Temperature-controlled ecological sand modifier, preparation method and application thereof

Abstract

This invention belongs to the field of ecological restoration technology and discloses a temperature-controlled ecological soil conditioner, its preparation method, and its application. The preparation method of the temperature-controlled ecological soil conditioner includes the following steps: S1, taking undehydrated municipal sludge in muddy state, removing impurities, adding a heavy metal passivating agent, and stirring to react, obtaining pretreated municipal sludge; S2, mixing the pretreated municipal sludge with sawdust, fly ash, and temperature-controlled biochar, then stirring evenly to obtain a mixture; S3, adding a compound fermentation agent to the mixture, mixing evenly, and then performing self-heating composting fermentation. After fermentation, the product is crushed, sieved, and then aerated and aged to obtain the temperature-controlled ecological soil conditioner. This invention uses undehydrated municipal sludge as the main raw material, supplemented with sawdust, fly ash, and temperature-controlled biochar, and through heavy metal passivation, microbial inoculation, and multi-stage self-heating composting, prepares a green soil conditioner that combines high-efficiency fermentation, ecological safety, and soil compatibility.

Description

Technical Field

[0001] This invention belongs to the field of ecological restoration technology, specifically relating to a temperature-controlled ecological sand soil conditioner, its preparation method, and its application. Background Technology

[0002] With the acceleration of urbanization and the advancement of ecological civilization construction, the resource utilization of solid waste and the remediation of desertified land have become urgent global ecological problems that need to be solved. Current sand improvement technologies mostly rely on chemical polymers. Although these materials can improve soil structure and enhance water and fertilizer retention capacity in the short term, they generally suffer from high costs, insufficient ecological adaptability, and the potential for soil compaction and secondary pollution with long-term use.

[0003] In the area of ​​solid waste resource utilization, the co-composting of municipal sludge and straw has been attempted for the remediation of desertified land. However, existing technologies require the addition of chemicals and dewatering to a moisture content of approximately 60% before using municipal sludge for subsequent composting. Otherwise, problems such as pile adhesion, poor aeration leading to anaerobic odor, and leachate overflow are likely to occur. The complex pre-process of chemical addition, filtration, dewatering and solidification, and secondary water replenishment after mixing the raw materials not only consumes a lot of time, space, and manpower and resources, but also causes serious water waste and wastewater secondary treatment costs. Furthermore, due to the high cellulose and lignin content in straw, which is difficult to degrade quickly, and the high moisture content, dense structure, and susceptibility to acidification of municipal sludge, the aeration during composting is poor, the heat of fermentation is insufficient, and the high-temperature stage is difficult to maintain stably, thus affecting the organic matter conversion efficiency and product stability. Existing composting technologies often have an organic matter conversion rate of less than 35%. In addition, to compensate for insufficient heating, some high-temperature composting processes rely on external heating to maintain the temperature, which not only increases energy consumption by 30% to 50%, but may also inhibit the activity of thermophilic bacteria, affect lignin degradation and pathogen inactivation, making it difficult to balance compost maturity and ecological safety. Summary of the Invention

[0004] The technical problem to be solved by this invention is to address the shortcomings of existing technologies by providing a temperature-controlled ecological sand soil conditioner, its preparation method, and its application. This invention overcomes the technical prejudice that sludge composting requires pre-dehydration. It directly uses undehydrated municipal sludge as the main raw material and constructs a loose, non-sticky, and oxygen-supplying framework through the synergistic use of multi-source drying additives. After heavy metal passivation, microbial inoculation, and self-heating composting, a green sand soil conditioner with high fermentation efficiency, ecological safety, dynamic water release and retention capacity, and soil compatibility is prepared, significantly reducing treatment energy consumption and costs.

[0005] To address the technical problem proposed in this invention, this invention provides a method for preparing a temperature-controlled ecological sand soil conditioner, comprising the following steps: S1. Take the undehydrated municipal sludge in mud state, remove impurities, add heavy metal passivating agent, stir and react to obtain pretreated municipal sludge; S2. The pretreated municipal sludge is mixed with sawdust, fly ash and temperature-controlled biochar, and then stirred evenly to obtain a mixture. S3. After adding compound fermentation agent to the mixture and mixing evenly, carry out self-heating composting fermentation. After fermentation, crush and screen the product and then ventilate and age it to obtain temperature-controlled ecological sand soil conditioner.

[0006] In the above scheme, the undehydrated municipal sludge has a water content of 92%~98%, an organic matter content of 20%~50% on a dry basis, a C / N ratio of 8~20, and a pH of 7~7.5. If the pH < 7, lime powder or fly ash is added to adjust it.

[0007] In the above scheme, the heavy metal passivating agent is one or two of calcium dihydrogen phosphate, phosphate rock powder, bentonite, and humate.

[0008] In the above scheme, the amount of heavy metal passivating agent added is 3% to 8% of the mass of municipal sludge.

[0009] In the above scheme, the stirring reaction time in step S1 is 2-4 hours.

[0010] In the above scheme, in step S1, after adding the heavy metal passivating agent and before stirring the reaction, when the sludge pH is <7, lime needs to be added to adjust the pH to 7~8 in order to ensure the environment of the passivating agent.

[0011] In the above scheme, the particle size of the wood chips is 2~5 mm and the moisture content is 10%~15%.

[0012] In the above scheme, the fly ash has a particle size of 0.1~1.0 mm and a moisture content of 1%~5%.

[0013] In the above scheme, the temperature-controlled biochar has a particle size of 1~3 mm and a moisture content of 5%~10%.

[0014] In the above scheme, the preparation method of the temperature-controlled biochar includes the following steps: 1) The biochar was first soaked and modified using nitric acid solution or hydrogen peroxide solution to obtain the first modified biochar; 2) The first modified biochar was subjected to a second soaking modification using ammonium persulfate solution to obtain the second modified biochar; 3) Mix the second modified biochar with a poly(N-isopropylacrylamide) (PNIPAM) solution and add a methylenebisacrylamide solution to react and obtain temperature-controlled biochar.

[0015] Furthermore, the biochar is obtained by pyrolysis of agricultural waste; the agricultural waste is one or more of straw, sawdust, rice husks, etc.; the pyrolysis temperature is 500~600℃, and the pyrolysis time is 30~60 min.

[0016] Furthermore, the concentration of the nitric acid solution is 1~3 mol / L.

[0017] Furthermore, the mass fraction of the hydrogen peroxide solution is 20% to 30%.

[0018] Furthermore, the soaking temperature for the first soaking modification is 60~80℃, the soaking time is 1~2h, and after soaking, the product is washed with water until neutral and then dried. The main function of the first soaking modification is to remove ash, open the pore structure of biochar, and introduce oxygen-containing functional groups to enhance the stability of subsequent polymer loading.

[0019] Furthermore, the concentration of the ammonium persulfate solution is 0.05~0.2 mol / L.

[0020] Furthermore, the soaking temperature for the second soaking modification is 20~25℃, and the soaking time is 30~60 min. After soaking, the solid and liquid are separated, and the solid product is allowed to drain naturally. The main function of the second soaking modification is to introduce free radical initiation sites on the surface of biochar.

[0021] Furthermore, the concentration of the poly-N-isopropylacrylamide solution is 0.5~2.0 mol / L.

[0022] Furthermore, the mass ratio of the poly(N-isopropylacrylamide) solution to the biochar is (3~10):1, preferably (4~8):1.

[0023] Furthermore, the concentration of the methylenebisacrylamide solution is 0.01~0.1 mol / L.

[0024] Furthermore, the amount of methylene bisacrylamide solution added is 0.5% to 2.0% of the mass of poly(N-isopropylacrylamide) solution, preferably 0.8% to 1.5%.

[0025] Furthermore, in step 3), the reaction temperature is 25~40℃, the reaction time is 3~6 h, and after the reaction is completed, the product is washed with water until neutral and then dried.

[0026] In the above scheme, in step S2, the mass ratio of the pretreated municipal sludge, sawdust, fly ash, and temperature-controlled biochar is 5:(1.5~2.5):(0.8~1.2):(0.8~1.2).

[0027] In the above scheme, the counter-flushing and mixing specifically involves using pretreated municipal sludge as the first stream and sawdust, fly ash, and temperature-controlled biochar as the second stream. The two streams are mixed by high-speed counter-flushing and impacting in opposite directions. After the counter-flushing and impacting, an instantaneous strong turbulent flow field is formed, which allows the high water content sludge slurry and dry auxiliary materials to be instantly dispersed and fully mixed. Under the action of gravity, the material falls naturally and further homogenizes and diffuses and restructures through the gravity settling process, forming a material with interconnected pores and uniform water content.

[0028] In the above scheme, the moisture content of the mixture is 55%~60%, and the C / N ratio is 20~30. This range can be adjusted by controlling the proportion of raw materials in the mixture. For example, when the C / N ratio is less than 20, the amount of wood chips can be increased; when the C / N ratio is greater than 30, municipal sludge can be added or the amount of wood chips can be reduced.

[0029] In the above scheme, the compound fermentation agent is a compound agent containing lactobacillus, yeast, nitrogen-fixing bacteria, phosphate-solubilizing bacteria and cellulose-decomposing bacteria, with a total effective viable count ≥ 1 × 10⁻⁶. 9 CFU / g.

[0030] Furthermore, based on the percentage of live bacteria, the compound fermentation agent contains 15% to 30% lactobacillus, 10% to 20% yeast, 8% to 15% nitrogen-fixing bacteria, 5% to 10% phosphate-solubilizing bacteria, and 5% to 10% cellulose-decomposing bacteria, with the remainder being one or more of actinomycetes or other facultative aerobic bacteria, which promotes the degradation of organic matter and other substances during composting.

[0031] In the above scheme, the mass of the compound fermentation agent is 0.05% to 0.15% of the mass of the premix.

[0032] In the above scheme, the compound fermentation agent is activated with brown sugar or molasses before being added. The amount of compound fermentation agent added to the brown sugar solution or molasses solution is 5% to 10%, and the activation time is 4 to 8 hours, so as to enhance metabolic activity and microbial stability.

[0033] In the above scheme, the self-heating composting fermentation adopts a windrow-type construction method, with a pile height of 2.3~2.8 m, a pile width of 2.0~2.5 m, and a pile density of 0.5~0.7 t / m³. 3 The initial moisture content of the pile was 55% to 60%.

[0034] In the above scheme, the self-heating composting fermentation includes a heating stage, a high-temperature stage, and a cooling stage. The entire fermentation process adopts intermittent forced aeration, and natural ventilation is carried out during the aeration pause.

[0035] Furthermore, the heating phase lasts 7-12 days, during which the pile temperature rises from ambient temperature to 50-55°C. This phase employs intermittent forced aeration at an intensity of 2.5-4.5 L / (min·kg), with each aeration lasting 10-15 minutes. Natural ventilation is maintained for 45-60 minutes between aeration cycles, and the pile is turned over once every 5-6 days.

[0036] Furthermore, the high-temperature stage lasts for 15-20 days, with the pile temperature maintained at 50-65℃. To meet the extremely high oxygen consumption caused by the vigorous metabolism of microorganisms during this stage and to accelerate water loss, high-frequency intermittent forced aeration is adopted, with an aeration intensity of 4.5-6.0 L / (min·kg). Each aeration lasts for 15-20 minutes, with a 30-40 minute break between aeration sessions for natural ventilation. The pile is turned over every 5-6 days.

[0037] Furthermore, the cooling phase lasts 15-25 days. During the first 5-10 days of this phase, the pile temperature gradually decreases to 30-40°C, and is then maintained at 30-40°C for 5-10 days before dropping to ambient temperature. During the cooling phase, the intensity of intermittent forced aeration is reduced daily to 90%-95% of the previous day's intensity, until it reaches 50%-65% of the aeration intensity during the high-temperature phase, and then remains stable. Simultaneously, the aeration frequency is adjusted to 5-10 minutes of continuous aeration each time, with a 60-90 minute break between aeration cycles for natural ventilation. During the cooling phase, the turning frequency is once every 3-5 days. Once the pile temperature drops below 35°C, the turning frequency is adjusted to once every 2-3 days.

[0038] In the above scheme, the self-heating composting fermentation process maintains the moisture content of the compost pile at 45% to 60%. If the moisture content is too low, water can be sprayed in an appropriate amount to replenish the moisture.

[0039] In the above scheme, the ventilation and aging process reduces the moisture content of the sand amendment to <30%, preferably between 25% and 30%.

[0040] The present invention also provides a temperature-controlled ecological sand soil conditioner, which is prepared by the above method.

[0041] In the above scheme, the temperature-controlled ecological sand soil conditioner has a pH value of 7.2~8.0, a moisture content of <30%, a water holding capacity of ≥50%, a porosity of 35%~45%, an organic matter content of >40%, a heavy metal available content accounting for <30% of the total heavy metal content, and a seed germination index (GI) of >80%.

[0042] In the above scheme, the particle size of the temperature-controlled ecological sand soil conditioner is mainly distributed in the range of 2 to 5 mm. Specifically, the particle size distribution is as follows: particles larger than 5 mm account for no more than 3% of the total mass, particles between 2 and 5 mm account for 70% to 80% of the total mass, and particles smaller than 2 mm account for 17% to 27% of the total mass.

[0043] This invention also provides an application of a temperature-controlled ecological sand soil conditioner in the improvement of desertified land. The application method is as follows: the temperature-controlled ecological sand soil conditioner is directly laid on the desertified land to form an improvement layer, and then a topsoil layer is covered on the improvement layer; or the temperature-controlled ecological sand soil conditioner is mixed with the topsoil layer and then laid on the desertified land to form an improvement layer.

[0044] In the above scheme, for extremely and severely desertified land, the temperature-controlled ecological sand soil conditioner is directly laid; for moderate and slightly desertified land, the temperature-controlled ecological sand soil conditioner is mixed with the surface sand before being laid.

[0045] In the above scheme, the thickness of the improved layer is 10~35 cm, the volume ratio of the temperature-controlled ecological sand soil conditioner in the improved layer is ≥14%, and the thickness of the improved layer and the mixing ratio of the temperature-controlled ecological sand soil conditioner are selected according to the degree of desertification and vegetation requirements.

[0046] Furthermore, for extremely and severely desertified land, the temperature-controlled ecological soil conditioner is directly laid, with a conditioner layer thickness of 25-35 cm and a surface layer of sand covering the conditioner layer thickness of 5-8 cm.

[0047] Furthermore, for moderately and mildly desertified land, the temperature-controlled ecological sand soil conditioner is mixed with the topsoil and then laid. The temperature-controlled ecological sand soil conditioner is mixed with the topsoil at a volume ratio of 1:3 to 1:6, and the thickness of the conditioner layer is 10 to 25 cm.

[0048] Furthermore, for moderately desertified land, when the temperature-controlled ecological soil conditioner is mixed with the topsoil at a volume ratio of 1:3 to 1:5, the thickness of the improved layer is 15 to 25 cm; for slightly desertified land, when the temperature-controlled ecological soil conditioner is mixed with the topsoil at a volume ratio of 1:5 to 1:6, the thickness of the improved layer is 10 to 20 cm.

[0049] In the above scheme, after the application of the temperature-controlled ecological sand soil conditioner, sand barriers can be further deployed to improve the effect of land sand fixation.

[0050] The main technical concept of this invention is as follows: In multi-source solid waste systems represented by municipal sludge, wood chips, and fly ash, there are generally defects such as relatively insufficient carbon sources, dense structure, easy initial acidification, high heavy metal activity, and poor water retention. Traditional composting processes cannot simultaneously achieve rapid heating, sustained high temperature, effective decomposition, and heavy metal stabilization without external heating. In addition, high water content sludge must be dehydrated in advance. These are the key technical difficulties that restrict the efficient utilization of this type of solid waste in the remediation of desertified land.

[0051] To address the aforementioned difficulties, the present invention adopts the following technical measures: 1. Overcoming the technical prejudice that "sludge must be dewatered," this invention constructs a self-balancing mechanism for dewatering-free mixing and skeletal oxygen supply: High-moisture (92%~98%) sludge is directly mixed with dried sawdust, fly ash, and temperature-controlled biochar after simple screen removal. Utilizing the high water absorption of the drying materials, a one-step self-balancing of moisture is achieved through the moisture content difference between solid wastes, eliminating the complex and energy-intensive steps of traditional processes such as pressure filtration dewatering, water replenishment, and wastewater treatment. To address the critical drawbacks of high-moisture sludge, which easily leads to anaerobic odor and leachate overflow, this invention utilizes the high porosity and rigid support of temperature-controlled biochar and fly ash to construct a three-dimensional, loose framework within the compost pile. Simultaneously, combined with counter-flushing and forced aeration, it completely breaks down the highly viscous state of the sludge, ensuring homogeneous oxygen mass transfer within the compost pile. This systematically overcomes industry pain points such as anaerobic digestion, odor, and leachate buildup associated with non-dehydration methods, achieving stable and efficient aerobic composting.

[0052] 2. Synergistic Coupling of Raw Materials for Aerobic Fermentation Composting: This technology is the first to couple municipal sludge, sawdust, fly ash, and temperature-controlled biochar, representing a multi-source solid waste process. Temperature-controlled biochar, obtained from straw or agricultural waste through high-temperature pyrolysis, possesses abundant micropores and functional groups, serving as a compost framework conditioner to improve the compost's pore structure and provide adsorption sites, thus facilitating moisture retention and heavy metal fixation. Fly ash acts as an alkaline conditioner to adjust pH and provides a silica-alumina framework to enhance the compost's structure. Sawdust, as the primary carbon source, increases the C / N ratio and improves permeability. This synergistic combination of multiple raw materials not only overcomes the shortcomings of single-source methods but also significantly enhances the compost's self-heating capacity and the physicochemical properties of the final product through their interactions.

[0053] 3. Temperature-Controlled Biochar with Dynamic Water Release and Retention: Sandy soil regions experience relatively low rainfall and high evaporation rates, resulting in highly unstable water supply for plant growth. Ordinary compost products can only passively retain water and cannot respond to environmental changes. Temperature-controlled biochar, formed by loading PNIPAM onto biochar, can gradually release some of its stored water during the day when soil surface temperature rises, alleviating short-term water stress in the plant rhizosphere; it can also reabsorb surrounding water at night or under cooling conditions. Compared to ordinary biochar or polymeric water-retaining agents that only passively adsorb water, temperature-controlled biochar can delay concentrated water evaporation under fluctuating temperature conditions, increasing the effective utilization time of limited water in the soil. This results in a more stable water retention effect in arid and semi-arid regions with scarce rainfall but significant temperature variations.

[0054] The temperature response threshold of this temperature-controlled biochar can fluctuate within the range of 30-35℃ due to the regulation of the compost and soil microenvironment. Even in areas with low average annual temperatures, it can still achieve periodic water absorption and dehydration under diurnal temperature variations and surface warming conditions, not limited to extreme high-temperature environments. Even in areas with low average annual temperatures, the soil surface can still reach or approach the phase transition range of PNIPAM during the day under sunlight conditions, and reabsorb water after the temperature drops at night, thus forming a cyclical regulation mechanism of water release during the day and water absorption at night. Furthermore, compared to directly adding PNIPAM, pre-loading can significantly reduce the risk of PNIPAM migration and loss in the compost and soil environment, avoiding degradation or aggregation failure of free polymers during high temperatures and turning during composting, ensuring the long-term stable existence of its temperature-controlled water release function in compost products and sandy soil environments. In addition, PNIPAM-loaded biochar can also serve as a skeletal conditioner in the compost and sandy soil, improving pore structure and aeration, and providing a stable physical space for plant roots and microbial activities.

[0055] 4. Enhanced Degradation with Compound Microbial Agent: The compound microbial agent, composed of lactobacillus, yeast, nitrogen-fixing bacteria, phosphate-solubilizing bacteria, and cellulose-decomposing bacteria, not only rapidly hydrolyzes proteins and polysaccharides in sludge but also efficiently degrades residual cellulose on the surface of sawdust and biochar, improving organic matter conversion rates. Phosphate-solubilizing bacteria dissolve inorganic phosphorus, making nutrients in compost more easily absorbed. Nitrogen-fixing bacteria increase nitrogen content through biological nitrogen fixation, slowing nitrogen loss. The compound microbial agent is activated with molasses before use, rapidly establishing a dominant microbial community in the early stages of composting, significantly increasing the heating rate and maintaining high temperatures for longer periods.

[0056] 5. Self-Heating Multi-Stage Composting Process: This invention, under the premise of controlling the C / N ratio and moisture content, utilizes the biodegradability of raw materials and the metabolic heat of compound microbial agents to achieve self-heating composting without relying on external heat sources. The compost pile rapidly rises from ambient temperature to 50-55℃ within 7-12 days, then enters a high-temperature stage of 50-65℃ for 15-20 days, and finally maintains a cooling and aging stage at 30-40℃ for 5-10 days to promote decomposition. The ventilation rate is precisely controlled through windrow stacks and automatic aeration devices. The pile is turned over every 5-6 days during the heating and high-temperature stages to ensure uniform oxygen distribution and prevent localized overheating. Throughout the composting process, the moisture content is maintained between 45% and 55%, resulting in minimal evaporation loss. Sustained high temperatures for more than 8 days can be achieved without an external heat source, effectively inactivating pathogens and accelerating lignin decomposition.

[0057] 6. Heavy Metal Passivation and Physicochemical Modification: During the pretreatment stage, heavy metal passivating agents such as calcium dihydrogen phosphate, phosphate rock powder, and bentonite are added. During composting, these agents complex with the surface functional groups of temperature-controlled biochar, fixing the heavy metals into insoluble forms. After composting, the proportion of available heavy metals in the total heavy metal content does not exceed 30%. Simultaneously, the porous structure of fly ash and biochar enhances the water and nutrient retention capacity of the modifier, resulting in a water holding capacity ≥50% and a stable porosity of 35%~45%, providing a stable framework structure and micro-ecological space for the sandy soil.

[0058] 7. Diverse Application Modes: The ecological sand soil conditioner of this invention can directly replace sand as a plant substrate, or it can be mixed with sand in different proportions and laid on the surface of desertified land. By adjusting the laying thickness and the specifications of the sand barriers, it can adapt to different degrees of desertification. In severely desertified areas, the conditioner can be laid to a thickness of 25-35 cm, allowing for the direct planting of sand-fixing shrubs. In moderately and mildly desertified areas, it can be mixed with sand at a volume ratio of 1:3 to 1:6 to form a 10-25 cm thick conditioner layer, which can significantly improve soil organic matter and water and fertilizer retention capacity, and promote vegetation restoration.

[0059] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention optimizes the proportion of multi-source solid waste to construct a pile framework structure with high porosity and good aeration; introduces a heavy metal passivating agent for pre-reaction to stabilize the sludge system and inhibit acidification; introduces temperature-controlled biochar to provide a stable microporous structure and surface functional group environment for the pile, enhancing adsorption and moisture regulation capabilities; and employs activated composite functional microbial agents to rapidly establish a dominant microbial community with high-efficiency metabolism. This synergistically solves common industry problems such as slow temperature rise in sludge piles, short duration of high-temperature periods, high heavy metal activity, and insufficient maturity and safety of final products. It achieves stable self-heating fermentation and efficient heavy metal passivation without an external heat source, and prepares a sand amendment with both good water retention and ecological safety. The application of this amendment in sand amendment has significant promotional value and can be widely used in ecological restoration and engineering construction in desertified and rocky desertified areas. Detailed Implementation

[0060] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0061] Example 1 This embodiment prepares a temperature-controlled ecological soil conditioner, including the following steps: (1) Municipal sludge pretreatment Undehydrated municipal sludge from a city wastewater treatment plant was collected and subjected to a simple screen to remove large debris. The sludge had a moisture content of 95%, a pH of 7.0, a C / N ratio of 12, and an organic matter content of 35% (dry basis). A heavy metal passivating agent composed of calcium dihydrogen phosphate and bentonite in a mass ratio of 3:2 was added at 6% of the sludge mass. Lime powder (1% of the sludge mass) was also added to adjust the pH to 7.5. The mixture was stirred and reacted for 3 hours to stabilize the heavy metals, resulting in pretreated municipal sludge. (2) Ingredients and mixing Pretreated municipal sludge in mud-like state, sawdust, fly ash, and temperature-controlled biochar were mixed in a mass ratio of 5:2:1:1 and thoroughly stirred. The mixture was then self-equilibrated using the difference in moisture content between the solid wastes to obtain a mixture with a moisture content of 56% and a C / N ratio of 25. Specifically, the sawdust had a particle size of 2-3 mm and a moisture content of 12%; the fly ash had a particle size of 0.2-0.8 mm and a moisture content of 2%; and the temperature-controlled biochar had a particle size of 1 mm and a moisture content of 6%. The preparation process was as follows: corn stalks were pyrolyzed at 500℃ for 60 min to obtain biochar. The biochar was then soaked in a 2 mol / L nitric acid solution at 80℃ for 1.5 h. The product was washed with deionized water until neutral and then dried. Subsequently, it was soaked in a 0.1 mol / L ammonium persulfate solution at 25℃ for 30 min, and the product was allowed to drain naturally. Finally, a 1.0 mol / L ammonium persulfate solution was added at 25℃. A 0.05 mol / L poly(N-isopropylacrylamide) solution was added to a poly(N-isopropylacrylamide) solution at a mass ratio of 5:1 to biochar. 1.0% of the poly(N-isopropylacrylamide) solution was then added to a 0.05 mol / L methylenebisacrylamide solution. The reaction was carried out for 4 h. The product was washed with deionized water until neutral and then dried. (3) Inoculation with compound microbial agent Add the compound fermentation agent at 0.1% of the premix mass and mix thoroughly; the total effective viable count of the compound fermentation agent used is 1.5 × 10⁻⁶. 9 The CFU / g of the compound fermentation agent contains 25% live Lactobacillus, 18% live yeast, 12% live nitrogen-fixing bacteria, 7% live phosphate-solubilizing bacteria and 8% live cellulosic bacteria, with the remainder being actinomycetes. The compound fermentation agent was pre-activated in a brown sugar solution for 6 hours before use. The amount of compound fermentation agent added to the brown sugar solution was 10%. After activation, the compound fermentation agent and the brown sugar solution were added to the mixture. (4) Composting The mixture with added compound fermentation agent was piled into windrows, with a height of 2.5 m, a width of 2.2 m, and a density of 0.6 t / m³. 3 The initial moisture content was 58%, and a ventilation duct and aeration system were installed for fermentation. The fermentation process included a heating stage, a high-temperature stage, and a cooling stage. The entire fermentation process was mainly based on intermittent forced aeration, supplemented by natural ventilation during aeration breaks. The heating phase lasted 8 days, during which the pile temperature rose from ambient temperature to about 55°C. During this phase, intermittent forced aeration was used, with an aeration intensity of 3.5 L / (min·kg). Each aeration lasted for 12 minutes, and there was a 50-minute break between two aeration sessions for natural ventilation. The turning frequency was once every 5 days. The high-temperature phase lasted 20 days, with the pile temperature maintained at 55~63℃. During this phase, high-frequency intermittent forced aeration was used, with an aeration intensity of 5.0 L / (min·kg). Each aeration lasted for 18 minutes, and there was a 35-minute break between two aeration sessions for natural ventilation. The turning frequency was once every 5 days. The cooling phase lasted 22 days. During the first 8 days of this phase, the pile temperature gradually decreased from 55-63°C in the high-temperature phase to 35°C. It was then maintained at 35°C for 8 days before dropping to the ambient temperature. After entering this phase, the intensity of intermittent forced aeration was reduced to 92% of the previous day's intensity each day until it reached 60% of the aeration intensity in the high-temperature phase and remained stable. The aeration frequency was adjusted to 8 minutes of continuous aeration each time, with a 75-minute break between aeration sessions for natural ventilation. After entering this phase, the turning frequency was once every 4 days. When the pile temperature dropped below 35°C, the turning frequency was adjusted to once every 2 days. During the above composting fermentation process, water can be sprayed in appropriate amounts to maintain the moisture content of the compost pile at 45% to 60%. (5) Breakage and aging When the temperature of the compost pile drops to the ambient temperature (20~30℃), the composting fermentation is considered to be over. The product is then crushed, sieved, and aged for 7 days under ventilated conditions to reduce the moisture content to 28%, thus obtaining a sand soil conditioner.

[0062] Testing of this batch of products revealed that the particle size was mainly distributed between 2 and 5 mm, specifically: particles larger than 5 mm accounted for 2% of the mass, particles between 2 and 5 mm accounted for 75%, and particles smaller than 2 mm accounted for 23%. Further testing showed a pH of 7.6, an organic matter content of 42.5%, a water holding capacity of 55.8%, a porosity of 40%, a heavy metal bioavailability of 26.4%, and a seed germination index of 85%. The bioavailability of heavy metals was determined using the BCR method, and the seed germination index was determined according to the NY / T 525-2021 standard. The results indicate that the product meets the requirements of NY / T 525-2021 "Organic Fertilizer" in terms of maturity, stability, and ecological safety.

[0063] Example 2 This embodiment prepares a temperature-controlled ecological sand soil conditioner, including the following steps: (1) Municipal sludge pretreatment Undehydrated municipal sludge from a city wastewater treatment plant was collected and subjected to a simple screen to remove large debris. The sludge had a water content of 97%, a pH of 7.2, a C / N ratio of 15, and an organic matter content of 40% (dry basis). A heavy metal passivating agent composed of phosphate rock powder and humate in a mass ratio of 1:1 was added to the sludge at a rate of 4% of the sludge mass. Lime was added to stabilize the pH of the system at 7.0-7.5. The mixture was stirred and reacted for 2 hours to stabilize the heavy metals, resulting in pretreated municipal sludge. (2) Ingredients and mixing Pretreated municipal sludge in mud-like form, sawdust, fly ash, and temperature-controlled biochar were mixed in a mass ratio of 5:2:1.2:0.8 and thoroughly stirred. The mixture was then self-equilibrated using the difference in moisture content between the solid wastes to obtain a mixture with a moisture content of 58% and a C / N ratio of 28. The sawdust had a particle size of 4-5 mm and a moisture content of 14%; the fly ash had a particle size of 0.5-1 mm and a moisture content of 4%; and the temperature-controlled biochar had a particle size of 2 mm and a moisture content of 8%. The preparation process was as follows: rice husks were pyrolyzed at 550℃ for 45 min to obtain biochar. The biochar was then soaked in a 25% hydrogen peroxide solution at 70℃ for 1.5 h. The product was washed with deionized water until neutral and then dried. Subsequently, it was soaked in a 0.15 mol / L ammonium persulfate solution at 22℃ for 45 min, and the product was allowed to drain naturally. Finally, a 1.5% hydrogen peroxide solution was added at 30℃. A 0.08 mol / L poly(N-isopropylacrylamide) solution was added to a poly(N-isopropylacrylamide) solution at a mass ratio of 6:1 to biochar. 1.2% of the poly(N-isopropylacrylamide) solution was then added to a 0.08 mol / L methylenebisacrylamide solution. The reaction was carried out for 5 h. The product was washed with deionized water until neutral and then dried. (3) Inoculation with compound microbial agent Add the compound fermentation agent at 0.07% of the premix weight and mix thoroughly; the total effective viable count of the compound fermentation agent used is 1×10⁻⁶. 9 The CFU / g of the compound fermentation agent contains 20% live Lactobacillus, 12% live yeast, 10% live nitrogen-fixing bacteria, 8% live phosphate-solubilizing bacteria, and 10% live cellulosic bacteria, with the remainder being facultative aerobic bacteria. The compound fermentation agent was pre-activated in a molasses solution for 5 hours before use. The amount of compound fermentation agent added to the molasses solution was 8%. After activation, the compound fermentation agent and the molasses solution were added to the mixture. (4) Composting The mixture with added compound fermentation agent was piled into windrows, with a height of 2.3 m, a width of 2.0 m, and a density of 0.7 t / m³. 3The initial moisture content was 55%, and a ventilation duct and aeration system were installed for fermentation. The fermentation process included a heating stage, a high-temperature stage, and a cooling stage. The entire fermentation process was mainly based on intermittent forced aeration, supplemented by natural ventilation during aeration breaks. The heating phase lasted 9 days, during which the temperature of the pile increased from the ambient temperature to about 50°C. During this phase, intermittent forced aeration was used, with an aeration intensity of 3.0 L / (min·kg). Each aeration lasted for 10 minutes, and there was a 45-minute break between two aeration sessions for natural ventilation. The pile was turned over once every 5 days. The high-temperature phase lasted 18 days, with the pile temperature maintained at 50~60℃. During this phase, high-frequency intermittent forced aeration was used, with an aeration intensity of 4.8 L / (min·kg). Each aeration lasted for 16 minutes, and there was a 40-minute break between two aeration sessions for natural ventilation. The turning frequency was once every 6 days. The cooling phase lasted 20 days. During the first 7 days of this phase, the pile temperature gradually decreased from 50-60°C in the high-temperature phase to 38°C, and then remained at 38°C for 7 days before dropping to the ambient temperature. After entering this phase, the intensity of intermittent forced aeration was reduced to 94% of the previous day's intensity each day until it reached 62.4% of the aeration intensity in the high-temperature phase and remained stable. The aeration frequency was adjusted to 6 minutes of continuous aeration each time, with an 80-minute break for natural ventilation between aeration sessions. After entering this phase, the turning frequency was once every 4 days. When the pile temperature dropped below 35°C, the turning frequency was adjusted to once every 3 days. During the above composting fermentation process, water can be sprayed in appropriate amounts to maintain the moisture content of the compost pile at 45% to 60%. (5) Breakage and aging When the temperature of the compost pile drops to the ambient temperature (20~30℃), the composting fermentation is considered to be over. The product is then crushed, sieved, and aged for 8 days under ventilated conditions to reduce the moisture content to 27%, thus obtaining a sand soil conditioner.

[0064] Testing of this batch of products revealed that the particle size was mainly distributed between 2 and 5 mm, specifically: particles larger than 5 mm accounted for 1.5% of the mass, particles between 2 and 5 mm accounted for 78%, and particles smaller than 2 mm accounted for 20.5%. Further testing showed a pH of 7.4, an organic matter content of 41%, a water holding capacity of 53%, a porosity of 38%, a heavy metal bioavailability of 27%, and a seed germination index of 82%. The bioavailability of heavy metals was determined using the BCR method, and the seed germination index was determined according to the NY / T 525-2021 standard. The results indicate that the product meets the requirements of NY / T 525-2021 "Organic Fertilizer" in terms of maturity, stability, and ecological safety.

[0065] Application Example 1 The soil conditioner prepared in Example 1 was applied to a severely desertified area of ​​the Mu Us Desert in Inner Mongolia.

[0066] When applying the soil conditioner, spread a 30 cm thick layer of sand on the ground surface, then cover it with a 5-8 cm layer of topsoil. Plant sand willows and caragana at a spacing of 2 m × 4 m, and set up straw checkerboard sand barriers (3 m × 5 m, 20 cm high). Use drip irrigation, watering 6 mm every 4 days. After 6 months, the survival rates of the two plants were 93% and 90%, respectively, and the surface wind erosion was reduced by 85%. After one year, the vegetation coverage reached 67%.

[0067] Application Example 2 The soil conditioner prepared in Example 2 was applied to a moderately desertified area.

[0068] When applying the treatment, mix the soil conditioner with topsoil at a volume ratio of 1:4 and spread it on the ground to a thickness of 20cm. Then, mechanically prepare the land and plant sand willows and caragana. Set up sand barriers and irrigate monthly with 10 mm of water during the growing season. After one year, the survival rates were 91% and 84% respectively, soil organic matter increased from 0.6% to 2.3%, and soil permeability and water retention capacity were significantly improved.

[0069] Application Example 3 The soil conditioner prepared in Example 1 was applied to a slightly desertified area.

[0070] When applying the solution, mix the soil conditioner with the topsoil at a volume ratio of 1:5 and spread it on the ground to a thickness of 15cm. Plant vegetation using a combination of aerial seeding and replanting, and set up straw sand barriers. Without artificial irrigation, the survival rates after one year were 89% and 78%, respectively, with a wind erosion inhibition rate increased by approximately 72%, and vegetation coverage significantly improved.

[0071] Comparative Example 1 The only difference between this comparative example and Example 1 is that no temperature-controlled biochar was added. During composting fermentation, due to the lack of pore adsorption and skeletal support from the temperature-controlled biochar, the high-moisture sludge mixed with the additives could not effectively achieve moisture self-balance, resulting in severe compaction and extremely poor aeration of the compost pile. The heating phase was extremely slow (the highest temperature only reached about 45°C and was difficult to maintain), and a large amount of leachate was generated at the bottom of the pile, accompanied by a strong anaerobic odor. After the final, barely completed fermentation, the resulting sand conditioner had a pH of 6.5 (acidification), an organic matter content of 28%, a water holding capacity of 35%, a porosity of 22%, a heavy metal availability rate of 42%, and a seed germination index of 55% (not meeting the safety standards for composting).

[0072] The soil conditioner prepared in this comparative example was applied under the conditions of Application Example 1. The results showed that after 6 months, the survival rates of sand willow and caragana were only 65% ​​and 60%, respectively, the surface wind erosion was reduced by only 50%, and the vegetation coverage was only 35% after one year.

[0073] The main reason why the comparative example was significantly worse than Example 1 is that no temperature-controlled biochar was added. On the one hand, it could not absorb the free water in the sludge and build a loose pile skeleton, resulting in severe anaerobic fermentation and leachate overflow during the composting process. The organic matter was not fully degraded and heavy metals could not be effectively complexed and fixed. On the other hand, the final product lacked a stable microporous structure and surface functional groups, and the water retention performance was greatly reduced. It could not respond to the drought microenvironment to achieve dynamic water release and absorption under temperature control, which caused severe drought and heavy metal stress, thus significantly reducing the survival rate of vegetation under drought conditions.

[0074] Comparative Example 2 The only difference between this comparative example and Example 1 is that poly-N-isopropylacrylamide was not pre-loaded onto the biochar; instead, the poly-N-isopropylacrylamide solution and biochar were directly mixed at a mass ratio of 6:1 for use as a temperature-controlled biochar. The resulting sand amendment had a pH of 7.5, an organic matter content of 38%, a water holding capacity of 45%, a porosity of 32%, a heavy metal availability of 28%, and a seed germination index of 70%.

[0075] The soil conditioner prepared in this comparative example was applied under the conditions of Application Example 1. The results showed that after 6 months, the survival rates of sand willow and caragana were only 72% and 68%, respectively, and after one year, the vegetation coverage was only 45%.

[0076] The reason why the comparative example is significantly worse than Example 1 is that poly(N-isopropylacrylamide) was not pre-loaded onto the biochar in situ. The free polymer material is easily degraded, lost, or agglomerated and ineffective under the high temperature and mechanical action of composting, and cannot stably perform the function of temperature-controlled water release. As a result, it cannot exist stably in the compost product for a long time and loses the function of dynamic temperature-controlled water release. In addition, the free polymer that is not chemically bonded is prone to block the original pores of biochar, weakening its role as a skeleton conditioner to improve soil permeability.

[0077] The above embodiments are merely examples for clear illustration and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, and any obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a temperature-controlled ecological soil conditioner, characterized in that, Includes the following steps: S1. After removing impurities from undehydrated municipal sludge, a heavy metal passivating agent is added, and the mixture is stirred to react, resulting in pretreated municipal sludge; the moisture content of the undehydrated municipal sludge is 92%~98%. S2. The pretreated municipal sludge is mixed with sawdust, fly ash, and temperature-controlled biochar, and then stirred evenly to obtain a mixture; the preparation method of the temperature-controlled biochar includes the following steps: 1) The biochar was first soaked and modified using nitric acid solution or hydrogen peroxide solution to obtain the first modified biochar; 2) The first modified biochar was subjected to a second soaking modification using ammonium persulfate solution to obtain the second modified biochar; 3) Mix the second modified biochar with poly(N-isopropylacrylamide) solution and add methylenebisacrylamide solution to react and obtain temperature-controlled biochar; S3. After adding compound fermentation agent to the mixture and mixing evenly, carry out self-heating composting fermentation. After fermentation, crush and screen the product and then ventilate and age it to obtain temperature-controlled ecological sand soil conditioner.

2. The preparation method of the temperature-controlled ecological sand soil conditioner according to claim 1, characterized in that, The organic matter content of the municipal sludge in slurry form is 20%~50% on a dry basis, the C / N ratio is 8~20, and the pH is 7~7.5; the heavy metal passivating agent is one or two of calcium dihydrogen phosphate, phosphate rock powder, bentonite, and humate; the amount of heavy metal passivating agent added is 3%~8% of the mass of the municipal sludge, and the mixture is stirred and reacted for 2~4 hours after addition.

3. The preparation method of the temperature-controlled ecological sand soil conditioner according to claim 1, characterized in that, The sawdust has a particle size of 2-5 mm and a moisture content of 10%-15%; the fly ash has a particle size of 0.1-1.0 mm and a moisture content of 1%-5%; the temperature-controlled biochar has a particle size of 1-3 mm and a moisture content of 5%-10%; the mass ratio of the pretreated municipal sludge, sawdust, fly ash and temperature-controlled biochar is 5:(1.5-2.5):(0.8-1.2):(0.8-1.2); the mixture has a moisture content of 55%-60% and a C / N ratio of 20-30.

4. The preparation method of the temperature-controlled ecological sand soil conditioner according to claim 1, characterized in that, The concentration of the nitric acid solution is 1~3 mol / L; the mass fraction of the hydrogen peroxide solution is 20%~30%; the soaking temperature for the first soaking modification is 60~80℃, and the soaking time is 1~2h; the concentration of the ammonium persulfate solution is 0.05~0.2 mol / L; the soaking temperature for the second soaking modification is 20~25℃, and the soaking time is 30~60 min.

5. The preparation method of the temperature-controlled ecological sand soil conditioner according to claim 1, characterized in that, The concentration of the poly(N-isopropylacrylamide) solution is 0.5~2.0 mol / L; the mass ratio of the poly(N-isopropylacrylamide) solution to biochar is (3~10):1; the concentration of the methylenebisacrylamide solution is 0.01~0.1 mol / L; the amount of methylenebisacrylamide solution added is 0.5%~2.0% of the mass of the poly(N-isopropylacrylamide) solution; the reaction temperature in step 3) is 25~40℃, the reaction time is 3~6 h, and after the reaction is completed, the product is washed with water until neutral and then dried.

6. The preparation method of the temperature-controlled ecological sand soil conditioner according to claim 1, characterized in that, The compound fermentation agent is a compound agent containing lactobacillus, yeast, nitrogen-fixing bacteria, phosphate-solubilizing bacteria, and cellulose-decomposing bacteria, with a total effective viable count ≥1×10⁻⁶. 9 CFU / g; based on the percentage of live bacteria, the proportions of lactobacillus, yeast, nitrogen-fixing bacteria, phosphate-solubilizing bacteria, and cellulose-decomposing bacteria are 15%~30%, 10%~20%, 8%~15%, 5%~10%, and 5%~10%, respectively, with the remainder being one or more of actinomycetes or other facultative aerobic bacteria; the mass of the compound fermentation agent is 0.05%~0.15% of the premix mass.

7. The preparation method of the temperature-controlled ecological sand soil conditioner according to claim 1, characterized in that, The self-heating composting fermentation adopts a windrow-type pile, with a pile height of 2.3~2.8 m, a pile width of 2.0~2.5 m, and a pile density of 0.5~0.7 t / m³. 3 The self-heating composting fermentation includes a heating stage, a high-temperature stage, and a cooling stage. The entire fermentation process adopts intermittent forced aeration, with natural ventilation during aeration breaks, and the moisture content of the compost pile is maintained at 45%~60%. The heating stage lasts 7~12 days, during which the compost pile temperature rises from ambient temperature to 50~55℃. The high-temperature stage lasts 15~20 days, during which the compost pile temperature is maintained at 50~65℃. The cooling stage lasts 15~25 days. During the first 5~10 days of this stage, the compost pile temperature gradually decreases to 30~40℃, and then remains at 30~40℃ for 5~10 days before dropping to ambient temperature.

8. The preparation method of the temperature-controlled ecological sand soil conditioner according to claim 7, characterized in that, During the heating phase, the aeration intensity is 2.5~4.5 L / (min·kg), with each aeration lasting 10~15 min, and a 45~60 min break between aerations. The turning frequency is once every 5~6 days. During the high-temperature phase, the aeration intensity is 4.5~6.0 L / (min·kg), with each aeration lasting 15~20 min, and a 30~40 min break between aerations. The turning frequency is once every 5~6 days. During the cooling phase, the aeration intensity is reduced to 90%~95% of the previous day's intensity each day, then stabilized at 50%~65% of the high-temperature phase aeration intensity. The aeration frequency is 5~10 min per aeration, with a 60~90 min break between aerations. The turning frequency is initially once every 3~5 days, and then once every 2~3 days after the pile temperature drops below 35℃.

9. A temperature-controlled ecological sand soil conditioner prepared by the method according to any one of claims 1 to 8, characterized in that, The temperature-controlled ecological sand soil conditioner has a particle size mainly distributed in the range of 2-5 mm, a pH value of 7.2-8.0, a moisture content of <30%, a water holding capacity of ≥50%, a porosity of 35%-45%, an organic matter content of >40%, a heavy metal available content accounting for <30% of the total heavy metal content, and a seed germination index of >80%.

10. A method for applying a temperature-controlled ecological soil conditioner prepared by any one of claims 1 to 8, characterized in that, The temperature-controlled ecological soil conditioner can be directly laid on the desertified land to form an improved layer, and then covered with a layer of topsoil; or the temperature-controlled ecological soil conditioner can be mixed with the topsoil and then laid on the desertified land to form an improved layer.