Method for slowing down membrane scaling and improving membrane treatment capacity in saline-alkali water treatment

Abstract

The invention discloses a method for slowing down membrane scaling and improving membrane treatment capacity in saline-alkali water treatment, and belongs to the technical field of agricultural saline-alkali water treatment and membrane separation, and the method comprises the following steps: (1) for hardness ions with the highest content in saline-alkali water to be treated, calculating the theoretical ion concentration # imgabs0 # of the hardness ions on the surface of a separation membrane and the inorganic scaling supersaturation index SI under a set working condition, predicting the membrane scaling trend in the separation process, and determining the target removal rate of the hardness ions in the agent softening process; (2) calculating the target removal rate of other hardness ions in the saline-alkali water to be treated; (3) optimizing the process parameters of the agent softening process so as to achieve the target removal rate of the hardness ions calculated in the above steps; and (4) carrying out agent softening on the saline-alkali water to be treated under the optimized process parameters, and filtering the saline-alkali water softened by the agent by using a separation membrane, thereby retarding membrane scaling and improving the membrane treatment capacity.

Description

Technical Field

[0001] The present invention relates to the technical fields of agricultural saline-alkali water treatment and membrane separation, and particularly relates to a method for slowing down membrane fouling and improving membrane treatment capacity in saline-alkali water treatment. Background Art

[0002] In the prior art, flooding and salt flushing methods are mostly used to alleviate soil salinization, resulting in a large amount of saline-alkali water with high salinity, high pH value and complex components, which is difficult to be directly reused. The pressure-driven membrane system coupling nanofiltration and reverse osmosis can efficiently separate mono- and multi-valent ions in saline-alkali water and desalinate it to achieve the purpose of recycling each component in the saline-alkali water. However, there are a large number of hardness ions (calcium ions, magnesium ions) in it, which are easy to scale on the membrane surface, resulting in reduced water treatment efficiency and increased costs, restricting the application of the pressure-driven membrane system in saline-alkali water treatment.

[0003] By means of technical means such as surface energy regulation, topological structure optimization and functional group grafting, the development of anti-fouling separation membranes provides an innovative solution for membrane system optimization. For example, the Chinese patent document with the publication number CN110433667A discloses an anti-pollution and anti-fouling separation membrane and its preparation method. This invention resists organic pollution and inorganic salt fouling by setting a metal-polybasic organic acid complex layer on the base membrane. The Chinese patent document with the publication number CN119701682A discloses an anti-fouling composite membrane, its preparation method and application. This invention sets a polyphenol-aminosulfonic acid grafting layer on the surface of the polyamide membrane to reduce the interaction force between the membrane surface and Ca scale and improve its own anti-fouling ability. Although the anti-fouling separation membrane shows significant advantages in pollution control, its technical promotion still faces multiple challenges, including cost issues, process batch-to-batch difference issues, coating stability issues, etc.

[0004] There are also studies on slowing down membrane scaling by adding antiscalants. For example, patent document with publication number CN103347594A discloses a method and system for controlling scaling in membrane system operation. The invention selects one or more antiscalants corresponding to the components of the scale based on water supply conditions, membrane materials, membrane scaling conditions and one or more items in a kinetic study of the reaction between the antiscalant and one or more components of the scale; estimates the composition of one or more selected antiscalants based on the total scaling rate constant and the objective function; and applies the estimated dosage of the composition of one or more antiscalants to control scaling in membrane system operation. The Chinese patent document with publication number CN105585076A discloses a method for preventing scaling of charged semipermeable membranes in water treatment applications. The invention adds a certain concentration of cationic polyelectrolyte to the feed liquid, so that hardness ions are first nucleated outside the semipermeable membrane, preventing high-concentration hardness ions from entering the semipermeable membrane. When the water flux decays to a certain extent, the membrane or membrane element is conventionally acid washed to wash out the scale and cationic polyelectrolyte together. When running again, cationic polyelectrolyte is still added to the feed liquid to circulate. The above inventions all require the addition of scale inhibitors, which can effectively delay the deposition of inorganic salts, but may cause secondary pollution and by-product generation.

[0005] Therefore, optimizing and improving the softening process of existing saline-alkali water treatment agents and constructing a method to slow down membrane scaling and improve membrane treatment capacity are of great significance for agricultural saline-alkali water treatment. Summary of the invention

[0006] The invention provides a method for slowing down membrane scaling and improving membrane treatment capacity in saline-alkali water treatment, which has broad application prospects in the field of water softening and is particularly suitable for the treatment of agricultural flooding saline-alkali water and wastewater containing high-concentration hardness ions.

[0007] The specific technical solutions adopted are as follows: A method for slowing down membrane scaling and improving membrane treatment capacity in saline-alkali water treatment specifically comprises the following steps: (1) For the hardness ion with the highest content in the saline-alkali water to be treated, calculate its theoretical ion concentration on the surface of the separation membrane based on the parameters of the separation membrane and the water quality indicators of the saline-alkali water to be treated. , based on the theoretical ion concentration obtained Calculate the inorganic scaling supersaturation index of the hardness ion under the set working conditions SI , obtained by the inorganic scaling supersaturation index SI Predict membrane fouling trends during separation using the inorganic fouling supersaturation index SI = 0 when the hardness ion removal rate is taken as the target removal rate of the hardness ion in the softening process; (2) For other hardness ions in the saline-alkali water to be treated, when the inorganic scaling supersaturation index SI = 0, the target removal rate of other hardness ions in the saline-alkali water to be treated is calculated by extrapolating from the relationship diagram between the pH value after chemical softening of the saline-alkali water to be treated and the removal rate of other hardness ions; (3) Optimize the process parameters of the chemical softening process to achieve the target removal rate of hardness ions calculated in steps (1) and (2); (4) Carry out chemical softening of the saline-alkali water to be treated under the optimized process parameters in step (3), and then filter the chemically softened saline-alkali water with a separation membrane, thereby slowing down membrane scaling and improving the membrane treatment capacity.

[0008] The present invention determines the hardness ion removal target in the chemical softening process through a specific method, optimizes the parameters to construct a chemical softening method with precise dosing, thereby slowing down membrane scaling and improving the membrane treatment capacity.

[0009] Optionally, the hardness ions in the saline-alkali water to be treated include calcium ions and magnesium ions.

[0010] Specifically, in the saline-alkali water to be treated, the calcium ion concentration ≥ 200 mg / L and the magnesium ion concentration ≥ 100 mg / L.

[0011] Optionally, the separation membrane is a nanofiltration membrane or a reverse osmosis membrane, and further preferably a nanofiltration membrane.

[0012] Optionally, in step (1), the theoretical ion concentration on the surface of the separation membrane is calculated by the following formula: ; where C F is the concentration of the corresponding ion in the saline-alkali water to be treated, mg / L; is the separation membrane recovery rate, %; is the rejection rate of the separation membrane for the corresponding ion, %.

[0013] Specifically, the inorganic scaling supersaturation index SI is calculated by the following formula: ; where IAP is the ionic activity product of inorganic scaling, K SP is the solubility product of inorganic scaling, IAP and K SP can be obtained by referring to the handbook according to the set pH value, temperature, the theoretical ion concentration on the surface of the separation membrane and the type of inorganic scaling.

[0014] Specifically, the inorganic scaling supersaturation index can be calculated by the software Visual MINTEQ 3.1 SI , inputting the set pH value, temperature, and the theoretical ion concentration on the surface of the separation membrane , selecting the correction model and the type of inorganic scaling, and then the inorganic scaling supersaturation index can be obtained SI .

[0015] Specifically, the method for predicting the membrane scaling trend during the separation process is as follows: If SI > 0, it means that the corresponding inorganic scaling is in a supersaturated state and has a tendency to scale on the membrane surface; if SI = 0, it means that the corresponding inorganic scaling is in a dynamic equilibrium state; if SI < 0, it means that the corresponding inorganic scaling is in an undersaturated state and has no tendency to scale on the membrane surface

[0016] In the saline-alkali water to be treated, the removal rate of other hardness ions will change with the change of the removal rate of the hardness ion with the highest content. On the basis that the hardness ion with the highest content reaches the target removal rate, when the inorganic scaling supersaturation index of other hardness ions SI = 0, determine the relationship diagram between the pH value after chemical softening of the saline-alkali water to be treated and the removal rate of other hardness ions, and further calculate the target removal rate of other hardness ions in the saline-alkali water to be treated

[0017] Preferably, in step (3), the optimized process parameters of the chemical softening process include but are not limited to the dosing amount of the softening agent, the softening time, or the softening stirring rate, etc

[0018] Preferably, the softening agent is trisodium phosphate

[0019] The present invention also provides an application of the method for reducing membrane scaling and improving membrane treatment capacity in the treatment of saline-alkali water in the field of water softening

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows The method of the present invention has simple steps and strong operability, provides a calculation method for the inorganic scaling supersaturation index of hardness ions SI , and uses the inorganic scaling supersaturation index SI to predict the membrane scaling trend during the separation process, thereby guiding the chemical softening process; compared with the traditional method of only calculating the dosing amount of the chemical agent through chemical equations or only from the solubility products of calcium carbonate and magnesium hydroxide, it can more accurately control the chemical softening process to slow down membrane scaling and improve membrane treatment capacity, providing strong technical support for engineering design and actual engineering applications Description of the Drawings

[0021] Figure 1 It is a flow chart of a method for reducing membrane fouling and improving membrane treatment capacity in saline-alkali water treatment.

[0022] Figure 2 It is a graph showing the change of the supersaturation index of calcium sulfate dihydrate with different calcium ion removal rates.

[0023] Figure 3 It is a graph showing the change of the influent pH with different magnesium ion removal rates when the supersaturation index of magnesium hydroxide is 0.

[0024] Figure 4 It is the influence of trisodium phosphate softening time, softening stirring rate and dosage on the removal rate of hardness ions. Among them, A is the influence of softening time on the removal rate of hardness ions, B is the influence of stirring rate on the removal rate of hardness ions, and C is the influence of dosage on the removal rate of hardness ions.

[0025] Figure 5 It is a SEM image of the nanofiltration membrane surface. Among them, A is the nanofiltration membrane without chemical softening treatment, and B is the nanofiltration membrane with chemical softening treatment (softening time 1 min, stirring rate 100 rpm, dosage 1200 mg / L). Detailed implementation manners

[0026] To make the objectives, features and advantages of the present invention more obvious and understandable, the following provides a detailed description through specific implementation manners. Many specific details are set forth in the following description in order to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described herein. Those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below. The technical features in each embodiment of the present invention can be combined correspondingly without conflict.

[0027] The operation methods without specific conditions indicated in the following embodiments are usually in accordance with conventional conditions or in accordance with the conditions recommended by the manufacturers. The content not described in detail in this specification belongs to the prior art well-known to those skilled in the art.

[0028] As Figure 1 shown, the present invention provides a method for reducing membrane fouling and improving membrane treatment capacity in saline-alkali water treatment, including the following steps: (1) Based on the dissolution equilibrium principle and the mass conservation principle, for the hardness ions with the highest content in the saline-alkali water to be treated, according to the parameters of the separation membrane and the water quality indexes of the saline-alkali water to be treated, calculate its theoretical ion concentration on the surface of the separation membrane , and calculate the inorganic scaling supersaturation index of the hardness ions under the set working conditions according to the obtained theoretical ion concentration SI, predicting the membrane fouling trend during the separation process based on the obtained inorganic scaling supersaturation index SI and using the hardness ion removal rate corresponding to the inorganic scaling supersaturation index SI = 0 as the target removal rate of the hardness ion during the chemical softening process; (2) In the saline-alkali water to be treated, the removal rates of other hardness ions will change with the change of the removal rate of the hardness ion with the highest content. On the basis that the hardness ion with the highest content reaches the target removal rate, for other hardness ions in the saline-alkali water to be treated, when the inorganic scaling supersaturation index SI = 0, determining the relationship diagram between the pH value after chemical softening of the saline-alkali water to be treated and the removal rates of other hardness ions, and further calculating the target removal rates of other hardness ions in the saline-alkali water to be treated; (3) Optimizing the process parameters of the chemical softening process to achieve the target removal rates of the hardness ions calculated in steps (1) and (2); (4) Conducting the chemical softening of the saline-alkali water to be treated under the optimized process parameters in step (3), and then filtering the chemically softened saline-alkali water with a separation membrane, thereby slowing down membrane fouling and improving the membrane treatment capacity.

[0029] In step (1), the theoretical ion concentration on the surface of the separation membrane is calculated by the following formula: ; where C F is the concentration of the corresponding ion in the saline-alkali water to be treated, mg / L; is the separation membrane recovery rate, %; is the rejection rate of the separation membrane for the corresponding ion, %.

[0030] The inorganic scaling supersaturation index SI is calculated by the following formula: ; where IAP is the ionic activity product of inorganic scaling, K SP is the solubility product of inorganic scaling, IAP and K SP can be obtained from the handbook according to the set pH value, temperature, the theoretical ion concentration on the surface of the separation membrane and the type of inorganic scaling. The target of removing hardness ions from saline-alkali water can be judged by the inorganic scaling supersaturation index. If SI > 0, it means that the corresponding inorganic scaling is in a supersaturated state and has a tendency to scale on the membrane surface; if SI= 0, it indicates that the corresponding inorganic scaling is in a dynamic equilibrium state; if SI < 0, it indicates that the corresponding inorganic scaling is in an undersaturated state and has no tendency to scale on the membrane surface. Taking the inorganic scaling supersaturation index SI = 0 as the target removal rate for the chemical softening process of hardness ions.

[0031] Example 1 (1) Measure the pH value, total dissolved solids (TDS) in water, calcium ion, and magnesium ion concentrations of agricultural saline-alkali water in a certain place. The specific data are shown in Table 1.

[0032] Table 1 Main water quality indicators of agricultural saline-alkali water in a certain place (concentration unit: mg / L)

[0033] (2) Query the rejection rate of a certain type of nanofiltration membrane for hardness ions. The calcium ion rejection rate is 75% and the magnesium ion rejection rate is 75%. Substitute the hardness ion rejection rate, calcium ion and magnesium ion concentrations in the saline-alkali water into the material balance equation to calculate the theoretical calcium and magnesium ion concentrations on the nanofiltration membrane surface. Input the ion concentrations on the membrane surface into the geochemical software, set the pH value, temperature, concentration unit, correction model, and inorganic scaling type under different working conditions, and thus obtain the supersaturation index of the inorganic scaling to be predicted SI .

[0034] (3) To determine the calcium ion removal rate, the target recovery rate of the nanofiltration process is set to 90%. Predict the scaling tendency of the nanofiltration membrane with a calcium ion removal rate between 0 and 99%, and set the step size to 2%. Except for the last point, there are a total of 51 data points. The results are as Figure 2 shown. As the calcium ion removal rate increases, at a recovery rate of 90%, the SI of calcium sulfate dihydrate gradually decreases. When the calcium ion removal rate increases to 82% or more, the SI of calcium sulfate dihydrate drops below 0, and at this time the scaling tendency is reversed. Therefore, it can be determined that in the nanofiltration salt separation process of agricultural saline-alkali water at a recovery rate of 90%, the target removal rate of calcium ions in the chemical softening process is 82%.

[0035] (4) On the basis of a nanofiltration recovery rate of 90% and a calcium ion removal rate set to 82%, investigate the ability of different magnesium ion removal rates (the investigation range is set the same as that of calcium ions) to resist the scaling of magnesium hydroxide caused by the increase in the inlet water pH (the pH value of the treated saline-alkali water after chemical softening). Fix the SI of magnesium hydroxide corresponding to magnesium ions to be 0, and obtain the inlet water pH that makes the magnesium hydroxide on the membrane surface just reach the equilibrium state at different magnesium ion removal rates, denoted as pHe. The results are as Figure 3As shown, as the magnesium ion removal rate increases from 0% to 99%, the pHe increases from 9.78 to 10.73. This indicates that the higher the magnesium ion removal rate in the softening step, the higher the inlet water pH that can cause magnesium hydroxide scaling on the membrane surface, that is, the stronger the ability to resist the increase in inlet water pH leading to magnesium hydroxide scaling (while achieving the target calcium ion removal rate and having a greater magnesium ion removal rate, the effect is better). Taking 40% as the target removal rate of magnesium ions, the corresponding pHe is 9.9, indicating that the nanofiltration membrane can be used to treat inlet water with pH ≤ 9.9, which can meet the vast majority of application scenarios.

[0036] (5) Sodium phosphate is selected as the softening agent, and the softening time of sodium phosphate, the dosage of sodium phosphate, and the softening stirring rate are changed to optimize the above process parameters to achieve the target removal rates of calcium ions and magnesium ions calculated in the above steps. The effects of the softening time of sodium phosphate, the softening stirring rate, and the dosage on the removal rate of hardness ions are as Figure 4 shown in A - C of [reference], and the softening parameters that can achieve the target removal rates of calcium ions and magnesium ions are determined as follows: the softening time is 1 - 30 min, the stirring rate is 100 - 500 rpm, and the dosage is 1200 - 1800 mg / L.

[0037] (6) Under the process parameters of a softening stirring rate of 100 rpm, a sodium phosphate dosage of 1200 mg / L, and a sodium phosphate softening time of 10 min, the medicament softening of the saline - alkali water to be treated is carried out, and then the nanofiltration membrane is used to filter the medicament - softened saline - alkali water, thereby slowing down membrane scaling and improving the membrane treatment capacity. Finally, an actual calcium ion removal rate of 84.5% and an actual magnesium ion removal rate of 44.8% can be achieved for the simulated agricultural saline - alkali water. The pH of the obtained softened water is about 7.9, and the change in TDS is about 0.07 mS / cm. The above results prove that the method of the present invention has obvious effects in the treatment of agricultural saline - alkali water.

[0038] Example 2 In this example, under the process parameters of a softening stirring rate of 100 rpm, a sodium phosphate dosage of 1200 mg / L, and a sodium phosphate softening time of 1 min, the medicament softening of the saline - alkali water to be treated is carried out, and then the nanofiltration membrane is used to filter the medicament - softened saline - alkali water, thereby slowing down membrane scaling and improving the membrane treatment capacity. Finally, an actual calcium ion removal rate of 87.2% and an actual magnesium ion removal rate of 44.5% can be achieved for the simulated agricultural saline - alkali water. The pH of the obtained softened water is about 7.70, and the change in TDS is about 0.09 mS / cm.

[0039] The SEM image of the nanofiltration membrane surface without medicament softening treatment is as Figure 5 shown in A of [reference], and the SEM image of the nanofiltration membrane surface with medicament softening treatment under the optimized process parameters of the present invention is as Figure 5As shown in B of , it can be seen that the method of the present invention can significantly slow down membrane fouling, thereby improving the membrane treatment capacity.

[0040] Example 3 In this example, the chemical softening of the saline-alkali water to be treated is carried out under the process parameters of a softening stirring rate of 100 rpm, a trisodium phosphate feeding amount of 1200 mg / L, and a trisodium phosphate softening time of 30 min. Then, the saline-alkali water after the above chemical softening is filtered by a nanofiltration membrane, so as to slow down membrane fouling and improve the membrane treatment capacity. Finally, an actual calcium ion removal rate of 86.2% and an actual magnesium ion removal rate of 41.9% can be achieved for the simulated agricultural saline-alkali water. The pH of the obtained softened water is about 8.69, and the change in TDS is about 0.10 mS / cm.

[0041] Example 4 In this example, the chemical softening of the saline-alkali water to be treated is carried out under the process parameters of a softening stirring rate of 500 rpm, a trisodium phosphate feeding amount of 1200 mg / L, and a trisodium phosphate softening time of 1 min. Then, the saline-alkali water after the above chemical softening is filtered by a nanofiltration membrane, so as to slow down membrane fouling and improve the membrane treatment capacity. Finally, an actual calcium ion removal rate of 85.6% and an actual magnesium ion removal rate of 43.8% can be achieved for the simulated agricultural saline-alkali water. The pH of the obtained softened water is about 8.62, and the change in TDS is about 0.06 mS / cm.

[0042] Example 5 In this example, the chemical softening of the saline-alkali water to be treated is carried out under the process parameters of a softening stirring rate of 100 rpm, a trisodium phosphate feeding amount of 1800 mg / L, and a trisodium phosphate softening time of 1 min. Then, the saline-alkali water after the above chemical softening is filtered by a separation membrane, so as to slow down membrane fouling and improve the membrane treatment capacity. Finally, an actual calcium ion removal rate of 97.9% and an actual magnesium ion removal rate of 83.9% can be achieved for the simulated agricultural saline-alkali water. The pH of the obtained softened water is about 9.48, and the change in TDS is about 0.19 mS / cm. Although the above parameters can achieve the best actual calcium ion removal rate and actual magnesium ion removal rate, the amount of trisodium phosphate fed is too much, and calcium ions or magnesium ions will be further removed in the subsequent membrane separation process.

[0043] The above-described embodiments have described the technical solutions of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, supplements, or substitutions in a similar manner within the scope of the principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for reducing membrane fouling and improving membrane treatment capacity in saline-alkali water treatment, characterized in that, It includes the following steps: (1) For the hardness ion with the highest content in the saline-alkali water to be treated, calculate its theoretical ion concentration on the surface of the separation membrane based on the parameters of the separation membrane and the water quality indicators of the saline-alkali water to be treated. , based on the theoretical ion concentration obtained Calculate the inorganic scaling supersaturation index of the hardness ion under the set working conditions SI , obtained by the inorganic scaling supersaturation index SI Predict membrane fouling trends during separation using the inorganic fouling supersaturation index SI = 0 when the hardness ion removal rate is taken as the target removal rate of the hardness ion in the softening process; (2)For other hardness ions in the saline-alkali water to be treated, the inorganic scaling supersaturation index of the corresponding hardness ions SI When = 0, the target removal rate of other hardness ions in the saline-alkali water to be treated is calculated by extrapolating from the relationship diagram between the pH value after chemical softening of the saline-alkali water to be treated and the removal rate of other hardness ions; (3) Optimize the process parameters of the chemical softening process to achieve the target removal rate of hardness ions calculated in steps (1) and (2); (4) Conduct chemical softening of the saline-alkali water to be treated under the optimized process parameters in step (3), and then use a separation membrane to filter the chemically softened saline-alkali water, thereby slowing down membrane fouling and improving the membrane treatment capacity.

2. The method for reducing membrane fouling and improving membrane treatment capacity in saline-alkali water treatment according to claim 1, characterized in that, The hardness ions in the saline-alkali water to be treated include calcium ions and magnesium ions, the calcium ion concentration ≥ 200 mg / L, and the magnesium ion concentration ≥ 100 mg / L.

3. The method for reducing membrane fouling and improving membrane treatment capacity in saline-alkali water treatment according to claim 1, characterized in that The separation membrane is a nanofiltration membrane or a reverse osmosis membrane.

4. The method for reducing membrane fouling and improving membrane treatment capacity in saline-alkali water treatment according to claim 1, characterized in that, In step (1), the theoretical ion concentration on the surface of the separation membrane is calculated by the following formula: ； wherein, C F is the concentration of the corresponding ion in the saline-alkali water to be treated, mg / L; is the separation membrane recovery rate, %; is the rejection rate of the separation membrane for the corresponding ion, %.

5. The method for reducing membrane fouling and improving membrane treatment capacity in saline-alkali water treatment according to claim 1, characterized in that Inorganic scaling supersaturation index SI Calculated by the following formula: ； Among them, IAP is the ion activity product of inorganic scaling, K SP is the solubility product of inorganic scaling.

6. The method for reducing membrane fouling and improving membrane treatment capacity in saline-alkali water treatment according to claim 1, characterized in that, The method for predicting the membrane fouling trend during the separation process is as follows: If SI > 0, it indicates that the corresponding inorganic fouling is in a supersaturated state and has a tendency to foul on the membrane surface; If SI = 0, it means that the corresponding inorganic scaling is in a dynamic equilibrium state; If SI < 0, it means that the corresponding inorganic scaling is in an undersaturated state and has no tendency to scale on the membrane surface.

7. The method for reducing membrane fouling and improving membrane treatment capacity in saline-alkali water treatment according to claim 1, characterized in that In the saline-alkali water to be treated, the removal rate of other hardness ions will change with the change of the removal rate of the hardness ion with the highest content. On the basis that the hardness ion with the highest content reaches the target removal rate, when the inorganic scaling supersaturation index of other hardness ions SI = 0, determine the relationship diagram between the pH value after chemical softening of the saline-alkali water to be treated and the removal rate of other hardness ions, and further calculate the target removal rate of other hardness ions in the saline-alkali water to be treated.

8. The method for reducing membrane fouling and improving membrane treatment capacity in saline-alkali water treatment according to claim 1, characterized in that The optimized process parameters of the chemical softening process include the dosage of softening agent, softening time or softening stirring rate.

9. Application of the method for slowing down membrane fouling and improving membrane treatment capacity in saline-alkali water treatment according to any one of claims 1-8 in the field of water softening.

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