Salt and alkali redistribution method based on artificial regulation of vertical stratification of salinity gradient

Abstract

The application provides a salt and alkali water salt distribution and redistribution method based on artificial regulation of vertical stratification of salinity gradient, and belongs to the technical field of utilization of salt and alkali water. The method comprises the following steps: extracting surface salt and alkali water or underground salt and alkali water; using a primary reverse osmosis system to desalinate the extracted salt and alkali water to obtain fresh water and concentrated salt and alkali water; and backfilling the concentrated salt and alkali water to the bottom layer of the salt and alkali water. The method is used to regenerate the salt and alkali water resources into fresh water resources in a sustainable manner by using the salt and alkali water desalination technology and the bottom backfilling technology of the concentrated salt and alkali water, to redistribute the salt and alkali water salt in the vertical spatial layer by artificially regulating the vertical stratification of the salinity gradient without changing the total amount of the salt and alkali water salt, so that the method has the dual functions of development and utilization of the salt and alkali water resources and ecological regulation of the salt, and the purpose of salt and alkali land treatment or comprehensive utilization of salt and alkali water can be achieved without relying on external fresh water, and the method has important popularization value in a salt and alkali area.

Description

Technical Field

[0001] This invention relates to the field of saline-alkali water utilization technology, and in particular to a method for saline-alkali water salt redistribution based on vertical stratification of salinity gradient artificially controlled. Background Technology

[0002] Saline-alkali water is a non-marine saline water resource distributed in terrestrial areas, with a mineralization ranging from 1 g / L to 50 g / L. It is widely present in nature and is characterized by high pH, ​​high carbonate alkalinity, imbalance of major ion ratios, and diverse water quality types. Furthermore, since saline-alkali land improvement often involves freshwater flooding to leach salt, a large amount of "newly added" saline-alkali water is generated during this process, consuming a significant amount of precious freshwater resources. Moreover, these lands often continue to become saline-alkali, requiring large amounts of freshwater to maintain a low salinity level the following year to meet planting needs. In the long run, this method of saline-alkali land improvement is unsustainable, and the scarcity of freshwater resources limits the effective management of saline-alkali land and regional development.

[0003] Because humans and livestock cannot directly drink saline-alkali water, and agricultural planting typically cannot directly utilize surface or groundwater saline-alkali water, the vast majority of saline-alkali land is forced into a state of idleness. Therefore, how to rationally and effectively develop and utilize this unconventional land resource of saline-alkali land and saline-alkali water to alleviate or solve food security problems has become an urgent and challenging common problem facing the world. Existing methods for improving saline-alkali land mainly include three categories:

[0004] (1) Improve saline-alkali land by flooding with external fresh water to leach salt. As mentioned above, this method exchanges external fresh water resources for farming opportunities, which is costly and unsustainable in the long run due to the limited fresh water resources.

[0005] (2) Selecting plants suitable for saline-alkali land or saline-alkali water to plant in suitable places is difficult because the selection of germplasm is difficult and the success rate of selection is relatively low for moderate to severe saline-alkali land. Also, suitable plants are not necessarily crops.

[0006] (3) The saline-alkali water freezing method involves freezing and thawing saline-alkali water to obtain a small amount of slightly brackish or fresh water, which is then used for irrigation to improve saline-alkali land. The disadvantage of this method is that the salinity of the saline-alkali water needs to be below 15‰, and the local area also needs to have low-temperature freezing conditions. It is subject to objective limitations of climate and hydrology. If artificial refrigeration is used to freeze the saline-alkali water, the energy consumption is too high, the cost is high, and it is not universally applicable.

[0007] Saline-alkali water desalination is the main approach to utilizing saline-alkali water resources, which involves using different technologies to convert saline-alkali water into fresh water and more concentrated saline-alkali water. Saline-alkali water desalination technologies share commonalities with seawater desalination. In practice, seawater desalination technologies considered effective mainly fall into the following categories: First, distillation methods, including multi-stage flash distillation, compressed gas distillation, and multi-effect distillation; second, membrane methods, including reverse osmosis, nanofiltration, and electrodialysis; and third, other methods, such as freezing, solvent extraction, and dew point evaporation desalination. Overall, due to water's high specific heat capacity, desalination technologies based on steam condensation or freezing principles are energy-intensive. Compared to other technologies, reverse osmosis offers higher recovery rates, lower investment, and lower overall water production costs, making it the mainstream direction for seawater desalination. It is reported that 80% of the world's seawater desalination plants use reverse osmosis technology.

[0008] Seawater desalination technology can be used for desalination of saline-alkali water, but the disposal of the concentrated saline-alkali water generated during the desalination process remains a challenge, limited by cost and environmental pollution caused by its discharge, and has not yet been widely adopted. Based on whether the total salt content in the ecosystem changes, the disposal of concentrated saline-alkali water can be divided into two main categories: methods that maintain the total salt content and methods that reduce the total salt content. Current methods that maintain the total salt content involve directly discharging the concentrated saline-alkali water into the environment, but this inevitably pollutes the environment and exacerbates secondary salinization at the discharge site, making this method unsustainable. The approach to reducing the total salt content involves concentrating and dehydrating the concentrated saline-alkali water to produce industrial salt. Due to water's high specific heat capacity, the methods used in reducing the total salt content are energy-intensive and costly, while the returns on industrial salts such as NaCl are low. This results in a high ecological value but a loss-making economic situation, making this method unsuitable for market promotion. Therefore, whether a new method can be found to treat the concentrated saline water that occurs during the desalination process is a common and difficult problem facing saline water desalination, saline-alkali land management and its promotion and application, and it is also an international challenge. Summary of the Invention

[0009] The purpose of this invention is to provide a method for saline redistribution of saline-alkali water based on artificially regulated vertical stratification of salinity gradient. This method utilizes a single-stage reverse osmosis system to desalinate saline-alkali water, producing freshwater that can be used for saline-alkali land remediation and domestic water supply. The associated concentrated saline-alkali water is directly reinjected into the bottom of the underground saline-alkali water aquifer or the surface saline-alkali water layer, thus artificially regulating the vertical stratification of salinity gradient. As desalination continues, the salinity is highest at the bottom of the underground saline-alkali water aquifer or the surface saline-alkali water layer, while the salinity of higher water levels remains at the original level to meet the needs of continuous desalination. This allows for the sustainable use of saline-alkali water to produce freshwater. Thus, while maintaining a constant total salinity, the method redistributes salinity in the vertical space by artificially regulating the vertical stratification of salinity gradient, achieving both saline-alkali water resource development and salinity ecological regulation, and realizing the effective utilization of saline-alkali land remediation and saline-alkali water. This invention can completely eliminate the need for external freshwater. Utilizing saline-alkali water desalination technology and concentrated saline-alkali water bottom-level reinjection technology, it redistributes the salinity of saline-alkali water by artificially controlling the vertical stratification of the salinity gradient without altering the total salinity. This not only sustainably regenerates saline-alkali water resources into freshwater resources, thereby achieving the goals of saline-alkali water desalination, saline-alkali land management, and comprehensive utilization of saline-alkali water, but also reduces the cost of saline-alkali water desalination because this method does not aim for a high recovery rate and does not require a reverse osmosis concentrate recirculation process. It also avoids the risk of reverse osmosis membrane scaling and clogging during the desalination process, making it highly valuable for promotion in saline-alkali areas.

[0010] To achieve the above objectives, this invention provides a method for salinity redistribution in saline-alkali water based on vertical stratification of salinity gradient artificially controlled, comprising the following steps:

[0011] Step S1: Extract the saline solution;

[0012] Step S2: Use a first-stage reverse osmosis system to desalinate the extracted brine water to obtain fresh water and concentrated brine water;

[0013] Step S3: Recycle concentrated brine solution back into the bottom layer of the brine solution.

[0014] Preferably, in step S1, the saline water is underground saline water or surface saline water.

[0015] Preferably, in step S2, the freshwater yield obtained through the primary reverse osmosis membrane is 30-45%.

[0016] Preferably, in step S2, the salinity of the associated concentrated alkaline water obtained after reverse osmosis desalination is not higher than 35‰.

[0017] Preferably, in step S3, when the extracted saline water is groundwater, the concentrated saline water is reinjected at the bottom of the groundwater layer; when the extracted saline water is surface water, the concentrated saline water is reinjected at the bottom layer of the surface water.

[0018] Therefore, the present invention employs the above-mentioned method for redistributing salinity in saline-alkali water based on vertical stratification of artificially regulated salinity gradients, and the beneficial technical effects are as follows:

[0019] (1) Unlike traditional freshwater flood irrigation methods that require freshwater from external sources, the saline-alkali land improvement water involved in this invention comes from saline-alkali water, completely independent of external freshwater. This makes it suitable for saline-alkali areas with limited freshwater resources, especially those lacking freshwater, and the method has strong universality. Compared with the "planting in suitable land" method, this invention actively improves saline-alkali land, rather than passively adapting it. The freshwater generated by this invention can actively improve saline-alkali land into arable land suitable for planting conventional crops, without the need for screening and creating salt-tolerant germplasm. It is applicable to the improvement of all saline-alkali land, has universality, and because the generated freshwater resources can effectively improve saline-alkali land, crops can be planted in the same year, making this invention highly effective. The "planting in suitable locations" approach essentially involves plants passively adapting to saline-alkali soil. This requires "selecting and breeding more salt-tolerant plants to adapt to saline-alkali soil" for different levels of salinity. It has the disadvantages of being time-consuming, difficult, and labor-intensive. Moreover, for severely saline-alkali soil, the cultivation of improved varieties is even more difficult, and even if successful, it often takes several years of planting to effectively improve the saline-alkali soil. Therefore, the "planting in suitable locations" approach has poor timeliness and universality in the treatment of saline-alkali soil.

[0020] (2) Due to the high specific heat capacity of water, traditional freezing methods for obtaining low-salinity irrigation water are energy-intensive and costly. Furthermore, the salinity of the saline water used cannot exceed 15‰, and it is highly dependent on climate factors, making it seasonal and unsuitable for the entire agricultural production season, thus limiting its application scenarios. In contrast, the method used in this invention is applicable to all mild, moderate, and severe saline-alkali lands, and the salinity of the saline water can exceed 15‰. This method can be used in all seasons, and more fresh water can be generated according to demand during the agricultural production season, demonstrating strong versatility and significant potential for promotion in saline-alkali areas.

[0021] (3) Existing methods only use saline water as a water source, merely "extracting" it without performing any other operations on the saline water "reservoir" itself. In contrast, this invention recharges the concentrated saline water generated during the desalination process into the bottom layer, achieving "replenishment". Unlike distillation and other methods that separate salt from saline water through high-energy consumption, this invention does not change the total salt content in the saline water body. Unlike discharging concentrated saline water to the surface, which would exacerbate surface salinization, this invention recharges the concentrated saline water into the saline water "reservoir" instead of discharging it to the surface, thus not exacerbating surface salinization or polluting the surface ecological environment. This invention creatively controls the salt content in the saline water "reservoir" to form a vertical stratification of salinity gradient, achieving a redistribution of salt.

[0022] Specifically, this invention achieves a stable spatial balance of salinity by artificially controlling the formation of a new salinity distribution where the bottom layer of the saline water has high salinity and the non-bottom (i.e., higher water layers) has low salinity. In this artificially controlled vertical stratification system of salinity gradient, the high-salinity concentrated saline water layer will spontaneously migrate the low-salinity saline water layer towards the surface or water surface. This process is energy-free and allows for the continuous use of the low-salinity saline water from the non-bottom layer for desalination. It avoids the problems that, as those skilled in the art believe, would occur when concentrated saline water is reinjected into the water body, resulting in a mixture of two salinities and causing the salinity of the non-bottom water layer in the saline water "reservoir" to increase, ultimately increasing the load on the reverse osmosis membrane, accelerating membrane wear, affecting membrane lifespan, and reducing freshwater yield. The method used in this invention achieves the stability and sustainability of the entire system.

[0023] In addition, since existing methods only "extract" from the saline-alkali water "reservoir", while the method used in this invention "replenishes" the saline-alkali water "reservoir", by re-injecting concentrated saline-alkali water, it not only does not cause secondary salinization of the surface, but also slows down or even avoids the decline of saline-alkali water level, and avoids geological disasters such as ground subsidence. Compared with existing methods, this method has obvious ecological advantages.

[0024] (4) This invention utilizes a reverse osmosis system for saline-alkali water desalination, but does not pursue a high recovery rate of the reverse osmosis membrane system, thus avoiding the risk of scaling and fouling of the reverse osmosis membrane during the saline-alkali water desalination process. Furthermore, it only requires a single-stage reverse osmosis system and does not require a reverse osmosis concentrate recirculation process, further reducing costs and operation steps.

[0025] (5) The method for treating the concentrated saline water that accompanies the desalination process of the present invention has the characteristics of low energy consumption, simple operation, good recycling performance, and outstanding sustainable development. It provides a new solution to the common and difficult problems faced by saline water desalination, saline-alkali land management, comprehensive utilization of saline water and its promotion and application, and has great promotion value in saline-alkali areas. Attached Figure Description

[0026] Figure 1 A schematic diagram showing the salt distribution of underground saline water before its salt content is determined.

[0027] Figure 2 A schematic diagram showing the salt distribution in underground saline-alkali water;

[0028] Figure 3 This is a schematic diagram showing the salt distribution of surface saline water before salt content is achieved.

[0029] Figure 4 This is a schematic diagram showing the distribution of salt in saline-alkali water on the surface. Detailed Implementation

[0030] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0031] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0032] Example 1

[0033] Taking a certain underground saline-alkali water in Alar City as an example, the groundwater at 50m and 100m is a shallow water layer. The location of the 100m underground recharge well is 100m south of the 50m underground pumping well. The main water ion indicators of the original water samples from the two locations are shown in Table 1.

[0034] Table 1. Main ion indicators of saline-alkali water after desalination and salt redistribution (concentration unit: mg / L)

[0035] <![CDATA[Na + ]]> <![CDATA[K + ]]> <![CDATA[Ca 2+ ]]> <![CDATA[Mg 2+ ]]> <![CDATA[Cl - ]]> <![CDATA[SO4 2- ]]> 50m underground saline water 2277.0 43.6 441.2 212.6 2963.8 2211.6 50m underground saline water reverse osmosis product water 157.8 0.0 0.0 0.0 243.6 0.0 Reverse osmosis accompanied by concentrated saline water 3984.3 79.7 805.0 387.1 5154.6 4027.1 Before reinjection, the reinjection well contained 100m of saline-alkali water. 2275.4 44.2 442.8 213.3 2965.4 2213.1 50m of saline-alkali water after reinjection 2275.0 44.1 442.9 213.1 2965.2 2209.2

[0036] like Figure 1 The diagram shows the pre-salt distribution of underground saline-alkali water. Saline-alkali water is drawn from 50m underground from a pumping well. After particle removal via microfiltration, the water passes through a booster pump and a security filter, then is pressurized by a high-pressure pump to become high-pressure saline-alkali water before entering the reverse osmosis membrane module. The resulting reverse osmosis permeate with approximately 45% recovery rate and the main ionic indicators of the high-pressure concentrated saline-alkali water are shown in Table 1. The high-pressure concentrated saline-alkali water is then transported to a reinjection well 100m underground for reinjection. The reinjection well receives 200 tons of concentrated saline-alkali water daily. After 30 days of continuous reinjection, the main ionic indicators of the saline-alkali water at 50m underground are shown in Table 1.

[0037] like Figure 2 The diagram shows the redistribution of salt in underground saline-alkali water. After redistribution, the bottom layer darkens, indicating an increase in salt concentration.

[0038] Example 2

[0039] Taking a surface saline-alkali water in Alar City as an example, the main water ion indicators of the original water sample of the surface saline-alkali water are shown in Table 2.

[0040] Table 2. Main water body ion indicators after surface saline-alkali water desalination and salt redistribution (concentration unit: mg / L)

[0041]

[0042]

[0043] like Figure 3The diagram shows the surface saline water before salt distribution. Saline water is extracted from 50cm below the surface water surface. After particle removal via microfiltration, the saline water is desalinated using a reverse osmosis membrane system, yielding approximately 30% recovery of reverse osmosis permeate (meta-water quality meets GB / T 14848-2017 Class III standard) and associated concentrated saline water. Water quality indicators are stable, as shown in Table 2. The concentrated saline water generated during desalination is transported to the bottom for reinjection. 200 tons of concentrated saline water are reinjected into the bottom layer daily. Table 2 shows the main water ion indicators of the saline water at 50cm below the bottom reinjection pipe and 50cm below the surface after 30 days of bottom reinjection. Subsequently, the concentrated saline water is reinjected at the surface, 30m south of the pump inlet, with the reinjection pipe facing downwards. Table 2 shows the main water ion indicators of the saline water at 50cm below the reinjection pipe and at the bottom after 5 days of surface reinjection.

[0044] like Figure 4 The diagram shows the redistribution of salt in surface saline water. After the salt redistribution, the bottom of the surface water layer becomes darker, indicating an increase in salt concentration at the bottom.

[0045] Using the above method, after the saline water is treated by the reverse osmosis membrane module, no salt precipitation occurs at the reverse osmosis membrane interface. The obtained reverse osmosis permeate can be directly used for saline-alkali land treatment, domestic water, or irrigation water. Saline-alkali water desalination can be carried out using reverse osmosis membrane method, or it can be done by distillation, nanofiltration, ultrafiltration, or a combination of different methods. The ultimate goal is to obtain fresh water (or saline-alkali water with reduced salinity) and even more concentrated saline-alkali water.

[0046] At the same time, this method can be used for the comprehensive utilization of underground saline water with different geological conditions and origins, such as deserts, Gobi deserts, and seawater intrusion into coastal areas.

[0047] Example 3

[0048] Located four kilometers from K104 of the No. 1 highway in the 14th Regiment of Alar City, on the northern edge of the Taklamakan Desert, the base exhibits typical desert saline-alkali land characteristics, including a high groundwater level (groundwater salinity of 9‰), a surface covered with white salt crystals, and extremely sparse vegetation. On April 7, 2025, an excavator was used to level a 1.2-acre experimental field. Starting from April 8, the freshwater prepared in Example 1 was used for flood irrigation to leach salt, with a total irrigation volume of 166 cubic meters. 3 After the saline solution had fully infiltrated, comprehensive improvements were made to the experimental field on April 14. These included applying base fertilizer, rotary tillage, leveling the land, laying drip irrigation tape, and covering with plastic film. Sowing and transplanting were also carried out simultaneously: Heilongjiang soybean variety "Heihe 35", as well as local peanut, cotton, and corn seeds were sown using a handheld seeder, and local sweet potato seedlings were transplanted and managed using conventional methods.

[0049] Planting results show that:

[0050] May 4: The overall germination rate of all types of seeds reached 70%.

[0051] May 26: Observations show that soybean plants are about 20cm tall and have entered the flowering and pod-setting stage. Some soybean plants that emerged earlier and have a longer growth process have already set pods. Peanut plants are about 10cm tall (some are flowering), cotton plants are about 15cm tall, corn plants are about 50cm tall, and sweet potato plants are about 10cm tall.

[0052] June 4: Soybean plants grew to about 40cm in height, and those that had formed pods began to fill out, with the beans gradually becoming fuller. Many flowers had formed pods, and the plant was in full bloom. Peanut plants grew to about 12cm in height, and the proportion of flowering plants increased. Cotton plants grew to about 20cm in height. Corn plants grew to about 80cm in height. Sweet potato plants grew to about 15cm in height. All crops were growing well overall.

[0053] June 9: Soybean plants grew to about 55cm in height, and the beans became increasingly plump (plump beans could be seen when the pods were opened). All the early-flowering plants had already formed pods, and the later-flowering plants also began to enter the flowering and pod-forming period. Peanut plants grew to about 14cm in height, and the proportion of flowering plants increased. Cotton plants grew to about 30cm in height. Corn plants grew to about 120cm in height. Sweet potato plants grew to about 20cm in height. All crops were growing well overall.

[0054] The above results fully demonstrate that:

[0055] Actively improve saline-alkali land: Using the fresh water generated by this invention for flood irrigation to wash away salt can effectively improve severely saline-alkali land into arable land suitable for the growth of conventional crops.

[0056] The crops showed normal growth: the tested crops (including non-salt-tolerant varieties such as Heihe 35 soybean) not only successfully emerged, but also completed the normal growth and development cycle, including growth, flowering and fruiting.

[0057] High technical applicability: This technology does not rely on the screening and creation of specific salt-tolerant varieties and is applicable to conventional crops.

[0058] Excellent timeliness of improvement: After using the freshwater washing method of this invention, crops can be planted and harvested in the same year, significantly shortening the improvement cycle of saline-alkali land.

[0059] It should be noted that, in the saline-alkali water salt redistribution system of the present invention, the fluids transported between the various parts of the device can generally be transported through pipelines, unless otherwise specified. Furthermore, when additional power is required during the transport process, suitable power equipment such as pumps or fans can be added to the necessary pipelines. Further, suitable valves can be added to the pipelines as needed to control the flow direction of the fluid.

[0060] It is worth noting that all content not described in detail in this invention is prior art and well known to those skilled in the art. In reverse osmosis systems, as long as there is no scaling or membrane blockage, the method used in this invention can be applied even if the salinity of the concentrated brine is greater than 35‰ or the freshwater yield is greater than 45%. This invention can also be combined with salt production from concentrated brine to achieve the comprehensive development and utilization of saline-alkali land / water.

[0061] Therefore, the present invention adopts the above-mentioned method of salinity redistribution of saline-alkali water based on vertical stratification of salinity gradient by artificial regulation. By using saline-alkali water desalination technology, the fresh water generated by saline-alkali water desalination can be used for saline-alkali land treatment or for fresh water-related production and living purposes such as domestic water use. The associated concentrated saline-alkali water is directly reinjected into the bottom of the underground saline-alkali water groundwater layer or the bottom layer of surface saline-alkali water, thus artificially regulating the vertical stratification of salinity gradient. As desalination of saline-alkali water continues, the salinity is highest at the bottom of the groundwater layer or the bottom layer of saline-alkali water on the surface. Utilizing the natural characteristic of high-salinity, high-density saline-alkali water, the associated concentrated saline-alkali water during reinjection can spontaneously migrate the lower-salinity saline-alkali water above it towards the surface or water level. This maintains the salinity of the higher-level saline-alkali water at its original level, meeting the needs of continuous desalination. This allows for the sustainable use of saline-alkali water to produce freshwater. Thus, while maintaining a constant total salinity, the salinity of the saline-alkali water is redistributed vertically by artificially controlling the salinity gradient. This method combines the dual functions of saline-alkali water resource development and salinity ecological regulation, achieving saline-alkali land improvement or comprehensive utilization of saline-alkali water. This method is completely independent of external desalination methods. Water can be used for comprehensive utilization of saline-alkali land or saline-alkali water. By utilizing saline-alkali water desalination technology and bottom-level reinjection technology of concentrated saline-alkali water, the salinity of saline-alkali water can be redistributed by artificially controlling the vertical stratification of salinity gradient without changing the total amount of salinity in the saline-alkali water. This not only allows saline-alkali water resources to be sustainably regenerated into freshwater resources, thereby achieving the goals of saline-alkali water desalination, saline-alkali land management, and comprehensive utilization of saline-alkali water, but also reduces the cost of saline-alkali water desalination because this method does not aim for a high recovery rate of saline-alkali water desalination and does not require reverse osmosis concentrate recirculation process. It also avoids the risk of reverse osmosis membrane scaling and clogging during the saline-alkali water desalination process, and improves the stability and sustainability of the entire system. It has great value for promotion in saline-alkali areas.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for salt redistribution in saline-alkali water based on vertical stratification of salinity gradient with artificial control, characterized in that, Includes the following steps: Step S1: Extract the saline solution; Step S2: Use a first-stage reverse osmosis system to desalinate the extracted brine water to obtain fresh water and concentrated brine water; Step S3: Recycle concentrated brine solution back into the bottom layer of the brine solution.

2. The method for salinity redistribution in saline-alkali water based on vertical stratification of artificially controlled salinity gradient according to claim 1, characterized in that, In step S1, the saline water is either underground saline water or surface saline water.

3. The method for salinity redistribution in saline-alkali water based on vertical stratification of artificially controlled salinity gradient according to claim 1, characterized in that, In step S2, the freshwater yield obtained through the first-stage reverse osmosis membrane is 30-45% or the reverse osmosis membrane is not fouled.

4. The method for salinity redistribution in saline-alkali water based on vertical stratification of artificially controlled salinity gradient according to claim 1, characterized in that, In step S3, when the extracted saline water is groundwater, the concentrated saline water is reinjected at the bottom of the unconfined layer; when the extracted saline water is surface water, the concentrated saline water is reinjected at the bottom layer of the surface water.

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