Application method of three-step nitrogen conservation synergistic composting product in contaminated soil remediation

Abstract

The invention discloses an application method of a three-step nitrogen conservation synergistic compost product in contaminated soil remediation, and belongs to the technical field of organic waste compost fermentation. Aiming at the problems of difficulty in low-temperature starting, long fermentation period, serious greenhouse gas emission and serious nitrogen loss in the existing composting technology, a temperature-control time-sharing inoculation technology is adopted: a low-temperature-resistant lignocellulose degrading bacterium LDT1 is added in a low-temperature starting period to realize quick starting at 10-15 DEG C; a multi-element synergistic emission reduction system composed of zeolite, calcium superphosphate and ferrous sulfate is added in the high-temperature stable period; an alkali-resistant ammonia assimilation strain JS2 is added in the nitrogen retention period, and free ammonia nitrogen is converted into mycoprotein. According to the method, the composting period is shortened from 90-270 days to 30-40 days, the NH3 emission amount is reduced by 70-76%, the N2O emission amount is reduced by 35-45%, the CO2 emission amount is reduced by 45-55%, the ammonia nitrogen content is increased by 3-5 times compared with that of a traditional method, and collaborative optimization of degradation, emission reduction and nitrogen conservation is achieved.

Description

Technical Field

[0001] This invention relates to the field of organic waste composting and fermentation technology, and in particular to a method for applying a three-step nitrogen-preserving synergistic compost product based on temperature-controlled time-segmented inoculation technology in the remediation of contaminated soil. Background Technology

[0002] Composting technology, as an important means of resource utilization of organic waste, plays a vital role in agricultural waste treatment and soil improvement. Currently, composting technologies mainly include staged composting technology, microbial inoculant enhancement technology, and synergistic additive technology.

[0003] Regarding staged composting technology, US Patent 2010112675A1 discloses a multi-stage composting method. This method sequentially passes organic matter through different composting ecosystems. The first stage creates a robust mixed thermophilic environment for primary aerobic composting, and the second stage transfers it to a stratified composting ecosystem. This technology optimizes the diversity of decomposing microorganisms and improves the efficiency of organic matter decomposition. However, this method does not involve the addition of specific microbial agents, lacks low-temperature start-up technology, and does not consider greenhouse gas emission reduction issues.

[0004] Regarding microbial inoculant enhancement technology, Chinese patent CN103497915A discloses a composting fermentation compound inoculant and its application. This compound inoculant contains multiple microorganisms such as *Phanerochaete chrysosporium*, *Streptomyces griseus*, and *Bacillus subtilis*, which can achieve rapid heating and effective decomposition of lignocellulose in livestock and poultry manure compost. However, this technology does not involve staged addition, lacks consideration for low-temperature adaptability, and is not specifically designed for greenhouse gas emission reduction.

[0005] Existing composting technologies generally suffer from the following technical defects: First, they are difficult to start up under low-temperature conditions (below 15℃), and traditional composting technologies rely on natural heating, which limits their application in cold regions; second, the fermentation cycle is long, with a conventional composting cycle of 90-270 days, resulting in low production efficiency; third, greenhouse gas emissions are serious, with large emissions of NH3, N2O, and CO2, causing environmental pollution and nitrogen loss; and fourth, there is a lack of precise control technologies for different composting stages, making it impossible to achieve synergistic optimization of degradation, emission reduction, and nitrogen retention. Summary of the Invention

[0006] The technical problem to be solved by this invention is that existing composting technologies are difficult to start under low temperature conditions, have long fermentation cycles, serious greenhouse gas emissions, and serious nitrogen loss. They also lack precise control technologies for different composting stages and cannot achieve synergistic optimization of rapid degradation, greenhouse gas emission reduction, and nitrogen retention.

[0007] To address the aforementioned technical problems, this invention provides a method for applying three-step nitrogen-preserving synergistic compost products in contaminated soil remediation. This method employs staged bioaugmentation technology, optimizing the composting process through temperature-controlled timed inoculation and multi-element synergistic regulation. The core of this technical solution lies in precisely adding specific functional strains and conditioners at different stages based on the temperature change patterns and microbial community succession characteristics during composting, achieving the synergistic goals of efficient organic matter degradation, greenhouse gas emission reduction, and effective nitrogen retention.

[0008] Specifically, this application method first involves pre-treating and conditioning the raw materials. By adjusting the physicochemical properties of the compost substrate, a suitable environment is created for subsequent microbial activity. The pH value of the raw materials is precisely controlled within the range of 6.5 to 7.5, while the moisture content is adjusted to the optimal level of 60% to 65%. The carbon-nitrogen ratio is maintained within the ideal range of 30:1 to 40:1 through ratio adjustments. Based on this, bran can be selectively added as a microbial carrier, with the addition amount controlled at 1% of the weight of the compost raw materials, to provide a substrate for microbial attachment and growth.

[0009] During the low-temperature start-up phase, when the ambient temperature is between 10 and 15°C, low-temperature lignocellulose-degrading bacteria optimized by atmospheric pressure room temperature plasma mutagenesis are added to the conditioned compost raw materials. The atmospheric pressure room temperature plasma mutagenesis optimization refers to mutagenesis treatment of the strain using room temperature plasma under atmospheric pressure conditions. The active particles generated by the plasma act on the strain cells, inducing gene mutations and screening for superior strains with low temperature resistance and high enzyme activity. The treatment conditions include the optimization and control of parameters such as plasma power, treatment time, and gas composition. This bacterium was named LDT1 (accession number CGMCC No. 31578), and the bacterial concentration reached 5 × 10⁻⁶ after incubation in LB medium at 37°C for 24 hours. 8The total addition amount was 1% of the weight of the compost raw materials, at a concentration of CFU / ml. The LDT1 strain achieved a CMCase enzyme activity of 70 U / mL at 10℃ and 210 U / mL at 15℃. Enzyme activity was determined using the DNS method with sodium carboxymethyl cellulose (CMC-Na) as the substrate at a concentration of 1%, a reaction system of 50 mL, and a reaction time of 30 min. Enzyme activity was calculated by measuring the amount of reducing sugar produced. One unit of enzyme activity was defined as the amount of enzyme required to produce 1 μmol of reducing sugar per minute under the above conditions, ensuring efficient initiation of the cellulose degradation process even at low temperatures. Molasses can also be added as a carbon source supplement at a concentration of 0.1%–0.5% of the weight of the compost raw materials. The total sugar content of the molasses used should be ≥45%, ensuring a sufficient supply of readily available carbon source. This provides the necessary energy basis for rapid microbial reproduction and enzyme activation under low-temperature conditions, while avoiding carbon source insufficiency due to excessively low sugar content. The low-temperature start-up period lasts for 3 days at 10℃ and for 1-2 days at 15℃.

[0010] When the composting system temperature rises to 55–65℃ and enters the high-temperature stable period, a multi-component synergistic emission reduction system should be added in a timely manner to control greenhouse gas emissions. This emission reduction system consists of zeolite, superphosphate, and ferrous sulfate, which can be used alone or in combination, with the total addition amount controlled within the range of 0.5%–2% of the weight of the composting raw materials. The zeolite particle size is 2–3 mm, the superphosphate has an effective phosphorus content ≥12%, and the ferrous sulfate purity is ≥98%. The 2–3 mm particle size of the zeolite ensures a suitable specific surface area and pore structure, which is beneficial for ammonia adsorption; the effective phosphorus content of superphosphate ≥12% ensures sufficient phosphate ions to combine with ammonia to form ammonium phosphate; and the ferrous sulfate purity ≥98% ensures sufficient ferrous ions to catalyze the oxidation and decomposition of organic matter. The synergistic effect of the three components achieves efficient greenhouse gas emission reduction. When the three components are used simultaneously, their weight ratio is zeolite:superphosphate:ferrous sulfate = 2:1:1. This high-temperature stable period lasts for 3–7 days, with the highest composting temperature reaching 55–65℃.

[0011] During the nitrogen retention stage, when the compost temperature naturally drops to 45℃ after the high-temperature stabilization period, the alkali-tolerant ammonia-assimilating strain JS2 (CGMCC No. 31577) is added at a rate of 1.0%–1.5% of the weight of the compost raw materials. This strain converts free ammonia nitrogen in the compost system into microbial proteins through an assimilation mechanism, thereby achieving nitrogen biofixation and retention and effectively reducing nitrogen loss.

[0012] This technical solution is suitable for composting materials including any combination of livestock and poultry manure, crop straw, vegetable waste, and mushroom residue. The initial carbon-to-nitrogen ratio is controlled at 30:1 to 40:1, and the entire fermentation cycle is 30 to 40 days. This method is suitable for areas with ambient temperatures of 5 to 25°C and relative humidity of 40 to 80%, and can shorten the fermentation cycle by 2.5 to 3.5 times compared to traditional composting methods.

[0013] The compost product prepared using the above technical solution exhibits a unique three-phase layered structure. This structure consists of a bottom layer of incompletely decomposed organic matter, a middle layer of semi-decomposed organic matter, and a top layer of stable humus. The thickness ratio of each layer is approximately bottom:middle:top = 3:2:1, with clearly distinguishable interlayer interfaces. The bottom layer maintains a certain porosity to facilitate aeration, the middle layer exhibits high microbial activity, and the top layer forms a dense protective humus layer. This layered structure is due to the differentiated distribution of microbial communities at different stages of composting and the gradient changes in the degree of organic matter degradation. Each layer possesses different physicochemical properties and microbial community characteristics, forming a gradient nutrient release system, with a stable humus layer on the surface. Product quality indicators are significantly optimized: Escherichia coli count ≤100 CFU / g, Ascaris egg mortality rate ≥95%, seed germination index ≥80%, C / N ratio controlled between 15 and 20, pH value stable within the range of 7.0 to 8.5, organic matter content ≥30%, and total nitrogen content ≥1.8%. Compared with traditional composting methods, according to GB / T 25246-2010 standard, NH3 emissions are reduced by 70-76%, N2O emissions by 35-45%, CO2 emissions by 45-55%, and ammonia nitrogen content is increased by 3-5 times. This method can reduce NH3 emissions by 70-76%, N2O emissions by 35-45%, and CO2 emissions by 45-55%, while increasing ammonia nitrogen content by 3-5 times compared with traditional methods, achieving a dual improvement in environmental friendliness and product quality.

[0014] The present invention has the following advantages over the prior art: 1. Significantly shortened fermentation cycle: Through temperature-controlled timed inoculation technology, the composting cycle is shortened from the traditional 90-270 days to 30-40 days, and the fermentation efficiency is increased by 2.5-7.5 times. The fermentation cycle is shortened from the traditional 90-270 days to 30-40 days, a reduction of 2.5-3.5 times. Rapid organic matter degradation is achieved through the synergistic effect of specific strains.

[0015] 2. Achieving low-temperature and high-efficiency start-up: Using atmospheric pressure and room temperature plasma-directed breeding strains, fermentation can be started rapidly at an ambient temperature of 10-15℃. The CMCase enzyme activity of the LDT1 strain reaches 70 U / mL at 10℃ and 210 U / mL at 15℃, which solves the technical bottleneck of difficult composting start-up in cold regions.

[0016] 3. Significant Synergistic Emission Reduction and Nitrogen Preservation Effects: Through the synergistic effect of a multi-element synergistic emission reduction system and alkali-tolerant ammonia assimilation strains, compared with traditional composting methods, according to GB / T 25246-2010 standard, NH3 emissions are reduced by 70-76%, N2O emissions by 35-45%, CO2 emissions by 45-55%, and ammonia nitrogen content is increased by 3-5 times.

[0017] 4. Improve the quality of compost products: The organic matter content of compost products is ≥30%, the total nitrogen content is ≥1.8%, the C / N ratio is 15-20, the number of Escherichia coli is ≤100 / g, the mortality rate of Ascaris eggs is ≥95%, the seed germination index is ≥80%, the pH value is 7.0-8.5, and the product quality is stable and reliable. Attached Figure Description

[0018] Figure 1 This is a temperature change curve during the composting process in an embodiment of the present invention; Figure 2 This is a graph showing the change in nitrogen content during the composting process in an embodiment of the present invention; Figure 3 This is a schematic diagram of the temperature-controlled time-sharing inoculation process of the present invention. Detailed Implementation

[0019] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0020] Example 1: The purpose of this example is to verify the application effect of temperature-controlled timed inoculation technology in cow manure composting and to demonstrate the phased bio-enhancing process scheme of low-temperature start-up period, high-temperature stabilization period and nitrogen retention period.

[0021] Fresh cow manure was selected as the composting material. The initial moisture content of the cow manure was 78%, the total nitrogen content was 1.2%, and the pH value was 7.8.

[0022] Step 1: Raw Material Preparation. Mix cow manure and crushed corn stalks at a weight ratio of 4:1, adjust the moisture content to 65%, the carbon-to-nitrogen ratio to 38:1, and the pH value to 7.2. Add wheat bran as a microbial carrier, at a rate of 1% of the weight of the compost raw materials.

[0023] Step Two: Low-Temperature Start-up Period. At an ambient temperature of 12℃, the low-temperature start-up cellulose-degrading bacterium LDT1 (accession number CGMCC No. 31578) was added to the composting material. LDT1 was cultured in LB medium (10 g / L peptone, 5 g / L yeast extract, 10 g / L NaCl, pH 7.0) at 37℃ and 150 rpm for 24 hours. The concentration was determined using the plate count method to be 5 × 10⁻⁶. 8 The total amount added is 1% of the weight of the compost raw materials, at a concentration of CFU / ml. Molasses is also added as a carbon source supplement at a concentration of 0.3% of the weight of the compost raw materials, with a total sugar content of 48%.

[0024] The CMCase enzyme activity of strain LDT1 was determined at 10℃ and 15℃ using the DNS method. Sodium carboxymethyl cellulose (CMC-Na) was used as the substrate at a concentration of 1%, with a reaction volume of 50 mL, pH 4.8, a reaction temperature of 10℃, and a reaction time of 30 min. The enzyme activity reached 70.5 U / mL. At 15℃ and pH 4.8, the enzyme activity reached 217.2 U / mL.

[0025] Step 3: High-Temperature Stabilization Period. Through the metabolic heat production of specific bacterial strains and external insulation measures, the compost temperature is gradually increased to above 55℃ within 72 hours. When the temperature reaches 60℃, a multi-component synergistic emission reduction system is added. The emission reduction system consists of zeolite, superphosphate, and ferrous sulfate in a weight ratio of 2:1:1. The zeolite particle size is 2.5mm, the specific surface area is 320m² / g, the available phosphorus content of superphosphate is 14%, and the purity of ferrous sulfate is 98.5%. The total amount of the emission reduction system added is 1.2% of the weight of the compost raw materials. The high-temperature period is maintained for 5 days, with the highest temperature reaching 62.3℃.

[0026] Step 4: Nitrogen Retention Period. When the composting temperature drops from the high-temperature period to 45℃, add the alkali-tolerant ammonia assimilation strain JS2 (CGMCC No. 31577) at a rate of 1.5% of the weight of the compost raw materials. This strain grows normally in an environment with an ammonia nitrogen concentration of 3000 mg / L, converting free ammonia nitrogen into bacterial protein through assimilation, achieving a nitrogen conversion efficiency of 90%.

[0027] The entire fermentation cycle takes 36 days. For example... Figure 1As shown, the temperature change curves during the composting process clearly demonstrate the temperature characteristics of three stages: the low-temperature start-up period (0-3 days) sees the temperature gradually rise from the ambient temperature of 12℃ to 50℃; the high-temperature stabilization period (4-8 days) maintains the temperature within the range of 55-65℃; and the nitrogen retention period (9-36 days) sees the temperature gradually decrease to below 45℃ and tend to stabilize. This temperature change pattern verifies the effectiveness of the temperature-controlled time-segmented inoculation technology. Temperature changes were monitored daily during fermentation using a portable thermometer (accuracy ±0.1℃); physicochemical indicators were periodically sampled and analyzed. Moisture content was determined using the 105℃ drying method, pH value was determined using a pH meter (PHS-3C type), and total nitrogen content was determined using the Kjeldahl method. Figure 2 As shown, the nitrogen content changes dynamically during composting, with the total nitrogen content increasing from an initial 1.2% to a final 2.1%, demonstrating the enrichment effect of nutrients.

[0028] Gas emission measurement: Gas samples were collected using the static chamber method, with sampling three times a day. NH3 was determined by Nessler's reagent spectrophotometry (HJ 533-2009), N2O was determined by gas chromatography, and CO2 was determined by infrared gas analyzer.

[0029] The above experiment was repeated three times. The results showed that the total nitrogen content of the compost product reached 2.1±0.15%, which was 75% higher than that of the initial raw material. NH3 emissions were reduced by 76.0±2.1%, N2O emissions by 40.1±1.8%, and CO2 emissions by 50.7±2.3%. The differences were statistically significant (P<0.05), which proved the superiority of the technical solution of the present invention.

[0030] Example 2: The purpose of this example is to verify the adaptability of temperature-controlled time-sharing inoculation technology under different ambient temperature conditions and to demonstrate the low-temperature start-up advantages of ambient pressure room temperature plasma directional breeding strains.

[0031] The same cow dung and corn stalks were used as composting materials, and the material preparation method was the same as in Example 1.

[0032] Composting experiments were conducted at an ambient temperature of 10°C. The low-temperature start-up period lasted for 3 days, during which LDT1 strain was added at the same concentration and amount as in Example 1.

[0033] The CMCase enzyme activity of strain LDT1 at 10℃ was measured to be 71.3 U / mL, demonstrating excellent low-temperature adaptability.

[0034] The high-temperature stability period was maintained for 7 days, with the highest temperature reaching 58℃ through insulation measures and heat generation from bacterial metabolism. The multi-element synergistic emission reduction system was added at 1.5% of the weight of the compost raw materials, including zeolite with a particle size of 2mm, a specific surface area of ​​310m² / g, superphosphate with an available phosphorus content of 12%, and ferrous sulfate with a purity of 98%.

[0035] The nitrogen retention period requires the addition of alkali-tolerant ammonia-assimilating strain JS2 at a rate of 1.5% of the weight of the compost raw materials. The entire fermentation cycle is 38 days.

[0036] The experiment was repeated three times. The test results showed that even at a low temperature of 10℃, the compost could still start and complete the fermentation process. The total nitrogen content of the compost product reached 1.9±0.12%, and the NH3 emission was reduced by 72±2.5%, which verified the effectiveness of the technology of the present invention in low temperature environment.

[0037] Example 3: The purpose of this example is to verify the application effect of temperature-controlled time-segmented inoculation technology under different raw material ratios and to demonstrate the applicability of the technical solution.

[0038] Pig manure, vegetable waste, and mushroom residue were selected as composting materials. The initial moisture content of the pig manure was 75%, the total nitrogen content was 1.5%, and the pH value was 8.2.

[0039] Raw material conditioning: Adjust the moisture content to 65%, the carbon-nitrogen ratio to 35:1, and the pH value to 6.8.

[0040] Low-temperature start-up period: The LDT1 strain was kept at an ambient temperature of 15℃ for one day. At 15℃, the cellulase activity reached 227.6 U / mL.

[0041] High-temperature stabilization period: maintained for 3 days, with a maximum temperature reaching 65℃. The amount of the multi-element synergistic emission reduction system added is 0.8% of the weight of the compost raw materials.

[0042] Nitrogen retention period: The amount of alkali-resistant ammonia assimilation strain JS2 added is 1.5% of the weight of compost raw materials.

[0043] The entire fermentation cycle was 32 days. The experiment was repeated 3 times. The compost product had an organic matter content of 32±1.2%, a total nitrogen content of 2.3±0.18%, a C / N ratio of 18, an E. coli count of 85 / g, a roundworm egg mortality rate of 96%, and a seed germination index of 85%. All indicators met the requirements of organic fertilizer standards.

[0044] Comparative Example 1: The purpose of this comparative example is to verify the difference in composting effect when the staged bio-fortification process is lacking. The traditional one-time addition method is used for comparison.

[0045] The same cow dung and corn stalk raw materials as in Example 1 were used, and the raw material conditioning method was the same. All bacterial strains and emission reduction agents were added at the beginning of composting, without phased addition. LDT1 and JS2 strains were added simultaneously, with a total addition amount of 2% of the weight of the compost raw materials, and the addition amount of the multi-element synergistic emission reduction system was 1.2%.

[0046] Monitoring was performed using the same test methods and conditions as in Example 1, and the experiment was repeated three times.

[0047] The comparison results show that: Heating rate: It takes 72 hours to reach 50°C (72 hours to reach 55°C in Example 1); Duration of high temperature period: only 2 days (5 days in Example 1); Maximum temperature: 56℃ (62.3℃ in Example 1); Fermentation cycle: extended to 65 days (36 days in Example 1); Total nitrogen content of compost product: 1.6±0.13% (2.1±0.15% in Example 1); NH3 emissions decreased by 45 ± 3.2% (76.0 ± 2.1% in Example 1); N2O emissions were reduced by 25 ± 2.8% (40.1 ± 1.8% in Example 1). The comparison shows that the lack of a phased bio-enhancing process leads to slow composting start-up, prolonged fermentation cycle, and a significant decrease in emission reduction and nitrogen retention effects, proving the necessity and superiority of the temperature-controlled time-sharing inoculation technology of this invention.

[0048] Comparative Example 2: The purpose of this comparative example is to verify the composting effect under low-temperature conditions when plasma-directed breeding strains are absent. Conventional strains are used for comparison.

[0049] The same raw materials and environmental conditions (10°C) as in Example 2 were used, but conventional cellulose-degrading bacteria were used instead of the LDT1 strain. The conventional strain was a commercially available cellulase-producing bacterium (a combination of Bacillus subtilis and Aspergillus niger), with an enzyme activity of only 15-20 U / mL at 10°C.

[0050] The other operating steps are the same as in Example 2, and the same testing method is used for monitoring. The experiment is repeated 3 times.

[0051] The comparison results show that: Heating time: It takes 7 days to reach 40°C (3 days to reach 50°C in Example 2); Duration of high temperature period: only 3 days (7 days in Example 2); Maximum temperature: 52℃ (58℃ in Example 2); Fermentation cycle: extended to 85 days (38 days in Example 2); Total nitrogen content of compost product: 1.4±0.11% (1.9±0.12% in Example 2); NH3 emissions were reduced by 35 ± 2.9% (72 ± 2.5% in Example 2); The comparison shows that the lack of plasma-directed breeding strains leads to difficulties in low-temperature start-up and low fermentation efficiency, demonstrating the important role and technical advantages of the specific strains of this invention.

[0052] Comparative Example 3: The purpose of this comparative example is to verify the greenhouse gas emissions in the absence of a multi-element synergistic emission reduction system. A scheme without adding emission reduction agents is used for comparison.

[0053] The same raw materials and strain addition scheme as in Example 1 were used, but the multi-element synergistic emission reduction system was not added during the high-temperature stability period.

[0054] The other operating procedures are the same as in Example 1, with a focus on monitoring greenhouse gas emissions. The experiment was repeated three times.

[0055] The comparison results show that: NH3 emissions decreased by 25 ± 2.1% (76.0 ± 2.1% in Example 1). N2O emissions were reduced by 15 ± 1.8% (40.1 ± 1.8% in Example 1). CO2 emissions were reduced by 20 ± 2.0% (50.7 ± 2.3% in Example 1). Ammonia nitrogen retention rate: 1.8 times higher than the initial level (3.5 times higher in Example 1); The comparison shows that the lack of a multi-faceted synergistic emission reduction system leads to a significant decrease in greenhouse gas emission reduction effectiveness, proving the key role of time-series compound conditioners in synergistic emission reduction.

[0056] Based on the above embodiments and comparative examples, such as Figure 3 As shown, this invention achieves multiple objectives—rapid start-up, efficient degradation, synergistic emission reduction, and nitrogen retention—through temperature-controlled time-segmented inoculation technology. Key innovations include: using plasma-guided breeding strains for low-temperature start-up; precisely adding a multi-element synergistic emission reduction system during the high-temperature period to achieve greenhouse gas emission reduction; and adding biological nitrogen-fixing coupled strains during the cooling period to achieve nitrogen retention. Compared with existing technologies, this invention significantly shortens the fermentation cycle, improves emission reduction and nitrogen retention effects, expands the scope of application, and provides an efficient and environmentally friendly technical solution for the resource utilization of organic waste.

Claims

1. A method for applying three-step nitrogen-retaining synergistic compost products in contaminated soil remediation, characterized in that, Includes the following steps: Step 1: Raw material conditioning. Adjust the pH value of the compost raw materials to 6.5-7.5, control the moisture content to 60%-65%, and control the carbon-nitrogen ratio to 30:1-40:

1. Step 2: Low-temperature start-up period. Under an ambient temperature of 10–15℃, add the low-temperature resistant lignocellulose-degrading bacteria LDT1 to the composting raw materials. The preservation number of LDT1 strain is CGMCC No. 31578. After culturing the degrading bacteria in LB medium at 37℃ for 24 hours, the concentration determined by plate counting method is 5 × 10⁻⁶. 8 CFU / ml, added at 1% of the weight of the compost raw materials; Step 3: High-temperature stabilization period. When the composting temperature rises to 55-65℃, add a multi-element synergistic emission reduction system. The emission reduction system includes one or more of zeolite, superphosphate, and ferrous sulfate, and the addition amount is 0.5-2% of the weight of the composting raw materials. Step 4: Nitrogen retention period. When the compost temperature drops to 45℃ after the high-temperature stable period ends, add the alkali-resistant ammonia assimilation strain JS2 (CGMCC No. 31577). Through assimilation, free ammonia nitrogen is converted into bacterial protein, thus achieving nitrogen fixation.

2. The method for applying the three-step nitrogen-retaining synergistic compost product according to claim 1 in contaminated soil remediation, characterized in that, The LDT1 strain exhibited a CMCase activity of 70 U / mL at 10°C and 210 U / mL at 15°C.

3. The method for applying the three-step nitrogen-retaining synergistic compost product in contaminated soil remediation according to claim 1, characterized in that, The low-temperature start-up period lasts for 3 days at 10℃ and for 1-2 days at 15℃. The high-temperature stabilization period lasts for 3-7 days, and the maximum composting temperature reaches 55-70℃. The amount of alkali-resistant ammonia-assimilating strains added during the nitrogen retention period is 1.0%-1.5% of the weight of the composting raw materials.

4. The method for applying the three-step nitrogen-retaining synergistic compost product according to claim 1 in contaminated soil remediation, characterized in that, In the multi-electrode synergistic emission reduction system, the zeolite has a particle size of 2-3 mm, the effective phosphorus content of superphosphate is ≥12%, the purity of ferrous sulfate is ≥98%, and the weight ratio of the three emission reduction agents is zeolite: superphosphate: ferrous sulfate = 2:1:

1.

5. The method for applying the three-step nitrogen-retaining synergistic compost product in contaminated soil remediation according to claim 1, characterized in that, Molasses is added as a carbon source supplement during the low-temperature start-up period. The amount of molasses added is 0.1% to 0.5% of the weight of the compost raw materials, and the total sugar content of the molasses is ≥45%.

6. The method for applying the three-step nitrogen-retaining synergistic compost product according to claim 1 in contaminated soil remediation, characterized in that, The composting materials include any combination of livestock and poultry manure, crop straw, vegetable waste and mushroom residue, with the initial carbon-nitrogen ratio controlled at 30:1 to 40:1, and the entire fermentation cycle is 30 to 40 days.

7. The method for applying the three-step nitrogen-retaining synergistic compost product according to claim 1 in contaminated soil remediation, characterized in that, The raw material conditioning step also includes adding wheat bran as a microbial carrier, with the amount of wheat bran added being 1% of the weight of the compost raw material.

8. The method for applying the three-step nitrogen-retaining synergistic compost product according to claim 1 in contaminated soil remediation, characterized in that, Compared with traditional composting methods, according to the GB / T 25246-2010 standard, the compost products obtained by the above method have NH3 emissions reduced by 70% to 76%, N2O emissions reduced by 35% to 45%, CO2 emissions reduced by 45% to 55%, and ammonia nitrogen content increased by 3 to 5 times compared with traditional composting methods.

9. The method for applying the three-step nitrogen-retaining synergistic compost product according to claim 1 in contaminated soil remediation, characterized in that, The method is suitable for areas with ambient temperatures of 5–25℃ and relative humidity of 40%–80%. The fermentation cycle is shortened by 2.5–3.5 times compared to traditional composting methods, and the compost product has an organic matter content of ≥30% and a total nitrogen content of ≥1.8%.

10. The compost product prepared by the method of claim 1, characterized in that, The compost product has a three-phase layered structure, with a stable humus layer on the surface, containing ≤100 Escherichia coli / g, ≥95% mortality rate of Ascaris eggs, ≥80% seed germination index, C / N ratio of 15-20, and pH value of 7.0-8.5.

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