Electrode-independent mfc-mec coupling device and application

Abstract

The application relates to an electrode-independent MFC-MEC coupling device and application and belongs to the field of microbial electrochemistry. The device changes the distribution state of the MFC self-generated electric field through the MEC external electric field, changes the single potential distribution of the MFC anode area and the MFC cathode area, realizes the same direction superposition of the electric fields of the two areas or shortens the ion migration distance, further promotes the MFC anode film formation, improves the electron transfer at the electrode / biological membrane interface and the biological membrane / solution interface and reduces the internal resistance of the system, so that the output power of the MFC is improved, and the electric energy and the methane co-production are realized. The application has high output power, excellent COD removal rate and Cr (VI) reduction rate, and effectively improves the overall performance of the MFC.

Description

Technical Field

[0001] This invention pertains to the resource utilization of organic waste in electrochemistry, and relates to microbial electrolysis cells and microbial fuel cells. Background Technology

[0002] In the following terms, the abbreviation for Microbial fuel cell is MFC; and the abbreviation for Microbial electrolysis cell is MEC.

[0003] MFCs generate electricity through the degradation and conversion of energy stored in the chemical bonds of fuel sources by microorganisms. Fuel sources are diverse, including domestic wastewater, industrial wastewater, and municipal wastewater. This differs from MECs, which use an external power source to create an electric field for hydrogen production via a reduction reaction at the cathode. Superficially, the MFC reaction involves electrochemical reaction kinetics processes such as liquid-phase mass transfer in the bulk solution, electron transfer in the external circuit, and electron transfer at the anode / biofilm / solution interface. The rate of any of these processes will affect the MFC reaction rate. However, current understanding of these processes is still abstract. For example, the idea of ​​using the electromotive force generated by the MFC's self-generated electric field as a power source for MEC to engineer biogas electricity for wastewater treatment is not an internal vector synthesis of the self-generated electric field formed by the MFC and the external electric field formed by the MEC power source. The theoretical output power of an MFC can reach 28 W·m. -2 The above figures, currently at approximately 12.8% of the theoretical output power, and the loss of over 85% of potential efficiency, render MFCs unsuitable for use in both civilian and industrial sectors. As a new technological solution to reduce over-reliance on fossil fuel power generation, it remains merely a potential avenue.

[0004] Research on the degradation of Cr(VI) from organic waste containing heavy metals aims to reduce Cr(VI) to Cr(III), and MFC, as a green technology, is an ideal choice for Cr(VI) reduction. Studies have shown that in acidic environments, Cr... 6+ The reduction process at the cathode can provide an electromotive force of approximately 1.33V-1.38V, which excites the expectation of significantly increasing the open-circuit voltage of the MFC. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to construct an MFC-MEC coupling device with independently usable electrodes by modifying the distribution of the self-generated electric field of the MFC based on the external electric field of the MEC. Another objective of this invention is to apply the device of this invention to degrade Cr(VI) contained in harmful heavy metal wastewater and improve the COD removal rate in organic wastewater, while obtaining electrical energy and methane, thus providing a basis for the large-scale production application of the device of this invention.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] (I) Electrode-independent MFC-MEC coupling device of the present invention

[0008] The device includes a microbial electrolyzer (hereinafter referred to as MEC) and a microbial fuel cell (hereinafter referred to as MFC), and:

[0009] The device achieves structural coupling between the MEC and the MFC by having the anode and cathode aligned in the same direction or crossing each other, through the vector superposition of the external electric field of the MEC and the self-generated electric field of the MFC.

[0010] Furthermore: This coupling device has two modes: a cathode and anode electrode unidirectional mode and a cathode and anode electrode cross-directional mode, wherein:

[0011] a) Same orientation mode for positive and negative electrodes:

[0012] A proton exchange membrane 8 separates the anode chamber 14 and the cathode chamber 15. The anode 16 of the MFC, the anode 17 of the MEC, and the cathode 18 of the MEC are arranged sequentially in the anode chamber 14. The cathode 19 of the MFC is arranged in the cathode chamber 15. The anode 16 of the MFC and the anode 17 of the MEC are separated by an insulating layer 20. The anode 16 is connected to the cathode 19 through a resistor 12, while the anode 17 is connected to the cathode 18 through an external power supply 13.

[0013] b) Crossover mode of positive and negative electrodes:

[0014] A proton exchange membrane 8 separates the anode chamber 14 and the cathode chamber 15. The anode 16 of the MFC, the cathode 18 of the MEC, and the anode 17 of the MEC are arranged in the anode chamber 14. The cathode 19 of the MFC is arranged in the cathode chamber 15. The anode 17 is connected to the cathode 18 through an external power supply 13, and the anode 16 is connected to the cathode 19 through a resistor 12.

[0015] Preferably:

[0016] a) In the aforementioned co-directional electrode mode, the insulating layer 20 between the anode 17 of the MEC and the anode 16 of the MFC has a thickness of 0.3 cm and an area of ​​16 cm². 2The distance between the anode 16 and the cathode 19 of the MFC is 6 cm, and the distance between the anode 17 and the cathode 18 of the MEC is 3 cm.

[0017] b) In the aforementioned cross-electrode mode, the distance between the cathode 18 and anode 17 of the MEC is 3 cm, the distance between the anode 16 and cathode 19 of the MFC is 6 cm, and the distance between the anode 16 of the MFC and cathode 18 of the MEC is 1 cm.

[0018] Preferably, the anode chamber 14 and the cathode chamber 15 have the same volume, which is 270 mL.

[0019] Preferably, the voltage of the external power supply 13 of the MEC is 0.5V, and the resistance of the resistor 12 of the MFC is 2000 Ω.

[0020] Preferably, the anodes 16 and 17 are 30mm×30mm×2mm graphite electrodes, and the cathodes 18 and 19 are 30mm×30mm×0.2mm platinum-plated electrodes. These two electrodes, together with the Ag / ClAg reference electrode, constitute a three-electrode in-situ testing system.

[0021] (II) Application of the electrode-independent MFC-MEC coupling device of the present invention

[0022] The method is as follows: 120g of acclimatized inoculum and anolyte with COD of 8281.15mg / L are placed into or pumped into anode chamber 14, respectively. The catholyte pumped into cathode chamber 15 is a solution containing 1g / L potassium dichromate. The pumping flow rate is 0.156L / h for both, in order to remove COD and reduce Cr(VI).

[0023] Preferably, the inoculum is prepared by electrolysis and acclimation of dried and pulverized pig manure at 0.5V for 3 months. The initial pH of the inoculum is 7.71, the total solids content is 15.12%, and the volatile solids content is 8.26%.

[0024] Preferably, the device operates continuously for 30 days under a 30°C circulating water bath insulation condition.

[0025] The technical solution of this invention has the following beneficial effects:

[0026] Under conditions of co-directional anode and cathode electrodes, cross-directional anode and cathode electrodes, and uncoupled MFC, a mixed microbial mixture containing electroactive bacteria and methanogenic bacteria was used as inoculum. The anolyte was wastewater with a COD of 8281.15 mg / L, which was continuously fed into the anode chamber as a carbon source for the growth of electroactive microorganisms; the catholyte was a 1 g / L potassium dichromate solution; and the pump flow rate was 0.156 L / h. The experimental results were compared, including:

[0027] 1) The optimal operating voltages for the same-direction mode and the cross-direction mode of the anode and cathode are 154mV and 215mV, respectively, which are 1.39 times and 1.94 times that of the uncoupled MFC (111mV).

[0028] Comparison of operating voltages between coupled MEC-MFC power generation systems and uncoupled MFC power generation systems

[0029]

[0030] 2) The maximum power density in both the same-polarity anode and cathode cross-polarity modes is 116 mW / m². 2 and 121.17mW / m 2 These are the values ​​of uncoupled MFC (55.6mW / m). 2 The output power of the MFC is 2.08 times and 2.18 times that of the MEC. Therefore, coupling the MFC with the MEC can effectively improve the output power of the MFC and effectively reduce the total internal resistance of the system.

[0031] Maximum power density and total internal resistance of the three modes

[0032] Anode and cathode in the same direction mode Anode-cathode crossover mode Uncoupled MFC Maximum power density <![CDATA[116mW / m 2 ]]> <![CDATA[121.17mW / m 2 ]]> <![CDATA[55.6mW / m 2 ]]> Total internal resistance 2095.32Ω 1850.84Ω 2884.9Ω

[0033] 3) The oxidation current i in the same-direction mode and the cross-direction mode of the anode and cathode is greater than that in the uncoupled MFC, and is related to the anode Tafel slope (k). t This corresponds to the relationship between the anode and cathode, and also corresponds to the charge transfer resistance at the anode / biofilm interface in both the co-directional and cross-directional anode / cathode modes. Therefore, both the coupled co-directional and cross-directional anode / cathode modes exhibit excellent electrochemical performance.

[0034] Oxidation current (i) and anodic Tafel slope (k) under three modes t and charge transfer internal resistance

[0035]

[0036] 4) The SECM response current shows that the external electric field of MEC provides more electrocatalytic active sites for the biofilm of MFC, and the maximum response current in the co-directional and cross-directional electrode modes is much higher than that of uncoupled MFC. Therefore, the MFC biofilm with electric field intervention provided by MEC has a stronger extracellular electron transfer capacity, and also increases the electroactive surface area at the biofilm / solution interface. In addition, the measurement results show that the biofilm with external electric field intervention by MEC is thicker, with biofilm thicknesses of 33.8 μm and 15.56 μm in the co-directional electrode mode and cross-directional electrode mode, respectively, which are 4.97 times and 2.29 times that of uncoupled MFC (6.79 μm).

[0037] Comparison of SECM response current in three modes

[0038]

[0039] 5) After 30 days of reduction, the reduction rate of Cr(VI) in both the anion-cathode unidirectional mode and the anion-cathode cross mode was higher than that of the uncoupled MFC, and the COD removal rate was also higher than that of the uncoupled MFC, making it an effective wastewater treatment system.

[0040] Comparison of Cr(VI) reduction rate and COD removal rate under three modes

[0041] Anode and cathode in the same direction mode Anode-cathode crossover mode Uncoupled MFC Cr(VI) reduction rate 69％ 71.34％ 62.39％ COD removal rate 62％ 68.24％ 54.84％

[0042] Therefore, the substantial progress of the present invention compared with the prior art lies in:

[0043] (1) The MFC-MEC coupling device of the present invention realizes the effective treatment of high-concentration wastewater and heavy metal wastewater containing Cr(VI), while recovering electrical energy and biogas.

[0044] (2) The biomembrane with MEC external electric field intervention of the present invention has more electrocatalytic active sites, larger active surface area and thicker biomembrane at the biomembrane / solution interface, while effectively reducing the extracellular electron transfer resistance at the anode / biomembrane interface, thus promoting the anode reaction rate.

[0045] (3) The coupling device of the present invention has a high COD removal rate and Cr(VI) reduction rate, and the system is simple to operate and has low operating requirements. It can usually operate efficiently at room temperature.

[0046] This invention is supported by the National Natural Science Foundation of China (Project No.: 21968038). Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the MFC-MEC coupling device with the same orientation of the anode and cathode electrodes according to the present invention. Wherein:

[0048] 1-Sampling port, 2-Exhaust port, 3-Insulated circulating water outlet, 4-Anodic solution outlet, 5-Water seal, 6-Anodic solution inlet, 7-Circulating water insulation layer, 8-Proton exchange membrane, 9-Insulated circulating water inlet, 10-Cathode solution inlet, 11-Cathode solution outlet, 12-Load resistor, 13-Power supply, 14-Anodic chamber, 15-Cathode chamber, 16-Anodic of MFC, 17-Anodic of MEC, 18-Cathode of MEC, 19-Cathode of MFC, 20-Insulating layer.

[0049] Figure 2This is a schematic diagram of the MFC-MEC coupling device with a cross-electrode mode according to the present invention. The meanings of the reference numerals are as follows: Figure 1 correspond.

[0050] Figure 3 This is a schematic diagram of the electric field vector and charge migration direction in the same-direction mode of the anode and cathode of this invention. Wherein, E MEC (dashed line) and E MFC (Solid lines) represent the electric fields of MEC and MFC, respectively; the straight lines with arrows represent the vector superposition of the electric fields; H + e - and CH3COO - It represents the charge and its migration direction; PEM represents the ion exchange membrane, and R is the load resistance.

[0051] Figure 4 This is a schematic diagram of the electric field vector and charge migration direction in the cross-electrode mode of the present invention. The meanings of the reference numerals are as follows: Figure 3 correspond.

[0052] Figure 5 The operating voltage across the load in the same polarity mode, cross polarity mode, and uncoupled MFC.

[0053] Figure 6 Methane content in co-directional mode, cross-directional mode, and uncoupled MEC

[0054] Figure 7 Polarization and power density curves for co-polarized and cross-polarized MFCs and uncoupled MFCs.

[0055] Figure 8 Cyclic voltammetry curves of electrochemical parameters for co-polarity mode, cross-polarity mode, and uncoupled MFC.

[0056] Figure 9 Tafel curves of electrochemical parameters for co-orientation mode, cross-orientation mode, and uncoupled MFC.

[0057] Figure 10 Anodic impedance spectra of electrochemical parameters for co-directional anode and cathode modes, cross-directional anode and cathode modes, and uncoupled MFCs.

[0058] Figure 11 High-resolution scanning electrochemical microscope images in the same orientation mode of the cathode and anode electrodes.

[0059] Figure 12 This is a high-scan image from a scanning electrochemical microscope in a cross-electrode mode.

[0060] Figure 13These are high-resolution images obtained by scanning electrochemical microscopy of uncoupled MFCs.

[0061] Figure 14 The asymptotic curves are for the same-direction mode of the anode and cathode, the cross-direction mode of the anode and cathode, and the uncoupled MFC.

[0062] Figure 15 COD degradation rate and Cr(VI) reduction rate for co-directional anode and cathode electrode mode, cross-directional anode and cathode electrode mode, and non-coupled MFC.

[0063] The present invention will be further described below with reference to specific embodiments thereof. Detailed Implementation

[0064] (i) The coupling device of the present invention for the same-direction mode and the cross-direction mode of the anode and cathode electrodes

[0065] Example 1:

[0066] The coupling device for the same-direction mode and the cross-direction mode of the anode and cathode electrodes includes: an anode chamber 14 and a cathode chamber 15. The anode chamber 14 has an anolyte inlet 6 and an outlet 4, and is connected to a water seal 5 to form a positive pressure exhaust system for gas-liquid separation. The top of the anode chamber 14 has an exhaust port 2 and a sampling port 1, which is connected to a gas flow meter and a gas collection bag. The bottom of the cathode chamber 15 has a cathode liquid inlet 10, and the top has an outlet 11. The anode chamber 14 and the cathode chamber 15 are surrounded by a circulating water insulation layer 7, and have a circulating water inlet 9 and a circulating water outlet 3.

[0067] As:

[0068] a) Same orientation mode for positive and negative electrodes:

[0069] like Figure 1 As shown, a proton exchange membrane 8 separates the anode chamber 14 and the cathode chamber 15. Within the anode chamber 14, the anode 16 of the MFC, the anode 17 of the MEC, and the cathode 18 of the MEC are sequentially arranged. Within the cathode chamber 15, the cathode 19 of the MFC is arranged. The anode 16 of the MFC and the anode 17 of the MEC are separated by an insulating layer 20. The anode 16 is connected to the cathode 19 via a resistor 12, while the anode 17 is connected to the cathode 18 via an external power supply 13. The MEC is a single-chamber unit, and the MFC is a dual-chamber unit.

[0070] like Figure 3 As shown, some of the protons generated by oxidation at MFC anode 16 and MEC anode 17 serve as electron acceptors at MEC cathode 18, while others are supplied to MFC cathode 19 after passing through a proton exchange membrane (PEM). The H₂... + e - and CH3COO - Equal charge at E MEC and EMFC They migrate towards the cathode or anode under the superimposed electric field formed in the same direction.

[0071] As:

[0072] b) Crossover mode of positive and negative electrodes:

[0073] like Figure 2 As shown, a proton exchange membrane 8 separates the anode chamber 14 and the cathode chamber 15. Within the anode chamber 14, the anode 16 of the MFC, the cathode 18 of the MEC, and the anode 17 of the MEC are arranged. The cathode 19 of the MFC is located within the cathode chamber 15. The anode 17 is connected to the cathode 18 via an external power supply 13, and the anode 16 is connected to the cathode 19 via a resistor 12. The MEC is a single-chamber unit, while the MFC is a dual-chamber unit.

[0074] like Figure 4 As shown, protons generated by oxidation at MFC anode 16 serve as electron acceptors at MEC cathode 18, while protons generated by oxidation at MEC anode 17 are supplied to MFC cathode 19 after passing through a proton exchange membrane (PEM). The H₂ in this process... + e - and CH3COO - Equal charge at E MEC and E MFC Under the superimposed electric field, protons migrate towards the cathode or anode. This migration is due to the shortened migration distance between the MFC anode 16 and the MEC cathode 18, and between the MEC anode 17 and the proton exchange membrane (PEM), which reduces internal energy loss.

[0075] Example 2:

[0076] The structural parameters of the coupling devices for the same-direction mode and the cross-direction mode of the anode and cathode are:

[0077] (a) Antenna and cathode in the same orientation mode:

[0078] like Figure 1 In the co-directional mode of the anode and cathode, the insulating layer 20 between the anode 17 of the MEC and the anode 16 of the MFC has a thickness of 0.3 cm and an area of ​​16 cm². 2 The distance between the anode 16 and the cathode 19 of the MFC is 6 cm, and the distance between the anode 17 and the cathode 18 of the MEC is 3 cm.

[0079] (b) Crossover mode of positive and negative electrodes:

[0080] like Figure 2 The distance between the cathode 18 and the anode 17 of the MEC is 3cm, the distance between the anode 16 and the cathode 19 of the MFC is 6cm, and the distance between the anode 16 of the MFC and the cathode 18 of the MEC is 1cm.

[0081] The anode electrodes 16 and 17 are block graphite electrodes; the cathode electrodes 18 and 19 are block platinum-plated electrodes. The anode chamber 14 contains inoculum and continuously fed high-concentration wastewater; the cathode chamber 15 contains continuously fed heavy metal wastewater.

[0082] Example 3: Except that the volumes of the anode chamber 14 and the cathode chamber 15 are equal (270 mL), the rest is the same as in Example 1.

[0083] Example 4: Except that the voltage of the external power supply 13 of MEC is 0.5V and the resistance of resistor 12 of MFC is 2000 Ω, the rest is the same as in Example 1.

[0084] Example 5: Except that the anodes 16 and 17 are 30mm×30mm×2mm graphite electrodes and the cathodes 18 and 19 are 30mm×30mm×0.2mm platinum-plated electrodes, which together with the Ag / ClAg reference electrode form a three-electrode in-situ testing system, the rest is the same as in Example 1.

[0085] (II) Application of the device of the present invention

[0086] 2.1 Inoculum

[0087] The inoculum used in this invention is derived from a biogas digester. First, the inoculum is mixed and stirred evenly, then passed through a 20-mesh sieve to remove impurities such as sand and gravel. Next, dried and pulverized pig manure is periodically and quantitatively fed into a 30°C constant-temperature incubator using an electrolytic acclimatization method at 0.5V for 3 months. Finally, the supernatant and bottom sludge of the acclimatized inoculum are removed, the intermediate portion is mixed evenly, weighed uniformly, bagged, and stored at a low temperature of 5°C for long-term use. Its initial pH value is 7.71, total solids content is 15.12%, and volatile solids content is 8.26%.

[0088] 2.2 Processing Method

[0089] (1) Preprocessing:

[0090] In this invention, all electrodes of the coupling device are immersed in a 25% H2O2 solution at 80°C for 1 hour to remove surface impurities; the proton exchange membrane (Nafion 117, DuPont) is treated in a 5% H2O2 solution at 80°C for 1 hour, then immersed in deionized water for 1 hour, followed by immersion in 5% dilute sulfuric acid at 80°C for 1 hour, and then immersed in deionized water for 1 hour.

[0091] (2) System startup:

[0092] When the coupling device of this invention is started, 120g of inoculum is inoculated into the anode chamber, and nitrogen gas is introduced for 15 minutes to remove air from the top of the anode chamber. The COD concentration of the anolyte feed is 8281.15mg / L, and organic wastewater containing acetate is continuously introduced as the sole carbon source for the growth of electroactive microorganisms in the anode chamber. Artificially simulated heavy metal wastewater containing 1.0g / L potassium dichromate is used as the cathode electrolyte in the cathode chamber. The system employs a positive pressure gas collection method. The electrolysis voltage of the MEC is 0.5V, and the load resistance of the MFC is 2000Ω. From startup, a peristaltic pump pumps the anolyte and cathode liquid into the anode and cathode chambers respectively at a feed rate of 0.156L / h, and the electrolytes are all in circulation. The MFC-MEC operates continuously for 30 days under a 30℃ circulating water bath insulation condition.

[0093] 2.3 System Analysis

[0094] Gas composition was measured every 2 days using a gas chromatograph with a stainless steel packed column and a thermally conductive detector (TCD). Test conditions were: TCD temperature 200℃, column oven temperature 110℃, carrier gas high-purity nitrogen, injection port temperature 200℃, and injection volume 200 μL. The operating voltage of the MFC was recorded every 0.5 days using a multi-function digital multimeter. After 30 days of system operation, the polarization curve was tested by changing the load resistance, starting from 1000Ω and increasing in increments of 500Ω up to 10000Ω. The operating current and areal power density were calculated using Ohm's law. The electrochemical characteristics of the biomembrane were measured using cyclic voltammetry and Tafel curves at a scan rate of 5 mV / s. -2 Hz-10 6 AC impedance testing was performed within a frequency range of Hz, with the solution resistance compensated for by iR, and a static time of 10 s. Asymptotic curve analysis of the anodic biofilm of the MFC was conducted using electrochemical scanning microscopy (SECM). After the asymptotic curve was completed, the probe crawled 50 μm along the +Z axis and then performed a contour scan within an 80 μm × 80 μm area to characterize the biofilm thickness and electrocatalytic active sites. A 25 μm diameter Pt electrode was used as the SECM probe, with a scan rate of 10 μm / s, and 1 mmol / L ferrocene methanol (FcMeOH) was used as the electrolyte. All electrochemical tests were performed in situ at 30 °C.

[0095] (III) Comparison and analysis of experimental results using the same inoculum, substrate, and catholyte in co-polar mode, cross-polar mode, and uncoupled MFC device.

[0096] like Figure 5As shown, due to the continuous addition of anolyte and cathode in the system, the operating voltage across the load exhibits a continuous distribution, initially increasing and then decreasing as the culture progresses. This is related to the gradual consumption of the substrate and the gradual formation of the biofilm. The optimal operating voltages for the unidirectional and cross-polarity electrode modes are 154 mV and 215 mV, respectively, which are 1.39 times and 1.94 times that of the uncoupled MFC (111 mV).

[0097] Comparison of operating voltages between coupled MEC-MFC power generation systems and uncoupled MFC power generation systems

[0098]

[0099] like Figure 6 The figure shows the methanogenesis performance of the system, regardless of whether the coupling system is in the same-direction mode or the cross-direction mode, in which the MEC is a single chamber and H + As the electron acceptor at the MEC cathode, the MEC produces hydrogen gas. This hydrogen gas is further reduced to carbon dioxide and converted to methane by hydrotrophic methanogens, resulting in a high methane content. The highest methane contents in the co-directional electrode mode, the cross-electrode mode, and the uncoupled MEC were 73.28%, 77.44%, and 83.34%, respectively, which are higher than the 50%-70% methane content of conventional anaerobic digestion. Simultaneously, this coupled system achieves the co-production of methane and electricity.

[0100] Maximum methane content in three modes and electron acceptor at the MEC cathode

[0101] Anode and cathode in the same direction mode Anode-cathode crossover mode Uncoupled MEC Maximum methane content 73.28％ 77.44％ 83.34％ Electron acceptor of MEC cathode <![CDATA[H + ]]> <![CDATA[H + ]]> <![CDATA[H + ]]>

[0102] like Figure 7 As shown, the maximum power density in the same-polarity mode and the cross-polarity mode is 116 mW / m. 2 and 121.17mW / m 2 These are the values ​​of uncoupled MFC (55.6mW / m). 2 The output power of the MFC is 2.08 times and 2.18 times that of the MEC. The total internal resistance of the co-directional mode and the cross-directional mode are 2095.32Ω and 1850.84Ω, respectively, which are 27.36% and 35.8% lower than that of the uncoupled MFC (2884.9Ω). In the MFC-MEC coupled system, the external electric field provided by the MEC is the only variable in the entire system. Therefore, coupling the MFC with the MEC can effectively improve the output power of the MFC and effectively reduce the total internal resistance of the system.

[0103] Maximum power density and total internal resistance of the three modes

[0104]

[0105]

[0106] like Figure 8 As shown, the oxidation current exists in i 阴阳电极同向模式 (-3.39mA) 阴阳电极交叉模式 (-3.22mA) 非耦合MFC The relationship between (-1.68mA) Figure 8 ), and the anode Tafel slope (k t The relationship is the same () Figure 9 ), that is, k t,阴阳电极同向模式 (134.33mV / dec) <k t,阴阳电极交叉模式 (135.08mV / dec) <k t,非耦合MFC (150.83mV / dec), while the charge transfer internal resistance at the anode / biofilm interface in the same-direction mode and the cross-direction mode are 81.05Ω and 84.28Ω, respectively, which are less than the 155.03Ω of the uncoupled MFC. Figure 10 Therefore, the coupled systems all exhibit excellent electrochemical performance.

[0107] Oxidation current (i) and anodic Tafel slope (k) under three modes t and charge transfer internal resistance

[0108]

[0109] like Figure 11 , Figure 12 and Figure 13 As shown, the surface current distribution of the uncoupled MFC biofilm is more uniform, while the surface current fluctuations and peak values ​​are larger in the co-directional and cross-directional electrode modes. This indicates that the external electric field of MEC provides more electrocatalytic active sites for the MFC biofilm. Furthermore, the maximum response currents in the co-directional and cross-directional electrode modes are 0.741 nA and 1.925 nA, respectively, significantly higher than the 0.176 nA of the control group MFC. Therefore, the MEC-mediated MFC biofilm exhibits stronger extracellular electron transfer capabilities and also increases the electroactive surface area at the biofilm / solution interface. In addition, the biofilms mediated by the MEC external electric field are thicker, with thicknesses of 33.8 μm and 15.56 μm in the co-directional and cross-directional electrode modes, respectively, which are 4.97 times and 2.29 times thicker than those in the uncoupled MFC (6.79 μm). Figure 14 ).

[0110] Comparison of SECM response current in three modes

[0111] ​​

[0112]

[0113] like Figure 15 As shown, after 30 days of reduction, the reduction rates of Cr(VI) in the co-directional electrode mode and the cross-directional electrode mode were 69% and 71.39%, respectively, both higher than the 62.39% of the uncoupled MFC. The COD removal efficiency showed a similar effect to the Cr(VI) reduction rate, with the co-directional electrode mode and the cross-directional electrode mode achieving 62% and 68.24% COD removal efficiencies, respectively, both higher than the 54.84% of the uncoupled MFC. Both the co-directional electrode mode and the cross-directional electrode mode effectively improved the COD removal rate and the Cr(VI) reduction rate, making them an effective wastewater treatment system.

[0114] Cr(VI) reduction rate and COD in symmetric mode, cross-symmetric mode and MFC mode

[0115] Removal rate comparison

[0116] Anode and cathode in the same direction mode Anode-cathode crossover mode Uncoupled MFC Cr(VI) reduction rate 69％ 71.34％ 62.39％ COD removal rate 62％ 68.24％ 54.84％

[0117] The above preferred embodiments only illustrate the technical solutions of the present invention in detail and are not intended to limit it. Those skilled in the art should understand that any substitutions or modifications made to the present invention within the scope of the technology disclosed herein shall fall within the protection and disclosure scope of the present invention.

Claims

1. An electrode-independent MFC-MEC coupling device, comprising a microbial electrolyzer (MEC) and a microbial fuel cell (MFC), has two modes: a co-directional anode and cathode mode and a cross-directional anode and cathode mode. a) Antenna and cathode unidirectional mode: A proton exchange membrane (8) separates the anode chamber (14) and the cathode chamber (15). The anode (16) of the MFC, the anode (17) of the MEC, and the cathode (18) of the MEC are arranged sequentially in the anode chamber (14). The cathode (19) of the MFC is arranged in the cathode chamber (15). The anode (16) of the MFC and the anode (17) of the MEC are separated by an insulating layer (20). The anode (16) of the MFC is connected to the cathode (19) of the MFC through a resistor (12), while the anode (17) of the MEC is connected to the cathode (18) of the MEC through an external power supply (13). b) Crossover mode of positive and negative electrodes: The anode chamber (14) and the cathode chamber (15) are separated by a proton exchange membrane (8). The anode (16) of the MFC, the cathode (18) of the MEC and the anode (17) of the MEC are arranged in the anode chamber (14). The cathode (19) of the MFC is set in the cathode chamber (15). The anode (17) of the MEC is connected to the cathode (18) of the MEC through an external power supply (13). The anode (16) of the MFC is connected to the cathode (19) of the MFC through a resistor (12).

2. The coupling device according to claim 1, characterized in that: a) The insulating layer (20) between the anode (17) of the MEC and the anode (16) of the MFC in the same polarity mode has a thickness of 0.3 cm and an area of ​​16 cm². 2 The distance between the anode (16) and cathode (19) of the MFC is 6cm, and the distance between the anode (17) and cathode (18) of the MEC is 3cm. b) In the cross-electrode mode, the distance between the cathode (18) of MEC and the anode (17) of MEC is 3 cm, the distance between the anode (16) of MFC and the cathode (19) of MFC is 6 cm, and the distance between the anode (16) of MFC and the cathode (18) of MEC is 1 cm.

3. The coupling device according to claim 1 or 2, characterized in that: The anode chamber (14) and the cathode chamber (15) have the same volume, which is 270 mL.

4. The coupling device according to claim 1 or 2, characterized in that: The external power supply (13) of the MEC has a voltage of 0.5V, and the resistance (12) of the MFC has a resistance of 2000Ω.

5. The coupling device according to claim 1 or 2, characterized in that: The anode (16) of the MFC and the anode (17) of the MEC are graphite electrodes with dimensions of 30 mm × 30 mm × 2 mm. The cathode (18) of the MEC and the cathode (19) of the MFC are platinum-plated electrodes with dimensions of 30 mm × 30 mm × 0.2 mm. These two electrodes, together with the Ag / AgCl reference electrode, constitute a three-electrode in-situ testing system.

6. The application of the electrode-independent MFC-MEC coupling device as described in any one of claims 1 to 5, characterized in that: 120g of the acclimated inoculum and an anolyte with a COD of 8281.15mg / L were placed into or pumped into the anode chamber (14), respectively. The catholyte pumped into the cathode chamber (15) was a solution containing 1g / L potassium dichromate. The pumping flow rate was 0.156L / h to remove COD and reduce Cr(VI).

7. The application of the coupling device according to claim 6, characterized in that: The inoculum was prepared by electrolysis of dried and pulverized pig manure at 0.5 V for 3 months. The initial pH of the inoculum was 7.71, the total solids content was 15.12%, and the volatile solids content was 8.26%.

8. The application of the coupling device according to claim 7, characterized in that: The device operated continuously for 30 days under a 30°C circulating water bath insulation condition.

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