Treatment method and treatment system for high-salinity wastewater zero-discharge evaporative crystallization mother liquor

Abstract

The invention relates to a treatment method and a treatment system for zero-discharge evaporative crystallization mother liquor of high-salinity wastewater, and the treatment method comprises the following steps: (1) after the zero-discharge evaporative crystallization mother liquor of the high-salinity wastewater is pretreated, carrying out primary loose nanofiltration treatment to obtain primary trapped fluid and primary permeated fluid; (2) carrying out advanced oxidation treatment on the primary permeate to obtain a treated solution; (3) carrying out secondary salt separation nanofiltration treatment on the treated solution to obtain a secondary trapped fluid and a secondary permeate; and (4) respectively carrying out evaporative crystallization treatment on the secondary trapped fluid and the secondary permeated fluid to obtain a salt product. The treatment method provided by the invention can simultaneously realize deep decolorization, efficient salt separation and resource recycling of the evaporative crystallization mother liquor, solves the problems of membrane pollution and inorganic scaling in a nanofiltration membrane process to a certain extent, and breaks through the difficult problem of mother liquor treatment with zero discharge of high-salinity wastewater.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and particularly relates to a treatment method and a treatment system for the evaporation crystallization mother liquor of zero-discharge of high-salt wastewater. Background Art

[0002] In the process of zero-discharge of industrial saline wastewater, a large amount of evaporation crystallization mother liquor is usually generated. This evaporation mother liquor has significant characteristics: extremely high salt concentration (total dissolved salts TDS≥20%), complex salt ion composition, containing Cl - , SO4 2- , Na + , K + and other mixed salts, residual refractory organic matters (such as benzene series compounds, heterocyclic compounds) and colloids in the zero-discharge process, resulting in a deep color (>500 times), high organic matter content; high calcium and magnesium content, and strong scaling tendency.

[0003] The above characteristics make the zero-discharge evaporation crystallization mother liquor extremely difficult to treat. At present, the main methods for treating the evaporation mother liquor are to add evaporation aids and then heat and evaporate to dryness to obtain miscellaneous salts for stacking or hand over to a professional company for treatment. If the evaporation mother liquor is directly reused without treatment, it will cause system scaling and a decrease in the purity of the product salt; the chemical softening + resin adsorption process has a high cost and will also generate secondary hazardous wastes; the flux of conventional nanofiltration membranes decays rapidly under the competitive adsorption conditions of high salt and high organic matter, and the salt separation selectivity is low, making it difficult to realize the resource utilization of salts.

[0004] CN115093081A discloses a method and a treatment system for deep treatment of coking wastewater in a steel plant, including pre-treating coking wastewater in a pretreatment module; the pre-treated coking wastewater enters a nanofiltration module for treatment; the water produced by the nanofiltration module enters a reverse osmosis module for treatment; the water produced by the reverse osmosis module enters an evaporation crystallization device for treatment, and the sodium chloride salt produced by the evaporation crystallization device is utilized as industrial salt.

[0005] CN118908471A discloses a method for treating coking wastewater, including subjecting coking wastewater to nanofiltration treatment; subjecting the nanofiltration-produced water to reverse osmosis treatment; subjecting the reverse osmosis concentrate to defluorination and desilication treatment; subjecting the reverse osmosis concentrate after the defluorination and desilication treatment to evaporation crystallization treatment; subjecting the nanofiltration concentrate and the evaporation crystallization mother liquor to electrocatalytic oxidation treatment, and using a boron-doped diamond electrode as the anode in the electrocatalytic oxidation, which solves the problem of treating the membrane concentrate of existing coking wastewater.

[0006] CN112624505A discloses a method for treating the evaporation mother liquor of high-salt wastewater, which includes subjecting the high-salt wastewater to nanofiltration treatment after pretreatment. After the filtrate is subjected to evaporation and crystallization treatment to precipitate sodium chloride product salt, a sodium chloride evaporation mother liquor is obtained. After the retentate is evaporated and concentrated and then subjected to freeze crystallization treatment to precipitate mirabilite, a sodium sulfate freeze mother liquor is obtained. Nanofiltration treatment can separate sodium chloride and sodium sulfate in the high-salt wastewater; reduce the salt content of the organic matter treatment and biochemical treatment mother liquor, thereby improving the effects of organic matter treatment and biochemical treatment.

[0007] Generally, for high-content organic wastewater, the biochemical method is considered the most economical disposal means, but the high salinity in the zero-discharge evaporation crystallization mother liquor limits the use of the biochemical method. Therefore, there is an urgent need for an effective method to achieve low-cost treatment of the zero-discharge evaporation crystallization mother liquor of high-salt wastewater. Summary of the Invention

[0008] To solve the above technical problems, the present invention provides a method and a treatment system for treating the zero-discharge evaporation crystallization mother liquor of high-salt wastewater. The treatment method of the present invention realizes the separation and recovery of organic and inorganic resources in the evaporation crystallization mother liquor with high organic matter and high salt through the core two-stage nanofiltration process, integrating advanced oxidation treatment and evaporation crystallization process, and solves the coexistence problem of high salt and high organic matter in the evaporation mother liquor.

[0009] To achieve this purpose, the present invention adopts the following technical solutions:

[0010] In the first aspect, the present invention provides a method for treating the zero-discharge evaporation crystallization mother liquor of high-salt wastewater, and the treatment method includes the following steps:

[0011] (1) After the zero-discharge evaporation crystallization mother liquor of high-salt wastewater is pretreated, it is subjected to first-stage loose nanofiltration treatment to obtain a first-stage retentate and a first-stage permeate;

[0012] (2) The first-stage permeate is subjected to advanced oxidation treatment to obtain a treated solution;

[0013] (3) The treated solution is subjected to second-stage salt separation nanofiltration treatment to obtain a second-stage retentate and a second-stage permeate;

[0014] (4) The second-stage retentate and the second-stage permeate are respectively subjected to evaporation crystallization treatment to obtain salt products.

[0015] The present invention treats the zero-discharge evaporation crystallization mother liquor of high-salt wastewater through an integrated process of two-stage nanofiltration - advanced oxidation - evaporation crystallization, realizing deep decolorization, efficient salt separation and resource recycling of the evaporation crystallization mother liquor, breaking through the "last mile" problem of zero-discharge of high-salt wastewater, solving the coexistence problem of high salt and high organic matter in the evaporation mother liquor, and at the same time, through the control of operating parameters, etc., enabling both stages of nanofiltration to operate stably.

[0016] It should be noted that in the present invention, the pretreated evaporation mother liquor is subjected to primary loose nanofiltration treatment. Among them, the salt components pass through the nanofiltration membrane, while most of the organic matters are intercepted by the nanofiltration membrane, so as to achieve the rough separation of organic matters and salts; the primary retentate changes from a high-salt and high-organic matter solution to a low-salt and high-organic matter solution, which can be returned to the biochemical system or the incineration system for disposal; the primary permeate becomes a high-salt and low-organic matter solution for advanced oxidation treatment.

[0017] As a preferred technical solution of the present invention, the pretreatment in step (1) includes adding a flocculant and a coagulant to the evaporation crystallization mother liquor with zero discharge of high-salt wastewater, and then performing solid-liquid separation treatment.

[0018] Through the pretreatment process, the present invention can remove suspended particles and macromolecular colloids in the evaporation crystallization mother liquor with zero discharge of high-salt wastewater.

[0019] Preferably, the flocculant includes any one or at least two combinations of polyaluminum chloride, polyferric sulfate, ferric trichloride or polyacrylamide. Typical but non-limiting examples of the combination are: polyaluminum chloride and polyferric sulfate, polyferric sulfate and ferric trichloride, ferric trichloride and polyacrylamide, polyaluminum chloride and polyacrylamide, etc.

[0020] Preferably, the solid-liquid separation treatment includes any one or at least two combinations of plate-and-frame filtration, multi-media filtration, ceramic membrane filtration or tubular membrane filtration. Typical but non-limiting examples of the combination are: plate-and-frame filtration and multi-media filtration, multi-media filtration and ceramic membrane filtration, ceramic membrane filtration and tubular membrane filtration, plate-and-frame filtration and tubular membrane filtration, etc.

[0021] Preferably, the operating precision of the solid-liquid separation treatment is not greater than 0.2 μm, such as 0.1 μm, 0.12 μm, 0.14 μm, 0.16 μm, 0.18 μm, etc., but is not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0022] As a preferred technical solution of the present invention, the cut-off molecular weight of the nanofiltration membrane used in the primary loose nanofiltration treatment in step (1) is 400-1000 Da, such as 400 Da, 500 Da, 600 Da, 700 Da, 800 Da, 900 Da, 1000 Da, etc., but is not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0023] The rejection rate of sodium sulfate is 10-50%, such as 10%, 20%, 30%, 40%, 50%, etc., but is not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0024] In the present invention, a loose nanofiltration membrane resistant to organic pollution and salt softening is selected for the first-stage loose nanofiltration, and the molecular weight cut-off (MWCO) is limited to 400-1000 Da, which can preferentially retain macromolecular organic matters (pigments) and colloids, and partially retain divalent salts (such as SO4 2- , Ca 2+ , Mg 2+ ), thereby reducing the subsequent scaling risk.

[0025] Preferably, the operating pH of the first-stage loose nanofiltration treatment is 7-10, such as 7, 7.5, 8, 8.5, 9, 9.5, 10, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0026] Preferably, the operating pressure of the first-stage loose nanofiltration treatment is 1.0-3.5 MPa, such as 1.0 MPa, 1.5 MPa, 2.0 MPa, 2.5 MPa, 3.0 MPa, 3.5 MPa, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0027] Preferably, the operating temperature of the first-stage loose nanofiltration treatment is 40-50 °C, such as 40 °C, 42 °C, 44 °C, 46 °C, 48 °C, 50 °C, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0028] The water production rate of the first-stage loose nanofiltration treatment is 75-90%, such as 75%, 80%, 85%, 90%, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0029] In the present invention, by regulating the pH of the first-stage loose nanofiltration, membrane surface fouling can be reduced and organic matter deposition can be inhibited; by regulating the operating pressure and operating temperature of the first-stage loose nanofiltration, the stable operation of the system can be ensured, and finally, an organic matter removal rate of more than 95% can be achieved, and the divalent salt retention rate is less than 30%.

[0030] Preferably, the first-stage retentate is subjected to biochemical treatment or incineration treatment.

[0031] As a preferred technical solution of the present invention, the first-stage loose nanofiltration treatment in step (1) includes a treatment method of adding water for nanofiltration; the washing and filtering multiple of the adding water for nanofiltration is 1-10 times, such as 1 time, 2 times, 4 times, 6 times, 8 times, 10 times, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0032] It should be noted that in the process of primary loose nanofiltration treatment, those skilled in the art can adopt the method of washing and filtering with water according to the concentration of the evaporation crystallization mother liquor of zero-discharge of high-salt wastewater, and the multiple of adding water can be adaptively adjusted according to the concentration of the evaporation crystallization mother liquor of zero-discharge of high-salt wastewater.

[0033] As a preferred technical solution of the present invention, before performing the primary loose nanofiltration treatment described in step (1), a complexing agent is further added to the pretreatment solution.

[0034] Preferably, the complexing agent includes any one or a combination of at least two of ethylenediaminetetraacetic acid, ethylene glycol bis(2-aminoethyl ether)-N,N,N',N'-tetraacetic acid, diethylenetriaminepentaacetic acid, or hydroxyethyl ethylenediamine triacetic acid. Typical but non-limiting examples of the combination are: ethylenediaminetetraacetic acid and ethylene glycol bis(2-aminoethyl ether)-N,N,N',N'-tetraacetic acid, ethylene glycol bis(2-aminoethyl ether)-N,N,N',N'-tetraacetic acid and diethylenetriaminepentaacetic acid, diethylenetriaminepentaacetic acid and hydroxyethyl ethylenediamine triacetic acid, hydroxyethyl ethylenediamine triacetic acid and ethylenediaminetetraacetic acid, etc.

[0035] By adding a complexing agent to the pretreatment solution, the present invention can form complexes with impurity ions such as calcium and magnesium, which are then intercepted by the primary loose nanofiltration.

[0036] As a preferred technical solution of the present invention, the advanced oxidation treatment described in step (2) includes any one or a combination of at least two of Fenton treatment, electrocatalytic oxidation treatment, or ozone oxidation treatment. Typical but non-limiting examples of the combination are: Fenton treatment and electrocatalytic oxidation treatment, electrocatalytic oxidation treatment and ozone oxidation treatment, Fenton treatment and ozone oxidation treatment.

[0037] Through the advanced oxidation treatment, the present invention can deeply remove the residual organic matter in the primary permeate, thereby reducing the risk of membrane fouling in the secondary salt separation nanofiltration and facilitating the subsequent secondary salt separation nanofiltration.

[0038] As a preferred technical solution of the present invention, the nanofiltration membrane used in the secondary salt separation nanofiltration treatment in step (3) has a cut-off molecular weight of 200 - 400 Da, such as 200 Da, 250 Da, 300 Da, 350 Da, 400 Da, etc., but is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0039] The rejection rate of sodium sulfate is above 95%, such as 95%, 96%, 97%, 98%, 99%, etc., but is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0040] The rejection rate of sodium chloride is 10 - 30%, such as 10%, 15%, 20%, 25%, 30%, etc., but is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0041] Preferably, the operating pH of the secondary salt-splitting nanofiltration treatment is 4 - 6, such as 4, 4.5, 5, 5.5, 6, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0042] Preferably, the operating temperature of the secondary salt-splitting nanofiltration treatment is 40 - 50 °C, such as 40 °C, 42 °C, 44 °C, 46 °C, 48 °C, 50 °C, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0043] Preferably, the operating pressure of the secondary salt-splitting nanofiltration treatment is 1.5 - 4.0 MPa, such as 1.5 MPa, 2.0 MPa, 2.5 MPa, 3.0 MPa, 3.5 MPa, 4.0 MPa, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0044] The water production rate of the secondary salt-splitting nanofiltration treatment is 75 - 90%, such as 75%, 80%, 85%, 90%, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0045] In the present invention, the secondary salt-splitting nanofiltration uses a negatively charged nanofiltration membrane, with the defined molecular weight cut-off (MWCO) of 200 - 400 Da. The salt-splitting nanofiltration membrane utilizes the charge repulsion effect to enhance the separation of monovalent / divalent ions; by regulating the operating pH of the secondary salt-splitting nanofiltration, the repulsive force of anions can be enhanced; by regulating the operating pressure and operating temperature of the secondary salt-splitting nanofiltration, the optimized and stable operation of the system can be ensured, and finally, the Cl - transmittance > 90%, SO4 2- retention rate > 95%, NaCl (purity ≥ 98%) is enriched on the water production side, and Na2SO4 (purity ≥ 90%) is enriched in the retentate, which can be directly recycled to the evaporation crystallization system or can be separately evaporated and crystallized according to the situation, thereby realizing the separation of miscellaneous salts.

[0046] As a preferred technical solution of the present invention, the evaporation crystallization treatment described in step (4) includes any one of multi-effect evaporation, vacuum flash evaporation crystallization, mechanical vapor recompression, spray drying, or freeze crystallization.

[0047] In the second aspect, the present invention provides a treatment system for use in the treatment method as described in the first aspect. The treatment system includes a pretreatment module, a primary loose nanofiltration module, an advanced oxidation module, a secondary salt-splitting nanofiltration module, and an evaporation crystallization module connected in series in sequence;

[0048] The retention zone and the water production zone of the secondary salt-splitting nanofiltration module are respectively connected to the evaporation crystallization module; the retention zone of the primary loose nanofiltration module is connected to the post-treatment module.

[0049] As a preferred technical solution of the present invention, the pretreatment module includes a chemical dosing tank and a filtering device; the post-treatment device includes a biochemical device or an incineration device.

[0050] Compared with the prior art, the present invention has at least the following beneficial effects:

[0051] (1) By integrally using a loose nanofiltration membrane and a salt-splitting nanofiltration membrane, the present invention solves the problem of separating organic substances and inorganic substances in the evaporation mother liquor. The separated primary retentate is easier to dispose of, thus realizing resource treatment.

[0052] (2) While separating organic substances in the primary loose nanofiltration treatment of the present invention, by adding a complexing agent, the pollution and scaling in the primary loose nanofiltration treatment process are inhibited, and the operation load of the secondary salt-splitting nanofiltration treatment is also reduced.

[0053] (3) After directional salt splitting and then concentration through secondary salt-splitting nanofiltration of the present invention, the total evaporation energy consumption can be greatly reduced.

[0054] (4) Through the integrated technology of primary loose nanofiltration and secondary salt-splitting nanofiltration, the present invention realizes the resource utilization and low-cost disposal of organic substances and inorganic salts in the evaporation crystallization mother liquor of high-salt wastewater zero discharge. The mother liquor is reduced by more than 90%, and the problem of mother liquor disposal in industrial wastewater zero discharge is solved at low cost, which is of great significance for promoting the popularization and implementation of zero discharge. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 is a process flow chart of a method for treating evaporation crystallization mother liquor of high-salt wastewater zero discharge provided by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0056] The technical solution of the present invention will be further described below with reference to the drawings and through specific embodiments. However, the following examples are only simple examples of the present invention and do not represent or limit the scope of the protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0057] Example 1

[0058] This example provides a method for treating evaporation crystallization mother liquor of high-salt wastewater zero discharge. The evaporation crystallization mother liquor of high-salt wastewater zero discharge is the evaporation mother liquor of printing and dyeing wastewater. The composition of the evaporation mother liquor of printing and dyeing wastewater is: 18% NaCl, 12% Na2SO4, chemical oxygen demand (COD) 2500 mg / L (including anthraquinone dyes), and chromaticity 600 times. The process flow chart of the treatment method is as Figure 1 shown;

[0059] The treatment method includes the following steps:

[0060] (1) Add 20 mg / L of polyaluminum chloride to the evaporation mother liquor of the printing and dyeing wastewater, and then filter it using a ceramic membrane; add an ethylenediaminetetraacetic acid complexing agent to the permeate of the ceramic membrane, and then perform primary loose nanofiltration treatment; the cut-off molecular weight of the nanofiltration membrane used in the primary loose nanofiltration treatment is 600 - 800 Da, the operating pressure is 3.0 MPa, the operating pH is 9.0, and the washing and filtration method is adopted twice; the COD of the primary retentate is 3000 mg / L, and the total salinity is 12%;

[0061] The COD of the primary permeate drops to 200 mg / L, the chromaticity drops to 30 times, the sodium sulfate concentration drops to 3.5%, and the sodium chloride concentration drops to 6%;

[0062] (2) Perform electrocatalytic oxidation treatment on the primary permeate, and the COD of the treated solution drops below 100 mg / L;

[0063] (3) Perform secondary salt separation nanofiltration treatment on the treated solution; the cut-off molecular weight of the nanofiltration membrane used in the secondary salt separation nanofiltration treatment is 300 Da, the operating pressure is 4.0 MPa, and the operating pH is 5.0; the NaCl concentration of the secondary permeate is 6.2%, and the NaCl recovery rate is 70%; the Na2SO4 concentration of the secondary retentate is 12.8%, and the Na2SO4 recovery rate is 60%;

[0064] (4) Perform multi-effect evaporation treatment on the secondary retentate and the secondary permeate respectively to obtain salt products.

[0065] Example 2

[0066] This example provides a treatment method for the evaporation crystallization mother liquor of high-salt wastewater with zero discharge. The evaporation crystallization mother liquor of high-salt wastewater with zero discharge is the evaporation mother liquor of coking wastewater; the composition of the evaporation mother liquor of coking wastewater is: 18% NaCl, 4% Na2SO4, 5% other miscellaneous salts, and chemical oxygen demand (COD) 60000 mg / L;

[0067] The treatment method includes the following steps:

[0068] (1) Add 40 mg / L of polyaluminum chloride and 4 ppm of polyacrylamide to the evaporation mother liquor of the printing and dyeing wastewater, and then filter it using a tubular membrane; the COD of the permeate of the tubular membrane drops to 40000 mg / L;

[0069] Ethylene glycol diethyletherdiamine tetraacetic acid complexing agent is added to the permeate of the tubular membrane, and then primary loose nanofiltration treatment is carried out; the cut-off molecular weight of the nanofiltration membrane used in the primary loose nanofiltration treatment is 800-1000 Da, the operating pressure is 3.5 MPa, the operating pH is 7.0, and the 3-fold washing and filtration method is adopted; the COD of the primary retentate obtained is 42000 mg / L, and the total salinity is less than 6%;

[0070] The COD of the primary permeate is reduced to 2000 mg / L, the concentration of sodium sulfate is reduced to 1.0%, the concentration of sodium chloride is reduced to 4%, and the concentration of miscellaneous salts is reduced to 1.2%;

[0071] (2) The primary permeate is subjected to electrocatalytic oxidation treatment, and the COD of the treated solution obtained is reduced to less than 200 mg / L;

[0072] (3) The treated solution is subjected to secondary salt separation nanofiltration treatment; the cut-off molecular weight of the nanofiltration membrane used in the secondary salt separation nanofiltration treatment is 300 Da, the operating pressure is 3.5 MPa, and the operating pH is 6.0; the NaCl concentration of the secondary permeate obtained is 5.5%, and the NaCl recovery rate is 76%; the Na2SO4 concentration of the secondary retentate is 4.0%, and the Na2SO4 recovery rate is 64%;

[0073] (4) The secondary retentate and the secondary permeate are respectively subjected to vacuum flash evaporation crystallization treatment to obtain salt products.

[0074] Example 3

[0075] This example provides a treatment method for the zero-discharge evaporation crystallization mother liquor of high-salt wastewater, and the zero-discharge evaporation crystallization mother liquor of high-salt wastewater is the evaporation mother liquor of coking wastewater; the composition of the evaporation mother liquor of coking wastewater is: 18% NaCl, 4% Na2SO4, 5% other miscellaneous salts, and chemical oxygen demand (COD) 60000 mg / L;

[0076] The treatment method includes the following steps:

[0077] (1) 40 mg / L of polyferric sulfate and 4 ppm of polyacrylamide are added to the evaporation mother liquor of the printing and dyeing wastewater, and then filtered by a tubular membrane; the COD of the permeate of the tubular membrane is reduced to 40000 mg / L;

[0078] Hydroxyethyl ethylenediamine triacetic acid complexing agent is added to the permeate of the tubular membrane, and then primary loose nanofiltration treatment is carried out; the cut-off molecular weight of the nanofiltration membrane used in the primary loose nanofiltration treatment is 400-600 Da, the operating pressure is 1.0 MPa, the operating pH is 7.0, and the 1-fold washing and filtration method is adopted; the COD of the primary retentate obtained is 45000 mg / L, and the total salinity is less than 13%;

[0079] The COD of the primary permeate is reduced to 1500 mg / L, the sodium sulfate concentration is reduced to 2%, the sodium chloride concentration is reduced to 9%, and the concentration of miscellaneous salts is reduced to 2%;

[0080] (2) The primary permeate is subjected to Fenton treatment, and the COD of the treated solution obtained is reduced to below 150 mg / L;

[0081] (3) The treated solution is subjected to secondary salt separation nanofiltration treatment; the nanofiltration membrane used in the secondary salt separation nanofiltration treatment has a cut-off molecular weight of 200 Da, an operating pressure of 1.5 MPa, and an operating pH of 6.0; the NaCl concentration of the secondary permeate obtained is 8%, and the NaCl recovery rate is 80%; the Na2SO4 concentration of the secondary retentate is 8%, and the Na2SO4 recovery rate is 75%;

[0082] (4) The secondary retentate and the secondary permeate are respectively subjected to mechanical vapor recompression treatment to obtain salt products.

[0083] Example 4

[0084] This example provides a method for treating the zero-discharge evaporation crystallization mother liquor of high-salt wastewater, and the zero-discharge evaporation crystallization mother liquor of high-salt wastewater is the evaporation mother liquor of coking wastewater; the composition of the evaporation mother liquor of coking wastewater is: 18% NaCl, 4% Na2SO4, 5% other miscellaneous salts, and chemical oxygen demand (COD) 60000 mg / L;

[0085] The treatment method includes the following steps:

[0086] (1) Add 40 mg / L of ferric chloride and 4 ppm of polyacrylamide to the evaporation mother liquor of the printing and dyeing wastewater, and then filter it using a tubular membrane; the COD of the permeate of the tubular membrane is reduced to 40000 mg / L;

[0087] Add a diethylenetriaminepentaacetic acid complexing agent to the permeate of the tubular membrane, and then perform primary loose nanofiltration treatment; the nanofiltration membrane used in the primary loose nanofiltration treatment has a cut-off molecular weight of 1000 Da, an operating pressure of 2.0 MPa, an operating pH of 7.0, and a washing and filtration method of 10 times; the COD of the primary retentate obtained is 30000 mg / L, and the total salinity is less than 1%;

[0088] The COD of the primary permeate is reduced to 2500 mg / L, the sodium sulfate concentration is reduced to 0.5%, the sodium chloride concentration is reduced to 2%, and the concentration of miscellaneous salts is reduced to 0.6%;

[0089] (2) The primary permeate is subjected to Fenton treatment, and the COD of the treated solution obtained is reduced to below 250 mg / L;

[0090] (3) The treated solution is subjected to secondary salt separation nanofiltration treatment; the molecular weight cut-off of the nanofiltration membrane used in the secondary salt separation nanofiltration treatment is 400 Da, the operating pressure is 3.5 MPa, and the operating pH is 6.0; the NaCl concentration of the secondary permeate obtained is 1.9%, and the NaCl recovery rate is 85.5%; the Na2SO4 concentration of the secondary retentate is 4.5%, and the Na2SO4 recovery rate is 90%;

[0091] (4) The secondary retentate and the secondary permeate are respectively subjected to freeze crystallization treatment to obtain salt products.

[0092] Example 5

[0093] This example provides a method for treating the zero-discharge evaporation crystallization mother liquor of high-salt wastewater. The difference from Example 2 is only that in step (1), no complexing agent is added, and the permeate of the tubular membrane is directly subjected to primary loose nanofiltration treatment, and other steps and parameter settings are the same as those in Example 2.

[0094] Comparative Example 1

[0095] This comparative example provides a method for treating the zero-discharge evaporation crystallization mother liquor of high-salt wastewater. The difference from Example 1 is only that the primary loose nanofiltration treatment in step (1) is omitted, and the solution after pretreatment is directly subjected to advanced oxidation treatment, and other steps and parameter settings are the same as those in Example 1.

[0096] Comparative Example 2

[0097] This comparative example provides a method for treating the zero-discharge evaporation crystallization mother liquor of high-salt wastewater. The difference from Example 1 is only that the secondary salt separation nanofiltration treatment in step (3) is omitted, and the solution after advanced oxidation treatment is directly subjected to evaporation crystallization treatment, and other steps and parameter settings are the same as those in Example 1.

[0098] Comparative Example 3

[0099] This comparative example provides a method for treating the zero-discharge evaporation crystallization mother liquor of high-salt wastewater. The difference from Example 1 is only that the primary loose nanofiltration treatment in step (1) is changed to primary salt separation nanofiltration treatment, and the nanofiltration membrane and operating parameters used are the same as those in the secondary salt separation nanofiltration treatment in step (3), and other steps and parameter settings are the same as those in Example 1.

[0100] Comparative Example 4

[0101] This comparative example provides a method for treating the zero-discharge evaporation crystallization mother liquor of high-salt wastewater. The difference from Example 1 is only that the secondary salt separation nanofiltration treatment in step (3) is changed to secondary loose nanofiltration treatment, and the nanofiltration membrane and operating parameters used are the same as those in the primary loose nanofiltration treatment in step (1), and other steps and parameter settings are the same as those in Example 1.

[0102] Performance test

[0103] The chemical oxygen demand (COD), NaCl recovery rate, and Na2SO4 recovery rate of the secondary permeate and secondary retentate in Examples 1-5 and Comparative Examples 1-4 were tested, and the test results are shown in Table 1.

[0104] Table 1

[0105]

[0106]

[0107] Performance analysis

[0108] (1) It can be seen from Examples 1-4 that through the integrated technology of primary loose nanofiltration and secondary salt-splitting nanofiltration in the present invention, the resource utilization and low-cost disposal of organic matters and inorganic salts in the evaporation mother liquor are realized. The recovery rate of sodium chloride in the secondary permeate is more than 70%, and the recovery rate of sodium sulfate in the secondary retentate is more than 60%. It solves the problem of mother liquor disposal in industrial wastewater zero discharge at low cost, which is of great significance for promoting the popularization and implementation of zero discharge.

[0109] (2) It can be seen from the comparison between Example 2 and Example 5 that no complexing agent was added in Example 5, resulting in poor removal of heterovalent salt ions, which affected the separation of monovalent / divalent ions in the secondary salt-splitting nanofiltration process and led to a decrease in the recovery rates of sodium chloride and sodium sulfate.

[0110] (3) It can be seen from Example 1 and Comparative Examples 1-4 that whether the primary loose nanofiltration treatment and secondary salt-splitting nanofiltration treatment were omitted in Comparative Examples 1 and 2, or the primary loose nanofiltration treatment was replaced by primary salt-splitting nanofiltration, or the secondary salt-splitting nanofiltration was replaced by secondary loose nanofiltration in Comparative Examples 3 and 4, the recovery rates of sodium chloride and sodium sulfate would be significantly reduced.

[0111] In summary, the present invention provides a treatment method and treatment system for the evaporation crystallization mother liquor of high-salt wastewater with zero discharge. The present invention treats the evaporation crystallization mother liquor of high-salt wastewater with zero discharge through an integrated process of secondary nanofiltration - advanced oxidation - evaporation crystallization, realizing the deep decolorization, efficient salt splitting, and resource recycling of the evaporation crystallization mother liquor, breaking through the "last mile" problem of high-salt wastewater zero discharge; the primary loose nanofiltration can remove most of the organic matters and colloids in the evaporation crystallization mother liquor, and the secondary salt-splitting nanofiltration separates monovalent / divalent ions, reducing the total energy consumption of evaporation crystallization and obtaining economically beneficial products; the treatment method of the present invention solves the problem of mother liquor disposal in industrial wastewater zero discharge at low cost, which is of great significance for promoting the popularization and implementation of zero discharge.

[0112] The applicant declares that the above description is only a specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A treatment method for the evaporation crystallization mother liquor of zero - discharge of high - salt wastewater, characterized in that, The described treatment method includes the following steps: (1) After the zero-discharge evaporation crystallization mother liquor of high-salt wastewater is pretreated, it is subjected to primary loose nanofiltration treatment to obtain a primary retentate and a primary permeate; (2) The primary permeate is subjected to advanced oxidation treatment to obtain a treated solution; (3) The treated solution is subjected to secondary salt separation nanofiltration treatment to obtain a secondary retentate and a secondary permeate; (4) The secondary retentate and the secondary permeate are respectively subjected to evaporation crystallization treatment to obtain salt products.

2. The processing method according to claim 1, wherein The pretreatment in step (1) includes adding a flocculant and a coagulant to the zero-discharge evaporation crystallization mother liquor of high-salt wastewater, and then performing solid-liquid separation treatment; Preferably, the flocculant includes any one or a combination of at least two of polyaluminum chloride, polyferric sulfate, ferric trichloride, or polyacrylamide; Preferably, the solid-liquid separation treatment includes any one or a combination of at least two of plate-and-frame filtration, multi-media filtration, ceramic membrane filtration, or tubular membrane filtration; Preferably, the operating precision of the solid-liquid separation treatment is not greater than 0.2 μm.

3. The processing method according to claim 1 or 2, characterized in that, The nanofiltration membrane used in the primary loose nanofiltration treatment in step (1) has a molecular weight cut-off of 400-1000 Da and a rejection rate of sodium sulfate of 10-50%; Preferably, the operating pressure of the primary loose nanofiltration treatment is 1.0-3.5 MPa; the water production rate of the primary loose nanofiltration treatment is 75-90%; Preferably, the primary retentate is subjected to biochemical treatment or incineration treatment.

4. The processing method according to any one of claims 1-3, characterized in that The primary loose nanofiltration treatment in step (1) includes a treatment method of adding water for nanofiltration; the washing and filtration multiple of the adding water for nanofiltration is 1-10 times.

5. The processing method according to any one of claims 1-4, characterized in that, Before performing the primary loose nanofiltration treatment in step (1), a complexing agent is further added to the pretreatment solution; Preferably, the complexing agent includes any one or a combination of at least two of ethylenediaminetetraacetic acid, ethylene glycol diethyl ether diamine tetraacetic acid, diethylenetriamine pentaacetic acid, or hydroxyethyl ethylenediamine triacetic acid.

6. The processing method according to any one of claims 1-5, characterized in that The advanced oxidation treatment in step (2) includes any one or a combination of at least two of Fenton treatment, electrocatalytic oxidation treatment, or ozone oxidation treatment.

7. The processing method according to any one of claims 1-6, characterized in that, The nanofiltration membrane used in the secondary salt separation nanofiltration treatment in step (3) has a molecular weight cut-off of 200-400 Da, a rejection rate of sodium sulfate of more than 95%, and a rejection rate of sodium chloride of 10-30%; Preferably, the operating pressure of the secondary salt separation nanofiltration treatment is 1.5-4.0 MPa; the water production rate of the secondary salt separation nanofiltration treatment is 75-90%.

8. The processing method according to any one of claims 1-7, characterized in that, The evaporation crystallization treatment in step (4) includes any one of multi-effect evaporation, vacuum flash evaporation crystallization, mechanical vapor recompression, spray drying, or freeze crystallization.

9. A processing system used for the processing method according to any one of claims 1-8, characterized in that The treatment system includes a pretreatment module, a primary loose nanofiltration module, an advanced oxidation module, a secondary salt separation nanofiltration module, and an evaporation crystallization module connected in series in sequence; The retentate area and the water production area of the secondary salt separation nanofiltration module are respectively connected to the evaporation crystallization module; the retentate area of the primary loose nanofiltration module is connected to the post-treatment module.

10. The processing system according to claim 9, wherein The pretreatment module includes a chemical dosing tank and a filtration device; the post-treatment device includes a biochemical device or an incineration device.

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