Microbial slow-release porous composite material for sewage treatment as well as preparation method and application thereof

Abstract

The invention provides a microbial slow-release porous composite material for sewage treatment as well as a preparation method and application thereof. The preparation method comprises the following steps: dropwise adding an organic ligand solution into a precursor solution consisting of a nanocellulose solution and a cobalt source solution; mixing the reaction solution with polyvinyl alcohol, injecting the mixture into a mold, and performing directional freezing to obtain an aerogel matrix; carrying out hydrophobic modification on the aerogel matrix to obtain a modified aerogel matrix; mixing the microbial suspension with sodium alginate, and homogenizing at high pressure to obtain a gel precursor emulsion; the preparation method comprises the following steps: dropwise adding a calcium chloride solution to gelatinize to obtain gel particles, and then cross-linking and drying by glutaraldehyde to obtain sustained-release capsule particles; dispersing the sustained-release capsule particles in deionized water to obtain dispersion liquid; and dipping the modified aerogel matrix in the dispersion liquid. An aerogel matrix with a hierarchical porous structure is compounded with a sustained-release capsule with a pH response mechanism, so that physical adsorption, chemical catalysis and biodegradation for sewage treatment are realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage treatment, and relates to a microbial slow-release porous composite material for sewage treatment, a preparation method thereof, and uses thereof. Background Art

[0002] In the context of global water resource shortage and increasing water pollution, the innovation of sewage treatment technology has become a core issue in the environmental field. Traditional sewage treatment methods such as physical filtration, chemical precipitation, and activated sludge method have achieved certain results in pollutant removal, but still face bottlenecks such as high sludge production, high risk of secondary pollution, and limited treatment efficiency. Taking biological treatment technology as an example, the activated sludge method relies on microbial metabolism to degrade organic matter, but microorganisms are easily lost with the effluent, requiring frequent addition of bacteria and being difficult to adapt to complex water quality fluctuations; the biofilm method is limited by the specific surface area of the carrier and the stability of microbial attachment, resulting in the difficulty of continuously improving the treatment efficiency. In recent years, the technology of immobilizing microorganisms has achieved slow-release applications by fixing functional bacteria in porous carriers, significantly reducing the frequency of adding bacteria. However, its carrier materials mostly use traditional porous media such as activated carbon and zeolite, which have problems such as single pore structure, limited adsorption capacity, low microbial loading efficiency, and rely on aeration equipment to maintain microbial release, resulting in high operating costs. In addition, existing slow-release materials such as ion adsorption carriers or embedding gels generally face defects such as insufficient mechanical strength and poor recyclability, and are difficult to meet the requirements of long-term stable operation.

[0003] With the improvement of environmental protection requirements, the demand for new materials with high pollutant removal ability, environmental friendliness, and economic feasibility in the field of sewage treatment is becoming increasingly urgent. Porous materials have become a research hotspot due to their high specific surface area and adjustable pore structure. For example, metal-organic framework materials (MOFs) and biochar composites have shown potential in adsorbing heavy metals and organic pollutants, but their synthesis processes are complex, costly, and lack mechanism design for synergistic action with microorganisms. At the same time, although the microbial slow-release technology can improve the treatment effect by extending the active period of the microbial community, existing solutions mostly focus on the immobilization of single strains, insufficient utilization of the synergistic effect of complex microbial co-metabolism, and the slow-release rate is difficult to match the dynamic water quality changes, resulting in large fluctuations in pollutant removal efficiency. In addition, the inhibition of microbial activity and the problem of carrier structure stability under extreme water quality conditions (such as high salt, high pH) are still the key challenges restricting the large-scale application of this technology. In this context, developing a composite functional material with a controllable pore structure, high microbial slow-release ability, and environmental adaptability has important scientific significance and engineering value for breaking through the performance bottlenecks of existing sewage treatment technologies. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technologies, the purpose of the present invention is to provide a microbial slow-release porous composite material for sewage treatment, its preparation method and uses. By combining an aerogel matrix with a multi-level pore structure and slow-release capsules with a pH-responsive mechanism, physical adsorption, chemical catalysis and biodegradation of sewage treatment are realized.

[0005] To achieve this purpose, the present invention adopts the following technical solutions:

[0006] In the first aspect, the present invention provides a preparation method of a microbial slow-release porous composite material for sewage treatment, and the preparation method includes:

[0007] (Ⅰ) Drop an organic ligand solution into a precursor solution composed of a nanocellulose solution and a cobalt source solution to obtain a reaction solution; mix the reaction solution with polyvinyl alcohol and then inject it into a mold for directional freezing to obtain an aerogel matrix; perform hydrophobic modification on the aerogel matrix to obtain a modified aerogel matrix;

[0008] (Ⅱ) Mix a microbial suspension with sodium alginate and then perform high-pressure homogenization to obtain a gel precursor emulsion; drop it into a calcium chloride solution for gelation to obtain gel particles, and then crosslink and dry them with glutaraldehyde to obtain slow-release capsule particles;

[0009] (Ⅲ) Disperse the slow-release capsule particles in deionized water to obtain a dispersion; immerse the modified aerogel matrix in the dispersion, take it out and dry it to obtain the microbial slow-release porous composite material.

[0010] The present invention combines an aerogel matrix with a multi-level pore structure and slow-release capsules with a pH-responsive mechanism, realizing physical adsorption, chemical catalysis and biodegradation of sewage treatment. The vertically penetrating pores of the modified aerogel matrix provide a high-speed channel for pollutant enrichment and mass transfer, and the Co 2+ nodes of the surface-loaded ZIF-67 provide Lewis acid sites, which specifically bind to sulfur, phosphorus or nitrogen-containing pollutants through coordination, enhancing the adsorption selectivity for polar or specific-structured pollutants. Slow-release capsule particles with a double-layer structure are prepared by a gradient crosslinking process, with its outer shell maintaining structural integrity under water flow impact, and the inner core reserving an active space for microbial colonization and metabolism.

[0011] In the present invention, nanocellulose is used as a biomass skeleton material, and its surface-rich hydroxyl functional groups coordinate with cobalt ions. When cobalt nitrate solution is mixed with nanocellulose, cobalt ions are preferentially adsorbed around the oxygen-containing groups of the cellulose molecular chain, forming a uniform metal ion distribution network. Subsequently, the introduced 2-methylimidazole organic ligand undergoes a self-assembly reaction with cobalt ions, generating metal-organic framework material ZIF-67 in the gaps of the nanocellulose network. The excessive organic ligand not only ensures the complete progress of the reaction but also inhibits the overgrowth of crystals through steric hindrance effect, ultimately forming regular dodecahedral crystals. These ZIF-67 crystals are tightly bound to the nanocellulose network through hydrogen bonding, retaining both the three-dimensional pore structure of the aerogel matrix and endowing it with catalytic active sites, capable of rapidly capturing heavy metal ions (such as Pb 2+ , Cd 2 + ), organic dye molecules, and oil pollutants in wastewater; meanwhile, its Lewis acid sites (Co 2+ nodes) can also bind to specific pollutants (such as sulfur- or nitrogen-containing compounds) through coordination, enhancing selective adsorption.

[0012] In the process of preparing the sustained-release capsule particles, a primary protection network is formed by the entanglement of sodium alginate molecular chains and the microbial cell suspension. The carboxylic acid groups on its molecular chains form a three-dimensional gel structure with calcium ions through the "egg box" cross-linking mechanism. This three-dimensional gel structure can not only maintain the metabolic activity of microorganisms but also reduce the mechanical damage of the external environment to the cells through a physical barrier. In the present invention, the gel precursor solution is dispersed into submicron-sized emulsion droplets with uniform particle size by high-pressure homogenization, so that the finally formed sustained-release capsule particles (1 - 5 μm) can match the 50 - 200 μm vertical pores of the modified aerogel matrix, and achieve uniform filling and stable loading of the sustained-release capsule particles in the pores of the modified aerogel matrix through capillary action and surface wettability. In the gelation stage, by vigorously stirring the calcium chloride solution, the secondary aggregation between gel particles can be effectively inhibited, ensuring the dispersion independence of individual gel particles and ensuring that the obtained sustained-release capsule particles have uniform size. The secondary cross-linking of glutaraldehyde solution constructs a covalent bond network through the condensation reaction of aldehyde groups and hydroxyl groups of sodium alginate. By adopting the process of calcium ion chelation and glutaraldehyde covalent cross-linking, the structural characteristics of the gel network are optimized, forming sustained-release capsule particles with a core-shell structure with a dense outer layer and a loose inner layer. This asymmetric structure can achieve pH-responsive release in a sewage environment - when the environmental pH fluctuation causes partial dissociation of the outer calcium alginate, the inner cross-linked network can still maintain structural stability, enabling the release rate of microorganisms to form a dynamic match with the pollutant load.

[0013] As a preferred technical solution of the present invention, in step (Ⅰ), the organic ligand solution is composed of 2-methylimidazole and methanol.

[0014] In some alternative examples, the concentration of 2-methylimidazole in the organic ligand solution is 0.9 to 1 mol / L. For example, it can be 0.9 mol / L, 0.91 mol / L, 0.92 mol / L, 0.93 mol / L, 0.94 mol / L, 0.95 mol / L, 0.96 mol / L, 0.97 mol / L, 0.98 mol / L, 0.99 mol / L or 1 mol / L. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0015] In some alternative examples, the mass fraction of the nanocellulose solution is 1 to 2 wt%. For example, it can be 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt% or 2.0 wt%. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0016] In some alternative examples, the cobalt source solution is composed of cobalt nitrate and deionized water.

[0017] In some alternative examples, the concentration of cobalt nitrate in the cobalt source solution is 0.15 to 0.25 mol / L. For example, it can be 0.15 mol / L, 0.16 mol / L, 0.17 mol / L, 0.18 mol / L, 0.19 mol / L, 0.2 mol / L, 0.21 mol / L, 0.22 mol / L, 0.23 mol / L, 0.24 mol / L or 0.25 mol / L. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0018] In some alternative examples, the volume ratio of the nanocellulose solution to the cobalt source solution is (2 to 3):1. For example, it can be 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1 or 3.0:1. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0019] The present invention specifically defines that the volume ratio of the nanocellulose solution to the cobalt source solution is (2 - 3):1. Within this range, the hydroxyl groups on the nanocellulose chains can form an appropriate coordination interaction with cobalt ions, ensuring that sufficient metal ions are anchored on the surface of the nanocellulose network while avoiding the destruction of the hydrogen bond cross-linking structure of nanocellulose by excessive cobalt salts. This enables the subsequent added 2-methylimidazole organic ligand to be evenly distributed in the gaps of the cellulose network and combine with cobalt ions to form ZIF-67 crystals with uniform size, constructing a stable hierarchical pore structure for the aerogel matrix.

[0020] When the addition amount of the nanocellulose solution is too low, the concentration of cobalt ions is too high, causing the coordination reaction to concentrate in local areas. The ZIF-67 crystals grow excessively to form large-size aggregates, which not only block the pores of the aerogel matrix and reduce its porosity but also weaken the mechanical strength of the nanocellulose network. At the same time, the unreacted free cobalt ions will crystallize out during the directional freezing process, destroying the regularity of the pore structure of the aerogel matrix.

[0021] When the addition amount of the nanocellulose solution is too high, the excessive nanocellulose chains hinder the uniform distribution of cobalt ions due to steric hindrance effects, resulting in insufficient nucleation sites for ZIF-67 crystals. The finally formed ZIF-67 crystals have poor dispersion and a reduced density of catalytic active sites. At the same time, the dense network formed by excessive cross-linking of nanocellulose will compress the pore space, significantly decreasing the specific surface area of the aerogel matrix.

[0022] It should be noted that the present invention does not make specific requirements or special limitations on the dropping rate of the organic ligand solution. Exemplarily, the dropping rate of the organic ligand solution is 1.5 - 2.5 mL / min, for example, it can be 1.5 mL / min, 1.6 mL / min, 1.7 mL / min, 1.8 mL / min, 1.9 mL / min, 2.0 mL / min, 2.1 mL / min, 2.2 mL / min, 2.3 mL / min, 2.4 mL / min, or 2.5 mL / min, but it is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0023] In some alternative examples, the molar ratio of 2-methylimidazole in the organic ligand solution to cobalt ions in the cobalt source solution is (5 - 6):1, for example, it can be 5.0:1, 5.1:1, 5.2:1, 5.3:1, 5.4:1, 5.5:1, 5.6:1, 5.7:1, 5.8:1, 5.9:1, or 6.0:1, but it is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0024] In some alternative examples, under stirring and heating conditions, the organic ligand solution is dropped into the precursor solution.

[0025] In some alternative examples, the heating temperature when the organic ligand solution is dropped is 60-70 °C. For example, it can be 60 °C, 61 °C, 62 °C, 63 °C, 64 °C, 65 °C, 66 °C, 67 °C, 68 °C, 69 °C or 70 °C. However, it is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0026] In some alternative examples, after all of the organic ligand solution is dropped, continue to mix and stir under heating conditions for 4-5 h to obtain the reaction solution. For example, it can be 4.0 h, 4.1 h, 4.2 h, 4.3 h, 4.4 h, 4.5 h, 4.6 h, 4.7 h, 4.8 h, 4.9 h or 5.0 h. However, it is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0027] As a preferred technical solution of the present invention, in step (I), the addition amount of the polyvinyl alcohol is 7-9 wt% of the mass of the reaction solution. For example, it can be 7.0 wt%, 7.2 wt%, 7.4 wt%, 7.6 wt%, 7.8 wt%, 8.0 wt%, 8.2 wt%, 8.4 wt%, 8.6 wt%, 8.8 wt% or 9.0 wt%. However, it is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0028] In some alternative examples, the mixing and stirring time of the reaction solution and the polyvinyl alcohol is 2-4 h. For example, it can be 2.0 h, 2.2 h, 2.4 h, 2.6 h, 2.8 h, 3.0 h, 3.2 h, 3.4 h, 3.6 h, 3.8 h or 4.0 h. However, it is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0029] In some alternative examples, the directional freezing process includes:

[0030] Cool down to the first freezing temperature at the first cooling rate and keep warm, and then continue to cool down to the second freezing temperature at the second cooling rate and keep warm.

[0031] In the present invention, in the first cooling stage, the temperature is rapidly decreased to -15~-20°C at a rate of -1~-2°C / min, which promotes the formation of a large number of tiny ice crystal nuclei in the solution. During the heat preservation process, the ice crystals initially extend and grow along the temperature gradient direction to form an initial pore framework with a diameter of about 50~150μm. In the second cooling stage, the temperature is slowly decreased to -30~-40°C at a rate of -0.5~-1°C / min. At this time, the solution viscosity increases significantly, and a secondary microporous structure is induced to form on the wall surface of the formed initial pores. During the heat preservation process, the solvent molecules in the remaining unfrozen liquid phase are fully crystallized, avoiding stress concentration caused by rapid deep cooling, and finally forming a hierarchical pore structure in which vertically arranged through pores are intertwined with wall micropores. This hierarchical pore structure directly affects the sewage treatment effect of the material. The through large-diameter channels greatly improve the pollutant adsorption rate, and the secondary microporous structure formed on the wall surface of the large-diameter channels provides a high-density anchoring site for the loading of ZIF-67 crystals.

[0032] In some optional examples, the first cooling rate is -1~-2°C / min. For example, it can be -1°C / min, -1.1°C / min, -1.2°C / min, -1.3°C / min, -1.4°C / min, -1.5°C / min, -1.6°C / min, -1.7°C / min, -1.8°C / min, -1.9°C / min or -2°C / min, but it is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0033] In some optional examples, the first freezing temperature is -15~-20°C. For example, it can be -15°C, -15.5°C, -16°C, -16.5°C, -17°C, -17.5°C, -18°C, -18.5°C, -19°C, -19.5°C or -20°C, but it is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0034] In some optional examples, the heat preservation time at the first freezing temperature is 0.5~1.5h. For example, it can be 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, 1.0h, 1.1h, 1.2h, 1.3h, 1.4h or 1.5h, but it is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0035] In some alternative examples, the second cooling rate is -0.5 to -1 °C / min. For example, it can be -0.5 °C / min, -0.55 °C / min, -0.6 °C / min, -0.65 °C / min, -0.7 °C / min, -0.75 °C / min, -0.8 °C / min, -0.85 °C / min, -0.9 °C / min, -0.95 °C / min or -1 °C / min. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0036] In some alternative examples, the second freezing temperature is -30 to -40 °C. For example, it can be -30 °C, -31 °C, -32 °C, -33 °C, -34 °C, -35 °C, -36 °C, -37 °C, -38 °C, -39 °C or -40 °C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0037] In some alternative examples, the holding time at the second freezing temperature is 3 to 4 h. For example, it can be 3.0 h, 3.1 h, 3.2 h, 3.3 h, 3.4 h, 3.5 h, 3.6 h, 3.7 h, 3.8 h, 3.9 h or 4.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0038] As a preferred technical solution of the present invention, in step (Ⅰ), the hydrophobic modification treatment includes:

[0039] Immerse the aerogel matrix in a silane coupling agent solution, oscillate and heat it, then take out the aerogel matrix, wash and dry it to obtain the modified aerogel matrix.

[0040] During the modification process, the silanol groups generated by the hydrolysis of the silane coupling agent undergo a condensation reaction with the hydroxyl groups on the surface of the aerogel matrix to form a dense Si-O-Si covalent bond network. The directional arrangement of the long-chain alkyl groups makes the surface contact angle of the modified aerogel matrix reach more than 145°. This chemical modification endows the aerogel matrix with superhydrophobic properties on the one hand, which can effectively block the penetration of water molecules and prevent the hydrolysis reaction of ZIF-67 crystals in the water environment, resulting in the dissolution of cobalt ions, so that the modified aerogel matrix maintains its structural integrity within a wide range of pH = 3 to 11. On the other hand, the silane layer grafted on the surface of the aerogel matrix can also reinforce the node connection of cellulose fibers through intermolecular forces, significantly improving the anti-swelling ability of the modified aerogel matrix in the aqueous environment.

[0041] In some alternative examples, the silane coupling agent solution is composed of a silane coupling agent and an ethanol aqueous solution.

[0042] In some alternative examples, the mass fraction of the silane coupling agent in the silane coupling agent solution is 1.8 - 2.2 wt%, for example, it can be 1.8 wt%, 1.85 wt%, 1.9 wt%, 1.95 wt%, 2.0 wt%, 2.05 wt%, 2.1 wt%, 2.15 wt% or 2.2 wt%, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0043] In some alternative examples, when the aerogel matrix is immersed in the silane coupling agent solution, the heating temperature is 35 - 45 °C, for example, it can be 35 °C, 36 °C, 37 °C, 38 °C, 39 °C, 40 °C, 41 °C, 42 °C, 43 °C, 44 °C or 45 °C, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0044] In some alternative examples, the immersion time of the aerogel matrix in the silane coupling agent solution is 12 - 24 h, for example, it can be 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 21 h, 22 h, 23 h or 24 h, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0045] It should be noted that after the immersion of the aerogel matrix is completed, it is taken out, washed with absolute ethanol, and then vacuum dried. The present invention does not make specific requirements and special limitations on the temperature and time of vacuum drying. Exemplarily, the temperature of vacuum drying is 45 - 55 °C, for example, it can be 45 °C, 46 °C, 47 °C, 48 °C, 49 °C, 50 °C, 51 °C, 52 °C, 53 °C, 54 °C or 55 °C; the time of vacuum drying is 10 - 12 h, for example, it can be 10 h, 10.2 h, 10.4 h, 10.6 h, 10.8 h, 11 h, 11.2 h, 11.4 h, 11.6 h, 11.8 h or 12 h, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0046] As a preferred technical solution of the present invention, in step (II), the microbial cell suspension is prepared by the following method:

[0047] Bacillus subtilis is inoculated into an LB liquid medium and cultured by shaking to obtain a Bacillus subtilis bacterial solution; then it is centrifuged, the supernatant is removed, and the bacterial cells precipitated at the bottom are collected for washing; the washed bacterial cells are resuspended in a pre-cooled buffer solution, and after mixing evenly, the microbial cell suspension is obtained.

[0048] It should be noted that the process of culturing the Bacillus subtilis strain has been disclosed in the prior art, and the present invention does not make specific requirements and special limitations on the process parameters involved. Exemplarily:

[0049] The inoculation amount of Bacillus subtilis in the LB liquid medium is 0.2 - 0.4 g / 100 mL of the LB liquid medium. For example, it can be 0.2 g / 100 mL, 0.22 g / 100 mL, 0.24 g / 100 mL, 0.26 g / 100 mL, 0.28 g / 100 mL, 0.3 g / 100 mL, 0.32 g / 100 mL, 0.34 g / 100 mL, 0.36 g / 100 mL, 0.38 g / 100 mL or 0.4 g / 100 mL.

[0050] The temperature for shaking culture is 35 - 37 °C. For example, it can be 35 °C, 35.2 °C, 35.4 °C, 35.6 °C, 35.8 °C, 36 °C, 36.2 °C, 36.4 °C, 36.6 °C, 36.8 °C or 37 °C.

[0051] The shaking speed for shaking culture is 180 - 200 rpm. For example, it can be 180 rpm, 182 rpm, 184 rpm, 186 rpm, 188 rpm, 190 rpm, 192 rpm, 194 rpm, 196 rpm, 198 rpm or 200 rpm.

[0052] The time for shaking culture is 12 - 24 h. For example, it can be 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 21 h, 22 h, 23 h or 24 h.

[0053] The centrifugation temperature of the Bacillus subtilis bacterial liquid is 4 - 6 °C. For example, it can be 4.0 °C, 4.2 °C, 4.4 °C, 4.6 °C, 4.8 °C, 5.0 °C, 5.2 °C, 5.4 °C, 5.6 °C, 5.8 °C or 6.0 °C.

[0054] The centrifugation speed of the Bacillus subtilis bacterial liquid is 4000 - 6000 rpm. For example, it can be 4000 rpm, 4200 rpm, 4400 rpm, 4600 rpm, 4800 rpm, 5000 rpm, 5200 rpm, 5400 rpm, 5600 rpm, 5800 rpm or 6000 rpm.

[0055] The centrifugation time of the Bacillus subtilis bacterial liquid is 5 - 10 min. For example, it can be 5.0 min, 5.5 min, 6.0 min, 6.5 min, 7.0 min, 7.5 min, 8.0 min, 8.5 min, 9.0 min, 9.5 min or 10.0 min.

[0056] In some alternative examples, the precooling temperature of the buffer solution is 4 to 6 °C. For example, it can be 4.0 °C, 4.2 °C, 4.4 °C, 4.6 °C, 4.8 °C, 5.0 °C, 5.2 °C, 5.4 °C, 5.6 °C, 5.8 °C or 6.0 °C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0057] In some alternative examples, the buffer solution is composed of trehalose, polyethylene glycol 6000 and deionized water.

[0058] In some alternative examples, the mass fraction of trehalose in the buffer solution is 5 to 10 wt%. For example, it can be 5.0 wt%, 5.5 wt%, 6.0 wt%, 6.5 wt%, 7.0 wt%, 7.5 wt%, 8.0 wt%, 8.5 wt%, 9.0 wt%, 9.5 wt% or 10.0 wt%. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0059] In some alternative examples, the mass fraction of polyethylene glycol 6000 in the buffer solution is 1 to 2 wt%. For example, it can be 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt% or 2.0 wt%. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0060] In some alternative examples, the ratio of the bacterial cells to the buffer solution is 1 g:(5 to 10) mL. For example, it can be 1 g:5.0 mL, 1 g:5.5 mL, 1 g:6.0 mL, 1 g:6.5 mL, 1 g:7.0 mL, 1 g:7.5 mL, 1 g:8.0 mL, 1 g:8.5 mL, 1 g:9.0 mL, 1 g:9.5 mL or 1 g:10.0 mL. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0061] As a preferred technical solution of the present invention, in step (II), the volume ratio of the microbial cell suspension to the sodium alginate solution during mixing is 1:(2 to 3). For example, it can be 1:2.0, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9 or 1:3.0. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0062] The present invention specifically limits the volume ratio of the microbial cell suspension to the sodium alginate solution to be 1:(2 - 3). When the volume ratio of the two is within this range, it can not only ensure the integrity of the gel shell but also maintain the mass transfer channels required for microbial metabolism. In the mixed system, the molecular chains of sodium alginate form a three-dimensional network structure with a moderate cross-linking density by the directional arrangement of carboxyl groups and chelation with calcium ions, which helps the penetration of nutrients and the diffusion of metabolites.

[0063] If the addition amount of the sodium alginate solution exceeds the upper limit of the range defined in the present invention, the entanglement of high-concentration sodium alginate molecular chains hinders the uniform penetration of calcium ions, and the gel shell quickly forms a dense cross-linked layer. However, due to insufficient calcium ion concentration in the inner core region, a loose flocculent structure appears. This non-uniform curing leads to an imbalance in the mechanical strength distribution of the slow-release capsule particles. The shell is hard and brittle and easily fragmented, while the inner core cannot effectively confine the microorganisms due to its loose structure.

[0064] If the addition amount of the sodium alginate solution is lower than the lower limit of the range defined in the present invention, the cross-linking density of the gel network is insufficient. The sparse molecular chain spacing causes the slow-release capsule particles to have too high a volume expansion rate during the swelling process, and repeated swelling-shrinking cycles lead to the expansion of structural fatigue cracks. In addition, the weak three-dimensional network cannot effectively block external hydrodynamic shear, resulting in an explosive diffusion of microorganisms at the initial stage of sewage treatment and a complete loss of the slow-release effect.

[0065] In some alternative examples, the mass fraction of the sodium alginate solution is 2 - 4 wt%, for example, it can be 2.0 wt%, 2.2 wt%, 2.4 wt%, 2.6 wt%, 2.8 wt%, 3.0 wt%, 3.2 wt%, 3.4 wt%, 3.6 wt%, 3.8 wt% or 4.0 wt%, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0066] In some alternative examples, the pressure of the high-pressure homogenization is 150 - 200 MPa, for example, it can be 150 MPa, 155 MPa, 160 MPa, 165 MPa, 170 MPa, 175 MPa, 180 MPa, 185 MPa, 190 MPa, 195 MPa or 200 MPa, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0067] In some alternative examples, the number of times of high-pressure homogenization is 5 - 7 times, for example, it can be 5 times, 6 times or 7 times, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0068] It should be noted that, preferably, before the gel precursor emulsion is dropped into the calcium chloride solution, the calcium chloride solution is stirred. Exemplarily, the stirring speed is 700 - 800 rpm, for example, it can be 700 rpm, 710 rpm, 720 rpm, 730 rpm, 740 rpm, 750 rpm, 760 rpm, 770 rpm, 780 rpm, 790 rpm or 800 rpm. The present invention does not make specific requirements and special limitations on the dropping speed of the gel precursor emulsion into the calcium chloride solution. Exemplarily, the dropping speed is 0.3 - 0.5 mL / min, for example, it can be 0.3 mL / min, 0.32 mL / min, 0.34 mL / min, 0.36 mL / min, 0.38 mL / min, 0.4 mL / min, 0.42 mL / min, 0.44 mL / min, 0.46 mL / min, 0.48 mL / min or 0.5 mL / min.

[0069] In some alternative examples, the mass fraction of the calcium chloride solution is 2 - 5 wt%, for example, it can be 2.0 wt%, 2.5 wt%, 3.0 wt%, 3.5 wt%, 4.0 wt%, 4.5 wt% or 5.0 wt%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0070] The present invention specifically limits the mass fraction of the calcium chloride solution to 2 - 5 wt%. When the mass fraction of the calcium chloride solution is lower than 2 wt%, the cross - linking sites between the alginate molecular chains cannot be fully saturated, and the formed gel network presents a loose flocculent structure, which is prone to deformation and collapse during the secondary cross - linking stage with glutaraldehyde, and the phenomenon of shell rupture and core disintegration will occur under hydraulic action.

[0071] When the mass fraction of the calcium chloride solution exceeds 5 wt%, the rapid cross - linking caused by high - concentration calcium ions will destroy the ordered assembly of the alginate molecular chains. Excessive calcium ions instantaneously form a dense cross - linking layer on the surface of the emulsion droplets, seriously hindering the diffusion of calcium ions to the inside, resulting in a non - uniform structure of the capsule with a "hard shell and liquid core". This structure will generate stress cracks due to the difference in shrinkage rate between the shell and the core during the drying process, significantly reducing the mechanical stability of the material.

[0072] As a preferred technical solution of the present invention, in step (II), the operation steps of glutaraldehyde cross - linking include: taking out the gel particles and immersing them in a glutaraldehyde solution, and obtaining microcapsule particles after cross - linking in the dark.

[0073] In some optional examples, the mass fraction of the glutaraldehyde solution is 1-2wt%, for example, it can be 1.0wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt% or 2.0wt%, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0074] The present invention particularly limits the mass fraction of the glutaraldehyde solution to 1-2wt%. Within the concentration range defined in the present invention, the glutaraldehyde molecules cross-link with the hydroxyl group and the carboxylic acid group of sodium alginate and the amino group on the surface of the microbial cells through the dialdehyde group thereof, and while strengthening the mechanical strength of the sustained-release capsule particles, the position of the bacteria can also be fixed by covalent bonding, so that the outer layer forms a dense protective layer, the inner layer maintains a moderate swelling space, and reserves a material exchange channel for the microbial metabolic activities.

[0075] When the mass fraction of glutaraldehyde solution is lower than 1wt%, the aldehyde supply is insufficient, the cross-linking reaction is limited, the density of connection points between the sodium alginate molecular chains is significantly reduced, and the insufficiently cross-linked gel network presents a loose flocculent structure, which is prone to structural collapse during sewage treatment. In addition, low concentrations of glutaraldehyde have a weak fixation effect on microbial cells. The internal stress generated when free bacteria migrate inside the sustained-release capsule particles will accelerate structural damage, causing most microorganisms to be released at the initial stage of sewage treatment, losing the sustained-release effect.

[0076] When the mass fraction of the glutaraldehyde solution exceeds 2wt%, the excessive cross-linking caused by the high concentration of aldehyde groups will destroy the gel network. Excessive glutaraldehyde molecules form a dense cross-linked layer on the surface of the gel particles, which seriously hinders the penetration and diffusion of subsequent reaction reagents, resulting in a large difference in the cross-linking density between the inner and outer layers. Microcracks are generated during the drying process due to uneven shrinkage stress, which significantly weakens the mechanical strength of the material. In addition, high concentrations of glutaraldehyde will penetrate the cell membrane and irreversibly cross-link with intracellular enzymes, destroying the metabolic active sites of microorganisms and causing the inactivation of a large number of functional bacteria.

[0077] In some optional examples, the immersion time of the gel particles in the glutaraldehyde solution is 2 to 4 hours, for example, it can be 2.0 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, 3.0 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours or 4.0 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0078] It should be noted that after the gel particles are cross-linked in the glutaraldehyde solution and taken out for drying, the present invention does not make specific requirements and special limitations on the drying temperature and drying time. Exemplarily, the drying temperature of the gel particles is 30-40°C, for example, it can be 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, 36°C, 37°C, 38°C, 39°C or 40°C, and the drying time of the gel particles is 12-24h, for example, it can be 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h or 24h, but it is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0079] As a preferred technical solution of the present invention, in step (III), the mass fraction of the sustained-release capsule particles in the dispersion liquid is 5-10wt%, for example, it can be 5.0wt%, 5.5wt%, 6.0wt%, 6.5wt%, 7.0wt%, 7.5wt%, 8.0wt%, 8.5wt%, 9.0wt%, 9.5wt% or 10.0wt%, but it is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0080] In some alternative examples, the impregnation process includes:

[0081] Adding the modified aerogel matrix and the dispersion liquid into a reaction kettle, completely submerging the modified aerogel matrix in the dispersion liquid, evacuating the reaction kettle, and then restoring it to normal pressure, and stirring the dispersion liquid under normal pressure; then continuing to evacuate; repeating the evacuation and restoration to normal pressure of the reaction kettle 5-8 times.

[0082] In some alternative examples, the mass ratio of the modified aerogel matrix to the sustained-release capsule particles in the dispersion liquid is 1:(1-2), for example, it can be 1:1.0, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2.0, but it is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0083] The present invention specifically limits the mass ratio of the modified aerogel matrix to the sustained-release capsule particles in the dispersion liquid to 1:(1-2). Within the mass ratio range defined by the present invention, the sustained-release capsule particles can be fully embedded in the inner wall of the micron-scale pores arranged vertically in the modified aerogel matrix, and form a stable bond through capillary adsorption and surface chemical bonding. This structure not only retains the mass transfer ability of the through-pores in the modified aerogel matrix, but also restricts the movement of the sustained-release capsule particles.

[0084] When the addition amount of the sustained-release capsule particles is lower than the lower limit of the range defined in the present invention, due to the too low loading amount of the sustained-release capsule particles, a large number of pores in the modified aerogel matrix are in a vacant state, and these unused micron-sized pores become secondary adsorption sites for pollutants in the sewage environment.

[0085] When the addition amount of the sustained-release capsule particles exceeds the upper limit of the range defined in the present invention, the excessive sustained-release capsule particles accumulate in the pores of the modified aerogel matrix, hindering the diffusion and penetration of microorganisms and metabolites. In addition, the over-accumulated sustained-release capsule particles will also cause plastic deformation of the modified aerogel matrix under continuous compressive strain, with too high stress concentration in local areas, leading to the expansion of microcracks under long-term hydraulic scouring and shortening the fatigue life of the material.

[0086] In some alternative examples, the reaction kettle is evacuated to -85 to -95 kPa, for example, it can be -85 kPa, -86 kPa, -87 kPa, -88 kPa, -89 kPa, -90 kPa, -91 kPa, -92 kPa, -93 kPa, -94 kPa or -95 kPa, but is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0087] In some alternative examples, the reaction kettle maintains the vacuum for 20 to 30 minutes, for example, it can be 20 minutes, 21 minutes, 22 minutes, 23 minutes, 24 minutes, 25 minutes, 26 minutes, 27 minutes, 28 minutes, 29 minutes or 30 minutes, but is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0088] In some alternative examples, during the normal pressure stage, the dispersion liquid is stirred for 10 to 15 minutes, for example, it can be 10 minutes, 10.5 minutes, 11 minutes, 11.5 minutes, 12 minutes, 12.5 minutes, 13 minutes, 13.5 minutes, 14 minutes, 14.5 minutes or 15 minutes, but is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0089] It should be noted that after the impregnation is completed, the impregnated modified aerogel matrix is taken out for drying. The present invention does not make specific requirements and special limitations on the drying temperature and time. Exemplarily, the drying temperature is 50-60 °C, for example, it can be 50 °C, 51 °C, 52 °C, 53 °C, 54 °C, 55 °C, 56 °C, 57 °C, 58 °C, 59 °C or 60 °C, and the drying time is 12-24 h, for example, it can be 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 21 h, 22 h, 23 h or 24 h, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0090] In a second aspect, the present invention provides a microbial slow-release porous composite material for sewage treatment prepared by using the preparation method described in the first aspect.

[0091] In a third aspect, the present invention provides a use of the microbial slow-release porous composite material for sewage treatment described in the second aspect, and the microbial slow-release porous composite material is used for sewage treatment.

[0092] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0093] The present invention composites an aerogel matrix with a hierarchical pore structure and a slow-release capsule with a pH-responsive mechanism, realizing physical adsorption, chemical catalysis and biodegradation of sewage treatment. The vertically through holes of the modified aerogel matrix provide a high-speed channel for pollutant enrichment and mass transfer, and the Co 2+ nodes of the surface-loaded ZIF-67 provide Lewis acid sites, which specifically bind to sulfur, phosphorus or nitrogen-containing pollutants through coordination, enhancing the adsorption selectivity for polar or specific-structured pollutants. A double-layer structured slow-release capsule particle is prepared by a gradient cross-linking process, the outer shell of which maintains the structural integrity under the impact of water flow, and the inner core retains the active space for microbial colonization and metabolism. Description of the Drawings

[0094] Figure 1 is the process flow chart of the preparation of the microbial slow-release porous composite material provided in Examples 1-15 of the present invention;

[0095] Figure 2 is the infrared spectrogram of nanocellulose, ZIF-67 and the aerogel matrix prepared in Example 1 of the present invention;

[0096] Figure 3 is the XRD spectrogram of nanocellulose, ZIF-67 and the aerogel matrix prepared in Example 1 of the present invention;

[0097] Figure 4The test curve graph of the water contact angle and oil contact angle of the modified aerogel matrix prepared in Example 1 of the present invention;

[0098] Figure 5 The swelling ratio curve graph of the sustained-release capsule particles prepared in Example 1 of the present invention under different pH values;

[0099] Figure 6 The scanning electron microscope image of the sustained-release capsule particles prepared in Example 1 of the present invention;

[0100] Figure 7 The cumulative release rate curve graph of the microbial sustained-release porous composite material prepared in Example 1 of the present invention under different pH environments. Detailed implementation manners

[0101] The technical solution of the present invention will be described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments described herein are specific specific implementation manners of the present invention and are used to illustrate the concept of the present invention; these descriptions are all explanatory and exemplary, and should not be construed as limiting the implementation manner of the present invention and the protection scope of the present invention. Except for the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims and the specification of the present application, and these technical solutions include technical solutions that make any obvious substitutions and modifications to the embodiments described herein.

[0102] Example 1

[0103] This example provides a preparation method of a microbial sustained-release porous composite material for sewage treatment. As Figure 1 shown, the preparation method specifically includes the following steps:

[0104] (1) Disperse cobalt nitrate in deionized water, and after mixing evenly, obtain a cobalt source solution with a concentration of 0.15 mol / L. Mix the nanocellulose solution with a mass fraction of 1 wt% and the cobalt source solution according to a volume ratio of 3:1, and mix evenly to obtain a precursor solution; Disperse 2-methylimidazole in methanol, and after mixing evenly, obtain an organic ligand solution with a concentration of 0.9 mol / L. Under the conditions of stirring and heating at 60 °C, drop the organic ligand solution into the precursor solution at a speed of 1.5 mL / min. The molar ratio of 2-methylimidazole to cobalt ions is 5:1. After all the organic ligand solution is dropped, continue to stir the obtained mixture at 60 °C for 5 h to obtain a reaction solution;

[0105] Mix the reaction solution with polyvinyl alcohol and stir for 2 h. The addition amount of polyvinyl alcohol is 7 wt% of the mass of the reaction solution. Inject the mixed solution into a mold for directional freezing. First, cool it to -15 °C at a cooling rate of -1 °C / min and hold for 1.5 h. Subsequently, continue to cool it to -30 °C at a cooling rate of -0.5 °C / min and hold for 4 h to obtain an aerogel matrix.

[0106] Add silane coupling agent KH550 to an ethanol aqueous solution (the volume ratio of absolute ethanol to deionized water in the ethanol aqueous solution is 9:1). After mixing evenly, obtain a silane coupling agent solution with a mass fraction of 1.8 wt%. Immerse the aerogel matrix in the silane coupling agent solution and oscillate at 35 °C for 24 h. Subsequently, take out the aerogel matrix, wash it with ethanol, and then place it in a vacuum dryer at 45 °C for 12 h to obtain a modified aerogel matrix.

[0107] (2) Inoculate Bacillus subtilis into LB liquid medium. The inoculation amount of Bacillus subtilis is 0.2 g / 100 mL of LB liquid medium. Subsequently, oscillate and culture it at an environmental temperature of 35 °C and an oscillation speed of 180 rpm for 24 h to obtain a Bacillus subtilis bacterial solution. Centrifuge the Bacillus subtilis bacterial solution at 4 °C and 4000 rpm for 10 min. After centrifugation, remove the supernatant and collect the precipitated cells at the bottom for washing. Mix trehalose, polyethylene glycol 6000, and deionized water evenly to obtain a buffer solution. The mass fraction of trehalose in the buffer solution is 5 wt%, and the mass fraction of polyethylene glycol 6000 is 1 wt%. Pre-cool the buffer solution to 4 °C, and then resuspend the washed cells in the pre-cooled buffer solution. The ratio of cells to buffer solution is 1 g:5 mL. After mixing evenly, obtain a microbial cell suspension.

[0108] Mix the microbial cell suspension with a 2 wt% sodium alginate solution. The volume ratio of the microbial cell suspension to the sodium alginate solution is 1:2. After mixing evenly, obtain a gel precursor solution. Perform high-pressure homogenization on the gel precursor solution 7 times at 150 MPa to obtain a gel precursor emulsion. Stir the calcium chloride solution at a speed of 700 rpm. Drop the gel precursor emulsion into the stirred 2 wt% calcium chloride solution at a dropping speed of 0.3 mL / min to obtain gel particles. Take out the gel particles and immerse them in a 1 wt% glutaraldehyde solution. After cross-linking in the dark for 4 h, obtain microcapsule particles. Take out the microcapsule particles and vacuum dry them at 30 °C for 24 h to obtain slow-release capsule particles.

[0109] (3) Disperse the sustained-release capsule particles obtained in step (2) in deionized water, and after mixing evenly, obtain a dispersion liquid with the mass fraction of the sustained-release capsule particles in the dispersion liquid being 5 wt%. Add the modified aerogel matrix obtained in step (1) and the dispersion liquid into a reaction kettle, with the mass ratio of the modified aerogel matrix to the sustained-release capsule particles being 1:1, ensuring that the modified aerogel matrix is completely immersed in the dispersion liquid. Vacuum the reaction kettle to -85 kPa and maintain it for 30 min. Subsequently, introduce nitrogen into the reaction kettle to restore it to normal pressure, and stir the dispersion liquid for 10 min. Then continue to vacuum the reaction kettle to -85 kPa and maintain it for 30 min. Repeat the operations of vacuuming and restoring to normal pressure for the reaction kettle 8 times, and then take it out and dry it in vacuum at 50 °C for 24 h to obtain the microbial sustained-release porous composite material.

[0110] Figure 2 are the infrared spectra of nanocellulose, ZIF-67, and the aerogel matrix prepared in this example. It can be seen from the figure that in the infrared spectrum of nanocellulose, the characteristic peaks at 3460 cm -1 and 1735 cm -1 are respectively attributed to the C-H stretching of cellulose hydroxyl and the C=O stretching vibration of carboxyl. In the infrared spectrum of the aerogel matrix obtained after in-situ growth of ZIF-67 nanoparticles, the absorption band appearing at 422 cm -1 is attributed to the Co-N stretching vibration of ZIF-67, and the vibration peaks at 1382 cm -1 , 1417 cm -1 and 1453 cm -1 are attributed to the C-N bond stretching vibration of 2-methylimidazole. The characteristic peaks at 689 cm -1 , 753 cm -1 and 1306 cm -1 are attributed to the bending vibration of 2-methylimidazole. The above results indicate that ZIF-67 nanoparticles are successfully loaded on the aerogel matrix.

[0111] Figure 3 are the XRD patterns of nanocellulose, ZIF-67, and the aerogel matrix prepared in this example. It can be seen from the figure that the main diffraction peaks at 2θ of 7.4°, 10.4°, 12.7°, 18.1°, and 26.7° respectively correspond to the (011), (002), (112), (222), and (134) crystal planes of ZIF-67. In addition, in the XRD pattern of the aerogel matrix, the weak characteristic peak at 22.6° belongs to the (002) crystal plane of nanocellulose. The above results indicate that ZIF-67 is successfully loaded on the aerogel matrix.

[0112] Figure 4The test curve graph of the water contact angle and oil contact angle of the modified aerogel matrix prepared in this example. It can be seen from the figure that as the test time extends, the surface water contact angle of the modified aerogel matrix decreases slightly, but its average value is 145°, still belonging to the superhydrophobic surface; similarly, as the test time extends, the surface oil contact angle of the modified aerogel matrix also decreases slightly, but its average value is 10°, belonging to the superoleophilic surface, which indicates that the modified aerogel matrix obtained after modification with silane coupling agent has hydrophobic and oleophilic properties.

[0113] Figure 5 The swelling ratio curve graph of the sustained-release capsule particles prepared in this example at different pH values. It can be seen from the figure that as the pH value in water increases, the swelling ratio of the sustained-release capsule particles shows a trend of first increasing and then decreasing. The swelling ratio in the water environment with pH = 4 is less than 1, while the swelling ratio in the water environment with pH = 6 can be as high as 20. This is because in the low pH region (pH < 5), a large number of carboxylic acid groups (-COOH) of sodium alginate are protonated, forming intramolecular and intermolecular hydrogen bonds. The existence of hydrogen bonds enhances the intermolecular force between polymer chains, resulting in the contraction and compaction of the gel network, the reduction of porosity, and the inhibition of the swelling ratio. At the same time, the covalent network formed by glutaraldehyde cross-linking has high stability under acidic conditions, further restricting the swelling space of the gel. In the medium pH region (pH value = 5 - 7), as the pH increases, the carboxylic acid groups are gradually deprotonated (-COO⁻), generating electrostatic repulsion. The repulsive force between negatively charged carboxylate ions causes the polymer chains to stretch, the network pores to expand, and the water molecule penetration to increase, so the swelling ratio rises rapidly and reaches the swelling peak near pH = 6. At this time, the ionization degree of the carboxylic acid groups is relatively high, and the electrostatic repulsion dominates the network expansion. At the same time, the cross-linked structure still maintains its integrity, forming the best balance between swelling and mechanical strength. In the high pH region (pH value > 7), excessive OH⁻ reacts with sodium alginate to cause the breakage of polysaccharide chains, resulting in the destruction of the integrity of the gel network. Although the carboxylic acid groups are completely ionized, the collapse of the network structure causes the swelling ability to decline. Therefore, the sustained-release capsule particles prepared in the present invention have a hydrogen bond contraction network at low pH values, structure destruction and charge shielding dominate at high pH values, while at medium pH values, the optimal swelling performance is achieved due to the maximization of electrostatic repulsion. This characteristic endows the sustained-release capsule particles with pH-responsive release ability, which can match the dynamically changing pollutant load in sewage treatment.

[0114] Figure 6 The scanning electron micrograph of the sustained-release capsule particles prepared in this example. It can be seen from the figure that the sustained-release capsule particles present a spherical structure with regular shape and uniform particle size. The particle size distribution is mainly concentrated in the range of 1 - 5 µm, and the average particle size is 2.5 µm.

[0115] Figure 7Cumulative release rate curve of the microbial slow-release porous composite material prepared in this example under different pH environments. As can be seen from the figure, the microbial slow-release porous composite material prepared in this example has excellent slow-release effect, can stably release microorganisms within 10 days. At the same time, the slow-release effect of the microbial slow-release porous composite material is different in different pH environments. It triggers rapid release in high-load sewage (pH = 6) (degrading 68.9% of COD in 5 days), avoiding pollutant accumulation, and maintains long-term release in conventional sewage (pH = 7.4) (continuous action for 10 days), reducing the frequency of supplementary bacteria.

[0116] Example 2

[0117] This example provides a preparation method of a microbial slow-release porous composite material for sewage treatment. As Figure 1 shown, the preparation method specifically includes the following steps:

[0118] (1) Disperse cobalt nitrate in deionized water, and after mixing evenly, obtain a cobalt source solution with a concentration of 0.18 mol / L. Mix the nanocellulose solution with a mass fraction of 1.2 wt% and the cobalt source solution according to a volume ratio of 2.8:1 to obtain a precursor solution; Disperse 2-methylimidazole in methanol, and after mixing evenly, obtain an organic ligand solution with a concentration of 0.92 mol / L. Under stirring and heating conditions at 62 °C, drop the organic ligand solution into the precursor solution at a rate of 1.8 mL / min. The molar ratio of 2-methylimidazole to cobalt ions is 5.2:1. After all the organic ligand solution is dropped, continue to stir the obtained mixture at 62 °C for 4.8 h to obtain a reaction solution;

[0119] Mix the reaction solution and polyvinyl alcohol and stir for 2.5 h. The addition amount of polyvinyl alcohol is 7.5 wt% of the mass of the reaction solution. Inject the mixed solution into a mold for directional freezing. First, cool down at a cooling rate of -1.2 °C / min to -16 °C and keep it warm for 1.2 h, and then continue to cool down at a cooling rate of -0.6 °C / min to -32 °C and keep it warm for 3.8 h to obtain an aerogel matrix;

[0120] Add silane coupling agent KH550 to the ethanol aqueous solution (the volume ratio of absolute ethanol to deionized water in the ethanol aqueous solution is 9:1), and after mixing evenly, obtain a silane coupling agent solution with a mass fraction of 1.9 wt%; Immerse the aerogel matrix in the silane coupling agent solution and oscillate at 38 °C for 21 h. Then take out the aerogel matrix, wash it with ethanol, and place it in a vacuum dryer at 48 °C for 11.5 h to obtain a modified aerogel matrix;

[0121] (2) Inoculate Bacillus subtilis into LB liquid medium. The inoculation amount of Bacillus subtilis is 0.25 g per 100 mL of LB liquid medium. Then, culture it by shaking at an environmental temperature of 35.5 °C and a shaking speed of 185 rpm for 21 h to obtain a Bacillus subtilis bacterial solution; centrifuge the Bacillus subtilis bacterial solution at 4.5 °C and a speed of 4500 rpm for 8 min. After centrifugation, remove the supernatant, collect the precipitated bacteria at the bottom for washing; mix trehalose, polyethylene glycol 6000, and deionized water evenly to obtain a buffer solution. The mass fraction of trehalose in the buffer solution is 6 wt%, and the mass fraction of polyethylene glycol 6000 is 1.2 wt%; pre-cool the buffer solution to 4.5 °C, and then resuspend the washed bacteria in the pre-cooled buffer solution. The ratio of bacteria to buffer solution is 1 g:6 mL. After mixing evenly, a microbial suspension is obtained;

[0122] Mix the microbial suspension with a 2.5 wt% sodium alginate solution. The volume ratio of the microbial suspension to the sodium alginate solution is 1:2.2. After mixing evenly, a pre-gel solution is obtained. Subject the pre-gel solution to high-pressure homogenization at 160 MPa for 6 times to obtain a pre-gel emulsion; stir the calcium chloride solution at a speed of 720 rpm, and drop the pre-gel emulsion into the stirred 3 wt% calcium chloride solution at a dropping speed of 0.35 mL / min to obtain gel particles; take out the gel particles and immerse them in a 1.2 wt% glutaraldehyde solution. After cross-linking in the dark for 3.5 h, microcapsule particles are obtained. Take out the microcapsule particles and vacuum dry them at 32 °C for 21 h to obtain slow-release capsule particles;

[0123] (3) Disperse the slow-release capsule particles obtained in step (2) in deionized water. After mixing evenly, a dispersion is obtained. The mass fraction of the slow-release capsule particles in the dispersion is 6 wt%; add the modified aerogel matrix obtained in step (1) and the dispersion into a reaction kettle. The mass ratio of the modified aerogel matrix to the slow-release capsule particles is 1:1.2, ensuring that the modified aerogel matrix is completely immersed in the dispersion. Vacuum the reaction kettle to -88 kPa and maintain it for 28 min; then introduce nitrogen into the reaction kettle to restore to normal pressure, and stir the dispersion for 12 min; then continue to vacuum the reaction kettle to -88 kPa and maintain it for 28 min; repeat the vacuuming and restoring to normal pressure of the reaction kettle 7 times, and then take it out and vacuum dry it at 52 °C for 21 h to obtain the microbial slow-release porous composite material.

[0124] Example 3

[0125] This example provides a preparation method of a microbial slow-release porous composite material for sewage treatment. As Figure 1 shown, the preparation method specifically includes the following steps:

[0126] (1) Disperse cobalt nitrate in deionized water. After mixing evenly, a cobalt source solution with a concentration of 0.2 mol / L is obtained. Mix the nanocellulose solution with a mass fraction of 1.5 wt% and the cobalt source solution evenly according to a volume ratio of 2.5:1 to obtain a precursor solution. Disperse 2-methylimidazole in methanol. After mixing evenly, an organic ligand solution with a concentration of 0.95 mol / L is obtained. Under stirring and heating at 65 °C, the organic ligand solution is dropped into the precursor solution at a rate of 2 mL / min. The molar ratio of 2-methylimidazole to cobalt ions is 5.5:1. After all the organic ligand solution is dropped, continue to stir the obtained mixture at 65 °C for 4.5 h to obtain a reaction solution;

[0127] Mix the reaction solution and polyvinyl alcohol and stir for 3 h. The addition amount of polyvinyl alcohol is 8 wt% of the mass of the reaction solution. Inject the mixed solution into a mold for directional freezing. First, cool down to -17 °C at a cooling rate of -1.5 °C / min and keep it warm for 1 h. Then continue to cool down to -35 °C at a cooling rate of -0.7 °C / min and keep it warm for 3.5 h to obtain an aerogel matrix;

[0128] Add the silane coupling agent KH550 to the ethanol aqueous solution (the volume ratio of absolute ethanol to deionized water in the ethanol aqueous solution is 9:1). After mixing evenly, a silane coupling agent solution with a mass fraction of 2 wt% is obtained. Immerse the aerogel matrix in the silane coupling agent solution and oscillate at 40 °C for 18 h. Then take out the aerogel matrix, wash it with ethanol, and place it in a vacuum dryer at 50 °C for 11 h to obtain a modified aerogel matrix;

[0129] (2) Inoculate Bacillus subtilis into LB liquid medium. The inoculation amount of Bacillus subtilis is 0.3 g / 100 mL of LB liquid medium. Then oscillate and culture at an environmental temperature of 36 °C and an oscillation speed of 190 rpm for 18 h to obtain a Bacillus subtilis bacterial solution. Centrifuge the Bacillus subtilis bacterial solution at 5 °C and 5000 rpm for 7 min. After centrifugation, remove the supernatant and collect the precipitated bacteria at the bottom for washing. Mix trehalose, polyethylene glycol 6000 and deionized water evenly to obtain a buffer solution. The mass fraction of trehalose in the buffer solution is 7 wt%, and the mass fraction of polyethylene glycol 6000 is 1.5 wt%. Pre-cool the buffer solution to 5 °C, and then resuspend the washed bacteria in the pre-cooled buffer solution. The ratio of bacteria to buffer solution is 1 g:7 mL. After mixing evenly, a microbial suspension is obtained;

[0130] Mix the microbial suspension with a sodium alginate solution with a mass fraction of 3 wt%, and the volume ratio of the microbial suspension to the sodium alginate solution is 1:2.5. After mixing evenly, a gel precursor solution is obtained. The gel precursor solution is subjected to high-pressure homogenization 6 times at 180 MPa to obtain a gel precursor emulsion; the calcium chloride solution is stirred at a high speed at a rotation speed of 750 rpm, and the gel precursor emulsion is dropped into the stirred calcium chloride solution with a mass fraction of 3 wt% at a dropping speed of 0.4 mL / min to obtain gel particles; the gel particles are taken out and immersed in a glutaraldehyde solution with a mass fraction of 1.5 wt%, and after cross-linking in the dark for 3 h, microcapsule particles are obtained. The microcapsule particles are taken out and vacuum dried at 35 °C for 18 h to obtain slow-release capsule particles;

[0131] (3)Disperse the slow-release capsule particles obtained in step (2) in deionized water, and after mixing evenly, a dispersion is obtained. The mass fraction of the slow-release capsule particles in the dispersion is 7 wt%; add the modified aerogel matrix obtained in step (1) and the dispersion into a reaction kettle, and the mass ratio of the modified aerogel matrix to the slow-release capsule particles is 1:1.5, ensuring that the modified aerogel matrix is completely immersed in the dispersion. The reaction kettle is evacuated to -90 kPa and maintained for 25 min; then nitrogen is introduced into the reaction kettle to return to normal pressure, and the dispersion is stirred for 13 min; then the reaction kettle is continuously evacuated to -90 kPa and maintained for 25 min; the reaction kettle is evacuated and restored to normal pressure 7 times, and then taken out and vacuum dried at 55 °C for 18 h to obtain the microbial slow-release porous composite material.

[0132] Example 4

[0133] This example provides a preparation method of a microbial slow-release porous composite material for sewage treatment, as Figure 1 shown. The preparation method specifically includes the following steps:

[0134] (1)Disperse cobalt nitrate in deionized water, and after mixing evenly, a cobalt source solution with a concentration of 0.22 mol / L is obtained. Mix the nanocellulose solution with a mass fraction of 1.8 wt% and the cobalt source solution evenly according to a volume ratio of 2.2:1 to obtain a precursor solution; disperse 2-methylimidazole in methanol, and after mixing evenly, an organic ligand solution with a concentration of 0.98 mol / L is obtained. Under stirring and heating conditions at 68 °C, the organic ligand solution is dropped into the precursor solution at a speed of 2.2 mL / min. The molar ratio of 2-methylimidazole to cobalt ions is 5.8:1. After all the organic ligand solution is dropped, continue to stir the obtained mixed solution at 68 °C for 4.2 h to obtain a reaction solution;

[0135] The reaction solution was mixed with polyvinyl alcohol and stirred for 3.5 h. The addition amount of polyvinyl alcohol was 8.5 wt% of the mass of the reaction solution. The mixed solution was injected into a mold for directional freezing. First, it was cooled to -18°C at a cooling rate of -1.8°C / min and held for 0.8 h. Subsequently, it was further cooled to -38°C at a cooling rate of -0.8°C / min and held for 3.2 h to obtain an aerogel matrix.

[0136] The silane coupling agent KH550 was added to an ethanol aqueous solution (the volume ratio of absolute ethanol to deionized water in the ethanol aqueous solution was 9:1). After mixing evenly, a silane coupling agent solution with a mass fraction of 2.1 wt% was obtained. The aerogel matrix was immersed in the silane coupling agent solution and oscillated at 42°C for 15 h. Subsequently, the aerogel matrix was taken out, washed with ethanol, and then placed in a vacuum dryer at 52°C for 10.5 h to obtain a modified aerogel matrix.

[0137] (2) Bacillus subtilis was inoculated into LB liquid medium. The inoculation amount of Bacillus subtilis was 0.35 g / 100 mL of LB liquid medium. Subsequently, it was oscillated and cultured at an environmental temperature of 36.5°C and an oscillation speed of 195 rpm for 15 h to obtain a Bacillus subtilis bacterial solution. The Bacillus subtilis bacterial solution was centrifuged at 5.5°C and a speed of 5500 rpm for 6 min. After centrifugation, the supernatant was removed, and the precipitated bacteria at the bottom were collected for washing. Trehalose, polyethylene glycol 6000, and deionized water were mixed evenly to obtain a buffer solution. The mass fraction of trehalose in the buffer solution was 8 wt%, and the mass fraction of polyethylene glycol 6000 was 1.8 wt%. The buffer solution was pre-cooled to 5.5°C. Subsequently, the washed bacteria were resuspended in the pre-cooled buffer solution. The ratio of bacteria to buffer solution was 1 g:8 mL. After mixing evenly, a microbial cell suspension was obtained.

[0138] The microbial cell suspension was mixed with a sodium alginate solution with a mass fraction of 3.5 wt%. The volume ratio of the microbial cell suspension to the sodium alginate solution was 1:2.8. After mixing evenly, a gel precursor solution was obtained. The gel precursor solution was subjected to high-pressure homogenization 5 times at 190 MPa to obtain a gel precursor emulsion. Calcium chloride solution was vigorously stirred at a speed of 780 rpm. The gel precursor emulsion was dropped into the stirred calcium chloride solution with a mass fraction of 4 wt% at a dropping speed of 0.45 mL / min to obtain gel particles. The gel particles were taken out and immersed in a glutaraldehyde solution with a mass fraction of 1.8 wt%. After cross-linking in the dark for 2.5 h, microcapsule particles were obtained. The microcapsule particles were taken out and vacuum dried at 38°C for 15 h to obtain slow-release capsule particles.

[0139] (3) Disperse the sustained-release capsule particles obtained in step (2) in deionized water, and after mixing evenly, obtain a dispersion liquid. The mass fraction of the sustained-release capsule particles in the dispersion liquid is 8 wt%. Add the modified aerogel matrix obtained in step (1) and the dispersion liquid into a reaction kettle. The mass ratio of the modified aerogel matrix to the sustained-release capsule particles is 1:1.8, ensuring that the modified aerogel matrix is completely immersed in the dispersion liquid. Vacuum the reaction kettle to -92 kPa and maintain for 22 min. Subsequently, introduce nitrogen into the reaction kettle to restore to normal pressure, and stir the dispersion liquid for 14 min. Then continue to vacuum the reaction kettle to -92 kPa and maintain for 22 min. Repeat the operations of vacuuming and restoring to normal pressure for the reaction kettle 6 times, and then take it out and vacuum dry at 58 °C for 15 h to obtain the microbial sustained-release porous composite material.

[0140] Example 5

[0141] This example provides a preparation method of a microbial sustained-release porous composite material for sewage treatment. As Figure 1 shown, the preparation method specifically includes the following steps:

[0142] (1) Disperse cobalt nitrate in deionized water, and after mixing evenly, obtain a cobalt source solution with a concentration of 0.25 mol / L. Mix the nanocellulose solution with a mass fraction of 2 wt% and the cobalt source solution according to a volume ratio of 2:1 to obtain a precursor solution. Disperse 2-methylimidazole in methanol, and after mixing evenly, obtain an organic ligand solution with a concentration of 1 mol / L. Under stirring and heating conditions at 70 °C, drop the organic ligand solution into the precursor solution at a rate of 2.5 mL / min. The molar ratio of 2-methylimidazole to cobalt ions is 6:1. After all the organic ligand solution is dropped, continue to stir the obtained mixed solution at 70 °C for 4 h to obtain a reaction solution;

[0143] Mix the reaction solution and polyvinyl alcohol and stir for 4 h. The addition amount of polyvinyl alcohol is 9 wt% of the mass of the reaction solution. Inject the mixed solution into a mold for directional freezing. First, cool at a cooling rate of -2 °C / min to -20 °C and keep warm for 0.5 h, and then continue to cool at a cooling rate of -1 °C / min to -40 °C and keep warm for 3 h to obtain an aerogel matrix;

[0144] Add the silane coupling agent KH550 to an ethanol aqueous solution (the volume ratio of absolute ethanol to deionized water in the ethanol aqueous solution is 9:1), and after mixing evenly, obtain a silane coupling agent solution with a mass fraction of 2.2 wt%. Immerse the aerogel matrix in the silane coupling agent solution and oscillate at 45 °C for 12 h. Then take out the aerogel matrix, wash it with ethanol, and place it in a vacuum dryer at 55 °C for 10 h to obtain a modified aerogel matrix;

[0145] (2) Inoculate Bacillus subtilis into LB liquid medium, with the inoculation amount of Bacillus subtilis being 0.4 g per 100 mL of LB liquid medium. Then, perform shaking culture at an environmental temperature of 37°C and a shaking speed of 200 rpm for 12 h to obtain a Bacillus subtilis bacterial solution. Centrifuge the Bacillus subtilis bacterial solution at 6°C and a speed of 6000 rpm for 5 min. After centrifugation, remove the supernatant and collect the precipitated cells at the bottom for washing. Mix trehalose, polyethylene glycol 6000, and deionized water evenly to obtain a buffer solution, where the mass fraction of trehalose in the buffer solution is 10 wt% and the mass fraction of polyethylene glycol 6000 is 2 wt%. Pre-cool the buffer solution to 6°C, and then resuspend the washed cells in the pre-cooled buffer solution at a ratio of 1 g of cells to 10 mL of buffer solution. After mixing evenly, obtain a microbial cell suspension.

[0146] Mix the microbial cell suspension with a 4 wt% sodium alginate solution at a volume ratio of 1:3. After mixing evenly, obtain a pre-gel solution. Perform high-pressure homogenization on the pre-gel solution 5 times at 200 MPa to obtain a pre-gel emulsion. Stir the calcium chloride solution at a speed of 800 rpm, and drop the pre-gel emulsion into the stirred 5 wt% calcium chloride solution at a dropping speed of 0.5 mL / min to obtain gel particles. Take out the gel particles and immerse them in a 2 wt% glutaraldehyde solution. After cross-linking in the dark for 2 h, obtain microcapsule particles. Take out the microcapsule particles and vacuum dry them at 40°C for 12 h to obtain slow-release capsule particles.

[0147] (3) Disperse the slow-release capsule particles obtained in step (2) in deionized water. After mixing evenly, obtain a dispersion, where the mass fraction of the slow-release capsule particles in the dispersion is 10 wt%. Add the modified aerogel matrix obtained in step (1) and the dispersion into a reaction kettle, with the mass ratio of the modified aerogel matrix to the slow-release capsule particles being 1:2, ensuring that the modified aerogel matrix is completely immersed in the dispersion. Vacuum the reaction kettle to -95 kPa and maintain for 20 min. Then, introduce nitrogen into the reaction kettle to restore to normal pressure, and stir the dispersion for 15 min. Subsequently, continue to vacuum the reaction kettle to -95 kPa and maintain for 20 min. Repeat the operations of vacuuming and restoring to normal pressure on the reaction kettle 5 times, and then take it out and vacuum dry it at 60°C for 12 h to obtain the microbial slow-release porous composite material.

[0148] Example 6

[0149] This example provides a preparation method of a microbial slow-release porous composite material for sewage treatment. The difference from Example 1 is that in step (1), the volume ratio of the nanocellulose solution to the cobalt source solution is adjusted to 1:1, and other operation steps and process parameters are exactly the same as those in Example 1.

[0150] Example 7

[0151] This example provides a method for preparing a microbial slow-release porous composite material for sewage treatment. The difference from Example 1 is that in step (1), the volume ratio of the nanocellulose solution to the cobalt source solution is adjusted to 4:1, and the other operation steps and process parameters are exactly the same as those in Example 1.

[0152] Example 8

[0153] This example provides a method for preparing a microbial slow-release porous composite material for sewage treatment. The difference from Example 1 is that in step (2), the volume ratio of the microbial cell suspension to the sodium alginate solution during mixing is adjusted to 1:1, and the other operation steps and process parameters are exactly the same as those in Example 1.

[0154] Example 9

[0155] This example provides a method for preparing a microbial slow-release porous composite material for sewage treatment. The difference from Example 1 is that in step (2), the volume ratio of the microbial cell suspension to the sodium alginate solution during mixing is adjusted to 1:4, and the other operation steps and process parameters are exactly the same as those in Example 1.

[0156] Example 10

[0157] This example provides a method for preparing a microbial slow-release porous composite material for sewage treatment. The difference from Example 1 is that in step (2), the mass fraction of the calcium chloride solution is adjusted to 1 wt%, and the other operation steps and process parameters are exactly the same as those in Example 1.

[0158] Example 11

[0159] This example provides a method for preparing a microbial slow-release porous composite material for sewage treatment. The difference from Example 1 is that in step (2), the mass fraction of the calcium chloride solution is adjusted to 7 wt%, and the other operation steps and process parameters are exactly the same as those in Example 1.

[0160] Example 12

[0161] This example provides a method for preparing a microbial slow-release porous composite material for sewage treatment. The difference from Example 1 is that in step (2), the mass fraction of the glutaraldehyde solution is adjusted to 0.1 wt%, and the other operation steps and process parameters are exactly the same as those in Example 1.

[0162] Example 13

[0163] This embodiment provides a preparation method of a microbial slow-release porous composite material for sewage treatment. The difference from Embodiment 1 is that in step (2), the mass fraction of the glutaraldehyde solution is adjusted to 3 wt%, and other operation steps and process parameters are exactly the same as those in Embodiment 1.

[0164] Embodiment 14

[0165] This embodiment provides a preparation method of a microbial slow-release porous composite material for sewage treatment. The difference from Embodiment 1 is that in step (3), the mass ratio of the modified aerogel matrix to the slow-release capsule particles is adjusted to 1:0.5, and other operation steps and process parameters are exactly the same as those in Embodiment 1.

[0166] Embodiment 15

[0167] This embodiment provides a preparation method of a microbial slow-release porous composite material for sewage treatment. The difference from Embodiment 1 is that in step (3), the mass ratio of the modified aerogel matrix to the slow-release capsule particles is adjusted to 1:3, and other operation steps and process parameters are exactly the same as those in Embodiment 1.

[0168] Using the microbial slow-release porous composite materials prepared in Embodiments 1 - 15 of the present invention to treat printing and dyeing wastewater and petrochemical wastewater, specifically including:

[0169] Put the microbial slow-release porous composite materials prepared in Embodiments 1 - 15 of the present invention into the printing and dyeing wastewater. In the printing and dyeing wastewater, the COD value is 824 mg / L, the NH₃-N value is 18.3 mg / L, the suspended solid content is 255 mg / L, the chromaticity value is 580 times (dilution multiple method), and the dosage is 2.5 kg / m 3 , and after 10 days, test the concentrations of various pollutants in the treated printing and dyeing wastewater. The concentrations of various pollutants in the treated printing and dyeing wastewater are shown in Table 1.

[0170] Put the microbial slow-release porous composite materials prepared in Embodiments 1 - 15 of the present invention into the petrochemical wastewater. In the petrochemical wastewater, the COD value is 2820 mg / L, the NH₃-N value is 58.6 mg / L, the suspended solid content is 236 mg / L, the petroleum content is 125.3 mg / L, and the dosage is 5 kg / m 3 , and after 10 days, test the concentrations of various pollutants in the treated petrochemical wastewater. The concentrations of various pollutants in the treated petrochemical wastewater are shown in Table 2.

[0171] Table 1

[0172]

[0173] Table 2

[0174]

[0175] It can be seen from the test data provided in Table 1 and Table 2 that the effluent water quality of Examples 1-5 is comprehensively better than the national standard requirements of printing and dyeing wastewater (GB 4287-2012 "Discharge Standard of Water Pollutants for the Textile Dyeing and Finishing Industry") and petrochemical wastewater (GB 31571-2015 "Discharge Standard of Pollutants for the Petrochemical Industry"). This technology combines a multi-level pore structure with microbial slow release to achieve efficient and stable sewage treatment performance, and is particularly suitable for the advanced treatment of high-difficulty printing and dyeing wastewater and petrochemical wastewater.

[0176] It can be seen from the test data of Example 1, Example 6 and Example 7 that the effluent water quality of Example 6 and Example 7 is inferior to that of Example 1. This is because the dosage of the nanocellulose solution in Example 6 is too small, resulting in the aggregation of ZIF-67 crystals, blocking the pores and reducing the adsorption and catalytic efficiency. In Example 7, the dosage of the nanocellulose solution is too large, affecting the structural stability, resulting in pore collapse and a decrease in the interception efficiency of pollutants.

[0177] It can be seen from the test data of Example 1, Example 8 and Example 9 that the effluent water quality of Example 8 and Example 9 is inferior to that of Example 1. This is because the dosage of the sodium alginate solution in Example 8 is too small, resulting in an unstable gel network structure formed, too fast release of microorganisms, and a deterioration of the treatment effect. In Example 9, the dosage of the sodium alginate solution is too large, the formed gel network is too dense, mass transfer is blocked, the microbial activity is low, and the treatment effect is poor.

[0178] It can be seen from the test data of Example 1, Example 10 and Example 11 that the effluent water quality of Example 10 and Example 11 is inferior to that of Example 1. This is because the mass fraction of the calcium chloride solution in Example 10 is too low, the cross-linking is insufficient, resulting in the easy rupture of the slow-release capsule particles and the loss of microorganisms, and the treatment effect deteriorates. In Example 11, the mass fraction of the calcium chloride solution is too high, the formed gel network is too dense, mass transfer is blocked, the microbial activity is low, and the treatment effect is poor.

[0179] It can be seen from the test data of Example 1, Example 12 and Example 13 that the effluent water quality of Example 12 and Example 13 is inferior to that of Example 1. This is because the mass fraction of the glutaraldehyde solution in Example 12 is too low, the cross-linking is insufficient, resulting in the easy rupture of the slow-release capsule particles and the loss of microorganisms, and the treatment effect deteriorates. In Example 13, the mass fraction of the glutaraldehyde solution is too high, the formed gel network is too dense, mass transfer is blocked, the microbial activity is low, and the treatment effect is poor.

[0180] It can be seen from the test data of Example 1, Example 14 and Example 15 that the effluent water quality of Example 14 and Example 15 is inferior to that of Example 1. This is because the dosage of the slow-release capsule particles in Example 14 is too small, resulting in insufficient loading and limited treatment capacity. In Example 15, the dosage of the slow-release capsule particles is too large, leading to the blockage of the pores of the modified aerogel matrix, hindering mass transfer and reducing the treatment effect.

[0181] The applicant declares that the above description is only a specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A preparation method of a microbial slow-release porous composite material for sewage treatment, characterized in that, The preparation method includes: (Ⅰ) Drop the organic ligand solution into the precursor solution composed of the nanocellulose solution and the cobalt source solution to obtain a reaction solution; mix the reaction solution with polyvinyl alcohol and then inject it into a mold for directional freezing to obtain an aerogel matrix; perform hydrophobic modification on the aerogel matrix to obtain a modified aerogel matrix; (Ⅱ) Mix the microbial cell suspension with sodium alginate and then perform high-pressure homogenization to obtain a gel precursor emulsion; drop it into calcium chloride solution for gelation to obtain gel particles, and then crosslink and dry them with glutaraldehyde to obtain slow-release capsule particles; (Ⅲ) Disperse the slow-release capsule particles in deionized water to obtain a dispersion; immerse the modified aerogel matrix in the dispersion, take it out and dry it to obtain the microbial slow-release porous composite material.

2. The preparation method according to claim 1, characterized in that, In step (Ⅰ), the organic ligand solution is composed of 2-methylimidazole and methanol; The concentration of 2-methylimidazole in the organic ligand solution is 0.9 - 1 mol / L; The mass fraction of the nanocellulose solution is 1 - 2 wt%; The cobalt source solution is composed of cobalt nitrate and deionized water; The concentration of cobalt nitrate in the cobalt source solution is 0.15 - 0.25 mol / L; The volume ratio of the nanocellulose solution to the cobalt source solution is (2 - 3):1; The molar ratio of 2-methylimidazole in the organic ligand solution to cobalt ions in the cobalt source solution is (5 - 6):1; Drop the organic ligand solution into the precursor solution under stirring and heating conditions; The heating temperature when the organic ligand solution is dropped is 60 - 70 °C; After all the organic ligand solution is dropped, continue to mix and stir under heating conditions for 4 - 5 h to obtain the reaction solution.

3. The preparation method according to claim 1, wherein In step (Ⅰ), the addition amount of polyvinyl alcohol is 7 - 9 wt% of the mass of the reaction solution; The mixing and stirring time of the reaction solution and polyvinyl alcohol is 2 - 4 h; The directional freezing process includes: Cool down to the first freezing temperature at the first cooling rate and keep warm, and then continue to cool down to the second freezing temperature at the second cooling rate and keep warm; The first cooling rate is -1 - -2 °C / min; The first freezing temperature is -15 - -20 °C; The holding time at the first freezing temperature is 0.5 - 1.5 h; The second cooling rate is -0.5 - -1 °C / min; The second freezing temperature is -30 - -40 °C; The holding time at the second freezing temperature is 3 - 4 h.

4. The preparation method according to claim 1, characterized in that, In step (Ⅰ), the hydrophobic modification treatment includes: Immerse the aerogel matrix in the silane coupling agent solution, oscillate and heat it, then take out the aerogel matrix, wash and dry it to obtain the modified aerogel matrix; The silane coupling agent solution is composed of a silane coupling agent and an ethanol aqueous solution; The mass fraction of the silane coupling agent in the silane coupling agent solution is 1.8 - 2.2 wt%; The heating temperature when the aerogel matrix is immersed in the silane coupling agent solution is 35 - 45 °C; The immersion time of the aerogel matrix in the silane coupling agent solution is 12 - 24 h.

5. The preparation method according to claim 1, characterized in that, In step (II), the microbial suspension is prepared by the following method: Inoculate Bacillus subtilis into LB liquid medium and shake culture to obtain Bacillus subtilis liquid; then centrifuge, remove the supernatant, and collect the precipitated cells at the bottom for washing; Resuspend the washed cells in a pre-cooled buffer solution, and mix evenly to obtain the microbial suspension; The pre-cooling temperature of the buffer solution is 4 - 6 °C; The buffer solution is composed of trehalose, polyethylene glycol 6000, and deionized water; The mass fraction of trehalose in the buffer solution is 5 - 10 wt%; The mass fraction of polyethylene glycol 6000 in the buffer solution is 1 - 2 wt%; The ratio of the cells to the buffer solution is 1 g:(5 - 10) mL.

6. The preparation method according to claim 1, wherein In step (II), the volume ratio of the microbial suspension to the sodium alginate solution during mixing is 1:(2 - 3); The mass fraction of the sodium alginate solution is 2 - 4 wt%; The pressure of the high-pressure homogenization is 150 - 200 MPa; The number of times of high-pressure homogenization is 5 - 7 times; The mass fraction of the calcium chloride solution is 2 - 5 wt%.

7. The preparation method according to claim 1, characterized in that, In step (II), the operation steps of glutaraldehyde cross-linking include: taking out the gel particles and immersing them in a glutaraldehyde solution, and cross-linking in the dark to obtain microcapsule particles; The mass fraction of the glutaraldehyde solution is 1 - 2 wt%; The soaking time of the gel particles in the glutaraldehyde solution is 2 - 4 h.

8. The preparation method according to claim 1, characterized in that, In step (III), the mass fraction of the slow-release capsule particles in the dispersion liquid is 5 - 10 wt%; The impregnation process includes: Adding the modified aerogel matrix and the dispersion liquid into a reaction kettle, completely submerging the modified aerogel matrix in the dispersion liquid, evacuating the reaction kettle, then restoring to normal pressure, and stirring the dispersion liquid under normal pressure; then continue to evacuate; repeat the evacuation and restoration to normal pressure of the reaction kettle 5 - 8 times; The mass ratio of the modified aerogel matrix to the slow-release capsule particles in the dispersion liquid is 1:(1 - 2); The reaction kettle is evacuated to -85 - -95 kPa; The time for the reaction kettle to maintain vacuum is 20 - 30 min; In the normal pressure stage, stir the dispersion liquid for 10 - 15 min.

9. A microbial slow-release porous composite material for sewage treatment prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the microbial slow-release porous composite material for sewage treatment according to claim 9, characterized in that, The microbial slow-release porous composite material is used for sewage treatment.

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