Coupling device of MEC and MFC with shared electrodes and its application

Abstract

The present invention relates to a coupling device and application of a shared-electrode MFC-MEC, belonging to the field of microbial electrochemistry. This device uses the same-direction superposition of the MEC's external electric field and the MFC's self-generated electric field to alter the single potential distribution in the MFC's anode and cathode regions, strengthening the system's internal electric field strength. This promotes biofilm formation on the MFC anode and improves electron transfer at the electrode / biofilm interface and the biofilm / solution interface, thereby enhancing MFC power generation performance and the co-production of electricity and methane. The present invention also achieves excellent COD removal and Cr(VI) reduction rates, effectively improving the overall performance of the MFC.

Description

Technical Field

[0001] The invention belongs to microbial electrochemistry and relates to a microbial electrolysis cell and a microbial fuel cell. Background Art

[0002] In the following terms, microbial fuel cell is abbreviated as MFC; microbial electrolysis cell is abbreviated as MEC.

[0003] In addition to reducing the consumption of traditional energy sources such as crude oil, natural gas and coal, we are also focusing on eco-friendly technology solutions such as MFC, which uses electrodes to catalyze microorganisms to degrade organic waste and generate electricity. However, the problem is that the theoretical power output of MFC can reach 28W·m -2 The current MFC output efficiency is only 12.8% of its theoretical output power. This loss of over 85% of potential efficiency makes MFCs unsuitable for civilian and industrial applications. To address the issue of low MFC output power, a method for treating dye wastewater has been disclosed. This method utilizes a microbial electrochemical coupling system, connecting an MFC and a MEC in series. The MFC supplies electricity to the dye wastewater within the MEC cathode chamber, degrading the dye wastewater. This invention separates two independent units, but does not couple the externally generated electric field of the MEC with the MFC electric field within the same system. This coupling does not utilize the electric field as an intrinsic link within the system.

[0004] The disorder and complexity of the MFC system, as well as the influence and laws of extracellular electron transfer and the migration of protons and substrates on MFC performance, remain elusive. The reason is that the energy output of the MFC depends on the redox potential distribution between the anode and cathode, which controls the process of extracellular electron transfer and proton migration after the oxidation of organic waste as a substrate. However, the reason that significantly affects the electrode performance and leads to the lower output power of the MFC is the electrochemical reaction between the anode and cathode involving the formation and consumption of protons and electrons, and the electric field driven ion migration formed by the spontaneous conduct of this reaction from the anode to the cathode.

[0005] Similar to the MFC, which has an electric field pointing from the anode to the cathode, the MEC, a reaction device that places the oxidation of organic matter at a lower oxidation potential for hydrogen production or improving methane conversion, also has an electrostatic field. The difference between the two is that the electric field of the former is spontaneously formed by the redox reaction of the reactants on the electrodes, while the electric field of the latter is formed by an externally applied electrolysis voltage. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of the present invention is to construct a coupling device of MEC and MFC with a common electrode to improve the power generation capacity of MFC and treat organic wastewater; at the same time, the purpose of the present invention is to efficiently apply the device to treat high-concentration Cr(VI) wastewater more efficiently to achieve the goals of green environmental protection and high efficiency energy saving.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] (1) Coupling device of MEC and MFC with shared electrodes

[0009] The device comprises a microbial electrolysis cell MEC and a microbial fuel cell MFC. Specifically, the device uses a common anode or a common cathode to superimpose the electric field provided by the MEC power supply and the electric field generated by the MFC in the same direction to form a structural coupling between the MEC and the MFC.

[0010] Furthermore, the coupling device has two modes: a common anode mode and a common cathode mode, wherein:

[0011] a) Common anode mode:

[0012] The anode chamber (14) and the cathode chamber (15) are separated by a proton exchange membrane (8), and the block-shaped graphite sheet in the anode chamber (14) is used as a common anode (16) connected to the positive end of the power supply (13) of the cathode (17) of the MEC in the anode chamber (14) and the parallel end of the load (12) of the cathode (18) of the MFC in the cathode chamber (15);

[0013] b) Common cathode mode:

[0014] An anode chamber (14) and a cathode chamber (15) are separated by a proton exchange membrane (8); two graphite sheets (20, 21) in the anode chamber (14) are separated by an insulating layer (19) and serve as the anode of the MEC and the anode of the MFC respectively; the anode of the MEC and the anode of the MFC are connected to the common cathode (22) of the MEC and the MFC in the cathode chamber through the parallel end of the power supply (13) of the MEC and the load resistor (12) of the MFC;

[0015] The voltage of the MEC power supply (13) is calculated based on the reaction kinetic equilibrium operating conditions according to the Nernst equation.

[0016] Preferably:

[0017] a) the distance between the anode (16) and cathode (17) of the microbial electrolysis cell in the shared anode mode is 3 cm, and the distance between the cathode (18) of the microbial fuel cell is 6 cm;

[0018] b) The insulating layer (19) between the graphite sheets (20, 21) of the microbial electrolysis cell with a common cathode mode as the anode (21) is 0.3 cm thick and has an area of 16 cm 2 The graphite sheets (20, 21) are spaced 5 cm and 5.3 cm apart from the cathode (22), respectively;

[0019] The anodes (16, 20, 21) are 30mm×30mm×2mm graphite electrodes, and the cathodes (17, 18, 22) are 30mm×30mm×0.2mm platinum-plated electrodes. The two electrodes and the Ag / ClAg reference electrode form a three-electrode in-situ test system.

[0020] Preferably, the effective volume of the anode chamber (14) and the cathode chamber (15) is 270 mL.

[0021] Preferably, the voltage of the power supply (13) of the MEC is 0.5V, and the load resistance (12) of the MFC is 2000Ω, so as to ensure the reaction kinetic balance of the microbial fuel cell.

[0022] (2) Application of coupling device between MEC and MFC with shared electrodes

[0023] The acclimated inoculum and anolyte are placed and pumped into the anode chamber (14) respectively to remove COD, and the cathode liquid pumped into the cathode chamber (15) is potassium dichromate solution to reduce Cr(VI).

[0024] Preferably, the inoculum of the anode chamber (14) is 120 g of anaerobic microorganisms, the initial pH value of the inoculum is 6.89, the total solid TS content is 12.36%, and the volatile solid VS content is 7.22%; the anolyte of the anode chamber (14) is 10 g·L -1 of sodium acetate solution;

[0025] The cathode liquid in the cathode chamber (15) is 1 g·L -1 The anolyte and catholyte were pumped by a peristaltic pump at a rate of 2.6 mL min -1 The flow rate is pumped into the anode chamber and cathode chamber respectively, and both the anode liquid and the cathode liquid are circulating.

[0026] Preferably, the device is operated continuously for 720 hours under the insulation condition of a 30°C circulating water bath.

[0027] The present invention has the following experimental results:

[0028] Comparison of experimental results conducted in shared anode mode, shared cathode mode, and uncoupled MFC conditions using the same inoculum, anolyte (sodium acetate solution), and catholyte (potassium dichromate solution), including:

[0029] 1) Both the common anode mode and the common cathode mode exhibited the best operating voltages of 184 mV and 170 mV, respectively, which were 34.3% and 24.1% higher than the 137 mV of the uncoupled MFC.

[0030] Comparison of operating voltages between coupled MEC-MFC power generation system and uncoupled MFC power generation system

[0031]

[0032] 2) The maximum power density in the common anode mode and the common cathode mode is 120.9 mW·m -2 and 72.8 mW·m -2 They are non-coupled MFC (55.6mW·m -2 ). In addition, the total internal resistance of the common anode mode and the common cathode mode is lower than that of the uncoupled MFC.

[0033] Comparison of maximum power density and total internal resistance of three modes

[0034] Common anode Common cathode Uncoupled MFC Maximum power density <![CDATA[120.9mW·m -2 ]]> <![CDATA[72.8mW·m -2 ]]> <![CDATA[55.6mW·m -2 ]]> Total internal resistance 1872.3Ω 2556.2Ω 2884.9Ω

[0035] 3) Oxidation current exists i 共用阴极模式 (-3.298mA) 共用阳极模式 (-2.831mA) 非耦合MFC (-1.875mA), and the anode Tafel slope (k t ) has the same relationship, that is, k t,共用阴极模式 (117.48 mV / dec) <k t,共用阳极模式 (118.12mV / dec) <k t,非耦合MFC (124.42 mV / dec). Meanwhile, the charge transfer internal resistance at the anode-biofilm interface in the shared anode mode and shared cathode mode was 84 Ω and 133 Ω, respectively, which was smaller than the 169 Ω of the uncoupled MFC.

[0036] Oxidation current (i), anodic Tafel slope (k t ) and internal resistance comparison

[0037]

[0038] 4) Compared to the maximum SECM response current of 0.176 nA for MFC, the maximum current values for the shared anode mode and shared cathode mode were 10.06 nA and 9.95 nA, respectively, much higher than those for MFC. Therefore, the MFC biofilm subjected to the electric field provided by the MEC exhibited a stronger extracellular electron transfer capacity.

[0039] ​​Comparison of SECM response current in three modes

[0040]

[0041]

[0042] 5) The Cr(VI) reduction rates of the shared anode mode and shared cathode mode were 70.1% and 68.9%, respectively, both higher than the 62.4% of the non-coupled MFC. The COD removal efficiency and Cr(VI) reduction rate also showed similar effects. The COD removal efficiencies of the shared anode mode and shared cathode mode were 69.2% and 66.3%, respectively, both higher than the 54.8% of the non-coupled MFC.

[0043] Comparison of Cr(VI) reduction rate and COD removal rate among shared anode, shared cathode and MFC modes

[0044] Common anode Common cathode Uncoupled MFC Cr(VI) reduction rate 70.1％ 68.9％ 62.4％ COD removal rate 69.2％ 66.3％ 54.8％

[0045] Therefore, compared with the uncoupled MFC, the present invention has the following beneficial effects:

[0046] (1) The MFC-MEC coupling system with a common electrode provided by the present invention changes the single potential distribution through the vector superposition of the external electric field of the MEC and the self-generated electric field of the MFC, strengthens the internal electric field of the MFC, increases the migration rate of charges at the electrode / biofilm interface and the biofilm / solution interface, increases the output power of the MFC, and realizes the co-production of methane.

[0047] (2) MEC provides an external electric field, which effectively reduces the charge transfer internal resistance and anodic Tafel slope at the electrode / biofilm interface, and provides more redox active sites at the MFC anode biofilm / solution interface, thereby effectively improving the extracellular electron transfer rate.

[0048] (3) The MFC-MEC system constructed using different coupling methods is easy to operate, has a simple structure, high power generation performance, high COD removal rate and Cr(VI) degradation efficiency, and is safe and environmentally friendly.

[0049] This invention is a project supported by the National Natural Science Foundation of China (Project No. 21968038). BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 Schematic diagram of the MFC-MEC coupling device in the shared anode mode of the present invention.

[0051] 1-sampling hole, 2-vent, 3-insulated circulating water outlet, 4-anolyte outlet, 5-water seal, 6-anolyte inlet, 7-circulating water insulation layer, 8-proton exchange membrane, 9-insulated circulating water inlet, 10-catholyte inlet, 11-catholyte outlet, 12-load resistor, 13-power supply, 14-anode chamber, 15-cathode chamber, 16-common anode, 17-MEC cathode, 18-MFC cathode, 19-insulating layer, 20-MFC anode, 21-MEC anode, 22-common cathode

[0052] Figure 2 Schematic diagram of the MFC-MEC coupling device in the common cathode mode of the present invention. Figure 1 correspond.

[0053] Figure 3 Schematic diagram of the electric field vector and charge migration direction of the common anode mode of the present invention. MEC (dashed line) and E MFC (solid lines) represent the electric fields of MEC and MFC, respectively, and the straight lines with arrows represent the vector superposition of the electric fields; H + 、e - and CH3COO - represents the charge and its migration direction; PEM represents the ion exchange membrane, and R is the load resistance.

[0054] Figure 4 Schematic diagram of the electric field vector and charge migration direction of the common cathode mode of the present invention. Figure 3 correspond.

[0055] Figure 5 is the operating voltage across the load of the common anode mode, common cathode mode and uncoupled MFC.

[0056] Figure 6 is the methane content in common anode mode, common cathode mode and non-coupled MEC.

[0057] Figure 7 Polarization curves and power density curves of common anode mode, common cathode mode and non-coupled MFC.

[0058] Figure 8 Cyclic voltammetry curves of electrochemical parameters of common anode mode, common cathode mode and non-coupled MFC.

[0059] Figure 9 Tafel plots of electrochemical parameters of common anode mode, common cathode mode and non-coupled MFC.

[0060] Figure 10Anodic impedance spectra of the electrochemical parameters of common anode mode, common cathode mode and non-coupled MFC.

[0061] Figure 11 This is a high-resolution scanning image of a scanning electrochemical microscope in common anode mode.

[0062] Figure 12 This is a high-resolution scanning image of a scanning electrochemical microscope in common cathode mode.

[0063] Figure 13 This is a scanning electrochemical microscope isometric image of an uncoupled MFC.

[0064] Figure 14 COD degradation rate and Cr(VI) reduction rate of common anode mode, common cathode mode and non-coupled MFC.

[0065] The present invention will be further described below in conjunction with specific embodiments of the present invention. DETAILED DESCRIPTION

[0066] (1) MFC-MEC coupling device of the present invention

[0067] The common structure of the device is:

[0068] The anode chamber 14, cathode chamber 15, and circulating water insulation layer 7 are separated from the cathode chamber 15 by a proton exchange membrane 8. The cathode chamber 15 has a cathode liquid feed port 10 and a discharge port 11 at the bottom; the anode chamber 14 has an anolyte feed port 6 at the bottom, a discharge port 4 in the middle connected to a water seal 5, a sampling port 1 and an exhaust port 2 at the top, and the exhaust port 2 is connected to a gas flow meter and a gas collection bag in sequence; the circulating water insulation layer is arranged around the anode chamber 14 and cathode chamber 15, and has a water inlet 9 at the bottom and a water outlet 3 at the top.

[0069] The effective volume of the anode chamber 14 and cathode chamber 15 of the MFC-MEC coupling device is 270 mL. These chambers are sealed with a sealing cap. A vent 2 is provided in the anode chamber 14 and connected to a gas flow meter and air bag. To eliminate the effects of electrolyte concentration gradients on the reaction system, a 5-L electrolyte transfer container is connected to a peristaltic pump outside each chamber 14 and 15, respectively, to ensure electrolyte recirculation.

[0070] in:

[0071] The device has a common anode mode and a common cathode mode, and its structures are:

[0072] a) If Figure 1 Common anode mode shown:

[0073] In this mode, anode chamber 14 contains a graphite sheet serving as a common anode 16 for the MEC and MFC, and a pure platinum electrode serves as the MEC's cathode 17. Cathode chamber 15 contains a pure platinum electrode serving as the MFC's cathode 18. The positive and negative electrodes of the MEC's power supply 13 are connected to the common anode 16 and MEC's cathode 17, respectively. The common anode 16 is connected to the MFC's cathode 18 via a load resistor 12.

[0074] Since the common anode 16 and the cathode 17 of the MEC are placed in the anode chamber 14, and the cathode of the MFC is placed in the cathode chamber, the MEC is a single chamber and the MFC is a double chamber, the combination of the two obtains an MFC-MEC coupling device in a common anode mode.

[0075] A portion of the protons produced by oxidation at the MFC anode 17 serves as an electron acceptor for the MEC cathode 17, and a portion of the protons is used by the MFC cathode 18 after passing through the proton exchange membrane (PEM). The MEC is a single chamber, while the MFC is a double chamber. Figure 3 As shown, H + 、e - and CH3COO - The equal charges migrate toward the cathode or anode under the vector superposition electric field formed by the EMEC and EMFC.

[0076] Furthermore, the common anode 16 is a 30 mm × 30 mm × 2 mm graphite electrode, the cathodes 17 and 18 are 30 mm × 30 mm × 0.2 mm platinum-plated electrodes, and together with the reference electrode form a three-electrode in-situ test system, and the load resistor 12 is 2000Ω.

[0077] b) If Figure 2 Common cathode mode shown:

[0078] In this model, two graphite sheets separated by an insulating layer 19 in the anode chamber 14 serve as the MEC anode 21 and the MFC anode 20, respectively, forming a "sandwich" composite electrode. In the cathode chamber, a platinum-plated electrode serves as the shared cathode 22 for the MEC and MFC. The insulating layer placed between the MFC anode 21 and the MEC anode 20 is secured with non-conductive adhesive. The negative and positive electrodes of the MEC power supply 13 are connected to the shared cathode 22 and the MEC anode 21, respectively. The shared cathode 22 is connected to the MFC anode 20 via a load resistor 12, resulting in a MFC-MEC coupled system in shared cathode mode.

[0079] The protons produced by oxidation of the MFC anode 20 and the MEC anode 21 are supplied to the common cathode 22 after passing through the proton exchange membrane (PEM). Figure 4 As shown, H + 、e - and CH3COO -The equal charges migrate toward the cathode or anode under the vector superposition electric field formed by the EMEC and EMFC.

[0080] Furthermore, the anodes 20 and 21 are 30 mm × 30 mm × 2 mm graphite electrodes, the common cathode 22 is a 30 mm × 30 mm × 0.2 mm platinum-plated electrode, and together with the reference electrode form a three-electrode in-situ test system, and the load resistor 12 is 2000 Ω.

[0081] Furthermore, the effective volume of the anode chamber 14 and the cathode chamber 15 is 270 mL.

[0082] Furthermore, the voltage of the power supply 13 of the MEC is 0.5V.

[0083] (2) Application of the device of the present invention

[0084] 2.1 Inoculum

[0085] The inoculum was anaerobic sludge after three months of acclimation with pig manure at 30°C, with an initial pH of 6.89, a total solids (TS) content of 12.36%, and a volatile solids (VS) content of 7.22%.

[0086] 2.2 Treatment methods

[0087] (1) Pretreatment: All electrodes were immersed in a 25% H2O2 solution at 50°C for 1 h to remove surface impurities; the proton exchange membrane (Nafion 117, DuPont) was treated in a 5% H2O2 solution at 80°C for 1 h, then immersed in deionized water for half an hour, then immersed in 5% dilute sulfuric acid at 80°C for 1 h, and then immersed in deionized water for half an hour.

[0088] (2) System operation: When the MFC-MEC was started, 120 g of inoculum was inoculated into the anode chamber, nitrogen was introduced for 15 min to remove the air at the top of the anode chamber, and 10 g·L -1 The sodium acetate solution was used as the carbon source. -1 The potassium dichromate solution was used as the cathode electrolyte. From the start, the peristaltic pump was used to pump the electrolyte at a rate of 2.6 mL min -1 Sodium acetate solution and potassium dichromate solution were pumped into the anode chamber 14 and cathode chamber 15, respectively, at a flow rate of 100 rpm. The electrolytes were circulated. The MFC-MEC was operated continuously for 720 h in a 30° C. circulating water bath.

[0089] (3) To ensure the reaction kinetics balance of the MFC, the electrolysis voltage 13 of the MEC is set to 0.5 V and the load resistor 12 of the MFC is set to 2,000 Ω, which are calculated according to the following Nernst equation based on the operating conditions:

[0090]

[0091] Where, E is the battery electromotive force; E θ is the standard cell electromotive force; R is the gas constant, R = 8.3144 J / (mol·K); T is the solution temperature, K; n is the number of electron transfers; F is the Faraday constant, F = 96485 C / mol; r and p are the stoichiometric coefficients of the reactants and products.

[0092] Anode reaction: CH3COO - +4H2O→2HCO - +9H + +8e - (E θ =-0.29V)

[0093] Cathode reaction: Cr2O7 2- +14H + +6e - =2Cr 3+ +7H2O(E θ =1.23V)

[0094] 2.3 System Analysis

[0095] The operating voltage across the load was recorded every 12 hours using a paperless recorder. Polarization curves and power density curves were obtained by voltammetry, and their values were calculated using Ohm's law. Asymptotic curves were measured using scanning electrochemical microscopy (SECM) in penetration mode to characterize biofilm thickness. After the asymptotic curve was completed, the probe crawled 30 μm along the +Z axis, and then contour scanning imaging was performed within an 80 μm × 80 μm area. A 10 μm diameter Pt electrode served as the SECM probe, and the scan rate was 10 μm s. -1 , 0.001mol·L -1 Ferrocene methanol (FcMeOH) was used as the redox mediator; all electrochemical tests were performed in situ at 30 °C. The electrochemical characteristics of the biofilm were determined by cyclic voltammetry (CV) and Tafel plots at 5 mV·S -1 Scan rate measurement; at 10 -2 Hz-10 6Electrochemical impedance spectroscopy (EIS) was performed in the frequency range of 100 Hz, and the solution resistance was compensated by iR. The gas composition was detected by a gas chromatograph (Fuli Company, Zhejiang) using a stainless steel column, and the detection was carried out every 48 h. Diphenylcarbazide was added to the analyte, and the Cr(VI) concentration was measured by UV-visible spectrophotometry, and the cathode reduction rate was calculated. The COD concentration of the anolyte at startup and after 720 h of incubation was measured by a COD online analyzer to calculate the COD removal rate. Finally, the performance of the MFC-MEC was compared with that of the uncoupled MFC and uncoupled MEC.

[0096] (III) Comparison and analysis of experimental results using the same inoculum, anolyte (sodium acetate solution), and catholyte (potassium dichromate solution) in shared anode mode, shared cathode mode, and uncoupled MFC devices

[0097] like Figure 5 As shown, the output voltage of the MEC-MFC power generation system cultivated in electrolyte recirculation mode exhibits a typical continuous distribution. With prolonged cultivation time, the operating voltage first increases and then decreases. The increase in voltage is due to the gradual formation of the anodic biofilm, while the subsequent decrease in voltage is caused by the gradual consumption of substrate and the reduction of Cr(VI). Both the shared anode and shared cathode modes exhibited optimal operating voltages of 184mV and 170mV, respectively, which are 34.3% and 24.1% higher than the 137mV of the uncoupled MFC.

[0098] Comparison of operating voltages between coupled MEC-MFC power generation system and uncoupled MFC power generation system

[0099]

[0100] like Figure 6 As shown in the figure, the common anode mode and the non-coupled MEC showed similar methane contents, with average contents of 63.37% and 64.55%, respectively; the methane content in the common cathode mode was 50.63%, which was because the cathode of the MEC was in the cathode chamber of the MFC-MEC coupling system and the electrolyte was potassium dichromate, while Cr in the standard state was 0. 6+ The reduction potential E θ =1.232V greater than H + The reduction potential E θ =0V,Cr 6+ It is reduced first, so no hydrogen is produced in the cathode chamber, and the gas production in the anode chamber is only equivalent to conventional anaerobic digestion. Therefore, the methane content is lower than that of the shared anode mode and non-coupled MFC system.

[0101] Comparison of average methane content and electron acceptor of MEC cathode in three models

[0102]

[0103] like Figure 7 As shown in the figure, the maximum power density in the common anode mode and the common cathode mode is 120.9 mW·m -2 and 72.8 mW·m -2 They are non-coupled MFC (55.6mW·m -2 ) by 2.17 times and 1.31 times respectively. Furthermore, the total internal resistance in the shared anode and shared cathode modes is 1872.3Ω and 2556.2Ω, respectively, lower than the 2884.9Ω of the uncoupled MFC. In the MFC-MEC coupled system, the MEC provides an additional electric field through an applied voltage, which is the only variable in the entire system. Therefore, coupling the MFC with the MEC effectively improves the MFC's power generation capacity.

[0104] Comparison of maximum power density and total internal resistance of three modes

[0105] Common anode Common cathode Uncoupled MFC Maximum power density <![CDATA[120.9mW·m -2 ]]> <![CDATA[72.8mW·m -2 ]]> <![CDATA[55.6mW·m -2 ]]> Total internal resistance 1872.3Ω 2556.2Ω 2884.9Ω

[0106] like Figure 8 As shown, the oxidation current exists i 共用阴极模式 (-3.298mA) 共用阳极模式 (-2.831mA) 非耦合MFC (-1.875mA) Figure 8 ), and the anodic Tafel slope (k t ) has the same relationship ( Figure 9 ), that is, k t,共用阴极模式 (117.48mV / dec) <k t,共用阳极模式 (118.12mV / dec) <k t,非耦合MFC (124.42 mV / dec). Meanwhile, the charge transfer internal resistance at the anode-biofilm interface in the shared anode mode and shared cathode mode was 84Ω and 133Ω, respectively, which was smaller than the 169Ω of the uncoupled MFC ( Figure 10 ).

[0107] Oxidation current (i), anodic Tafel slope (k t ) and internal resistance comparison

[0108]

[0109] like Figure 11 、 Figure 12 and Figure 13 ​​As shown, the surface current distribution of the biofilm in the uncoupled MFC was more uniform, while the surface current of the biofilm in the shared anode and shared cathode modes fluctuated greatly and had more current peaks, indicating that the electric field of the MEC provided more electrocatalytic active sites for the MFC biofilm. Because the biofilm's response to SECM current is affected by the transfer of electrons across the biofilm, the magnitude of the SECM response current can reflect the biofilm's electron conductivity. The maximum current values in the shared anode and shared cathode modes were 10.06nA and 9.95nA, respectively, much higher than the 0.176nA of the control MFC. Therefore, the MFC biofilm with the MEC providing electric field intervention has a stronger extracellular electron transfer capacity.

[0110] Comparison of SECM response current in three modes

[0111]

[0112] like Figure 14 As shown in the figure, the Cr(VI) reduction rates of the shared anode mode and the shared cathode mode were 70.1% and 68.9%, respectively, both higher than the 62.4% of the non-coupled MFC, while the COD removal efficiency and the Cr(VI) reduction rate also showed similar effects. The COD removal efficiencies of the shared anode mode and the shared cathode mode were 69.2% and 66.3%, respectively, both higher than the 54.8% of the non-coupled MFC.

[0113] Comparison of Cr(VI) reduction rate and COD removal rate among shared anode, shared cathode and MFC modes

[0114] Common anode Common cathode Uncoupled MFC Cr(VI) reduction rate 70.1％ 68.9％ 62.4％ COD removal rate 69.2％ 66.3％ 54.8％

[0115] The above preferred implementation cases only illustrate the technical solutions of the present invention in detail and are not limiting. Those skilled in the art should understand that any simple replacement or modification of the present invention by any person skilled in the art within the technical scope disclosed in the present invention falls within the protection scope and disclosure scope of the present invention.

Claims

1. A coupling device for a MEC and a MFC with a common electrode, comprising a microbial electrolysis cell MEC and a microbial fuel cell MFC, characterized in that: The device uses a common anode or a common cathode to form a structural coupling between the MEC and the MFC by superposing the electric field provided by the MEC power supply and the MFC self-generated electric field in the same direction. The coupling device has two modes: a common anode mode and a common cathode mode, wherein: a) Common anode mode: The anode chamber (14) and cathode chamber (15) are separated by a proton exchange membrane (8), and the block graphite sheet in the anode chamber (14) is used as a common anode (16) connected to the positive end of the power supply (13) of the cathode (17) of the MEC in the anode chamber (14) and the parallel end of the load (12) of the cathode (18) of the MFC in the cathode chamber (15); b) Common cathode mode: An anode chamber (14) and a cathode chamber (15) are separated by a proton exchange membrane (8), and two graphite sheets (20, 21) in the anode chamber (14) are separated by an insulating layer (19) to serve as the anode of the MEC and the anode of the MFC respectively. The anode of the MEC and the anode of the MFC are connected to the common cathode (22) of the MEC and the MFC in the cathode chamber through the parallel end of the power supply (13) of the MEC and the load resistor (12) of the MFC; The voltage value of the MEC power supply (13) is calculated based on the reaction kinetic equilibrium operating conditions according to the Nernst equation.

2. The coupling device according to claim 1, characterized in that: a) The distance between the anode (16) of the MEC and the cathode (17) of the shared anode mode is 3 cm, and the distance between the anode (16) and the cathode (17) of the MFC is 6 cm; b) The insulating layer (19) between the graphite sheet (21) serving as the anode of the MEC and the graphite sheet (20) serving as the anode of the MFC in the common cathode mode has a thickness of 0.3 cm and an area of 16 cm 2 The graphite sheet (21) as the anode of MEC and the graphite sheet (20) as the anode of MFC are spaced 5 cm and 5.3 cm from the cathode (22), respectively; The anodes (16, 20, 21) are graphite electrodes of 30 mm × 30 mm × 2 mm, and the cathodes (17, 18, 22) are platinum-plated electrodes of 30 mm × 30 mm × 0.2 mm. The two electrodes and an Ag / AgCl reference electrode form a three-electrode in-situ test system.

3. The coupling device according to claim 1 or 2, characterized in that: The voltage of the power supply (13) of the MEC is 0.5 V, and the load resistance (12) of the MFC is 2000Ω to ensure the reaction kinetic balance of the microbial fuel cell.

4. The use of one of the coupling devices for MEC and MFC with a common electrode as claimed in claims 1 to 3, characterized in that: The acclimated inoculum and anolyte are placed and pumped into the anode chamber (14) to remove COD, and the cathode liquid pumped into the cathode chamber (15) is potassium dichromate solution to reduce Cr (VI).

5. The use of the coupling device according to claim 4, characterized in that: The inoculum of the anode chamber (14) is 120 g of anaerobic microorganisms, the initial pH value of the inoculum is 6.89, the total solid TS content is 12.36%, and the volatile solid VS content is 7.22%; the anolyte of the anode chamber (14) is 10 g·L -1 of sodium acetate solution; The cathode liquid in the cathode chamber (15) is 1 g·L -1 The anolyte and catholyte were pumped by a peristaltic pump at a rate of 2.6 mL min -1 The flow rate is pumped into the anode chamber and cathode chamber respectively, and both the anode liquid and the cathode liquid are circulating.

6. Use of the coupling device according to claim 4 or 5, characterized in that: The device was operated continuously for 720 h in a 30° C. circulating water bath.

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