodium citrate, nickel sulfate, cobalt sulfate, stannous mono-sulphate, boric acid and sodium chloride. According to the method, the stainless steel mesh which is cheap and more beneficial to struvite crystal attachment is selected as the cathode, the stainless steel mesh cathode is modified through nickel, cobalt and tin, the phosphorus recovery rate is increased by improving the hydrogen evolution performance of the stainless steel mesh cathode, the reaction time is shortened, and the purpose of obtaining the high phosphorus recovery rate within a short time is achieved.

Description

Technical Field

[0001] The invention relates to the field of wastewater phosphorus recovery, and in particular to a modification method of a stainless steel mesh cathode and application thereof in wastewater phosphorus recovery in a microbial electrolysis cell. Background Art

[0002] Phosphorus (P) is an essential element for all organisms and an irreplaceable element in fertilizer production. It supports the development of modern agriculture and is also used in other industrial production. As the demand for phosphorus increases year by year, the existing global phosphorus rock reserves may be exhausted in the next 50 to 100 years. 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, which destroys 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. Their final products (chemical or biological sludge) are unsafe and cannot be reused in agriculture. Therefore, a more sustainable phosphorus utilization model should be explored.

[0003] Microbial electrolytic 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, while protons are released into the solution. The electrons then travel through the wire to the cathode and combine with free protons in the solution to produce hydrogen. The consumption of protons in the cathode chamber increases the pH of the solution, so phosphorus can be precipitated in the form of struvite. Struvite can simultaneously recover nitrogen and phosphorus from sewage and is an efficient slow-release phosphate fertilizer that can avoid the "seedling burn" phenomenon caused by fast-acting ammonium phosphate fertilizers. Using microbial electrolytic cells to recover phosphorus in the form of struvite, without the need to add sodium hydroxide to provide alkaline conditions, can achieve the purpose of simultaneously reducing drug consumption and energy consumption and efficiently recovering phosphorus resources.

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

[0005] 8H2O+8e - →8OH - +4H2↑

[0006]

[0007] Improving the hydrogen production effect by changing the cathode of MECs has been a hot topic in recent years. The enhancement of hydrogen production also significantly affects the phosphorus recovery performance of MECs. Similar to traditional electrolytic cells, MECs cathodes require catalysts to accelerate the kinetically slow 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 electrolytic cells. Summary of the invention

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

[0009] The present invention first provides a method for modifying a stainless steel mesh cathode for recovering phosphorus from wastewater in a microbial electrolysis cell, comprising the following steps:

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

[0011] The above modification method, in the electrolyte, the concentration of sodium citrate 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, in the electrolyte, the concentration of sodium citrate 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; and the concentration of sodium chloride is 17.5 g / L.

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

[0015] The temperature of the electrodeposition is 20 to 65°C; preferably 20 to 50°C, more preferably 50°C;

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

[0017] The electrodeposition time is 1200 to 2100 s; specifically, it may be 1500 s or 1800 s.

[0018] Second, the present invention further provides a Ni-Co-Sn modified stainless steel mesh cathode prepared by the above modification method.

[0019] The application of the above-mentioned Ni-Co-Sn modified stainless steel mesh cathode in the recovery of phosphorus from wastewater in a microbial electrolysis cell also falls within the protection scope of the present invention.

[0020] Finally, the present invention provides a method for recovering phosphorus from sewage, comprising the following steps:

[0021] Electrogenic bacteria are inoculated in the anode chamber of a double-chamber microbial electrolytic cell, and phosphorus-containing wastewater to be treated is added to the cathode chamber; the 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 recover phosphorus in the wastewater.

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

[0023] The electrogenic bacteria is Geobacter sulfurreducens PCA, whose deposit number is ATCC51573;

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

[0025] The anode solution in the anode chamber is composed of: 0.2-0.5 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;

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

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

[0028] In the above recovery method, the operating temperature of the double-chamber microbial electrolysis cell is 20-35°C;

[0029] The applied voltage for operating the dual-chamber microbial electrolysis cell is 0.7 to 1.1 V, specifically 0.9 V;

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

[0031] The above-mentioned recovery method also includes the step of starting the microbial electrolysis cell before operation;

[0032] In the step of starting the microbial electrolysis cell, the anode solution is composed of: 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, 5-7 mM sodium selenate, 5-25 mM sodium acetate, 5-15 mL / L trace element solution and 5-15 mL / L vitamin solution;

[0033] 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 to 1:10, specifically 1:10;

[0034] The OD of the electrogenic bacteria solution 600 0.5~0.6;

[0035] The electrogenic bacteria liquid is taken from electrogenic bacteria in the logarithmic growth phase;

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

[0037] In the above-mentioned recovery method, in the step of starting the microbial electrolytic cell, the double-chamber microbial electrolytic cell is operated, and when the voltage is close to zero, the cathode chamber and the anode chamber solutions are replaced, and when the three-cycle power generation time and the maximum voltage tend to be stable, the startup is successful;

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

[0039] The microbial electrolysis cell is started up and operated under anaerobic conditions.

[0040] In the above recovery method, the composition and concentration of the trace element solution are as follows: 0.5-2g / L trisodium nitrilotriacetate (NTA), 2-4g / L MgSO4·7H2O, 0.2-1g / L MnSO4·H2O, 0.5-2g / L NaCl, 0.1-0.2g / L FeSO4·7H2O, 0.1-0.2g / L CaCl2·2H2O, 0.1-0.2g / L CoCl2·6H2O, 0.1-0.15g / L ZnCl2, 0.01-0.02g / L CuSO4·5H2O, 0.01-0.02g / L AlK(SO4)2·12H2O, 0.01-0.02g / L H3BO3, 0.025-0.03g / L Na2MoO4·2H2O, 0.02~0.03g / L NiCl2·6H2O, 0.02~0.03g / LNa2WO4·2H2O; the solvent is water;

[0041] Specifically, the composition and concentration of the trace element solution are as follows: 1.5g / L trisodium nitrilotriacetate (NTA), 3g / LMgSO4·7H2O, 0.5g / L MnSO4·H2O, 1g / L NaCl, 0.1g / L FeSO4·7H2O, 0.1g / L CaCl2·2H2O, 0.1g / L CoCl2·6H2O, 0.13g / L ZnCl2, 0.01g / L CuSO4·5H2O, 0.01g / L AlK(SO4)2·12H2O, 0.01g / L H3BO3, 0.025g / L Na2MoO4·2H2O, 0.024g / L NiCl2·6H2O, 0.025g / L Na2WO4·2H2O;

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

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

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

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

[0046] The present invention has the following advantages:

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

[0048] (2) The reactor of the present invention has a simple structure and the cathode stainless steel mesh is inexpensive. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is a diagram of the constant current deposition device of the present invention: in the figure, 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 This is a polarization curve diagram of the linear sweep voltammetry in Example 1 of the present invention.

[0051] Figure 3 This is the electrochemical impedance spectroscopy diagram in Example 1 of the present invention.

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

[0053] Figure 5 This is a diagram showing the phosphorus recovery effect in Example 1 of the present invention.

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

[0055] Figure 7 This is the electrochemical impedance spectroscopy diagram in Example 2 of the present invention.

[0056] Figure 8 This is a diagram showing the phosphorus recovery effect in Example 2 of the present invention.

[0057] Fig. 9 1 is the XRD diagram of the cathode of the nickel-cobalt-tin modified stainless steel mesh and the original stainless steel mesh in Example 2 of the present invention.

[0058] Fig.10 This is the XPS spectrum of nickel in the nickel-cobalt-tin modified stainless steel mesh cathode in Example 2 of the present invention.

[0059] Fig.11 This is the XPS spectrum of cobalt in the nickel-cobalt-tin modified stainless steel mesh cathode in Example 2 of the present invention.

[0060] Fig.12This is the XPS spectrum of tin in the nickel-cobalt-tin modified stainless steel mesh cathode in Example 2 of the present invention.

[0061] Fig.13 This is the XRD diagram of the product after the microbial electrolysis cell in Example 2 of the present invention runs for one cycle.

[0062] Fig.14 This is a graph showing the change in phosphorus recovery rates over time for four different cathodes, namely, SSM before modification, Ni-Co-SSM, Ni-Co-P-SSM, and Ni-Co-Sn-SSM in Example 3 of the present invention. DETAILED DESCRIPTION

[0063] The present invention is further described in detail below in conjunction with specific embodiments. The given examples are only for illustrating the present invention, but not for limiting the scope of the present invention.

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

[0065] The quantitative tests in the following examples were all repeated three times, and the results were averaged.

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

[0067] The Geobacter sulfurreducens PCA used in the following examples is commercially available from the American Type Culture Collection with a collection number of ATCC51573.

[0068] Example 1: Phosphorus recovery effect of nickel-cobalt-tin stainless steel mesh cathode microbial electrolysis cell at different electrodeposition current densities

[0069] Step 1: Modification of cathode stainless steel mesh

[0070] Constant current deposition device such as Figure 1 : It 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 a 60×60 mesh 304 stainless steel mesh with a geometric area of ​​3×4 cm 2 , the anode is 4×4cm 2 Nickel plate, the reference electrode is Ag / AgCl electrode;

[0072] The electrolyte preparation method is as follows: first, 32.25 g of sodium citrate is dissolved in water, then 19.7 g of nickel sulfate hexahydrate (NiSO4·6H2O), 10.5 g of cobalt sulfate heptahydrate (CoSO4·7H2O), 2.4 g of stannous sulfate (SnSO4), 4.625 g of boric acid and 4.375 g of sodium chloride are added, and finally, the pH is adjusted to 4.5 with sodium hydroxide solution and the volume is fixed to 250 mL;

[0073] The electrochemical workstation (Shanghai Chenhua CHI 660E) was used for constant current deposition using the chronopotentiometry method. A magnetic stirrer was used to keep the deposition temperature and electrolyte concentration uniform. The electrodeposition temperature and magnetic stirring speed were 20°C and 400 rpm, respectively. At a current density of 0.2 to 0.35 A / dm 2 The electrodeposition was carried out for 1500 s under the conditions of , and then the deposited cathode was rinsed with deionized water.

[0074] All electrochemical tests were performed using a three-electrode system of an electrochemical workstation (Shanghai Chenhua CHI 660E) in 50 mM phosphate buffer at pH 7. The electrodeposited samples were cut into 1×2 cm 2 The rectangular part is used as the working electrode, the platinum mesh is used as the counter electrode, and the Ag / AgCl is used as the reference electrode (filled with 3M KCl). The electrochemical test temperature is maintained at 30°C in a constant temperature water bath. Nitrogen is passed through the phosphate buffer for 20 minutes before each test, and then left for 10 minutes. The buffer is replaced after each electrochemical test of a sample. The experiment obtained 0.3A / dm 2 The stainless steel mesh electrode prepared under the current density (j) is 10mA / cm 2 The cathode overpotential is the smallest, which is 1.36V ( Figure 2 ), the charge transfer resistance is the smallest, which is 60.12ohm ( Figure 3 ).

[0075] Step 2: Construction of microbial electrolysis cell

[0076] The structure of the microbial electrolysis cell is as follows: Figure 4As shown, it 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 the cathode chamber 6 are separated by the cation exchange membrane 7 to form a double-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 by stainless steel screws; a sampling port 19 is provided above the anode chamber 5 and the cathode chamber 6, and a sampling needle is inserted into the sampling port 19, and the switch is controlled by a two-way valve 11; the water inlet 12 and the water outlet 13 are located on both sides of the anode chamber 5 and the cathode chamber 4, the water inlet 12 is on the top, and the water outlet 13 is at the bottom, and is sealed with a rubber cover when not in use; a gas collecting port 1 14 and a gas collecting port 2 18 are provided above the anode chamber 5 and the cathode chamber 6, and the gas collecting port 1 14 and the gas collecting port 2 18 are provided above the anode chamber 5 and the cathode chamber 6. Air bags are connected at 18 to store the gas produced by the anode and cathode respectively; the cathode and cathode are connected by a copper conductor 15, with a high-precision resistor 16 in between; a power supply 17 is connected in series in the circuit to power 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] The 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 the bacterial solution was 1:10 (the total volume was 100 mL). A sterile anaerobic environment must be ensured during the inoculation process. All solutions except the vitamin solution must be sterilized at high temperature. After the inoculation is completed, an anaerobic workstation must be used for aeration for 20 minutes (N2:CO2 volume ratio 8:2); the total volume of the cathode solution is 100 mL.

[0079] Among them, the OD of Geobacter sulfurreducens PCA bacterial solution 600 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 0.7 V during the startup period. The inoculum was Geobacter sulfurreducens in the logarithmic growth period (24-48 h), and the substrate was sodium acetate (NaAc). The effective volumes of the anode and cathode chambers were both 118 mL, the anode was a carbon fiber brush, and the cathode was the stainless steel mesh prepared above (area 3×4 cm 2 ). Run the dual-chamber microbial electrolytic cell. When the voltage is close to zero, replace the cathode chamber and anode chamber solutions. When the three-cycle power generation time and the maximum voltage tend to be stable, the startup is successful. After the startup is successful, the current density of the dual-chamber microbial electrolytic cell in this study can reach 1.9A / m 2 about.

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

[0083] 0.25g / L NH4Cl, 0.1g / L KCl, 2.5g / L NaHCO3, 0.6g / L NaH2PO4·H2O, 5mM Na2SeO4, 10mM sodium acetate, 10mL / L vitamin solution and 10mL / L trace element solution, 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] 10g / L pyridoxine hydrochloride, 0.1g / L vitamin B12, 2g / L biotin, 2g / L folic acid, 5g / L pantothenic acid, 5g / L thiamine, 5g / L riboflavin, 5g / L niacin, 5g / L p-aminobenzoic acid, 5g / L lipoic acid; the solvent is water;

[0087] The cathode solution composition is as follows:

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

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

[0090] When the reactor is successfully started, the anode solution and cathode solution are replaced to start phosphorus recovery. No bacterial solution is added in each experiment. The composition of the anode solution is the same as that in the startup period. 0.27g / L potassium dihydrogen phosphate, 0.43g / L ammonium chloride and 0.61g / L magnesium chloride are used as cathode solutions to simulate phosphorus-rich sewage. The sodium acetate concentration of the anode solution is 10mM, the Mg / P molar ratio of the cathode solution is 1.5, the N / P molar ratio is 4.0, and the phosphorus concentration is 60mg / L. A 10Ω resistor is connected between the anode and the cathode, and the reactor temperature is maintained at 30°C. All operations still ensure sterile anaerobic conditions. The applied voltage of the power supply adjustment experiment is 0.9V. The current is recorded every 30 seconds in each experiment. The phosphorus concentration is measured from the sampling port 19 every 12h, and the reaction time is 48h. After the reaction is completed, the cathode is taken out, and the electrodeposition current density is 0.3A / dm 2 The recovery rate of phosphorus in the stainless steel net cathode can reach 94% in 48 hours. Figure 5 shown.

[0091] Example 2: Phosphorus recovery effect of a nickel-cobalt-tin stainless steel mesh cathode microbial electrolysis cell at different electrodeposition temperatures Step 1: Modification of the cathode stainless steel mesh

[0092] Constant current deposition device such as Figure 1 The modification method and conditions are the same as those in Example 1 except for the following. The electrodeposition temperature in the experiment is 20°C to 65°C, and the magnetic stirring speed is 400 rpm. 2 Electrodeposition was carried out under the condition of 1800s electrodeposition time; then the cathode was prepared by rinsing the deposited cathode with deionized water. The electrode overpotential was the smallest at 50℃, which was 1.15V ( Figure 6 ), the charge transfer resistance is the smallest, which is 34ohm ( Figure 7 ).

[0093] Steps 2 and 3 are the same as those in Example 1 and are not described in detail here.

[0094] Step 4: Phosphorus recovery from the nickel-cobalt-tin stainless steel mesh cathode microbial electrolysis cell at different electrodeposition temperatures

[0095] The experimental conditions are the same as those in step 4 of Example 1. After the reaction is completed, the cathode is taken out. The phosphorus recovery rate of the stainless steel mesh cathode at an electrodeposition temperature of 50° C. can reach 97.88% in 36 hours. Figure 8 shown.

[0096] Step 5: Characterization of Ni-Co-Tin Modified Stainless Steel Mesh Cathode and Phosphorus Recovery Products in 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 shown in Fig. 9 As shown, both show the same characteristic peaks as austenite. The diffraction peaks at 43.8, 50.9 and 74.8° at 2θ match the (111), (200) and (220) crystal planes of austenitic steel (PDF 33-0945), respectively, indicating that the main components of SSM are Ni, Fe and Cr. The diffraction angle of 33.9° in the XRD of Ni-Co-Sn-SSM corresponds to the (101) crystal plane of SnO2, and the characteristic peak of Sn appears at 30.65°, which is attributed to the (200) plane of tin. In order 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. Fig.10 is the XPS pattern of Ni, Ni 2p 3 / 2 The peak at 855.3 eV is the partially charged Ni (Ni δ+ , δ is likely close to 0), and the peak at 876.2 eV is the characteristic peak of Ni in nickel oxide. 2+ The peaks at 859.88eV and 883.43eV are the characteristic peaks of Ni 2p 3 / 2 and Ni 2p 1 / 2 Satellite peaks. Fig.11 This is the XPS graph of Co. The two peaks at 782.5eV and 797.2eV come from Co. δ+ and cobalt oxide (Co 2+ / 3+ ), the peaks at 787.0eV and 804.89eV correspond to satellite peaks. Fig.12 The XPS spectrum of Sn shows two peaks, which appear at the binding energies of 486.88 eV and 496.5 eV. 496.5 eV corresponds to Sn 3d 3 / 2 According to the literature, the two peaks correspond to Sn 0 and Sn 4+ , indicating that the Sn in the prepared Ni-Co-Sn-SSM electrode mainly exists in the form of Sn metal and SnO2.

[0098] Fig.13 This is the XRD diagram of the cathode product in the Ni-Co-Sn-SSM microbial electrolysis cell at an electrodeposition temperature of 50°C. The product generated in the experiment has a high degree of consistency with the struvite standard card, indicating that the generated product is mainly struvite crystals.

[0099] The cathode products were collected after the operation of the reactor was completed, and then dried in a forced air drying oven at 40°C for 24 hours, and then XRD characterization was performed to analyze the crystal structure of the products.

[0100] Example 3: Phosphorus recovery effect of microbial electrolysis 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 The modification method and conditions are the same as those in Example 1 except for the following. When preparing the Ni-Co-SSM stainless steel mesh cathode, the electrolyte is prepared as follows: first, 32.25 g of sodium citrate is dissolved in water, then 19.7 g of nickel sulfate hexahydrate (NiSO4·6H2O), 10.5 g of cobalt sulfate heptahydrate (CoSO4·7H2O), 4.625 g of boric acid and 4.375 g of sodium chloride are added, and finally, sodium hydroxide solution is used to prepare the electrolyte. The pH was adjusted to 4.5 and the volume was adjusted to 250 mL. When preparing the Ni-Co-P-SSM stainless steel mesh cathode, the electrolyte was prepared as follows: 19.7 g of nickel sulfate hexahydrate (NiSO4·6H2O), 10.5 g of cobalt sulfate heptahydrate (CoSO4·7H2O), 2.4 g of potassium dihydrogen phosphate, 4.625 g of boric acid and 4.375 g of sodium chloride were added, and finally the pH was adjusted to 4.5 with sodium hydroxide solution and the volume was adjusted to 250 mL.

[0103] The electrochemical workstation (Shanghai Chenhua CHI 660E) was used for constant current deposition using the chronopotentiometry method. A magnetic stirrer was used to keep the deposition temperature and electrolyte concentration uniform. The electrodeposition temperature was 50°C and the magnetic stirring speed was 400 rpm. At a current density of 0.3 A / dm 2 Two types of stainless steel mesh cathodes, Ni-Co-SSM and Ni-Co-P-SSM, were prepared by electrodeposition under the condition of electrodeposition time of 1800s; the deposited cathodes were then rinsed with deionized water.

[0104] Steps 2 and 3 are the same as those in Example 1 and are not described in detail here.

[0105] Step 4: Phosphorus recovery in modified stainless steel mesh cathode microbial electrolysis cell

[0106] 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 changes in the phosphorus recovery rate of the original SSM and four stainless steel mesh cathodes, Ni-Co-SSM, Ni-Co-P-SSM, and Ni-Co-Sn-SSM, over time were compared. The results are as follows Fig.14 As shown in the figure, it can be seen that the phosphorus recovery rate of Ni-Co-Sn-SSM is the fastest, reaching about 90% after 12 hours of reaction. Ni-Co-P-SSM and Ni-Co-SSM cathodes both reach about 90% after 36 hours of reaction. The phosphorus recovery rate of Ni-Co-P-SSM in the first 24 hours is slightly faster than that of Ni-Co-SSM. The phosphorus recovery rate of the original SSM in the first 24 hours is the slowest, and the recovery rate is also the lowest, reaching only about 50%.

Claims

1. A method for modifying a stainless steel mesh cathode for recovering phosphorus from wastewater in a microbial electrolysis cell, comprising the following steps: The stainless steel mesh is used as the cathode and the Ni-Co-Sn modified stainless steel mesh cathode is prepared by an electrodeposition method; the electrolyte used in the electrodeposition method includes sodium citrate, nickel sulfate, cobalt sulfate, stannous sulfate, boric acid and sodium chloride.

2. The modification method according to claim 1, characterized in that: In the electrolyte, the concentration of sodium citrate 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; The pH value of the electrolyte is 4.5-7.

3. The modification method according to claim 1 or 2, characterized in that: In the electrodeposition method, the material of the anode is nickel or graphite; The temperature of the electrodeposition is 20 to 65°C; preferably 20 to 50°C, more preferably 50°C; The current density of electrodeposition is 0.2~0.35A / dm 2 ; preferably 0.30A / dm 2 ; The electrodeposition time is 1200 to 2100 s.

4. A Ni-Co-Sn modified stainless steel mesh cathode prepared by the modification method according to any one of claims 1 to 3.

5. Use of the Ni-Co-Sn modified stainless steel mesh cathode according to claim 4 in phosphorus recovery from wastewater in a microbial electrolysis cell.

6. A method for recovering phosphorus from sewage, comprising the following steps: Electrogenic bacteria are inoculated in the anode chamber of a double-chamber microbial electrolytic cell, and phosphorus-containing wastewater to be treated is added to the cathode chamber; the Ni-Co-Sn modified stainless steel mesh cathode described in claim 4 is used as the cathode of the electrolytic cell; and the double-chamber microbial electrolytic cell is operated to recover phosphorus from the wastewater.

7. The recycling method according to claim 6, characterized in that: 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 PCA, whose deposit number is ATCC51573; The anode is a carbon fiber brush or carbon felt; The anode solution in the anode chamber is composed of: 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 nitrilotriacetate, 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, 0.02~0.03g / L Na2WO4·2H2O; the solvent is water; The composition and concentration of the vitamin solution are as follows: 10-15g / L pyridoxine hydrochloride, 0.1-0.3g / L vitamin B12, 1-2g / L biotin, 1-2g / L folic acid, 3-5g / L pantothenic acid, 3-5g / L thiamine, 3-5g / L riboflavin, 3-5g / L nicotinic acid, 3-5g / L p-aminobenzoic acid, 3-5g / L lipoic acid; the solvent is water; The initial phosphorus concentration of the phosphorus-containing wastewater is 1-4 mM, the magnesium-phosphorus molar ratio is 1-1.5, and the nitrogen-phosphorus molar ratio is 1-4.

8. The recycling method according to claim 6 or 7, characterized in that: The operating temperature of the double-chamber microbial electrolysis cell is 20-35°C; The applied voltage for operating the dual-chamber microbial electrolysis cell is 0.7 to 1.1 V; The double-chamber microbial electrolysis cell operates under anaerobic conditions.

9. The recovery method according to any one of claims 6 to 8, characterized in that: The recovery method also includes the step of starting the microbial electrolysis cell before operation; In the step of starting the microbial electrolysis cell, the anode solution is composed of: 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, 5-7 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: 0.5~2g / L trisodium nitrilotriacetate, 2~4g / L MgSO4·7H2O, 0.2~1g / L MnSO4·H2O, 0.5~2g / LNaCl, 0.1~0.2g / L FeSO4·7H2O, 0.1~0.2g / L CaCl2·2H2O, 0.1~0.2g / L CoCl2·6H2O, 0.1~0.15g / L ZnCl2, 0.01~0.02g / L CuSO4·5H2O, 0.01~0.02g / L AlK(SO4)2·12H2O, 0.01~0.02g / L H3BO3, 0.025~0.03g / L Na2MoO4·2H2O, 0.02~0.03g / L NiCl2·6H2O, 0.02~0.03g / L Na2WO4·2H2O; the solvent is water; The composition and concentration of the vitamin solution are as follows: 10-15g / L pyridoxine hydrochloride, 0.1-0.3g / L vitamin B12, 1-2g / L biotin, 1-2g / L folic acid, 3-5g / L pantothenic acid, 3-5g / L thiamine, 3-5g / L riboflavin, 3-5g / L nicotinic acid, 3-5g / L p-aminobenzoic acid, 3-5g / 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 to 1:10; The OD of the electrogenic bacteria solution 600 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 according to claim 9, characterized in that: In the step of starting the microbial electrolysis cell, the dual-chamber microbial electrolysis cell is operated, and when the voltage is close to zero, the solutions in the cathode chamber and the anode chamber are replaced, and when the power generation time and the maximum voltage of each cycle tend to be stable, the start-up is completed; The microbial electrolysis cell is started up and operated under anaerobic conditions.

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