Method for preparing organic matrix for greening from sludge

Abstract

The invention discloses a method for preparing an organic matrix for greening from sludge, which comprises the following steps: carrying out pyrohydrolysis, dehydration and crushing on the sludge to obtain sludge particles; mixing the sludge particles, structural auxiliary materials and nutritional auxiliary materials, and conditioning; inoculating the mixed material with a composite functional bacterial agent for aerobic fermentation; mixing the material obtained after aerobic fermentation with a composite passivating agent, and carrying out passivating treatment; and aging and screening the passivated material to obtain the organic matrix for greening. Compared with a conventional preparation process, the method disclosed by the invention adopts a combined process of sludge pretreatment, ingredient conditioning, inoculated fermentation, synergistic passivation and aging screening; the prepared organic matrix product for greening has the characteristics of capability of fixing plants, water and fertilizer retention, good air permeability, stable property, no toxicity, light weight, high ion exchange capacity, proper carbon-nitrogen ratio, easiness in pH value adjustment, capability of promoting the growth of green plants and the like, and is high in use value and good in application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of solid waste resource utilization, and relates to a method for preparing an organic substrate for greening from sludge. BACKGROUND

[0002] Currently, the mainstream process methods for preparing the organic substrate from the municipal sludge include aerobic composting, anaerobic digestion, thermal drying and carbonization, etc. The aerobic composting process is relatively simple and has low equipment investment, but needs a large site and a long period, has problems of odor emission and incomplete heavy metal passivation, has a greater impact on the surrounding environment, and does not consider potential toxic elements such as soluble chlorine and soluble sodium of the substrate. The anaerobic digestion process can produce biogas and has the advantage of carbon emission reduction, but has problems of relatively high investment, unstable operation condition, complex operation and regulation, and the need for further treatment of the digestion product. The thermal drying and carbonization process has the most significant reduction effect, has a short treatment period, and the product can be prepared into sludge carbon as a high-end greening substrate, but has high energy consumption, large investment and high operation cost.

[0003] In addition, the existing organic fertilizer prepared from the sludge also has the following problems: the EC value is too high, which is easy to burn seedlings; the nutrient balance is unbalanced, such as improper ratio of nutrient available / retardant; the pore structure is unreasonable, the air permeability is poor, and it is easy to be hardened; and there are potential toxic elements such as soluble chlorine and soluble sodium, so it cannot be used as a direct planting substrate.

[0004] Based on the above reasons, the present application is proposed. SUMMARY

[0005] The technical problem solved by the present application is to overcome the deficiencies of the prior art and provide a method for preparing an organic substrate for greening from sludge.

[0006] To solve the above technical problems, the present application adopts the following technical scheme: A method for preparing an organic substrate for greening from sludge, comprising the following steps: S1, heat hydrolysis, dehydration and crushing of the sludge to obtain sludge particles; S2, mixing the sludge particles obtained in step S1, structural auxiliary materials and nutritional auxiliary materials to obtain a mixture; S3, inoculating a composite functional bacteria agent into the mixture obtained in step S2 to perform aerobic fermentation; the composite functional bacteria agent is composed of white rot fungi, Bacillus subtilis, actinomycetes, lactic acid bacteria and thermophilic sulfate-reducing bacteria; S4, mixing the material obtained after the aerobic fermentation in step S3 with a composite passivation agent to perform passivation treatment; the composite passivation agent is composed of modified sepiolite, struvite and modified vermiculite; the modified sepiolite is prepared by heat modification treatment of sepiolite; the modified vermiculite is prepared by soaking and calcining vermiculite and urea solution; S5, aging and screening the material obtained after the passivation treatment in step S4 to obtain an organic substrate for greening.

[0007] The method is further improved, and in step S4, the adding amount of the composite passivation agent is 10%-15% of the mass of the material obtained after the aerobic fermentation; and the mass ratio of the modified sepiolite, struvite and modified vermiculite in the composite passivation agent is 1-1.5:1.5-2:5-10.

[0008] The method is further improved, and the preparation method of the modified sepiolite comprises the following steps: heating sepiolite to 250-300 DEG C and keeping the temperature for 2-3 hours, crushing, and passing through a 100-mesh screen to obtain the modified sepiolite; and the particle size of the modified sepiolite is less than or equal to 0.15 mm.

[0009] The method is further improved, and the preparation method of the struvite comprises the following steps: mixing sludge pretreatment filtrate containing ammonium ions and phosphate ions with magnesium to react, drying at a temperature less than or equal to 60 DEG C for 3-4 hours, crushing, and passing through a 10-mesh to 50-mesh screen to obtain the struvite; and the particle size of the struvite is 0.5-2 mm.

[0010] The method is further improved, and the preparation method of the modified vermiculite comprises the following steps: mixing vermiculite and urea solution, soaking, and calcining at 600-800 DEG C for 1-2 min to obtain the modified vermiculite; and the particle size of the modified vermiculite is 3-6 mm.

[0011] The method is further improved, and in step S1, the thermal hydrolysis is performed under alkaline conditions; lime is added to the sludge in the thermal hydrolysis system; the adding amount of the lime is 5% of the mass of the sludge; the operating pressure of the thermal hydrolysis is 0.3-0.6 MPa; the temperature of the thermal hydrolysis is 110-130 DEG C; the filtrate generated in the dewatering process is used for preparing struvite; the particle size of the sludge particles is less than or equal to 10 mm; and the moisture content of the sludge particles is 40%-60%.

[0012] The method is further improved, and in step S2, the mass ratio of the sludge particles, the structural auxiliary material and the nutritional auxiliary material is 4-6:1-2:2.5-4; the structural auxiliary material is sawdust; and the nutritional auxiliary material is at least one of pig manure and chicken manure.

[0013] The method is further improved, and in step S2, the carbon-nitrogen ratio of the mixture is 25-30:1; the water content in the mixture is 50%-60%; the pH value of the mixture is 5.5-8.5; and the spray humidification method is used to control the water content in the conditioning process.

[0014] The method is further improved, and in the step S3, the inoculation amount of the compound functional bacterial agent is 0.2%-0.5% of the mass of the mixture; and the mass ratio of the white rot fungus, the bacillus subtilis, the actinomycete, the lactic acid bacteria and the thermophilic sulfur-oxidizing bacteria in the compound functional bacterial agent is 2-5:15-25:10-20:5-10:1-5.

[0015] The method is further improved, and in the step S3, the aerobic fermentation is carried out at a temperature of 60-70 DEG C; and the aerobic fermentation time is 7-10 days.

[0016] The method is further improved, and in the step S5, the aging time is 10-20 days; the particle size of the organic substrate for greening is 5-10 mm; and the water content of the organic substrate for greening is less than or equal to 40%.

[0017] Compared with the prior art, the method has the advantages that: The present application creatively provides a method for preparing green organic substrate from sludge, which adopts a combined process of sludge pretreatment, ingredient conditioning, inoculation fermentation, synergistic passivation and aging screening, and obtains a green organic substrate with low EC value, balanced nutrients, rich pore structure, good air permeability, low hardening tendency and low content of toxic and harmful elements, and specifically, the sludge is first subjected to hot hydrolysis treatment, during which most of the pathogenic bacteria in the sludge are inactivated at high temperature, the heavy metals are preliminarily stabilized, the hydroxide precipitate and organic combined state are formed, and the soluble chlorine and soluble sodium and other potential toxic and harmful elements in the sludge enter the dewatering filtrate, further reducing the content of potential toxic and harmful elements in the sludge, and at the same time, part of the organic matter and protein in the sludge enter the filtrate after the sludge is subjected to hot hydrolysis, the organic matter content of the sludge is reduced, the difficulty and period of subsequent fermentation treatment are further shortened, and the odor and sanitation problems are also obviously improved, then the sludge particles are conditioned, and under the conditioning effect of the sludge particles, structural auxiliary materials and nutritional auxiliary materials, the carbon-nitrogen ratio and pH value of the material are within a reasonable range, no additional pH chemical conditioner is needed, which is beneficial to reducing the salt intake of the material, further, the mixed material is subjected to aerobic fermentation by using a composite functional bacterial agent, the white rot fungus can secrete lignin-degrading enzymes to efficiently decompose lignin and cellulose in the sawdust, improve the material structure, prolong the high-temperature period and assist in heavy metal passivation, especially the fixation of Pb, the Bacillus subtilis secretes protease and lipase to rapidly decompose organic matter, generate high temperature (60-70 DEG C) to further kill pathogenic bacteria and degrade part of pollutants, the actinomycete decomposes cellulose and other refractory organic matter, produces antibiotics to inhibit pathogenic bacteria, promotes the formation of humus and improves the soil structure, the lactic acid bacteria can produce lactic acid to reduce the pH value, inhibit the growth of spoilage bacteria, effectively remove odor and improve the fermentation environment, and the thermophilic sulfate-reducing bacteria reduce sulfate to hydrogen sulfide at the high-temperature period (45-75 DEG C), and form stable sulfide precipitate with heavy metal ions (such as Cu, Pb, Cd, etc.) to realize heavy metal passivation, it can be seen that under the joint action of the white rot fungus, Bacillus subtilis, actinomycete, lactic acid bacteria and thermophilic sulfate-reducing bacteria, the organic matter and lignin and cellulose can be rapidly and efficiently decomposed, and the heavy metal can be passivated by microorganisms, more importantly, the material obtained after aerobic fermentation is subjected to passivation treatment by using a composite passivation agent, which can construct a strategy of slow-release nutrient embedding and pore gradient improvement, thereby controlling the ratio of available nutrients and slow-release nutrients, realizing the sustained release of fertilizer efficiency, and improving the air permeability and drainage property of the substrate to prevent the substrate from hardening, specifically, the vermiculite is modified by urea assisted calcination, on the one hand, the coarse particle expanded vermiculite is prepared by urea assisted expansion, and the layered structure of the vermiculite forms a porous and loose property after high-temperature expansion,Very suitable for building aeration pores, preventing compaction, responsible for building pore framework, providing cation exchange sites and loading nutrients, on the other hand, can also adsorb part of NH4 in vermiculite, + , to supplement the loss of nitrogen in the later stage of material fermentation; struvite provides a slow-release nutrient source, and its crystal structure has low solubility, which can slowly release nitrogen, phosphorus and magnesium in the soil; through the heat modification treatment of sepiolite, the adsorbed water and part of the crystal water in the sepiolite can be removed, the porosity is increased, the specific surface area is increased, the heavy metal ions can be adsorbed, and the heavy metals can be effectively passivated, and the structure of the vermiculite is improved, the unique needle-like structure of the vermiculite is interwoven in the substrate, the compressive resistance of the substrate is enhanced, and the substrate is prevented from being compacted, so it can be seen that the slow-release nutrient embedding is to use the huge specific surface area and pore structure of vermiculite and sepiolite to embed the slow-release fertilizer struvite particles and adsorb and fix the readily available nutrients (such as NH4 + , K + and the like) in the fermentation material on the surface and inside, so as to establish a "storage" for the easily lost nutrients; on the one hand, the high specific surface area and high cation exchange capacity of vermiculite and sepiolite can adsorb and hold ammonium nitrogen and potassium ions, reducing leaching loss; when the nutrient concentration in the substrate decreases, the adsorbed ions will gradually desorb and be absorbed by plants, thereby achieving slow release; on the other hand, struvite slowly dissolves under the action of microbial activity and organic acid secreted by roots, and continuously releases nutrients; the pore gradient improvement is that the interlayer structure of vermiculite and the fibrous structure of sepiolite can form a complex pore network with organic materials, the micropores enhance the water and fertilizer retention capacity, the macropores guarantee aeration and drainage, and finally through aging, the material properties are completely stabilized, and impurities are removed through screening, so that a homogeneous and loose organic substrate for greening is obtained. In the present application, sludge is used as the main raw material to prepare the directly usable organic substrate for greening, and the proportion of sludge is more than 50%, so that the organic matter and nutrient elements such as nitrogen, phosphorus and potassium in the sludge can be fully utilized, and the product meets the relevant performance indicators of "Organic Substrate for Greening" (GB / T 33891-2017), realizing the resource utilization of sludge, and overcoming the problems of high EC value, nutrient imbalance, unreasonable pore structure, poor aeration porosity, easy compaction and potential toxic elements in the prior art. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application.

[0019] Figure 1 The process flow diagram for preparing the organic substrate for greening by sludge in the embodiment 1 of the present application is shown. DETAILED DESCRIPTION

[0020] The technical solutions of the present application will be clearly and completely described below with reference to the drawings. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of the present application.

[0021] Embodiment 1 A method for preparing an organic substrate for sludge greening, a process flow chart of which is shown in Figure 1 The method comprises the following steps: S1, performing thermal hydrolysis on sludge, dewatering, and crushing to obtain sludge particles, specifically as follows: S11, taking sludge (water content: 80%) from a municipal sludge treatment plant, adding lime to the sludge to form an alkaline environment according to a lime addition amount of 5% of the mass of the sludge, and performing alkaline thermal hydrolysis on the sludge under the conditions of a temperature of 120℃ and an operating pressure of 0.5MPa for 120min.

[0022] S12, performing pressure filtration dewatering on the product after the alkaline thermal hydrolysis to form a sludge cake.

[0023] In this step, the chemical indexes of the obtained sludge particles are as follows: pH: 8.5, water content: 34%, organic matter: 35.6%, organic nitrogen: 142g / kg, total nutrient: 2.08% (dry basis), total nitrogen: 0.75%, total phosphorus (calculated as P2O5): 0.48%, total potassium (calculated as K2O): 0.849%, and heavy metals (dry basis): total mercury: 7.87mg / kg, total arsenic: 32.7mg / kg, total cadmium: 1.89mg / kg, total lead: 227mg / kg, and total chromium: 78mg / kg.

[0024] In this step, the filtrate generated in the pressure filtration dewatering process is used to prepare struvite.

[0025] S13, sending the sludge cake into a crusher to perform crushing to obtain sludge particles with a particle size of ≤10mm.

[0026] S2, mixing the sludge particles obtained in step S1, structural auxiliary materials, and nutritional auxiliary materials to perform conditioning to obtain a mixture, specifically as follows: 12kg of main material sludge particles, 2.2kg of structural auxiliary materials (sawdust), and 6.5kg of nutritional auxiliary materials (pig manure) are respectively weighed and mixed to perform batching, and water is appropriately sprayed for humidification in a spray humidification manner to control the water content of the materials, control the carbon-nitrogen ratio to be 28:1, control the water content to be 52%, and control the pH to be 6.73.

[0027] In this step, under the matching of sludge particles, structural auxiliary materials and nutritional auxiliary materials, the carbon-nitrogen ratio and pH value of the material are within a reasonable range, without the need to add new pH chemical conditioners, which is conducive to reducing the salt intake of the material.

[0028] S3, inoculate the mixture obtained in step S2 with a complex functional bacteria agent for aerobic fermentation, specifically as follows: The mixed material is inoculated with 100g of complex functional bacteria agent, and the inoculation amount is 0.48% of the mass of the mixed material. The complex functional bacteria agent is soaked in warm water with brown sugar for 6 hours before inoculation. The composition and ratio of the complex functional bacteria agent are 3:20:16:8:3 of white rot fungus, Bacillus subtilis, actinomycetes, lactic acid bacteria and thermophilic sulfate-reducing bacteria. These bacteria agents are commercially available. During the aerobic fermentation process, forced ventilation is used, and the temperature of the pile is raised to 65℃ after 3 days, covered with white mycelium. The color becomes significantly darker after 5 days, and there is no odor after 7 days. The pH gradually decreases to 5.68 during the period. The main fermentation period is 10 days. In this step, white rot fungus can secrete lignin-degrading enzymes to efficiently decompose lignin and cellulose in wood chips, improve material structure, extend the high-temperature period, and assist in heavy metal passivation, especially Pb fixation. Bacillus subtilis secretes protease and lipase to rapidly decompose organic matter, generate high temperature (60℃-70℃), further kill pathogenic bacteria, degrade some pollutants, actinomycetes decompose cellulose and other refractory organic matter, produce antibiotics to inhibit pathogenic bacteria, promote the formation of humus, and improve soil structure. Lactic acid bacteria can produce lactic acid to lower the pH value, inhibit the growth of spoilage bacteria, effectively remove odors, and improve the fermentation environment. Thermophilic sulfate-reducing bacteria reduce sulfate to hydrogen sulfide at high temperatures (45℃-75℃), forming stable sulfide precipitates with heavy metal ions (such as Cu, Pb, Cd, etc.), achieving heavy metal passivation. It can be seen that under the combined action of white rot fungus, Bacillus subtilis, actinomycetes, lactic acid bacteria and thermophilic sulfate-reducing bacteria, organic matter and lignin and cellulose can be rapidly and efficiently decomposed, and the heavy metal passivation effect of microorganisms can be achieved.

[0029] S4, mix the material obtained after aerobic fermentation in step S3 with a complex passivation agent for passivation treatment, specifically as follows: The fermented material is added with a complex passivation agent, and the addition amount of the complex passivation agent is 10% of the mass of the fermented material. The composition of the complex passivation agent is 300g of modified sepiolite powder, 500g of struvite and 1.5kg of modified vermiculite, which is used for heavy metal synergistic passivation and simultaneously designed for slow-release nutrient embedding and pore gradient improvement.

[0030] In this step, the modified sepiolite is prepared by heat modification treatment of sepiolite. The preparation method of the modified sepiolite includes the following steps: heating the sepiolite to 250℃ and keeping it for 2 hours, crushing, and passing through a 100 mesh screen to obtain the modified sepiolite. The particle size of the modified sepiolite is ≤0.15mm.

[0031] The preparation method of struvite adopted in this step includes the following steps: mixing the filtrate containing ammonium ions and phosphate ions with magnesium source and reacting, drying at a temperature ≤60℃ for 4 hours, crushing, and passing through a 10-50 mesh screen to obtain struvite with a particle size of 0.5-2 mm. In the preparation method of struvite, the filtrate is the filtrate obtained after dewatering of sludge, or the filtrate obtained after pressure filtration and dewatering in step S1.

[0032] In the preparation method of struvite adopted in this step, ammonium ions and phosphate ions in the filtrate are reacted by adding magnesium source (such as magnesium chloride) to generate struvite precipitate, thereby separating nitrogen and phosphorus nutrients from the liquid phase. In particular, after removal of nitrogen and phosphorus from the sludge filtrate, high-quality carbon sources can be prepared for further resource utilization, and the precipitated struvite can be used as a slow-release fertilizer supplement for preparing organic substrates for greening from sludge, ensuring the maximum utilization of nitrogen and phosphorus elements in sludge.

[0033] In this step, the modified vermiculite is prepared by impregnating and calcining vermiculite and urea solution, and the preparation method of the modified vermiculite includes the following steps: mixing vermiculite and urea solution, impregnating, and calcining at 700℃ for 2 min to obtain modified vermiculite with a particle size of 3-6 mm.

[0034] In this step, a strategy for embedding slow-release nutrients and improving pore gradient is constructed to control the ratio of available nutrients to slow-release nutrients, achieve sustained release of fertilizer efficiency, and improve the air permeability and drainage of the substrate to prevent the substrate from hardening. Specifically, the vermiculite is modified by urea-assisted calcination. On the one hand, coarse-grained expanded vermiculite is prepared by urea-assisted expansion, and the layered structure of vermiculite forms a porous and loose property after expansion at high temperature, which is very suitable for constructing air pores, preventing hardening, constructing pore framework, providing cation exchange sites and loading nutrients. On the other hand, part of NH4 + + in the vermiculite can also be adsorbed to supplement the loss of nitrogen in the later stage of material fermentation; struvite provides a slow-release nutrient source, and its crystal structure has low solubility, which can slowly release nitrogen, phosphorus, and magnesium in the soil; heat modification treatment of sepiolite can remove adsorbed water and part of the crystal water in sepiolite, increase porosity, increase specific surface area, adsorb heavy metal ions, effectively passivate heavy metals, and assist vermiculite in structure modification. The unique acicular structure of sepiolite interweaves in the substrate, enhancing the compressive resistance of the substrate and preventing the substrate from compacting. Therefore, slow-release nutrient embedding utilizes the large specific surface area and pore structure of vermiculite and sepiolite to embed slow-release fertilizer struvite particles and available nutrients (such as NH4 + , K +The vermiculite and the sepiolite are adsorbed, fixed on the surface and the inside, and a "storage" for the easily lost nutrients is established, on one hand, the high specific surface area and the high cation exchange capacity characteristics of the vermiculite and the sepiolite can adsorb and hold ammonium nitrogen, potassium ions and the like, so that the leaching loss is reduced, when the nutrient concentration in the substrate is reduced, the adsorbed ions are gradually desorbed, and are absorbed by plants, so that slow release is realized; on the other hand, the struvite slowly dissolves under the action of microbial activity and organic acid secreted by the root system, and nutrients are continuously released; the pore gradient improvement is that the interlayer structure of the vermiculite and the fibrous structure of the sepiolite can form a complex pore network with different sizes with the organic material, the micropore enhances the water and fertilizer retention capacity, and the macropore guarantees ventilation and drainage.

[0035] It can be seen that, in the present application, the modified sepiolite, the struvite and the modified vermiculite particles are added, the air permeability and the drainage of the substrate are improved by different porosities and specific surface areas of the natural minerals, and the required nutrient elements such as nitrogen, phosphorus, potassium and magnesium for plants are supplemented, the loss of nitrogen in the later fermentation stage is supplemented, the organic matter of the sludge itself and the humus of the fermentation product are used as carriers to embed the slow-release nutrients, the ratio of available nutrients / slow-release nutrients is controlled, and the fertilizer efficiency is continuously released. In this stage, the whole of the passivation agent is alkaline, and the pH rises to about 7.2.

[0036] S5, the material obtained after the passivation treatment in step S4 is aged and screened to obtain the organic substrate for greening, specifically: The material after the fermentation and the synergistic passivation treatment is aged and placed in an open space for 15 days, so that the properties are completely stable, the water content is 34%, the pH is 6.6, and there is no peculiar smell. The roller screen with a size of 5-10 mm is selected for screening to remove impurities, and a homogeneous and loose final product, the organic substrate for greening, is obtained. The performance technical indexes and the heavy metal limit values of the product all meet the national standard "Organic Substrate for Greening" (GB / T 33891-2017).

[0037] Comparative Example 1 A method for preparing the organic substrate for greening from sludge is basically the same as that in Example 1, and the difference is only that: In Comparative Example 1, the structural auxiliary material is replaced by corn straw, and the mass of the sludge particles, the structural auxiliary material and the nutrient auxiliary material is 12 kg, 2.5 kg and 6.0 kg respectively, the carbon-nitrogen ratio of the material is controlled to be 27:1, the water content is 51%, and the pH is 6.78.

[0038] In Comparative Example 1, the compound functional microbial agent is replaced by yeast, bacillus subtilis and actinomycetes, and the ratio of the yeast, the bacillus subtilis and the actinomycetes is 5-10:15-25:10-20. The temperature of the pile rises slowly, and reaches 65℃ after about 5 days, the mycelium is less, the color is obviously deep after 10 days, and there is no peculiar smell after 15 days. During the period, the pH gradually decreases to 6.22, and the main fermentation period is about 18 days.

[0039] In the comparative example 1, the composite passivation agent is replaced by lime and biochar, wherein the composite passivation agent contains 200 g of lime and 800 g of biochar, and at the same time, 40 g of urea is added to supplement the nitrogen loss in the later stage of fermentation during the passivation process. At this stage, the overall passivation agent is alkaline, and the pH rises to about 7.8.

[0040] In the comparative example 1, the material after fermentation and synergistic passivation treatment is placed in the open space for 20 days to make its properties completely stable, with a moisture content of 36%, a pH of 7.2, and no odor. A 5-10 mm roller screen is selected for screening to remove impurities, and a homogeneous and loose final product, i.e., an organic substrate for greening, is obtained.

[0041] Product testing: The organic substrate for greening products obtained in the example 1 and the comparative example 1 are subjected to index detection, and the detection results are as follows: From the product testing results and the preparation process of the example 1 and the comparative example 1, it can be found that after the auxiliary substrate in the comparative example 1 is changed from sawdust to straw, and the special composite functional microbial agent is not added, but the conventional aerobic compost microbial agent is used, the temperature rising rate becomes slow, and the fermentation period becomes long. In the comparative example 1, the conventional passivation agent lime and biochar are used, and the targeted composite functional microbial agent + composite passivation agent is not used for synergistic passivation of heavy metals, resulting in that part of the heavy metal indicators do not meet the product I-level index requirements. In the comparative example 1, the slow-release nutrient embedding and pore gradient modification are not designed synchronously, and the porosity of the final product does not meet the requirements. Although the overall EC value meets the requirements, it is higher than that of the example 1. Under the condition that the total nutrients are equivalent, the proportion of available nutrients is higher, and the proportion of slow-release nutrients will decrease, which is easy to cause rapid loss of nutrients in the early stage and insufficient supply in the later stage, and is easy to cause burn or nutrient loss of seedlings, and cannot realize balanced and slow-release supply of nutrients.

[0042] Table 1 Technical indexes of the organic substrate for greening in the example 1 and the comparative example 1

[0043] Table 2 Heavy metal indexes of the organic substrate for greening in the example 1 and the comparative example 1

[0044] From the above results, compared with the conventional preparation process, the method for preparing the organic substrate for greening from sludge according to the present application adopts the combined process of sludge pretreatment, ingredient conditioning, inoculation fermentation, synergistic passivation, and aging screening, and obtains an organic substrate for greening with low EC value, balanced nutrients, rich pore structure, good air permeability, low risk of compaction, low content of toxic and harmful elements, and the like, which can achieve the following unexpected technical effects: (1) The sludge is used as the main raw material to prepare the directly usable green organic substrate, and the sludge accounts for more than 50%, so that the organic matter and nutrient elements such as nitrogen, phosphorus and potassium in the sludge can be fully utilized, the product meets the relevant performance indicators of the "Green Organic Substrate" (GB / T33891-2017), and the resource utilization of the sludge is realized.

[0045] (2) The heat hydrolysis + high dry dehydration + aerobic fermentation are combined, the main material sludge particles, structural auxiliary material sawdust and nutrient auxiliary material pig manure are proportioned and conditioned, and the specific composite functional inoculant is inoculated, so that the difficulty and period of fermentation treatment are further shortened, and the odor and sanitation problems are obviously improved.

[0046] (3) The potential toxic elements such as soluble chlorine and soluble sodium in the sludge are introduced into the dewatering filtrate, so that the content of the potential toxic elements in the sludge is further reduced, and the EC value of the substrate is controlled.

[0047] (4) In view of the difficulty of heavy metal stabilization of the green substrate, the synergistic graded passivation of the composite functional inoculant + composite passivation agent is designed, the passivation effect of the heavy metal is improved through the synergistic effect of the microorganism and the natural mineral, the specific passivation agent combination is designed for different heavy metals, the precise passivation is realized, and the biological availability and migration of the heavy metal are further reduced.

[0048] (5) The slow-release nutrient embedding and pore gradient improvement are simultaneously designed, the ratio of available nutrients and slow-release nutrients is controlled to realize the sustained release of the fertilizer effect, the air permeability and drainage of the substrate are improved, the substrate is prevented from being hardened, and at the same time, no excessive chemical reagent is added in the whole treatment process, and the nitrogen, phosphorus and potassium nutrients and the medium elements such as calcium and magnesium required by plants are supplemented by the mineral, so that the plants are not burned by the nutrient accumulation.

[0049] (6) The struvite can be obtained from the by-product sludge filtrate treatment section of the sludge heat hydrolysis + high dry dehydration pretreatment process, the struvite precipitate is generated by adding a magnesium source (such as magnesium chloride), so that the nitrogen and phosphorus nutrients are separated from the liquid phase. After the nitrogen and phosphorus in the sludge filtrate are removed, the high-quality carbon source can be prepared for further resource utilization, and the precipitated struvite can be used as a slow-release fertilizer supplement for the preparation of the green organic substrate from the sludge, so that the nitrogen and phosphorus elements in the sludge are maximized.

[0050] Therefore, the green organic substrate product prepared by the method of the present application meets the characteristics of fixing plants, water and fertilizer retention, good air permeability, stable properties, non-toxicity, light texture, high ion exchange capacity, appropriate carbon-nitrogen ratio, easy to adjust pH value, and promoting the growth of green plants, and has high use value and good application prospect.

[0051] The above examples are only preferred embodiments of the present application, and the protection scope of the present application is not limited to the above examples. Any technical scheme falling within the concept of the present application belongs to the protection scope of the present application. It should be pointed out that improvements and refinements made by those of ordinary skill in the art without departing from the principles of the present application should also be considered as falling within the protection scope of the present application.

Claims

1. A method for preparing organic substrate for landscaping from sludge, characterized in that, Includes the following steps: S1. The sludge is subjected to hot hydrolysis, dewatering, and crushing to obtain sludge particles; S2. Mix and condition the sludge particles, structural additives and nutritional additives obtained in step S1 to obtain a mixture. S3. Inoculate the mixture obtained in step S2 with a compound functional microbial agent for aerobic fermentation; the compound functional microbial agent is composed of white rot fungi, Bacillus subtilis, actinomycetes, lactic acid bacteria and thermophilic sulfate-reducing bacteria. S4. The material obtained after aerobic fermentation in step S3 is mixed with a composite passivating agent for passivation treatment; the composite passivating agent is composed of modified sepiolite, struvite, and modified vermiculite; the modified sepiolite is prepared by thermally modifying sepiolite; the modified vermiculite is prepared by impregnation and calcination of vermiculite and urea solution as raw materials; S5. The material obtained after passivation treatment in step S4 is aged and screened to obtain an organic substrate for landscaping.

2. The method according to claim 1, characterized in that, In step S4, the amount of the composite passivating agent added is 10% to 15% of the mass of the material obtained after aerobic fermentation; the mass ratio of modified sepiolite, struvite, and modified vermiculite in the composite passivating agent is 1 to 1.5: 1.5 to 2: 5 to 10.

3. The method according to claim 2, characterized in that, The preparation method of the modified sepiolite includes the following steps: heating sepiolite to 250℃~300℃ and holding it at that temperature for 2 hours~3 hours, crushing it, and passing it through a 100-mesh sieve to obtain modified sepiolite; the particle size of the modified sepiolite is ≤0.15mm; The preparation method of the struvite includes the following steps: mixing sludge pretreatment filtrate containing ammonium ions and phosphate ions with magnesium oxide and reacting, drying at a temperature ≤60℃ for 3 to 4 hours, pulverizing, and passing through a 10-50 mesh sieve to obtain struvite; the particle size of the struvite is 0.5 mm to 2 mm. The preparation method of the modified vermiculite includes the following steps: mixing vermiculite and urea solution, impregnating the mixture, and calcining it at 600℃~800℃ for 1min~2min to obtain modified vermiculite; the particle size of the modified vermiculite is 3mm~6mm.

4. The method according to any one of claims 1 to 3, characterized in that, In step S1, the hot hydrolysis is carried out under alkaline conditions; lime is added to the sludge in the hot hydrolysis system; the amount of lime added is 5% of the sludge mass; the operating pressure of the hot hydrolysis is 0.3MPa~0.6MPa; the temperature of the hot hydrolysis is 110℃~130℃; the time of the hot hydrolysis is 100min~150min; the filtrate produced during the dewatering process is used to prepare struvite; the particle size of the sludge particles is ≤10mm; the moisture content of the sludge particles is 40%~60%.

5. The method according to any one of claims 1 to 3, characterized in that, In step S2, the mass ratio of the sludge particles, structural additives, and nutritional additives is 4-6:1-2:2.5-4; the structural additives are sawdust; and the nutritional additives are at least one of pig manure and chicken manure.

6. The method according to claim 5, characterized in that, In step S2, the carbon-to-nitrogen ratio of the mixture is 25-30:1; the moisture content of the mixture is 50%-60%; the pH value of the mixture is 5.5-8.5; and the moisture content is controlled by spray humidification during the conditioning process.

7. The method according to any one of claims 1 to 3, characterized in that, In step S3, the inoculation amount of the compound functional microbial agent is 0.2% to 0.5% of the mass of the mixture; the mass ratio of white rot fungi, Bacillus subtilis, actinomycetes, lactic acid bacteria and thermophilic sulfate-reducing bacteria in the compound functional microbial agent is 2 to 5: 15 to 25: 10 to 20: 5 to 10: 1 to 5.

8. The method according to claim 7, characterized in that, In step S3, the aerobic fermentation is carried out at a temperature of 60℃~70℃; the aerobic fermentation time is 7 days~10 days.

9. The method according to any one of claims 1 to 3, characterized in that, In step S5, the aging time is 10 to 20 days; the particle size of the organic substrate for landscaping is 5 mm to 10 mm; and the moisture content of the organic substrate for landscaping is ≤40%.

Images