Zero-discharge treatment process for salt-containing wastewater

Abstract

A zero-discharge treatment process for salt-containing wastewater belongs to the field of water treatment, and comprises the following steps: high-salt wastewater enters a primary reaction device, ettringite precipitation is generated by using an ultrahigh lime aluminum method and the wastewater to remove sulfate ions in the water, and a flocculating agent is added for precipitation; the second-stage reaction device adopts a dual-alkali method to remove hardness, calcium and magnesium ions in water and metal ions generated by an ultrahigh lime-aluminum method; hydrochloric acid is added behind an effluent weir of the inclined tube sedimentation tank, and effluent enters a sand filter; the high-salinity wastewater is filtered by the sand filter, and the effluent enters an ultrafiltration device; an ion exchanger deeply removes metal cations or sulfate ions in water, and effluent enters an ozone nano microbubble reactor; organic matters in water are removed by the ozone nano microbubble reactor, and effluent enters a reverse osmosis device; the reverse osmosis device is used for concentrating and reducing the wastewater, and evaporative crystallization is carried out; water is concentrated through evaporative crystallization, and produced sodium chloride resources are recycled. The method is used for zero discharge treatment of salt-containing wastewater.

Description

Technical Field

[0001] The present invention belongs to the technical field of water treatment, and particularly relates to a zero-discharge treatment process for saline wastewater. Background Art

[0002] High-salt wastewater refers to wastewater with a total salt content greater than 1%, which has a wide range of sources, including industrial water drainage in coastal cities, industrial production drainage such as printing and dyeing refining, saline domestic sewage generated by seawater utilization, and high-salt groundwater in some areas. Its composition is complex, often containing various salts, organic substances, heavy metal ions, etc., with poor biodegradability and high treatment difficulty.

[0003] Nanofiltration membrane desalination technology uses the pressure difference as the driving force, and utilizes the selective permeability of the nanofiltration membrane to different valence ions and the interception effect on specific solutes to synchronize concentration and desalination, and can effectively intercept organic substances and part of the salts. However, the nanofiltration membrane is easily contaminated during use, has relatively strict requirements for the quality of the influent water, and moreover, the overall investment cost and operating cost of the nanofiltration membrane are relatively high, and the resource utilization rate of the miscellaneous salts prepared from the concentrated solution is not high.

[0004] Existing zero-discharge technologies for high-salt wastewater mostly use nanofiltration membranes to intercept divalent miscellaneous salts. However, the overall investment cost of the nanofiltration membrane is relatively high, and the resource utilization rate of the miscellaneous salts prepared from the nanofiltration membrane concentrated solution is not high, and additional external treatment is required, increasing the cost. During the desalination process of the nanofiltration membrane, it is easy to cause pollution, the maintenance cost is relatively high, and it needs to be replaced regularly, resulting in a high overall operating cost. The salt content of high-salt wastewater is relatively high, and its biodegradability is poor. Using traditional biological methods to treat the organic substances in the water has poor effects and is easy to cause organic pollution of the reverse osmosis membrane, making it difficult to meet the reuse index. Summary of the Invention

[0005] The purpose of the present invention is to provide a zero-discharge treatment process for saline wastewater to solve the above problems existing in the use of nanofiltration membrane technology in zero-discharge technology and the organic pollution of the reverse osmosis membrane by organic substances.

[0006] 1. The present invention uses the ultra-high lime-aluminum method combined with the double-alkali method for pretreatment to remove sulfate ions, fluoride ions, silicon dioxide, calcium, magnesium and other metal ions in the water, remove the miscellaneous salts in the water, and replace the effect of nanofiltration membrane desalination, facilitating the zero-discharge treatment of high-salt wastewater;

[0007] 2. The present invention uses ozone nano-microbubble technology to remove organic pollutants in the water, not only reducing the organic pollution of the reverse osmosis membrane, but also having an antibacterial effect.

[0008] 3. After reverse osmosis treatment, the produced water is used for process reuse, and the concentrated solution is subjected to evaporation and concentration treatment to generate high-purity sodium chloride, realizing resource recovery and achieving zero discharge of wastewater.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] A zero-discharge treatment process for saline wastewater, comprising the following steps:

[0011] Step 1: The high-salt wastewater first enters a primary reaction device, and ettringite is generated with the wastewater by using the ultra-high lime-aluminum method, and its chemical formula is Ca6Al2(SO4)3(OH) 12 , the sulfate ions in the water are removed by precipitation, and a flocculant is added to assist precipitation. The supernatant generated by the precipitation enters a secondary reaction device, and the sludge enters the sludge thickening tank of the sludge treatment system;

[0012] Step 2: The secondary reaction device uses the double-alkali method to remove hardness to remove calcium and magnesium ions in the wastewater and additional metal ions generated by the ultra-high lime-aluminum method. Magnesium oxide is added to remove SiO2 in the wastewater. The supernatant enters the inclined tube sedimentation tank for sedimentation, and the sludge enters the sludge thickening tank of the sludge treatment system;

[0013] Step 3: Hydrochloric acid is added after the water outlet weir of the inclined tube sedimentation tank to adjust the pH to 7-9 to adjust the wastewater to neutral. The effluent enters the sand filter, and the sludge enters the sludge thickening tank of the sludge treatment system;

[0014] Step 4: The effluent of the high-salt wastewater after being filtered by the sand filter enters the ultrafiltration device. The ultrafiltration device further removes impurities in the water, and the effluent enters the ion exchanger;

[0015] Step 5: The ion exchanger deeply removes metal cations or sulfate ions in the water, and the effluent enters the ozone nano-microbubble reactor;

[0016] Step 6: The ozone nano-microbubble reactor removes organic matter in the water, and at the same time uses ozone for sterilization and disinfection. The effluent treated by the ozone nano-microbubble reactor enters the reverse osmosis device;

[0017] Step 7: The reverse osmosis device conducts concentration and reduction treatment on the wastewater, the effluent is recycled, and the concentrated liquid enters the evaporation crystallizer;

[0018] Step 8: The evaporation crystallizer conducts evaporation and crystallization treatment on the wastewater concentrated liquid, and the produced sodium chloride resources are recycled.

[0019] Furthermore, in Step 1, Step 2 and Step 3, the sludge entering the sludge thickening tank is concentrated and then enters the sludge dewatering machine for dewatering treatment, and the dewatered sludge is transported out;

[0020] The filtrate after dewatering is refluxed to the primary reaction device to enhance the flocculation effect of the flocculant.

[0021] Furthermore, the primary reaction device and the secondary reaction device have the same structure, both including a housing, a first chemical addition pipe, a second chemical addition pipe, a water inlet pipe, a low-speed stirrer, and a high-speed stirrer; in the middle of the inner cavity of the housing, there are a first reaction zone, a second reaction zone, and a sedimentation and clarification zone from inside to outside;

[0022] Inside the first reaction zone, a high-speed stirrer with a rotation speed of 100 - 300 r / min is arranged. At the bottom of the first reaction zone, the water inlet pipe and the first chemical addition pipe are connected to each other, and the water inlet pipe evenly distributes water through a water distribution plate arranged at the bottom of the first reaction zone; inside the second reaction zone, a low-speed stirrer with a rotation speed of 50 - 80 r / min is arranged, and a second chemical addition pipe is arranged at the bottom of the second reaction zone; at the upper side of the sedimentation and clarification zone, a water outlet is arranged, and at the bottom of the sedimentation and clarification zone is a sludge collection hopper; the motors of the low-speed stirrer and the high-speed stirrer are both fixedly installed on the top cover of the housing.

[0023] Furthermore, in step one, calcium oxide or calcium hydroxide, and sodium aluminate or aluminum chloride are added to the first reaction zone of the primary reaction device through the first chemical addition pipe, and the flocculant polyacrylamide is added to the second reaction zone of the primary reaction device through the second chemical addition pipe to generate Ca6Al2(SO4)3(OH) 12 precipitation; the dosage of the chemicals in the first chemical addition pipe is nCa / nAl = 2 - 4, and the dosage of polyacrylamide in the second chemical addition pipe is 3 - 10 mg / L. The addition concentration of calcium oxide is 2 - 5%, the addition concentration of polyacrylamide is 0.5% - 1%, and the addition concentrations of other chemicals are 5 - 20%.

[0024] Furthermore, in step two, sodium hydroxide and sodium carbonate are added to the first reaction zone of the secondary reaction device through the first chemical addition pipe, the addition of sodium hydroxide is up to pH = 10.5 - 12, and the dosage of sodium carbonate is 50 - 500 mg / L; calcium carbonate precipitation and magnesium hydroxide are generated to remove the water hardness;

[0025] Magnesium oxide is added to the second reaction zone of the secondary reaction device through the second chemical addition pipe to remove SiO2 in the water; the dosage of magnesium oxide is: the mass ratio of MgO / SiO2 is 15 - 30.

[0026] Furthermore, the sand filtration is one of single-layer sand filtration, multi-layer sand filtration, and mixed sand filtration; the particle size of the filter material is 0.5 - 1.2 mm.

[0027] Furthermore, the ultrafiltration device is one of hollow fiber ultrafiltration, tubular ultrafiltration, or spiral wound ultrafiltration.

[0028] Furthermore, the ion exchanger is filled with strongly acidic cation exchange resin or strongly basic anion exchange resin.

[0029] Furthermore, the ozone nano-microbubble reactor uses ozone as the dosing gas, and the dosing method is hydraulic cavitation or pressure dissolution - pressure release method; the ozone dosing amount is 1 - 10 mg / L.

[0030] Furthermore, the reverse osmosis device adopts secondary reverse osmosis, the reverse osmosis recovery rate is between 70% - 90%, and the produced water is recycled after passing through secondary reverse osmosis; mechanical vapor recompression evaporation is used for evaporation crystallization, and the sodium chloride product of evaporation crystallization is recycled.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] 1. The present invention uses the ultra-high lime-aluminum method plus the double-alkali method to pretreat the wastewater, removing sulfate ions, fluoride ions, silicate, calcium, magnesium and other metal ions in the water, which not only improves the effluent standard, but also prevents the fouling problem of reverse osmosis membrane treatment and prolongs the service life of the reverse osmosis membrane;

[0033] 2. The pretreatment process of the ultra-high lime-aluminum method plus the double-alkali method removes the miscellaneous salts in the water, eliminating the need for nanofiltration membrane treatment, saving investment costs. At the same time, there is no need to separately treat the miscellaneous salts generated by the nanofiltration membrane, which are directly treated with the sludge, saving the operating cost of membrane treatment;

[0034] 3. After pretreatment with the ultra-high lime-aluminum method plus the double-alkali method, the salt in the reverse osmosis concentrate is sodium chloride, which can be recycled resourcefully after evaporation crystallization for industrial applications of high-purity sodium chloride;

[0035] 4. The ozone nano-microbubble technology is used to remove organic pollutants in the water, which not only improves the contact effect between ozone and wastewater, but also has a long-term antibacterial effect, while preventing organic pollution of the reverse osmosis membrane and bacterial growth in the effluent. Description of the Drawings

[0036] Figure 1 is a flow chart of a zero-discharge treatment process for saline wastewater of the present invention;

[0037] Figure 2 is a structural schematic diagram of the first reaction device and the second reaction device;

[0038] The names of the components and the reference numerals involved in the above drawings are as follows:

[0039] First reaction device 1, second reaction device 2, inclined tube sedimentation tank 3, sludge thickening tank 4, ultrafiltration device 5, ion exchanger 6, ozone nano-microbubble reactor 7, reverse osmosis device 8, housing 9, first dosing pipe 10, water inlet pipe 11, second dosing pipe 12, first reaction zone 13, second reaction zone 14, high-speed stirrer 15, low-speed stirrer 16, water outlet 17, evaporation crystallizer 18, precipitation clarification zone 19. Detailed Embodiments

[0040] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0041] Specific Embodiment 1: As Figure 1 shown, this embodiment records a zero-discharge treatment process for saline wastewater, including the following steps:

[0042] Step 1: The high-salt wastewater first enters the first-stage reaction device 1, and ettringite is generated with the wastewater by using the ultra-high lime-aluminum method, and its chemical formula is Ca6Al2(SO4)3(OH) 12 , the sulfate ions in the water are removed by precipitation and a flocculant is added to assist precipitation. The supernatant of the precipitation enters the second-stage reaction device 2, and the sludge enters the sludge thickening tank 4 of the sludge treatment system;

[0043] Step 2: The second-stage reaction device 2 uses the double-alkali method to remove hardness to remove calcium and magnesium ions in the wastewater and the additional metal ions generated by the ultra-high lime-aluminum method. Magnesium oxide is added to remove SiO2 in the wastewater. The supernatant enters the inclined tube sedimentation tank 3 for precipitation, and the sludge enters the sludge thickening tank 4 of the sludge treatment system;

[0044] Step 3: Hydrochloric acid is added after the effluent weir of the inclined tube sedimentation tank 3 to adjust the pH to 7-9 to adjust the wastewater to neutral. The effluent enters the sand filter (used to remove impurities in the water), and the sludge enters the sludge thickening tank 4 of the sludge treatment system;

[0045] Step 4: The effluent of the high-salt wastewater after being filtered by the sand filter enters the ultrafiltration device 5. The ultrafiltration device 5 further removes impurities in the water, and the effluent enters the ion exchanger 6;

[0046] Step 5: The ion exchanger 6 deeply removes metal cations or sulfate anions in the water, and the effluent enters the ozone nano-microbubble reactor 7;

[0047] Step 6: The ozone nano-microbubble reactor 7 removes organic matter in the water, and at the same time uses ozone for disinfection (to prevent the growth of microorganisms to eliminate the risk of organic pollution of the reverse osmosis membrane). The effluent treated by the ozone nano-microbubble reactor 7 enters the reverse osmosis device 8;

[0048] Step 7: The reverse osmosis device 8 concentrates and reduces the volume of the wastewater, the effluent is recycled, and the concentrated liquid enters the evaporation crystallizer 18;

[0049] Step 8: The evaporation crystallizer 18 performs evaporation crystallization treatment on the wastewater concentrated liquid, and the produced sodium chloride resources are recycled.

[0050] Embodiment 2, as Figure 1 and Figure 2 shown, this embodiment is a further description of Embodiment 1. In Steps 1, 2, and 3, the sludge entering the sludge thickening tank 4 is thickened and then enters a sludge dewatering machine for dewatering. The dewatered sludge is transported out.

[0051] The filtrate after dewatering is refluxed to the first reaction device 1 to enhance the flocculation effect of the flocculant.

[0052] The sludge dewatering machine is one of a belt filter press, a plate and frame filter press, a chamber filter press, and a centrifugal sludge dewatering machine.

[0053] Embodiment 3, as Figure 2 shown, this embodiment is a further description of Embodiment 1. The first reaction device 1 and the second reaction device 2 have the same structure, and both include a housing 9, a first chemical addition pipe 10, a second chemical addition pipe 12, a water inlet pipe 11, a low-speed stirrer 16, and a high-speed stirrer 15. In the middle of the inner cavity of the housing 9, a first reaction zone 13, a second reaction zone 14, and a sedimentation and clarification zone 19 are provided from the inside to the outside.

[0054] Inside the first reaction zone 13, a high-speed stirrer 15 with a speed of 100 - 300 r / min is provided. At the bottom of the first reaction zone 13, the water inlet pipe 11 and the first chemical addition pipe 10 are communicated with each other. The water inlet pipe 11 uniformly distributes water through a water distribution plate provided at the bottom of the first reaction zone 13. Inside the second reaction zone 14, a low-speed stirrer 16 with a speed of 50 - 80 r / min is provided. At the bottom of the second reaction zone 14, the second chemical addition pipe 12 is provided. At the upper side of the sedimentation and clarification zone 19, a water outlet 17 is provided. At the bottom of the sedimentation and clarification zone 19 is a sludge collection hopper. The motors of the low-speed stirrer 16 and the high-speed stirrer 15 are both fixedly installed on the top cover of the housing 9.

[0055] Embodiment 4, as Figure 2 shown, this embodiment is a further description of Embodiment 3. In Step 1, calcium oxide or calcium hydroxide, and sodium aluminate or aluminum chloride are added through the first chemical addition pipe 10 in the first reaction zone 13 of the first reaction device 1, and the flocculant polyacrylamide is added through the second chemical addition pipe 12 in the second reaction zone 14 of the first reaction device 1 to generate Ca6Al2(SO4)3(OH) 12 precipitate; the dosage of the chemical in the first chemical addition pipe 10 is nCa / nAl = 2 - 4, and the dosage of polyacrylamide in the second chemical addition pipe 12 is 3 - 10 mg / L. The addition concentration of calcium oxide is 2 - 5%, the addition concentration of polyacrylamide is 0.5% - 1%, and the addition concentration of other chemicals is 5 - 20%.

[0056] Add the flocculant polyacrylamide (to assist in forming larger precipitate flocs) to the second reaction zone 14 of the primary reaction device 1.

[0057] Specific Embodiment 5, as Figure 2 shown, this embodiment is a further description of Specific Embodiment 3 or Specific Embodiment 4. In step 2, add sodium hydroxide and sodium carbonate to the first reaction zone 13 of the secondary reaction device 2 through the first chemical addition pipe 10. The addition of sodium hydroxide is adjusted to pH = 10.5 - 12, and the addition amount of sodium carbonate is 50 - 500 mg / L; calcium carbonate precipitate and magnesium hydroxide are generated to remove the water hardness by precipitation.

[0058] Add magnesium oxide to the second reaction zone 14 of the secondary reaction device 2 through the second chemical addition pipe 12 to remove SiO2 in the water; the addition amount of magnesium oxide is: the mass ratio of MgO / SiO2 is 15 - 30.

[0059] Specific Embodiment 6, as Figure 1 shown, this embodiment is a further description of Specific Embodiment 1. The sand filtration is one of single - layer sand filtration, multi - layer sand filtration (anthracite on the upper layer and quartz sand on the lower layer), and mixed sand filtration (quartz sand mixed with iron - based materials); the particle size of the filter media is 0.5 - 1.2 mm.

[0060] Specific Embodiment 7, as Figure 1 shown, this embodiment is a further description of Specific Embodiment 1. The ultrafiltration device 5 is one of hollow - fiber ultrafiltration, tubular ultrafiltration, or spiral - wound ultrafiltration.

[0061] Specific Embodiment 8, as Figure 1 shown, this embodiment is a further description of Specific Embodiment 1. The ion exchanger 6 is filled with strongly acidic cation exchange resin or strongly basic anion exchange resin.

[0062] When the ion exchanger 6 is filled with strongly acidic cation exchange resin, the ionic form is sodium ion; when the ion exchange resin is filled with strongly basic anion exchange resin, the ionic form is chloride ion. Further remove the high - valence cations or anions in the wastewater, and displace sodium ions or chloride ions to improve the purity of the evaporation product sodium chloride of the subsequent concentrated wastewater.

[0063] Specific Embodiment 9, as Figure 1 shown, this embodiment is a further description of Specific Embodiment 1. The ozone nano - microbubble reactor 7 uses ozone as the dosing gas, and the dosing method is hydrodynamic cavitation or pressure - dissolution - decompression release method; the ozone dosing amount is 1 - 10 mg / L.

[0064] Due to the very small diameter of micro-nano bubbles, their surface area is relatively large, so the solubility of ozone in micro-nano bubbles increases significantly. This enables ozone to more effectively contact and react with pollutants in water, thereby improving the utilization rate and treatment effect of ozone. Moreover, nano-micro bubbles maintain stability in water for a long time, thus enhancing the effect of ozone.

[0065] Specific Embodiment Ten, as Figure 1 shown, this embodiment is a further elaboration on Specific Embodiment One. The reverse osmosis device 8 adopts a two-stage reverse osmosis process, with a reverse osmosis recovery rate between 70% and 90%. The produced water is recycled after passing through the two-stage reverse osmosis. Evaporation crystallization uses mechanical vapor recompression evaporation (MVR evaporation), and the sodium chloride product obtained from evaporation crystallization is recycled and utilized (can be used in industrial applications of high-purity sodium chloride).

[0066] The innovation of the present invention lies in: using the ultra-high lime-aluminum method + double-alkali method for pretreatment to replace the nanofiltration membrane to remove divalent sulfate ions and metal ions such as calcium and magnesium, saving the investment and operating costs of the nanofiltration device; using the ozone nano-micro bubble technology to treat organic matter in wastewater and achieving the purpose of sterilization at the same time; membrane treatment for concentration reduction + evaporation concentration to achieve zero discharge of wastewater and resource recovery of high-purity sodium chloride. Specifically:

[0067] 1. Using the ultra-high lime-aluminum method + double-alkali method for pretreatment of sulfate ions and metal ions such as calcium and magnesium to replace the nanofiltration membrane for concentrating and removing impurity salts;

[0068] 2. Using the ozone nano-micro bubble technology to remove organic matter in water and prevent organic pollution of the membrane concentration in subsequent zero-discharge treatment;

[0069] 3. Reverse osmosis membrane + evaporation concentration to achieve the effect of zero discharge and complete the recovery of pure salt sodium chloride.

[0070] The ultra-high lime-aluminum method is also known as the Friedel's salt method. In this method, saline wastewater is added with calcium oxide and sodium meta-aluminate, and through reactions under certain conditions, insoluble ettringite (Ca6Al2(SO4)3(OH) 12 ) precipitate is formed to remove sulfate ions. At the same time, the ultra-high lime-aluminum method can also remove chloride ions in water to form Ca4Al2Cl2(OH) 12 precipitate. However, in the ultra-high lime-aluminum method process, removing SO4 2- and Cl - from the desalination concentrated water, there is a competitive relationship between SO4 2- and Cl - . SO4 2- is preferentially removed over Cl - , and the coexisting divalent ion SO4 2- has a higher affinity for the intermediate layer region.

[0071] The nano - microbubble technology is a technology that disperses gas in a solution to form tiny bubble particles. The diameter of the generated bubbles is below 100 nm, and they have characteristics such as a large specific surface area, a slow rising speed, self - pressurized dissolution, surface charging, and the ability to generate hydroxyl radicals. This can greatly improve the solubility of gas in water and the mass transfer efficiency, and has functions such as deodorization, cleaning, catalysis, adsorption, sterilization, and disinfection. It is widely used in the fields of water treatment, cosmetics, agriculture, petroleum, semiconductor cleaning, food processing, medical and health, etc.

[0072] For the treatment of high - salt wastewater in a certain chemical plant, after the reverse osmosis concentrate is evaporated and crystallized, the purity of sodium chloride is above 99%. The main water quality and treatment results are as follows in the table:

[0073]

[0074] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above - mentioned exemplary embodiments, and the present invention can be implemented in other forms of the device without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non - restrictive. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent conditions of the claims are intended to be included in the present invention. Any reference signs in the claims should not be regarded as limiting the claimed claims.

[0075] In addition, it should be understood that although this specification is described according to the embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A zero-discharge treatment process for saline wastewater, characterized in that: It includes the following steps: Step 1: The high-salt wastewater first enters the first-stage reaction device (1). Using the ultra-high lime-aluminum method, ettringite is generated with the wastewater, and its chemical formula is Ca6Al2(SO4)3(OH) 12 , and the sulfate ions in the water are removed by precipitation. A flocculant is added to assist in precipitation. The supernatant produced by the precipitation enters the second-stage reaction device (2), and the sludge enters the sludge thickening tank (4) of the sludge treatment system; Step 2: The secondary reaction device (2) uses the double-alkali method to remove hardness to remove calcium and magnesium ions in the wastewater and additional metal ions generated by the ultra-high lime-aluminum method. Magnesium oxide is added to remove SiO2 in the wastewater. The supernatant enters the inclined tube sedimentation tank (3) for sedimentation, and the sludge enters the sludge thickening tank (4) of the sludge treatment system; Step 3: Hydrochloric acid is added after the water outlet weir of the inclined tube sedimentation tank (3) to adjust the pH to 7-9 to adjust the wastewater to neutral. The effluent enters the sand filter, and the sludge enters the sludge thickening tank (4) of the sludge treatment system; Step 4: The effluent of the high-salt wastewater after passing through the sand filter enters the ultrafiltration device (5). The ultrafiltration device (5) further removes impurities in the water, and the effluent enters the ion exchanger (6); Step 5: The ion exchanger (6) deeply removes metal cations or sulfate anions in the water, and the effluent enters the ozone nano-microbubble reactor (7); Step 6: The ozone nano-microbubble reactor (7) removes organic matter in the water and uses ozone for sterilization and disinfection. The effluent treated by the ozone nano-microbubble reactor (7) enters the reverse osmosis device (8); Step 7: The reverse osmosis device (8) conducts concentration reduction treatment on the wastewater. The effluent is recycled, and the concentrated liquid enters the evaporation crystallizer (18); Step 8: The evaporation crystallizer (18) conducts evaporation crystallization treatment on the wastewater concentrated liquid, and the produced sodium chloride resources are recycled.

2. The zero-discharge treatment process for saline wastewater according to claim 1, characterized in that: In Step 1, Step 2, and Step 3, the sludge entering the sludge thickening tank (4) is concentrated and then enters a sludge dehydrator for dehydration treatment. The dehydrated sludge is transported out; The filtrate after dehydration flows back to the primary reaction device (1) to enhance the flocculation effect of the flocculant.

3. The zero-discharge treatment process for saline wastewater according to claim 1, wherein: The primary reaction device (1) has the same structure as the secondary reaction device (2), and both include a housing (9), a chemical addition pipe 1 (10), a chemical addition pipe 2 (12), a water inlet pipe (11), a low-speed stirrer (16), and a high-speed stirrer (15); in the middle of the inner cavity of the housing (9), there are a first reaction zone (13), a second reaction zone (14), and a sedimentation and clarification zone (19) from inside to outside; Inside the first reaction zone (13), a high-speed stirrer (15) with a rotation speed of 100-300 r / min is arranged. At the bottom of the first reaction zone (13), the water inlet pipe (11) and the chemical addition pipe 1 (10) are connected to each other. The water inlet pipe (11) distributes water evenly through a water distribution plate arranged at the bottom of the first reaction zone (13); inside the second reaction zone (14), a low-speed stirrer (16) with a rotation speed of 50-80 r / min is arranged, and a chemical addition pipe 2 (12) is arranged at the bottom of the second reaction zone (14); at the upper side of the sedimentation and clarification zone (19), a water outlet (17) is arranged, and at the bottom of the sedimentation and clarification zone (19) is a sludge collection hopper; the motors of the low-speed stirrer (16) and the high-speed stirrer (15) are both fixedly installed on the top cover of the housing (9).

4. A zero-discharge treatment process for saline wastewater according to claim 3, characterized in that: In the first step, calcium oxide or calcium hydroxide, and sodium aluminate or aluminum chloride are added through the first chemical addition pipe (10) to the first reaction zone (13) of the primary reaction device (1), and the flocculant polyacrylamide is added through the second chemical addition pipe (12) to the second reaction zone (14) of the primary reaction device (1) to generate Ca6Al2(SO4)3(OH) 12 precipitate; the dosage of the chemicals in the first chemical addition pipe (10) is nCa / nAl = 2 - 4, the dosage of polyacrylamide in the second chemical addition pipe (12) is 3 - 10 mg / L, the addition concentration of calcium oxide is 2 - 5%, the addition concentration of polyacrylamide is 0.5% - 1%, and the addition concentration of other chemicals is 5 - 20%.

5. A zero-discharge treatment process for saline wastewater according to claim 3 or 4, characterized in that: In Step 2, sodium hydroxide and sodium carbonate are added through the first dosing pipe (10) in the first reaction zone (13) of the secondary reaction device (2). The sodium hydroxide is added until the pH reaches 10.5 - 12, and the dosage of sodium carbonate is 50 - 500 mg / L; calcium carbonate precipitate and magnesium hydroxide are generated, and the precipitate removes the hardness in the water. Magnesium oxide is added through the second dosing pipe (12) in the second reaction zone (14) of the secondary reaction device (2) to remove SiO2 in the water; the dosage of magnesium oxide is such that the mass ratio of MgO / SiO2 is 15 - 30.

6. The zero-discharge treatment process for saline wastewater according to claim 1, characterized in that: The sand filtration is one of single - layer sand filtration, multi - layer sand filtration, and mixed sand filtration; the particle size of the filter material is 0.5 - 1.2 mm.

7. A zero-discharge treatment process for saline wastewater according to claim 1, characterized in that: The ultrafiltration device (5) is one of hollow - fiber ultrafiltration, tubular ultrafiltration, or spiral - wound ultrafiltration.

8. The zero - discharge treatment process for saline wastewater according to claim 1, wherein: The ion exchanger (6) is filled with strongly acidic cation exchange resin or strongly basic anion exchange resin.

9. A zero-discharge treatment process for saline wastewater according to claim 1, characterized in that: The ozone nano - microbubble reactor (7) uses ozone as the dosing gas, and the dosing method is hydraulic cavitation or pressure - dissolution and decompression - release method; the ozone dosage is 1 - 10 mg / L.

10. A zero-discharge treatment process for saline wastewater according to claim 1, characterized in that: The reverse osmosis device (8) adopts two - stage reverse osmosis, and the reverse osmosis recovery rate is between 70% - 90%. The produced water is reused after passing through two - stage reverse osmosis; mechanical vapor recompression evaporation is used for evaporation crystallization, and the sodium chloride product obtained from evaporation crystallization is recycled.

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