Multi-stage saline-alkali soil circular agricultural system and method based on multi-stage resource utilization of saline-alkali water

Abstract

The application belongs to the technical field of comprehensive management of saline-alkali land and circular agriculture, and particularly relates to a multi-stage circular agriculture system and method for saline-alkali land based on multi-stage resource utilization of saline-alkali water, which comprises the following steps: through the technical chain of terrace land reclamation, seawater-like regulation, reverse osmosis desalination, planting and breeding coupling and tail water circulation, efficient cyclic utilization of natural resources in the saline-alkali area is realized. The method mainly comprises the following steps: after the saline-alkali water in the saline-alkali area is detected, the saline-alkali water is extracted for seawater-like regulation, the regulated saline-alkali water is obtained, and then the saline-alkali water is desalinated through a reverse osmosis system, and fresh water and seawater-like water are obtained, which are used for crop planting and aquatic product breeding, respectively, and the breeding tail water is recycled after solid-liquid separation. The system and method have the advantages that the system does not need external supply of fresh water, is self-contained, achieves win-win of ecological benefit, social benefit and economic benefit, realizes green and sustainable development, and has universal popularization value for comprehensive development and utilization of saline-alkali land.

Description

Technical Field

[0001] This invention relates to the field of comprehensive management of saline-alkali land and circular agriculture technology, and in particular to a multi-level circular agriculture system and method for saline-alkali land based on multi-level resource utilization of saline-alkali water. Background Technology

[0002] Saline-alkali land is land in which excessive salt and alkali components accumulate on the surface layer of the soil under the influence of natural and human factors, resulting in a continuous increase in the salt and alkali concentration and osmotic pressure of the surface soil. This causes crops to experience "physiological drought" and have difficulty absorbing water, thus affecting the growth of agricultural crops.

[0003] Existing methods for saline-alkali land management include physical, chemical, and biological measures, as well as combinations of these three categories, to reduce the salinity and alkali content in the soil, thereby converting saline-alkali land into arable land.

[0004] Physical engineering improvement methods include three types: open ditch drainage, vertical well drainage, and underground pipe drainage. Open ditch drainage results in high evaporation and occupies surface area, reducing the effective arable land area; underground pipe drainage has high installation costs, is prone to clogging, and has high maintenance costs; vertical well drainage only transfers salt and alkali from underground to the surface, but the salt and alkali will still return to the groundwater through surface seepage, causing secondary salinization, or the discharge of groundwater into rivers will lead to an increase in the salinity of downstream soils or even the transformation into saline-alkali land.

[0005] Agronomic improvement methods refer to the use of agronomic measures such as applying topsoil, straw interlayers, and sand in saline-alkali land, especially in areas with high evaporation, to create a loose isolation layer in the soil, cut off soil capillaries, reduce the upward movement of water and salt, break up soil compaction, reduce the degree of salinization of the soil surface, and improve soil structure. However, this method is aimed at the current season and has a short time effect. It fails to solve the problem at the root cause of groundwater level, and the effect of saline-alkali land improvement varies depending on natural conditions.

[0006] Chemical amendment method: This method mainly relies on the principle of ion exchange, which involves replacing ions in the soil with ions in the amendment. Once the soil's physical and chemical properties reach an ideal state, water is used for leaching to remove saline-alkali components. Chemical amendment measures have the advantages of rapid effectiveness, flexible and varied formulations, a wide range of material choices, and strong targeting. However, their effects are singular, short-lasting, expensive, and prone to causing secondary pollution to saline-alkali land. Furthermore, leaching requires a large amount of water resources.

[0007] Biological improvement method: This method involves planting new salt-tolerant varieties or microorganisms that can directly utilize saline-alkali soil, removing some salt from the roots or altering the diversity of soil microbial communities, thereby improving soil quality and enabling saline-alkali land to achieve ecological balance and long-term stability. Essentially, it involves selecting salt-tolerant varieties suitable for planting in saline-alkali land. For moderately to severely saline-alkali land, it is difficult to grow major food crops such as rice, wheat, soybeans, and corn in the short term.

[0008] Comprehensive improvement methods: Current viewpoints suggest that engineering improvement methods are mostly used for moderate to severe saline-alkali land improvement, biological and chemical improvement methods are mostly used for mild to moderate saline-alkali land improvement, and agronomic improvement methods are particularly effective in areas with high evaporation. However, none of these measures alone can completely remediate saline-alkali land; therefore, the comprehensive utilization of various improvement measures is gradually gaining importance. For example, the "terraced field-shallow pond" integrated land use model, suitable for coastal areas, combines engineering improvement measures such as digging soil to form ponds and building earthen platforms with biological improvement measures such as terraced field planting and shallow pond aquaculture. This method of raising the land and digging ponds to lower the groundwater level is suitable for areas with high rainfall or external freshwater replenishment, but not for areas with high evaporation, low rainfall, and no external freshwater replenishment. In other words, the suitability of saline-alkali land improvement methods needs to be assessed based on local hydrological conditions.

[0009] Furthermore, since many saline-alkali land improvement projects primarily rely on freshwater flood irrigation to leach salt, water-soluble salts move from higher to lower elevations with the water, accumulating in low-lying areas and generating a large amount of newly added saline-alkali water. Low-lying saline-alkali soils are generally prone to waterlogging, have high salt content, and develop a crust on the surface, making water infiltration difficult and severely hindering normal crop growth.

[0010] In summary, resources such as saline-alkali land and surface saline-alkali water collected by drainage ditches have not been effectively utilized. Given the limitations of the aforementioned methods in effectively utilizing saline-alkali land and water, there is an urgent need for a new type of saline-alkali land and / or saline-alkali water circular agriculture system and method to achieve efficient utilization of natural resources in saline-alkali areas and improve the integrated production capacity of saline-alkali land / water-based agriculture and fisheries. Summary of the Invention

[0011] The purpose of this invention is to provide a multi-level circular agriculture system and method for saline-alkali land based on the multi-level resource utilization of saline-alkali water. The entire system is self-contained and does not require external supply of fresh water. Based on the multi-level resource utilization of saline-alkali water, a multi-level circular agriculture system for saline-alkali land with good economic benefits is formed, achieving a win-win situation of ecological, social and economic benefits, realizing green and sustainable development, and having universal promotion value for the comprehensive development and utilization of saline-alkali land.

[0012] To achieve the above objectives, this invention provides a multi-level circular agriculture method for saline-alkali land based on multi-level resource utilization of saline-alkali water, comprising the following steps:

[0013] Step S1: After testing the saline-alkali water in the saline-alkali area, extract the saline-alkali water for seawater-like regulation, that is, adjust the ionic composition and ratio of the saline-alkali water according to the needs of aquaculture water to obtain the regulated saline-alkali water.

[0014] Step S2: Desalinate the adjusted saline water through a primary reverse osmosis system to obtain fresh water and seawater-like water;

[0015] Seawater-like water is a concentrated saline-alkali water produced by desalination after the adjustment of saline-alkali water. It refers to the main ionic components and contents of saline-alkali water that are similar to seawater of the same salinity and can be used for aquaculture.

[0016] Step S3: The obtained freshwater is used for planting and freshwater aquaculture, and the obtained seawater-like water is used for aquaculture.

[0017] Step S4: After the aquatic products are harvested, the aquaculture wastewater is separated into solid and liquid components. The residue obtained from the filtration is used as fertilizer for crop cultivation, while the filtered wastewater is discharged into an outer pond or used for recycling aquaculture.

[0018] Preferably, before implementing seawater-like regulation, land reclamation should be carried out in saline-alkali areas.

[0019] Preferably, the distance between the surface soil and the groundwater level after land reclamation is 2.5 to 5 meters, which can block the formation of soil capillaries and avoid repeated salinization.

[0020] Preferably, in step S1, the outer ponds created after the land reclamation are used as ponds / greenhouses for aquaculture, reservoirs for water storage, or for storing aquaculture wastewater.

[0021] Preferably, in step S1, the saline-alkali water is regulated using a seawater-like regulation method to obtain regulated saline-alkali water, including the following two cases:

[0022] Scenario 1: When the calcium hardness of the extracted saline water is greater than that of the aquaculture water, calculate the calcium ion concentration that needs to be removed based on the original calcium ion concentration of the saline water and the calcium, potassium, and magnesium ion concentrations to be adjusted for aquaculture water. Then remove the calcium ions and increase the potassium and magnesium ions.

[0023] The method to remove calcium ion concentration is to add potassium oxalate or sodium oxalate to the water to precipitate calcium ions;

[0024] Scenario 2: When the calcium hardness of the extracted saline water is less than that of the water used for aquaculture, calcium, potassium, and magnesium ions are added to the saline water according to the adjusted concentrations of calcium, potassium, and magnesium ions intended for use in aquaculture.

[0025] Preferably, in step S2, the freshwater yield obtained through the reverse osmosis system is 45-50%.

[0026] Preferably, in step S2, the salinity of the aquaculture water obtained through the reverse osmosis system is not higher than 35‰.

[0027] Preferably, in step S3, once the volume of seawater meets the needs of aquaculture, the remaining saline-alkali water is directly desalinated without being regulated by seawater, and the resulting concentrated saline-alkali water is directly reinjected into the bottom of the saline-alkali water layer.

[0028] The present invention also provides a system for realizing the above-mentioned multi-level circular agriculture method for saline-alkali land based on multi-level resource utilization of saline-alkali water, a seawater regulation module for adjusting saline-alkali water to be similar to or the same as seawater with the same salinity and ion composition and content as aquaculture water.

[0029] The saline-alkali water desalination module is used to desalinate the conditioned saline-alkali water through a reverse osmosis system, simultaneously producing fresh water and seawater-like water.

[0030] Planting module, equipped with drip irrigation system under film;

[0031] Aquaculture module, used for aquaculture;

[0032] Terraced fields are used to increase the distance between the topsoil and the groundwater level, while creating an outer pond and / or reservoir.

[0033] Photovoltaic power generation modules are used to supply power to seawater regulation modules, saline-alkali water desalination modules, planting modules, and aquaculture modules.

[0034] Therefore, the present invention employs the above-mentioned multi-level circular agriculture system and method for saline-alkali land based on multi-level resource utilization of saline-alkali water, and the beneficial technical effects are as follows:

[0035] (1) Terraced land reclamation has multiple benefits. On the one hand, by raising the surface height to regulate the relative height between the surface layer and the groundwater level, the problem of soil salinization can be solved at its root, avoiding repeated salinization. On the other hand, the soil supply area can provide a site for aquaculture, eliminating the need to dig ponds separately. Thirdly, the excavated ponds can also be used as reservoirs for water storage. When a large amount of freshwater is produced, it can be collected into a freshwater reservoir to prepare freshwater reserves for subsequent applications.

[0036] (2) By using seawater-like regulation technology, the calculated calcium salt removal agent or the required ions in the water can be added in advance to regulate the concentration of calcium ions in the water, thereby accurately regulating the water hardness. It can also avoid the problem of reverse osmosis system clogging caused by the precipitation of high concentrations of calcium salts in the water during saline-alkali water desalination.

[0037] (3) The freshwater yield of the reverse osmosis system can be 45%–50%, avoiding salt precipitation that could clog the reverse osmosis membrane. Furthermore, the adjusted saline-alkali water is converted into seawater-like water, unlike the 65%–85% freshwater yield of industrial wastewater desalination. The method used in this invention does not result in reverse osmosis membrane fouling due to salt saturation precipitation. Additionally, traditional reverse osmosis systems for desalinating saline-alkali water / seawater often require a secondary reverse osmosis system (i.e., re-reverse osmosis treatment of the first reverse osmosis permeate) to obtain high-purity freshwater. Similarly, to increase the overall freshwater yield, a reverse osmosis concentrate recirculation process is needed to perform secondary reverse osmosis treatment on the concentrated saline-alkali water to obtain freshwater and even higher-concentration saline-alkali water. Therefore, the method used in this invention has low cost and fewer equipment requirements or limitations.

[0038] (4) Multi-level resource utilization of saline-alkali water: ① After being treated with seawater-like regulation, the regulated saline-alkali water can be directly used for aquaculture, converting idle saline-alkali water resources into aquaculture water and generating economic benefits. ② After being treated with seawater-like regulation, the regulated saline-alkali water is desalinated using a reverse osmosis system. The resulting freshwater is used for crop cultivation or used for freshwater aquaculture and then for crop cultivation. ③ After being treated with a reverse osmosis system, the regulated saline-alkali water becomes seawater-like water, which is used for high-value aquaculture, resulting in good economic benefits (compared with traditional planting, the yield per mu of seafood in seawater-like aquaculture can be increased by more than 100 times), making the entire circular agriculture sustainable. ④ The aquaculture is a factory-style recirculating aquaculture system. The water consumption for aquaculture is far less than that for concentrated saline-alkali water. Once the volume of seawater-like water meets the needs of aquaculture, the remaining saline-alkali water is directly desalinated without seawater-like water regulation. The resulting concentrated saline-alkali water is directly reinjected into the bottom of the saline-alkali water layer, without polluting the original saline-alkali water (the concentrated saline-alkali water is only obtained by concentrating the saline-alkali water, and its composition is the same as the original saline-alkali water). Moreover, the reinjection can stabilize the groundwater or surface water level, preventing geological disasters such as ground subsidence caused by excessive extraction of groundwater. ⑤ The obtained seawater-like water is used for aquaculture. Using conventional solid-liquid separation technology, organic matter such as feces and uneaten feed in the aquaculture water is removed and can be used as fertilizer for crops. The filtered aquaculture tailwater is saline-alkali water, which can be reused in aquaculture or discharged into external ponds. The stability of the original saline-alkali water level is achieved by balancing indicators such as surface water evaporation, saline-alkali water reinjection volume, external pond evaporation, and external pond groundwater replenishment.

[0039] (5) Desalination of saline-alkali water is energy-intensive and the cost of producing fresh water is high. When used for open-field crop cultivation, the income from cultivation is often lower than the cost, resulting in an economic loss. This is a key factor preventing the widespread adoption of the idea of ​​using desalinated water for cultivation. Secondly, the discharge of concentrated saline-alkali water associated with desalination leads to environmental pollution. These two objective drawbacks hinder the promotion and application of single saline-alkali water desalination technology in saline-alkali areas. Directly using saline-alkali water for aquaculture is also problematic. Firstly, the main ions in saline-alkali water differ significantly from those in seawater, making it unsuitable for directly cultivating high-value seafood. Secondly, saline-alkali water aquaculture cannot be coupled with crop cultivation on saline-alkali land, making it impossible to develop saline-alkali land into arable land. However, the method used in this invention creatively integrates modules such as seawater-like regulation, saline-alkali water desalination, terraced fields, planting, aquaculture, and photovoltaics to form a circular agricultural system with good economic benefits, achieving unexpected results. Attached Figure Description

[0040] Figure 1 This is a flowchart of a multi-level circular agriculture method for saline-alkali land based on multi-level resource utilization of saline-alkali water according to the present invention;

[0041] Figure 2 This is a schematic diagram of the structure of a multi-level circular agriculture system for saline-alkali land based on multi-level resource utilization of saline-alkali water, according to the present invention. Detailed Implementation

[0042] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0043] 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.

[0044] Example 1

[0045] like Figure 1 The diagram shows a flowchart of a circular agriculture method based on saline-alkali water desalination according to the present invention, which specifically includes the following steps:

[0046] Step S1: Terracing and land reclamation.

[0047] Specifically, when the evaporation rate in saline-alkali areas is low, consider digging ponds on raised platforms and using vertical wells to drain water to lower the groundwater level. When the evaporation rate is high, only raised platforms should be considered, without open-air aquaculture ponds. Increasing the distance between the surface soil and the groundwater level can effectively block the formation of soil capillaries and prevent soil salinization. The distance between the surface soil and the groundwater level should ideally be controlled between 2.5 and 5 meters.

[0048] Earthwork can be supplied by digging ponds locally, avoiding or reducing transportation costs. The earthwork generated from pond digging is used for terraced fields, and the excavated foundations or pond openings can be used as factory farming bases for aquatic products, as reservoirs for water storage, or as outer ponds for storing aquaculture wastewater.

[0049] The terraced land reclamation method in this invention has multiple benefits. On the one hand, by increasing and regulating the distance between the surface and groundwater levels, it addresses the problem of soil salinization at its source. On the other hand, it provides level ground for aquaculture. Thirdly, the excavated ponds can be used to build freshwater reservoirs to store freshwater. When there is a surplus of freshwater produced from the desalination of saline-alkali water, it can be discharged into the reservoir for storage, preparing for subsequent freshwater applications.

[0050] Groundwater level control is achieved through the drainage function of vertical wells. If the groundwater level is too high, saline water is extracted and more fresh water is generated using a reverse osmosis system (step S3 below) to accelerate the transformation of saline-alkali land.

[0051] Step S2: Seawater-like regulation.

[0052] Before implementing seawater-like regulation, the saline water is tested, primarily focusing on the composition of major ions within it. In this invention, the saline water can be either surface or underground saline water.

[0053] This invention addresses the regulation of saline-alkali water. The purpose of detecting the salinity of saline-alkali water is to determine suitable aquaculture species based on the actual salinity. Based on actual testing, field tests were conducted in a region of Xinjiang, and the salinity range of the saline-alkali water was generally between 3‰ and 18‰.

[0054] The purpose of detecting ions in saline-alkali water is to adjust the ion composition and ratio of saline-alkali water based on the ion status, and then compare the existing ion status with seawater of the same salinity to supplement or remove ions.

[0055] Specifically, seawater-like regulation includes the following two situations:

[0056] 1) When the calcium hardness of the extracted saline water is greater than that of the aquaculture water, the calcium ion concentration to be removed is calculated based on the original calcium ion concentration in the water and the calcium, potassium, and magnesium ion concentrations to be adjusted for aquaculture. The increase in the concentration of calcium ions, potassium ions, and magnesium ions is also calculated.

[0057] The method to remove calcium ion concentration is to add potassium oxalate or sodium oxalate to the water to precipitate calcium ions;

[0058] 2) When the calcium hardness of the extracted saline water is less than that of the aquaculture water, calculate the required concentrations of calcium, magnesium, and potassium ions to be added based on the concentrations of calcium, magnesium, and potassium ions to be added to the aquaculture water after adjustment.

[0059] After the above adjustment steps, seawater with ionic properties similar to seawater of the same salinity was obtained. In addition, the water hardness was adjusted to reduce the precipitation of calcium salts during the subsequent reverse osmosis membrane desalination, thereby preventing reverse osmosis membrane fouling.

[0060] The following are some specific examples of regulation.

[0061] 1) Oxalate precipitation of calcium ions in high-hardness saline-alkali water

[0062] 1. Prepare oxalic acid, sodium oxalate, and potassium oxalate solutions separately: (1) Dissolve 19.80g of H2C2O4 in 900mL of water, then bring the volume to 1000mL and mix well to obtain an oxalic acid solution with a concentration of 19.80g / L (220mmol / L). (2) Dissolve 29.48g of Na2C2O4 in 900mL of water, then bring the volume to 1000mL and mix well to obtain a sodium oxalate solution with a concentration of 29.48g / L (220mmol / L). (3) Dissolve 22.10g of K2C2O4·H2O in 900mL of water, then bring the volume to 1000mL and mix well to obtain a potassium oxalate solution with a concentration of 120mmol / L.

[0063] 2. The salinity of underground saline water in region B is approximately 9‰. The sodium content in the water is... + K + Ca 2+ Mg 2+ Cl - SO4 2- The ion concentrations were 2277.0 mg / L, 43.6 mg / L, 441.2 mg / L, 212.6 mg / L, 2963.8 mg / L, and 2211.6 mg / L, respectively. Meanwhile, the corresponding Na concentrations in seawater at 9‰ were... + K + Ca 2+ Mg 2+ Cl - SO4 2- The ion concentrations were 2771.5 mg / L, 99.5 mg / L, 108.3 mg / L, 332.5 mg / L, 4990.0 mg / L, and 696.8 mg / L, respectively. It is evident that, regarding the four main cations, compared to seawater at the same salinity, the 9‰ salinity water is deficient in potassium (K). + Mg 2+ Ions, while Ca 2+However, it has four times the salinity of seawater at the same level, and its ion composition and ratio are very different from seawater. In order to use saline water for marine aquaculture, it is necessary to adjust the saline water to resemble seawater.

[0064] 3. Take three 2L beakers and add 1000mL of saline water from a certain area (B). Add 10mL of oxalic acid, sodium oxalate, and potassium oxalate solutions to each beaker. The results show that with the addition of the sodium oxalate and potassium oxalate solutions, white suspended matter immediately appears. After mixing, white suspended matter is present throughout the water. After standing overnight, a white precipitate accumulates at the bottom of the beaker, and the water changes from cloudy white to transparent. Inductively coupled plasma mass spectrometry (ICP-MS) analysis reveals that oxalate treatment can precipitate an equimolar amount of Ca. 2+ Ions: After treatment with sodium oxalate, the Ca in the saline-alkali water... 2+ The ion concentration decreased by nearly 88.0 mg / L (2.2 mmol / L), Mg 2+ and K + The ion concentration remained unchanged; after treatment with potassium oxalate, the Ca in the water... 2+ The ion concentration decreased by nearly 48.0 mg / L (1.2 mmol / L), Mg 2+ The ion concentration remains constant, while K + The ion concentration increased by nearly 93.6 mg / L (2.4 mmol / L). This indicates that sodium oxalate can precisely reduce calcium hardness in saline water without affecting magnesium hardness; potassium oxalate can not only precisely reduce calcium hardness in saline water without affecting magnesium hardness, but also precisely increase K+ ion concentration. + The ion concentration was relatively stable; however, the situation was completely different for the oxalic acid group. With the addition of oxalic acid solution, no white suspended matter appeared in the saline-alkali water, and even a tenfold increase in oxalic acid concentration did not result in the formation of white suspended matter. This indicates that oxalates (sodium oxalate and potassium oxalate) can accurately precipitate Ca in water. 2+ It contains ions, but oxalic acid does not have this function.

[0065] 2) Potassium oxalate and sodium oxalate solutions regulate calcium hardness and potassium ion concentration in high-hardness saline-alkali water.

[0066] 1. Preparation of sodium oxalate and potassium oxalate solutions: (1) Dissolve 30.55g of Na2C2O4 in 900mL of water, then bring the volume to 1000mL. Mix well to obtain a sodium oxalate solution with a concentration of 30.55g / L (228mmol / L). (2) Dissolve 53.05g of K2C2O4·H2O in 900mL of water, then bring the volume to 1000mL. Mix well to obtain a potassium oxalate solution with a concentration of 288mmol / L. (3) Take 334mL of the sodium oxalate solution prepared above, add 25mL of the potassium oxalate solution prepared above, mix well, and use as a potassium oxalate / sodium oxalate mixed solution.

[0067] 2. Take three 2L beakers and add 1000mL of saline-alkali water from area B of a certain region to each beaker, labeled #1, #2, and #3. For sample #1, first add 2.5mL of potassium oxalate solution. It was observed that white suspended matter immediately appeared in the water upon addition of the solution. After mixing, the white suspended matter was present throughout the entire water sample. Then, add 33.4mL of sodium oxalate solution. It was found that more white precipitate formed in the saline-alkali water. After standing overnight or filtering the precipitate, saline-alkali water with reduced calcium and increased potassium was obtained. For sample #2, first add 33.4mL of sodium oxalate solution. It was observed that a large amount of white suspended matter immediately appeared in the water upon addition of the solution. After mixing, the white suspended matter was present throughout the entire water sample. Then, add 2.5mL of potassium oxalate solution. White precipitate continued to form in the saline-alkali water. After standing overnight or filtering the precipitate, saline-alkali water with reduced calcium and increased potassium was obtained. Adding 35.9 mL of a potassium oxalate / sodium oxalate mixed solution to #3 immediately resulted in the appearance of a large amount of white suspended matter in the water. After mixing, the solution was allowed to stand overnight or filtered to precipitate, yielding calcium-reducing and potassium-enhancing saline-alkali water. Inductively coupled plasma mass spectrometry (ICP-MS) analysis revealed that the Na+ content of the calcium-reducing and potassium-enhancing saline-alkali water obtained after treatments #1, #2, and #3 was significantly higher. + K + Ca 2+ Mg 2+ The ion concentrations were 2536.2 mg / L, 96.3 mg / L, 104.1 mg / L, and 205.2 mg / L. This indicates that treating saline-alkali water with potassium oxalate solution sequentially or simultaneously does not affect the final result of water quality conditioning; both solutions effectively reduce Ca2+. 2+ Ion concentration, precisely increase K + Ion concentration, without affecting Mg 2+ Ion concentration. When adding a potassium oxalate / sodium oxalate mixed solution to saline-alkali water, the goal of precisely reducing calcium and increasing potassium can be achieved in a single operation, achieving two goals at once, and the operation is simple. In addition, ion chromatography detection of oxalate ions showed that the oxalate ion concentration was <10mg / L, less than 1.5% of the original added concentration, indicating that calcium oxalate precipitation was sufficient and oxalate ion residue was low.

[0068] 3) Based on K + Ca 2+ Mg 2+ Seawater regulation methods based on ions in saline-alkali water

[0069] 1. Preparation of sodium oxalate, potassium oxalate and magnesium chloride solutions: (1) Dissolve 30.55g of Na2C2O4 in 900mL of water, then bring the volume to 1000mL and mix well to obtain a sodium oxalate solution with a concentration of 30.55g / L (228mmol / L). (2) Dissolve 53.05g of K2C2O4·H2O in 900mL of water, then bring the volume to 1000mL and mix well to obtain a potassium oxalate solution with a concentration of 288mmol / L. (3) Take 334mL of the sodium oxalate solution prepared above, add 25mL of the potassium oxalate solution prepared above, mix well, and use as a potassium oxalate / sodium oxalate mixed solution. (4) Dissolve 304.95g of MgCl2·6H2O in 900mL of water, then bring the volume to 1000mL and mix well to obtain a magnesium chloride solution with a concentration of 1500mmol / L.

[0070] 2. Take three 2L beakers and add 1000mL of saline-alkali water from a certain area B to each beaker, labeled #1, #2, and #3. In #1, first add 2.5mL of potassium oxalate solution. It was observed that white suspended matter immediately appeared in the water upon addition of the solution. After mixing, the entire water body contained white suspended matter. Then, add 33.4mL of sodium oxalate solution, generating more white precipitate. After letting it stand overnight or filtering the precipitate, add 3.5mL of magnesium chloride solution to the clear solution to obtain saline-alkali water that reduces calcium, increases potassium, and increases magnesium. In #2, first add 33.4mL of sodium oxalate solution. It was observed that a large amount of white suspended matter immediately appeared in the water upon addition of the solution. After mixing, the entire water body contained white suspended matter. Then, add 2.5mL of potassium oxalate solution, which continued to generate white precipitate. After letting it stand overnight or filtering the precipitate, add 3.5mL of magnesium chloride solution to the clear solution to obtain saline-alkali water that reduces calcium, increases potassium, and increases magnesium. Adding 35.9 mL of potassium oxalate / sodium oxalate mixed solution to #3 immediately resulted in a large amount of white suspended matter appearing in the water. After mixing, the solution was allowed to stand overnight or filtered to precipitate. Then, 3.5 mL of magnesium chloride solution was added to the clear solution to obtain saline-alkali water with reduced calcium, increased potassium, and increased magnesium. Inductively coupled plasma mass spectrometry (ICP-MS) analysis revealed that the Na+ content of the saline-alkali water obtained after treatments #1, #2, and #3 was significantly higher than that obtained after treatments #1, #2, and #3. + K + Ca 2+ Mg 2+ The ion concentrations were approximately 2527.7 mg / L, 96.0 mg / L, 103.7 mg / L, and 325.8 mg / L, respectively. Except for Na... + Apart from the ions, the concentrations of the other three cations are basically consistent with the ion concentrations corresponding to 9‰ seawater, thus achieving the adjustment of saline water to K+. + Ca 2+ Mg 2+ Seawater-like at the ion level.

[0071] 3. Scale up the system, prepare and utilize the aforementioned K + Ca 2+ Mg 2+ Adjusted saline-alkaline water with ion concentrations matching those of seawater at a salinity of 9‰ was used for the culture of Litopenaeus vannamei from southern Xinjiang. Except for the use of adjusted saline-alkaline water, all other operations were consistent with those described in "Industrialized Culture Technology of Litopenaeus vannamei" (Shi Chaobin & Sun Yanhui. Henan Fisheries, 2023, Vol. 2: 14-15, 20). Results showed that although the adjusted saline-alkaline water... + Ion concentration is not related to salinity (9‰ seawater Na+). + The ion concentrations are exactly the same, and its Na + The ion concentration was 91.5% of that of seawater with the same salinity, yet normal cultivation of Litopenaeus vannamei was still possible, indicating that the Na+ concentration in the regulated saline-alkaline water was significantly reduced. + K + Ca 2+ Mg 2+ When the plasma concentration is roughly equivalent to that of seawater with the same salinity, successful cultivation of Litopenaeus vannamei can be achieved. This adjusted saline-alkaline water can be used as aquaculture water for Litopenaeus vannamei. After 60 days of feeding and management, no diseases occurred during the entire cultivation process. The Litopenaeus vannamei reached a size of 70-80 shrimp / kg, with a yield of 3000 kg per mu (approximately 0.16 acres) and a single-crop cultivation output value exceeding 180,000 yuan per mu.

[0072] 4. Scale up the system, prepare and utilize the aforementioned K + Ca 2+ Mg 2+ Adjusted saline-alkaline water with ion concentrations consistent with those of seawater at a salinity of 9‰ was used for the cultivation of pearl grouper in southern Xinjiang. Except for the use of 1.2m deep adjusted saline-alkaline water and a stocking size of 100g for the fish fry, the other operations were consistent with the "Experimental Study on Factory Farming Technology of Giant Grouper" (Tian Lili et al., Fisheries Wealth Guide, 2023(11): 50-52). The results showed that the adjusted saline-alkaline water was suitable for the cultivation of pearl grouper. After 5 months of feeding and management, the pearl grouper reached a size of 500-900g / fish, with a yield value of 500,000 yuan per mu.

[0073] 4) Based on Na + K + Ca 2+ Mg 2+ Seawater regulation methods for saline-alkali water with ions

[0074] 1. Preparation of sodium oxalate, potassium oxalate, magnesium chloride, and sodium chloride solutions: (1) Dissolve 30.55g of Na2C2O4 in 900mL of water, then bring the volume to 1000mL and mix well to obtain a sodium oxalate solution with a concentration of 30.55g / L (228mmol / L). (2) Dissolve 53.05g of K2C2O4·H2O in 900mL of water, then bring the volume to 1000mL and mix well to obtain a potassium oxalate solution with a concentration of 288mmol / L. (3) Take 334mL of the sodium oxalate solution prepared above, add 25mL of the potassium oxalate solution prepared above, mix well, and use this as a potassium oxalate / sodium oxalate mixed solution. (4) Dissolve 304.95g of MgCl2·6H2O in 900mL of water, then bring the volume to 1000mL and mix well to obtain a magnesium chloride solution with a concentration of 1500mmol / L. (5) Dissolve 360g of NaCl in 900mL of water, then bring the volume up to 1000mL. Mix well to obtain a sodium chloride solution with a concentration of 360g / L (6160mmol / L). (6) Take 350mL of the magnesium chloride solution prepared above, add 130mL of the sodium chloride solution prepared above, mix well, and use it as a magnesium chloride / sodium chloride mixed solution.

[0075] 2. Take three 2L beakers and add 1000mL of saline-alkali water from a certain area B to each beaker, labeled #1, #2, and #3. Add 35.9mL of a potassium oxalate / sodium oxalate mixed solution to sample #1. Upon addition of the solution, a large amount of white suspended matter immediately appears in the water. After mixing, let the solution stand overnight or filter to precipitate. First, add 3.5mL of magnesium chloride solution, mix well, then add 1.3mL of sodium chloride solution and mix well to obtain Na+. + K + Ca 2+ Mg 2+ The composition and ratio of the four ions are consistent with seawater of the same salinity. In sample #2, 35.9 mL of a potassium oxalate / sodium oxalate mixed solution was added. Immediately upon addition, a large amount of white suspended matter appeared in the water. After mixing, the solution was allowed to stand overnight or filtered to precipitate. Then, 1.3 mL of sodium chloride solution was added, mixed, and then 3.5 mL of magnesium chloride solution was added and mixed to obtain Na+. + K + Ca 2+ Mg 2+ The composition and ratio of the four ions are consistent with seawater of the same salinity. In sample #3, 35.9 mL of a potassium oxalate / sodium oxalate mixed solution was added. Immediately upon addition, a large amount of white suspended matter appeared in the water. After mixing, the solution was allowed to stand overnight or filtered to precipitate. Then, 4.8 mL of a magnesium chloride / sodium chloride mixed solution was added and mixed to obtain Na+. + K + Ca 2+ Mg2+ The four ion compositions and proportions were consistent with seawater of the same salinity. Inductively coupled plasma mass spectrometry (ICP-MS) analysis revealed that the Na+ content of the seawater obtained after treatments #1, #2, and #3 was significantly higher. + K + Ca 2+ Mg 2+ The ion concentrations were approximately 2701.5 mg / L, 96.0 mg / L, 103.6 mg / L, and 325.4 mg / L, respectively. The concentrations of the four cations were essentially consistent with the ion concentrations corresponding to 9‰ seawater, thus achieving the goal of adjusting the saline water to Na+. + K + Ca 2+ Mg 2+ Seawater-like water with ion concentrations and proportions consistent with seawater of the same salinity.

[0076] 3. Scale up the system, prepare and utilize the aforementioned Na + K + Ca 2+ Mg 2+ Adjusted saline-alkaline water with ion concentrations matching those of seawater at a salinity of 9‰ was used for the cultivation of Litopenaeus vannamei in southern Xinjiang. Except for the use of adjusted saline-alkaline water, all other operations were consistent with the principles described in "Industrialized Cultivation Technology of Litopenaeus vannamei" (Shi Chaobin & Sun Yanhui. Henan Fisheries, 2023, Vol. 2: 14-15, 20). Results showed that precisely adjusting the salinity of the water to Na+ concentration... + K + Ca 2+ Mg 2+ Adjusted saline-alkaline water with ion concentrations matching those of seawater at the same salinity can be used for the normal cultivation of Litopenaeus vannamei. This adjusted saline-alkaline water can be used as aquaculture water for Litopenaeus vannamei. After 60 days of feeding and management, no diseases occurred during the entire cultivation process. The shrimp reached a size of 70-80 shrimp / kg, with a yield of 3200 kg per mu (approximately 0.16 acres), and a single-crop cultivation output value exceeding 190,000 yuan per mu.

[0077] Step S3: Desalinate the brine water using the reverse osmosis system.

[0078] In this invention, the desalinated brine water produced by the reverse osmosis system is regulated brine water obtained through step S2. Its purpose is to simultaneously obtain freshwater needed for crop cultivation and seawater-like water for aquaculture, without considering a high freshwater yield. In this invention, the freshwater yield is controlled at 45%–50%, unlike traditional industrial brine water purification, which achieves a freshwater yield of 65%–85%.

[0079] In addition, traditional reverse osmosis systems for desalinating brine water often require a secondary reverse osmosis system (i.e., the permeate from the first reverse osmosis process is treated again by reverse osmosis) to obtain high-purity fresh water. Similarly, to improve the overall fresh water yield, a reverse osmosis concentrate recirculation process is needed to treat concentrated brine water a second time by reverse osmosis to obtain fresh water and brine water with even higher concentrations.

[0080] In this invention, only a single-stage reverse osmosis system is used, and the freshwater yield is controlled at 45%–50%, resulting in concentrated brine with a salinity of 6‰–35‰, which is suitable for marine aquaculture species. Furthermore, when the freshwater yield is controlled at 45–50%, the brine will not precipitate salt, thus preventing fouling of the reverse osmosis membrane.

[0081] Therefore, by combining the seawater-like regulation in step S2 with the novel reverse osmosis strategy in step S3, the problem of reverse osmosis membrane fouling during the desalination of saline-alkali water was solved.

[0082] Experiments were conducted in two areas of the First Division of the Xinjiang Production and Construction Corps. The main ion composition of the water in areas A and B is shown in Table 1.

[0083] Table 1. Main ionic composition and concentration of saline water in two regions (concentration unit: mg / L)

[0084] <![CDATA[Na + ]]> <![CDATA[K + ]]> <![CDATA[Ca 2+ ]]> <![CDATA[Mg 2+ ]]> <![CDATA[Cl - ]]> <![CDATA[SO4 2- ]]> salinity‰ Region A 4612.6 52.2 409.9 274.7 5647.1 3334.8 15.3 Region B 2198.5 43 418.3 213.2 2906.8 2105.3 8.9

[0085] In area A, the salinity of the underground saline water is 15.3‰, and the main ion composition is shown in Table 1. When the saline water is concentrated to twice its original concentration, i.e., the salinity becomes 30.6‰, no salt precipitates; when the saline water is concentrated to 2.5 times its original concentration, the salinity becomes 38.3‰, and still no salt precipitates; when the saline water is concentrated to 3.3 times its original concentration, the salinity becomes 50.9‰, fine crystals precipitate.

[0086] In area B, the salinity of the underground saline water is 8.9‰, and the main ion composition is shown in Table 1. When the saline water is concentrated to twice its original concentration, i.e., the salinity becomes 17.8‰, no salt precipitates; when it is concentrated to three times its original concentration, the salinity becomes 26.7‰, and still no salt precipitates; when it is concentrated to four times its original concentration, the salinity becomes 35.6‰, and still no salt precipitates; when it is concentrated to five times its original concentration, the salinity becomes 44.5‰, fine and elongated crystals precipitate.

[0087] The main ionic composition and concentration indicators of the desalinated water in region B are shown in Table 2.

[0088] Table 2. Main ionic composition and concentration of saline-alkali water in Region B before and after desalination (concentration unit: mg / L)

[0089]

[0090] Step S4: Crop planting and aquaculture.

[0091] In this invention, the freshwater obtained from the reverse osmosis system is used for crop cultivation or domestic water use. During non-irrigation periods, crops require less water, and the excess freshwater can be pumped into the reservoir obtained in step S1 for storage. When irrigation is needed, the water is pumped out for irrigation. The seawater-like water obtained from the reverse osmosis system is used for factory-scale recirculating aquaculture of aquatic products. Since recirculating aquaculture requires a small amount of water, the concentrated saline-alkali water obtained over a long period will far exceed the seawater-like water demand for aquaculture. At this time, once the amount of seawater-like water meets the needs of aquaculture, the remaining saline-alkali water is directly desalinated without seawater-like water regulation. The resulting concentrated saline-alkali water is directly reinjected into the bottom of the saline-alkali water layer, which will not pollute the original saline-alkali water and is also conducive to the relative stability of groundwater or surface water levels, preventing geological disasters such as ground collapse.

[0092] The aforementioned seawater-like material was prepared and used for the cultivation of Litopenaeus vannamei in southern Xinjiang. Except for the use of seawater-like material as the culture water, the other operations were consistent with those described in "Industrialized Culture Technology of Litopenaeus vannamei" (Shi Chaobin & Sun Yanhui. Henan Fisheries, 2023, Vol. 2: 14-15, 20). The results showed that the seawater-like material could support the normal cultivation of Litopenaeus vannamei, indicating that it can be used as culture water. After 60 days of feeding and management, no diseases occurred during the entire cultivation process. The shrimp reached a size of 60-70 shrimp / kg, with a yield of 3700 kg per mu (approximately 0.16 acres), and a single-crop output value exceeding 220,000 yuan per mu.

[0093] The aforementioned seawater-like environment was prepared and used for the cultivation of pearl grouper in southern Xinjiang. Except for the use of seawater with a depth of 1.2m and a stocking size of 100g for the fish fry, the other operations were consistent with the "Experimental Study on Factory Farming Technology of Giant Grouper" (Tian Lili et al., Fisheries Wealth Guide, 2023(11): 50-52). The results showed that after 5 months of feeding and management, the pearl grouper reached a size of 550-950g / fish, with a yield value of over 530,000 yuan per mu.

[0094] The reason why excess concentrated saline water can be directly recharged is that it has not been used for aquaculture and is only a concentration of the original saline water. It will not add extra bacteria or other exogenous substances, so direct recharge is safe and reliable.

[0095] When the extracted saline water is groundwater, the concentrated saline water is reinjected at the bottom of the subsurface water layer; when the extracted saline water is surface water, the concentrated saline water is reinjected at the bottom of the surface water layer. The different reinjection locations of the concentrated saline water will have different effects on the salinity of saline water at different depths. Taking a surface saline water source in Alar City as an example, the main water ion indicators of the original surface saline water sample are shown in Table 3.

[0096] Table 3. Main ion indicators of surface saline water after desalination and salt redistribution (concentration unit: mg / L)

[0097] <![CDATA[Na + ]]> <![CDATA[K + ]]> <![CDATA[Ca 2+ ]]> <![CDATA[Mg 2+ ]]> <![CDATA[Cl - ]]> <![CDATA[SO4 2- ]]> 50cm below the water surface, saline water 4777.1 27.1 784.5 558.4 6833.2 3943.1 saline water reverse osmosis permeate 63.2 0.0 0.0 0.0 97.6 0.0 Reverse osmosis accompanied by concentrated saline water 6736.2 38.7 1121.1 798.0 9625.2 5634.7 Bottom saline water before bottom recharge 4779.8 27.5 786.4 557.7 6835.4 3946.7 Subsurface saline water after bottom recharge 5948.0 34.2 980.4 696.3 8521.7 4953.5 50cm of saline-alkali water after bottom recharge 4776.3 27.2 784.8 559.1 6834.4 3942.7 After water surface recharge, 50cm of saline-alkali water below the water surface 5364.6 30.8 884.6 631.2 7672.2 4451.2 After surface recharge, the bottom of the water is saline-alkali water 6007.8 34.7 990.3 703.4 8606.5 5003.4

[0098] Saline-alkali water was extracted from 50 cm below the surface water surface. After particle removal by microfiltration, the saline-alkali water was desalinated using a reverse osmosis membrane system, yielding reverse osmosis permeate with a recovery rate of approximately 30% (permeate water quality meets GB / T 14848-2017 Class III standard) and associated concentrated saline-alkali water. The water quality indicators were stable, as shown in Table 3. The concentrated saline-alkali water generated during the desalination process was transported to the bottom for reinjection. 200 tons of concentrated saline-alkali water were reinjected into the bottom layer daily. The main water ion indicators of the saline-alkali water at 50 cm below the bottom reinjection pipe and 50 cm below the surface after 30 days of bottom reinjection are shown in Table 3. Subsequently, the concentrated saline-alkali water was reinjected at the surface, 30 m south of the pump outlet, with the reinjection pipe opening facing downwards. The main water ion indicators of the saline-alkali water at 50 cm below the reinjection pipe and at the bottom layer after 5 days of surface reinjection are shown in Table 3.

[0099] Water-saving measures such as drip irrigation under mulch film are adopted during crop cultivation. In arid regions, where the average annual evaporation is 2-3 cubic meters, mulching technology can save 1250-1950 tons of freshwater per acre. Combined with drip irrigation technology, freshwater can be supplied to crops in a personalized manner, solving the problem of freshwater scarcity and potentially alleviating or even solving the problem of declining groundwater levels.

[0100] Traditional mulching methods aim to maintain the temperature inside the membrane and reduce evaporation, thereby minimizing water consumption. This invention differs from traditional mulching methods. The purpose of reducing water consumption in this invention is to maintain a stable groundwater level without disrupting the original hydrogeological conditions. Unlike traditional methods that lead to groundwater level decline or even ground collapse, this invention represents a green and sustainable land reclamation method.

[0101] Wastewater or tailwater from aquaculture (the aquaculture water remaining after seafood harvesting) undergoes solid-liquid separation. The solid organic matter, such as feces and uneaten feed, is used as organic fertilizer for crop growth. The filtered aquaculture water or tailwater can be used for recycling or fed into the outer ponds dug in step S1. Evaporation from the outer ponds also increases the water vapor content in the local air, and salt-tolerant plants and animals can be cultivated in the ponds. The tailwater in this invention is not directly used for groundwater recharge because it contains exogenous substances such as bacteria, which differ from the original groundwater; direct recharge could cause groundwater pollution. After being filtered through sand and gravel, the water in the outer ponds can replenish the groundwater level or, after being blocked by a waterproof layer, precipitate salt as the salinity increases, which can then be used to prepare and sell industrial salt.

[0102] Step S5: Photovoltaic power generation.

[0103] This invention also includes a photovoltaic power generation module, which generates electricity for saline-alkali water desalination, crop cultivation, and aquaculture. By incorporating the photovoltaic power generation module, the entire system can achieve self-sufficiency in electricity, eliminating the need for external power connections.

[0104] In addition, the energy in the entire system is basically recycled, and the saline water and fresh water in the system are also recycled, which is conducive to the stability of the local ecology and the development of the region.

[0105] Example 2

[0106] like Figure 2 As shown, the present invention also provides a multi-level circular agriculture system for saline-alkali land based on multi-level resource utilization of saline-alkali water, including a seawater-like regulation module, a saline-alkali water desalination module, a planting module, an aquaculture module, a terraced field module, and a photovoltaic power generation module.

[0107] Among them, the seawater-like regulation module is used to adjust the underground saline water to be similar or the same as the saline water with the same ionic composition and content and salinity as seawater used in aquaculture.

[0108] The saline-alkali water desalination module is used to desalinate the conditioned saline-alkali water through a reverse osmosis system, simultaneously producing fresh water and seawater-like water.

[0109] The planting module is used to grow local crops and can be equipped with corresponding drip irrigation technology or water evaporation prevention technology.

[0110] The aquaculture module is used to cultivate aquatic products adapted to seawater. Freshwater can be used in the planting module or for cultivating freshwater aquatic products, or it can be used first for cultivating freshwater aquatic products and then the aquaculture wastewater can be used in the planting module.

[0111] Terraced fields are used to increase the distance between the topsoil and the groundwater level, while creating an outer pond and / or reservoir.

[0112] Photovoltaic power generation modules are used to supply power for seawater regulation, saline-alkali water desalination, crop planting, and aquaculture.

[0113] Example 3

[0114] 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. 3After 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.

[0115] Planting results show that:

[0116] May 4: The overall germination rate of all types of seeds reached 70%.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] The above results fully demonstrate that:

[0121] 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.

[0122] 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.

[0123] High technical applicability: This technology does not rely on the screening and creation of specific salt-tolerant varieties and is applicable to conventional crops.

[0124] 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.

[0125] It is worth noting that all contents not described in detail in this invention are existing technologies and are well known to those skilled in the art. Before treatment by the reverse osmosis system, if the concentration of potassium and / or magnesium ions is higher than that of seawater with the same salinity, it is not necessary to reduce the concentration of potassium and / or magnesium ions. During reverse osmosis treatment, as long as the reverse osmosis membrane is not fouled, the method used in this invention can be applied even if the salinity of seawater is greater than 35‰ or the freshwater yield is greater than 50%. Under conditions where groundwater levels or surface evaporation can be controlled, saline-alkali land can be reclaimed without terraces. Before irrigation, freshwater aquaculture can be carried out, and the aquaculture wastewater can be used for planting, which not only increases economic benefits but also fertilizes the land and reduces alkali. Since photovoltaic power generation can not only supply power to modules such as saline-alkali water desalination but also generate profits through grid connection, a simplified model consisting only of photovoltaic modules, saline-alkali water desalination and recharge modules, and planting modules can be selected. This "energy-for-agriculture" approach can achieve sustainable development of saline-alkali land or desert land reclamation, enabling rapid and large-scale utilization and transformation of saline-alkali land or deserts.

[0126] Therefore, the present invention adopts the above-mentioned multi-level circular agriculture system and method for saline-alkali land based on multi-level resource utilization of saline-alkali water. That is, a multi-level circular agriculture system for saline-alkali land is constructed based on multi-level resource utilization of saline-alkali water. The entire system does not require external supply of fresh water and external power supply, and is self-contained, achieving a win-win situation of ecological, social and economic benefits, realizing green and sustainable development, and has universal promotion value for the comprehensive development and utilization of saline-alkali land.

[0127] 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 multi-level circular agriculture method for saline-alkali land based on multi-level resource utilization of saline-alkali water, characterized in that, Includes the following steps: Step S1: After testing the saline-alkali water in the saline-alkali area, extract the saline-alkali water for seawater-like regulation, that is, adjust the ionic composition and ratio of the saline-alkali water according to the needs of aquaculture water to obtain the regulated saline-alkali water. Step S2: Desalinate the adjusted saline water through a primary reverse osmosis system to obtain both fresh water and seawater-like water. Step S3: The obtained freshwater is used for crop cultivation, and the obtained seawater-like water is used for aquaculture. Step S4: After the aquatic products are harvested, the aquaculture tailwater is separated into solid and liquid components. The residue obtained from the filtration is used as fertilizer for crop planting, and the filtered tailwater is discharged into the outer pond or used for recycling aquaculture. In step S1, the saline-alkali water is regulated using a seawater-like regulation method to obtain regulated saline-alkali water, including the following two cases: Scenario 1: When the calcium hardness of the extracted saline water is greater than that of the aquaculture water, calculate the calcium ion concentration that needs to be removed based on the original calcium ion concentration of the saline water and the adjusted calcium, potassium, and magnesium ion concentrations to be used in the aquaculture water. Then remove the calcium ions and increase the potassium and magnesium ions. The method to remove calcium ion concentration is to add potassium oxalate or sodium oxalate to the water to precipitate calcium ions; Scenario 2: When the calcium hardness of the extracted saline water is less than that of the water used for aquaculture, calcium, potassium, and magnesium ions are added to the saline water according to the adjusted concentrations of calcium, potassium, and magnesium ions intended for use in the aquaculture water. In step S3, once the amount of seawater meets the needs of aquaculture, the remaining saline-alkali water is directly desalinated without being regulated by seawater, and the resulting concentrated saline-alkali water is directly reinjected into the bottom of the saline-alkali water layer.

2. The method for multi-level circular agriculture of saline-alkali land based on multi-level resource utilization of saline-alkali water according to claim 1, characterized in that, In step S2, the freshwater yield of the reverse osmosis system is 45-50%.

3. The method for multi-level circular agriculture of saline-alkali land based on multi-level resource utilization of saline-alkali water according to claim 1, characterized in that, In step S2, the salinity of the seawater obtained through the reverse osmosis system is no higher than 35‰.

4. A multi-level circular agricultural system for saline-alkali land based on multi-level resource utilization of saline-alkali water, characterized in that, A method for implementing a multi-level circular agriculture method for saline-alkali land based on multi-level resource utilization of saline-alkali water as described in any one of claims 1-3, comprising: A seawater regulation module is used to adjust saline water to be similar to or the same as seawater with the same salinity and ion composition and content as aquaculture water. The saline-alkali water desalination module is used to desalinate the conditioned saline-alkali water through a reverse osmosis system, simultaneously producing fresh water and seawater-like water. Planting module, equipped with drip irrigation system under film; Aquaculture module, used for aquaculture; Terraced fields are used to increase the distance between the topsoil and the groundwater level, while creating an outer pond and / or reservoir. Photovoltaic power generation modules are used to supply power to seawater regulation modules, saline-alkali water desalination modules, planting modules, and aquaculture modules.

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