Fluidized bed-double membrane method deep fluorine removal device and use method

Abstract

The application discloses a kind of fluidized bed-double membrane method deep fluorine removal device, including several fluidized bed reactors, the water inlet of fluidized bed reactor is connected with water inlet pipe by first electromagnetic valve, stainless steel filter screen is equipped at the lower end of fluidized bed reactor, load layer seed is equipped below stainless steel filter screen, and fluidized bed clarification zone is above stainless steel filter screen, the ultrafiltration water inlet of first ultrafiltration membrane column is connected with the water outlet of fluidized bed by first high-pressure diaphragm pump, the ultrafiltration water outlet of first ultrafiltration membrane column is communicated with adjusting tank, adjusting tank is connected with the reverse osmosis water inlet of reverse osmosis membrane column by second high-pressure diaphragm pump, and the reverse osmosis water outlet of reverse osmosis membrane column is connected with water production tank.The fluoride ion concentration of the present application is far higher than 10mg / L of GB 30484-2013 battery industry pollutant discharge standard, and reaches 1mg / L below stably, so that the water quality of effluent meets semiconductor industry reuse water standard, and the reuse rate of industrial water is improved.

Description

Technical Field

[0001] This invention relates to a fluidized bed-dual membrane deep defluorination device and its usage method, belonging to the field of wastewater treatment. Background Technology

[0002] Fluoride-containing wastewater refers to wastewater containing fluorides generated during industrial production processes. With the accelerating pace of global industrialization and the rapid development of industries such as fluorochemicals, electronics, metallurgy, steelmaking, aluminum electrolysis, chemicals, and pesticides, the discharge of fluoride-containing wastewater has increased year by year. The treatment of fluoride-containing wastewater has become a crucial issue in the current environmental protection field. Due to the high biotoxicity and environmental persistence of fluorides, if fluoride-containing wastewater is discharged directly without proper treatment, it will cause serious harm to water bodies, soil, and human health. The fluorochemical industry is one of the main sources of fluoride-containing wastewater. During the production of fluoride salts and hydrofluoric acid, large amounts of fluorides enter the wastewater, resulting in extremely high concentrations of fluoride ions, sometimes reaching several thousand milligrams per liter. In electronic manufacturing processes such as semiconductors and electroplating, the generation of fluoride-containing wastewater is unavoidable due to the use of fluoride chemicals. This wastewater typically contains high concentrations of fluoride ions. In metallurgical and steelmaking processes, especially in aluminum electrolysis and steel production, fluorides are widely used as fluxes, leading to large-scale discharges of fluoride-containing wastewater.

[0003] Fluoride is a potent bioaccumulative toxin that can accumulate through the food chain, causing severe harm to aquatic organisms and soil microorganisms. If fluoride-containing wastewater seeps into the soil, fluoride can form insoluble compounds with calcium and magnesium ions, leading to soil structure damage, affecting crop growth, and consequently impacting agricultural production. Excessive fluoride intake in humans can cause fluorosis, leading to a range of health problems such as osteoporosis, arthritis, and dental fluorosis. The World Health Organization sets the upper limit for fluoride content in drinking water at 1.5 mg / L, while my country's "Standards for Drinking Water Quality" (GB5749-2022) sets the limit at 1 mg / L.

[0004] Commonly used methods for treating fluoride-containing wastewater include chemical precipitation, electrochemical methods, adsorption, and ion exchange resin methods. Chemical precipitation involves adding chemical agents to the wastewater, causing fluorides to react with the agents to form insoluble calcium fluoride precipitates, thus removing fluoride ions from the water. Lime is typically used as a precipitant. However, due to the low solubility of calcium fluoride in water, this method has limited removal efficiency, and the fluoride concentration in the treated effluent often fails to meet environmental protection requirements. Electrochemical methods utilize electrode reactions to remove fluoride ions, achieving high defluorination efficiency, but typically involve high equipment costs and complex operation, making them suitable for high-precision wastewater treatment applications. Adsorption methods use adsorbents (such as activated carbon and bauxite) to adsorb fluoride ions from the water, thereby reducing the fluoride content. They offer advantages such as simple operation and relatively low cost, but adsorbent regeneration and post-treatment disposal remain challenges. Ion exchange removes fluoride ions from wastewater using ion exchange resins, achieving a high fluoride removal efficiency. However, the resins are expensive and require regular regeneration, making it suitable for treating small volumes of high-concentration fluoride-containing wastewater.

[0005] Although the aforementioned defluoridation methods have been widely used in practice, several problems remain to be addressed. First, while traditional methods such as chemical precipitation and coagulation sedimentation are low-cost, they produce large amounts of sludge, leading to significant secondary pollution, and sometimes the treatment effect fails to meet emission standards. Second, while newer technologies such as electrochemical and ion exchange offer high defluoridation efficiency, they are costly and have limited applicability. The treatment of fluoride-containing wastewater should focus on developing more efficient, economical, and environmentally friendly treatment technologies, combining multiple treatment methods in a multi-stage process to achieve efficient treatment of fluoride-containing wastewater of varying concentrations and sources. Furthermore, the selection of treatment technologies should emphasize resource recovery and recycling to further reduce environmental impact. Summary of the Invention

[0006] Purpose of the invention: In order to overcome the shortcomings of the existing technology, the present invention provides a fluidized bed-dual membrane deep defluorination device and its usage method. The effluent fluoride concentration is much higher than the 10 mg / L of the GB 30484-2013 battery industry pollutant emission standard, and is stably below 1 mg / L, so that the effluent water quality meets the semiconductor industry's water reuse standards and improves the reuse rate of industrial water.

[0007] Technical Solution: To solve the above-mentioned technical problems, the present invention provides a fluidized bed-dual membrane deep defluorination device, comprising several fluidized bed reactors. The inlet of each fluidized bed reactor is connected to an inlet pipe via a first solenoid valve. A stainless steel filter screen is provided at the lower end of the fluidized bed reactor, and seed crystals are placed below the stainless steel filter screen. A fluidized bed clarification zone is located above the stainless steel filter screen. The outlet of the fluidized bed is connected to the ultrafiltration inlet of a first ultrafiltration membrane column via a first high-pressure diaphragm pump. The ultrafiltration product outlet of the first ultrafiltration membrane column is connected to a regulating tank. The regulating tank is connected to a second high-pressure diaphragm pump via a third high-pressure diaphragm pump. Two high-pressure diaphragm pumps are connected to the reverse osmosis inlet of the reverse osmosis membrane column, and the reverse osmosis outlet of the reverse osmosis membrane column is connected to the product water tank. The system also includes a concentrate tank, whose inlet is connected to the upper end of the ultrafiltration membrane column and the lower end of the reverse osmosis membrane column, and whose outlet is connected to the inlet of the fluidized bed reactor. The bottom of the product water tank has a backwash water inlet, which is connected to the upper end of the reverse osmosis membrane column and the lower end of the ultrafiltration membrane column via a third high-pressure diaphragm pump. The fluidized bed reactor is connected to a precipitant dosing tank via a pipeline, and the precipitant dosing tank contains a stirring device.

[0008] Preferably, the seed crystal layer comprises several layers of nonwoven fabric, with seed crystal particles placed on each layer of nonwoven fabric.

[0009] Preferably, the stainless steel filter screen is 100 or 150 mesh.

[0010] Preferably, the ultrafiltration membrane module of the ultrafiltration membrane column is an external pressure PVDF ultrafiltration membrane, with a single-column water production capacity of 1-4 m³ / h. 3 The flow rate is [ / h], the operating pressure is below 0.3 MPa, the reverse osmosis membrane module is a polyamide thin-film composite membrane, and the permeate flow rate of a single module is 0.25-1.2 m³ / h. 3 / h, operating pressure between 0.7-1.0 MPa.

[0011] A method of using a fluidized bed-dual membrane deep defluorination device, characterized by comprising the following steps:

[0012] The first step is to determine the optimal values ​​for seed crystal dosage, seed crystal type, calcium chloride dosage, and fluidized bed upflow velocity under the following conditions: influent concentration, temperature, and pH value. After adding the precipitant calcium chloride and pH adjuster sodium hydroxide to the precipitant dosing tank and fully dissolving them under the action of the stirring device, the inlet valve on the fluoride wastewater inlet pipe is opened to introduce the raw water to be treated. At the same time, the inlet valve of the lower inlet pipe of the precipitant dosing tank is opened to form a continuous mixed flow in the fluidized bed.

[0013] The second step involves the raw water and precipitant entering a fluidized bed, where heterogeneous crystallization occurs on the seed crystals in the substrate layer. Calcium and fluoride ions react on the seed crystals, and then the water passes through a stainless steel filter. Based on a feed solution of 300 mg / L sodium fluoride, the turbidity of the clarified effluent is generally less than 10 NTU, and the fluoride ion concentration is generally 10-20 mg / L. The effluent from the fluidized bed flows by gravity into the ultrafiltration membrane pipeline, is pressurized by the first high-pressure diaphragm pump, and enters the ultrafiltration membrane column. The number of ultrafiltration membrane modules is determined based on the required water volume and the permeate output of a single membrane module. Generally, the total permeate output is designed to be no less than 1.2 times the required water volume, and the reverse osmosis membrane module output is generally no less than 3 times the ultrafiltration membrane output. The diameter of free fluoride ions after ultrafiltration is 0.266 nm, and the effective treatment range of the reverse osmosis membrane is around 0.1 nm. A sealed stainless steel water volume regulating tank is installed between the ultrafiltration and reverse osmosis units, allowing residual pressure from the effluent to enter, and then it is pumped by the second high-pressure diaphragm pump into the reverse osmosis membrane column.

[0014] The third step involves closing the inlet solenoid valve of the ultrafiltration membrane column, opening the backwash solenoid valve at the bottom of the product water tank, and starting the third high-pressure diaphragm pump for backwashing. Based on the built-in opening and closing cycles of the solenoid valves on the backwash branch, individual membrane modules for ultrafiltration or reverse osmosis are cleaned. The cleaning process does not affect the water production of other membrane modules. The backwash water enters the concentrate tank through the transmembrane residual pressure. Once the concentrate tank reaches half its storage capacity, the solenoid valve at the bottom of the concentrate tank is opened, and the water flows back to the bottom of the fluidized bed via a self-priming pump, forming a mixed flow. The amount of calcium chloride added to the fluidized bed in step one is optimized through small-scale experiments to match changes in water quality. At this point, the entire treatment system is fully operational, and each section forms a continuous flow system.

[0015] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0016] 1. The fluidized bed-dual membrane deep defluorination device of the present invention can achieve a high degree of defluorination. Under the condition of 300 mg / L sodium fluoride in the influent, the fluoride ion concentration in the test water is less than 0.3 mg / L, which is better than the fluoride ion concentration of about 10 mg / L in the effluent of the general multi-stage internal circulation sedimentation method, and better than the fluoride ion concentration of about 5 mg / L in the effluent of ion exchange resin.

[0017] 2. The fluidized bed-dual membrane deep defluorination device of the present invention has a good seed configuration effect. Generally, fluidized bed defluorination devices need to be equipped with a stirring device to keep the reaction zone in a turbulent state so that the seed crystals do not sink to the bottom, so as to maintain more growth sites for fluoride ions and calcium ions on the seed crystal surface. This device uses a carrier seed crystal, which grows through the upward flow formed by the self-priming pump with three water inlets, through the fine seed crystals between the layers of non-woven fabric.

[0018] 3. The fluidized bed-dual membrane deep defluorination device of the present invention has a strong ability to cope with changes in water quality. The process can make a variety of responses to changes in water quality. For example, the pH value in the fluidized bed reaction zone can be adjusted without adding additional facilities. Multiple crystal seeds can be replaced to remove chromium ions on the basis of precipitation. Polyaluminum chloride, calcium carbonate, calcium oxide, calcium hydroxide, sodium hydroxide, etc. can be added to the precipitant addition tank to form a composite precipitate. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of the present invention.

[0020] Figure 2 This is a schematic diagram of the structure of the seed crystal layer.

[0021] In the diagram: 1-Inlet; 2-Horizontal self-priming pump; 3-Solenoid valve; 4-Crystal seed layer; 5-Stainless steel filter screen; 6-Fluorescent bed clarification zone; 7-Fluorescent bed outlet; 8-High-pressure diaphragm pump; 9-Ultrafiltration inlet; 10-Ultrafiltration product outlet; 11-Ultrafiltration water tank inlet; 12-Reverse osmosis inlet; 13-Reverse osmosis outlet; 14-Process product outlet; 15-Backwash water inlet; 16-Reverse osmosis backwash pipeline; 17-Ultrafiltration backwash Piping; 18-Reverse osmosis backwash drainage; 19-Ultrafiltration backwash drainage; 20-Concentrate reflux; 21-Flocculant dosing tank; 22-Agitator; 23-Fluidized bed reactor; 24-Ultrafiltration membrane column; 25-Reverse osmosis membrane column; 26-Balancing tank; 27-Concentrate tank; 28-Permeate tank; 29-Wastewater inlet piping system; 30-Flocculant dosing piping system; 31-Fluidized bed effluent piping system; 32-Ultrafiltration permeate piping system; 33-Reverse osmosis permeate piping system. Detailed Implementation

[0022] The invention will now be further described with reference to the accompanying drawings.

[0023] like Figure 1As shown, the fluidized bed-dual membrane deep defluorination device of the present invention includes a fluidized bed reactor, an ultrafiltration membrane unit, a regulating tank, a reverse osmosis membrane unit, and a concentrate tank. Fluoride-containing wastewater is connected to the bottom of the fluidized bed reactor via pipelines. An n-stage parallel fluidized bed is configured according to the fluoride-containing wastewater; this invention has four stages, each with a secondary inlet pipe controlled by an electromagnetic valve. The bottom of the fluidized bed reactor is also connected to a precipitant dosing tank and equipped with a self-priming pump and electromagnetic valve. The bottom of the fluidized bed reactor is also connected to the concentrate tank, which is also equipped with a self-priming pump and electromagnetic valve. A high-pressure diaphragm pump is connected to the upper part of the fluidized bed reactor. The pump outlet is connected to 2-6 stages of parallel ultrafiltration membrane columns. The ultrafiltration membrane outlet is connected to the regulating tank. The outlet of the regulating tank is connected to the high-pressure diaphragm pump, which is connected to 6-18 stages of parallel reverse osmosis membrane columns. The reverse osmosis effluent is stored in a tank, which is connected to a self-priming pump as the system's product water. A high-pressure diaphragm pump is connected to the bottom of the tank, providing backwashing for both the ultrafiltration and reverse osmosis membrane units. The backwash outlet is connected to a concentrate storage tank, whose bottom is connected to a pipeline that returns the concentrate to the bottom of the fluidized bed reactor via a self-priming pump. Valves on each pipeline control the on / off switching of the pipeline and the operation / backwashing process.

[0024] The fluidized bed reactor is equipped with a main shell, baffles, seed crystals, and a stainless steel filter. The seed crystals cover the reaction zone below the stainless steel filter, while the clarification zone is above the stainless steel filter. The lower part is equipped with three inlets connected to fluoride-containing wastewater, a precipitant dosing tank, and membrane concentrate. The upper part is equipped with one outlet connected to the ultrafiltration feed water. The stainless steel filter is 100 or 150 mesh. The fluidized bed material is generally fiberglass or 304 stainless steel. The reaction zone dimensions are generally 1500-2500 mm in height and 200-300 mm in diameter, while the clarification zone dimensions are 1200-2000 mm in height and 600-800 mm in diameter.

[0025] The precipitant dosing tank is equipped with a tank body, a stirring device, a self-priming pump, and a level gauge. Its bottom is connected to the bottom of the fluidized bed reactor, and its volume is generally not less than 8 m³. 3 .

[0026] The regulating tank is equipped with a tank body, a level gauge, and an inspection port, and its volume generally ranges from 10 to 20 cubic meters. 3 .

[0027] Ultrafiltration membrane modules are generally external pressure PVDF ultrafiltration membranes, with a single unit producing 1-4 m³ of water. 3 The flow rate is [ / h], the operating pressure is below 0.3 MPa, the reverse osmosis membrane module is a polyamide thin-film composite membrane, and the permeate flow rate of a single module is 0.25-1.2 m³ / h. 3 / h, operating pressure between 0.7-1.0 MPa.

[0028] The product water tank is equipped with a tank body and a level gauge. The bottom is connected to a backwash line, which is connected to the ultrafiltration backwash line and the reverse osmosis backwash line via a tee and a solenoid valve, respectively. A product water outlet is located at a certain height on the bottom side, with a volume of not less than 5 m³. 3 That is, the backwash water volume of each membrane unit should be met.

[0029] The concentrate tank is equipped with a tank body, a level gauge, and a self-priming pump. The concentrate tank is connected to the concentrate of 2-6 parallel ultrafiltration membrane columns and 6-18 parallel reverse osmosis membrane columns.

[0030] The fluidized bed-dual membrane deep defluorination device of the present invention can effectively reduce the fluoride ion concentration to below 0.3 mg / L, effectively improve the removal efficiency of suspended solids, and has higher water treatment efficiency compared with existing sewage treatment equipment.

[0031] All pipes in this invention are made of polyethylene.

[0032] The method of using the fluidized bed-dual membrane deep defluorination device of the present invention includes the following steps:

[0033] The first step involves determining the optimal seed crystal dosage, seed crystal type, calcium chloride dosage, and fluidized bed upflow velocity under specific conditions, including influent concentration, temperature, and pH, through small-scale experiments. The pH adjustment via the precipitant dosing tank is also investigated. Generally, the equipment is designed to handle influent concentrations of 50-1000 mg / L, temperatures of 10-45℃, and pH values ​​of 2-9. Typically, the seed crystal dosage is [amount missing] per m³. 3 The fluidized bed reactor is fed with 3-15 kg of calcium fluoride or silicon dioxide as seed crystals. The calcium chloride dosage depends on the average fluoride ion concentration in the influent. The calcium-fluoride molar ratio is between 0.8 and 0.5. The fluidized bed upflow velocity is approximately 60-120 mm / min, and the water treatment capacity per stage is approximately 0.45-0.9 m³. 3 / h.

[0034] After the dosage of calcium chloride, the precipitant, and sodium hydroxide, the pH adjuster, determined in the small-scale test, are added to the precipitant dosing tank and fully dissolved under the action of the stirring device, the inlet valve on the fluoride-containing wastewater inlet pipe is opened to introduce the raw water to be treated. At the same time, the inlet valve of the lower inlet pipe of the precipitant dosing tank is opened to form a continuous mixed flow in the fluidized bed.

[0035] Combination Figure 2This invention explains that by placing seed crystals in the reaction zone, the fluidized bed reactor below the stainless steel filter screen is constructed using multiple layers of circularly cut hydrophilic nonwoven fabric, typically made of polyester or polylactic acid. Seed crystals are uniformly added between the nonwoven fabric layers. The fluoride-containing wastewater to be treated enters from the bottom of the fluidized bed and passes through each layer of nonwoven fabric, reacting with it. Conventional fluidized bed reactors require a stirring device to maintain a turbulent flow, preventing suspended seed crystal particles from agglomerating and settling in the reaction zone, thus increasing nucleation sites for fluoride and calcium ions. This invention, however, disperses the seed crystals in the reaction zone through the stacking of permeable hydrophilic nonwoven fabric, saving the need for a stirring device.

[0036] In the second step, the raw water and precipitant enter the fluidized bed, where heterogeneous crystallization occurs on the seed crystals in the supported layer. Calcium and fluoride ions react on the seed crystals, and then the water passes through a stainless steel filter screen. The turbidity is further reduced in the fluidized bed clarification zone. Using a 300 mg / L sodium fluoride feed solution, the turbidity of the clarified effluent is generally less than 10 NTU, and the fluoride ion concentration is generally 10-20 mg / L. The effluent from the fluidized bed flows by gravity into the ultrafiltration membrane pipeline, where it is pressurized by a diaphragm pump. The number of ultrafiltration membrane modules is determined based on the required water volume and the permeate output of each module. Generally, the total designed permeate output is not less than 1.2 times the required water volume, and the number of reverse osmosis membrane modules is generally not less than 3 times the number of ultrafiltration membrane modules. The diameter of free fluoride ions after ultrafiltration is 0.266 nm, while the effective treatment range of reverse osmosis membranes is around 0.1 nm. Therefore, in the deep defluorination stage of reverse osmosis, fluoride ions are mainly removed by size sieving effect. Reverse osmosis membranes have a higher tendency to foul, and in actual operation, a margin must be allowed for the impact of a decrease in reverse osmosis membrane flux on the total system treatment capacity. A sealed stainless steel water flow regulating tank is installed between the ultrafiltration and reverse osmosis units, with residual pressure water entering and then passing through a high-pressure diaphragm pump into the reverse osmosis membrane module. The ultrafiltration membrane and reverse osmosis membrane module are existing technologies; therefore, the specific structural composition of the membrane module will not be described in detail in this invention.

[0037] The third step involves closing the inlet solenoid valve of the ultrafiltration membrane module, opening the backwash solenoid valve at the bottom of the permeate tank, and starting the backwash high-pressure diaphragm pump. Based on the built-in opening and closing cycles of the solenoid valves on the backwash branch, individual ultrafiltration or reverse osmosis membrane modules are cleaned. The cleaning process does not affect the water production of other membrane modules. The backwash water enters the concentrate tank through the transmembrane residual pressure. Once the concentrate tank reaches half its capacity, the bottom solenoid valve is opened, and the concentrate is returned to the bottom of the fluidized bed via a self-priming pump, forming a mixed flow. The amount of calcium chloride added to the fluidized bed in step one is optimized through small-scale experiments to match changes in water quality. At this point, the entire treatment system is fully operational, and each section forms a continuous flow system.

[0038] The fourth step is to ensure that the effluent quality consistently meets the standards of GB / T 19923-2024 for industrial water reuse of urban wastewater. The effluent fluoride concentration is significantly higher than the GB 30484-2013 standard for pollutant discharge from the battery industry (10 mg / L), consistently below 1 mg / L. This ensures that the effluent quality meets the standards for recycled water in the semiconductor industry and improves the reuse rate of industrial water.

[0039] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A fluidized bed-dual membrane deep defluorination device, characterized in that: The system comprises several fluidized bed reactors. The inlet of each fluidized bed reactor is connected to an inlet pipe via a first solenoid valve. A stainless steel filter screen is installed at the lower end of the fluidized bed reactor, and seed crystals are placed below the filter screen. Above the filter screen is a fluidized bed clarification zone. The fluidized bed outlet is connected to the ultrafiltration inlet of a first ultrafiltration membrane column via a first high-pressure diaphragm pump. The ultrafiltration permeate outlet of the first ultrafiltration membrane column is connected to a regulating tank. The regulating tank is connected to the reverse osmosis inlet of a reverse osmosis membrane column via a second high-pressure diaphragm pump. The reverse osmosis effluent from the reverse osmosis membrane column... The system includes a product water tank and a concentrate tank. The inlet of the concentrate tank is connected to the upper end of the ultrafiltration membrane column and the lower end of the reverse osmosis membrane column. The outlet of the concentrate tank is connected to the inlet of the fluidized bed reactor. The bottom of the product water tank is equipped with a backwash water inlet, which is connected to the upper end of the reverse osmosis membrane column and the lower end of the ultrafiltration membrane column via a third high-pressure diaphragm pump. The fluidized bed reactor is connected to a precipitant dosing tank via a pipeline. The precipitant dosing tank contains a stirring device. The seed crystal layer consists of several layers of nonwoven fabric, with seed crystal particles placed on each layer of nonwoven fabric.

2. The fluidized bed-dual membrane deep defluorination device according to claim 1, characterized in that: The stainless steel filter screen is 100 or 150 mesh.

3. The fluidized bed-dual membrane deep defluorination device according to claim 1, characterized in that: The ultrafiltration membrane module of the ultrafiltration membrane column is an external pressure PVDF ultrafiltration membrane, with a single unit producing 1-4 m³ of water. 3 The flow rate is [ / h], the operating pressure is below 0.3 MPa, the reverse osmosis membrane module is a polyamide thin-film composite membrane, and the permeate flow rate of a single module is 0.25-1.2 m³ / h. 3 / h, operating pressure between 0.7-1.0 MPa.

4. A method of using the fluidized bed-dual membrane deep defluorination device as described in any one of claims 1 to 3, characterized in that, Includes the following steps: (1) The seed dosage, seed type, calcium chloride dosage, and fluidized bed upflow velocity were determined by small-scale experiments under the following conditions: concentration of influent, temperature and pH value. After the dosage of calcium chloride and sodium hydroxide determined by the small-scale experiment were added to the precipitant dosing tank, they were fully dissolved under the action of the stirring device. Then, the inlet valve on the fluoride wastewater inlet pipe was opened to introduce the raw water to be treated. At the same time, the inlet valve of the inlet pipe at the bottom of the precipitant dosing tank was opened to form a continuous mixed flow in the fluidized bed. (2) The raw water to be treated and the precipitant enter the fluidized bed, where heterogeneous crystallization occurs in the seed crystals of the substrate layer. Calcium ions and fluoride ions react on the seed crystals and then pass through the stainless steel filter screen. Based on a feed solution of 300 mg / L sodium fluoride, the turbidity of the clarified effluent is generally less than 10 NTU, and the fluoride ion concentration is generally 10-20 mg / L. The effluent from the fluidized bed flows into the ultrafiltration membrane pipeline by gravity, and is pressurized by the first high-pressure diaphragm pump before entering the ultrafiltration membrane column. The diameter of the free fluoride ions after passing through the ultrafiltration membrane is 0.266 nm. A closed stainless steel water flow regulating tank is set between the ultrafiltration and reverse osmosis units. The residual pressure of the effluent enters and then enters the reverse osmosis membrane column by the second high-pressure diaphragm pump. (3) Close the inlet solenoid valve of the ultrafiltration membrane column, open the backwash solenoid valve at the bottom of the product water tank, and turn on the third high-pressure diaphragm pump for backwashing. According to the opening and closing cycle of the solenoid valve on the backwash branch, clean the individual membrane modules of ultrafiltration or reverse osmosis. The cleaning process does not affect the water production of other membrane modules. The backwash water enters the concentrate tank through the transmembrane residual pressure. After the concentrate tank reaches half of its storage capacity, open the solenoid valve at the bottom of the concentrate tank and return it to the bottom of the fluidized bed through the self-priming pump to form a mixed flow. Optimize the amount of calcium chloride added to the fluidized bed in step one through a small-scale test to match the water quality changes. At this point, the entire treatment system is fully turned on, and each section forms a continuous flow system.

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