Fluorine-containing wastewater advanced treatment system and method with synergy of chemical precipitation and membrane method

Abstract

The invention discloses a fluorine-containing wastewater advanced treatment system and a fluorine-containing wastewater advanced treatment method based on cooperation of chemical precipitation and a membrane method. Comprising a sedimentation tank, a dynamic filter and a double-membrane system which are arranged in sequence, wherein in the sedimentation tank, a modified calcium salt precipitator and CaF2 seed crystals are added into the fluorine-containing wastewater for reflux, and large calcium fluoride particle precipitates are formed through an induced crystallization adsorption-sedimentation mechanism; the dynamic filter is used for intercepting sediments from effluent of the sedimentation tank through a gradient aperture structure to realize solid-liquid separation and preliminary fluorine removal; and the double-membrane system is used for removing residual fluorine-containing particles, colloids and ions in the wastewater treated by the dynamic filter by utilizing an ultrafiltration membrane and a reverse osmosis membrane. Through cooperation of a modified calcium salt adsorption-precipitation mechanism and a membrane gradient interception method, efficient trapping and solid-liquid separation of fluorine ions are achieved, the fluorine removal precipitation reaction is enhanced, the medicine consumption is reduced, and near-zero external water consumption is achieved.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, and in particular to a system and method for the deep treatment of fluoride-containing wastewater by combining chemical precipitation and membrane technology, which is applicable to the treatment of high-fluoride wastewater generated in industries such as photovoltaics, metallurgy, and chemicals. Background Technology

[0002] Fluoride-containing wastewater widely originates from industries such as photovoltaics, metallurgy, chemicals, and electronics, and is characterized by high toxicity, difficulty in degradation, and high treatment costs. Traditional chemical precipitation methods typically involve reacting lime (Ca(OH)₂) with fluoride ions to form CaF₂ precipitate. However, due to the high solubility of CaF₂ (Ksp = 3.9 × 10⁻⁶), this method is problematic. - ¹¹), incomplete precipitation often results in fluoride concentrations in the effluent exceeding 10 mg / L, making it difficult to meet the requirement of ≤1.5 mg / L for fluoride in the "Integrated Wastewater Discharge Standard" (GB 8978-1996). In some areas, the Class III limit (<1 mg / L) of the "Surface Water Environmental Quality Standard" is even used as the discharge standard.

[0003] While membrane technologies (such as ultrafiltration and reverse osmosis) can achieve deep defluoridation, they suffer from problems such as severe membrane fouling, difficulty in treating concentrate, and high operating costs. In particular, the high concentration of fluoride ions in reverse osmosis concentrate can cause secondary pollution if directly discharged. Therefore, there is an urgent need to develop a highly efficient, low-consumption, and sustainable method for deep treatment of fluoride-containing wastewater, balancing defluoridation efficiency, reagent consumption, water recovery rate, and sludge resource utilization. Summary of the Invention

[0004] To overcome the above-mentioned shortcomings, this invention proposes a system and method for the deep treatment of fluoride-containing wastewater that combines chemical precipitation and membrane technology. The aim is to overcome the deficiencies of existing technologies and achieve efficient fluoride removal, low chemical consumption, low water consumption, and sludge resource utilization.

[0005] To achieve the above objectives, the present invention provides a synergistic chemical precipitation and membrane method for the advanced treatment of fluoride-containing wastewater, comprising: a sedimentation tank, a dynamic filter, and a dual-membrane system arranged sequentially; wherein, In the sedimentation tank, modified calcium salt precipitant and CaF2 seed crystals are added to the fluoride-containing wastewater and refluxed to form large calcium fluoride precipitates through an induced crystallization adsorption-precipitation mechanism. Dynamic filters are used to trap sediment in sedimentation tank effluent through a gradient pore structure, achieving solid-liquid separation and preliminary defluorination. The dual-membrane system uses ultrafiltration and reverse osmosis membranes to remove residual fluoride particles, colloids, and ions from wastewater treated by the dynamic filtration unit.

[0006] Furthermore, the dynamic filter and dual-membrane system are equipped with a backwashing unit, which is used to backwash the dynamic filter and ultrafiltration membrane.

[0007] Furthermore, it also includes a hydrocyclone separator, wherein the backwash water from the backwashing unit of the dynamic filter and the ultrafiltration membrane is combined and then enters the hydrocyclone separator.

[0008] Furthermore, it also includes a sludge return device, wherein the cyclone separator classifies the backwash sludge according to particle size, and the precipitate with a particle size >50μm is returned to the chemical precipitation tank as seed crystals.

[0009] To achieve the above objectives, the present invention provides a method for advanced treatment of fluoride-containing wastewater using a combination of chemical precipitation and membrane technology, characterized by comprising the following steps: (1) Chemical precipitation: Modified calcium salt precipitant and CaF2 seed crystals are added to fluoride-containing wastewater and refluxed to form large calcium fluoride precipitates through induced crystallization adsorption-precipitation mechanism; (2) Dynamic filter: The effluent from the sedimentation enters the dynamic filter, which uses a gradient pore structure to trap the sediment, thereby achieving solid-liquid separation and preliminary defluorination; (3) Ultrafiltration treatment: The water effluent from the dynamic filter enters the ultrafiltration system to remove residual fine particles and colloids. The ultrafiltration backwash water and the dynamic filter backwash water are combined and enter the hydrocyclone separator. (4) Sludge return: The hydrocyclone separator classifies the backwash sludge according to particle size. The precipitate with a particle size >50μm is returned to the chemical sedimentation tank as seed crystals to promote the sedimentation reaction; the remaining sludge enters the sludge treatment system. (5) Reverse osmosis concentration: The ultrafiltration effluent enters the reverse osmosis membrane. The purified water is discharged or reused after meeting the standards, and the concentrated water is returned to the raw water equalization tank for circulation treatment. Some of the purified water is used for backwashing of the membrane system.

[0010] Furthermore, the modified calcium salt is a composite modification of Ca(OH)2 or CaO and a coagulant aid, with a particle size of 0.1-0.5 mm and a specific surface area >15 m² / g.

[0011] Furthermore, the dynamic filter filling material is a diatomaceous earth polymer with a pore size gradient of 0.5-5 μm, an operating throughput of 80-120 L / (m²·h), and a backwashing cycle of 30-60 min.

[0012] Furthermore, the hydrocyclone is a hydrocyclone with a diameter of 75 mm and a cone angle of 20°, a feed pressure of 0.2-0.3 MPa, and a classifiable particle size range of 30-100 μm.

[0013] Furthermore, the reverse osmosis membrane operates at a pressure of 1.2-1.8 MPa, has a water recovery rate of 75-85%, and a concentrate reflux ratio of 30-50%. The present invention has the following advantages: 1. Synergistic fluoride removal mechanism: By combining the modified calcium salt adsorption-precipitation mechanism with the membrane gradient interception method, efficient capture and solid-liquid separation of fluoride ions are achieved. 2. Seed reflux to enhance precipitation: Using a hydrocyclone separator to screen and reflux large particles of precipitate as seed crystals significantly improves precipitation efficiency and reduces reagent consumption by more than 20%. 3. Concentrate internal circulation and clean water reuse: The concentrate from the reverse osmosis membrane is returned to the sedimentation tank to enrich fluoride ions, increasing the system water recovery rate to over 80%. Some of the clean water is reused for backwashing, achieving near-zero external water consumption. 4. Membrane fouling control optimization: By pre-retaining large particles through dynamic filters, the load on ultrafiltration and reverse osmosis membranes is reduced, membrane life is extended, and operating costs are reduced. Attached Figure Description

[0014] Figure 1 This is a flowchart of a system and method for advanced treatment of fluoride-containing wastewater using a combination of chemical precipitation and membrane technology, according to the present invention. Detailed Implementation

[0015] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0016] In the description of this invention, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0017] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0018] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0019] like Figure 1As shown, the present invention provides a synergistic chemical precipitation and membrane method for the advanced treatment of fluoride-containing wastewater, comprising: a sedimentation tank, a dynamic filter, and a dual-membrane system arranged sequentially; wherein, In the sedimentation tank, a modified calcium salt precipitant and CaF2 seed crystals are added to the fluoride-containing wastewater and refluxed to form large calcium fluoride particles through an induced crystallization adsorption-precipitation mechanism. The modified calcium salt is Ca(OH)2 or CaO modified with a coagulant aid, with a particle size of 0.1-0.5 mm and a specific surface area >15 m² / g.

[0020] A dynamic filter is used to trap sediment in the effluent from a sedimentation tank through a gradient pore structure, achieving solid-liquid separation and preliminary defluorination. The filter filling material is diatomaceous earth polymer with a pore size gradient of 0.5-5μm, an operating throughput of 80-120L / (m²·h), and a backwashing cycle of 30-60min.

[0021] The dual-membrane system utilizes ultrafiltration and reverse osmosis membranes to remove residual fluoride particles, colloids, and ions from wastewater treated by a dynamic filter. The dynamic filter and dual-membrane system are equipped with a backwashing unit for backwashing the dynamic filter and ultrafiltration membrane.

[0022] It also includes a hydrocyclone separator, where the backwash water from the backwashing unit of the dynamic filter and ultrafiltration membrane is combined and then enters the hydrocyclone separator. The hydrocyclone separator is a hydrocyclone with a diameter of 75 mm and a cone angle of 20°, a feed pressure of 0.2-0.3 MPa, and a classifiable particle size range of 30-100 μm.

[0023] It also includes a sludge return device, wherein the cyclone separator classifies the backwash sludge according to particle size, and the precipitate with a particle size >50μm is returned to the chemical precipitation tank as seed crystals.

[0024] This invention provides a method for advanced treatment of fluoride-containing wastewater, characterized by comprising the following steps: 1) Chemical precipitation stage: Adding a modified calcium salt precipitant (such as modified Ca(OH)2 or CaO) to fluoride-containing wastewater will form CaF2 precipitate under stirring conditions. The precipitate will preferentially adsorb fluoride ions through the functional groups on the surface of the modifier, promoting the formation of large precipitate particles. 2) Dynamic filtering stage: After sedimentation, the wastewater enters the dynamic filter, where dynamic packing material with gradient pore size (such as diatomaceous earth polymer) is used to retain the precipitate, achieving preliminary solid-liquid separation and deep defluorination. During the operation of the dynamic filter, the flow rate is maintained by intermittent backwashing. 3) Ultrafiltration membrane treatment stage: The water effluent from the dynamic filter enters the ultrafiltration membrane for further removal of fine particles and colloids. The ultrafiltration membrane and the backwash water from the dynamic filter are mixed and then enter the hydrocyclone separator. 4) Sludge recirculation and seed crystal enhancement: The hydrocyclone separator classifies the backwash sludge according to particle size. Larger particles are returned to the chemical sedimentation tank as seed crystals to promote the sedimentation reaction and reduce the amount of precipitant to be added. The remaining sludge enters the sludge thickening system. 5) Reverse osmosis concentration and reuse: Ultrafiltration effluent enters the reverse osmosis membrane. The purified water meets the standards for discharge or reuse, while the concentrated water is returned to the raw water equalization tank for further enrichment and concentration to improve the system's water recovery rate. Some of the reverse osmosis purified water is used for membrane system backwashing to reduce external purified water consumption.

[0025] Example 1: A photovoltaic industry in an industrial park discharges 100 m³ of fluoride-containing wastewater daily. The raw water is F - With a concentration of 85 mg / L, pH 6.5, and TDS concentration of 2200 mg / L, 200 mg / L Ca(OH)2 was first added and stirred for 30 min to raise the pH to 8.5 to complete chemical precipitation. The solution was then sequentially passed through a diatomaceous earth-PAM packing material with a pore size of 2 μm and a flux of 100 L / (m²•h) and a PVDF hollow fiber ultrafiltration membrane with a flux of 60 L / (m²•h). All backwash water from the dynamic filter and ultrafiltration membrane was sent to a hydrocyclone separator with a feed pressure of 0.25 MPa. Returned sludge with a particle size greater than 50 μm was used as seed crystals and returned to the sedimentation tank at a 40% reflux ratio to enhance solid-liquid separation. The ultrafiltration membrane filtered water was then treated by a 1.5 MPa reverse osmosis membrane with a water recovery rate of 80% and a concentrate reflux ratio of 40%. The clarified water was used for backwashing, and the final effluent was F... - The concentration was reduced to 0.48 mg / L, reducing the amount of reagent used by 25%, achieving a total water recovery rate of 92%, and decreasing operating costs by 32%.

[0026] Example 2: A certain industrial park discharges 200 m³ of high-fluoride wastewater from the metallurgical industry daily. The raw water is F -At a concentration of 120 mg / L and pH 5.8, 250 mg / L CaO (containing 0.1% PAM modification) was first added, and the mixture was stirred and reacted for 30 min until the pH was raised to 7.5 to complete chemical precipitation. Subsequently, the solution was passed sequentially through a diatomaceous earth-PAM packing material with a pore size of 2 μm and a flux of 100 L / (m²•h) and a PVDF hollow fiber ultrafiltration membrane with a flux of 60 L / (m²•h). All backwash water from the dynamic filter and ultrafiltration membrane was sent to a hydrocyclone separator with a feed pressure of 0.25 MPa. Returned sludge with a particle size greater than 50 μm was used as seed crystals and returned to the sedimentation tank at a 35% reflux ratio to enhance solid-liquid separation. The ultrafiltration membrane filtered water was then treated by a 1.5 MPa reverse osmosis membrane with a water recovery rate of 85% and a concentrate reflux ratio of 40%. The clarified water was used for backwashing, and the final effluent was F. - The concentration was reduced to 0.75 mg / L, reducing the amount of chemicals used by 22%, eliminating the need for external clean water replenishment, and decreasing sludge production by 28%.

[0027] The present invention has been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described above. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Many other changes and modifications made without departing from the concept and scope of the present invention should be considered within the scope of protection of the present invention.

[0028] In the description of this specification, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

[0029] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A system for the advanced treatment of fluoride-containing wastewater using a combination of chemical precipitation and membrane technology, characterized in that, include: Set in sequence Sedimentation tank, dynamic filter, and dual-membrane system; among which, In the sedimentation tank, modified calcium salt precipitant and CaF2 seed crystals are added to the fluoride-containing wastewater and refluxed to form large calcium fluoride precipitates through an induced crystallization adsorption-precipitation mechanism. Dynamic filters are used to trap sediment in sedimentation tank effluent through a gradient pore structure, achieving solid-liquid separation and preliminary defluorination. The dual-membrane system uses ultrafiltration and reverse osmosis membranes to remove residual fluoride particles, colloids, and ions from wastewater treated by the dynamic filtration unit.

2. The advanced treatment system for fluoride-containing wastewater combining chemical precipitation and membrane technology according to claim 1, characterized in that, The dynamic filtration unit and dual-membrane system are equipped with a backwashing unit, which is used to backwash the dynamic filter and ultrafiltration membrane.

3. The advanced treatment system for fluoride-containing wastewater combining chemical precipitation and membrane technology according to claim 2, characterized in that, It also includes a hydrocyclone separator, and the backwash water from the backwashing unit after backwashing the dynamic filter and ultrafiltration membrane is combined and then enters the hydrocyclone separator.

4. The advanced treatment system for fluoride-containing wastewater combining chemical precipitation and membrane methods according to claim 3, characterized in that, It also includes a sludge return device, wherein the cyclone separator classifies the backwash sludge according to particle size, and the precipitate with a particle size >50μm is returned to the chemical precipitation tank as seed crystals.

5. A method for advanced treatment of fluoride-containing wastewater using a synergistic combination of chemical precipitation and membrane technology, characterized in that, Includes the following steps: (1) Chemical precipitation: Modified calcium salt precipitant and CaF2 seed crystals are added to fluoride-containing wastewater and refluxed to form large calcium fluoride precipitates through induced crystallization adsorption-precipitation mechanism; (2) Dynamic filtration: The effluent from sedimentation enters the dynamic filter, which uses the gradient pore structure to trap the sediment, thereby achieving solid-liquid separation and preliminary defluorination; (3) Ultrafiltration treatment: The water effluent from the dynamic filter enters the ultrafiltration membrane to remove residual fine particles and colloids. The ultrafiltration backwash water and the dynamic membrane backwash water are combined and enter the hydrocyclone separator. (4) Sludge return: The hydrocyclone separator classifies the backwash sludge according to particle size. The precipitate with a particle size >50μm is returned to the chemical sedimentation tank as seed crystals to promote the sedimentation reaction; the remaining sludge enters the sludge treatment system. (5) Reverse osmosis concentration: The ultrafiltration effluent enters the reverse osmosis membrane and the purified water is discharged or reused after meeting the standards. The concentrated water is returned to the raw water equalization tank for circulation treatment, and part of the purified water is used for backwashing of the membrane system.

6. The method for advanced treatment of fluoride-containing wastewater by synergistic chemical precipitation and membrane methods according to claim 5, characterized in that, The modified calcium salt is a composite modification of Ca(OH)2 or CaO and a coagulant aid, with a particle size of 0.1-0.5 mm and a specific surface area >15 m² / g.

7. The method for advanced treatment of fluoride-containing wastewater by synergistic chemical precipitation and membrane methods according to claim 5, characterized in that, The dynamic filter packing is made of diatomaceous earth polymer with a pore size gradient of 0.5-5μm, an operating throughput of 80-120 L / (m²·h), and a backwashing cycle of 30-60min.

8. The method for advanced treatment of fluoride-containing wastewater by synergistic chemical precipitation and membrane methods according to claim 5, characterized in that, The hydrocyclone separator is a hydrocyclone with a diameter of 75 mm and a cone angle of 20°, a feed pressure of 0.2-0.3 MPa, and a classifiable particle size range of 30-100 μm.

9. The method for advanced treatment of fluoride-containing wastewater by synergistic chemical precipitation and membrane methods according to claim 5, characterized in that, The reverse osmosis membrane operates at a pressure of 1.2-1.8 MPa, has a water recovery rate of 75-85%, and a concentrate reflux ratio of 30-50%.

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