Method for promoting decay, preserving nitrogen and immobilizing heavy metals in organic solid waste compost

Abstract

The invention relates to a method for promoting decay, preserving nitrogen and fixing heavy metals in organic solid waste compost, and belongs to the technical field of organic solid waste recycling. The compound additive is prepared by combining a compound fungicide of white-rot fungi and sulfur reduction geobacter with phosphate, and compost humification synergism, nitrogen retention and heavy metal immobilization are achieved through the synergistic effect of biodegradation and chemical passivation. The method specifically comprises the following steps: (1) preparing a compound fermentation inoculant; (2) uniformly mixing a compound fermentation inoculant with phosphate, and adding the mixture into the compost raw material; and (3) carrying out aerobic composting treatment. The organic solid waste compost can promote decomposition and protect nitrogen and fix heavy metals, realizes safe land utilization of compost products, and has a good application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of resource treatment of organic waste, and particularly relates to a composite additive of a composite fermentation bacterium agent and phosphate, and a method for realizing the synergistic effects of compost humification enhancement, nitrogen retention and heavy metal fixation through biodegradation and chemical passivation. Background Art

[0002] With the growth of population and the improvement of living standards, the demand for livestock products has increased, leading to the expansion of the livestock industry. The intensive farming mode has generated a large amount of livestock manure. The annual output of livestock manure in China reaches 3.8 billion tons, making it an important agricultural pollution source. Promoting the resource utilization of livestock manure by returning it to the field can not only effectively alleviate the environmental pollution problems caused by livestock breeding, but also provide organic fertilizers for planting and reduce the use of chemical fertilizers. However, direct application or improper treatment of manure will introduce toxic substances such as heavy metals, antibiotics and pathogens into the environment, posing risks to human health and environmental safety. To ensure the safe utilization of livestock manure and achieve effective resource conversion, it is usually necessary to carry out composting treatment on livestock manure before returning it to the field. However, during the conventional composting process, a large amount of NH3 volatilization will cause serious nitrogen loss, thereby reducing the quality of organic fertilizers. Therefore, how to control nitrogen loss and environmental risks such as heavy metals while promoting compost maturity has been the focus of compost technology research and application in recent years.

[0003] During the composting process, in order to shorten the fermentation cycle, reduce nitrogen loss and control environmental risks, various microorganisms, organic or inorganic substances are often added to the compost pile as additives. Most inorganic additives have the characteristics of porosity and large specific surface area. They can not only act as Lewis acids to catalyze the Maillard reaction of amino acids and reducing sugars to form humus, but also prevent the degradation of humus by microorganisms through ion adsorption or chemical interactions. Both natural and synthetic organic additives can promote compost humification by enhancing the activity of microorganisms and enzymes, reducing the production of CO2, and directly participating in humification pathways such as the Maillard reaction. Microbial additives such as white rot fungi can promote the degradation of lignocellulose and various aromatic compounds, releasing polyphenols, sugars and nitrogen-containing compounds, thus promoting the formation of humus. Although inorganic and organic additives have good humification promotion effects, they also have problems of high cost and non-reusability. In addition, due to the drastic changes in the compost environment and the evolution of the microbial community, it is also difficult to control the effect of exogenous microbial additives on promoting humification. The composite additive can reduce the dosage of the additive, save costs, and at the same time combine the advantages of different additives to promote compost humification. Therefore, developing a high-efficiency and low-cost compost composite additive is the key technology for promoting compost humification and nitrogen preservation and safe utilization of land at present.

[0004] Microorganisms play a crucial role in the humification and nitrogen cycling processes during composting. Previous studies have shown that adding microbial inoculants to compost optimizes the microbial community structure, accelerates the degradation of lignocellulose, promotes the humification process, and enhances the nitrogen retention capacity, thereby improving the quality of compost products. The white-rot fungus Phanerochaete chrysosporium, as an efficient lignocellulose-degrading functional bacterium, secretes a non-specific oxidase system composed of manganese peroxidase (MnP), lignin peroxidase (LiP), and laccase (Lac), which targets the cleavage of the lignin-cellulose composite structure and degrades aromatic compounds, releasing humus precursor substances such as polyphenols, reducing sugars, and nitrogen-containing compounds, directly driving the synthesis of humic acids, significantly enhancing the compost humification efficiency and shortening the cycle. Geobacter sulfurreducens is a humus-reducing bacterium that can reduce sulfates, sulfites, etc. to sulfides through the sulfur reduction metabolic pathway, combine with heavy metal ions to form stable metal sulfide precipitates. In addition, it can mediate the electron transfer of high-valent heavy metals and reduce them to low-toxicity low-valent forms, significantly reducing the bioavailability and ecological toxicity of heavy metals, and has been widely used in scenarios such as acid mine wastewater treatment and polluted soil remediation. Although white-rot fungi have been proven to have high lignocellulose degradation ability, their specific role in compost nitrogen transformation is still unclear. Although Geobacter sulfurreducens is widely used in heavy metal bioremediation, its contribution to humus synthesis and organic carbon stabilization has not been clarified. In the existing technology, due to the limitations of the functions and insufficient environmental adaptability of single inoculants, it is difficult to simultaneously achieve the enhancement of compost humification, nitrogen retention, and heavy metal risk control. Composite microbial inoculants combine microorganisms with different functions and provide a more comprehensive method for regulating the composting process compared with single inoculants, thus accelerating the maturity of compost. Therefore, the synergistic effect of white-rot fungi and Geobacter sulfurreducens in livestock manure composting is also worthy of in-depth study.

[0005] Adding acidic chemicals such as phosphates during composting can not only effectively reduce the pH value of the materials and inhibit the conversion of NH4 + to NH3, but also combine with NH4 + to stabilize it and reduce nitrogen loss during composting. Some studies have found that adding phosphogypsum and superphosphate can promote the formation of humus and further improve the maturity of compost. However, there are relatively few reports on whether microbial composite inoculants and phosphates can synergistically enhance the quality of compost during the composting process, and the research in this field remains to be explored in depth.

[0006] In summary, aiming at the problems of poor composting maturity, nitrogen loss during composting, and heavy metal residues in organic solid waste, a composite microbial inoculant is prepared and phosphate is mixed and added to construct a "rotting promotion - nitrogen fixation - pollution control" synergistic system in composting, which is of great significance for improving the quality of organic solid waste composting and realizing the safe land use of compost products. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to propose a method for promoting the rotting, preserving nitrogen and fixing heavy metals in organic solid waste composting in view of problems such as poor composting maturity, nitrogen loss during composting, and heavy metal residues.

[0008] To achieve the above object, the present invention adopts the following technical solutions: A method for promoting the rotting, preserving nitrogen and fixing heavy metals in organic solid waste composting, comprising the following steps: (1) Prepare a white rot fungus - Geobacter sulfurreducens composite fermentation inoculant; (2) Mix the white rot fungus - Geobacter sulfurreducens composite fermentation inoculant with a phosphate additive to obtain a composite additive; add the composite additive to the compost raw materials, adjust the initial C / N ratio to 20, and adjust the initial moisture content to 60% - 65% to obtain a compost pile; (3) Carry out aerobic composting treatment on the compost pile.

[0009] Further, the preparation method of the above-mentioned white rot fungus - Geobacter sulfurreducens composite fermentation inoculant comprises the following steps: S1: Inoculate white rot fungus and Geobacter sulfurreducens into slant media respectively, and carry out constant temperature culture at 33 - 36 °C for 24 - 48 hours to obtain activated strains of white rot fungus and Geobacter sulfurreducens respectively; S2: Inoculate the activated strains of white rot fungus and Geobacter sulfurreducens obtained in step S1 into seed media respectively, and carry out shaking culture at 33 - 36 °C and a rotation speed of 120 rpm for 18 - 24 hours until the logarithmic phase to obtain a white rot fungus seed solution and a Geobacter sulfurreducens seed solution respectively; S3: Mix the white rot fungus seed solution and the Geobacter sulfurreducens seed solution obtained in step S2 according to a volume ratio of 1:0.5 - 1:2, then inoculate them into the fermentation medium at an inoculation amount of 10 vol%, and carry out aeration fermentation at 33 - 36 °C, a rotation speed of 150 rpm, an air ventilation rate of 0.8 vvm, and a tank pressure of 0.08 Mpa for 18 - 24 hours to obtain a white rot fungus - Geobacter sulfurreducens composite fermentation inoculant; The formula of the slant medium is as follows: per 1 L volume, it contains 5 g of yeast extract, 10 g of tryptone, 10 g of NaCl, 15 - 20 g of agar, and the rest is distilled water; the formula of the seed medium is as follows: per 1 L volume, it contains 4 - 8 g of yeast extract, 8 - 12 g of tryptone, 18 - 20 mL of potato extract, 8 - 12 g of sodium chloride, 15 - 20 g of agar, and the rest is distilled water; the formula of the fermentation medium is as follows: per 1 L volume, it contains 800 - 900 mL of pig manure extract and 100 - 200 mL of potato extract; the preparation method of the potato extract is as follows: after peeling and slicing fresh potatoes, mix them with distilled water at a ratio of 1:3 - 5 w / v, boil for 30 - 40 minutes, filter to obtain the filtrate, which is the potato extract; the preparation method of the pig manure extract is as follows: dry pig manure at 105 °C for 24 hours, then mix it with distilled water at a ratio of 1:5 - 10 w / v, extract at 25 - 30 °C for 24 - 48 hours, centrifuge to obtain the supernatant, which is the pig manure extract. Among them, the potato extract can supply easily degradable carbon sources such as starch and glucose, as well as growth factors such as vitamin B group and biotin, stimulating the metabolic activity of microorganisms; the pig manure extract can provide sulfur source and organic nitrogen source, providing metabolic substrates for microorganisms, and at the same time having a slow-release property to avoid the inhibition of the activity of the bacterial community due to excessive ammonia concentration; the fermentation medium contains potato extract and pig manure extract, with characteristics such as complementary nutrition and metabolic synergy, which can enable the bacterial community to adapt to complex substrates in advance and enhance the functional expression of the subsequent compound microbial agent.

[0010] Further, the mass ratio of the above-mentioned white rot fungus - Geobacter sulfurreducens composite fermentation microbial agent to the phosphate additive is 1:0.2 - 1.

[0011] Further, the above-mentioned phosphate additive is any one or more of phosphogypsum, superphosphate, and calcium dihydrogen phosphate.

[0012] Further, the addition amount of the above-mentioned composite additive is 0.5 wt% - 5 wt% of the dry weight of the compost raw materials.

[0013] Further, the process of the above-mentioned aerobic composting treatment lasts for 42 days, and is divided into a heating period, a high-temperature period, a cooling period, and a maturity period; during the heating period and the high-temperature period, the compost is turned over once a day, and the turning time each time is 30 - 40 minutes. After entering the cooling period, the compost is turned over twice a day, the turning time each time is 30 - 40 minutes, and the time interval between turnings is 8 - 12 hours.

[0014] Further, the above-mentioned promoting decay means increasing the humic acid content and the humic acid - fulvic acid ratio of the compost; nitrogen preservation means increasing the nitrate nitrogen content and the total nitrogen content of the compost; heavy metal fixation means passivating heavy metals and reducing the bioavailability and environmental mobility of heavy metals.

[0015] The application of the above-mentioned method for promoting decay, preserving nitrogen, and fixing heavy metals in organic solid waste composting in any one or more of the following: 1) Applications in the treatment of organic solid waste; 2) Applications in promoting the decomposition and nitrogen preservation of compost; 3) Applications in heavy metal immobilization.

[0016] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: (1) The present invention significantly improves the humification efficiency through the synergistic effect of "compound fermentation inoculant - phosphate". White rot fungi secrete lignocellulose-degrading enzymes such as laccase to degrade lignocellulose and release humus precursors. Geobacter sulfurreducens participates in the electron transfer of quinone humus intermediates through its extracellular electron transfer system, thereby accelerating the synthesis of humus. As a key nutrient for microbial growth, phosphate can promote the metabolic activity of the compound inoculant, and thus affect the synthesis process of humus. After the composting is completed, the humic acid content increases by 13.1% - 53.2%, and the degree of polymerization (DP = HA / FA) is significantly improved, shortening the composting fermentation cycle.

[0017] (2) The present invention effectively reduces nitrogen loss through the synergistic effect of "compound fermentation inoculant - phosphate". White rot fungi significantly increase the nitrate nitrogen content by promoting nitrification. Geobacter sulfurreducens realizes nitrogen fixation by accelerating the synthesis of nitrogen-containing humus through its extracellular electron transfer system. Phosphate inhibits the conversion of ammonium nitrogen to ammonia by regulating the pH of the compost pile, reducing nitrogen loss. After the composting is completed, the total nitrogen content increases by 16.79% - 28.31%, promoting nitrogen retention in the compost.

[0018] (3) The present invention reduces the bioavailability and environmental mobility of heavy metals through the synergistic effect of "compound fermentation inoculant - phosphate", reducing the environmental risk of compost products. The S produced by the metabolism of Geobacter sulfurreducens 2- forms insoluble sulfides with heavy metals such as Cd 2+ , Pb 2+ etc. In addition, highly toxic heavy metal forms such as Cr(VI) are reduced to Cr(III). The PO4 of phosphate 3- forms compounds with heavy metals such as Cu 2+ , Zn 2+Heavy metals such as generate stable phosphates. The bioavailability of Zn and Cu decreased by 4.71% - 17.17% and 4.32% - 44.36% respectively, and the heavy metal content after composting met the "Technical Specification for Composting of Livestock and Poultry Manure" (NY / T 3442—2019). (4) The method of the present invention has the advantages of environmental friendliness and economy. The composite fermentation inoculant reduces the emissions of compost nitrogen gases such as NH3 and N2O through enhanced nitrification, reduces air pollution, improves the quality of compost, is beneficial to the safe utilization of land, and reduces environmental risks. The use of phosphates such as phosphogypsum and superphosphate not only reduces the treatment cost of waste, but also converts it into a valuable compost additive, realizing the high value-added of industrial by-products, can replace high-cost passivators such as zeolite and diatomite, and the raw material cost is reduced by 30% - 50%, with significant economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a graph showing the change of the temperature at the center of the compost pile with time during the composting process of Examples 1 - 4 and Comparative Examples 1 - 4.

[0020] Figure 2 It is the content of humic acid (HA) during the composting process of Examples 1 - 4 and Comparative Examples 1 - 4.

[0021] Figure 3 It is a graph showing the change of the degree of polymerization (HA / FA) during the composting process of Examples 1 - 4 and Comparative Examples 1 - 4.

[0022] Figure 4 It is the graph of the content change of nitrate nitrogen (NO3 - -N) during the composting process of Examples 1 - 4 and Comparative Examples 1 - 4.

[0023] Figure 5 It is a graph showing the change of the total nitrogen (TN) content during the composting process of Examples 1 - 4 and Comparative Examples 1 - 4.

[0024] Figure 6 It is a graph showing the change of the bioavailability of Cu and Zn during the composting process of Examples 1 - 4 and Comparative Examples 1 - 4. DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention will be further described in detail below in conjunction with the specific embodiments. The examples given are only for clarifying the present invention, rather than limiting the scope of the present invention. The following examples can be used as a guide for those of ordinary skill in the art to make further improvements, and do not limit the present invention in any way.

[0026] The present invention places no special restrictions on the sources of the white-rot fungus Phanerochaete chrysosporium and Geobacter sulfurreducens. Commercially available products can be used, or strains isolated and purified from nature can also be used. In a specific embodiment of the present invention, Phanerochaete chrysosporium is preferably BNCC336257 from the Henan Provincial Engineering and Technology Research Center for Industrial Microbial Strains, and Geobacter sulfurreducens is preferably ATCC51573 from the American Type Culture Collection.

[0027] In the present invention, pig manure was collected from a pig farm in Fuzhou, Fujian Province; sawdust was purchased from a wood factory in Xiamen, Fujian Province. The physical and chemical indicators are shown in Table 1.

[0028] Table 1 Physical and chemical indicators of pig manure and sawdust The preparation steps of the white-rot fungus-Geobacter sulfurreducens composite fermentation agent of the present invention are as follows: S1: Inoculate the white-rot fungus and Geobacter sulfurreducens into slant media respectively, and incubate them at a constant temperature of 33-36°C for 24-48 hours to obtain the activated strains of the white-rot fungus and Geobacter sulfurreducens respectively; S2: Inoculate the activated strains of the white-rot fungus and Geobacter sulfurreducens obtained in step S1 into seed media respectively, and shake-culture them at a temperature of 33-36°C and a rotation speed of 120 rpm for 18-24 hours until the logarithmic phase to obtain the seed solutions of the white-rot fungus and Geobacter sulfurreducens respectively; S3: Mix the seed solutions of the white-rot fungus and Geobacter sulfurreducens obtained in step S2 at a volume ratio of 1:1, and then inoculate them into the fermentation medium at an inoculation amount of 10 vol%, and conduct aeration fermentation at a temperature of 33-36°C, a rotation speed of 150 rpm, an air ventilation rate of 0.8 vvm, and a tank pressure of 0.08 Mpa for 18 hours to obtain the white-rot fungus-Geobacter sulfurreducens composite fermentation agent.

[0029] The preparation steps of the white-rot fungus fermentation agent of the present invention are as follows: S1: Inoculate the white-rot fungus into slant media, and incubate it at a constant temperature of 33-36°C for 24-48 hours to obtain the activated strain of the white-rot fungus; S2: Inoculate the activated strain of the white-rot fungus obtained in step S1 into seed media, and shake-culture it at a temperature of 33-36°C and a rotation speed of 120 rpm for 18-24 hours until the logarithmic phase to obtain the seed solution of the white-rot fungus; S3: Inoculate the white-rot fungus seed liquid from step S2 into the fermentation medium at an inoculation amount of 10 vol%, and perform aerated fermentation at a temperature of 33 - 36°C, a rotation speed of 150 rpm, an air ventilation rate of 0.8 vvm, and a tank pressure of 0.08 Mpa for 18 hours to obtain a white-rot fungus fermentation inoculant.

[0030] The preparation steps of the Geobacter sulfurreducens fermentation inoculant of the present invention are as follows: S1: Inoculate Geobacter sulfurreducens into the slant medium and perform constant-temperature cultivation at a temperature of 33 - 36°C for 24 - 48 hours to obtain an activated Geobacter sulfurreducens strain. S2: Inoculate the activated Geobacter sulfurreducens strain from step S1 into the seed medium and perform shaking cultivation at a temperature of 33 - 36°C and a rotation speed of 120 rpm for 18 - 24 hours until the logarithmic phase to obtain a Geobacter sulfurreducens seed liquid. S3: Inoculate the Geobacter sulfurreducens seed liquid from step S2 into the fermentation medium at an inoculation amount of 10 vol%, and perform aerated fermentation at a temperature of 33 - 36°C, a rotation speed of 150 rpm, an air ventilation rate of 0.8 vvm, and a tank pressure of 0.08 Mpa for 18 hours to obtain a Geobacter sulfurreducens fermentation inoculant.

[0031] The preparation steps of the white-rot fungus - Geobacter sulfurreducens mixed seed liquid of the present invention are as follows: S1: Inoculate white-rot fungus and Geobacter sulfurreducens into the slant medium respectively, and perform constant-temperature cultivation at a temperature of 33 - 36°C for 24 - 48 hours to obtain an activated white-rot fungus strain and an activated Geobacter sulfurreducens strain respectively. S2: Inoculate the activated white-rot fungus strain and the activated Geobacter sulfurreducens strain from step S1 into the seed medium respectively, and perform shaking cultivation at a temperature of 33 - 36°C and a rotation speed of 120 rpm for 18 - 24 hours until the logarithmic phase to obtain a white-rot fungus seed liquid and a Geobacter sulfurreducens seed liquid respectively. S3: Mix the white-rot fungus seed liquid and the Geobacter sulfurreducens seed liquid from step S2 at a volume ratio of 1:1 to obtain a white-rot fungus - Geobacter sulfurreducens mixed seed liquid.

[0032] The formula of the slant medium of the present invention is: containing 5 g of yeast extract, 10 g of tryptone, 10 g of NaCl, 15 g of agar in every 1 L volume, and the rest is distilled water; pH = 7.0 - 7.6; autoclave at 121°C for 20 minutes.

[0033] The formula of the seed medium of the present invention is: containing 6 g of yeast extract, 10 g of tryptone, 20 mL of potato extract, 8 g of sodium chloride, 20 g of agar in every 1 L volume, and the rest is distilled water; pH = 7.0 - 7.6; autoclave at 121°C for 20 minutes.

[0034] The formula of the fermentation medium of the present invention is as follows: in every 1 L volume, it contains 800 mL of pig manure extract and 200 mL of potato extract; pH = 7.0 - 7.6; autoclaving at 121 °C for 20 minutes.

[0035] The preparation method of the potato extract of the present invention is: after peeling and slicing fresh potatoes, mix them with distilled water at a ratio of 1:5 (w / v), boil for 40 minutes, filter to obtain the filtrate, and thus obtain the potato extract.

[0036] The preparation method of the pig manure extract of the present invention is: dry pig manure at 105 °C for 24 hours, then mix it with distilled water at a ratio of 1:10 (w / v), extract at 25 °C for 24 hours, centrifuge to obtain the supernatant, and thus obtain the pig manure extract.

[0037] Example 1: A method for promoting composting, preserving nitrogen and fixing heavy metals is carried out according to the following steps: S1: Mix the white rot fungus - Geobacter sulfurreducens complex fermentation agent and calcium dihydrogen phosphate at a mass ratio of 1:0.5 to obtain a composite additive; add the composite additive to the compost raw materials at an addition amount of 5 wt% of the dry weight of the compost raw materials, adjust the initial C / N ratio to 20 with sawdust, and adjust the initial moisture content to 60% - 65% with sterilized water to obtain a compost pile. Among them, the compost raw materials consist of 25 kg of pig manure and 9.6 kg of sawdust.

[0038] S2: Carry out aerobic composting treatment on the compost pile. Among them, the composting method is: the entire composting process lasts for 42 days and is divided into 4 periods: the temperature - rising period, the high - temperature period, the cooling period and the maturity period. The temperature - rising period is the number of days when the center temperature of the compost pile rises from the initial temperature to 50 °C, the high - temperature period is the number of days when the center temperature of the compost pile is between 50 - 74 °C, the cooling period is the number of days when the center temperature of the compost pile drops from 50 °C to 40 °C, and the maturity period is the number of days when the center temperature of the compost pile drops from 40 °C to 32 °C; the aeration volume during the composting process is controlled at 0.1 L / min; turn the pile once a day during the temperature - rising period and the high - temperature period, and the turning time each time is 30 - 40 minutes; after entering the cooling period, turn the pile twice a day, and the turning time each time is 30 - 40 minutes, and the turning time interval is 8 - 12 hours.

[0039] Example 2: A method for promoting composting, preserving nitrogen and fixing heavy metals is carried out according to the following steps: S1: Mix the white rot fungus fermentation agent and calcium dihydrogen phosphate at a mass ratio of 1:0.5 to obtain a composite additive; add the composite additive to the compost raw materials at an addition amount of 5 wt% of the dry weight of the compost raw materials, adjust the initial C / N ratio to 20 with sawdust, and adjust the initial moisture content to 60% - 65% with sterilized water to obtain a compost pile. Among them, the compost raw materials consist of 25 kg of pig manure and 9.6 kg of sawdust.

[0040] S2: Perform aerobic composting on the compost heap. Among them, the composting method is as follows: The entire composting process lasts for 42 days and is divided into 4 periods: the heating period, the high-temperature period, the cooling period, and the maturity period. The heating period is the number of days when the central temperature of the compost heap rises from the initial temperature to 50 °C. The high-temperature period is the number of days when the central temperature of the compost heap is between 50 and 71 °C. The cooling period is the number of days when the central temperature of the compost heap drops from 50 °C to 40 °C. The maturity period is the number of days when the central temperature of the compost heap drops from 40 °C to 32 °C. The ventilation volume during the composting process is controlled at 0.1 L / min. During the heating period and the high-temperature period, the compost heap is turned over once a day, and the turning time each time is 30 - 40 minutes. After entering the cooling period, the compost heap is turned over twice a day, and the turning time each time is 30 - 40 minutes, and the turning time interval is 8 - 12 hours.

[0041] Example 3: A method for promoting compost decay, preserving nitrogen, and fixing heavy metals is carried out according to the following steps: S1: Mix Geobacter sulfurreducens fermentation inoculant and calcium dihydrogen phosphate in a mass ratio of 1:0.5 to obtain a composite additive. Add the composite additive to the compost raw materials at an addition amount of 5 wt% of the dry weight of the compost raw materials, adjust the initial C / N ratio to 20 with sawdust, and adjust the initial moisture content to 60% - 65% with sterilized water to obtain a compost heap. Among them, the compost raw materials consist of 25 kg of pig manure and 9.6 kg of sawdust.

[0042] S2: Perform aerobic composting on the compost heap. Among them, the composting method is as follows: The entire composting process lasts for 42 days and is divided into 4 periods: the heating period, the high-temperature period, the cooling period, and the maturity period. The heating period is the number of days when the central temperature of the compost heap rises from the initial temperature to 50 °C. The high-temperature period is the number of days when the central temperature of the compost heap is between 50 and 69 °C. The cooling period is the number of days when the central temperature of the compost heap drops from 50 °C to 40 °C. The maturity period is the number of days when the central temperature of the compost heap drops from 40 °C to 32 °C. The ventilation volume during the composting process is controlled at 0.1 L / min. During the heating period and the high-temperature period, the compost heap is turned over once a day, and the turning time each time is 30 - 40 minutes. After entering the cooling period, the compost heap is turned over twice a day, and the turning time each time is 30 - 40 minutes, and the turning time interval is 8 - 12 hours.

[0043] Example 4: A method for promoting compost decay, preserving nitrogen, and fixing heavy metals is carried out according to the following steps: S1: Add the white rot fungus - Geobacter sulfurreducens composite fermentation inoculant to the compost raw materials at an addition amount of 5 wt% of the dry weight of the compost raw materials, adjust the initial C / N ratio to 20 with sawdust, and adjust the initial moisture content to 60% - 65% with sterilized water to obtain a compost heap. Among them, the compost raw materials consist of 25 kg of pig manure and 9.6 kg of sawdust.

[0044] S2: Aerobically compost the heap. Among them, the composting method is as follows: The entire composting process lasts for 42 days and is divided into 4 periods: the heating period, the high-temperature period, the cooling period, and the maturity period. The heating period is the number of days when the central temperature of the heap rises from the initial temperature to 50 °C. The high-temperature period is the number of days when the central temperature of the heap is between 50 and 68 °C. The cooling period is the number of days when the central temperature of the heap drops from 50 °C to 40 °C. The maturity period is the number of days when the central temperature of the heap drops from 40 °C to 28 °C. The aeration volume during the composting process is controlled at 0.1 L / min. During the heating period and the high-temperature period, the heap is turned over once a day, and the turning time each time is 30 - 40 minutes. After entering the cooling period, the heap is turned over twice a day, and the turning time each time is 30 - 40 minutes, and the time interval between turnings is 8 - 12 hours.

[0045] Comparative Example 1: A method for promoting compost decay, preserving nitrogen, and fixing heavy metals is carried out according to the following steps: S1: Mix the white rot fungus - Geobacter sulfurreducens mixed seed solution and calcium dihydrogen phosphate in a mass ratio of 1:0.5 to obtain a composite additive. Add the composite additive to the compost raw materials at an addition amount of 5 wt% of the dry weight of the compost raw materials, adjust the initial C / N ratio to 20 with sawdust, and adjust the initial moisture content to 60% - 65% with sterilized water to obtain a heap. Among them, the compost raw materials consist of 25 kg of pig manure and 9.6 kg of sawdust.

[0046] S2: Aerobically compost the heap. Among them, the composting method is as follows: The entire composting process lasts for 42 days and is divided into 4 periods: the heating period, the high-temperature period, the cooling period, and the maturity period. The heating period is the number of days when the central temperature of the heap rises from the initial temperature to 50 °C. The high-temperature period is the number of days when the central temperature of the heap is between 50 and 66 °C. The cooling period is the number of days when the central temperature of the heap drops from 50 °C to 40 °C. The maturity period is the number of days when the central temperature of the heap drops from 40 °C to 28 °C. The aeration volume during the composting process is controlled at 0.1 L / min. During the heating period and the high-temperature period, the heap is turned over once a day, and the turning time each time is 30 - 40 minutes. After entering the cooling period, the heap is turned over twice a day, and the turning time each time is 30 - 40 minutes, and the time interval between turnings is 8 - 12 hours.

[0047] Comparative Example 2: A method for promoting compost decay, preserving nitrogen, and fixing heavy metals is carried out according to the following steps: S1: Add the white rot fungus fermentation inoculant to the compost raw materials at an addition amount of 5 wt% of the dry weight of the compost raw materials, adjust the initial C / N ratio to 20 with sawdust, and adjust the initial moisture content to 60% - 65% with sterilized water to obtain a heap. Among them, the compost raw materials consist of 25 kg of pig manure and 9.6 kg of sawdust.

[0048] S2: Aerobically compost the heap. Among them, the composting method is as follows: The entire composting process lasts for 42 days and is divided into 4 periods: the temperature-rising period, the high-temperature period, the cooling period, and the maturity period. The temperature-rising period is the number of days when the central temperature of the heap rises from the initial temperature to 50 °C. The high-temperature period is the number of days when the central temperature of the heap is between 50 and 65 °C. The cooling period is the number of days when the central temperature of the heap drops from 50 °C to 40 °C. The maturity period is the number of days when the central temperature of the heap drops from 40 °C to 28 °C. The ventilation volume during the composting process is controlled at 0.1 L / min. During the temperature-rising period and the high-temperature period, the heap is turned over once a day, and the turning time each time is 30 - 40 minutes. After entering the cooling period, the heap is turned over twice a day, and the turning time each time is 30 - 40 minutes, and the time interval between turnings is 8 - 12 hours.

[0049] Comparative Example 3: A composting method for promoting decay, nitrogen preservation, and heavy metal fixation is carried out according to the following steps: S1: Add Geobacter sulfurreducens fermentation inoculum to the compost raw materials at an addition amount of 5 wt% of the dry weight of the compost raw materials, adjust the initial C / N ratio to 20 with sawdust, and adjust the initial moisture content to 60% - 65% with sterilized water to obtain the heap. Among them, the compost raw materials consist of 25 kg of pig manure and 9.6 kg of sawdust.

[0050] S2: Aerobically compost the heap. Among them, the composting method is as follows: The entire composting process lasts for 42 days and is divided into 4 periods: the temperature-rising period, the high-temperature period, the cooling period, and the maturity period. The temperature-rising period is the number of days when the central temperature of the heap rises from the initial temperature to 50 °C. The high-temperature period is the number of days when the central temperature of the heap is between 50 and 63 °C. The cooling period is the number of days when the central temperature of the heap drops from 50 °C to 40 °C. The maturity period is the number of days when the central temperature of the heap drops from 40 °C to 28 °C. The ventilation volume during the composting process is controlled at 0.1 L / min. During the temperature-rising period and the high-temperature period, the heap is turned over once a day, and the turning time each time is 30 - 40 minutes. After entering the cooling period, the heap is turned over twice a day, and the turning time each time is 30 - 40 minutes, and the time interval between turnings is 8 - 12 hours.

[0051] Comparative Example 4: S1: Add calcium dihydrogen phosphate to the compost raw materials at an addition amount of 5 wt% of the dry weight of the compost raw materials, adjust the initial C / N ratio to 20 with sawdust, and adjust the initial moisture content to 60% - 65% with sterilized water to obtain the heap. Among them, the compost raw materials consist of 25 kg of pig manure and 9.6 kg of sawdust.

[0052] S2: Aerobically compost the heap. Among them, the composting method is as follows: The entire composting process lasts for 42 days and is divided into 4 periods: the heating period, the high-temperature period, the cooling period, and the maturity period. The heating period is the number of days when the central temperature of the heap rises from the initial temperature to 50 °C. The high-temperature period is the number of days when the central temperature of the heap is between 50 and 65 °C. The cooling period is the number of days when the central temperature of the heap drops from 50 °C to 40 °C. The maturity period is the number of days when the central temperature of the heap drops from 40 °C to 28 °C. The ventilation volume during the composting process is controlled at 0.1 L / min. During the heating period and the high-temperature period, the heap is turned over once a day, and the turning time each time is 30 - 40 minutes. After entering the cooling period, the heap is turned over twice a day, and the turning time each time is 30 - 40 minutes, and the time interval between turnings is 8 - 12 hours.

[0053] For the examples and comparative examples, the central temperature of the heap and the ambient temperature are measured every day. Sampling is carried out on the 0th, 7th, 14th, 21st, 28th, and 42nd days of composting. The nitrate nitrogen (NO3 - -N) content of the new compost sample is determined by "Determination of Nitrate Nitrogen, Ammonium Nitrogen, and Amide Nitrogen Contents in Fertilizers" (NYT1116 - 2014). The total nitrogen (TN) content of the heap is determined by an elemental analyzer. The humic acid (HA) content of the heap is extracted and determined by the method of the International Humic Substances Society (IHSS), and the polymerization degree (HA / FA) of the compost sample is calculated.

[0054] Heavy metals in the compost sample are continuously fractionated and separated by an improved European Commission Bureau of Reference (BCR) process. All solid-liquid extraction steps are carried out under continuous stirring. The solution is adjusted to the target pH value with nitric acid. Between each extraction step, the residue is centrifuged at 6000 r / min for 20 minutes and then dried at 85 °C for 18 hours.

[0055] (1) Acid-extractable fraction (F1): At 25 °C, 0.1 g of dehydrated biogas residue is extracted with 20 mL of acetic acid solution with a concentration of 0.11 M for 16 hours.

[0056] (2) Reducible fraction (F2): At 25 °C, the residue obtained in step (1) is extracted with 20 mL of hydroxylamine hydrochloride solution with a concentration of 0.5 M and a pH value of 1.5 for 16 hours.

[0057] (3) First, place the residue obtained in step (2) in 5 mL of hydrogen peroxide solution with a concentration of 30% and a pH value of 2, digest at 25 °C for 1 hour, and then continue to digest in the same solution at 85 °C with intermittent stirring for 1 hour. Subsequently, at 25 °C, the digested residue is extracted with 25 mL of ammonium acetate solution with a concentration of 1 M containing 20 vol% nitric acid and a pH value of 2 for 16 hours to obtain the oxidizable fraction (F3).

[0058] (4) Residual state (F4): The residue obtained in step (3) was placed in a mixed solution of 10 mL of nitric acid and hydrogen peroxide with a volume ratio of 4:1, and digested at 180 °C for 40 minutes to obtain.

[0059] The F1 fraction is sensitive to the pH value and ionic strength of the water environment and can be regarded as having mobility and being bioavailable to organisms. The F2 and F3 fractions are still available under both reducing and oxidizing conditions. The F4 fraction makes little contribution to the bioavailability of heavy metals in the environment. The bioavailable components of heavy metals include the F1 and F2 fractions.

[0060] The changes in the central temperature of the compost piles in Examples 1 to 4 and Comparative Examples 1 to 4 are as Figure 1 shown. Compared with Comparative Example 1, the highest central temperature of the compost pile in Example 4 during the high-temperature period increased by 2.5 °C, and the high-temperature period was extended by 1 day, confirming that fermentation pre-culture can enhance the adaptability of the microbial community to complex substrates and significantly improve the functional expression efficiency. Compared with Comparative Examples 2 and 3, the highest central temperature of the compost pile in Example 4 during the high-temperature period increased by 3 - 6 °C, and the high-temperature period was extended by 1 - 2 days, confirming that the dual-bacteria combination significantly enhances the metabolic activity of the microbial community and shortens the composting period through carbon-sulfur metabolic interaction. Compared with Comparative Example 4, the highest central temperature of the compost pile in Examples 1 to 3 during the high-temperature period increased by 4 - 9 °C, and the high-temperature period was extended by 3 - 7 days, verifying the synergistic effect of "compound fermentation inoculant - phosphate", that is, phosphate provides phosphorus nutrition and regulates pH, promoting the functional expression of the inoculant, while the heat released by the metabolism of the inoculant and the exothermic reaction of phosphate are superimposed, accelerating the processes of organic matter mineralization and humification.

[0061] The changes in the HA content and polymerization degree (HA / FA) of the composts in Examples 1 to 4 and Comparative Examples 1 to 4 are shown in Figures 2 - 3During the pig manure composting process, the HA content increased in all examples and comparative examples. At the initial stage of composting, the HA content was generally low, and it gradually increased as composting proceeded. After composting ended, compared with Comparative Examples 2-3, the HA content in Example 4 increased by 7.41 and 11.95% respectively, indicating that the composite microbial agent had a synergistic advantage compared with the single microbial agent. Through the metabolic complementarity and microenvironment regulation of white rot fungi and Geobacter sulfurreducens, the humification efficiency was improved; the HA content in Example 4 was higher than that in Comparative Example 1, which indicated that the composite microbial agent could improve the metabolic activity of microorganisms and the expression of functional genes after fermentation culture, promoting the decomposition of organic matter and the formation of humus; the HA content in Examples 1-3 increased by 23.88%-56.95% compared with Comparative Example 4, indicating that the composite microbial agent and phosphate could significantly improve the humification efficiency through synergistic effects. Among them, white rot fungi secreted lignocellulose-degrading enzymes such as laccase to degrade lignocellulose and release humus precursors, and Geobacter sulfurreducens participated in the electron transfer of quinone humus intermediates through its extracellular electron transfer system, thus accelerating the synthesis of humus. As a key nutrient for microbial growth, phosphate could promote the metabolic activity of the composite microbial agent, thereby promoting the synthesis of humus and shortening the composting fermentation cycle. The compost polymerization degree (DP = HA / FA) had a similar change trend to the HA content.

[0062] The changes in the compost nitrate nitrogen (NO3 - -N) and total nitrogen (TN) contents of Examples 1-4 and Comparative Examples 1-4 are shown in Figures 4 - 5。The contents of nitrate nitrogen and total nitrogen showed a gradually increasing trend. After the composting ended, the total nitrogen content of Example 4 was 7.17% and 10.66% higher than that of Comparative Example 2 and Comparative Example 3 respectively (p < 0.05), indicating that compared with the single fermentation inoculant, the composite fermentation inoculant optimized the microenvironment of the compost pile through microbial co-metabolism and redox regulation, inhibited nitrogen gas volatilization and the denitrification pathway, and significantly improved the nitrogen retention efficiency; the total nitrogen content of Example 4 was higher than that of Comparative Example 1, indicating that the fermentation and cultivation process significantly enhanced the performance of the inoculant, improved the fixation and conversion efficiency of nitrogen, reduced nitrogen loss, and thus improved the quality and fertilizer efficiency of the compost; the total nitrogen content of Examples 1-3 was 24.71% - 36.97% higher than that of Comparative Example 4, indicating that the synergistic effect of the composite fermentation inoculant and phosphate significantly increased the total nitrogen retention rate of the compost through "biological metabolism regulation + chemical adsorption and fixation". The chemical regulation effect of phosphate included adjusting the pH of the compost pile to 6.5 - 7.5, inhibiting the volatilization of ammonium nitrogen to ammonia, and the formation of hydroxyapatite by phosphate ions and calcium ions to adsorb and fix ammonium nitrogen, reducing nitrogen gaseous loss; while the biological strengthening effect of the composite fermentation inoculant included the degradation of lignocellulose by white rot fungi to release organic nitrogen, increasing the availability of nitrogen sources, the inhibition of the activity of denitrifying bacteria by Geobacter sulfurreducens through sulfur metabolism, promoting nitrification, reducing nitrate nitrogen loss, and white rot fungi providing carbon sources to support the metabolism of sulfur-reducing bacteria, and the reducing substances such as S produced by the latter 2- Inhibiting denitrification and promoting nitrogen fixation.

[0063] The changes in heavy metal contents, passivation rates, and the bioavailability of copper and zinc before and after composting are shown in Table 2 and Figure 6 。As can be seen from Table 2, after the composting ended, the contents of heavy metals in all examples and comparative examples increased compared with before composting, showing an obvious "concentration effect". The contents of heavy metals met the "Technical Specification for Livestock and Poultry Manure Composting" (NY / T 3442—2019), where Cd ≤ 3 mg / kg, Cr ≤ 150 mg / kg, Cu ≤ 100 mg / kg, Pb ≤ 50 mg / kg, and Zn ≤ 400 mg / kg. From the perspective of the passivation rate, all examples and comparative examples had a certain passivation effect on heavy metals. The passivation effects of all treatment groups on Cu, Zn, Cr, and Cd were as follows: Example 1 > Example 3 > Example 2 > Comparative Example 4 > Example 4 > Comparative Example 1 > Comparative Example 3 > Comparative Example 2; the passivation effect on Pb was as follows: Example 1 > Example 3 > Comparative Example 4 > Example 2 > Example 4 > Comparative Example 3 > Comparative Example 1 > Comparative Example 2. From Figure 6It can be seen that "compound fermentation inoculant - phosphate" promoted the transformation of Zn and Cu towards low bioavailability, reducing the bioavailability of Zn by 8.93% - 17.17% and 4.71% - 13.34%, while the bioavailability of Cu was reduced by 33.08% - 44.36% and 4.32% - 20.44%. This indicates that the synergistic effect of "compound fermentation inoculant - phosphate" can reduce the bioavailability and environmental mobility of heavy metals, thereby reducing the environmental risks of compost products. The S produced by the metabolism of Geobacter sulfurreducens 2- and Cd 2+ , Pb 2+ and other heavy metals form insoluble sulfides. In addition, highly toxic heavy metal forms such as Cr(VI) are reduced to Cr(III), while the PO4 3- of phosphate combines with Cu 2+ , Zn 2+ and other heavy metals to form stable phosphates. The heavy metal content after composting meets the "Technical Specification for Composting of Livestock and Poultry Manure" (NY / T 3442 - 2019). Table 2 Heavy metal content and passivation rate before and after composting in Examples 1 - 4 and Comparative Examples 1 - 4 In summary, through the synergistic effect of "compound fermentation inoculant - phosphate", it can help promote the decomposition and nitrogen preservation of livestock and poultry manure compost, fix heavy metals, reduce the bioavailability and environmental mobility of heavy metals, achieve the safe land use of compost, and solve environmental risk problems such as nitrogen loss, poor composting effect, and heavy metal pollution during the composting process of organic solid waste.

Claims

1. A method for promoting nitrogen preservation and fixing heavy metals by composting organic solid waste, characterized in that: The following steps are involved: (1) Preparation of white rot fungus-Geobacterium sulfurreducens composite fermentation agent; (2) mixing the white rot fungus-Geobacterium sulfurreducens composite fermentation agent with the phosphate additive to obtain a composite additive; adding the composite additive to the compost raw material, adjusting the initial C / N ratio to 20, and adjusting the initial moisture content to 60% to 65%, to obtain a pile; (3) Carry out aerobic composting on the pile.

2. The method according to claim 1, characterized in that: The preparation method of the white rot fungus-Geobacterium sulfurreducens composite fermentation agent comprises the following steps: S1: white rot fungi and Geobacter sulfurreducens are inoculated into slant culture medium respectively, and cultured at a constant temperature of 33-36°C for 24-48 hours to obtain activated strains of white rot fungi and activated strains of Geobacter sulfurreducens respectively; S2: inoculating the activated strains of white rot fungi and activated strains of Geobacter sulphurreducens from step S1 into seed culture medium respectively, and culturing with shaking at a temperature of 33-36° C. and a rotation speed of 120 rpm for 18-24 hours until the logarithmic phase, to obtain white rot fungi seed solution and Geobacter sulphurreducens seed solution respectively; S3: The white rot fungus seed solution and the sulfur-reducing Geobacter seed solution of step S2 are mixed in a volume ratio of 1:0.5-1:2, and then inoculated into the fermentation medium at an inoculation amount of 10 vol%, and aerated fermentation is carried out for 18-24 hours at a temperature of 33-36°C, a rotation speed of 150 rpm, a ventilation volume of 0.8 vvm, and a tank pressure of 0.08 MPa to obtain a white rot fungus-sulfur-reducing Geobacter composite fermentation agent.

3. The method according to claim 2, characterized in that: The slant culture medium formula is: 5g yeast extract, 10g tryptone, 10g NaCl, 15-20g agar per 1L volume, and the rest is distilled water; the seed culture medium formula is: 4-8g yeast extract, 8-12g tryptone, 18-20mL potato extract, 8-12g sodium chloride, 15-20g agar per 1L volume, and the rest is distilled water; the fermentation culture medium formula is: 800-900mL pig manure extract and 100-200mL potato extract per 1L volume; the preparation method of the potato extract is: peel and slice fresh potatoes, mix them with distilled water at a ratio of 1:3-5 w / v, boil for 30-40 minutes, filter and take the filtrate to obtain the potato extract; the preparation method of the pig manure extract is: after the pig manure is dried at 105°C for 24 hours, mix it with distilled water at a ratio of 1:5-10 Mix them in a w / v ratio, extract at 25-30℃ for 24-48 hours, and centrifuge to obtain the supernatant to obtain the pig manure extract.

4. The method according to claim 1, characterized in that: The mass ratio of the white rot fungus-Geobacterium sulfurreducens composite fermentation agent to the phosphate additive is 1:0.2-1.

5. The method according to claim 1, characterized in that: The phosphate additive is any one or more of phosphogypsum, superphosphate and monocalcium phosphate.

6. The method according to claim 1, characterized in that: The added amount of the composite additive is 0.5wt% to 5wt% of the dry weight of the compost raw material.

7. The method according to claim 1, characterized in that: The aerobic composting process lasts for 42 days and is divided into a heating period, a high temperature period, a cooling period and a maturity period; the compost is turned once a day during the heating period and the high temperature period, and each turning time is 30 to 40 minutes. After entering the cooling period, the compost is turned twice a day, and each turning time is 30 to 40 minutes. The time interval between turnings is 8 to 12 hours.

8. The method according to claim 1, characterized in that: The decomposition promotion is to increase the humic acid content and the humic acid-fulvic acid ratio of the compost; the nitrogen retention is to increase the nitrate nitrogen content and the total nitrogen content of the compost; and the heavy metal fixation is to passivate the heavy metals and reduce the biological effectiveness and environmental mobility of the heavy metals.

9. Application of the method according to any one of claims 1 to 8 in any one or more of the following: 1) Application in the treatment of organic solid waste; 2) Application in promoting decomposition and retaining nitrogen in composting; 3) Application in heavy metal fixation.

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