Method for electrocatalytic ozone treatment of coking wastewater nanofiltration concentrate

Abstract

This invention discloses a method for treating nanofiltration concentrate of coking wastewater using electrocatalytic ozone, belonging to the field of advanced industrial wastewater treatment technology. Addressing the issues of high color and low purity of sodium sulfate and sodium chloride byproducts after nanofiltration concentration, this invention develops a treatment technology that can efficiently remove organic matter from nanofiltration concentrate, thereby improving byproduct purity and reducing environmental risks associated with the effluent. This invention designs an electrocatalytic ozone oxidation technology, using a BDD electrode as the anode and a Mn@C-PTFE electrode as the cathode, constructing a strong oxidation system with multiple free radicals. Through electron transfer, active species such as ·OH and free chlorine are formed, directly participating in pollutant degradation and significantly improving the removal efficiency of recalcitrant organic pollutants by ozone. Furthermore, intermediate products such as H2O2 can effectively inhibit the formation of toxic and harmful substances such as brominated and chlorinated byproducts in the water.

Description

Technical Field

[0001] This invention belongs to the field of coking wastewater treatment technology, specifically relating to a method for treating nanofiltration concentrate of coking wastewater with electrocatalytic ozone. Background Technology

[0002] In recent years, with the development of membrane separation technology, nanofiltration (NF) technology has been widely used in the advanced treatment of coking wastewater. By converting the membrane concentrate into sodium sulfate and sodium chloride that meet industrial standards, and then packaging and selling them, the by-products are utilized as resources. However, the sodium sulfate and sodium chloride products generally suffer from high color and low purity. The main reason for this is that wastewater accumulates sulfate ions, chloride ions, and organic pollutants simultaneously during nanofiltration concentration. These organic compounds cause scaling in the evaporator during subsequent crystallization, increasing equipment instability and uncertainty, and affecting the quality of the final product salt. Therefore, there is an urgent need to develop treatment technologies that can efficiently remove organic matter from nanofiltration concentrate, improve the purity of by-products, and reduce environmental risks associated with the effluent.

[0003] Currently, traditional ozone (O3) oxidation is commonly used to remove organic matter from nanofiltration concentrates. O3 is a selective oxidant that can efficiently degrade pollutants containing electron-rich groups (such as unsaturated double bonds and amine groups). Furthermore, O3 decomposes in water to produce reactive oxygen species (ROS) such as hydroxyl radicals (·OH). These reactive species can react with pollutants that are difficult to oxidize with ozone, causing their degradation. However, because the amount of ROS produced during the natural decomposition of O3 in water is relatively small, traditional ozone oxidation technology has a low removal rate for recalcitrant organic matter and also produces toxic intermediate products. In contrast, electrocatalytic ozone oxidation technology can enhance ozone mass transfer through electron transfer, promoting the decomposition of O3 into ROS and significantly improving the removal efficiency of recalcitrant pollutants. In addition, intermediate products such as hydrogen peroxide (H2O2) effectively inhibit the formation of toxic byproducts in the water. Therefore, electrocatalytic ozone oxidation technology has broad application prospects in the treatment of nanofiltration concentrates from coking wastewater. Summary of the Invention

[0004] To address the problem of low organic matter removal efficiency in nanofiltration concentration of coking wastewater, this invention provides a method for treating nanofiltration concentrate of coking wastewater with electrocatalytic ozone.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A method for electrocatalytic ozone treatment of nanofiltration concentrate from coking wastewater, using BDD as the anode and Mn@C-PTFE as the cathode, powered by a DC power supply with a current density of 40–80 mA / cm³. 2 The ozone dosage is 40–100 g / m³. 3The aeration rate is 0.125–0.5 L / min; the hydraulic retention time is 60–180 min; and the electrode spacing is 1 cm. The anode BDD generates hydroxyl radicals (·OH) and free chlorine through electron transfer, while the cathode Mn@C-PTFE generates hydrogen peroxide through two-electron oxygen reduction, which further reacts with ozone to generate ·OH. Through the combined action of multiple oxide species, organic matter in the nanofiltration concentrate of coking wastewater is removed efficiently and with low consumption.

[0007] Furthermore, the preparation method of the Mn@C-PTFE includes the following steps:

[0008] Step 1: Cut the nickel mesh, wash and dry it;

[0009] Step 2: Take carbon black, add it to ethanol and PTFE emulsion, and mix ultrasonically to obtain a mixture;

[0010] Step 3: Heat the mixture to evaporate the ethanol; then roll it into a 2mm thin sheet, place it on both sides of the nickel mesh and press it to obtain the electrode sheet;

[0011] Step 4: Place the electrode sheet in a muffle furnace and calcine it at 300°C for 2 hours to obtain a carbon substrate;

[0012] Step 5: Weigh a certain mass of carbon powder and uniformly disperse it in ultrapure water to obtain a carbon solution; then add manganese nitrate solution dropwise to the carbon solution, stir thoroughly, and freeze-dry with liquid nitrogen to obtain carbon material; then place the carbon material in a tube furnace and calcine it at high temperature in an argon atmosphere, keeping the argon gas flowing until the tube furnace cools to room temperature to obtain Mn catalyst layer powder.

[0013] Step 6: Disperse the Mn catalyst layer powder in a mixture of ethanol and PTFE to obtain a catalyst mixture, and uniformly spray the catalyst mixture onto a carbon substrate to obtain a modified carbon electrode.

[0014] Step 7: Place the modified carbon electrode in a muffle furnace and calcine it at high temperature;

[0015] Step 8: Repeat steps 6 and 7 to obtain Mn@C-PTFE with different loads.

[0016] Furthermore, in step 2, the ratio of carbon black, ethanol, and emulsion is 3g:35mL:4mL.

[0017] Furthermore, in step 3, the evaporation temperature is 80℃ and the evaporation time is 20 minutes;

[0018] Furthermore, in step 5, the volume ratio of manganese nitrate solution to carbon solution is 20 mL: 200 mL; the concentrations of manganese nitrate solution and carbon solution are 0.45 g / L and 1.5 g / L, respectively.

[0019] Furthermore, in step 5, the high-temperature calcination in an argon atmosphere is carried out at a temperature of 500°C for 3 hours.

[0020] Furthermore, in step 6, the ratio of Mn catalyst powder, ethanol, and PTFE is 0.05g:10mL:200μL.

[0021] Furthermore, in step 7, the high-temperature calcination temperature is 350°C and the time is 1 hour.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] In the Mn@C-PTFE electrode prepared in this invention, oxygen-containing functional groups and metallic manganese jointly regulate the two-electron oxygen reduction reaction of oxygen to produce H2O2. Oxygen-containing functional groups such as carbonyl and carboxyl groups give adjacent carbon atoms a positive charge, which can enhance the terminal adsorption of oxygen molecules and promote the two-electron oxygen reduction reaction. Furthermore, metallic manganese can further enhance the activity of the two-electron oxygen reduction reaction by increasing the binding energy between adjacent carbon atoms and the oxygen reduction intermediate (OOH*). This electrode is applied to electrocatalytic ozone oxidation technology, using a BDD electrode as the anode and a Mn@C-PTFE electrode as the cathode, constructing a strong oxidation system with multiple free radicals. The BDD electrode forms non-selective ·OH and free chlorine through electron transfer, while the cathode converts the O2 wasted during ozone aeration into H2O2 through two-electron oxygen reduction, which further reacts with O3 to generate ·OH. These active species, such as ·OH and free chlorine, can directly react with pollutants, degrading them and significantly improving the removal efficiency of recalcitrant pollutants by ozone. In addition, intermediate products such as H2O2 can effectively inhibit the formation of toxic and harmful substances such as brominated byproducts in water. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 Schematic diagram of the electrocatalytic ozone generation principle in this invention;

[0026] Figure 2 During the treatment of nanofiltration concentrate by anodizing, conventional ozone, and electrocatalytic ozone technologies, (a) removal of p-chlorobenzoic acid (·OH probe) and (b) ·OH exposure;

[0027] Figure 3 The removal efficiency of organic matter in nanofiltration concentrate by anodizing, conventional ozone, and electrocatalytic ozone technologies;

[0028] Figure 4 3D-EEM images of nanofiltration concentrate before and after treatment with electrocatalytic ozone technology.

[0029] Figure 5 Production of chloroacetic acid in anodizing, conventional ozone, and electrocatalytic ozone systems. Detailed Implementation

[0030] To gain a deeper understanding of this invention, we will provide a comprehensive and detailed description. However, this invention has various implementations and is not limited to the specific examples listed herein. These examples are presented to enhance a full understanding of the disclosure of this invention.

[0031] Example 1

[0032] A method for treating nanofiltration concentrate of coking wastewater with electrocatalytic ozone, the principle diagram of electrocatalytic ozone is shown below. Figure 1 As shown, BDD was used as the anode, Mn@C-PTFE as the cathode, and a DC power supply was used with a current density of 60 mA / cm². 2 The ozone dosage is 70 g / m³. 3 The aeration rate was 0.25 L / min; the hydraulic retention time was 120 min; and the electrode spacing was 1 cm. The anode, BDD, generated hydroxyl radicals (·OH) and free chlorine through electron transfer. The cathode, Mn@C-PTFE, produced hydrogen peroxide through two-electron oxygen reduction, which further reacted with ozone to generate ·OH. Through the combined action of multiple oxide species, organic matter in the nanofiltration concentrate of coking wastewater was removed efficiently and with low consumption. 3D-EEM images of the nanofiltration concentrate before and after treatment with electrocatalytic ozone technology are shown below. Figure 4 As shown.

[0033] The preparation method of Mn@C-PTFE includes the following steps:

[0034] Step 1: Cut the nickel mesh, wash and dry it;

[0035] Step 2: Take carbon black, add it to ethanol and PTFE emulsion and mix ultrasonically to obtain a mixture; the ratio of carbon black, ethanol and emulsion is 3g:35mL:4mL.

[0036] Step 3: Heat the mixture in an electric furnace and evaporate the ethanol at 80°C for 20 minutes; then roll it into a 2mm thin sheet, place it on both sides of the nickel mesh and press it to obtain the electrode sheet;

[0037] Step 4: Place the electrode sheet in a muffle furnace and calcine it at 300°C for 2 hours to obtain a carbon substrate;

[0038] Step 5: Weigh a certain mass of carbon powder and uniformly disperse it in ultrapure water to obtain a carbon solution; then add manganese nitrate solution dropwise to the carbon solution, stir thoroughly, and freeze-dry with liquid nitrogen to obtain carbon material; then place the carbon material in a tube furnace and calcine it at 500℃ for 3 hours in an argon atmosphere, keeping the argon gas flowing in until the tube furnace cools to room temperature to obtain Mn catalyst layer powder; the volume ratio of manganese nitrate solution to carbon solution is 20mL:200mL; the concentrations of manganese nitrate solution and carbon solution are 0.45g / L and 1.5g / L, respectively.

[0039] Step 6: Disperse the Mn catalyst layer powder in a mixture of ethanol and PTFE to obtain a catalyst mixture. Then, use an electric spray gun to uniformly spray the catalyst mixture onto a carbon substrate to obtain a modified carbon electrode. The ratio of Mn catalyst layer powder, ethanol and PTFE is 0.05g:10mL:200μL.

[0040] Step 7: Place the modified carbon electrode in a muffle furnace and calcine it at 350°C for 1 hour;

[0041] Step 8: Repeat steps 6 and 7 to obtain Mn@C-PTFE with different loads.

[0042] Example 2

[0043] The difference from Example 1 is that the current density is 70 mA / cm². 2 The ozone dosage is 70 g / m³. 3 The aeration rate is 0.2 L / min; the hydraulic retention time is 90 min.

[0044] Example 3

[0045] The difference from Example 1 is that the current density is 40 mA / cm². 2 The ozone dosage is 40 g / m³. 3 The aeration rate is 0.1 L / min; the hydraulic retention time is 180 min.

[0046] Example 4

[0047] The difference from Example 1 is that the current density is 50 mA / cm². 2 The ozone dosage is 100g / m³. 3 The aeration rate was 0.2 L / min; the hydraulic retention time was 130 min.

[0048] Example 5

[0049] The difference from Example 1 is that the current density is 60 mA / cm². 2 The ozone dosage is 90 g / m³. 3The aeration rate was 0.125 L / min; the hydraulic retention time was 150 min.

[0050] Example 6

[0051] The difference from Example 1 is that the current density is 80 mA / cm². 2 The ozone dosage is 80 g / m³. 3 The aeration rate is 0.4 L / min; the hydraulic retention time is 60 min.

[0052] Example 7

[0053] The difference from Example 1 is that the current density is 60 mA / cm². 2 The ozone dosage is 60 g / m³. 3 The aeration rate is 0.5 L / min; the hydraulic retention time is 110 min.

[0054] Experimental Test

[0055] We also tested the removal of ·OH probes and the exposure of ·OH during the treatment of nanofiltration concentrate using anodizing, conventional ozone, and electrocatalytic ozone technologies, respectively. The test results are as follows: Figure 2 As shown in the figure, compared with traditional ozone and anodizing, electrocatalytic ozone significantly enhanced the degradation of p-chlorobenzoic acid, resulting in a significant increase in the exposure of ·OH in the system. The removal efficiencies of anodizing, traditional ozone, and electrocatalytic ozone technologies for organic matter removal from nanofiltration concentrates are as follows: Figure 3 As shown in the figure, compared with traditional ozone and anodic oxidation, the COD removal efficiency of the electrocatalytic ozone system is significantly increased, with a COD removal rate >95% after 60 minutes of reaction. Furthermore, as... Figure 4 As shown, in the electrocatalytic ozone system, the effluent showed no fluorescence peak at an excitation wavelength of 340 nm, indicating that a large amount of humic substances can be completely oxidized and degraded by ·OH.

[0056] In summary, the electrocatalytic ozone treatment method for nanofiltration concentrate of coking wastewater of the present invention significantly improves the removal efficiency of recalcitrant organic pollutants by ozone oxidation. Furthermore, intermediate products such as H₂O₂ can effectively inhibit the formation of toxic and harmful substances such as brominated byproducts in the water. Figure 5 As shown, compared to traditional ozone and anodic oxidation, the production of dichloroacetic acid is significantly reduced in the electrocatalytic ozone system, while there is no production of trichloroacetic acid.

[0057] Contents not described in detail in this specification are prior art known to those skilled in the art. Although illustrative specific embodiments of the invention have been described above to facilitate understanding by those skilled in the art, it should be understood that the invention is not limited to the scope of the specific embodiments. Various modifications are readily apparent to those skilled in the art as long as they fall within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of this invention are protected.

Claims

1. A method for treating nanofiltration concentrate of coking wastewater with electrocatalytic ozone, characterized in that: Using BDD as the anode and Mn@C-PTFE as the cathode, powered by a DC power supply with a current density of 40~80 mA / cm² 2 The ozone dosage is 40~100 g / m³. 3 The aeration rate is 0.125~0.5 L / min; the hydraulic retention time is 60~180 min; and the electrode spacing is 1 cm. The anode BDD generates hydroxyl radicals (•OH) and free chlorine through electron transfer. The cathode Mn@C-PTFE generates hydrogen peroxide through two-electron oxygen reduction, which further reacts with ozone to generate •OH. Through the combined action of multiple oxide species, organic matter in the nanofiltration concentrate of coking wastewater is removed. The preparation method of Mn@C-PTFE includes the following steps: Step 1: Cut the nickel mesh, wash and dry it; Step 2: Take carbon black, add it to ethanol and PTFE emulsion, and mix ultrasonically to obtain a mixture; Step 3: Heat the mixture to evaporate the ethanol; then roll it into a 2 mm thin sheet, place it on both sides of the nickel mesh and press it to obtain the electrode sheet; Step 4: Place the electrode sheet in a muffle furnace and calcine at 300°C for 2 hours to obtain a carbon substrate; Step 5: Weigh a certain amount of carbon powder and disperse it evenly in ultrapure water to obtain a carbon solution; then add manganese nitrate solution dropwise to the carbon solution, stir thoroughly, and freeze dry with liquid nitrogen to obtain carbon material; then place the carbon material in a tube furnace and calcine it at high temperature in an argon atmosphere, keeping the argon gas flowing in until the tube furnace cools down to room temperature to obtain Mn catalyst layer powder. Step 6: Disperse the Mn catalyst layer powder in a mixture of ethanol and PTFE to obtain a catalyst mixture, and uniformly spray the catalyst mixture onto a carbon substrate to obtain a modified carbon electrode. Step 7: Place the modified carbon electrode in a muffle furnace and calcine it at high temperature; Step 8: Repeat steps 6 and 7 to obtain Mn@C-PTFE with different loads.

2. The method for treating coking wastewater nanofiltration concentrate with electrocatalytic ozone according to claim 1, characterized in that: In step 2, the ratio of carbon black, ethanol, and emulsion is 3 g: 35 mL: 4 mL.

3. The method for treating coking wastewater nanofiltration concentrate with electrocatalytic ozone according to claim 1, characterized in that: In step 3, the evaporation temperature is 80℃ and the evaporation time is 20 min.

4. The method for treating nanofiltration concentrate of coking wastewater with electrocatalytic ozone according to claim 1, characterized in that: In step 5, the volume ratio of manganese nitrate solution to carbon solution is 20 mL: 200 mL; the concentrations of manganese nitrate solution and carbon solution are 0.45 g / L and 1.5 g / L, respectively.

5. The method for treating coking wastewater nanofiltration concentrate with electrocatalytic ozone according to claim 1, characterized in that: In step 5, the high-temperature calcination in an argon atmosphere is carried out at a temperature of 500°C for 3 hours.

6. The method for treating coking wastewater nanofiltration concentrate with electrocatalytic ozone according to claim 1, characterized in that: In step 6, the ratio of Mn catalyst powder, ethanol, and PTFE is 0.05 g: 10 mL: 200 μL.

7. The method for treating nanofiltration concentrate of coking wastewater with electrocatalytic ozone according to claim 1, characterized in that: In step 7, the high-temperature calcination temperature is 350℃ and the time is 1 hour.

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