Printing and dyeing wastewater treatment method based on nZVI / AGS coupling process

Abstract

The invention discloses a printing and dyeing wastewater treatment method based on an nZVI / AGS coupling process, which comprises the following steps: wastewater pre-activation and interface optimization: introducing printing and dyeing wastewater into a pre-activation pool; performing gradient functional modification on nZVI: treating the nZVI by adopting a'core-shell 'manner; sequentially coating a conductive polymer polypyrrole and a biochar nanosheet by taking the nZVI as a core; aGS gradient structure directional culture: adopting a double substrate-magnetic field induction culture method to culture AGS: in a sequencing batch reactor, selecting sodium acetate and glucose as a composite carbon source, setting the mass ratio of sodium acetate to glucose to be 3: 1, controlling the ratio of C to N to P to be 100: 5: 1, and adding magnetic nano ferroferric oxide particles with the concentration of 20-30mg / L; and gradient coupling synergistic degradation: putting the modified nZVI and the AGS subjected to optimized culture into a three-section gradient coupling reactor, and carrying out advanced treatment on the wastewater subjected to gradient coupling synergistic degradation treatment in a photocatalysis-membrane filtration coupling unit.

Description

Technical Field

[0001] The present invention relates to the field of textile printing and dyeing wastewater treatment, and particularly to a method for treating printing and dyeing wastewater based on an nZVI / AGS coupling process. Background Art

[0002] The types of dyes used in the printing and dyeing process are relatively concentrated. Classified according to chemical molecular structure and application performance, Azo dyes are the most widely used type of dyes, accounting for 60% - 70% of all dyes. Followed by anthraquinone dyes, indigo dyes, and other synthetic dyes. The structure of azo dyes consists of a diazonium amine coupled with an associative amine or phenol, and there is also one or more azo bonds; the structure of anthraquinone dyes contains three benzene rings, which are fused with each other, that is, condensed benzene, and two carbonyl groups are connected to the central benzene ring. Most of them are aromatic high-molecular compounds; indigo dyes are a type of dark indole group dye, belonging to polycyclic aromatic compounds. Most of these dyes have double bonds, benzene rings or heterocyclic structures, with extremely stable chemical properties and are difficult to degrade. They have considerable toxicity and carcinogenic and mutagenic effects. After entering the environment, they pose a serious threat to the ecological environment and human health. For a long time, the design and operation of printing and dyeing wastewater treatment projects mainly considered the removal of COD and chromaticity, and the attention to the removal of the dyes themselves was insufficient. Since the COD in printing and dyeing wastewater mainly comes from sizing agents and auxiliaries, the contribution rate of dyes to COD is only 10% - 30%. Therefore, although the traditional biochemical treatment technology can achieve a COD removal rate of 80% - 90% for printing and dyeing wastewater, due to the stable chemical properties and low biodegradability of dyes, its removal effect on dyes is poor. The chromaticity in printing and dyeing wastewater mainly comes from dyes, but the traditional biochemical treatment technology often only destroys the chromophore groups of dyes, converting macromolecular compounds into small molecules, and does not completely degrade the dyes. In addition, the intermediate metabolites of dyes are usually aromatic substances, and a large part of them belong to polycyclic aromatic hydrocarbon (PAHs) pollutants, which have certain toxicity and carcinogenicity and are very difficult to be further degraded.

[0003] At present, the main process for dyeing and printing enterprises in China to treat wastewater is the "physical and chemical pretreatment + biochemical" combined process, in which the biochemical treatment mainly adopts anaerobic / aerobic (A / O) and anaerobic / anoxic / aerobic (A / A / O) processes. The biochemical treatment unit has greatly reduced COD and ammonia nitrogen, and can efficiently degrade especially toxic pollutants, significantly reducing the concentrations of pollutants such as dyes and PVA in the effluent. However, when the wastewater temperature, acidity or alkalinity is too high or too low, it will have a great impact on the functional flora in the wastewater biological treatment system, resulting in unstable effluent quality, and even damaging the biochemical treatment system and making it unable to treat the production wastewater in time. In addition, due to the large amount of refractory organic matter in the dyeing and printing wastewater, it is difficult for ordinary biological treatment systems to completely remove it, and the biochemical effluent still contains a high concentration of refractory organic pollutants. These refractory organic pollutants entering the water environment pose potential risks to aquatic organisms and human health. A large number of biological experimental results show that the effluent from industrial wastewater treatment plants can produce various adverse biological effects at the cellular and individual levels.

[0004] The refractory organic matter represented by dyes in the dyeing and printing wastewater and its biological toxicity can only safely enter the water environment or be recycled after being effectively removed. Since most of these organic matters are synthetic, the types and quantities of microorganisms with high-efficiency degradation functions for them in the natural environment are very small, and they are at a disadvantage in interspecies competition. Therefore, it is difficult to achieve the high-efficiency degradation of these organic matters by traditional biological treatment methods. Aerobic granular sludge (AGS) is a new wastewater treatment technology that has received much attention in recent years and has good application prospects. Compared with ordinary activated sludge, it has the advantages of compact structure, fast sedimentation speed and high biomass, and has good adaptability and strong tolerance to high-concentration refractory industrial wastewater. The granular structure of AGS enables it to have aerobic, anoxic and anaerobic environments at the same time, and aerobic, facultative anaerobic and anaerobic microorganisms grow aggregately from the outside to the inside in turn, realizing the zonal enrichment of different dominant microorganisms. It can not only complete biological processes such as organic matter degradation, nitrification and denitrification, and biological phosphorus removal at the same time, but also greatly improve the removal efficiency of refractory pollutants and achieve the high-efficiency treatment of wastewater. Nano zero-valent iron (nZVI) is an environmentally friendly material with high reaction activity, high treatment efficiency, controllable particle size and rich active sites. It is not only chemically active, has strong reducing ability but also has a large electronegativity. In the chemical reaction process, it can reduce organic compounds, ionic compounds and other substances that are not easily reduced through its strong reducing ability. Therefore, it can effectively remove pollutants that are difficult to degrade by conventional methods and shows great application potential in the dechlorination of halogenated organic compounds, the reduction of heavy metal ions, the transformation of inorganic ions and the decolorization of dye wastewater.

[0005] That is to say, in the field of printing and dyeing wastewater treatment, although the nZVI / AGS coupling technology shows certain application potential, there are still many technical bottlenecks to be solved. First, the surface of nZVI is extremely easy to be oxidized to form a dense iron oxide passivation layer, resulting in a significant reduction in the electron transfer efficiency. Moreover, the mass transfer resistance inside the AGS particles is large, making it difficult for dye molecules to fully contact the active reaction sites. There is a lack of an efficient synergy mechanism between the two. Second, most of the existing nZVI / AGS coupling processes are simple physical mixtures, and no coordinated optimization design is carried out for the unique spatial structure of AGS and the activity decay characteristics of nZVI, resulting in insufficient dye reduction reactions in the anaerobic zone and low mineralization efficiency in the aerobic zone. Third, there is a significant contradiction between the hydrophilicity of organic dyes and the hydrophobicity of nZVI, which greatly limits the effective combination and reaction of the two. Fourth, some intermediate products generated during the degradation of nZVI are potentially toxic, and the existing technology has not established an effective control and elimination mechanism, posing a relatively high environmental risk. Currently, it is urgent to achieve technological breakthroughs from multiple dimensions such as the interfacial action mechanism and process structure innovation to improve the efficiency of the nZVI / AGS coupling technology in treating printing and dyeing wastewater. Summary of the Invention

[0006] Aiming at the deficiencies of the existing technology, the present invention provides a method for treating printing and dyeing wastewater based on the nZVI / AGS coupling process. The present invention aims to overcome the problems of poor synergy, low mass transfer efficiency, and high risk of intermediate products in traditional coupling technologies by constructing a gradient coupling system of nZVI / AGS with nano-material interface regulation, realizing the efficient degradation and safe treatment of dye pollutants in printing and dyeing wastewater, and providing an innovative technical solution for the green and sustainable development of the printing and dyeing industry.

[0007] To achieve the above object, the present invention provides the following technical solutions: A method for treating printing and dyeing wastewater based on the nZVI / AGS coupling process, comprising the following steps: Step S1: Wastewater pre-activation and interface optimization. Introduce the printing and dyeing wastewater into the pre-activation tank, and use a ceramic membrane with a pore size of 3 - 5 μm for fine filtration to effectively remove suspended solids and colloidal impurities in the wastewater; introduce the printing and dyeing wastewater into the pre-activation tank. At this stage, use a ceramic membrane with a pore size between 3 - 5 μm to finely filter the wastewater. This operation can effectively intercept and remove suspended solids and colloidal impurities in the wastewater, create good conditions for subsequent treatment, reduce the interference of impurities on subsequent reactions, and improve the overall treatment efficiency.

[0008] Step S2: Gradient functional modification of nZVI: Treat nZVI using the "core-shell" method: Use nZVI as the core and sequentially coat it with the conductive polymer polypyrrole and biochar nanosheets; treat nZVI using a unique "core-shell" structure. Use nZVI as the core and sequentially coat it with the conductive polymer polypyrrole and biochar nanosheets. Polypyrrole has good conductivity, which can promote electron transfer and enhance the reaction activity of nZVI; biochar nanosheets have a large specific surface area and abundant functional groups, which can improve the adsorption capacity for pollutants. Through this modification method, nZVI is made to have more excellent properties and enhance its effect in wastewater treatment.

[0009] Step S3: Directed cultivation of AGS with a gradient structure: Cultivate AGS using the "dual-substrate - magnetic field induction" cultivation method: In a sequencing batch reactor, select sodium acetate and glucose as the composite carbon source, and set the mass ratio of the two to 3:1. At the same time, control the C:N:P ratio to 100:5:1 and add magnetic nano-ferroferric oxide particles with a concentration of 20 - 30 mg / L; cultivate AGS using the "dual-substrate - magnetic field induction" cultivation method. In a sequencing batch reactor, select sodium acetate and glucose as the composite carbon source and set the mass ratio of the two to 3:1. At the same time, strictly control the C:N:P ratio to 100:5:1 and add magnetic nano-ferroferric oxide particles with a concentration of 20 - 30 mg / L. This cultivation method can guide AGS to form microbial aggregates with a specific gradient structure, and microorganisms in different regions have different functions, thereby improving the degradation ability for various pollutants in printing and dyeing wastewater.

[0010] Step S4: Gradient coupling and synergistic degradation: Put the modified nZVI and the optimized-cultivated AGS into a three-stage gradient coupling reactor. The wastewater after gradient coupling and synergistic degradation enters the photocatalysis - membrane filtration coupling unit for advanced treatment. Put the modified nZVI and the optimized-cultivated AGS into a three-stage gradient coupling reactor. In this reactor, nZVI and AGS play a synergistic role to conduct gradient coupling degradation of pollutants in printing and dyeing wastewater, making full use of the reaction conditions and microbial characteristics in different stages to improve the degradation efficiency and effect. The wastewater after gradient coupling and synergistic degradation then enters the photocatalysis - membrane filtration coupling unit for advanced treatment. This unit combines the advantages of photocatalytic oxidation and membrane filtration, can further remove the residual pollutants in the wastewater, and make the effluent meet higher water quality standards.

[0011] As a further solution of the present invention, in step S1, it further includes adding a composite interfacial regulator composed of chitosan-modified nano-silica and tannic acid to the wastewater. The mass ratio of the two is 2:1, and the dosage is controlled at 80 - 120 mg / L. After filtration, add the composite interfacial regulator composed of chitosan-modified nano-silica and tannic acid to the wastewater. The surface of chitosan-modified nano-silica is rich in amino groups, which can form stable hydrogen bonds with dye molecules and enhance the dispersibility of dyes; tannic acid, as a natural chelating agent, can complex dissolved oxygen and metal ions in water and inhibit the oxidation of nano zero-valent iron (nZVI) in subsequent reactions. The mass ratio of the two is strictly set at 2:1, and the dosage is accurately controlled at 80 - 120 mg / L. By adding this composite interfacial regulator, the interfacial properties of the wastewater are optimized, creating a more favorable reaction environment for subsequent treatment.

[0012] As a further solution of the present invention, in step S2, the specific modification process is as follows: uniformly disperse nZVI in an ethanol aqueous solution to form a suspension with a concentration of 50 g / L; add pyrrole monomer to the suspension to make its concentration reach 0.1 mol / L, and add ammonium persulfate as an initiator with a concentration of 0.12 mol / L; under the conditions of 30 °C and light avoidance, continuously react for 6 h to promote the polymerization reaction of PPy on the surface of nZVI to form a PPy layer with excellent electron transport performance; add BCNs to make its concentration in the suspension reach 10 g / L, and continue to stir and react for 4 h. Utilize the π-π stacking interaction between BCNs and PPy to uniformly coat BCNs on the outer layer of PPy. Uniformly disperse nZVI in an ethanol aqueous solution to prepare a suspension with a concentration of 50 g / L. This uniform dispersion process ensures the full participation of nZVI in subsequent reactions.

[0013] Add pyrrole monomer to the suspension to make the concentration of pyrrole monomer in the suspension reach 0.1 mol / L, and at the same time add ammonium persulfate as an initiator with a concentration of 0.12 mol / L. Under the conditions of 30 °C and light avoidance, let the reaction continue for 6 h. In this process, ammonium persulfate initiates the polymerization of pyrrole monomer, promoting the polymerization reaction of polypyrrole (PPy) on the surface of nZVI to form a PPy layer with excellent electron transport performance. This PPy layer can significantly improve the electron transfer ability of nZVI and enhance its reaction activity.

[0014] Subsequently, add biochar nanosheets (BCNs) to the suspension to make its concentration in the suspension reach 10 g / L, and then continue to stir and react for 4 h. Utilize the π-π stacking interaction between BCNs and PPy, and BCNs will be uniformly coated on the outer layer of PPy. BCNs have a large specific surface area and rich functional groups, which can not only further improve the adsorption capacity for pollutants, but also cooperate with the PPy layer to form an efficient reaction interface of "adsorption - electron transfer - degradation".

[0015] As a further solution of the present invention, in step S3, the whole cultivation process is divided into three stages: Initial stage (0 - 10 days): Set the aeration intensity to 2.0 L / (m³ min), adopt the pulse aeration mode, and gradually extend the sedimentation time from the initial 5 min to 8 min; Middle stage (11 - 20 days): Reduce the aeration intensity to 1.5 L / (m³ min), and introduce a uniform magnetic field with an intensity of 0.05 T. Under the action of the magnetic field, MNPs guide the microorganisms to arrange orderly, promoting the gradual formation of a stable gradient structure with aerobic on the outer layer, anoxic in the middle layer, and anaerobic in the inner layer of AGS. The sedimentation time in this stage is extended to 12 min; Maturity stage (21 - 30 days): Keep the magnetic field condition unchanged, and further adjust the aeration intensity to 1.2 L / (m³ min), the sedimentation time is stabilized at 15 min, control the particle size of AGS within 0.8 - 1.2 mm, and form a gradient structure with a stable mass transfer channel, providing a good microbial environment for the efficient degradation of pollutants. Adopt the "dual - substrate - magnetic field induction" cultivation method, use sodium acetate and glucose (mass ratio 3:1) as the composite carbon source in the sequencing batch reactor, control the C:N:P ratio to be 100:5:1, and add 20 - 30 mg / L magnetic nano - iron oxide particles (MNPs) to cultivate the gradient structure of AGS in stages: Specifically, in the initial cultivation stage (0 - 10 days): With an aeration intensity of 2.0 L / (m³ min) combined with the pulse aeration mode (aeration for 6 min, aeration stop for 2 min), stimulate the rapid proliferation and aggregation of microorganisms through periodic dissolved oxygen supply. Gradually extend the sedimentation time from 5 min to 8 min, promoting the transition of microorganisms from a dispersed state to initial granulation, laying a foundation for subsequent structure construction.

[0016] Structure formation stage (11 - 20 days): Reduce the aeration intensity to 1.5 L / (m³ min), and at the same time introduce a uniform magnetic field with an intensity of 0.05 T. In this stage, MNPs act as a "magnetic guiding agent", driving the microorganisms to arrange orderly under the action of the magnetic field, promoting the gradual formation of a stable gradient structure with aerobic on the outer layer, anoxic in the middle layer, and anaerobic in the inner layer inside the AGS particles. Extend the sedimentation time to 12 min to ensure the stability of the oxygen concentration gradient inside the particles and strengthen the spatial distribution of different functional microbial communities.

[0017] Maturity optimization stage (21 - 30 days): Keep the magnetic field condition unchanged, and further reduce the aeration intensity to 1.2 L / (m³ min), slowing down the damage of water shear force to particles. The sedimentation time is fixed at 15min, and the AGS particle size is precisely controlled at 0.8-1.2mm through long-term hydraulic screening and microbial self-immobilization. The internal mass transfer channel of the particles formed in this particle size range is stable, which not only guarantees the demand of outer aerobic bacteria for dissolved oxygen, but also creates an oxygen-free environment for inner anaerobic bacteria, significantly improving the graded degradation efficiency of pollutants in printing and dyeing wastewater.

[0018] As a further solution of the present invention, in step S4, the reactor is specifically divided into the following three functional areas: Pre-reduction zone: A high-efficiency static mixer is used to fully and evenly mix nZVI and wastewater. The residence time of wastewater in this zone is 1.5h; Gradient coupling zone: A circular magnetic field with a magnetic field strength of 0.1 T is set in this zone. Under the action of the magnetic field, the directional adsorption of nZVI and AGS particles is promoted to form stable "nZVI-AGS" microaggregates; Deep mineralization area: Micro-nano aeration technology is used to maintain the dissolved oxygen at 4-6 mg / L, and iron-manganese composite oxides with a concentration of 30-50 mg / L are added as efficient electron carriers for microbial metabolism. The wastewater stays in this area for 2 hours.

[0019] Specifically, in the present invention, the modified nZVI and the optimized cultured AGS are put into a three-stage gradient coupling reactor, which is specifically divided into the following three functional zones, and each functional zone works synergistically to achieve efficient treatment of printing and dyeing wastewater: Pre-reduction zone: This zone is equipped with a high-efficiency static mixer, which is used to fully and evenly mix nZVI with wastewater. During the 1.5-hour residence time, the modified nZVI, with its strong reducing property, preliminarily destroys the conjugated structure of the dye molecule. This process reduces the chromaticity and complexity of the dye, creating favorable conditions for subsequent deep treatment.

[0020] Gradient coupling zone: A circular magnetic field with an intensity of 0.1T is set to promote the directional adsorption of nZVI and AGS particles to form "nZVI-AGS" microaggregates. By precisely controlling the rising flow rate of the water flow, the microaggregates are placed in a suspended fluidized state. In this state, the microaggregates can fully contact the wastewater, greatly increasing the effective area of ​​the reaction. The wastewater stays in this area for 3 hours. In the anaerobic-anoxic-aerobic gradient environment constructed by AGS, nZVI and the microorganisms in AGS achieve efficient synergy. In an anaerobic environment, microorganisms use the electrons provided by nZVI to reduce difficult-to-degrade organic matter; in an anaerobic environment, denitrifying bacteria use nZVI and organic matter to carry out denitrification reactions; in an aerobic environment, aerobic microorganisms further decompose organic matter. Through this multi-environment and multi-mechanism collaboration, pollutants are deeply degraded, significantly improving the treatment effect of printing and dyeing wastewater.

[0021] Deep mineralization area: The micro-nano aeration technology is adopted to maintain the dissolved oxygen at 4 - 6 mg / L. Meanwhile, iron-manganese composite oxide with a concentration of 30 - 50 mg / L is added as an efficient electron carrier for microbial metabolism. During the 2-hour residence time, the mineralization of refractory intermediate products such as aromatic amines is further enhanced. The iron-manganese composite oxide promotes the microbial metabolism process, enabling these refractory substances to be decomposed more thoroughly, ensuring the deep purification of the wastewater.

[0022] The wastewater after gradient coupling and synergistic degradation treatment enters the photocatalysis-membrane filtration coupling unit for in-depth treatment. With the hollow fiber membrane loaded with titanium dioxide nanotubes as the core component, under the irradiation of ultraviolet light (wavelength 254 nm, light intensity 15 W / m²), the titanium dioxide nanotubes generate strongly oxidizing hydroxyl radicals to oxidize and degrade the residual pollutants. At the same time, the hollow fiber membrane intercepts the potentially toxic substances generated by the degradation of nZVI to ensure the compliance of the effluent quality.

[0023] The present invention has the following beneficial effects: The novel technical principle and synergistic mechanism in the present invention: Most of the existing nZVI / AGS coupling technologies are simple physical mixtures, relying on the independent action of the reducibility of nZVI and the biodegradability of AGS, lacking systematic synergistic design. The present invention creatively proposes a "nanomaterial interface regulation-gradient functional zoning" synergistic mechanism: By constructing an nZVI-CS-SiO2 composite interface with CS-SiO2 and tannic acid, the hydrophobic contradiction between the dye and nZVI is solved; The "core-shell" structure is used to modify nZVI with PPy and BCNs to achieve a three-in-one synergistic effect of "adsorption-electron transfer-degradation"; At the same time, the "dual-substrate-magnetic field induction" is used to cultivate AGS to form a gradient structure, combined with a three-stage reactor to achieve hierarchical degradation of anaerobic-anoxic-aerobic. This multi-dimensional synergistic mechanism is a fundamental breakthrough in traditional coupling technologies, forming a new technical principle system.

[0024] The present invention innovatively integrates a variety of technologies, such as nanomaterial modification, magnetic field-induced microbial cultivation, and photocatalysis-membrane filtration coupling. A ring-shaped magnetic field is utilized to promote the directional adsorption of nZVI and AGS, forming "nZVI-AGS" microaggregates; potential toxic substances generated by the degradation of nZVI are removed directionally through the photocatalysis-membrane filtration unit. In view of the problems in the prior art, such as the easy oxidation and inactivation of nZVI, the limited mass transfer of AGS, and the incomplete degradation of dyes, the present invention proposes a series of targeted solutions. For example, the oxidation of nZVI is inhibited by compounding an interface regulator and modifying the core-shell structure, and its specific surface area is increased to 82 m² / g; the structure of AGS is optimized by gradient cultivation and micro-nano aeration, and the proportion of the anaerobic zone reaches 35%, significantly improving the mass transfer efficiency; through a three-stage reactor and the addition of electron carriers, the hierarchical treatment of dyes from pre-reduction to deep mineralization is realized, and the COD removal rate is increased to more than 98%.

[0025] The present invention has achieved a qualitative leap in terms of treatment efficiency and effect. Experimental data show that its COD removal rate for printing and dyeing wastewater reaches more than 98%, and the dye removal rate is as high as 99.5%, which is 30%-40% higher than that of traditional processes; the decolorization rate of refractory azo dyes is increased by 35%, and the hydraulic retention time is shortened by 40%. This benefits from the efficient mass transfer and synergistic reaction of the gradient coupling process, as well as the strong degradation ability of modified nZVI and optimized AGS.

[0026] Through the gradient functional zoning design and precise regulation of nanomaterials, the present invention effectively improves the stability of the process and its adaptability to different water qualities. For example, the core-shell structure of modified nZVI significantly enhances its antioxidant ability and extends its service life; the gradient structure of AGS makes the distribution of the microbial community more reasonable and improves the shock load resistance of the system; the three-stage reactor can flexibly adjust parameters according to the wastewater quality. These characteristics enable the process to be applicable to various complex printing and dyeing wastewaters, overcoming the defect of traditional technologies being sensitive to water quality fluctuations.

[0027] To more clearly elaborate the structural features and efficacy of the present invention, the following will combine the drawings with specific embodiments to illustrate the present invention in detail. Description of the Drawings

[0028] Figure 1 It is the overall flow chart of a method for treating printing and dyeing wastewater based on the nZVI / AGS coupling process of the present invention. Detailed Embodiments

[0029] The following will further illustrate the present invention in combination with the drawings and relevant knowledge, and describe it clearly and completely. Obviously, the described applications are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0030] Refer to Figure 1As shown in the figure, the present invention provides a method for treating printing and dyeing wastewater based on the nZVI / AGS coupling process, including the following steps: Step S1: Introduce the printing and dyeing wastewater into the pre-activation tank. First, use a ceramic membrane with a pore size of 3 - 5 μm for fine filtration to effectively remove suspended solids and colloidal impurities in the wastewater, creating good conditions for subsequent treatment. Subsequently, add a composite interfacial regulator composed of chitosan-modified nano-silica (CS-SiO2) and tannic acid to the wastewater. The mass ratio of the two is 2:1, and the dosage is controlled at 80 - 120 mg / L. The abundant amino groups on the surface of CS-SiO2 can form stable hydrogen bonds with dye molecules, significantly enhancing the dispersibility of dyes in water. At the same time, its nano-scale structure has a strong adsorption capacity and can firmly adsorb nZVI, thus constructing a stable nZVI-CS-SiO2 composite interface. Tannic acid, as a natural and efficient chelating agent, can quickly complex dissolved oxygen and metal ions in water, effectively inhibiting the oxidation reaction of nZVI. Under the condition of a stirring speed of 200 - 300 r / min, allow the wastewater to react fully with the composite interfacial regulator for 40 - 60 min. Then, adjust the pH value of the wastewater to 7.0 - 7.5 and maintain the temperature at 28 - 32 °C to provide suitable environmental conditions for the subsequent treatment process. Step S2: Treat nZVI using a unique "core-shell" structure modification strategy: Use nZVI as the core and sequentially coat conductive polymer polypyrrole (PPy) and biochar nanosheets (BCNs). The specific modification process is as follows: First, uniformly disperse nZVI in an ethanol aqueous solution (the volume ratio of ethanol to water is 1:1) to form a suspension with a concentration of 50 g / L. Then, add pyrrole monomer to the suspension to make its concentration reach 0.1 mol / L, and add ammonium persulfate as an initiator with a concentration of 0.12 mol / L. Under the conditions of 30 °C and darkness, continuously react for 6 h to promote the polymerization reaction of PPy on the surface of nZVI, forming a PPy layer with excellent electron transport performance. Subsequently, add BCNs to make its concentration in the suspension 10 g / L, and continue to stir and react for 4 h. Utilize the π-π stacking interaction between BCNs and PPy to uniformly coat BCNs on the outer layer of PPy. The phenolic hydroxyl groups and carboxyl groups rich on the surface of BCNs can undergo specific adsorption with dye molecules; while the PPy layer can significantly promote the electron transfer efficiency from nZVI to AGS microorganisms. Through this modification method, a synergistic reaction interface of "adsorption - electron transfer - degradation" in one entity is formed. The modified nZVI is separated by centrifugation (centrifugation speed 6000 r / min, time 15 min) and then freeze-dried for standby. Step S3: The AGS is cultured by using the "dual-substrate - magnetic field induction" culture method: In a sequencing batch reactor, sodium acetate and glucose are selected as the composite carbon source, and the mass ratio of the two is set to 3:1. At the same time, the C:N:P ratio is strictly controlled to be 100:5:1, and magnetic nano-ferroferric oxide particles (MNPs) with a concentration of 20 - 30 mg / L are added. The entire culture process is divided into three stages: Initial stage (0 - 10 days): The aeration intensity is set to 2.0 L / (m³ min), and the pulse aeration method is used (aeration for 6 min, aeration stop for 2 min). The sedimentation time gradually increases from the initial 5 min to 8 min. This stage mainly promotes the rapid aggregation and initial agglomeration of microorganisms; Middle stage (11 - 20 days): The aeration intensity is reduced to 1.5 L / (m³ min), and a uniform magnetic field with an intensity of 0.05 T is introduced. Under the action of the magnetic field, MNPs guide the microorganisms to be arranged orderly, promoting the AGS to gradually form a stable gradient structure with aerobic on the outer layer, anoxic in the middle layer, and anaerobic in the inner layer. The sedimentation time in this stage is extended to 12 min; Mature stage (21 - 30 days): The magnetic field conditions are maintained unchanged, and the aeration intensity is further adjusted to 1.2 L / (m³ min), and the sedimentation time is stabilized at 15 min. Finally, the particle size of the AGS is controlled within 0.8 - 1.2 mm, forming a gradient structure with a stable mass transfer channel, providing a good microbial environment for the efficient degradation of pollutants.

[0031] Step S4: Gradient coupling and synergistic degradation; The modified nZVI (dosage of 150 - 200 mg / L) and the optimized cultured AGS are put into a three-stage gradient coupling reactor. This reactor is specifically divided into the following three functional zones: Pre-reduction zone: A high-efficiency static mixer is used to make the nZVI and the wastewater fully and evenly mixed. The residence time of the wastewater in this area is 1.5 h. Utilizing the strong reducibility of the modified nZVI, the conjugated structure of the dye molecules is initially destroyed, reducing the chroma and complexity of the dye; Gradient coupling zone: An annular magnetic field with a magnetic field intensity of 0.1 T is set in this area. Under the action of the magnetic field, it promotes the directional adsorption of nZVI and AGS particles to form stable "nZVI - AGS" micro-aggregates. By precisely controlling the upward flow velocity of the water flow (0.5 m / h), the micro-aggregates are in a suspended fluidized state. The residence time of the wastewater in this area is 3 h. Under the unique anaerobic - anoxic - aerobic gradient environment of the AGS, the nZVI and the microorganisms in the AGS cooperate to deeply degrade the pollutants; Deep mineralization area: The micro-nano aeration technology (bubble diameter less than 100 μm) is adopted to maintain the dissolved oxygen at 4-6 mg / L, and iron-manganese composite oxide (Fe-Mn-Ox) with a concentration of 30-50 mg / L is added as an efficient electron carrier for microbial metabolism. The residence time of the wastewater in this area is 2 h, which further strengthens the mineralization of refractory intermediate products such as aromatic amines, ensuring the complete decomposition of pollutants.

[0032] Further preferably, the wastewater after gradient coupling and synergistic degradation treatment enters the photocatalysis-membrane filtration coupling unit for advanced treatment: Using a hollow fiber membrane loaded with titanium dioxide nanotubes (TiO2NTs) as the core treatment component, under the irradiation of ultraviolet light (wavelength 254 nm, light intensity 15 W / m²), TiO2NTs generate a large number of highly oxidizing hydroxyl radicals, which can rapidly oxidize and degrade the remaining pollutants. At the same time, the hollow fiber membrane plays a role in filtration and interception, effectively removing the potentially toxic substances generated during the nZVI degradation process.

[0033] More preferably, under the irradiation of ultraviolet light (wavelength 254 nm, light intensity 15 W / m²), a photocatalytic reaction occurs on TiO2NTs. After the valence band electrons of TiO2NTs absorb photon energy, they jump to the conduction band, leaving holes in the valence band, forming electron-hole pairs. Since electrons and holes have strong activity, they will quickly migrate to the surface of TiO2NTs. Among them, the holes react with water molecules to generate highly oxidizing hydroxyl radicals ( •OH). The redox potential of hydroxyl radicals is as high as 2.8 V, second only to fluorine gas, and can react non-selectively with various refractory organic pollutants remaining in the wastewater. Through a series of redox processes, the molecular structure of these pollutants is gradually destroyed and finally mineralized into carbon dioxide, water and other harmless small molecule substances.

[0034] At the same time, the hollow fiber membrane exerts its physical filtration and interception function. It has a specific pore size structure, which can effectively intercept the unreacted nZVI particles in the wastewater, various solid oxides generated during the nZVI degradation process, and other possible suspended impurities. In particular, for the potentially toxic intermediate products generated during the nZVI degradation process, such as some bio-toxic aromatic amines and azo small molecule substances, the hollow fiber membrane, by virtue of its sieving effect, intercepts these substances on one side of the membrane, preventing them from flowing out with the treated water, thus avoiding secondary pollution. Through the synergistic effect of photocatalytic oxidation degradation and membrane filtration interception, this coupling unit realizes the advanced purification of wastewater, ensuring that the effluent quality meets strict discharge standards or reuse requirements.

[0035] Example 1, A method for treating printing and dyeing wastewater based on the nZVI / AGS coupling process, comprising the following steps: Step S1: Pretreatment and Interface Optimization of Wastewater: Select 10 m³ of printing and dyeing wastewater containing reactive brilliant red X-3B from a certain printing and dyeing factory. After introducing it into the pre-activation tank, first filter it through a ceramic membrane filter with a pore size of 3 μm. Subsequently, add 800 g of CS-SiO₂ and 400 g of tannic acid according to the mass ratio of CS-SiO₂ to tannic acid in the composite interface modifier of 2:1. Under the condition of a stirring speed of 250 r / min, allow the wastewater and the reagent to react fully for 50 min. After the reaction, use a pH adjustment device to adjust the pH value of the wastewater to 7.2, and maintain the temperature at 30 °C through a temperature control system.

[0036] Step S2: Gradient Functionalization Modification of nZVI: Weigh 1 kg of nZVI, disperse it in an ethanol aqueous solution (volume ratio 1:1) to prepare a suspension with a concentration of 50 g / L. Add pyrrole monomer (to make its concentration reach 0.1 mol / L) and ammonium persulfate (concentration 0.12 mol / L) in sequence, and react for 6 h in a light-tight environment at 30 °C to polymerize PPy on the surface of nZVI. Then add 100 g of BCNs and continue to stir and react for 4 h. After the reaction is completed, centrifuge the modified nZVI (rotation speed 6000 r / min, time 15 min), and then perform freeze-drying treatment for standby. After testing, the specific surface area of the modified nZVI increases from 35 m² / g to 82 m² / g, and the Zeta potential changes from -12 mV to +8 mV, significantly improving its reaction activity and adsorption performance.

[0037] Step S3: Directed Cultivation of AGS Gradient Structure: In a sequencing batch reactor, add a composite carbon source according to the mass ratio of sodium acetate to glucose of 3:1, while ensuring that the C:N:P ratio is 100:5:1, and add 250 g of MNPs. In the initial stage of cultivation (0 - 10 days), set the aeration intensity to 2.0 L / (m³ min), adopt a pulsed aeration method (aeration for 6 min, aeration stop for 2 min), and gradually extend the sedimentation time from 5 min to 8 min; in the middle stage of cultivation (11 - 20 days), reduce the aeration intensity to 1.5 L / (m³ min), and introduce a uniform magnetic field of 0.05 T, and extend the sedimentation time to 12 min; in the mature stage of cultivation (21 - 30 days), maintain the magnetic field condition, adjust the aeration intensity to 1.2 L / (m³ min), and the sedimentation time is stabilized at 15 min. Finally, obtain AGS with a particle size of about 1.0 mm and an obvious gradient structure. After testing, the proportion of the anaerobic zone inside it reaches 35%, providing a good microbial environment for the efficient degradation of pollutants.

[0038] Step S4: Gradient-coupled synergistic degradation: The modified nZVI is put into a three-stage gradient-coupled reactor together with the optimized AGS cultured at a dosage of 180 mg / L. In the pre-reduction zone, a static mixer is used to fully mix nZVI with the wastewater, and the wastewater residence time is 1.5 h. In the gradient-coupled zone, with the aid of an annular magnetic field (intensity 0.1 T), the formation of "nZVI-AGS" micro-aggregates between nZVI and AGS is promoted. By controlling the upward water flow velocity at 0.5 m / h, the micro-aggregates are kept in a suspended fluidized state, and the wastewater residence time is 3 h. In the deep mineralization zone, a micro-nano aeration technique is adopted to maintain the dissolved oxygen at 4-6 mg / L, and 40 mg / L of Fe-Mn-Ox is added, and the wastewater residence time is 2 h. After this treatment, it is detected that the COD of the wastewater drops from the initial 1200 mg / L to 20 mg / L, and the dye removal rate reaches 99.6%, and the treatment effect is remarkable.

[0039] Directional detoxification: The treated wastewater enters the photocatalysis-membrane filtration coupling unit. Under the irradiation of ultraviolet light (wavelength 254 nm, intensity 15 W / m²), the hollow fiber membrane loaded with TiO2NTs plays the roles of photocatalytic oxidation and filtration interception. After detection, the concentration of toxic substances in the effluent is lower than the detection limit, meeting the reclaimed water standard.

[0040] Synergistic enhancement of multiple processes in the present invention: In the wastewater pre-activation, the composite interfacial regulator optimizes the water quality, creating conditions for subsequent treatment; the gradient functionalization modification of nZVI improves its activity and adsorption performance, which is complementary to the microbial gradient environment formed by the directional cultivation of the gradient structure of AGS, realizing the synergistic degradation of pre-reduction, gradient coupling and deep mineralization in the three-stage reactor; the photocatalysis-membrane filtration coupling unit deeply treats the residual pollutants and toxic substances. Each step is closely linked to form a complete treatment chain. Synergistic effect of substances and microorganisms: The modified nZVI acts as an electron donor and adsorption carrier in the reactor, synergizing with different functional microbial communities in AGS. In the anaerobic zone, nZVI provides electrons for microorganisms to reduce dyes, and in the aerobic zone, microorganisms use nZVI to degrade intermediate products for further mineralization; at the same time, the gradient structure of AGS provides a stable reaction environment for nZVI, preventing it from being oxidized and inactivated too quickly, and the two promote each other. Synergistic effect of physical-chemical and biological processes: Physical means such as ceramic membrane filtration, magnetic field induction, and micro-nano aeration, chemical processes such as nZVI modification and photocatalytic oxidation, are organically combined with biological treatment (AGS degradation). For example, magnetic field induction promotes the structural optimization of AGS and the formation of nZVI-AGS aggregates, micro-nano aeration improves the dissolved oxygen transfer efficiency, creating conditions for biological reactions, and the hydroxyl radicals generated by photocatalysis strengthen the biodegradation of pollutants that are difficult to remove.

[0041] The present invention proposes an nZVI "core-shell" gradient functionalization modification method, which significantly improves its performance through the coating of PPy and BCNs; and develops a "dual-substrate - magnetic field-induced" AGS gradient structure directional cultivation technique.

[0042] Design of new reactors and treatment units: Construct a three-stage gradient coupling reactor, divide it into a pre-reduction zone, a gradient coupling zone, and a deep mineralization zone to achieve hierarchical treatment of pollutants; design a photocatalysis-membrane filtration coupling unit, combine photocatalytic oxidation with membrane filtration to directionally remove toxic substances, which has a creative breakthrough in the structural design of reactors and treatment units. Aiming at industry problems such as the easy oxidation of nZVI, the mass transfer limitation of AGS, and the difficult degradation of dyes, inhibit the oxidation of nZVI through a composite interfacial regulator, optimize the structure of AGS to improve mass transfer, and synergistically improve the degradation efficiency through multiple processes.

[0043] Example 2, A method for treating printing and dyeing wastewater based on the nZVI / AGS coupling process, includes the following steps: Step S1: Wastewater pre-activation and interface optimization: Select 8 m³ of printing and dyeing wastewater containing disperse blue 2BLN from another printing and dyeing factory. After filtering through a ceramic membrane with a pore size of 4 μm, add 640 g of CS-SiO2 and 320 g of tannic acid. Under the condition of a stirring speed of 230 r / min, react for 45 min, then adjust the pH value of the wastewater to 7.3 and maintain the temperature at 29°C.

[0044] Step S2: nZVI gradient functionalization modification: Modify 800 g of nZVI, and the specific steps are the same as in Example 1. After testing after modification, the adsorption rate constant of nZVI and the dye increased by 2.3 times, significantly enhancing its adsorption ability for the dye.

[0045] Step S3: AGS gradient structure directional cultivation: During the cultivation process, appropriately adjust the parameters according to the actual situation. Finally, obtain AGS with a particle size of 0.9 mm. Through microbial community analysis, it is found that the aerobic layer microorganisms are mainly Nitrobacter, and a large number of Desulfovibrio are enriched in the anaerobic layer, forming a good gradient microbial structure.

[0046] Step S4: Gradient coupling synergistic degradation: The operating parameters are the same as in Example 1. After treatment, the COD of the wastewater drops to 25 mg / L, and the dye removal rate reaches 99.2%, also achieving excellent treatment effects.

[0047] The above describes the technical principle of the present invention in combination with specific embodiments, which is only the preferred embodiment of the present invention. The protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the concept of the present invention belong to the protection scope of the present invention. Those skilled in the art can easily think of other specific embodiments of the present invention without creative labor, and these embodiments will all fall within the protection scope of the present invention.

Claims

1. A method for treating printing and dyeing wastewater based on the nZVI / AGS coupling process, characterized in that, Including the following steps: Step S1: Pretreatment activation and interface optimization of wastewater. Introduce the printing and dyeing wastewater into the pre-activation tank, and use a ceramic membrane with a pore size of 3 - 5 μm for fine filtration to effectively remove suspended solids and colloidal impurities in the wastewater. Step S2: nZVI gradient functional modification: Treat nZVI using the "core - shell" method: Use nZVI as the core, and sequentially coat the conductive polymer polypyrrole and biochar nanosheets. Step S3: Directed cultivation of AGS gradient structure: Cultivate AGS using the "dual - substrate - magnetic field induction" cultivation method: In a sequencing batch reactor, select sodium acetate and glucose as the composite carbon source, and set their mass ratio to 3:

1. At the same time, control the C:N:P ratio to 100:5:1, and add magnetic nano - iron oxide particles with a concentration of 20 - 30 mg / L. Step S4: Gradient coupling and synergistic degradation: Put the modified nZVI and the optimized - cultivated AGS into a three - stage gradient coupling reactor. The wastewater after gradient coupling and synergistic degradation enters the photocatalysis - membrane filtration coupling unit for advanced treatment.

2. The method for treating printing and dyeing wastewater based on the nZVI / AGS coupling process according to claim 1, wherein In step S1, it also includes adding a composite interface regulator composed of chitosan - modified nano - silica and tannic acid to the wastewater. The mass ratio of the two is 2:1, and the dosage is controlled at 80 - 120 mg / L.

3. The method for treating printing and dyeing wastewater based on the nZVI / AGS coupling process according to claim 2, characterized in that, In step S2, the specific modification process is as follows: Uniformly disperse nZVI in an ethanol - aqueous solution to form a suspension with a concentration of 50 g / L; Add pyrrole monomer to the suspension to make its concentration reach 0.1 mol / L, and add ammonium persulfate as the initiator with a concentration of 0.12 mol / L; Under the conditions of 30 °C and in the dark, continuously react for 6 h to promote the polymerization reaction of PPy on the surface of nZVI to form a PPy layer with electron - transport performance; Add BCNs to make its concentration in the suspension 10 g / L, and continue to stir and react for 4 h. Utilize the π - π stacking effect between BCNs and PPy to uniformly coat BCNs on the outer layer of PPy.

4. The method for treating printing and dyeing wastewater based on the nZVI / AGS coupling process according to claim 3, characterized in that, In step S3, the entire cultivation process is divided into three stages: Initial 0 - 10 days: Set the aeration intensity to 2.0 L / (m³ min), adopt the pulsed aeration mode, and gradually extend the sedimentation time from the initial 5 min to 8 min; Medium term, 11 - 20 days: Reduce the aeration intensity to 1.5 L / (m³ min), and introduce a uniform magnetic field with an intensity of 0.05 T. Under the action of the magnetic field, MNPs guide the microorganisms to arrange orderly, promoting the gradual formation of a stable gradient structure with aerobic in the outer layer, anoxic in the middle layer, and anaerobic in the inner layer of AGS. The sedimentation time in this stage is extended to 12 min; Maturity period: 21 - 30 days. Keeping the magnetic field conditions unchanged, adjust the aeration intensity to 1.2 L / (m³ min), keep the sedimentation time stable at 15 min, control the AGS particle size within 0.8 - 1.2 mm, form a gradient structure with a stable mass transfer channel, and provide a good microbial environment for the efficient degradation of pollutants.

5. The method for treating printing and dyeing wastewater based on the nZVI / AGS coupling process according to claim 4, wherein In step S4, the reactor is specifically divided into the following three functional zones: Pre - reduction zone: Use a high - efficiency static mixer to make nZVI and the wastewater fully and uniformly mixed. The residence time of the wastewater in this area is 1.5 h. Gradient coupling zone: Set an annular magnetic field in this area with a magnetic field intensity of 0.1 T. Under the action of the magnetic field, promote the directional adsorption of nZVI and AGS particles to form stable "nZVI - AGS" micro - aggregates. Deep mineralization zone: Use the micro - nano aeration technology to maintain the dissolved oxygen at 4 - 6 mg / L, and add iron - manganese composite oxides with a concentration of 30 - 50 mg / L as an efficient electron carrier for microbial metabolism. The residence time of the wastewater in this area is 2 h.

6. The method for treating printing and dyeing wastewater based on the nZVI / AGS coupling process according to claim 5, wherein In the gradient coupling zone, by controlling the upward flow velocity of the water flow, the micro - aggregates are in a suspended fluidized state. The residence time of the wastewater in this area is 3 h. Under the anaerobic - anoxic - aerobic gradient environment of AGS, nZVI and the microorganisms in AGS cooperate to deeply degrade the pollutants.

7. The method for treating printing and dyeing wastewater based on the nZVI / AGS coupling process according to claim 6, characterized in that, In step S4, the hollow fiber membrane loaded with titanium dioxide nanotubes is used as a treatment component, and under the irradiation of ultraviolet light, hydroxyl radicals with strong oxidizing properties are generated for the oxidative degradation of residual pollutants.

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