Coal chemical high-salt high-phenol wastewater treatment method and system

Abstract

The application discloses a coal chemical high-salt high-phenol wastewater treatment method and system, and the method comprises the following steps: detoxification pretreatment, salt-tolerant biochemical treatment, deep desalination and crystallization, and resource recovery. The application adopts a process route of "front-end deep detoxification and impurity removal + middle-end salt-tolerant biochemical synergy". First, through the precise pretreatment of "ammonia evaporation and ammonia removal" and "extraction and phenol extraction", ammonia nitrogen and phenols and other toxic substances are efficiently removed at the source, and the inhibiting factors of the subsequent biochemical unit are fundamentally removed. Then, combined with the domesticated salt-tolerant microbial flora (Halomonas and Chromohalobacter), the biochemical system can stably operate in a high-salt environment with TDS>15000 mg / L, and the COD removal rate is stably above 80%, so that the combined inhibition problem of high salt, high phenol and high ammonia nitrogen to biochemical treatment is solved, and the long-term stable operation of the whole process is ensured.

Description

Technical Field

[0001] The invention relates to the field of industrial wastewater treatment and resource utilization technology, specifically to a treatment process for high-concentration organic wastewater from coal chemical industry, and in particular, a method and system for treating high-salt and high-phenol wastewater from coal chemical industry. Background Technology

[0002] Wastewater generated from coal chemical processes is characterized by high ammonia nitrogen, high phenol, high salt, poor degradation, and large fluctuations in water quality. The total dissolved solids (TDS) often exceed 15,000 mg / L, the phenol concentration can reach 500-2,000 mg / L, the ammonia nitrogen concentration is 100-500 mg / L, and the biodegradability is extremely poor (B / C < 0.3). Existing wastewater treatment technologies suffer from the following key challenges: Poor stability of biological systems: Conventional biological treatments struggle to withstand the toxic effects of high salt and phenol concentrations, severely inhibiting microbial activity and resulting in low removal efficiency for pollutants such as COD and ammonia nitrogen, making it impossible to consistently meet standards. Insufficient economic viability of physicochemical methods: Single evaporation and membrane separation processes incur extremely high investment and operating costs, and are prone to scaling, membrane fouling, and other problems, leading to difficult equipment maintenance and short service life. Low resource utilization: Existing processes primarily aim for "compliant discharge," lacking a systematic resource recovery design. Valuable components such as ammonia, phenols, and salts in wastewater are not effectively recovered and utilized, failing to achieve true zero wastewater discharge and thus not meeting the requirements for green and low-carbon industrial development.

[0003] Currently, the mainstream coal chemical wastewater treatment process in the industry involves several steps: First, ammonia nitrogen is removed from the front end using an ammonia stripping tower, and phenols are recovered from an extraction tower to reduce wastewater toxicity. Second, conventional activated sludge processes are used for biological treatment to degrade organic pollutants. Finally, advanced oxidation processes such as Fenton oxidation are used to further remove recalcitrant organic matter, followed by RO membrane separation for wastewater reuse. The concentrated wastewater undergoes evaporation and crystallization to achieve zero discharge. However, this process has the following drawbacks: poor shock resistance of the biological system; conventional microbial communities cannot adapt to high-salt environments with TDS > 10000 mg / L; high salt and residual phenols continuously inhibit microbial activity, leading to large fluctuations in biological treatment efficiency and COD. The removal rate can only be maintained at 60%-70%, which cannot guarantee the stable operation of the subsequent membrane system; membrane fouling and scaling problems are prominent: the front-end pretreatment does not completely remove hardness ions such as calcium and magnesium and residual organic matter, which makes the RO membrane module prone to scaling and organic pollution, resulting in short membrane cleaning cycles, significantly shortened service life, and high operation and maintenance costs; resource recovery is incomplete: only ammonia and phenol are initially recovered, and the impurities produced by evaporation and crystallization have low purity and cannot be reused as industrial salt, but can only be disposed of as hazardous waste, which increases environmental protection costs; energy consumption and costs are too high: the energy consumption of traditional multi-effect evaporation process is as high as 30-40 kWh / t of water, and the insufficient front-end impurity removal leads to serious scaling of the evaporator, which further increases the operating cost and has poor economic efficiency; the effluent water quality does not meet the standards: the COD, phenol and other indicators of the final freshwater of conventional processes are difficult to consistently meet the coal chemical circulating cooling water makeup water standards, which limits the scope of reuse.

[0004] In summary, existing coal chemical high-salt and high-phenol wastewater treatment processes generally suffer from the following technical bottlenecks: (1) poor process synergy, with toxic substances (phenol, ammonia nitrogen) and high salinity exerting a dual inhibitory effect on the biochemical system, leading to unstable system operation; (2) high operating costs, with low biochemical efficiency resulting in a heavy burden on advanced oxidation, high evaporation energy consumption, and scaling problems increasing maintenance costs; and (3) low resource utilization, with incomplete recovery of ammonia and phenol, and crystalline salt being hazardous waste, failing to achieve true zero discharge and resource recycling. Therefore, developing an integrated treatment process that can synergistically detoxify and desalinate, operate efficiently and stably, achieve simultaneous recovery of reclaimed water and resources, and has controllable operating costs has become an urgent technical challenge to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a method and system for treating high-salt and high-phenol wastewater from coal chemical industry, so as to at least partially solve the above-mentioned problems of the prior art.

[0006] To achieve the above objectives, the present invention provides a method for treating high-salt, high-phenol wastewater from coal chemical industry, characterized by comprising the following steps: (1) Detoxification pretreatment: The raw water is successively subjected to ammonia stripping and deammoniation, phenol extraction and chemical softening to obtain pretreated effluent; (2) Salt-tolerant biochemical treatment: The pretreated effluent is introduced into a biological reactor and acclimated salt-tolerant microbial community is added for degradation; the salt-tolerant microbial community is composed of Halomonas genus and Chlorobacter genus, and the total dissolved solids tolerance concentration of the community in a high-salt environment is greater than 15000 mg / L; (3) Deep desalination and crystallization: After Fenton oxidation, the biochemical effluent enters the two-stage RO membrane device and the MVR evaporation crystallization device in sequence to recover the crystallized salt slurry and the evaporation condensate; (4) Resource recovery: The two-stage RO permeate and the evaporation condensate are combined and then subjected to deep treatment to produce recycled water that meets the standards for coal chemical circulating cooling water makeup water. In this process, phenolic substances are reduced to below a specific threshold through a pre-treatment to match the metabolic characteristics of the specific salt-tolerant bacterial community, thereby achieving a synergistic detoxification of high salt and high phenolic toxicity.

[0007] Furthermore, in step (1), the chemical softening treatment adopts the lime-sodium carbonate softening method to control the calcium and magnesium hardness of the pretreated effluent entering step (2) to <200 mg / L, so as to prevent scaling of the subsequent membrane system and evaporator.

[0008] Furthermore, in step (1), the ammonia stripping process uses steam stripping, and the top gas phase of the tower is absorbed and recovered using dilute sulfuric acid; the phenol extraction process uses countercurrent extraction, and the extract phase is regenerated by distillation while recovering the crude phenol product and the regenerated extractant.

[0009] Furthermore, in step (2), the COD removal rate of the salt-tolerant microbial community can reach more than 80%, and the residence time of the biochemical treatment is 48 to 72 hours.

[0010] Furthermore, in step (3), ferrous salt and hydrogen peroxide are added in the Fenton oxidation step to degrade the recalcitrant organic matter in the biochemical effluent through hydroxyl radical degradation; in the two-stage RO membrane device, the first-stage RO concentrate enters the second-stage RO treatment, and the second-stage RO concentrate enters the MVR evaporation and crystallization device.

[0011] Furthermore, in step (4), the deep treatment step includes ultrafiltration and activated carbon adsorption, and the produced reusable freshwater has the following indicators: COD≤50mg / L, phenols≤5mg / L, and pollution index SDI≤3.

[0012] Another objective of this invention is to provide a coal chemical high-salt and high-phenol wastewater treatment system for implementing the method, characterized in that it includes an ammonia stripping and deammoniation device, an extraction and phenol extraction device, a chemical softening treatment device, a biological reaction tank, a Fenton oxidation device, a two-stage RO membrane device, an MVR evaporation and crystallization device, a deep treatment device, and a salt separation and drying device connected sequentially by pipelines. The outlet of the ammonia stripping and deammoniation device is connected to the inlet of the extraction and phenol extraction device, and the outlet of the extraction and phenol extraction device is connected to the inlet of the chemical softening treatment device. The outlet of the chemical softening treatment device is connected to the inlet of the biological reaction tank; The outlet of the biological reactor is connected to the inlet of the Fenton oxidation device; The outlet of the Fenton oxidation device is connected to the inlet of the two-stage RO membrane device. The permeate outlet of the two-stage RO membrane device and the condensate outlet of the MVR evaporation crystallization device are both connected to the inlet of the deep treatment device. The salt slurry outlet of the MVR evaporation crystallization device is connected to the feed inlet of the salt separation and drying device.

[0013] Furthermore, the extraction and phenol extraction device includes an extraction tower and a distillation and regeneration tower connected in series. The extract phase outlet of the extraction tower is connected to the feed inlet of the distillation and regeneration tower. The distillation and regeneration tower is provided with a crude phenol outlet, and the regeneration extractant outlet of the distillation and regeneration tower is connected to the extractant inlet of the extraction tower through a circulation pipeline. The raffinate outlet of the extraction tower constitutes the water outlet of the extraction and phenol extraction device.

[0014] Furthermore, the two-stage RO membrane device includes a primary RO membrane group and a secondary RO membrane group connected in series. Both the primary and secondary RO membrane groups are provided with independent concentrate outlets, and the concentrate outlets are connected to the feed inlet of the MVR evaporation crystallization device.

[0015] Furthermore, the advanced treatment device includes an ultrafiltration device and an activated carbon adsorption tower connected in series via pipelines. The inlet of the ultrafiltration device serves as the inlet of the advanced treatment device, used to collect the permeate from the two-stage RO membrane device and the condensate from the MVR evaporation and crystallization device.

[0016] Compared with the prior art, the present invention has at least the following advantages.

[0017] First, the system exhibits strong synergy and stable, reliable operation. This invention innovatively adopts a process route of "deep detoxification and impurity removal at the front end + mid-stage salt-tolerant biochemical synergy." Firstly, through precise pretreatment of "ammonia stripping and deammonia removal" and "phenol extraction," toxic substances such as ammonia nitrogen and phenols are efficiently removed at the source, fundamentally eliminating inhibitory factors on subsequent biochemical units. Subsequently, combined with domesticated salt-tolerant microbial communities (Haloxylon ammodendron and Chromobacterium), the biochemical system can operate stably in a high-salt environment with TDS > 15000 mg / L, maintaining a COD removal rate consistently above 80%. This solves the combined inhibitory problem of high salt, high phenol, and high ammonia nitrogen on biochemical treatment, ensuring long-term stable operation of the entire process.

[0018] Secondly, it achieves true zero wastewater discharge and resource recovery. This invention deeply integrates "treatment" and "recycling," realizing comprehensive resource recovery of water, salt, and valuable components. Specifically, this is reflected in: ① Water resource recovery: Through "two-stage RO + MVR evaporation and crystallization + deep treatment," the produced reclaimed water has excellent quality (COD ≤ 50 mg / L, phenols ≤ 5 mg / L, SDI ≤ 3), which can be directly reused as makeup water for circulating cooling water, significantly reducing the consumption of fresh water. ② Valuable component recovery: Ammonia nitrogen is recovered in the form of ammonium salt, and phenols are recovered in the form of crude phenol products, turning waste into treasure. ③ Salt resource recovery: Finally, through MVR crystallization and purification, the hazardous waste "mixed salts" generated by traditional processes are refined into industrial salt products that can be utilized for resource recovery, completely solving the problem of mixed salt disposal and realizing "zero liquid discharge" and "solid waste resource recovery" throughout the entire process.

[0019] Third, it boasts low operating costs and significant energy-saving and consumption-reducing effects. This is reflected in: ① Significantly reduced energy consumption: The main evaporation unit employs mechanical vapor recompression technology, fully utilizing the latent heat of secondary steam to effectively control energy consumption per ton of water evaporated to 15-25 kWh, saving over 50% energy compared to traditional multi-effect evaporation (typically >50 kWh / t of water), thus greatly improving operational economics. ② Reduced maintenance costs: Through upstream "chemical softening" and "coagulation sedimentation" processes, calcium and magnesium hardness ions and colloidal substances are efficiently removed, greatly alleviating scaling and contamination problems in subsequent RO membrane systems and MVR evaporators from the source. This significantly extends membrane cleaning and equipment maintenance cycles, reducing reagent consumption and operation and maintenance costs.

[0020] Fourth, it boasts high treatment efficiency and produces excellent and stable effluent quality. This invention constructs a highly efficient organic matter removal chain through the effective integration of "salt-tolerant biochemical degradation" and "Fenton deep oxidation." The biochemical stage removes most degradable organic matter, while the advanced oxidation stage specifically targets and breaks down recalcitrant components, ensuring excellent water quality entering the membrane system and reducing membrane fouling. Finally, through the dual deep treatment guarantee of "ultrafiltration + activated carbon adsorption," it ensures that the product water quality not only consistently meets but also exceeds the standards for coal chemical circulating cooling water makeup water, resulting in low reuse risk and high reliability.

[0021] Fifth, it offers significant environmental benefits and aligns with the requirements of green and low-carbon development. The entire process of this invention is guided by "resource recovery" and "zero emissions," not only solving the pollution problem of highly challenging wastewater from coal chemical industries but also achieving the recycling of water, salt, ammonia, and phenol. This minimizes the environmental risks of wastewater discharge and the land occupation and secondary pollution risks associated with landfilling of miscellaneous salts, resulting in significant environmental and social benefits. Attached Figure Description

[0022] Figure 1 This is a flowchart of a method for treating high-salt, high-phenol wastewater used in coal chemical industry according to the present invention.

[0023] Figure 2 This is a schematic diagram of an embodiment of a high-salt, high-phenol wastewater treatment system for coal chemical industry according to the present invention.

[0024] Schematic diagram of the attached diagram: 1—Acid absorption tower; 2—Ammonium salt recovery; 5—Ammonia stripping tower; 6—Distillation regeneration tower; 7—Extraction tower; 8—Crude phenol recovery; 9—Salt-tolerant biological reactor; 10—Fenton oxidation unit; 11—First-stage RO membrane unit; 12—Second-stage RO membrane unit; 13—Homogenization and conditioning tank; 14—Chemical softening tank; 15—Coagulation and sedimentation tank; 16—Raw water; 17—MVR evaporation and crystallization unit; 18—Salt separation and drying unit; 20—Industrial salt recovery; 21—Ultrafiltration unit; 22—Fresh water reuse; 23—Activated carbon adsorption tower. Detailed Implementation

[0025] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0026] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be used interchangeably where appropriate to understand the embodiments of the invention described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a product or device comprising a series of units is not necessarily limited to those explicitly listed, but may include other units not explicitly listed or inherent to such product or device.

[0027] In this invention, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," and "longitudinal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing the invention and its embodiments, and are not intended to limit the indicated devices, elements, or components to having a specific orientation, or to be constructed and operated in a specific orientation.

[0028] Furthermore, in addition to indicating direction or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in certain situations to indicate a dependency or connection. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0029] Furthermore, the terms "installation," "setup," "equipped with," "connection," "linking," and "socketing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral structure; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium, or an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0030] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments. Example 1

[0031] Please refer to Figure 1 and Figure 2 The method for treating high-salt, high-phenol wastewater from coal chemical industry in this embodiment includes: Ammonia stripping and deammoniation: Raw water 16 enters ammonia stripping tower 5, where ammonia nitrogen in the wastewater is removed by steam stripping. The gas phase at the top of the tower enters acid absorption tower 1, where dilute sulfuric acid is used to absorb ammonia nitrogen, and finally ammonium salt products are recovered. The liquid phase at the bottom of the tower (deammoniation wastewater) enters extraction tower 7.

[0032] Extraction of phenols: The deammoniation wastewater is contacted countercurrently with the extractant in the extraction tower 7 to extract phenolic substances from the wastewater; the extracted phase enters the distillation regeneration tower 6, where phenols and extractant are separated by distillation, crude phenol product is recovered, and the regenerated extractant is returned to the extraction tower 7 for recycling; the residual aqueous phase (dephenolization wastewater) enters the homogenization equalization tank 13.

[0033] Water conditioning and softening: The phenol removal wastewater is homogenized and equalized in the equalization tank 13 to stabilize the water quality and quantity; then it enters the chemical softening tank 14, where lime, sodium carbonate and other agents are added to remove hardness ions such as calcium and magnesium and prevent scaling of the subsequent membrane system and evaporator; finally, it enters the coagulation sedimentation tank 15, where flocculants (such as PAC, PAM) are added to remove suspended solids, colloids and residual organic matter, and the supernatant enters the main treatment stage.

[0034] Salt-tolerant biochemical treatment: The pretreated wastewater enters the salt-tolerant biological reactor 9, where acclimatized salt-tolerant microbial flora (Haloxylon ammodendron and Chromobacterium spp.) are added. This flora can stably tolerate the high-salt environment with TDS > 15000 mg / L and efficiently degrade organic pollutants in the wastewater. The COD removal rate can reach more than 80%, solving the problem of high salt inhibiting the biochemical system.

[0035] Fenton deep oxidation: The biochemical effluent enters the Fenton oxidation unit 10, where the hydroxyl radicals generated by the Fenton reagent deeply degrade recalcitrant organic matter (such as polycyclic aromatic hydrocarbons and heterocyclic compounds) that are difficult to remove by biochemical methods, further reducing COD and ensuring the quality of the influent water for the subsequent membrane system.

[0036] Two-stage RO membrane desalination: The effluent from oxidation sequentially enters the first-stage RO membrane group 11 and the second-stage RO membrane group 12, where the fresh water and concentrated water are separated through membrane separation; the permeate from the two stages is combined and then enters the advanced treatment stage, while the concentrated water enters the MVR evaporation and crystallization unit 17.

[0037] MVR Evaporation and Crystallization: RO concentrate enters the MVR evaporation and crystallization unit 17, and wastewater is concentrated and crystallized through mechanical vapor recompression technology. The condensate is returned to the deep treatment stage, and the crystallized salt slurry enters the salt separation and drying unit 18.

[0038] Deep freshwater treatment: The permeate from the two-stage RO system is combined with the condensate from the MVR system and enters the ultrafiltration unit 21 to remove residual suspended solids and colloids; then it enters the activated carbon adsorption tower 23 to adsorb and remove residual organic matter and phenols. The final freshwater produced has a COD ≤ 50 mg / L, phenols ≤ 5 mg / L, and SDI ≤ 3, which meets the standards for make-up water for coal chemical circulating cooling water and realizes freshwater reuse.

[0039] Salt resource recovery: The salt slurry generated by MVR evaporation enters the salt separation and drying unit 18. Through separation, drying and purification processes, the miscellaneous salt is refined into industrial salt products, realizing the resource recovery of salt and truly achieving zero wastewater discharge.

[0040] Preferably, in this embodiment, the ammonia stripping and deammoniation unit, the phenol extraction and extraction unit, the chemical softening treatment unit, the biological reactor, the Fenton oxidation unit, the two-stage RO membrane unit, the MVR evaporation and crystallization unit, the deep treatment unit, and the salt separation and drying unit are connected sequentially via pipelines. The outlet of the ammonia stripping and deammoniation unit is connected to the inlet of the phenol extraction and extraction unit, and the outlet of the phenol extraction and extraction unit is connected to the inlet of the chemical softening treatment unit. The outlet of the chemical softening treatment unit is connected to the inlet of the biological reactor. The outlet of the biological reactor is connected to the inlet of the Fenton oxidation unit. The outlet of the Fenton oxidation unit is connected to the inlet of the two-stage RO membrane unit. The permeate outlet of the two-stage RO membrane unit and the condensate outlet of the MVR evaporation and crystallization unit are both connected to the inlet of the deep treatment unit. The salt slurry outlet of the MVR evaporation and crystallization unit is connected to the inlet of the salt separation and drying unit.

[0041] Preferably, the ammonia stripping and deammoniation device described in this embodiment includes an ammonia stripping tower 5 and an acid absorption tower 1 connected in series. The gas inlet pipe of the acid absorption tower 1 is connected to the gas phase outlet at the top of the ammonia stripping tower 5. The bottom of the acid absorption tower 1 is provided with an ammonium salt recovery outlet. The bottom liquid phase outlet of the ammonia stripping tower 5 constitutes the water outlet of the ammonia stripping and deammoniation device.

[0042] Preferably, the extraction and phenol extraction device of this embodiment includes an extraction tower 7 and a distillation and regeneration tower 6 connected in series. The extract phase outlet of the extraction tower 7 is connected to the feed inlet of the distillation and regeneration tower 6. The distillation and regeneration tower 6 is provided with a crude phenol outlet, and the regeneration extractant outlet of the distillation and regeneration tower 6 is connected to the extractant inlet of the extraction tower 7 through a circulation pipeline. The raffinate aqueous phase outlet of the extraction tower 7 constitutes the water outlet of the extraction and phenol extraction device.

[0043] Preferably, the chemical softening treatment device described in this embodiment includes a homogenization conditioning tank 13, a chemical softening tank 14, and a coagulation sedimentation tank 15 connected in series via pipelines.

[0044] Preferably, the two-stage RO membrane device in this embodiment includes a primary RO membrane group 11 and a secondary RO membrane group 12 connected in series. Both the primary RO membrane group 11 and the secondary RO membrane group 12 are provided with independent concentrate outlets, and the concentrate outlets are connected to the feed inlet of the MVR evaporation crystallization device 17.

[0045] Preferably, the deep treatment device in this embodiment includes an ultrafiltration device 21 and an activated carbon adsorption tower 23 connected in series by pipelines. The inlet of the ultrafiltration device 21 serves as the inlet of the deep treatment device, and is used to collect the permeate from the two-stage RO membrane device and the condensate from the MVR evaporation and crystallization device 17.

[0046] Preferably, the inlet of the extraction and phenol extraction device described in this embodiment is connected to the bottom liquid phase outlet of the ammonia stripping tower 5.

[0047] Preferably, the inlet of the chemical softening treatment device described in this embodiment is connected to the raffinate outlet of the extraction tower 7.

[0048] Preferably, the salt-tolerant bioreactor 9 described in this embodiment is an aeration tank or sequencing batch reactor structure used to accommodate salt-tolerant microbial communities.

[0049] Preferably, the system described in this embodiment further includes a pump for conveying materials and a control valve for controlling the operating status of each device, wherein the pump and the control valve are installed on corresponding connecting pipelines.

[0050] Specifically, the object of treatment in this embodiment is wastewater from a coal chemical gasification-liquefaction combined unit (example of water quality indicators in Table 1), which corresponds to the high-salt and high-phenol wastewater treatment system for coal chemical industry described in this invention.

[0051] Table 1 COD 8200 mg / L ammonia nitrogen 3600 mg / L volatile phenols 1100 mg / L TDS 23000 mg / L Calcium magnesium hardness 460 mg / L .

[0052] The process steps in this embodiment include the following.

[0053] (1) Detoxification pretreatment: Raw water first enters the ammonia stripping tower 5, where steam stripping is used to control the gas-liquid ratio at 120 m³ / h. The gas phase at the top of the tower enters the acid absorption tower 1, where it is absorbed by 20% dilute sulfuric acid to generate ammonium sulfate solution. After crystallization and drying, the industrial-grade ammonium salt product is recovered. The deammonia-removed wastewater enters the extraction tower 7, where it is contacted countercurrently with methyl isobutyl ketone (MIBK) at an O / A ratio of 1:3. The extracted phase enters the distillation regeneration tower 6 to separate and recover crude phenol product (purity ≥95%), and the regenerated extractant is returned to the extraction tower. The raffinate phase enters the homogenization equalization tank 13, where it is retained for 12 h. Then it enters the chemical softening tank 14, where lime 350 mg / L and sodium carbonate 250 mg / L are added to control the effluent hardness <180 mg / L. Finally, it enters the coagulation sedimentation tank 15, where PAC = 30 mg / L and PAM = 1 mg / L are added to remove suspended solids.

[0054] (2) Targeted Salt-Tolerant Biochemical Treatment: The pretreated effluent enters the salt-tolerant bioreactor 9, inoculated with a salt-tolerant microbial community composed of *Haloxylon ammodendron* and *Halomycin* at a biomass ratio of 3:1. DO is controlled at 2.5–3.5 mg / L, HRT at 60 h, and MLSS at 4500 mg / L. This microbial community maintains high activity under high-salt conditions (TDS > 20000 mg / L), achieving a COD removal rate of 81.5%, thus resolving the synergistic inhibition of biochemical treatment by high salt and phenolic toxicity.

[0055] (3) Deep desalination and crystallization: The biochemical effluent enters the Fenton oxidation unit 10, with Fe²⁺=80mg / L, H₂O₂=200mg / L, pH=3.5, and oxidation time of 45min. The Fenton effluent sequentially enters the primary RO membrane group 11 and the secondary RO membrane group 12: the primary RO recovery rate is 70%, and the concentrate enters the secondary RO; the secondary RO recovery rate is 85%, and the concentrate TDS>80000 mg / L enters the MVR evaporation crystallization unit 17. The condensate generated by the MVR evaporation is recycled to the deep treatment unit, and the crystallized salt slurry enters the salt separation and drying unit 18.

[0056] (4) Advanced treatment and resource recovery: The permeate from the two-stage RO system and the condensate from the MVR system are combined and then sequentially fed into the ultrafiltration unit 21 and the activated carbon adsorption tower 23. The ultrafiltration system has a molecular weight cutoff of 100 kDa, and the activated carbon adsorbs residual organic matter and phenols. The final permeate has the following characteristics: COD = 38 mg / L, phenols = 0.6 mg / L, and SDI = 2.4, which meets the standards for make-up water for circulating cooling water in coal chemical industry. The MVR crystallized salt slurry is separated and dried to obtain NaCl industrial salt with a purity of 98.7%, thus realizing the resource recovery of salt. Example 2

[0057] This embodiment focuses on semi-coke wastewater with extremely high phenol concentration but relatively low salinity, and aims to verify the adaptability of "front-end detoxification + salt-tolerant biochemical treatment" to highly toxic substances.

[0058] This embodiment treats wastewater from a semi-coke enterprise in Northwest China (see Water Quality Indicators Example Table 2). The system described in this invention is used, and the system connection is the same as in Embodiment 1. The key difference lies in the adjustment of process parameters.

[0059] Table 2 COD 12500 mg / L ammonia nitrogen 2800 mg / L volatile phenols 3200 mg / L TDS 8500 mg / L CN⁻ 2g / L .

[0060] The process steps of the embodiment include the following.

[0061] (1) Detoxification Pretreatment: Ammonia stripping: Raw water enters ammonia stripping tower 5, with steam pressure controlled at 0.25 MPa. The gas phase at the top of the tower is absorbed by dilute sulfuric acid to recover ammonium sulfate. Phenol extraction: Due to the high phenol concentration of 3200 mg / L, a two-stage countercurrent extraction process is adopted. After the deammoniation wastewater and MIBK extractant are in countercurrent contact in the first-stage extraction tower, the raffinate phase enters the second-stage extraction tower for further extraction. The extraction ratio O / A = 1:4. The crude phenol recovery rate is increased to 92%. Water quality conditioning: Due to the low TDS, the dosage of chemical softening agent is appropriately reduced to control the effluent hardness to <150 mg / L.

[0062] (2) Targeted Salt-Tolerant Biochemical Treatment: Pretreated effluent enters salt-tolerant bioreactor 9. To address the biotoxicity caused by extremely high phenol concentrations, the microbial community structure is adjusted: *Haloxylon ammodendron* : *Halomycinobacter* = 1:2. Principle: *Halomycinobacter* has a stronger metabolic pathway for phenolic compounds; increasing its proportion enhances the buffering capacity against high phenol shocks. Operating parameters: HRT extended to 72h, MLSS controlled at 5000 mg / L. Technical results: Despite extremely high influent toxicity, no sludge disintegration occurred in the system, and the COD removal rate reached 87.2%.

[0063] (3) Deep desalination and crystallization: Fenton oxidation: The biochemical effluent enters the Fenton oxidation unit 10. Due to the increase in recalcitrant organic matter, H2O2=300 mg / L and Fe²⁺=100 mg / L are added, and the oxidation reaction time is extended to 60 min. Two-stage RO+MVR: Due to the low TDS of the influent, the salt content of the RO concentrate is relatively low, the MVR evaporation load is reduced, and the energy consumption is reduced by 15%.

[0064] (4) Advanced treatment and resource utilization: The permeate from the two-stage RO system and the condensate from the MVR system are combined and then treated by ultrafiltration and activated carbon. Permeate indicators: COD = 45 mg / L, volatile phenols = 0.8 mg / L, SDI = 2.6. Resource utilization: The amount of crude phenol recovered increased by 18% compared to Example 1; all freshwater was reused in the coke quenching section. Example 3

[0065] This embodiment focuses on verifying the anti-scaling design of "chemical softening + two-stage RO + MVR" for brine processing wastewater with extremely high calcium and magnesium hardness and high chloride ion content.

[0066] This embodiment treats brine wastewater from a salt lake resource development enterprise (see Water Quality Indicators Example Table 3). The system described in this invention is used, with a particularly enhanced configuration of the chemical softening tank and the MVR evaporation crystallization device.

[0067] Table 3 TDS 62000 mg / L Cl⁻ 28000 mg / L Ca²⁺ 1200 mg / L Mg²⁺ 480 mg / L <![CDATA[SiO2]]> 80 mg / L .

[0068] The process steps of this embodiment include the following: (1) Detoxification pretreatment: Ammonia stripping and extraction: conventional operation, recovery of ammonium salts and trace phenols. Water quality conditioning and softening: Wastewater enters chemical softening tank 14, and lime 600 mg / L and sodium carbonate 400 mg / L are added. Introduction of seed crystal-induced crystallization technology: Quartz sand is added to the reaction tank as crystal nuclei to promote the precipitation of Ca²⁺ and Mg²⁺ in the form of crystals, rather than forming colloidal flocs. Control index: The calcium and magnesium hardness of the effluent is reduced to 160 mg / L. Scale prevention mechanism: By thoroughly removing hardness ions, the risk of subsequent CaSO4 and SiO2 scaling on the membrane surface is blocked.

[0069] (2) Targeted Salt Tolerance Biochemical Treatment: Due to the high TDS of 62000 mg / L, an ultra-high salt acclimatization mode was initiated. Microbial Community Status: Halomonas and Chromobacterium secreted large amounts of extracellular polymeric substances (EPS) in a hyperosmotic environment to maintain cell osmotic pressure. Operational Results: Under a high chloride ion environment, the COD removal rate remained stable at 78.5%.

[0070] (3) Deep desalination and crystallization: Fenton oxidation: Normal operation, further reducing organic matter. Two-stage RO membrane desalination: The concentrate from the first-stage RO enters the second-stage RO. Due to thorough softening at the front end, the flux decline rate of the RO membrane is only 8% after 180 days of operation. MVR evaporation crystallization: The concentrate from the second-stage RO enters the MVR evaporation crystallization unit. Since the hardness has been removed, the MVR heat exchanger has been running continuously for 180 days without significant scaling, and the cleaning cycle has been extended to 12 months.

[0071] (4) Advanced Treatment and Resource Utilization: Freshwater Reuse: After ultrafiltration and activated carbon treatment, the COD of the RO permeate and condensate is 48 mg / L, meeting the reuse standard. Salt Resource Utilization: The main component of the salt slurry discharged from the MVR is NaCl. After purification by a salt separation and drying device, industrial salt products are obtained with a purity of 99.1%, which is superior to the first-grade standard of "Industrial Salt" (GB / T 5462-2015).

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for treating high-salt, high-phenol wastewater from coal chemical industry, characterized in that, Includes the following steps: (1) Detoxification pretreatment: The raw water is successively subjected to ammonia stripping and deammoniation, phenol extraction and chemical softening to obtain pretreated effluent; (2) Salt-tolerant biochemical treatment: The pretreated effluent is introduced into a biological reactor and acclimated salt-tolerant microbial community is added for degradation; the salt-tolerant microbial community is composed of Halomonas genus and Chlorobacter genus, and the total dissolved solids tolerance concentration of the community in a high-salt environment is greater than 15000 mg / L; (3) Deep desalination and crystallization: After Fenton oxidation, the biochemical effluent enters the two-stage RO membrane device and the MVR evaporation crystallization device in sequence to recover the crystallized salt slurry and the evaporation condensate; (4) Resource recovery: The two-stage RO permeate and the evaporation condensate are combined and then subjected to deep treatment to produce recycled water that meets the standards for coal chemical circulating cooling water makeup water. In this process, phenolic substances are reduced to below a specific threshold through a pre-treatment to match the metabolic characteristics of the specific salt-tolerant bacterial community, thereby achieving a synergistic detoxification of high salt and high phenolic toxicity.

2. The method for treating high-salt, high-phenol wastewater from coal chemical industry according to claim 1, characterized in that, In step (1), the chemical softening treatment adopts the lime-sodium carbonate softening method to control the calcium and magnesium hardness of the pretreated effluent entering step (2) to be <200 mg / L.

3. The method for treating high-salt, high-phenol wastewater from coal chemical industry according to claim 1, characterized in that, In step (1), ammonia stripping is performed using steam stripping, and the top gas phase is absorbed and recovered using dilute sulfuric acid; phenol extraction is performed using countercurrent extraction, and the extract phase is regenerated by distillation while recovering crude phenol products and regenerated extractant.

4. The method for treating high-salt, high-phenol wastewater from coal chemical industry according to claim 1, characterized in that, In step (2), the COD removal rate of the salt-tolerant microbial community reaches more than 80%, and the residence time of the biochemical treatment is 48 to 72 hours.

5. The method for treating high-salt, high-phenol wastewater from coal chemical industry according to claim 1, characterized in that, In step (3), ferrous salt and hydrogen peroxide are added in the Fenton oxidation step to degrade the recalcitrant organic matter in the biochemical effluent through hydroxyl radical degradation; in the two-stage RO membrane device, the first-stage RO concentrate enters the second-stage RO treatment, and the second-stage RO concentrate enters the MVR evaporation and crystallization device.

6. The method for treating high-salt, high-phenol wastewater from coal chemical industry according to claim 1, characterized in that, In step (4), the deep treatment steps include ultrafiltration and activated carbon adsorption, and the resulting reusable freshwater has the following indicators: COD≤50mg / L, phenols≤5mg / L, and SDI≤3.

7. A coal chemical high-salt, high-phenol wastewater treatment system implementing the method of any one of claims 1 to 6, characterized in that, It includes an ammonia stripping and deaming unit, an extraction and phenol extraction unit, a chemical softening treatment unit, a biological reactor, a Fenton oxidation unit, a two-stage RO membrane unit, an MVR evaporation and crystallization unit, a deep treatment unit, and a salt separation and drying unit, which are connected sequentially by pipelines. The outlet of the ammonia stripping and deammoniation device is connected to the inlet of the extraction and phenol extraction device, and the outlet of the extraction and phenol extraction device is connected to the inlet of the chemical softening treatment device. The outlet of the chemical softening treatment device is connected to the inlet of the biological reaction tank; The outlet of the biological reactor is connected to the inlet of the Fenton oxidation device; The outlet of the Fenton oxidation device is connected to the inlet of the two-stage RO membrane device. The permeate outlet of the two-stage RO membrane device and the condensate outlet of the MVR evaporation crystallization device are both connected to the inlet of the deep treatment device. The salt slurry outlet of the MVR evaporation crystallization device is connected to the feed inlet of the salt separation and drying device.

8. The coal chemical high-salt, high-phenol wastewater treatment system according to claim 7, characterized in that, The extraction and phenol extraction device includes an extraction tower and a distillation and regeneration tower connected in series. The extract phase outlet of the extraction tower is connected to the feed inlet of the distillation and regeneration tower. The distillation and regeneration tower is provided with a crude phenol outlet, and the regeneration extractant outlet of the distillation and regeneration tower is connected to the extractant inlet of the extraction tower through a circulation pipeline. The raffinate outlet of the extraction tower constitutes the water outlet of the extraction and phenol extraction device.

9. The coal chemical high-salt, high-phenol wastewater treatment system according to claim 7, characterized in that, The two-stage RO membrane device includes a primary RO membrane group and a secondary RO membrane group connected in series. Both the primary and secondary RO membrane groups are provided with independent concentrate outlets, and the concentrate outlets are connected to the feed inlet of the MVR evaporation and crystallization device.

10. The coal chemical high-salt, high-phenol wastewater treatment system according to claim 7, characterized in that, The advanced treatment device includes an ultrafiltration device and an activated carbon adsorption tower connected in series via pipelines. The inlet of the ultrafiltration device serves as the inlet of the advanced treatment device, used to collect the permeate from the two-stage RO membrane device and the condensate from the MVR evaporation and crystallization device.

Images