New method for generating electricity by treating aged landfill leachate through Co3O4 / Ni-MOF anode single-chamber MFC

Abstract

The invention discloses a novel method for generating electricity by treating aged landfill leachate through a Co3O4 / Ni-MOF anode single-chamber MFC, and belongs to the technical field of inorganic environment materials and waste water resource utilization. The method comprises the following steps: firstly preparing different materials and taking the different materials as an anode catalyst of a microbial fuel cell (MFC), then constructing a single-chamber MFC, taking anaerobic activated sludge obtained by culturing aerobic activated sludge of a sewage treatment plant as anolyte, adding a nutrient solution, stabilizing for several periods, replacing an anaerobic sludge matrix in an anode chamber with the aged landfill leachate, and finally preparing the aged landfill leachate in the single-chamber MFC. The MFC is operated at room temperature and constant pressure, organic pollutants and ammonia nitrogen in the aged landfill leachate can be removed, and meanwhile electric energy can be recycled. The method is simple in equipment, convenient to operate, energy-saving and free of secondary pollution. When the anode catalyst is Co3O4 / Ni-MOF, the maximum power density of the single-chamber MFC reaches 882 mW / m < 2 >, the maximum output voltage is 524 mV, the COD removal rate can reach 35.3%, and the ammonia nitrogen removal rate can reach 48.5%.

Description

Technical Field

[0001] The present invention relates to a new method for generating electricity by treating aged landfill leachate through a single-chamber microbial fuel cell, belonging to the technical field of inorganic environmental materials and wastewater resource utilization. Background Art

[0002] With the rapid development of society and the over-exploitation and utilization of resources, wastewater treatment has become a key part of current environmental safety issues. Among them, the aged landfill leachate brought about by landfill treatment usually pollutes the soil, groundwater, surface drinking water sources and the surrounding environment. Currently, the treatment methods for landfill leachate include physical methods, chemical methods, biological methods, etc., but they all have certain deficiencies; while the microbial fuel cell (MFC) technology is a new type of wastewater treatment method that can convert the chemical energy of organic matter into electrical energy through microbial catalytic reactions, and can generate electricity while degrading the organic matter in the wastewater. Compared with traditional methods, MFC not only saves costs but also is very environmentally friendly, and realizes the resource utilization of wastewater.

[0003] Currently, electrode catalysts are a major research hotspot in MFC technology. In particular, efficient anode catalysts can significantly improve the overall performance of MFC. In recent years, the semiconductor material Co3O4 has been widely used in MFC. For example, in "Enhanced oxygen reduction reaction in air-cathode microbial fuel cells using flower-like Co3O4 as an efficient cathode catalyst" on pages 19287-19295 of Volume 42 of "International Journal of Hydrogen Energy" (Comparative Document 1), flower-like Co3O4 was prepared by a hydrothermal method and used as the cathode catalyst of MFC. Compared with the bare cathode, it has more oxygen reduction reaction (ORR) active sites and stronger electron transfer characteristics. However, the deficiencies of this method are as follows: (1) The constructed double-chamber MFC only explored the power generation performance of the cathode catalyst, and only detected the output voltage after microbial inoculation, without testing the degradation effect of actual wastewater; (2) The prepared flower-like Co3O4 was not analyzed for the influence of different ratios or multiple factors; (3) The maximum power density of the flower-like Co3O4 cathode MFC is relatively low, only 248 mW / m 2 .

[0004] In addition, a metal-organic framework (MOF) refers to a porous crystalline material formed by the self-assembly of metal ions or metal clusters and organic ligands. It has characteristics such as a highly ordered porous structure, adjustable pore size and specific surface area, and rich chemical functionality. For example, in "Robust bimetallic metal-organic framework cathode catalyst to boost oxygen reduction reaction in microbial fuel cell" (Comparative Document 2) in Volume 547, Issue 231947 of "Journal of Power Sources", a new type of bimetallic metal-organic framework (Zr / Ni-MOF) was synthesized and used as the cathode catalyst of MFC, showing good catalytic activity. However, the deficiencies of this method are as follows: (1) The performance of nickel metal-organic framework (Ni-MOF) has not been studied; (2) In MFC, only cultured bacteria are used as the treatment substrate of MFC, and actual wastewater has not been treated; (3) The maximum power density of the Zr / Ni-MOF cathode MFC is relatively small, only 0.8 W / m 2 。

[0005] Therefore, the composite of Co3O4 and MOF as the electrode material of MFC still has great research potential. In the present invention, a composite catalyst Co3O4 / Ni-MOF of Co3O4 and nickel-based metal-organic framework (Ni-MOF) was prepared and made into the anode electrode of a single-chamber MFC to treat aged landfill leachate. While achieving efficient power generation, it also has good pollutant removal effects. Summary of the Invention

[0006] The object of the present invention is to provide a new preparation method of an anode catalyst Co3O4 / Ni-MOF that is simple in steps, low in cost, and efficient, and apply it to the green and environmentally friendly MFC technology to treat aged landfill leachate, so that the wastewater can be effectively degraded while the organic matter energy in the wastewater can be converted into electric energy. The new method for the Co3O4 / Ni-MOF anode single-chamber MFC to treat aged landfill leachate and generate electricity is as follows:

[0007] (1) Preparation of Co3O4

[0008] Weigh 1.46 g of cobalt nitrate hexahydrate, 3 g of urea, and 0.74 g of ammonium fluoride, dissolve them in 70 mL of distilled water, transfer the solution to a 100 mL autoclave after magnetic stirring for 1 h, and carry out hydrothermal reaction at 120 °C for 12 h; cool it naturally to room temperature, filter, wash the filter cake by low-speed centrifugation with distilled water, then place it in an oven and dry at 60 °C for 12 h, grind it and transfer it to a muffle furnace, calcine it at 350 °C for 2 h, and after cooling to room temperature, grind it to obtain the black powder Co3O4.

[0009] (2) Preparation of anode catalyst Co3O4 / Ni-MOF

[0010] Measure 20 mL of DMF, 20 mL of absolute ethanol, and 20 mL of distilled water into a 100 mL beaker, and stir magnetically to obtain a homogeneous solution A; weigh 0.88 g of cobalt nitrate hexahydrate, 0.24 g of terephthalic acid, and 1.2 g of polyvinylpyrrolidone and add them to solution A in sequence, and continue to stir for 30 min to obtain solution B; weigh 0.362 g of Co3O4 powder and add it to solution B, stir magnetically for 30 min to obtain a mixed solution; transfer the mixed solution to a 100 mL high-pressure autoclave, place it in an oven and carry out hydrothermal reaction at 150 °C for 10 h; cool it naturally to room temperature, filter, wash the filter cake by high-speed centrifugation alternately with distilled water and absolute ethanol for 3 times, then place it in a vacuum drying oven and dry at 80 °C for 12 h to obtain the Co3O4 / Ni-MOF composite catalyst material; without adding Co3O4, prepare the Ni-MOF catalyst according to the above method.

[0011] (3) Construction of single-chamber MFC

[0012] Select plexiglass to construct a single-chamber MFC device. The device is as Figure 1 shown. The device is a three-section design. The cathode side has a central circular hollow design to enable the air cathode to be in full contact with air; the chamber part has a cylindrical hollow design for holding liquid; the other side is solid and the interior of the chamber can be observed; each section is connected by a rubber pad with a hollow middle to play a role in sealing and waterproofing. The effective volume of the device is 50 mL. The cathode and anode are connected in series with a 0.5 cm titanium wire and a 1000 Ω external resistor to form a closed loop, and a data acquisition card is connected in parallel at both ends of the external resistor to record the voltage data during the operation of the MFC.

[0013] (4) Start-up of single-chamber MFC

[0014] Use the cultured anaerobic sludge as the substrate in the anode chamber to start the microbial fuel cell; the reactor operates in an intermittent mode; after three operation cycles, the output voltage of the MFC can remain stable for a long time and the maximum output voltage of each cycle is close, then the start-up of the MFC is completed.

[0015] (5) Operation of Microbial Fuel Cell with Aged Landfill Leachate as Substrate

[0016] Replace the anaerobic sludge substrate in the anode chamber with aged landfill leachate, operate the MFC at room temperature and constant pressure, and use a data acquisition instrument to record its output voltage; measure the COD and ammonia nitrogen concentrations of the mixed wastewater before and after the operation starts.

[0017] The beneficial effects of the above technical solutions of the present invention are as follows:

[0018] First, the present invention directly treats the actual aged landfill leachate, not only tests its power generation performance, but also detects its effect on degrading actual wastewater, which is better than Comparative Document 1 and Comparative Document 2.

[0019] Second, the cultured bacterial flora is used in Comparative Document 1 and Comparative Document 2, and neither of them treats the actual wastewater, so the practical value is relatively low. However, the actual wastewater used in the present invention has a better application prospect.

[0020] Third, the Co3O4 / Ni-MOF anode catalyst can significantly enhance the power generation performance of the single-chamber MFC system and maintain a good pollutant removal effect. Description of the Drawings

[0021] Figure 1 It is a schematic diagram of a single-chamber microbial fuel cell device. In the figure: 1 - anode, 2 - anode chamber, 3 - cathode, 4 - wire, 5 - resistance box;

[0022] Figure 2 It is the X-ray diffraction pattern of Co3O4, Ni-MOF and Co3O4 / Ni-MOF;

[0023] Figure 3 It is the curve of the output voltage of the single-chamber MFC with different anode catalysts changing with time;

[0024] Figure 4 It is the power density curve of the single-chamber MFC with different anode catalysts. Detailed Embodiments

[0025] The present invention will be further described below in conjunction with specific embodiments.

[0026] Example 1

[0027] A new method for power generation by treating aged landfill leachate with a Co3O4 / Ni-MOF anode single-chamber MFC, the specific steps are as follows:

[0028] (1) Preparation of Co3O4

[0029] Weigh 1.46 g of cobalt nitrate hexahydrate, 3 g of urea, and 0.74 g of ammonium fluoride, dissolve them in 70 mL of distilled water, transfer them to a 100 mL autoclave after magnetic stirring for 1 h, and carry out hydrothermal reaction at 120 °C for 12 h; cool naturally to room temperature, filter, wash the filter cake by low-speed centrifugation with distilled water, then place it in an oven and dry at 60 °C for 12 h, grind it and transfer it to a muffle furnace, calcine at 350 °C for 2 h, and after cooling to room temperature, grind it to obtain black powder Co3O4.

[0030] (2) Preparation of anode catalyst Co3O4 / Ni-MOF

[0031] Measure 20 mL of DMF, 20 mL of absolute ethanol, and 20 mL of distilled water into a 100 mL beaker, stir magnetically to obtain a homogeneous solution A; weigh 0.88 g of cobalt nitrate hexahydrate, 0.24 g of terephthalic acid, and 1.2 g of polyvinylpyrrolidone and add them to solution A in sequence, continue stirring for 30 min to obtain solution B; weigh 0.362 g of Co3O4 powder and add it to solution B, stir magnetically for 30 min to obtain a mixed solution; transfer the mixed solution to a 100 mL autoclave, place it in an oven and carry out hydrothermal reaction at 150 °C for 10 h; cool naturally to room temperature, filter, wash the filter cake by alternately high-speed centrifugation with distilled water and absolute ethanol for 3 times, then place it in a vacuum drying oven and dry at 80 °C for 12 h to obtain the Co3O4 / Ni-MOF composite catalyst material; without adding Co3O4, prepare the Ni-MOF catalyst according to the above method.

[0032] (3) Electrode pretreatment method

[0033] Cut the carbon cloth, with the anode size of 2×2 cm and the cathode size of 5×5 cm. Immerse the cut carbon cloth in absolute ethanol, ultrasonically clean it for 15 min and then soak it for 30 min, carefully rinse it with deionized water and then immerse it in a mixed solution of 10% nitric acid solution and 10% sulfuric acid solution with a volume ratio of 3:1, ultrasonically for 15 min, soak for 5 h and then carefully rinse it with deionized water; immerse the carbon cloth in deionized water, ultrasonically for 15 min, soak for 30 min, then carefully wash it with deionized water and put it in an oven at 60 °C to dry, and then place it in a muffle furnace and calcine at 300 °C for 4 h to obtain the carbon cloth electrode.

[0034] (4) Fabrication of air cathode

[0035] Measure 1 mL of deionized water and 1 mL of 60% polytetrafluoroethylene emulsion (PTFE) into a 10 mL beaker. Weigh 30 mg of carbon black and add it to the beaker in small portions multiple times, then stir evenly to obtain suspension A. Gently brush suspension A onto a 5×5 cm carbon cloth, let it air dry for 2 hours, then place it in a muffle furnace and calcine at 370 °C for 25 minutes. After cooling, evenly coat a layer of 60% PTFE on the carbon-coated surface. After drying until the PTFE turns white, calcine at 370 °C for 12 minutes. After the carbon cloth cools, continue to coat a layer of PTFE and calcine, for a total of 4 brush coatings. Use a pipette to transfer 400 μL of Nafion solution, 200 μL of isopropanol, and 200 μL of deionized water into a 10 mL beaker. Weigh 40 mg of 20% platinum-carbon powder, ultrasonicate for 10 min and then brush it onto the other side of the carbon cloth. Let it stand for 24 h to air dry to obtain the air cathode.

[0036] (5) Fabrication of the anode

[0037] Weigh 8 mg of Co3O4 / Ni-MOF catalyst into a 2.5 mL test tube. Measure 300 μL of absolute ethanol, 200 μL of ethylene glycol, and 20 μL of Nafion solution and add them to the test tube. Place the test tube in an ultrasonic cleaner and ultrasonicate for 30 min to mix evenly to obtain a suspension. Drop the suspension evenly onto a 2×2 cm carbon cloth and dry it to obtain the anode.

[0038] (6) Construction of the single-chamber microbial fuel cell

[0039] The outer length, width, and height of the single-chamber MFC are 8.5, 8.5, and 8 cm respectively. The cavity is a cylindrical shape with a bottom diameter of 4 cm and a height of 4 cm, and the effective volume is 50 mL. The entire device is made of plexiglass and is designed in a three-section style. The cathode side has a central circular hollow design to enable the air cathode to fully contact with air. The chamber part has a cylindrical hollow design for containing liquid. The other side is solid, allowing the internal part of the chamber to be observed. Each section is connected by a rubber pad with a hollow middle to play a role in sealing and waterproofing. There are small holes at the top for placing the cathode and anode wires and adding liquid, etc. Place the anode carbon cloth loaded with the prepared catalyst and the air cathode loaded with the platinum-carbon catalyst in sequence. The cathode and anode are connected in series with a 1000 Ω external resistor through 0.5 cm titanium wires to form a closed loop. A data acquisition card is connected in parallel at both ends of the external resistor to record the voltage data during the operation of the MFC.

[0040] (7) Startup of the single-chamber microbial fuel cell

[0041] Mix the phosphate buffer solution with the already cultivated active anaerobic sludge in a volume ratio of 1:1 as the anolyte, and then add 1.6 g / L of sodium acetate, 0.05 g / L of ammonium chloride, 12.5 mL / L of trace metal solution, and 5 mL / L of vitamin solution to maintain the growth of microorganisms in the anolyte. The trace metal solution consists of 6.15 g / L of magnesium sulfate, 0.5 g / L of manganese sulfate, 1 g / L of sodium chloride, and 0.1 g / L of ferrous sulfate, and the vitamin solution consists of 2 mg / L of biotin, 2 mg / L of folic acid, 10 mg / L of vitamin B6, and 5 mg / L of riboflavin. After sealing the chamber, use a data acquisition instrument to record the voltage data of the MFC. When the voltage data drops rapidly, it indicates that the nutrients in the MFC are exhausted and nutrients need to be added again. After several voltage cycles, if its output voltage can be stable at a relatively high voltage for a long time and the maximum stable voltage of each cycle is close, it indicates that the MFC is successfully started and the biofilm on the electrode material has grown mature.

[0042] (8) Operation of a microbial fuel cell using aged landfill leachate as a substrate

[0043] Replace the anaerobic sludge substrate in the anode chamber with aged landfill leachate, operate the MFC at room temperature and constant pressure, use a data acquisition instrument to record its output voltage, and measure the COD and ammonia nitrogen concentrations of the mixed wastewater before and after the operation starts.

[0044] Example 2

[0045] A new method for electricity generation by treating aged landfill leachate using a Co3O4 / Ni-MOF anode single-chamber MFC, the specific steps are as follows:

[0046] (1) Preparation of Co3O4

[0047] Same as step (1) in Example 1.

[0048] (2) Preparation of the anode catalyst Co3O4 / Ni-MOF

[0049] Same as step (2) in Example 1.

[0050] (3) Electrode pretreatment

[0051] Same as step (3) in Example 1.

[0052] (4) Fabrication of the cathode

[0053] Same as step (4) in Example 1.

[0054] (5) Fabrication of the anode

[0055] Weigh 8 mg of the Ni-MOF catalyst into a 2.5 mL test tube. Measure 300 μL of absolute ethanol, 200 μL of ethylene glycol, and 20 μL of Nafion solution and add them to the test tube. Place the test tube in an ultrasonic cleaner and ultrasonicate for 30 min to make the mixture uniform to obtain a suspension; uniformly drop-coat the suspension on a 2×2 cm carbon cloth and dry it to prepare the anode.

[0056] (6) Construction of a single-chamber microbial fuel cell

[0057] Same as step (6) in Example 1.

[0058] (7) Start-up of a single-chamber microbial fuel cell

[0059] Same as step (7) in Example 1.

[0060] (8) Operation of a microbial fuel cell using aged landfill leachate as a substrate

[0061] Same as step (8) in Example 1.

[0062] Example 3

[0063] A new method for electricity generation by a Co3O4 / Ni-MOF anode single-chamber MFC treating aged landfill leachate, the specific steps are as follows:

[0064] (1) Preparation of Co3O4

[0065] Same as step (1) in Example 1.

[0066] (2) Preparation of the anode catalyst Co3O4 / Ni-MOF

[0067] Same as step (2) in Example 1.

[0068] (3) Electrode pretreatment

[0069] Same as step (3) in Example 1.

[0070] (4) Fabrication of the cathode

[0071] Same as step (4) in Example 1.

[0072] (5) Fabrication of the anode

[0073] Weigh 8 mg of the Co3O4 catalyst into a 2.5 mL test tube. Measure 300 μL of absolute ethanol, 200 μL of ethylene glycol, and 20 μL of Nafion solution and add them to the test tube. Place the test tube in an ultrasonic cleaner and ultrasonicate for 30 min to make the mixture uniform to obtain a suspension; uniformly drop-coat the suspension on a 2×2 cm carbon cloth and dry it to prepare the anode.

[0074] (6) Construction of a single-chamber microbial fuel cell

[0075] Same as step (6) in Example 1.

[0076] (7) Start-up of the single-chamber microbial fuel cell

[0077] Same as step (7) in Example 1.

[0078] (8) Operation of the microbial fuel cell with aged landfill leachate as the substrate

[0079] Same as step (8) in Example 1.

[0080] Example 4

[0081] A new method for power generation by treating aged landfill leachate using a Co3O4 / Ni-MOF anode single-chamber MFC, the specific steps are as follows:

[0082] (1) Preparation of Co3O4

[0083] Same as step (1) in Example 1.

[0084] (2) Preparation of the anode catalyst Co3O4 / Ni-MOF

[0085] Same as step (2) in Example 1.

[0086] (3) Electrode pretreatment

[0087] Same as step (3) in Example 1.

[0088] (4) Fabrication of the cathode

[0089] Same as step (4) in Example 1.

[0090] (5) Fabrication of the anode

[0091] Use the carbon cloth anode prepared in step (3) of Example 1 without drop-coating the catalyst.

[0092] (6) Construction of the single-chamber microbial fuel cell

[0093] Same as step (6) in Example 1.

[0094] (7) Start-up of the single-chamber microbial fuel cell

[0095] Same as step (7) in Example 1.

[0096] (8) Operation of the microbial fuel cell with aged landfill leachate as the substrate

[0097] Same as step (8) in Example 1.

[0098] Experimental results

[0099] The power generation performance and degradation performance of the single-chamber MFC with the Co3O4 / Ni-MOF anode prepared in Example 1 for treating aged landfill leachate are the best.

[0100] Figure 2 The XRD diffraction patterns of Co3O4, Ni-MOF, and Co3O4 / Ni-MOF are shown in the figure. It can be seen from the XRD pattern of Co3O4 that characteristic diffraction peaks belonging to Co3O4 appear at 2θ = 31.33°, 36.89°, and 44.85°, corresponding to the crystal planes of (220), (311), and (400) respectively. The peak shapes are sharp and there are no impurity peaks, which is consistent with the Co3O4 standard card PDF#43-1003. From the XRD pattern of Ni-MOF, Ni-MOF has strong diffraction peaks, and strong diffraction peaks of Ni-MOF and Co3O4 are observed in the XRD diffraction pattern of Co3O4 / Ni-MOF, indicating that the composite sample Co3O4 / Ni-MOF is successfully prepared.

[0101] For the MFC system started and operated with different anode catalysts, the curve of the output voltage changing with time is as Figure 3 shown. When the anode catalyst is Co3O4 / Ni-MOF, the maximum stable output voltage of the battery is 524 mV, which is 1.27 times, 2.38 times, and 3.74 times that of the single samples Ni-MOF, Co3O4, and the blank sample respectively. The maximum power density of the anode catalyst Co3O4 / Ni-MOF is up to 882 mW / m 2 ( Figure 4 )), which is 1.36 times, 2.75 times, and 11.45 times that of the single samples Ni-MOF, Co3O4, and the blank sample respectively.

[0102] Tests show that when the anode catalysts are the blank sample, Co3O4, Ni-MOF, and Co3O4 / Ni-MOF respectively, the COD removal rates of the MFC system for aged landfill leachate are 29.6%, 31.4%, 32.4%, and 35.3% respectively; the ammonia nitrogen removal rates are 37.4%, 38.7%, 46.9%, and 48.5% respectively. It shows that the constructed single-chamber microbial fuel cell has a good removal effect on the pollutants in aged landfill leachate.

Claims

1. A new method for electricity generation by treating aged landfill leachate using a Co3O4 / Ni-MOF anode single-chamber MFC, characterized in that, It includes the following steps: (1) Preparation of Co3O4 Weigh 1.46 g of cobalt nitrate hexahydrate, 3 g of urea, and 0.74 g of ammonium fluoride, dissolve them in 70 mL of distilled water, transfer them to a 100 mL autoclave after magnetic stirring for 1 h, and carry out hydrothermal reaction at 120 °C for 12 h; naturally cool to room temperature, filter, wash the filter cake by low-speed centrifugation with distilled water, then place it in an oven and dry at 60 °C for 12 h, grind it and transfer it to a muffle furnace, calcine it at 350 °C for 2 h, cool to room temperature, and then grind to obtain black powder Co3O4; (2) Preparation of anode catalyst Co3O4 / Ni-MOF Measure 20 mL of DMF, 20 mL of absolute ethanol, and 20 mL of distilled water into a 100 mL beaker, stir magnetically to obtain a homogeneous solution A; weigh 0.88 g of cobalt nitrate hexahydrate, 0.24 g of terephthalic acid, and 1.2 g of polyvinylpyrrolidone and add them to solution A in sequence, continue to stir for 30 min to obtain solution B; weigh 0.362 g of Co3O4 powder and add it to solution B, stir magnetically for 30 min to obtain a mixed solution; transfer the mixed solution to a 100 mL autoclave, place it in an oven and carry out hydrothermal reaction at 150 °C for 10 h; naturally cool to room temperature, filter, wash the filter cake by alternating high-speed centrifugation with distilled water and absolute ethanol for 3 times, then place it in a vacuum drying oven and dry at 80 °C for 12 h to obtain Co3O4 / Ni-MOF composite catalyst material; without adding Co3O4, prepare Ni-MOF catalyst according to the above method; (3) Construction and startup of single-chamber MFC Select plexiglass to construct a single-chamber MFC device. The device is shown in Figure 1. The device is of a three-section design. The cathode side has a central circular hollow design to enable the air cathode to fully contact with air; the chamber part has a cylindrical hollow design for containing liquid; the other side is solid and the interior of the chamber can be observed; each section is connected by a rubber pad with a hollow middle to play a role in sealing and waterproofing. The effective volume of the device is 50 mL. The cathode and anode use 0.5 cm titanium wires to form a closed circuit with an external resistor of 1000 Ω, and a data acquisition card is connected in parallel at both ends of the external resistor to record the voltage data during the operation of the MFC; Use the cultivated anaerobic sludge as the substrate in the anode chamber to start the microbial fuel cell; The reactor operates in an intermittent mode; after three cycles of operation, the output voltage of the MFC can remain stable for a long time and the maximum output voltage of each cycle is close, then the startup of the MFC is completed; (4) Operation of microbial fuel cell with aged landfill leachate as substrate Replace the anaerobic sludge substrate in the anode chamber with aged landfill leachate, operate the MFC at room temperature and constant pressure, and use a data acquisition instrument to record its output voltage; Measure the COD and ammonia nitrogen concentrations of the mixed wastewater before and after the operation starts.

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