A reverse osmosis-electrodialysis-nanofiltration combined desalting system and application thereof

Abstract

The application discloses a kind of reverse osmosis-electrodialysis-nanofiltration combined salt separation systems, including wastewater collection pond, pretreatment system, filtration system, reverse osmosis system, primary nanofiltration system and evaporation crystallization system A sequentially arranged along wastewater flow direction;The water side of the primary nanofiltration system is sequentially connected with electrodialysis system, secondary nanofiltration system and evaporation crystallization system B;The concentrated water side of the secondary nanofiltration system is connected to the evaporation crystallization system A;The water of the reverse osmosis system and the water of the electrodialysis system are recycled to the wastewater collection pond;The condensed water of the evaporation crystallization system A and the evaporation crystallization system B is recycled to the wastewater collection pond.The system process has the characteristics of simple operation, stable operation, high salt separation efficiency, etc.Compared with existing salt separation technology, it realizes ultra-high concentration salt water salt separation and achieves high-efficiency salt separation effect, while greatly reducing energy consumption and operating cost, suitable for further engineering popularization and application.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-salinity wastewater treatment, and particularly relates to a reverse osmosis-electrodialysis-nanofiltration combined salt separation system and application thereof. BACKGROUND

[0002] Chemical industry wastewater, especially wastewater generated in the processes of coal-to-oil, coal-to-methanol, coal-to-olefin and coal-to-gas, has the characteristics of high salt content, high hardness, complex composition and difficult treatment. There is an urgent need for a coal chemical industry wastewater treatment process with good treatment effect, low treatment cost and stable operation.

[0003] In recent years, according to the characteristics of high-salinity wastewater, a batch of "zero discharge" treatment processes for high-salinity wastewater have emerged through continuous research and improvement by domestic and foreign scholars. However, in the actual operation process, these "zero discharge" treatment processes often only achieve liquid zero discharge, while the dissolved inorganic salts and organic matter contained in the high-salinity water are evaporated and crystallized as mixed salts. This part of the mixed salt cannot be reused due to the mutual doping of various inorganic salts, organic matter and heavy metal ions, and is instead treated and disposed as hazardous waste. This not only increases the cost of later hazardous waste treatment, but also increases the risk of secondary pollution to the surrounding environment. Therefore, it is urgent to develop a salt separation treatment process for high-salinity wastewater to achieve low-cost and efficient separation of sodium chloride and sodium sulfate in high-salinity water, which is the key to achieving the "zero discharge" goal of high-salinity wastewater in a true sense. SUMMARY

[0004] Based on the above problems, the purpose of the present application is to provide a reverse osmosis-electrodialysis-nanofiltration combined salt separation system and application thereof. Compared with the existing salt separation technology, the present application realizes the separation of ultra-high concentration salt-containing water and achieves high-efficiency salt separation, while greatly reducing energy consumption and operation cost, and is suitable for further engineering promotion and application.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical solutions.

[0006] One embodiment of the present application provides a reverse osmosis-electrodialysis-nanofiltration combined salt separation system, which comprises, in sequence along the flow direction of wastewater, a wastewater collection tank, a pretreatment system, a filtration system, a reverse osmosis system, a primary nanofiltration system and an evaporation crystallization system 6A; the water production side of the primary nanofiltration system is connected in sequence with an electrodialysis system, a secondary nanofiltration system and an evaporation crystallization system 9B; the concentrated water side of the secondary nanofiltration system is connected to the evaporation crystallization system 6A; the water production of the reverse osmosis system and the water production of the electrodialysis system are returned to a reuse water collection tank for reuse; and the condensed water of the evaporation crystallization system 6A and the evaporation crystallization system 9B is returned to the wastewater collection tank.

[0007] According to the above-mentioned one embodiment of the present application, the reverse osmosis-electrodialysis-nanofiltration combined salt separation system is provided, and the wastewater collecting tank is provided with a stirrer or a pre-aeration stirring device.

[0008] According to the above-mentioned one embodiment of the present application, the reverse osmosis-electrodialysis-nanofiltration combined salt separation system is provided, and the pretreatment system comprises a combination of one or more removal units for removing organic matter, ammonia nitrogen, total nitrogen, hardness, alkalinity, suspended matter and colloidal pollutants.

[0009] According to the above-mentioned one embodiment of the present application, the reverse osmosis-electrodialysis-nanofiltration combined salt separation system is provided, and the filtration system comprises one or more filtering devices selected from sand filtration, multi-medium filtration and ultrafiltration.

[0010] According to the above-mentioned one embodiment of the present application, the reverse osmosis-electrodialysis-nanofiltration combined salt separation system is provided, and the reverse osmosis system adopts a tubular reverse osmosis membrane, and the membrane assembly of the tubular reverse osmosis membrane is a combination of one or more membrane assemblies.

[0011] According to the above-mentioned one embodiment of the present application, the reverse osmosis-electrodialysis-nanofiltration combined salt separation system is provided, and the primary nanofiltration system and the secondary nanofiltration system adopt a common or high-pressure nanofiltration membrane, and the membrane assembly of the nanofiltration membrane is a combination of one or more membrane assemblies.

[0012] According to the above-mentioned one embodiment of the present application, the reverse osmosis-electrodialysis-nanofiltration combined salt separation system is provided, and the evaporation crystallization system 6A and the evaporation crystallization system 9B are evaporators in a primary or multi-stage combination, and the evaporators comprise multi-effect evaporation and / or MVR evaporators.

[0013] Another embodiment of the present application further provides a high-salinity wastewater treatment method of the reverse osmosis-electrodialysis-nanofiltration combined salt separation system, which is characterized by adopting the reverse osmosis-electrodialysis-nanofiltration combined salt separation system for treating the high-salinity wastewater, and the method comprises the following steps:

[0014] S1: The high-salinity wastewater is collected through a pipeline into a wastewater collecting tank, and the high-salinity wastewater in the wastewater collecting tank is subjected to homogenization and homoeostasis through a stirrer or a pre-aeration stirring device in the wastewater collecting tank;

[0015] S2: The homogenized and homoeostatic high-salinity wastewater is lifted to a pretreatment system through a wastewater lifting pump, so as to remove organic matter, ammonia nitrogen, total nitrogen, hardness, alkalinity, suspended matter and colloidal pollutants and the like;

[0016] S3: The high-salinity wastewater after the pretreatment is pumped into a filtration system to further remove suspended matter, colloidal matter and the like in the wastewater;

[0017] S4: Pumping the filtered effluent into the reverse osmosis system, and obtaining high-salt wastewater and product water after desalination by concentration, wherein the product water enters a recycled water collection tank;

[0018] S5: Pumping the high-salt wastewater obtained in step S4 into a primary nanofiltration system after further removing hardness and organic matter, etc., and obtaining concentrated water and product water through the separation of monovalent and divalent ions by the nanofiltration membrane, wherein the divalent ions are retained on the concentrated water side, and the monovalent ions are separated to the product water side; the concentrated water then enters an evaporation crystallization system 6A;

[0019] S6: Pumping the product water obtained in step S5 into an electrodialysis system to obtain high-salt wastewater and product water after desalination by concentration; pumping the product water into a recycled water collection tank; and pumping the high-salt wastewater into a secondary nanofiltration system after further removing hardness and organic matter, etc., and obtaining concentrated water and product water through the separation of monovalent and divalent ions by the nanofiltration membrane, wherein the divalent ions are retained on the concentrated water side, and the monovalent ions are separated to the product water side;

[0020] S7: Pumping the concentrated water obtained in step S6 into an evaporation crystallization system 6A to evaporate and crystallize sodium sulfate products, and returning the condensed water to a wastewater collection tank; and pumping the product water into an evaporation crystallization system 9B to evaporate and crystallize sodium chloride products, and returning the condensed water to the wastewater collection tank.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] 1. The present application solves the problems of the mixed salt produced in the high-salt wastewater "zero discharge" process, such as being unable to be utilized, having no economic value, and causing accumulation of hazardous waste and secondary pollution;

[0023] 2. The present application utilizes the selective permeability of nanofiltration membranes to different ions to separate the high-salt industrial wastewater concentrated by the reverse osmosis system and the electrodialysis system into monovalent sodium chloride concentrated water and divalent sodium sulfate concentrated water, and then evaporates and crystallizes to obtain industrial-grade standard sodium chloride and sodium sulfate;

[0024] 3. The present application can effectively reduce or avoid the problems of fouling and plugging of membranes and evaporators, the product water of reverse osmosis and electrodialysis can be fully recycled, the condensed water of the evaporation system is returned to the wastewater collection tank, and the problems of wastewater zero discharge and water resource recycling are truly solved;

[0025] 4. The process has the characteristics of simple operation, high salt separation efficiency, and stable operation, and compared with the existing salt separation technology, the present application realizes the effect of efficient salt separation of ultra-high concentration salt-containing wastewater, greatly reduces energy consumption and operation cost, and is suitable for further engineering promotion and application. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The present application is a process flow diagram of the system. DETAILED DESCRIPTION

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1: As Figure 1 As shown, the present invention discloses a reverse osmosis-electrodialysis-nanofiltration combined salt separation system, which includes a wastewater collection tank 1, a pretreatment system 2, a filtration system 3, a reverse osmosis system 4, a primary nanofiltration system 5, an evaporation crystallization system 6A, an electrodialysis system 7, a secondary nanofiltration system 8, an evaporation crystallization system 9B, and a recycled water collection tank 10 arranged sequentially along the wastewater flow direction.

[0029] The primary nanofiltration system 5 is sequentially connected to the electrodialysis system 7, the secondary nanofiltration system 8, and the evaporation crystallization system 9B on its permeate side. The concentrate side of the secondary nanofiltration system 8 is connected to the evaporation crystallization system 6A. The permeate from the reverse osmosis system 4 and the electrodialysis system 7 is recycled to the reclaimed water collection tank 10. The evaporation crystallization system 6A produces sodium sulfate crystals, and the evaporation crystallization system 9B produces sodium chloride crystals. The condensate from the evaporation crystallization systems 6A and 9B is returned to the wastewater collection tank 1. The permeate from the reverse osmosis system 4 and the electrodialysis system 7 is connected to the reclaimed water collection tank 10. The condensate from the evaporation crystallization systems 6A and 9B is connected to the wastewater collection tank 1.

[0030] Wastewater collection tank 1 is equipped with a stirrer or pre-aeration stirring device for homogenizing and regulating the wastewater. Pretreatment system 2 includes a combination of one or more removal units for removing pollutants such as organic matter, ammonia nitrogen, total nitrogen, hardness, alkalinity, suspended solids, and colloids. Filtration system 3 includes one or more filtration devices such as sand filtration, multi-media filtration, and ultrafiltration. Reverse osmosis system 4 uses tubular reverse osmosis membranes, and the membrane modules are a combination of one or more membrane modules. Primary nanofiltration system 5 and secondary nanofiltration system 8 use ordinary or high-pressure nanofiltration membranes, and the membrane modules are a combination of one or more membrane modules. Evaporation crystallization system 6A and evaporation crystallization system 9B are single-stage or multi-stage evaporators, including one or more of multi-effect evaporators and MVR evaporators. One or more units are also provided upstream of the nanofiltration membrane modules to further remove hardness and organic matter from the concentrated high-salinity water, effectively reducing or avoiding fouling problems caused by fouling and scaling of the nanofiltration membrane and evaporation crystallization system during the process.

[0031] The monovalent sodium chloride product water produced by the nanofiltration membrane assembly enters the subsequent evaporation crystallization system 9B to obtain industrial-grade sodium chloride crystals with a purity of more than 95%. The divalent sodium sulfate concentrated water produced by the nanofiltration membrane assembly enters the subsequent evaporation crystallization system 6A to obtain industrial-grade sodium sulfate crystals with a purity of more than 97%.

[0032] The specific steps of the wastewater treatment of the embodiment include:

[0033] (1) The high-salinity wastewater is collected by pipelines into a wastewater collection tank 1, which is provided with a stirrer or a pre-aeration stirring device for homogenizing and equalizing the high-salinity wastewater in the tank;

[0034] (2) The homogenized and equalized high-salinity wastewater is lifted by a wastewater lifting pump to a pretreatment system 2, which realizes the removal of pollutants such as organic matter, ammonia nitrogen, total nitrogen, hardness, alkalinity, suspended matter and colloid through one or more removal units in combination, thereby reducing the pollution and scaling of membranes and evaporators;

[0035] (3) The pretreated high-salinity wastewater is pumped into a filtration system 3, which further removes suspended matter, colloid and the like in the wastewater through one or more filtering devices such as sand filtration, multi-medium filtration and ultrafiltration;

[0036] (4) The effluent of the filtration system 3 is pumped into a reverse osmosis system 4, and the product water after concentration and desalination is collected in a reuse water collection tank 10 through one or more reverse osmosis membrane assemblies, and the concentrated high-salinity wastewater enters the next unit;

[0037] (5) The high-salinity wastewater concentrated by the reverse osmosis system 4 is further removed of hardness and organic matter and the like and then pumped into a primary nanofiltration system 5, which separates monovalent and divalent ions through nanofiltration membranes, and the combination of one or more nanofiltration assemblies retains the divalent ions on the concentrated water side and separates the monovalent ions to the product water side;

[0038] (6) The concentrated water of the primary nanofiltration system 5 enters an evaporation crystallization system 6A, which evaporates and crystallizes sodium sulfate products through one or more evaporators in combination, and the condensed water returns to the wastewater collection tank 1;

[0039] (7) The product water of the primary nanofiltration system 5 enters an electrodialysis system 7, and the product water after concentration and desalination enters the reuse water collection tank 10 through one or more electrodialysis systems, and the concentrated high-salinity wastewater enters the next unit;

[0040] (8) The high-salinity wastewater concentrated by the electrodialysis system 7 is further removed of hardness and organic matter and the like and then pumped into a secondary nanofiltration system 8, which separates monovalent and divalent ions through nanofiltration membranes, and the combination of one or more nanofiltration membrane assemblies retains the divalent ions on the concentrated water side and separates the monovalent ions to the product water side;

[0041] (9) The concentrated water of the secondary nanofiltration system 8 enters the evaporation crystallization system 6A, and sodium sulfate products are evaporated and crystallized through one or more stages of combined evaporators, and the condensed water returns to the wastewater collection tank 1; The water produced by the secondary nanofiltration system 8 enters the evaporation crystallization system 9B, and sodium chloride products are evaporated and crystallized through one or more stages of combined evaporators, and the condensed water returns to the wastewater collection tank 1.

[0042] Example 2: In order to verify the effect of the reverse osmosis-electrodialysis-nanofiltration combined salt separation system and engineering application of high-salinity wastewater according to the present application, as shown in the following, a high-salinity wastewater treatment project of a certain coal chemical enterprise is taken as an example to illustrate the system and method of the present application. Figure 1

[0043] (1) The high-salinity wastewater has large fluctuations in quality and quantity, is collected and homogenized in the wastewater collection tank, and is lifted by a pump to the pretreatment system, which has a treatment capacity of 500 t / d. The water quality after pretreatment is as follows: TDS is 20000-30000 mg / L, COD is about 50 mg / L, TN is about 15 mg / L, and hardness is about 10 mg / L;

[0044] (2) The pretreated high-salinity wastewater flows to the filtration system by itself, and the filtration system uses submerged MBR ultrafiltration membranes to further remove suspended solids in the wastewater to below 1 mg / L;

[0045] (3) The ultrafiltration water is lifted by a pump to the reverse osmosis system, concentrated and desalinated by multiple reverse osmosis membrane assemblies, with a design recovery rate of 75%, and the wastewater is concentrated by about 4 times. The reverse osmosis concentrated water is pumped into the primary nanofiltration system after further removing hardness and organic matter, and the reverse osmosis water is used for reuse by entering the reuse water collection tank;

[0046] (4) The high-salinity concentrated water after concentration by the reverse osmosis system is divided into monovalent salt concentrated water and divalent salt concentrated water by the different selectivity of the nanofiltration membrane assembly, wherein the monovalent salt concentrated water is sodium chloride concentrated water, and the divalent salt concentrated water is sodium sulfate concentrated water. The nanofiltration membrane has different selectivity to different ions, and the charge intensity of various electrolyte salt ions in the high-salinity concentrated water is different, resulting in different ion retention rates of the nanofiltration membrane assembly. Therefore, in a multi-component system containing different valence ions, the proportion of different ions passing through the nanofiltration membrane assembly is also different, so that the high-salinity wastewater to be treated is divided into two kinds of concentrated water mainly containing sodium chloride and mainly containing sodium sulfate;

[0047] ​(5) In the process, the nanofiltration membrane assembly used has a rejection rate of 5%~15% for sodium chloride and a rejection rate of 90%~99% for sodium sulfate, that is, after nanofiltration membrane treatment, 85%~95% of sodium chloride can penetrate the nanofiltration membrane into the product water side, while only 1%~10% of sodium sulfate penetrates, and most of it is retained, remaining in the concentrated water side, so that the nanofiltration membrane realizes efficient separation of sodium chloride and sodium sulfate, and two different ionic valence concentrated waters of sodium chloride and sodium sulfate are obtained;

[0048] (6) Through the membrane separation of the primary nanofiltration system, sodium sulfate is mainly retained on the nanofiltration concentrated water side, and sodium chloride is mainly retained on the nanofiltration product water side; the primary nanofiltration concentrated water is pumped into the MVR evaporation crystallization system 6A to produce sodium sulfate crystals through concentration and crystallization, and the purity of the sodium sulfate crystals is above 97%, meeting the "II qualified product" standard in "Industrial anhydrous sodium sulfate" (GB / T 6009-2014);

[0049] (7) The product water of the primary nanofiltration is pumped to the electrodialysis system for further concentration and desalination, with a design recovery rate of 70%, and the wastewater is concentrated by about 3.3 times; the concentrated water of the electrodialysis is pumped into the secondary nanofiltration system for salt separation through multiple high-pressure nanofiltration membrane assemblies after further removal of hardness and organic matter, and the product water of the electrodialysis enters the recycled water collection tank for recycling;

[0050] (8) Through the membrane separation of the secondary nanofiltration system, sodium sulfate is mainly retained on the nanofiltration concentrated water side, and sodium chloride is mainly retained on the nanofiltration product water side; the secondary nanofiltration concentrated water is pumped into the MVR evaporation crystallization system 6A to produce sodium sulfate crystals through concentration and crystallization, and the purity of the sodium sulfate crystals is above 97%, meeting the "II qualified product" standard in "Industrial anhydrous sodium sulfate" (GB / T 6009-2014); the product water of the secondary nanofiltration is pumped into the MVR evaporation crystallization system 9B to produce sodium chloride crystals through concentration and crystallization, and the purity of the sodium chloride crystals is above 95%, meeting the "sunlight industrial salt level I" standard in "Industrial salt" (GB / T 5462-2003);

[0051] (9) The condensed water of the evaporation crystallization system 6A and the evaporation crystallization system 9B returns to the wastewater collection tank for collection and further treatment, and the product water of the reverse osmosis and the electrodialysis enters the recycled water collection tank for collection and recycling;

[0052] (10) The flushing, backwashing, regeneration and other wastewater of the entire system are collected by the wastewater collection tank and treated, and the entire system realizes zero wastewater discharge.

[0053] The details not described in the present application are known to those skilled in the art.

[0054] Finally, it should be noted that the above detailed description is only used to explain the technical solutions of the present application and not to limit the present application. Although the present application has been described in detail with reference to the examples, those skilled in the art should understand that the technical solutions of the present application can be modified and replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application, and all modifications and replacements should be included in the scope of the claims of the present application.

Claims

1. A method for treating high-salinity wastewater using a reverse osmosis-electrodialysis-nanofiltration combined salt separation system, characterized in that the reverse osmosis-electrodialysis-nanofiltration combined salt separation system comprises, in sequence along the flow direction of the wastewater, a wastewater collection tank, a pretreatment system, a filtration system, a reverse osmosis system, a primary nanofiltration system, and an evaporation crystallization system 6A; the water production side of the primary nanofiltration system is connected in sequence with an electrodialysis system, a secondary nanofiltration system, and an evaporation crystallization system 9B; the concentrated water side of the secondary nanofiltration system is connected to the evaporation crystallization system 6A; the water produced by the reverse osmosis system and the water produced by the electrodialysis system are used in a reuse water collection tank; and the condensed water from the evaporation crystallization systems 6A and 9B is returned to the wastewater collection tank. The reverse osmosis system uses a tubular reverse osmosis membrane, and the membrane assembly of the tubular reverse osmosis membrane is one or more membrane assembly combinations. The primary nanofiltration system and the secondary nanofiltration system use ordinary or high-pressure nanofiltration membranes, and the membrane assembly of the nanofiltration membrane is one or more membrane assembly combinations. The method comprises the following steps: S1: high-salinity wastewater is collected by a pipeline into a wastewater collection tank, and the high-salinity wastewater in the wastewater collection tank is homogenized and homogenized by a stirrer or a pre-aeration stirring device in the wastewater collection tank; S2: the homogenized and homogenized high-salinity wastewater is lifted by a wastewater lifting pump to a pretreatment system to remove organic matter, ammonia nitrogen, total nitrogen, hardness, alkalinity, suspended matter, and colloidal pollutants; S3: the pretreated high-salinity wastewater is pumped into a filtration system to further remove suspended matter and colloidal matter in the wastewater; S4: the filtered water is pumped into a reverse osmosis system, and after concentration and desalination, high-salinity wastewater and water are obtained, and the water is introduced into a reuse water collection tank; S5: the high-salinity wastewater obtained in step S4 is further removed of hardness and organic matter and then pumped into a primary nanofiltration system, and through the separation of monovalent and divalent ions by the nanofiltration membrane, the divalent ions are retained on the concentrated water side, and the monovalent ions are separated to the water production side to obtain concentrated water and water; the concentrated water is then introduced into a crystallization system 6A; S6: the water obtained in step S5 is introduced into an electrodialysis system to concentrate and desalinate to obtain high-salinity wastewater and water; the water is introduced into a reuse water collection tank; and the high-salinity wastewater is further removed of hardness and organic matter and then pumped into a secondary nanofiltration system, and through the separation of monovalent and divalent ions by the nanofiltration membrane, the divalent ions are retained on the concentrated water side, and the monovalent ions are separated to the water production side to obtain concentrated water and water; S7: the concentrated water obtained in step S6 is introduced into a crystallization system 6A to evaporate and crystallize sodium sulfate products, and the condensed water is returned to the wastewater collection tank; and the water is introduced into a crystallization system 9B to evaporate and crystallize sodium chloride products, and the condensed water is returned to the wastewater collection tank. The wastewater collection tank is provided with a stirrer or a pre-aeration stirring device.

2. The method of claim 1, wherein, The pretreatment system comprises one or more combinations of removal units for removing organic matter, ammonia nitrogen, total nitrogen, hardness, alkalinity, suspended matter, and colloidal pollutants.

3. The method of claim 1, wherein, The filtration system comprises one or more filtration devices such as sand filtration, multi-media filtration, and ultrafiltration.

4. The method of claim 1, wherein, ​ 5. The method of claim 1, wherein, The evaporation crystallization system 6A and the evaporation crystallization system 9B are single- or multi-stage combined evaporators, including multiple-effect evaporation and / or MVR evaporators.

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