A method for electrocatalytic enhancement of degradation of pollutants in nitrobenzene and phenolic wastewater

Abstract

The present application relates to wastewater treatment technical field, specifically to a kind of electrocatalysis enhanced method for degrading pollutants in nitrobenzene and phenol wastewater, comprising the following steps: S1, electrochemical system coupling two-phase anaerobic reactor, S2, pollutant degradation;The present application is a kind of processing method by combining electrochemistry and biotechnology, uses electrode as electron acceptor or donor, directional reinforcement microbial metabolic process, synchronous cracking two types of pollutants degradation inhibition, strengthen electron transfer efficiency and finally realize the efficient recovery of methane, can stably and efficiently realize the synergistic treatment and resource utilization of multiple pollutants, while reducing processing cost and environmental risk, it is a kind of efficient, economic, environmental protection nitrobenzene-containing wastewater and phenol-containing wastewater processing method.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wastewater treatment, in particular to a method for electrocatalytic enhancement of pollutant degradation in nitrobenzene and phenolic wastewater. BACKGROUND

[0002] Nitrobenzene-containing wastewater and phenolic wastewater are widely derived from petrochemical, pesticide, pharmaceutical, dye and explosive manufacturing industries, and have complex components, high biological toxicity and poor biodegradability, belonging to typical refractory organic wastewater. At present, the treatment methods for these two kinds of wastewater mainly include physical method (such as adsorption, extraction), chemical method (such as advanced oxidation, incineration) and biological method (such as anaerobic digestion, aerobic biological treatment). Physical and chemical methods often have problems such as high treatment cost, easy secondary pollution or high energy consumption, and are difficult to be applied on a large scale. Although the biological method has relatively low cost and is environmentally friendly, the traditional anaerobic biological treatment technology has many problems such as long start-up period, low treatment efficiency and unstable system operation when facing high toxicity and high concentration of nitrobenzene and phenol. The nitro group of nitrobenzene is a strong electron-withdrawing group, which is difficult to be directly degraded by microorganisms; while phenol is relatively easy to be degraded, but its inhibition threshold to microorganisms is low. When the two coexist, their combined toxicity effect further inhibits the activity of anaerobic microorganisms (especially methanogenic archaea), leading to metabolic imbalance between the hydrolysis acidification stage and the methanogenesis stage in the traditional two-phase anaerobic process, and finally causing treatment failure.

[0003] In the prior art, some studies have tried to improve the treatment effect by adding special bacterial agents or optimizing process parameters, but the improvement is limited, and the resistance to impact load is weak. In recent years, the treatment method combining electrochemistry and biotechnology (i.e. microbial electrochemical system) has shown broad prospects. The core is to use electrodes as electron acceptors or donors to direct the metabolic process of microorganisms, simultaneously break down the degradation inhibition of the two types of pollutants, strengthen the electron transfer efficiency and finally realize the efficient recovery of methane. However, most of the studies focus on single pollutant or simulated wastewater, and there is still a lack of efficient and stable solutions for the simultaneous treatment and methane recovery of nitrobenzene-containing wastewater and phenolic wastewater commonly found in actual industries.

[0004] Therefore, it is urgent to develop a new and efficient wastewater treatment method to realize the simultaneous degradation of nitrobenzene and phenolic wastewater and energy recovery and resource utilization, so as to achieve the dual purposes of pollution control and energy recovery. SUMMARY

[0005] In order to solve the above problems, the present application provides a method for electrocatalytic enhancement of pollutant degradation in nitrobenzene and phenolic wastewater.

[0006] The technical scheme of the present application is: a method for electrocatalytic enhancement of pollutant degradation in nitrobenzene and phenolic wastewater, comprising the following steps:

[0007] S1, coupling an electrochemical system to a two-phase anaerobic reactor

[0008] Electrodes are arranged in the hydrolysis-acidification tank and the methane production tank of the two-phase anaerobic reactor, and the electrodes in the hydrolysis-acidification tank are connected to the anode of the electrochemical system, and the electrodes in the methane production tank are connected to the cathode of the electrochemical system; the electrodes in the hydrolysis-acidification tank and the methane production tank are both nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2 heterojunction electrodes; the electrodes optimize the electronic structure by constructing Co3O4 / Co(OH)2 heterojunctions, enhance the electrical conductivity by using nitrogen-doped carbon, and improve the mass transfer efficiency by the porous structure, thereby improving the electrocatalytic performance; the nitrogen-doped carbon-coated porous structure can provide more active sites and exhibit excellent OER performance under acidic conditions, and is suitable for strengthening the electron transfer in the hydrolysis-acidification process;

[0009] S2, pollutant degradation

[0010] The nitrobenzene wastewater and the phenolic wastewater are mixed and injected into the two-phase anaerobic reactor, and an anaerobic biological reaction is carried out in the two-phase anaerobic reactor to degrade the pollutants in the mixed wastewater.

[0011] Further, the step of the anaerobic biological reaction is:

[0012] (1) sludge inoculation

[0013] Anaerobic sludge is inoculated into the bottom of the hydrolysis-acidification tank and the methane production tank to form a sludge bed, and the amount of anaerobic sludge added is such that the liquid level of the sludge bed is located at 1 / 2~2 / 3 of the height of the hydrolysis-acidification tank and the methane production tank;

[0014] (2) sludge cultivation and domestication

[0015] The nitrobenzene wastewater and the phenolic wastewater are injected into the hydrolysis-acidification tank through the water inlet pipe, and an external power source is turned on, and under the condition that the organic load is 0.2~1 kg COD / (m 3 ·d), the system is operated for 7~15 days, and then discharged along the water outlet at the top of the methane production tank, wherein the injection speed of the wastewater is 0.001~0.05 V1 mL / min, and the discharge speed is 0.001~0.05 V2 mL / min, V1 is the volume of the hydrolysis-acidification tank, and V2 is the volume of the methane production tank.

[0016] Description: Phenolic wastewater is degraded by microorganisms in the hydrolysis acidification tank, and the potential difference applied by the electrochemical system promotes the release of electrons to supply the nitrobenzene degrading bacteria, promotes the co-degradation of nitrobenzene and phenolic wastewater, and the electrons generated by the destruction of nitrobenzene and phenolic pollutants are transmitted to the methane production tank through the external circuit, and the intermediates (such as butyric acid and acetic acid) produced by them are transported into the methane production tank through the material transport channel between the two phases, and the anaerobic sludge utilizes the electrons transmitted by the hydrolysis acidification tank through the external circuit and the intermediates (such as butyric acid and acetic acid) produced by them to synthesize methane, keeping the pH of the hydrolysis acidification tank stable at 5.5-6.5, and the pH of the methane production tank stable at 7.0-7.5.

[0017] Further, the voltage of the electrochemical system is 1.2-2.5V, the electrode height is 3 / 4-1 of the sludge bed height, and the electrode width is 1 / 2-2 / 3 of the sludge bed height.

[0018] Description: The size of the electrode determines the area of the microorganisms stimulated by the electrode for catalysis, and the larger the area, the better the degradation effect of the microorganisms catalyzed by the electrode on the pollutants.

[0019] Further, the mass concentration ratio of nitrobenzene pollutants to phenolic pollutants after mixing the nitrobenzene wastewater and phenolic wastewater is 2-1:1.

[0020] Description: The phenol content under the above-mentioned ratio can effectively produce H2O2 and ·OH, while also reducing the competition of ·OH with nitrobenzene, causing excessive consumption of oxidants, and further improving the degradation effect of the mixed wastewater pollutants.

[0021] Further, the anaerobic sludge is washed 3-5 times with physiological saline with a mass concentration of 0.7-0.9% before inoculation, and the washing is performed until the volatile suspended solids (VSS) content in the anaerobic sludge is 2-5%.

[0022] Description: After the anaerobic sludge is washed with physiological saline, a suitable osmotic pressure environment is created for the microorganisms, thereby optimizing their activity and adaptability in degrading pollutants.

[0023] Further, the preparation method of the nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2 heterojunction electrode is as follows:

[0024] Preparation of precursor solution: Co(NO3)2·6H2O is dissolved in ethanol to obtain Co 2+ The concentration of the composite solution is 0.1-0.5M, then ammonia water with a volume concentration of 25-28% is added to adjust the pH of the composite solution to 9-10, and Co(OH)2 nanoparticle sol is obtained by water bath stirring at a temperature of 55-60℃, then polypyrrole is added to the Co(OH)2 nanoparticle sol to obtain the nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2 heterojunction electrode. 2+The molar ratio of the surfactant to Co(OH)2 is 0.1-1:1, and the surfactant is added to obtain the precursor solution. 2+ The molar ratio of the surfactant to Co(OH)2 is 0.1-1:1, and the surfactant is added to obtain the precursor solution.

[0025] Hydrothermal treatment: The precursor solution is transferred to a reaction kettle, and is reacted at 120-180℃ for 8-12h. After natural cooling to 25-30℃, centrifugal treatment is performed at a parameter of 7000-8000rpm for 8-10min, and the precipitate is washed with deionized water and ethanol alternately for 3-5 times.

[0026] Carbonization treatment: Finally, the precipitate is heated to 750-800℃ at a rate of 5-8℃ / min under nitrogen protection, and is naturally cooled at constant temperature for 2-4h to obtain the nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2 composite material.

[0027] Electrode preparation: The nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2 composite material, a conductive agent and a binder are mixed in a mass ratio of 7-8:2-3:1, and then N-methyl pyrrolidone is added to prepare a slurry with a viscosity of 5000-7000mPa·s. The slurry is coated on a foam nickel current collector in a coating amount of 3-5mg / cm 2 2

[0028] Description: The Co3O4(semiconductor) / Co(OH)2(hydroxide) heterojunction forms a built-in electric field, which can reduce the energy barrier of the H + + / H2 and O2 / H2O reaction in the hydrolysis and acidification process, and the electron transfer rate of Co3O4 / Co(OH)2 is higher than that of a single component. The nitrogen-doped carbon layer formed by carbonization of polypyrrole (containing pyridine nitrogen and pyrrole nitrogen) can improve the conductivity while providing additional active sites, further strengthening the electron transfer in the hydrolysis and acidification process. The slurry with the above viscosity can meet the requirements of smooth surface and no obvious leveling marks after the coating is scraped.

[0029] Further, the surfactant is F127; the conductive agent is Super P or acetylene black; and the binder is polyvinylidene fluoride.

[0030] Description: F127 can form an ordered mesoporous structure to improve the mass transfer efficiency. Super P has a chain structure and a large specific surface area, and can form a conductive network with acetylene black very effectively; polyvinylidene fluoride has strong adhesion, good chemical stability and good film-forming property.

[0031] Compared with the prior art, the present application has the beneficial effects that:

[0032] The present application organically couples an electrochemical system with a two-phase anaerobic reactor, sets an anode and a cathode in a hydrolysis acidification tank and a methane production tank respectively, and uses electrocatalysis to strengthen the synergistic treatment of nitrobenzene wastewater and phenolic wastewater. On the one hand, the anode as an electron sink significantly promotes the degradation of phenolic substances and the release of electrons, provides driving force for the reductive degradation of nitrobenzene, and strengthens the co-metabolism of the two pollutants; on the other hand, the cathode directly receives the electrons transmitted by the external circuit, efficiently drives the CO2 reduction to produce methane, and effectively consumes the volatile fatty acids (such as acetic acid, butyric acid, etc.) produced in the hydrolysis acidification stage, avoiding the accumulation of intermediate products leading to system acidification, and significantly improving the methane production rate and system operation stability. This method has a significant effect on the removal of typical refractory pollutants, with a removal rate of nitrobenzene pollutants exceeding 98% and a removal rate of phenolic pollutants exceeding 95%. At the same time, by converting pollutants into methane, wastewater is recycled and energy is recovered, reducing the cost of subsequent treatment and the risk of secondary pollution. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a structural schematic diagram of the electrochemical system coupled with the two-phase anaerobic reactor of the present application;

[0034] Figure 2 is a diagram of electrocatalysis strengthening nitrobenzene pollutant degradation of the present application;

[0035] Figure 3 is a diagram of electrocatalysis strengthening phenolic pollutant degradation of the present application;

[0036] Figure 4 is a diagram of electrocatalysis strengthening methane synthesis of the present application. DETAILED DESCRIPTION

[0037] To further illustrate the manner of carrying out the present application and to facilitate an understanding thereof, the technical solutions of the present application will be described in detail below with reference to experiments.

[0038] The nitrobenzene wastewater used in the present application includes, in terms of mass percentage: 2-5% of nitrobenzene, 1.5-2.5% of nitroso benzene, 1-2% of phenylhydroxylamine, 0.3-1.0% of aniline, ≤100 mg / L of suspended solids in the nitrobenzene wastewater, 2000-10000 mg / L of COD, and 6.0-7.0 of pH value.

[0039] The phenol wastewater used in the present application comprises, in terms of mass percentage: 1-4% of phenol, 0.5-1% of p-hydroxybenzoic acid, 0.2-5% of benzoic acid, ≤80 mg / L of suspended solids in the phenol wastewater, 1500-8000 mg / L of COD, and 6.5-7.0 of pH value (referred to as NBs and PhOHs with ES).

[0040] Embodiment 1: A method for electrocatalytically enhancing the degradation of pollutants in nitrobenzene and phenol wastewater, comprising the following steps:

[0041] S1, coupling an electrochemical system to a two-phase anaerobic reactor

[0042] Electrodes are arranged in the hydrolysis acidification tank and the methane production tank of the two-phase anaerobic reactor, and the electrodes in the hydrolysis acidification tank are connected to the anode of the electrochemical system, and the electrodes in the methane production tank are connected to the cathode of the electrochemical system; in the present embodiment, the electrodes in the hydrolysis acidification tank and the methane production tank are both carbon felt electrodes;

[0043] S2, pollutant degradation

[0044] After mixing the nitrobenzene wastewater and the phenol wastewater, the mixed wastewater is injected into the two-phase anaerobic reactor, and an anaerobic biological reaction is carried out in the two-phase anaerobic reactor to degrade the pollutants in the mixed wastewater.

[0045] In S2, the steps of the anaerobic biological reaction are:

[0046] (1) sludge inoculation

[0047] Anaerobic sludge is inoculated at the bottom of the hydrolysis acidification tank and the methane production tank to form a sludge bed, and the amount of the anaerobic sludge added is such that the liquid level of the sludge bed is located at 2 / 3 of the height of the hydrolysis acidification tank and the methane production tank; before inoculation, the anaerobic sludge is washed with physiological saline with a mass concentration of 0.8% for 4 times until the volatile suspended solids (VSS) content of the anaerobic sludge is 3%;

[0048] (2) sludge cultivation and domestication

[0049] Nitrobenzene wastewater and phenol wastewater are injected into the hydrolysis acidification tank through the water inlet pipe, and an external power source is turned on, and the system is operated for 11 days under the condition that the organic load is 0.6 kg COD / (m 3 ·d); then the effluent is discharged along the effluent port at the top of the methane production tank, wherein the injection speed of the wastewater is 0.02V1 mL / min, and the discharge speed is 0.02V2 mL / min, V1 is the volume of the hydrolysis acidification tank, and V2 is the volume of the methane production tank; the mass concentration ratio of the nitrobenzene pollutants to the phenol pollutants after mixing the nitrobenzene wastewater and the phenol wastewater is 3:1;

[0050] The voltage of the electrochemical system is 1.8 V, the electrode height is 7 / 8 of the sludge bed height, and the electrode width is 7 / 12 of the sludge bed height.

[0051] Example 2: Different from example 1, the anaerobic sludge is washed with 0.7% physiological saline for 5 times before inoculation, so that the volatile suspended solids VSS content in the anaerobic sludge is 2%.

[0052] Example 3: Different from example 1, the anaerobic sludge is washed with 0.9% physiological saline for 3 times before inoculation, so that the volatile suspended solids VSS content in the anaerobic sludge is 5%.

[0053] Example 4: Different from example 1, the organic load is 0.2 kg COD / (m 3 ·d) for 7 days, and then discharged along the effluent outlet at the top of the methane production tank, wherein the wastewater injection speed is 0.001V1 mL / min, and the discharge speed is 0.05V2 mL / min.

[0054] Example 5: Different from example 1, the organic load is 1 kg COD / (m 3 ·d) for 15 days, and then discharged along the effluent outlet at the top of the methane production tank, wherein the wastewater injection speed is 0.05V1 mL / min, and the discharge speed is 0.001V2 mL / min.

[0055] Example 6: Different from example 1, the voltage of the electrochemical system is 1.2 V, the electrode height is 3 / 4 of the sludge bed height, and the electrode width is 1 / 2 of the sludge bed height.

[0056] Example 7: Different from example 1, the voltage of the electrochemical system is 2.5 V, the electrode height is equal to the sludge bed height, and the electrode width is 2 / 3 of the sludge bed height.

[0057] Example 8: Different from example 1, the mass concentration ratio of nitrobenzene pollutants to phenolic pollutants is 2:1 after mixing the nitrobenzene wastewater and the phenolic wastewater.

[0058] Example 9: Different from example 1, the mass concentration ratio of nitrobenzene pollutants to phenolic pollutants is 1:1 after mixing the nitrobenzene wastewater and the phenolic wastewater.

[0059] Example 10: Different from example 1, the electrodes in the hydrolysis acidification tank and the methane production tank are nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2 heterojunction electrodes.

[0060] The preparation method of the nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2 heterojunction electrode is as follows:

[0061] Precursor solution preparation: Co(NO3)2·6H2O was dissolved in ethanol to obtain Co 2+ concentration of 0.3M, and then ammonia water with a volume concentration of 27% was added to adjust the pH of the complex solution to 9.5. Co(OH)2nanoparticle sol was obtained by stirring in a water bath at a temperature of 58℃. Then, polypyrrole was added according to a molar ratio of polypyrrole to Co 2+ , and finally F127 was added according to a molar ratio of F127 to Co 2+ , to obtain the precursor solution.

[0062] Hydrothermal treatment: the precursor solution was transferred to a reaction kettle and reacted at 150℃ for 10h. After natural cooling to 28℃, centrifugal treatment was performed at a parameter of 7500rpm for 9min, and the precipitate was washed with deionized water and ethanol alternately for 4 times.

[0063] Carbonization treatment: finally, the precipitate was heated to 775℃ at a rate of 7℃ / min under nitrogen protection, and kept at a constant temperature for 3h, and then naturally cooled to obtain nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2composite material.

[0064] Electrode preparation: the nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2composite material, a conductive agent and a binder were mixed according to a mass ratio of 15:5:2, and then N-methyl pyrrolidone was added to prepare a slurry with a viscosity of 6000mPa·s. Then, the slurry was coated on a foam nickel current collector according to a coating amount of 4mg / cm 2 , and then vacuum dried at 110℃ for 11h, and finally pressed into a sheet under a pressure of 15MPa for 45s to obtain a nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2heterojunction electrode. The conductive agent was Super P, and the binder was polyvinylidene fluoride.

[0065] Example 11: different from example 10, Co(NO3)2·6H2O was dissolved in ethanol to obtain Co 2+ concentration of 0.1M, and then ammonia water with a volume concentration of 25% was added to adjust the pH of the complex solution to 9. In a water bath, Co(OH)2nanoparticle sol was obtained by stirring at a temperature of 55℃. Then, polypyrrole was added according to a molar ratio of polypyrrole to Co 2+ , and finally F127 was added according to a molar ratio of F127 to Co 2+ , to obtain the precursor solution.

[0066] Example 12: different from example 10, Co(NO3)2·6H2O was dissolved in ethanol to obtain Co 2+The complex solution with a concentration of 0.5 M was then adjusted to a pH of 10 by adding ammonia water with a volume concentration of 28%, and a Co(OH)2nanoparticle sol was obtained by stirring in a water bath at a temperature of 60°C. Then, polypyrrole was added according to a molar ratio of 1:3 of polypyrrole to Co(OH)2. Finally, F127 was added according to a molar ratio of 1:1 of F127 to Co(OH)2, and a precursor solution was obtained by mixing. 2+ 2+

[0067] Example 13: Different from Example 10, the precursor solution was transferred to a reaction kettle, reacted at 120°C for 8 h, naturally cooled to 25°C, centrifuged at a parameter of 7000 rpm for 8 min, washed with deionized water and ethanol alternately for 3 times, and the precipitate was collected. Finally, the precipitate was heated to 750°C at a rate of 5°C / min under nitrogen protection, kept at 750°C for 2 h, and naturally cooled to obtain a nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2composite material.

[0068] Example 14: Different from Example 10, the precursor solution was transferred to a reaction kettle, reacted at 180°C for 12 h, naturally cooled to 30°C, centrifuged at a parameter of 8000 rpm for 10 min, washed with deionized water and ethanol alternately for 5 times, and the precipitate was collected. Finally, the precipitate was heated to 800°C at a rate of 8°C / min under nitrogen protection, kept at 800°C for 4 h, and naturally cooled to obtain a nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2composite material.

[0069] Example 15: Different from Example 10, the nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2composite material, a conductive agent, and a binder were mixed according to a mass ratio of 7:2:1, and then N-methyl pyrrolidone was added to prepare a slurry with a viscosity of 5000 mPa·s.

[0070] Example 16: Different from Example 10, the nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2composite material, a conductive agent, and a binder were mixed according to a mass ratio of 8:3:1, and then N-methyl pyrrolidone was added to prepare a slurry with a viscosity of 7000 mPa·s; the conductive agent was acetylene black.

[0071] Example 17: Different from Example 10, the slurry was then coated on a foam nickel current collector according to a coating amount of 3 mg / cm 2 , vacuum dried at 100°C for 10 h, and finally pressed into a sheet under a pressure of 10 MPa for 30 s to obtain a nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2heterojunction electrode.

[0072] Example 18: Different from Example 10, the slurry was then coated on a foam nickel current collector according to a coating amount of 5 mg / cm 2 ​​The coating amount of the coating solution of the above-mentioned coating solution is coated on a foamed nickel current collector, vacuum dried at 120°C for 12h, and finally pressed into a sheet under a pressure of 20MPa for 60s to obtain a nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2 heterojunction electrode.

[0073] Experimental Example: The description of this experimental example is based on the description in Example 1, and is intended to illustrate the practical application effect of the present application. Gas component test method: The gases to be determined in this system include methane. The data obtained by this method is detected by gas chromatography (Agilent 6890N, USA). Pollutant detection: The concentration changes of nitrobenzene and phenolic toxic substances (nitrobenzene, nitrosobenzene, phenylhydroxylamine, aniline, phenol, hydroxybenzoic acid, benzoic acid) are directly detected by HPLC and GC-MS.

[0074] 1. Experimental design: In order to illustrate the treatment effect of the method of the present application on wastewater, the following experimental groups are designed:

[0075] Control group 1: Different from Example 1, the voltage of the electrochemical system is 0 V.

[0076] Control group 2: Different from Example 1, during the sludge cultivation and domestication process, only nitrobenzene-containing wastewater is injected through the water inlet pipe.

[0077] Control group 3: Different from Example 1, during the sludge cultivation and domestication process, only phenol-containing wastewater is injected through the water inlet pipe.

[0078] As shown in Figure 2 and Figure 3 , after the electrocatalysis (NBs and PhOHs with ES) of the mixed wastewater containing nitrobenzene and phenol, the removal efficiencies of nitrobenzene and phenol pollutants are more than 98% and 95%, respectively. Compared with the mixed wastewater group (NBs and PhOHs without ES) without electrocatalysis, the removal efficiencies of nitrobenzene and phenol pollutants are increased by more than 15% and 25%, respectively. In addition, the pollutant removal efficiency of the mixed wastewater in the control group 1 is higher than that of the nitrobenzene or phenol wastewater pollutants in the control group 2 or the control group 3, which indicates that when these two types of wastewater coexist, there is a synergistic effect of promoting degradation, and electrocatalysis further promotes the utilization of electrons released during the degradation of pollutants by applying a potential difference, and promotes the co-degradation of nitrobenzene and phenol wastewater.

[0079] As shown in Figure 4As shown, the electrocatalysis promotes the conversion of nitrobenzene and phenolic pollutants to intermediate products (such as butyric acid, acetic acid, etc.) that can be easily utilized by methanogens, and the methanogens in the methane production tank utilize the electrons transmitted by the external circuit from the hydrolytic acidification tank and the intermediate products (such as butyric acid, acetic acid, etc.) generated thereby to synthesize methane, and the methane production is increased by more than 30% relative to the case without electrocatalysis. Therefore, it is shown that the electrocatalysis method of the present application has a positive effect on the removal of pollutants in nitrobenzene and phenolic wastewater, and can further promote methane synthesis.

[0080] 2. Explore the effect of nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2 heterojunction electrodes on wastewater treatment

[0081] Control group 4: the electrode in the hydrolytic acidification tank is a carbon felt electrode, and the electrode in the methane production tank is a nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2 heterojunction electrode.

[0082] Control group 5: the electrode in the hydrolytic acidification tank is a nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2 heterojunction electrode, and the electrode in the methane production tank is a carbon felt electrode.

[0083] Table 1: Effect of treatment methods of Example 1, Example 10-Example 18 and Control Group 4-Control Group 5 on wastewater treatment

[0084]

[0085] From the data in Table 1 and the comparison with Control Group 4, it can be seen that, relative to the carbon felt electrode, the nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2 heterojunction electrode has better conductivity efficiency, thereby promoting the electron transfer efficiency of the microbial community, and the pollutant degradation efficiency is increased by more than 20%, and the connection of the nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2 heterojunction electrode in the hydrolytic acidification tank is more effective, and the pollutant removal efficiency and methane production rate are increased by 53% and 26%, while the connection of the nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2 heterojunction electrode in the hydrolytic acidification tank and the methane production tank only increases the pollutant removal efficiency and methane production rate by 63% and 30%. The electrode in the methane production tank in Control Group 5 is a carbon felt electrode, which limits the wastewater treatment, mainly because the methane production tank is the most critical place for the degradation of nitrobenzene, but the catalytic activity of the cathode (carbon felt) is low, resulting in a "bottleneck" in the reduction efficiency of the entire system, a small amount of H2 is produced and the efficiency is low, the rate of reduction of nitrobenzene to aniline is slow, and the nitrobenzene that is not degraded in time will strongly inhibit the activity of methanogens, making the methane production of the entire anaerobic system difficult.

[0086] The reason for the above phenomenon is that the nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2 heterojunction electrode optimizes the electronic structure by constructing a Co3O4 / Co(OH)2 heterojunction electrode, enhances the electrical conductivity by using nitrogen-doped carbon, and improves the mass transfer efficiency by the porous structure, thereby improving the electrocatalytic performance. The nitrogen-doped carbon-coated porous structure provides more active sites, which is suitable for strengthening the electron transfer in the hydrolysis acidification process. And because the degradation of pollutants is mainly concentrated in the acidification phase, connecting the nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2 heterojunction electrode in the hydrolysis acidification tank has better conductivity and pollutant degradation efficiency. Therefore, this electrode structure can significantly promote the decomposition and conversion of organic pollutants and improve the overall treatment efficiency of the system.

[0087] In summary, the nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2 heterojunction electrode has excellent electron conduction ability, rich active interface and efficient mass transfer characteristics. The Co3O4 / Co(OH)2 heterojunction electrode itself is an excellent hydrogen evolution reaction catalyst. The nitrogen-doped carbon layer further improves its electrical conductivity and stability. This means that at the same voltage, the cathode of the methane production tank can produce more and more active H2 and electrons. These abundant reducing agents can greatly accelerate the process of reducing nitrobenzene (highly toxic and difficult to degrade) to aniline (less toxic and easy to degrade), thereby relieving its inhibition on methanogens and promoting the complete mineralization of subsequent pollutants such as phenol (CH4 / CO2). It is especially suitable for wastewater treatment processes and has important application value in enhancing the degradation of nitrobenzene and phenol pollutants in the wastewater treatment process.

Claims

1. A method for electrocatalytically enhancing the degradation of pollutants in nitrobenzene and phenolic wastewater, characterized in that, The method comprises the following steps: S1, coupling the electrochemical system to the two-phase anaerobic reactor Electrodes are arranged in the hydrolysis acidification tank and the methane production tank of the two-phase anaerobic reactor respectively, and the electrodes in the hydrolysis acidification tank are connected to the anode of the electrochemical system, and the electrodes in the methane production tank are connected to the cathode of the electrochemical system; the electrodes in the hydrolysis acidification tank and the methane production tank are both nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2 heterojunction electrodes; S2, pollutant degradation After mixing the nitrobenzene wastewater and the phenolic wastewater, the mixed wastewater is injected into the two-phase anaerobic reactor, and an anaerobic biological reaction is carried out in the two-phase anaerobic reactor to degrade the pollutants in the mixed wastewater.

2. A method of electro-catalytic enhanced degradation of pollutants in nitrobenzene and phenolic waste water as claimed in claim 1, wherein, The step of the anaerobic biological reaction is: (1) sludge inoculation Anaerobic sludge is inoculated at the bottom of the hydrolysis acidification tank and the methane production tank to form a sludge bed, and the amount of the anaerobic sludge added is such that the liquid level of the sludge bed is located at 1 / 2~2 / 3 of the height of the hydrolysis acidification tank and the methane production tank. (2) sludge cultivation and domestication The nitrobenzene series wastewater and phenol series wastewater are injected into the hydrolysis acidification tank through the water inlet pipe, an external power supply is turned on, and the operation is carried out under the condition that the organic load is 0.2-1 kg COD / (m 3 ·d) for 7-15 days, and then discharged along the effluent outlet at the top of the methane production tank, wherein the injection speed is 0.001-0.05 V1 mL / min, the discharge speed is 0.001-0.05 V2 mL / min, V1 is the volume of the hydrolysis acidification tank, and V2 is the volume of the methane production tank.

3. The method for electrocatalytically enhanced degradation of pollutants in nitrobenzene and phenol wastewater as described in claim 2, characterized in that, The voltage of the electrochemical system is 1.2~2.5V, the height of the electrode is 3 / 4~1 of the height of the sludge bed, and the width of the electrode is 1 / 2~2 / 3 of the height of the sludge bed.

4. A method of electro-catalytic enhanced degradation of pollutants in nitrobenzene and phenolic waste water as claimed in claim 1 wherein, After mixing, the mass concentration ratio of the nitrobenzene pollutants to the phenolic pollutants is 2~1:

1. ​ 5. The method for electrocatalytically enhanced degradation of pollutants in nitrobenzene and phenol wastewater as described in claim 2, characterized in that, Before inoculation of the anaerobic sludge, the physiological saline with a mass concentration of 0.7~0.9% is used to clean 3~5 times.

6. A method of electro-catalytic enhanced degradation of pollutants in nitrobenzene and phenolic waste water as claimed in claim 1 wherein, The preparation method of the nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2 heterojunction electrode is: The precursor solution is prepared as follows: Co(NO3)2-6H2O is dissolved in ethanol to obtain Co 2+ The complex solution with a concentration of 0.1-0.5 M is prepared, then ammonia water with a volume concentration of 25-28% is added to adjust the pH of the complex solution to 9-10, and the Co(OH)2nanoparticle sol is obtained by water bath stirring at a temperature of 55-60°C. 2+ The polypyrrole is added according to a molar ratio of 1:1-3 of polypyrrole to Co 2+ The surfactant is added according to a molar ratio of 0.1-1:1 of surfactant to Co 2+ , and the precursor solution is obtained by mixing. hydrothermal treatment: the precursor solution is transferred to a reaction kettle, reacted at 120~180℃ for 8~12h, naturally cooled to 25~30℃, centrifuged at 7000~8000rpm for 8~10min, and washed with deionized water and ethanol alternately for 3~5 times, and the precipitate is collected; carbonization treatment: finally, the precipitate is heated to 750~800℃ at 5~8℃ / min under nitrogen protection, kept at constant temperature for 2~4h, and naturally cooled to obtain a nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2 composite material; Electrode preparation: the nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2 composite material, a conductive agent and a binder are mixed in a mass ratio of 7-8:2-3:1, then N-methyl pyrrolidone is added to prepare a slurry with a viscosity of 5000-7000 mPa·s, then the slurry is coated on a foamed nickel current collector at a coating amount of 3-5 mg / cm 2 , vacuum dried at 100-120 °C for 10-12 h, and finally pressed into a sheet under a pressure of 10-20 MPa for 30-60 s to obtain the nitrogen-doped carbon-coated porous Co3O4 / Co(OH)2 heterojunction electrode.

7. A method of electro-catalytically enhancing degradation of pollutants in nitrobenzene and phenolic waste water as claimed in claim 6 wherein, the surfactant is F127; the conductive agent is Super P or acetylene black; and the binder is polyvinylidene fluoride.

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