A method for degrading toluene using a microbial electrolytic cell

Abstract

The invention discloses a method for degrading toluene in a microbial electrolytic cell, comprising the following steps: 1) using low-cost pulp as raw material, preparing a cellulose carbon aerogel / polypyrrole composite material (CA-ppy) by a sol-gel method and conductive polymer loading; 2) using the CA-ppy composite electrode material as a bioanode, constructing a packed bed microbial electrolytic cell for degrading toluene; 3) taming and starting the bioanode, forming an anode biofilm on the anode electrode, and taming electroactive microorganisms capable of degrading toluene; 4) investigating the performance of the microbial electrolytic cell in treating toluene under different potentials and residence times, and determining optimal operating parameters.

Description

Technical Field

[0001] The invention belongs to the field of microbial electrochemistry, and in particular relates to a method for degrading toluene in a microbial electrolytic cell. Background Art

[0002] Toluene is a volatile organic compound (VOCs) known to be harmful to human health and the environment. Toluene is, of course, present in tolu trees and crude oil. It is produced in several anthropogenic activities, such as the manufacturing process of fuel and coke. It is commonly used in the production of paints, adhesives, nail polish, rubber, varnishes, etc. It is also used in the production of benzene, plastics, nylon and polyurethane and in the synthesis reaction of toluene diisocyanate, benzoic acid, trinitrotoluene and benzoyl chloride, thus playing a vital role in human daily life and industrial development over the past decades. However, due to its toxicity and volatility, toluene has been recorded in the Pollutant Release and Transfer Registers of many countries. Toluene has been found to be carcinogenic, mutagenic, developmental and teratogenic to humans and animals. Toluene is also harmful to the environment, and it contributes to the formation of photochemical smog, climate change and the destruction of the ozone layer. Therefore, effective technologies are needed to remove toluene from polluted air streams to improve ambient air quality and protect human health.

[0003] Bioelectrochemical System (BES) is a new and efficient pollutant removal method. Some bacteria have electrochemical activity, which can reduce the redox overpotential and facilitate the efficient degradation of difficult-to-degrade pollutants. Microbial Electrolysis Cell (MEC) can convert any biodegradable waste into hydrogen, biofuels and other value-added products. Compared with other biotechnologies, it not only produces higher hydrogen yields, but also requires significantly lower external energy input (theoretically >0.14V), even compared with water electrolysis (>1.2V). In addition, since MEC can use various organic wastewaters as substrates to produce hydrogen, it has the advantage of treating pollutants. In the process of converting biological waste into hydrogen, exogenous electrobacteria first oxidize organic matter and transfer electrons to the bioanode. Then the electrons pass through the external circuit and combine with protons at the anaerobic cathode to produce hydrogen or other required substances. These characteristics have attracted widespread attention to the MEC system. The use of MEC to produce biohydrogen is considered an energy-saving option, and the construction of microbial electrolysis cells has good research prospects.

[0004] Carbon aerogel (CA) has excellent physicochemical properties such as high specific surface area, rich pore structure, excellent electron conduction ability, stable chemical properties and adjustable surface chemistry. CA is usually obtained by carbonizing organic aerogel under an inert atmosphere. Its porosity makes it very significant in adsorption, energy storage and catalysis. There are still many challenges in the preparation of CA, such as expensive manufacturing costs, redundant preparation processes and toxic precursors, which limit the commercialization of CA. Biomass is not only easy to obtain and has low raw material costs, but also avoids the cellulose extraction step, making it cost-effective and environmentally friendly. Biomass is essentially a phenolic substance with extremely low price. Its high reactivity is attributed to the presence of various reactive functional groups, such as carboxyl, carbonyl and hydroxyl. Similar to traditional porous carbon materials, biomass carbon-based materials have the characteristics of adjustable micro- and macroscopic architectures, huge specific surface area and high porosity, and have applications in many aspects. Due to the above advantages of biomass, cheap and green biomass CA can be prepared.

[0005] The present invention uses volatile organic pollutant toluene as the target pollutant, constructs a MEC system with three-dimensional porous biomass carbon aerogel as an electrode, inoculates a mixed bacterial community with toluene degradation ability into the anode chamber, and stably and efficiently removes toluene under an applied potential condition. By further adjusting conditions such as toluene concentration and applied potential, the performance of MEC is improved. The MEC system can stably and effectively remove toluene under the drive of an applied potential, achieving a more efficient degradation efficiency. Summary of the invention

[0006] The purpose of the present invention is to provide a method for degrading toluene in a microbial electrolytic cell. With low-cost pulp as raw material, a cellulose carbon aerogel / polypyrrole composite material (CA@ppy) with a hierarchical void structure is prepared by a sol-gel method and conductive polymer loading. The prepared CA@ppy is used as a filling bioanode of a microbial electrolytic cell. Under the promotion of an applied potential, the microbial electrolytic cell can stably and efficiently degrade toluene.

[0007] A method for degrading toluene in a microbial electrolytic cell comprises the following steps:

[0008] 1) A microbial electrolysis cell separated by a proton exchange membrane is used, anaerobic activated sludge obtained from a sewage treatment plant and an anolyte containing microbial nutrients are added to the anode chamber, a continuous mixture of toluene and air is introduced into the anode chamber as the only carbon source, and an inorganic salt buffer solution is added to the cathode chamber;

[0009] The anode chamber uses carbon aerogel or carbon aerogel grown with conductive polymer polypyrrole as an anode electrode, and the cathode chamber uses carbon cloth as an electrode and is connected to an electrochemical workstation through a wire. The electrochemical workstation provides an applied voltage to start the microbial electrolysis cell for domestication, so that an anode biofilm is formed on the anode electrode, which serves as the domesticated anode.

[0010] 2) transforming the anode into a packed bed electrode, the outer surface of which is non-conductive polytetrafluoroethylene, breaking the tamed anode obtained in step 1) into blocks, filling the blocks into polytetrafluoroethylene, using a graphite rod as a current collector, connecting the graphite rod to the shell of the microbial electrolysis cell with a conductive glue, and connecting the anode and the cathode with a wire to form a closed loop;

[0011] Anode liquid, domesticated anaerobic activated sludge containing electroactive bacteria, and toluene are added to the anode chamber;

[0012] The cathode chamber is an inorganic salt buffer solution;

[0013] During operation, an external potential is provided by the electrochemical workstation, and electrons are conducted from the circuit on the anode to the cathode, driving the anode microorganisms to degrade toluene.

[0014] Further preferably, the method for degrading toluene by a microbial electrolytic cell comprises the following process:

[0015] 1) Acclimation and start-up of bioanode

[0016] The microbial electrolysis cell MEC is domesticated using Nafion 117 as a proton exchange membrane separator, anaerobic activated sludge obtained from a sewage treatment plant and anolyte are added to the anode chamber, a continuous mixture of toluene and air is introduced into the anode chamber as the only carbon source, wherein trace vitamin solution and trace minerals are added to the anolyte to meet the basic conditions for the growth of anode microorganisms; an inorganic salt buffer solution is added to the cathode chamber; the prepared CA-ppy is used as an electrode in the anode chamber, and the cathode chamber is used as an electrode using carbon cloth and connected to an electrochemical workstation through a wire, and an applied voltage is provided by the electrochemical workstation to start the microbial electrolysis cell for domestication, so that an anodic biofilm is formed on the anode electrode as a biological anode;

[0017] 2) Construction and operation of microbial electrolysis cell MEC

[0018] The anode electrode in the MEC with the domesticated bioanode in step 1) is upgraded, and the anode chamber is transformed into a packed bed electrode, the outside is non-conductive polytetrafluoroethylene, the middle is filled with CA-ppy, a graphite rod is used as a current collector, and the connection between the graphite rod and the shell is connected with a conductive glue. The aerogel electrode in the anode chamber uses biomass as a material as a matrix, and the bioanode and the cathode are connected with a wire to form a closed loop; anolyte and domesticated anaerobic activated sludge containing electroactive bacteria and toluene are added to the anode chamber, and the cathode chamber is an inorganic salt buffer solution; during operation, an external potential is provided by an electrochemical workstation, and electrons are conducted from the circuit on the anode to the cathode, driving the anode microorganisms to degrade toluene.

[0019] In the method for degrading toluene by a microbial electrolytic cell, in step 1), the anolyte is an inorganic salt buffer solution added with trace vitamins and trace minerals; and the catholyte is an inorganic salt solution.

[0020] In the method for degrading toluene using a microbial electrolytic cell, step 2) 60 mL of PBS solution is added to both the anode and cathode.

[0021] In the method for reducing toluene in a microbial electrolytic cell, the inorganic salt buffer solution is composed of Na2HPO4, NaH2PO4·2H2O, KCl, NH4Cl and deionized water, wherein the concentration of Na2HPO4 in the inorganic salt buffer solution is 27.2-37.2 mM, the concentration of NaH2PO4·2H2O is 12.8-22.8 mM, the concentration of KCl is 1.2-2.2 mM, and the concentration of NH4Cl is 3.8-7.8 mM. More preferably, the inorganic salt buffer solution is composed of: 32.2 mM Na2HPO4, 17.8 mM NaH2PO4·2H2O, 1.7 mM KCl, 5.8 mM NH4Cl, and the solvent is deionized water.

[0022] In the method for degrading toluene using a microbial electrolytic cell, in step 1), the external constant potential provided by the electrochemical workstation is 0.3-1.2 V vs. SHE, preferably 0.6 V vs. SHE anode potential.

[0023] The method for degrading toluene in a microbial electrolytic cell, in step 1), when the constant current potential is controlled by an electrochemical workstation to start the microbial electrolytic cell for domestication, a cycle is formed every 3-5 days, and the solutions in the two chambers are replaced after each cycle. After multiple cycles of batch domestication, the toluene removal rate is close to stable, and the anode biofilm is fully formed on the anode electrode, that is, the startup is completed.

[0024] The preparation of carbon aerogel specifically includes:

[0025] S1: Mix sodium hydroxide, urea and deionized water evenly, put them in a refrigerator at 2-6°C for precooling for 10-30 minutes, then add natural cotton that has been crushed by a wall-breaking machine and stir for 2-4 hours, then add epichlorohydrin and stir for 0.5-2 hours, put the obtained material into a mold and then age it in a water bath at 70-90°C for 6-10 hours, then replace it with deionized water to a neutral pH, then put it in a refrigerator at -75°C to -85°C for freezing, and then put it in a freeze dryer to form aerogel;

[0026] S2: placing the aerogel obtained in step S1 in a tubular furnace and annealing it in a nitrogen atmosphere for 1 to 3 hours, and after cooling, preparing a carbon aerogel with a three-dimensional porous structure.

[0027] Further preferably, the method for degrading toluene in a microbial electrolytic cell, using CA material as a matrix, and the preparation method of distributing conductive polymer ppy particles on the surface of the matrix comprises the following steps:

[0028] S1: Mix sodium hydroxide, urea and deionized water evenly, put them in a 4°C refrigerator for precooling for 20 minutes, slowly add the pulp that has been broken by a wall breaker and stir for 3 hours, then add epichlorohydrin and stir for another hour, put the obtained material into a mold and then age it in an 80°C water bath for 8 hours, then replace it with deionized water to a neutral pH; then put it in a -80°C refrigerator for freezing, and then put it in a freeze dryer to form aerogel.

[0029] S2: placing the sample obtained in step S1 in a tubular furnace and annealing it in a nitrogen atmosphere for 1 to 3 hours, and cooling it to room temperature to prepare a carbon aerogel electrode with a three-dimensional porous structure.

[0030] In step S1, the mass ratio of urea, sodium hydroxide and pulp is 10-14:5-9:3-5, and more preferably, the mass ratio of urea, sodium hydroxide, pulp and water is 12:7:4:81;

[0031] In step S2, the temperature of the tube furnace is 800-900°C.

[0032] Growth of carbon aerogel of conductive polymer polypyrrole, specifically comprising:

[0033] M1: Pyrrole was added to hydrochloric acid and carbon aerogel was immersed in the solution under magnetic stirring to obtain a pyrrole solution;

[0034] M2: FeCl3 is added to hydrochloric acid to obtain a ferric chloride solution, and the ferric chloride solution is dripped into the pyrrole solution. After polymerization for 20 to 40 minutes, the carbon aerogel sheet is taken out and washed with deionized water until neutral. After drying, a carbon aerogel with grown conductive polymer polypyrrole is obtained.

[0035] The usage ratio of pyrrole to FeCl3 is 0.5-2 mL: 2-4 g.

[0036] Further preferably, the preparation method of the CA-ppy material having the conductive polymer polypyrrole grown on the carbon aerogel comprises the following steps:

[0037] M1: 1 mL of pyrrole was added to 20 mL of hydrochloric acid (0.1 M), and the carbon aerogel was immersed in the solution for 20 min under magnetic stirring;

[0038] M2: 3 g of FeCl3 was added to 20 mL of hydrochloric acid (0.1 M) for 30 min, and then the ferric chloride solution was dripped into the pyrrole solution at room temperature. After polymerization for 30 min, the carbon aerogel sheet was taken out and washed with excess deionized water until neutral. The sample was dried at 80 ° C for 12 h to obtain the conductive polymer-supported CA-ppy;

[0039] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in:

[0040] The present invention constructs a microbial electrolytic cell based on CA-ppy three-dimensional porous electrodes. Under the promotion of an applied potential, more efficient degradation of toluene pollutants is achieved, and the microbial electrolytic cell can stably and effectively degrade toluene. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1(a)(b) is the scanning electron microscopy image of CA-ppy.

[0042] Figure 2 It is the impedance curve of CA and CA-ppy.

[0043] Figure 3 It is the change of removal rate of the reactor under various inlet gas concentration conditions.

[0044] Figure 4 This is a degradation effect diagram showing the effect of different residence times on the degradation rate of toluene.

[0045] Figure 5 This is a diagram of toluene degradation effect under different applied potential conditions.

[0046] Figure 6 is a schematic diagram of the MEC reactor. DETAILED DESCRIPTION

[0047] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0048] Example 1: Preparation of cellulose carbon aerogel / polypyrrole composite electrode

[0049] 1) 12 g, 7 g, 81 g of sodium hydroxide, urea and deionized water were mixed evenly, placed in a 4°C refrigerator for precooling for 20 minutes, 4 g of pulp was slowly added thereto, wherein the pulp had been broken by a wall breaking machine, stirred under magnetic stirring for 3 hours, 1 mL of epichlorohydrin was added thereto for aging for one hour, the obtained material was put into a 2.5 cm × 2.5 cm × 1 cm mold and then aged in a 80°C water bath for 8 hours, and then replaced with deionized water to a neutral pH; then placed in a -80°C refrigerator for freezing for 3 hours, and then placed in a freeze dryer to form an aerogel.

[0050] 2) The sample obtained in step 1 is placed in a tubular furnace and annealed in a nitrogen atmosphere for 1 to 3 hours. The temperature in the tubular furnace is raised from room temperature to 200°C at a rate of 5°C / min and maintained for 1 hour, then raised to 900°C at a rate of 5°C / min and maintained for 2 hours, and then cooled to room temperature, thereby preparing a carbon aerogel electrode with a three-dimensional porous structure.

[0051] 3) Add 1 mL of pyrrole to 20 mL of hydrochloric acid (0.1 M), and immerse a piece of 2.5 cm × 2.5 cm × 1 cm carbon aerogel in the solution under magnetic stirring for 20 minutes; add 3 g of FeCl3 to 20 mL of hydrochloric acid (0.1 M) and stir for 30 minutes, then slowly drip the ferric chloride solution into the pyrrole solution at room temperature, stir for 30 minutes, take out the carbon aerogel sheet, and wash it with excess deionized water until neutral, and dry the sample at 80 ° C for 12 hours to obtain CA-ppy loaded with conductive polymer.

[0052] The scanning electron microscope image of the CA-ppy anode prepared in Example 1 is as follows: Figure 1a , 1b As shown. Figure 1b It can be seen that polypyrrole particles grow on the carbon substrate with a size of about 1 μm. Ppy nanoparticles are irregularly distributed on the surface of carbon aerogels, and close contact is generated between CA and ppy, which can promote the transfer of charges and thus improve the efficiency of electron transfer and degradation performance.

[0053] Figure 2 It is a comparison chart of the impedance curves of CA and CA-ppy prepared in Example 1. Generally, the smaller the semicircular arc in the high-frequency region, the smaller the charge transfer resistance and the more the interfacial charge transfer. A three-electrode system is adopted, and the CA or CA-ppy sample prepared in Example 1 is the working electrode, the platinum sheet electrode (20×20×0.3mm) and the Ag / AgCl electrode are used as the counter electrode and the reference electrode respectively, and the electrolyte is a phosphate buffer solution. The prepared electrodes are subjected to electrochemical impedance testing using an electrochemical workstation, and the parameters are: the initial voltage is the open circuit potential, and the frequency range is 0.1Hz-100kHz. By the attached Figure 2It can be seen that compared with CA, the semicircle of CA-ppy is significantly smaller, indicating that the modification of polypyrrole reduces the charge transfer resistance of CA. CA-ppy has a lower mass transfer resistance and is more conducive to the transmission of electrons, thereby improving the electrochemical performance of the electrode.

[0054] Example 2: Toluene removal effect during MEC startup

[0055] The construction and operation of MEC (the mechanism diagram of toluene degradation by microbial electrolysis cell system is shown in Figure 2) Figure 6 shown):

[0056] A microbial electrolysis cell separated by a proton exchange membrane was used, anaerobic activated sludge (pH 6.8, BOD 55400, COD = 1500) obtained from the Qige Wastewater Treatment Plant in Hangzhou was added to the anode chamber and an anolyte containing microbial nutrients was added, a continuous mixture of toluene and air was introduced into the anode chamber as the only carbon source, and an inorganic salt buffer solution was added to the cathode chamber;

[0057] The anode chamber uses carbon aerogel or carbon aerogel grown with conductive polymer polypyrrole as an anode electrode, and the cathode chamber uses carbon cloth as an electrode and is connected to an electrochemical workstation through a wire. The electrochemical workstation provides an applied voltage to start the microbial electrolysis cell for domestication. The domestication cycle is 4 days. After each cycle, the solutions in the two chambers are replaced. After multiple batches of domestication, the toluene removal rate is close to stable, so that a biofilm with stable and efficient toluene degradation ability is formed on the anode electrode, which serves as the domesticated anode;

[0058] The air inlet at the left end of the anode chamber is set outside the reactor, and a sand core is added to the bottom of the reactor to ensure uniform intake of toluene simulated exhaust gas. The prepared 2.5×2.5×1cm CA-ppy is broken into uniform small pieces and filled into a polytetrafluoroethylene cylinder. A graphite rod is used as a current collector. The graphite rod and polytetrafluoroethylene are connected by conductive glue. There are four-mesh holes on the polytetrafluoroethylene cylinder. The cathode is a carbon cloth electrode. 60mL of inorganic salt buffer solution is added to the anode and cathode. During operation, the constant potential is controlled by an electrochemical workstation. The electrons on the anode are conducted to the cathode through the circuit to promote the degradation of toluene by anode microorganisms. The inorganic salt buffer solution is composed of: 32.2mM Na2HPO4, 17.8mM NaH2PO4·2H2O, 1.7mM KCl, 5.8mM NH4Cl, the solvent is deionized water; the simulated toluene exhaust gas is carried by a part of the air in the stripping bottle, fully mixed with another part of the air in the mixing bottle, and then enters the anode chamber. After each cycle, the cathode liquid and the anode liquid are completely replaced; sampling is taken through the gas sampling port, and the concentration of 1,2-dichloroethane in the reactor is detected by a gas chromatograph.

[0059] The start-up phase of bioanode acclimation: CA-ppy reactor was heated at various inlet gas concentrations (600-1500 mg / m 3 The changes in removal rate under different conditions and the stability of removal rate under different conditions are shown in the attached figure. Figure 3 As shown. Within the range of inlet concentration, the MEC system can achieve a removal rate of more than 90%. The inlet concentration is 900mg / m 3 When the removal rate is compared with 600mg / m 3 There is basically no change, maintaining above 94%; the intake air concentration is 1200mg / m 3 When the inlet concentration is 1500mg / m 3 When the removal rate drops to about 90%, the removal rate can quickly reach stability after the MEC system changes the intake air concentration conditions, and the stability is better when dealing with small fluctuations in intake air concentration.

[0060] Example 3: Effect of different applied potentials on toluene degradation rate

[0061] The strength of the applied potential affects the growth and activity of microorganisms and is an important factor affecting the toluene treatment effect of the microbial electrolytic cell. The experiment was carried out according to the operating steps of the construction and operation of the MEC in Example 2. The residence time was set to 2 minutes. At a toluene concentration of 1500 mg / m 3 Under the same conditions, the applied potential was adjusted to 0.3, 0.6, 0.9 and 1.2 V vs. SHE, and the temperature was 30°C. The treatment effect of the microbial electrolytic cell on toluene under different applied potentials was investigated. Samples were taken at three time points every day to measure the concentration of toluene in the microbial electrolytic cell and calculate the degradation rate.

[0062] The results refer to the attached Figure 5 , as the voltage increases from 0.3V to 1.2V, the degradation of toluene in the two reactors first increases and then decreases. At an applied potential of 0.6V, the degradation rate of toluene in CA-ppy can reach an average of 92.86%, while the degradation rate of toluene in CA can only reach an average of 82.11%, an increase of 10.75%. At this time, the degradation rate reaches the highest. With the continuous increase of the applied potential, at an applied potential of 1.2V, the degradation rate of toluene in CA-ppy can only reach an average of 84.05%, while the degradation rate of toluene in CA is only 75.01%, which is about 8% lower than that of 0.6V, indicating that the excessively high applied potential inhibits the degradation of toluene by microorganisms. Therefore, an excessively high applied potential may cause side reactions at the anode, which is not conducive to the degradation of toluene by microorganisms.

[0063] Example 4: Effect of different residence times on toluene degradation rate

[0064] Residence time affects the mass transfer rate of the reaction and is an important influencing factor in a continuous flow reactor. After the MEC of Example 2 was successfully started, the voltage was set at 0.6 V. By changing the air inlet flow rate, the effect of different residence times on the toluene treatment effect of the microbial electrolysis cell was investigated. The experiment was carried out according to the operating steps of the construction and operation of the MEC in Example 2. When the toluene concentration was set to 1500 mg / m 3 Under the same conditions, the inlet flow rate was adjusted to 30, 45, and 60 mL / min, and the solution temperature was 30°C, and the adaptability of the reactor to different initial concentrations was investigated. Samples were taken at three time points each day to measure the concentration of toluene in the microbial electrolysis cell and calculate the degradation rate.

[0065] The results refer to the attached Figure 5 , with the increase of inlet flow rate, toluene degradation gradually decreased. When the initial residence time was reduced from 2 minutes to 1 minute, the toluene degradation rate in CA-ppy decreased from an average of 92.86% to 85.67%, while the toluene degradation rate in CA decreased from an average of 84.56% to 76.78%, which was about 8% lower than that of CA-ppy. The reduction of residence time was not conducive to the degradation of toluene. Therefore, the excessively high flow rate may affect the mass transfer between gas and liquid, limiting the biodegradability.

[0066] The contents described in this specification are merely an enumeration of implementation forms of the inventive concept, and the protection scope of the present invention should not be regarded as being limited to the specific forms described in the embodiments.

Claims

1. A method for degrading toluene using a microbial electrolytic cell, characterized in that: The following steps are involved: 1) A microbial electrolysis cell separated by a proton exchange membrane is used, anaerobic activated sludge obtained from a sewage treatment plant and an anolyte containing microbial nutrients are added to the anode chamber, a continuous mixture of toluene and air is introduced into the anode chamber as the only carbon source, and an inorganic salt buffer solution is added to the cathode chamber; The anode chamber uses carbon aerogel or carbon aerogel grown with conductive polymer polypyrrole as an anode electrode, and the cathode chamber uses carbon cloth as an electrode and is connected to an electrochemical workstation through a wire. The electrochemical workstation provides an applied voltage to start the microbial electrolysis cell for domestication, so that an anode biofilm is formed on the anode electrode, which serves as the domesticated anode. The preparation of carbon aerogel specifically includes: S1: Mix sodium hydroxide, urea and deionized water evenly, put them in a refrigerator at 2-6°C for precooling for 10-30 minutes, then add the pulp that has been broken by a wall-breaking machine and stir for 2-4 hours, then add epichlorohydrin and stir for 0.5-2 hours, put the obtained material into a mold and age it in a water bath at 70-90°C for 6-10 hours, then replace it with deionized water until the pH is neutral, then put it in a refrigerator at -75°C to -85°C for freezing, and then put it in a freeze dryer to form aerogel; S2: placing the aerogel obtained in step S1 in a tubular furnace and annealing it in a nitrogen atmosphere for 1 to 3 h, and after cooling, preparing a carbon aerogel with a three-dimensional porous structure; Growth of carbon aerogel of conductive polymer polypyrrole, specifically comprising: M1: adding pyrrole to hydrochloric acid, and immersing the prepared carbon aerogel into the solution under magnetic stirring to obtain a pyrrole solution; M2: FeCl3 is added to hydrochloric acid to obtain a ferric chloride solution, and the ferric chloride solution is dripped into the pyrrole solution, wherein the ratio of pyrrole to FeCl3 is 0.5-2 mL: 2-4 g. After polymerization for 20-40 min, the carbon aerogel sheet is taken out and washed with deionized water until neutral, and then dried to obtain a carbon aerogel with a growing conductive polymer polypyrrole; 2) The anode is transformed into a packed bed electrode, the outer surface of which is non-conductive polytetrafluoroethylene. The tamed anode obtained in step 1) is broken into pieces and filled into polytetrafluoroethylene. A graphite rod is used as a current collector. The graphite rod is connected to the shell of the microbial electrolysis cell with conductive glue, and the anode and the cathode are connected with a wire to form a closed loop. Anode liquid, domesticated anaerobic activated sludge containing electroactive bacteria, and toluene are added to the anode chamber; The cathode chamber is an inorganic salt buffer solution; During operation, an external potential is provided by the electrochemical workstation, and electrons are conducted from the circuit on the anode to the cathode, driving the anode microorganisms to degrade toluene.

2. The method for degrading toluene by a microbial electrolytic cell according to claim 1, characterized in that: In step 1), the proton exchange membrane uses Nafion 117 as the proton exchange membrane.

3. The method for degrading toluene by a microbial electrolytic cell according to claim 1, characterized in that: In step 1), the anode liquid containing microbial nutrients is an inorganic salt buffer solution added with vitamins and mineral elements.

4. The method for degrading toluene by a microbial electrolytic cell according to claim 1, characterized in that: In step 1), the inorganic salt buffer solution is composed of Na2HPO4, NaH2PO4·2H2O, KCl, NH4Cl and deionized water, wherein the concentration of Na2HPO4 in the inorganic salt buffer solution is 27.2~37.2 mM, the concentration of NaH2PO4·2H2O is 12.8~22.8 mM, the concentration of KCl is 1.2~2.2 mM, and the concentration of NH4Cl is 3.8~7.8 mM.

5. The method for degrading toluene by a microbial electrolytic cell according to claim 1, characterized in that: In step 1), the external constant potential provided by the electrochemical workstation is 0.3~1.2 V vs. SHE anode potential.

6. The method for degrading toluene by a microbial electrolytic cell according to claim 1, characterized in that: In step 1), the microbial electrolytic cell is started for domestication. The domestication cycle is 3-5 days. The solutions in the two chambers are replaced after each cycle. After multiple batches of domestication, the toluene removal rate is close to stable and the domestication is completed.

7. The method for degrading toluene by a microbial electrolytic cell according to claim 1, characterized in that: In step S1, the mass ratio of urea, sodium hydroxide and pulp is 10-14:5-9:3-5; In step S2, the temperature of the tube furnace is 700-900°C.

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