A zero-emission system and method for high-hardness salt-containing wastewater

Abstract

The application relates to a zero-emission system and method for high-hardness salt-containing wastewater, the zero-emission system comprising a membrane concentration system, a regenerated waste liquid treatment system and an evaporation crystallization system, the membrane concentration system comprising an ion exchange hardening removal unit, a first-stage membrane concentration module and a second-stage membrane concentration module; a membrane concentration concentrated water outlet of the membrane concentration system is connected with a regenerated liquid inlet of the ion exchange hardening removal unit, a regenerated waste liquid outlet of the ion exchange hardening removal unit is connected with a liquid inlet of the regenerated waste liquid treatment system, and a liquid outlet of the regenerated waste liquid treatment system is connected with a liquid inlet of the evaporation crystallization system; the evaporation crystallization system comprises two or more than two units in a sodium chloride evaporation crystallization unit, a sodium sulfate evaporation crystallization unit and a mixed salt drying unit. The application regenerates saturated resin of the membrane concentration system concentrated water by taking sodium sulfate as a main component, simplifies a process flow of the zero-emission system, reduces a reagent adding amount, and solves the problem of calcium sulfate scale deposition and blockage caused by regenerated sodium sulfate resin.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of salt-containing wastewater treatment, and particularly relates to a zero-emission system and method for high-hardness salt-containing wastewater. BACKGROUND

[0002] High-hardness salt-containing wastewater is usually derived from industrial production processes such as power generation, metallurgy, coal mining, chemical industry, desalination, printing and dyeing, and papermaking. Such wastewater contains high hardness and salt content. The high hardness mainly refers to the high total concentration of calcium and magnesium ions in the wastewater. If the salt-containing wastewater is directly discharged without treatment, it will cause salinization of water bodies and soil, endangering the natural environment. Salt-containing wastewater usually requires reuse after treatment and cannot be discharged, or the discharge water is required to meet the salt content limit value. Therefore, the salt-containing wastewater needs to be treated for zero or near-zero emission, so that the salts in the water are concentrated and crystallized to form crystalline salt for resource utilization, and other pollutants in the water are discharged in the form of filter cake to be landfilled or incinerated in a waste treatment plant. High hardness will cause serious scaling and even blockage of the concentration and crystallization equipment and pipelines, reduce the water production rate of the equipment, and seriously affect the system operation.

[0003] The conventional hardness removal treatment process for high-hardness salt-containing wastewater is to add a large amount of hardness removal agent in the pretreatment section to remove the hardness of the high-hardness salt-containing wastewater by chemical precipitation, and then use ion exchange resin to further remove the hardness in the reverse osmosis concentrated water to meet the requirements of the membrane concentration system and the evaporation crystallization system for the hardness of the inlet water.

[0004] Although the conventional treatment process is relatively mature, it still has many problems. For example, a large amount of hardness removal agent needs to be added during the hardness removal process by chemical precipitation. In order to ensure the hardness removal effect, an excessive amount of agent is usually added, which results in high cost of the hardness removal agent and a large amount of chemical sludge. In addition, excessive addition of the agent will increase the salt content of the wastewater, increase the operating load of the membrane concentration and evaporation crystallization, and increase the investment and operating costs.

[0005] The ion exchange resin hardness removal process, which is relatively mature at present, can only treat low-hardness wastewater. Therefore, it can only be used as a subsequent process combined with the chemical precipitation method for hardness removal. When ion exchange is used to treat high-hardness wastewater, frequent regeneration is required, which requires a large amount of acid, alkali, or salt as a regeneration agent. Therefore, ion exchange is basically not used to treat high-hardness salt-containing wastewater. In addition, the regeneration agent needs to be returned to the system after use, which also increases the operating load of the membrane concentration and evaporation crystallization.

[0006] When salt regeneration is used for resin regeneration, sodium chloride is generally used instead of sodium sulfate. The reason is that when the product of the concentrations of calcium ions and sulfate ions in the solution is greater than the solubility product of calcium sulfate, crystals will be generated and precipitated in the resin column. The calcium sulfate scale layer is dense and has high hardness, and is difficult to dissolve. SUMMARY

[0007] In view of the defects in the prior art, the purpose of the present application is to provide a zero-emission system and method for high-hardness salt-containing wastewater, wherein the ion exchange hardness removal unit uses concentrated water of a membrane concentration system mainly composed of sodium sulfate as a saturated resin regeneration liquid, and the hardness in the high-hardness salt-containing wastewater is completely removed through the combination of different ion exchange bed types, and the regeneration waste liquid forms calcium sulfate precipitation, which simplifies the process flow of the zero-emission system, greatly reduces the amount of chemicals added, and significantly reduces the overall salt content compared with the conventional zero-emission chemical hardness removal system; and the problem of deposition and blockage of calcium sulfate scale formed by the regeneration of sodium sulfate resin is solved.

[0008] To achieve the above purpose, the technical scheme adopted by the present application is: a zero-emission system for high-hardness salt-containing wastewater, the zero-emission system comprising a membrane concentration system, a regeneration waste liquid treatment system, and an evaporation crystallization system, wherein:

[0009] The membrane concentration system comprises an ion exchange hardness removal unit, a first membrane concentration module, and a second membrane concentration module.

[0010] The membrane concentration concentrated water outlet of the membrane concentration system is connected to the regeneration liquid inlet of the ion exchange hardness removal unit, the regeneration waste liquid outlet of the ion exchange hardness removal unit is connected to the liquid inlet of the regeneration waste liquid treatment system, and the liquid outlet of the regeneration waste liquid treatment system is connected to the liquid inlet of the evaporation crystallization system.

[0011] The evaporation crystallization system comprises two or more of a sodium chloride evaporation crystallization unit, a sodium sulfate evaporation crystallization unit, and a mixed salt drying unit.

[0012] Further, when the hardness of the wastewater is higher than the upper limit of the water inlet of the first membrane concentration module, the ion exchange hardness removal unit, the first membrane concentration module, and the second membrane concentration module are sequentially connected in the membrane concentration system.

[0013] When the hardness of the wastewater is lower than the upper limit of the water inlet of the first membrane concentration module, the wastewater directly enters the first membrane concentration module for concentration treatment, and the first membrane concentration module, the ion exchange hardness removal unit, and the second membrane concentration module are sequentially connected in the membrane concentration system.

[0014] Further, the ion exchange hardness removal unit comprises an exchange unit, a regeneration unit, and a water washing unit, and the exchange unit, the regeneration unit, and the water washing unit achieve hardness removal and resin regeneration by using the combination of different ion exchange bed types.

[0015] Further, the different ion exchange bed types comprise fixed bed, intermittent or continuous moving bed, and fluidized bed; according to the calcium and magnesium ion concentration in the wastewater entering the water inlet of the ion exchange hardness removal unit, the ion exchange bed type, the number of stages, and the connection mode of the exchange unit, the regeneration unit, and the water washing unit are selected.

[0016] Further, in the regeneration unit, saturated resin is regenerated by using sodium sulfate solution or concentrated water from the membrane concentration system as the regeneration liquid;

[0017] The sodium ion concentration in the regeneration liquid is greater than 15000 mg / L;

[0018] The dosage of the regeneration liquid is 5% to 20% of the influent of the ion exchange unit.

[0019] Further, the zero discharge system further comprises a pretreatment system arranged before the membrane concentration system, and the pretreatment system comprises one or a combination of one or more of an adjusting unit, a first sedimentation unit, a first filtration unit, a first organic matter removal unit, and a first resin fluoride removal unit.

[0020] Further, in the membrane concentration system, one or a combination of one or more of a second sedimentation unit, a second filtration unit, a second organic matter removal unit, and a second resin fluoride removal unit is arranged between the ion exchange hardening removal unit and the first membrane concentration module and / or between the first membrane concentration module and the second membrane concentration module.

[0021] Further, the zero discharge system further comprises a dosing unit, and the dosing unit comprises one or a combination of one or more of a coagulant dosing device, a flocculant dosing device, a desiliconizing agent dosing device, a defluorination agent dosing device, and a chemical oxidant dosing device;

[0022] The coagulant dosing device, the flocculant dosing device, the desiliconizing agent dosing device, and the defluorination agent dosing device are respectively connected to the first sedimentation unit; and the chemical oxidant dosing device is connected to the first organic matter removal unit.

[0023] The coagulant dosing device, the flocculant dosing device, the desiliconizing agent dosing device, and the defluorination agent dosing device are respectively connected to the second sedimentation unit; and the chemical oxidant dosing device is connected to the second organic matter removal unit.

[0024] Further, the regeneration waste liquid treatment system comprises a third sedimentation unit, a third filtration unit, and a cation bed softening unit connected in sequence.

[0025] The influent port of the third sedimentation unit is connected to the regeneration waste liquid outlet of the ion exchange hardening removal unit.

[0026] If the TDS of the effluent port of the cation bed softening unit is higher than the lower limit of the design influent TDS range of the evaporation crystallization system, the effluent port of the cation bed softening unit is directly connected to the influent port of the evaporation crystallization system.

[0027] If the TDS of the liquid outlet of the cation bed softening unit is lower than the lower limit of the design water inlet TDS range of the evaporative crystallization system, a membrane concentration module is arranged between the liquid outlet of the cation bed softening unit and the liquid inlet of the evaporative crystallization system; or the liquid outlet of the cation bed softening unit is connected with the liquid inlet of the secondary membrane concentration module of the membrane concentration system.

[0028] Further, the primary membrane concentration module comprises a primary ultrafiltration unit and a primary reverse osmosis unit connected in sequence; and the secondary membrane concentration module comprises a secondary ultrafiltration unit and a secondary reverse osmosis unit connected in sequence.

[0029] Further, the secondary reverse osmosis unit comprises a nanofiltration unit and a product water reverse osmosis unit; wherein the water inlet of the nanofiltration unit is connected with the water outlet of the secondary ultrafiltration unit, the product water outlet of the nanofiltration unit is connected with the liquid inlet of the product water reverse osmosis unit, and the concentrated water outlet of the nanofiltration unit is connected with the regeneration liquid inlet of the ion exchange hardness removal unit.

[0030] The concentrated water outlet of the product water reverse osmosis unit is connected with the sodium chloride evaporative crystallization unit.

[0031] Further, the membrane concentration system comprises a multi-stage membrane concentration module, and the multi-stage membrane concentration module comprises the primary membrane concentration module, the secondary membrane concentration module, …, and an n-stage membrane concentration module, wherein n is greater than or equal to 3.

[0032] The multi-stage membrane concentration module is formed by connecting the primary membrane concentration module, the secondary membrane concentration module, …, and the n-stage membrane concentration module in series, and the n-stage membrane concentration module comprises an n-stage ultrafiltration unit and an n-stage reverse osmosis unit connected in sequence.

[0033] The application also provides a zero-emission method for high-hardness salt-containing wastewater, which is realized based on the zero-emission system for high-hardness salt-containing wastewater and comprises the following steps:

[0034] S1, pretreating wastewater: adjusting the water volume and balancing the water quality through an adjusting unit, removing suspended solids, silicon compounds, fluorine compounds and the like in the wastewater through a first sedimentation unit, a first filtration unit and a dosing unit, and obtaining pretreated wastewater;

[0035] S2, membrane concentration treatment of wastewater: when the hardness of the wastewater is higher than the upper limit of the water inlet of the primary membrane concentration module, the pretreated wastewater is first treated by an ion exchange hardness removal unit to remove hardness, and then treated by a primary membrane concentration module and a secondary membrane concentration module for concentration treatment, and the obtained membrane concentration concentrated water is used as a regeneration liquid to regenerate saturated resin in the ion exchange hardness removal unit.

[0036] When the hardness of the wastewater is lower than the upper limit of the inlet water of the first-stage membrane concentration module, the pretreated wastewater directly enters the first-stage membrane concentration module for concentration treatment. The obtained first-stage membrane concentrate is then passed through the ion exchange hardening unit to remove hardness, and then through the second-stage membrane concentration module for further concentration treatment. The obtained membrane concentrate is used as a regenerator to regenerate the saturated resin in the ion exchange hardening unit.

[0037] S3. Wastewater Treatment of Regenerated Wastewater: The regenerated wastewater discharged from the ion exchange hardening unit enters the regenerated wastewater treatment system for treatment. After passing through the third precipitation unit, the third filtration unit, and the cation bed softening unit to remove hardness, the wastewater is then selected based on the TDS at the outlet of the cation bed softening unit to either directly enter the evaporation crystallization system, further concentrate it through a membrane before entering the evaporation crystallization system, or return to the secondary membrane concentration module for concentration and then be treated by the regenerated wastewater treatment system before entering the evaporation crystallization system.

[0038] Furthermore, step S1 also includes removing organic matter from the wastewater through the first organic matter removal unit and removing fluoride compounds from the wastewater through the first resin defluorination unit.

[0039] Furthermore, in step S2, before the pretreated wastewater enters the primary membrane concentration module, the organic matter in the pretreated wastewater is removed by the second organic matter removal unit; before entering the secondary membrane concentration module, the fluoride compounds in the pretreated wastewater are also removed by the second resin defluorination unit.

[0040] The beneficial effects of this invention are as follows: The zero-discharge system and method for treating high-hardness, saline wastewater provided by this invention comprises a membrane concentration system, a regenerated wastewater treatment system, and an evaporation crystallization system. The membrane concentration system includes an ion exchange hardening unit, a primary membrane concentration module, and a secondary membrane concentration module. The concentrated water outlet of the membrane concentration system is connected to the regenerated liquid inlet of the ion exchange hardening unit. The regenerated wastewater outlet of the ion exchange hardening unit is connected to the inlet of the regenerated wastewater treatment system, and the outlet of the regenerated wastewater treatment system is connected to the inlet of the evaporation crystallization system. The evaporation crystallization system includes two or more units selected from a sodium chloride evaporation crystallization unit, a sodium sulfate evaporation crystallization unit, and a mixed salt drying unit. In the zero-discharge system and method provided by this invention, the concentrated water from the membrane concentration system, whose main component is sodium sulfate, regenerates the saturated resin in the ion exchange hardening unit. The regenerated wastewater forms calcium sulfate precipitate, simplifying the zero-discharge system process and significantly reducing the amount of reagents required. Compared with conventional zero-discharge chemical reagent hardening systems, the overall salt content is significantly reduced.

[0041] The beneficial effects of the zero-emission system and method provided by this invention also include:

[0042] (1) The ion exchange hardening unit thoroughly removes hardness, reducing the hardness (calculated as CaCO3) from a relatively high level of 300mg / L to 4000mg / L in the influent to below 20mg / L in the effluent. It can replace the multi-stage chemical hardening process, simplifying the zero-discharge system process. Compared with chemical hardening, it can save about 3 to 10 yuan / ton in hardening agent costs (related to the unit price of the agent and the hardness of the influent). At the same time, it reduces the increase in total salt content caused by excessive addition of hardening agents, impurity of agents, and pH adjustment, thereby reducing the overall total salt content of the system and thus reducing the working pressure of reverse osmosis and saving energy consumption. Moreover, compared with the chemical hardening system, the ion exchange hardening unit in this invention adopts modular equipment, which is compact and can save a lot of space.

[0043] (2) Since the hardness of the effluent from the ion exchange hardness removal unit can reach below 20 mg / L, it can reduce the scaling tendency of the first-stage reverse osmosis unit, reduce the addition of scale inhibitor, and extend the service life of the membrane.

[0044] (3) Compared with the traditional cation bed softening process, which uses acid, alkali or sodium chloride regeneration, which increases the amount of salt entering the system, the ion exchange de-hardening unit in this invention uses the concentrated water from the membrane concentration system to regenerate the resin, without introducing salt. Therefore, compared with the traditional zero-discharge system, the zero-discharge system provided by this invention can reduce the scale of the subsequent evaporation and crystallization system. In addition, the ion exchange de-hardening unit in this invention innovatively uses the concentrated water from the membrane concentration system, which mainly contains sodium sulfate, as the regeneration liquid, which solves the problem of calcium sulfate scale deposition and blockage, and realizes the resource utilization of salt in wastewater. Attached Figure Description

[0045] Figure 1 A schematic diagram of the overall process flow of a zero-discharge system for high-hardness saline wastewater provided for an embodiment of the present invention;

[0046] Figure 2 A schematic diagram of the overall process flow of another zero-discharge system for high-hardness saline wastewater provided for an embodiment of the present invention;

[0047] Figure 3 A schematic diagram of the specific process flow of a zero-discharge system for high-hardness saline wastewater provided for an embodiment of the present invention;

[0048] Figure 4 A schematic diagram of the specific process flow of another zero-discharge system for high-hardness saline wastewater provided for an embodiment of the present invention;

[0049] 1-preprocessing system; 2-membrane concentration system; 3-regeneration waste liquid treatment system; 4-evaporation crystallization system; 101-adjusting unit; 102-first precipitation unit; 103-first filtration unit; 104-second organic matter removal unit; 105-dosing unit; 106-ion exchange hardness removal unit; 107-first-stage ultrafiltration unit; 108-first-stage reverse osmosis unit; 109-second resin fluorine removal unit; 110-second-stage ultrafiltration unit; 111-second-stage reverse osmosis unit; 112-third precipitation unit; 113-third filtration unit; 114-cation bed softening unit; 201-nanofiltration unit; 202-product water reverse osmosis unit; 203-sodium chloride evaporation crystallization unit; 204-sodium sulfate evaporation crystallization unit; 205-mixed salt drying unit. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present application will be further clearly and completely described below with reference to the drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0051] As shown in Figure 1 The zero-emission system for high-hardness salt-containing wastewater provided by the embodiments of the present application comprises a membrane concentration system 2, a regeneration waste liquid treatment system 3, and an evaporation crystallization system 4.

[0052] The regeneration waste liquid outlet of the membrane concentration system 2 is connected to the liquid inlet of the regeneration waste liquid treatment system 3, and the liquid outlet of the regeneration waste liquid treatment system 3 is connected to the liquid inlet of the evaporation crystallization system 4.

[0053] The membrane concentration system 2 comprises an ion exchange hardness removal unit 106, a first-stage membrane concentration module, and a second-stage membrane concentration module. The first-stage membrane concentration module comprises a first-stage ultrafiltration unit 107 and a first-stage reverse osmosis unit 108 connected in sequence, and the first-stage ultrafiltration unit 107 provides high-quality water guarantee for the first-stage reverse osmosis unit 108. The second-stage membrane concentration module comprises a second-stage ultrafiltration unit 110 and a second-stage reverse osmosis unit 111 connected in sequence, and the second-stage ultrafiltration unit 110 provides high-quality water guarantee for the second-stage reverse osmosis unit 111.

[0054] When the hardness of the wastewater (calcium and magnesium ion content in the wastewater to be treated) is higher than the upper limit of the influent of the primary membrane concentration module, the ion exchange hardness removal unit 106, the primary membrane concentration module, and the secondary membrane concentration module are sequentially connected in the membrane concentration system 2; when the hardness of the wastewater is lower than the upper limit of the influent of the primary membrane concentration module, the wastewater directly enters the primary membrane concentration module for concentration treatment, and the primary membrane concentration module, the ion exchange hardness removal unit 106, and the secondary membrane concentration module are sequentially connected in the membrane concentration system 2.

[0055] The ion exchange hardness removal unit 106 includes an ion exchange unit, a regeneration unit, and a water washing unit, which are combined to remove hardness and regenerate the resin, so as to ensure that the effluent hardness is at a low level.

[0056] Specifically, the ion exchange resin in the ion exchange hardness removal unit 106 is preferably a sodium type cation exchange resin.

[0057] Specifically, the different ion exchange bed types include fixed bed, intermittent or continuous moving bed, and fluidized bed; according to the hardness (i.e. calcium and magnesium ion concentration) of the wastewater entering the influent of the ion exchange hardness removal unit 106, the ion exchange bed type, the number of stages, and the arrangement and combination connection mode of the ion exchange unit, the regeneration unit, and the water washing unit are selected to remove the high hardness of the wastewater and regenerate the ion exchange resin.

[0058] In a specific embodiment, the ion exchange unit has one stage, the regeneration unit has two stages, and the water washing unit has one stage. The calcium and magnesium ions in the wastewater are exchanged with sodium ions on the ion exchange resin in the ion exchange unit to remove the hardness of the wastewater; the movement of the ion exchange resin in the ion exchange unit and the transfer between the resin columns can be intermittent or continuous. In the regeneration unit, countercurrent regeneration is used to improve the regeneration degree of the resin, i.e. the saturated resin passes through the primary regeneration unit and the secondary regeneration unit in sequence to complete regeneration, the regeneration liquid enters the secondary regeneration unit and the primary regeneration unit in sequence to regenerate the resin, the resin in the primary regeneration unit and the secondary regeneration unit adopts fluidized bed, the secondary regenerated resin obtained from the secondary regeneration unit enters the water washing unit through a pipeline, the resin in the water washing unit adopts fixed bed, and the regenerated resin obtained after water washing returns to the ion exchange unit again to perform ion exchange with the wastewater in the next cycle; the regeneration waste liquid formed after the regeneration liquid regenerates the resin is transferred to the regeneration waste liquid treatment system 3 through a pipeline for treatment.

[0059] Optionally, in the regeneration unit, saturated resin is regenerated by using sodium sulfate solution or the membrane concentration concentrated water of the membrane concentration system 2 as the regeneration liquid.

[0060] Preferably, the concentration of sodium ions in the regeneration solution is above 15000 mg / L; more preferably, the concentration of sodium ions in the regeneration solution is between 17000 mg / L and 25000 mg / L, and the regeneration effect and economy are optimal. The dosage of the regeneration solution is preferably 5% to 20% of the influent of the ion exchange unit; more preferably, the dosage of the regeneration solution is between 8% and 15% of the influent of the ion exchange unit, and the regeneration effect and economy are optimal.

[0061] When the membrane-concentrated concentrated water is used as the regeneration solution, and the concentration of sodium ions in the regeneration solution is insufficient or the amount of the regeneration solution is insufficient, commercially available sodium sulfate solids can be dissolved to supplement the concentration of sodium ions or the amount of the regeneration solution; when the membrane-concentrated concentrated water contains more components other than sodium chloride and sodium sulfate, the sodium sulfate obtained in the evaporation crystallization system 4 can be dissolved to be used as the regeneration solution.

[0062] When the membrane-concentrated concentrated water or the sodium sulfate solution is used as the regeneration solution, the ion exchange unit removes the hardness of the high-hardness wastewater according to the influent hardness by using a fixed bed or an intermittent moving bed or a continuous moving bed; the ion exchange hardness removal unit 106 is suitable for treating wastewater with calcium hardness (in terms of CaCO3) ranging from 250 mg / L to 3000 mg / L, total hardness (in terms of CaCO3) ranging from 300 mg / L to 4000 mg / L, and TDS (total salt content) less than 12000 mg / L; the ion exchange hardness removal unit 106 has the optimal hardness removal effect and economy for wastewater with calcium hardness (in terms of CaCO3) ranging from 500 mg / L to 2000 mg / L, total hardness (in terms of CaCO3) ranging from 600 mg / L to 2500 mg / L, and total salt content less than 8000 mg / L; the high-hardness salt-containing wastewater is treated by a combination of fluidized bed, intermittent or continuous moving bed, and fixed bed in the regeneration unit, so that the calcium ions regenerated form precipitates with sulfate ions in the regeneration solution and are discharged from the system in time.

[0063] When the hardness of the wastewater is lower than the upper limit of the inlet water of the primary membrane concentration module (i.e. the upper limit of the inlet water hardness), the wastewater directly enters the primary membrane concentration module for concentration treatment, and in the membrane concentration system 2, the primary membrane concentration module, the ion exchange hardness removal unit 106, and the secondary membrane concentration module are sequentially connected in order. That is, the concentrated water outlet of the primary membrane concentration module is connected with the inlet water of the ion exchange hardness removal unit 106 through a pipeline, and the outlet water of the ion exchange hardness removal unit 106 is connected with the inlet water of the secondary membrane concentration module through a pipeline. Specifically, the outlet water of the primary ultrafiltration unit 107 is connected with the inlet water of the primary reverse osmosis unit 108 through a pipeline; the outlet water of the primary reverse osmosis unit 108 is connected with the inlet water of the ion exchange hardness removal unit 106 through a pipeline, the outlet water of the ion exchange hardness removal unit 106 is connected with the inlet water of the secondary ultrafiltration unit 110 through a pipeline, and the outlet water of the secondary ultrafiltration unit 110 is connected with the inlet water of the secondary reverse osmosis unit 111 through a pipeline; the wastewater first enters the inlet water of the primary ultrafiltration unit 107, is concentrated by the primary reverse osmosis unit 108, and then enters the inlet water of the ion exchange hardness removal unit 106. The sodium ions on the ion exchange resin are exchanged with the calcium and magnesium ions in the wastewater to remove the hardness in the wastewater, so that the hardness of the outlet water of the ion exchange hardness removal unit 106 meets the inlet water requirement of the secondary membrane concentration module.

[0064] When the hardness of the wastewater (the content of calcium and magnesium ions in the wastewater to be treated) is higher than the upper limit of the inlet water of the primary membrane concentration module, in the membrane concentration system 2, the ion exchange hardness removal unit 106, the primary membrane concentration module, and the secondary membrane concentration module are sequentially connected in order, that is, the outlet water of the ion exchange hardness removal unit 106 is connected with the inlet water of the primary ultrafiltration unit 107 through a pipeline, the outlet water of the primary ultrafiltration unit 107 is connected with the inlet water of the primary reverse osmosis unit 108 through a pipeline; the concentrated water outlet of the primary reverse osmosis unit 108 is connected with the inlet water of the secondary ultrafiltration unit 110 through a pipeline, and the outlet water of the secondary ultrafiltration unit 110 is connected with the inlet water of the secondary reverse osmosis unit 111 through a pipeline; the wastewater first enters the inlet water of the ion exchange hardness removal unit 106, and the sodium ions on the ion exchange resin are exchanged with the calcium and magnesium ions in the wastewater to remove the hardness in the wastewater, so that the hardness of the outlet water of the ion exchange hardness removal unit 106 meets the inlet water requirement of the primary membrane concentration module.

[0065] Optionally, according to the TDS (total salt content) of the concentrated water outlet of the secondary reverse osmosis unit 111, in order to make the membrane concentration concentrated water obtained by the membrane concentration system 2 meet the concentration requirement of the evaporation crystallization system 3 in the zero discharge process, the membrane concentration system 1 comprises a multi-stage membrane concentration module, the multi-stage membrane concentration module comprises the primary membrane concentration module, the secondary membrane concentration module, …, and an n-stage membrane concentration module, wherein n≥3; the multi-stage membrane concentration module is connected in series by the primary membrane concentration module, the secondary membrane concentration module, …, and the n-stage membrane concentration module, and the n-stage membrane concentration module comprises a first n-stage ultrafiltration unit and a first n-stage reverse osmosis unit connected in sequence. Therefore, when the hardness of the wastewater is lower than the upper limit of the water inlet of the primary membrane concentration module, the membrane concentration system 2 comprises the primary membrane concentration module, the ion exchange hardening removal unit 106, the secondary membrane concentration module, …, and the n-stage membrane concentration module connected in sequence. When the hardness of the wastewater is higher than the upper limit of the water inlet of the primary membrane concentration module, the membrane concentration system 2 comprises the ion exchange hardening removal unit 106, the primary membrane concentration module, the secondary membrane concentration module, …, and the n-stage membrane concentration module connected in sequence.

[0066] Optionally, the secondary reverse osmosis unit 111 in the secondary membrane concentration module comprises a nanofiltration unit 201 and a product water reverse osmosis unit 202, the water inlet of the nanofiltration unit 201 is connected to the water outlet of the secondary ultrafiltration unit 110, the product water outlet of the nanofiltration unit 201 is connected to the liquid inlet of the product water reverse osmosis unit 202, and the concentrated water outlet of the nanofiltration unit 201 is connected to the regeneration liquid inlet of the ion exchange hardening removal unit 106. The concentrated water of the nanofiltration unit 201 is used as the regeneration liquid to regenerate the saturated resin in the ion exchange hardening removal unit 106. The nanofiltration unit 201 uses the selective interception characteristics of the nanofiltration membrane to separate sodium chloride and sodium sulfate in the liquid phase. Therefore, the sodium chloride in the wastewater mainly enters the nanofiltration permeate (i.e., product water), and after being concentrated by the product water reverse osmosis unit 202, enters the sodium chloride evaporation crystallization unit 204 for evaporation crystallization, and finally obtains sodium chloride crystals; the sodium sulfate in the wastewater is in the nanofiltration concentrated liquid (i.e., concentrated water), and is used as the regeneration liquid to regenerate the resin in the ion exchange hardening removal unit 106.

[0067] Optionally, the embodiment provides another zero discharge system for high-hardness and high-salt wastewater as shown in Figure 2 The zero discharge system further comprises a pretreatment system 1 arranged before the membrane concentration system 2, and the pretreatment system comprises one or a combination of multiple of the adjusting unit 101, the first precipitation unit 102, the first filtration unit 103, the first organic matter removal unit, and the first resin fluorine removal unit.

[0068] The adjusting unit 101 is used for adjusting the water volume and balancing the water quality of the wastewater; specifically, when the water volume and the water quality of the wastewater are unstable, the pretreatment system 1 comprises the adjusting unit 101.

[0069] Optionally, when the suspended solids content is high, the adjusting unit 101 can select the pool type of the horizontal flow sedimentation tank, which is arranged before the first sedimentation unit 102 to increase the sedimentation function to achieve the purpose of suspended solids primary sedimentation, and reduce the subsequent processing load of the first sedimentation unit 102.

[0070] Optionally, the zero discharge system further comprises a dosing unit 105, wherein the dosing unit 105 comprises one or a combination of a coagulant dosing device, a flocculant dosing device, a silicon removal agent dosing device, a fluorine removal agent dosing device, and a chemical oxidant dosing device; the coagulant dosing device, the flocculant dosing device, the silicon removal agent dosing device, and the fluorine removal agent dosing device are connected with the first sedimentation unit 102; and the chemical oxidant dosing device is connected with the first organic matter removal unit.

[0071] The first sedimentation unit 102 and the first filtration unit 103 are sequentially connected and can be used to remove suspended solids and other impurities in the wastewater. In addition, when the content of silicon compounds or fluorine compounds in the wastewater is high, the silicon removal agent or the fluorine removal agent can be added to the first sedimentation unit 102 through the dosing unit 105, so that the silicon compounds or the fluorine compounds are chemically precipitated and then removed together with the suspended solids, the silicon compounds, and the fluorine compounds by the first filtration unit 103.

[0072] When the wastewater contains organic matter, the pretreatment system 1 comprises a first organic matter removal unit. The first organic matter removal unit comprises one or a combination of a biochemical unit, a chemical oxidation unit, and an activated carbon adsorption unit, and the first organic matter removal unit is arranged in the preferred order of the biochemical unit, the chemical oxidation unit, and the activated carbon adsorption unit according to the concentration of the organic matter in the wastewater.

[0073] The first resin fluorine removal unit is used to remove fluorine compounds in the wastewater. When the concentration of the fluorine compounds in the wastewater is higher than 10 mg / L, the first resin fluorine removal unit is used as a deep treatment process for removing fluorine compounds by using a reagent. When the concentration of the fluorine compounds in the wastewater is lower than 10 mg / L, no fluorine removal agent is added to the first sedimentation unit 102, and only the first resin fluorine removal unit is used to remove the fluorine compounds.

[0074] Optionally, the membrane concentration system 2 further comprises one or a combination of a second sedimentation unit, a second filtration unit, a second organic matter removal unit 104, and a second resin fluorine removal unit 109.

[0075] Since the primary membrane concentration module, the secondary membrane concentration module, … the n-level membrane concentration module in the membrane concentration system 2 concentrate the wastewater, some water quality indexes after concentration may exceed the influent limit value of the membrane concentration or the subsequent evaporation crystallization system, therefore, the second sedimentation unit 102, the second filtration unit 103, the second organic matter removal unit 104, and the second resin fluoride removal unit 109 need to be arranged at the inlet of the influent pipeline of the primary membrane concentration module, the secondary membrane concentration module, … the n-level membrane concentration module according to the water quality; that is, the first sedimentation unit 102, the first filtration unit 103, the second organic matter removal unit 104, and the second resin fluoride removal unit 109 are combined with the multi-level membrane concentration module in a cross manner to remove other components except sodium chloride and sodium sulfate.

[0076] The coagulant dosing device, the flocculant dosing device, the desilication agent dosing device, and the defluorination agent dosing device of the dosing unit 105 are connected with the second sedimentation unit respectively; and the chemical oxidant dosing device is connected with the second organic matter removal unit 104.

[0077] The regeneration waste liquid treatment system 3 includes a third sedimentation unit 112, a third filtration unit 113, and a cation bed softening unit 114, which are combined in a preferred manner to realize the sedimentation and hardness removal of the regeneration waste liquid. The sodium ions in the regeneration liquid replace the calcium ions and magnesium ions from the resin, so the regeneration waste liquid mainly consists of sodium ions, calcium ions, magnesium ions, sulfate ions, and chloride ions. The high-concentration calcium ions and sulfate ions form a precipitate in the regeneration unit, which is discharged from the regeneration unit in time and then enters the regeneration waste liquid treatment system 3. Most of the calcium ions are precipitated in the form of calcium sulfate in the third sedimentation unit 112, and the precipitate sludge is concentrated and dewatered to be discharged from the system in the form of gypsum to realize resource utilization. The supernatant of the sedimentation tank still contains high hardness, which is further chemically precipitated and removed by adding hardness removal agents through the third sedimentation unit 112 and then enters the third filtration unit 113.

[0078] The filtered water of the third filtration unit 113 enters the cation bed softening unit 114 to further remove the remaining hardness, and then is directly introduced into the evaporation crystallization system 4 according to the TDS of the liquid outlet of the cation bed softening unit 114 (when the TDS of the liquid outlet of the cation bed softening unit 114 is higher than the lower limit of the design influent TDS range of the evaporation crystallization system 4); or is further introduced into the evaporation crystallization system 4 after being concentrated by a membrane (when the TDS of the liquid outlet of the cation bed softening unit 114 is lower than the lower limit of the design influent TDS range of the evaporation crystallization system 4); or returns to the membrane concentration system 2 (when the TDS of the liquid outlet of the cation bed softening unit 114 is lower than the lower limit of the design influent TDS range of the evaporation crystallization system 4). The TDS of the regeneration waste liquid after treatment is reduced.

[0079] Depending on the wastewater composition, the evaporation crystallization system 4 includes at least two of the following units: sodium chloride evaporation crystallization unit 203, sodium sulfate evaporation crystallization unit 204, and mixed salt drying unit 205.

[0080] Optionally, when the membrane concentration system 2 contains a nanofiltration unit 201, the nanofiltration permeate, mainly containing sodium chloride, is further concentrated by the permeate through the product water reverse osmosis unit 202 and then enters the evaporation crystallization system 4. Sodium chloride is obtained through the sodium chloride evaporation crystallization unit 203, and the mixed salt mother liquor enters the mixed salt drying unit 205 for evaporation and drying to form mixed salt. The wastewater treated by the regenerated wastewater treatment system 3 mainly contains sodium sulfate and sodium chloride. When sodium sulfate has a larger proportion, direct evaporation crystallization can be used. The wastewater enters the sodium sulfate evaporation crystallization unit 204, where sodium sulfate crystallizes out, and the mixed salt mother liquor enters the mixed salt drying unit 205 for evaporation and drying to form mixed salt. When there is no dominant salt component in the wastewater, salt-nitrate co-production fractional crystallization or low-temperature fractional crystallization process can be used to fractionally crystallize sodium sulfate and sodium chloride. Sodium chloride is obtained through the sodium chloride evaporation crystallization unit 203, and sodium sulfate is obtained through the sodium sulfate evaporation crystallization unit 204. The mixed salt mother liquor enters the mixed salt drying unit 205 for evaporation and drying to form mixed salt.

[0081] In one specific embodiment, the following is adopted: Figure 3 The diagram illustrates a specific process flow for a zero-discharge system for high-hardness, saline wastewater. The pretreatment system 1 includes a regulating unit 101, a first sedimentation unit 102, and a first filtration unit 103 connected in sequence. The membrane concentration system 2 includes a second organic matter removal unit 104, an ion exchange hardening unit 106, a primary membrane concentration module (a primary ultrafiltration unit 107 and a primary reverse osmosis unit 108), a second resin defluorination unit 109, and a secondary membrane concentration module (a secondary ultrafiltration unit 110 and a secondary reverse osmosis unit 111, with the concentrated membrane water obtained from the secondary reverse osmosis unit 111 used as regenerator to regenerate the saturated resin in the ion exchange hardening unit 106). The regenerated wastewater treatment system 3 includes a third sedimentation unit 112, a third filtration unit 113, and a cation bed softening unit 114 connected in sequence. The outlet of the cation bed softening unit 114 is connected to an evaporation crystallization system 4.

[0082] Specifically, when the hardness of the wastewater exceeds the upper limit of the inlet water of the first-stage membrane concentration module, the outlet of the first filtration unit 103 is connected to the inlet of the ion exchange hardening unit 106. The high-hardness, saline wastewater is treated sequentially by the regulating unit 101, the first sedimentation unit 102, the first filtration unit 103, the second organic matter removal unit 104, and the ion exchange hardening unit 106 before entering the first-stage ultrafiltration unit 107. When the fluoride content in the outlet concentrate of the first-stage reverse osmosis unit 108 is high, a second resin defluorination unit 109 is installed between the concentrate outlet pipeline of the first-stage reverse osmosis unit 108 and the inlet pipeline of the second-stage ultrafiltration unit 110. The regenerated wastewater discharged from the ion exchange de-hardening unit 106 is treated by the regenerated wastewater treatment system 3. The resulting regenerated wastewater mainly contains sodium sulfate and sodium chloride. Since there is no dominant salt component in the regenerated wastewater, salt-nitrate co-production and salt separation crystallization or low-temperature salt separation crystallization process can be used to separate and crystallize sodium sulfate and sodium chloride. Sodium chloride is obtained through the sodium chloride evaporation crystallization unit 203, and sodium sulfate is obtained through the sodium sulfate evaporation crystallization unit 204. The mixed salt mother liquor enters the mixed salt drying unit 205 for evaporation and drying to form mixed salt.

[0083] In another specific embodiment, the following is adopted: Figure 4 The following is a specific process flow diagram of another zero-discharge system for high-hardness saline wastewater, wherein the pretreatment system 1 includes a regulating unit 101, a first sedimentation unit 102, and a first filtration unit 103 connected in sequence; the membrane concentration system 2 includes a second organic matter removal unit 104, an ion exchange hardness removal unit 106, a primary membrane concentration module (a primary ultrafiltration unit 107 and a primary reverse osmosis unit 108), a second resin defluorination unit 109, and a secondary membrane concentration module (a secondary ultrafiltration unit 110, a nanofiltration unit 201, and a permeate unit) connected in sequence. The reverse osmosis unit 202 is included. The inlet of the nanofiltration unit 201 is connected to the outlet of the secondary ultrafiltration unit 110. The product water outlet of the nanofiltration unit 201 is connected to the product water reverse osmosis unit 202. The concentrate outlet of the nanofiltration unit 201 is connected to the regeneration liquid inlet of the ion exchange hardening unit 106. The nanofiltration concentrate is used as the regeneration liquid to regenerate the saturated resin in the ion exchange hardening unit 106. The regeneration waste liquid treatment system 3 includes a third precipitation unit 112, a third filtration unit 113, and a cation bed softening unit 114 connected in sequence. The evaporation crystallization system 4 includes a sodium chloride evaporation crystallization unit 203, a sodium sulfate evaporation crystallization unit 204, and a mixed salt drying unit 205. The outlet of the product water reverse osmosis unit 202 is connected to the inlet of the sodium chloride evaporation crystallization unit 204, and the outlet of the cation bed softening unit 114 is connected to the inlet of the sodium sulfate evaporation crystallization unit 204.

[0084] Specifically, when the hardness (calcium and magnesium ion content in the wastewater to be treated) of the wastewater is higher than the upper limit of the influent of the primary membrane concentration module, the high-hardness salt-containing wastewater is sequentially treated by the adjusting unit 101, the first precipitation unit 102, the first filtration unit 103, the second organic matter removal unit 104, and the ion exchange hardness removal unit 106, and then enters the primary ultrafiltration unit 107 and the primary reverse osmosis unit 108; the second resin fluorine removal unit 109 is arranged between the concentrated water outlet pipeline of the primary reverse osmosis unit 108 and the influent pipeline of the secondary ultrafiltration unit 110.

[0085] The nanofiltration product water mainly containing sodium chloride is further concentrated by membrane concentration (product water reverse osmosis unit 202) and then enters the sodium chloride evaporation crystallization unit 203 in the evaporation crystallization system 4 to obtain sodium chloride; the mixed salt mother liquor enters the mixed salt drying unit 205 to be evaporated and dried to form mixed salt. The regenerated waste liquid discharged from the ion exchange hardness removal unit 106 is treated by the regenerated waste liquid treatment system 3, mainly containing sodium sulfate and sodium chloride, and when the proportion of sodium sulfate is dominant, a direct evaporation crystallization method is used, the regenerated waste liquid enters the sodium sulfate evaporation crystallization unit 204, and sodium sulfate is crystallized and separated out; the mixed salt mother liquor enters the mixed salt drying unit 205 to be evaporated and dried to form mixed salt.

[0086] The embodiment also provides a zero-emission method for high-hardness salt-containing wastewater, which is realized based on the zero-emission system for high-hardness salt-containing wastewater and includes the following steps.

[0087] S1, pretreating wastewater: adjusting the water quantity and balancing the water quality of the wastewater by the adjusting unit, removing suspended solids, silicon compounds, fluorine compounds and the like in the wastewater by the first precipitation unit and the first filtration unit in combination with the dosing unit, and obtaining pretreated wastewater;

[0088] Optionally, in step S1, the method further includes removing organic matter in the wastewater by the first organic matter removal unit and removing fluorine compounds in the wastewater by the first resin fluorine removal unit.

[0089] S2, membrane concentration treatment of wastewater: when the hardness of the wastewater is higher than the upper limit of the influent of the primary membrane concentration module, the pretreated wastewater is first treated by the ion exchange hardness removal unit to remove hardness, and then treated by the primary membrane concentration module and the secondary membrane concentration module for concentration treatment, and the obtained membrane concentration concentrated water is used as a regeneration liquid to regenerate saturated resin in the ion exchange hardness removal unit;

[0090] When the hardness of the wastewater is lower than the upper limit of the influent of the primary membrane concentration module, the pretreated wastewater is directly treated by the primary membrane concentration module for concentration treatment, the obtained primary membrane concentration concentrated water is treated by the ion exchange hardness removal unit to remove hardness, and then treated by the secondary membrane concentration module for concentration treatment, and the obtained membrane concentration concentrated water is used as a regeneration liquid to regenerate saturated resin in the ion exchange hardness removal unit;

[0091] Optionally, in step S2, the organic matter in the pretreated wastewater is removed by a second organic matter removal unit before the pretreated wastewater enters the primary membrane concentration module; and the fluorine compounds in the pretreated wastewater are removed by a second resin fluorine removal unit before the pretreated wastewater enters the secondary membrane concentration module.

[0092] S3, treating the wastewater with regenerated waste liquid: the regenerated waste liquid discharged from the ion exchange hardness removal unit enters a regenerated waste liquid treatment system for treatment, sequentially passes through a third precipitation unit, a third filtration unit, and a cation bed softening unit to remove hardness, and then is directly introduced into an evaporation crystallization system according to the TDS of the liquid outlet of the cation bed softening unit, or is further introduced into the evaporation crystallization system after being concentrated by a membrane, or is introduced into the evaporation crystallization system after being treated by the regenerated waste liquid treatment system and the secondary membrane concentration module.

[0093] Embodiment:

[0094] The present application will be described in detail below with reference to an industrial project. The embodiment is used to illustrate the present application, but is not used to limit the scope of the present application.

[0095] Inlet water quality: total hardness (in terms of CaCO3) is 1200-1500 mg / L, and TDS is 5-6 g / L.

[0096] The product water is used as reclaimed water, and the crystallized salt is industrial anhydrous sodium sulfate I-class third-grade product.

[0097] The process flow of the zero discharge system for the high-hardness salt-containing wastewater provided in the embodiment for treating the above project is as follows:

[0098] The incoming water is adjusted in the adjusting pre-sedimentation tank (adjusting unit 101) to adjust the water volume and balance the water quality, and then enters the high-efficiency sedimentation tank (first sedimentation unit 102) after pre-sedimentation. The adjusting pre-sedimentation tank has an adjusting volume of 6h of incoming water, and is in the form of a horizontal-flow sedimentation tank. A mud scraper is arranged to scrape the sludge to a sludge hopper for continuous sludge discharge by a sludge pump. The high-efficiency sedimentation tank mainly comprises a reaction zone, a water distribution zone and an inclined plate sedimentation zone. The reaction zone is provided with a silicon removal agent, a coagulant and a flocculant to remove suspended solids, silicon compounds and part of organic matters. After the turbidity is further reduced in the V-type filter (first filtration unit 103), the water enters the ion exchange hardness removal system (ion exchange hardness removal unit 106) to remove hardness. The total hardness (in terms of CaCO3) of the water discharged from the ion exchange hardness removal system is less than 10mg / L. After ultrafiltration (first-stage ultrafiltration unit 107), the water enters the first-stage reverse osmosis system (first-stage reverse osmosis unit 108). The TDS of the concentrated water of the first-stage reverse osmosis is 20-23g / L. After the concentrated water of the first-stage reverse osmosis is subjected to second-stage ultrafiltration (second-stage ultrafiltration unit 110), the water enters the second-stage reverse osmosis system (second-stage reverse osmosis unit 111) to further concentrate the concentrated water by using a high-pressure reverse osmosis membrane. The TDS of the concentrated water of the second-stage reverse osmosis is 65-70g / L. The concentrated water of the second-stage reverse osmosis is used as the regeneration liquid of the ion exchange hardness removal system. After the regeneration waste liquid is subjected to two-stage sedimentation (third sedimentation unit 112 and third filtration unit 113) and the hardness is removed by the cationic bed softening resin (cationic bed softening unit 114), the liquid enters the decarbonization tower to reduce the alkalinity of the water, so as to reduce the non-condensable gas in the subsequent evaporation crystallization and reduce the risk of scaling. Then, the liquid enters the MVR evaporation and concentration system for further concentration. The TDS of the water discharged from the MVR concentrated water is 200-230g / L. The MVR concentrated water is used to produce sodium sulfate in the sodium sulfate three-effect evaporation crystallizer (sodium sulfate evaporation and crystallization unit 204). The mother liquor enters the mixed salt crystallization system (mixed salt drying unit 205) to produce mixed salt.

[0099] The direct operation cost of the project described in the present embodiment is about 12yuan / ton, which is 4-5yuan / ton lower than the conventional zero-discharge system using chemical hardness removal and resin softening.

[0100] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application belong to the scope of the claims of the present application and their equivalents, the present application also intends to include these modifications and variations.

Claims

1. A zero-discharge system for high-hardness, saline wastewater, characterized in that, The zero-emission system includes a membrane concentration system, a regenerated wastewater treatment system, and an evaporation crystallization system, wherein: The zero-emission system also includes a pretreatment system, which is located before the membrane concentration system. The pretreatment system includes one or more of the following: a regulating unit, a first precipitation unit, a first filtration unit, a first organic matter removal unit, and a first resin defluorination unit. The membrane concentration system includes an ion exchange de-hardening unit, a primary membrane concentration module, and a secondary membrane concentration module. The membrane concentrate outlet of the membrane concentration system is connected to the regenerated liquid inlet of the ion exchange hardening unit, the regenerated waste liquid outlet of the ion exchange hardening unit is connected to the inlet of the regenerated waste liquid treatment system, and the outlet of the regenerated waste liquid treatment system is connected to the inlet of the evaporation crystallization system. The ion exchange hardening unit includes an exchange unit, a regeneration unit, and a water washing unit. The exchange unit, regeneration unit, and water washing unit achieve hardness removal and resin regeneration by using a combination of different ion exchange bed types. In the regeneration unit, sodium sulfate solution or the concentrated water from the membrane concentration system is used as the regeneration solution to regenerate the saturated resin. The ion exchange unit uses a fixed bed, intermittent moving bed, or continuous moving bed to remove hardness from high-hardness wastewater, depending on the hardness of the influent. The ion exchange hardness removal unit is suitable for treating wastewater with calcium hardness (calculated as CaCO3) ranging from 250 mg / L to 3000 mg / L, total hardness (calculated as CaCO3) ranging from 300 mg / L to 4000 mg / L, and TDS (total salinity) less than 12000 mg / L. The evaporation crystallization system includes two or more units selected from the following: a sodium chloride evaporation crystallization unit, a sodium sulfate evaporation crystallization unit, and a mixed salt drying unit.

2. The zero-discharge system for high-hardness saline wastewater according to claim 1, characterized in that, When the hardness of the wastewater exceeds the upper limit of the inlet water of the primary membrane concentration module, the ion exchange hardness removal unit, the primary membrane concentration module, and the secondary membrane concentration module are connected in sequence in the membrane concentration system. When the hardness of the wastewater is lower than the upper limit of the inlet water of the primary membrane concentration module, the wastewater directly enters the primary membrane concentration module for concentration treatment. In the membrane concentration system, the primary membrane concentration module, the ion exchange hardening unit, and the secondary membrane concentration module are connected in sequence.

3. The zero-discharge system for high-hardness saline wastewater according to claim 1, characterized in that, The different ion exchange bed types include fixed beds, intermittent or continuous moving beds, and fluidized beds; the ion exchange bed type, number of stages, and connection method of the exchange unit, regeneration unit, and washing unit are selected according to the concentration of calcium and magnesium ions in the wastewater entering the inlet of the ion exchange hardening unit.

4. The zero-discharge system for high-hardness saline wastewater according to claim 1, characterized in that, The sodium ion concentration in the regenerated solution is greater than 15000 mg / L; The amount of regenerated liquid used is 5% to 20% of the influent volume of the exchange unit.

5. A zero-discharge system for high-hardness saline wastewater according to claim 1, characterized in that, In the membrane concentration system, the ion exchange de-hardening unit and the primary membrane concentration module, and / or the primary membrane concentration module and the secondary membrane concentration module, further include one or more of the following: a second precipitation unit, a second filtration unit, a second organic matter removal unit, and a second resin defluorination unit.

6. A zero-discharge system for high-hardness saline wastewater according to claim 5, characterized in that, The zero-emission system also includes a dosing unit, which includes a combination of one or more of the following: a coagulant dosing device, a flocculant dosing device, a silicate dosing device, a fluoride removal agent dosing device, and a chemical oxidant dosing device. The coagulant dosing device, flocculant dosing device, silicate dosing device, and fluoride dosing device are respectively connected to the first precipitation unit; the chemical oxidant dosing device is connected to the first organic matter removal unit. The coagulant dosing device, flocculant dosing device, silicate dosing device, and fluoride dosing device are respectively connected to the second precipitation unit; the chemical oxidant dosing device is connected to the second organic matter removal unit.

7. A zero-discharge system for high-hardness saline wastewater according to claim 1, characterized in that, The regenerated waste liquid treatment system includes a third sedimentation unit, a third filtration unit, and a cation bed softening unit connected in sequence. The inlet of the third precipitation unit is connected to the outlet of the regenerated waste liquid of the ion exchange hardening unit; If the TDS at the outlet of the cation bed softening unit is higher than the lower limit of the design inlet TDS range of the evaporation crystallization system, then the outlet of the cation bed softening unit is directly connected to the inlet of the evaporation crystallization system. If the TDS at the outlet of the cation bed softening unit is lower than the lower limit of the design inlet TDS range of the evaporation crystallization system, then a membrane concentration module shall be installed between the outlet of the cation bed softening unit and the inlet of the evaporation crystallization system. Alternatively, the outlet of the cation bed softening unit may be connected to the inlet of the secondary membrane concentration module of the membrane concentration system.

8. A zero-discharge system for high-hardness saline wastewater according to claim 1, characterized in that, The primary membrane concentration module includes a primary ultrafiltration unit and a primary reverse osmosis unit connected in sequence; the secondary membrane concentration module includes a secondary ultrafiltration unit and a secondary reverse osmosis unit connected in sequence.

9. A zero-discharge system for high-hardness saline wastewater according to claim 8, characterized in that, The secondary reverse osmosis unit includes a nanofiltration unit and a permeate reverse osmosis unit; wherein, the inlet of the nanofiltration unit is connected to the outlet of the secondary ultrafiltration unit, the permeate outlet of the nanofiltration unit is connected to the inlet of the permeate reverse osmosis unit, and the concentrate outlet of the nanofiltration unit is connected to the regenerant inlet of the ion exchange hardening unit. The concentrate outlet of the permeate reverse osmosis unit is connected to the sodium chloride evaporation and crystallization unit.

10. A zero-discharge system for high-hardness saline wastewater according to claim 1, characterized in that, The membrane concentration system includes a multi-stage membrane concentration module, which includes a first-stage membrane concentration module, a second-stage membrane concentration module, ..., n-stage membrane concentration modules, where n≥3; The multi-stage membrane concentration module is composed of the first-stage membrane concentration module, the second-stage membrane concentration module, ..., n-stage membrane concentration modules connected in series. The n-stage membrane concentration module includes an nth-stage ultrafiltration unit and an nth-stage reverse osmosis unit connected in sequence.

11. A method for zero discharge of high-hardness, saline wastewater, characterized in that, This is achieved using the zero-discharge system for high-hardness saline wastewater as described in any one of claims 1-10, and the method includes the following steps: S1. Pre-treated wastewater: The wastewater volume is adjusted and the water quality is balanced by the regulating unit. The wastewater is then treated by removing suspended solids, silicon compounds, fluoride compounds, etc., through the first sedimentation unit, the first filtration unit and the dosing unit to obtain pre-treated wastewater. S2. Wastewater Concentration Treatment: When the hardness of the wastewater is higher than the upper limit of the inlet water of the first-stage membrane concentration module, the pretreated wastewater first passes through the ion exchange hardness removal unit to remove hardness, and then passes through the first-stage membrane concentration module and the second-stage membrane concentration module for concentration treatment. The obtained membrane concentrate is used as a regenerator to regenerate the saturated resin in the ion exchange hardness removal unit. When the hardness of the wastewater is lower than the upper limit of the inlet water of the first-stage membrane concentration module, the pretreated wastewater directly enters the first-stage membrane concentration module for concentration treatment. The obtained first-stage membrane concentrate is then passed through the ion exchange hardening unit to remove hardness, and then through the second-stage membrane concentration module for further concentration treatment. The obtained membrane concentrate is used as a regenerator to regenerate the saturated resin in the ion exchange hardening unit. S3. Wastewater Treatment of Regenerated Wastewater: The regenerated wastewater discharged from the ion exchange hardening unit enters the regenerated wastewater treatment system for treatment. After passing through the third precipitation unit, the third filtration unit, and the cation bed softening unit to remove hardness, the wastewater is then selected based on the TDS at the outlet of the cation bed softening unit to either directly enter the evaporation crystallization system, further concentrate it through a membrane before entering the evaporation crystallization system, or return to the secondary membrane concentration module for concentration and then be treated by the regenerated wastewater treatment system before entering the evaporation crystallization system.

12. A method for zero discharge of high-hardness saline wastewater according to claim 11, characterized in that, Step S1 also includes removing organic matter from the wastewater through the first organic matter removal unit and removing fluoride compounds from the wastewater through the first resin defluorination unit.

13. A method for zero discharge of high-hardness saline wastewater according to claim 11, characterized in that, In step S2, before the pretreated wastewater enters the primary membrane concentration module, it passes through a second organic matter removal unit to remove organic matter from the pretreated wastewater; before entering the secondary membrane concentration module, it also passes through a second resin defluorination unit to remove fluoride compounds from the pretreated wastewater.

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