A device and method for mitigating inorganic salt fouling on the surface of a nanofiltration membrane

Abstract

The application relates to a device for relieving inorganic salt scaling on the surface of a nanofiltration membrane, which comprises a raw water stabilizing unit, a water quality synergistic adjusting unit, a nanofiltration separation unit and a product water buffering and collecting unit which are sequentially connected by pipelines; wherein the water quality synergistic adjusting unit can synergistically add sodium chloride and natural organic polymers into raw water according to water quality monitoring feedback; the device adopts the above-mentioned sodium chloride and natural organic polymer synergistic relieving inorganic salt scaling on the surface of a nanofiltration membrane technology and method, can effectively reduce the inorganic salt deposition scaling tendency on the surface of the nanofiltration membrane, improve the system operation stability, reduce the membrane cleaning frequency, realize efficient low-consumption and sustainable operation in the drinking water advanced treatment process.

Description

Technical Field

[0001] This invention relates to the field of drinking water treatment technology, and in particular to an apparatus and method for mitigating inorganic salt scaling on the surface of nanofiltration membranes. Background Technology

[0002] According to statistics from the World Health Organization and related international organizations, as of 2024, more than a quarter of the world's population still lacked access to safe and clean drinking water, and water scarcity and pollution have become one of the global public health challenges. Against this backdrop, pressure-driven membrane separation technologies, especially nanofiltration (NF) technology, have shown broad application prospects in the field of advanced drinking water treatment due to their unique separation characteristics.

[0003] Nanofiltration membranes typically have a molecular weight cutoff between 200 and 2000 Da, enabling them to filter divalent and higher-valent ions in water (such as Ca). 2+ Mg 2+ SO4 2- HCO3 - (etc.) to achieve a high rejection rate, while partially retaining monovalent ions beneficial to the human body (such as Na+, etc.). + K + Nanofiltration combines the absorption of low-valence minerals with low-valence minerals, ensuring both the safety and taste of the treated water. At the same time, nanofiltration operates at relatively low pressure and consumes less energy, offering significant economic advantages and making it one of the most competitive technologies in the field of advanced drinking water treatment.

[0004] However, in practical engineering applications, nanofiltration membrane systems face serious membrane fouling problems during long-term operation, especially inorganic salt scaling, which has become a core bottleneck restricting the stable operation of nanofiltration processes and extending membrane lifespan. Its formation mechanism lies in the fact that as divalent cations (Ca) in the feed water... 2+ Mg 2+ (etc.) and anions (SO4) 2- CO3 2- HCO3 - Insoluble salts (such as gypsum CaSO4·2H2O, calcium carbonate CaCO3, etc.) continuously accumulate within the concentration polarization layer on the membrane surface. When the local ion concentration exceeds its solubility limit, sparingly soluble salts nucleate and grow on the membrane surface, gradually forming a dense scale layer, leading to a series of negative consequences: 1. Continuous decline in membrane flux: Scale buildup blocks membrane pores and flow channels, resulting in a significant decrease in water flux, and even irreversible loss. 2. Increased operating pressure: In order to maintain water production, the inlet water pressure needs to be continuously increased, which increases the system's energy consumption; 3. Damage to membrane materials: The physical embedding and chemical corrosion of inorganic salt crystals can lead to structural damage to membrane materials and shorten the replacement cycle of membrane modules; 4. Increased operation and maintenance costs: Frequent chemical cleaning (acid washing, alkaline washing) shortens the membrane's lifespan and causes secondary pollution and increases the cost of chemical agents.

[0005] To address the aforementioned scaling problem, commonly used control strategies in existing technologies mainly include the following categories: First, pretreatment enhancement, such as lime softening, ion exchange, and activated carbon adsorption, to reduce the concentration of scaling ions in the influent; Second, chemical cleaning, periodically using acid solutions (hydrochloric acid, citric acid, etc.) or alkaline solutions and chelating agents (EDTA, etc.) to clean the membrane surface to dissolve and remove the scale layer; Third, membrane material modification, improving the membrane's antifouling performance through surface hydrophilic modification, charge regulation, or special coating technologies; Fourth, optimizing operating conditions, such as adjusting the recovery rate, operating pressure, or flow rate to mitigate concentration polarization and scaling tendency.

[0006] However, the above methods all have limitations to varying degrees: the pretreatment process is long and the investment cost is high; chemical cleaning operations are frequent, which can easily generate secondary pollution and affect membrane life; membrane modification technology is complex and difficult to prepare on a large scale; and optimizing operating conditions sacrifices water production rate or treatment efficiency. Under complex and variable raw water quality conditions, the above methods are difficult to simultaneously achieve multiple objectives such as efficient scale inhibition, economical operation, and ease of operation.

[0007] Recent studies have shown that introducing natural organic polymers (such as humic acid) can be a potential scale inhibition strategy, as they can interfere with the growth of sparingly soluble salt crystal nuclei through adsorption and complexation. However, under long-term operating conditions, the accumulation of introduced natural organic polymers on the membrane surface may form an organic fouling layer. This layer can act as a heterogeneous nucleation interface and promote inorganic salt scaling, increasing the difficulty of cleaning. Therefore, there is an urgent need to develop a novel, efficient, and cost-effective nanofiltration membrane scale inhibition method that combines interface regulation and solution chemistry adjustment. This method should effectively solve the problem of inorganic salt scaling while avoiding the irreversible complex fouling defects caused by individual organic substances, thus comprehensively improving the long-term operational stability and sustainability of nanofiltration membrane systems. Summary of the Invention

[0008] The purpose of this invention is to provide a technology and method for synergistically mitigating inorganic salt scaling on nanofiltration membrane surfaces using sodium chloride and natural organic polymers for advanced drinking water treatment. The core idea is to simultaneously and precisely add sodium chloride and natural organic polymers during the pre-membrane water conditioning stage. Through the synergistic effect of charge shielding, ion strength regulation, complexation, and steric hindrance, the tendency of inorganic salts to deposit and scale on the nanofiltration membrane surface is reduced from two dimensions: ion morphology control and crystal nucleation inhibition. This achieves efficient and stable operation of the membrane system without altering the nanofiltration membrane material itself.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: On one hand, the present invention provides a device for mitigating inorganic salt scaling on the surface of a nanofiltration membrane, comprising a raw water flow stabilization unit, a water quality co-regulation unit, a nanofiltration separation unit, and a product water buffer collection unit connected in sequence by pipelines; the raw water flow stabilization unit is equipped with a liquid level balancing component to eliminate raw water flow fluctuations and output raw water with a stable flow rate; the water quality co-regulation unit is equipped with a water quality monitoring feedback component, a stirring and mixing component, and a dual-component dosing component, the dual-component dosing component being used to co-add sodium chloride and natural organic polymers to the raw water according to the water quality monitoring feedback; the nanofiltration separation unit is internally equipped with a nanofiltration membrane assembly and connected to a pressure stabilizing drive component to provide a stable filtration drive pressure; the product water buffer collection unit is equipped with an anti-backflow structure and a buffer flow stabilization structure for collecting nanofiltration product water.

[0010] Preferably, the raw water flow stabilization unit specifically includes a collection tank and a constant-level water tank connected in series. The constant-level water tank is equipped with a water level sensor, and the flow rate is stabilized through dynamic balance of inlet and outlet water. Specifically, the upper side wall of the collection tank has a collection tank inlet for receiving raw water from the raw water source; the lower end of the collection tank has a collection tank outlet. The collection tank inlet is connected to an inlet booster pump and an inlet valve, and the booster pump provides power to stably introduce raw water. The collection tank, as the primary buffer unit of the system, provides temporary storage and preliminary water volume regulation functions through its physical volume.

[0011] The constant-level water tank is equipped with a water level sensor to monitor water level changes in real time. The upper part of the side wall of the constant-level water tank has an inlet, and the lower part has an outlet. The outlet of the collection tank is connected to the inlet of the constant-level water tank via a connecting pipe. The constant-level water tank controls the opening and closing of the inlet valve through feedback signals from the water level sensor to maintain a constant water level, ensuring that the downstream water quality conditioning tank and nanofiltration membrane module receive a stable and uniform influent flow rate, and avoiding shock loads on the membrane module caused by flow fluctuations.

[0012] The water quality synergistic regulation unit includes a water quality regulation tank. The water quality monitoring and feedback component, stirring and mixing component, and two-component dosing component are all located within the water quality regulation tank. The inlet of the water quality regulation tank is connected to the outlet of the constant-level water tank via a pipeline. Specifically, the lower part of the side wall of the water quality regulation tank has an inlet, and the upper part has an outlet. The side wall of the water quality regulation tank is connected to the water quality monitoring and feedback component for real-time online monitoring of raw water quality parameters. The inlet of the water quality regulation tank is connected to the outlet of the constant-level water tank via a pipeline. This unit is the core functional unit for achieving synergistic scale inhibition in this invention. Through online water quality parameter acquisition and control, it achieves precise and dynamic dosing of the regulator, and the stirring device ensures thorough homogeneous mixing of the regulator and the raw water.

[0013] Preferably, the nanofiltration separation unit includes a pressure-driven membrane filter and a nanofiltration membrane module disposed therein. The membrane filter has a membrane filter inlet on its side wall, a vent at its bottom, and a pressurization port at its upper side wall. The membrane filter inlet is connected to the outlet of the water quality conditioning tank through an inlet valve and a booster pump. The nanofiltration membrane module is connected to the outlet pipeline of the pressure-driven membrane filter. The pressurization port is connected to an air pressurization device to provide a stable operating pressure to drive the nanofiltration separation process.

[0014] Preferably, the product water tank is equipped with an overflow tank and a collection tank. The overflow tank has an inlet on the upper side wall, and the collection tank has an outlet on the lower side wall, both connected to subsequent process units. The overflow tank inlet is connected to the outlet pipe of the pressure-driven membrane filter, and a check valve is installed on the outlet pipe to prevent backflow of product water. An overflow weir with a height difference of 15-30 cm is provided between the overflow tank and the collection tank. After being buffered and stabilized by the overflow tank, the product water overflows smoothly into the collection tank, ensuring stable product water quality.

[0015] Furthermore, the raw water can be surface water, groundwater, or slightly polluted water sources, and is especially suitable for raw water with high hardness, high alkalinity, or containing more natural organic polymers and scale-forming ions.

[0016] Furthermore, the water collection tank, constant water tank, water quality conditioning tank, pressure-driven membrane filter tank and product water tank are all equipped with maintenance manholes and drain valves to facilitate daily maintenance and thorough drainage when the system is shut down.

[0017] Furthermore, a backwashing interface can be provided above the membrane module of the pressure-driven membrane filter, which can periodically or automatically start the backwashing program according to the change of transmembrane pressure difference, and use the product water or clean water source to backwash the membrane surface, thereby further extending the continuous operation cycle.

[0018] Furthermore, the connecting pipes between the water collection tank, constant water tank, water quality conditioning tank and pressure-driven membrane filter are all made of UPVC material with smooth inner walls to reduce water flow resistance, and are all equipped with flow regulating valves to facilitate precise control of the flow between each unit.

[0019] On the other hand, the present invention also provides a method for performing advanced drinking water treatment using the above-mentioned apparatus, which is carried out in sequence according to the following steps: S1. Stabilization Treatment. Raw water is driven by the inlet booster pump and enters the collection tank through the inlet valve and the inlet of the collection tank to complete the initial collection. Subsequently, the raw water flows into the constant level tank through the outlet of the collection tank. The water level sensor inside the constant level tank monitors the water level in the tank in real time. By dynamically adjusting the opening and closing of the inlet valve, a constant water level is maintained to ensure a stable flow of water entering the subsequent treatment units and effectively avoid the impact load on the membrane module caused by the flow fluctuation at the water source.

[0020] S2. Modification and Conditioning. Water from the constant-level water tank flows into the water quality conditioning tank through the outlet. The water quality monitoring and feedback component collects the water quality parameters of the incoming water in real time, including key indicators such as pH value, conductivity, hardness, and total organic carbon (TOC) concentration. Based on the real-time monitoring data, sodium chloride and natural organic polymers (humic acid, sodium alginate, etc.) are precisely and dynamically added by the two-component dosing component. The stirring device operates continuously at a speed of 100 to 600 rpm to ensure that the conditioning agent and the raw water are fully homogenized and mixed to achieve water quality homogenization treatment.

[0021] S3. Stable Pressure Filtration. The effluent from the water conditioning tank is pumped through the tank outlet to the inlet of the pressure-driven membrane filter via a booster pump and inlet valve. An air pressurization device provides a stable operating pressure of 0.3-1.2 MPa through the pressurization port, driving water molecules through the nanofiltration membrane module for deep purification. During this process, the previously added sodium chloride and natural organic polymers work synergistically to inhibit scale buildup, significantly reducing inorganic salt deposition and scaling on the nanofiltration membrane surface, maintaining stable filtration flux and separation efficiency.

[0022] S4. Buffer Collection. Nanofiltration permeate enters the overflow tank of the permeate tank through the outlet pipeline. The check valve installed on the outlet pipeline effectively prevents backflow of permeate. The overflow weir plate between the overflow tank and the collection tank buffers and stabilizes the permeate flow, eliminating secondary disturbances caused by water flow impact. Finally, the buffered and stabilized permeate overflows smoothly into the collection tank, and is then transported to subsequent processes through the outlet of the collection tank to complete the safe and advanced treatment of drinking water.

[0023] Based on the above-described invention, the water purification and scale inhibition mechanism of the present invention can be explained from the following levels: 1. Physical buffering and water stabilization mechanism: The two-stage buffering system consisting of the collection tank and the constant water level tank eliminates the impact of raw water source flow fluctuations on the downstream membrane system through physical volume regulation and closed-loop control by water level sensors, ensuring that the nanofiltration membrane module operates stably under constant feed water conditions, and laying the foundation for suppressing concentration polarization and scaling from an operational perspective.

[0024] 2. Charge shielding and ionic strength regulation mechanism: Sodium chloride, as a strong electrolyte, completely dissociates into Na+ in water. + and Cl - This significantly increases the ionic strength of the water. According to the double-layer theory, the increase in ionic strength compresses the Ca2+ layer. 2+ Mg 2+The thickness of the electrostatic double layer between divalent cations and the negatively charged nanofiltration membrane surface reduces the electrostatic adsorption force between ions and the membrane surface (charge shielding effect), thereby inhibiting the initial adsorption and enrichment of scaling ions on the membrane surface. Simultaneously, the change in ionic strength affects the activity product of sparingly soluble salts such as CaSO4 and CaCO3, increasing their apparent solubility within a certain range and delaying the occurrence of supersaturated precipitation.

[0025] 3. Complexation and Free Ion Consumption Mechanism: Natural organic polymers (such as humic acid) contain abundant active functional groups such as carboxyl groups (—COOH), hydroxyl groups (—OH), and phenolic hydroxyl groups, which can react with free Ca in water. 2+ Mg 2+ Divalent cations undergo complexation reactions to form stable, soluble organometallic complexes. By consuming free scaling ions and reducing their effective concentration, the number of ions in the solution that can participate in nucleation and crystallization is reduced, thereby delaying the time for sparingly soluble salts such as CaSO4 and CaCO3 to reach a supersaturated critical state and effectively slowing down the scaling process.

[0026] 4. Steric Hinderation and Crystal Nucleation Inhibition Mechanism: Natural organic macromolecules adsorb onto the surface of sparingly soluble salt crystal nuclei such as CaSO4 or form steric barriers around them, hindering the contact and binding of crystal nuclei with free ions in the solution, thereby interfering with further crystal growth and aggregation. The steric hindrance effect of organic macromolecules such as humic acid can effectively inhibit the crystal nucleation rate (nucleation inhibition) and crystal growth rate (growth inhibition), keeping CaSO4 and other substances in the solution in a metastable state with low crystallinity and reducing their tendency to deposit on the nanofiltration membrane surface.

[0027] 5. Dual synergistic effect mechanism: The charge shielding and ionic strength regulation of sodium chloride, together with the complexation-steric inhibition of natural organic polymers, complement each other in terms of mechanism of action and have a synergistic effect in terms of effect. They work together to inhibit scale by reducing ion adsorption on the membrane surface (macro-interface behavior regulation) and inhibiting crystal nucleus formation and growth (micro-crystallization process regulation). The overall effect is significantly better than that of any one component used alone.

[0028] Compared with the prior art, the present invention has the following beneficial effects: 1. Effectively inhibits inorganic salt scaling: Through the synergistic effect of sodium chloride and natural organic polymers, the deposition and crystallization of inorganic salts such as calcium and magnesium on the nanofiltration membrane surface are inhibited by a quadruple mechanism of charge shielding, ionic strength regulation, complexation and steric hindrance, which significantly reduces the risk of membrane fouling and scaling and improves the long-term operational stability of nanofiltration membranes.

[0029] 2. Improve the safety of effluent water quality: Through pre-membrane water quality optimization, ensure the stable operation of nanofiltration membrane under high flux and low pressure loss conditions, effectively remove hardness ions, heavy metals and macromolecular organic matter, and improve the safety and drinking taste of the produced water.

[0030] 3. Reduced operation and maintenance costs: Reduces fouling and contaminant accumulation on membrane surfaces, significantly reduces membrane cleaning frequency and chemical cleaning intensity, slows down membrane performance degradation, extends membrane module replacement cycle, and comprehensively reduces system operation and maintenance costs.

[0031] 4. Intelligent dynamic control with strong adaptability: The online water quality monitoring and closed-loop intelligent control mechanism realizes dynamic response and precise regulation agent addition under water quality fluctuation conditions, improves the system's adaptability to complex raw water quality, and ensures long-term continuous and stable operation.

[0032] 5. Modular design and wide applicability: The system features a modular design and is easy to operate. It can be flexibly integrated with conventional drinking water treatment processes (such as coagulation, sedimentation, and sand filtration), making it suitable for different scale scenarios such as rural areas, towns, and emergency water supply. It has broad prospects for promotion and application.

[0033] The technical solution of the present invention will be further described in detail below through embodiments. Attached Figure Description

[0034] Figure 1 A schematic diagram of the structure of a device for alleviating inorganic salt fouling on the surface of a nanofiltration membrane provided by the present invention; Figure 2 This is a flux diagram of the nanofiltration process after adding different concentrations of sodium chloride and natural organic polymeric humic acid in an embodiment of the present invention.

[0035] Figure label: 1. Water collection tank; 2. Constant-level water tank; 3. Water quality equalization tank; 4. Pressure-driven membrane filter; 5. Product water tank; 11. Water collection tank inlet; 12. Water collection tank outlet; 13. First inlet valve; 14. Inlet booster pump; 21. Water level sensor; 22. Constant-level water tank inlet; 23. Constant-level water tank outlet; 31. Two-component dosing assembly; 32. Stirring device; 33. Water quality equalization tank inlet... 34. Water outlet; 35. Water quality regulating tank outlet; 46. Water quality monitoring feedback component; 47. Nanofiltration membrane module; 48. Membrane filter inlet; 49. Vent outlet; 40. Pressurization port; 41. Outlet pipeline; 42. Second inlet valve; 53. Booster pump; 54. Air pressurization device; 55. Overflow tank; 56. Collection tank; 57. Overflow tank inlet; 58. Collection tank outlet; 59. Check valve. Detailed Implementation

[0036] To enable those skilled in the art to better understand the present application, the technical solutions in specific embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by those skilled in the art.

[0037] The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects.

[0038] Example 1 Combination Figure 1 As shown, this embodiment provides a device for alleviating inorganic salt scaling on the surface of a nanofiltration membrane. The specific structure includes a water collection tank 1, a constant water tank 2, a water quality conditioning tank 3, a pressure-driven membrane filter tank 4, and a product water tank 5. The upper part of the side wall of the water collection tank 1 is provided with a water collection tank inlet 11, and the lower part is provided with a water collection tank outlet 12. The water collection tank inlet 11 is connected to the water inlet booster pump 14 and the first water inlet valve 13. The constant level water tank 2 is provided with a water level sensor 21 inside. The upper part of the side wall is provided with a constant level water tank inlet 22, and the lower part is provided with a constant level water tank outlet 23. The water collection tank outlet 12 is connected to the constant level water tank inlet 22 through a pipe. The water quality conditioning tank 3 is provided with a dual-component dosing component 31 and a stirring device 32. The lower part of the side wall is provided with a water quality conditioning tank inlet 33, and the upper part is provided with a water quality conditioning tank outlet 34. The side wall is connected to a water quality monitoring feedback component 35. The inlet 33 is connected to the outlet 23 of the constant water level tank via a pipeline; the pressure-driven membrane filter 4 is equipped with a nanofiltration membrane module 41, a membrane filter inlet 42 on the side wall, a vent 43 at the bottom, and a pressurization port 44 at the upper part of the side wall. The membrane filter inlet 42 is connected to the outlet 34 of the water quality conditioning tank via a second inlet valve 46 and a lift pump 47. The nanofiltration membrane module 41 is connected to the outlet pipeline 45, and the pressurization port 44 is connected to the air pressurization device 48. The product water tank 5 is equipped with an overflow tank 51 and a collection tank 52. The overflow tank inlet 53 is connected to the outlet pipeline 45, and a check valve 55 is installed on the outlet pipeline. The collection tank outlet 54 is connected to the subsequent process.

[0039] The following steps are taken to carry out advanced drinking water treatment using the above-mentioned device: S1. Stabilization Treatment: In this embodiment, the raw water is high-hardness surface water (total hardness approximately 450 mg / L, calculated as CaCO3, pH 7.5, conductivity approximately 800 μS / cm). The raw water enters the collection tank 1 through the inlet 11 of the collection tank via the inlet pump 14 and the first inlet valve 13; subsequently, the raw water flows into the constant-level water tank 2 through the outlet 12 of the collection tank. The water level sensor 21 monitors the water level in real time, and dynamic balance adjustment ensures stable water flow, effectively avoiding shock loads on the membrane module.

[0040] S2. Modification and Adjustment: Water from the constant-level water tank 2 flows into the water quality adjustment tank 3. The water quality monitoring feedback component 35 collects water quality parameters in real time, including pH value, conductivity, hardness, and TOC concentration. Based on the feedback of the above parameters, sodium chloride (dosage 10 g / L) and natural organic high molecular weight humic acid (dosage 50 mg / L) are precisely added through the two-component dosing component 31. The stirring device 32 runs continuously at a speed of 300 rpm to ensure that the conditioner and the raw water are fully homogeneously mixed.

[0041] S3. Stable pressure filtration: The regulated effluent is delivered to the pressure-driven membrane filter 4 via the booster pump 47 and the second inlet valve 46. The air pressurization device 48 provides a stable operating pressure of 1.0 MPa through the pressurization port 44 for nanofiltration. The nanofiltration membrane module 41 uses a commercial NF270 membrane with the following parameters: molecular weight cutoff of 250 to 350 Da, surface roughness of 3.5 nm, and isoelectric point of 3.2. The membrane fouling problem is effectively alleviated through the synergistic effect of sodium chloride and humic acid.

[0042] S4. Buffer Collection: Nanofiltration permeate enters overflow tank 51 through outlet pipe 45, and check valve 55 prevents backflow of permeate; an overflow weir plate with a height difference of 30 cm is set between overflow tank 51 and collection tank 52, and permeate overflows smoothly to collection tank 52 after buffering and stabilizing the flow; outlet 54 of collection tank transports permeate to subsequent water supply processes, realizing safe deep treatment of drinking water and long-term stable operation of membrane system.

[0043] Example 2 The main difference between this embodiment and Example 1 is that the natural organic polymer is replaced with sodium alginate at a concentration of 30 mg / L; the sodium chloride dosage is adjusted to 5 g / L, while the remaining structure and steps are the same as in Example 1. This embodiment verifies that when the type of natural organic polymer is changed, the synergistic scale inhibition effect of sodium chloride and sodium alginate is equally significant, and the membrane flux and recovery rate are better than the control group without any regulators.

[0044] Example 3 The main difference between this embodiment and Embodiment 1 is that the stirring speed is adjusted to 500 rpm to accommodate higher viscosity influent; the remaining structure and steps are the same as in Embodiment 1. This embodiment verifies that the present invention has good scale inhibition effect and system stability under different combinations of operating parameters.

[0045] Example 4 The main difference between this embodiment and Embodiment 1 is that the air pressurization device provides a stable air pressure adjusted to 0.5 MPa, suitable for low-pressure nanofiltration membrane modules; the overflow weir plate height difference is set to 15 cm, and the remaining structure and steps are the same as in Embodiment 1. This embodiment verifies that the present invention has good scale inhibition effect and system stability under different combinations of operating parameters.

[0046] Specific experimental content: To verify the technical effects of the present invention, the following systematic experiments were conducted: Raw water preparation: A CaSO4 solution with a concentration of 21 mmol / L was prepared using CaCl2 and Na2SO4 to simulate the gypsum (CaSO4·H2O) scaling scenario commonly encountered in actual nanofiltration treatment, in order to evaluate the inhibitory effect of different combinations of regulators on inorganic salt scaling during nanofiltration.

[0047] Nanofiltration membrane selection: Commercial NF270 flat sheet nanofiltration membrane was adopted, with a molecular weight cutoff of 250 to 350 Da, a membrane surface roughness of 3.5 nm, and an isoelectric point of 3.2. It is one of the most widely used polyamide composite nanofiltration membranes in the field of advanced drinking water treatment.

[0048] Experimental settings: Different concentrations of sodium chloride (0, 3, 5, 10 g / L) and natural organic polymeric humic acid (0, 10, 50 mg / L), as well as combinations thereof, were added to the raw water. Nanofiltration experiments were conducted under a stable operating pressure of 1.0 MPa, and the changes in normalized flux and water recovery rate under each condition were recorded.

[0049] The test results are as follows: 1. When the sodium chloride concentration was 0 g / L, the nanofiltration membrane experienced severe scaling when the water recovery rate was only 57.5%, and the normalized flux was as low as 0.03, indicating that the gypsum scaling was extremely serious.

[0050] 2. When the sodium chloride concentration was increased to 3, 5 and 10 g / L, the final water recovery rate increased to 65.0%, 67.5% and 70.0%, respectively, with corresponding normalized fluxes of 0.04, 0.12 and 0.40, respectively. This indicates that sodium chloride effectively delayed gypsum crystallization nucleation and film deposition by increasing ionic strength and reducing electrostatic adsorption.

[0051] 3. When 10 mg / L humic acid was added alone, scaling was slightly delayed, and the water recovery rate increased to 62.5%, with a normalized flux of 0.09. When the humic acid concentration was increased to 50 mg / L, the inhibitory effect on flux decay was significantly enhanced, and the normalized flux reached as high as 0.33 when the water recovery rate reached 70.0%, indicating that humic acid complexes Ca... 2+ The steric hindrance effect has a significant inhibitory effect on the formation and growth of gypsum crystals.

[0052] 4. When sodium chloride and humic acid are added simultaneously, the synergistic scale inhibition effect is most prominent, the water recovery rate is always maintained at 70.0%, and the normalized flux remains at a high level, showing significantly better scale inhibition performance than adding either component alone.

[0053] For details, please refer to Figure 2 As shown, Figure 2 The first table, from left to right, shows the effect of adding different concentrations of sodium chloride on membrane flux and water recovery rate during nanofiltration without the addition of humic acid. The second table shows the effect of adding 10 mg / L humic acid and different concentrations of sodium chloride on membrane flux and water recovery rate during nanofiltration. The third table shows the effect of adding 50 mg / L humic acid and different concentrations of sodium chloride on membrane flux and water recovery rate during nanofiltration.

[0054] Figure 2 The three tables in the paper collectively demonstrate the mechanism of this technology: NaCl increases ionic strength, thereby improving the solubility of sparingly soluble salts (solubility product effect). Natural organic polymers complex free calcium ions and hinder crystal growth (steric hindrance effect). The combined use of these two methods achieves a synergistic scale inhibition effect of "1+1>2", solving the problem of single methods easily failing at high recovery rates.

[0055] The above experimental results fully verify the scientific nature and effectiveness of the proposed technology of synergistic mitigation of inorganic salt scaling on nanofiltration membrane surface by sodium chloride and natural organic polymers, and provide a solid experimental basis for the promotion and application of this technology in the practice of drinking water deep treatment engineering.

[0056] Finally, it should be noted that the described embodiments are merely some, not all, of the embodiments of the present invention. Those skilled in the art will understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the claims and their equivalents; that is, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A device for mitigating inorganic salt scaling on the surface of a nanofiltration membrane, characterized in that, It includes a raw water flow stabilization unit, a water quality coordination and regulation unit, a nanofiltration separation unit, and a product water buffer and collection unit connected in sequence by pipelines; The raw water flow stabilization unit is equipped with a liquid level balancing component to eliminate raw water flow fluctuations and output raw water with a stable flow rate. The water quality synergistic adjustment unit is equipped with a water quality monitoring feedback component, a stirring and mixing component, and a two-component dosing component. The two-component dosing component is used to synergistically add sodium chloride and a natural organic polymer with ion complexing and crystal growth inhibition effects to the raw water according to the water quality monitoring feedback. The nanofiltration separation unit is equipped with a nanofiltration membrane assembly and is connected to a voltage stabilizing drive assembly to provide a stable filtration drive pressure. The product water buffer collection unit is equipped with an anti-backflow structure and a buffer flow stabilization structure for collecting nanofiltration product water.

2. The apparatus according to claim 1, characterized in that, The raw water flow stabilization unit specifically includes a water collection tank and a constant-level water tank connected in series; the constant-level water tank is equipped with a water level sensor, and the flow rate is stabilized through the dynamic balance of inlet and outlet water.

3. The apparatus according to claim 1, characterized in that, The water quality co-regulation unit includes a water quality regulation tank. The water quality monitoring and feedback component, the stirring and mixing component, and the two-component dosing component are all installed in the water quality regulation tank. The inlet of the water quality regulation tank is connected to the outlet of the constant-level water tank through a pipeline.

4. The apparatus according to claim 3, characterized in that, The water quality monitoring feedback component includes one or more of the following: an online pH meter, a conductivity meter, a hardness sensor, and a TOC analyzer.

5. The apparatus according to claim 3, characterized in that, The mixing component is a variable speed mixing device with an operating speed range of 100-600 rpm.

6. The apparatus according to claim 1, characterized in that, The natural organic polymer is one or more of humic acid and sodium alginate.

7. The apparatus according to claim 1, characterized in that, The pressure stabilizing drive component is an air pressurization device configured to provide a stable air pressure of 0.3-1.2 MPa to the nanofiltration separation unit; the nanofiltration separation unit is provided with an air vent at the bottom for discharging concentrated water.

8. The apparatus according to claim 1, characterized in that, The water production buffer collection unit specifically includes an overflow tank and a collection tank; the buffer flow stabilization structure is an overflow weir plate set between the overflow tank and the collection tank, and the height difference of the overflow weir plate is 15-30 cm.

9. The apparatus according to claim 1, characterized in that, The inner walls of the connecting pipes between each unit are smooth and each is equipped with a flow regulating valve.

10. A method for advanced drinking water treatment using the apparatus as described in any one of claims 1-9, characterized in that, Includes the following steps: S1. Stabilization treatment: Raw water enters the raw water stabilization unit, and through dynamic balance adjustment of liquid level, a continuous and stable water volume is ensured to enter the subsequent units; S2. Modification and Adjustment: In the water quality co-regulation unit, based on real-time monitored water quality parameters, sodium chloride and natural organic polymers are precisely added and mixed evenly to construct an influent system with low scaling risk. S3. Stable pressure filtration: The regulated water enters the nanofiltration separation unit and is filtered under the stable pressure provided by the pressure stabilization drive component. The synergistic effect of sodium chloride and natural organic polymers inhibits the scaling of inorganic salts on the membrane surface. S4, Buffer Collection: Nanofiltration permeate is output after being buffered and stabilized by the permeate buffer collection unit.

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