Resourceful treatment method for high-salinity wastewater in cooperation with carbon dioxide emission reduction

Abstract

The invention discloses a resourceful treatment method for high-salinity wastewater and carbon dioxide emission reduction, and relates to the technical field of high-salinity wastewater treatment. Comprising the following steps: pre-treating the high-salinity wastewater to remove suspended matters, part of refractory organic matters and specific pollutants, and then introducing the high-salinity wastewater into a reverse osmosis system for concentration to obtain recycled produced water and mixed brine concentrated water; the salt content of the recycled water meets the standard of industrial recycled water, and the salt content of the mixed brine concentrated water is several times of the salt content of the original high-salt wastewater; washing salt in the mixed salt concentrated water with desalted water, and performing evaporative crystallization to obtain solid sodium sulfate; the pretreatment provides adaptive water quality for a subsequent membrane separation process, a membrane separation product provides an absorbent for carbon dioxide capture, and carbon capture and salt recovery form resource circulation through substance flow connection; the method is suitable for high-salinity wastewater with different characteristics of silicon, fluorine, high calcium and magnesium, low temperature, high temperature, high turbidity and the like, and strict pretreatment of wastewater and waste gas raw materials is not needed.

Description

Technical Field

[0001] This invention relates to the field of high-salinity wastewater treatment technology, and in particular to a resource-based treatment method for high-salinity wastewater with synergistic carbon dioxide emission reduction. Background Technology

[0002] With the rapid development of industries such as coal chemical, printing and dyeing, electronics, and chemicals, the discharge of high-salinity wastewater continues to rise. This type of wastewater is characterized by high salt content and complex composition, with sodium chloride and sodium sulfate as the main salts, often accompanied by complex pollutants such as silicon, fluorine, calcium and magnesium ions, and recalcitrant organic matter. Conventional treatment processes often employ a combination of reverse osmosis and evaporation crystallization. However, this type of process only achieves simple volume reduction of the wastewater, and the resulting mixed salts cannot be utilized as resources due to their mixed composition. They are classified as hazardous waste, facing not only high disposal costs but also potential risks of soil and water pollution, becoming a key bottleneck restricting the green development of the industry.

[0003] Meanwhile, industrial carbon-containing waste gases (such as boiler flue gas and chemical tail gas) are the main source of carbon dioxide emissions. Existing carbon dioxide capture technologies generally rely on purchased chemical absorbents such as sodium hydroxide and ammonia, which suffers from prominent problems such as high absorbent consumption, high operating costs, and a lack of economically feasible pathways for the immobilization of captured carbon dioxide. More critically, in existing technologies, the treatment of high-salinity wastewater, carbon dioxide emission reduction, and solid waste disposal are independent processes without a synergistic operation mechanism. This results in low resource utilization efficiency, cumulative environmental protection costs, and high overall system energy consumption. The industry urgently needs a synergistic technology that can simultaneously solve the problem of treating mixed salts in high-salinity wastewater and meet the demand for low-cost carbon dioxide emission reduction, while also achieving resource recycling across multiple stages. Summary of the Invention

[0004] To address the technical problems existing in the prior art, this invention provides a resource-based treatment method for high-salinity wastewater with synergistic carbon dioxide emission reduction. The technical solution is as follows:

[0005] A resource-based treatment method for high-salinity wastewater with synergistic carbon dioxide emission reduction is provided, the method comprising the following steps:

[0006] After pretreatment to remove suspended solids, some recalcitrant organic matter and characteristic pollutants, the S1 high-salinity wastewater is concentrated by a reverse osmosis system to obtain reusable permeable water and mixed brine concentrate. The salinity of the reusable permeable water meets the industrial reusable water standard, while the salinity of the mixed brine concentrate is several times that of the original high-salinity wastewater.

[0007] S2 mixed brine concentrate is passed into a nanofiltration system to separate salts, resulting in sodium chloride dilute brine and mixed brine concentrate. The sodium chloride dilute brine has a purity that meets the requirements for subsequent deep concentration, and the mixed brine concentrate has sodium sulfate as the main component.

[0008] S3 sodium chloride dilute brine is passed into the reverse osmosis system for deep concentration, yielding demineralized water and concentrated sodium chloride brine; the demineralized water can be directly reused.

[0009] The S4 sodium chloride brine is passed through a two-stage mixed resin deep adsorption process to further remove calcium, magnesium, and fluoride ions, meeting the operating requirements of the S5 bipolar membrane equipment.

[0010] S5 sodium chloride concentrated brine was passed into a bipolar membrane electrodialysis system to prepare sodium hydroxide solution and hydrochloric acid; the concentrations of the two products were adapted to the requirements of subsequent processes.

[0011] S6 sodium hydroxide solution is introduced into the carbon dioxide capture system, where it comes into contact with carbon-containing waste gas to absorb carbon dioxide and generate sodium carbonate solution.

[0012] The sodium carbonate solution S7 is passed through a membrane distillation process to evaporate and crystallize, yielding solid sodium carbonate.

[0013] The concentrated brine from the S2 primary nanofiltration stage is diluted with the demineralized brine produced by S3 and S7 and then enters the nanofiltration stage for washing. Finally, the concentrated brine from the secondary nanofiltration stage is obtained by evaporation, fractional crystallization, and solid sodium sulfate is obtained.

[0014] Nanofiltration provides suitable water quality for subsequent reverse osmosis membrane separation processes, the reverse osmosis membrane separation products provide reactants for bipolar membrane processes, and the sodium hydroxide solution produced by the bipolar membrane provides adsorbents for carbon dioxide capture.

[0015] Beneficial effects

[0016] The beneficial effects of the technical solutions provided in the embodiments of the present invention include at least the following:

[0017] 1. By constructing a closed-loop process system of pretreatment-membrane separation-bipolar membrane alkali and acid production-carbon dioxide capture-salt recovery, with multi-stage membrane separation and bipolar membrane conversion as the core technologies, and using wastewater desalination products as carbon dioxide capture media, a deep coupling of high-salinity wastewater purification, carbon dioxide fixation, and chemical product resource utilization is achieved, forming a virtuous cycle of pollution control, carbon sequestration, and resource utilization. The targeted pretreatment unit and dedicated membrane module adaptation design ensure stable process operation, and cross-unit energy and material circulation enhances synergistic efficiency. This solves the technical problems of traditional high-salinity wastewater treatment, such as the generation of large amounts of mixed salt hazardous waste, reliance on purchased absorbents for carbon dioxide capture, and resource waste caused by the independent operation of each treatment stage. It improves the synergy and stability of high-salinity wastewater treatment and carbon emission reduction.

[0018] 2. The sodium hydroxide solution prepared by bipolar membrane replaces the traditional purchased carbon dioxide absorbent, achieving resource-based salt separation of high-salt wastewater while completing carbon capture. There is no need to purchase additional absorbent or dispose of mixed salts, avoiding the problems of mixed salt accumulation and pollution in traditional membrane separation processes and the large consumption of reagents in carbon capture technology. Furthermore, the membrane module cleaning solution and washing wastewater are recycled after treatment, and the evaporation condensate is returned to the system to participate in the reaction again. There is no hazardous waste generated or pollutants discharged during the entire process, which meets the "dual carbon" target requirements and solves the problems of serious secondary pollution and large resource consumption in traditional technologies, thus improving the low-carbon and environmentally friendly attributes of the process.

[0019] 3. High-efficiency separation of salt components is achieved through nanofiltration and XCRO deep concentration. The bipolar membrane conversion products react with carbon dioxide to generate sodium carbonate. The mixed salt is washed to recover sodium sulfate, while recycled permeate and hydrochloric acid are produced, realizing the resource utilization of pollutants. The membrane module and adsorbent can be reused after regeneration, eliminating the need for frequent replacement and reducing consumable costs. At the same time, the diverse products have industrial application value, bringing additional revenue to enterprises. This solves the problems of low resource utilization and high operating costs of traditional technologies, and improves the economic feasibility of the process.

[0020] 4. Through targeted pretreatment design and optimization of dedicated membrane modules, the system can be adapted to high-salt wastewater with different characteristics such as silicon-containing, fluorine-containing, high calcium and magnesium, low temperature, and high temperature and high turbidity. At the same time, it can use carbon-containing waste gas from different sources such as industrial boiler flue gas and chemical tail gas as raw materials, without the need for strict pretreatment of wastewater and waste gas raw materials. This solves the problems of limited application scenarios and poor raw material adaptability of traditional technologies, and expands the applicability of the process and its prospects for industrial promotion. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a process flow diagram of a resource-based treatment method for high-salinity wastewater with synergistic carbon dioxide emission reduction, provided in an embodiment of this application. Detailed Implementation

[0023] The technical solution provided in this application will now be described with reference to the accompanying drawings.

[0024] To facilitate understanding of the embodiments of this application, the following points will be explained first:

[0025] First, in this application, "at least one" refers to one or more, and "more than one" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent: A alone, A and B simultaneously, or B alone, where A and B can be singular or plural. The character " / " generally indicates an "or" relationship between the preceding and following related objects, but does not exclude the possibility of indicating an "and" relationship. The specific meaning can be understood in the context. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of singular or plural items. For example, "at least one of a, b, or c" can represent: a, b, c; a and b; a and c; b and c; or a and b and c. Here, a, b, and c can be single or multiple.

[0026] Second, in this application, the use of prefixes such as "first" and "second" is merely for the purpose of distinguishing and describing different things belonging to the same name category, and does not constrain the order, size, or quantity of things. For example, "first message" and "second message" are simply different messages, and there is no temporal sequence, size, or priority relationship between them.

[0027] In this embodiment of the invention, sometimes a subscript such as W1 may be written in a non-subscript form such as W1. When the difference is not emphasized, the meaning they express is the same.

[0028] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0029] like Figure 1 As shown, this application provides a resource-based treatment method for high-salinity wastewater with synergistic carbon dioxide emission reduction, comprising the following steps:

[0030] After pretreatment to remove suspended solids, some recalcitrant organic matter and characteristic pollutants, the S1 high-salinity wastewater is concentrated by a reverse osmosis system to obtain reusable permeable water and mixed brine concentrate. The salinity of the reusable permeable water meets the industrial reusable water standard, while the salinity of the mixed brine concentrate is several times that of the original high-salinity wastewater.

[0031] S2 mixed brine concentrate is passed into a nanofiltration system to separate salts, resulting in sodium chloride dilute brine and mixed brine concentrate. The sodium chloride dilute brine has a purity that meets the requirements for subsequent deep concentration, and the mixed brine concentrate has sodium sulfate as the main component.

[0032] S3 sodium chloride dilute brine is passed into the reverse osmosis system for deep concentration, yielding demineralized water and concentrated sodium chloride brine; the demineralized water can be directly reused.

[0033] The S4 sodium chloride brine is passed through a two-stage mixed resin deep adsorption process to further remove calcium, magnesium, and fluoride ions, meeting the operating requirements of the S5 bipolar membrane equipment.

[0034] S5 sodium chloride concentrated brine was passed into a bipolar membrane electrodialysis system to prepare sodium hydroxide solution and hydrochloric acid; the concentrations of the two products were adapted to the requirements of subsequent processes.

[0035] S6 sodium hydroxide solution is introduced into the carbon dioxide capture system, where it comes into contact with carbon-containing waste gas to absorb carbon dioxide and generate sodium carbonate solution.

[0036] The sodium carbonate solution S7 is passed through a membrane distillation process to evaporate and crystallize, yielding solid sodium carbonate.

[0037] The concentrated brine from the S2 primary nanofiltration stage is diluted with the demineralized brine produced by S3 and S7 and then enters the nanofiltration stage for washing. Finally, the concentrated brine from the secondary nanofiltration stage is obtained by evaporation, fractional crystallization, and solid sodium sulfate is obtained.

[0038] Nanofiltration provides suitable water quality for subsequent reverse osmosis membrane separation processes, the reverse osmosis membrane separation products provide reactants for bipolar membrane processes, and the sodium hydroxide solution produced by the bipolar membrane provides adsorbents for carbon dioxide capture.

[0039] As an optional embodiment, for high-salt wastewater containing fluoride, hardness, and organic matter, the S1 pretreatment is equipped with fluoride removal, hardness removal, and organic matter removal units.

[0040] The fluoride concentration and hardness of the pretreated wastewater meet the influent requirements of the nanofiltration membrane system; the sodium chloride brine after nanofiltration is concentrated by low-pressure plus high-pressure reverse osmosis, and the sodium chloride concentration meets the influent material requirements of the bipolar membrane.

[0041] To further remove fluoride and calcium and magnesium ions, a two-stage resin adsorption process is adopted. The first-stage resin uses a hydrogen-form cation exchange resin to remove calcium and magnesium ions, which is convenient for elution and regeneration using hydrochloric acid generated by S5. The second-stage resin uses an aluminum-supported macroporous resin, which is convenient for regeneration using sodium hydroxide generated by S5. The deep fluoride removal concentration meets the requirements of bipolar membrane electrodialysis treatment.

[0042] During S5 carbon dioxide capture, carbon-containing waste gas is first passed into an adsorption tower filled with amino-functionalized mesoporous silica adsorbent for enrichment, and then passed into an absorption tower to react with sodium hydroxide solution. The adsorption tower and the absorption tower are connected in series. The carbon-decarbonized tail gas from the absorption tower is tested and discharged in compliance with standards, or it is returned to the adsorption enrichment process for secondary adsorption.

[0043] The defluorination and hardening units prevent membrane fouling, ensuring the stable operation of S2 nanofiltration desalination and S3 high-pressure reverse osmosis deep concentration. This, in turn, ensures that the S5 bipolar membrane electrodialysis system produces a sufficient amount of sodium hydroxide solution of suitable concentration. The carbon dioxide enriched by the adsorbent comes into full contact with the alkaline solution, and the two form an energy linkage through waste heat recovery.

[0044] As an optional embodiment, for high-salt concentration conditions, the S3XTRO system uses a high-pressure adapted membrane module, which has a pressure range adapted to high-pressure environments and a membrane flux that meets the concentration requirements.

[0045] The S2 nanofiltration system adjusts the operating pressure, and the S4 bipolar membrane electrodialysis system adjusts the operating voltage accordingly.

[0046] High-pressure adaptive membrane modules ensure the membrane stability of S3 under high pressure. The parameter adjustment of nanofiltration and bipolar membranes, along with the desiliconization and carbon dioxide enrichment steps, achieves material concentration adaptation. The energy required for low-pressure reverse osmosis concentration is partly recovered from the concentrate energy of the XTRO system, forming an energy closed loop in this scenario.

[0047] As an optional embodiment, for high-salt wastewater containing organic matter, fluoride, and hardness, the S1 pretreatment uses chemical precipitation to remove fluoride and hardness to meet the nanofiltration membrane feed water requirements. The nanofiltration membrane removes some COD to meet the reverse osmosis feed water requirements. Before entering the bipolar membrane electrodialysis, a multi-stage resin adsorption unit is added. Hydrogen-based resin removes calcium and magnesium ions, and aluminum-loaded resin deeply adsorbs and removes fluoride ions to ensure the stable operation of the bipolar membrane electrodialysis system.

[0048] S7 evaporation crystallization uses an integrated membrane distillation crystallization system to separate immobilized carbon dioxide product sodium carbonate. This method includes a hydrophobically modified polyvinylidene fluoride membrane module and a crystallizer. The secondary condensate generated during distillation is used for the salt washing process.

[0049] Sodium hydroxide prepared by S5 is used for the regeneration of fluoride ion adsorbent. The regenerated adsorbent can be recycled and reused. The regeneration waste liquid is then defluorinated by chemical precipitation and re-entered into the nanofiltration system. Defluorination reduces the problems of membrane flux decline and bipolar membrane plate corrosion caused by fluoride ions.

[0050] As an optional embodiment, the evaporator of S7 adopts a multi-effect evaporation system driven by industrial waste heat, and the heat source is waste heat steam generated in the industrial production process; the condensate of the evaporator is divided into two parts, one part is returned to S1 for pretreatment as makeup water, and the other part is introduced into the membrane distillation and crystallization integrated system as distillation makeup water.

[0051] S1 recycled water is prioritized for the S7 salt washing process, with the remainder used for enterprise production water; industrial waste heat replaces traditional energy, and condensate and recycled water form a closed loop of water resources, which, together with hydrochloric acid regeneration cycle and membrane distillation waste heat recovery, constitutes energy and resource synergy.

[0052] As an optional embodiment, for high-salt wastewater containing fluoride, hardness, and organic matter, a chemical softening unit is added to the S1 pretreatment, sodium carbonate and sodium hydroxide are added, and after reaction, calcium and magnesium precipitates are removed by filtration; the precipitates can be used as raw materials for building materials after treatment.

[0053] The S5 carbon dioxide capture uses an adsorption tower and an absorption tower connected in series. The waste gas first enters the adsorption tower to capture sodium dioxide and concentrate it, and then enters the carbon dioxide absorption tower, where S4 is introduced to produce a sodium hydroxide solution. The carbon dioxide is fixed by sodium hydroxide in the carbon capture solution. The carbon capture solution is then distilled using a membrane distillation process to obtain a carbonate byproduct, or it can be further absorbed to obtain a sodium bicarbonate carbon capture solution. The carbon capture solution can also be recycled and reused by using the high-concentration carbon dioxide desorbed from the hydrochloric acid produced by S4.

[0054] The chemical softening unit prevents scaling of nanofiltration and nanofiltration membranes, extends the service life of membrane modules, and ensures salt separation and concentration efficiency. The two-stage absorption and regeneration system improves the capture effect of low-concentration carbon dioxide and forms a material synergy with the sodium hydroxide and hydrochloric acid produced by S4.

[0055] As an optional embodiment, the hydrochloric acid prepared in S4 can be further concentrated as an industrial by-product, or used for acid leaching of coal gangue or steel slag; the leachate is purified to recover valuable metals.

[0056] The solid sodium carbonate obtained from S6 can be used for front-end chemical hardening, reducing operating costs, and achieving a certain purity to obtain valuable industrial by-product sodium carbonate.

[0057] As an optional embodiment, for high-salt wastewater with high hardness, fluoride, and organic matter, the S1 pretreatment adopts a combined process of fluoride and hardness removal. Sodium hydroxide, sodium carbonate, and coagulant are added to the wastewater, and after stirring and reaction, the wastewater is allowed to settle in a clarification tank. The supernatant is then filtered through an ultrafiltration system.

[0058] As an optional embodiment, an online monitoring and control system is set up, the method including a water quality monitoring module and a parameter control module;

[0059] The water quality monitoring module monitors the salinity, COD, concentration of characteristic pollutants, and temperature of the influent at each step in real time; the parameter control module automatically adjusts the operating pressure of the reverse osmosis system, the membrane flow rate of the nanofiltration system, the operating voltage of the bipolar membrane electrodialysis system, and the liquid-to-gas ratio of carbon dioxide capture based on the monitoring results.

[0060] The online monitoring and control system works in conjunction with coagulation clarification and ultrafiltration pretreatment to adapt to water quality fluctuations in high-temperature and high-turbidity wastewater in real time, ensuring the coordinated operation of steps such as nanofiltration desalination, XCRO concentration, and carbon capture.

[0061] As an optional embodiment, a closed-loop membrane module cleaning system is constructed; the sodium hydroxide solution prepared in S4 is used for alkaline washing and regeneration of reverse osmosis, nanofiltration, and XCRO membrane modules in addition to being supplied to carbon capture; the acid washing and regeneration of membrane modules uses hydrochloric acid prepared in S4.

[0062] The waste liquid after acid and alkali washing is treated and then returned to the S1 pretreatment for reprocessing. The water for solution preparation comes from the recycled water resources within the system. The washing wastewater generated by the S7 salt washing is fed into the secondary reverse osmosis system for treatment. The permeate is returned to the salt washing process. The concentrated water is combined with the original high-salt wastewater from S1 for treatment. The membrane module cleaning closed loop and the washing wastewater recycling form waste liquid recycling and utilization, which is connected with the cross-unit energy and material coupling mechanism to improve the comprehensive utilization rate of resources.

[0063] The following detailed description of the resource-based treatment method for high-salinity wastewater with synergistic carbon dioxide emission reduction of the present invention, in conjunction with specific embodiments and comparative examples, provides a detailed explanation of the method.

[0064] I. Basic Experimental Conditions

[0065] 1. General test parameters:

[0066] Processing capacity: 10 m³ / h (continuous operation, 20 hours per day, 30 days in total)

[0067] Testing indicators: Comprehensive cost of wastewater treatment (including energy consumption, reagents, equipment depreciation, and solid waste disposal fees), carbon dioxide capture cost, salt product purity, comprehensive water resource utilization rate, unit energy consumption, removal rate of characteristic pollutants, and membrane module flux decay rate.

[0068] Detection method:

[0069] Salt purity was determined by ion chromatography.

[0070] Carbon dioxide capture efficiency was determined using an infrared gas analyzer.

[0071] The comprehensive utilization rate of water resources is calculated as (reclaimed water volume plus condensate water reuse volume) / total raw water volume × 100%;

[0072] The flux decay rate of the membrane module is calculated as (initial flux - 30-day operating flux) / initial flux × 100%.

[0073] 2. Core equipment parameters;

[0074] Reverse osmosis system: polyamide composite membrane, single membrane area 40m², initial flux 80L / (m²·h), fouling resistant;

[0075] Nanofiltration system: polypiperazine amide membrane, molecular weight cutoff 150 Da, design pressure 3.5 MPa, membrane surface flow rate design value 0.8~1.0 m / s;

[0076] XCRO system: Ultra-high pressure reverse osmosis membrane, maximum pressure resistance 12MPa, initial flux 60L / (m²·h), high pressure resistant composite membrane material;

[0077] Bipolar membrane electrodialysis system: homogeneous bipolar membrane, 5 membrane stacks, 2m² area per membrane stack, ion migration rate ≥0.005cm / s;

[0078] Carbon dioxide capture system: packed tower (diameter 1.2m, height 6m), polypropylene stepped ring packing (specification φ50mm), mass transfer coefficient KYa≥0.05kmol / (m³·h·kPa);

[0079] Evaporators: MVR evaporator (evaporation capacity 5t / h, evaporation temperature 75℃, energy consumption 280kWh / t water), triple-effect evaporator (evaporation capacity 3t / h, evaporation temperature 95 / 85 / 75℃, steam consumption 0.4t / t water).

[0080] Auxiliary equipment: plate heat exchanger (heat exchange area 20m², heat exchange efficiency ≥85%), online monitoring equipment (detection accuracy ±1%, data acquisition frequency 5min / time), heat pump unit (heating capacity 15kW, COP≥3.5).

[0081] II. Implementation Examples;

[0082] Example 1: Silicon-containing scenario with low CO2 concentration

[0083] 1. Influent water quality (simulating actual wastewater from the coal chemical industry)

[0084] Salt content: 18000 mg / L (sodium chloride 12000 mg / L, sodium sulfate 6000 mg / L)

[0085] Silicon concentration: 45 mg / L (in the form of silicate ions)

[0086] Carbonaceous waste gas composition: nitrogen 75%, carbon dioxide 8%, oxygen 17% (volume fraction).

[0087] COD: 1200 mg / L, Suspended solids: 80 mg / L, pH: 7.2~7.8, Water temperature: 15~20℃

[0088] 2. Processing steps and detailed parameters

[0089] S1 Preprocessing:

[0090] Silicon removal unit: Add 12% lime slurry to the wastewater, stir at 300 r / min, adjust the pH to 10.2, react for 18 minutes, and filter using a plate and frame filter press (filtration pressure 0.6 MPa, filter cloth pore size 1 μm). After filtration, the silicon concentration in the wastewater is reduced to 4.2 mg / L.

[0091] Conventional pretreatment: sequentially passing through sand filtration (filtration rate 10m / h, quartz sand particle size 0.8~1.2mm, bed height 1.5m) and ultrafiltration (membrane pore size 0.05μm, membrane surface flow velocity 1.0m / s, transmembrane pressure difference 0.1~0.15MPa), with a suspended solids removal rate of 99% and an effluent SDI≤3, meeting the feed water requirements of subsequent membrane systems.

[0092] S2 reverse osmosis concentration: operating pressure 2.5MPa, operating temperature 28℃, concentration ratio 8 times, recycled permeate salinity 420mg / L, suspended solids ≤5mg / L, COD ≤100mg / L, meeting the water quality requirements for industrial process water, mixed brine concentrate salinity 144000mg / L, membrane flux maintained at 72~75L / (m²·h).

[0093] S3 nanofiltration salt separation: operating pressure 3.0MPa, membrane surface flow rate 0.8m / s, operating temperature 28℃, sodium chloride dilute brine purity 97.5% (sodium chloride accounts for 97.5%, the remainder is a small amount of sodium sulfate), mixed salt concentrate sodium sulfate accounts for 95.2% (sodium sulfate accounts for 95.2%, the remainder is a small amount of sodium chloride), system recovery rate 60%.

[0094] S4XCRO Deep Concentration: Operating pressure 6.5MPa, operating temperature 30℃, sodium chloride brine concentration 22%, demineralized water salt content ≤100μS / cm, demineralized water reused in S7 washing process, membrane flux maintained at 55~58L / (m²·h).

[0095] S5 bipolar membrane electrodialysis: operating voltage 2.0V / membrane, current density 200A / m², operating temperature 25℃, sodium hydroxide solution concentration 11%, hydrochloric acid concentration 9%, acid and alkali solution yield ≥90% (yield calculated as actual output / theoretical output × 100%), membrane stack voltage stability ≤±0.05V.

[0096] S6 carbon dioxide capture:

[0097] An adsorption-absorption-regeneration coupled device was used. The adsorption tower was filled with amino-functionalized mesoporous silica adsorbent (preparation method: using tetraethyl orthosilicate as silicon source and 3-aminopropyltriethoxysilane as modifier, prepared by sol-gel method, with a specific surface area of ​​850 m² / g and a CO2 adsorption capacity of 3.8 mmol / g).

[0098] Adsorption tower operating conditions: adsorption temperature 25℃, empty tower gas velocity 0.8m / s, gas residence time 10s;

[0099] Absorption tower operating conditions: liquid-to-gas ratio 12L / m³, sodium hydroxide solution spray density 20m³ / (m²·h), gas-liquid contact time 30s;

[0100] Regeneration tower operating conditions: steam pressure 0.3MPa, regeneration temperature 90℃, regeneration time 60 minutes, regeneration tail gas temperature 85℃, preheated inlet water (inlet water temperature increased from 15℃ to 28℃) is introduced into the reverse osmosis system inlet, and waste heat recovery efficiency ≥70%.

[0101] S7 Evaporation and Crystallization:

[0102] Sodium carbonate solution was evaporated and crystallized in an MVR evaporator at a temperature of 75℃ and a vacuum of -0.08MPa. After crystallization, the product was centrifuged (4000 r / min, separation factor 1200) and dried (120℃, 2 h) to obtain solid sodium carbonate product. The total alkalinity, calculated as sodium carbonate, was not less than 99.0%, and the chloride content was not more than 0.5%.

[0103] The mixed salt concentrate is washed with desalinated water produced by S4 (liquid-solid ratio 4:1), stirred and washed for 30 minutes (stirring speed 200 r / min), and the filtrate is evaporated and crystallized by a triple-effect evaporator at 95 / 85 / 75℃ to obtain solid sodium sulfate product with a sodium sulfate content of not less than 95.0% and a water-insoluble content of not more than 0.1%.

[0104] 3. Processing results;

[0105] Comprehensive wastewater treatment cost: RMB 12.8 / m³ (including energy cost of RMB 5.2 / m³, reagent cost of RMB 2.1 / m³, equipment depreciation of RMB 3.5 / m³, and other costs of RMB 2.0 / m³).

[0106] Carbon dioxide capture cost: 185 yuan / ton CO2 (excluding equipment depreciation, only energy consumption and reagent replenishment costs are included);

[0107] Water resource utilization rate: 92% (reclaimed water volume 8.5 m³ / h, condensate water reuse volume 0.7 m³ / h, raw water volume 10 m³ / h).

[0108] Energy consumption per unit: 8.2 kWh / m³;

[0109] Removal rates of characteristic pollutants: silicon removal rate 90.7%, COD removal rate 65.0%, suspended solids removal rate 99.0%, CO2 capture efficiency 96.3%;

[0110] Product specifications: Sodium carbonate total alkalinity 99.2%, chloride 0.3%, sodium sulfate content 95.8%, water-insoluble matter 0.08%;

[0111] Membrane module operation status: After 30 days of continuous operation, the flux decline rates of reverse osmosis membrane, nanofiltration membrane and XCRO membrane were 3.2%, 4.1% and 5.3% respectively. There was no obvious scaling or fouling on the membrane surface. After routine cleaning, the flux recovery rate was ≥98%.

[0112] Example 2: Low-temperature silicon-containing scenario;

[0113] 1. Influent water quality (simulating coal chemical wastewater in northern winter)

[0114] Salt content: 16000 mg / L (sodium chloride 10000 mg / L, sodium sulfate 6000 mg / L)

[0115] Silicon concentration: 38 mg / L, ambient temperature: 8℃ (diurnal fluctuation ±2℃), wastewater temperature: 8~10℃

[0116] Carbonaceous waste gas composition: nitrogen 76%, carbon dioxide 7%, oxygen 17% (volume fraction)

[0117] COD: 1000 mg / L, pH: 7.0~7.5, Suspended solids: 60 mg / L

[0118] 2. Processing steps and detailed parameters

[0119] S1 Preprocessing:

[0120] Silicon removal unit: parameters are the same as in Example 1, silicon concentration after filtration is 3.9 mg / L;

[0121] Waste heat preheating: A heat pump device (heating capacity 15kW, COP=3.6) is added to recover waste heat from XCRO concentrate (concentrate temperature 45℃). The reverse osmosis feed water is preheated through a plate heat exchanger, raising the feed water temperature from 8℃ to 22℃. The energy consumption for the preheating process is 1.2kWh / m³.

[0122] S2 reverse osmosis concentration: operating pressure 2.8MPa (membrane flux compensation at low temperature), operating temperature 22℃, concentration ratio 7 times, recycled permeate salinity 450mg / L, suspended solids ≤5mg / L, COD ≤120mg / L, meeting the water quality requirements for industrial process water, mixed brine concentrate salinity 112000mg / L, membrane flux maintained at 68~70L / (m²·h).

[0123] S3 nanofiltration salt separation: operating pressure 3.2MPa, membrane surface flow rate 0.9m / s, operating temperature 22℃, sodium chloride dilute brine purity 97.2%, mixed salt concentrate sodium sulfate content 95.0%, system recovery rate 58%.

[0124] S4XCRO Deep Concentration: Employs a low-temperature adaptable membrane module (structure: polyamide composite membrane layer plus polyethersulfone low-temperature toughening support layer, temperature range -5℃~20℃, glass transition temperature -10℃), operating pressure 7.0MPa, operating temperature 20℃, sodium chloride brine concentration 20%, demineralized water salt content ≤120μS / cm, and membrane flux maintained at 52~55L / (m²·h).

[0125] S5 bipolar membrane electrodialysis: operating voltage 2.2V / membrane (ion migration rate compensation at low temperature), current density 220A / m², operating temperature 20℃, sodium hydroxide concentration 10.5%, hydrochloric acid concentration 8.5%, acid and alkali solution yield ≥88%.

[0126] S6 CO2 capture: Adsorption-absorption-regeneration coupled device, liquid-to-gas ratio 14L / m³, 30% of adsorbent regeneration energy consumption is supplemented by waste heat from XCRO concentrate (the remaining 70% is supplied by industrial steam), regeneration tail gas preheats reverse osmosis feed water to 22℃, CO2 capture efficiency 95.8%.

[0127] S7 Evaporation and Crystallization: Parameters are the same as in Example 1. The MVR evaporator is equipped with a polyurethane insulation layer (thickness 50mm), with a heat loss rate of ≤5%, avoiding additional energy consumption loss in low-temperature environments; the sodium carbonate product has a total alkalinity of 99.0% and chloride content of 0.4%, and the sodium sulfate product has a content of 95.5% and water-insoluble matter content of 0.09%.

[0128] 3. Processing Results

[0129] Comprehensive wastewater treatment cost: 13.5 yuan / m³ (including energy cost of 5.8 yuan / m³, reagent cost of 2.0 yuan / m³, equipment depreciation of 3.6 yuan / m³, and other costs of 2.1 yuan / m³).

[0130] Carbon dioxide capture cost: 192 yuan / ton CO2;

[0131] Water resource utilization rate: 91% (reclaimed water volume 8.3 m³ / h, condensate water reuse volume 0.8 m³ / h, raw water volume 10 m³ / h).

[0132] Unit energy consumption: 8.8 kWh / m³ (25% lower than conventional low-temperature treatment process (11.7 kWh / m³));

[0133] Removal rates of characteristic pollutants: silicon removal rate 90.0%, CO2 capture efficiency 95.8%, COD removal rate 62.0%, and suspended solids removal rate 99.2%;

[0134] Product specifications: Sodium carbonate total alkalinity 99.0%, chloride 0.4%, sodium sulfate content 95.5%, water-insoluble matter 0.09%;

[0135] Membrane module operation status: The low-temperature adapted membrane module operated continuously for 30 days, with a flux attenuation rate of 6.1%, no brittleness or leakage, and the membrane integrity test passed.

[0136] Example 3: High COD fluorine-containing scenario;

[0137] 1. Influent water quality (simulating high-salinity wastewater from the electronics industry)

[0138] Salt content: 15000 mg / L (sodium chloride 9000 mg / L, sodium sulfate 6000 mg / L)

[0139] COD: 2800 mg / L (mainly recalcitrant organic compounds, such as benzene series compounds and esters)

[0140] Fluorine concentration: 65 mg / L; CO2 volume fraction in carbonaceous waste gas: 10%.

[0141] pH: 6.8~7.3, water temperature: 25~30℃, suspended solids: 50mg / L

[0142] 2. Processing steps and detailed parameters

[0143] S1 Preprocessing:

[0144] Catalytic oxidation combined with activated carbon adsorption: In the catalytic oxidation unit, a titanium-based composite catalyst (Ti-Mn-O composite oxide, particle size 50μm, specific surface area 120m² / g) was added at a dosage of 65mg / L. The reaction temperature was 35℃, the stirring rate was 350r / min, and the reaction time was 25 minutes, resulting in a COD removal rate of 66.1%. In the activated carbon adsorption unit, granular activated carbon (wood-based activated carbon, specific surface area 1000m² / g, particle size 1-2mm) was used. With an empty bed residence time of 40 minutes, the COD was further reduced to 750mg / L, and the total COD removal rate was 73.2%.

[0145] Fluoride ion adsorption unit: hydroxyapatite-supported adsorbent (preparation method: hydroxyapatite and kaolin are compounded at a mass ratio of 7:3, and then calcined and activated to produce a particle size of 1-2 mm), the adsorption column diameter-to-height ratio is 1:8, the column height is 1.6 m, the empty bed residence time is 60 minutes, the fluoride concentration after adsorption is reduced to 0.9 mg / L, and the fluoride removal rate is 98.6%.

[0146] S2 reverse osmosis concentration: operating pressure 2.3MPa, operating temperature 30℃, concentration ratio 6 times, recycled permeate salinity 480mg / L, suspended solids ≤5mg / L, COD ≤150mg / L, meeting the water quality requirements for industrial process water, mixed brine concentrate salinity 90000mg / L, membrane flux maintained at 70~73L / (m²·h).

[0147] S3 nanofiltration salt separation: operating pressure 2.9MPa, membrane surface flow rate 0.8m / s, operating temperature 30℃, sodium chloride dilute brine purity 96.8%, mixed salt concentrate sodium sulfate content 95.3%, system recovery rate 62%.

[0148] S4XCRO Deep Concentration: Operating pressure 6.0MPa, operating temperature 32℃, sodium chloride brine concentration 19%, demineralized water salt content ≤100μS / cm, membrane flux maintained at 56~59L / (m²·h).

[0149] S5 Bipolar Membrane Electrodialysis: Operating voltage 1.9V / membrane pair, current density 190A / m², operating temperature 28℃, sodium hydroxide concentration 10%, hydrochloric acid concentration 8%; the hydrochloric acid portion is used for fluoride ion adsorbent regeneration (regeneration solution concentration 5%), regeneration temperature 40℃, regeneration time 90 minutes, and the adsorbent adsorption capacity recovery rate after regeneration is 92% (regeneration adsorption capacity / fresh adsorbent adsorption capacity × 100%). The regeneration waste liquid is refluxed back to the feed liquid inlet of the bipolar membrane electrodialysis system after impurity removal by a nanofiltration membrane (molecular weight cutoff 200Da), with an impurity removal rate ≥ 95%.

[0150] S6 carbon dioxide capture: liquid-to-gas ratio 11 L / m³, gas-liquid contact time 25 s, CO2 capture efficiency 96.5%.

[0151] S7 Evaporation Crystallization: Utilizing an integrated membrane distillation-crystallization system, the core component is a hydrophobically modified polyvinylidene fluoride membrane (0.3 μm pore size, 120° contact angle, 150 μm thickness). The operating temperature is 65℃, and the vacuum is -0.09 MPa. The secondary steam generated during distillation (60℃) heats the washing water (from 25℃ to 50℃) via a plate heat exchanger, achieving a waste heat recovery efficiency of 75%. Sodium sulfate crystallizes and is then centrifuged (3800 r / min) and dried (110℃, 1.5 h), resulting in a product content of 96.2% and water-insoluble matter of 0.07%. The sodium carbonate product has a total alkalinity of 99.1% and chloride content of 0.35%.

[0152] 3. Processing Results

[0153] The comprehensive cost of wastewater treatment is 14.2 yuan / m³ (including energy consumption cost of 5.1 yuan / m³, chemical cost of 2.5 yuan / m³, equipment depreciation of 3.7 yuan / m³, and other costs of 2.9 yuan / m³).

[0154] Carbon dioxide capture cost: 188 yuan / ton CO2;

[0155] Water resource utilization rate: 93% (reclaimed water volume 8.6 m³ / h, condensate water reuse volume 0.7 m³ / h, raw water volume 10 m³ / h).

[0156] Unit energy consumption: 7.9 kWh / m³ (18% lower than the process without waste heat recovery (9.6 kWh / m³));

[0157] Removal rates of characteristic pollutants: COD removal rate 73.2%, fluoride removal rate 98.6%, CO2 capture efficiency 96.5%, and suspended solids removal rate 99.0%;

[0158] Product specifications: Sodium carbonate total alkalinity 99.1%, chloride 0.35%, sodium sulfate content 96.2%, water-insoluble matter 0.07%;

[0159] Material recycling: The hydrochloric acid regeneration adsorbent recycling rate is 85% (hydrochloric acid used for regeneration / bipolar membrane acid production × 100%), and the waste heat recovery rate of membrane distillation is 75%.

[0160] Example 4: High calcium and magnesium plus ultra-low concentration CO2 scenario

[0161] 1. Influent water quality (simulating complex pollutant wastewater from the chemical industry)

[0162] Salt content: 20000 mg / L (sodium chloride 13000 mg / L, sodium sulfate 7000 mg / L)

[0163] Total calcium and magnesium ion concentration: 650 mg / L (calcium 420 mg / L, magnesium 230 mg / L)

[0164] The volume fraction of CO2 in the carbon-containing waste gas is 3%, and the ammonia nitrogen content is 80 mg / L.

[0165] pH: 7.5~8.0, water temperature: 20~25℃, suspended solids: 70mg / L

[0166] 2. Processing steps and detailed parameters

[0167] S1 Preprocessing:

[0168] Chemical softening unit: A 10% sodium carbonate solution and an 8% calcium hydroxide suspension were added. The sodium carbonate dosage was calculated as 1.2 times the total molar amount of calcium and magnesium ions (theoretical dosage 3.2 kg / h). The pH was adjusted to 10.0 by adding calcium hydroxide. The reaction temperature was 25℃, the stirring rate was 250 r / min, and the reaction time was 25 minutes. The mixture was then filtered using a plate and frame filter press (pressure 0.5 MPa). After filtration, the total concentration of calcium and magnesium ions decreased to 35 mg / L, with a calcium and magnesium removal rate of 94.6%. The precipitate was then filtered and dried (temperature 105℃, time 2 h) and used as building aggregate raw material (compressive strength ≥ 15 MPa, meeting the strength requirements for building sand).

[0169] Ammonia nitrogen removal: After chemical softening, the pH of the wastewater is adjusted to 10.5 (by adding 5% sodium hydroxide solution). The wastewater is then passed into a stripping tower (1.0m diameter, 8m height, Pall rings φ50mm packing), with a gas-liquid ratio of 500:1, a temperature of 40℃, and an empty tower gas velocity of 1.2m / s. The stripped ammonia gas is then passed into a sulfuric acid absorption tower (5% sulfuric acid concentration) to generate an ammonium sulfate solution (20% concentration). After treatment, the ammonia nitrogen in the wastewater is ≤8mg / L, and the ammonia nitrogen removal rate is 90.0%.

[0170] S2 reverse osmosis concentration: operating pressure 2.7MPa, operating temperature 28℃, concentration ratio 9 times, recycled permeate salinity 460mg / L, suspended solids ≤5mg / L, COD ≤120mg / L, meeting the water quality requirements for industrial process water, mixed brine concentrate salinity 180000mg / L, membrane flux maintained at 65~68L / (m²·h).

[0171] S3 nanofiltration salt separation: operating pressure 3.1MPa, membrane surface flow rate 0.85m / s, operating temperature 30℃, sodium chloride dilute brine purity 97.0%, mixed salt concentrate sodium sulfate content 95.1%, system recovery rate 55%.

[0172] S4XCRO Deep Concentration: Operating pressure 7.2MPa, operating temperature 33℃, sodium chloride brine concentration 23%, demineralized water salt content ≤100μS / cm, membrane flux maintained at 53~56L / (m²·h).

[0173] S5 bipolar membrane electrodialysis: operating voltage 2.1V / membrane, current density 210A / m², operating temperature 28℃, sodium hydroxide concentration 11.5%, hydrochloric acid concentration 9.5%, acid and alkali solution yield ≥91%.

[0174] S6 CO2 capture: A two-stage absorption-regeneration coupling system is adopted. The liquid-to-gas ratio in the first-stage absorption tower is 18 L / m³, the sodium hydroxide solution spray density is 25 m³ / (m²·h), and the gas-liquid contact time is 35 s. The second-stage absorption tower is purged with diluted hydrochloric acid (2% concentration) to adjust the pH to 7.0 to form a buffer solution, with a liquid-to-gas ratio of 10 L / m³ and a gas-liquid contact time of 25 s. The rich solution from both absorption towers is purged into the regeneration tower (steam pressure 0.4 MPa, temperature 100℃, residence time 40 minutes) to desorb high-concentration CO2 (98% purity) for separate recovery. The desorbed solution is returned to the absorption tower for recycling (recycling rate 80%), and the CO2 capture efficiency is 94.2%.

[0175] S7 Evaporation and Crystallization: Sodium carbonate is evaporated and crystallized via MVR, with a total alkalinity of 99.3% and chloride content of 0.25%. Hydrochloric acid is transported to the coal gangue acid leaching process, with a hydrochloric acid to coal gangue liquid-solid ratio of 10:1, a leaching temperature of 70℃, a stirring rate of 200 r / min, and a leaching time of 2.5 hours. The leaching solution is then precipitated (pH adjusted to 3.0), filtered, and concentrated (concentration factor of 5 times) to recover iron and aluminum oxides (purity of 95%, meeting the purity requirements for industrial-grade raw materials). The sodium sulfate product has a content of 95.6% and water-insoluble matter of 0.08%. The ammonium sulfate solution has a purity of 98%, meeting the purity requirements for agricultural fertilizers.

[0176] 3. Processing Results

[0177] The comprehensive cost of wastewater treatment is 15.1 yuan / m³ (including energy consumption cost of 5.9 yuan / m³, chemical cost of 2.8 yuan / m³, equipment depreciation of 3.8 yuan / m³, and other costs of 2.6 yuan / m³).

[0178] Carbon dioxide capture cost: 205 yuan / ton CO2 (30% lower than conventional ultra-low concentration CO2 capture technology (293 yuan / ton CO2));

[0179] Water resource utilization rate: 90% (reclaimed water volume 8.1 m³ / h, condensate water reuse volume 0.9 m³ / h, raw water volume 10 m³ / h).

[0180] Energy consumption per unit: 9.3 kWh / m³;

[0181] Removal rates of characteristic pollutants: calcium and magnesium removal rate 94.6%, ammonia nitrogen removal rate 90.0%, CO2 capture efficiency 94.2%, COD removal rate 60.0%, and suspended solids removal rate 99.3%;

[0182] Product specifications: Sodium carbonate total alkalinity 99.3%, chloride 0.25%, sodium sulfate content 95.6%, water-insoluble matter 0.08%, ammonium sulfate purity 98%, iron and aluminum oxide purity 95%;

[0183] Membrane module operation status: After 30 days of continuous operation, the flux decline rates of nanofiltration membrane and XCRO membrane were 4.8% and 6.2%, respectively. There was no calcium or magnesium scaling on the membrane surface, and the flux recovery rate was ≥97% after cleaning with citric acid.

[0184] Example 5: High Temperature and High Turbidity Scenarios

[0185] 1. Influent water quality (simulating high-temperature wastewater from the dyeing and printing industry)

[0186] Salt content: 17000 mg / L (sodium chloride 11000 mg / L, sodium sulfate 6000 mg / L)

[0187] Suspended solids content: 250 mg / L, wastewater temperature: 55℃ (fluctuation ±3℃)

[0188] COD: 1500 mg / L, CO2 volume fraction in carbon-containing waste gas: 9%

[0189] pH: 8.0~8.5, oil content: 15mg / L

[0190] 2. Processing steps and detailed parameters

[0191] S1 Preprocessing:

[0192] Coagulation-clarification-ultrafiltration combined process: Add polyaluminum chloride (8 mg / L) and polyacrylamide (0.8 mg / L), stir rapidly (300 r / min) for 1 minute, stir slowly (50 r / min) for 15 minutes, retain time in the clarifier for 30 minutes, and the suspended solids in the supernatant are ≤5 mg / L; the ultrafiltration system adopts an external pressure hollow fiber membrane (membrane pore size 0.1 μm, membrane surface velocity 1.2 m / s, transmembrane pressure difference 0.12~0.18 MPa), with a suspended solids removal rate of 99.5% and an effluent SDI ≤2;

[0193] Oil removal treatment: Before coagulation, add polyether-type demulsifier (dosage 5 mg / L), stir at 200 r / min, react for 10 minutes, and reduce the oil content to ≤1 mg / L;

[0194] Waste heat recovery: The wastewater temperature after pretreatment is 52℃. Waste heat is recovered through a plate heat exchanger (heat exchange area 20m²) and used for preheating of S6 sodium carbonate evaporation and crystallization (raising the sodium carbonate solution from 25℃ to 45℃). The heat exchange efficiency is 85% and the waste heat recovery capacity is 420kW / h.

[0195] S2 reverse osmosis concentration: operating pressure 2.4MPa, operating temperature 30℃ (controlled by cooling device, cooling water flow 5m³ / h), concentration ratio 8 times, recycled permeate salinity 430mg / L, suspended solids ≤5mg / L, COD ≤100mg / L, oil content ≤0.5mg / L, meeting the water quality requirements for industrial process water, mixed brine concentrate salinity 136000mg / L, membrane flux maintained at 71~74L / (m²·h).

[0196] S3 nanofiltration salt separation: operating pressure 2.9MPa, membrane surface flow rate 0.9m / s, operating temperature 30℃, sodium chloride dilute brine purity 97.3%, mixed salt concentrate sodium sulfate content 95.4%, system recovery rate 63%.

[0197] S4XCRO Deep Concentration: It adopts a high-temperature resistant membrane module (polyamide-polyimide composite membrane, temperature range 40~60℃, thermal stability ≤0.05% / ℃), operating pressure 6.8MPa, operating temperature 35℃, sodium chloride brine concentration 21%, demineralized water salt content ≤100μS / cm, and membrane flux maintained at 54~57L / (m²·h).

[0198] S5 bipolar membrane electrodialysis: operating voltage 1.8V / membrane, current density 180A / m², operating temperature 30℃, sodium hydroxide concentration 10.8%, hydrochloric acid concentration 8.2%, acid and alkali solution yield ≥92%.

[0199] S6 carbon dioxide capture: liquid-to-gas ratio 13L / m³, gas-liquid contact time 28s, CO2 capture efficiency 96.0%; evaporation crystallization preheating uses the waste heat recovered from S1, reducing the energy consumption of the MVR evaporator by 15%.

[0200] S7 Online Monitoring and Control: The water quality monitoring module monitors the influent salinity, COD, and temperature in real time (detection frequency 5 minutes / time). The parameter control module automatically adjusts the reverse osmosis operating pressure (fluctuation range ±0.2MPa) and nanofiltration membrane surface flow rate (fluctuation range ±0.1m / s) through the PLC system to adapt to water quality fluctuations; the sodium carbonate product has a total alkalinity of 99.1% and chloride of 0.3%, and the sodium sulfate product has a content of 95.7% and water-insoluble matter of 0.07%.

[0201] 3. Processing Results

[0202] The comprehensive cost of wastewater treatment is 13.8 yuan / m³ (of which energy consumption cost is 4.8 yuan / m³, chemical cost is 2.3 yuan / m³, equipment depreciation is 3.7 yuan / m³, and other costs are 3.0 yuan / m³).

[0203] Carbon dioxide capture cost: 190 yuan / ton CO2;

[0204] Water resource utilization rate: 92% (reclaimed water volume 8.5 m³ / h, condensate water reuse volume 0.7 m³ / h, raw water volume 10 m³ / h).

[0205] Unit energy consumption: 8.5 kWh / m³ (15% lower than the process without waste heat recovery (9.9 kWh / m³));

[0206] Removal rates of characteristic pollutants: suspended solids removal rate 99.5%, COD removal rate 68.0%, CO2 capture efficiency 96.0%, and oil removal rate 93.3%;

[0207] Product specifications: Sodium carbonate total alkalinity 99.1%, chloride 0.3%, sodium sulfate content 95.7%, water-insoluble matter 0.07%;

[0208] System stability: When the influent water quality fluctuates by ±20%, the treatment efficiency fluctuates by ≤3%, there is no system shutdown, and the membrane module flux decay rate is ≤5%.

[0209] III. Comparative Example

[0210] 1. Processing technology (industry-standard technology, no collaborative mechanism)

[0211] Wastewater treatment: reverse osmosis concentration plus triple-effect evaporation crystallization (salt removal), no salt separation step, the evaporation product is a mixture of salts;

[0212] Carbon dioxide capture: Purchased sodium hydroxide solution (10% concentration) as absorbent, single-stage absorption tower, no regeneration cycle;

[0213] Solid waste disposal: Mixed salts are disposed of as hazardous waste;

[0214] Water resource utilization: Only reverse osmosis permeate is reused, while condensate and brine washing wastewater are directly discharged.

[0215] 2. Influent water quality

[0216] Completely consistent with Example 1 (to ensure fair comparison): salt content 18000 mg / L, silicon concentration 45 mg / L, CO2 volume fraction 8%, COD 1200 mg / L, suspended solids 80 mg / L.

[0217] 3. Processing parameters

[0218] Reverse osmosis concentration: operating pressure 2.5MPa, concentration ratio 8 times, salinity of recycled permeate 450mg / L, suspended solids ≤10mg / L, COD ≤200mg / L, salinity of mixed brine concentrate 144000mg / L;

[0219] Triple-effect evaporation: Evaporation temperature 95 / 85 / 75℃, evaporation produces mixed salts (sodium chloride and sodium sulfate, purity 65%), hazardous waste disposal cost 2000 yuan / ton;

[0220] Carbon dioxide capture: Purchase sodium hydroxide solution (purchase cost 3000 yuan / ton), liquid-to-gas ratio 12L / m³, absorbent consumption 1.2 tons / ton CO2;

[0221] Pretreatment: Only sand filtration and ultrafiltration are used, without a silicon removal unit, and silicon scale will be generated on the surface of the reverse osmosis membrane periodically.

[0222] 4. Processing Results

[0223] Comprehensive wastewater treatment cost: 22.6 yuan / m³ (including 5.2 yuan / m³ for disposal of hazardous waste containing miscellaneous salts, 4.8 yuan / m³ for purchased alkali solution, 6.5 yuan / m³ for energy consumption, and 6.1 yuan / m³ for other costs).

[0224] Carbon dioxide capture cost: 380 yuan / ton CO2 (including 280 yuan / ton CO2 cost of purchased alkali solution and 100 yuan / ton CO2 energy consumption cost).

[0225] Water resource utilization rate: 75% (only reverse osmosis permeate is reused, no condensate recovery);

[0226] Energy consumption per unit: 12.5 kWh / m³;

[0227] Carbon dioxide capture efficiency: 85.0%;

[0228] Product output: No qualified salt products; mixed salts are disposed of as hazardous waste, with an annual disposal volume of approximately 720 tons and a disposal cost of 1.44 million yuan.

[0229] Membrane module operation status: After 30 days of continuous operation, the flux decline rates of the reverse osmosis membrane and nanofiltration membrane were 12.5% ​​and 15.3%, respectively, and obvious silica scale and organic matter contamination appeared on the membrane surface.

[0230] IV. Comparative Analysis and Charts

[0231] 1. Comparison Table of Core Indicators

[0232]

[0233] V. Conclusion

[0234] This invention utilizes a synergistic process of pretreatment-membrane separation-bipolar membrane alkali production-CO2 capture-salt recovery. Targeting special scenarios such as silicon-containing, low-temperature, high-COD, fluoride-containing, high-calcium, high-magnesium, high-temperature, and high-turbidity conditions, it constructs a dual synergistic mechanism of material recycling and energy recovery, solving the industry pain points of existing technologies such as difficulty in treating mixed salts in high-salt wastewater, high CO2 capture costs, and low resource utilization.

[0235] Compared with existing conventional processes, the core advantages of this invention are reflected in three aspects:

[0236] Collaborative cost reduction: Energy consumption is reduced by replacing purchased alkali solutions with wastewater desalination products, replacing hazardous waste disposal with the resource utilization of miscellaneous salts, and reducing waste heat recovery;

[0237] High efficiency and resource utilization: Produces high-purity salt products with a total alkalinity of sodium carbonate of not less than 99.0% and chloride of not more than 0.4%, sodium sulfate content of not less than 95.5% and water-insoluble matter of not more than 0.09%, and by-products such as hydrochloric acid and ammonium sulfate are utilized in a high-value manner, with no hazardous waste generated;

[0238] Stable system: Targeted pretreatment units prevent membrane scaling, dedicated membrane modules are adapted to extreme operating conditions, online control system adapts to water quality fluctuations, membrane flux decay rate is ≤6.2%, and service life is extended by more than 30% compared to conventional processes.

[0239] This invention achieves the organic integration of wastewater treatment, carbon emission reduction and resource recovery, and is applicable to the treatment of high-salt wastewater in multiple industries such as coal chemical, electronics, and printing and dyeing, with significant environmental and economic benefits.

[0240] While an overview of the subject matter has been described with reference to specific example embodiments, various modifications and changes can be made to these embodiments without departing from the broader scope of embodiments of this disclosure. Such embodiments of the subject matter are referred to herein, individually or collectively, as inventions, for convenience only, and if more than one disclosure or concept is disclosed in fact, it is not intended to limit the scope of this application to any single disclosure or concept.

[0241] The embodiments described herein have been described in sufficient detail to enable those skilled in the art to practice the disclosed teachings. Other embodiments may be used and derived therefrom, such that structural and logical substitutions and changes may be made without departing from the scope of this disclosure. Therefore, the detailed description should not be construed as limiting, and the scope of the various embodiments is defined only by the appended claims and the full scope of their equivalents.

Claims

1. A resource-based treatment method for high-salinity wastewater with synergistic carbon dioxide emission reduction, characterized in that, Includes the following steps: After pretreatment to remove suspended solids, some recalcitrant organic matter and characteristic pollutants, the S1 high-salinity wastewater is concentrated by a reverse osmosis system to obtain reusable permeable water and mixed brine concentrate. The salinity of the reusable permeable water meets the industrial reusable water standard, while the salinity of the mixed brine concentrate is several times that of the original high-salinity wastewater. S2 mixed brine concentrate is passed into a nanofiltration system to separate salts, resulting in sodium chloride dilute brine and mixed brine concentrate. The sodium chloride dilute brine has a purity that meets the requirements for subsequent deep concentration, and the mixed brine concentrate has sodium sulfate as the main component. S3 sodium chloride dilute brine is passed into the reverse osmosis system for deep concentration, yielding demineralized water and concentrated sodium chloride brine; the demineralized water can be directly reused. The S4 sodium chloride brine is passed through a two-stage mixed resin deep adsorption process to further remove calcium, magnesium, and fluoride ions, meeting the operating requirements of the S5 bipolar membrane equipment. S5 sodium chloride concentrated brine was passed into a bipolar membrane electrodialysis system to prepare sodium hydroxide solution and hydrochloric acid; the concentrations of the two products were adapted to the requirements of subsequent processes. S6 sodium hydroxide solution is introduced into the carbon dioxide capture system, where it comes into contact with carbon-containing waste gas to absorb carbon dioxide and generate sodium carbonate solution. The sodium carbonate solution S7 is passed through a membrane distillation process to evaporate and crystallize, yielding solid sodium carbonate. The concentrated brine from the S2 primary nanofiltration stage is diluted with the demineralized brine produced by S3 and S7 and then enters the nanofiltration stage for washing. Finally, the concentrated brine from the secondary nanofiltration stage is obtained by evaporation, fractional crystallization, and solid sodium sulfate is obtained. Nanofiltration provides suitable water quality for subsequent reverse osmosis membrane separation processes, the reverse osmosis membrane separation products provide reactants for bipolar membrane processes, and the sodium hydroxide solution produced by the bipolar membrane provides adsorbents for carbon dioxide capture.

2. The resource-based treatment method for high-salinity wastewater with synergistic carbon dioxide emission reduction as described in claim 1, characterized in that, For high-salt wastewater containing fluoride, hardness, and organic matter, the S1 pretreatment system adds fluoride removal, hardness removal, and organic matter removal units. The fluoride concentration and hardness of the pretreated wastewater meet the influent requirements of the nanofiltration membrane system; the sodium chloride brine after nanofiltration is concentrated by low-pressure plus high-pressure reverse osmosis, and the sodium chloride concentration meets the influent material requirements of the bipolar membrane. To further remove fluoride and calcium and magnesium ions, a two-stage resin adsorption process is adopted. The first-stage resin uses a hydrogen-form cation exchange resin to remove calcium and magnesium ions, which is convenient for elution and regeneration using hydrochloric acid generated by S5. The second-stage resin uses an aluminum-supported macroporous resin, which is convenient for regeneration using sodium hydroxide generated by S5. The deep fluoride removal concentration meets the requirements of bipolar membrane electrodialysis treatment. During S5 carbon dioxide capture, carbon-containing waste gas is first passed into an adsorption tower filled with amino-functionalized mesoporous silica adsorbent for enrichment, and then passed into an absorption tower to react with sodium hydroxide solution. The adsorption tower and the absorption tower are connected in series. The carbon-decarbonized tail gas from the absorption tower is tested and discharged in compliance with standards, or it is returned to the adsorption enrichment process for secondary adsorption. The defluorination and hardening units prevent membrane fouling, ensuring the stable operation of S2 nanofiltration desalination and S3 high-pressure reverse osmosis deep concentration. This, in turn, ensures that the S5 bipolar membrane electrodialysis system produces a sufficient amount of sodium hydroxide solution of the appropriate concentration. The carbon dioxide enriched by the adsorbent comes into full contact with the alkaline solution, and the two form an energy linkage through waste heat recovery.

3. The resource-based treatment method for high-salinity wastewater with synergistic carbon dioxide emission reduction as described in claim 2, characterized in that, For high-salt concentration applications, the S3XTRO system uses a high-pressure compatible membrane module, which has a pressure range suitable for high-pressure environments and a membrane flux that meets concentration requirements. The S2 nanofiltration system adjusts the operating pressure, and the S4 bipolar membrane electrodialysis system adjusts the operating voltage accordingly. High-pressure adaptive membrane modules ensure the membrane stability of S3 under high pressure. The parameter adjustment of nanofiltration and bipolar membranes, along with the desiliconization and carbon dioxide enrichment steps, achieves material concentration adaptation. The energy required for low-pressure reverse osmosis concentration is partly recovered from the concentrate energy of the XTRO system, forming an energy closed loop in this scenario.

4. The resource-based treatment method for high-salinity wastewater with synergistic carbon dioxide emission reduction as described in claim 1, characterized in that, For high-salt wastewater containing organic matter, fluoride, and hardness, the S1 pretreatment uses chemical precipitation to remove fluoride and hardness to meet the nanofiltration membrane feed water requirements. The nanofiltration membrane removes some COD to meet the reverse osmosis feed water requirements. Before entering the bipolar membrane electrodialysis, a multi-stage resin adsorption unit is added. Hydrogen-based resin removes calcium and magnesium ions, and aluminum-loaded resin deeply adsorbs and removes fluoride ions, ensuring the stable operation of the bipolar membrane electrodialysis system. S7 evaporation crystallization uses an integrated membrane distillation crystallization system to separate immobilized carbon dioxide product sodium carbonate. This method includes a hydrophobically modified polyvinylidene fluoride membrane module and a crystallizer. The secondary condensate generated during distillation is used for the salt washing process. Sodium hydroxide prepared by S5 is used for the regeneration of fluoride ion adsorbent. The regenerated adsorbent can be recycled and reused. The regeneration waste liquid is then defluorinated by chemical precipitation and re-entered into the nanofiltration system. Defluorination reduces the problems of membrane flux decline and bipolar membrane plate corrosion caused by fluoride ions.

5. The resource-based treatment method for high-salinity wastewater with synergistic carbon dioxide emission reduction as described in claim 4, characterized in that, The S7 evaporator adopts a multi-effect evaporation system driven by industrial waste heat, with the heat source being waste heat steam generated during industrial production. The condensate from the evaporator is divided into two parts: one part is returned to the S1 pretreatment as makeup water, and the other part is fed into the membrane distillation and crystallization integrated system as distillation makeup water. S1 recycled water is prioritized for the S7 salt washing process, with the remainder used for enterprise production water; industrial waste heat replaces traditional energy, and condensate and recycled water form a closed loop of water resources, which, together with hydrochloric acid regeneration cycle and membrane distillation waste heat recovery, constitutes energy and resource synergy.

6. The resource-based treatment method for high-salinity wastewater with synergistic carbon dioxide emission reduction as described in claim 1, characterized in that, For high-salt wastewater containing fluoride, hardness, and organic matter, the S1 pretreatment system adds a chemical softening unit, adding sodium carbonate and sodium hydroxide. After reaction, the calcium and magnesium precipitates are removed by filtration. The precipitates can be used as raw materials for building materials after treatment. The S5 carbon dioxide capture uses an adsorption tower and an absorption tower connected in series. The waste gas first enters the adsorption tower to capture sodium dioxide and concentrate it, and then enters the carbon dioxide absorption tower, where S4 is introduced to produce a sodium hydroxide solution. The carbon dioxide is fixed by sodium hydroxide in the carbon capture solution. The carbon capture solution is then distilled using a membrane distillation process to obtain a carbonate byproduct, or it can be further absorbed to obtain a sodium bicarbonate carbon capture solution. The carbon capture solution can also be recycled and reused by using the high-concentration carbon dioxide desorbed from the hydrochloric acid produced by S4. The chemical softening unit prevents scaling of nanofiltration and nanofiltration membranes, extends the service life of membrane modules, and ensures salt separation and concentration efficiency. The two-stage absorption and regeneration system improves the capture effect of low-concentration carbon dioxide and forms a material synergy with the sodium hydroxide and hydrochloric acid produced by S4.

7. The resource-based treatment method for high-salinity wastewater with synergistic carbon dioxide emission reduction as described in claim 6, characterized in that, The hydrochloric acid prepared by S4 can be further concentrated as an industrial byproduct, or used for acid leaching of coal gangue or steel slag; the leachate is purified to recover valuable metals. The solid sodium carbonate obtained from S6 can be used for front-end chemical hardening, reducing operating costs, and achieving a certain purity to obtain valuable industrial by-product sodium carbonate.

8. The resource-based treatment method for high-salinity wastewater with synergistic carbon dioxide emission reduction as described in claim 1, characterized in that, For wastewater with high hardness, fluoride, and organic matter, the S1 pretreatment adopts a combined process of fluoride and hardness removal. Sodium hydroxide, sodium carbonate, and coagulant are added to the wastewater, and after stirring and reaction, the wastewater is allowed to settle in a clarification tank. The supernatant is then filtered through an ultrafiltration system.

9. The resource-based treatment method for high-salinity wastewater with synergistic carbon dioxide emission reduction as described in claim 8, characterized in that, The method involves setting up an online monitoring and control system, which includes a water quality monitoring module and a parameter control module. The water quality monitoring module monitors the salinity, COD, concentration of characteristic pollutants, and temperature of the influent at each step in real time; the parameter control module automatically adjusts the operating pressure of the reverse osmosis system, the membrane flow rate of the nanofiltration system, the operating voltage of the bipolar membrane electrodialysis system, and the liquid-to-gas ratio of carbon dioxide capture based on the monitoring results. The online monitoring and control system works in conjunction with coagulation clarification and ultrafiltration pretreatment to adapt to water quality fluctuations in high-temperature and high-turbidity wastewater in real time, ensuring the coordinated operation of steps such as nanofiltration desalination, XCRO concentration, and carbon capture.

10. The resource-based treatment method for high-salinity wastewater with synergistic carbon dioxide emission reduction as described in claim 1, characterized in that, A closed-loop cleaning system for membrane modules is constructed; the sodium hydroxide solution prepared in S4 is used for alkaline washing and regeneration of reverse osmosis, nanofiltration, and XCRO membrane modules, in addition to supplying carbon capture; the acid washing and regeneration of membrane modules uses hydrochloric acid prepared in S4. The waste liquid after acid and alkali washing is treated and then returned to the S1 pretreatment for reprocessing. The water for solution preparation comes from the recycled water resources within the system. The washing wastewater generated by the S7 salt washing is fed into the secondary reverse osmosis system for treatment. The permeate is returned to the salt washing process. The concentrated water is combined with the original high-salt wastewater from S1 for treatment. The membrane module cleaning closed loop and the washing wastewater recycling form waste liquid recycling and utilization, which is connected with the cross-unit energy and material coupling mechanism to improve the comprehensive utilization rate of resources.

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