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

Abstract

This invention discloses a method for treating dyeing and printing wastewater based on an nZVI / AGS coupling process, comprising the following steps: wastewater pre-activation and interface optimization, wherein the dyeing and printing wastewater is introduced into a pre-activation tank; nZVI gradient functionalization modification: nZVI is treated using a "core-shell" approach, with nZVI as the core, and conductive polymer polypyrrole and biochar nanosheets are sequentially coated on it; AGS gradient structure directional cultivation: AGS is cultivated using a "dual substrate-magnetic field induced" cultivation method, wherein sodium acetate and glucose are selected as composite carbon sources in a sequencing batch reactor, with a mass ratio of 3:1, and the C:N:P ratio is controlled at 100:5:1, and magnetic nano-iron oxide particles at a concentration of 20-30 mg / L are added; gradient coupling synergistic degradation: the modified nZVI and the optimized cultured AGS are fed into a three-stage gradient coupling reactor, and the wastewater treated by gradient coupling synergistic degradation enters a photocatalysis-membrane filtration coupling unit for further treatment.

Description

Technical Field

[0001] This invention relates to the field of textile dyeing and printing wastewater treatment, specifically a method for treating dyeing and printing wastewater based on the nZVI / AGS coupling process. Background Technology

[0002] The types of dyes used in the printing and dyeing process are relatively concentrated, and they can be classified according to their chemical molecular structure and application properties.

[0003] Azo dyes are the most widely used class 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 diazoamine coupled with an associative amine or phenol, plus one or more azo bonds. Anthraquinone dyes contain three fused benzene rings, i.e., fused benzene, with two carbonyl groups attached to the central benzene ring; most are aromatic polymers. Indigo dye is a dark indole group dye, belonging to polycyclic aromatic compounds. Most of these dyes have double bonds, benzene rings, or heterocyclic structures, are extremely chemically stable and difficult to degrade, and possess considerable toxicity, carcinogenicity, and mutagenicity. Once released into the environment, they pose a serious threat to the ecological environment and human health. For a long time, the design and operation of dyeing and printing wastewater treatment projects have mainly focused on COD and color removal, while insufficient attention has been paid to the removal of the dyes themselves. Since the COD in dyeing and printing wastewater mainly originates from sizing agents and auxiliaries, with dyes contributing only 10% to 30%, traditional biological treatment technologies can achieve COD removal rates of 80% to 90%. However, due to the stable chemical properties and low biodegradability of dyes, their removal effect is relatively poor. The color in dyeing and printing wastewater primarily comes from dyes, but traditional biological treatment technologies often only destroy the chromophores of dyes, converting large molecules into smaller ones, without completely degrading the dyes. Furthermore, the intermediate metabolites of dyes are usually aromatic substances, a large portion of which belong to polycyclic aromatic hydrocarbons (PAHs), which are toxic and carcinogenic and difficult to further degrade.

[0004] Currently, my country's dyeing and printing enterprises mainly adopt a combined "physicochemical pretreatment + biological treatment" process for wastewater treatment, with biological treatment primarily using anaerobic / aerobic (A / O) and anaerobic / anoxic / aerobic (A / A / O) processes. Biological treatment units significantly reduce COD and ammonia nitrogen, especially toxic pollutants, resulting in a significant reduction in the concentration of dyes, PVA, and other pollutants in the effluent. However, when the wastewater temperature, pH, or alkalinity is too high or too low, it can significantly impact the functional microbial community in the wastewater biological treatment system, leading to unstable effluent quality and even damaging the biological treatment system, preventing timely treatment of production wastewater. Furthermore, because dyeing and printing wastewater contains a large amount of recalcitrant organic matter, ordinary biological treatment systems struggle to completely remove it, leaving high concentrations of recalcitrant organic pollutants in the biological effluent. These recalcitrant organic pollutants pose potential risks to aquatic organisms and human health when they enter the aquatic environment. Numerous biological experiments have shown that industrial wastewater treatment plant effluent can produce various adverse biological effects at the cellular and individual levels.

[0005] In dyeing and printing wastewater, recalcitrant organic matter, represented by dyes, and its biotoxicity must be effectively removed before it can safely enter the aquatic environment or be reused. Since most of these organic compounds are artificially synthesized, the types and numbers of microorganisms capable of efficiently degrading them in the natural environment are very limited, and they are at a disadvantage in interspecies competition. Therefore, traditional biological treatment methods struggle to achieve efficient degradation of these organic compounds. Aerobic granular sludge (AGS) is a promising new wastewater treatment technology that has attracted considerable attention in recent years. Compared to ordinary activated sludge, it has advantages such as compact structure, fast settling speed, and high biomass, and exhibits good adaptability and strong tolerance to high-concentration recalcitrant industrial wastewater. The granular structure of AGS allows for the simultaneous existence of aerobic, anoxic, and anaerobic environments. Aerobic, facultative anaerobic, and anaerobic microorganisms aggregate and grow sequentially from the outside in, achieving the regional enrichment of different dominant microorganisms. This not only enables the simultaneous completion of biological processes such as organic matter degradation, nitrification / denitrification, and biological phosphorus removal, but also significantly improves the removal efficiency of recalcitrant pollutants, achieving highly efficient wastewater treatment. Nano-zero valent iron (nZVI) is an environmentally friendly material with high reactivity, high treatment efficiency, controllable particle size, and abundant active sites. It is not only chemically active with strong reducing power and high electronegativity, but also can reduce organic compounds, ionic compounds, and other substances that are not easily reduced in chemical reactions. Therefore, it can effectively remove pollutants that are difficult to degrade by conventional methods. It has shown great application potential in the dechlorination of halogenated organic compounds, the reduction of heavy metal ions, the conversion of inorganic ions, and the decolorization of dye wastewater.

[0006] In other words, while the nZVI / AGS coupling technology has shown some application potential in the field of dyeing and printing wastewater treatment, there are still many technical bottlenecks that urgently need to be addressed. Firstly, the surface of nZVI is easily oxidized to form a dense iron oxide passivation layer, leading to a significant reduction in electron transfer efficiency. Meanwhile, the high mass transfer resistance within AGS particles makes it difficult for dye molecules to fully contact the active reaction sites, resulting in a lack of efficient synergistic mechanisms between the two. Secondly, existing nZVI / AGS coupling processes are mostly simple physical mixing processes, without synergistic optimization design considering the unique spatial structure of AGS and the activity decay characteristics of nZVI, leading to insufficient dye reduction reactions in the anaerobic zone and low mineralization efficiency in the aerobic zone. Thirdly, there is a significant contradiction between the hydrophilicity of organic dyes and the hydrophobicity of nZVI, greatly limiting their effective binding and reaction. Fourthly, some intermediate products generated during the degradation of nZVI have potential toxicity, and current technologies have not yet established effective control and elimination mechanisms, posing a high environmental risk. Currently, there is an urgent need to achieve technological breakthroughs from multiple dimensions, such as interface interaction mechanisms and process structure innovation, in order to improve the efficiency of nZVI / AGS coupling technology in treating dyeing and printing wastewater. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a method for treating dyeing and printing wastewater based on an nZVI / AGS coupling process. This 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 an nZVI / AGS gradient coupling system regulated by nanomaterial interfaces. This will achieve efficient degradation and safe treatment of dye pollutants in dyeing and printing wastewater, providing an innovative technical solution for the green and sustainable development of the dyeing and printing industry.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for treating dyeing and printing wastewater based on an nZVI / AGS coupling process includes the following steps:

[0010] Step S1: Wastewater Pre-activation and Interface Optimization. The dyeing and printing wastewater is introduced into a pre-activation tank and finely filtered using a ceramic membrane with a pore size of 3-5 μm to effectively remove suspended solids and colloidal impurities. In this stage, the wastewater is finely filtered using a ceramic membrane with a pore size of 3-5 μm. This operation effectively intercepts and removes suspended solids and colloidal impurities from the wastewater, creating favorable conditions for subsequent treatment, reducing interference from impurities in subsequent reactions, and improving overall treatment efficiency.

[0011] Step S2: nZVI Gradient Functionalization Modification: nZVI is treated using a "core-shell" structure. nZVI serves as the core, sequentially coated with the conductive polymer polypyrrole and biochar nanosheets. Polypyrrole possesses excellent conductivity, promoting electron transfer and enhancing the reactivity of nZVI; biochar nanosheets have a large specific surface area and abundant functional groups, improving the adsorption capacity for pollutants. This modification method gives nZVI superior performance, enhancing its effectiveness in wastewater treatment.

[0012] Step S3: AGS Gradient Structure Directed Cultivation: AGS is cultivated using a "dual-substrate-magnetic field induced" cultivation method. In a sequencing batch reactor (SBR), sodium acetate and glucose are selected as a composite carbon source, with a mass ratio of 3:1. The C:N:P ratio is controlled at 100:5:1, and magnetic nano-iron oxide particles at a concentration of 20-30 mg / L are added. This cultivation method guides AGS to form microbial aggregates with a specific gradient structure. Microorganisms in different regions possess different functions, thereby improving the degradation capacity of various pollutants in dyeing and printing wastewater.

[0013] Step S4: Gradient Coupling Synergistic Degradation: Modified nZVI and optimized AGS are added to a three-stage gradient coupling reactor. The wastewater, after gradient coupling synergistic degradation, then enters a photocatalytic-membrane filtration coupling unit for further treatment. In this reactor, nZVI and AGS work synergistically to degrade pollutants in the dyeing and printing wastewater through gradient coupling, fully utilizing the reaction conditions and microbial characteristics at different stages to improve degradation efficiency and effectiveness. The wastewater after gradient coupling synergistic degradation then enters the photocatalytic-membrane filtration coupling unit for further treatment. This unit combines the advantages of photocatalytic oxidation and membrane filtration, further removing residual pollutants from the wastewater and achieving higher water quality standards for the effluent.

[0014] As a further aspect of the present invention, step S1 further includes adding a composite interface modifier composed of chitosan-modified nano-silica and tannic acid to the wastewater, with a mass ratio of 2:1 and a dosage controlled at 80-120 mg / L. After filtration, the composite interface modifier composed of chitosan-modified nano-silica and tannic acid is added to the wastewater. The surface of chitosan-modified nano-silica is rich in amino groups, which can form stable hydrogen bonds with dye molecules, enhancing dye dispersibility; tannic acid, as a natural chelating agent, can complex dissolved oxygen and metal ions in water, inhibiting 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 precisely controlled at 80-120 mg / L. By adding this composite interface modifier, the interface properties of the wastewater are optimized, creating a more favorable reaction environment for subsequent treatment.

[0015] As a further aspect of the present invention, the specific modification process in step S2 is as follows: nZVI is uniformly dispersed in an ethanol-water solution to form a suspension with a concentration of 50 g / L; pyrrole monomer is added to the suspension to achieve a concentration of 0.1 mol / L, and ammonium persulfate is added as an initiator with a concentration of 0.12 mol / L; the reaction is continued for 6 hours at 30°C in the dark to promote the polymerization reaction of PPy on the surface of nZVI, forming a PPy layer with excellent electron transport properties; BCNs are added to achieve a concentration of 10 g / L in the suspension, and the reaction is continued with stirring for 4 hours. Utilizing the π-π stacking effect between BCNs and PPy, BCNs uniformly coat the outer layer of PPy. The uniform dispersion process ensures the full participation of nZVI in subsequent reactions.

[0016] Pyrrole monomer was added to the suspension to achieve a concentration of 0.1 mol / L, and ammonium persulfate was added as an initiator at a concentration of 0.12 mol / L. The reaction was allowed to proceed for 6 hours at 30°C in the dark. During this process, ammonium persulfate initiated the polymerization of pyrrole monomer, promoting the polymerization of polypyrrole (PPy) on the nZVI surface to form a PPy layer with excellent electron transport properties. This PPy layer significantly improves the electron transport capacity of nZVI and enhances its reactivity.

[0017] Subsequently, biochar nanosheets (BCNs) were added to the suspension to achieve a concentration of 10 g / L, and the reaction was continued with stirring for 4 hours. Utilizing the π-π stacking interaction between BCNs and PPy, BCNs uniformly coat the outer layer of PPy. BCNs possess a large specific surface area and abundant functional groups, which not only further enhances the adsorption capacity for pollutants but also synergistically interacts with the PPy layer to form a highly efficient reaction interface of "adsorption-electron transfer-degradation".

[0018] As a further aspect of the present invention, in step S3, the entire cultivation process is divided into three stages:

[0019] Initial 0-10 days: Set the aeration intensity to 2.0 L / (m³) Using pulse aeration, the settling time was gradually increased from the initial 5 minutes to 8 minutes.

[0020] Mid-term (days 11-20): Reduce aeration intensity to 1.5 L / (m³) (min), and a uniform magnetic field with an intensity of 0.05T is introduced. Under the action of the magnetic field, MNPs guide the microorganisms to arrange themselves in an orderly manner, which promotes the AGS to gradually form a stable gradient structure with an outer aerobic layer, a middle hypoxic layer, and an inner anaerobic layer. The settling time in this stage is extended to 12min.

[0021] Maturity period 21-30 days: Maintaining the magnetic field conditions unchanged, further adjust the aeration intensity to 1.2 L / (m³). The sedimentation time was stabilized at 15 min, allowing the AGS particle size to be controlled at 0.8-1.2 mm, forming a gradient structure with stable mass transfer channels, providing a favorable microbial environment for the efficient degradation of pollutants. A "dual-substrate-magnetic field-induced" culture method was employed in a sequencing batch reactor using sodium acetate and glucose (mass ratio 3:1) as a composite carbon source, controlling the C:N:P ratio at 100:5:1, and adding 20-30 mg / L of magnetic nano-iron oxide particles (MNPs) to directionally cultivate the gradient structure of AGS in stages.

[0022] Specifically, during the initial cultivation stage (0-10 days): at a rate of 2.0 L / (m³) The aeration intensity (6 min) combined with the pulse aeration mode (6 min aeration, 2 min pause) stimulates rapid microbial proliferation and aggregation through periodic dissolved oxygen supply. The settling time is gradually extended from 5 min to 8 min, prompting the microorganisms to transition from a dispersed state to initial granulation, laying the foundation for subsequent structure construction.

[0023] Structure formation stage (11-20 days): Reduce aeration intensity to 1.5 L / (m³) (min) Simultaneously, a uniform magnetic field with an intensity of 0.05T is introduced. During this stage, MNPs act as "magnetic guides," driving the orderly arrangement of microorganisms under the influence of the magnetic field, promoting the gradual formation of a stable gradient structure within the AGS particles: an outer aerobic layer, a middle hypoxic layer, and an inner anaerobic layer. Extending the settling time to 12 min ensures the stability of the oxygen concentration gradient within the particles and enhances the spatial distribution of different functional microbial communities.

[0024] Maturity and optimization phase (21-30 days): Maintaining the magnetic field conditions unchanged, further reduce the aeration intensity to 1.2 L / (m³). The settling time is fixed at 15 minutes, which reduces the shear force of the water flow on the particles. Through long-term hydraulic screening and microbial self-immobilization, the particle size of AGS is precisely controlled within 0.8-1.2 mm. The internal mass transfer channels formed within this particle size range are stable, ensuring the dissolved oxygen requirements of the outer aerobic bacteria while creating an anaerobic environment for the inner anaerobic bacteria, significantly improving the efficiency of graded degradation of pollutants in dyeing and printing wastewater.

[0025] As a further aspect of the present invention, in step S4, the reactor is specifically divided into the following three functional areas:

[0026] Pre-reduction zone: A high-efficiency static mixer is used to ensure that nZVI and wastewater are fully and uniformly mixed. The residence time of wastewater in this zone is 1.5 hours.

[0027] Gradient coupling region: A ring magnetic field with a strength of 0.1T is set in this region. Under the action of the magnetic field, the nZVI and AGS particles are oriented to adsorb and form stable “nZVI-AGS” micro-aggregates.

[0028] Deep mineralization zone: Micro-nano aeration technology is used to maintain dissolved oxygen at 4-6 mg / L, and iron-manganese composite oxide at a concentration of 30-50 mg / L is added as an efficient electron carrier for microbial metabolism. Wastewater stays in this zone for 2 hours.

[0029] Specifically, in this invention, modified nZVI and optimized cultured AGS are introduced into a three-stage gradient coupled reactor. This reactor is divided into three functional zones, which work synergistically to achieve efficient treatment of dyeing and printing wastewater.

[0030] Pre-reduction zone: This zone is equipped with a high-efficiency static mixer, whose function is to ensure thorough and uniform mixing of nZVI and wastewater. During the 1.5-hour residence time, the modified nZVI, with its strong reducing properties, initially disrupts the conjugated structure of the dye molecules. This process reduces the dye's chroma and complexity, creating favorable conditions for subsequent advanced treatment.

[0031] Gradient Coupling Zone: A ring-shaped magnetic field with an intensity of 0.1T is set up to promote the directional adsorption of nZVI and AGS particles, forming "nZVI-AGS" micro-aggregates. By precisely controlling the upward flow velocity of the water, the micro-aggregates are kept in a suspended fluidized state. In this state, the micro-aggregates can fully contact the wastewater, greatly increasing the effective reaction area. The wastewater stays in this zone for 3 hours. In the anaerobic-anoxic-aerobic gradient environment constructed by AGS, nZVI and the microorganisms in AGS achieve highly efficient synergistic effects. In the anaerobic environment, microorganisms use the electrons provided by nZVI to reduce recalcitrant organic matter; in the anoxic environment, denitrifying bacteria use nZVI and organic matter to carry out denitrification; in the aerobic environment, aerobic microorganisms further decompose organic matter. Through this synergistic effect of multiple environments and mechanisms, pollutants are deeply degraded, significantly improving the treatment effect of dyeing and printing wastewater.

[0032] Deep mineralization zone: Micro-nano aeration technology is used to maintain dissolved oxygen at 4-6 mg / L. Simultaneously, iron-manganese composite oxides at a concentration of 30-50 mg / L are added as highly efficient electron carriers for microbial metabolism. During the 2-hour retention time, the mineralization of recalcitrant intermediates such as aromatic amines is further enhanced. The iron-manganese composite oxides promote microbial metabolic processes, enabling these recalcitrant substances to be decomposed more thoroughly, ensuring deep purification of the wastewater.

[0033] Wastewater treated by gradient coupling synergistic degradation then enters the photocatalysis-membrane filtration coupling unit for further treatment. Using a hollow fiber membrane loaded with titanium dioxide nanotubes as the core component, under ultraviolet light (wavelength 254nm, light intensity 15W / m²), the titanium dioxide nanotubes generate highly oxidizing hydroxyl radicals, oxidizing and degrading residual pollutants. Simultaneously, the hollow fiber membrane traps potentially toxic substances produced by nZVI degradation, ensuring that the effluent meets quality standards.

[0034] The present invention has the following beneficial effects:

[0035] This invention presents a novel technical principle and synergistic mechanism. Existing nZVI / AGS coupling technologies are mostly simple physical mixtures, relying on the independent action of nZVI's reducibility and AGS's biodegradation ability, lacking a systematic synergistic design. This invention innovatively proposes a "nanomaterial interface regulation-gradient functional partitioning" synergistic mechanism: an nZVI-CS-SiO2 composite interface is constructed using CS-SiO2 and tannic acid to resolve the hydrophobicity conflict between the dye and nZVI; a "core-shell" structure is used to modify nZVI with PPy and BCNs, achieving a three-in-one synergistic effect of "adsorption-electron transfer-degradation"; simultaneously, a "dual substrate-magnetic field induction" method is used to cultivate AGS to form a gradient structure, combined with a three-stage reactor to achieve anaerobic-anoxic-aerobic graded degradation. This multi-dimensional synergistic mechanism represents a fundamental breakthrough from traditional coupling technologies, forming a completely new technical principle system.

[0036] This invention innovatively integrates multiple technologies, including nanomaterial modification, magnetic field-induced microbial culture, and photocatalysis-membrane filtration coupling. A toroidal magnetic field is used to promote the directional adsorption of nZVI and AGS, forming "nZVI-AGS" micro-aggregates. A photocatalysis-membrane filtration unit then directionally removes potentially toxic substances generated during nZVI degradation. Addressing the problems of easy oxidation and inactivation of nZVI, limited mass transfer of AGS, and incomplete dye degradation in existing technologies, this invention proposes a series of targeted solutions. For example, by using composite interface modifiers and core-shell structure modification to inhibit nZVI oxidation, its specific surface area is increased to 82 m² / g; gradient culture and micro / nano aeration are used to optimize the AGS structure, achieving an anaerobic zone ratio of 35%, significantly improving mass transfer efficiency; and a three-stage reactor and electron carrier addition are used to achieve staged treatment of the dye from pre-reduction to deep mineralization, increasing the COD removal rate to over 98%.

[0037] This invention represents a qualitative leap in treatment efficiency and effectiveness. Experimental data shows that it achieves a COD removal rate of over 98% and a dye removal rate of up to 99.5% for dyeing and printing wastewater, representing a 30%-40% improvement compared to traditional processes. It also increases the decolorization rate of recalcitrant azo dyes by 35% and shortens the hydraulic retention time by 40%. This is attributed to the efficient mass transfer and synergistic reaction of the gradient coupling process, as well as the strong degradation capabilities of modified nZVI and optimized AGS.

[0038] Through gradient functional zoning design and precise control of nanomaterials, this 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 capacity and extends its service life; the AGS gradient structure makes the distribution of microbial communities more rational, improving the system's resistance to shock loads; and the three-stage reactor allows for flexible adjustment of parameters according to wastewater quality. These characteristics make this process suitable for various complex dyeing and printing wastewaters, overcoming the shortcomings of traditional technologies that are sensitive to water quality fluctuations.

[0039] To more clearly illustrate the structural features and effects of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0040] Figure 1 This is a flowchart illustrating a dyeing and printing wastewater treatment method based on the nZVI / AGS coupling process according to the present invention. Detailed Implementation

[0041] The present invention will now be further described in conjunction with the accompanying drawings and relevant knowledge, and will be described clearly and completely. Obviously, the described applications are only some embodiments of the present invention, and not all embodiments.

[0042] Reference Figure 1 As shown, the present invention provides a method for treating dyeing and printing wastewater based on an nZVI / AGS coupling process, comprising the following steps:

[0043] Step S1: The dyeing and printing wastewater is introduced into a pre-activation tank. First, a ceramic membrane with a pore size of 3-5 μm is used for fine filtration to effectively remove suspended solids and colloidal impurities, creating favorable conditions for subsequent treatment. Then, a composite interface modifier consisting of chitosan-modified nano-silica (CS-SiO2) and tannic acid is added to the wastewater at a mass ratio of 2:1, with the dosage 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. Simultaneously, its nanoscale structure possesses strong adsorption capacity, firmly adsorbing nZVI, thereby constructing a stable nZVI-CS-SiO2 composite interface. Tannic acid, as a natural and highly efficient chelating agent, can rapidly complex dissolved oxygen and metal ions in the water, effectively inhibiting the oxidation reaction of nZVI. Under the condition of stirring speed of 200-300 r / min, allow the wastewater and composite interface conditioner to react fully for 40-60 min. Then adjust the pH value of the wastewater to 7.0-7.5 and maintain the temperature at 28-32℃ to provide suitable environmental conditions for subsequent treatment processes.

[0044] Step S2: A unique "core-shell" structure modification strategy was employed to treat nZVI: using nZVI as the core, conductive polymer polypyrrole (PPy) and biochar nanosheets (BCNs) were sequentially coated. The specific modification process is as follows: First, nZVI was uniformly dispersed in an ethanol-water solution (ethanol to water volume ratio of 1:1) to form a suspension with a concentration of 50 g / L; then, pyrrole monomer was added to the suspension to achieve a concentration of 0.1 mol / L, and ammonium persulfate was added as an initiator with a concentration of 0.12 mol / L; the reaction was continued for 6 hours at 30°C in the dark, promoting the polymerization reaction of PPy on the surface of nZVI to form a PPy layer with excellent electron transport properties. Subsequently, BCNs were added to achieve a concentration of 10 g / L in the suspension, and the reaction was continued with stirring for 4 hours. Utilizing the π-π stacking effect between BCNs and PPy, BCNs were uniformly coated on the outer layer of PPy. The phenolic hydroxyl and carboxyl groups abundant on the surface of BCNs enable specific adsorption of dye molecules; while the PPy layer significantly promotes the electron transfer efficiency of nZVI to AGS microorganisms. This modification method creates a synergistic reaction interface integrating adsorption, electron transfer, and degradation. The modified nZVI was then centrifuged (6000 r / min for 15 min) and freeze-dried for later use.

[0045] Step S3: AGS is cultured using a "dual-substrate-magnetic field-induced" culture method: In a sequencing batch reactor, sodium acetate and glucose are selected as a composite carbon source, with a mass ratio of 3:1. The C:N:P ratio is strictly controlled at 100:5:1, and magnetic nano-iron oxide particles (MNPs) at a concentration of 20-30 mg / L are added. The entire culture process is divided into three stages:

[0046] Initial stage (0-10 days): Set the aeration intensity to 2.0 L / (m³). The settling time was gradually increased from the initial 5 minutes to 8 minutes using pulse aeration (6 minutes of aeration followed by 2 minutes of aeration stop). This stage mainly promoted the rapid aggregation and initial clumping of microorganisms.

[0047] Mid-term (11-20 days): Reduce aeration intensity to 1.5 L / (m³) (min), and a uniform magnetic field with an intensity of 0.05T is introduced. Under the action of the magnetic field, MNPs guide the orderly arrangement of microorganisms, causing AGS to gradually form a stable gradient structure with an outer aerobic layer, a middle hypoxic layer, and an inner anaerobic layer. During this stage, the settling time is extended to 12min;

[0048] Maturity period (21-30 days): Maintaining the magnetic field conditions unchanged, further adjust the aeration intensity to 1.2 L / (m³). The settling time was stabilized at 15 min, ultimately controlling the AGS particle size to 0.8-1.2 mm, forming a gradient structure with stable mass transfer channels, providing a favorable microbial environment for the efficient degradation of pollutants.

[0049] Step S4: Gradient coupling synergistic degradation;

[0050] The modified nZVI (dosage of 150-200 mg / L) and the optimized cultured AGS were introduced into a three-stage gradient coupled reactor, which was specifically divided into the following three functional zones:

[0051] Pre-reduction zone: A high-efficiency static mixer is used to ensure thorough and uniform mixing of nZVI and wastewater. The wastewater residence time in this zone is 1.5 hours. Utilizing the strong reducing properties of modified nZVI, the conjugated structure of dye molecules is initially disrupted, reducing the dye's chroma and complexity.

[0052] Gradient Coupling Zone: A ring-shaped magnetic field with a strength of 0.1T is set in this zone. Under the influence of the magnetic field, nZVI and AGS particles undergo directional adsorption, forming stable "nZVI-AGS" micro-aggregates. By precisely controlling the upward flow velocity of the water (0.5 m / h), the micro-aggregates are kept in a suspended fluidized state, and the wastewater residence time in this zone is 3 hours. In the unique anaerobic-anoxic-aerobic gradient environment of AGS, nZVI and the microorganisms in AGS work synergistically to deeply degrade pollutants.

[0053] Deep mineralization zone: Micro-nano aeration technology (bubble diameter less than 100μm) is used to maintain dissolved oxygen at 4-6mg / L, and iron-manganese composite oxide (Fe-Mn-Ox) at a concentration of 30-50mg / L is added as an efficient electron carrier for microbial metabolism. Wastewater stays in this zone for 2 hours, which further enhances the mineralization of recalcitrant intermediate products such as aromatic amines and ensures that pollutants are completely decomposed.

[0054] Further optimization involves the wastewater, after gradient coupling synergistic degradation treatment, entering a photocatalysis-membrane filtration coupling unit for advanced treatment. A hollow fiber membrane loaded with titanium dioxide nanotubes (TiO2NTs) serves as the core treatment component. Under ultraviolet light irradiation (wavelength 254nm, light intensity 15W / m²), TiO2NTs generate a large number of highly oxidizing hydroxyl radicals, which can rapidly oxidize and degrade residual pollutants. Simultaneously, the hollow fiber membrane performs filtration and retention, effectively removing potentially toxic substances generated during the nZVI degradation process.

[0055] Further optimization revealed that TiO2NTs underwent a photocatalytic reaction under ultraviolet light irradiation (wavelength 254 nm, light intensity 15 W / m²). After absorbing photon energy, the valence band electrons of TiO2NTs transitioned to the conduction band, leaving holes in the valence band and forming electron-hole pairs. Due to the high reactivity of electrons and holes, they rapidly migrated to the TiO2NTs surface. Among these, the holes reacted with water molecules to generate highly oxidizing hydroxyl radicals (…). OH). The redox potential of hydroxyl radicals is as high as 2.8V, second only to fluorine gas. It can react non-selectively with various recalcitrant organic pollutants remaining in wastewater. Through a series of redox processes, it gradually destroys the molecular structure of these pollutants and eventually mineralizes them into carbon dioxide, water and other harmless small molecules.

[0056] Meanwhile, the hollow fiber membrane performs its physical filtration function. With its specific pore structure, it effectively intercepts unreacted nZVI particles, various solid oxides generated during nZVI degradation, and other potential suspended impurities in the wastewater. In particular, for potentially toxic intermediates generated during nZVI degradation, such as some biotoxic aromatic amines and azo compounds, the hollow fiber membrane, through its sieving action, retains these substances on one side of the membrane, preventing them from flowing out with the treated water and thus avoiding secondary pollution. Through the synergistic effect of photocatalytic oxidation degradation and membrane filtration, this coupled unit achieves deep purification of wastewater, ensuring that the effluent quality meets stringent discharge standards or reuse requirements.

[0057] Example 1: A method for treating dyeing and printing wastewater based on an nZVI / AGS coupling process, comprising the following steps:

[0058] Step S1: Wastewater Pre-activation and Interface Optimization: 10 m³ of dyeing and printing wastewater containing Reactive Brilliant Red X-3B from a dyeing and printing factory was selected and introduced into a pre-activation tank. First, it was filtered through a ceramic membrane filter with a pore size of 3 μm. Subsequently, 800 g of CS-SiO2 and 400 g of tannic acid were added according to a 2:1 mass ratio of CS-SiO2 to tannic acid in the composite interface modifier. The wastewater and the reagent were allowed to react fully for 50 minutes at a stirring speed of 250 r / min. After the reaction, the pH of the wastewater was adjusted to 7.2 using a pH adjustment device, and the temperature was maintained at 30℃ using a temperature control system.

[0059] Step S2: nZVI gradient functionalization modification: Weigh 1 kg of nZVI and disperse it in an ethanol-water solution (volume ratio 1:1) to prepare a suspension with a concentration of 50 g / L. Add pyrrole monomer (to a concentration of 0.1 mol / L) and ammonium persulfate (concentration of 0.12 mol / L) sequentially, and react at 30℃ in the dark for 6 h to allow PPy to polymerize on the nZVI surface. Then add 100 g of BCNs and continue stirring for another 4 h. After the reaction is complete, centrifuge the modified nZVI (6000 r / min, 15 min) and then freeze-dry it for later use. Testing showed that the specific surface area of ​​the modified nZVI increased from 35 m² / g to 82 m² / g, and the Zeta potential changed from -12 mV to +8 mV, significantly improving its reactivity and adsorption performance.

[0060] Step S3: AGS Gradient Structure Directed Culture: In a sequencing batch reactor, a composite carbon source is added at a sodium acetate to glucose mass ratio of 3:1, ensuring a C:N:P ratio of 100:5:1, and 250g of MNPs is added. During the initial culture period (0-10 days), the aeration rate is set to 2.0L / (m³). During the first 6 minutes of cultivation (11-20 days), a pulse aeration method was used (aeration for 6 minutes, followed by a 2-minute pause), with the settling time gradually increased from 5 minutes to 8 minutes. During the second 6 minutes of cultivation (11-20 days), the aeration intensity was reduced to 1.5 L / (m³). During the maturation period (21-30 days), a uniform magnetic field of 0.05T was introduced, and the settling time was extended to 12 minutes. The magnetic field conditions were maintained, and the aeration intensity was adjusted to 1.2 L / (m³). The settling time was stabilized at 15 minutes. The final product was AGS with a particle size of approximately 1.0 mm and a distinct gradient structure. Analysis showed that the anaerobic zone accounted for 35% of its internal structure, providing a favorable microbial environment for the efficient degradation of pollutants.

[0061] Step S4: Gradient Coupling Synergistic Degradation: Modified nZVI was added to a three-stage gradient coupling reactor at a dosage of 180 mg / L along with optimized cultured AGS. In the pre-reduction zone, a static mixer was used to thoroughly mix nZVI with the wastewater, with a wastewater retention time of 1.5 h. In the gradient coupling zone, a toroidal magnetic field (strength 0.1 T) was used to promote the formation of "nZVI-AGS" micro-aggregates between nZVI and AGS. By controlling the upward flow velocity of the water at 0.5 m / h, the micro-aggregates were kept in a suspended fluidized state, with a wastewater retention time of 3 h. In the deep mineralization zone, micro-nano aeration technology was used to maintain dissolved oxygen at 4-6 mg / L, and 40 mg / L of Fe-Mn-Ox was added, with a wastewater retention time of 2 h. After this treatment, the COD of the wastewater decreased from the initial 1200 mg / L to 20 mg / L, and the dye removal rate reached 99.6%, demonstrating a significant treatment effect.

[0062] Targeted detoxification: The treated wastewater enters the photocatalytic-membrane filtration coupling unit. Under ultraviolet light irradiation (wavelength 254nm, intensity 15W / m²), the TiO2NTs-loaded hollow fiber membrane performs photocatalytic oxidation and filtration. Testing showed that the concentration of toxic substances in the effluent was below the detection limit, meeting the standards for reused water.

[0063] This invention features synergistic effects across multiple processes: In wastewater pre-activation, a composite interface regulator optimizes water quality, creating conditions for subsequent treatment; nZVI gradient functionalization enhances its activity and adsorption performance, complementing the microbial gradient environment formed by the directional cultivation of the AGS gradient structure, achieving synergistic degradation of pre-reduction, gradient coupling, and deep mineralization in a three-stage reactor; the photocatalytic-membrane filtration coupling unit deeply treats residual pollutants and toxic substances, with each step interconnected to form a complete treatment chain. Synergistic effects between substances and microorganisms: Modified nZVI acts as an electron donor and adsorbent carrier in the reactor, synergizing with different functional microbial communities within the AGS. In the anaerobic zone, nZVI provides electrons to reduce the dye for microorganisms, while in the aerobic zone, microorganisms utilize nZVI to degrade intermediate products for further mineralization; simultaneously, the gradient structure of the AGS provides a stable reaction environment for nZVI, preventing its rapid oxidation and deactivation, thus promoting mutual benefit. Synergistic effects of physicochemical and biological processes: Physical methods such as ceramic membrane filtration, magnetic field induction, and micro / nano aeration, along with chemical processes such as nZVI modification and photocatalytic oxidation, are organically combined with biological treatment (AGS degradation). For example, magnetic field induction promotes AGS structure optimization and nZVI-AGS aggregate formation, micro-nano aeration improves dissolved oxygen transfer efficiency, creating conditions for biological reactions, and photocatalysis generates hydroxyl radicals that enhance the biodegradation of pollutants that are difficult to remove.

[0064] This invention proposes a core-shell gradient functionalization modification method for nZVI, which significantly improves its performance through PPy and BCNs coating; and develops a dual-substrate-magnetic field induced AGS gradient structure directional culture technology.

[0065] Novel Reactor and Treatment Unit Design: A three-stage gradient-coupled reactor is constructed, divided into a pre-reduction zone, a gradient coupling zone, and a deep mineralization zone to achieve graded treatment of pollutants. A photocatalysis-membrane filtration coupling unit is designed, combining photocatalytic oxidation with membrane filtration to directionally remove toxic substances, representing a creative breakthrough in reactor and treatment unit structural design. Addressing industry challenges such as easy oxidation of nZVI, limited mass transfer in AGS, and difficult degradation of dyes, the design utilizes composite interface modifiers to inhibit nZVI oxidation, optimizes the AGS structure to improve mass transfer, and employs multi-process synergy to enhance degradation efficiency.

[0066] Example 2: A method for treating dyeing and printing wastewater based on an nZVI / AGS coupling process, comprising the following steps:

[0067] Step S1: Wastewater pre-activation and interface optimization: 8 m³ of dyeing wastewater containing Disperse Blue 2BLN from another dyeing and printing plant was selected, filtered through a ceramic membrane with a pore size of 4 μm, and then 640 g of CS-SiO2 and 320 g of tannic acid were added. The reaction was carried out for 45 min at a stirring speed of 230 r / min, and then the pH of the wastewater was adjusted to 7.3 and the temperature was maintained at 29℃.

[0068] Step S2: nZVI gradient functionalization modification: 800gnZVI was modified using the same steps as in Example 1. After modification, the adsorption rate constant of nZVI and the dye was increased by 2.3 times, significantly enhancing its adsorption capacity for the dye.

[0069] Step S3: Directed Cultivation of AGS in a Gradient Structure: During the cultivation process, parameters were adjusted appropriately according to the actual situation. Finally, AGS with a particle size of 0.9 mm was obtained. Microbial community analysis revealed that the aerobic layer was dominated by *Nitrobacterium*, while the anaerobic layer was enriched with a large number of *Desulfovibrio*, forming a well-developed gradient microbial structure.

[0070] Step S4: Gradient Coupling Synergistic Degradation: Operating parameters remained consistent with Example 1. After treatment, the COD of the wastewater decreased to 25 mg / L, and the dye removal rate reached 99.2%, achieving excellent treatment results.

[0071] The technical principles of the present invention have been described above with reference to specific embodiments, which are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments; all technical solutions falling within the scope of the present invention's concept are within its protection scope. Those skilled in the art can conceive of other specific embodiments of the present invention without creative effort, and these embodiments will all fall within the protection scope of the present invention.

Claims

1. A method for treating dyeing and printing wastewater based on an nZVI / AGS coupling process, characterized in that, Includes the following steps: Step S1: Wastewater pre-activation and interface optimization. The dyeing and printing wastewater is introduced into the pre-activation tank and finely filtered using a ceramic membrane with a pore size of 3-5μm to effectively remove suspended solids and colloidal impurities from the wastewater. A composite interface regulator composed of chitosan-modified nano-silica and tannic acid is added to the wastewater at a mass ratio of 2:1 and the dosage is controlled at 80-120mg / L. Step S2: nZVI gradient functionalization modification: nZVI is treated using a "core-shell" method: using nZVI as the core, conductive polymer polypyrrole and biochar nanosheets are sequentially coated. The specific modification process is as follows: nZVI is uniformly dispersed in an ethanol aqueous solution to form a suspension with a concentration of 50 g / L; pyrrole monomer is added to the suspension to achieve a concentration of 0.1 mol / L, and ammonium persulfate is added as an initiator with a concentration of 0.12 mol / L; the reaction is continued for 6 hours at 30°C in the dark to promote the polymerization reaction of PPy on the surface of nZVI, forming a PPy layer with electron transport properties; BCNs are added to achieve a concentration of 10 g / L in the suspension, and the reaction is continued with stirring for 4 hours. Utilizing the π-π stacking effect between BCNs and PPy, BCNs are uniformly coated on the outer layer of PPy. Step S3: AGS Gradient Structure Directed Cultivation: AGS was cultivated using a "dual substrate-magnetic field induced" cultivation method. In a sequencing batch reactor, sodium acetate and glucose were selected as a composite carbon source, with a mass ratio of 3:

1. The C:N:P ratio was controlled at 100:5:1, and magnetic nano-iron oxide particles at a concentration of 20-30 mg / L were added. The entire cultivation process was divided into three stages: Initial 0-10 days: Set the aeration intensity to 2.0 L / (m³) Using pulse aeration, the settling time was gradually increased from the initial 5 minutes to 8 minutes. Mid-term (days 11-20): Reduce aeration intensity to 1.5 L / (m³) (min), and a uniform magnetic field with an intensity of 0.05T is introduced. Under the action of the magnetic field, MNPs guide the microorganisms to arrange themselves in an orderly manner, which promotes the AGS to gradually form a stable gradient structure with an outer aerobic layer, a middle hypoxic layer, and an inner anaerobic layer. The settling time in this stage is extended to 12min. Maturity period 21-30 days: Maintain the magnetic field conditions unchanged, and adjust the aeration intensity to 1.2 L / (m³). The settling time was stabilized at 15 min, which controlled the AGS particle size to 0.8-1.2 mm, forming a gradient structure with stable mass transfer channels, providing a good microbial environment for the efficient degradation of pollutants; Step S4: Gradient Coupling Synergistic Degradation: The modified nZVI and the optimized cultured AGS are fed into a three-stage gradient coupling reactor. The wastewater treated by gradient coupling synergistic degradation then enters the photocatalysis-membrane filtration coupling unit for further treatment. The reactor is specifically divided into the following three functional zones: Pre-reduction zone: A high-efficiency static mixer is used to ensure that nZVI and wastewater are fully and uniformly mixed. The residence time of wastewater in this zone is 1.5 hours. Gradient coupling region: A ring magnetic field with a strength of 0.1T is set in this region. Under the action of the magnetic field, the nZVI and AGS particles are oriented to adsorb and form stable "nZVI-AGS" micro-aggregates. Deep mineralization zone: Micro-nano aeration technology is used to maintain dissolved oxygen at 4-6 mg / L, and iron-manganese composite oxide at a concentration of 30-50 mg / L is added as an efficient electron carrier for microbial metabolism. Wastewater stays in this zone for 2 hours.

2. The method for treating dyeing and printing wastewater based on the nZVI / AGS coupling process as described in claim 1, characterized in that, In the gradient coupling zone, the upward flow velocity of the water is controlled to keep the micro-aggregates in a suspended fluidized state. The wastewater stays in this zone for 3 hours. Under the anaerobic-anoxic-aerobic gradient environment of AGS, nZVI works synergistically with the microorganisms in AGS to deeply degrade pollutants.

3. The method for treating dyeing and printing wastewater based on the nZVI / AGS coupling process as described in claim 2, characterized in that, In step S4, a hollow fiber membrane loaded with titanium dioxide nanotubes is used as a processing component. Under ultraviolet light irradiation, hydroxyl radicals with strong oxidizing properties are generated to oxidize and degrade residual pollutants.

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