Sludge in-situ solidification-nitrogen and phosphorus removal dual-function coupling material as well as preparation method and application thereof

Abstract

The invention discloses a sludge in-situ solidification-nitrogen and phosphorus removal dual-function coupling material as well as a preparation method and application thereof, and belongs to the technical field of water pollution control. In-situ sludge is used as a core base material, and is matched with a multi-source mineral-based gelling agent, a composite nitrogen and phosphorus removal functional filler, modified biomass fibers and an ecological adjuvant. A steel slag / fly ash-based gelling system reacts with an alkaline activator to form a compact skeleton, and modified fibers construct a three-dimensional bridging network to improve the crack resistance; the composite functional filler realizes triple purification of physical adsorption, chemical precipitation and biodegradation: zeolite adsorbs ammonia nitrogen, Fe-K-CT iron-carbon filler performs micro-electrolysis oxidation on pollutants and releases iron ions to precipitate phosphate, and a carbon source is slowly released to maintain denitrification. The material can be prefabricated into a riverway revetment module, an ecological filter dam component or a wetland foundation cushion layer, in-situ resource utilization of sludge and synchronous improvement of a water ecological function are achieved, the engineering cost is remarkably reduced, and ecological system restoration is promoted.

Description

Technical Field

[0001] This invention relates to the field of water pollution control technology, specifically to a dual-functional coupled material for in-situ solidification of sludge, nitrogen and phosphorus removal, its preparation method, and its application. Background Technology

[0002] Current aquatic ecological governance and engineering construction face three major challenges. First, there is immense pressure from sludge disposal. The amount of sludge accumulating at the bottom of rivers and wetlands is increasing. The traditional "dredging-transportation-landfilling" model not only occupies valuable land resources but also easily causes secondary pollution, and the costs of dredging, transportation, and subsequent disposal remain high. Second, engineering materials cannot keep up with ecological needs. Traditional structural materials like concrete and masonry must be produced off-site and transported long distances to the construction site, increasing costs and disrupting the ecological connection between land and water, rendering them ineffective in purifying water. Finally, the limited functionality leads to compounded costs. Materials specifically designed for nitrogen and phosphorus removal, such as filter media and floating islands, require additional installation and cannot be integrated with structural support materials, increasing both project complexity and costs significantly.

[0003] Patent CN118495771A discloses a slow-release material and method for sludge treatment. By coating the surface of an iron-carbon micro-electrolysis packing material with a water-soluble slow-release membrane, it slowly releases ferrous ions from the sludge, thereby catalyzing and activating persulfate to generate free radicals, achieving the oxidative degradation of nitrogen-containing organic matter. Simultaneously, ferric ions react with phosphate to form ferric phosphate precipitate, achieving the simultaneous removal of nitrogen, phosphorus, and heavy metals. While this method possesses a certain nitrogen and phosphorus removal capability, its core is an additive slow-release agent, without addressing the structural forming or mechanical property construction of the material. Therefore, it cannot be used as an engineering structure and is not suitable for in-situ solidification applications.

[0004] Currently, there is considerable research in the industry on the preparation of denitrification or phosphorus removal materials from sludge resources, but there are still significant shortcomings in the integration of material functions. On the one hand, while slow-release reagents can achieve purification through chemical reactions, they lack structural support and cannot be solidified in situ. On the other hand, pyrolytic carbon-based adsorbents have good phosphorus removal effects, but their preparation process is energy-intensive, and they are all in powder form, making it difficult to meet the requirements of mechanical properties and ease of construction in engineering applications. More importantly, neither of these technologies has been able to combine the functions of "in-situ solidification" and "denitrification and phosphorus removal" within the same material system. This results in the need for separate structural construction and water purification in actual engineering projects, increasing both system complexity and overall cost. Therefore, there is an urgent need to develop a material that can be solidified in situ under normal or low-temperature conditions, possessing both sufficient mechanical strength and efficient denitrification and phosphorus removal capabilities. Through this dual-functional integrated material, the goal of simultaneously improving the on-site resource utilization of sludge and the aquatic ecological function can be achieved. Summary of the Invention

[0005] One of the objectives of this invention is to provide a dual-functional coupled material for in-situ solidification of sludge and denitrification and phosphorus removal, which solves the problems of high cost of sludge transportation and disposal, separation of engineering structure and ecological function, and system redundancy caused by the need for independent construction of denitrification and phosphorus removal units in traditional technologies.

[0006] The second objective of this invention is to provide a method for preparing a dual-functional coupled material for in-situ solidification, denitrification, and phosphorus removal of sludge, which is used to prepare the aforementioned dual-functional coupled material for in-situ solidification, denitrification, and phosphorus removal of sludge.

[0007] The third objective of this invention is to apply a dual-functional coupled material for in-situ solidification, denitrification, and phosphorus removal of sludge in riverbank protection modules, ecological filter dam components, and wetland foundation cushion layers.

[0008] In a first aspect, the present invention provides a dual-functional coupling material for in-situ solidification of sludge and denitrification and phosphorus removal. The raw material composition, based on in-situ sludge by mass percentage, includes the following components: 60%~75% in-situ sludge, 15%~25% multi-source mineral-based gelling agent, 5%~10% composite denitrification and phosphorus removal functional filler, 3%~6% modified biomass fiber, and 1%~3% ecological auxiliary agent.

[0009] Furthermore, the in-situ sludge is river or wetland sediment with a moisture content of 65% to 85%, and is screened on-site to remove impurities with a particle size greater than 20 mm. The 65% to 85% moisture content of the in-situ sludge ensures plasticity and gelation reactivity, while screening to remove impurities >20 mm avoids structural stress concentration.

[0010] Furthermore, the multi-source mineral-based cementitious agent is composed of 40% steel slag, 30% fly ash, 20% alkaline activator, and 10% penetrating crystallizer. In the multi-source mineral-based cementitious agent, the steel slag / fly ash depolymerizes the silica-alumina components through the alkaline activator to generate CSH gel, and the penetrating crystallizer fills the micropores to improve density.

[0011] Furthermore, the composite denitrification and phosphorus removal functional packing is composed of 30% zeolite powder, 25% Fe-K-CT iron-carbon packing, 25% modified ceramsite, and 20% slow-release carbon source. The composite denitrification and phosphorus removal functional packing adsorbs ammonia nitrogen through zeolite ion exchange, generates ·OH through Fe-K-CT micro-electrolysis to oxidize pollutants, and releases Fe... 2+ Precipitated phosphates and modified ceramsite reinforced PO4 3- Coordination adsorption and slow-release carbon source maintain the electron donor for denitrification.

[0012] Furthermore, the modified biomass fiber is straw fiber that has been soaked in 5wt% NaOH solution for 30 min, then treated with 1wt% silane coupling agent KH550 ethanol solution for 1 h, dried, and cut to a length of 8-10 mm. The modified biomass fiber is treated with NaOH to remove hemicellulose and improve surface activity, and the silane coupling agent forms -Si-O-Me chemical bonds to enhance the interfacial bonding force with the inorganic matrix.

[0013] Furthermore, the ecological auxiliary agent consists of 0.5%~1.5% water-retaining agent and 0.5%~1.5% compound microbial agent, wherein the compound microbial agent is a mixture of nitrifying bacteria, denitrifying bacteria and polyphosphate-accumulating bacteria in a volume ratio of 1:1:1, and the concentration of live bacteria is not less than 1×10⁻⁶. 8 CFU / g. The water-retaining agent in the ecological auxiliary agent maintains pore moisture through high water absorption, while the compound microbial agent synergistically completes nitrification (NH4+) in a 1:1:1 ratio. + →NO3 - ), denitrification (NO3) - →N2), polyphosphate (excess phosphorus uptake) nitrogen-phosphorus conversion closed loop.

[0014] Furthermore, by using in-situ sludge as the core substrate, a dense framework is formed through depolymerization-condensation reaction with a multi-source mineral-based coagulant. Simultaneously, modified biomass fibers are introduced to construct a three-dimensional bridging network, enhancing crack resistance. The composite denitrification and phosphorus removal functional filler forms a triple purification pathway within the material: physical adsorption, chemical precipitation, and biodegradation. Water-retaining agents in the ecological auxiliary agent maintain pore moisture, while composite microbial agents colonize the porous carrier surface and continuously metabolize nitrogen and phosphorus pollutants. The multi-source mineral-based coagulant utilizes industrial solid waste to replace cement, reducing carbon emissions. The modified biomass fibers undergo alkali-silane dual treatment to enhance interfacial bonding with the inorganic matrix. The Fe-K-CT iron-carbon filler spontaneously forms micro-galvanic cells in the aquatic environment, releasing Fe... 2+ / Fe 3+It participates in phosphate precipitation; the slow-release carbon source provides a continuous electron donor for the denitrification process; the compound microbial agent forms a biofilm in the pores of the material, realizing the full conversion of nitrogen.

[0015] Furthermore, the alkaline activator is composed of water glass and sodium hydroxide mixed at a mass ratio of 3:1; the penetrating crystallizer is composed of sodium silicate and activated silica micropowder compounded at a mass ratio of 2:1. The slow-release carbon source is polyhydroxyalkanoate (PHA) particles with a particle size of 0.5~1.5mm; the water-retaining agent is sodium polyacrylate crosslinked resin with a water absorption ratio ≥300g / g. Water glass and NaOH synergistically activate the active silica-alumina components in steel slag and fly ash; sodium silicate and active SiO2 generate CSH and NASH gels in the capillary channels to block the pores; PHA particles slowly hydrolyze and release organic acids as a denitrification carbon source; sodium polyacrylate repeatedly absorbs and releases water in the dry-wet cycle to maintain the humidity environment required for microbial activity.

[0016] Furthermore, the Fe-K-CT iron-carbon filler is prepared by mechanically ball milling zero-valent iron filings, activated carbon, and potassium feldspar powder at a mass ratio of 5:3:2 for 2 hours, followed by heat treatment at 300℃ under a nitrogen atmosphere for 1 hour; the modified ceramsite is obtained by impregnating commercially available ceramsite with a 1mol / L FeCl3 solution for 12 hours and then drying it at 60℃. The iron-carbon micro-electrolysis system utilizes Fe... 0 →Fe 2+ +2e - O2 + 2H2O + 4e - →4OH - The reaction produces ·OH radicals that oxidize ammonia nitrogen and release iron ions to precipitate phosphate; Fe 3+ Modified ceramsite reinforces PO4 3- Its coordination adsorption capacity.

[0017] Furthermore, the composite microbial agent is fixed using a sodium alginate-chitosan double-layer encapsulation method: first, the bacterial solution is mixed with 2% sodium alginate solution at a ratio of 1:4 and dropped into a 0.1 mol / L CaCl2 solution to form gel beads, which are then immersed in a 1% chitosan acetate solution for cross-linking for 10 min, and vacuum dried at 40°C until the moisture content is ≤10%. This encapsulation structure protects the bacteria from the initial high pH gelation environment and allows the material to slowly swell and release active bacteria after contact with water.

[0018] Secondly, a method for preparing a dual-functional coupled material for in-situ sludge solidification, nitrogen and phosphorus removal includes the following steps: S1. In-situ sludge pretreatment: Treat river or wetland bottom sludge using a 20mm mesh screen; if the moisture content is >75%, add 5%~10% fly ash by weight of sludge to adjust; if the moisture content is <65%, spray deionized water to bring the moisture content to 65%~75%; S2. Dry material premixing: Mix multi-source mineral-based gelling agent, composite denitrification and phosphorus removal functional filler and modified biomass fiber at 30 r / min speed for 2 min to obtain pretreated sludge; S3. Wet material mixing: Pretreated sludge and ecological additives are mixed at 60 r / min for 3-5 min to obtain a castable slurry; S4. In-situ molding: Inject the castable grout into the precast mold and vibrate for 30-60 seconds, then cover the surface with geotextile to keep it moist. S5. Natural curing: Allow to stand for 7-10 days at an ambient temperature ≥10℃, spray with clean water once in the morning and once in the evening. After the curing period, remove the mold to obtain the dual-function coupling material.

[0019] Furthermore, the composite denitrification and phosphorus removal functional filler is added in two steps in step S2: first, zeolite powder and modified ceramsite are added and stirred for 1 minute, and then Fe-K-CT iron-carbon filler and slow-release carbon source are added and stirred for 1 minute to avoid premature contact of the iron-carbon filler with moisture and triggering a pre-reaction.

[0020] Furthermore, the mold is prefabricated into the shape of a riverbank protection module, an ecological filter dam component, or a wetland foundation cushion layer, depending on the application scenario.

[0021] Furthermore, the resulting bifunctional material forms a composite framework of "sludge particles-gel network-fiber bridging" within its interior, with functional fillers and colonizing microorganisms distributed within the pores. When water flows through the material's pores, ammonia nitrogen is captured by zeolite ion exchange, and phosphate is absorbed by Fe... 3+ Modified ceramsite adsorbs and converts nitrates into FePO4 precipitate. Nitrate is reduced to nitrogen by denitrifying bacteria with the support of a slow-release carbon source (PHA). Polyphosphate-accumulating bacteria excessively absorb phosphorus under alternating wet and dry conditions and enter the sedimentary phase along with biofilm renewal. This material eliminates the need for sludge transportation, prefabricated component transport, and separate purification facilities, achieving integrated in-situ construction of engineering structure and ecological function.

[0022] Thirdly, the application of a dual-functional coupled material for in-situ solidification, denitrification, and phosphorus removal of sludge in riverbank protection modules, ecological filter dam components, and wetland foundation cushion layers.

[0023] In the application of riverbank protection modules, the material is made into a hexahedral module with dimensions of 500mm×300mm×200mm. The water-facing side is provided with a vegetation trough with an inclination angle of 15°~25°, a trough depth of 50~80mm and a width of 60~100mm. The side of the module is provided with a trapezoidal tenon and mortise structure. The internal porosity of the component is ≥25%, and the pore diameter is 2~8mm, ensuring space for water exchange and microbial attachment. In the application of ecological filter dam components, the material is made into a porous block with an external size of 400mm×400mm×300mm and an internal porosity of ≥30%. The channels are in a three-dimensional interconnected network structure. When stacked, they are joined by staggered joints. After stacking, they form the main body of the filter dam. When water flows from top to bottom or horizontally through the filter dam, it undergoes a triple purification process of physical adsorption, chemical precipitation and biodegradation. In its application in wetland foundation cushion layers, the material is made into a sheet structure with a thickness of 15-20cm, laid at the bottom of the wetland as a bearing layer, with a compressive strength of not less than 2.5MPa. Before laying, the original soil compaction degree is ≥90%, and the joints of the cushion layer are treated with grout of the same proportion. At the same time, the functional filler and microbial system inside the material simultaneously intercept and transform nitrogen and phosphorus pollutants in infiltrated rainwater or wetland water.

[0024] The beneficial effects of this invention are: (1) The sludge in-situ solidification-denitrification and phosphorus removal dual-function coupled material of the present invention is characterized in that the raw material composition, based on the in-situ sludge as a mass percentage, includes: 60%~75% in-situ sludge, 15%~25% multi-source mineral-based gelling agent, 5%~10% composite denitrification and phosphorus removal functional filler, 3%~6% modified biomass fiber, and 1%~3% ecological auxiliary agent. This proportion design achieves the on-site resource utilization of river / wetland sediment through the high proportion of in-situ sludge, avoiding land occupation and secondary pollution caused by off-site transportation and landfill. At the same time, the multi-source mineral-based gelling agent and modified biomass fiber work together to form a dense mechanical skeleton and maintain high porosity. The composite denitrification and phosphorus removal functional filler constructs a triple purification path of physical adsorption-chemical precipitation-biodegradation. The ecological auxiliary agent ensures the activity of microorganisms, so that the material can simultaneously achieve structural support and efficient denitrification and phosphorus removal during in-situ molding at room temperature. This completely eliminates the system redundancy of traditional technology where structural materials and purification functions are separated and denitrification and phosphorus removal units need to be constructed independently, reducing the overall cost and promoting the restoration of aquatic ecosystems.

[0025] (2) The synergistic effect of this invention is reflected in the entire process of material composition, preparation and application. Each component forms a synergistic mechanism through interfacial bonding, chemical reaction and biological interaction. The in-situ sludge and the cementation system form a dense skeleton through chemical reaction. The modified biomass fiber constructs a three-dimensional bridging network to improve crack resistance, while retaining suitable interconnected pores, taking into account both mechanical strength and pore structure requirements. The composite denitrification and phosphorus removal functional filler works synergistically through adsorption, micro-electrolysis oxidation, chemical precipitation and other effects, combined with the supply of slow-release carbon source, to form a complementary physicochemical purification pathway. The water-retaining agent in the ecological auxiliary agent and the embedded and fixed composite bacterial agent cooperate with each other to maintain the environment required for microbial survival, promote the biodegradation process, and achieve a joint improvement of physicochemical purification and biological purification.

[0026] (3) This collaborative design in the present invention enables the material to be applied to scenarios such as riverbank protection, ecological filter dams, and wetland foundation treatment. In practical applications, the material can not only provide structural support as an engineering component, but also intercept and transform nitrogen and phosphorus pollutants through an internal purification system, while relying on vegetation planting and microbial colonization to build an ecological interaction system. This technology eliminates the need for sludge transportation and prefabricated component transportation, realizing the integrated in-situ construction of engineering structures and ecological functions, and reducing overall costs. Detailed Implementation

[0027] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0028] Example 1

[0029] This embodiment provides a dual-functional coupled material for in-situ sludge solidification, nitrogen and phosphorus removal, which is prepared through the following steps: S1. In-situ sludge pretreatment: Take 100 kg (wet weight) of riverbed sediment and screen it using a 20 mm aperture vibrating screen (power 1.5 kW, vibration frequency 50 Hz) to remove impurities such as gravel, dead branches, and plastic, and collect 85 kg of sludge that passes through the screen; the moisture content is measured to be 70% using an infrared moisture analyzer, i.e., 25.5 kg of dry sludge and 59.5 kg of water. Take 70 kg of pretreated sludge for later use (21 kg dry basis, 49 kg water). S2, Dry Material Premixing: S2.1 Preparation of Multi-Source Mineral-Based Cementitious Agent: Based on a total usage of 20 kg, weigh out 8 kg of steel slag, 6 kg of fly ash, 4 kg of alkaline activator, and 2 kg of penetrating crystallizer. Among them, 3 kg of alkaline activator is prepared by mixing water glass and 1 kg of sodium hydroxide and stirring at 200 r / min for 5 min, and the penetrating crystallizer is prepared by mixing and grinding 1.33 kg of sodium silicate and 0.67 kg of active silica micro powder to a fineness of 200 mesh. Put the above four components into a double helical conical mixer and mix at 30 r / min for 10 min to obtain the multi-source mineral-based cementitious agent. S2.2 Preparation of composite denitrification and phosphorus removal functional filler: The dosage of each component is as follows: zeolite powder 30%, Fe-K-CT iron-carbon filler 25%, modified ceramsite 25%, and slow-release carbon source 20%; the preparation details of each component are as follows: Fe-K-CT iron-carbon filler: Weigh 0.875 kg of zero-valent iron filings, 0.525 kg of activated carbon, and 0.35 kg of potassium feldspar powder, put them into a planetary ball mill at a ball-to-material ratio of 3:1, use alumina balls as the grinding medium, and mechanically ball mill at a speed of 200 r / min for 2 h. Then transfer it to a tube furnace and heat treat it at 300℃ for 1 h in a nitrogen atmosphere. After cooling to room temperature, pass it through a 100-mesh sieve to obtain Fe-K-CT iron-carbon filler. Modified ceramsite: Take 1.75 kg of commercially available ceramsite (particle size 2~5 mm), immerse it in 1 mol / L FeCl3 solution at a solid-liquid ratio of 1:15, soak it in a constant temperature water bath at 25℃ for 12 h, and after soaking, dry it at 60℃ to constant weight (weight loss of 0.5%) to obtain modified ceramsite. The slow-release carbon source is polyhydroxyalkanoate (PHA) particles with a particle size of 0.5~1.5mm; S2.4, Material Mixing First, 70 kg of pretreated in-situ sludge was added to a mixer and stirred at 30 r / min for 1 min. Then, 20 kg of multi-source mineral-based coagulant was added and stirred for another 2 min. Subsequently, composite denitrification and phosphorus removal functional filler was added in batches: the first batch consisted of 2.1 kg of zeolite powder and 1.75 kg of modified ceramsite, stirred at 30 r / min for 1 min; the second batch consisted of 1.75 kg of Fe-K-CT iron-carbon filler and 1.4 kg of slow-release carbon source, stirred at 30 r / min for 1 min; finally, 4 kg of modified biomass fiber was added and dry-mixed at 30 r / min for 1 min to obtain the pretreated sludge mixture. S3, Wet material mixing: S3.1 Preparation of ecological auxiliary agents: Based on a total usage of 2kg, weigh out 1kg of water-retaining agent (sodium polyacrylate crosslinking resin, water absorption ratio 350g / g) and 1kg of compound microbial agent; the compound microbial agent is prepared as follows: Microbial culture preparation: Take 333.3 mL each of nitrifying bacteria culture, denitrifying bacteria culture, and polyphosphate-accumulating bacteria culture (volume ratio 1:1:1), mix them to obtain 1 L of composite bacterial culture, with a viable bacteria concentration of 2 × 10⁻⁶. 8 CFU / g; Double-layer encapsulation: 1 L of composite bacterial solution and 4 L of 2 wt% sodium alginate solution were mixed and stirred at 150 r / min for 10 min to obtain a mixture. The mixture was then dropped into 20 L of 0.1 mol / L CaCl2 solution and allowed to stand for 30 min to solidify to obtain gel beads. Subsequently, the gel beads were transferred into 20 L of 1 wt% chitosan acetate solution and crosslinked in the shell for 10 min. The solid was collected by vacuum filtration, and the surface residual solution was rinsed with deionized water. The mixture was dried at 40 °C until the water content was 10%, and then ground to a particle size of 0.1 mm to obtain the composite microbial agent. S3.2, Material Mixing Add 2 kg of ecological auxiliary agent (1 kg of water-retaining agent + 1 kg of compound microbial agent) to the pretreated sludge mixture obtained from S2, adjust the mixer speed to 60 r / min, and stir for 4 min. During the stirring process, control the pH of the system to 10.5. After stirring, take a small amount of slurry and place it on a glass plate. The slurry should be a uniform paste without obvious lumps, and the natural flow speed should be 6 cm / min to obtain a castable slurry. S4, In-situ molding: A prefabricated hexahedral steel mold (500mm×300mm×200mm, with a 15°~25° inclined vegetation trough and trapezoidal tenon and mortise structure) is selected. A layer of water-based release agent is applied to the inner wall of the mold, with a coating amount of 0.5g / cm². 2 Place the mold on a level workbench and calibrate it with a level. Evenly fill the mold with the pourable grout using a shovel, filling it in three stages, each stage filling one-third of the mold's volume. After each stage, vibrate with an immersion vibrator (1.1kW power, 50Hz frequency) for 20 seconds, inserting the vibrator to two-thirds of the grout layer, avoiding contact with the mold's inner wall. After all three stages, vibrate the entire mold for 45 seconds until no obvious air bubbles overflow and the surface is smooth. Use a scraper to smooth the grout surface along the mold's edge, removing excess grout. Then, lightly brush the surface with a brush to create a rough interface, facilitating moisture retention during subsequent curing. Immediately cover the mold surface with a 200g / m² layer of grout. 2 The geotextile must completely cover the surface of the mold, with the edges hanging down to the bottom of the mold to prevent rapid evaporation of moisture. S5. Natural Curing and Post-Treatment: After molding, the mold is transferred to a natural curing area. The ambient temperature in the curing area is controlled at 15℃ and the relative humidity at 60%. Direct sunlight, rain, and strong winds are avoided. The mold is sprayed with clean water twice a day, morning and evening, using a sprayer at a pressure of 0.3MPa. The amount of water sprayed should be enough to moisten the geotextile but not to cause water accumulation. After each spraying, the geotextile coverage is checked and adjusted as needed. The mold is left to cure for 10 days. After the curing period, the bolts on the side of the mold are removed first, and then the edge of the mold is gently pried to separate the material from the inner wall of the mold. The mold is then slowly removed to avoid damaging the material due to violent demolding, thus obtaining the dual-function coupling material.

[0030] Example 2

[0031] The difference between this embodiment and Example 1 is that the amount of in-situ sludge used is 65 kg, the amount of multi-source mineral-based gelling agent used is 25 kg, and the remaining raw materials and preparation process are the same as in Example 1.

[0032] Example 3

[0033] The difference between this embodiment and Example 1 is that the amount of in-situ sludge used is 75 kg, the amount of multi-source mineral-based gelling agent used is 15 kg, and the remaining raw materials and preparation process are the same as in Example 1.

[0034] Example 4

[0035] The difference between this embodiment and Example 1 is that the amount of composite denitrification and phosphorus removal functional filler is 5 kg, the amount of ecological auxiliary agent is 3 kg, and the remaining raw materials and preparation process are the same as in Example 1.

[0036] Example 5

[0037] The difference between this embodiment and Example 1 is that the amount of composite denitrification and phosphorus removal functional filler is 9 kg, the amount of modified biomass fiber is 3 kg, and the remaining raw materials and preparation process are the same as in Example 1.

[0038] Example 6

[0039] The difference between this embodiment and Example 1 is that the amount of modified biomass fiber used is 6 kg, the amount of ecological auxiliary agent used is 1 kg, and the remaining raw materials and preparation process are the same as in Example 1.

[0040] Comparative Example 1

[0041] The difference between this comparative example and Example 1 is that 20 kg of multi-source mineral-based cementitious agent was replaced with 20 kg of ordinary Portland cement (PO 42.5), while the other raw materials and preparation process remained the same as in Example 1.

[0042] Comparative Example 2

[0043] Compared with Example 1, the difference in this comparative example is that 7 kg of composite denitrification and phosphorus removal functional filler is replaced with 7 kg of single zeolite powder, while the other raw materials and preparation process remain the same as in Example 1.

[0044] Comparative Example 3

[0045] The difference between this comparative example and Example 1 is that the Fe-K-CT iron-carbon filler is removed, while the remaining raw materials and preparation process remain the same as in Example 1.

[0046] Comparative Example 4

[0047] The difference between this comparative example and Example 1 is that 1.4 kg of slow-release carbon source was replaced with 1.4 kg of glucose, while the other raw materials and preparation process remained the same as in Example 1.

[0048] Comparative Example 5

[0049] The difference between this comparative example and Example 1 is that 4 kg of modified biomass fiber was replaced with 4 kg of unmodified straw fiber, while the other raw materials and preparation process remained the same as in Example 1.

[0050] Comparative Example 6

[0051] Compared with Example 1, the difference in this comparative example is that 2 kg of ecological auxiliary agent was replaced with 2 kg of single water-retaining agent (sodium polyacrylate crosslinked resin), while the other raw materials and preparation process remained the same as in Example 1.

[0052] Comparative Example 7

[0053] The difference between this comparative example and Example 1 is that the composite microbial agent was not immobilized by encapsulation, and the preparation of the composite microbial agent only involved the compounding of bacterial strains. Nitrifying bacteria, denitrifying bacteria, and polyphosphate-accumulating bacteria were mixed in a 1:1:1 ratio, with a viable bacteria concentration of 2×10⁻⁶. 8 The compound bacterial solution was obtained at CFU / g. 1L of the compound bacterial solution was mixed with 1kg of water-retaining agent as an ecological auxiliary agent. The remaining raw materials and preparation process were the same as in Example 1.

[0054] Comparative Example 8

[0055] The difference between this comparative example and Example 1 is that the 1.75 kg modified ceramsite in the composite denitrification and phosphorus removal functional filler is replaced with 1.75 kg ordinary unmodified ceramsite, while the other raw materials and preparation process remain the same as in Example 1.

[0056] Performance testing

[0057] The bifunctional coupling materials prepared in all embodiments and comparative examples were subjected to the following performance tests: 1. Compressive strength: Referring to GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete", the castable grout was injected into a 50mm×50mm×50mm cube mold, vibrated for 30s, and cured for 7d and 28d before demolding. The compressive strength of the sample was tested using an electronic universal testing machine.

[0058] 2. Erosion resistance test: Prepare 100mm×100mm×50mm cuboid specimens, cure for 28 days, and use a circulating water erosion test device. The water flow velocity gradient is set to 1.0~5.0m / s, and each velocity gradient is used for 2 hours. Record the mass loss rate and surface morphology changes of the specimens. Erosion resistance flow velocity: the maximum water flow velocity when the mass loss rate of the specimen is ≤5%.

[0059] 3. Porosity test: Take the core part of the sample after 28 days of curing, cut it into small pieces of 5mm×5mm×5mm, and vacuum dry at 60℃ for 24h. Use a fully automatic mercury porosimeter with a pressure range of 0.001~414MPa to record the pore volume and pore size distribution. Total porosity (%) = total pore volume / apparent volume of sample × 100%.

[0060] 4. Performance test of nitrogen and phosphorus removal function: Ammonia nitrogen (NH4) + -N) Removal rate test: A static immersion test was conducted. A sample (50mm×50mm×50mm) after 28 days of curing was placed in 1L of simulated wastewater with a concentration of 50mg / L NH4Cl, and the water temperature was controlled at 25℃. Samples were taken at 1d, 3d, 7d, 14d, and 28d of immersion. After filtration through a 0.45μm filter membrane, the absorbance was measured at a wavelength of 420nm using a spectrophotometer. The ammonia nitrogen concentration and removal rate were calculated. Total phosphorus (TP) removal rate test: Same as ammonia nitrogen removal rate test, simulated wastewater is KH2PO4 solution with a concentration of 10 mg / L, water temperature 25℃; test cycle is the same as ammonia nitrogen removal rate test, after sampling and digestion treatment, absorbance is measured at a wavelength of 700 nm using a spectrophotometer, and total phosphorus concentration and removal rate are calculated. Total nitrogen (TN) removal rate test: Same as ammonia nitrogen removal rate test, simulated wastewater is 50 mg / L KNO3 solution (supplemented with 10 mg / L NH4Cl), water temperature 25℃; test cycle is the same as ammonia nitrogen removal rate test, after sampling, it is digested with alkaline potassium persulfate, and the absorbance is measured at wavelengths of 220 nm and 275 nm using a UV spectrophotometer, and the total nitrogen concentration and removal rate are calculated.

[0061] 5. Microbial activity test: The viable count of nitrifying bacteria, denitrifying bacteria, and polyphosphate-accumulating bacteria on the material surface was determined by plate counting. Samples were scraped from the surface after 7 and 28 days of curing and diluted with sterile physiological saline by shaking. Nitrifying bacteria were cultured aerobically at 28°C for 7 days using a nitrifying selective medium; denitrifying bacteria were cultured anaerobically at 28°C for 7 days using a denitrifying selective medium; and polyphosphate-accumulating bacteria were cultured aerobically at 28°C for 7 days using a polyphosphate-accumulating selective medium. Plates with colony counts between 30 and 300 were selected, and the viable count concentration (CFU / g) was calculated.

[0062] 6. Material durability test: The sample cured for 28 days was placed in a wet-dry cycle chamber. After soaking in tap water for 24 hours, it was dried at 60℃ for 24 hours as one cycle. After 50 cycles, the compressive strength loss rate was tested.

[0063] The results are shown in Tables 1 and 2: Table 1

[0064] Table 2

[0065] As can be seen from the data in Tables 1 and 2, the realization of this invention relies on the synergistic curing effect among multiple components. Specifically, the core gelling system matches the substrate, forming a stable structure; modified fibers construct a three-dimensional support network, thereby enhancing the material's mechanical properties; simultaneously, suitable curing conditions ensure the full progress of the curing reaction; the material relies on the synergistic mechanism of adsorption, chemical action, and biodegradation, providing multi-level pollutant removal pathways through composite functional fillers; the addition of a slow-release carbon source ensures the long-term effectiveness of the treatment process, and static and dynamic test results also verify its practical applicability. Furthermore, ecological aids help regulate the microbial living environment, double-layer encapsulation technology improves the stability of the bacterial cells, and a suitable pore structure supports biofilm formation.

[0066] The performance degradation in Comparative Example 1 may be due to the use of ordinary silicate cement instead of multi-source mineral-based binders. While ordinary cement systems can improve structural density, their excessive alkalinity can disrupt the living environment of the composite microbial agents, leading to decreased microbial activity and hindered biodegradation. Simultaneously, the excessively dense pores in the cement system limit the contact between pollutants and internal functional fillers, reduce water exchange and microbial attachment space, and hinder the purification effects of physical adsorption and chemical precipitation. Furthermore, ordinary cement lacks the synergistic binding effect of industrial solid waste and sludge particles found in multi-source mineral-based binders. While it exhibits high short-term strength, its long-term stability is insufficient, making it prone to performance degradation under wet-dry cycles, ultimately resulting in a significant decrease in denitrification, phosphorus removal, and durability.

[0067] The performance degradation in Comparative Example 2 may be due to the replacement of the composite nitrogen and phosphorus removal filler with a single zeolite powder, which disrupts the original synergistic purification mechanism of "adsorption-precipitation-biodegradation". Single zeolite powder can only adsorb ammonia nitrogen through ion exchange, lacking chemical precipitation sites for phosphates and the functional carriers required for denitrification, making it difficult to achieve efficient removal of total phosphorus. Simultaneously, the single filler cannot provide a stable attachment and growth environment for the composite microbial agent, resulting in an unsustainable biodegradation process and limited total nitrogen conversion efficiency. Furthermore, the adsorption capacity of zeolite powder is limited and easily reaches saturation; with prolonged use, the overall purification capacity rapidly declines.

[0068] The performance degradation in Comparative Example 3 may be due to the removal of the Fe-K-CT iron-carbon filler, resulting in the loss of the chemical precipitation and micro-electrolysis oxidation pathways. The iron-carbon filler can form a micro-galvanic cell system in water, converting some ammonia nitrogen through oxidation, while the released metal ions can form insoluble precipitates with phosphates. The absence of this crucial chemical purification step directly weakens the removal capacity for total phosphorus and ammonia nitrogen. Furthermore, the porous structure of the iron-carbon filler could serve as an auxiliary carrier for microbial attachment; its removal reduces microbial colonization sites, indirectly affecting biodegradation and causing an overall decline in purification performance.

[0069] The performance degradation in Comparative Example 4 may be due to the replacement of the slow-release carbon source with glucose, which affected the stable supply of carbon source during denitrification. Glucose is a readily degradable carbon source that is rapidly consumed by microorganisms in water, making it difficult to provide a continuous electron donor for denitrifying bacteria. This leads to the inability to sustain the denitrification process and a significant reduction in total nitrogen conversion efficiency. In contrast, the original slow-release carbon source can release carbon slowly, matching the denitrification rate and ensuring the long-term effectiveness of biological nitrogen removal. The rapid degradation of glucose may also cause excessive proliferation of local microorganisms, clogging the pores of the material and further hindering pollutant transfer and water exchange, indirectly affecting the overall purification function.

[0070] The performance degradation in Comparative Example 5 may be due to the use of unmodified straw fiber instead of modified biomass fiber, which weakens the interfacial bonding between the fiber and the inorganic matrix. Unmodified straw fiber has fewer surface-active groups, making it difficult to form stable chemical bonds with the sludge-cementation system and thus hindering the construction of an effective three-dimensional bridging network. This leads to a decrease in the material's ability to suppress microcracks, weakened crack resistance and impact resistance, and increased susceptibility to crack propagation and structural damage under water erosion and wet-dry cycles. Impaired structural integrity causes the loss of internal functional fillers and disrupts the microbial environment, ultimately significantly reducing the material's support and purification capabilities.

[0071] The performance degradation in Comparative Example 6 may be due to the replacement of the ecological auxiliary agent with a single water-retaining agent, thus lacking the biodegradation effect of the composite microbial agent. The composite microbial agent in the ecological auxiliary agent is the core of biodegradation, capable of efficiently converting nitrogen and phosphorus through nitrification, denitrification, and excessive phosphorus uptake. The single water-retaining agent can only maintain pore moisture and cannot replace the biodegradation function, leading to a significant decrease in total nitrogen removal efficiency. Furthermore, the water-retaining agent and the microbial agent originally have a synergistic effect; the moist environment maintained by the water-retaining agent helps the microbial agent maintain its activity. A single water-retaining agent cannot achieve this synergy, further weakening the material's ecological purification capacity.

[0072] The performance degradation in Comparative Example 7 may be due to the lack of encapsulation and fixation treatment for the composite microbial agent, making it unable to withstand the high pH environment during the initial stage of material curing. The original sodium alginate-chitosan double-layer encapsulation structure provides protection for the bacteria, preventing their inactivation under the strongly alkaline conditions of the gelation system. If the unencapsulated bacterial solution is used directly, a large number of bacteria will die in the high pH environment, leading to a sharp decline in microbial activity. The reduced number of active bacteria makes the biodegradation process difficult to carry out effectively, significantly reducing the bioconversion efficiency of nitrogen and phosphorus, ultimately affecting the overall purification performance.

[0073] The performance degradation in Comparative Example 8 may be due to the use of ordinary unmodified ceramsite instead of modified ceramsite, which resulted in the loss of the modified ceramsite's targeted adsorption capacity for phosphates. After iron salt treatment, modified ceramsite forms numerous active sites on its surface capable of coordinating with phosphates, a crucial step in chemical adsorption for phosphorus removal. Ordinary ceramsite lacks these active sites, relying solely on its porous structure for physical adsorption, resulting in limited adsorption capacity and poor selectivity, thus failing to efficiently remove phosphates. Furthermore, while modified ceramsite can serve as a good carrier for microbial attachment, ordinary ceramsite has weaker carrier properties, indirectly affecting microbial colonization and metabolism within the material, further weakening the biological phosphorus removal effect and leading to overall performance degradation.

[0074] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A dual-functional coupled material for in-situ sludge solidification, denitrification, and phosphorus removal, characterized in that, Its raw material composition, based on in-situ sludge, includes the following components by mass percentage: 60%~75% in-situ sludge, 15%~25% multi-source mineral-based coagulant, 5%~10% composite denitrification and phosphorus removal functional filler, 3%~6% modified biomass fiber, and 1%~3% ecological auxiliary agent.

2. The dual-functional coupled material for in-situ solidification, denitrification, and phosphorus removal of sludge as described in claim 1, characterized in that, The in-situ sludge is riverbed or wetland sediment with a water content of 65% to 85%.

3. The dual-functional coupled material for in-situ sludge solidification, denitrification, and phosphorus removal as described in claim 1, characterized in that, The multi-source mineral-based cementitious agent is composed of 40% steel slag, 30% fly ash, 20% alkaline activator, and 10% penetrating crystallizer. The alkaline activator is composed of water glass and sodium hydroxide in a mass ratio of 3:1; the penetrating crystallizer is composed of sodium silicate and active silica micro powder in a mass ratio of 2:

1.

4. The dual-functional coupled material for in-situ sludge solidification, denitrification, and phosphorus removal as described in claim 1, characterized in that, The composite denitrification and phosphorus removal functional filler is composed of 30% zeolite powder, 25% Fe-K-CT iron-carbon filler, 25% modified ceramsite, and 20% slow-release carbon source; The Fe-K-CT iron-carbon filler is prepared by mechanically ball milling zero-valent iron filings, activated carbon, and potassium feldspar powder at a mass ratio of 5:3:2 for 2 hours, followed by heat treatment at 300℃ under a nitrogen atmosphere for 1 hour; the modified ceramsite is obtained by impregnating commercially available ceramsite with 1 mol / L FeCl3 solution for 12 hours and then drying it at 60℃; the slow-release carbon source is polyhydroxy fatty acid ester particles with a particle size of 0.5~1.5 mm.

5. The dual-functional coupled material for in-situ sludge solidification, denitrification, and phosphorus removal as described in claim 1, characterized in that, The modified biomass fiber is straw fiber that has been soaked in 5wt% NaOH solution for 30 minutes, then treated with 1wt% silane coupling agent KH550 ethanol solution for 1 hour, dried, and cut to a length of 8-10 mm.

6. The dual-functional coupled material for in-situ sludge solidification, denitrification, and phosphorus removal as described in claim 1, characterized in that, The ecological auxiliary agent consists of 0.5%~1.5% water-retaining agent and 0.5%~1.5% compound microbial agent, wherein the compound microbial agent is a mixture of nitrifying bacteria, denitrifying bacteria and polyphosphate-accumulating bacteria in a volume ratio of 1:1:1, and the concentration of live bacteria is not less than 1×10⁻⁶. 8 CFU / g; The water-retaining agent is sodium polyacrylate crosslinked resin with a water absorption ratio ≥300g / g.

7. The dual-functional coupled material for in-situ sludge solidification, denitrification, and phosphorus removal as described in claim 6, characterized in that, The fixation method of the composite microbial agent includes the following steps: first, the bacterial solution and 2% sodium alginate solution are mixed at a ratio of 1:4 and dropped into 0.1 mol / L CaCl2 solution to form gel beads, then immersed in 1% chitosan acetate solution for cross-linking for 10 min, and vacuum dried at 40°C until the moisture content is ≤10%.

8. A method for preparing a dual-functional coupled material for in-situ sludge solidification, nitrogen and phosphorus removal, characterized in that, The preparation of the sludge in-situ solidification-denitrification and phosphorus removal dual-functional coupled material according to any one of claims 1-7 includes the following steps: S1. In-situ sludge pretreatment: Treat river or wetland bottom sludge using a 20mm mesh screen; if the moisture content is >75%, add 5%~10% fly ash by weight of sludge to adjust; if the moisture content is <65%, spray deionized water to bring the moisture content to 65%~75%; S2. Dry material premixing: Mix multi-source mineral-based gelling agent, composite denitrification and phosphorus removal functional filler and modified biomass fiber at 30 r / min for 2 min to obtain pretreated sludge; S3. Wet material mixing: Pretreated sludge and ecological additives are mixed at 60 r / min for 3-5 min to obtain a castable slurry; S4. In-situ molding: Inject the castable grout into the precast mold and vibrate for 30-60 seconds, then cover the surface with geotextile to keep it moist. S5. Natural curing: Allow to stand for 7-10 days at an ambient temperature ≥10℃, spray with clean water once in the morning and once in the evening. After the curing period, remove the mold to obtain the dual-function coupling material.

9. The preparation method of a dual-functional coupled material for in-situ solidification, denitrification, and phosphorus removal of sludge according to claim 8, characterized in that, The composite denitrification and phosphorus removal functional filler is added in two steps: first, zeolite powder and modified ceramsite are added and stirred for 1 minute, then Fe-K-CT iron-carbon filler and slow-release carbon source are added and stirred for 1 minute.

10. The application of a dual-functional coupled material for in-situ sludge solidification, nitrogen and phosphorus removal in riverbank protection modules, ecological filter dam components, and wetland foundation layers, characterized in that... The sludge in-situ solidification-denitrification and phosphorus removal dual-functional coupled material is prepared by the preparation method described in any one of claims 8-9; In riverbank protection engineering, the material is made into a hexahedral module with dimensions of 500mm×300mm×200mm. The water-facing side is provided with a vegetation trough with an inclination angle of 15°~25°, a trough depth of 50~80mm and a width of 60~100mm. The side of the module is provided with a trapezoidal tenon and mortise structure. The internal porosity of the component is ≥25%, and the pore diameter is 2~8mm. In the application of ecological filter dam components, the material is made into a porous block with external dimensions of 400mm×400mm×300mm, internal porosity ≥30%, and the channels form a three-dimensional interconnected network structure. When stacked, a staggered overlapping method is adopted. In the application of wetland foundation cushion layer, the material is made into a sheet structure with a thickness of 15~20cm, and laid at the bottom of the wetland as a bearing layer. The compressive strength is not less than 2.5MPa, the original soil compaction degree is ≥90% before laying, and the joints of the cushion layer are treated with grout of the same proportion.

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