An artificial wetland-microbial fuel cell coupling device

Abstract

This invention discloses an artificial wetland-microbial fuel cell coupling device. The device consists of an plexiglass tank and, from bottom to top, a bottom layer, an anode layer, an intermediate layer, and a cathode layer arranged therein. The bottom layer is filled with quartz sand or ceramsite. The anode layer has a cage as a current collector, and a biofilm composite electrode is fixedly installed on the surface of the cage. The intermediate layer is filled with quartz sand or ceramsite. The cathode layer is formed by placing activated carbon in a mesh bag. An overflow weir of 2-3 cm is provided on the upper surface of the cathode layer. The bottom layer, anode layer, intermediate layer, and cathode layer are all provided with side outlet holes. The bottom surface of the bottom layer has a water inlet hole, and the top surface of the cathode layer has a top outlet hole. The side outlet holes, water inlet holes, and top outlet holes are all connected to rubber hoses. This invention effectively improves pollutant removal efficiency, reduces the operating cost of biofuel cells, and is easy to mass-produce.

Description

Technical Field

[0001] This invention belongs to the field of constructed wetland-microbial fuel cell technology, specifically a constructed wetland-microbial fuel cell coupling device based on a biofilm composite three-dimensional electrode. Background Technology

[0002] Constructed wetlands (CWs) mimic the structure and function of natural wetlands, utilizing the synergistic effects of packing materials, plants, and microorganisms. This system simultaneously engages in physical, chemical, and biological processes. Through the physicochemical actions of the packing materials—interception, filtration, co-precipitation, adsorption, complexation reactions, and ion exchange—as well as the absorption by plants and the decomposition by microorganisms, it achieves highly efficient wastewater purification. This technology boasts advantages such as low investment cost, simple process, and good treatment effect, and is widely used for the treatment of domestic sewage, industrial wastewater, polluted surface water, landfill leachate, and wastewater treatment plant effluent. Microbial fuel cell (MFC) technology uses microorganisms as catalysts to decompose organic matter in wastewater into electrical energy, simultaneously achieving pollutant removal and energy recovery.

[0003] The constructed wetland coupled with microbial fuel cell (CW-MFC) system is a novel wastewater treatment process based on bioelectrochemical technology. The upper part of the CW is an aerobic environment, while the lower part is an anaerobic environment. Significant redox potential (ORP) gradients exist at different heights within the CW, providing the necessary ORP gradient for the MFC. Furthermore, root exudates from the plants within the CW provide chemical energy to the MFC. The introduction of the MFC forms a closed loop, and the current enhances the activity of the microorganisms, resulting in more efficient pollutant removal. Studies have shown that this system can effectively improve the degradation rate of pollutants and enhance power generation performance. Currently, low power output, high construction costs, and low nitrogen removal rates are the main obstacles to the widespread application of CW-MFC.

[0004] The anode region serves as both a carrier for microbial attachment and a primary site for anaerobic reactions and total nitrogen degradation. Anode materials play a crucial role in the power output and COD, total nitrogen, and ammonia nitrogen removal performance of CW-MFCs. Developing high-performance anode materials with large specific surface area, good conductivity, high biocompatibility, and large biomass loading capacity is one of the main strategies for improving the energy recovery efficiency and pollutant removal efficiency of CW-MFCs.

[0005] Three-dimensional anode materials can accommodate more microbial growth than one-dimensional and two-dimensional materials. These microorganisms loaded on the electrode have shorter electron transport paths than microorganisms suspended in solution. However, since the microbial cell membrane is non-conductive, multi-layered stacked biological cells are not conducive to improving electron transport efficiency. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide an artificial wetland-microbial fuel cell coupling device.

[0007] An artificial wetland-microbial fuel cell coupling device, the device comprising an plexiglass tank and, from bottom to top, a bottom layer, an anode layer, an intermediate layer, and a cathode layer arranged therein;

[0008] The bottom layer is filled with quartz sand or ceramsite; the anode layer is provided with a cage as a current collector, and a biofilm composite electrode is fixedly installed on the surface of the cage to form a three-dimensional structure; the middle layer is filled with quartz sand or ceramsite; the cathode layer is formed by filling activated carbon into a mesh bag; and a 2-3cm overflow weir is provided on the upper surface of the cathode layer.

[0009] A perforated plexiglass plate is used for support and separation between the bottom layer and the anode layer, between the anode layer and the intermediate layer, and between the intermediate layer and the cathode layer.

[0010] The bottom layer, anode layer, intermediate layer and cathode layer are all provided with side water outlet holes, the bottom of the bottom layer is provided with a water inlet hole, and the top of the cathode layer is provided with a top water outlet hole. The side water outlet holes, water inlet holes and top water outlet holes are all connected to the rubber hose.

[0011] In the anode layer, the cage is made of stainless steel mesh, and a biofilm composite electrode is attached to each surface of the cage by binding titanium wire.

[0012] As a further improvement, the biofilm composite electrode is an HCCF composite anode with a reduced graphene oxide biofilm loaded on its surface, where HCCF is a hierarchical porous carbon-modified composite carbon felt.

[0013] As a further improvement, the HCCF composite anode with a reduced graphene oxide biofilm loaded on its surface is prepared by the following steps:

[0014] 10 mL of sludge microbial suspension was transferred to a container containing 66 mL of sodium acetate culture medium to form an electrolyte. The sodium acetate culture medium contained graphene oxide, and the volume ratio of sludge microbial suspension to sodium acetate culture medium was 1:6-7.

[0015] A hierarchical porous carbon-modified composite carbon felt (HCCF) was immersed in an electrolyte to serve as a supporting substrate for the formation of the anode biofilm. Under sealed conditions, the mixture was stirred at 50 rpm for 40-50 hours using a magnetic stirrer, allowing graphene oxide and microorganisms to gradually adhere to the HCCF. When the electrolyte changed from brown to black and formed polymers attached to the HCCF surface, it indicated that the graphene oxide on the electrode surface was reduced to rGO by microorganisms, which is black and water-insoluble. After continuous stirring for 6-8 days, an HCCF composite anode with a biofilm of reduced graphene oxide loaded on its surface was obtained.

[0016] As a further improvement, the sodium acetate culture medium consists of a phosphate buffer solution and a graphene oxide solution in a volume ratio of 12-16:1.

[0017] As a further improvement, the sodium acetate culture medium contains a 0.05 M phosphate buffer solution, and contains 1.0-1.5 g L of [unspecified ingredient] in the 0.05 M phosphate buffer solution. -1 Sodium acetate solution, 12.5-13.0 mL / L -1 Mineral solution and 12.5-13.0 mL -1 Vitamin solution.

[0018] As a further improvement, the hierarchical porous carbon-modified composite carbon felt HCCF is prepared using the following steps:

[0019] The carbon felt was cut to a preset size, cleaned and dried to obtain a blank control carbon felt electrode, named CF.

[0020] Weigh 0.47-0.50g NiCl2 and 2-2.5g PVA-1799 and add them to 20-25mL 1M KOH solution. Heat in a water bath at 90-100℃ with stirring. A uniform hydrogel will form after 25-35 minutes.

[0021] Then the blank carbon felt is completely immersed in the hydrogel, allowing the blank carbon felt to absorb the hydrogel.

[0022] Freeze for 4-5 hours, then freeze-dry for 20-26 hours; then anneal in nitrogen at 800-850℃ for 2-3 hours.

[0023] Finally, the impurities were removed by soaking in 3M hydrochloric acid for 10-15 hours, and the mixture was washed with deionized water until the pH was neutral and then dried to obtain a hierarchical porous carbon-modified composite carbon felt, named HCCF.

[0024] As a further improvement, when cleaning the carbon felt, use anhydrous ethanol and deionized water for ultrasonic cleaning for 20-25 minutes respectively.

[0025] As a further improvement, the height of the bottom layer is the same as the height of the middle layer, and the height of the anode layer is less than the height of the bottom layer, and the height of the cathode layer is less than the height of the anode layer.

[0026] As a further improvement, the acrylic bucket is a square bucket with the same length and width, and the height of the acrylic bucket is greater than its length.

[0027] Compared with the prior art, the present invention has the following beneficial technical effects:

[0028] Using a three-dimensional electrode composite with a growth membrane as a substrate, the surface roughness of the electrode is improved through methods such as hierarchical porous carbon composites. Then, a three-dimensional composite anode encapsulating microorganisms in reduced graphene is constructed using in-situ assembly technology. On one hand, the three-dimensional electrode can accommodate more microbial attachment, and the rough surface can form more microbial attachment sites. The in-situ composite of reduced graphene can encapsulate the microorganisms to form a highly conductive layer, thereby improving the electron transfer efficiency of the multi-layered stacked microorganisms. The formation of the three-dimensional composite biofilm also facilitates the formation of a micro-anaerobic reaction zone in the anode layer, allowing total nitrogen to decompose organic matter under the action of denitrifying bacteria while simultaneously converting nitrogen into nitrogen gas to complete denitrification. Therefore, the industrial wetland-microbial fuel cell device developed based on this anode has high pollutant removal efficiency and power generation performance, showing promising application prospects. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the main structure of the device of the present invention;

[0030] Figure 2 A schematic diagram of the original carbon felt CF;

[0031] Figure 3 This is a schematic diagram of SEM of HCCF in this invention;

[0032] Figure 4 The nitrogen adsorption-desorption isotherm of the sample prepared in this invention and the original carbon felt CF;

[0033] Figure 5 The BJH pore volume distribution diagrams of the sample prepared in this invention and the original carbon felt CF are shown.

[0034] Figure 6 CV plots for different samples;

[0035] Figure 7 This is a schematic diagram of the output voltage during the startup phase of the device of the present invention and prior art devices;

[0036] Figure 8 This is a schematic diagram showing the power density output of the device of the present invention and existing technology devices under different external resistance conditions.

[0037] Figure reference numerals: bottom layer 1, anode layer 2, intermediate layer 3, cathode layer 4, overflow weir 5, side outlet hole 6, inlet hole 7, top outlet hole 8. Detailed Implementation

[0038] To further understand the features, technical means, and specific objectives and functions achieved by the present invention, the present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments.

[0039] Example 1

[0040] refer to Figure 1 As shown, an artificial wetland-microbial fuel cell coupling device is provided. The device consists of an plexiglass tank and, from bottom to top, a bottom layer 1, an anode layer 2, an intermediate layer 3, and a cathode layer 4 arranged therein. The plexiglass tank is 30cm long and wide, and 50cm high. The bottom layer 1 and the intermediate layer 3 are both 20cm high, the anode layer 2 is 10cm high, and the cathode layer 4 extends upwards to a height of 3.5cm.

[0041] The anode layer is provided with a cage as a current collector, and a biofilm composite electrode is fixedly installed on the surface of the cage to form a three-dimensional structure; the middle layer is filled with quartz sand or ceramsite; the cathode layer is formed by filling activated carbon into a mesh bag; an overflow weir of 2-3 cm is provided on the upper surface of the cathode layer; the cage of the anode layer is formed by welding stainless steel mesh, and the biofilm composite electrode is bound and fixed on the surface of the stainless steel mesh with titanium wire.

[0042] A perforated plexiglass plate is used for support and separation between the bottom layer 1 and the anode layer 2, between the anode layer 2 and the intermediate layer 3, and between the intermediate layer 3 and the cathode layer 4.

[0043] The bottom layer 1, anode layer 2, intermediate layer 3, and cathode layer 4 are all equipped with side water outlets 6, the bottom of the bottom layer 1 is equipped with a water inlet 7, and the top of the cathode layer 4 is equipped with a top water outlet 8. The side water outlets, water inlet, and top water outlet are all connected to rubber hoses. Simulated wastewater flows through the device from bottom to top using a peristaltic pump.

[0044] Example 2

[0045] The biomembrane composite electrode needs to be prepared accordingly.

[0046] First, a three-dimensional biomembrane electrode is prepared:

[0047] The carbon felt was cut into 2cm×3cm×5mm pieces, ultrasonically cleaned with anhydrous ethanol and deionized water for 20 minutes each, and dried to obtain a blank control carbon felt electrode, named CF.

[0048] 0.47 g NiCl2 and 2 g PVA-1799 were weighed and added to 20 mL of 1 M KOH solution. The mixture was heated and stirred in a water bath at 95 °C for 30 minutes to form a uniform hydrogel. The blank carbon felt was then completely immersed in the hydrogel to allow it to fully absorb the hydrogel. The mixture was frozen for 4 hours and then freeze-dried for 24 hours. It was then annealed in nitrogen at 800 °C for 2 hours. Finally, it was soaked in 3 M hydrochloric acid for 12 hours to remove impurities, washed with deionized water until the pH was neutral, and then dried to obtain a hierarchical porous carbon-modified composite carbon felt, named HCCF.

[0049] Of course, in addition to carbon felt, other biomass, commercial three-dimensional materials, or other three-dimensional support materials, as well as their further modified three-dimensional materials, are all within the scope of electrode support materials referred to in this invention.

[0050] The three-dimensional reduced graphene oxide composite biofilm anode was constructed using an in-situ self-assembly method.

[0051] Specifically, 10 mL of sludge microbial suspension was transferred to a container containing 66 mL of sodium acetate culture medium, and then 4 mL of graphene oxide (GO) solution (5 mg / mL) was added. The sodium acetate culture medium contained 0.05 M phosphate buffer solution, and the 0.05 M phosphate buffer solution contained 1.0-1.5 g L / L of... -1 Sodium acetate solution, 12.5-13.0 mL / L -1 Mineral solution and 12.5-13.0 mL L -1 Vitamin solution.

[0052] HCCF was immobilized in an electrolyte using titanium wire, serving as a support substrate for the formation of the anode biofilm. Under sealed conditions, the mixture was slowly stirred at 50 rpm for 48 hours using a magnetic stirrer, allowing graphene oxide and microorganisms to gradually adhere to the HCCF. When the electrolyte gradually changed from brown to black and formed polymers on the HCCF surface, it indicated that GO was reduced to rGO (black, water-insoluble) by microorganisms on the electrode surface. After continuous stirring for 7 days, an HCCF composite anode with a surface-loaded reduced graphene oxide biofilm was obtained, named mrGO / HCCF.

[0053] Example 3

[0054] Electrochemical performance was tested using cyclic voltammetry (CV) in a three-electrode system, with Ag / AgCl as the reference electrode, mrGO / HCCF as the working electrode, and Pt as the counter electrode. EIS measurements were performed at open-circuit potential, with a frequency range of 0.05–105 Hz and an amplitude of 10 mV. The CV scan potential range was -0.6–0.6 V (relative to Ag / AgCl), and the electrolyte was sodium acetate medium (0.05 M phosphate buffer containing 1.0 g L). -1 Sodium acetate solution, 12.5 mL -1 Mineral solution and 12.5 mL L -1 (Vitamin solution), scan rate 5mV / s.

[0055] For ease of comparison, the electrochemical performance of several different electrode samples was tested. Study on the electrochemical performance of blank carbon felt anode.

[0056] 1. Preparation of blank carbon felt anode

[0057] Commercial carbon felt (or other three-dimensional materials) were cut into 2cm×3cm×5mm sizes, ultrasonically cleaned with anhydrous ethanol and deionized water for 20 minutes each, and dried to obtain a blank control carbon felt electrode, named CF.

[0058] II: Preparation of Reduced Graphene / Biofilm / Carbon Felt Anode

[0059] The three-dimensional reduced graphene oxide composite biofilm anode is constructed using an in-situ self-assembly method, wherein the electrode is CF, that is, CF is immersed in the electrolyte. Everything else is the same as in this invention, except that the electrode is CF.

[0060] 3. Testing of the electrochemical performance of reduced graphene / biofilm carbon felt anodes

[0061] A battery device was fabricated using mrGO / CF as the electrode.

[0062] Sample of this invention: Performance testing of an artificial wetland-microbial fuel cell device based on a biofilm composite anode.

[0063] The HCCF prepared in this invention is used to assemble a battery-coupled CW-MFC device.

[0064] The CW-MFC device is primarily a 30cm x 30cm rectangular plexiglass tank, 50cm high, divided into a bottom layer, an anode layer, a middle layer, and a cathode layer. The bottom layer is 20cm high and uses quartz sand. The anode layer is 10cm high and uses a stainless steel cage (25cm x 25cm x 10cm) welded from stainless steel mesh as a current collector. 158 pieces of HCCF are sequentially bound to the stainless steel surface with titanium wire, forming a rectangular three-dimensional structure. The middle layer is 20cm high and uses the same packing as the bottom layer. The cathode layer is 3.5cm high, with activated carbon placed in a stainless steel mesh bag. A 3cm overflow weir is provided at the top. Each layer is supported and separated by perforated plexiglass plates. Each layer has an outlet, connected to a hose and clamped in place. There is an inlet at the bottom and an outlet at the top, all connected by long hoses. Simulated wastewater flows through the device from bottom to top using a peristaltic pump.

[0065] Start-up of the apparatus: Sludge was taken from the sludge thickening tank of Niushan Wastewater Treatment Plant in Dongguan City. After being sealed and cultured for one month, it was diluted and injected into the anode chamber. The peristaltic pump was turned on to allow water to enter, and the apparatus began operation. The influent COD concentration was set to 1500 mg / L; the total nitrogen concentration was set to 700 mg / L; and the ammonia nitrogen concentration was set to 400 mg / L. The voltage of the apparatus under a constant load of 1000 Ω external resistance was continuously recorded using a Newwell battery testing system. Effluent samples were collected daily for monitoring, and fresh influent was added daily. When the voltage displayed on the electrochemical instrument tended to stabilize, the apparatus was considered to have started up successfully, and the sludge had been acclimated. At this point, experiments were conducted under different operating conditions.

[0066] Detection of pollutant indicators: COD was determined by rapid digestion spectrophotometry (HJ / T 399-2007); ammonia nitrogen concentration was determined by Nessler's reagent spectrophotometry (GB 7479-87); and total nitrogen concentration was determined by alkaline potassium persulfate ultraviolet spectrophotometry (GB11894-1989).

[0067] Performance of an artificial wetland-microbial fuel cell device based on a blank carbon felt anode.

[0068] The apparatus and startup are the same as in Example 3, except that the anode material is different; blank carbon felt (CF) is used as the anode material.

[0069] Figure 2 and 3 The images provided are SEM images of CF and HCCF materials at 1000x magnification. As can be seen, Figure 2 The blank carbon felt surface shown is flat and smooth; while Figure 3The HCCF material shown exhibits a large number of porous carbon particles on the surface of the carbon felt after treatment with organic-inorganic hybrid gel. These particles encapsulate most of the carbon fibers and fill the gaps between them, forming a loose and porous structure. This rough surface structure is conducive to the adhesion of microorganisms to form a biofilm, thereby promoting anodic denitrification and COD removal.

[0070] Figure 4 and 5 The nitrogen adsorption-desorption isotherm (77 K) and pore size distribution are shown for CF and HCCF material samples. The results show that... Figure 4 The BET specific surface area of ​​the blank carbon felt (CF) shown is 1.17 m². 2 / g, and Figure 5 The specific surface area of ​​HCCF shown is 126.84 m². 2 / g, which is 108.4 times that of CF, indicating that the specific surface area of ​​the treated material was significantly improved. From Figure 4 The isotherms of the two materials show that CF material is Type-II (non-porous), while HCCF material is Type-I (porous). This means that CF is non-porous, but after activation, it forms HCCF with a rich porous structure. The pore size distribution diagram shows that the cumulative desorption pore volume of HCCF is 0.075 cm³. 3 / g is the original size (0.001cm). 3 The carbon material exhibits a 75-fold increase in adsorption capacity ( / g), with a significantly increased number of micropores (less than 2 nm) and mesopores (2–50 nm). The average adsorption pore diameter is 2.38 nm, with the largest number of micropores (1.1 nm) and mesopores (3.9 nm). This hierarchical pore structure, composed of micropores and mesopores, can facilitate mass transfer and diffusion, and also increase the double-layer capacitance of the carbon material. Previous studies have shown that the presence of double-layer capacitance can effectively improve the power density of the device.

[0071] Figure 6 This is a CV diagram showing the formation of rGO biofilms by different types of electrodes in sodium acetate culture medium. The inset shows electrodes suspended in a solution containing mixed bacteria from wastewater, sodium acetate culture medium, and a brown graphene oxide suspension. After magnetic stirring for a period of time, the brown graphene was reduced to black rGO and attached to the electrode along with the microorganisms. This indicates that negatively charged microorganisms attract and encapsulate the positively charged graphene oxide on the electrode surface, resulting in in-situ polymerization and self-assembly to form a biofilm composite electrode (abbreviated as mrGO) coated with a "conductive" rGO layer. Figure 6It is evident that the peak current density of both CF and HCCF electrodes significantly increased after the growth of mrGO, indicating that the formation of the mrGO composite biofilm is beneficial for constructing a high-performance anode. Calculations show that, with the same biofilm loading, the CV curve area of ​​the modified mrGO / HCCF electrode is 8.9 times that of the unmodified mrGO / CF. Furthermore, the CV curve area of ​​the modified mrGO / HCCF electrode with superimposed composite reduced graphene biofilm is 150 times higher than that of the original carbon felt CF. This further demonstrates that the rough and loose porous structure formed on the surface of the material after porous carbon composite is more conducive to the formation of a highly active biofilm, thereby significantly promoting the improvement of electrochemical performance.

[0072] Figure 7 The voltage output of CW-MFC devices with different anodes during the start-up period is given (hydraulic residence time is 1.5 days, external resistance is 1000Ω). It can be seen that the voltage of CW-MFC battery with HCCF as anode steadily increases over time, and gradually stabilizes at about 500mV when the start-up time is 100 hours. Its voltage output is far superior to that of CW-MFC device with blank carbon felt.

[0073] Table 1 shows the average removal efficiencies of the two devices for COD, ammonia nitrogen, and total nitrogen under different operating conditions (each condition was tested continuously for 10 days, and the average value was calculated). It can be seen that the modified HCCF has a higher average removal efficiency for pollutants than the blank CF under all conditions. This may be because the microbial adhesion performance of the anode is better after treatment, which is more conducive to the formation of biofilm and shortens the electron transfer path and mass transfer diffusion, which is more conducive to the catalytic oxidation of organic matter and improves the COD removal rate. The increase in current density promotes the utilization and conversion of nitrogen source by nitrifying and denitrifying bacteria in the device, making its treatment effect on ammonia nitrogen and total nitrogen more significant.

[0074] Table 1. Removal efficiency of CW-MFC unit for COD, ammonia nitrogen and total nitrogen under different operating conditions.

[0075]

[0076] Compared with the 1000Ω external resistance of the load in the closed-circuit state, the COD removal rate of the device in the open-circuit state is not much different, but the ammonia nitrogen removal rate is reduced. This may be because the lack of directional flow of electrons in the open-circuit state inhibits the nitrification of ammonia nitrogen, resulting in a decrease in the denitrification effect.

[0077] The power density variation of CW-MFC under different resistances is as follows: Figure 8 As shown, the power density of HCCF-CW-MFC with gel-activated carbon felt as the anode is significantly higher than that of CF-CW-MFC with blank carbon felt as the anode, with the maximum power density reaching a maximum of 0.66 mW / m at 330 Ω.3 .

[0078] Furthermore, the results for different hydraulic retention times (HRT) (Table 1) show that the decontamination performance of the device is generally better when the HRT is 3 than when it is 2. This indicates that the extended HRT increases the contact time between microorganisms and organic wastewater, thereby enhancing the denitrification of microorganisms in the anaerobic zone and improving the total nitrogen removal rate. A longer HRT allows nitrogen sources more time to diffuse into the aerobic cathode layer. Under suitable dissolved oxygen conditions, the nitrogen sources are nitrified by aerobic nitrifying bacteria, thus promoting the ammonia nitrogen removal rate.

[0079] Therefore, the CW-MFC device based on HCCF biofilm anode has better power density, power output, and removal efficiency of COD, ammonia nitrogen, and total nitrogen, making it a low-cost and high-efficiency CW-MFC device.

[0080] It should be noted that the above description is not intended to limit the present invention. Any obvious substitutions without departing from the inventive concept of the present invention are within the protection scope of the present invention.

Claims

1. An artificial wetland-microbial fuel cell coupling device, characterized in that, The device consists of an plexiglass barrel and, from bottom to top, a bottom layer, an anode layer, an intermediate layer, and a cathode layer arranged therein; The bottom layer is filled with quartz sand or ceramsite; the anode layer is provided with a cage as a current collector, and a biofilm composite electrode is fixedly installed on the surface of the cage to form a three-dimensional structure; the middle layer is filled with quartz sand or ceramsite; the cathode layer is formed by filling activated carbon into a mesh bag; and a 2-3cm overflow weir is provided on the upper surface of the cathode layer. A perforated plexiglass plate is used for support and separation between the bottom layer and the anode layer, between the anode layer and the intermediate layer, and between the intermediate layer and the cathode layer. The bottom layer, anode layer, intermediate layer and cathode layer are all provided with side water outlet holes, the bottom of the bottom layer is provided with a water inlet hole, and the top of the cathode layer is provided with a top water outlet hole. The side water outlet holes, water inlet holes and top water outlet holes are all connected to the rubber hose. The biofilm composite electrode is an HCCF composite anode with a reduced graphene oxide biofilm loaded on its surface. HCCF is a hierarchical porous carbon-modified composite carbon felt. The HCCF composite anode with a reduced graphene oxide biofilm loaded on its surface is prepared through the following steps: 10 mL of sludge microbial suspension was transferred to a container containing 66 mL of sodium acetate culture medium to form an electrolyte. The sodium acetate culture medium contained graphene oxide, and the volume ratio of sludge microbial suspension to sodium acetate culture medium was 1:6-7. A hierarchical porous carbon-modified composite carbon felt (HCCF) was immersed in an electrolyte to serve as a supporting substrate for the formation of the anode biofilm. Under sealed conditions, the mixture was stirred at 50 rpm for 40-50 hours using a magnetic stirrer, allowing graphene oxide and microorganisms to gradually attach to the HCCF. When the electrolyte changed from brown to black and a polymer formed on the HCCF surface, it indicated that the graphene oxide had been reduced to rGO by microorganisms on the electrode surface, resulting in a black and water-insoluble substance. Stirring was continued for 6-8 days to obtain an HCCF composite anode with a surface-loaded reduced graphene oxide biofilm. The sodium acetate culture medium consisted of a phosphate buffer solution and a graphene oxide solution at a volume ratio of 12-16:

1. The sodium acetate culture medium contained 0.05 M phosphate buffer solution and 1.0-1.5 g L of [unspecified substance] in the 0.05 M phosphate buffer solution. -1 Sodium acetate solution, 12.5-13.0 mL / L -1 Mineral solution and 12.5-13.0 mL L -1 Vitamin solution; The hierarchical porous carbon-modified composite carbon felt HCCF was prepared using the following steps: The carbon felt was cut to a preset size, cleaned and dried to obtain a blank control carbon felt electrode, named CF. Weigh 0.47-0.50g NiCl2 and 2-2.5g PVA-1799 and add them to 20-25mL 1M KOH solution. Heat in a water bath at 90-100℃ with stirring. A uniform hydrogel will form after 25-35 minutes. Then the blank carbon felt is completely immersed in the hydrogel, allowing the blank carbon felt to absorb the hydrogel. Freeze for 4-5 hours, then freeze-dry for 20-26 hours; then anneal in nitrogen at 800-850℃ for 2-3 hours. Finally, the impurities were removed by soaking in 3M hydrochloric acid for 10-15 hours, and the mixture was washed with deionized water until the pH was neutral and then dried to obtain a hierarchical porous carbon-modified composite carbon felt, named HCCF.

2. The constructed wetland-microbial fuel cell coupling device according to claim 1, characterized in that, In the anode layer, the cage is made of stainless steel mesh, and a biofilm composite electrode is attached to each surface of the cage by titanium wire.

3. The constructed wetland-microbial fuel cell coupling device according to claim 2, characterized in that, When cleaning carbon felt, use anhydrous ethanol and deionized water for ultrasonic cleaning for 20-25 minutes respectively.

4. The constructed wetland-microbial fuel cell coupling device according to claim 3, characterized in that, The bottom layer has the same height as the middle layer, and the anode layer has a lower height than the bottom layer, while the cathode layer has a lower height than the anode layer.

5. The constructed wetland-microbial fuel cell coupling device according to claim 4, characterized in that, The acrylic bucket is a square bucket, and its length and width are the same, while its height is greater than its length.

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