Solid waste-based soil ecological restoration substrate and preparation method thereof

Abstract

The present application relates to the field of soil conditioning material and contaminated soil remediation technology, and particularly relates to a kind of solid waste base type soil ecological remediation substrate and a preparation method thereof.The substrate includes a nutrient core and a reaction outer layer coated on the outside of the nutrient core;The nutrient core is composed of phosphorus-rich sludge incineration ash, agroforestry waste biochar, humification digestion residue and phosphorus-activated bacteria fixed in the pores of biochar, the reaction outer layer is composed of water treatment iron and aluminum sludge, carbonized steel slag and desulfurization gypsum, and is provided with microporous channels in communication with the nutrient core.Form the nutrient core first, then coat the reaction outer layer and solidify during preparation.The substrate is connected through the partition of the nutrient activation area and the mineral reaction area, reduces the component competition and local environmental disturbance, maintains the adhesion of microorganisms and the migration of substances, and enhances the stable fixation of contaminated components in the composite contaminated soil and the stability of the substrate structure.

Description

Technical Field

[0001] This invention relates to the field of soil conditioning materials and contaminated soil remediation technology, specifically to a solid waste-based soil ecological remediation matrix and its preparation method. Background Technology

[0002] Existing solid waste-based soil remediation materials typically use one or more of the following raw materials: sludge incineration ash, biochar, steel slag, desulfurization gypsum, or water treatment sludge. These materials are crushed, mixed, granulated, or directly applied to the soil. Sludge incineration ash provides a phosphorus-containing mineral phase, biochar provides pores and an organic matter loading interface, steel slag and desulfurization gypsum provide calcareous minerals and acid-base buffering components, and iron-aluminum minerals from water treatment sludge adsorb migratable pollutants from the soil. Conventional solutions often employ a uniform mixing structure, with each raw material in disordered contact within the same particle, exposing phosphorus-containing components, iron-aluminum minerals, and calcareous minerals to the soil solution. Some solutions also directly spray functional bacterial solutions onto the surface of the mixture, relying on the carrier pores for adhesion, and then achieving nutrient release, pollutant fixation, and microbial colonization through natural diffusion.

[0003] The aforementioned uniform mixed structure allows the activation of phosphate-bearing phases, the adsorption of iron-aluminum minerals, and the dissolution and release of calcareous minerals to occur simultaneously in the same area. Phosphate ions and anionic pollutants in the soil easily compete for iron-aluminum active sites, and the local dissolution of steel slag may alter the pH environment around functional bacteria, leading to interference between microbial activity and mineral fixation processes. When insoluble phosphorus in sludge incineration ash lacks a controlled activation interface, the release process is discontinuous; when functional bacteria are directly dispersed on the outer surface of the material, they are easily affected by fluctuations in soil salinity, pollutants, and moisture. Therefore, the main technical problem to be solved is: how to establish interconnected yet distinct nutrient activation zones and mineral reaction zones within the same solid waste remediation matrix, enabling phosphorus-bearing components, functional bacteria, iron-aluminum minerals, and calcareous minerals to synergistically contact at predetermined interfaces, avoiding competition for reaction sites and local environmental conflicts. Summary of the Invention

[0004] To address the shortcomings of existing solid waste-based soil remediation materials, which use a uniform mixture of multiple solid waste components, leading to competition for reaction sites and localized environmental conflicts among phosphorus-containing components, iron-aluminum minerals, calcareous minerals, and functional bacteria in the same area, this invention provides a solid waste-based soil ecological remediation matrix and its preparation method, in order to establish interconnected and partitioned nutrient activation zones and mineral reaction zones.

[0005] To address the aforementioned technical problems, this invention provides a solid waste-based soil ecological remediation matrix, comprising a nutrient core and a reaction outer layer covering the outside of the nutrient core; the nutrient core comprises phosphorus-rich sludge incineration ash, agricultural and forestry waste biochar, humification digestion residue, and phosphorus-activating bacteria immobilized in the pores of the agricultural and forestry waste biochar; the reaction outer layer comprises water treatment iron-aluminum sludge, carbonized steel slag, and desulfurization gypsum, and has microporous channels communicating with the nutrient core.

[0006] The pores of the agricultural and forestry waste biochar provide attachment space for the phosphorus-activating bacteria. The humification and digestion residue is distributed within the nutrient core and forms an organic matter interface. The phosphorus-activating bacteria remain fixed within the organic matter interface and the biochar pores, and contact the phosphate-containing mineral phase in the phosphorus-rich sludge incineration ash. After the substrate is applied to the soil, soil moisture enters the nutrient core, and the phosphorus-activating bacteria participate in the activation process of the phosphate-containing mineral phase. The activated and migratory components migrate to the outer reaction layer through the microporous channels. The water treatment iron-aluminum sludge, carbonized steel slag, and desulfurized gypsum form a mineral reaction interface in the outer reaction layer. Migratory pollutants in the soil undergo adsorption, ion exchange, or mineral binding at this mineral reaction interface. The coating relationship between the nutrient core and the outer reaction layer separates the biological activation zone and the mineral reaction zone. The microporous channels maintain the material exchange between the two zones, allowing different solid waste components to participate in the reaction along an inside-out path.

[0007] Furthermore, in the above technical solution, the phosphorus-rich sludge incineration ash is composed of mutually separated phosphorus-containing mineral phase particles, the agricultural and forestry waste biochar forms a through-pore framework, the humification digestion residue fills the space between the through-pore framework and the phosphorus-containing mineral phase particles, and the phosphorus-activating bacteria are attached to the pore walls of the through-pore framework and distributed at the organic matter interface formed by the humification digestion residue.

[0008] In practice, the separated phosphate-containing mineral phase particles are distributed within the interconnected porous framework, maintaining contact interfaces between each particle and the liquid phase and the phosphorus-activating bacteria. The interconnected porous framework forms a continuous migration path for water and dissolved components within the nutrient core. The humification and digestion residue fills the space between the interconnected porous framework and the phosphate-containing mineral phase particles, ensuring that the attachment site of the phosphorus-activating bacteria is adjacent to the phosphate-containing mineral phase particles. After soil moisture enters along the interconnected porous framework, it sequentially contacts the organic matter interface, the phosphorus-activating bacteria, and the phosphate-containing mineral phase particles, thereby forming a continuous biological activation and liquid phase migration process.

[0009] Furthermore, in the above technical solution, the water treatment iron-aluminum sludge forms a continuous iron-aluminum mineral phase in the outer reaction layer, the carbide steel slag is embedded in the continuous iron-aluminum mineral phase as discrete particles, the desulfurization gypsum is dispersed at the contact interface between the continuous iron-aluminum mineral phase and the discrete particles, and the microporous channel passes through the continuous iron-aluminum mineral phase and surrounds the outer periphery of the discrete particles.

[0010] In practice, the continuous iron-aluminum mineral phase constitutes the continuous mineral framework of the outer reaction layer, allowing the liquid phase entering the outer reaction layer to continuously contact the iron-aluminum mineral surface. The carbide steel slag is embedded in discrete particles, preventing it from forming concentrated areas in the outer reaction layer. The desulfurized gypsum is located at the interface between the continuous iron-aluminum mineral phase and the discrete particles, allowing different mineral components to contact each other at the interface. The liquid phase passes through the continuous iron-aluminum mineral phase along the microporous channels and bypasses the discrete particles, contacting different mineral surfaces sequentially during its migration, thereby forming a continuously distributed multiphase mineral reaction path.

[0011] Furthermore, in the above technical solution, an interface transition layer is provided between the nutrient core and the reaction outer layer. The interface transition layer includes an inner porous phase formed by the agricultural and forestry waste biochar and an outer mineral phase formed by the water treatment iron-aluminum sludge. The inner porous phase and the outer mineral phase are interlocked, and the pores in the interface transition layer are respectively connected to the pores of the nutrient core and the micropore channels.

[0012] In specific implementation, the inner porous phase is in contact with the agricultural and forestry waste biochar in the nutrient core, and the outer mineral phase is in contact with the iron-aluminum sludge for water treatment in the outer reaction layer. The inner porous phase and the outer mineral phase are interlocked, forming a continuous interface between the nutrient core and the outer reaction layer. The liquid phase in the nutrient core enters the interface transition layer through its pores, and then enters the microporous channels through the pores in the interface transition layer. This continuous porous structure ensures that substances maintain a predetermined migration path when crossing the inner and outer layer interfaces and reduces interfacial separation between the nutrient core and the outer reaction layer during water absorption and drying.

[0013] Furthermore, in the above technical solution, the microporous channel includes a main connecting hole extending radially along the outer reaction layer and a diversion hole extending circumferentially along the outer reaction layer. The diversion hole intersects with the adjacent main connecting hole. The orifices of the main connecting hole are staggered on the inner and outer surfaces of the outer reaction layer. The water treatment iron-aluminum sludge, carbonized steel slag, and desulfurization gypsum together form the pore walls of the main connecting hole and the diversion hole.

[0014] In specific implementation, the main connecting hole facilitates radial material migration between the nutrient core and the external soil. The diversion hole connects adjacent main connecting holes, allowing the liquid phase entering a single main connecting hole to be dispersed circumferentially to other main connecting holes. The staggered arrangement of the inner and outer orifices prevents the liquid phase from directly passing through the outer reaction layer in a straight line, instead requiring it to migrate along the connecting path formed by the main connecting hole and the diversion hole. The iron-aluminum sludge, carbonized steel slag, and desulfurized gypsum used in the water treatment process collectively constitute the pore wall, allowing the migrating liquid phase to come into contact with various mineral components as it flows through the pores.

[0015] Furthermore, in the above technical solution, the pore walls of the agricultural and forestry waste biochar are covered with a humic membrane layer formed by the humification digestion residue, the phosphorus-activating bacteria are fixed on the surface of the humic membrane layer in the form of a biofilm, the phosphorus-containing mineral phase particles are embedded between adjacent agricultural and forestry waste biochar, and a release gap is maintained between the phosphorus-containing mineral phase particles and the humic membrane layer to the outer reaction layer.

[0016] In practice, the humic film layer covers the pore walls of the agricultural and forestry waste biochar, forming a continuous organic matter attachment interface within the porous framework. After the phosphorus-activating bacteria are fixed in the form of a biofilm, the bacteria remain on the surface of the humic film layer and are not directly lost with the liquid phase entering the pores. The phosphorus-containing mineral phase particles are located between adjacent agricultural and forestry waste biochar and maintain a release gap with the humic film layer, allowing soil moisture to enter the release gap and contact the phosphorus-containing mineral phase particles. Components released from the phosphorus-containing mineral phase particles into the liquid phase enter the outer reaction layer along the release gap.

[0017] Furthermore, in the above technical solution, the continuous iron-aluminum mineral phase forms an iron-aluminum enrichment zone on the side near the nutrient core, the carbide steel slag and the desulfurized gypsum form a calcareous mineral enrichment zone on the side near the outer surface of the reaction outer layer, and a mutually penetrating mixing zone is formed between the iron-aluminum enrichment zone and the calcareous mineral enrichment zone, and the microporous channel passes through the iron-aluminum enrichment zone, the mixing zone and the calcareous mineral enrichment zone in sequence.

[0018] In practice, the liquid phase migrating outward from the nutrient core first enters the iron-aluminum enrichment zone, contacts the continuous iron-aluminum mineral phase, then enters the mixing zone, simultaneously contacting the interpenetrating iron-aluminum and calcareous minerals, subsequently entering the calcareous mineral enrichment zone and reaching the outer surface of the reaction outer layer. When external soil moisture enters the reaction outer layer in the reverse direction, it sequentially passes through the calcareous mineral enrichment zone, the mixing zone, and the iron-aluminum enrichment zone. The microporous channels penetrate different enrichment zones, enabling the mineral components to form a continuous and layered contact interface radially.

[0019] Furthermore, in the above technical solution, the interface transition layer includes, in the radial direction, an inner bonding zone, a middle interpenetrating zone, and an outer bonding zone. The inner bonding zone is formed by the interweaving of the agricultural and forestry waste biochar and the humification digestion residue. The outer bonding zone is formed by the solidification of the water treatment iron-aluminum sludge and the fine particles of the carbonized steel slag. The middle interpenetrating zone includes interlaced biochar branches and iron-aluminum mineral branches.

[0020] In specific implementation, the inner binding region is continuous with the porous organic structure in the nutrient core, and the outer binding region is continuous with the mineral structure in the reaction outer layer. The central interpenetrating region connects the inner and outer binding regions through the interlacing extensions of the biochar branches and the iron-aluminum mineral branches. When the liquid phase enters the interface transition layer from the nutrient core, it enters the central interpenetrating region along the pores between the biochar branches, and then enters the outer binding region along the pores between the iron-aluminum mineral branches. This radial interpenetrating structure allows for a gradual transition from the organic porous phase to the mineral phase.

[0021] Furthermore, in the above technical solution, the main connecting hole is formed by sequentially connecting a diffusion hole section near the nutrient core, a bent hole section located in the middle of the reaction outer layer, and an exchange hole section penetrating the outer surface of the reaction outer layer. The diversion hole connects adjacent bent hole sections. The desulfurized gypsum is distributed around the orifices of the diffusion hole section and the exchange hole section. The water treatment iron-aluminum sludge is distributed on the pore wall of the bent hole section.

[0022] In practice, the liquid phase migrating from the nutrient core first enters the diffusion pore section, then the bend pore section, and can migrate between adjacent bend pore sections through the diversion holes. Subsequently, it enters the external soil through the exchange pore section. The bend pore section alters the linear migration direction of the liquid phase, and the diversion holes expand the contact range of the liquid phase in the middle of the outer reaction layer. The desulfurized gypsum is disposed around the orifices of the diffusion and exchange pore sections, and the iron-aluminum sludge for water treatment is disposed on the pore wall of the bend pore section, allowing the liquid phase to contact the corresponding mineral components during its entry into the pores, passage through the middle of the pores, and exit from the pores.

[0023] To address the aforementioned technical problems, this invention also provides a method for preparing a solid waste-based soil ecological restoration matrix, comprising: combining phosphorus-rich sludge incineration ash, agricultural and forestry waste biochar, and humification digestion residue; inoculating and immobilizing phosphorus-activating bacteria into the pores of the agricultural and forestry waste biochar to form a nutrient core; preparing a coating material from water treatment iron-aluminum sludge, carbonized steel slag, and desulfurization gypsum; coating the outside of the nutrient core with the coating material, forming microporous channels communicating with the nutrient core in the coating material; and solidifying to obtain the solid waste-based soil ecological restoration matrix.

[0024] After the phosphorus-rich sludge incineration ash, agricultural and forestry waste biochar, and humic digestion residue are combined, the agricultural and forestry waste biochar forms a porous structure to support the phosphorus-activating bacteria, and the humic digestion residue is distributed between the agricultural and forestry waste biochar and the phosphorus-rich sludge incineration ash. The phosphorus-activating bacteria are inoculated into the pores of the agricultural and forestry waste biochar and fixed, so that the bacteria and the phosphorus-rich sludge incineration ash are distributed in close proximity. The water treatment iron-aluminum sludge, carbonized steel slag, and desulfurization gypsum form a coating material and coat the outside of the nutrient core. During the solidification process, a reaction outer layer is formed, and microporous channels communicating with the nutrient core are retained. After the prepared matrix is ​​applied to the soil, soil moisture migrates between the nutrient core and the external soil through the microporous channels. The biological activation process in the nutrient core and the mineral reaction process in the reaction outer layer are connected along the microporous channels.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The remediation matrix employs a nutrient core and a reactive outer layer encapsulation structure. Phosphorus-rich sludge incineration ash, agricultural and forestry waste biochar, humification digestion residue, and phosphorus-activating bacteria are concentrated in the nutrient core, while water treatment iron-aluminum sludge, carbonized steel slag, and desulfurization gypsum are placed in the reactive outer layer, connected by microporous channels. This structure allows the bioactivation of phosphorus-containing mineral phases to occur within the core pores. The generated migratory components gradually enter the outer layer through the microporous channels, forming a continuous reactive interface between iron-aluminum and calcareous minerals in the outer layer, spatially reducing direct, disordered contact between phosphorus-containing components and iron-aluminum active sites. The interface transition layer and radially and circumferentially connected channels maintain restricted exchange between the inner and outer layers, reducing the impact of local mineral dissolution on the attachment environment of phosphorus-activating bacteria, and ensuring continuous integration of nutrient release, pollutant fixation, and acid-base buffering within the same particle.

[0026] 2. Agricultural and forestry waste biochar forms a permeable porous framework. Humic digestion residue fills the spaces between the porous framework and phosphate-bearing mineral particles, creating a humic interface on the pore walls for phosphorus-activating bacteria to attach, thus reducing direct exposure of the bacteria to the external soil environment. Release gaps are maintained between the phosphate-bearing mineral particles and the humic membrane layer, keeping the liquid phase migration pathways in the core connected. The continuous iron-aluminum mineral phase, discrete carbonized steel slag particles, and desulfurized gypsum distributed at the contact interface in the outer reaction layer constitute a multiphase mineral framework. Iron-aluminum enrichment zones, mixed zones, and calcareous mineral enrichment zones are arranged radially, with diffusion pores, bend pores, and exchange pores extending the material migration pathways. This structure also reduces interfacial separation of particles during water absorption, drying, and transportation, maintaining a relatively stable pore connectivity and component distribution in the remediation matrix. Detailed Implementation

[0027] In the following examples, the amounts of each solid raw material are based on dry weight. Phosphorus-rich sludge incineration ash is crushed and freed from visible impurities before use; agricultural and forestry waste biochar, humic digestion residue, water treatment iron-aluminum sludge, carbonized steel slag, and desulfurization gypsum are dried, pulverized, and sieved before use. Phosphorus-activating bacteria are selected from bacteria capable of growing and forming phosphate-solubilizing zones under culture conditions using insoluble phosphorus as the phosphorus source; the viable cell count in the bacterial solution is adjusted to a predetermined level before inoculation.

[0028] Example 1: This example prepares a solid waste-based soil ecological restoration matrix, which, based on 100 parts by weight of solid raw materials, includes 55 parts by weight of nutrient core raw materials and 45 parts by weight of reaction outer layer raw materials.

[0029] The 55 parts by weight of the nutrient core raw material consists of 24.2 parts by weight of phosphorus-rich sludge incineration ash, 18.2 parts by weight of agricultural and forestry waste biochar, and 12.6 parts by weight of humification digestion residue. The 45 parts by weight of the reaction outer layer raw material consists of 25.2 parts by weight of water treatment iron-aluminum sludge, 12.2 parts by weight of carbonized steel slag, and 7.6 parts by weight of desulfurization gypsum.

[0030] The specific preparation method is as follows: The phosphorus-rich sludge incineration ash is pulverized to a particle size of 80–150 μm, causing the phosphorus-containing mineral phases to form separated particles. The agricultural and forestry waste biochar is sieved to a particle size of 0.30–0.80 mm, and the humification digestion residue is sieved to a particle size of 0.15–0.50 mm. The agricultural and forestry waste biochar and the humification digestion residue are mixed, water is added and stirred to bring the moisture content of the mixture to 35%, and then allowed to stand for 4 hours to allow the humification digestion residue to adhere to the pore walls of the agricultural and forestry waste biochar and form a humic film layer.

[0031] Add phosphorus-activated bacteria solution to the above mixture to achieve a viable bacteria count of 8.0 × 10⁻⁶ per gram of agricultural and forestry waste biochar. 8 Mix the phosphorus-rich sludge under low-speed agitation for 20 minutes, then let it stand for 6 hours to allow phosphorus-activating bacteria to be fixed on the surface of the humic film layer in the form of a biofilm. Add the phosphorus-rich sludge incineration ash in three portions, mixing for 5 minutes after each addition, so that the phosphorus-containing mineral phase particles are dispersed between adjacent agricultural and forestry waste biochar, and a release gap for liquid phase to enter is maintained between the phosphorus-containing mineral phase particles and the humic film layer.

[0032] The moisture content of the above mixture was adjusted to 38%, and nutrient cores with a diameter of 4-6 mm were formed by roll forming. The cores were then dried at 32°C until the moisture content was 15%. The extrusion pressure was controlled during the forming process to maintain the interconnected pore framework of the agricultural and forestry waste biochar.

[0033] Five percent of each of the agricultural and forestry waste biochar and the water treatment iron-aluminum sludge were taken and mixed to prepare an interface transition material. The interface transition material was uniformly attached to the surface of the nutrient core to form an interface transition layer with a thickness of 0.20-0.35 mm. The inner side of the interface transition layer retained the porous structure of biochar, the outer side formed a mineral structure from the water treatment iron-aluminum sludge, and the middle part formed interwoven biochar branches and iron-aluminum mineral branches.

[0034] The remaining iron-aluminum sludge from the water treatment process is pulverized to a particle size of 50–180 μm, the steel carbide slag is sieved to a particle size of 100–300 μm, and the desulfurization gypsum is pulverized to a particle size of 50–150 μm. The iron-aluminum sludge, steel carbide slag, and desulfurization gypsum from the water treatment process are mixed, and water is added to prepare a coating material with a moisture content of 42%. This allows the steel carbide slag to be distributed as discrete particles within the continuous iron-aluminum mineral phase formed by the iron-aluminum sludge from the water treatment process, while the desulfurization gypsum is distributed at the interface between the continuous iron-aluminum mineral phase and the steel carbide slag particles.

[0035] The coating material is applied to the outside of the nutrient core in three layers. After each coating, the material is rolled at low speed and ventilated for 8 minutes to allow mineral particles in adjacent coating layers to accumulate in a staggered manner. The first coating forms an iron-aluminum enriched zone near the nutrient core, the second coating forms a mixed zone where iron-aluminum minerals and calcareous minerals interpenetrate, and the third coating forms a calcareous mineral enriched zone near the outer surface.

[0036] During the coating process, the supply speed of the coating material and the rolling state of the particles are controlled to maintain radially extending main connecting pores between mineral particles and to connect the interlayer pores formed by each coating step circumferentially, forming diversion pores. Adjacent coating layers are staggered so that the orifices of the main connecting pores on the inner and outer surfaces of the reaction outer layer are not on the same straight line. The main connecting pores are formed by connecting a diffusion pore section near the nutrient core, a bending pore section located in the middle of the reaction outer layer, and an exchange pore section penetrating the outer surface of the reaction outer layer. The diversion pores connect adjacent bending pore sections.

[0037] After coating, the substrate was cured at 35℃ for 24 hours to obtain a solid waste-based soil ecological remediation matrix with a diameter of 6–9 mm and a reaction outer layer thickness of 0.8–1.5 mm. The resulting matrix consists of a nutrient core, an interface transition layer, and a reaction outer layer connected sequentially, with the interconnected pores of the nutrient core communicating with the microporous channels in the reaction outer layer.

[0038] Example 2: In this example, the mass ratio of the nutrient core to the reaction outer layer is adjusted. Based on 100 parts by mass of solid raw materials, the nutrient core raw material is 50 parts by mass, and the reaction outer layer raw material is 50 parts by mass.

[0039] In the nutrient core, the mass ratio of phosphorus-rich sludge incineration ash, agricultural and forestry waste biochar, and humification digestion residue is the same as in Example 1; in the reaction outer layer, the mass ratio of water treatment iron-aluminum sludge, carbonized steel slag, and desulfurization gypsum is the same as in Example 1. The phosphorus-activating bacteria loading, raw material particle size, moisture content of the nutrient core, moisture content of the coating material, number of coatings, curing temperature, and curing time are all the same as in Example 1.

[0040] In this embodiment, the proportion of the reaction outer layer in the total mass of the matrix is ​​increased to make the thickness of the resulting reaction outer layer 1.1 to 1.7 mm. The other conditions are the same as in Example 1.

[0041] Example 3: In this example, the mass ratio of the nutrient core to the reaction outer layer is adjusted. Based on 100 parts by mass of solid raw materials, the nutrient core raw material is 60 parts by mass, and the reaction outer layer raw material is 40 parts by mass.

[0042] The relative proportions of the components in the nutrient core and the reaction outer layer are the same as in Example 1. The phosphorus-activating bacteria loading and all preparation conditions are the same as in Example 1. This example only increases the proportion of the nutrient core in the total mass of the matrix, so that the thickness of the resulting reaction outer layer is 0.7-1.2 mm. All other conditions are the same as in Example 1.

[0043] Example 4: This example adjusts the mass ratio of each component in the nutrient core. Based on 55 parts by mass of nutrient core raw materials, it includes 27.5 parts by mass of phosphorus-rich sludge incineration ash, 16.5 parts by mass of agricultural and forestry waste biochar, and 11.0 parts by mass of humic digestion residue.

[0044] The composition and amount of raw materials for the outer reaction layer are the same as in Example 1. The total mass ratio of the nutrient core to the outer reaction layer is the same as in Example 1. The phosphorus-activating bacteria loading and all preparation conditions are the same as in Example 1. This example only increases the proportion of phosphorus-rich sludge incineration ash in the nutrient core; all other conditions are the same as in Example 1.

[0045] Example 5: This example adjusts the mass ratio of each component in the nutrient core. Based on 55 parts by mass of nutrient core raw materials, it includes 20.9 parts by mass of phosphorus-rich sludge incineration ash, 20.9 parts by mass of agricultural and forestry waste biochar, and 13.2 parts by mass of humification digestion residue.

[0046] The composition and amount of raw materials for the outer reaction layer are the same as in Example 1. The total mass ratio of the nutrient core to the outer reaction layer is the same as in Example 1. The phosphorus-activating bacteria loading and all preparation conditions are the same as in Example 1. This example only increases the proportion of agricultural and forestry waste biochar in the nutrient core; all other conditions are the same as in Example 1.

[0047] Example 6: In this example, the mass ratio of each component in the outer reaction layer is adjusted. Based on 45 parts by mass of the outer reaction layer raw materials, it includes 27.9 parts by mass of water treatment iron-aluminum sludge, 10.4 parts by mass of carbide steel slag, and 6.7 parts by mass of desulfurization gypsum.

[0048] The composition and dosage of the nutrient core raw materials are the same as in Example 1, the total mass ratio of the nutrient core to the outer reaction layer is the same as in Example 1, and the phosphorus-activating bacteria loading and all preparation conditions are the same as in Example 1. This example only increases the proportion of iron-aluminum sludge from water treatment in the outer reaction layer; all other conditions are the same as in Example 1.

[0049] Example 7: In this example, the mass ratio of each component in the outer reaction layer is adjusted. Based on 45 parts by mass of the outer reaction layer raw materials, it includes 22.5 parts by mass of water treatment iron-aluminum sludge, 14.4 parts by mass of carbide steel slag, and 8.1 parts by mass of desulfurization gypsum.

[0050] The composition and amount of the nutrient core raw materials are the same as in Example 1, the total mass ratio of the nutrient core to the outer reaction layer is the same as in Example 1, and the phosphorus-activating bacteria loading and all preparation conditions are the same as in Example 1. This example only increases the proportion of carbide steel slag and desulfurized gypsum in the outer reaction layer; all other conditions are the same as in Example 1.

[0051] Example 8: In this example, the loading of phosphorus-activating bacteria was adjusted. The number of viable phosphorus-activating bacteria per gram of agricultural and forestry waste biochar was 5.0 × 10⁻⁶. 8 indivual.

[0052] The composition, dosage, and particle size of each solid raw material are the same as in Example 1. The moisture content of the nutrient core molding, the moisture content of the coating material, the number of coatings, the curing temperature, and the curing time are also the same as in Example 1. This example only reduces the phosphorus-activating bacteria load; all other conditions are the same as in Example 1.

[0053] Example 9: In this example, the loading of phosphorus-activating bacteria was adjusted. The number of viable phosphorus-activating bacteria per gram of agricultural and forestry waste biochar was 1.2 × 10⁻⁶. 9 indivual.

[0054] The composition, dosage, and particle size of each solid raw material are the same as in Example 1. The moisture content of the nutrient core molding, the moisture content of the coating material, the number of coatings, the curing temperature, and the curing time are also the same as in Example 1. This example only increases the phosphorus-activating bacteria loading; all other conditions are the same as in Example 1.

[0055] Example 10: This example maintains the same composition, amount and phosphorus-activating bacteria load as Example 1, only adjusting the moisture content of the nutrient core before rolling molding from 38% to 32%.

[0056] The premixed moisture content, settling time, inoculation method, interface transition layer preparation method, coating material moisture content, coating times, curing temperature, and curing time of the agricultural and forestry waste biochar and humification digestion residue were all the same as in Example 1. The resulting nutrient core diameter was 4–6 mm, and the remaining conditions were the same as in Example 1.

[0057] Example 11: This example maintains the same composition, dosage and phosphorus-activating bacteria load as Example 1, except that the moisture content of the coating material formed by the iron-aluminum sludge, carbonized steel slag and desulfurization gypsum for water treatment is adjusted from 42% to 36%.

[0058] The preparation method of the nutrient core, the moisture content of the nutrient core molding, the preparation method of the interface transition layer, the number of coatings, the curing temperature, and the curing time are all the same as in Example 1. During the coating process, the method of three coatings and interlayer ventilation is still used, and the other conditions are the same as in Example 1.

[0059] Example 12: This example maintains the same composition and dosage of each solid raw material, the loading of phosphorus-activated bacteria, the nutrient core molding conditions, and the coating conditions as Example 1, except that the curing conditions after coating are adjusted from 35℃ for 24 hours to 30℃ for 36 hours.

[0060] After curing, the matrix was placed at room temperature for equilibration for 12 hours. The particle size and outer layer thickness of the resulting matrix were the same as in Example 1, and the other conditions were the same as in Example 1.

[0061] Comparative Example 1: This comparative example was not inoculated with phosphorus-activating bacteria. The composition and dosage of phosphorus-rich sludge incineration ash, agricultural and forestry waste biochar, humic digestion residue, water treatment iron and aluminum sludge, carbonized steel slag, and desulfurization gypsum were the same as in Example 1.

[0062] In preparation, an equal amount of water was added to the mixture of agricultural and forestry waste biochar and humification digestion residue instead of the phosphorus-activating bacteria solution. The conditions for nutrient core formation, interface transition layer formation, reaction outer layer coating, and solidification were the same as in Example 1. This comparative example only omits the phosphorus-activating bacteria; all other conditions are the same as in Example 1.

[0063] Comparative Example 2: This comparative example uses a conventional preparation method with uniform mixing. The composition and total amount of phosphorus-rich sludge incineration ash, agricultural and forestry waste biochar, humic digestion residue, water treatment iron and aluminum sludge, carbonized steel slag, and desulfurization gypsum are the same as in Example 1, and the phosphorus-activating bacteria loading is the same as in Example 1.

[0064] All solid raw materials were mixed at once, and phosphorus-activating bacteria solution was added. The moisture content was adjusted to 38%, and the mixture was directly rolled to form homogeneous particles with a diameter of 6-9 mm. The particles were then cured at 35°C for 24 hours. The resulting particles do not have a nutrient core, a reaction outer layer, or an interface transition layer; all components are uniformly dispersed within the particles. This comparative example only changes the spatial partitioning of each component; all other conditions are the same as in Example 1.

[0065] Comparative Example 3: This comparative example maintains the same composition and dosage of each solid raw material, the loading of phosphorus-activated bacteria, and the preparation conditions of the nutrient core as in Example 1, except that the moisture content of the coating material is adjusted to 58%.

[0066] The coating material was applied to the outer side of the nutrient core in three stages. The rolling and shaping time and ventilation time after each coating were the same as in Example 1, and the curing conditions were the same as in Example 1. The higher moisture content allowed the fine particles of iron-aluminum sludge from the water treatment to enter between the carbonized steel slag particles along with the liquid phase and form a relatively dense reaction outer layer after curing. The remaining conditions were the same as in Example 1.

[0067] Comparative Example 4: This comparative example maintains the same composition, dosage, phosphorus-activated bacteria load, and coating material moisture content as Example 1 for each solid raw material. However, after coating, the particles are compacted and shaped to make the mineral particles in the outer reaction layer tightly arranged, without retaining continuous main connecting holes and branch holes.

[0068] The preparation of the interface transition layer, the number of coatings, the curing temperature, and the curing time were all the same as in Example 1. This comparative example only omits the retention of the microporous channels; all other conditions are the same as in Example 1.

[0069] Test method: 1. Test soil and treatment method Compositely contaminated soil was selected as the test soil. After being naturally air-dried, the test soil was sieved through a 2mm sieve. Its initial pH was 6.42, and its lead content was 826 mg / kg, cadmium content was 8.35 mg / kg, arsenic content was 96.4 mg / kg, and chromium content was 184.7 mg / kg.

[0070] The substrates prepared in each example and comparative example were added to the soil at 5% of the dry weight of the tested soil, with three replicates for each treatment. Soil moisture content was maintained at 60% of field capacity, and the soil was incubated at 25°C for 60 days. Lost water was replenished every 7 days during the incubation period. After 30 days of incubation, five wet-dry cycles were performed, each cycle including natural water loss to 30% of field capacity and replenishment to restore 60% of field capacity.

[0071] 2. Detection Method After cultivation, the available lead and available cadmium in the soil were determined by diethylenetriaminepentaacetic acid extraction method, and the reduction rate of available content was calculated using synchronously cultivated soil without the addition of remediation matrix as a reference.

[0072] Soil leachate was prepared using a horizontal oscillating leaching method. The arsenic and chromium contents in the leachate were measured, and the leaching concentration reduction rate was calculated using synchronously cultured soil without the addition of remediation matrix as a reference.

[0073] After culture, the substrate particles were collected, the nutrient cores were broken, and serial dilutions and plate counts were performed to determine the viable count of phosphorus-activated bacteria. The viable count was calculated after 60 days, using the initial viable count at the end of preparation as a baseline.

[0074] Matrix particles that have completed 5 wet-dry cycles were randomly selected, and cut open along the center of the particle. The proportion of the interface length in which the nutrient core and the reaction outer layer are continuously bonded to the total interface length was counted as the interface integrity rate.

[0075] Soil pH was measured every 5 days during the cultivation period, and the difference between the highest and lowest values ​​measured within 60 days for each treatment was taken as the pH fluctuation range.

[0076] The test results are shown in Table 1.

[0077] Table 1 Performance test results of each embodiment and comparative example

[0078] In Example 1, phosphorus-rich sludge incineration ash, agricultural and forestry waste biochar, humification digestion residue, and phosphorus-activating bacteria are concentrated in the nutrient core, while iron-aluminum sludge from water treatment, carbonized steel slag, and desulfurized gypsum are concentrated in the outer reaction layer. The phosphorus-activating bacteria remain attached to the humic film layer and biochar pores, maintaining release gaps between the phosphorus-containing mineral particles and the bacterial attachment interface, allowing the bioactivation of the phosphorus-containing mineral phase to occur within the nutrient core. The iron-aluminum and calcareous mineral phases in the outer reaction layer are connected to the nutrient core through microporous channels, enabling the soil solution to migrate between different reaction zones. Example 1 exhibits high fixation levels for lead, cadmium, arsenic, and chromium, while maintaining a 78.4% viable count of phosphorus-activating bacteria and a 94.5% interface integrity rate, indicating that this formulation and hierarchical structure achieve a relatively balanced state between pollutant fixation, bacterial cell maintenance, and particle structure stability.

[0079] In Example 2, increasing the proportion of the outer reaction layer resulted in a reduction rate of 61.8% for arsenic leaching and 58.4% for chromium leaching, higher than in Example 1. This change corresponds to the increased relative amount of iron-aluminum sludge in the substrate for water treatment. Due to the decreased proportion of the nutrient core, the reduction rates of lead and cadmium bioavailability and the retention rate of phosphorus-activated bacteria were slightly lower than in Example 1, indicating that the increased proportion of the outer reaction layer mainly enhanced the contact between anionic pollutants and the iron-aluminum mineral phase.

[0080] In Example 3, increasing the proportion of the nutrient core resulted in a 76.2% and 66.1% reduction in the bioavailable forms of lead and cadmium, respectively, while maintaining an 80.1% viable phosphorus-activating bacteria rate. This result corresponds to the increase in the total amount of phosphorus-rich sludge incineration ash, biochar porosity, and humic digestion residue in the nutrient core. Decreasing the proportion of the outer reaction layer led to a lower reduction in arsenic and chromium leaching rates compared to Example 1, indicating that the mass ratio of the nutrient core to the outer reaction layer alters the fixed emphasis of different pollutant components.

[0081] In Example 4, increasing the proportion of phosphorus-rich sludge incineration ash resulted in a reduction rate of 77.0% for lead and 66.8% for cadmium biomass, higher than in Example 1. However, the viable bacteria retention rate and interface integrity rate decreased. These results indicate that increasing the phosphate rock phase expands the contact area between phosphorus-activating bacteria and phosphate rock phase particles. However, the relative reduction in biochar and humic digestion residue leads to a corresponding decrease in the space for bacterial attachment and the organic matter interface.

[0082] In Example 5, after increasing the proportion of biochar in agricultural and forestry waste, the retention rate of phosphorus-activated bacteria and the interface integrity rate reached 82.6% and 95.7%, respectively, and the pH fluctuation range decreased to 0.33. The increase in the proportion of biochar increased the surface area of ​​the interconnected pore skeleton and bacterial attachment in the nutrient core, but the relative proportion of phosphorus-rich sludge incineration ash decreased, so the reduction rate of available lead and cadmium was lower than that in Example 1.

[0083] In Example 6, after increasing the proportion of iron-aluminum sludge in the water treatment process, the reduction rates of arsenic leaching and chromium leaching reached 64.3% and 60.8%, respectively, which are among the highest levels in the examples. This result indicates that increasing the proportion of continuous iron-aluminum mineral phases increases the number of mineral interfaces available for arsenic and chromium contact in the outer reaction layer. Example 6 maintained a 94.8% interface integrity rate, demonstrating that adjusting the proportion of iron-aluminum sludge in the water treatment process did not disrupt the connection between the outer reaction layer and the nutrient core.

[0084] In Example 7, increasing the proportion of carbide steel slag and desulfurized gypsum reduced the pH fluctuation to 0.29, and decreased the effective forms of lead and cadmium by 75.5% and 65.7%, respectively. The increased calcareous mineral enrichment zone formed on the outer side of the reaction layer by carbide steel slag and desulfurized gypsum stabilized the buffer state of the mineral reaction interface. After the relative decrease in the proportion of iron-aluminum sludge in the water treatment, the reduction rates of arsenic and chromium leaching were slightly lower than in Example 1.

[0085] In Example 8, after reducing the phosphorus-activating bacteria load, the viable bacteria retention rate decreased to 64.8%, and the reduction rates of lead and cadmium availability decreased to 69.2% and 58.7%, respectively. The reduction rates of arsenic and chromium leaching showed little change, indicating that the phosphorus-activating bacteria load mainly affects the activation process of the phosphorus-containing mineral phase in the nutrient core, while the fixation of arsenic and chromium in the outer reaction layer is still undertaken by the iron-aluminum mineral phase.

[0086] In Example 9, after increasing the phosphorus-activating bacteria load, the viable cell retention rate reached 81.7%, and the reduction rate of lead and cadmium effective states was higher than that in Example 8. The data are similar to those in Example 1, indicating that as the initial bacterial count continues to increase, the pores of the nutrient core and the humic membrane layer gradually approach a stable state in terms of bacterial load capacity, and the increase in bacterial load does not cause a proportional change in any of the indicators.

[0087] In Example 10, after adjusting the moisture content of the nutrient core molding to 32%, the fixed indices of lead, cadmium, arsenic, and chromium remained at high levels, but the interface integrity rate decreased to 91.6%. The lower molding moisture content slightly reduced the bonding between nutrient core particles, and a small number of interface cracks appeared after wet-dry cycles. This result indicates that when the moisture content of the nutrient core molding varies within a certain range, the matrix can still maintain its basic zoning structure and repair performance.

[0088] In Example 11, after adjusting the moisture content of the coating material to 36%, the outer reaction layer could still be formed, but the interface integrity rate and the reduction rate of arsenic and chromium leaching were lower than in Example 1. After reducing the moisture content of the coating material, the continuity of the coating of the iron-aluminum sludge in the water treatment onto the surface of the carbide steel slag particles and the nutrient core decreased, and the degree of bonding between local mineral phases decreased accordingly.

[0089] Example 12 was cured at 30℃ for 36 hours, and its various indicators were similar to those of Example 1, with an interface integrity rate of 95.0% and a viable cell retention rate of 79.1% for phosphorus-activated bacteria. These results indicate that under conditions of lower curing temperature and extended curing time, the outer reaction layer can be solidified, and the bacteria in the nutrient core can maintain their activity. The preparation method described has a certain degree of adaptability to curing conditions.

[0090] After removing phosphorus-activating bacteria in Comparative Example 1, the reduction rates of available lead and cadmium forms decreased to 51.8% and 42.6%, respectively, significantly lower than in Example 1, while the reduction rates of arsenic and chromium leaching remained at 56.7% and 53.0%, respectively. This difference indicates that the outer reaction layer composed of iron-aluminum sludge, carbonized steel slag, and desulfurized gypsum in water treatment can still bear some arsenic and chromium fixation. However, without phosphorus-activating bacteria, the phosphorus-containing mineral phase in the phosphorus-rich sludge incineration ash lacks a biological activation process, and the synergy between the nutrient core and the outer reaction layer decreases.

[0091] In Comparative Example 2, after adopting a uniform mixing structure, the fixed indices of lead, cadmium, arsenic, and chromium were all at the lowest levels among the samples, the viability retention rate of phosphorus-activating bacteria decreased to 33.8%, and the pH fluctuation range increased to 1.32. With all components in direct contact within the same area, the phosphorus-rich sludge incineration ash, iron-aluminum mineral phase, calcareous mineral phase, and phosphorus-activating bacteria lacked spatial partitioning, and the phosphorus activation process and mineral reaction process occurred simultaneously in the same pore environment. These results indicate that simply maintaining the same composition while eliminating the nutrient core, reaction outer layer, and interfacial transition layer cannot achieve the comprehensive indices of Example 1.

[0092] In Comparative Example 3, after increasing the moisture content of the coating material to 58%, the outer reaction layer tended to be denser during the curing process. The fixation indices of lead, cadmium, arsenic, and chromium were all lower than in Example 1, and the viability retention rate of phosphorus-activating bacteria decreased to 59.6%. With the reduction in the number of micropores in the outer reaction layer, the migration of substances between the nutrient core and the external soil was restricted. Soil moisture could not fully enter the nutrient core, and the migratory components generated by the nutrient core could not easily pass through the outer reaction layer.

[0093] In Comparative Example 4, even without retaining the main connecting pores and branch pores, the interface integrity rate still reached 92.6%, but the contaminant fixation index and the retention rate of phosphorus-activated bacteria were both lower than in Example 1. This result indicates that maintaining particle integrity does not equate to maintaining normal material exchange between the inner and outer layers. After the microporous channels were compacted, the bio-activated region in the nutrient core and the mineral reaction region in the reaction outer layer could not form a continuous migration path.

[0094] The comparison between Example 1 and Comparative Examples 1, 2, 3, and 4 shows that the spatial partitioning of the phosphorus-activating bacteria, the nutrient core and the reaction outer layer, the interface transition layer, and the connecting microporous channels each play a different role, and the absence of any one of these roles will cause a decrease in some indicators. The nutrient core concentrates phosphorus-rich sludge incineration ash, agricultural and forestry waste biochar, humification digestion residue, and phosphorus-activating bacteria in a relatively stable porous environment. The reaction outer layer organizes iron-aluminum sludge from water treatment, carbonized steel slag, and desulfurization gypsum into a continuous mineral reaction interface. The microporous channels maintain limited connectivity between the two types of regions. The comprehensive results obtained when all the techniques are used together are higher than those obtained when the same components are uniformly mixed or when only a portion of the structure is retained, indicating that the partitioned composite structure produces a synergistic effect that goes beyond the simple superposition of the components.

Claims

1. A solid waste-based soil ecological remediation substrate, characterized in that, It includes a nutrient core and a reaction outer layer covering the outside of the nutrient core; The nutrient core includes phosphorus-rich sludge incineration ash, agricultural and forestry waste biochar, humification digestion residue, and phosphorus-activating bacteria fixed in the pores of the agricultural and forestry waste biochar. The outer reaction layer comprises water treatment iron-aluminum sludge, carbonized steel slag, and desulfurization gypsum, and has microporous channels communicating with the nutrient core.

2. The solid waste-based soil ecological remediation substrate according to claim 1, characterized in that, The phosphorus-rich sludge incineration ash consists of mutually separated phosphorus-containing mineral phase particles, the agricultural and forestry waste biochar forms a through-pore framework, the humification digestion residue fills the space between the through-pore framework and the phosphorus-containing mineral phase particles, and the phosphorus-activating bacteria attach to the pore walls of the through-pore framework and are distributed at the organic matter interface formed by the humification digestion residue.

3. The solid waste-based soil ecological remediation substrate according to claim 1, characterized in that, The iron-aluminum sludge used for water treatment forms a continuous iron-aluminum mineral phase in the outer reaction layer. The carbide steel slag is embedded in the continuous iron-aluminum mineral phase as discrete particles. The desulfurized gypsum is dispersed at the contact interface between the continuous iron-aluminum mineral phase and the discrete particles. The microporous channels pass through the continuous iron-aluminum mineral phase and are arranged around the outer periphery of the discrete particles.

4. The solid waste-based soil ecological remediation substrate according to claim 1, characterized in that, An interface transition layer is provided between the nutrient core and the reaction outer layer. The interface transition layer includes an inner porous phase formed by the agricultural and forestry waste biochar and an outer mineral phase formed by the water treatment iron-aluminum sludge. The inner porous phase and the outer mineral phase are interlocked, and the pores in the interface transition layer are respectively connected to the pores of the nutrient core and the micropore channels.

5. The solid waste-based soil ecological remediation substrate according to claim 1, characterized in that, The microporous channel includes a main connecting hole extending radially along the outer reaction layer and a diversion hole extending circumferentially along the outer reaction layer. The diversion hole intersects with the adjacent main connecting hole. The orifices of the main connecting hole are staggered on the inner and outer surfaces of the outer reaction layer. The iron-aluminum sludge, carbonized steel slag, and desulfurized gypsum used for water treatment together form the pore walls of the main connecting hole and the diversion hole.

6. The solid waste-based soil ecological remediation substrate according to claim 2, characterized in that, The pore walls of the agricultural and forestry waste biochar are covered with a humic membrane layer formed by the humification digestion residue. The phosphorus-activating bacteria are fixed on the surface of the humic membrane layer in the form of a biofilm. The phosphorus-containing mineral phase particles are embedded between adjacent agricultural and forestry waste biochar, and a release gap is maintained between the phosphorus-containing mineral phase particles and the humic membrane layer to connect to the outer reaction layer.

7. The solid waste-based soil ecological remediation substrate according to claim 3, characterized in that, The continuous iron-aluminum mineral phase forms an iron-aluminum enrichment zone on the side near the nutrient core, and the carbide steel slag and the desulfurized gypsum form a calcareous mineral enrichment zone on the side near the outer surface of the reaction outer layer. The iron-aluminum enrichment zone and the calcareous mineral enrichment zone form a mutually penetrating mixed zone, and the microporous channel passes through the iron-aluminum enrichment zone, the mixed zone and the calcareous mineral enrichment zone in sequence.

8. The solid waste-based soil ecological remediation substrate according to claim 4, characterized in that, The interface transition layer includes, in radial order, an inner bonding zone, a middle interpenetrating zone, and an outer bonding zone. The inner bonding zone is formed by the interweaving of the agricultural and forestry waste biochar and the humification digestion residue. The outer bonding zone is formed by the solidification of the water treatment iron-aluminum sludge and the fine particles of the carbonized steel slag. The middle interpenetrating zone contains interlaced biochar branches and iron-aluminum mineral branches.

9. The solid waste-based soil ecological remediation substrate according to claim 5, characterized in that, The main connecting hole is formed by sequentially connecting a diffusion hole section near the nutrient core, a bend hole section located in the middle of the outer reaction layer, and an exchange hole section penetrating the outer surface of the outer reaction layer. The diversion hole connects adjacent bend hole sections. The desulfurized gypsum is distributed around the orifices of the diffusion hole section and the exchange hole section. The water treatment iron-aluminum sludge is distributed on the pore wall of the bend hole section.

10. A method for preparing a solid waste-based soil ecological remediation substrate, characterized in that, include: Phosphorus-rich sludge incineration ash, agricultural and forestry waste biochar, and humification digestion residue are combined, and phosphorus-activating bacteria are inoculated and fixed into the pores of the agricultural and forestry waste biochar to form a nutrient core. Iron-aluminum sludge from water treatment, carbonized steel slag, and desulfurized gypsum are made into a coating material. The coating material is then applied to the outside of the nutrient core, and microporous channels communicating with the nutrient core are formed in the coating material. The mixture is then solidified to obtain the solid waste-based soil ecological restoration matrix.

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