A coking wastewater membrane filtration concentrate treatment system and method

Abstract

The application discloses a coking wastewater membrane filtration concentrate treatment system, which comprises a first adsorption device, a micro-electrolysis device, a Fenton device, a neutralization tank, a flocculation and precipitation tank, an electro-oxidation device, a first hardness removal device, a nanofiltration device, a second vacuum membrane distillation device, a low-temperature crystallizer, a second adsorption device, a second hardness removal device and a bipolar membrane electrodialysis device which are connected in sequence, and further comprises a first vacuum membrane distillation device, a water production tank, a crystallizer and a sodium ferrate preparation device. The application further discloses a coking wastewater membrane filtration concentrate treatment method, which removes organic matters in the concentrate by adopting adsorption+micro-electrolysis+Fenton+electro-oxidation, and realizes resource utilization of the concentrate by adopting nanofiltration+vacuum membrane distillation+bipolar membrane electrodialysis. Meanwhile, waste gas generated in the electro-oxidation treatment process and sludge generated in the micro-electrolysis+Fenton treatment are effectively utilized to prepare a sodium ferrate solution, so that the coking wastewater has a high recycling rate.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, and specifically relates to a coking wastewater membrane filtration concentrate treatment system and a coking wastewater membrane filtration concentrate treatment method. Background Technology

[0002] Coking wastewater is a typical type of recalcitrant organic wastewater, characterized by high toxicity and poor biodegradability, making it one of the most difficult wastewaters to treat in the steel industry. Currently, steel companies commonly employ a treatment method combining biological treatment, nanofiltration, and reverse osmosis. During this process, the membrane technology generates a concentrate.

[0003] Currently, the recovery rate of membrane treatment for coking wastewater is generally around 70%, and the concentrated brine with a mass concentration of about 30% is mostly consumed internally by the enterprises, mainly for coal blending, slag flushing, and coke quenching. To meet the requirements of energy conservation, emission reduction, and water pollutant discharge standards, relevant enterprises need to improve their wastewater treatment processes and adopt wastewater reduction measures.

[0004] When coking wastewater is used as flushing water, toxic and harmful substances volatilize under high temperatures, causing air pollution. Effective treatment of the concentrate is an indispensable and crucial part of the entire treatment system, and also one of the bottlenecks in the current application of membrane treatment technology.

[0005] In the steel manufacturing process, only 30% to 50% of the energy is effectively utilized, with the remaining large amount existing as waste heat, indicating significant potential for recovery. Achieving efficient recovery and utilization of waste heat resources and reducing energy costs for enterprises is a major issue that steel companies need to consider in their research. For the treatment of high-salinity wastewater, the traditional method is to first reduce the volume and concentrate the wastewater, then use evaporation technology to crystallize the salt, ultimately achieving wastewater desalination and salt resource recovery. Currently, the main industrialized concentration methods are thermal methods and membrane separation methods. Thermal methods mainly use heating to evaporate the water from high-salinity wastewater to achieve concentration and volume reduction. This method typically uses steam as a heat source, thus consuming enormous amounts of energy and incurring very high operating costs. Membrane distillation technology is a novel separation technology that combines traditional thermal evaporation with membrane separation technology. Its principle is that the waste liquid is prevented from penetrating the membrane pores in liquid form by the interception effect of the hydrophobic microporous membrane. Only the volatile components penetrate the membrane pores under the impetus of the vapor pressure difference on both sides of the membrane, while the non-volatile components are intercepted, thus achieving the separation and purification of the mixture. It has the characteristics of high concentration ratio and low energy consumption (using a low-grade heat source of 30-70℃).

[0006] A small number of coking plants evaporate and crystallize the concentrated membrane filtrate of coking wastewater to obtain industrial water and mixed salts. Thermal salt separation and crystallization processes can recover 60-70% of sodium sulfate, with a comprehensive recovery rate of 40-50% for the crystalline salt products. Membrane salt separation and crystallization can recover approximately 90% of sodium sulfate, with a comprehensive recovery rate of around 80% for the crystalline salts. Current salt separation and crystallization processes still require the treatment of 15% of the mixed salts. Because these mixed salts contain organic matter and other impurities, they are classified as hazardous waste, resulting in high disposal costs. Therefore, developing technologies to remove organic matter and other pollutants from coking wastewater, and to utilize the salts as resources to achieve zero-discharge technology for coking wastewater, is of great significance. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, this invention provides a coking wastewater membrane filtration concentrate treatment system and method. The system uses adsorption + micro-electrolysis + Fenton + electro-oxidation to remove organic matter from the concentrate, and nanofiltration + vacuum membrane distillation + bipolar membrane electrodialysis to utilize the concentrate for resource recovery. At the same time, the system effectively utilizes the waste gas generated during the electro-oxidation process and the sludge generated during the micro-electrolysis + Fenton treatment to prepare sodium ferrate solution, thereby achieving zero discharge of coking wastewater.

[0008] To solve the above problems, the present invention provides the following solution:

[0009] A coking wastewater membrane filtration concentrate treatment system includes a first adsorption device. The outlet of the first adsorption device is connected to the inlet pipe of a micro-electrolysis device. The outlet of the micro-electrolysis device is connected to the inlet of a Fenton device. The outlet of the Fenton device is connected to the inlet of a neutralization tank. The outlet of the neutralization tank is connected to the inlet of a flocculation sedimentation tank. The ferric hydroxide outlet of the flocculation sedimentation tank is connected to a sodium ferrate preparation device. The outlet of the flocculation sedimentation tank is connected to the inlet of an electro-oxidation device. The sodium hypochlorite outlet of the electro-oxidation device is connected to the sodium ferrate preparation device. The outlet of the electro-oxidation device is connected to the inlet of a first hardening device. The outlet of the first hardening device is connected to the inlet of a nanofiltration device. The nanofiltration permeate outlet of the nanofiltration device is connected to the inlet of a first vacuum membrane distillation device. The concentrate outlet of the first vacuum membrane distillation device is connected to a crystallizer. The mother liquor outlet of the crystallizer is connected to both the inlet of the first vacuum membrane distillation device and a second adsorption device. The inlet is connected to the product water outlet of the first vacuum membrane distillation unit, which is connected to the product water tank. The concentrate outlet of the nanofiltration unit is connected to the inlet of the second vacuum membrane distillation unit. The product water outlet of the second vacuum membrane distillation unit is connected to the product water tank. The concentrate outlet of the second vacuum membrane distillation unit is connected to the low-temperature crystallizer. The mother liquor outlet of the low-temperature crystallizer is connected to the inlet of the second vacuum membrane distillation unit and the inlet of the second adsorption unit, respectively. The outlet of the second adsorption unit is connected to the inlet of the second hardening removal unit. The outlet of the second hardening removal unit is connected to the inlet of the bipolar membrane electrodialysis unit. The alkali outlet of the bipolar membrane electrodialysis unit is connected to the alkali dosing pipe of the neutralization tank, the alkali input port of the electro-oxidation unit, the alkali dosing pipe of the first hardening removal unit, and the sodium ferrate preparation device, respectively. The acid outlet of the bipolar membrane electrodialysis unit is connected to the acid dosing pipe of the micro-electrolysis unit. The fresh water outlet of the bipolar membrane electrodialysis unit is connected to the inlet of the nanofiltration unit.

[0010] As described above, the first adsorption device includes a first adsorption device inlet tank. The inlet of the first adsorption device inlet tank serves as the inlet of the first adsorption device. The first adsorption device inlet tank is connected to the first water tank of the adsorption reaction tank via an inlet pump. The bottom of the first water tank and the bottom of the second water tank of the adsorption reaction tank are connected via a flow channel. Aeration pipes are installed at the bottom of both the first and second water tanks of the adsorption reaction tank. The inlet of the aeration pipe is connected to a first blower. The second water tank of the adsorption reaction tank is connected to the inlet of the filter device via a first lift pump. The concentrated water outlet of the filter device is connected to the first water tank of the adsorption reaction tank. The product water outlet of the filter device (5) is connected to the first product water tank. The drain outlet of the filter device is connected to an external sludge dewatering machine. The outlet of the first product water tank is the outlet of the first adsorption device.

[0011] As described above, the micro-electrolysis device includes a pipeline mixer. One inlet of the pipeline mixer is connected to the outlet of the micro-electrolysis inlet pipe, and the other inlet of the pipeline mixer is connected to the acid dosing pipe. The outlet of the pipeline mixer is connected to the inlet of the micro-electrolysis reactor inlet pipe. The outlet of the micro-electrolysis reactor inlet pipe extends to the lower part of the micro-electrolysis reactor. Multiple packing support layers are provided inside the micro-electrolysis reactor, and block packing is provided on the packing support layers. An aeration pipe for the micro-electrolysis reactor is provided below each packing support layer. A first baffle is provided at the bottom of the micro-electrolysis reactor, located directly below the outlet of the micro-electrolysis reactor inlet pipe. A micro-electrolysis reactor maintenance port is provided on the side wall of the micro-electrolysis reactor corresponding to each packing support layer. A first separator is provided above the uppermost packing support layer, and a first overflow weir is provided above the first separator. The first overflow weir is located in the upper part of the micro-electrolysis reactor and is connected to the micro-electrolysis reactor outlet pipe. The outlet of the micro-electrolysis reactor outlet pipe serves as the outlet of the micro-electrolysis device.

[0012] As described above, the Fenton device includes a Fenton reactor inlet pipe, the inlet of which serves as the inlet of the Fenton reactor and is connected to the outlet of the micro-electrolysis reactor outlet pipe. The outlet of the Fenton reactor inlet pipe extends to the lower part of the Fenton reactor. An aeration pipe and a second baffle are installed at the bottom of the Fenton reactor. The second baffle is located directly below the outlet of the Fenton reactor inlet pipe. A second overflow weir is located at the upper part of the Fenton reactor. A second separator is located below the second overflow weir. The second overflow weir is connected to the inlet of the Fenton reactor outlet pipe. The outlet of the Fenton reactor outlet pipe is the outlet of the Fenton device. A hydrogen peroxide solution dosing pipe is connected to the bottom of the Fenton reactor.

[0013] As described above, the neutralization tank is connected to the outlet of the Fenton reactor effluent pipe. An aeration pipe is installed at the bottom of the neutralization tank, which is connected to a second blower. The bottom of the neutralization tank and the bottom of the flocculation tank are connected through a flow channel, which serves as the outlet of the neutralization tank and the inlet of the flocculation sedimentation tank.

[0014] The flocculation sedimentation tank includes a flocculation tank equipped with a flocculation tank agitator and a flocculant dosing pipe connected to it. The overflow port at the top of the flocculation tank is connected to the inlet of the sedimentation tank inlet pipe. The outlet of the sedimentation tank inlet pipe extends to the middle of the sedimentation tank. A sedimentation tank sludge hopper is located at the bottom of the sedimentation tank, below the outlet of the sedimentation tank inlet pipe. The sedimentation tank sludge hopper is connected to the inlet of a sludge discharge pump. The outlet of the sludge discharge pump serves as the ferric hydroxide output port of the flocculation sedimentation tank. A sedimentation tank outlet is located at the top of the sedimentation tank, serving as the outlet of the flocculation sedimentation tank.

[0015] As described above, the electro-oxidation device includes an electro-oxidation inlet tank. The inlet of the inlet tank serves as the inlet for the electro-oxidation device. The top of the inlet tank is closed, and an aeration pipe is installed at the bottom. The aeration pipe is connected to a third blower. The inlet of a second exhaust blower is connected to the space above the liquid surface in the inlet tank, and the outlet of the second exhaust blower is connected to the air inlet of the absorption tower. The inlet of an electro-oxidation inlet pump is connected to the outlet of the inlet tank, and the outlet of the pump is connected to the inlet of a filter. The outlet of the filter is connected to the inlet of the electrolytic cell. The outlet of the electrolytic cell is connected to the inlet tank via an exhaust pipe, and the outlet of the exhaust pipe is located below the liquid surface in the inlet tank. The outlet of the electrolytic cell is connected to the electro-oxidation product water tank. The top of the product water tank is closed. The unit is partially enclosed. The inlet of the first exhaust fan is connected to the space above the liquid surface in the electro-oxidation product water tank. The outlet of the first exhaust fan is connected to the air inlet of the absorption tower. The bottom of the absorption tower is connected to the alkali solution tank. Multiple alkali solution tanks are set up. When the alkali solution tank is empty, the inlet of the alkali solution tank serves as the alkali input port of the electro-oxidation device. When the alkali solution tank is filled with sodium hydroxide solution, the inlet of the alkali solution tank is disconnected from the alkali output port of the bipolar membrane electrodialysis device, and the outlet of the alkali solution tank is connected to the inlet of the spray pump. The outlet of the spray pump is connected to the upper water inlet of the absorption tower. The inlet of the alkali solution tank is connected to the water outlet of the absorption tower. When the concentration of sodium hypochlorite solution in the alkali solution tank reaches the set value, the outlet of the alkali solution tank becomes the sodium hypochlorite outlet of the electro-oxidation device, and the outlet of the electro-oxidation product water tank serves as the water outlet of the electro-oxidation device.

[0016] As described above, the first hardening device includes a first reaction tank connected in sequence. The bottom of the first reaction tank and the bottom of the second reaction tank are connected through a flow channel. The upper part of the second reaction tank and the upper part of the third reaction tank are connected through an overflow channel. The first reaction tank is equipped with a first agitator, the second reaction tank is equipped with a second agitator, and the third reaction tank is equipped with a third agitator. The inlet of the first reaction tank serves as the inlet of the first hardening device. The first reaction tank is equipped with an alkali dosing pipe, which also serves as the alkali dosing pipe for the first hardening device. The second reaction tank is connected to a sodium carbonate dosing pipe. The third reaction tank is connected to the inlet of the ultrafiltration membrane via an ultrafiltration feed pump. The ultrafiltration membrane concentrate outlet is connected to the third reaction tank. The ultrafiltration membrane product outlet is connected to a second product water tank. The second product water tank is connected to the resin tank of the first hardening device via a second booster pump. The resin tank of the first hardening device is filled with a strong acidic cation exchange resin. The outlet of the resin tank serves as the outlet of the first hardening device.

[0017] A method for treating coking wastewater membrane filtration concentrate, utilizing the coking wastewater membrane filtration concentrate treatment system described above, characterized by the following steps:

[0018] S1. First, activated carbon is used in the first adsorption unit to remove most of the organic pollutants in the membrane filtration concentrate of coking wastewater. The effluent from the first adsorption unit enters the micro-electrolysis unit. An acid solution is added to adjust the pH of the influent to the micro-electrolysis unit to 2-3, which further removes organic pollutants and color from the wastewater while generating ferrous ions. The permeate from the micro-electrolysis unit enters the Fenton unit. The Fenton unit uses ferrous ions and hydrogen peroxide to further oxidize and remove organic pollutants and color from the wastewater, while generating ferric ions.

[0019] S2. The effluent from the Fenton unit enters the neutralization tank, where the pH is adjusted to 7-8 using an alkaline solution. After adding flocculant to the flocculation tank, the effluent from the sedimentation tank undergoes sedimentation. The effluent from the sedimentation tank enters the electro-oxidation unit, and the ferric hydroxide precipitate in the sedimentation tank enters the sodium ferrate preparation unit.

[0020] S3. The electro-oxidation unit removes ammonia nitrogen, COD and color from the wastewater. At the same time, it uses an alkaline solution to generate sodium hypochlorite solution. The sodium hypochlorite solution enters the sodium ferrate preparation unit. The electro-oxidation product enters the first hardening removal unit. The first hardening removal unit uses chemical precipitation and resin softening to remove hardness from the wastewater. The hardened effluent enters the nanofiltration unit.

[0021] S4. The permeate from the first hardening unit is filtered through a nanofiltration unit to obtain nanofiltration permeate with sodium chloride as the main component. The nanofiltration permeate enters the first vacuum membrane distillation unit. The concentrate from the first vacuum membrane distillation unit enters the crystallizer to obtain sodium chloride crystals. Part of the mother liquor output from the crystallizer is returned to the first vacuum membrane distillation unit, and the other part of the mother liquor output from the crystallizer enters the second adsorption unit. The permeate from the first vacuum membrane distillation unit enters the permeate tank. The nanofiltration concentrate enters the second vacuum membrane distillation unit for further concentration. The concentrate from the second vacuum membrane distillation unit enters the low-temperature crystallizer to obtain sodium sulfate decahydrate crystals. The permeate from the second vacuum membrane distillation unit enters the permeate tank. Most of the mother liquor from the low-temperature crystallizer is returned to the second vacuum membrane distillation unit, and the remaining part of the mother liquor from the low-temperature crystallizer enters the second adsorption unit.

[0022] S5. In the second adsorption unit, granular activated carbon and macroporous adsorption resin are used to adsorb and remove organic matter in the mother liquor output from the low-temperature crystallizer. The effluent from the second adsorption unit enters the second hardening removal unit and the hardness in the wastewater is removed by resin softening. The effluent from the second hardening removal unit enters the bipolar membrane electrodialysis unit.

[0023] S6. The bipolar membrane electrodialysis device produces a mixed acid of hydrochloric acid and sulfuric acid, as well as a sodium hydroxide solution. The mixed acid is recycled to the micro-electrolysis device. Part of the sodium hydroxide solution is used in the neutralization tank to adjust the pH, part is used in the alkaline water tank of the electro-oxidation device to absorb the tail gas, and the remaining part is used in the sodium ferrate preparation device to prepare a sodium ferrate solution with ferric hydroxide from the flocculation sedimentation tank and sodium hypochlorite from the electro-oxidation device.

[0024] As described above, in step S3, multiple sets of alkaline water tanks are set up. When the mass concentration of sodium hypochlorite solution reaches 10%, the system switches to the next set of alkaline water tanks to continue operation. Then, the solution is transported to the sodium ferrate preparation device via a booster pump. The resin tank of the first hardening device is filled with strong acidic cation exchange resin, which releases hydrogen ions to adjust the pH of the wastewater. In step S6, the mass concentration of sodium hydroxide solution prepared by bipolar membrane electrodialysis is 8-10%. The mixed acid is used for pH adjustment in the micro-electrolysis device, regeneration of resin inside or outside the system, and membrane cleaning inside or outside the system.

[0025] As described above, in step S4, the heat source for the first and second vacuum membrane distillation devices is the waste heat from the steel plant, which keeps the wastewater operating temperature at 50-70°C.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. This invention utilizes a pretreatment process combining adsorption, micro-electrolysis, Fenton chromatography, and electro-oxidation to effectively remove recalcitrant organic matter and color from water. The acids and alkalis used in the treatment are derived from the bipolar membrane electrodialysis unit within this system. The combined application of micro-electrolysis and Fenton chromatography eliminates the need for ferrous sulfate addition, thereby reducing the amount of external reagents that could increase the salinity in the wastewater and effectively improving the water quality for subsequent salt separation and crystallization processes. Simultaneously, chemical precipitation and resin hardening effectively remove calcium and magnesium hardness from the concentrate, reducing impurities in the wastewater and improving the purity of the subsequent salt separation and crystallization products.

[0028] 2. The concentration process employed in this invention combines nanofiltration, vacuum membrane distillation, and crystallization. Nanofiltration is used to separate salts from wastewater, utilizing the selective retention characteristics of nanofiltration membranes for divalent salts to achieve the separation of monovalent sodium chloride and divalent sodium sulfate in the liquid phase. Sodium chloride primarily enters the nanofiltration permeate, while sodium sulfate is concentrated in the nanofiltration concentrate. The nanofiltration permeate and concentrate are then further concentrated by vacuum membrane distillation and crystallized to obtain sodium chloride and sodium sulfate, respectively. The vacuum membrane distillation unit uses waste heat from the steel plant as a heat source, effectively reducing energy consumption, improving the steel plant's thermal energy utilization efficiency, and achieving energy conservation and emission reduction. It features high recovery rate, low operating cost, stable permeate water quality, and effluent water quality consistently meeting reuse standards, with a high overall recovery rate of crystallized salts.

[0029] 3. After salt separation and crystallization, the remaining mixed salts are processed through adsorption, hardening removal, and bipolar membrane electrodialysis to produce mixed acid and sodium hydroxide solution, further improving the resource recovery rate of the concentrate. The mixed acid and sodium hydroxide solution are used for internal consumption within the treatment system. The chlorine gas and iron sludge generated during the treatment process are further utilized. Sodium ferrate is synthesized at low temperature using ferric hydroxide, sodium hypochlorite, and sodium hydroxide. The resulting sodium ferrate solution can be used in the treatment of coking wastewater. This invention applies bipolar membrane electrodialysis technology to the resource utilization of mixed salts, combined with the iron sludge generated by the micro-electrolysis-Fenton process and the sodium hypochlorite solution generated by electro-oxidation, to prepare a sodium ferrate solution with significant economic benefits, further improving the resource utilization rate of the concentrate. This technology can achieve zero discharge of the concentrate. Attached Figure Description

[0030] Figure 1 This is a process flow diagram of a coking wastewater membrane filtration concentrate treatment system.

[0031] Figure 2 This is a schematic diagram of the first adsorption device.

[0032] Figure 3 This is a schematic diagram of the micro-electrolysis-Fenton reactor-neutralization tank-flocculation sedimentation tank device.

[0033] Figure 4 This is a schematic diagram of the electro-oxidation device.

[0034] Figure 5 This is a schematic diagram of the first hardening device.

[0035] In the diagram: 1-Inlet tank of the first adsorption device; 2-Inlet pump; 3-First blower; 4-Adsorption reaction tank; 5-Filter device; 6-First product water tank; 7-First booster pump; 10-Micro electrolysis reactor; 11-Micro electrolysis inlet pipe; 12-Acid dosing pipe; 13-Pipe mixer; 14-Inlet pipe of the micro electrolysis reactor; 15-First separator; 16-First overflow weir; 17-Exhaust port of the micro electrolysis reactor; 18-Maintenance port of the micro electrolysis reactor; 19-Aeration pipe of the micro electrolysis reactor; 20-First baffle; 21-First air compressor; 22-First air storage tank; 23-Packing support layer; 24-Outlet pipe of the micro electrolysis reactor; 25-Inlet pipe of the Fenton reactor; 26-Fenton reactor; 27-Second overflow weir; 28-Maintenance port of the Fenton reactor; 29-Second air compressor; 30-Second air storage tank; 31-Second baffle; 32- Second separator; 33-Fenton reactor outlet pipe; 34-Second blower; 35-Neutralization tank; 36-Flocculation tank; 37-Sedimentation tank; 38-Sludge pump; 39-Flocculation tank agitator; 40-Sedimentation tank outlet; 41-Electro-oxidation inlet tank; 42-Third blower; 43-Electro-oxidation inlet pump; 44-Filter; 45-Electrolytic cell; 46-Power supply; 47-Electrolytic cell exhaust pipe; 48-Electro-oxidation product water tank ; 49-First exhaust fan; 50-Second exhaust fan; 51-Absorption tower; 52-Alkali solution tank; 53-Spray pump; 61-First reaction tank; 62-Second reaction tank; 63-Third reaction tank; 64-Ultrafiltration feed pump; 65-Ultrafiltration membrane; 66-First mixer; 67-Second mixer; 68-Third mixer; 69-Second product water tank; 70-Second booster pump; 71-First hardening device resin tank. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0037] Example 1

[0038] In specific implementation, the process flow of the coking wastewater membrane filtration concentrate treatment system of the present invention is as follows: Figure 1 As shown.

[0039] A coking wastewater membrane filtration concentrate treatment system includes a first adsorption device, a micro-electrolysis device, a Fenton device, a neutralization tank 35, a flocculation sedimentation tank, an electro-oxidation device, a first hardening removal device, a nanofiltration device, a second vacuum membrane distillation device, a low-temperature crystallizer, a second adsorption device, a second hardening removal device, and a bipolar membrane electrodialysis device connected in sequence. It also includes a first vacuum membrane distillation device, a product water tank, a crystallizer, and a sodium ferrate preparation device.

[0040] The effluent from the coking wastewater membrane filtration concentrate is fed into the inlet of the first adsorption unit. The outlet of the first adsorption unit is connected to the micro-electrolysis inlet pipe 11 of the micro-electrolysis unit. The outlet of the micro-electrolysis unit is connected to the inlet of the Fenton unit. The outlet of the Fenton unit is connected to the inlet of the neutralization tank 35. The outlet of the neutralization tank 35 is connected to the inlet of the flocculation sedimentation tank. The ferric hydroxide outlet of the flocculation sedimentation tank is connected to the sodium ferrate preparation device. The outlet of the flocculation sedimentation tank is connected to the inlet of the electro-oxidation unit. The sodium hypochlorite outlet of the electro-oxidation unit is connected to the sodium ferrate preparation device. The outlet of the electro-oxidation unit is connected to the inlet of the first hardening removal unit. The outlet of the first hardening removal unit is connected to the inlet of the nanofiltration unit. The nanofiltration permeate outlet of the nanofiltration unit is connected to the inlet of the first vacuum membrane distillation unit. The concentrate outlet of the first vacuum membrane distillation unit is connected to the crystallizer. The mother liquor outlet of the crystallizer is connected to the inlet of the first vacuum membrane distillation unit and the second adsorption unit, respectively. The inlet of the first vacuum membrane distillation unit is connected to the product water tank, the concentrate outlet of the nanofiltration unit is connected to the inlet of the second vacuum membrane distillation unit, the product water outlet of the second vacuum membrane distillation unit is connected to the product water tank, the concentrate outlet of the second vacuum membrane distillation unit is connected to the low-temperature crystallizer, the mother liquor outlet of the low-temperature crystallizer is connected to the inlet of the second vacuum membrane distillation unit and the inlet of the second adsorption unit, respectively, the outlet of the second adsorption unit is connected to the inlet of the second hardening removal unit, the outlet of the second hardening removal unit is connected to the inlet of the bipolar membrane electrodialysis unit, the alkali outlet of the bipolar membrane electrodialysis unit is connected to the alkali dosing pipe of the neutralization tank 35, the alkali input port of the electro-oxidation unit, the alkali dosing pipe of the first hardening removal unit, and the sodium ferrate preparation device, respectively, the acid outlet of the bipolar membrane electrodialysis unit is connected to the acid dosing pipe 12 of the micro-electrolysis unit, and the fresh water outlet of the bipolar membrane electrodialysis unit is connected to the inlet of the nanofiltration unit.

[0041] like Figure 2As shown, the first adsorption device includes a first adsorption device inlet tank 1, an inlet pump 2, an adsorption reaction tank 4, a first lift pump 7, a filter device 5, and a first product water tank 6 connected in sequence. The inlet of the first adsorption device inlet tank 1 serves as the inlet of the first adsorption device. The inlet of the inlet pump 2 is connected to the first adsorption device inlet tank 1, and the outlet of the inlet pump 2 is connected to the adsorption reaction tank 4. Specifically, the adsorption reaction tank 4 is divided into a first tank and a second tank by a partition. A flow channel is provided between the lower part of the partition and the bottom of the adsorption reaction tank 4. The bottom of the first tank and the bottom of the second tank are connected through the flow channel, changing the adsorption reaction tank 4 from a general completely mixed type to a partially plug flow type, which can improve the removal efficiency to a certain extent. The outlet of the inlet pump 2 is connected to the first tank of the adsorption reaction tank 4. Aeration pipes are installed at the bottom of the first and second tanks of the adsorption reaction tank 4. The inlets of the aeration pipes of the first and second tanks are connected to a first blower 3. The aeration rate is 3-5 L / (m²) depending on the area of ​​the liquid surface. 2 The inlet of the first booster pump 7 is connected to the second water tank of the adsorption reaction tank 4, the outlet of the first booster pump 7 is connected to the inlet of the filter device 5, the concentrate outlet of the filter device 5 is connected to the first water tank of the adsorption reaction tank 4, and the product water outlet of the filter device 5 is connected to the first product water tank 6; the filter device 5 adopts a rotary disc filter, the filter material of the disc is filter cloth, the filtration accuracy is 5μm, the operating pressure is 0.1~0.4Mpa, the disc rotation speed is 60~300r / min, and the drain outlet of the filter device 5 is connected to an external... After a period of operation, the sludge dewatering machine and filter unit 5 require cleaning and maintenance, necessitating the discharge of some effluent containing activated carbon (sludge) through the drain outlet. This effluent then returns to the sludge dewatering machine, which employs a plate and frame filter press. The filtered effluent is returned to the first product water tank 6. The wastewater in the first product water tank 6 is pumped to the micro-electrolysis device. The outlet of the first product water tank 6 is the outlet of the first adsorption device, and it is connected to the inlet of the micro-electrolysis inlet pipe 11. In the adsorption reaction tank 4 of the first adsorption device, activated carbon removes most of the organic pollutants from the coking wastewater membrane filtration concentrate.

[0042] like Figure 3As shown, the micro-electrolysis device includes a micro-electrolysis reactor 10, a micro-electrolysis water inlet pipe 11, an acid dosing pipe 12, a pipeline mixer 13, a micro-electrolysis reactor water inlet pipe 14, a micro-electrolysis reactor exhaust port 17, a first separator 15, a first overflow weir 16, a micro-electrolysis reactor maintenance port 18, a micro-electrolysis reactor aeration pipe 19, a first baffle 20, a first air compressor 21, a first air storage tank 22, a packing support layer 23, and a micro-electrolysis reactor water outlet pipe 24. One inlet of the pipe mixer 13 is connected to the outlet of the micro-electrolysis inlet pipe 11, and the other inlet of the pipe mixer 13 is connected to the acid dosing pipe 12. The outlet of the pipe mixer 13 is connected to the inlet of the micro-electrolysis reactor inlet pipe 14. The outlet of the micro-electrolysis reactor inlet pipe 14 extends to the lower part of the micro-electrolysis reactor 10. Multiple packing support layers 23 are arranged from top to bottom inside the micro-electrolysis reactor 10. Each packing support layer 23 is equipped with packing material, and an aeration pipe for the micro-electrolysis reactor is installed below each packing support layer 23. 19. A first baffle 20 is provided at the bottom of the micro-electrolysis reactor 10. The first baffle 20 is located directly below the bottom outlet of the micro-electrolysis reactor inlet pipe 14. The first baffle 20 is conical and can create a swirling flow of the water effluent from the micro-electrolysis reactor inlet pipe 14. A micro-electrolysis reactor maintenance port 18 is provided on the side wall of the micro-electrolysis reactor 10 corresponding to each packing support layer 23. The aeration pipe 19 of each micro-electrolysis reactor is connected to the outlet of the first air storage tank 22, and the inlet of the first air storage tank 22 is connected to the first air compressor 2. 1. A first separator 15 is installed above the uppermost packing support layer 23, and a first overflow weir 16 is installed above the first separator 15. The first overflow weir 16 is located in the upper part of the micro-electrolysis reactor 10 and is connected to the outlet pipe 24 of the micro-electrolysis reactor. The outlet of the outlet pipe 24 of the micro-electrolysis reactor serves as the outlet of the micro-electrolysis device. The micro-electrolysis reactor 10 uses high-temperature sintered iron-carbon packing. The packing installed on the packing support layer 23 is block-shaped with a diameter of 3-5 cm. The packing flows from the micro-electrolysis reactor... The equipment is fed through inspection port 18, where compressed air supplied by the first air compressor 21 and the first air storage tank 22 is used to aerate and flush the surface of the packing material, thereby stirring the packing and improving mass transfer. The pressure of the compressed air is 0.4–0.7 MPa. The separator 15 at the top uses two triangular plates, with exhaust pipes installed at the top of the triangular plates. All exhaust pipes converge into a first exhaust manifold extending above the liquid surface, which connects to the exhaust port 17 of the micro-electrolysis reactor. The hydraulic retention time of the micro-electrolysis reactor 10 is 2–4 hours. Organic pollutants and color are further removed from the wastewater in the micro-electrolysis reactor 10, while a large amount of ferrous ions are generated. The permeate from the micro-electrolysis reactor 10 then enters the Fenton unit.

[0043] The Fenton apparatus includes a Fenton reactor inlet pipe 25, a Fenton reactor 26, a second overflow weir 27, a Fenton reactor access port 28, a second air compressor 29, a second air storage tank 30, a second baffle 31, a second separator 32, and a Fenton reactor outlet pipe 33. The top inlet of the Fenton reactor inlet pipe 25 serves as the inlet of the Fenton reactor apparatus and is connected to the outlet of the micro-electrolysis reactor outlet pipe 24 via a water supply pipe. The bottom outlet of the Fenton reactor inlet pipe 25 extends to the lower part of the Fenton reactor 26. An aeration pipe and a second baffle 31 are installed at the bottom of the Fenton reactor 26, with the second baffle 31 located directly below the bottom outlet of the Fenton reactor inlet pipe 25. The aeration pipe of the Fenton reactor 26 is connected to the outlet of the second air storage tank 30, and the inlet of the second air storage tank 30 is connected to the second air compressor 29. The second overflow weir 27 is located at the upper part of the Fenton reactor 26, and the second separator 32 is located below the second overflow weir 27. Weir 27 is connected to the inlet of Fenton reactor outlet pipe 33, and the outlet of Fenton reactor outlet pipe 33 is the outlet of Fenton device; separator 32 is composed of two triangular plates, with an exhaust pipe at the top of the triangular plates, and the exhaust pipes are collected into a second exhaust manifold that connects to the liquid surface and to the Fenton reactor outlet at the top of Fenton reactor 26; Fenton reactor inspection port 28 is provided on the lower side wall of Fenton reactor 26 for internal maintenance; dosing pipe is connected to the bottom of Fenton reactor 26 for adding hydrogen peroxide solution, and the aeration rate of Fenton reactor 26 is calculated based on the liquid surface area, with a value ranging from 0.6 to 3 L / (m²). 2 The aeration pressure is 0.3–0.4 MPa; the hydraulic retention time of the Fenton reactor 26 is 1–2 hours.

[0044] The neutralization tank 35 is connected to the outlet of the Fenton reactor effluent pipe 33. The neutralization tank 35 is equipped with an alkali dosing pipe, which is connected to the alkali output port of the bipolar membrane electrodialysis unit. An aeration pipe is installed at the bottom of the neutralization tank 35. The aeration rate of the neutralization tank 35 is calculated based on the liquid surface area and is taken as 3–5 L / (m²). 2 ·s), the aeration pipe of the neutralization tank 35 is connected to the second blower 34, and the bottom of the neutralization tank 35 and the bottom of the flocculation tank 36 are connected through a flow channel, which serves as the outlet of the neutralization tank 35 and the inlet of the flocculation tank 36 (that is, the inlet of the flocculation sedimentation tank).

[0045] The flocculation sedimentation tank includes a flocculation tank 36 and a sedimentation tank 37. The flocculation tank 36 is equipped with a flocculation tank agitator 39 and is connected to a flocculant dosing pipe. The overflow port at the top of the flocculation tank 36 is connected to the inlet of the sedimentation tank 37. The outlet of the inlet of the sedimentation tank 37 extends to the middle of the sedimentation tank 37. A sedimentation tank sludge hopper is set at the bottom of the sedimentation tank 37, located below the outlet of the inlet of the sedimentation tank 37. The inlet of the sludge pump 38 is connected to the sedimentation tank sludge hopper, and the outlet of the sludge pump 38 serves as the ferric hydroxide output port of the flocculation sedimentation tank, connected to the sodium ferrate preparation device. The sedimentation tank outlet 40 is located at the top of the sedimentation tank 37 and serves as the outlet of the flocculation sedimentation tank, connected to the inlet of the electro-oxidation device. Specifically, the hydraulic retention time of the neutralization tank 35 is 15-30 minutes, the hydraulic retention time of the flocculation tank 36 is 5-10 minutes, and the hydraulic retention time of the sedimentation tank 37 is 2 hours.

[0046] like Figure 4As shown, the electro-oxidation device includes an electro-oxidation inlet tank 41, a third blower 42, an electro-oxidation inlet pump 43, a filter 44, an electrolytic cell 45, a power supply 46, an electrolytic cell exhaust pipe 47, an electro-oxidation product water tank 48, a first exhaust fan 49, a second exhaust fan 50, an absorption tower 51, an alkaline water tank 52, and a spray pump 53. The inlet of the electro-oxidation inlet tank 41 serves as the inlet of the electro-oxidation device. The top of the electro-oxidation inlet tank 41 is closed, and an aeration pipe is installed at the bottom of the electro-oxidation inlet tank 41. The aeration pipe of the electro-oxidation inlet tank 41 is connected to the third blower 42. The inlet of the second exhaust fan 50 is connected to the space above the liquid surface inside the electro-oxidation inlet tank 41 via an air supply pipe. The outlet of the second exhaust fan 50 is connected to the air inlet of the absorption tower 51. The inlet of the electro-oxidation inlet pump 43 is connected to the outlet of the electro-oxidation inlet tank 41, and the outlet of the electro-oxidation inlet pump 43 is connected to the inlet of the filter 44. The outlet of electrolytic cell 45 is connected to the inlet of electrolytic cell 45. The outlet of electrolytic cell 45 is connected to electro-oxidation water tank 41 through electrolytic cell exhaust pipe 47, and the outlet of electrolytic cell exhaust pipe 47 is located below the liquid surface of electro-oxidation water tank 41. The outlet of electrolytic cell 45 is connected to the electro-oxidation product water tank 48. The top of electro-oxidation product water tank 48 is closed. Each electrolytic cell 45 is powered by power supply 46. The inlet of the first exhaust fan 49 is connected to the space above the liquid surface in the electro-oxidation product water tank 48 through a gas transmission pipe. The outlet of the first exhaust fan 49 is connected to the air inlet of absorption tower 51. The bottom of 51 is connected to an alkaline water tank 52. Multiple alkaline water tanks 52 are installed. When the alkaline water tank 52 is empty, its inlet serves as both the alkaline input port of the electro-oxidation device and the alkaline output port of the bipolar membrane electrodialysis device. After sodium hydroxide solution is added, the inlet of the alkaline water tank 52 is disconnected from the alkaline output port of the bipolar membrane electrodialysis device and connected to the inlet of the spray pump 53 at the outlet of the alkaline water tank 52 to absorb chlorine gas. The outlet of the spray pump 53 is connected to the upper inlet of the absorption tower 51. At this time, the inlet of the alkaline water tank 52 is connected to the lower outlet of the absorption tower 51. The generated sodium hypochlorite solution is collected; when the sodium hypochlorite solution produced by the alkaline water tank 52 absorbing chlorine gas reaches the set concentration, the outlet of the alkaline water tank 52 containing the set concentration of sodium hypochlorite solution becomes the sodium hypochlorite outlet of the electro-oxidation device. At this time, the next alkaline water tank 52 containing sodium hydroxide solution is connected to the inlet of the spray pump 53 to continue operating the absorption tower 51. The alkaline water tank 52 containing sodium hypochlorite solution is connected to an external booster pump to send the sodium hypochlorite solution to the sodium ferrate preparation device; the outlet of the electro-oxidation product water tank 48 serves as the outlet of the electro-oxidation device.The electro-oxidation inlet tank 41 and the electro-oxidation product tank 48 are equipped with microporous aeration and stirring. The second exhaust fan 50 and the first exhaust fan 49 are used to draw chlorine gas generated in the electro-oxidation inlet tank 41 and the electro-oxidation product tank 48 respectively, and the chlorine gas is transported to the absorption tower 51. In the absorption tower 51, the chlorine gas is absorbed by alkaline solution to obtain sodium hypochlorite solution. The electrode plates of the electrolytic cell 45 are porous electrode plates with a pore size of 20-50 μm and a thickness of 3-5 mm. The water flow direction in the electrolytic cell 45 is perpendicular to the electrode plates, and the wastewater passes through each electrode plate in sequence. The anode plate and the cathode plate are arranged alternately in sequence with a plate spacing of 1-2 cm. The current density of the electrolytic cell 45 is 600-800 A / m. 2 .

[0047] like Figure 5 As shown, the first hardening device includes a first reaction tank 61, a second reaction tank 62, a third reaction tank 63, an ultrafiltration feed water pump 64, an ultrafiltration membrane 65, a second product water tank 69, a second booster pump 70, and a first hardening device resin tank 71 connected in sequence. The bottoms of the first reaction tank 61 and the second reaction tank 62 are connected by a flow channel, and the upper parts of the second reaction tank 62 and the upper parts of the third reaction tank 63 are connected by an overflow channel. The first reaction tank 61 is equipped with a first agitator 66, the second reaction tank 62 with a second agitator 67, and the third reaction tank 63 with a third agitator 68. The outlet of the electro-oxidation product water tank 48 is connected to the inlet of the first reaction tank 61, which serves as the inlet of the first hardening removal device. The first reaction tank 61 is equipped with an alkali dosing pipe, which is connected to the alkali output port of the bipolar membrane electrodialysis device as the alkali dosing pipe for the first hardening removal device. The second reaction tank 62 is connected to a sodium carbonate dosing pipe. The inlet of the ultrafiltration feed pump 64 is connected to the third reaction tank 63, and the outlet of the ultrafiltration feed pump 64 is connected to the inlet of the ultrafiltration membrane 65. The concentrate outlet of filter membrane 65 is connected to the third reaction tank 63, the product water outlet of ultrafiltration membrane 65 is connected to the second product water tank 69, the inlet of the second booster pump 70 is connected to the second product water tank 69, and the outlet of the second booster pump 70 is connected to the resin tank 71 of the first hardening device. The outlet of the resin tank 71 of the first hardening device serves as the outlet of the first hardening device. The ultrafiltration membrane 65 of the first hardening device is a tubular ultrafiltration membrane with a filtration accuracy of 50nm. The resin tank 71 of the first hardening device uses a strong acid cation exchange resin. During operation, the ultrafiltration membrane 65 needs to discharge a portion of concentrate. The discharged concentrate enters an external sludge dewatering machine, which is a plate and frame filter press. The effluent after filtration by the plate and frame filter press is returned to the second product water tank 69. When the resin in the resin tank 71 of the first hardening device needs to be regenerated during use, it is regenerated using a mixed acid produced by a bipolar membrane electrodialysis device.

[0048] After the first hardening device removes hardness, the concentration of calcium and magnesium hardness is low. However, after the wastewater is concentrated by the second vacuum membrane distillation device, the concentration of calcium and magnesium hardness increases. Therefore, it is necessary to use the resin of the second hardening device to reduce the concentration of calcium and magnesium hardness and ensure the quality of the feed water for bipolar membrane electrodialysis. In this embodiment, the second hardening device has the same structure as the first hardening device.

[0049] Example 2

[0050] In specific implementation, the process flow of the coking wastewater membrane filtration concentrate treatment method of the present invention is as follows: Figure 1 As shown.

[0051] A method for treating coking wastewater membrane filtration concentrate, utilizing the coking wastewater membrane filtration concentrate treatment system described in Example 1, includes the following steps:

[0052] S1. Removal of organic pollutants and color from coking wastewater membrane filtration concentrate. First, activated carbon is used in the first adsorption unit to remove most of the organic pollutants from the coking wastewater membrane filtration concentrate. The effluent from the first adsorption unit enters a micro-electrolysis unit, where a mixed acid solution from bipolar membrane electrodialysis is added to adjust the pH of the influent to 2-3, further removing organic pollutants and color while generating ferrous ions. The permeate from the micro-electrolysis unit enters a Fenton unit, where ferrous ions and hydrogen peroxide further oxidize and remove organic pollutants and color from the wastewater, while also generating ferric ions. The specific process is as follows:

[0053] The coking wastewater membrane filtration concentrate is first stored in a concentrate tank, then pumped to the inlet tank 1 of the first adsorption device by a booster pump, and then pumped to the adsorption reaction tank 4 by an inlet pump 2. A powdered activated carbon solution with a mass concentration of 5-10% is added to the adsorption reaction tank 4 to remove most of the organic pollutants in the wastewater. The wastewater in the adsorption reaction tank 4 is sent to the filtration device 5 by the first booster pump 7. The powdered activated carbon is separated by filtration in the filtration device 5. Part of the concentrated water after separation is returned to the adsorption reaction tank 4, and part is discharged to the external powdered activated carbon dewatering device (such as the plate and frame filter press in this embodiment) during maintenance and cleaning. The dewatered clear liquid flows to the first product water tank 6. The wastewater in the first product water tank 6 is pumped to the micro-electrolysis device.

[0054] Wastewater from the first product tank 6 enters the pipeline mixer 13 through the micro-electrolysis inlet pipe 11. At the same time, acid solution is added to the pipeline mixer 13 through the acid dosing pipe 12. The acid solution comes from the output port of the mixed acid solution (HCl solution and H2SO4 solution) of the bipolar membrane electrodialysis. The micro-electrolysis reactor 10 is equipped with a pH meter to control the pH of the influent to the micro-electrolysis reactor 10 to be 2-3. The micro-electrolysis reactor 10 is filled with iron-carbon packing material. The iron-carbon micro-electrolysis reaction is used to further remove organic pollutants and color from the wastewater, while generating a large amount of ferrous ions. The product water from the micro-electrolysis reactor 10 enters the Fenton reactor 26.

[0055] The Fenton reactor 26 utilizes ferrous ions and hydrogen peroxide solution added in the bottom dosing pipe of the Fenton reactor 26 to further oxidize and remove organic pollutants and color from the wastewater, while generating a large amount of ferric ions.

[0056] Both the micro-electrolysis reactor 10 and the Fenton reactor 26 use air compressors for aeration and stirring. The inlet air pressure of the micro-electrolysis reactor 10 is 0.4-0.7 MPa, and the aeration pressure of the Fenton reactor 26 is 0.3-0.4 MPa.

[0057] S2. Removal of iron ions. The effluent from the Fenton unit enters neutralization tank 35. The pH in neutralization tank 35 is adjusted to 7-8 using an alkaline solution from the bipolar membrane electrodialysis unit. After adding flocculant to flocculation tank 36, sedimentation occurs in sedimentation tank 37. The effluent from sedimentation tank 37 enters the electro-oxidation unit. The ferric hydroxide precipitate in sedimentation tank 37 enters the sodium ferrate preparation unit.

[0058] The effluent from the Fenton unit enters the neutralization tank 35 from the Fenton reactor effluent pipe 33. An alkaline solution is added to the neutralization tank 35. The alkaline solution comes from the alkaline solution output port of the bipolar membrane electrodialysis. The pH of the wastewater in the neutralization tank 35 is adjusted to 7-8. The neutralization tank 35 is aerated and stirred by the second blower 34 to further oxidize the unoxidized ferrous iron to ferric iron. After that, the effluent from the neutralization tank 35 overflows into the flocculation tank 36.

[0059] Flocculant (anionic polyacrylamide PAM with a mass concentration of 0.1-0.2%) is added to flocculation tank 36 and stirred by flocculation tank agitator 39. The mixture then enters sedimentation tank 37 through sedimentation tank inlet pipe. After sedimentation in sedimentation tank 37, the effluent from sedimentation tank 37 enters electro-oxidation device. The ferric hydroxide precipitate in the sludge hopper of sedimentation tank 37 is transported to sodium ferrate preparation device by sludge discharge pump 38.

[0060] S3. Removes ammonia nitrogen, COD, color, and hardness from wastewater, producing sodium hypochlorite solution. The electro-oxidation unit removes ammonia nitrogen, COD, and color from the wastewater, while simultaneously generating sodium hypochlorite solution using alkaline solution from the bipolar membrane electrodialysis unit. The sodium hypochlorite solution enters the sodium ferrate preparation unit, and the electro-oxidation permeate enters the first hardness removal unit. The first hardness removal unit uses chemical precipitation and resin softening to remove hardness from the wastewater. The effluent after hardness removal enters the nanofiltration unit.

[0061] The effluent from sedimentation tank 37 is first stored in electro-oxidation inlet tank 41, and then pumped to electrolytic cell 45 by electro-oxidation inlet pump 43. Electrolytic cell 45 is equipped with porous electrode plates, each 3–5 mm thick, with alternating anode and cathode plates spaced 1–2 cm apart. Electrolytic cell 45 is connected to power supply 46, and the current density of electrolytic cell 45 is 600–800 A / m³. 2 When wastewater passes through porous electrode plates, it is oxidized to remove ammonia nitrogen, COD, and color. The tail gas generated during the oxidation process (mainly containing air, chlorine, and a small amount of hydrogen) first enters the electro-oxidation feed tank 41 and is absorbed by the solution. The unabsorbed tail gas is sent to the absorption tower 51 by the second exhaust fan 50. At the same time, the product water of the electro-oxidation device first enters the electro-oxidation product water tank 48 and then is sent to the first hardening removal device. Both the electro-oxidation feed tank 41 and the electro-oxidation product water tank 48 are aerated, blown off, and stirred by the third blower 42. The tail gas in the electro-oxidation product water tank 48 is sent to the absorption tower 51 by the first exhaust fan 49. The absorption tower 51 uses alkaline spray to absorb chlorine and produce sodium hypochlorite solution. The alkaline solution in the alkaline solution tank 52 comes from the alkaline solution of the bipolar membrane electrodialysis device. The alkaline solution is sent to the absorption tower 51 by the spray pump 53. Multiple sets of alkaline water tanks 52 are set up. First, the empty alkaline water tank 52 is connected to the alkaline output port of the bipolar membrane electrodialysis device to collect sodium hydroxide solution. Then, the alkaline water tank 52 containing sodium hydroxide solution is connected to the inlet of the spray pump 53 to absorb chlorine. When the sodium hypochlorite solution produced by the absorption of chlorine by one set of alkaline water tanks 52 reaches a mass concentration of 10%, the next set of alkaline water tanks 52 containing sodium hydroxide solution is switched to the inlet of the spray pump 53 to continue running the absorption tower 51. The alkaline water tank 52 containing sodium hypochlorite solution is connected to an external booster pump to send the sodium hypochlorite solution to the sodium ferrate preparation device. In addition to the alkaline solution obtained from the bipolar membrane electrodialysis, sodium hydroxide solid can also be added to the alkaline water tank 52 to increase the concentration of the alkaline solution, thereby improving the efficiency of chlorine absorption. The electro-oxidation produced water enters the first reaction tank 61 of the first hardening device. The tail gas after the absorption tower 51 absorbs chlorine is mainly air and a small amount of hydrogen, which is discharged from the exhaust port of the absorption tower 51 to the outside of the system.

[0062] Alkali solution is added to the first reaction tank 61 from the alkali output port of the bipolar membrane electrodialysis device. Sodium carbonate solution is added to the second reaction tank 62. Wastewater in the third reaction tank 63 is sent to the ultrafiltration membrane 65 for filtration and separation via the ultrafiltration feed pump 64. Part of the concentrated water produced by the ultrafiltration membrane 65 is returned to the third reaction tank 63, and part is discharged to the sludge dewatering machine for dewatering. The dewatered clear liquid flows to the second product water tank 69. The product water of the ultrafiltration membrane 65 enters the second product water tank 69. The wastewater in the second product water tank 69 is sent to the first hardening device resin tank 71 by the second lift pump 70. The first hardening device resin tank 71 is filled with strong acid cation exchange resin. After the resin exchanges calcium and magnesium ions in the wastewater, it releases hydrogen ions to adjust the pH of the wastewater. The product water of the first hardening device resin tank 71 enters the feed water tank of the nanofiltration device.

[0063] S4. Obtain sodium chloride crystals and sodium sulfate decahydrate crystals. The permeate from the first hardening unit is filtered through a nanofiltration unit to obtain nanofiltration permeate, whose main component is sodium chloride. This nanofiltration permeate enters the first vacuum membrane distillation unit. The concentrated water from the first vacuum membrane distillation unit enters the crystallizer to obtain sodium chloride crystals. A portion of the mother liquor output from the crystallizer is returned to the first vacuum membrane distillation unit, and the other portion enters the second adsorption unit. The permeate from the first vacuum membrane distillation unit enters the permeate tank. The nanofiltration concentrate enters the second vacuum membrane distillation unit for further concentration. The concentrated water from the second vacuum membrane distillation unit enters the low-temperature crystallizer to obtain sodium sulfate decahydrate crystals. The permeate from the second vacuum membrane distillation unit enters the permeate tank. Most of the mother liquor from the low-temperature crystallizer is returned to the second vacuum membrane distillation unit, and the remaining portion of the mother liquor from the low-temperature crystallizer enters the second adsorption unit.

[0064] The permeate from the first hardening unit enters the nanofiltration unit, which separates monovalent and divalent salts in the wastewater to obtain permeate and concentrate. The main component of the nanofiltration permeate is sodium chloride. This permeate then enters the first vacuum membrane distillation unit, which uses waste heat from the steel plant to heat the influent, maintaining its temperature between 50 and 70°C. The heated influent is then separated into concentrate and water vapor. The water vapor is condensed to obtain permeate. The concentrate from the first vacuum membrane distillation unit enters the crystallizer to obtain sodium chloride crystals. Part of the output mother liquor is returned to the first vacuum membrane distillation unit for further concentration, and the other part of the mother liquor output from the crystallizer enters the second adsorption unit. The permeate from the first vacuum membrane distillation unit enters the permeate tank, and the concentrated water output from the nanofiltration unit enters the second vacuum membrane distillation unit. The second vacuum membrane distillation unit also uses the waste heat from the steel plant for heating, so that the inlet water temperature of the second vacuum membrane distillation unit is controlled at 50-70°C. The concentrated water output from the nanofiltration unit is further concentrated by the second vacuum membrane distillation unit and then enters the low-temperature crystallizer to obtain sodium sulfate decahydrate crystals. Most of the mother liquor output from the low-temperature crystallizer is returned to the second vacuum membrane distillation unit, and the remaining part of the mother liquor enters the second adsorption unit.

[0065] S5. Sequential removal of organic matter and hardness. In the second adsorption unit, granular activated carbon and macroporous adsorption resin are used to adsorb and remove organic matter from the mother liquor output from the low-temperature crystallizer. The effluent from the second adsorption unit enters the second hardness removal unit, where resin softening is used to remove hardness. The effluent from the second hardness removal unit then enters the bipolar membrane electrodialysis unit.

[0066] The second adsorption device includes an inlet tank, a booster pump, an adsorption tank, and a resin tank. The second adsorption device uses granular activated carbon and resin for adsorption. The mother liquor output from the low-temperature crystallizer first enters the inlet tank of the second adsorption device and is then pumped to the adsorption tank. The adsorption tank is filled with granular activated carbon. The effluent from the adsorption tank enters the resin tank, which is filled with macroporous adsorption resin. This macroporous adsorption resin is a moderately polar macroporous adsorption resin containing ester groups, using multifunctional methacrylate as a crosslinking agent. Its surface has both hydrophobic and hydrophilic parts. The organic matter in the mother liquor is removed through adsorption by the granular activated carbon and resin of the second adsorption device. The resin tank structure of the second adsorption device is the same as that of the resin tank 71 of the first hardening device, but the type of resin filled is different (the resin tank 71 of the first hardening device is filled with ion exchange resin, and the second adsorption device is filled with macroporous adsorption resin). The resin adsorption is increased to enhance the removal effect. Two-stage adsorption (activated carbon adsorption + resin adsorption) is used to improve the removal effect of organic matter. The bipolar membrane electrodialysis device has high requirements for the quality of the influent water. The organic matter concentration is low after the treatment in step S1, but the organic matter concentration increases after the second vacuum membrane distillation device and the low temperature crystallizer. Therefore, it is still necessary to further reduce the organic matter concentration in step S5.

[0067] The effluent from the second adsorption device enters the second hardening removal device. The resin tank of the second hardening removal device is filled with strong acidic cation exchange resin. The hardness in the effluent from the second adsorption device is removed by the resin of the second hardening removal device. The effluent from the second hardening removal device then enters the bipolar membrane electrodialysis device.

[0068] S6. A bipolar membrane electrodialysis device produces a mixed acid of hydrochloric acid and sulfuric acid, as well as a sodium hydroxide solution. The mixed acid is recycled to the micro-electrolysis device. Part of the sodium hydroxide solution is used to adjust the pH in the neutralization tank 35, part is used to absorb tail gas in the alkaline water tank 52 of the electro-oxidation device, and the remaining part is used in the sodium ferrate preparation device to prepare a sodium ferrate solution together with ferric hydroxide from the flocculation sedimentation tank and sodium hypochlorite from the electro-oxidation device.

[0069] In a bipolar membrane electrodialysis unit, sodium, sulfate, and chloride ions in wastewater are separated by an ion exchange membrane to obtain a mixed acid of hydrochloric acid and sulfuric acid, as well as a sodium hydroxide solution. The sodium hydroxide solution has a mass concentration of 8-10%. The mixed acid is reused in the micro-electrolysis unit for acid adjustment, resin regeneration (internal or external), and membrane cleaning (internal or external). Part of the alkaline solution is used in the neutralization tank 35 to adjust the pH and in the alkaline water tank 52 of the electro-oxidation unit to absorb tail gas. The other part is used in a sodium ferrate preparation unit, where ferric hydroxide is first washed and filtered, and then sodium ferrate solution is prepared at low temperature using sodium hydroxide solution, washed ferric hydroxide, and sodium hypochlorite solution. The resulting sodium ferrate solution is used in the treatment of coking wastewater or other wastewater, and can be used as a strong oxidant and flocculant. Sodium chloride impurities in the sodium ferrate solution can be removed by recrystallization, thereby purifying the sodium ferrate solution.

[0070] Fe 3+ +3OH - →Fe(OH)3

[0071] 2Fe(OH)3+3NaClO+4NaOH→2Na2FeO4+3NaCl+5H2O

[0072] Example 3

[0073] The coking wastewater membrane filtration concentrate from a steel plant in Hubei Province was selected as the treatment object of this invention. Example 2 was implemented. The water quality of the coking wastewater membrane filtration concentrate was as follows: pH 7.0–8.5, SS concentration 20–70 mg / L, conductivity 15500–18000 μS / cm, COD (chemical oxygen demand) concentration 480–650 mg / L, TDS (total dissolved solids) concentration 12800–15500 mg / L, ammonia nitrogen concentration 35–60 mg / L, sulfate concentration 5000–7000 mg / L, chloride ion concentration 3500–5000 mg / L, and Ca... 2+ Concentration of 260–280 mg / L, Mg 2+ The concentration is 80–100 mg / L.

[0074] In step S1: After the coking wastewater membrane filtration concentrate is treated by the first adsorption device, the effluent COD is 150-170 mg / L. The product water from the first adsorption device enters the micro-electrolysis reactor 10 and the Fenton reactor 26 for further treatment.

[0075] In step S2: the COD of the effluent from sedimentation tank 37 is 100-120 mg / L. After treatment by the electro-oxidation device, the COD of the effluent from sedimentation tank 37 is less than 30 mg / L and the ammonia nitrogen is less than 0.2 mg / L.

[0076] In step S3: the effluent from the electro-oxidation device first undergoes chemical precipitation to remove hardness in the first hardness removal device. The hardness of the effluent from the ultrafiltration membrane 65 in the first hardness removal device is less than 20 mg / L, and the hardness of the effluent from the resin tank 71 of the first hardness removal device is less than 5 mg / L.

[0077] In step S4: the effluent from the first hardening device is treated by a nanofiltration device, the nanofiltration permeate is concentrated by a first vacuum membrane distillation, the concentrated water from the first vacuum membrane distillation is crystallized in a crystallizer to obtain sodium chloride, and the permeate from the first vacuum membrane distillation enters a permeate tank for storage, where the permeate meets the standards for reuse; the nanofiltration concentrated water is treated by a second vacuum membrane distillation device and then crystallized in a low-temperature crystallizer to obtain sodium sulfate decahydrate.

[0078] In step S5: Part of the mother liquor discharged from the low-temperature crystallizer is returned to the second vacuum membrane distillation device, and part of it enters the second adsorption device. The COD of the water effluent from the second adsorption device is less than 10 mg / L. The water effluent from the second adsorption device enters the second hardness removal device. The hardness of the water effluent from the second hardness removal device is less than 5 mg / L.

[0079] In step S6: the effluent from the second hardening device enters the bipolar membrane electrodialysis device, and finally a mixed acid of sulfuric acid solution and hydrochloric acid solution and a sodium hydroxide solution with a mass concentration of 8-10% are obtained; the sodium ferrate preparation device uses the iron hydroxide, sodium hydroxide and sodium hypochlorite generated by the system to prepare sodium ferrate solution at low temperature, and the sodium ferrate solution is used in the pretreatment of coking wastewater.

[0080] This process achieves a resource utilization rate of over 95% for coking wastewater membrane filtration concentrate, reducing the operating costs of the treatment system and essentially achieving zero discharge of the concentrate.

[0081] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A coking wastewater membrane filtration concentrate treatment system, comprising a first adsorption device, characterized in that, The outlet of the first adsorption device is connected to the micro-electrolysis inlet pipe (11) of the micro-electrolysis device, the outlet of the micro-electrolysis device is connected to the inlet of the Fenton device, the outlet of the Fenton device is connected to the inlet of the neutralization tank (35), the outlet of the neutralization tank (35) is connected to the inlet of the flocculation sedimentation tank, the ferric hydroxide outlet of the flocculation sedimentation tank is connected to the sodium ferrate preparation device, the outlet of the flocculation sedimentation tank is connected to the inlet of the electro-oxidation device, the sodium hypochlorite outlet of the electro-oxidation device is connected to the sodium ferrate preparation device, the outlet of the electro-oxidation device is connected to the inlet of the first hardening device, the outlet of the first hardening device is connected to the inlet of the nanofiltration device, the nanofiltration product outlet of the nanofiltration device is connected to the inlet of the first vacuum membrane distillation device, the concentrated water outlet of the first vacuum membrane distillation device is connected to the crystallizer, and the mother liquor outlet of the crystallizer is connected to the inlet of the first vacuum membrane distillation device and the inlet of the second adsorption device, respectively. The product water outlet of the membrane distillation device is connected to the product water tank, the concentrate outlet of the nanofiltration device is connected to the inlet of the second vacuum membrane distillation device, the product water outlet of the second vacuum membrane distillation device is connected to the product water tank, the concentrate outlet of the second vacuum membrane distillation device is connected to the low temperature crystallizer, the mother liquor outlet of the low temperature crystallizer is connected to the inlet of the second vacuum membrane distillation device and the inlet of the second adsorption device, respectively, the outlet of the second adsorption device is connected to the inlet of the second hardening device, the outlet of the second hardening device is connected to the inlet of the bipolar membrane electrodialysis device, the alkaline outlet of the bipolar membrane electrodialysis device is connected to the alkaline dosing pipe of the neutralization tank (35), the alkaline input port of the electro-oxidation device, the alkaline dosing pipe of the first hardening device and the sodium ferrate preparation device, respectively, the acid outlet of the bipolar membrane electrodialysis device is connected to the acid dosing pipe (12) of the micro-electrolysis device, and the fresh water outlet of the bipolar membrane electrodialysis device is connected to the inlet of the nanofiltration device; The heat source for both the first and second vacuum membrane distillation units is waste heat from the steel plant, which keeps the wastewater operating temperature at 50–70°C.

2. The coking wastewater membrane filtration concentrate treatment system according to claim 1, characterized in that, The first adsorption device includes a first adsorption device inlet tank (1), the inlet of the first adsorption device inlet tank (1) serves as the inlet of the first adsorption device, the first adsorption device inlet tank (1) is connected to the first water tank of the adsorption reaction tank (4) through an inlet pump (2), the bottom of the first water tank of the adsorption reaction tank (4) and the bottom of the second water tank of the adsorption reaction tank (4) are connected through a flow channel, aeration pipes are installed at the bottom of the first water tank and the second water tank of the adsorption reaction tank (4), the inlet of the aeration pipe is connected to the first blower (3), the second water tank of the adsorption reaction tank (4) is connected to the inlet of the filter device (5) through a first lift pump (7), the concentrated water outlet of the filter device (5) is connected to the first water tank of the adsorption reaction tank (4), the product water outlet of the filter device (5) is connected to the first product water tank (6), the drain outlet of the filter device (5) is connected to an external sludge dewatering machine, and the outlet of the first product water tank (6) is the outlet of the first adsorption device.

3. The coking wastewater membrane filtration concentrate treatment system according to claim 2, characterized in that, The micro-electrolysis device includes a pipe mixer (13), one inlet of which is connected to the outlet of the micro-electrolysis water inlet pipe (11), and the other inlet of which is connected to the acid dosing pipe (12). The outlet of the pipe mixer (13) is connected to the inlet of the micro-electrolysis reactor water inlet pipe (14). The outlet of the micro-electrolysis reactor water inlet pipe (14) extends to the lower part of the micro-electrolysis reactor (10). Multiple packing support layers (23) are provided inside the micro-electrolysis reactor (10). Block packing is provided on the packing support layers (23). A micro-electrolysis reactor aeration pipe (19) is provided below each packing support layer (23). The bottom of the reactor is provided with a first baffle (20), which is located directly below the outlet of the inlet pipe (14) of the micro-electrolysis reactor. The micro-electrolysis reactor inspection port (18) is provided on the side wall of the micro-electrolysis reactor (10) corresponding to each packing support layer (23). A first separator (15) is provided above the uppermost packing support layer (23). A first overflow weir (16) is provided above the first separator (15). The first overflow weir (16) is located in the upper part of the micro-electrolysis reactor (10). The first overflow weir (16) is connected to the outlet pipe (24) of the micro-electrolysis reactor. The outlet of the outlet pipe (24) of the micro-electrolysis reactor serves as the outlet of the micro-electrolysis device.

4. The coking wastewater membrane filtration concentrate treatment system according to claim 3, characterized in that, The Fenton device includes a Fenton reactor inlet pipe (25), the inlet of which serves as the inlet of the Fenton reactor and is connected to the outlet of the micro-electrolysis reactor outlet pipe (24). The outlet of the Fenton reactor inlet pipe (25) extends to the lower part of the Fenton reactor (26). An aeration pipe and a second baffle (31) are installed at the bottom of the Fenton reactor (26). The second baffle (31) is located directly below the outlet of the Fenton reactor inlet pipe (25). A second overflow weir (27) is located at the upper part of the Fenton reactor (26). A second separator (32) is located below the second overflow weir (27). The second overflow weir (27) is connected to the inlet of the Fenton reactor outlet pipe (33). The outlet of the Fenton reactor outlet pipe (33) is the outlet of the Fenton device. A hydrogen peroxide solution dosing pipe is connected to the bottom of the Fenton reactor (26).

5. The coking wastewater membrane filtration concentrate treatment system according to claim 4, characterized in that, The neutralization tank (35) is connected to the outlet of the Fenton reactor outlet pipe (33). An aeration pipe is installed at the bottom of the neutralization tank (35). The aeration pipe of the neutralization tank (35) is connected to the second blower (34). The bottom of the neutralization tank (35) and the bottom of the flocculation tank (36) are connected through a flow channel. The flow channel serves as the outlet of the neutralization tank (35) and the inlet of the flocculation sedimentation tank. The flocculation sedimentation tank includes a flocculation tank (36), which is equipped with a flocculation tank agitator (39). The flocculation tank (36) is connected to a flocculant dosing pipe. The overflow port at the top of the flocculation tank (36) is connected to the inlet of the sedimentation tank (37). The outlet of the inlet of the sedimentation tank (37) extends to the middle of the sedimentation tank (37). A sedimentation tank sludge hopper is provided at the bottom of the sedimentation tank (37). The sedimentation tank sludge hopper is located below the outlet of the inlet of the sedimentation tank (37). The sedimentation tank sludge hopper is connected to the inlet of a sludge pump (38). The outlet of the sludge pump (38) serves as the output port of ferric hydroxide for the flocculation sedimentation tank. A sedimentation tank outlet (40) is provided at the top of the sedimentation tank (37). The sedimentation tank outlet (40) serves as the outlet of the flocculation sedimentation tank.

6. The coking wastewater membrane filtration concentrate treatment system according to claim 5, characterized in that, The electro-oxidation device includes an electro-oxidation inlet tank (41), the inlet of which serves as the inlet for the electro-oxidation device. The top of the electro-oxidation inlet tank (41) is closed, and an aeration pipe is installed at the bottom. The aeration pipe of the electro-oxidation inlet tank (41) is connected to a third blower (42). The inlet of a second exhaust fan (50) is connected to the space above the liquid surface inside the electro-oxidation inlet tank (41), and the outlet of the second exhaust fan (50) is connected to the air inlet of the absorption tower (51). The inlet of the inlet pump (43) is connected to the outlet of the electro-oxidation inlet tank (41), and the outlet of the electro-oxidation inlet pump (43) is connected to the inlet of the filter (44). The outlet of the filter (44) is connected to the inlet of the electrolytic cell (45). The outlet of the electrolytic cell (45) is connected to the electro-oxidation inlet tank (41) through the electrolytic cell exhaust pipe (47), and the outlet of the electrolytic cell exhaust pipe (47) is located below the liquid surface of the electro-oxidation inlet tank (41). The outlet of the electrolytic cell (45) is connected to the electro-oxidation product water tank (48). The top of the box (48) is closed. The inlet of the first exhaust fan (49) is connected to the space above the liquid surface inside the electro-oxidation product water tank (48). The outlet of the first exhaust fan (49) is connected to the air inlet of the absorption tower (51). The bottom of the absorption tower (51) is connected to the alkaline water tank (52). Multiple alkaline water tanks (52) are provided. When the alkaline water tank (52) is empty, the inlet of the alkaline water tank (52) serves as the alkaline input port of the electro-oxidation device. When the alkaline water tank (52) is filled with sodium hydroxide solution, the inlet of the alkaline water tank (52) serves as the alkaline input port of the electro-oxidation device. The outlet of the alkaline solution in the bipolar membrane electrodialysis device is disconnected from the alkaline solution outlet, and the outlet of the alkaline solution tank (52) is connected to the inlet of the spray pump (53). The outlet of the spray pump (53) is connected to the upper inlet of the absorption tower (51), and the inlet of the alkaline solution tank (52) is connected to the outlet of the absorption tower (51). When the concentration of sodium hypochlorite solution in the alkaline solution tank (52) reaches the set value, the outlet of the alkaline solution tank (52) becomes the sodium hypochlorite outlet of the electro-oxidation device, and the outlet of the electro-oxidation product water tank (48) becomes the outlet of the electro-oxidation device.

7. The coking wastewater membrane filtration concentrate treatment system according to claim 6, characterized in that, The first hardening removal device includes a first reaction tank (61) connected in sequence. The bottom of the first reaction tank (61) and the bottom of the second reaction tank (62) are connected through a flow channel. The upper part of the second reaction tank (62) and the upper part of the third reaction tank (63) are connected through an overflow channel. The first reaction tank (61) is equipped with a first stirrer (66), the second reaction tank (62) is equipped with a second stirrer (67), and the third reaction tank (63) is equipped with a third stirrer (68). The inlet of the first reaction tank (61) serves as the inlet of the first hardening removal device. The first reaction tank (61) is equipped with an alkali dosing pipe, and the alkali in the first reaction tank (61) is... The liquid dosing pipe serves as the alkali dosing pipe for the first hardening device. The second reaction tank (62) is connected to the sodium carbonate dosing pipe. The third reaction tank (63) is connected to the inlet of the ultrafiltration membrane (65) via the ultrafiltration feed pump (64). The concentrate outlet of the ultrafiltration membrane (65) is connected to the third reaction tank (63). The product water outlet of the ultrafiltration membrane (65) is connected to the second product water tank (69). The second product water tank (69) is connected to the resin tank (71) of the first hardening device via the second booster pump (70). The resin tank (71) of the first hardening device is filled with strong acidic cation exchange resin. The outlet of the resin tank (71) of the first hardening device serves as the outlet of the first hardening device.

8. A method for treating coking wastewater membrane filtration concentrate, utilizing the coking wastewater membrane filtration concentrate treatment system described in claim 7, characterized by the following steps: include: S1. First, most of the organic pollutants in the coking wastewater membrane filtration concentrate are removed by activated carbon in the first adsorption device. The effluent from the first adsorption unit enters the micro-electrolysis unit. An acid solution is added to adjust the pH of the influent to the micro-electrolysis unit to 2-3, which further removes organic pollutants and color from the wastewater while generating ferrous ions. The product water from the micro-electrolysis unit enters the Fenton unit. The Fenton unit uses ferrous ions and hydrogen peroxide to further oxidize and remove organic pollutants and color from the wastewater, while generating ferric ions. S2. The effluent from the Fenton device enters the neutralization tank (35). The pH in the neutralization tank (35) is adjusted to 7-8 using an alkaline solution. After adding flocculant in the flocculation tank (36), the effluent is settled in the sedimentation tank (37). The effluent from the sedimentation tank (37) enters the electro-oxidation device. The ferric hydroxide precipitate in the sedimentation tank (37) enters the sodium ferrate preparation device. S3. The electro-oxidation unit removes ammonia nitrogen, COD and color from the wastewater. At the same time, it uses an alkaline solution to generate sodium hypochlorite solution. The sodium hypochlorite solution enters the sodium ferrate preparation unit. The electro-oxidation product enters the first hardening removal unit. The first hardening removal unit uses chemical precipitation and resin softening to remove hardness from the wastewater. The hardened effluent enters the nanofiltration unit. S4. The permeate from the first hardening unit is filtered through a nanofiltration unit to obtain nanofiltration permeate with sodium chloride as the main component. The nanofiltration permeate enters the first vacuum membrane distillation unit. The concentrate from the first vacuum membrane distillation unit enters the crystallizer to obtain sodium chloride crystals. Part of the mother liquor output from the crystallizer is returned to the first vacuum membrane distillation unit, and the other part of the mother liquor output from the crystallizer enters the second adsorption unit. The permeate from the first vacuum membrane distillation unit enters the permeate tank. The nanofiltration concentrate enters the second vacuum membrane distillation unit for further concentration. The concentrate from the second vacuum membrane distillation unit enters the low-temperature crystallizer to obtain sodium sulfate decahydrate crystals. The permeate from the second vacuum membrane distillation unit enters the permeate tank. Most of the mother liquor from the low-temperature crystallizer is returned to the second vacuum membrane distillation unit, and the remaining part of the mother liquor from the low-temperature crystallizer enters the second adsorption unit. S5. In the second adsorption unit, granular activated carbon and macroporous adsorption resin are used to adsorb and remove organic matter in the mother liquor output from the low-temperature crystallizer. The effluent from the second adsorption unit enters the second hardening removal unit and the hardness in the wastewater is removed by resin softening. The effluent from the second hardening removal unit enters the bipolar membrane electrodialysis unit. S6. A mixed acid of hydrochloric acid and sulfuric acid and a sodium hydroxide solution are prepared by a bipolar membrane electrodialysis device. The mixed acid is recycled to a micro-electrolysis device. Part of the sodium hydroxide solution is used in a neutralization tank (35) to adjust the pH, part is used in an alkaline water tank (52) of an electro-oxidation device to absorb tail gas, and the remaining part is used in a sodium ferrate preparation device to prepare a sodium ferrate solution with ferric hydroxide from a flocculation sedimentation tank and sodium hypochlorite from an electro-oxidation device.

9. A method for treating coking wastewater membrane filtration concentrate according to claim 8, characterized in that: In step S3, multiple sets of alkaline water tanks (52) are set up. When the mass concentration of sodium hypochlorite solution reaches the set concentration, the solution is switched to the next set of alkaline water tanks (52) and then transported to the sodium ferrate preparation device by a booster pump. In step S6, the mass concentration of sodium hydroxide solution prepared by bipolar membrane electrodialysis is 8-10%. The mixed acid is used for pH adjustment of the micro-electrolysis device, regeneration of resin inside or outside the system, and membrane cleaning inside or outside the system.

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