Coking wastewater treatment system and method based on BDD electrocatalytic oxidation gradient current

Abstract

The present invention provides a coking wastewater treatment system and method based on BDD electrocatalytic oxidation gradient current. The treatment system includes a sequentially connected sedimentation and filtration device, a first BDD electrocatalytic oxidation unit, an ultrafiltration unit, a nanofiltration unit, and a reverse osmosis unit. The concentrate outlet of the nanofiltration unit is connected to a second BDD electrocatalytic oxidation unit, and the concentrate outlet of the reverse osmosis unit is connected to a third BDD electrocatalytic oxidation unit, for treating organic matter in the high-conductivity membrane concentrate. The first, second, and third BDD electrocatalytic oxidation units each include an electrocatalytic oxidation reactor and a regulated power supply. The regulated power supply has a gradient current mode that outputs a set current to the electrocatalytic oxidation reactor according to the solution's conductivity and COD index. By dynamically regulating the current density, the reaction rate and pollutant degradation efficiency can be optimized, overall energy consumption can be reduced, and the electrode service life can be increased.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and in particular to a coking wastewater treatment system and method based on BDD electrocatalytic oxidation gradient current. Background Art

[0002] Coking wastewater is high-concentration, difficult-to-degrade industrial wastewater produced during the coal coking process. It mainly comes from coal gas purification (residual ammonia water, final cooling wastewater, crude benzene separation water), tar processing and equipment cleaning. It is characterized by complex composition and strong toxicity, containing high concentrations of phenols, polycyclic aromatic hydrocarbons (PAHs), cyanide, ammonia nitrogen and difficult-to-degrade organic matter.

[0003] The main existing treatment processes include Fenton oxidation, ozone oxidation, traditional electrocatalytic oxidation, etc. Fenton oxidation uses Fe 2+ / H2O2 reaction generates hydroxyl radicals to degrade organic matter, which will increase the iron ion concentration in the sewage and produce sludge, causing secondary pollution; the ozone oxidation method has limited COD removal ability, with a removal rate of only 50%-70%; traditional electrocatalytic oxidation electrodes use DSA electrodes, which are easily passivated in a high-chlorine environment, resulting in decreased catalytic activity, increased treatment energy consumption, and shortened electrode life.

[0004] A coking wastewater treatment system and method in the prior art includes an electrocatalytic oxidation unit and a nanofiltration unit, a reverse osmosis unit, a fluorine removal and silicon removal unit, and an evaporation crystallization unit connected in sequence. The electrocatalytic oxidation unit is connected to the nanofiltration unit and the evaporation crystallization unit to receive nanofiltration concentrated water and evaporation crystallization mother liquor respectively. The electrocatalytic oxidation unit is used to perform electrocatalytic oxidation treatment on the nanofiltration concentrated water and the evaporation crystallization mother liquor.

[0005] The applicant has discovered that the existing technologies present at least the following technical problems: All coking wastewater treatment systems and methods, including the aforementioned existing technologies, employ a constant current mode, setting a constant current density in the electrocatalytic oxidation unit. This results in rapid consumption of pollutants near the electrodes, leading to concentration polarization and an increased proportion of oxygen and hydrogen evolution side reactions, resulting in low oxidation efficiency and high treatment energy consumption. Summary of the Invention

[0006] The present invention aims to provide a coking wastewater treatment system and method based on BDD electrocatalytic oxidation gradient current, addressing the low electrocatalytic oxidation efficiency and high energy consumption inherent in existing coking wastewater treatment systems and methods. The various technical benefits achieved by the preferred technical solutions provided by the present invention are detailed below.

[0007] To achieve the above objectives, the present invention provides the following technical solutions:

[0008] The coking wastewater treatment system based on BDD electrocatalytic oxidation gradient current provided by the present invention is characterized by comprising a sedimentation and filtration device, a first BDD electrocatalytic oxidation unit, an ultrafiltration unit, a nanofiltration unit, and a reverse osmosis unit connected in sequence according to the wastewater treatment order, wherein the first BDD electrocatalytic oxidation unit is used to treat large molecular refractory organic matter in the coking wastewater;

[0009] The concentrated water outlet of the nanofiltration unit is connected to the second BDD electrocatalytic oxidation unit, and the concentrated water outlet of the reverse osmosis unit is connected to the third BDD electrocatalytic oxidation unit. The second BDD electrocatalytic oxidation unit and the third BDD electrocatalytic oxidation unit are used to treat organic matter in the high conductivity membrane concentrated water;

[0010] The first BDD electrocatalytic oxidation unit, the second BDD electrocatalytic oxidation unit and the third BDD electrocatalytic oxidation unit each include an electrocatalytic oxidation reactor and an adjustment configuration power supply, the adjustment configuration power supply having a gradient variable current mode, and the gradient variable current mode can output a variable set current to the electrocatalytic oxidation reactor according to the conductivity and COD index of the solution.

[0011] Preferably, the gradient current mode refers to:

[0012] When the COD index of the water body is constant, the set current increases in a gradient as the conductivity of the solution increases; when the conductivity of the solution is constant, the set current increases in a gradient as the COD index of the water body increases;

[0013] Furthermore, the set current has a maximum current limit, and the maximum current limit no longer changes with the increase of the conductivity of the solution and the COD index of the water body.

[0014] Preferably, the sedimentation and filtration device includes a high-density sedimentation tank and a sand filter tank connected in sequence according to the wastewater treatment order, and the high-density sedimentation tank is connected to a PAC dosing device and a PAM dosing device for removing part of the COD and suspended matter;

[0015] A buffer tank is connected between the first BDD electrocatalytic oxidation unit and the ultrafiltration unit, and the buffer tank is connected to a dosing device;

[0016] An ion exchange resin unit is connected between the ultrafiltration unit and the nanofiltration unit to deeply remove calcium, magnesium and fluoride ions.

[0017] Preferably, the electrode structure in the electrocatalytic oxidation reactor is as follows: the anode is a BDD electrode, the substrate is any one of silicon-based, titanium-based, and niobium-based, and the cathode material is a corrosion-resistant titanium plate or a titanium-based iridium dioxide coated electrode.

[0018] Preferably, the water outlet of the reverse osmosis unit is connected to a reuse water pool;

[0019] The water outlet of the second BDD electrocatalytic oxidation unit is sequentially connected to the first pH adjustment tank and the sodium sulfate evaporation unit;

[0020] The water outlet of the third BDD electrocatalytic oxidation unit is sequentially connected to the second pH adjustment tank and the sodium chloride evaporation unit.

[0021] The present invention also provides a coking wastewater treatment method based on BDD electrocatalytic oxidation gradient current, using the above-mentioned BDD electrocatalytic oxidation gradient current coking wastewater treatment system, the treatment method includes:

[0022] When the first BDD electrocatalytic oxidation unit, the second BDD electrocatalytic oxidation unit, and the third BDD electrocatalytic oxidation unit are used to treat water, the regulating configuration power supply is placed in the gradient variable current mode, and a set current that changes according to the conductivity and COD index of the solution is output to the electrocatalytic oxidation reactor;

[0023] Among them, when the COD index of the water body is constant, the set current increases gradiently with the increase of the conductivity of the solution; when the conductivity of the solution is constant, the set current increases gradiently with the increase of the COD index of the water body; the set current has a maximum current, and the maximum current no longer changes with the increase of the conductivity of the solution and the COD index of the water body.

[0024] Preferably, when the first BDD electrocatalytic oxidation unit, the second BDD electrocatalytic oxidation unit, and the third BDD electrocatalytic oxidation unit are in a water body, the treatment method includes:

[0025] Real-time detection of water conductivity and COD, and input signals to the control unit;

[0026] The control unit controls the regulating configuration power supply to be in the gradient current mode according to the conductivity and COD signals, and controls the regulating configuration power supply to output the changed set current to the electrocatalytic oxidation reactor.

[0027] Preferably, the processing method further comprises:

[0028] Passing the biochemical effluent of the coking wastewater through the sedimentation and filtration device to perform sedimentation filtration on the biochemical effluent of the coking wastewater;

[0029] The effluent from the precipitation and filtration device enters the first BDD electrocatalytic oxidation unit, so that the first BDD electrocatalytic oxidation unit treats the macromolecular refractory organic matter in the coking wastewater;

[0030] The effluent from the first BDD electrocatalytic oxidation unit enters the ultrafiltration unit to intercept macromolecular organic matter, colloids, suspended matter and other substances to reduce turbidity;

[0031] The effluent from the ultrafiltration unit enters the nanofiltration unit, and the selective permeability of the nanofiltration membrane is used to intercept multivalent ions and small molecular organic matter, while allowing monovalent ions to partially pass through;

[0032] Passing the nanofiltration concentrated water through the second BDD electrocatalytic oxidation unit to further treat organic matter and remove COD;

[0033] The reverse osmosis concentrated water is passed through the third BDD electrocatalytic oxidation unit to further process organic matter and remove COD.

[0034] Preferably, the processing method further comprises:

[0035] Before the effluent from the ultrafiltration unit enters the nanofiltration unit, the effluent from the ultrafiltration unit enters an ion exchange resin unit to deeply remove calcium, magnesium and fluoride ions.

[0036] Preferably, the processing method further comprises:

[0037] Allow the effluent from the reverse osmosis unit to enter the reuse water pool;

[0038] The effluent from the second BDD electrocatalytic oxidation unit enters the first pH adjustment tank to adjust the pH of the effluent;

[0039] The effluent from the first pH adjustment tank enters the sodium sulfate evaporation unit for salt concentration and crystallization to produce anhydrous sodium sulfate or sodium sulfate decahydrate crystals;

[0040] The effluent from the third BDD electrocatalytic oxidation unit enters a second pH regulating tank to adjust the pH of the effluent;

[0041] The effluent from the second pH regulating tank enters the sodium chloride evaporation unit for salt concentration and crystallization to precipitate high-purity sodium chloride crystals;

[0042] The water outlet of the second BDD electrocatalytic oxidation unit is sequentially connected to the first pH regulating tank and the sodium sulfate evaporation unit;

[0043] The water outlet of the third BDD electrocatalytic oxidation unit is sequentially connected to the second pH regulating tank and the sodium chloride evaporation unit.

[0044] The coking wastewater treatment system and treatment method based on BDD electrocatalytic oxidation gradient variable current provided by the present invention have the following beneficial effects compared with the existing technology: the first BDD electrocatalytic oxidation unit is used to treat large molecular difficult-to-degrade organic matter in coking wastewater, reduce COD, avoid membrane system blockage caused by large molecular organic matter and alleviate the treatment pressure of the membrane system; the second BDD electrocatalytic oxidation unit and the third BDD electrocatalytic oxidation unit are used to treat organic matter in high-conductivity membrane concentrated water to improve the purity of evaporated crystallized salt and reduce the hazardous waste rate of miscellaneous salts (such as mixed salts containing organic matter); and the regulating configuration power supply in each BDD electrocatalytic oxidation unit has a gradient variable current mode, which can prevent the pollutants near the electrode from being rapidly consumed, causing concentration polarization, and an increase in the proportion of oxygen evolution side reactions and hydrogen evolution side reactions. By dynamically controlling the current density, the reaction rate and pollutant degradation efficiency can be optimized, and while ensuring the treatment efficiency, the overall energy consumption can be reduced and the service life of the electrode can be increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0046] Figure 1 This is a flow chart of a coking wastewater treatment method based on BDD electrocatalytic oxidation gradient current;

[0047] Figure 2 This is a schematic diagram of the overall structure of the coking wastewater treatment system based on BDD electrocatalytic oxidation gradient current.

[0048] In the figure, 1. high-density sedimentation tank; 2. sand filter; 3. first BDD electrocatalytic oxidation unit; 4. buffer tank; 5. ultrafiltration unit; 6. ion exchange resin unit; 7. nanofiltration unit; 8. reverse osmosis unit; 9. recycled water tank; 10. second BDD electrocatalytic oxidation unit; 11. first pH adjustment tank; 12. sodium sulfate evaporation unit; 13. third BDD electrocatalytic oxidation unit; 14. second pH adjustment tank; 15. sodium chloride evaporation unit; 16. PAC dosing device; 17. PAM dosing device; 18. dosing device; 19. electrocatalytic oxidation reactor. DETAILED DESCRIPTION

[0049] To make the objectives, technical solutions, and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other implementations obtained by those of ordinary skill in the art without inventive effort are within the scope of protection of the present invention.

[0050] In the description of the present invention, it should be understood that the terms "center," "length," "width," "height," "up," "down," "front," "back," "left," "right," "vertical," "horizontal," "top," "bottom," "inside," "outside," and "side" and the like, indicating positions or location relationships, are based on the positions or location relationships shown in the accompanying drawings and are intended only to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore should not be construed as limiting the present invention. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0051] The embodiment of the present invention provides a coking wastewater treatment system and method based on BDD electrocatalytic oxidation gradient variable current. By dynamically controlling the current density, the reaction rate and pollutant degradation efficiency can be optimized. While ensuring the treatment efficiency, the overall energy consumption can be reduced and the service life of the electrode can be increased.

[0052] The following combination Figure 1 and Figure 2 The technical solution provided by the present invention is described in more detail.

[0053] See also Figure 1 and Figure 2 As shown, the coking wastewater treatment system based on BDD electrocatalytic oxidation gradient variable current provided by the present invention includes a sedimentation filtration device, a first BDD electrocatalytic oxidation unit 3, an ultrafiltration unit 5, a nanofiltration unit 7, and a reverse osmosis unit 8 connected in sequence according to the wastewater treatment order. The first BDD electrocatalytic oxidation unit 3 is used to treat large molecular refractory organic matter in the coking wastewater; the concentrated water outlet of the nanofiltration unit 7 is connected to the second BDD electrocatalytic oxidation unit 10, and the concentrated water outlet of the reverse osmosis unit 8 is connected to the third BDD electrocatalytic oxidation unit 13. The second BDD electrocatalytic oxidation unit 10 and the third BDD electrocatalytic oxidation unit 13 are used to treat organic matter in the high conductivity membrane concentrated water; the first BDD electrocatalytic oxidation unit 3, the second BDD electrocatalytic oxidation unit 10 and the third BDD electrocatalytic oxidation unit 13 all include an electrocatalytic oxidation reactor 19 and an adjustable configuration power supply. The adjustable configuration power supply has a gradient variable current mode. The gradient variable current mode can output a set current that changes according to the conductivity and COD index of the solution to the electrocatalytic oxidation reactor 19.

[0054] The electrocatalytic oxidation reactor 19 is the core component of the system. It houses electrodes, typically made of boron-doped diamond (BDD) or metal oxides. These electrodes exhibit high catalytic activity and stability, and indirectly degrade pollutants through direct electron transfer or the generation of strong oxidizing free radicals (such as •OH) on the electrode surface. A regulated power supply provides stable current and voltage to the electrocatalytic reactor, ensuring controllable reaction conditions. Adjusting the current density optimizes the reaction rate and pollutant degradation efficiency.

[0055] In existing technologies, the power supply provides a constant current to the electrocatalytic reactor. In constant current mode, the current density is fixed, but the pollutant diffusion rate decreases as the concentration decreases. This results in the rapid consumption of pollutants near the electrodes, causing concentration polarization, increasing the proportion of oxygen and hydrogen evolution side reactions, and leading to low oxidation efficiency and high treatment energy consumption. Therefore, it is necessary to dynamically match the current and mass transfer capacity according to the COD and conductivity of the treated wastewater to effectively suppress concentration polarization at low COD levels and achieve efficient and low-energy pollutant degradation.

[0056] To address the above problem, in this embodiment, the adjustment configuration power supply has a gradient variable current mode, which can output a variable set current to the electrocatalytic oxidation reactor 19 according to the conductivity and COD index of the solution.

[0057] Current density refers to the current passing through the electrode surface per unit area, that is, the current per unit cross-sectional area, generally expressed in A / m 2 or mA / cm 2 It is an important process parameter in the electrocatalytic process.

[0058] Conductivity is the ease with which charges move in an electrolyte solution, and can indirectly reflect the salt content in the solution to be treated.

[0059] COD, or Chemical Oxygen Demand, is an important indicator of water pollution. The more polluted the water, the higher the COD index.

[0060] The current density in the gradient current mode of this embodiment is gradient-varied according to the following table:

[0061] Table 1 Current density adjustment table

[0062]

[0063] As the reaction proceeds, the concentration of the pollutants decreases, and the diffusion rate of the pollutants decreases as the concentration decreases, resulting in: the pollutants near the electrode are quickly consumed, causing concentration polarization, an increase in the proportion of oxygen evolution side reactions and hydrogen evolution side reactions, and problems such as low oxidation efficiency and high processing energy consumption. Therefore, in this embodiment, as shown in Table 1, the gradient variable current mode refers to: when the COD index of the water body is constant, the set current increases in a gradient as the conductivity of the solution increases; when the conductivity of the solution is constant, the set current increases in a gradient as the COD index of the water body increases; and the set current has a maximum current, and the maximum current no longer changes with the increase of the conductivity of the solution and the COD index of the water body.

[0064] By dynamically matching the current and mass transfer capacity according to the COD and conductivity of the treated wastewater, it can effectively suppress concentration polarization under low COD and achieve efficient and low-cost pollutant degradation.

[0065] In this embodiment, the current is set to have a maximum current, with a current density of 100 mA / cm 2 The maximum value is taken into account the effect of current density on life, and the current density is greater than 100mA / cm 2 Water treatment can cause significant damage to the electrodes, thereby reducing their lifespan. This embodiment can effectively increase their lifespan.

[0066] As an alternative embodiment, see Figure 1 and Figure 2 As shown, the sedimentation and filtration device includes a high-density sedimentation tank 1 and a sand filter 2, connected in sequence according to the wastewater treatment process. The high-density sedimentation tank 1 is connected to a PAC dosing device 16 and a PAM dosing device 17 for removing some COD and suspended solids. A buffer tank 4 is connected between the first BDD electrocatalytic oxidation unit 3 and the ultrafiltration unit 5, and is also connected to a dosing device 18. Oxidizing substances such as residual chlorine and ozone generated by the first BDD electrocatalytic oxidation unit are removed through aeration or the addition of sodium bisulfite to prevent oxidative damage to the ultrafiltration membrane. Simultaneously, the pH is adjusted to a stable range of 6.5-7.5 by adding dilute hydrochloric acid or an alkaline agent to prevent scaling or corrosion in the subsequent membrane system (ultrafiltration / RO) due to pH fluctuations. An ion exchange resin unit 6 is connected between the ultrafiltration unit 5 and the nanofiltration unit 7 for deep removal of calcium, magnesium, and fluoride ions.

[0067] As an alternative embodiment, see Figure 1 and Figure 2 As shown, the water outlet of the reverse osmosis unit 8 is connected to the reuse water pool 9; the water produced by the reverse osmosis unit 8 enters the reuse water pool 9 and can be directly used as circulating cooling water, boiler feed water or process water, thereby realizing the reuse of coking wastewater.

[0068] The outlet of the second BDD electrocatalytic oxidation unit 10 is connected to the first pH regulating tank 11 and the sodium sulfate evaporation unit 12 in sequence. The outlet of the second BDD electrocatalytic oxidation unit 10 enters the first pH regulating tank 11 to adjust the pH of the outlet water and serve as an emergency storage of flow buffer. The outlet of the first pH regulating tank 11 enters the sodium sulfate evaporation unit 12 to concentrate and crystallize the salt to produce anhydrous sodium sulfate or sodium sulfate decahydrate crystals.

[0069] The outlet of the third BDD electrocatalytic oxidation unit 13 is connected in sequence to the second pH adjustment tank 14 and the sodium chloride evaporation unit. The effluent from the third BDD electrocatalytic oxidation unit 13 enters the second pH adjustment tank 14, where the pH is adjusted and it also serves as an emergency flow buffer. The effluent from the second pH adjustment tank 14 enters the sodium chloride evaporation unit 15 (existing equipment), where salt is concentrated and crystallized to produce high-purity sodium chloride crystals. The crystallized salt can be used as a raw material in the chlor-alkali industry, as a deicing agent, and other applications, thus realizing waste resource utilization.

[0070] In this embodiment, the electrode structure of the electrocatalytic oxidation unit is as follows: the anode is a BDD electrode, which can be based on silicon, titanium, or niobium; the cathode material is a corrosion-resistant titanium plate or a titanium-based iridium dioxide-coated electrode. The plate spacing is 2-3 mm. The BDD electrode has a boron doping level of 5 g / L-50 g / L, a grain size of 1-10 μm, and a shape of one of rectangular, disc, mesh, and foam. The BDD electrode thickness is 5-50 μm.

[0071] In electrocatalytic oxidation technology, commonly used electrode materials include titanium-based DSA electrodes, graphite electrodes, sub-titanium oxide electrodes, MOS electrodes, BDD electrodes, etc. Among them, boron-doped diamond electrodes (BDD) have significant advantages:

[0072] 1. Wide electrochemical window and high oxygen evolution potential. The BDD electrode has an electrochemical window of over 3.5 V (compared to only approximately 2 V for conventional electrodes such as glassy carbon electrodes) and a high oxygen evolution potential. This effectively inhibits side reactions (such as oxygen evolution) when oxidizing pollutants. Consequently, the BDD electrode is significantly more efficient at generating hydroxyl radicals (•OH) than other materials, making it suitable for treating high-concentration, complex wastewater.

[0073] 2. Excellent chemical stability. BDD electrodes remain stable in extreme environments such as strong acid, strong alkali, high salt and high temperature, hardly react with the medium, and have strong corrosion resistance.

[0074] 3. Low adsorption properties and anti-pollution capabilities. The catalytic mechanism of traditional electrodes relies on surface adsorption. Physically adsorbed active oxygen on the anode surface appears as highly active M-OH, while chemically adsorbed oxygen appears as metal transition oxides (MO). Pollutants combine with M-OH or MO and are oxidized. During the reaction, some MO undergoes oxygen evolution reaction to generate oxygen. However, the low adsorption of BDD makes it difficult for hydroxyl radicals (•OH) to stably adsorb on the electrode surface, diffuse in the solution, and oxidize pollutants. This process hinders the continuous reaction step of the oxygen evolution reaction. Considering the aforementioned oxygen evolution overpotential of the BDD electrode (>2.3 V vs. SHE) is much higher than that of traditional metal oxide electrodes (such as RuO2's -1.5 V), a higher applied potential is required to trigger the oxygen evolution reaction. This allows the BDD electrocatalytic oxidation system to prioritize the oxidation and degradation of pollutants within the potential range required for pollutant oxidation, rather than wasting energy on side reactions (oxygen evolution reaction).

[0075] During use, conventional electrodes absorb reaction intermediates or contaminants, resulting in some active sites becoming occupied or clogged, hindering the normal progress of electrochemical reactions. This phenomenon is known as electrode "poisoning." For example, when treating phenol-containing wastewater, phenolic polymers adsorb on the surface of graphite electrodes, resulting in reduced performance. During the phenol oxidation process, intermediates such as benzoquinone and polyphenols are easily adsorbed on the electrode surface, forming a dense layer that hinders further oxidation. BDD's low adsorption capacity makes it less susceptible to adsorption of reaction intermediates or contaminants, keeping active sites open and effectively avoiding "poisoning," demonstrating significant advantages in the field of electrocatalytic oxidation. This property is particularly suitable for treating industrial wastewater containing complex organic compounds (such as phenols and pesticides), reducing the frequency of electrode cleaning and maintenance.

[0076] See also Figure 1 and Figure 2 As shown, this embodiment provides a coking wastewater treatment method based on BDD electrocatalytic oxidation gradient variable current, using the coking wastewater treatment system based on BDD electrocatalytic oxidation gradient variable current of the above-mentioned embodiment 1, the treatment method includes: when using the first BDD electrocatalytic oxidation unit 3, the second BDD electrocatalytic oxidation unit 10 and the third BDD electrocatalytic oxidation unit 13 to treat the water body, the adjustment configuration power supply is in a gradient variable current mode, and the set current that changes according to the conductivity and COD index of the solution is output to the electrocatalytic oxidation reactor 19; wherein, when the COD index of the water body is constant, the set current increases gradiently with the increase of the conductivity of the solution; when the conductivity of the solution is constant, the set current increases gradiently with the increase of the COD index of the water body; the set current has a maximum current, and the maximum current no longer changes with the increase of the conductivity of the solution and the COD index of the water body.

[0077] In this embodiment, the first BDD electrocatalytic oxidation unit 3 is used to treat large molecular refractory organic matter in coking wastewater, reduce COD, avoid membrane system clogging caused by large molecular organic matter, and alleviate the treatment pressure of the membrane system. The second BDD electrocatalytic oxidation unit 10 and the third BDD electrocatalytic oxidation unit 13 are used to treat organic matter in high-conductivity membrane concentrated water to improve the purity of evaporated crystallized salt and reduce the hazardous waste rate of miscellaneous salts (such as mixed salts containing organic matter); and the regulating configuration power supply in each BDD electrocatalytic oxidation unit has a gradient variable current mode, which can prevent the pollutants near the electrode from being rapidly consumed, causing concentration polarization, and increasing the proportion of oxygen evolution side reactions and hydrogen evolution side reactions. By dynamically controlling the current density, the reaction rate and pollutant degradation efficiency can be optimized, and while ensuring the treatment efficiency, the overall energy consumption can be reduced and the service life of the electrode can be increased.

[0078] As an alternative embodiment, see Figure 1 and Figure 2 As shown, the corresponding outlet water is lifted to the electrocatalytic oxidation reactor 19 by the water inlet pump, and a water quality and water quantity monitoring instrument is provided in the water inlet pipe, and the monitoring instrument includes an automatic conductivity detection probe, an online COD monitor and an online pressure meter; when the first BDD electrocatalytic oxidation unit 3, the second BDD electrocatalytic oxidation unit 10, and the third BDD electrocatalytic oxidation unit 13 are in the water body, the treatment method includes: real-time detection of the conductivity and COD of the water body, and inputting the signal to the control unit; the control unit controls the adjustment configuration power supply to be in a gradient variable current mode according to the conductivity and COD signals, and controls the adjustment configuration power supply to output the changed set current to the electrocatalytic oxidation reactor 19.

[0079] As an optional embodiment, the treatment method also includes: passing the biochemical effluent of the coking wastewater through a sedimentation filtration device to perform sedimentation filtration on the biochemical effluent of the coking wastewater; passing the effluent of the sedimentation filtration device into the first BDD electrocatalytic oxidation unit 3, so that the first BDD electrocatalytic oxidation unit 3 treats the large molecular refractory organic matter in the coking wastewater; passing the effluent of the first BDD electrocatalytic oxidation unit 3 into the ultrafiltration unit 5, intercepting large molecular organic matter, colloids and suspended matter and other substances to reduce turbidity; passing the effluent of the ultrafiltration unit 5 into the nanofiltration unit 7, utilizing the selective permeability of the nanofiltration membrane to intercept multivalent ions and small molecular organic matter, and allowing monovalent ions to partially pass through; passing the nanofiltration concentrate through the second BDD electrocatalytic oxidation unit 10, further treating the organic matter and removing COD; passing the reverse osmosis concentrate through the third BDD electrocatalytic oxidation unit 13, further treating the organic matter and removing COD.

[0080] As an optional embodiment, the treatment method further includes: before the effluent of the ultrafiltration unit 5 enters the nanofiltration unit 7, the effluent of the ultrafiltration unit 5 enters the ion exchange resin unit 6 to deeply remove calcium, magnesium and fluoride ions.

[0081] As an optional embodiment, the treatment method also includes: allowing the effluent of the reverse osmosis unit 8 to enter the reuse water tank 9; allowing the effluent of the second BDD electrocatalytic oxidation unit 10 to enter the first pH regulating tank 11 to adjust the pH of the effluent; allowing the effluent of the first pH regulating tank 11 to enter the sodium sulfate evaporation unit 12 for salt concentration and crystallization to produce anhydrous sodium sulfate or sodium sulfate decahydrate crystals; allowing the effluent of the third BDD electrocatalytic oxidation unit 13 to enter the second pH regulating tank 14 to adjust the pH of the effluent; allowing the effluent of the second pH regulating tank 14 to enter the sodium chloride evaporation unit 15 for salt concentration and crystallization to precipitate high-purity sodium chloride crystals; the outlet of the second BDD electrocatalytic oxidation unit 10 is sequentially connected to the first pH regulating tank 11 and the sodium sulfate evaporation unit 12; the outlet of the third BDD electrocatalytic oxidation unit 13 is sequentially connected to the second pH regulating tank 14 and the sodium chloride evaporation unit.

[0082] The coking wastewater treatment method based on BDD electrocatalytic oxidation gradient current in this embodiment specifically includes the following steps:

[0083] S1: The biochemical effluent of coking wastewater is used as the inlet water and enters the high-density sedimentation tank 1. Lime milk and sodium carbonate are added to the high-density sedimentation tank 1 to remove hardness. A polyaluminium chloride (PAC) solution with a concentration of 5-10% is used as a flocculant, and a PAM with a concentration of 0.1-0.3% is used as a coagulant aid for flocculation. The sedimentation takes 60-90 minutes to ensure that the flocs are fully settled, remove 20%-30% of COD and suspended solids, reduce turbidity, and reduce the load of the sand filter 2 unit and the load and energy consumption of the BDD electrocatalytic oxidation unit.

[0084] S2: The sand filter 2 intercepts the suspended particulate matter remaining in the wastewater (such as colloids and flocs that have not been completely settled in the sedimentation tank), reduces the pollution load of the subsequent BDD electrocatalytic oxidation unit, reduces the cleaning frequency of the electrode, and prevents suspended matter from causing problems such as blockage of the BDD electrocatalytic oxidation equipment pipeline or short circuit of the plate.

[0085] The thickness of the sand layer in unit 2 of the sand filter is 800-1000mm, the filtration flow rate is 10-20m / h, and the backwash cycle is adjusted between 24-48h according to the turbidity of the influent.

[0086] S3: The effluent from the sand filter 2 enters the first BDD electrocatalytic oxidation unit 3 for treatment. The stubborn organic substances such as phenols, quinoline, polycyclic aromatic hydrocarbons (PAHs) in the coking wastewater are oxidized by •OH free radicals, and highly toxic substances such as phenol and cyanide are converted into low-toxic / easily biodegradable products (such as CO2 and H2O). Pollutants such as COD, ammonia nitrogen and cyanide are removed, the fouling of the ultrafiltration membrane is alleviated, and the frequency of ultrafiltration membrane cleaning is reduced.

[0087] The specific processing steps of step S3 are as follows:

[0088] S301 The effluent from the sand filter 2 is pumped to the buffer tank of the first BDD electrocatalytic oxidation unit 3 by the water inlet pump.

[0089] The water inlet pipe is equipped with water quality and water quantity monitoring instruments, including conductivity automatic detection probe, online COD monitor and online pressure meter.

[0090] The S302 monitoring instrument detects conductivity and COD in real time and inputs the signal to the BDD electrocatalytic oxidation equipment.

[0091] The wastewater in the S303 buffer tank is circulated by a circulating pump. The first BDD electrocatalytic oxidation unit 3 establishes a "COD-Conductivity Dual-Factor Adaptive BDD Gradient Current Control Model" based on Table 1. This model adjusts the power supply to output the appropriate treatment current based on the input conductivity and COD output current density. This is suitable for electrochemical treatment of highly volatile industrial wastewater, optimizing both efficiency and energy consumption.

[0092] S304 After the wastewater is treated to the target COD, the circulation is stopped and the treated wastewater is discharged to the regulating tank through the drainage pump.

[0093] S4: The effluent from the first BDD electrocatalytic oxidation unit 3 enters the buffer tank 4. Aeration or the addition of sodium bisulfite removes oxidizing substances such as residual chlorine and ozone generated by the first BDD electrocatalytic oxidation unit 3, preventing oxidative damage to the ultrafiltration membrane. Simultaneously, the pH is adjusted by adding dilute hydrochloric acid or an alkaline agent, stabilizing it at 6.5-7.5 to prevent scaling or corrosion in the subsequent membrane system (ultrafiltration / RO) due to pH fluctuations.

[0094] An online pH meter and an online ORP sensor are configured in the buffer tank 4.

[0095] S5: The effluent from buffer tank 4 is further filtered through ultrafiltration to intercept macromolecular organic matter, colloids, suspended solids and other substances, reducing turbidity (effluent turbidity ≤ 0.5 NTU), avoiding contamination of the resin surface and ensuring ion exchange capacity; preventing nanofiltration (NF) or reverse osmosis (RO) membranes from being blocked by colloids and particulate matter, extending membrane life; reducing scaling (such as CaCO3 and silicates) on the NF / RO membrane surface and reducing the frequency of chemical cleaning.

[0096] The ultrafiltration concentrate can be returned to the BDD unit for secondary oxidation to achieve closed-loop treatment of pollutants.

[0097] S6: Ultrafiltration water passes through ion exchange resin unit 6 to deeply remove calcium, magnesium and fluoride ions to prevent Ca 2+ / Mg 2+ With SO4 2- / CO3 2-Combined with the formation of calcium sulfate, magnesium carbonate and other scaling substances, resulting in a decrease in membrane flux; prevent F⁻ from forming insoluble fluorides (such as CaF2) in high-salt concentrated water, which will block the membrane pores. Reduce the impurity content (such as Ca 2 + ), improve salt purity.

[0098] S7: The effluent from the ion exchange resin unit 6 passes through the nanofiltration unit 7 for salt separation, and the selective permeability of the nanofiltration membrane is used to intercept multivalent ions (such as SO4 2- 、CO3 2- ) and small organic molecules (molecular weight 200-1000 Da), allowing monovalent ions (Cl - 、Na - ) partially penetrates; the salinity of the produced water is reduced by 60%-80% (raw water conductivity 5000-8000 μS / cm → produced water 1000-2000 μS / cm); the salinity of the concentrate is increased to 15000-20000 μS / cm, facilitating subsequent evaporation and crystallization to recover sodium sulfate / sodium chloride.

[0099] S7-A: The concentrated water from the nanofiltration unit 7 passes through the second BDD electrocatalytic oxidation unit 10 to further treat organic matter, remove COD, and decolorize, thereby preventing coking and scaling of organic matter during the evaporation process, improving heat exchange efficiency, reducing steam energy consumption, and improving the purity of sodium sulfate in subsequent evaporation crystallization.

[0100] For specific processing steps, please refer to S3.

[0101] S7-B: The effluent from the second BDD electrocatalytic oxidation unit 10 enters the first pH regulating tank 11 to regulate the pH of the effluent and serve as an emergency storage of flow buffer.

[0102] S7-C: The effluent from the first pH regulating tank 11 enters the sodium sulfate evaporation equipment for salt concentration and crystallization to produce anhydrous sodium sulfate or sodium sulfate decahydrate crystals.

[0103] Evaporative crystallization is a physical and chemical process that involves evaporating the solvent to supersaturate a solution, thereby precipitating solute crystals. Its core principle is to continuously remove the solvent (usually water) through an external heat source (such as steam or electricity), gradually increasing the solute concentration in the solution until it exceeds its solubility limit. This causes the solute molecules to arrange themselves into crystal particles, achieving solute separation, purification, and resource recovery.

[0104] The evaporation crystallization process includes multi-effect evaporation, mechanical vapor recompression, and thermal vapor recompression.

[0105] S8: The water produced by the nanofiltration unit 7 enters the reverse osmosis unit 8 (RO), which uses high pressure to drive water molecules through the semipermeable membrane (pore size 0.1-1 nm) to intercept monovalent ions (such as Cl- 、Na - ) and small molecule organic matter (molecular weight > 100 Da). Product water conductivity < 100 μS / cm (raw water > 2000 μS / cm), desalination rate > 98%.

[0106] S8-A: The concentrated water from the reverse osmosis unit 8 (RO) passes through the third BDD electrocatalytic oxidation unit 13 to further treat organic matter, remove COD, and decolorize, thereby preventing coking and scaling of organic matter during the evaporation process, improving heat exchange efficiency, reducing steam energy consumption, and improving the purity of subsequent evaporation crystals.

[0107] For specific processing steps, please refer to S3.

[0108] S8-B: The effluent from the third BDD electrocatalytic oxidation unit 13 enters the second pH regulating tank 14 to adjust the pH of the effluent and serve as an emergency storage of flow buffer.

[0109] S8-C: The effluent from the second pH regulating tank 14 enters the sodium chloride evaporation equipment for salt concentration and crystallization to precipitate high-purity sodium chloride crystals. The crystallized salt can be used as raw materials for the chlor-alkali industry, snow melting agents, etc., realizing waste resource utilization.

[0110] S9: The water produced by the reverse osmosis unit 8 (RO) enters the reuse water pool 9 and can be directly used as circulating cooling water, boiler feed water or process water, realizing the reuse of coking wastewater.

[0111] Example 1

[0112] The biochemical effluent from a coking wastewater plant was taken as the treatment object. After pretreatment in the high-density sedimentation tank 1 and the sand filter 2, the influent quality of the first BDD electrocatalytic oxidation unit 3 was as shown in Table 2.

[0113] Table 2 Influent quality of Example 1

[0114]

[0115] Through three-stage gradient variable current treatment (parameters see Table 2), the final effluent COD can be reduced to 45 mg / L, and the total removal rate can reach more than 90%.

[0116] Table 3 Treatment of COD by gradient current mode

[0117]

[0118] Comparative Example

[0119] This comparative example examines the energy consumption of constant-current BDD electrocatalytic oxidation under the conditions of identical pretreatment steps, consistent plate spacing, electrode area, circulation flow rate, and consistent effluent COD (parameters see Table 3).

[0120] Table 4. COD treatment in constant current parameter mode

[0121]

[0122] Comparing Example 1 with the comparative example, it can be concluded that the gradient current mode is significantly superior to the traditional constant current mode. By dynamically controlling the current density, this process reduces the overall energy consumption by more than 22% while maintaining the processing efficiency, and the electrode service life can be increased by more than 5 months.

[0123] In the description of this specification, specific features, structures or characteristics may be combined in an appropriate manner in any one or more embodiments or examples.

[0124] In the description of this specification, the reference terms "one embodiment," "some embodiments," "example," "specific example," or "some examples" mean that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0125] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A coking wastewater treatment system based on BDD electrocatalytic oxidation gradient current, characterized in that: It includes a sedimentation and filtration device, a first BDD electrocatalytic oxidation unit, an ultrafiltration unit, a nanofiltration unit, and a reverse osmosis unit which are connected in sequence according to the wastewater treatment order. The first BDD electrocatalytic oxidation unit is used to treat large molecular refractory organic matter in coking wastewater. The concentrated water outlet of the nanofiltration unit is connected to the second BDD electrocatalytic oxidation unit, and the concentrated water outlet of the reverse osmosis unit is connected to the third BDD electrocatalytic oxidation unit. The second BDD electrocatalytic oxidation unit and the third BDD electrocatalytic oxidation unit are used to treat organic matter in the high conductivity membrane concentrated water; The first BDD electrocatalytic oxidation unit, the second BDD electrocatalytic oxidation unit, and the third BDD electrocatalytic oxidation unit each include an electrocatalytic oxidation reactor and a regulating configuration power supply, wherein the regulating configuration power supply has a gradient variable current mode, and the gradient variable current mode can output a variable set current to the electrocatalytic oxidation reactor according to the conductivity and COD index of the solution; The gradient current mode refers to: When the COD index of the water body is constant, the set current increases in a gradient as the conductivity of the solution increases; when the conductivity of the solution is constant, the set current increases in a gradient as the COD index of the water body increases; Furthermore, the set current has a maximum current limit, and the maximum current limit no longer changes with the increase of the conductivity of the solution and the COD index of the water body.

2. The coking wastewater treatment system based on BDD electrocatalytic oxidation gradient current according to claim 1 is characterized in that: The sedimentation and filtration device includes a high-density sedimentation tank and a sand filter tank connected in sequence according to the wastewater treatment order. The high-density sedimentation tank is connected to a PAC dosing device and a PAM dosing device for removing part of the COD and suspended matter. A buffer tank is connected between the first BDD electrocatalytic oxidation unit and the ultrafiltration unit, and the buffer tank is connected to a dosing device; An ion exchange resin unit is connected between the ultrafiltration unit and the nanofiltration unit to deeply remove calcium, magnesium and fluoride ions.

3. The coking wastewater treatment system based on BDD electrocatalytic oxidation gradient current according to claim 1 is characterized in that: The electrode structure in the electrocatalytic oxidation reactor is as follows: the anode adopts a BDD electrode, the substrate is any one of silicon-based, titanium-based, and niobium-based, and the cathode material adopts a corrosion-resistant titanium plate or a titanium-based iridium dioxide coated electrode.

4. The coking wastewater treatment system based on BDD electrocatalytic oxidation gradient current according to claim 1 is characterized in that: The water outlet of the reverse osmosis unit is connected to a reuse water pool; The water outlet of the second BDD electrocatalytic oxidation unit is sequentially connected to the first pH adjustment tank and the sodium sulfate evaporation unit; The water outlet of the third BDD electrocatalytic oxidation unit is sequentially connected to the second pH adjustment tank and the sodium chloride evaporation unit.

5. A coking wastewater treatment method based on BDD electrocatalytic oxidation gradient current, characterized in that: Using the coking wastewater treatment system based on BDD electrocatalytic oxidation gradient current according to any one of claims 1 to 4, the treatment method includes: When the first BDD electrocatalytic oxidation unit, the second BDD electrocatalytic oxidation unit, and the third BDD electrocatalytic oxidation unit are used to treat water, the regulating configuration power supply is placed in the gradient variable current mode, and a set current that changes according to the conductivity and COD index of the solution is output to the electrocatalytic oxidation reactor; Among them, when the COD index of the water body is constant, the set current increases gradiently with the increase of the conductivity of the solution; when the conductivity of the solution is constant, the set current increases gradiently with the increase of the COD index of the water body; the set current has a maximum current, and the maximum current no longer changes with the increase of the conductivity of the solution and the COD index of the water body.

6. The method for treating coking wastewater based on BDD electrocatalytic oxidation gradient current according to claim 5, characterized in that: When the first BDD electrocatalytic oxidation unit, the second BDD electrocatalytic oxidation unit, and the third BDD electrocatalytic oxidation unit are in a water body, the treatment method includes: Real-time detection of water conductivity and COD, and input signals to the control unit; The control unit controls the regulating configuration power supply to be in the gradient current mode according to the conductivity and COD signals, and controls the regulating configuration power supply to output the changed set current to the electrocatalytic oxidation reactor.

7. The method for treating coking wastewater based on BDD electrocatalytic oxidation gradient current according to claim 5, characterized in that: The processing method further comprises: Passing the biochemical effluent of the coking wastewater through the sedimentation and filtration device to perform sedimentation filtration on the biochemical effluent of the coking wastewater; The effluent from the precipitation and filtration device enters the first BDD electrocatalytic oxidation unit, so that the first BDD electrocatalytic oxidation unit treats the macromolecular refractory organic matter in the coking wastewater; The effluent from the first BDD electrocatalytic oxidation unit enters the ultrafiltration unit to intercept macromolecular organic matter, colloids and suspended matter, thereby reducing turbidity; The effluent from the ultrafiltration unit enters the nanofiltration unit, and the selective permeability of the nanofiltration membrane is used to intercept multivalent ions and small molecular organic matter, while allowing monovalent ions to partially pass through; Passing the nanofiltration concentrated water through the second BDD electrocatalytic oxidation unit to further treat organic matter and remove COD; The reverse osmosis concentrated water is passed through the third BDD electrocatalytic oxidation unit to further process organic matter and remove COD.

8. The method for treating coking wastewater based on BDD electrocatalytic oxidation gradient current according to claim 7, characterized in that: The processing method further comprises: Before the effluent from the ultrafiltration unit enters the nanofiltration unit, the effluent from the ultrafiltration unit enters an ion exchange resin unit to deeply remove calcium, magnesium and fluoride ions.

9. The method for treating coking wastewater based on BDD electrocatalytic oxidation gradient current according to claim 7, characterized in that: The processing method further comprises: Allow the effluent from the reverse osmosis unit to enter the reuse water pool; The effluent from the second BDD electrocatalytic oxidation unit enters the first pH adjustment tank to adjust the pH of the effluent; The effluent from the first pH adjustment tank enters the sodium sulfate evaporation unit for salt concentration and crystallization to produce anhydrous sodium sulfate or sodium sulfate decahydrate crystals; The effluent from the third BDD electrocatalytic oxidation unit enters a second pH regulating tank to adjust the pH of the effluent; The effluent from the second pH regulating tank enters the sodium chloride evaporation unit for salt concentration and crystallization to precipitate high-purity sodium chloride crystals; The water outlet of the second BDD electrocatalytic oxidation unit is sequentially connected to the first pH regulating tank and the sodium sulfate evaporation unit; The water outlet of the third BDD electrocatalytic oxidation unit is sequentially connected to the second pH regulating tank and the sodium chloride evaporation unit.

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