System and method for treating salt-laden wastewater

Abstract

The application provides a system and method for treating salt-containing wastewater. The system comprises: a pretreatment unit for pretreating the salt-containing wastewater; a membrane separation unit connected with the pretreatment unit, comprising a gradient coupling membrane separation structure and a scale inhibitor dosing device, for dosing scale inhibitors to the effluent of the pretreatment unit and gradient separation, to obtain a divalent salt-rich liquid; the scale inhibitor dosing device is connected to a chemical dosing port of the gradient coupling membrane separation structure; the scale inhibitor is a dendritic scale inhibitor, which is a polyamide-amine series dendrimer with alkyl diamine as the core, and does not contain organic phosphonate and inorganic phosphate in the molecule; a hardness and silicon removal unit connected with a concentrated water outlet of the membrane separation unit; a crystallization unit comprising parallel monovalent salt crystallization devices and divalent salt crystallization devices; the monovalent salt crystallization device is connected with a water outlet of the membrane separation unit; the divalent salt crystallization device is connected with a water outlet of the hardness and silicon removal unit. The system and method are stable in operation, have good quality of crystallized salt, low energy consumption and excellent scale inhibition performance.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment and resource utilization technology, specifically relating to a system and method for treating saline wastewater, applicable to near-zero discharge and resource utilization of saline wastewater such as high-salt industrial wastewater, coal mine water, coal-fired power plant wastewater, and seawater. Background Technology

[0002] With global population growth, accelerated industrialization, and the impact of extreme weather events brought about by climate change, freshwater scarcity has become a global challenge. The resource utilization of typical high-salinity unconventional water sources such as seawater and mine water has become an important way to alleviate freshwater shortages. Retaining salt and pollutants from high-salinity water, promoting the domestic substitution of core equipment, and achieving wastewater reuse or compliant discharge have become key approaches to industrial wastewater treatment. Seawater and mine water share the commonality of containing various mineral components. Seawater is rich in sodium chloride and also contains elements such as magnesium, calcium, potassium, and silicon; mine water commonly contains sodium sulfate, sodium chloride, calcium, magnesium, and silicon. The biggest problem affecting operational stability and economy in membrane treatment for both is the scaling problem caused by calcium, magnesium, and silicon. When water passes through the membrane module, as water continuously permeates the membrane pores, the solute concentration on the membrane surface gradually increases, forming concentration polarization. At this time, if the ion concentration exceeds its solubility product (such as CaCO3, CaSO4, etc.), it will precipitate and deposit on the membrane surface, forming hard scale, leading to a decrease in membrane flux, a reduction in desalination rate, and even damage to the membrane element. Silica scale typically originates from dissolved silica and colloidal silica compounds in water. Under conditions of circulation concentration, pH changes, and sudden pressure drops, it precipitates out as supersaturation, forming hard, insoluble precipitates that easily clog membrane elements and evaporators, and are difficult to remove with conventional acids and alkalis. Furthermore, coal mine water and seawater generally exhibit high hardness, high mineralization, and silica content, presenting technical challenges due to objective fluctuations in water quality. They also face economic difficulties such as high energy consumption, short membrane lifespan, and high initial investment costs.

[0003] To address the aforementioned issues, there is an urgent need in this field to develop a saline wastewater treatment system and method with good stability, high-quality crystallized salt, and low energy consumption. This system would solve the problems of membrane fouling and scaling under complex water quality conditions such as high hardness, high mineralization, and silicon content, enabling the recycling of water and salt resources and the long-term stable operation of the system. This would provide technical support for resolving the contradictions between "water-industry-ecology" in areas with abundant coal resources but scarce water resources and coastal regions.

[0004] Currently, there are no reports of technologies that can solve the aforementioned problems. Summary of the Invention

[0005] The first objective of this invention is to provide a system for treating saline wastewater, thereby solving at least one of the aforementioned technical problems, and providing stable operation, high-quality crystalline salt, reduced energy consumption, and excellent scale inhibition performance.

[0006] A second objective of this invention is to provide a method for treating saline wastewater.

[0007] To achieve the first objective of this invention, the following technical solution is adopted: A system for treating saline wastewater includes: A system for treating saline wastewater, characterized in that the system comprises: The pretreatment unit is used to pretreat saline wastewater to remove any one or more of suspended solids, colloids, and organic pollutants to obtain pretreated permeate. A membrane separation unit, connected to the pretreatment unit, includes a gradient-coupled membrane separation structure and a scale inhibitor dosing device. This unit is used to add scale inhibitor and perform gradient separation on the effluent from the pretreatment unit, yielding a monovalent salt enriched solution and a divalent salt enriched solution. The scale inhibitor dosing device is connected to the reagent dosing port of the gradient-coupled membrane separation structure and is used to add scale inhibitor to the structure. The scale inhibitor is a dendritic scale inhibitor, a polyamide-amine series dendritic macromolecule with an alkyl diamine core, and its molecules do not contain organic phosphonates or inorganic phosphates. The hardening and desiliconization unit is connected to the concentrate outlet of the membrane separation unit and is used to perform hardening and desiliconization treatment on the divalent salt enrichment solution to remove calcium, magnesium ions and silicon impurities, and obtain calcium carbonate, magnesium hydroxide and silicate precipitates. The crystallization unit includes a monovalent salt crystallization device and a divalent salt crystallization device connected in parallel. The monovalent salt crystallization device is connected to the permeate outlet of the membrane separation unit and is used to crystallize the permeate of the membrane separation unit to obtain monovalent salt crystals. The divalent salt crystallization device is connected to the outlet of the hardening and desiliconizing unit and is used to crystallize the effluent after hardening and desiliconizing to obtain divalent salt crystals.

[0008] The system for treating saline wastewater of the present invention preferably further includes an intelligent control unit; the intelligent control unit is connected to the pretreatment unit, the membrane separation unit, the hardening and silicon removal unit and the crystallization unit respectively, and includes temperature sensors, TDS sensors, residual chlorine sensors and pH sensors disposed at the inlet and outlet of each membrane separation device in the gradient coupling membrane separation structure of the membrane separation unit, for collecting real-time data and adjusting the operating parameters in a coordinated manner.

[0009] The system for treating saline wastewater of the present invention, preferably, further includes a scaling risk early warning module and a linkage adjustment module in the intelligent control unit; wherein... The scaling risk warning module is connected to the membrane separation unit and the crystallization unit respectively, and is used to detect the calcium hydroxide concentration in the effluent of the membrane separation unit and the calcium hydroxide concentration in the mother liquor of the crystallization unit respectively. The signal receiving end of the linkage adjustment module is connected to the scaling risk warning module, and the signal output end of the linkage adjustment module is connected to the scale inhibitor dosing device and the inlet valve of the saline wastewater. In the system for treating saline wastewater of the present invention, preferably, the linkage adjustment module automatically performs one or more of the following operations based on the detection data: When the concentration of calcium hydroxide in the water reaches the set value, the scale inhibitor is automatically released, the water temperature is increased, and the water flow rate is increased to prevent scale from depositing on the membrane surface. Preferably, the set values ​​are: calcium hydroxide concentration in the water 0.165±0.1%, water temperature increase of 4~7 ℃, and flow rate increase of 1.5~3%. When scaling is detected in the crystallization unit, reduce the inlet water flow rate; preferably, reduce the inlet water flow rate by 20-40%.

[0010] The system for treating saline wastewater of the present invention preferably further includes a refluxing pipeline, wherein the inlet end of the refluxing pipeline is connected to the mother liquor outlet of the crystallization unit and the outlet end is connected to the inlet pipeline of the membrane separation unit, for refluxing the mother liquor of the crystallization unit.

[0011] The system for treating saline wastewater of the present invention preferably includes a pretreatment unit comprising one or more of a flocculation sedimentation device, an ozone oxidation device, and a membrane bioreactor, for treating saline wastewater by flocculation sedimentation, ozone oxidation, and membrane bioreactor treatment.

[0012] The system for treating saline wastewater of the present invention preferably includes a monovalent salt crystallization device that is a sodium chloride crystallization device; and / or, The divalent salt crystallization device is a sodium sulfate crystallization device and / or a magnesium salt crystallization device.

[0013] The hardening and desiliconizing unit includes a divalent brine tank and a filtration device connected in sequence. The divalent brine tank is connected to the divalent salt enrichment outlet of the membrane separation unit and is connected to a dosing pipeline for introducing the divalent salt enrichment and adding chemicals to generate calcium carbonate, magnesium hydroxide, and silicate precipitates. The filtration device is used to filter the material in the divalent brine tank to remove calcium carbonate, magnesium hydroxide, and silicate precipitates, and outputs the filtrate as effluent.

[0014] The system for treating saline wastewater of the present invention preferably includes a gradient-coupled membrane separation structure comprising a first membrane treatment device and a dual-stage nanofiltration device connected in sequence. The first membrane treatment is performed on the effluent from the pretreatment unit, and then the concentrated water from the first membrane treatment is subjected to salt separation treatment to obtain a monovalent salt enriched solution and a divalent salt enriched solution. The membrane pore sizes of the first membrane treatment device and the dual-stage nanofiltration device are arranged in a decreasing order.

[0015] The system for treating saline wastewater of the present invention preferably includes an ultrafiltration device and / or a reverse osmosis device in the first membrane treatment device; more preferably, the first membrane treatment device includes an ultrafiltration device and a reverse osmosis device connected in sequence.

[0016] The system for treating saline wastewater of the present invention preferably includes a two-stage nanofiltration device comprising a primary nanofiltration device and a secondary nanofiltration device connected in sequence, for performing salt separation treatment on the concentrate from the first membrane treatment device to obtain a monovalent salt enriched solution and a divalent salt enriched solution.

[0017] In the system for treating saline wastewater of the present invention, preferably, the membrane pore sizes of the ultrafiltration device, the reverse osmosis device, the first-stage nanofiltration device, and the second-stage nanofiltration device are arranged in descending order.

[0018] In the system for treating saline wastewater of the present invention, preferably, the scale inhibitor dosing device is connected to the reagent dosing port of each membrane separation device in the gradient coupling membrane separation structure.

[0019] In this invention, each membrane separation device in the gradient coupling membrane separation structure refers to an ultrafiltration device, a reverse osmosis device, a primary nanofiltration device, and a secondary nanofiltration device.

[0020] To achieve the second objective of this invention, this invention also provides a method for treating saline wastewater, the method employing the aforementioned system; the method includes: S1. Pretreatment: The saline wastewater is passed into the pretreatment unit for pretreatment to remove one or more of suspended solids, colloids and organic pollutants to obtain pretreated wastewater. S2, Membrane separation: The pretreated permeate obtained in step S1 is passed into the membrane separation unit, and gradient separation is performed through the gradient coupling membrane separation structure in the presence of scale inhibitor to obtain monovalent salt enriched solution and divalent salt enriched solution; the scale inhibitor is a dendritic scale inhibitor, which is a polyamide-amine series dendritic macromolecule with alkyl diamine as the core, and its molecule does not contain organic phosphonates and inorganic phosphates. S3. Hardening and silicon removal: The divalent salt enrichment solution obtained in step S2 is passed into the hardening and silicon removal unit to remove calcium, magnesium ions and silicon impurities. The filtered filtrate is used as the hardening and silicon removal effluent. S4. Crystallization: The monovalent salt enrichment solution obtained in step S2 and the desiliconized water obtained in step S3 are respectively fed into the crystallization unit for crystallization to obtain monovalent salt crystals and divalent salt crystals.

[0021] The method for treating saline wastewater according to the present invention preferably further includes step S5, which involves using an intelligent control unit to collect real-time data from the temperature sensors, TDS sensors, residual chlorine sensors, and pH sensors at the inlet and outlet of each membrane separation device and to adjust the operating parameters accordingly.

[0022] The present invention provides a method for treating saline wastewater, which preferably utilizes a linkage adjustment module to automatically perform one or more of the following operations based on detection data: when the concentration of calcium hydroxide in the water body reaches a set value, the scale inhibitor is automatically released, the water body is heated, and the water flow rate is increased to prevent scale from depositing on the membrane surface. When scaling is detected in the crystallization unit, reduce the influent flow rate.

[0023] The method for treating saline wastewater according to the present invention preferably further includes step S6, in which the mother liquor from the crystallization unit in step S4 is returned to the inlet pipeline of the membrane separation unit in step S2 via a return pipeline for recycling.

[0024] The present invention relates to a method for treating saline wastewater, wherein the scale inhibitor is preferably a compound of a polyamide-amine dendritic polymer grafted with diethylenetriaminepentaacetic acid and a terpolymer, preferably in a weight percentage ratio of 50-85% and 5-10% respectively, with the remainder being water; wherein the terpolymer is an acrylic acid / acrylamidopropanesulfonic acid / hydroxypropyl acrylate copolymer.

[0025] The present invention provides a method for treating saline wastewater. Preferably, in step S2, the gradient-coupled membrane separation structure includes a first membrane treatment device and a dual-stage nanofiltration device connected in sequence; the membrane pore sizes of the first membrane treatment device and the dual-stage nanofiltration device are arranged in descending order; the dual-stage nanofiltration device includes a primary nanofiltration device and a secondary nanofiltration device; the membrane pore sizes of the primary nanofiltration device and the secondary nanofiltration device are arranged in descending order. The pretreated permeate is first treated by a first membrane treatment device to obtain first membrane treated permeate and first membrane treated concentrate. In step S2, membrane separation includes: The concentrate from the first membrane treatment is fed into a two-stage nanofiltration device for salt separation. Monovalent salts pass through the nanofiltration membrane into the permeate side, while divalent salts are retained in the concentrate side, resulting in monovalent salt enriched solution and divalent salt enriched solution, respectively.

[0026] The present invention provides a method for treating saline wastewater, preferably in a two-stage nanofiltration device. The operating temperature of the primary nanofiltration unit is 20~50 ℃, and / or the operating pressure is 15~20 bar, and / or the membrane flux is 15~20 LMH, and / or the recovery rate is 60~70%, and / or the retention rate of sulfate is 98~99.5%, and / or the retention rate of chloride is 0~25%. The operating temperature of the secondary nanofiltration device is 20~50 ℃, and / or the operating pressure is 6~15 bar, and / or the membrane flux is 12~20 LMH, and / or the recovery rate is 50~75%, and / or the retention rate of sulfate is 98~99.5%, and / or the retention rate of chloride is 10~30%.

[0027] The beneficial effects of this invention are as follows: This invention relates to a system and method for treating saline wastewater, capable of addressing membrane fouling and scaling problems under complex water quality conditions such as high hardness, high mineralization, and silicon content. It achieves the recycling of water and salt resources and the system's adaptive long-term stable operation, providing technical support for resolving the "water-industry-ecology" contradiction in coal-rich, water-scarce, and coastal areas. Specifically, (1) The system and method for treating saline wastewater of the present invention have high operational stability. Through the gradient coupling configuration of the membrane separation unit and the application of scale inhibitor, the continuous operation stability of the system can be improved to over 90%, which is significantly better than the level of about 65% of the traditional process. The amount of scale inhibitor used is small, which is safe for the membrane system.

[0028] (2) The system and method for treating saline wastewater of the present invention significantly reduce energy consumption. By optimizing the membrane pore size and functional cascade configuration through the gradient coupling configuration of the membrane separation unit, the energy consumption per unit of produced water can be reduced to below 2.8 kW·h / m³, which is far lower than the average level of 3.5~4.0 kW·h / m³ of similar international technologies.

[0029] (3) The system and method of the present invention for treating saline wastewater produce high-quality crystalline salt and significantly reduce impurities. Through the technical route of "membrane separation and salt separation + hardening and silicon removal + crystallization", it can produce super-grade industrial crystalline salt (NaCl purity ≥ 99.1%, Na2SO4 purity ≥ 99.4%), with an impurity reduction rate of ≥ 90%, solving the problems of low purity of crystalline salt and difficulty in handling impurities in traditional processes.

[0030] (4) The system and method of the present invention for treating saline wastewater exhibit excellent scale inhibition performance. By employing a dendritic scale inhibitor with a large internal and external surface area and a large number of terminal functional groups, a high scale inhibition load can be provided, controlling various metal ions, organic matter, and inorganic molecules. The scale inhibitor molecule does not contain any organic phosphonates or inorganic phosphates, which can reduce the risk of microbial contamination in membrane separation devices and the impact of sewage discharge on the environment. The terpolymer in the scale inhibitor has a good dispersion effect on highly mineralized wastewater and can inhibit the influence of heavy metal ions on the polyamide-amine dendritic polymer grafted with diethylenetriaminepentaacetic acid.

[0031] (5) The system and method of the present invention for treating saline wastewater can intelligently prevent scale formation and extend equipment life. The multi-sensor real-time monitoring and linkage intelligent control system, combined with dendritic scale inhibitor, can effectively inhibit scale formation on the membrane surface and crystallization equipment, extend the equipment cleaning cycle by 2 to 6 times, and reduce maintenance costs.

[0032] (6) The system and method for treating saline wastewater of the present invention have high integration and low investment cost. The pretreatment, membrane separation, hardening and silicon removal, crystallization and intelligent control units are organically integrated, resulting in high system integration, small footprint, low investment cost and low operating cost, and are suitable for the resource-based treatment of saline wastewater. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the system for treating saline wastewater according to one embodiment of the present invention; Figure 2 This is a schematic diagram of another embodiment of the system for treating saline wastewater according to the present invention. Detailed Implementation

[0034] The technical solution and its effects of the present invention will be further described below with reference to specific embodiments / examples. The following embodiments / examples are only for illustrating the content of the present invention, and the invention is not limited to the following embodiments or examples. Simple modifications made to the present invention based on the concept of the present invention are all within the scope of protection claimed by the present invention.

[0035] like Figures 1-2 As shown, the present invention provides a system for treating saline wastewater, comprising: Pretreatment unit 1 is used to pretreat saline wastewater to remove any one or more of suspended solids, colloids and organic pollutants to obtain pretreated wastewater; Membrane separation unit 2, connected to pretreatment unit 1, includes a gradient-coupled membrane separation structure and a scale inhibitor dosing device (not shown in the figure, only the scale inhibitor dosing pipeline is shown). It is used to add scale inhibitor and perform gradient separation on the effluent from pretreatment unit 1 to obtain monovalent salt enriched solution and divalent salt enriched solution. The scale inhibitor dosing device is connected to the reagent dosing port of the gradient-coupled membrane separation structure and is used to add scale inhibitor to the gradient-coupled membrane separation structure. The scale inhibitor is a dendritic scale inhibitor, which is a polyamide-amine series dendritic macromolecule with an alkyl diamine core, and its molecules do not contain organic phosphonates or inorganic phosphates. The hardening and desiliconization unit 3 is connected to the concentrate outlet of the membrane separation unit 2 and is used to perform hardening and desiliconization treatment on the divalent salt enrichment solution to remove calcium, magnesium ions and silicon impurities, and obtain calcium carbonate, magnesium hydroxide and silicate precipitates. Crystallization unit 4 includes a monovalent salt crystallization device and a divalent salt crystallization device connected in parallel; the monovalent salt crystallization device is connected to the product water outlet of the membrane separation unit 2 and is used to crystallize the product water of the membrane separation unit 2 to obtain monovalent salt crystals; the divalent salt crystallization device is connected to the outlet of the hardening and desiliconizing unit 3 and is used to crystallize the effluent after hardening and desiliconizing to obtain divalent salt crystals.

[0036] This invention relates to a system for treating saline wastewater. Through a gradient-coupled membrane separation structure, the membrane modules of each stage of the membrane separation unit have clearly defined functions and synergistic effects, significantly improving salt separation efficiency and creating the prerequisite for obtaining high-purity crystalline salt. By removing calcium, magnesium, and silicon impurities from the divalent salt enriched solution before it enters the crystallization unit, the deposition and scaling of hardness ions and silicon on the surface of the crystallization equipment is avoided, protecting the crystallization unit and extending its service life. Simultaneously, it prevents impurities from contaminating the crystalline salt product. By adding a dendritic scale inhibitor with an alkyl diamine core, PAMAM series dendritic macromolecules, to the membrane separation unit, its large internal and external surface area and numerous terminal functional groups provide a high scale inhibition load. Furthermore, because this scale inhibitor does not contain organic phosphonates or inorganic phosphates, it avoids eutrophication problems caused by phosphorus discharge and reduces the risk of microbial contamination of the membrane system. Compared to conventional scale inhibitors, which suffer from rapid performance degradation in high-salinity environments, this scale inhibitor is particularly suitable for treating high-salinity wastewater. By organically integrating the pretreatment unit, membrane separation unit, hardening and silica removal unit, and crystallization unit, it achieves high integration, small footprint, and low investment and operating costs.

[0037] This invention incorporates a scale inhibitor dosing device in the membrane separation unit, thereby enabling the added scale inhibitor to work synergistically with the crystallization unit to form phase change-enhanced crystallization.

[0038] Those skilled in the art will understand that the saline wastewater includes mine wastewater and / or seawater, and the salinity of both, calculated according to total dissolved solids (TDS), is as follows: I. Mine water (salt-containing wastewater from highly mineralized mines in coal-rich areas) TDS (total dissolved solids) ranges from 1,000 to 35,000 mg / L; among them, the TDS of shallow, low-mineralized mine water ranges from 1,000 to 5,000 mg / L, while the TDS of deep old mine water and high-sulfur mine water can reach 10,000 to 35,000 mg / L. II. Seawater (Routine nearshore seawater) TDS (total dissolved solids) ranges from 20,000 to 36,000 mg / L; among them, the TDS of standard seawater is approximately 32,000 to 36,000 mg / L; and the TDS of nearshore seawater affected by tides and freshwater inflow is 20,000 to 32,000 mg / L.

[0039] In some specific embodiments, the system further includes an intelligent control unit; the intelligent control unit is connected to the pretreatment unit, the membrane separation unit, the hardening and desiliconizing unit and the crystallization unit respectively, and includes temperature sensors, TDS sensors, residual chlorine sensors and pH sensors disposed at the inlet and outlet of each membrane separation device in the gradient coupling membrane separation structure of the membrane separation unit, for collecting real-time data and adjusting the operating parameters in a coordinated manner.

[0040] This invention relates to a system for treating saline wastewater. By installing multi-parameter sensors (temperature, TDS, residual chlorine, pH) at the inlet and outlet of each membrane separation unit, the system's operating status can be monitored and dynamically controlled in real time. Compared to existing technologies where operating parameters are mostly statically set, this system can dynamically adjust in real time according to water quality fluctuations, significantly enhancing the system's adaptability and stability.

[0041] In some specific embodiments, the intelligent control unit further includes a scaling risk warning module and a linkage adjustment module; wherein, The scaling risk warning module is connected to the membrane separation unit and the crystallization unit respectively, and is used to detect the calcium hydroxide concentration in the effluent of the membrane separation unit and the calcium hydroxide concentration in the mother liquor of the crystallization unit respectively. The signal receiving end of the linkage adjustment module is connected to the scaling risk warning module, and the signal output end of the linkage adjustment module is connected to the scale inhibitor dosing device and the inlet valve of the saline wastewater.

[0042] In some specific implementations, the linkage adjustment module automatically performs one or more of the following operations based on the detection data: When the concentration of calcium hydroxide in the water reaches the set value, the scale inhibitor is automatically released, the water temperature is increased, and the water flow rate is increased to prevent scale from depositing on the membrane surface. Preferably, the set value of the calcium hydroxide concentration in the water is 0.165±0.1%; the water temperature is increased by 4~7 ℃, such as 4 ℃, 5 ℃, 6 ℃, and 7 ℃, and any value or range within this range; the flow rate is increased by 1.5~3%, such as 1.5%, 2%, 2.5%, and 3%, and any value or range within this range. When scaling risk is detected in the crystallization unit, the inlet water flow rate is reduced; preferably, the inlet water flow rate is reduced by 20% to 40%, such as 20%, 25%, 30%, 35% and 40%, and any value and range within this range.

[0043] This invention relates to a system for treating saline wastewater. Through the setup of a scaling risk early warning module and a linkage regulation module, it achieves closed-loop control of "monitoring-early warning-response." The scaling risk early warning module and the linkage regulation module work together to intervene at the initial stage of scaling risk, preventing large-scale scale formation that could damage equipment or cause system shutdown, thus achieving adaptive long-term stable operation of the system. Regarding membrane scaling risk, the linkage regulation module simultaneously performs three operations: scale inhibitor release, temperature increase, and acceleration. The scale inhibitor chemically inhibits scale formation, the temperature increase thermodynamically improves salt solubility, and the acceleration reduces particulate matter adhesion from a fluid dynamics perspective. These three actions work synergistically to intervene before scale precipitation, resulting in a scale inhibition effect superior to any single method. When scaling risk is detected in the crystallization unit, the influent flow rate is automatically reduced, decreasing the crystallization load and extending the residence time to prevent explosive nucleation and scale buildup on the vessel walls caused by a rapid increase in supersaturation. Combined with the above membrane anti-scaling strategies, unified anti-scaling management is achieved for all units in the system, realizing proactive protection of the crystallization unit. Through intelligent linkage control, the membrane cleaning cycle can be extended by 2 to 6 times, which greatly reduces the difficulty of operation and management and maintenance costs, extends equipment life and reduces manual intervention.

[0044] In some specific embodiments, the system further includes a refluxing line 5, the inlet end of which is connected to the mother liquor outlet of the crystallization unit and the outlet end of which is connected to the inlet line of the membrane separation unit, for refluxing the mother liquor of the crystallization unit.

[0045] The present invention provides a system for treating saline wastewater. By re-dissolving the mother liquor of the crystallization unit through the re-dissolution pipeline 5, the total salt recovery rate can be improved, the discharge of impurities can be reduced, continuous production can be achieved, and it can be coordinated with intelligent control.

[0046] Those skilled in the art understand that the crystallization mother liquor still contains a certain amount of uncrystallized salt, and direct discharge will cause salt loss and secondary pollution. This invention returns the mother liquor to the membrane separation unit for reprocessing via a refluxing pipeline, allowing the residual salt in the mother liquor to be recovered again, significantly improving the overall salt recovery rate. Furthermore, the mother liquor refluxing and recycling process reduces the amount of final discharged impurities, achieving a technical effect of ≥90% reduction in impurities, and lowering the disposal cost of impurities as hazardous waste. The refluxing pipeline 5 allows the mother liquor from the crystallization unit to be circulated back to the front end of the system, enabling mother liquor treatment without interrupting system operation and ensuring continuous and stable system operation. The operating status of the refluxing pipeline 5 can be uniformly monitored and adjusted by the intelligent control unit. When the mother liquor return flow rate changes, the system can automatically adjust the front-end influent parameters to achieve dynamic optimization of the overall system material balance and achieve synergy with intelligent control.

[0047] In some specific embodiments, the pretreatment unit includes one or more of a flocculation sedimentation device, an ozone oxidation device, and a membrane bioreactor, for treating saline wastewater by flocculation sedimentation, ozone oxidation, and membrane bioreactor treatment; in a preferred embodiment, the pretreatment unit sequentially includes a flocculation sedimentation device, an ozone oxidation device, and a membrane bioreactor connected in series, for treating saline wastewater by flocculation sedimentation, ozone oxidation, and membrane bioreactor treatment in sequence.

[0048] In this invention, the flocculation sedimentation tank is used to flocculate and settle saline wastewater to remove suspended solids; the ozone oxidation device is used to treat the flocculated sedimentation effluent with ozone oxidation, breaking the ring-chain of organic matter in it, thereby converting recalcitrant organic matter into easily biodegradable small molecule intermediates; the membrane bioreactor is used to perform aerobic biochemical treatment on the ozone oxidation effluent, using activated sludge to mineralize and remove biodegradable organic matter, and achieving sludge-water separation through built-in membrane modules.

[0049] In some specific embodiments, the monovalent salt crystallization device is a sodium chloride crystallization device.

[0050] In some specific embodiments, the divalent salt crystallization device is a sodium sulfate crystallization device and / or a magnesium salt crystallization device.

[0051] In some specific embodiments, the sodium chloride crystallization device uses an evaporator crystallizer with an operating temperature of 90~100 ℃, such as 95 ℃, 96 ℃, 97 ℃, 98 ℃, 99 ℃, and 100 ℃, as well as any value and range within this range, to evaporate and crystallize the monovalent salt enrichment solution to obtain sodium chloride crystals.

[0052] In some specific embodiments, the sodium sulfate crystallization device uses a cryogenic crystallizer with an operating temperature of 5~20℃, such as 5℃, 10℃, 15℃ and 20℃, and any value and range within this range, for the precipitation of sodium sulfate crystals.

[0053] In some specific embodiments, the magnesium salt crystallization device employs a hot-press crystallizer with an operating temperature of 90~100℃, such as 95℃, 96℃, 97℃, 98℃, 99℃, and 100℃, and any value or range within this range; and an operating pressure of 2~5 MPa, such as 2 MPa, 3 MPa, 4 MPa, and 5 MPa, and any value or range within this range, for the precipitation of magnesium sulfate or magnesium hydroxide crystals.

[0054] In some specific embodiments, the hardening and desiliconizing unit includes a divalent brine tank and a filtration device connected in sequence; the divalent brine tank is connected to the divalent salt enrichment outlet of the membrane separation unit and is connected to a dosing pipeline for introducing the divalent salt enrichment and adding chemicals to generate calcium carbonate, magnesium hydroxide and silicate precipitates; the filtration device is used to filter the material in the divalent brine tank to remove calcium carbonate, magnesium hydroxide and silicate precipitates, and output the filtrate as effluent.

[0055] In this invention, "the divalent saline tank is connected to the divalent salt enrichment outlet of the membrane separation unit and is connected to a dosing line" means "the divalent saline tank is connected to the divalent salt enrichment outlet of the membrane separation unit and is connected to a dosing line".

[0056] This invention relates to a system for treating saline wastewater. The aforementioned pretreatment combination ensures the stable operation of the subsequent membrane treatment unit. Specifically, flocculation and sedimentation remove suspended solids and colloids, ozone oxidation breaks down recalcitrant organic matter into easily degradable small-molecule intermediates through ring-opening and chain breaking, and the MBR utilizes high-concentration activated sludge to mineralize and remove organic matter. This ensures that the pretreated effluent meets the influent requirements of the nanofiltration membrane (SDI≤3, turbidity≤0.1 NTU), guaranteeing the long-term stable operation of the subsequent membrane separation unit from the source.

[0057] This invention relates to a system for treating saline wastewater. Through the aforementioned hardness and silicate removal unit, the quality of the effluent is guaranteed. Specifically, after adding chemicals to the divalent salt tank to generate calcium carbonate, magnesium hydroxide, and silicate precipitates, the precipitates are removed by a filtration device. The output filtrate serves as the hardness and silicate removal effluent, ensuring that the feed solution entering the divalent salt crystallization unit is free of hardness ions and silica impurities, thereby guaranteeing the purity of sodium sulfate / magnesium salt crystals.

[0058] Those skilled in the art will understand that the agents added during the addition of chemicals in the hardening and desiliconization unit are commonly used agents in the art, such as magnesium agents (e.g., magnesium oxide (MgO) or magnesium chloride (MgCl2) and other magnesium-containing agents), aluminum agents (e.g., sodium aluminate (NaAlO2) or polyaluminum chloride (PAC) and other aluminum-containing coagulants), and soda ash (Na2CO3, i.e., sodium carbonate), etc.

[0059] In some specific implementations, the dosing process for the hardening and silicon removal unit is as follows: Adjust the pH to the alkaline range (e.g., 10-11). First, add a silicon removal agent (such as magnesium or aluminum agent), react and flocculate to remove silicon; Then, a hardening agent (such as soda ash) is added to generate calcium carbonate and magnesium hydroxide precipitates, which remove the calcium and magnesium hardness.

[0060] In some specific embodiments, the gradient-coupled membrane separation structure includes a first membrane treatment device 21 and a two-stage nanofiltration device 22 connected in sequence. The first membrane treatment is performed on the effluent from the pretreatment unit, and then the concentrated water from the first membrane treatment is subjected to salt separation treatment to obtain a monovalent salt enriched solution and a divalent salt enriched solution. The membrane pore sizes of the first membrane treatment device 21 and the two-stage nanofiltration device 22 are arranged in a decreasing order.

[0061] In some specific embodiments, the first membrane treatment device 21 includes an ultrafiltration device 211 and / or a reverse osmosis device 212; preferably, the first membrane treatment device 21 includes an ultrafiltration device 211 and a reverse osmosis device 212 connected in sequence.

[0062] In some specific embodiments, the dual-stage nanofiltration device 22 includes a primary nanofiltration device 221 and a secondary nanofiltration device 222, which are used to perform salt separation treatment on the concentrated water of the first membrane treatment device 21 to obtain a monovalent salt enriched solution and a divalent salt enriched solution.

[0063] In some specific embodiments, the membrane pore sizes of the ultrafiltration device 211, the reverse osmosis device 212, the first-stage nanofiltration device 221, and the first-stage nanofiltration device 222 are arranged in descending order.

[0064] This invention relates to a system for treating saline wastewater. On one hand, it achieves functional division through a gradient configuration of membrane pore sizes. Specifically, the membrane pore sizes decrease sequentially from large to small: ultrafiltration 211 (0.01~0.1 μm) → reverse osmosis 212 (<0.001 μm) → primary nanofiltration 221 → secondary nanofiltration 222. The functions of each membrane module are progressively enhanced: ultrafiltration intercepts suspended solids and colloids, reverse osmosis performs preliminary desalination and concentration, and primary / secondary nanofiltration selectively separates ions of different valence states. Each membrane layer performs its specific function and works synergistically, avoiding rapid fouling and performance degradation caused by a single membrane module bearing an excessive separation load. On the other hand, the purity of the separated salts is improved through two-stage nanofiltration. Specifically, the primary nanofiltration treats the first membrane; after preliminary salt separation of the concentrate, the secondary nanofiltration further retains residual divalent salts in the primary nanofiltration permeate, further improving the relative purity of NaCl in the monovalent salt enrichment solution, creating conditions for the subsequent production of high-purity NaCl crystals.

[0065] In some specific embodiments, the scale inhibitor dosing device is connected to the agent dosing port of each membrane separation device in the gradient coupling membrane separation structure.

[0066] The present invention provides a system for treating saline wastewater. Through the aforementioned setup of the scale inhibitor dosing device, scale inhibitor can be added separately according to the actual scaling risk of each membrane module, thereby achieving precise control of the scale inhibitor dosage and reducing reagent consumption while ensuring scale inhibition effect.

[0067] The present invention also provides a method for treating saline wastewater, the method employing the aforementioned system; the method includes: S1. Pretreatment: The saline wastewater is passed into the pretreatment unit for pretreatment to remove any one or more of suspended solids, colloids and organic pollutants to obtain pretreated wastewater. S2, Membrane separation: The pretreated permeate obtained in step S1 is passed into the membrane separation unit, and gradient separation is performed through the gradient coupling membrane separation structure in the presence of scale inhibitor to obtain monovalent salt enriched solution and divalent salt enriched solution; the scale inhibitor is a dendritic scale inhibitor, which is a polyamide-amine series dendritic macromolecule with alkyl diamine as the core, and its molecule does not contain organic phosphonates and inorganic phosphates. S3. Hardening and silicon removal: The divalent salt enrichment solution obtained in step S2 is passed into the hardening and silicon removal unit to remove calcium, magnesium ions and silicon impurities. The filtered filtrate is used as the hardening and silicon removal effluent. S4. Crystallization: The monovalent salt enrichment solution obtained in step S2 and the desiliconized water obtained in step S3 are respectively fed into the crystallization unit for crystallization to obtain monovalent salt crystals and divalent salt crystals.

[0068] This invention provides a method for treating saline wastewater. Through a sequence of steps—pretreatment, membrane separation, hardening and desilting, and crystallization—the treatment effect is ensured. Specifically, pretreatment first guarantees the quality of the influent to the membrane separation; membrane separation first separates monovalent and divalent salts, allowing them to enter different channels; hardening and desilting only treats the divalent salt-enriched solution, rather than treating all the concentrated water, reducing the amount of chemicals needed and the treatment load; crystallization is the final step to obtain a high-purity product. Each step is interconnected and indispensable; by using the aforementioned phosphorus-free dendritic scale inhibitor, the long-term stable operation of the membrane separation process is ensured, avoiding frequent shutdowns for cleaning due to scaling.

[0069] Those skilled in the art will understand that in conventional technologies, hardening and desilication units may be located at different points in the system, and the treatment target may be "all concentrate" or "all feed liquid entering the crystallization unit." In the technical solution of this invention, the hardening and desilication unit is located on the pipeline of the divalent salt enrichment solution, treating only the divalent salt enrichment solution (i.e., nanofiltration concentrate), while the monovalent salt enrichment solution (nanofiltration permeate) directly enters the monovalent salt crystallization device without passing through the hardening and desilication unit. Since the flow rate of the divalent salt enrichment solution is typically less than the total concentrate flow rate of the system, treating only a portion of it naturally requires less reagent dosage, thus reducing the amount of reagent needed. Furthermore, the hardening and desilication unit has a smaller processing capacity, smaller equipment size, and lower investment and operating costs, thus reducing overall treatment costs.

[0070] In this invention, the scale inhibitor is dendritic, possessing a large internal and external surface area and a large number of terminal functional groups, which can provide a higher scale inhibition load than conventional scale inhibitors, enabling it to control various metal ions, organic and inorganic molecules; the scale inhibitor molecules do not contain any organic phosphonates or inorganic phosphates, reducing the risk of microbial contamination on membrane modules and the impact of environmental pollution.

[0071] In some specific embodiments, the method further includes step S5, which uses an intelligent control unit to collect real-time data from the temperature sensors, TDS sensors, residual chlorine sensors and pH sensors at the inlet and outlet of each membrane separation device and adjusts the operating parameters accordingly. Preferably, the linkage adjustment module automatically performs one or more of the following operations based on the detection data: When the concentration of calcium hydroxide in the water reaches the set value, the scale inhibitor is automatically released, the water temperature is increased, and the water flow rate is increased to prevent scale from depositing on the membrane surface. Preferably, the set value of the calcium hydroxide concentration in the water is 0.165±0.1%; the water temperature is increased by 4~7 ℃, such as 4 ℃, 5 ℃, 6 ℃, and 7 ℃, and any value or range within this range; the flow rate is increased by 1.5~3%, such as 1.5%, 2%, 2.5%, and 3%, and any value or range within this range. When scaling risk is detected in the crystallization unit, the inlet water flow rate is reduced; preferably, the inlet water flow rate is reduced by 20% to 40%, such as 20%, 25%, 30%, 35% and 40%, and any value and range within this range.

[0072] This invention provides a method for treating saline wastewater, in which the intelligent control step S5 enables adaptive operation. Step S5 formalizes the intelligent control method, realizing a closed-loop control logic of "monitoring-early warning-response," which is beneficial for the automated control and continuous stable operation of the system. In some specific embodiments, the method further includes step S6, in which the crystallization mother liquor from the crystallization unit in step S4 is returned to the inlet pipeline of the membrane separation unit in step S2 via the return pipeline 5 for recycling.

[0073] This invention provides a method for treating saline wastewater. Through the mother liquor re-dissolution step S6, the mother liquor is returned to the membrane separation unit for reprocessing, allowing residual salts in the mother liquor to be recovered again, significantly improving the overall salt recovery rate. Furthermore, the mother liquor re-dissolution and recycling process reduces the amount of residual salts ultimately discharged, achieving a reduction of ≥90% in residual salts and lowering the disposal costs of residual salts as hazardous waste.

[0074] In some specific embodiments, the scale inhibitor in the method is a compound of diethylenetriaminepentaacetic acid-grafted polyamide-amine (DTPA-PAMAM) dendritic polymer and terpolymer, preferably in a weight percentage ratio of 50-85% (e.g., 50%, 55%, 60%, 65%, 70%, 75%, 80%, and 85%, and any value and range within this range) and 5-10% (e.g., 5%, 6%, 7%, 8%, 9%, and 10%, and any value and range within this range), with the balance being water; wherein the terpolymer is acrylic acid / acrylamidopropanesulfonic acid / hydroxypropyl acrylate copolymer (AA / AMPS / HPA).

[0075] In this invention, the dendritic polymer in the scale inhibitor possesses a large internal and external surface area and a large number of terminal functional groups, which can provide a higher scale inhibition load than conventional scale inhibitors, enabling it to control various metal ions, organic and inorganic molecules. The terpolymer in the scale inhibitor has a good dispersion effect on highly mineralized wastewater and can inhibit the influence of heavy metal ions on the dendritic polymer. The DTPA-PAMAM dendritic polymer inhibits scale crystal growth through steric hindrance, while the terpolymer (AA / AMPS / HPA) has a good dispersion effect on highly mineralized wastewater and can inhibit the influence of heavy metal ions on the dendritic polymer. The combination of the two produces a synergistic effect, and the scale inhibition performance is better than that of a single component. The two have a synergistic effect. Moreover, this scale inhibitor does not contain organophosphonates and inorganic phosphates, making it environmentally friendly. In some specific embodiments, the dosage of the scale inhibitor is 1~2 ppm, such as 1 ppm, 1.5 ppm and 2 ppm, as well as any value and range within this range.

[0076] In some specific embodiments, in step S2, the gradient-coupled membrane separation structure includes a first membrane treatment device 21 and a two-stage nanofiltration device 22 connected in sequence; the membrane pore sizes of the first membrane treatment device 21 and the two-stage nanofiltration device 22 are arranged in a decreasing order; the two-stage nanofiltration device 22 includes a first-stage nanofiltration device 221 and a first-stage nanofiltration device 222; the membrane pore sizes of the first-stage nanofiltration device 221 and the first-stage nanofiltration device 222 are arranged in a decreasing order. In step S2, membrane separation includes: The pretreated permeate is first subjected to first membrane treatment via the first membrane treatment device 21 to obtain first membrane treated permeate and first membrane treated concentrate. Then, the concentrated water from the first membrane treatment is sent to a two-stage nanofiltration device 22 for salt separation treatment. The monovalent salts pass through the nanofiltration membrane into the product water side, while the divalent salts are retained in the concentrated water side, resulting in monovalent salt enriched solution and divalent salt enriched solution, respectively.

[0077] This invention provides a method for treating saline wastewater. By connecting a first membrane treatment device 21 (such as ultrafiltration or reverse osmosis) in series with a dual-stage nanofiltration device 22, and setting their membrane pore sizes in a decreasing sequence, a synergistic gradient of physical interception and ion separation is formed. This structure is not a simple superposition of units, but rather constructs a complete separation chain from "coarse filtration" to "fine salt separation." Specifically, the first membrane treatment device 21 removes residual suspended solids, colloids, and macromolecular organic matter from the pretreated permeate, effectively reducing the risk of organic fouling and clogging of the subsequent nanofiltration membrane, thus providing pre-treatment protection. The first membrane treatment device 21 (especially reverse osmosis) performs preliminary concentration of the wastewater, reducing the amount of water entering the dual-stage nanofiltration device 22 and increasing the salt concentration, creating more favorable conditions for subsequent nanofiltration salt separation, thus forming a staged concentration. The dual-stage nanofiltration device 22 is placed after the "first membrane treatment" to specifically treat its concentrate, achieving the treatment of high-concentration divalent salts (SO42-). 2- Ca, Mg 2+ Selective retention of monovalent salts (such as Na+, etc.). Through the series connection of primary and secondary nanofiltration, monovalent salts (Na+, etc.) are selectively retained. + Cl - Nanofiltration permeate (NO) is allowed to pass through to the permeate side, while divalent salts are efficiently retained on the concentrate side. This configuration results in high purity of the monovalent salt enrichment (nanofiltration permeate), which is the fundamental guarantee for the subsequent production of high-purity (≥99.1%) sodium chloride crystals, thus achieving precise salt separation. The divalent salt enrichment (nanofiltration concentrate) then enters the hardening and silicate removal unit and the subsequent divalent salt crystallization device, providing pure raw materials for obtaining high-purity (≥99.4%) sodium sulfate or magnesium salt crystals. This fundamentally avoids mutual interference between salts of different valence states during crystallization, ensuring quality.

[0078] In some specific embodiments, the first membrane treatment device 21 includes an ultrafiltration device 211 and / or a reverse osmosis device 212. In step S2, the first membrane treatment is to perform ultrafiltration and / or reverse osmosis treatment on the pretreated permeate.

[0079] In some specific embodiments, the first membrane treatment device 21 includes an ultrafiltration device 211 and a reverse osmosis device 212 connected in sequence, with the membrane pore sizes of the ultrafiltration device 211 and the reverse osmosis device 212 decreasing sequentially; in step S2, the first membrane treatment is to sequentially perform ultrafiltration treatment and reverse osmosis treatment on the pretreated permeate.

[0080] In some specific embodiments, the operating temperature of the primary nanofiltration unit 221 is 20~50 °C, such as 20 °C, 30 °C, 40 °C, and 50 °C, and any value or range within this range; and / or the operating pressure is 15~20 bar, such as 15 bar, 16 bar, 17 bar, 18 bar, 19 bar, and 20 bar, and any value or range within this range; and / or the membrane flux is 15~20 LMH, such as 15 LMH, 16 LMH, 17 LMH, 18 LMH, 19 LMH, and 20 LMH, and any value or range within this range; and / or the recovery rate is 60~70%, such as 60%, 65%, and 70%, and any value or range within this range; and / or the sulfate rejection rate is 98~99.5%, such as 98%, 98.5%, 99%, and 99.5%. % and any value and range within that range; and / or a chloride ion rejection rate of 0 to 25%, such as 0%, 5%, 10%, 15%, 20% and 25% and any value and range within that range.

[0081] In some specific embodiments, the operating temperature of the primary nanofiltration unit 222 is 20~50 °C, such as 20 °C, 30 °C, 40 °C, and 50 °C, and any value or range within this range; and / or the operating pressure is 6~15 bar, such as 6 bar, 8 bar, 10 bar, 12 bar, 14 bar, and 15 bar, and any value or range within this range; and / or the membrane flux is 12~20 LMH, such as 12 LMH, 14 LMH, 16 LMH, 18 LMH, and 20 LMH, and any value or range within this range; and / or the recovery rate is 50~75%, such as 50%, 55%, 60%, 65%, and 70%, and any value or range within this range; and / or the sulfate rejection rate is 98~99.5%, such as 98%, 98.5%, 99%, and 99.5%. % and any value and range within that range; and / or a chloride ion rejection rate of 10-30%, such as 10%, 15%, 20%, 25% and 30% and any value and range within that range.

[0082] This invention, by limiting the parameters of the primary nanofiltration unit 221 and the secondary nanofiltration unit, can further achieve efficient and selective separation of monovalent / divalent salts, ensure the production of high-quality crystalline salts, extend membrane life and reduce operating costs, significantly reduce system energy consumption, and improve system operational stability.

[0083] The system and method for treating saline wastewater of the present invention have the following beneficial effects: (1) The system and method for treating saline wastewater of the present invention have high operational stability. Through the gradient coupling configuration of the membrane separation unit and the application of scale inhibitor, the continuous operation stability of the system can be improved to over 90%, which is significantly better than the level of about 65% of the traditional process. The amount of scale inhibitor used is small, which is safe for the membrane system.

[0084] (2) The system and method for treating saline wastewater of the present invention significantly reduce energy consumption. By optimizing the membrane pore size and functional cascade configuration through the gradient coupling configuration of the membrane separation unit, the energy consumption per unit of produced water can be reduced to below 2.8 kW·h / m³, which is far lower than the average level of 3.5~4.0 kW·h / m³ of similar international technologies.

[0085] (3) The system and method of the present invention for treating saline wastewater produce high-quality crystalline salt and significantly reduce impurities. Through the technical route of "membrane separation and salt separation + hardening and silicon removal + crystallization", it can produce super-grade industrial crystalline salt (NaCl purity ≥ 99.1%, Na2SO4 purity ≥ 99.4%), with an impurity reduction rate of ≥ 90%, solving the problems of low purity of crystalline salt and difficulty in handling impurities in traditional processes.

[0086] (4) The system and method of the present invention for treating saline wastewater exhibit excellent scale inhibition performance. By employing a dendritic scale inhibitor with a large internal and external surface area and a large number of terminal functional groups, a high scale inhibition load can be provided, controlling various metal ions, organic matter, and inorganic molecules. The scale inhibitor molecule does not contain any organic phosphonates or inorganic phosphates, which can reduce the risk of microbial contamination in membrane separation devices and the impact of sewage discharge on the environment. The terpolymer in the scale inhibitor has a good dispersion effect on highly mineralized wastewater and can inhibit the influence of heavy metal ions on the polyamide-amine dendritic polymer grafted with diethylenetriaminepentaacetic acid.

[0087] (5) The system and method of the present invention for treating saline wastewater can intelligently prevent scale formation and extend equipment life. The multi-sensor real-time monitoring and linkage intelligent control system, combined with dendritic scale inhibitor, can effectively inhibit scale formation on the membrane surface and crystallization equipment, extend the equipment cleaning cycle by 2 to 6 times, and reduce maintenance costs.

[0088] (6) The system and method for treating saline wastewater of the present invention have high integration and low investment cost. The pretreatment, membrane separation, hardening and silicon removal, crystallization and intelligent control units are organically integrated, resulting in high system integration, small footprint, low investment cost and low operating cost, and are suitable for the resource-based treatment of saline wastewater.

[0089] The present invention will be further illustrated by the following examples.

[0090] Example 1 (S1) A system A1 for treating saline wastewater, such as Figures 1-2 As shown, it includes: The pretreatment unit is used to pretreat saline wastewater, removing one or more of suspended solids, colloids, and organic pollutants to obtain pretreated permeable water; wherein, The pretreatment unit includes a flocculation sedimentation device, an ozone oxidation device, and a membrane bioreactor connected in sequence, which are used to sequentially treat saline wastewater by flocculation sedimentation, ozone oxidation, and membrane bioreactor. A membrane separation unit, connected to the pretreatment unit, includes a gradient-coupled membrane separation structure and a scale inhibitor dosing device. It is used to add scale inhibitor and perform gradient separation on the effluent from the pretreatment unit to obtain a monovalent salt enriched solution and a divalent salt enriched solution. The scale inhibitor dosing device is connected to the reagent dosing port of the gradient-coupled membrane separation structure and is used to add scale inhibitor to the gradient-coupled membrane separation structure. The scale inhibitor is a dendritic scale inhibitor, which is a polyamide-amine series dendritic macromolecule with an alkyl diamine core, and its molecules do not contain organic phosphonates and inorganic phosphates. The gradient-coupled membrane separation structure includes a first membrane treatment device 21 and a dual-stage nanofiltration device 22 connected in sequence; the first membrane treatment device 21 includes an ultrafiltration device 211 and a reverse osmosis device 212 connected in sequence; the dual-stage nanofiltration device 22 includes a first-stage nanofiltration device 221 and a first-stage nanofiltration device 222 connected in sequence; the membrane pore sizes of the ultrafiltration device 211, reverse osmosis device 212, first-stage nanofiltration device 221, and first-stage nanofiltration device 222 decrease sequentially; the scale inhibitor dosing device is connected to the reagent dosing port of each membrane separation device in the gradient-coupled membrane separation structure. The hardening and desiliconization unit is connected to the concentrate outlet of the membrane separation unit and is used to perform hardening and desiliconization treatment on the divalent salt enrichment solution to remove calcium, magnesium ions, and silicon impurities, yielding calcium carbonate, magnesium hydroxide, and silicate precipitates; wherein, The hardening and desiliconizing unit includes a divalent brine tank and a filtration device connected in sequence. The divalent brine tank is connected to the divalent salt enrichment outlet of the membrane separation unit and is connected to a dosing pipeline for introducing the divalent salt enrichment and adding chemicals to generate calcium carbonate, magnesium hydroxide, and silicate precipitates. The filtration device is used to filter the material in the divalent brine tank to remove calcium carbonate, magnesium hydroxide, and silicate precipitates, and outputs the filtrate as effluent. The crystallization unit includes a monovalent salt crystallization device and a divalent salt crystallization device connected in parallel. The monovalent salt crystallization device is connected to the permeate outlet of the membrane separation unit and is used to crystallize the permeate from the membrane separation unit to obtain monovalent salt crystals. The divalent salt crystallization device is connected to the outlet of the hardening and desiliconizing unit and is used to crystallize the effluent after hardening and desiliconizing to obtain divalent salt crystals. The monovalent salt crystallization device is a sodium chloride crystallization device, used to generate sodium chloride crystals; The divalent salt crystallization apparatus includes a sodium sulfate crystallization apparatus and a magnesium salt crystallization apparatus connected in parallel, used to generate sodium sulfate crystals and magnesium salt crystals.

[0091] Example 2 (S2) A system A2 for treating saline wastewater differs from system A1 in Example 1 as follows: The first membrane treatment device 21 includes only an ultrafiltration device 211; the membrane pore sizes of the ultrafiltration device 211, the first-stage nanofiltration device 221, and the first-stage nanofiltration device 222 are arranged in descending order.

[0092] Example 3 (S3) A system A3 for treating saline wastewater differs from system A1 in Example 1 as follows: The first membrane treatment device 21 includes only a reverse osmosis device 212; the membrane pore sizes of the reverse osmosis device 212, the first-stage nanofiltration device 221, and the first-stage nanofiltration device 222 are arranged in descending order.

[0093] Example 4 (S4) A system A4 for treating saline wastewater differs from system A1 in Example 1 as follows: The system also includes a refluxing line 5, the inlet of which is connected to the mother liquor outlet of the crystallization unit and the outlet of which is connected to the inlet of the membrane separation unit, for refluxing the mother liquor of the crystallization unit.

[0094] Example 5 (S5) A system A5 for treating saline wastewater differs from system A1 in Example 1 as follows: It also includes an intelligent control unit; the intelligent control unit is connected to the pretreatment unit, the membrane separation unit, the hardening and desiliconizing unit and the crystallization unit respectively, and includes temperature sensors, TDS sensors, residual chlorine sensors and pH sensors at the inlet and outlet of each membrane separation device in the gradient coupling membrane separation structure in the membrane separation unit, for collecting real-time data and linking and regulating operating parameters.

[0095] Example 6 (S6) A system A6 for treating saline wastewater differs from system A5 in Example 5 as follows: The intelligent control unit also includes a scaling risk early warning module and a linkage adjustment module; wherein... The scaling risk warning module is connected to the membrane separation unit and the crystallization unit respectively, and is used to detect the calcium hydroxide concentration in the effluent of the membrane separation unit and the calcium hydroxide concentration in the mother liquor of the crystallization unit respectively. The signal receiving end of the linkage adjustment module is connected to the scaling risk warning module, and the signal output end of the linkage adjustment module is connected to the scale inhibitor dosing device and the inlet valve of the saline wastewater. The linkage adjustment module automatically performs the following operations based on the detection data: When the concentration of calcium hydroxide in the water reaches the set value of 0.165±0.1%, the scale inhibitor is automatically released, the water temperature is increased by 5°C, and the water flow rate is increased by 2%. When scaling risk is detected in the crystallization unit, reduce the influent flow rate (by 30%).

[0096] Example 7 (S7) A system A7 for treating saline wastewater differs from system A6 in Example 6 as follows: When the concentration of calcium hydroxide in the water reaches the set value of 0.165±0.1%, the scale inhibitor is automatically released, the water temperature is raised by 4°C, and the water flow rate is increased (by 3%). When scaling risk is detected in the crystallization unit, reduce the influent flow rate (by 20%).

[0097] Example 8 (S8) A system A8 for treating saline wastewater differs from system A6 in Example 6 as follows: When the concentration of calcium hydroxide in the water reaches the set value of 0.165±0.1%, the scale inhibitor is automatically released, the water temperature is raised by 7°C, and the water flow rate is increased (by 1.5%). When scaling risk is detected in the crystallization unit, reduce the influent flow rate (by 40%).

[0098] Application Example 1 The saline wastewater 1 (mine water from the Shendong Coal Supply Tower Area Mine Water Project) was treated, and the TDS in saline wastewater 1 was approximately 3010 mg / L.

[0099] Application Examples 11-13 (Y11-13) For saline wastewater 1 (mine water from the Shendong Coal Mine Water Project in the Bulian Tower Area), the following methods were used to treat it using systems A1-3 described in Examples 1-3: S1. Pretreatment: The saline wastewater is passed into the pretreatment unit for pretreatment to remove any one or more of suspended solids, colloids and organic pollutants to obtain pretreated wastewater. S2. Membrane Separation: The pretreated permeate obtained in step S1 is passed into a membrane separation unit. In the presence of a scale inhibitor, gradient separation is performed through a gradient-coupled membrane separation structure to obtain a monovalent salt enriched solution and a divalent salt enriched solution. The scale inhibitor is a compound of a polyamide-amine dendritic polymer grafted with diethylenetriaminepentaacetic acid and a terpolymer. The compounding ratio of the two is 65% and 8% by weight (or 50% and 10%, or 85% and 5%), with the balance being water. The terpolymer is an acrylic acid / acrylamidopropanesulfonic acid / hydroxypropyl acrylate copolymer. S3. Hardening and silicon removal: The divalent salt enrichment solution obtained in step S2 is passed into the hardening and silicon removal unit to remove calcium, magnesium ions and silicon impurities. The filtered filtrate is used as the hardening and silicon removal effluent. S4. Crystallization: The monovalent salt enrichment solution obtained in step S2 and the desiliconized water obtained in step S3 are respectively fed into the crystallization unit for crystallization to obtain monovalent salt crystals and divalent salt crystals.

[0100] Application Examples 14-17 (Y14-17) For saline wastewater 1 (mine water from the Shendong Coal Mine Water Project in the Bulian Tower Area), the systems A5-8 described in Examples 4-7 for treating saline wastewater were used for treatment. The only difference between these systems and those used in Examples 11-13 (Y11-13) is that: The method also includes step S5, which uses an intelligent control unit to collect real-time data from the temperature sensors, TDS sensors, residual chlorine sensors and pH sensors at the inlet and outlet of each membrane separation device and adjusts the operating parameters accordingly.

[0101] Application Example 18 (Y18) For saline wastewater 1 (mine water from the Shendong Coal Mine Water Project in the Bulian Tower Area), the systems A1-3 described in Examples 1-3 for treating saline wastewater were used for treatment. The only difference between these systems and those used in Examples 11-13 (Y11-13) is that: The method further includes step S6, in which the mother liquor from the crystallization unit in step S4 is returned to the inlet water pipeline of the membrane separation unit in step S2 via the return pipeline 5 for recycling.

[0102] Application Result 1 For saline wastewater 1 (mine water in the Shendong Coal Supplement Tower Area Mine Water Project), after treatment using Examples 11-18 (Y11-18), the TDS in the effluent is ≤100 mg / L.

[0103] For saline wastewater 1 (mine water from the Shendong Coal Mine Water Project in the Bulian Tower Area), the treatment volume in 2024 is approximately 10 million tons, with an annual output value of approximately 150 million yuan at a price of 15 yuan / ton; the discharge of miscellaneous salts will be reduced by approximately 13,000 tons / year, with a treatment unit price of 3,000 yuan / ton, resulting in a reduction of treatment costs of approximately 39 million yuan; the production of sodium chloride crystallized salts will be approximately 3,000 tons / year, and the production of sodium sulfate crystallized salts will be approximately 10,000 tons / year, generating an annual economic benefit of approximately 1.3 million yuan; the total benefit of zero-discharge treatment of wastewater for the entire plant is approximately 200 million yuan / year, and with an operation and maintenance period of 15 years, the total benefit is approximately 3 billion yuan.

[0104] Meanwhile, in terms of cost, it can reduce labor costs by about 1.5 million yuan per year; by monitoring and optimizing the energy consumption of the sewage treatment plant, it can reduce the annual operating electricity cost by nearly 800,000 yuan per year; and in terms of chemical consumption, it can reduce chemical consumption by about 977,600 yuan per year, for a total reduction in operating costs of about 3.28 million yuan per year.

[0105] Application Example 2 The saline wastewater 2 (seawater from the seawater desalination project of Penglai Power Generation Co., Ltd.) was treated, and the TDS in saline wastewater 2 was approximately 32,000 mg / L.

[0106] Application Examples 21-28 (Y21-28) For saline wastewater 2 (seawater from the seawater desalination project of Penglai Power Generation Co., Ltd.), it was treated according to application examples 11-18 (Y11-18).

[0107] Application Result 2 For saline wastewater 2 (seawater from the seawater desalination project of Penglai Power Generation Co., Ltd.), after treatment using Examples 21-28 (Y21-28), the TDS in the effluent is ≤400 mg / L.

[0108] For saline wastewater 2 (seawater from the seawater desalination project of Penglai Power Generation Co., Ltd.), the actual annual reduction of municipal tap water is 3 million cubic meters, saving water costs of about 5.76 million yuan per year, and annual electricity savings of 11.08 million kWh, saving electricity costs of about 4.43 million yuan per year.

[0109] In this seawater desalination project, the chemical cost per ton of water is 0.29 yuan, and the total cost of producing water per ton of water is 3.09 yuan. Compared to the traditional thermal method, applications of Examples 21-28 (Y21-28) can reduce the chemical cost per ton of water by 39% and the cost of producing water per ton of water by 84%. Compared to ordinary all-membrane seawater desalination technology, applications of Examples 21-28 (Y21-28) can achieve a 73% reduction in chemical cost per ton of water and a 63% reduction in cost of producing water per ton of water.

[0110] Application Example 3 The saline wastewater 3 (mine water from the National Energy Group mine water project) was treated, and the TDS in saline wastewater 3 was approximately 20,000 mg / L.

[0111] Application Examples 31-38 (Y31-38) For saline wastewater 3 (mine water from the National Energy Group mine water project), it was treated according to application examples 11-18 (Y11-18).

[0112] Application Result 3 For saline wastewater 3 (mine water from the National Energy Group mine water project), after treatment using Examples 31-38 (Y31-38), the TDS in the effluent is ≤300 mg / L.

[0113] For saline wastewater 3 (mine water in the National Energy Group mine water project), the treatment volume in 2023 is about 200 million tons. By adopting the application example 3, the operating cost can be reduced by more than 291 million yuan per year, and the economic benefits are extremely significant.

[0114] Based on the application results of various embodiments and application examples, it is evident that the technical solution of this invention has a promising market application prospect in the fields of mine water and seawater desalination. In mine water treatment, it offers significant cost reduction and returns, and can be widely applied in coal, coal-fired power, chemical, and metallurgical industries, particularly in coal-fired power plants, coal-fired power-chemical energy bases, and industrial parks. Regarding seawater desalination, the group's annual desalination capacity exceeds 30 million tons, while the demand for seawater desalination outside the group is substantial, with a market size of approximately US$18 billion.

[0115] The above embodiments / examples are only used to illustrate the content of the present invention and are not limited thereto. Any simple changes made to the present invention based on the concept of the present invention are within the scope of protection claimed by the present invention.

Claims

1. A system for treating saline wastewater, characterized in that, The system includes: The pretreatment unit is used to pretreat saline wastewater to remove any one or more of suspended solids, colloids, and organic pollutants to obtain pretreated permeate. A membrane separation unit, connected to the pretreatment unit, includes a gradient-coupled membrane separation structure and a scale inhibitor dosing device. This unit is used to add scale inhibitor and perform gradient separation on the effluent from the pretreatment unit, yielding a monovalent salt enriched solution and a divalent salt enriched solution. The scale inhibitor dosing device is connected to the reagent dosing port of the gradient-coupled membrane separation structure and is used to add scale inhibitor to the structure. The scale inhibitor is a dendritic scale inhibitor, a polyamide-amine series dendritic macromolecule with an alkyl diamine core, and its molecules do not contain organic phosphonates or inorganic phosphates. The hardening and desiliconization unit is connected to the concentrate outlet of the membrane separation unit and is used to perform hardening and desiliconization treatment on the divalent salt enrichment solution to remove calcium, magnesium ions and silicon impurities, and obtain calcium carbonate, magnesium hydroxide and silicate precipitates. The crystallization unit includes a monovalent salt crystallization device and a divalent salt crystallization device connected in parallel. The monovalent salt crystallization device is connected to the permeate outlet of the membrane separation unit and is used to crystallize the permeate of the membrane separation unit to obtain monovalent salt crystals. The divalent salt crystallization device is connected to the outlet of the hardening and desiliconizing unit and is used to crystallize the effluent after hardening and desiliconizing to obtain divalent salt crystals.

2. The system according to claim 1, characterized in that, It also includes an intelligent control unit; the intelligent control unit is connected to the pretreatment unit, the membrane separation unit, the hardening and desiliconizing unit and the crystallization unit respectively, and includes temperature sensors, TDS sensors, residual chlorine sensors and pH sensors at the inlet and outlet of each membrane separation device in the gradient coupling membrane separation structure in the membrane separation unit, for collecting real-time data and linking and regulating operating parameters; Preferably, the intelligent control unit further includes a scaling risk early warning module and a linkage adjustment module; wherein, The scaling risk warning module is connected to the membrane separation unit and the crystallization unit respectively, and is used to detect the calcium hydroxide concentration in the effluent of the membrane separation unit and the calcium hydroxide concentration in the mother liquor of the crystallization unit respectively. The signal receiving end of the linkage adjustment module is connected to the scaling risk warning module, and the signal output end of the linkage adjustment module is connected to the scale inhibitor dosing device and the inlet valve of the saline wastewater. Preferably, the linkage adjustment module automatically performs one or more of the following operations based on the detection data: When the concentration of calcium hydroxide in the water reaches the set value, the scale inhibitor is automatically released, the water temperature is increased, and the water flow rate is increased to prevent scale from depositing on the membrane surface. Preferably, the set values ​​are: calcium hydroxide concentration in the water 0.165±0.1%, water temperature increase of 4~7 ℃, and flow rate increase of 1.5~3%. When scaling is detected in the crystallization unit, reduce the inlet water flow rate; preferably, reduce the inlet water flow rate by 20-40%.

3. The system according to claim 1 or 2, characterized in that, It also includes a refluxing pipeline, the inlet end of which is connected to the mother liquor outlet of the crystallization unit and the outlet end of which is connected to the inlet pipeline of the membrane separation unit, for refluxing the mother liquor of the crystallization unit.

4. The system according to any one of claims 1-3, characterized in that, The pretreatment unit includes one or more of a flocculation sedimentation device, an ozone oxidation device, and a membrane bioreactor, used for treating saline wastewater using one or more of the following methods: flocculation sedimentation treatment, ozone oxidation treatment, and membrane bioreactor treatment; and / or, The monovalent salt crystallization apparatus is a sodium chloride crystallization apparatus; and / or, The divalent salt crystallization device is a sodium sulfate crystallization device and / or a magnesium salt crystallization device; And / or, The hardening and desiliconizing unit includes a divalent brine tank and a filtration device connected in sequence. The divalent brine tank is connected to the divalent salt enrichment outlet of the membrane separation unit and is connected to a dosing pipeline for introducing the divalent salt enrichment and adding chemicals to generate calcium carbonate, magnesium hydroxide, and silicate precipitates. The filtration device is used to filter the material in the divalent brine tank to remove calcium carbonate, magnesium hydroxide, and silicate precipitates, and outputs the filtrate as effluent.

5. The system according to any one of claims 1-4, characterized in that, The gradient-coupled membrane separation structure includes a first membrane treatment device and a dual-stage nanofiltration device connected in sequence. It is used to first treat the effluent from the pretreatment unit with a first membrane, and then to perform salt separation treatment on the concentrate from the first membrane treatment to obtain a monovalent salt enriched solution and a divalent salt enriched solution. The membrane pore sizes of the first membrane treatment device and the dual-stage nanofiltration device are arranged in a decreasing order. Preferably, the first membrane treatment device includes an ultrafiltration device and / or a reverse osmosis device; more preferably, the first membrane treatment device includes an ultrafiltration device and a reverse osmosis device connected in sequence; and / or, The dual-stage nanofiltration device includes a primary nanofiltration device and a secondary nanofiltration device connected in sequence, used to perform salt separation treatment on the concentrate from the first membrane treatment device to obtain a monovalent salt enriched solution and a divalent salt enriched solution. Preferably, the membrane pore sizes of the ultrafiltration unit, reverse osmosis unit, first-stage nanofiltration unit, and second-stage nanofiltration unit are arranged in descending order; Preferably, the scale inhibitor dosing device is connected to the reagent dosing port of each membrane separation device in the gradient coupling membrane separation structure.

6. A method for treating saline wastewater, characterized in that, The method is performed using the system described in any one of claims 1-5; the method includes: S1. Pretreatment: The saline wastewater is passed into the pretreatment unit for pretreatment to remove one or more of suspended solids, colloids and organic pollutants to obtain pretreated wastewater. S2, Membrane separation: The pretreated permeate obtained in step S1 is passed into the membrane separation unit, and gradient separation is performed through the gradient coupling membrane separation structure in the presence of scale inhibitor to obtain monovalent salt enriched solution and divalent salt enriched solution; the scale inhibitor is a dendritic scale inhibitor, which is a polyamide-amine series dendritic macromolecule with alkyl diamine as the core, and its molecule does not contain organic phosphonates and inorganic phosphates. S3. Hardening and silicon removal: The divalent salt enrichment solution obtained in step S2 is passed into the hardening and silicon removal unit to remove calcium, magnesium ions and silicon impurities. The filtered filtrate is used as the hardening and silicon removal effluent. S4. Crystallization: The monovalent salt enrichment solution obtained in step S2 and the desiliconized water obtained in step S3 are respectively fed into the crystallization unit for crystallization to obtain monovalent salt crystals and divalent salt crystals.

7. The method according to claim 6, characterized in that, The method further includes step S5, which involves using an intelligent control unit to collect real-time data from the temperature sensors, TDS sensors, residual chlorine sensors, and pH sensors at the inlet and outlet of each membrane separation device and adjusting the operating parameters accordingly; preferably, the linkage adjustment module automatically performs one or more of the following operations based on the detection data: When the concentration of calcium hydroxide in the water reaches the set value, the scale inhibitor is automatically released, the water temperature is increased, and the water flow rate is increased to prevent scale from depositing on the membrane surface. When scaling risk is detected in the crystallization unit, reduce the influent flow rate; And / or, The method further includes step S6, in which the crystallization mother liquor from the crystallization unit in step S4 is returned to the inlet water pipeline of the membrane separation unit in step S2 via the refluxing pipeline for recycling.

8. The method according to claim 6 or 7, characterized in that, The scale inhibitor is a compound of a polyamide-amine dendritic polymer grafted with diethylenetriaminepentaacetic acid and a terpolymer, preferably in a weight ratio of 50-85% and 5-10% respectively, with the remainder being water; wherein the terpolymer is an acrylic acid / acrylamidopropanesulfonic acid / hydroxypropyl acrylate copolymer.

9. The method according to any one of claims 6-8, characterized in that, In step S2, the gradient-coupled membrane separation structure includes a first membrane treatment device and a two-stage nanofiltration device connected in sequence; the membrane pore sizes of the first membrane treatment device and the two-stage nanofiltration device are arranged in a decreasing order; the two-stage nanofiltration device includes a first-stage nanofiltration device and a second-stage nanofiltration device. The membrane pore sizes of the primary nanofiltration unit and the secondary nanofiltration unit are set in a decreasing order. In step S2, membrane separation includes: The pretreated permeate is first treated by a first membrane treatment device to obtain first membrane treated permeate and first membrane treated concentrate. The concentrate from the first membrane treatment is fed into a two-stage nanofiltration device for salt separation. Monovalent salts pass through the nanofiltration membrane into the permeate side, while divalent salts are retained in the concentrate side, resulting in monovalent salt enriched solution and divalent salt enriched solution, respectively.

10. The method according to claim 9, characterized in that, In a two-stage nanofiltration unit, The operating temperature of the primary nanofiltration unit is 20~50 ℃, and / or the operating pressure is 15~20 bar, and / or the membrane flux is 15~20 LMH, and / or the recovery rate is 60~70%, and / or the retention rate of sulfate is 98~99.5%, and / or the retention rate of chloride is 0~25%. The operating temperature of the secondary nanofiltration device is 20~50 ℃, and / or the operating pressure is 6~15 bar, and / or the membrane flux is 12~20 LMH, and / or the recovery rate is 50~75%, and / or the retention rate of sulfate is 98~99.5%, and / or the retention rate of chloride is 10~30%.

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