Method for electrocatalytic ozonation of organic phosphorus in tannery wastewater using modified foamed iron electrode as cathode

Abstract

The application provides a method for treating organic phosphorus in tanning wastewater by electrocatalytic ozone treatment with a modified foam iron electrode as a cathode, and the method comprises at least one pair of electrodes; the electrodes comprise a modified foam iron cathode and a modified graphite felt anode, the modified foam iron cathode is modified 40ppi foam iron; the method for treating organic phosphorus in tanning wastewater is as follows: the modified foam iron cathode and the modified graphite felt anode are placed in a reactor, the cathode and the anode are connected to a direct current power supply; the wastewater containing tetramethylphosphonium sulfate to be treated is added into the reactor, and the pH value of the wastewater is controlled in the range of 5-9; the mixed gas of ozone and oxygen is continuously introduced into the reactor, and the flow rate of the mixed gas of ozone and oxygen is controlled to be 0.1-0.5L / min per liter of wastewater; the direct current power supply is started to supply power to the graphite anode and the modified foam iron cathode, and the tetramethylphosphonium sulfate in the wastewater is continuously oxidized into orthophosphate salt between the electrodes; the crystallized orthophosphate salt is separated from the wastewater, and the organic phosphorus component in the tanning wastewater is removed.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a method for electrocatalytic ozone treatment of organophosphorus compounds in tanning wastewater using a modified foamed iron electrode as the cathode. Background Technology

[0002] With the increasing severity of eutrophication in water bodies, the presence of organophosphorus compounds in aquatic environments has garnered significant attention. Tanning wastewater contains substantial amounts of organophosphorus compounds, primarily tetramethylolphosphine sulfate (THPS), requiring proper treatment before discharge into water bodies. Traditional chrome tanning processes generate chromium-containing wastewater and solid waste. The Cr3+ in finished leather carries the potential risk of oxidation into the toxic and carcinogenic Cr6+. Therefore, THPS, as a high-performance new tanning agent, is increasingly used in the leather industry. While THPS addresses the heavy metal pollution problem associated with traditional chrome tanning, its synthesis and use generate large quantities of recalcitrant organophosphorus wastewater, primarily composed of THPS. This wastewater not only contains high levels of recalcitrant organophosphorus compounds but also exhibits strong biotoxicity, and its indiscriminate discharge can damage natural aquatic ecosystems. Due to the bactericidal properties of THPS, biological treatment methods are ineffective. Therefore, a safe, reliable, and efficient treatment method for THPS wastewater is urgently needed to address its environmental pollution.

[0003] Currently, commonly used methods for removing THPS from tanning wastewater include physical methods such as adsorption, filtration, and flocculation, as well as chemical methods such as wet oxidation, electrochemical oxidation, photochemical oxidation, and ozone oxidation.

[0004] Electrocatalytic ozone technology is a novel advanced oxidation process that has attracted considerable attention in recent years. In this process, the oxygen in the ozone and oxygen mixture introduced into the system is first reduced to hydrogen peroxide at the cathode surface, and then reacts with ozone to generate a large number of hydroxyl radicals. Therefore, it features strong oxidation capacity and no secondary pollution. Iron is often used as a sacrificial anode due to its low cost, but it generates a large amount of iron sludge during treatment, causing secondary pollution and significant electrode wear, resulting in a very short battery life. Therefore, it is essential to develop an electrocatalytic ozone technology that results in no or only minimal metal leaching during wastewater treatment. Summary of the Invention

[0005] To address the above-mentioned issues and overcome the shortcomings of existing technologies, this invention provides a method for electrocatalytic ozone treatment of organophosphorus compounds in tanning wastewater using a modified foamed iron electrode as the cathode. This method solves the problems of low ozone utilization, short electrode lifespan, and susceptibility to secondary pollution associated with electrocatalytic technology in treating tanning wastewater. This invention provides a method for electrocatalytic treatment of organophosphorus compounds in tanning wastewater using a modified foamed iron electrode as the cathode. While ensuring the degradation efficiency and effectiveness of THPS in tanning wastewater, it reduces the leaching of metal ions. This method can effectively protect the electrode, increase electrode lifespan, and reduce wastewater treatment costs.

[0006] The technical solution is that the present invention includes at least one pair of electrodes; the electrodes include a cathode made of modified foamed iron and an anode made of modified graphite felt, wherein the modified foamed cathode is modified 40ppi foamed iron; the method for treating organophosphates in tanning wastewater is as follows:

[0007] The modified foamed iron cathode and the modified graphite felt anode are placed in the reactor, and the cathode and anode are connected to a DC power supply.

[0008] The tetrahydroxymethylphosphoric acid wastewater to be treated was added to the reactor, and the pH value of the wastewater was adjusted to the range of 5 to 9.

[0009] A mixture of ozone and oxygen is continuously introduced into the reactor, wherein the flow rate of the ozone and oxygen mixture is controlled to be 0.1-0.5 L / min per liter of wastewater.

[0010] When the DC power supply is turned on, electricity is supplied to the graphite anode and the modified foamed iron cathode, and the tetrahydroxymethylphosphonic acid in the wastewater is continuously oxidized to orthophosphate between the electrodes; during the reaction, the wastewater is continuously disturbed in the reactor by the action of a magnetic stirrer.

[0011] The process involves separating crystalline orthophosphates from wastewater, which is essentially removing organophosphate components from tanning wastewater.

[0012] The modified foamed iron is a product obtained by calcining foamed iron at 500°C for 120 min, resulting in a nanowire array on its surface.

[0013] The modified graphite felt electrode is the product of immersing graphite felt in polytetrafluoroethylene (PTFE) emulsion for 10 minutes and then calcining it at 360 degrees Celsius for 30 minutes.

[0014] The modified foamed iron cathode and the modified graphite felt anode have the same shape and area, and the distance between the cathode and the anode in each set of electrodes is 20 mm.

[0015] In the ozone and oxygen mixture, the ozone volume percentage is 8% to 16%.

[0016] To ensure that the ozone and oxygen mixture is fully dispersed in the reactor, it is preferable to continuously introduce the ozone and oxygen mixture into the wastewater through a titanium aerator with a micropore size of 1-100 μm.

[0017] Before starting the DC power supply, electrolytes need to be added to the tanning wastewater to be treated. The amount of electrolyte added should be based on the actual wastewater. This scheme uses anhydrous sodium sulfate as the electrolyte, with an addition amount of 50 mmol / L, based on the actual wastewater indicators.

[0018] The above embodiments of the present invention have the following beneficial effects:

[0019] 1. This method features high hydroxyl radical production, strong oxidizing power, no secondary pollution, and simple operation. The ozone and oxygen mixture introduced into the wastewater first passes through a modified graphite felt anode, where electrochemical oxidation catalyzes the production of ·OH from the ozone. The introduced oxygen undergoes a reduction reaction at the cathode to generate hydrogen peroxide, which then reacts with the ozone to produce ·OH and O2. 2- Ozone and water can also react directly to produce ·OH, and the ·OH produced in the reaction reacts with O. 2- They work together to degrade pollutants.

[0020] 2. This method can oxidize THPS in tanning wastewater to orthophosphate. The resulting orthophosphate can be recovered through other substances and then separated from the water body.

[0021] 3. This method uses modified foamed iron as the cathode and modified graphite felt as the anode, and introduces a mixture of ozone and gas for wastewater treatment. After 10 cycles, the degradation effect of THPS in tanning wastewater did not change significantly. After 10 cycles, the growth rate of orthophosphate remained at 80%, demonstrating excellent persistence.

[0022] 4. This method uses modified foamed iron as the cathode and graphite felt as the anode, and introduces a mixture of ozone and gas for wastewater treatment. Compared with electrocatalysis and ozonation alone, the degradation rate of this method is significantly improved.

[0023] 5. This method uses modified foamed iron as the cathode and graphite felt as the anode, and introduces a mixture of ozone and gas for wastewater treatment. Increasing the ozone concentration entering the reactor can improve the degradation effect of THPS in tanning wastewater. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of wastewater treatment in Example 1.

[0025] Figure 2 The degradation rates of THPS are those of Example 1, Comparative Example 1, and Comparative Example 2, respectively.

[0026] Figure 3 The experiment showed the degradation rates of organophosphorus compounds in wastewater by cathodes of different materials.

[0027] Figure 4 Example 2 is an electrode scanning electron microscope image of the modified foamed iron.

[0028] Figure 5 Example 2 is an XPS image of the modified foamed iron.

[0029] Figure 6 The degradation rate of organophosphorus THPS is measured when graphite felt and modified graphite felt are used as anodes, respectively.

[0030] Figure 7 The results are from the recycling performance test of modified foamed iron as the cathode and modified graphite as the anode in Example 4.

[0031] Figure 8 This is a diagram showing the treatment effect of THPS simulated wastewater under different ozone concentrations in Example 5.

[0032] Figure 9 This is the degradation rate of organophosphorus compounds in actual wastewater as shown in Example 6. Detailed Implementation

[0033] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0034] Example 1

[0035] A THPS solution with a total phosphorus concentration of 10 mmol / L and a pH of 8 was used as the simulated wastewater (self-prepared wastewater);

[0036] refer to Figure 1 In this embodiment, a pair of electrodes is used for the experiment, which specifically includes the following steps:

[0037] Step 1: Place the modified foamed iron cathode and the modified graphite felt anode in the reactor, and connect the cathode and anode to a DC power supply;

[0038] The electrode includes a cathode made of modified foamed iron and an anode made of modified graphite felt. The modified foamed iron is a product obtained by calcining foamed iron at 500°C for 120 min to produce a nanowire array on its surface.

[0039] The modified foam cathode is modified 40ppi foam iron, and the modified graphite felt electrode is the product of immersing graphite felt in polytetrafluoroethylene (PTFE) emulsion for 10 min and then calcining it at 360 degrees Celsius for 30 min.

[0040] In this example, the modified foamed iron cathode and the modified graphite felt anode are of the same shape and area, so that the cathode and anode with the largest area face each other and are parallel to each other, and the distance between the cathode and the anode is 20mm.

[0041] Step 2: Add the tetramethylolphosphine sulfate wastewater to be treated into the reactor and adjust the pH value of the wastewater to the range of 5-9;

[0042] In this embodiment, the pH value of actual tanning wastewater is approximately 8, indicating that the wastewater is weakly alkaline.

[0043] Step 3: Continuously introduce a mixture of ozone and oxygen into the reactor, wherein the flow rate of the ozone and oxygen mixture is controlled to be 0.3 L / min per liter of wastewater;

[0044] In this embodiment, an oxygen cylinder is used to supply oxygen to the ozone generator, which generates a mixed gas of ozone and oxygen, wherein the ozone volume fraction is 8%. The mixed gas enters the reactor through a gas flow meter and a microporous titanium aerator with a pore size of 50 μm, and is uniformly dispersed into the wastewater under the action of a magnetic rotor.

[0045] Step 4: Turn on the DC power supply to energize the graphite anode and the modified foamed iron cathode. The tetrahydroxymethyl phosphate in the wastewater is continuously oxidized to orthophosphate between the electrodes.

[0046] In this embodiment, before starting the DC power supply, an electrolyte needs to be added to the tanning wastewater to be treated. The amount of electrolyte added is based on the actual wastewater conditions. This scheme uses anhydrous sodium sulfate as the electrolyte, with an addition amount of 50 mmol / L, referencing the actual wastewater indicators.

[0047] In this embodiment, the current density during power-on is set to 1 mA / cm2, and the power-on duration is set to 30 min.

[0048] Step 5: Separate the crystallized orthophosphate from the wastewater, i.e. remove the organic phosphorus components from the tanning wastewater;

[0049] According to the test results, the organophosphorus removal rate in this embodiment is approximately 85%.

[0050] Comparative Example 1

[0051] Without turning on the ozone generator, the rest of the operation is the same as in Example 1, except that electrocatalysis is used to treat the tanning wastewater. After 30 minutes, the organic phosphorus removal rate is about 10%.

[0052] Comparative Example 2

[0053] Without turning on the DC power supply connected to the modified foamed iron cathode and the modified graphite felt anode, the rest of the operation is the same as in Example 1, except that a mixture of ozone and oxygen is used to treat the tanning wastewater. After 30 minutes, the organic phosphorus removal rate is about 22%.

[0054] refer to Figure 2 In the line graphs of the experimental data of Example 1, Comparative Example 1 and Comparative Example 2, it can be seen that the removal efficiency of electrocatalytic ozone in tanning wastewater is much greater than the sum of the efficiencies of ozone alone and electrochemical reaction alone. Therefore, it can be determined that the electrocatalytic ozone technology is not simply a superposition of electrochemical and ozone technologies, but rather a mutually reinforcing effect between the two.

[0055] Comparative Example 3

[0056] In this comparative example, foamed iron was soaked in alcohol and distilled water for 10 minutes each, and then calcined in a vacuum tube furnace at 500°C with a heating rate of 12°C / min, followed by cooling to room temperature at a cooling rate of 15°C / min. Using modified foamed iron as the cathode and modified graphite felt electrode as the anode, and with all other conditions remaining unchanged from Example 1, tanning wastewater was treated.

[0057] refer to Figure 3 , Figure 3 The figure shows the degradation rates of organophosphorus compounds in wastewater by cathodes of different materials during the experiment. It can be seen that the removal rate of organophosphorus compounds in tanning wastewater treated with ordinary foamed iron as cathode is about 80%, while the removal rate of organophosphorus compounds treated with modified foamed iron as cathode is about 85%. Therefore, the modified foamed iron electrode has a better removal rate of organophosphorus compounds.

[0058] Table 1 - Fe content in the cathode of the wastewater solution after the reaction

[0059] electrode Foamed iron Modified foamed iron Total Fe content (mg / L) 6.8932 ＜0.01

[0060] As shown in Table 1, after the reaction, the total Fe content in the solution with ordinary foamed iron as the cathode was 6.8932 mg / L, while that of modified foamed iron was only 0.524 mg / L, which is 13 times that of modified foamed iron.

[0061] Therefore, using modified foamed iron as a cathode not only improves the removal rate of organophosphorus THPS in wastewater, but also greatly reduces the precipitation of Fe ions, reduces electrode wear, and avoids secondary pollution of water bodies.

[0062] Example 2

[0063] In this embodiment, the calcined foamed iron electrode was subjected to scanning electron microscopy and X-ray photoelectron spectroscopy.

[0064] refer to Figure 4 , Figure 4The image shown is a scanning electron microscope image of the modified foamed iron electrode in Example 2. It can be seen that the surface of the modified foamed iron is covered with a nanowire array, which increases the contact area with water and mixed gas, and an iron oxide film is formed on the surface, thereby greatly reducing the precipitation of Fe ions.

[0065] refer to Figure 5 , Figure 5 The X-ray photoelectron spectra of the foamed iron electrodes calcined at different temperatures in Example 2 show the fine XPS spectra of Fe 2p.

[0066] It can be seen that the peaks at 710.1 eV and 723.7 eV are attributed to the 2p3 / 2 and 2p1 / 2 spin orbitals of Fe2+; those at 712.7 eV and 727.5 eV are attributed to the 2p3 / 2 and 2p1 / 2 spin orbitals of Fe3+; and the satellite peaks at 717.4 eV and 732.4 eV are attributed to Fe. The Fe2+ to Fe3+ content ratio of the calcined electrode is 61.95%:38.05%; therefore, it can be concluded that the formation of an iron oxide film on the surface of the modified foamed iron electrode hinders the precipitation of iron, resulting in a low total Fe content in the modified foamed iron electrode reaction system.

[0067] Example 3

[0068] In this embodiment, the graphite felt was immersed in distilled water and polytetrafluoroethylene (PTFE) emulsion for 10 min each, and then calcined at 360 degrees Celsius for 30 min. Modified foamed iron was used as the cathode, and the modified graphite felt electrode was used as the anode, with all other conditions remaining unchanged from Example 1, to treat the tanning wastewater.

[0069] refer to Figure 6 It can be seen that when ordinary graphite felt is used as the cathode to treat organophosphorus in tanning wastewater, the removal rate is about 76%, while when modified foamed iron is used as the cathode, the removal rate is about 85%. The modified graphite felt electrode has a better removal rate for organophosphorus.

[0070] Example 4

[0071] In this embodiment, the recycling performance of modified foamed iron was investigated when modified foamed iron was used as the cathode, modified graphite felt electrode as the anode, and a mixture of ozone and oxygen was introduced. The operation in Example 1 was repeated 10 times, and the removal rate of THPS in tanning wastewater for each cycle was calculated.

[0072] refer to Figure 7Using the method in Example 1, modified foamed iron was used as the cathode and graphite felt as the anode, and a mixture of ozone and oxygen was introduced for wastewater treatment. After 10 cycles, the degradation effect of THPS in tanning wastewater did not change. After 10 cycles, the removal rate of THPS remained at 80%, indicating that the modified foamed iron electrode material is relatively stable.

[0073] Example 5

[0074] In this example, different ozone flow rates were used to investigate the effect of ozone flow rate on pollutant degradation. The operation of this example is basically the same as that of Example 1, except that the flow rate entering the reactor was 0.1 L / min, 0.2 L / min, 0.3 L / min, 0.4 L / min, and 0.5 L / min, and water quality was measured every 5 minutes to calculate the growth rate of orthophosphate.

[0075] refer to Figure 8 As the ozone flow rate increases, the removal rate of THPS (organophosphorus compounds) in tanning wastewater also increases, showing a positive correlation. The organophosphorus removal efficiency increases most rapidly when the ozone flow rate increases from 0.2 L / min to 0.3 L / min.

[0076] Example 6

[0077] The self-prepared wastewater in Example 1 was replaced with actual wastewater from a leather factory area. All other conditions were exactly the same as in Example 1. Modified foamed iron electrode was used as the cathode and modified graphite felt was used as the anode to treat the organic phosphorus in the actual wastewater.

[0078] refer to Figure 9 Using modified foamed iron electrodes as the cathode and modified graphite felt as the anode, the electrocatalytic ozone treatment achieved a removal efficiency of approximately 70% for organophosphorus compounds in actual wastewater. This removal efficiency is lower than that for self-prepared simulated wastewater due to the complex composition and numerous side reactions in actual wastewater. However, compared to other technologies, this technique still maintains high efficiency and stability in removing organophosphorus compounds from actual wastewater.

Claims

1. A method for electrocatalytic treatment of organic phosphorus in tannery wastewater using modified foamed iron electrode as cathode, characterized in that, comprise at least one pair of electrodes; the electrodes comprise a cathode made of modified foam iron and an anode made of modified graphite felt, the modified foam cathode is modified 40 ppi foam iron; the method for treating organic phosphorus in tanning wastewater is as follows: S1, placing the modified foam iron cathode and the modified graphite felt anode in a reactor, and connecting the cathode and the anode to a direct current power supply; S2, adding the tetrakis hydroxymethyl phosphonium sulfate wastewater to be treated into the reactor, and controlling the pH value of the wastewater in the range of 5-9; S3, continuously introducing a mixed gas of ozone and oxygen into the reactor, wherein the flow rate of the mixed gas of ozone and oxygen is controlled to be 0.1-0.5 L / min per liter of wastewater; S4, starting the direct current power supply to pass electricity to the graphite anode and the modified foam iron cathode, and continuously oxidizing the tetrakis hydroxymethyl phosphonium sulfate in the wastewater into orthophosphate between the electrodes; S5, separating the crystallized orthophosphate from the wastewater, i.e. removing the organic phosphorus component in the tanning wastewater.

2. The method of claim 1, wherein, The modified foam iron is a product obtained by calcining the foam iron at 500 DEG C for 120 min to produce a nano-wire array on the surface.

3. The method of claim 1, wherein, The modified graphite felt electrode is a product obtained by immersing the graphite felt in a polytetrafluoroethylene emulsion for 10 min and then calcining at 360 DEG C for 30 min.

4. The method of claim 1, wherein, The modified foam iron cathode and the modified graphite felt anode have the same shape and area, and the distance between the cathode and the anode in each group of electrodes is 20 mm.

5. The method of claim 1, wherein, The volume percentage of ozone in the mixed gas of ozone and oxygen in step 3 is 8%-16%.

6. The method of claim 3, wherein, In step 3, the mixed gas of ozone and oxygen is continuously introduced into the wastewater through a metal titanium aeration head; The pore size of the metal titanium aeration head is 1-100 μm.

7. The method of claim 1, wherein, In step 4, the direct current power supply is started to pass electricity to the graphite anode and the modified foam iron cathode, which further comprises, Before electrification, an electrolyte is added to the wastewater, and the concentration of the electrolyte is 50 mmol / L.

8. The method of claim 1, wherein, In step 4, the tetrakis hydroxymethyl phosphonium sulfate in the wastewater is continuously oxidized into orthophosphate between the electrodes, which further comprises, During the reaction, the wastewater is continuously disturbed in the reactor by a magnetic stirrer.

9. The method as claimed in claim 1, wherein, In step 4, the direct current power supply is started to pass electricity to the graphite anode and the modified foam iron cathode, wherein the current density of the electrification is 0.5-10 mA / cm2, and the length of each electrification cycle is 30 min.

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