Integrated treatment method for desalination of chemical wastewater

Abstract

The present application relates to sewage treatment technical field, specifically to a kind of chemical wastewater desalination integrated processing method.The present application overcomes the problem of low resource utilization efficiency of chemical wastewater desalination in prior art;The present application first synthesizes three-dimensional catalytic aerogel microspheres, which are loaded in a fixed bed to target adsorption and catalytic chain scission of macromolecular polymers in high-salinity wastewater with persulfate;Subsequently, a salt-tolerant membrane bioreactor is introduced to form small-molecule organic compounds through deep metabolism;The effluent is sequentially subjected to target complexation and precipitation of heavy metals using modified chitosan and amphoteric polyacrylamide, pre-implantation of polyepoxysuccinic acid scale inhibitor, and finally subjected to nanofiltration and reverse osmosis systems, freeze crystallization and MVR evaporation to extract high-purity sodium sulfate and sodium chloride.The present application effectively solves the problem of membrane fouling caused by heavy metal leakage and organic matter residue in traditional process, and realizes the deep purification of chemical wastewater and the high-value resource recovery of salt.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to an integrated method for desalination of chemical wastewater. Background Technology

[0002] In the preparation of modern fine chemicals, polymers, and special thin film materials, the discharged chemical wastewater is generally characterized by extremely high salinity and is rich in long-chain polymers and recalcitrant aromatic organic compounds. Currently, the industry mostly uses a linear process route of "traditional advanced oxidation pretreatment + conventional flocculation sedimentation + evaporation crystallization" to treat this type of wastewater. However, in actual engineering operations, problems such as low desalination and resource recovery efficiency and secondary impurities interfering with the treatment efficiency have been exposed.

[0003] Traditional oxidation processes lack interfacial catalytic enrichment effects and have short free radical half-lives, making it impossible to completely open and break the chains of sterically hindered polymers. This results in a large amount of residual organic macromolecules and colloids in the wastewater. When these recalcitrant organic compounds enter subsequent mechanical vapor recompression or multi-effect evaporation crystallization systems, they trigger complex co-solubility effects and increased boiling points. Furthermore, organic matter is prone to thermal decomposition and carbonization during high-temperature forced crystallization and is densely encapsulated within the crystal lattice of inorganic salts, leading to a severely black and yellow mixed salt that fails to meet the standards for refined industrial salt.

[0004] The frequent introduction of secondary impurities severely disrupts the long-term stability and efficiency of water treatment systems. To drastically increase the degradation rate of organic matter at the front end, existing homogeneous Fenton systems require the addition of massive amounts of metal salt catalysts. This not only generates huge quantities of hazardous chemical sludge during the neutralization stage but also causes a large number of free heavy metal ions to leak into the downstream stages. In extremely high-salt environments, the strong electrostatic shielding effect of the water causes severe coiling of the molecular chains of conventional water treatment flocculants, completely eliminating their ability to trap, bridge, and complex impurities. Simultaneously, the continuous deposition of metal impurities easily triggers the catalytic oxidative degradation of desalination membrane materials and the adhesion of hard scale to the walls of crystallizer heat exchange tubes, significantly shortening the service life of high-value equipment.

[0005] In summary, existing technologies utilize various processes to improve the treatment efficiency of chemical wastewater; however, ensuring the long-term stability of the desalination and separation system and the high-purity resource extraction of waste salt remain significant challenges in the wastewater treatment field.

[0006] Therefore, this invention proposes an integrated treatment method for desalination of chemical wastewater. Summary of the Invention

[0007] The purpose of this invention is to provide an integrated method for desalination of chemical wastewater. This invention first synthesizes three-dimensional catalytic aerogel microspheres, which are then packed into a fixed bed to synergistically adsorb and catalytically break down macromolecular polymers in high-salt wastewater with persulfate. Subsequently, these microspheres are introduced into a halophilic membrane bioreactor for deep metabolism, forming small-molecule organic matter. The effluent is then subjected to targeted complexation and precipitation of heavy metals using modified chitosan and amphoteric polyacrylamide, pre-implanted with polyepoxysuccinic acid scale inhibitors, and finally, through nanofiltration and reverse osmosis systems, freeze crystallization and MVR evaporation are used to extract high-purity sodium sulfate and sodium chloride, respectively. This invention effectively solves the problems of membrane fouling and low-quality waste salt caused by heavy metal leakage and organic residue in traditional processes, achieving deep purification of chemical wastewater and high-value resource recovery of salts.

[0008] To achieve the above objectives, the present invention provides the following technical solution: This invention provides an integrated treatment method for desalination of chemical wastewater, comprising the following steps: A 20% sulfuric acid aqueous solution was added to high-salinity chemical wastewater with a chemical oxygen demand (COD) of 20,000-30,000 mg / L to adjust the pH to 3.5-4.5. This solution was then pumped into a fixed-bed catalytic reaction tower with an internal aerogel microsphere packing rate of 60%-70% at a continuous flow rate of 0.5-1.0 m³ / h. Simultaneously, a 10% sodium persulfate solution was continuously added via a metering pump at a ratio of 3.0-5.0 g / L. The temperature inside the reaction tower was maintained at 65-75℃ using a water bath jacket, and the hydraulic residence time was controlled to be 90-120 min to obtain the reaction solution. This process achieves catalytic chain scission of macromolecular polymers and in-situ targeted adsorption and degradation of organic salts, resulting in an improved B / C ratio in the effluent. The pH is raised to above 0.4; the reaction solution is cooled through a heat exchanger and adjusted to 7.0-7.5 using a 20% sodium hydroxide solution. It is then introduced into a membrane bioreactor inoculated with Haloxylon ammodendron microorganisms. The total dissolved solids salinity is controlled at 8%-12%, the water temperature is maintained at 30-35℃, dissolved oxygen is controlled at 2.0-3.0 mg / L through bottom microporous aeration discs, and the sludge concentration is maintained at 4000-6000 mg / L. The microbial community's metabolism deeply degrades the small-molecule organic matter generated by chain scission, and the dialysis supernatant is obtained through a polytetrafluoroethylene hollow fiber membrane with a transmembrane pressure difference controlled at 0.02 MPa and a pore size of 0.1 μm. The effluent chemical composition is controlled... The oxygen demand was reduced to below 80 mg / L; a 20% sodium hydroxide solution was added to the dialysis supernatant to adjust the pH to 8.0-8.5, followed by the addition of 10-20 mg / L modified chitosan aqueous solution and rapid mechanical stirring at 200 rpm for 5 min; then, 3-5 mg / L polyacrylamide aqueous solution was added and stirred at 40 rpm for 15 min, followed by standing precipitation for 2 h to obtain the supernatant; the DTC groups targeted and captured residual heavy metal ions to form extremely insoluble chelates, removing residual heavy metal ions, and the turbidity of the supernatant was reduced to below 1 NTU; finally, 30-50 mg / L polyepoxysuccinic acid was added to the supernatant as a pre-implanted scale inhibitor, maintaining a rotation speed of 100 rpm for a time of [missing information]. After 10 minutes of stirring and mixing, a mixed solution is obtained. The mixed solution is then pumped sequentially into a nanofiltration membrane module with an operating pressure of 1.5-2.5 MPa. Divalent sulfate ions with a rejection rate greater than 95% form nanofiltration concentrate, which is then sent through pipelines to a cryogenic crystallizer where it is forcibly cooled at 0-5℃ to precipitate sodium sulfate decahydrate crystals, which are then separated by centrifugation. The nanofiltration permeate, rich in monovalent chloride ions, enters the reverse osmosis system and is concentrated to a total salinity of 10% at an operating pressure of 4.0-6.0 MPa. It is then introduced into a mechanical vapor recompression evaporator and boiled and evaporated to crystallize under a system vacuum of -0.06 MPa and a boiling point of 90℃. The purified sodium chloride is recovered by centrifugation and drying. The freezing and evaporation mother liquor is returned to the raw water equalization tank to form a closed loop system.

[0009] Preferably, the dithiocarbamate-modified chitosan of the present invention is prepared by conventional methods, including alkali swelling, nucleophilic addition, isothermal ripening, precipitation and purification, and alternating washing and drying. The primary amino groups on the chitosan molecular chain undergo nucleophilic addition with carbon disulfide in a strongly alkaline medium, converting it into dithiocarbamate groups with extremely strong heavy metal chelating ability.

[0010] Preferably, the TEMPO-modified nanocellulose of the present invention is prepared using conventional methods, including homogeneous dispersion and system construction, initial pH adjustment, initiation of oxidation and constant pH control, reaction termination and quenching, purification and desalting, and ultrasonic exfoliation. The TEMPO / NaBr / NaClO-mediated catalytic oxidation system exhibits extremely high regioselectivity, specifically oxidizing the primary hydroxyl group at the C6 position of the cellulose glucose ring to a carboxylic acid group, thereby achieving nanoscale exfoliation through electrostatic repulsion.

[0011] Preferably, the preparation of the aerogel microspheres includes the following steps: dispersing 10-15 parts of graphene oxide and 15-20 parts of modified nanocellulose in 1000 parts of deionized water, and ultrasonically treating for 30 minutes under ultrasonic power of 500W and frequency of 40kHz to form a uniform suspension; adding 20-25 parts of sodium alginate to the suspension, stirring at 300rpm until completely dissolved, then slowly adding 4-6 parts of copper sulfate crystals and 15-20 parts of ferrous sulfate heptahydrate, and magnetically stirring at 25°C for 2 hours to obtain a mixed slurry; allowing metal ions and oxygen-containing functional groups to fully undergo electrostatic adsorption and coordination complexation. The mixed slurry was added dropwise at a rate of 10 mL / min to a crosslinking coagulation bath composed of 50 parts anhydrous calcium chloride, 2 parts ascorbic acid, and 1000 parts deionized water using a high-pressure injection pump with a 2 mm inner diameter needle at an operating pressure of 0.4 MPa. The droplets solidified instantly upon contact with the coagulation bath to obtain hydrogel microspheres; the radial diameter of the hydrogel microspheres was 2.5-3.5 mm. The microspheres were then aged at 25°C for 12 hours, washed with deionized water until neutral, pre-frozen at -80°C for 12 hours, and then transferred to a vacuum freeze dryer for freeze-drying under an absolute vacuum of less than 10 Pa for 48 hours to obtain the aerogel microspheres. The specific surface area of ​​the aerogel microspheres was 450-650 m² / g, and the mesopore size distribution was 20-50 nm.

[0012] Preferably, the purity of the recovered sodium sulfate in this invention is 98.9%-99.4%; and the purity of the recovered sodium chloride is 99.1%-99.6%.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention pre-implants polyepoxysuccinic acid into the MBR dialysis solution. It does not participate in flocculation and sedimentation at the front end, but enters the desalination membrane system and evaporation section with the water flow, exerting a highly efficient lattice distortion and scale inhibition effect. Combined with the deep reduction of organic colloids by the front-end MBR, the increase in transmembrane pressure difference after 30 days of continuous system operation is reduced, which is far superior to the traditional process, and significantly extends the cleaning cycle and service life of the membrane module.

[0014] 2. This invention uses porous Cu-Fe@MNC / GO aerogel microspheres as a heterogeneous catalyst, with bimetallic sites firmly anchored within a mesoporous framework of modified nanocellulose and graphene oxide crosslinking. This not only avoids catalyst aggregation and loss in strongly disturbed water bodies, achieving self-sustaining catalyst circulation, but also minimizes the leakage rate of heavy metals. Combined with the precise capture of targeted reagents at the back end, the system produces significantly less sludge than traditional processes, avoiding the introduction of secondary pollution.

[0015] 3. This invention tightly couples the catalytic chain scission of the front-end aerogel microspheres with the deep metabolic consumption of the halophilic MBR system, thoroughly eliminating the organic carbon source that induces evaporator foaming and blackening of crystallized salts; at the same time, it utilizes modified chitosan to remove trace heavy metal impurities and eliminate color interference caused by metal ions entering the crystal lattice, ultimately improving the purity of the recovered sodium chloride and sodium sulfate and reducing TOC content, successfully converting traditional high-cost hazardous waste salts into refined industrial salt that meets national standards, maximizing resource value.

[0016] 4. This invention breaks down the boundaries between physicochemical and biodegradation. The high specific surface area aerogel microspheres generate a strong interfacial salt-monomonas siphon effect on macromolecular resins and locally enrich sulfate free radicals for precise molecular-level ring-opening shaving. The sterically hindered macromolecules that are originally lethal to microorganisms are efficiently converted into easily biodegradable small molecules such as formic acid and acetic acid, increasing the B / C ratio. This provides an extremely high-quality metabolic carbon source for downstream high-salinity tolerance, resulting in a stable increase in the overall COD removal rate of the system.

[0017] 5. This invention utilizes the byproducts of the oxidation stage to provide nutrients for the biochemical stage; the precipitation stage removes heavy metals, clearing away complexation interference for the scale inhibition stage; and the scale inhibitor's penetration directly protects the final membrane separation and heat exchange interface. Through this interconnected material flow design, the system's tolerance and buffering capacity in the face of drastic fluctuations in upstream water quality are greatly improved, ensuring the safety of continuous industrial-grade operation and the absolute stability of the effluent water quality. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the process flow for chemical wastewater in an embodiment of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] The graphene oxide of this invention has CAS number 1034343-98-0, a monolayer ratio >80%, an oxygen content ≥40%, a lateral dimension of 0.5-5 μm, and a thickness of 0.8-1.2 nm; the modified nanocellulose is TEMPO oxidized microcrystalline cellulose with a diameter of 5-20 nm and a length of 100-500 nm, a surface carboxyl substitution degree of 1.0-1.5 mmol / g, and an aspect ratio >20; the sodium alginate has CAS number 9005-38-3, a weight-average molecular weight (Mw) of 200,000 Da, and a G / M ratio of 0.4-0.6; the modified chitosan is dithiocarbamate-modified chitosan, wherein the degree of deacetylation is ≥ 85%, with the degree of grafting substitution of dithiocarbamate groups controlled at 0.5-0.8; PESA is polyepoxysuccinic acid, CAS number 51274-37-4, with a weight-average molecular weight (Mw) controlled at 400-1500 Da; amphoteric polyacrylamide CAS number 25085-02-3, with a weight-average molecular weight (Mw) of 8,000,000-12,000,000 Da, cationicity 15-20%, and anionicity 25-30%; Halomonas spp. are preferred, exhibiting extremely high metabolic activity towards short-chain organic acids under high salinity and high osmotic pressure environments of 8%-12%, with accession number CGMCC1.2315.

[0021] Please see Figure 1 This invention provides an integrated treatment method for desalination of chemical wastewater, the technical solution of which is as follows: Example

[0022] Preparation of aerogel microspheres: 12 parts of graphene oxide and 18 parts of modified nanocellulose were dispersed in 1000 parts of deionized water and ultrasonically treated for 30 minutes at an ultrasonic power of 500W and a frequency of 40kHz to form a uniform suspension. 24 parts of sodium alginate were added to the suspension and stirred at 300rpm until completely dissolved. Then, 5 parts of copper sulfate crystals and 18 parts of ferrous sulfate heptahydrate were slowly added, and the mixture was magnetically stirred at 25°C for 2 hours to obtain a mixed slurry. This allowed for sufficient electrostatic adsorption and coordination complexation between metal ions and oxygen-containing functional groups. The mixed slurry was added dropwise at a rate of 10 mL / min to a crosslinking coagulation bath composed of 50 parts anhydrous calcium chloride, 2 parts ascorbic acid, and 1000 parts deionized water using a high-pressure injection pump with a 2 mm inner diameter needle. The droplets solidified instantly upon contact with the coagulation bath to obtain hydrogel microspheres. Subsequently, the microspheres were aged at 25 °C for 12 h, washed with deionized water until neutral, pre-frozen at -80 °C for 12 h, and then transferred to a vacuum freeze dryer. The microspheres were freeze-dried for 48 h under an absolute vacuum of less than 10 Pa to obtain the aerogel microspheres.

[0023] Chemical wastewater treatment process: A 20% sulfuric acid aqueous solution was added to high-salinity chemical wastewater with a chemical oxygen demand (COD) of 25000 mg / L to adjust the pH to 4. This solution was then pumped into a fixed-bed catalytic reaction tower with an internal aerogel microsphere packing ratio of 65% at a continuous flow rate of 0.8 m³ / h. Simultaneously, a 10% sodium persulfate solution was continuously added via a metering pump at a ratio of 4 g / L. The temperature inside the reaction tower was maintained at 70°C using a water bath jacket, and the hydraulic residence time was controlled to be 100 min to obtain the reaction solution. The reaction solution was then cooled through a heat exchanger and... A 20% sodium hydroxide solution was adjusted to pH 7.2 and introduced into a membrane bioreactor inoculated with Halomonas microorganisms. The total dissolved solids salinity was controlled at 10%, the water temperature was maintained at 35℃, dissolved oxygen was controlled at 2.5 mg / L through bottom microporous aeration discs, and the sludge concentration was maintained at 5000 mg / L. Dialysate was obtained through a polytetrafluoroethylene hollow fiber membrane with a transmembrane pressure differential controlled at 0.02 MPa and a pore size of 0.1 μm. The effluent chemical oxygen demand was reduced to below 80 mg / L. Subsequently, a 20% sodium hydroxide solution was added to the dialysate... The pH was adjusted to 8.0 with a 20% sodium hydroxide solution, and a 15 mg / L modified chitosan aqueous solution was added. The mixture was mechanically stirred rapidly at 200 rpm for 5 min. Subsequently, a 4 mg / L polyacrylamide aqueous solution was added, and the mixture was stirred at 40 rpm for 15 min. The mixture was allowed to stand for 2 h to obtain a supernatant. Finally, 40 mg / L polyepoxysuccinic acid was precisely added to the supernatant as a pre-implanted scale inhibitor, and the mixture was stirred at 100 rpm for 10 min to obtain a mixed solution. The mixed solution was then pumped sequentially into a nanofiltration membrane operating at a pressure of 2 MPa. The system uses nanofiltration to collect divalent sulfate ions with a rejection rate greater than 95%, forming concentrated nanofiltration water. This concentrated water is then piped into a cryogenic crystallizer where it is forcibly cooled at 0°C to precipitate sodium sulfate decahydrate crystals, which are then separated by centrifugation. The nanofiltration permeate, rich in monovalent chloride ions, enters the reverse osmosis system and is concentrated to a total salinity of 10% under an operating pressure of 5 MPa. It is then introduced into a mechanical vapor recompression evaporator and boiled and evaporated under a system vacuum of -0.06 MPa and a boiling point of 90°C to crystallize the water. Industrial-grade refined sodium chloride is recovered through centrifugation and drying. The freezing and evaporation mother liquor is returned to the raw water equalization tank to form a closed-loop system.

[0024] Examples 2-4 follow the same preparation method and parameter conditions as Example 1, with differences shown in Table 1.

[0025] Table 1. Parameter variations in Examples 1-5 Key process parameters Example 1 Example 2 Example 3 Example 4 Initial chemical oxygen demand (COD) / mg / L 25000 20000 30000 28000 Graphene oxide mass dosage / part 12 10 14 15 Modified nanocellulose mass dosage / part 18 15 17 20 Copper sulfate crystal mass usage / part 5 4 4.5 6 Sodium alginate dosage (per serving) 24 20 25 20 Ferrous sulfate heptahydrate mass dosage / part 18 15 16 20 Sodium persulfate solution continuous feed ratio / g / L 4 3 3.5 5 Temperature inside the fixed-bed catalytic reactor / °C 70 65 68 75 Aerogel microsphere filling rate / % 65 60 70 62 Hydraulic retention time / min 100 90 120 110 Total dissolved solids salinity / % 10 8 12 10 Modified chitosan dosage (mg / L) 15 10 12 20 Polyepoxysuccinic acid dosage (mg / L) 40 30 35 50 Amphoteric polyacrylamide dosage (mg / L) 4 3 5 4 Nanofiltration membrane pressure / MPa 2 1.5 2.5 1.8 Reverse osmosis system operating pressure / MPa 5 4 6 4

[0026] Comparative Example 1 is the same as Example 1, except that it does not use modified nanocellulose and graphene oxide to prepare aerogel microspheres, but directly adds free powdered Cu-Fe bimetallic catalyst powder to the reaction tank for catalytic oxidation.

[0027] Comparative Example 2 is the same as Example 1, except that it skips the halophilic membrane bioreactor section inoculated with Halomonas spp., that is, the effluent from the fixed bed catalytic reaction tower directly enters the subsequent nanofiltration and reverse osmosis desalination system after targeted complexation sedimentation.

[0028] Comparative Example 3 is the same as Example 1, except that no modified chitosan complexing agent and amphoteric polyacrylamide are added, and they are replaced in equal amounts with polyaluminum chloride and anionic polyacrylamide commonly used in traditional water treatment.

[0029] Comparative Example 4 is the same as Example 1, except that polyepoxysuccinic acid pre-implanted scale inhibitor is not added, while the rest of the process remains unchanged.

[0030] Comparative Example 5 is the same as Example 1, except that the sodium persulfate added in the oxidation section is replaced with a conventional 30% hydrogen peroxide solution that provides an equimolar amount of oxidation.

[0031] Comparative Example 6 is the same as Example 1, except that the MBR system is not inoculated with Halomonas, but instead uses ordinary activated sludge from a conventional municipal wastewater treatment plant that has not been acclimated to high salt.

[0032] Experiment Example 1: Stability Performance Test

[0033] The chemical wastewater treatment processes of Examples 1-4 and Comparative Examples 1-6 were subjected to relevant stability performance tests. The supernatant after settling in the targeted sedimentation tank was filtered through a 0.45 μm aqueous microporous membrane and acidified with 1% nitric acid. The residual total copper / iron concentration was quantitatively determined using inductively coupled plasma mass spectrometry. This index directly reflects the target capture limit of the compounded reagent of this invention for heavy metals in free or weakly complexed catalysts, and is related to the degree to which the desalination system is protected from heavy metal penetration poisoning. The feed water and permeate of the nanofiltration membrane module were collected daily, and the sulfate ion concentration was determined using ion chromatography. The average value over 30 days was taken as the sulfate rejection rate. Additionally, the transmembrane pressure difference value under the initial stable operating state of the nanofiltration / reverse osmosis membrane system was read and recorded. After 30 days of continuous operation without cleaning, the final transmembrane pressure difference value was recorded, and the increase in membrane pressure difference before and after was calculated. The significant effects of the MBR's complete consumption of organic carbon sources and the anti-scaling effect of the PESA phosphorus-free scale inhibitor were evaluated. The test results are shown in Table 2.

[0034] Table 2 Test results of the examples and comparative examples Example Total residual copper / iron concentration (μg / L) Divalent sulfate rejection rate (%) Transmembrane pressure gradient (TMP) increase (%) Example 1 12.3 98.7 8.4 Example 2 18.5 96.2 11.1 Example 3 15.8 97.4 9.6 Example 4 10.1 98.9 7.2 Comparative Example 1 245.6 91.5 35.8 Comparative Example 2 14.2 82.3 87.9 Comparative Example 3 850.4 88.6 28.3 Comparative Example 4 11.9 85.1 95.7 Comparative Example 5 45.2 89.4 62.5 Comparative Example 6 16.7 84.8 78.1

[0035] As shown in Table 2, the comparative example, through adjustments to the components and process, exhibited significantly different results in heavy metal removal from chemical wastewater and long-term stability of the membrane separation system compared to the example. In the example, Cu-Fe@MNC / GO aerogel microspheres were introduced at the front end, which adsorbed macromolecular polymers in situ through a three-dimensional porous network and completely severed the chains through a persulfate system. The subsequently inoculated Haloxylon ammodendron MBR system was able to deeply metabolize the small molecule organic carbon sources generated by the chain severance. Combined with the mid-stage modified chitosan's exclusive chelation of trace heavy metals and the pre-implantation of polyepoxysuccinic acid as a phosphorus-free scale inhibitor, each stage achieved close cross-domain synergy at the physical, chemical, and biological levels, thereby ensuring extremely low heavy metal residues, high-purity salt removal rate, and extremely excellent long-term anti-fouling ability of the membrane.

[0036] In Comparative Example 1, the lack of modified nanocellulose and graphene oxide structural support components prevented the formation of aerogel interface chemical bridges. The directly added free Cu-Fe bimetallic catalyst was easily lost and aggregated in the continuous water flow, resulting in insufficient exposure of catalytic sites and a significant decrease in front-end chain scission efficiency. Heavy metals escaping with the water flow increased the removal load on the sedimentation tank, while incompletely scissioned organic matter increased the burden on subsequent membrane modules, leading to a significant increase in transmembrane pressure. Comparative Example 2, which did not pass through a bioreactor stage, resulted in a large amount of small-molecule organic acids generated by the upstream advanced oxidation process. Nanofiltration and reverse osmosis systems are prone to causing severe biological / organic fouling, which also reduces the membrane's retention accuracy. In Comparative Example 3, although a flocculation stage was added, the polymeric aluminum chloride and anionic polyacrylamide commonly used in traditional water treatment undergo severe chain curling due to the strong polyelectrolyte effect in high-salt systems, completely losing their bridging and chelating abilities. This prevents Cu / Fe ions from settling, and these high-concentration heavy metal ions then directly enter the membrane module, causing severe inorganic fouling and metal oxidation degradation on the membrane surface. In Comparative Example 4, no... Adding polyepoxysuccinic acid as a pre-implanted scale inhibitor, although removing organic matter and heavy metals at the upstream end, under the high concentration ratio of reverse osmosis and nanofiltration systems, trace amounts of hardness ions and high concentrations of sulfate ions quickly reach a supersaturated state on the membrane surface and precipitate crystalline scale, affecting the stability of the membrane module. In Comparative Example 5, replacing the sodium persulfate fed into the oxidation section with traditional hydrogen peroxide providing an equimolar amount of oxidation, the hydroxyl radicals generated by hydrogen peroxide have a weak chain-breaking ability on polymer macromolecules with high steric hindrance and complex aromatic ring structures, resulting in limited improvement in the biodegradability of the wastewater. The recalcitrant components in the liquid cannot be effectively utilized by microorganisms in the subsequent MBR. Ultimately, this residual organic matter accumulates on the membrane surface, leading to a significant increase in transmembrane pressure. In Comparative Example 6, conventional activated sludge from a municipal wastewater treatment plant that has not been acclimated to high salt levels was used in the MBR system. Due to the huge osmotic pressure difference generated by the high-salt wastewater, the water in the cells of ordinary microorganisms was rapidly extracted, resulting in severe plasmolysis and large-scale death of the microbial community. The dead sludge mixed with undegraded small-molecule organic matter and flushed into the membrane system, resulting in a decrease in retention rate and reduced membrane module stability.

[0037] Experiment Example 2: Waste Salt Recovery Performance Test The wastewater treatment performance and waste salt recovery performance of the chemical wastewater treatment processes in Examples 1-4 and Comparative Examples 1-6 were tested. Effluent from the fixed-bed catalytic converter during stable operation was used to determine COD using potassium dichromate titration (according to HJ828-2017) and BOD5 using dilution and inoculation method (according to HJ 505-2009). The ratio of these two methods is the B / C ratio. The COD concentration of the raw water influent and the COD concentration at the influent of the reverse osmosis system were measured, and the overall COD removal rate was calculated. The treated crystalline salt was used to determine the sodium chloride mass fraction using the silver titration method in GB / T 5462-2015, and the sodium sulfate mass fraction was determined using the gravimetric method in GB / T 6009-2014. Additionally, 1g of dried crystalline salt sample was accurately weighed, dissolved in carbon-free ultrapure water, and brought to a final volume. The TOC was measured using a combustion oxidation-non-dispersive infrared absorption analyzer and converted to the concentration in solid salt. The test results are shown in Table 3.

[0038] Table 3. Test results of the examples and comparative examples Example Fixed bed effluent B / C ratio Overall COD removal rate (%) Sodium chloride purity (%) Sodium sulfate recovery purity (%) TOC content (ppm) in crystalline salts Example 1 0.45 99.8 99.5 99.2 6.3 Example 2 0.41 99.4 99.1 98.8 8.7 Example 3 0.43 99.6 99.3 98.9 7.5 Example 4 0.48 99.9 99.6 99.4 5.2 Comparative Example 1 0.22 85.3 94.7 93.1 156.4 Comparative Example 2 0.46 72.1 91.2 89.5 452.9 Comparative Example 3 0.44 98.5 96.8 95.3 24.1 Comparative Example 4 0.47 99.2 97.4 96.6 9.8 Comparative Example 5 0.29 88.7 95.9 94 112.5 Comparative Example 6 0.4 78.4 92.5 90.7 345.6

[0039] As shown in Table 3, the comparative example, through adjustments to the components and process, exhibited significantly different performance in organic matter degradation and waste salt recovery of the chemical wastewater compared to the example. In the example, Cu-Fe@MNC / GO aerogel microspheres and a halophilic MBR biochemical system were introduced at the front and middle stages, respectively. Through the physicochemical synergy between the three-dimensional mesoporous framework and high-density functional groups of the aerogel, a local high-concentration sulfate radical enrichment zone was formed at the interface between the liquid and solid phases. This completely opened and broke the chain of macromolecular polymers, converting them into easily biodegradable small-molecule organic acids, which were then tightly bonded to the carbon source utilization chain for subsequent biochemical degradation. In addition, the unicellular bacteria underwent efficient metabolism in the MBR. The low TOC water quality after metabolism not only endowed the salt separation system with antifouling properties, but its extremely low organic matter residue also significantly eliminated co-solution interference during the crystallization process, which is beneficial to the subsequent high-purity extraction process of by-product salts.

[0040] In Comparative Example 1, lacking the three-dimensional interfacial chemical support framework of modified nanocellulose and graphene oxide, macromolecules in the catalytic system rely solely on random collisions and free bimetallic reactions, resulting in an extremely low B / C ratio in the effluent. The insufficiently shrunk polymer macromolecules cannot be effectively metabolized by the subsequent MBR and easily penetrate the biochemical system to the downstream end, causing a sharp drop in the overall COD removal rate. Furthermore, during high-temperature evaporation, they are carbonized and encapsulated within the crystal lattice, causing a surge in TOC. Combined with Comparative Example 2, the system lacks the biological metabolic consumption process of halophilic bacteria for carbon sources. In the front-end catalytic oxidation effluent, due to the presence of a large amount of small-molecule organic acids generated by ring-opening, its physicochemical properties are significantly different from those of directly crystallized pure organic matter. Incomplete salt solution matching leads to complex co-solubility and boiling point elevation when high concentrations of small-molecule organic carbon merge in the evaporator distributor. Furthermore, this significantly reduces overall crystallization purity and causes the salt to darken during subsequent high-temperature forced crystallization. In Comparative Example 3, although the primary function of the coagulant is to remove heavy metals to prevent membrane fouling, its replacement with traditional PAC and APAM, along with a slight adjustment to the electrostatic shielding effect in the high-salt background and the absence of modified chitosan, means a higher proportion of weakly complexed metal ions in the water. This results in slight changes in the sedimentation rate and complexation stability of impurities, leading to differences in the penetration depth of metal impurities into the crystallizer compared to when DTC targeting groups are present. The most significant difference is... The risk lies in the fact that trace amounts of copper / iron ions entering the crystal lattice cause changes in the redox potential, resulting in yellow-green spots on the crystalline salt, directly leading to a failure to meet the purity standards for refined industrial salt. In Comparative Example 4, inorganic hardness ions rapidly adhere and form scale on the high-temperature evaporator tube wall. The uneven inorganic scale layer leads to extremely uneven local heat flux distribution on the heat exchange tube wall, causing violent boiling of the evaporator liquid at the gas-liquid interface. Fine droplets are directly mixed into the secondary steam and finished crystals in the form of mist, destroying the purity of liquid-solid separation and causing varying degrees of decrease in the purity of sodium sulfate and sodium chloride. In Comparative Example 5, when sodium persulfate is replaced with hydrogen peroxide, the hydroxyl radicals generated by the Fenton system affect the high steric hindrance. Complex aromatic ring systems exhibit poor electrophilic addition selectivity, and their redox potential is severely suppressed in high-salt systems, leading to incomplete macromolecular chain scission, a significant decrease in the B / C ratio of the effluent, and the breakage of biochemically synergistic chains. Undegraded long-chain colloidal organic matter directly penetrates into the salt separation and crystallization system, causing a double deterioration in purity and TOC indicators. In Comparative Example 6, ordinary activated sludge was used. Under extreme osmotic pressure, the extravasation of microbial cell fluid led to membrane fouling. The dead cells released a large amount of extracellular polymers and soluble microbial metabolites into the water. These secondary macromolecular polysaccharides and proteins are extremely difficult to remove by conventional methods, directly resulting in a significant decrease in the overall COD removal rate.

[0041] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An integrated treatment method for desalination of chemical wastewater, characterized in that, The process includes the following steps: adjusting the pH of chemical wastewater to weakly acidic using sulfuric acid, passing it into a fixed-bed catalytic reaction tower containing aerogel microspheres, and treating it with sodium persulfate to obtain a reaction solution; then adjusting the pH to neutral using sodium hydroxide, and placing it in a membrane bioreactor for deep biochemical treatment to obtain dialysis supernatant; adjusting the pH of the dialysis supernatant and adding modified chitosan. Amphoteric polyacrylamide was added and stirred, then allowed to settle. Polyepoxysuccinic acid was added and stirred to obtain a mixture. The mixture was pumped into a nanofiltration membrane module for separation and treatment to obtain sodium sulfate and sodium chloride. The remaining mother liquor was refluxed and treated again in proportion. The aerogel microspheres were obtained by mixing graphene oxide, modified nanocellulose, copper sulfate and ferrous sulfate, crosslinking coagulation bath, washing and drying. The modified chitosan was dithiocarbamate modified chitosan.

2. The integrated treatment method for desalination of chemical wastewater according to claim 1, characterized in that, The preparation of the aerogel microspheres includes the following steps: dispersing 10-15 parts of the graphene oxide and 15-20 parts of the modified nanocellulose in deionized water, and ultrasonically treating to form a uniform suspension; then adding 20-25 parts of sodium alginate, stirring to dissolve, adding 4-6 parts of the copper sulfate crystals and 15-20 parts of ferrous sulfate heptahydrate, and stirring to obtain a mixed slurry; adding the mixed slurry dropwise into a crosslinking coagulation bath composed of anhydrous calcium chloride, ascorbic acid and the deionized water, and solidifying to obtain hydrogel microspheres; allowing static aging, washing with deionized water, and freeze-drying to obtain the aerogel microspheres.

3. The integrated treatment method for desalination of chemical wastewater according to claim 1, characterized in that, The treatment of the reaction solution includes the following steps: adjusting the pH value of the chemical wastewater and pumping it into a fixed-bed catalytic reaction tower filled with aerogel microspheres; continuously adding sodium persulfate solution at a ratio of 3.0-5.0 g / L through a metering pump; using a water bath jacket to keep the temperature inside the reaction tower constant at 65-75℃; and controlling the hydraulic residence time to be 90-120 min to obtain the reaction solution.

4. The integrated treatment method for desalination of chemical wastewater according to claim 1, characterized in that, The treatment of the dialysis solution includes the following steps: the reaction solution is cooled by a heat exchanger and the pH value is adjusted by sodium hydroxide solution. It is then introduced into a membrane bioreactor inoculated with salt-tolerant microorganisms. The total dissolved solids salinity of the system is controlled to be 8%-12%. Oxygen is supplied through a bottom microporous aeration disc, and the dialysis solution is obtained by filtration through a polytetrafluoroethylene hollow fiber membrane.

5. The integrated treatment method for desalination of chemical wastewater according to claim 1, characterized in that, The treatment of the mixture includes the following steps: adding sodium hydroxide solution to the dialysis solution to adjust the pH value, adding 10-20 mg / L of the modified chitosan, then adding 3-5 mg / L of the amphoteric polyacrylamide, stirring and mixing, and allowing it to stand to precipitate; then adding 30-50 mg / L of the polyepoxysuccinic acid, stirring and mixing to obtain the mixture.

6. The integrated treatment method for desalination of chemical wastewater according to claim 1, characterized in that, The separation process includes the following steps: pumping the mixture into a nanofiltration membrane module with an operating pressure of 1.5-2.5 MPa to form nanofiltration concentrate, which is then sent through a pipeline to a cryogenic crystallizer to cool and precipitate sodium sulfate crystals, followed by centrifugation; the chloride-rich nanofiltration permeate enters a reverse osmosis system with an operating pressure of 4.0-6.0 MPa, boils at 90°C to evaporate and crystallize, and is then centrifuged and dried to obtain the sodium chloride.

7. The integrated treatment method for desalination of chemical wastewater according to claim 1, characterized in that: The purity of the recovered sodium sulfate is 98.9%-99.4%; the purity of the recovered sodium chloride is 99.1%-99.6%.

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