Reinforced resourceful treatment process for coking high-salinity wastewater

Abstract

The invention belongs to the technical field of industrial wastewater treatment, and particularly relates to an enhanced resourceful treatment process for coking high-salinity wastewater. According to the process, wastewater treatment and recycling are realized through an integrated process of alkali softening, ultrafiltration salt separation, electro-catalysis coupling ozone oxidation and bipolar membrane electrodialysis. Bicarbonate and calcium carbonate are used as softening agents for alkali softening, and the total hardness removal rate is larger than or equal to 95%; the circulating flow is controlled to be 5-10 times of the water production flow by ultrafiltration salt separation, and the water recovery rate is greater than or equal to 85%; the COD (Chemical Oxygen Demand) removal rate is greater than or equal to 92% through electro-catalysis coupled ozone The salt recovery rate of bipolar membrane electrodialysis is greater than or equal to 80%, and produced acid and alkali can be reused for membrane cleaning and coke oven gas desulfurization. According to the invention, self-circulation of resources can be realized, the treatment cost is greatly reduced, and the economic benefits of enterprises are improved.

Description

Technical Field

[0001] This invention belongs to the field of industrial wastewater treatment technology, specifically relating to an enhanced resource utilization treatment process for high-salt coking wastewater. Background Technology

[0002] The coal chemical industry generates large amounts of saline wastewater during production processes, primarily originating from coal gasification, shift conversion, and deacidification. This wastewater is characterized by high total dissolved solids (TDS) concentrations, high salinity, hardness, and alkalinity, making desalination treatment extremely challenging. Furthermore, the presence of aromatic and heterocyclic organic compounds in the wastewater, coupled with its poor biodegradability, further complicates treatment. Direct discharge would cause severe water pollution, impacting the ecological environment and human health. Efficient treatment of high-salinity coking wastewater has become a critical challenge and key focus for the industry.

[0003] Currently, the coal chemical industry has established a basic zero-discharge technology route for wastewater treatment through classified collection, differentiated treatment, and multi-stage reuse: "pretreatment - biochemical treatment - saline wastewater treatment - salt separation - deep concentration - crystallization." First, high-salinity wastewater undergoes pretreatment, including chemical softening, adsorption, and membrane filtration, to remove suspended solids, oils, organic matter, and calcium and magnesium ions. Second, concentration and desalination are performed, primarily using methods such as electrodialysis, reverse osmosis, and nanofiltration. Finally, the concentrated saline wastewater is evaporated and crystallized. However, the current practice of treating high-salinity coking wastewater generally suffers from long treatment processes, high operating costs, and extremely low added value of the produced Na₂SO₄ and NaCl, resulting in poor economic benefits. This severely restricts the green development of the coal chemical industry and has become a critical problem that urgently needs to be solved.

[0004] For example, Chinese patent application CN110606612A discloses a resource-based treatment process for high-salt wastewater from coal coking. The main process flow includes defluorination + desiliconization + hardening pretreatment + multi-media filter + ultrafiltration + resin softening + FDG + nanofiltration for salt separation + reverse osmosis concentration + ozone oxidation + evaporation crystallization. This process is lengthy, has high operating costs, and results in low added value for Na2SO4 and NaCl during salt recovery. CN105800885B discloses a resource-based recycling system for high-concentration, recalcitrant saline organic wastewater, including a crystallization defluorination reactor, a comprehensive wastewater equalization tank, a biochemical treatment system, an advanced oxidation unit, a filtration unit, an ultrafiltration device, a resin softening device, a reverse osmosis device, a concentration-type electrodialysis device, a nanofiltration device, a first bipolar membrane electrodialysis device, and a second bipolar membrane electrodialysis device. This process involves multiple units such as crystallization defluorination, biochemical treatment, resin softening, reverse osmosis, and concentration electrodialysis. The process is complex, requires significant equipment investment, and the interconnection of multiple units can easily lead to low wastewater treatment efficiency and cumbersome operation and maintenance. The current method of using resin softening to treat hardness is problematic because the resin is easily contaminated by high-salinity wastewater, requires frequent regeneration, and has poor adaptability to high-salinity, high-hardness (e.g., 300-2500 mg / L high-hardness coking wastewater) conditions. This process involves multiple membrane separation steps, including reverse osmosis, concentration electrodialysis, and bipolar membrane electrodialysis, resulting in significantly high energy consumption. Its advanced oxidation unit includes a modified Fenton oxidation system and / or a targeted catalytic oxidation system. The modified Fenton oxidation system requires ferrous sulfate and hydrogen peroxide, leading to high reagent costs, and the iron reagent entering the wastewater or sludge can cause secondary pollution. The targeted catalytic oxidation system uses catalysts and ozone, but its catalytic efficiency remains low, making it difficult to adapt to large-volume, continuously outputting high-COD, high-salinity coking wastewater. Organic matter can also contaminate various treatment membranes, affecting the overall system's operational stability. In summary, existing coking high-salinity wastewater treatment technologies suffer from long process flows, high operating costs, and poor resource recovery efficiency, necessitating an enhanced resource-based treatment process for coking high-salinity wastewater. Summary of the Invention

[0005] (a) Technical problems to be solved To address the technical pain points of existing coking high-salinity wastewater treatment technologies, such as long process flow, high operating costs, and poor resource recovery efficiency, this invention provides an enhanced resource recovery treatment process for coking high-salinity wastewater. Specifically, it achieves synergistic improvement in the quality and efficiency of coking high-salinity wastewater treatment by innovatively integrating core technologies such as high-efficiency softening, organic matter degradation, salt conversion, and salt recovery. This results in improved resource recovery efficiency, reduced treatment costs, reduced environmental pressure, and increased economic benefits for enterprises.

[0006] (II) Technical Solution The technical solution of the present invention is as follows: A process for enhanced resource recovery treatment of high-salt coking wastewater includes the following steps: S1, Alkali softening The total molar concentration of calcium and magnesium ions in the raw water of high-salt coking wastewater was detected; a mixture of sodium bicarbonate and calcium chloride at a mass ratio of 2-5:1 was used as a softening agent, and the softening agent was added at a molar ratio of bicarbonate to calcium and magnesium ions in the raw water of 1.2-2.0:1. After stirring and reacting, alkaline softened water was obtained. S2, Ultrafiltration Salt Separation The alkaline softened water treated by S1 is fed into a ceramic ultrafiltration membrane device to remove suspended solids through ultrafiltration. The operating parameters of the ultrafiltration device are as follows: the wastewater flow rate continuously circulating inside the ultrafiltration device is 5-10 times the product water flow rate, the transmembrane pressure difference is 0.10-0.30 MPa, the ultrafiltration product water membrane flux is maintained at 100-150 L / m²·h, the turbidity of the ultrafiltration effluent is below 0.2 NTU, and the water recovery rate is not less than 85%. S3, Organic matter removal An electrocatalytic oxidation coupled with ozone was used to enhance the oxidation of organic matter in ultrafiltration effluent containing sulfur dioxide (S2). Conditions were controlled to ensure an organic matter removal rate of at least 92%, yielding catalytically oxidized effluent. Electrocatalysis was achieved using an electrocatalytic device. The anode of the device was a composite coated electrode on a titanium substrate, consisting of a Sn(Sb)O2 coating and a TiO2-γ-MnO2 coating. The cathode was a graphite electrode or a porous carbon electrode. The electrocatalytic current density was 100-300 A / m³. 2 The voltage is 4.0-6.0V, the electrode spacing is 2.0-4.0cm, and the spacing is filled with visible light modified particle electrodes based on iron tailings; while electrocatalytically oxidizing the wastewater, ozone is introduced into the wastewater using micro-nano bubble aerators, with an ozone mass concentration of 5.0-20.0mg / L in the wastewater and a treatment time of 20-40min. S4, Salt Recovery The effluent from the catalytic oxidation of S3 was treated using bipolar membrane electrodialysis technology, with controlled conditions to ensure a salt recovery rate of no less than 80%, and to produce acid and alkali.

[0007] In its S2, the ultrafiltration unit is designed with a circulation flow rate of 5-10 times the product water flow rate, which ensures that the turbulence intensity on the membrane surface can meet the pollution control requirements no matter how the product water flow rate is adjusted (such as increasing / decreasing the treatment capacity).

[0008] Preferably, before alkali softening, the coking high-salt wastewater is temporarily stored and collected in a wastewater equalization tank, and then transported at a uniform rate to the alkali softening process. The alkali softening is carried out in a sedimentation tank with an inclined plate inside. A softening agent is added above the inclined plate so that the alkali softening reaction takes place above the inclined plate. The inclined plate accelerates sedimentation, and the bottom conical trough collects the settled sludge. The settled sludge is discharged at predetermined intervals, dewatered, and then subjected to solidification / stabilization treatment (such as adding a solidifying agent to reduce the leaching of pollutants) before being transported to a dedicated hazardous waste landfill for landfilling.

[0009] According to a preferred embodiment of the present invention, in S1, the total hardness of the raw coking high-salt wastewater, calculated as calcium carbonate, is 300-2500 mg / L; the stirring reaction time is 10-20 minutes; the stirring speed is automatically adjusted according to the hardness of the raw water during the stirring process: 250-350 rpm when the total hardness is >1500 mg / L, and 100-150 rpm when the total hardness is <500 mg / L. Following this method, the total hardness removal rate of the raw coking high-salt wastewater can reach over 95%.

[0010] A faster stirring speed is used under high hardness conditions, mainly to enhance mass transfer, while a slower stirring speed is used under low hardness conditions to avoid the flocs being sheared and broken, resulting in larger floc particle size, faster sedimentation, reduced sludge moisture content, and lower subsequent sludge treatment costs.

[0011] According to a preferred embodiment of the present invention, in S1, the hardness of the raw water is monitored online in real time, and the addition ratio of sodium bicarbonate and calcium chloride is automatically adjusted. When the total hardness is >1500mg / L, the mass ratio of sodium bicarbonate to calcium chloride is 5:1, and when the total hardness is <500mg / L, the mass ratio of sodium bicarbonate to calcium chloride is 2:1, thereby significantly improving the utilization rate of the softening agent.

[0012] According to a preferred embodiment of the present invention, in step S2, the pore size of the ceramic ultrafiltration membrane is 0.1-0.5 μm; the surface of the ultrafiltration membrane is cleaned by physical cleaning followed by chemical cleaning with 0.3% HCl, with a backwashing time of 60-200 s and a backwashing cycle of 20-40 min. This method can control the effluent turbidity below 0.2 NTU, and the water recovery rate is not less than 85%. The wastewater generated during backwashing is collected and recycled in a wastewater equalization tank.

[0013] According to a preferred embodiment of the present invention, in S3, electrocatalysis is achieved using an electrocatalytic device. The anode of the electrocatalytic device is a composite coated electrode consisting of a Sn(Sb)O2 coating and a TiO2-γ-MnO2 coating supported on a titanium substrate; the cathode is a graphite electrode or a porous carbon electrode; and the electrocatalytic current density is 100-300 A / m. 2 The system operates at a voltage of 4.0-6.0V and an electrode spacing of 2.0-4.0cm, with the spacing filled with visible light-modified particles based on iron tailings. Simultaneously with the electrocatalytic oxidation of wastewater, ozone is introduced into the wastewater using micro-nano bubble aeration heads, achieving an ozone concentration of 5.0-20.0 mg / L. Under these conditions, the removal rate of organic matter in the wastewater is no less than 92%. Micro-nano bubble aeration significantly improves ozone utilization, reduces ozone input costs, and enhances the removal rate of organic matter in wastewater.

[0014] The anode is prepared by the following method: (1) The titanium substrate is processed into a plate shape, and then mechanically ground (SiC sandpaper is used to grind the oxide layer step by step), degreased, ultrasonically cleaned with acetone for 10-30 min, and dried to ensure conductivity and surface flatness. (2) Sn(Sb)O2 is electrodeposited on the titanium substrate using an electrolyte containing SnCl4 and SbCl3. After that, it is calcined at 450-500℃ for 1-3 h to enhance the electrocatalytic oxidation ability by utilizing its high oxygen overpotential and abundant electroactive sites. (3) The surface is coated with a composite film of Fe-Ni co-doped TiO2 and γ-MnO2, with a mass ratio of TiO2 to γ-MnO2 of 7:3. Fe(NO3)3, Ni(NO3)2, tetrabutyl titanate, and Mn(NO3)2 were mixed to prepare a sol, which was then spin-coated onto the surface of a Sn(Sb)O2 coating. After drying at 100-120℃, the coating was calcined at 400-500℃ for 1-3 hours. This process was repeated 3 times to obtain a uniform coating.

[0015] Fe-Ni co-doped TiO2 is used to achieve visible light response, and γ-MnO2 narrow bandgap (~1.8eV) enhances light absorption and charge separation. The three form a heterojunction to improve photoelectric synergy efficiency.

[0016] The preparation method of the visible light modified particle electrode based on iron tailings is as follows: (1) After ball milling the iron tailings particles, boil them with dilute hydrochloric acid and dilute NaOH solution to remove impurities, rinse them with distilled water, dry them and pass them through a 60-mesh sieve, and dry them to obtain fine iron tailings particles; (2) Prepare 55% fine iron tailings particles, 15% dry fine clay, 15% starch (pore-forming agent) and 15% MnO2 by mass percentage. Mix the iron tailings, clay, starch and MnO2 evenly, impregnate them in SnCl4-Mn(NO3)2 sol for 3-5h, dry them at 100-120℃ and then extrude them into balls; (3) Bake the raw material balls at 120℃ for 24h, heat them at 300℃ for 2h, activate them at 550℃ for 20min, and finally calcine them at 850℃ for 15-25min. After natural cooling, impregnate them with Fe-Co co-doped TiO2 sol, calcine them again to shape them and obtain particle electrodes with a particle size of 3-5mm. The preferred filling amount of the particle electrode is 100-150 g / L, which is filled in the area between the anode and cathode. This electrode can achieve surface photoelectrocatalysis under visible light and promote the regeneration of the particle electrode.

[0017] This invention employs a three-dimensional photoelectric synergistic electro-Fenton system consisting of a titanium-based composite coated anode, a carbon cathode, and a visible light modified particle electrode. Combining the advantages of electrocatalysis, photocatalysis, and electro-Fenton technology, it achieves efficient and low-energy degradation of organic matter, reaching an organic matter removal rate of over 92%.

[0018] Among them, electrocatalysis (100-300A / m²) and ozone generation are both high-energy-consuming units. At the same time, a hydrogen bubble recovery device is integrated into the cathode of the electrocatalytic device to reuse the generated H2 as fuel for the ozone generator, achieving partial energy self-sufficiency and reducing energy consumption and energy costs.

[0019] According to a preferred embodiment of the present invention, in S4, bipolar membrane electrodialysis is achieved using a bipolar membrane electrodialysis device, wherein the electrodes of the bipolar membrane electrodialysis device are metal electrodes, non-metal electrodes, and doped modified electrodes; the current density is 30-100 A / m 2 The voltage is 1.5-5.0V, and the liquid volume passing through the membrane stack is 10-50mL per minute. The salt recovery rate of this scheme is no less than 80%.

[0020] According to a preferred embodiment of the present invention, in S4, the salinity of the feed water to the bipolar membrane electrodialysis unit is monitored online in real time, and the current density and flow rate are dynamically matched. When the sum of the chloride and sulfate ion concentrations in the wastewater exceeds 10000 mg / L, the flow rate is increased to 40-50 mL / min and the current density is reduced to 30-50 A / m². This reduces energy consumption while ensuring that the salt recovery rate is increased to over 85%. When the salt ion concentration in the wastewater is high, increasing the flow rate can alleviate polarization by enhancing mass transfer, allowing the membrane system to ensure effective ion migration even at a lower current density, without a significant decrease in desalination efficiency due to reduced driving force. Reducing the current density further amplifies the effect of high flow rate, reduces Joule heating and side reactions, avoids increased polarization caused by high current, and makes the inhibitory effect of high flow rate on scaling / salting out more significant. - +SO4 2- The coking wastewater with a concentration exceeding 10,000 mg / L and high total hardness not only solved the mass transfer and membrane fouling problems caused by high salt content, but also balanced desalination efficiency and energy consumption, ultimately achieving a salt recovery rate of over 85% and reduced energy consumption.

[0021] According to a preferred embodiment of the present invention, in S4, the metal electrode is an Ir electrode, a Ru electrode, a Pt electrode, or a ruthenium-iridium electrode; the non-metal electrode is a graphite electrode; the doped and modified electrode is an Ir-based doped electrode, a Ru-based doped electrode, a Pt-based doped electrode, or a graphite-based doped and modified electrode; the doping element of the Ir-based doped electrode is Ta, Ti, or Sn; the doping element of the Ru-based doped electrode is Ti, Mn, or Co; the doping element of the Pt-based doped electrode is Ir or Pd; and the doping element of the graphite-based doped and modified electrode is N, P, B, Mn, Sn, or Ti.

[0022] Among doped electrodes, Ir-Ta alloy electrodes exhibit low oxygen evolution overpotential and high corrosion resistance. Ir-SnO2 coated electrodes have a service life more than twice that of pure Ir electrodes. Ru-TiO2 composite electrodes demonstrate high electrocatalytic activity, making them suitable for treating low-salt wastewater; Ru-MnOx electrodes achieve a current efficiency exceeding 90% at 3.0V; Pt-based doped electrodes, such as Pt-Ir alloy electrodes, exhibit good corrosion resistance and are suitable for preparing high-purity acids and alkalis. N-doped graphite electrodes demonstrate excellent oxidation and corrosion resistance when treating sulfate-containing wastewater, with a service life more than three times that of pure graphite electrodes. PB co-doped graphite electrodes exhibit higher conductivity compared to pure graphite electrodes. MnO2-doped graphite composite electrodes consume less energy than pure graphite electrodes at the same current density.

[0023] According to a preferred embodiment of the present invention, in S4, before performing bipolar membrane electrodialysis, a separation treatment of monovalent anion salt and divalent anion salt is performed using a charged nanofiltration membrane to obtain salts containing Cl. - Salt solutions and those containing SO4 2- The salt solutions are then fed into different bipolar membrane electrodialysis units for bipolar membrane electrodialysis treatment. This allows for the production of sulfuric acid and hydrochloric acid with higher purity (hydrochloric acid can be used as a cleaning agent for ultrafiltration units), thereby increasing the added value of the products.

[0024] According to a preferred embodiment of the present invention, in step S4, the produced acid, after dilution, is used for chemical cleaning of the ultrafiltration membrane in step S2, achieving reagent self-circulation, reducing process reagent costs, and partially serving as an acid product; the produced alkaline solution is partially used to replace 20%-30% of the calcium chloride in the softening process in step S1, or concentrated to 10-15 wt% and reused in the coke oven gas desulfurization tower. This reduces reagent costs, further improves hardness removal efficiency, achieves a residual hardness of ≤40 mg / L in the softened water, and reduces the risk of subsequent membrane scaling.

[0025] According to a preferred embodiment of the present invention, in S1, the raw water quality of the coking high-salt wastewater is as follows: pH 7-8, chloride ion 2000-8500 mg / L, sulfate ion 2000-10000 mg / L, total hardness (calculated as calcium carbonate) 300-2500 mg / L, TDS 13000-30000 mg / L, and COD 300-600 mg / L.

[0026] (III) Beneficial Effects This invention employs an integrated process combining alkali softening, ultrafiltration desalination, electrocatalytic ozone oxidation, and bipolar membrane electrodialysis to achieve enhanced resource-based treatment and differentiated resource utilization of high-salt coking wastewater. Compared to existing technologies, it achieves the following significant technical advantages: (1) The pretreatment process is greatly simplified and the processing efficiency is significantly improved. The combined pretreatment method of alkali softening and ultrafiltration desalination eliminates the mechanical filtration step in the traditional process, reducing the sedimentation tank volume by more than 80%; it does not require excessive addition of chemicals, achieves a total hardness removal rate of over 95%, and a system water recovery rate of no less than 85%, thus simplifying the process while improving the pretreatment effect.

[0027] (2) Enhanced removal efficiency of recalcitrant organic matter and reduced operating costs The synergistic oxidation effect of electrocatalysis and micro / nano-scale ozone, employing a three-dimensional photoelectric synergistic electro-Fenton system consisting of a titanium-based composite coated anode, a carbon cathode, and a visible-light modified particle electrode, can efficiently degrade recalcitrant organic compounds such as phenol in wastewater, achieving an organic matter removal rate of no less than 92% and significantly reducing TOC and color in wastewater. Compared to the traditional ozone + hydrogen peroxide oxidation process, it significantly reduces the amount of reagents required, improving treatment efficiency while lowering reagent costs. Specifically, the Sn(Sb)O2 on the anode surface exhibits high electrocatalytic oxidation activity, while the TiO2-γ-MnO2 heterojunction provides visible-light photoelectric catalysis. The particle electrode enhances mass transfer and free radical generation, significantly improving the degradation rate of organic pollutants. Most organic compounds can be degraded by more than 90%, even 95%, within 30 minutes, and organic pollutants are mineralized into CO2 and H2O, effectively reducing organic pollution on the bipolar membrane surface and improving the purity and added value of acids and alkalis.

[0028] (3) High utilization rate of salt resources and improved economic benefits for enterprises: The bipolar membrane electrodialysis process ensures the purity of acid, alkali and salt through water dissociation process, realizing the resource utilization of high-value salts; it avoids the hazardous waste disposal problem caused by mixed salt crystallization in existing zero-emission projects, which not only reduces the cost of hazardous waste disposal, but also creates additional income for enterprises by selling by-product pure salt. Attached Figure Description

[0029] Figure 1 This is a flow chart of the enhanced resource utilization process for coking high-salt wastewater according to the present invention. Detailed Implementation

[0030] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below through specific embodiments.

[0031] Example 1 This embodiment provides a highly efficient photoelectric synergistic three-dimensional electrocatalytic electrode for degrading organic matter, comprising an anode, a cathode, and a particle electrode. The cathode is a graphite electrode.

[0032] The anode is a composite coated electrode consisting of a Sn(Sb)O2 coating and a visible light modified TiO2-γ-MnO2 coating supported on a titanium substrate surface. The preparation method is as follows: (1) The titanium substrate is processed into a plate shape, mechanically ground, the oxide layer is removed, degreased, ultrasonically cleaned with acetone for 10-30 min, and dried for pretreatment to ensure conductivity and surface smoothness. (2) Sn(Sb)O2 is electrodeposited on the titanium substrate using an electrolyte containing SnCl4 and SbCl3 under constant current, followed by calcination at 450-500℃ for 1-3 h. (3) Fe(NO3)3, Ni(NO3)2, tetrabutyl titanate, and Mn(NO3)2 are mixed to prepare a sol, which is spin-coated onto the surface of the Sn(Sb)O2 coating. After drying at 100-120℃, it is calcined at 400-500℃ for 1-3 h. This process is repeated 3 times to obtain a uniform coating. The mass ratio of TiO2 to γ-MnO2 in the coating is approximately 7:3.

[0033] The particle electrode is an iron tailings-based visible light modified particle electrode, and its preparation method is as follows: (1) After ball milling the iron tailings particles, they were boiled in 10% hydrochloric acid and 10% NaOH solution to remove impurities, rinsed with distilled water, dried at 105℃ and passed through a 60-mesh sieve, and dried to obtain fine iron tailings particles. (2) By mass, prepare 55% fine iron tailings particles, 15% dry fine clay, 15% starch, and 15% MnO2. Mix the iron tailings, clay, starch, and MnO2 evenly, impregnate them in SnCl4-Mn(NO3)2 sol for 4 hours, dry them at 120℃, and then extrude them into balls. (3) The raw material balls are dried at 120℃ for 24 hours, heated at 300℃ for 2 hours, activated at 550℃ for 20 minutes, and finally calcined at 850℃ for 15-25 minutes. After natural cooling, they are impregnated with Fe-Co co-doped TiO2 sol and calcined again to shape them, resulting in particle electrodes with a particle size of about 3-4 mm.

[0034] Assemble the electrocatalytic device, setting up a tank to contain wastewater. Install the anode and cathode with a 3cm gap, filling the gap with the particle electrodes at a density of 100g / L. Add coking high-salt wastewater to the tank, with the following water characteristics: pH 7.5, chloride ion 2000mg / L, sulfate 6050mg / L, total hardness (as calcium carbonate) 400mg / L, TDS 14000mg / L, COD 300mg / L. Connect the anode and cathode to a 5.0V operating voltage and a current density of 150A / m. 2 When the ozone concentration was 10.0 mg / L and the electrocatalytic and ozone synergistic treatment lasted for 25 minutes, the COD removal rate in the wastewater reached 92.7%.

[0035] Comparative Example 1 This comparative example uses a conventional electrocatalytic device. The anode is made of activated carbon fiber, and the cathode material is a carbon-polytetrafluoroethylene composite material. The dimensions and specifications of the anode and cathode plates are the same as in Example 1. The anode and cathode are installed with a 3cm gap, and the gap is not filled with particle electrodes. High-salt coking wastewater with the following characteristics is added to the tank: pH 7.5, chloride ion 2000 mg / L, sulfate ion 6050 mg / L, total hardness (calculated as calcium carbonate) 400 mg / L, TDS 14000 mg / L, COD 300 mg / L. The anode and cathode are connected to a 5.0V operating voltage and a current density of 200A / m². 2 When the ozone concentration was 10.0 mg / L and the electrocatalytic and ozone synergistic treatment lasted for 25 minutes, the COD removal rate in the wastewater reached 81%.

[0036] As can be seen from the above embodiments and comparative examples, the novel electrocatalytic system designed in this invention has extremely high COD removal efficiency, and is especially suitable for treating high-salt coking wastewater.

[0037] Example 2 In this embodiment, the coking high-salt wastewater to be treated has the following characteristics: pH 7.5, chloride ion 2400 mg / L, sulfate 6250 mg / L, total hardness (as calcium carbonate) 400 mg / L, TDS 14000 mg / L, and COD 400 mg / L. The wastewater flow rate is 1 t / h, and the system operates for 20 hours per day. The treatment process is described in [reference needed]. Figure 1 It includes the following steps: (1) The total hardness of the raw water was 400 mg / L (<500 mg / L). Sodium bicarbonate and calcium chloride were added at a mass ratio of 2:1, while the molar ratio of bicarbonate to calcium carbonate was controlled at 1.5:1. Sodium bicarbonate of 504 mg / L and calcium chloride of 252 mg / L were added, and the mixture was stirred at 150 rpm for 15 minutes. The total hardness removal rate was 97%, and alkaline softened water was obtained.

[0038] (2) Ultrafiltration desalination: Alkali-softened water is fed into a ceramic ultrafiltration membrane device (membrane pore size 0.2μm). The operating parameters are controlled as follows: circulation flow rate 5t / h, backwash time 100s, backwash cycle 30min, transmembrane pressure difference 0.20MPa, and ultrafiltration permeate membrane flux is maintained at 135L / m²·h. The membrane surface is cleaned by physical cleaning + chemical cleaning with 0.3% HCl. The final effluent turbidity is 0.1NTU, and the system water recovery rate is 89%.

[0039] (3) Organic matter removal: The ultrafiltration effluent was treated by electrocatalysis coupled with ozone synergistic oxidation. The anode was a composite coated electrode consisting of Sn(Sb)O2 coating and TiO2-γ-MnO2 coating on a titanium substrate, and the cathode material was a porous carbon electrode. The electrocatalytic current density was controlled at 150A / m², the voltage at 5.0V, and the electrode spacing at 2.0cm. The spacing was filled with visible light modified particles based on iron tailings at a density of 100g / L. At the same time, ozone was introduced into the wastewater to a mass concentration of 10.0mg / L. After treatment for 30min, the final COD removal rate was 93.0%, and the catalytic oxidation effluent was obtained.

[0040] (4) Salt recovery: The catalytic oxidation effluent is treated by a bipolar membrane electrodialysis device. The electrodes of the electrodialysis device are ruthenium-iridium metal electrodes. The current density is controlled at 60A / m², the voltage at 2.5V, and the flow rate at 25mL / min. After treatment, the salt recovery rate is 85%, and acid and alkali solutions are produced. The purity of both acid and alkali solutions is greater than 97%. The produced HCl acid solution is diluted to a concentration of 0.3% and then reused for chemical cleaning of the ceramic ultrafiltration membrane in step (2) to achieve self-circulation of the reagent. The produced NaOH alkali solution is concentrated to 12wt% and then reused in the coke oven gas desulfurization tower to complete the resource recycling.

[0041] Example 3 In this embodiment, the coking high-salt wastewater to be treated has the following characteristics: pH 8.0, chloride ion 3250 mg / L, sulfate ion 7250 mg / L, total hardness (as calcium carbonate) 2100 mg / L, TDS 19000 mg / L, and COD 500 mg / L. The wastewater flow rate is 1.2 t / h, and the system operates for 20 hours per day. The treatment process is as follows: (1) Alkali softening: The total hardness of the raw water was 2100 mg / L. Sodium bicarbonate and calcium chloride were added at a mass ratio of 5:1, while the molar ratio of bicarbonate to calcium carbonate was controlled at 1.8:1. The dosage of sodium bicarbonate was 3175 mg / L, and the dosage of calcium chloride was 635.04 mg / L. The reaction time was 20 minutes with stirring at 350 rpm, and the total hardness removal rate was 96%.

[0042] (2) Ultrafiltration desalination: circulation flow rate 10t / h, backwash time 150s, backwash cycle 40min, transmembrane pressure difference 0.25MPa, ceramic ultrafiltration permeate membrane flux maintained at 110L / (m²·h), membrane surface is physically cleaned + 0.3%HCl chemically cleaned, effluent turbidity is 0.15NTU, system water recovery rate is 86%.

[0043] (3) Organic matter removal: The anode is a composite coating electrode consisting of Sn(Sb)O2 coating and TiO2-γ-MnO2 coating supported on a titanium substrate, and the cathode is a graphite electrode. The electrocatalytic current density is 200A / m², the voltage is 5.5V, the electrode spacing is 2.5cm, and the spacing is filled with iron tailings-based visible light modified particle electrodes at a density of 100g / L. The ozone mass concentration is 15.0mg / L. After 30min of treatment, the COD removal rate is 96.8%.

[0044] (4) Salt recovery: The bipolar membrane electrodialysis device uses ruthenium-iridium electrodes, with a current density of 80A / m², voltage of 3.0V, and flow rate of 30mL / min. The salt recovery rate is 83%, and the recovered salt is converted into acid and alkali solutions with a purity of >97%.

[0045] Example 4 In this embodiment, the coking high-salt wastewater to be treated has the following characteristics: pH 7.8, chloride ion 2750 mg / L, sulfate ion 6750 mg / L, total hardness (as calcium carbonate) 900 mg / L, TDS 17000 mg / L, and COD 450 mg / L. The wastewater flow rate is 1 t / h, and the system operates for 20 hours per day. The treatment process is as follows: (1) Alkali softening: The total hardness of the raw water was 900 mg / L. Sodium bicarbonate and calcium chloride were added at a mass ratio of 3:1, while the molar ratio of bicarbonate to calcium carbonate was controlled at 1.6:1. The dosage of sodium bicarbonate was 1209.6 mg / L, and the dosage of calcium chloride was 403.2 mg / L. The reaction time was 15 minutes with stirring at 200 rpm, and the total hardness removal rate was 95%.

[0046] (2) Ultrafiltration desalination: circulation flow rate 7t / h, backwash time 120s, backwash cycle 35min, transmembrane pressure difference 0.20MPa, ceramic ultrafiltration permeate membrane flux maintained at 130L / (m²·h), membrane surface is physically cleaned + 0.3%HCl chemically cleaned, effluent turbidity is 0.12NTU, and system water recovery rate is 88%.

[0047] (3) Organic matter removal: The anode is a composite coating electrode consisting of Sn(Sb)O2 coating and TiO2-γ-MnO2 coating supported on a titanium substrate, and the cathode is a graphite electrode. At the same time, a hydrogen bubble recovery device is integrated on the cathode to recover the generated H2 as fuel for the ozone generator. The electrocatalytic current density is 180A / m², the voltage is 4.5V, the electrode spacing is 2.0cm, and the spacing is filled with iron tailings-based visible light modified particle electrodes at a density of 100g / L. The ozone mass concentration is 12.0mg / L (fuel is supplied by recovered H2). After 30min of treatment, the COD removal rate is 95.2%.

[0048] (4) Salt recovery: The bipolar membrane electrodialysis device uses ruthenium-iridium electrodes, with a current density of 60A / m², voltage of 2.5V, and flow rate of 25mL / min. The salt recovery rate is 84%, and the recovered salt is converted into acid and alkali solutions with a purity of >98%.

[0049] Example 5 In this embodiment, the coking high-salt wastewater to be treated has the following characteristics: pH 7.6, chloride ion 4250 mg / L, sulfate ion 8250 mg / L, total hardness (as calcium carbonate) 700 mg / L, TDS 23000 mg / L, and COD 550 mg / L. The wastewater flow rate is 1.5 t / h, and the system operates for 20 hours per day. The treatment process is as follows: (1) Alkali softening: The total hardness of the raw water was 700 mg / L. Sodium bicarbonate and calcium chloride were added at a mass ratio of 3:1, while the molar ratio of bicarbonate to calcium carbonate was controlled at 1.7:1. The dosage of sodium bicarbonate was 999.6 mg / L, and the dosage of calcium chloride was 333.2 mg / L. The reaction was carried out at 200 rpm for 18 minutes, and the total hardness removal rate was 96%.

[0050] (2) Ultrafiltration desalination: circulation flow rate 12t / h, backwash time 180s, backwash cycle 40min, transmembrane pressure difference 0.30MPa, ceramic ultrafiltration permeate membrane flux maintained at 120L / (m²·h), membrane surface is physically cleaned + 0.3%HCl chemically cleaned, effluent turbidity is 0.18NTU, system water recovery rate is 85%.

[0051] (3) Organic matter removal: The anode is a composite coating electrode consisting of Sn(Sb)O2 coating and TiO2-γ-MnO2 coating supported on a titanium substrate, and the cathode is a graphite electrode; the electrocatalytic current density is 250A / m², the voltage is 6.0V, the electrode spacing is 3.0cm, and the spacing is filled with iron tailings-based visible light modified particle electrodes at a density of 100g / L. The ozone mass concentration is 20.0mg / L, and the treatment time is 30min. The COD removal rate is 98.3%.

[0052] (4) Salt separation: First, a charged nanofiltration membrane is used for salt separation to obtain Cl-containing salts. - Salt solutions (chloride ion concentration enriched to 12500 mg / L) and solutions containing SO4 2- The salt solution (sulfate concentration enriched to 24500 mg / L).

[0053] (5) Recovery: The Cl-containing... - The salt solution was fed into a bipolar membrane electrodialysis unit: current density 50 A / m², voltage 2.0 V, flow rate 20 mL / min, salt recovery rate 82%, producing HCl acid solution with a purity greater than 99%, which can be used as a cleaning agent for the ultrafiltration membrane after dilution; containing SO4. 2-The salt solution was fed into another bipolar membrane electrodialysis unit: current density 70A / m², voltage 3.5V, flow rate 30mL / min, recovery rate 81%, producing H2SO4 acid solution with a purity greater than 98%; at the same time, a sodium hydroxide solution with a purity greater than 99% was obtained.

[0054] Example 6 In this embodiment, the coking high-salt wastewater to be treated has the following characteristics: pH 7.2, chloride ion 8250 mg / L, sulfate ion 9250 mg / L, total hardness (as calcium carbonate) 500 mg / L, TDS 29000 mg / L, and COD 600 mg / L. The wastewater flow rate is 0.8 t / h, and the system operates for 20 hours per day. The treatment process is as follows: (1) Alkali softening: The total hardness of the raw water was 500 mg / L. Sodium bicarbonate and calcium chloride were added at a mass ratio of 2:1, while the molar ratio of bicarbonate to calcium carbonate was controlled at 1.4:1. The dosage of sodium bicarbonate was 588 mg / L, and the dosage of calcium chloride was 294 mg / L. The reaction was carried out at 150 rpm for 10 minutes, and the total hardness removal rate was 98%.

[0055] (2) Ultrafiltration salt separation: circulation flow rate 6t / h, backwash time 60s, backwash cycle 20min, transmembrane pressure difference 0.15MPa, ceramic ultrafiltration permeate membrane flux maintained at 140L / (m²·h), and subsequent chemical cleaning was performed after dilution of the acid produced in step (4); the effluent turbidity was 0.1NTU, and the system water recovery rate was 90%.

[0056] (3) Organic matter removal: The anode is a composite coating electrode consisting of Sn(Sb)O2 coating and TiO2-γ-MnO2 coating supported on a titanium substrate, and the cathode is a porous carbon electrode; the electrocatalytic current density is 300A / m², the voltage is 5.0V, the electrode spacing is 2.5cm, and the spacing is filled with iron tailings-based visible light modified particle electrodes at a density of 100g / L. The ozone mass concentration is 18.0mg / L, and the COD removal rate is 96.3% after 30min of treatment.

[0057] (4) Salt recovery: Online monitoring of the salinity of the influent to the membrane stack (chloride + sulfate ion concentration 17500mg / L), dynamically adjusting the flow rate to 45mL / min and the current density to 40A / m²; the salt recovery rate after bipolar membrane electrodialysis treatment is 82%, and the recovered salt is converted into acid and alkali solutions, both with a purity greater than 96%. The produced acid is diluted and reused for chemical cleaning of the ultrafiltration membrane in step (2), and part of the produced alkali solution is returned to step (1) to replace 20% of calcium chloride, thereby softening the water, reducing the amount of calcium chloride used and the introduction of calcium ions. Part of the alkali solution can also be concentrated to 12wt% and reused in the coke oven gas desulfurization tower.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features. These modifications or substitutions, or combinations of technical features in the above embodiments that do not conflict with each other, can be made in accordance with the manner described in the embodiments. These modifications, substitutions or combinations do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A process for enhanced resource recovery treatment of coking high-salinity wastewater, characterized in that, It comprises the following steps: S1, alkali softening The total molar concentration of calcium and magnesium ions in the raw coking high-salt wastewater is detected; a mixture of sodium bicarbonate and calcium chloride with a mass ratio of 2-5:1 is used as the softening agent, and the softening agent is added in a molar ratio of bicarbonate to calcium and magnesium ions in the raw water of 1.2-2.0:1, and after stirring and reaction, the alkali softening water is obtained; S2, ultrafiltration and salt separation The alkali softening water treated by S1 is sent to a ceramic ultrafiltration membrane device for removing suspended solids by ultrafiltration treatment; the operation parameters of the ultrafiltration device are as follows: the internal continuous circulation wastewater flow of the ultrafiltration device is 5-10 times the water production flow, the transmembrane pressure difference is 0.10-0.30 MPa, the ultrafiltration water production membrane flux is maintained at 100-150 L / m²·h, the ultrafiltration effluent turbidity is below 0.2 NTU, and the water recovery rate is not less than 85%; S3, organic matter removal The organic matter in the ultrafiltration effluent of S2 is removed by electro-catalysis coupled with ozone and synergistic oxidation, and the removal rate of organic matter is controlled to be not less than 92%, and the catalytic oxidation effluent is obtained; electro-catalysis is realized by using an electro-catalysis device, and the anode of the electro-catalysis device is a composite coating electrode composed of Sn(Sb)O2 coating and TiO2-γ-MnO2 coating on a titanium substrate; The cathode is a graphite electrode or a porous carbon electrode; the electrocatalytic current density is 100-300 A / m 2 The voltage is 4.0-6.0 V, the electrode plate spacing is 2.0-4.0 cm, and the spacing is filled with iron tailing-based visible light modified particle electrodes; and at the same time of electrocatalytic oxidation of the wastewater, ozone is introduced into the wastewater by using a micro-nano bubble aeration head, the ozone mass concentration in the wastewater is 5.0-20.0 mg / L, and the treatment time is 20-40 min. S4, salt recovery The catalytic oxidation effluent of S3 is treated by bipolar membrane electrodialysis technology, and the salt recovery rate is controlled to be not less than 80%, and acid and alkali are produced.

2. The process for enhanced resource recovery of coking high salinity wastewater according to claim 1, characterized in that, In S1, the total hardness of the raw coking high-salt wastewater is 300-2500 mg / L in terms of calcium carbonate; the stirring reaction time is 10-20 minutes.

3. The process for enhanced resource recovery of coking high salinity wastewater according to claim 2, characterized in that, In S1, the hardness of the raw water is monitored in real time online, and the addition ratio of sodium bicarbonate and calcium chloride is automatically adjusted; when the total hardness is greater than 1500 mg / L in terms of calcium carbonate, the mass ratio of sodium bicarbonate to calcium chloride is 5:1, and when the total hardness is less than 500 mg / L, the mass ratio of sodium bicarbonate to calcium chloride is 2:

1.

4. The process for enhanced resource recovery of coking high salinity wastewater according to claim 1, characterized in that, In S2, the pore size of the ceramic ultrafiltration membrane is 0.1-0.5 μm; the surface of the ultrafiltration membrane is physically cleaned and chemically cleaned with 0.3% HCl, and the backwashing time is 60-200 s and the backwashing period is 20-40 min.

5. The process for enhanced resource recovery of coking high salinity wastewater according to claim 1, characterized in that, In S3, the preparation method of the anode comprises: (1) The titanium substrate is processed into a plate shape, and is pretreated by mechanical grinding, degreasing, acetone ultrasonic cleaning for 10-30 min, and drying; (2) A electrolyte containing SnCl4 and SbCl3 is used for constant current electrodeposition on the titanium substrate, and then calcination at 450-500°C for 1-3h; (3) A sol prepared by mixing Fe(NO3)3, Ni(NO3)2, tetrabutyl titanate, and Mn(NO3)2 is coated on the surface to obtain a composite film of Fe-Ni co-doped TiO2 and γ-MnO2, and the mass ratio of TiO2 to γ-MnO2 in the composite film is 7:3; The preparation method of the iron tailings-based visible light modified particle electrode is as follows: (1) The iron tailings particles are ball milled, then impurities are removed by boiling in dilute hydrochloric acid and dilute NaOH solution, washed with distilled water, dried, and sieved through a 60-mesh sieve to obtain fine iron tailings particles; (2) 55% fine iron tailings, 15% dry fine clay, 15% starch, and 15% MnO2 by mass ratio were prepared; the iron tailings, clay, starch, and MnO2 were mixed uniformly, immersed in SnCl4-Mn(NO3)2 sol for 3-5 h, dried at 100-120°C, and then extruded into balls; (3) the green balls were baked at 120°C for 24 h, heated at 300°C for 2 h, activated at 550°C for 20 min, and finally calcined at 850°C for 15-25 min, and then immersed in Fe-Co co-doped TiO2 sol for loading, and then calcined and shaped to obtain a particle electrode with a particle size of 3-5 mm.

6. The process for enhanced resource recovery treatment of coking high salinity wastewater according to claim 5, characterized in that, A hydrogen bubble recovery device was integrated with the cathode of the electro-catalytic device to recover the generated H2 as fuel for the ozone generator.

7. The process for intensified resource recovery of coking high salinity wastewater as claimed in claim 1, wherein, In S4, the bipolar membrane electrodialysis is achieved by using a bipolar membrane electrodialyzer, and the electrodes of the bipolar membrane electrodialyzer are metal electrodes, non-metal electrodes, and doped modified electrodes; Current density 30-100 A / m 2 Voltage 1.5-5.0 V, liquid volume through the membrane stack per minute 10-50 mL.

8. The process for enhanced resource recovery treatment of coking high salinity wastewater according to claim 7, characterized in that, In S4, the membrane stack water salinity of the bipolar membrane electrodialyzer is monitored in real time, and the current density and flow rate are dynamically matched; when the sum of the concentrations of chloride ions and sulfate ions in the wastewater exceeds 10000 mg / L, the flow rate is increased to 40-50 mL / min and the current density is reduced to 30-50 A / m².

9. The process for enhanced resource recovery treatment of coking high salinity wastewater according to claim 1 or 7, characterized in that, In S4, before the bipolar membrane electrodialysis treatment, including the use of charged nanofiltration membrane monovalent anion salt and divalent anion salt saltation treatment, respectively containing Cl - of salt solution and SO4 2- of salt solution, respectively transported to different bipolar membrane electrodialysis for bipolar membrane electrodialysis treatment.

10. The process for enhanced resource recovery treatment of coking high salinity wastewater according to claim 1, characterized in that, The produced acid is diluted and used for chemical cleaning of the S2 ultrafiltration membrane, and part of it is used as an acid product; part of the produced lye is used to replace 20%-30% of the calcium chloride in the S1 softening process, or is concentrated to 10-15 wt% and then returned to the coke oven gas desulfurization tower, and part of it is used as an alkali product.

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