An apparatus and method for upflow electrochemical treatment of wastewater containing hexavalent chromium

Abstract

This invention discloses an upflow electrochemical treatment device and method for treating wastewater containing hexavalent chromium. The device includes a cylindrical inner reaction chamber and a double-layer reaction chamber. The inner reaction chamber contains a mesh-like ruthenium-iridium-titanium anode and a carbon fiber felt membrane cathode. The double-layer reaction chamber includes an external overflow chamber and an internal upflow chamber. The method includes the following steps: S1, preliminary preparation; S2, wastewater injection; S3, continuous wastewater treatment; S4, detection. This invention mainly uses an upflow electrochemical water purification membrane for wastewater treatment, which can efficiently reduce highly toxic hexavalent chromium to less toxic trivalent chromium, effectively reducing the toxicity of the wastewater. Simultaneously, it utilizes the oxygen released during the reduction of hexavalent chromium to achieve the simultaneous generation of hydrogen peroxide, improving resource utilization and reducing treatment costs.

Description

Technical Field

[0001] This invention relates to the field of chromium-containing wastewater treatment technology, specifically to an upflow electrochemical treatment apparatus and method for hexavalent chromium wastewater. Background Technology

[0002] Hexavalent chromium is a highly toxic pollutant widely found in wastewater from electroplating, leather tanning, and metallurgical industries, posing a serious threat to human health and aquatic ecosystems. In recent years, electrochemical reduction has attracted widespread attention due to its ability to convert highly toxic hexavalent chromium into less toxic trivalent chromium. However, current research largely focuses on improving the reduction efficiency of hexavalent chromium, neglecting the potential value of hexavalent chromium wastewater in resource utilization. As a strong oxidizing pollutant, the reduction of hexavalent chromium involves the release of chemical energy. Simultaneously, the oxygen produced by the anodic oxygen evolution reaction also contains chemical energy. Recovering the chemical energy of both hexavalent chromium and oxygen simultaneously not only contributes to the effective treatment of pollutants but also provides an innovative and economically feasible strategy for achieving low-carbon management.

[0003] Hydrogen peroxide is a widely used, green water purification oxidant. The large amount of oxygen generated during the reduction of hexavalent chromium can serve as an ideal precursor for the synthesis of hydrogen peroxide. Previous studies have shown that in electrochemical systems based on redox reactions, the chemical energy of hexavalent chromium can be converted into electrical energy, suggesting that the reduction of hexavalent chromium to assist in the synthesis of hydrogen peroxide is feasible.

[0004] Traditional electrochemical filtration processes typically employ a top-down gravity-assisted flow model, suitable for water purification processes that do not require enhanced gas management. However, in electrochemical reactions involving gas generation, this design can lead to poor water purification results due to gas retention and low mass transfer efficiency. In contrast, bottom-up upflow electrochemical filtration significantly enhances reaction efficiency by utilizing the buoyancy of rising bubbles, making it more suitable for process conditions involving gas generation. Therefore, it is necessary to develop a method that can efficiently reduce hexavalent chromium in wastewater and simultaneously generate hydrogen peroxide. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides an upflow electrochemical treatment apparatus and method for treating wastewater containing hexavalent chromium.

[0006] The technical solution of this invention is:

[0007] An upflow electrochemical treatment device for hexavalent chromium wastewater includes a cylindrical inner reaction chamber and a double-layer reaction chamber located outside the inner reaction chamber.

[0008] The inner reaction chamber is hollow to form a flow channel. A mesh ruthenium-iridium titanium anode and a carbon fiber felt film cathode are arranged in the middle of the inner reaction chamber. The carbon fiber felt film cathode is located above the mesh ruthenium-iridium titanium anode, and the mesh ruthenium-iridium titanium anode and the carbon fiber felt film cathode are arranged parallel to each other. Both the mesh ruthenium-iridium titanium anode and the carbon fiber felt film cathode cover the flow channel of the inner reaction chamber.

[0009] The double-layer reaction chamber includes an outer overflow chamber and an inner rising chamber. The top of the inner rising chamber is sealed to the top of the inner reaction chamber through a sealing top plate. The upper surface of the sealing top plate is provided with several overflow channels loaded with biomass activated carbon. The overflow channels extend from the top of the inner reaction chamber to the top of the outer overflow chamber. A groove is provided at the bottom of the inner rising chamber where it communicates with the outer overflow chamber.

[0010] The mesh ruthenium-iridium-titanium anode is provided with several first sealing connection points to the inner wall of the inner reaction chamber. The mesh ruthenium-iridium-titanium anode is connected one-to-one with several arc-shaped mesh ruthenium-iridium-titanium extended anodes provided inside the inner riser chamber through the first sealing connection points. The carbon fiber felt cathode is provided with several second sealing connection points to the inner wall of the inner reaction chamber. The carbon fiber felt cathode is connected one-to-one with several arc-shaped carbon fiber felt extended cathodes provided inside the inner riser chamber through the second sealing connection points.

[0011] The bottom of the inner reaction chamber is provided with a water inlet pipe, and the top of the inner riser chamber is provided with a drain pipe that passes through the outer overflow chamber and extends outward.

[0012] Furthermore, the mesh ruthenium-iridium-titanium anode and the carbon fiber felt cathode are each connected to a wire by conductive adhesive. The conductive adhesive is located in a cavity provided inside the inner reaction chamber. The cavity is located between two adjacent first sealing connection points or two adjacent second sealing connection points. The wire is externally insulated and passes through the inner current riser cavity and the outer overflow cavity in sequence before being connected to an external power source.

[0013] Note: A mesh ruthenium-iridium titanium electrode is used as the anode, and a carbon fiber felt film electrode is used as the cathode. The mesh ruthenium-iridium titanium electrode, as the anode for the oxygen evolution reaction (OER), exhibits extremely high OER performance. Its ruthenium-iridium coating significantly reduces the overpotential of the OER, improving reaction efficiency and making oxygen generation faster and more efficient. Furthermore, the stability of the ruthenium-iridium coating ensures high-efficiency OER performance at high current densities, with minimal performance degradation over long-term operation, demonstrating excellent stability and continuous OER capability. Due to its excellent two-electron oxygen reduction activity, carbon fiber felt is used as the film cathode, as it does not adsorb hexavalent chromium.

[0014] Furthermore, an annular first PTFE pad is provided between the mesh ruthenium-iridium-titanium anode and the carbon fiber felt cathode, and an annular second PTFE pad is provided below the mesh ruthenium-iridium-titanium anode and above the carbon fiber felt cathode. Both the first and second PTFE pads are fixedly connected to the inner wall of the inner reaction chamber. The thickness of the mesh ruthenium-iridium-titanium anode is 1-3 cm, the thickness of the carbon fiber felt cathode is 2-4 cm, the thickness of the mesh ruthenium-iridium-titanium extended anode is 2-4 cm, the thickness of the carbon fiber felt cathode extended cathode is 3-5 cm, and the distance between the mesh ruthenium-iridium-titanium anode and the carbon fiber felt cathode is 5-20 cm.

[0015] Explanation: The PTFE pad ensures that the two electrodes do not interfere with each other and provides support. The optimized spacing between the mesh ruthenium-iridium-titanium anode and the carbon fiber felt cathode can reduce resistance loss and ensure efficient ion conduction in the electrolyte.

[0016] Furthermore, there are 6 to 12 overflow channels, and each overflow channel extends outward from the center of the inner reaction chamber. The interior of the overflow channel is alternately lined with 2 to 3 layers of biomass activated carbon and 2 to 3 layers of pebbles. The thickness of the biomass activated carbon layer is 2 to 6 cm, and the thickness of the pebbles layer is 2 to 6 cm.

[0017] Explanation: By optimizing the internal structure of the overflow channel, it is made to have an adsorption function, which helps to purify sewage.

[0018] Furthermore, there are 3 to 5 first sealing connection points and 3 to 5 second sealing connection points, and the first and second sealing connection points are arranged in a crisscross pattern along the longitudinal direction.

[0019] Explanation: By optimizing and adjusting the position and number of the first and second sealing connection points, the overall structural position of the device is made more reasonable while ensuring sealing.

[0020] Furthermore, the inlet pipe is equipped with an inlet valve, and the outlet pipe is equipped with a outlet valve.

[0021] The present invention also provides a method for treating hexavalent chromium-containing wastewater using an upflow electrochemical process, based on the apparatus for treating hexavalent chromium-containing wastewater as described in any one of the above claims, comprising the following steps:

[0022] S1. Preliminary preparation: Add Na2SO4 to the hexavalent chromium-containing wastewater to be treated, and adjust the pH of the hexavalent chromium-containing wastewater to be treated to 2±0.1. Alternately lay biomass activated carbon layers and cobblestone layers inside each overflow channel.

[0023] S2. Wastewater injection: Inject the hexavalent chromium-containing wastewater to be treated through the inlet pipe, and then energize the mesh ruthenium-iridium titanium anode and carbon fiber felt cathode.

[0024] S3. Continuous Wastewater Treatment: Wastewater containing hexavalent chromium enters the inner reaction chamber and moves from bottom to top, passing sequentially through the mesh ruthenium-iridium-titanium anode and carbon fiber felt cathode. An external power supply is turned on to apply a voltage of 5-15V to the mesh ruthenium-iridium-titanium anode and carbon fiber felt cathode to complete the first electrochemical purification. Subsequently, the wastewater containing hexavalent chromium overflows into the outer overflow chamber through various overflow channels at the top of the inner reaction chamber. It is then adsorbed and purified by the biomass activated carbon loaded in the overflow channels. Afterward, it enters the inner upflow chamber through the slot and rises again, passing sequentially through the arc-shaped sheet-like mesh ruthenium-iridium-titanium anode and carbon fiber felt cathode to complete the second electrochemical purification.

[0025] S4. Detection: The concentrations of hexavalent chromium and hydrogen peroxide in the treated wastewater are measured.

[0026] Furthermore, in S1, the injection rate of the hexavalent chromium wastewater to be treated is 0.5–5 L / min, the molar concentration of Na2SO4 is controlled at 0.1–0.5 mol / L, and a 40% NaOH solution or HCl solution is added when adjusting the pH of the hexavalent chromium wastewater to be treated.

[0027] Note: By adding Na2SO4 and adjusting its concentration within a reasonable range, a suitable ion concentration can be provided, ensuring that the system has low resistance, thereby reducing power loss and improving current efficiency; the initial pH of the wastewater to be treated is adjusted to acidic to prevent the trivalent chromium generated by reduction from depositing on the cathode surface.

[0028] Furthermore, in S1, the biomass activated carbon layer includes several biomass activated carbon particles with a particle size of 0.3 to 0.8 cm, and the pebble layer includes several pebbles with a particle size of 0.3 to 0.8 cm.

[0029] The preparation method of the biomass activated carbon granules is as follows: straw or rice husks are collected and crushed into small pieces less than 2 cm. After rinsing and drying, they are placed in a pyrolysis furnace and pyrolyzed at 600-800℃ for 1-2 hours to obtain biomass activated carbon powder. After cooling, the biomass activated carbon powder is mixed with bentonite powder at a mass ratio of 1:1. Water is added to maintain a moisture content of 3-5%. The mixture is stirred and then granulated by an extrusion granulator to obtain biomass activated carbon granules that meet the particle size requirements. The granules are then dried at 75-80℃.

[0030] Explanation: By optimizing the preparation method of biomass activated carbon particles, they can be attached to the surface of the overflow channel to achieve the purpose of auxiliary purification and adsorption.

[0031] The beneficial effects of this invention are:

[0032] (1) The apparatus and method for treating hexavalent chromium wastewater by upflow electrochemical treatment of the present invention mainly uses upflow electrochemical water purification membrane to treat wastewater, which can efficiently reduce highly toxic hexavalent chromium to low-toxic trivalent chromium, effectively reducing the toxicity of wastewater. At the same time, the oxygen released during the reduction of hexavalent chromium is used to realize the synchronous generation of hydrogen peroxide, improve resource utilization and reduce treatment costs.

[0033] (2) The device for treating hexavalent chromium wastewater by upflow electrochemical treatment of the present invention adopts a two-step upflow water flow treatment mode, which helps oxygen bubbles to concentrate and move towards the electrode active area, significantly enhances the two-electron oxygen reduction reaction, thereby improving the efficiency of hydrogen peroxide generation. In particular, the staggered electrode plates during the second upflow can further improve the concentration of oxygen bubbles towards the electrode active area.

[0034] (3) The device for treating hexavalent chromium wastewater by upflow electrochemical treatment of the present invention also optimizes and adjusts the structure of the overflow channel and the internal filling material. After filling with a specially made biomass activated carbon layer, it can be purified by adsorption with assistance. Moreover, the adsorption and purification occurs between two electrochemical treatments, which further improves the overall purification efficiency.

[0035] (4) The method of upflow electrochemical treatment of hexavalent chromium wastewater of the present invention achieves the most stable continuous treatment purpose by adjusting the parameter settings, and provides a system stability analysis experiment to prove that the electrochemical reactor of the present invention has stable performance during long-term operation and is suitable for practical application. It not only effectively treats pollutants, but also realizes the combination of wastewater treatment and resource utilization, providing an innovative and economical solution for low-carbon management. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the overall structure of an upflow electrochemical treatment device for treating hexavalent chromium wastewater according to the present invention;

[0037] Figure 2 This is a top view of an upflow electrochemical treatment device for hexavalent chromium wastewater according to the present invention;

[0038] Figure 3 This is a schematic diagram of the internal structure of an upflow electrochemical treatment device for hexavalent chromium wastewater, omitting the double-layer reaction chamber, according to the present invention.

[0039] Figure 4 This is a cross-sectional view of the overall internal structure of an upflow electrochemical treatment device for hexavalent chromium wastewater according to the present invention.

[0040] Figure 5This is a top view of the internal structure of an upflow electrochemical treatment device for hexavalent chromium wastewater, omitting the double-layer reaction chamber, according to the present invention.

[0041] Figure 6 This is a cross-sectional view of the internal structure of an upflow electrochemical treatment device for hexavalent chromium wastewater, omitting the double-layer reaction chamber, according to the present invention.

[0042] Figure 7 This is a cross-sectional view of the cavity of an upflow electrochemical treatment device for hexavalent chromium wastewater according to the present invention;

[0043] Figure 8 This is a schematic diagram of the internal structure of the overflow channel of an upflow electrochemical treatment device for hexavalent chromium wastewater according to the present invention;

[0044] Figure 9 These are SEM images and EDS elemental analysis diagrams of the mesh ruthenium-iridium-titanium anode in the experimental examples of this invention;

[0045] Figure 10 This is a SEM image of the carbon fiber felt film cathode in the experimental example of this invention;

[0046] Figure 11 This is a diagram showing the adsorption effect of carbon fiber felt on hexavalent chromium in the experimental example of this invention without the application of an electric field;

[0047] Figure 12 This is a comparison chart of the actual effects of treating hexavalent chromium simulated wastewater before and after treatment in the experimental examples of this invention;

[0048] Figure 13 This is a graph showing the changes in the reduction efficiency of hexavalent chromium and the concentration of hydrogen peroxide during 24 consecutive days of operation in the experimental example of this invention.

[0049] Among them, 1-inner reaction chamber, 11-first sealing connection point, 12-second sealing connection point, 13-water inlet pipe, 14-drain pipe, 15-cavity, 16-first PTFE pad, 17-second PTFE pad, 2-double-layer reaction chamber, 21-external overflow chamber, 22-inner upflow chamber, 23-groove, 3-mesh ruthenium-iridium-titanium anode, 4-carbon fiber felt cathode, 5-sealed top plate, 51-overflow channel, 52-biomass activated carbon layer, 53-pebble layer, 6-mesh ruthenium-iridium-titanium extended anode, 7-carbon fiber felt extended cathode, 8-conductive adhesive, 81-wire, 9-external power supply. Detailed Implementation

[0050] Example 1

[0051] like Figure 1 As shown, an upflow electrochemical treatment device for hexavalent chromium wastewater includes a cylindrical inner reaction chamber 1 and a double-layer reaction chamber 2 located outside the inner reaction chamber 1.

[0052] like Figure 6 As shown, the inner reaction chamber 1 is hollow to form a flow channel. A mesh ruthenium-iridium-titanium anode 3 and a carbon fiber felt cathode 4 are provided in the middle of the inner reaction chamber 1. The carbon fiber felt cathode 4 is located above the mesh ruthenium-iridium-titanium anode 3, and the mesh ruthenium-iridium-titanium anode 3 and the carbon fiber felt cathode 4 are arranged parallel to each other. Both the mesh ruthenium-iridium-titanium anode 3 and the carbon fiber felt cathode 4 cover the flow channel of the inner reaction chamber 1.

[0053] like Figure 2 , Figure 4 , Figure 8 As shown, the double-layer reaction chamber 2 includes an outer overflow chamber 21 and an inner rising chamber 22. The top of the inner rising chamber 22 is sealed to the top of the inner reaction chamber 1 through a sealing top plate 5. The upper surface of the sealing top plate 5 is provided with 9 overflow channels 51 loaded with biomass activated carbon. The overflow channels 51 extend from the top of the inner reaction chamber 1 to the top of the outer overflow chamber 21. The bottom of the inner rising chamber 22 is provided with a slot 23 at the connection between it and the outer overflow chamber 21. Each overflow channel 51 extends outward from the center of the inner reaction chamber 1. The interior of the overflow channel 51 is alternately lined with 3 layers of biomass activated carbon 52 and 2 layers of pebble 53. The thickness of the biomass activated carbon layer 52 is 6 cm and the thickness of the pebble layer 53 is 6 cm.

[0054] like Figures 3-6 As shown, the mesh ruthenium-iridium-titanium anode 3 has four first sealing connection points 11 on the inner wall of the inner reaction chamber 1. The mesh ruthenium-iridium-titanium anode 3 is connected one-to-one with four arc-shaped mesh ruthenium-iridium-titanium extended anodes 6 inside the inner riser cavity 22 through the first sealing connection points 11. The carbon fiber felt cathode 4 has four second sealing connection points 12 on the inner wall of the inner reaction chamber 1. The carbon fiber felt cathode 4 is connected to four arc-shaped carbon fiber felt extended cathodes 7 inside the inner riser cavity 22 through the second sealing connection points 12. The connections are made in a one-to-one correspondence, and the first sealing connection point 11 and the second sealing connection point 12 are arranged in a cross pattern along the longitudinal direction. The distance between the mesh ruthenium-iridium-titanium anode 3 and the carbon fiber felt film cathode 4 is 10cm. The mesh ruthenium-iridium-titanium extended anode 6 and the mesh ruthenium-iridium-titanium anode 3 are purchased from Suzhou Shuertai Industrial Technology Co., Ltd., with the item number SZT20230615001. The carbon fiber felt film cathode 4 and the carbon fiber felt film extended cathode 7 are purchased from Inner Mongolia Wanxing Carbon Co., Ltd., with the item number SMZ20231218002.

[0055] like Figure 3 , Figure 6 and 7As shown, the mesh ruthenium-iridium-titanium anode 3 and the carbon fiber felt cathode 4 are respectively connected by a wire 81 through conductive adhesive 8. The conductive adhesive 8 is located in the cavity 15 provided inside the inner reaction chamber 1. The cavity 15 is located between two adjacent first sealing connection points 11 or between two adjacent second sealing connection points 12. The wire 81 is externally insulated and passes through the inner current riser cavity 22 and the outer overflow cavity 21 in sequence before being connected to the external power supply 9. An annular first PTFE pad 16 is provided between the mesh ruthenium-iridium-titanium anode 3 and the carbon fiber felt cathode 4. An annular second PTFE pad 17 is provided below the mesh ruthenium-iridium-titanium anode 3 and above the carbon fiber felt cathode 4. The first PTFE pad 16 and the second PTFE pad 17 are both fixedly connected to the inner wall of the inner reaction chamber 1. The thickness of the mesh ruthenium-iridium-titanium anode 3 is 2cm, the thickness of the carbon fiber felt cathode 4 is 3cm, the thickness of the mesh ruthenium-iridium-titanium extended anode 6 is 3cm, and the thickness of the carbon fiber felt extended cathode 7 is 4cm.

[0056] like Figure 1 As shown, the bottom of the inner reaction chamber 1 is provided with a water inlet pipe 13, and the top of the inner riser chamber 22 is provided with a drain pipe 14 that passes through the outer overflow chamber 21 and extends outward. The water inlet pipe 13 is provided with a water inlet valve, and the drain pipe 14 is provided with a drain valve.

[0057] Example 2

[0058] The difference between this embodiment and Embodiment 1 is that:

[0059] The upper surface of the sealed top plate 5 is provided with 6 overflow channels 51 loaded with biomass activated carbon. The interior of the overflow channels 51 is alternately lined with 3 layers of biomass activated carbon 52 and 3 layers of pebble 53. The biomass activated carbon layer 52 is 5cm thick and the pebble layer 53 is 2cm thick.

[0060] Example 3

[0061] The difference between this embodiment and Embodiment 1 is that:

[0062] The upper surface of the sealed top plate 5 is provided with 12 overflow channels 51 loaded with biomass activated carbon. The interior of the overflow channel 51 is alternately lined with two layers of biomass activated carbon 52 and two layers of pebble 53. The biomass activated carbon layer 52 is 2cm thick and the pebble layer 53 is 3cm thick.

[0063] Note: If too many overflow channels 51 are provided, the surface area of ​​the sealing top plate 5 will be compressed, resulting in a shallower depth. Consequently, the number of biomass activated carbon layers 52 and pebble layers 53 will also decrease. When fewer overflow channels 51 are provided, the surface area occupied by the sealing top plate 5 is smaller, and the depth can be further increased. Consequently, the number of biomass activated carbon layers 52 and pebble layers 53 will also increase. The appropriate selection can be made according to the needs.

[0064] Example 4

[0065] The difference between this embodiment and Embodiment 1 is that:

[0066] There are 3 first sealing connection points 11, 3 mesh ruthenium-iridium-titanium extended anodes 6, 3 second sealing connection points 12, and 3 carbon fiber felt cathodes 4.

[0067] Example 5

[0068] The difference between this embodiment and Embodiment 1 is that:

[0069] There are 5 first sealing connection points 11, 5 mesh ruthenium-iridium-titanium extended anodes 6, 5 second sealing connection points 12, and 5 carbon fiber felt cathodes 4.

[0070] Example 6

[0071] The difference between this embodiment and Embodiment 1 is that:

[0072] The mesh ruthenium-iridium-titanium anode 3 has a thickness of 1 cm, the carbon fiber felt cathode 4 has a thickness of 2 cm, the mesh ruthenium-iridium-titanium extended anode 6 has a thickness of 2 cm, the carbon fiber felt extended cathode 7 has a thickness of 3 cm, and the distance between the mesh ruthenium-iridium-titanium anode 3 and the carbon fiber felt cathode 4 is 5 cm.

[0073] Example 7

[0074] The difference between this embodiment and Embodiment 1 is that:

[0075] The mesh ruthenium-iridium-titanium anode 3 has a thickness of 3cm, the carbon fiber felt cathode 4 has a thickness of 4cm, the mesh ruthenium-iridium-titanium extended anode 6 has a thickness of 4cm, the carbon fiber felt extended cathode 7 has a thickness of 5cm, and the distance between the mesh ruthenium-iridium-titanium anode 3 and the carbon fiber felt cathode 4 is 20cm.

[0076] Note: Based on the overall size of the device according to the present invention and the volume of wastewater to be treated, the thickness of each electrode is appropriately adjusted. The larger the treatment volume, the larger the required electrode thickness.

[0077] Example 8

[0078] This embodiment provides a method for treating hexavalent chromium-containing wastewater using an upflow electrochemical process, based on an apparatus for treating hexavalent chromium-containing wastewater in Embodiment 1, and includes the following steps:

[0079] S1. Preliminary preparation: Add Na2SO4 to the wastewater containing hexavalent chromium to be treated, and adjust the pH of the wastewater to be treated to 2. Alternately lay biomass activated carbon layer 52 and pebble layer 53 inside each overflow channel 51. The injection rate of the wastewater containing hexavalent chromium to be treated is 2L / min. Control the molar concentration of Na2SO4 to be 0.3mol / L. Add 40% NaOH solution or HCl solution when adjusting the pH of the wastewater containing hexavalent chromium to be treated.

[0080] The biomass activated carbon layer 52 includes several biomass activated carbon particles with a particle size of 0.5 cm, and the pebble layer 53 includes several pebbles with a particle size of 0.5 cm. The preparation method of the biomass activated carbon particles is as follows: straw or rice husks are collected and crushed into small pieces of 1 cm. After washing and drying, they are placed in a pyrolysis furnace and pyrolyzed at 700℃ for 1.5 h to obtain biomass activated carbon powder. After cooling, the biomass activated carbon powder is mixed with bentonite powder at a mass ratio of 1:1. Water is added to maintain a moisture content of 4%. The mixture is stirred and then granulated by an extrusion granulator to obtain biomass activated carbon particles that meet the particle size requirements. The particles are then dried at 78℃.

[0081] S2, Wastewater Injection: Inject the hexavalent chromium-containing wastewater to be treated through the inlet pipe 13, and then energize the mesh ruthenium-iridium-titanium anode 3 and the carbon fiber felt cathode 4;

[0082] S3. Continuous wastewater treatment: Wastewater containing hexavalent chromium enters the inner reaction chamber 1 and moves from bottom to top, passing sequentially through the mesh ruthenium-iridium-titanium anode 3 and the carbon fiber felt cathode 4. An external power supply 9 is turned on to apply a 10V voltage to the mesh ruthenium-iridium-titanium anode 3 and the carbon fiber felt cathode 4 to complete the first electrochemical purification. Subsequently, the wastewater containing hexavalent chromium overflows into the outer overflow chamber 21 through the overflow channels 51 at the top of the inner reaction chamber 1. It is then adsorbed and purified by the biomass activated carbon loaded in the overflow channels 51. Afterward, it enters the inner rising chamber 22 through the slot 23 and rises again, passing sequentially through the arc-shaped mesh ruthenium-iridium-titanium anode 3 and the carbon fiber felt cathode 4 to complete the second electrochemical purification.

[0083] S4. Detection: The concentrations of hexavalent chromium and hydrogen peroxide in the treated wastewater are measured.

[0084] Example 9

[0085] The difference between this embodiment and embodiment 8 is that:

[0086] S1. Preliminary preparation: Add Na2SO4 to the hexavalent chromium-containing wastewater to be treated, and adjust the pH of the wastewater to 1.9. Alternately lay biomass activated carbon layer 52 and pebble layer 53 inside each overflow channel 51. The injection rate of the hexavalent chromium-containing wastewater to be treated is 0.5L / min. Control the molar concentration of Na2SO4 to 0.1mol / L. Add a 40% NaOH solution or HCl solution when adjusting the pH of the hexavalent chromium-containing wastewater to be treated.

[0087] Example 10

[0088] The difference between this embodiment and embodiment 8 is that:

[0089] S1. Preliminary preparation: Add Na2SO4 to the hexavalent chromium-containing wastewater to be treated, and adjust the pH of the wastewater to 2.1. Alternately lay biomass activated carbon layer 52 and pebble layer 53 inside each overflow channel 51. The injection rate of the hexavalent chromium-containing wastewater to be treated is 5L / min. Control the molar concentration of Na2SO4 to 0.5mol / L. Add a 40% NaOH solution or HCl solution when adjusting the pH of the hexavalent chromium-containing wastewater to be treated.

[0090] Note: The faster the wastewater is injected, the more important it is to maintain the stability of the wastewater and ensure that the system has low resistance, thereby reducing power loss and improving current efficiency. The higher the concentration of Na2SO4 required, the more recommended it is to use a larger flow rate to improve treatment efficiency when the volume of wastewater to be treated is large.

[0091] Example 11

[0092] The difference between this embodiment and embodiment 8 is that:

[0093] The biomass activated carbon layer 52 includes several biomass activated carbon particles with a particle size of 0.3 cm, and the pebble layer 53 includes several pebbles with a particle size of 0.3 cm. The preparation method of the biomass activated carbon particles is as follows: straw or rice husks are collected and crushed into small segments of 0.5 cm. After washing and drying, they are placed in a pyrolysis furnace and pyrolyzed at 600°C for 1 hour to obtain biomass activated carbon powder. After cooling, the biomass activated carbon powder is mixed with bentonite powder at a mass ratio of 1:1. Water is added to maintain a moisture content of 3%. The mixture is stirred and then granulated by an extrusion granulator to obtain biomass activated carbon particles that meet the particle size requirements. The particles are then dried at 75°C.

[0094] Example 12

[0095] The difference between this embodiment and embodiment 8 is that:

[0096] The biomass activated carbon layer 52 includes several biomass activated carbon particles with a particle size of 0.8 cm, and the pebble layer 53 includes several pebbles with a particle size of 0.8 cm. The preparation method of the biomass activated carbon particles is as follows: straw or rice husks are collected and crushed into small pieces of 2 cm. After washing and drying, they are placed in a pyrolysis furnace and pyrolyzed at 800°C for 2 hours to obtain biomass activated carbon powder. After cooling, the biomass activated carbon powder is mixed with bentonite powder at a mass ratio of 1:1. Water is added to maintain a moisture content of 5%. The mixture is stirred and then granulated by an extrusion granulator to obtain biomass activated carbon particles that meet the particle size requirements. The particles are then dried at 80°C.

[0097] Example 13

[0098] The difference between this embodiment and embodiment 8 is that:

[0099] S3. Continuous wastewater treatment: Turn on the external power supply 9 and apply a 5V voltage to the mesh ruthenium-iridium titanium anode 3 and the carbon fiber felt cathode 4.

[0100] Example 14

[0101] The difference between this embodiment and embodiment 8 is that:

[0102] S3. Continuous wastewater treatment: Turn on the external power supply 9 and apply a 15V voltage to the mesh ruthenium-iridium-titanium anode 3 and the carbon fiber felt cathode 4.

[0103] Experimental Example

[0104] The feasibility of the apparatus and method of this invention is studied through actual tests. Hexavalent chromium is determined using the 1,5-diphenylcarbazide (DPC) colorimetric method. The pH of the sample is adjusted to acidic, DPC reagent is added, and the mixture reacts with hexavalent chromium to form a red compound. The absorbance is measured at 540 nm using a UV-Vis spectrophotometer. Hydrogen peroxide concentration is determined using the titanium(IV) oxysulfuric acid method. Titanium(IV) oxysulfuric acid reagent is added to the treated wastewater, causing it to react with hydrogen peroxide to form a yellow titanium peroxide complex. The absorbance is measured at 408 nm using a UV-Vis spectrophotometer. Based on the linear relationship between absorbance and hydrogen peroxide concentration, the hydrogen peroxide concentration in the sample can be accurately calculated using a standard curve.

[0105] System stability analysis: A 24-day system stability analysis experiment was conducted, with daily monitoring of hexavalent chromium concentration and hydrogen peroxide concentration to assess reaction efficiency. After the experiment, the long-term reliability of the system was evaluated by comparing the performance changes of the electrodes before and after operation.

[0106] like Figure 9As shown, the surface morphology and elemental composition of the reticulated ruthenium-iridium titanium anode 3 were investigated and analyzed using field emission scanning electron microscopy (FEI-F50) and energy dispersive X-ray spectroscopy (EDS). The reticulated ruthenium-iridium titanium anode 3 consists of a dense monolithic structure and cracks. This morphology provides a large specific surface area, which can improve the electrochemical activity of the electrode. EDS mapping confirmed that the substrate is Ti, and the surface coating consists of Ru and Ir elements.

[0107] like Figure 10 As shown, the surface morphology of the carbon fiber felt cathode 4 was investigated and analyzed using a field emission scanning electron microscope (FEI-F50). The carbon fiber felt is composed of interwoven fiber bundles with a diameter of 10-20 μm, and has the characteristics of large specific surface area and high porosity.

[0108] like Figure 11 As shown, the adsorption effect of carbon fiber felt cathode 4 on hexavalent chromium was investigated without applying an electric field. 900 mL of hexavalent chromium wastewater was filtered over 60 min, and samples were taken every 10 min to test the hexavalent chromium concentration. The results showed that the hexavalent chromium concentration remained consistently around 100 mg / L, indicating that the carbon fiber felt cathode does not adsorb hexavalent chromium, thus ruling out hexavalent chromium removal due to adsorption.

[0109] Under the same applied voltage and peristaltic pump flow rate, 900 mL of simulated wastewater containing 100 mg / L hexavalent chromium was filtered using the conventional top-down mode, the apparatus of Example 1, and the method of Example 8. In the conventional mode, the hydrogen peroxide concentration was 0.79 mmol / L after 90 minutes, while in the upflow mode, the concentration was 1.43 mmol / L after 90 minutes, an increase of approximately 80% compared to the conventional mode. This indicates that the upflow method can significantly increase the amount of hydrogen peroxide generated.

[0110] like Figure 12 As shown, the initial aqueous solution of the simulated hexavalent chromium wastewater was orange-yellow, while the effluent was dark green after upflow electrochemical treatment. This indicates that the hexavalent chromium was completely reduced during the treatment process.

[0111] like Figure 13 As shown, the experimental results indicate that hexavalent chromium was completely reduced within a 24-day operating period. The initial hydrogen peroxide concentration was lower because the new carbon fiber felt electrode required a certain amount of time to activate and reach a stable state. The hydrogen peroxide concentration reached 1.68 mmol / L on day 8 of operation, and then gradually decreased, maintaining around 1.4 mmol / L between days 13 and 24, demonstrating the reliability of the equipment and its suitability for industrial applications.

Claims

1. An apparatus for the upflow electrochemical treatment of wastewater containing hexavalent chromium, characterized in that, It includes a cylindrical inner reaction chamber (1) and a double-layered reaction chamber (2) located outside the inner reaction chamber (1); The inner reaction chamber (1) is hollow to form a flow channel. A mesh ruthenium-iridium titanium anode (3) and a carbon fiber felt cathode (4) are provided in the middle of the inner reaction chamber (1). The carbon fiber felt cathode (4) is located above the mesh ruthenium-iridium titanium anode (3), and the mesh ruthenium-iridium titanium anode (3) and the carbon fiber felt cathode (4) are arranged in parallel to each other. Both the mesh ruthenium-iridium titanium anode (3) and the carbon fiber felt cathode (4) cover the flow channel of the inner reaction chamber (1). The double-layer reaction chamber (2) includes an outer overflow chamber (21) and an inner rising chamber (22). The top of the inner rising chamber (22) is sealed to the top of the inner reaction chamber (1) through a sealing top plate (5). The upper surface of the sealing top plate (5) is provided with several overflow channels (51) loaded with biomass activated carbon. The overflow channels (51) extend from the top of the inner reaction chamber (1) to the top of the outer overflow chamber (21). The bottom of the inner rising chamber (22) is provided with a groove (23) at the connection between it and the outer overflow chamber (21). The mesh ruthenium-iridium-titanium anode (3) is provided with a plurality of first sealing connection points (11) on the inner wall of the inner reaction chamber (1). The mesh ruthenium-iridium-titanium anode (3) is connected one-to-one with a plurality of arc-shaped mesh ruthenium-iridium-titanium extended anodes (6) provided in the inner riser chamber (22) through the first sealing connection points (11). The carbon fiber felt cathode (4) is provided with a plurality of second sealing connection points (12) on the inner wall of the inner reaction chamber (1). The carbon fiber felt cathode (4) is connected one-to-one with a plurality of arc-shaped carbon fiber felt extended cathodes (7) provided in the inner riser chamber (22) through the second sealing connection points (12). The bottom of the inner reaction chamber (1) is provided with a water inlet pipe (13), and the top of the inner riser chamber (22) is provided with a drain pipe (14) that passes through the outer overflow chamber (21) and extends outward.

2. The apparatus for the upflow electrochemical treatment of wastewater containing hexavalent chromium according to claim 1, characterized in that The mesh ruthenium-iridium-titanium anode (3) and the carbon fiber felt cathode (4) are respectively connected to a wire (81) by conductive adhesive (8). The conductive adhesive (8) is located in a cavity (15) provided inside the inner reaction chamber (1). The cavity (15) is located between two adjacent first sealing connection points (11) or between two adjacent second sealing connection points (12). The wire (81) is externally insulated and passes through the inner current riser cavity (22) and the outer overflow cavity (21) in sequence before being connected to an external power supply (9).

3. The apparatus for upflow electrochemical treatment of hexavalent chromium-containing wastewater according to claim 1, characterized in that, An annular first PTFE pad (16) is provided between the mesh ruthenium-iridium-titanium anode (3) and the carbon fiber felt cathode (4). An annular second PTFE pad (17) is provided below the mesh ruthenium-iridium-titanium anode (3) and above the carbon fiber felt cathode (4). The first PTFE pad (16) and the second PTFE pad (17) are fixedly connected to the inner wall of the inner reaction chamber (1). The thickness of the mesh ruthenium-iridium-titanium anode (3) is 1-3 cm, the thickness of the carbon fiber felt cathode (4) is 2-4 cm, the thickness of the mesh ruthenium-iridium-titanium extended anode (6) is 2-4 cm, the thickness of the carbon fiber felt cathode (7) is 3-5 cm, and the distance between the mesh ruthenium-iridium-titanium anode (3) and the carbon fiber felt cathode (4) is 5-20 cm.

4. The apparatus for upflow electrochemical treatment of hexavalent chromium-containing wastewater according to claim 1, characterized in that, There are 6 to 12 overflow channels (51), and each overflow channel (51) extends outward from the center of the inner reaction chamber (1). The interior of the overflow channel (51) is alternately lined with 2 to 3 layers of biomass activated carbon (52) and 2 to 3 layers of pebble (53). The thickness of the biomass activated carbon layer (52) is 2 to 6 cm, and the thickness of the pebble layer (53) is 2 to 6 cm.

5. The apparatus for upflow electrochemical treatment of hexavalent chromium-containing wastewater according to claim 4, characterized in that, There are 3 to 5 first sealing connection points (11), 3 to 5 mesh ruthenium-iridium-titanium extended anodes (6), 3 to 5 second sealing connection points (12), and 3 to 5 carbon fiber felt film extended cathodes (7), and the first sealing connection points (11) and the second sealing connection points (12) are arranged in a cross pattern along the longitudinal direction.

6. The apparatus for upflow electrochemical treatment of hexavalent chromium-containing wastewater according to claim 1, characterized in that, The inlet pipe (13) is equipped with an inlet valve, and the drain pipe (14) is equipped with a drain valve.

7. A method for treating hexavalent chromium-containing wastewater using an upflow electrochemical process, based on the apparatus for treating hexavalent chromium-containing wastewater according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Preliminary preparation: Add Na2SO4 to the wastewater containing hexavalent chromium to be treated, and adjust the pH of the wastewater to be treated to 2±0.

1. Alternately lay biomass activated carbon layer (52) and pebble layer (53) inside each overflow channel (51). S2, Wastewater Injection: The wastewater containing hexavalent chromium to be treated is injected through the inlet pipe (13), and then the mesh ruthenium-iridium-titanium anode (3) and carbon fiber felt cathode (4) are energized. S3. Continuous wastewater treatment: The wastewater containing hexavalent chromium enters the inner reaction chamber (1), moves from bottom to top, and passes through the mesh ruthenium-iridium titanium anode (3) and carbon fiber felt cathode (4) in sequence. The external power supply (9) is turned on to apply a voltage of 5-15V to the mesh ruthenium-iridium titanium anode (3) and carbon fiber felt cathode (4) to complete the first electrochemical purification. Then the wastewater containing hexavalent chromium overflows into the outer overflow chamber (21) through the overflow channels (51) at the top of the inner reaction chamber (1). It is adsorbed and purified by the biomass activated carbon loaded in the overflow channel (51). Then it enters the inner upflow chamber (22) through the slot (23) and rises again. It passes through the arc-shaped mesh ruthenium-iridium titanium anode (3) and carbon fiber felt cathode (4) in sequence to complete the second electrochemical purification. S4. Detection: The concentrations of hexavalent chromium and hydrogen peroxide in the treated wastewater are measured.

8. The method for upflow electrochemical treatment of hexavalent chromium-containing wastewater according to claim 7, characterized in that, In step S1, the injection rate of the hexavalent chromium wastewater to be treated is 0.5–5 L / min, the molar concentration of Na2SO4 is controlled at 0.1–0.5 mol / L, and a 40% NaOH solution or HCl solution is added to adjust the pH of the hexavalent chromium wastewater.

9. The method for upflow electrochemical treatment of hexavalent chromium-containing wastewater according to claim 7, characterized in that, In S1, the biomass activated carbon layer (52) includes several biomass activated carbon particles with a particle size of 0.3 to 0.8 cm, and the pebble layer (53) includes several pebbles with a particle size of 0.3 to 0.8 cm. The preparation method of the biomass activated carbon granules is as follows: straw or rice husks are collected and crushed into small pieces less than 2 cm. After rinsing and drying, they are placed in a pyrolysis furnace and pyrolyzed at 600-800℃ for 1-2 hours to obtain biomass activated carbon powder. After cooling, the biomass activated carbon powder is mixed with bentonite powder at a mass ratio of 1:

1. Water is added to maintain a moisture content of 3-5%. The mixture is stirred and then granulated by an extrusion granulator to obtain biomass activated carbon granules that meet the particle size requirements. The granules are then dried at 75-80℃.

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