Method for strengthening degradation of nitrogen-containing heterocyclic compounds by electrocatalytic coupling of nitrate to build aerobic / anoxic microenvironment

Abstract

The application discloses a method for strengthening degradation of nitrogen-containing heterocyclic compounds by constructing aerobic / anoxic microenvironment through electrocatalysis coupling nitrate nitrogen. The method uses a transition metal hydroxyl oxide / graphite felt modified electrode material as an anode and is arranged at the bottom of a cross-flow upflow microbial reactor, nitrogen-containing heterocyclic compound wastewater is introduced from the lower end of the anode, nitrate nitrogen is added into the water as an electron acceptor, and the aerobic / anoxic microenvironment is constructed through an applied voltage to strengthen degradation of the nitrogen-containing heterocyclic compounds. The application introduces electrocatalysis to construct the aerobic / anoxic microenvironment in the microbial system, and simultaneously adds the nitrate nitrogen to supplement the electron acceptor under the anoxic condition, so that the ability of the biological system to resist external environmental fluctuations can be effectively improved, and the long-term stability of the biological system is promoted, and under the optimal condition, the removal rate of the nitrogen-containing heterocyclic compounds in the wastewater can reach more than 96%. The method is low in cost, efficient and simple, reduces high energy consumption under ordinary mechanical aeration, and reduces volatilization of organic pollutants.

Description

Technical Field

[0001] This invention belongs to the field of nitrogen-containing heterocyclic compound wastewater treatment technology, and relates to a method for enhancing the degradation of nitrogen-containing heterocyclic compounds by constructing an aerobic / anoxic microenvironment through electrocatalysis coupled with nitrate nitrogen. Background Technology

[0002] Nitrogen-containing heterocyclic compounds are common pollutants in industrial wastewater. Because the ring structure of nitrogen-containing heterocyclic compounds is a closed conjugated system, they are usually structurally stable and difficult to degrade, and can exist in the environment for a long time, posing potential hazards to the ecology and human health.

[0003] The main methods for treating wastewater containing nitrogen heterocyclic compounds are physicochemical and biological methods. Physicochemical methods include photocatalytic degradation, ozone oxidation, membrane separation, and electrochemical oxidation. While these methods are effective and fast, they suffer from high costs and energy consumption, and can even lead to secondary pollution. Commonly used biological treatment technologies include anaerobic, anoxic, and aerobic biological technologies. Anaerobic biological technologies have low degradation efficiency and poor stability; anoxic biological technologies lack electron acceptors such as nitrates and nitrites in the microorganisms to promote the ring-opening of nitrogen heterocyclic compounds; while aerobic biological technologies have high degradation efficiency and good effluent quality, and are widely used in wastewater treatment. However, for traditional aerobic biological treatment technologies, the dissolved oxygen content in the water is crucial to the entire degradation system. To maintain sufficient dissolved oxygen in the biodegradation system, additional aeration devices are needed to continuously replenish dissolved oxygen, which increases operating costs and equipment energy consumption, and can also easily lead to the volatilization of pollutants, causing secondary air pollution. Physical, chemical, and biological methods have all been applied to the treatment of recalcitrant organic wastewater. In recent years, research on novel biological treatment technologies that enhance the biological treatment effect through physicochemical means has also attracted increasing attention.

[0004] Chinese patent application 202110280792.2 discloses an apparatus and method for treating wastewater containing nitrogen-containing heterocyclic compounds. The apparatus includes an upflow reactor and a temperature control structure. The reactor is equipped with assembled electrodes and filled with anaerobic sludge. Following the direction from inlet to outlet within the reactor, the assembled electrodes sequentially include an electrochemical anode, a reference electrode, and an electrochemical cathode. The electrochemical anode is constructed by binding a titanium mesh of Ru and Ir oxides with graphite felt. The anaerobic sludge must completely submerge the surfaces of the anode and cathode. The method utilizes an externally applied voltage to construct an electrically assisted micro-aerobic system to enhance the degradation of wastewater containing N-methylpyrrolidone. This method couples electrochemical and biotechnology, using an anode coated with an oxygen evolution catalyst to catalyze oxygen evolution under a certain voltage, providing a micro-aerobic environment for the enhanced degradation of pollutants, promoting the growth of functional microorganisms, and strengthening electron transfer between pollutants, electrodes, and microorganisms. While this method improves the biodegradation performance of nitrogen-containing heterocyclic compounds to some extent, the anode raw materials used are precious metals, resulting in high costs and making practical application difficult. The degradation efficiency of nitrogen-containing heterocyclic compounds in the anoxic environment of the reactor cannot be guaranteed. At the same time, the upflow reactor is greatly affected by the fluctuation of the influent flow rate, which can easily cause sludge to float to the surface and there is also the problem of insufficient contact between pollutants and electrode surfaces. Summary of the Invention

[0005] To address the problems of high energy consumption, high gas loss, and gas volatilization pollution associated with existing aerobic biological treatment methods for nitrogen-containing heterocyclic compound wastewater, as well as the high cost and poor oxygen evolution capacity of electrode materials in electrocatalytic oxygen production, and the lack of electron acceptors for microorganisms in anoxic environments, this invention provides a method for enhancing the degradation of nitrogen-containing heterocyclic compounds by constructing an aerobic / anoxic microenvironment through electrocatalysis coupled with nitrate nitrogen. This method utilizes an electrode material loaded with transition metal hydroxyl oxides for oxygen evolution. Oxygen directly passes through a biofilm loaded on the anode surface, achieving in-situ mass transfer and creating an aerobic / anoxic environment. Combined with the fact that nitrate nitrogen can act as an electron acceptor under anoxic conditions, aerobic / anoxic biodegradation of nitrogen-containing heterocyclic compound wastewater is achieved. Furthermore, the use of a cross-flow upflow reactor reduces the reactor volume, improves the reactor's resistance to shock loads, and promotes greater contact between organic pollutants and microorganisms on the electrode surface, thereby improving degradation efficiency.

[0006] The technical solution adopted in this invention is as follows:

[0007] A method for enhancing the degradation of nitrogen-containing heterocyclic compounds by constructing an aerobic / anoxic microenvironment through electrocatalysis coupled with nitrate nitrogen involves first preparing a transition metal hydroxyl oxide / graphite felt modified electrode material, then constructing an electrocatalytic aerobic / anoxic biological system. Oxygen generated from the electrocatalytic decomposition of water by transition metal hydroxyl oxides is passed through a biofilm loaded on the electrode material surface to create the aerobic / anoxic environment, coupled with nitrate nitrogen for the degradation of nitrogen-containing heterocyclic compound wastewater. The specific steps are as follows:

[0008] Step 1: Using a three-electrode system, the anode is graphite felt, the cathode is platinum sheet, the reference electrode is Ag / AgCl electrode, and the transition metal salt solution is the electrolyte. A constant current density is applied to the three-electrode system using an electrochemical workstation, and transition metal hydroxy oxides are attached to the surface of graphite felt by electrodeposition. After deposition, the graphite felt is removed, cleaned, and dried to obtain the transition metal hydroxy oxide / graphite felt modified electrode material.

[0009] Step 2: The transition metal hydroxyl oxide / graphite felt modified electrode material is placed at the bottom of the cross-flow rising microbial reactor as the anode, and ordinary graphite felt is placed at the top of the cross-flow rising microbial reactor as the cathode. A reference electrode is placed between the two. Anaerobic sludge is added to completely cover the anode. A constant voltage is applied to the anode and cathode. At the same time, wastewater containing nitrogen-containing heterocyclic compounds and nitrate nitrogen is introduced from the lower end of the anode to realize the electrocatalytic construction of an aerobic / anoxic system coupled with enhanced microbial degradation of nitrate nitrogen.

[0010] Preferably, in step 1, the transition metal is selected from one or more of Co, Fe, and Ni.

[0011] Preferably, in step 1, the transition metal salt is selected from one or more of Co(NO3)2·6H2O, FeCl2·4H2O, and Ni(NO3)2·6H2O.

[0012] Preferably, in step 1, the concentration of transition metal ions in the transition metal salt solution is 0.1 M.

[0013] Preferably, in step 1, the constant current density is -16 to -32 mA·cm⁻¹. -2 The electrodeposition time is 30~120 min, the drying temperature is 80℃, and the drying time is 5~48 h.

[0014] Preferably, in step 2, the inoculated sludge is taken from a bioreactor treating wastewater containing nitrogen heterocyclic compounds, and the initial sludge inoculation amount is 6.0~10.0 g·L⁻¹. -1 .

[0015] Preferably, in step 2, the constant voltage is 1.2~1.6 V, and the concentration of nitrate nitrogen in the wastewater is 10~100 mg·L⁻¹. -1 .

[0016] Preferably, in step 2, the nitrate nitrogen is a nitrate such as sodium nitrate or potassium nitrate. In a specific embodiment of the present invention, sodium nitrate is used as an example.

[0017] Preferably, in step 2, the nitrogen-containing heterocyclic compound is quinoline, indole, pyridine, etc. In a specific embodiment of the present invention, pyridine is taken as an example.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) This invention couples electrocatalysis with biotechnology. It constructs an aerobic / anoxic microenvironment to enhance the degradation of nitrogen-containing heterocyclic compounds by electrocatalysis coupled with nitrate nitrogen. The anode is a transition metal hydroxyl oxide / graphite felt modified electrode material. The transition metal hydroxyl oxide material decomposes water to release oxygen under a certain applied voltage. Since the modified electrode material has strong hydrophilicity, looseness and pores, the generated oxygen directly reaches the biolayer in the microbial reaction system (attached to the surface of the electrode material), forming an aerobic-anoxic microbial layer structure. This is conducive to the in-situ utilization of aerobic microorganisms and the rapid decomposition of organic matter. It changes the traditional oxygen supply mode and improves the utilization rate of O2. After a period of selection, the microbial structure evolves in a direction that is more conducive to the degradation of pollutants, which improves the system's tolerance and activity to pollutants and greatly improves the system's stability. It solves the problems of traditional nitrogen-containing heterocyclic compounds such as pyridine being volatile and having high gas loss and cost in aerobic biological treatment. At the same time, the microorganisms in the anoxic layer use nitrate nitrogen in the influent as an electron acceptor to further open the ring of nitrogen-containing heterocyclic compounds, converting them from large molecular organic matter into small molecular inorganic matter.

[0020] (2) The aerobic / anoxic microenvironment formed by electrocatalytic coupling of nitrate nitrogen constructed in this invention promotes the growth of functional microorganisms, strengthens the electron transfer between pollutants and microorganisms, reduces the energy waste and gas pollution caused by mechanical aeration in traditional biodegradation, and the cross-flow rising reactor increases the contact time between pollutants and microorganisms, improves degradation efficiency, and has the potential for large-scale industrial application. Attached Figure Description

[0021] Figure 1 This is a simplified schematic diagram of the device used in this invention, wherein an inlet ① is provided at one end of the bottom of the reactor, an outlet ⑤ is provided at the other end of the top, and an anode ②, a reference electrode ③ and a cathode ④ are provided inside, and anaerobic sludge ⑥ is filled inside.

[0022] Figure 2 This is a graph showing the pyridine removal performance of different reaction systems in Example 1.

[0023] Figure 3 These are linear voltammetric scan curves of different modified electrode materials. Detailed Implementation

[0024] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings. These embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the invention.

[0025] The graphite felt with strong hydrophilicity and high porosity used in the following embodiments was purchased from Sichuan Junrui Carbon Fiber Materials Co., Ltd.

[0026] Example 1

[0027] 1. Preparation of CoOOH / graphite felt modified electrode material: Co(NO3)2·6H2O was dissolved in ultrapure water aerated with N2 for 15 min to achieve a Co ion concentration of 0.1 M. The solution was magnetically stirred for 30 min until completely dissolved, and then aerated with N2 for 15 min. Strongly hydrophilic and porous graphite felt was cut into 6 cm diameter circles to synthesize the anode, a 2 × 2 cm platinum sheet was used as the cathode, and Ag / AgCl was used as the counter electrode. The current density was set to -16 mA·cm². -2 The deposition time was 30 min. CoOOH was deposited on the surface of graphite felt using a constant current method. The graphite felt was then removed, rinsed with ultrapure water, and dried in an 80℃ oven for 12 h to obtain the CoOOH / graphite felt modified electrode material. This electrode material is characterized by its ease of synthesis, high biocompatibility, presence of electrocatalytic materials, and strong hydrophilicity.

[0028] 2. Four cross-flow reactors were set up: an electrocatalytic oxygen evolution coupled with nitrate nitrogen bioreactor, an electrocatalytic oxygen evolution bioreactor, an anoxic coupled with nitrate nitrogen bioreactor, and an anaerobic control bioreactor, for which pyridine degradation experiments were conducted. See the bioreactor schematic diagram below. Figure 1 The reactor has an inlet ① at one end of its bottom and an outlet ⑤ at the other end of its top. Inside the reactor are an anode ②, a reference electrode ③, and a cathode ④, filled with anaerobic sludge ⑥. Following the direction of water flow from inlet to outlet within the reactor, the anode consists of two sets of CoOOH / graphite felt modified electrode materials. The two graphite felt pieces in each set are bound together with titanium wire, and the anaerobic sludge must completely submerge the anode surface. Specifically, the setup of each cross-flow reactor is as follows:

[0029] (1) Electrocatalytic oxygen evolution coupled nitrate nitrogen bioreactor: This consists of a microbial reaction system and a CoOOH / graphite felt modified electrode. The CoOOH / graphite felt modified electrode is placed at the bottom of the bioreactor as the anode, the middle part is an Ag / AgCl reference electrode, and the top part is an unmodified graphite felt as the cathode. Simulated wastewater is introduced into the microbial reaction system, and an external voltage is applied to the oxygen evolution potential. The applied voltage is 1.4 V, and an additional 80 mg·L⁻¹ of oxygen is added to the reactor influent. -1Sodium nitrate acts as an electron acceptor.

[0030] (2) Electrocatalytic oxygen evolution bioreactor: It has the same structure as the electrocatalytic oxygen evolution coupled nitrate nitrogen bioreactor, and no additional sodium nitrate is added to the influent.

[0031] (3) Anoxic coupled nitrate nitrogen bioreactor: The structure is the same as that of the electrocatalytic oxygen evolution coupled nitrate nitrogen bioreactor, with an applied voltage of 0 and an influent sodium nitrate concentration of 80 mg·L. -1 .

[0032] (4) Anaerobic control bioreactor: It has the same structure as the electrocatalytic oxygen evolution coupled nitrate nitrogen bioreactor, with an applied voltage of 0 and an influent sodium nitrate concentration of 0.

[0033] The microbial reaction systems of the four reactors described above all consisted of equal volumes of simulated wastewater and inoculated sludge. The simulated wastewater was 300 mg·L⁻¹. -1 pyridine solution, phosphate buffer at pH 7, and 1 mL·L -1 SL-4. The inoculum sludge was taken from a bioreactor treating pyridine-containing wastewater, with an initial inoculum size of 10 g·L⁻¹. -1 .

[0034] The pyridine removal performance of different reaction systems, such as Figure 2 As shown, the pyridine degradation rate in the electrocatalytic oxygen evolution coupled nitrate nitrogen reactor at an applied voltage of 1.4 V was significantly higher than that in the other three reactor groups. Comparison with the anoxic bioreactor and the anaerobic control bioreactor under the same conditions revealed that their pyridine degradation rates were relatively slow. This suggests that the removal of some pyridine may be due to the oxygen generated by electrocatalysis reaching the microbial layer, which facilitates in-situ utilization by aerobic microorganisms and rapid decomposition of organic matter. Comparison with the electrocatalytic oxygen evolution bioreactor without added nitrate nitrogen showed that the addition of nitrate nitrogen effectively enhanced the pyridine degradation rate, and the bioreactor was more stable with minimal fluctuations in the pyridine removal rate.

[0035] In the electrocatalytic oxygen evolution coupled nitrate nitrogen reactor, oxygen generated from the electrocatalytic decomposition of water by CoOOH is transferred to the biofilm on the electrode surface, forming an aerobic-anoxic biolayer structure. Pyridine is oxidized and decomposed in the aerobic layer and then reaches the anoxic layer, where it is further decomposed and mineralized under the action of nitrate nitrogen as an electron acceptor. This achieves the purpose of aerobic / anoxic coupled nitrate nitrogen biodegradation of nitrogen-containing heterocyclic compound wastewater. It not only promotes the growth of functional microorganisms and enhances electron transfer between pollutants and microorganisms, but also reduces the energy waste and gas pollution caused by mechanical aeration in traditional biodegradation. At the same time, it increases the system's resistance to shock loads, providing a certain theoretical and practical basis for industrial applications.

[0036] Comparative Example 1

[0037] Five different electrode materials were prepared to investigate their oxygen evolution performance, as detailed below:

[0038] (1) Co 0.4 Fe 0.6 OOH / graphite felt modified electrode material: The preparation method is basically the same as that of CoOOH / graphite felt modified electrode material in Example 1, except that Co(NO3)2 is replaced with Co(NO3)2·6H2O and FeCl2·4H2O, and the molar ratio of Co ions to Fe ions is 2:3.

[0039] (2) CoOOH / foam titanium modified electrode material: The preparation method is basically the same as that of CoOOH / graphite felt modified electrode material in Example 1, except that graphite felt is replaced with foam titanium.

[0040] (3) CoOOH / pure titanium modified electrode material: The preparation method is basically the same as that of CoOOH / graphite felt modified electrode material in Example 1, except that graphite felt is replaced with pure titanium.

[0041] (4) Spinel Co3O4 / graphite felt electrode material: synthesized by sol-gel method, the specific process is as follows: Co(NO)3·6H2O is added to 9 mL of 1.5 M citric acid solution to control the Co ion content at 9 mmol. The resulting solution is stirred and heated at 80℃ for 3 h to convert it into a thick gel. The gel is placed in a 120℃ constant temperature drying oven and dried for 12 h, and then calcined in air at 800℃ for 5 h to obtain spinel Co3O4. Spinel Co3O4 and binder PTFE with a mass ratio of 8:2 are added to a mixed solution of water and isopropanol with a volume ratio of 1:1. The resulting mixture is homogenized in an ultrasonic bath to prepare catalyst ink. The catalyst ink is uniformly coated on graphite felt and dried in a 80℃ constant temperature drying oven for 10 h to obtain spinel Co3O4 / graphite felt electrode material.

[0042] (5) Spinel Co3O4 / graphite felt S electrode material: The above spinel Co3O4 / graphite felt was calcined in air at 325°C for 15 min to obtain spinel Co3O4 / graphite felt S electrode material.

[0043] Linear current-voltage (LSV) curves of six modified electrode materials are shown below. Figure 3 As shown. The LSV test was performed in a phosphate buffer solution saturated with N2 and at pH 7, with a scan rate of 5 mV·s. -1 Within the measured potential range, it can be seen that graphite felt, as a substrate material, not only has good biocompatibility but also low electrical resistance. This results in the lowest onset potential for CoOOH / graphite felt and the steepest slope of the curve. 0.4Fe 0.6 The OOH / graphite felt modified electrode material also exhibits excellent oxygen evolution performance, showing a very small difference compared to CoOOH / graphite felt, confirming the wide applicability of transition metal hydroxyl oxide catalysts prepared by electrodeposition. As a control, spinel Co3O4 electrode materials cannot be directly deposited on graphite felt using electrodeposition. They are synthesized via a sol-gel method and then coated onto the graphite felt with a PTFE binder. This inevitably increases their resistance, making the oxygen evolution reaction more difficult to occur. In conclusion, the CoOOH / graphite felt modified electrode material prepared by electrodeposition exhibits excellent oxygen evolution performance.

Claims

1. A method for enhancing the degradation of nitrogen-containing heterocyclic compounds by constructing an aerobic / anaerobic microenvironment through electrocatalytic coupling of nitrate nitrogen, characterized in that, The specific steps are as follows: Step 1: Using a three-electrode system, the anode is graphite felt, the cathode is a platinum sheet, the reference electrode is an Ag / AgCl electrode, and the electrolyte is a transition metal salt solution. A constant current density is applied to the three-electrode system using an electrochemical workstation, and transition metal hydroxyl oxides are deposited onto the surface of the graphite felt using an electrodeposition method. After deposition, the graphite felt is removed, cleaned, and dried to obtain a transition metal hydroxyl oxide / graphite felt modified electrode material. The transition metal salt is selected from one or more of Co(NO3)2·6H2O, FeCl2·4H2O, and Ni(NO3)2·6H2O. Step 2: The transition metal hydroxyl oxide / graphite felt modified electrode material is placed at the bottom of the cross-flow rising microbial reactor as the anode, and ordinary graphite felt is placed at the top of the cross-flow rising microbial reactor as the cathode. A reference electrode is placed between the two. Anaerobic sludge is added to completely cover the anode. A constant voltage is applied to the anode and cathode. At the same time, wastewater containing nitrogen-containing heterocyclic compounds and nitrate nitrogen is introduced from the lower end of the anode to realize the electrocatalytic construction of an aerobic / anoxic system coupled with enhanced microbial degradation of nitrate nitrogen.

2. The method according to claim 1, characterized in that, In step 1, the concentration of transition metal ions in the transition metal salt solution is 0.1 M.

3. The method according to claim 1, characterized in that, In step 1, the constant current density is -16 to -32 mA·cm⁻¹ -2 The electrodeposition time is 30~120 min, the drying temperature is 80℃, and the drying time is 5~48 h.

4. The method according to claim 1, characterized in that, In step 2, the inoculated sludge is taken from a bioreactor treating wastewater containing nitrogen heterocyclic compounds, and the initial sludge inoculation amount is 6.0~10.0 g·L. -1 .

5. The method according to claim 1, characterized in that, In step 2, the constant voltage is 1.2~1.6 V, and the concentration of nitrate nitrogen in the wastewater is 10~100 mg·L. -1 .

6. The method according to claim 1, characterized in that, In step 2, the nitrate nitrogen is sodium nitrate or potassium nitrate.

7. The method according to claim 1, characterized in that, In step 2, the nitrogen-containing heterocyclic compound is quinoline, indole, or pyridine.

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