Method for improving desert soil through cooperation of coal gasification slag and forestry and agricultural residues

Abstract

The invention discloses a method for improving desert soil through cooperation of coal gasification slag and forestry and agricultural residues, and belongs to the field of solid waste resource utilization. The method comprises the following steps: carrying out oxygen-limited carbonization on part of agricultural and forestry wastes to prepare biomass charcoal; performing mixed fermentation on the residual agricultural and forestry wastes and livestock and poultry manure to obtain a fermentation base material; mixing and curing the coal gasification slag, the biomass charcoal and the fermentation base material according to the mass ratio of (20-70%): (10-40%): (10-40%) to obtain an improved material; and finally, applying the material into desert soil according to the mass ratio of 1: 1. Through multi-waste cooperation and staged treatment, a four-dimensional improvement mechanism of mineral framework supporting, organic nutrient slow release, microbial activation and heavy metal passivation is constructed, the soil structure is remarkably improved, the fertility and the water binding capacity are improved, vegetation growth is promoted, and meanwhile solid waste recycling and safe utilization are achieved.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization, and in particular to a method for improving desert soil by co-processing coal gasification slag with agricultural and forestry waste. Background Technology

[0002] Desertification is a major global ecological challenge. As an important ecological barrier in Northwest China, Ningxia has more than half of its total land area affected by desertification. Its ecological security is not only related to the sustainable development of the region, but also directly affects the climate pattern from Northwest China to the Yellow River and Huai River basins.

[0003] Currently, Ningxia faces two prominent challenges in combating desertification: The soil is infertile and fragile: the sandy soil has an extremely loose structure, with an organic matter content generally below 1%, poor water and fertilizer retention capacity, and a vegetation survival rate of less than 30%.

[0004] Dilemma of solid waste utilization: Agricultural and forestry waste (such as wine lees, corn stalks, edible fungus lees, fruit tree branches), livestock and poultry manure, and coal gasification slag and other industrial and agricultural by-products are piled up on a large scale in the region, which not only occupy land, but also cause resource waste and secondary pollution due to traditional incineration or simple composting.

[0005] Studies have shown that coal gasification slag is rich in minerals such as silicon, aluminum, and calcium, which can improve the physical and chemical structure of soil. However, it lacks organic matter and readily available nutrients, making it difficult to sustain plant growth when applied alone. Current technologies often employ a simple mixture of organic fertilizer and solid waste, failing to establish a synergistic physical-chemical-biological mechanism. This results in slow and unstable soil aggregate formation. Furthermore, direct application of industrial solid waste may trigger heavy metal migration, posing risks to plant and ecological safety. In addition, existing methods have not yet achieved in-situ high-value utilization of waste. Summary of the Invention

[0006] To address the aforementioned problems, this invention proposes a method for synergistically improving desert soil based on coal gasification slag, agricultural and forestry waste, and livestock manure. Through the synergistic utilization of multiple wastes, combined with natural fermentation and partial carbonization processes, a four-dimensional mechanism is constructed: "mineral framework support - slow release of organic nutrients - microbial activation - heavy metal passivation." This mechanism simultaneously improves soil structure and fertility, promotes vegetation restoration, and achieves high-value utilization of solid waste, thus realizing the dual effects of desert ecological restoration and resource recycling.

[0007] The method for improving desert soil using coal gasification slag and agricultural and forestry waste provided by the present invention is characterized by comprising the following steps: (1) Take a portion of agricultural and forestry waste and carbonize it at 500-650℃ under oxygen-limited conditions to obtain biochar. The porosity of the biochar is ≥60% and the specific surface area is ≥120m². 2 / g; (2) Take the remaining agricultural and forestry waste, crush it and mix it with livestock and poultry manure, adjust the C / N ratio to 20-25, the moisture content to 50-60%, add compound microbial agent, ferment it at 45-65℃ for 30-40 days, turn the pile every 2-5 days to obtain fermentation base material; (3) The acid-washed coal gasification slag, the biochar obtained in step (1), and the fermentation substrate obtained in step (2) are mixed in a mass ratio of 20-70%: 10-40%: 10-40%, and matured for 20-30 days. The mixture is turned over every 7-10 days to obtain the improved material. The coal gasification slag is composed of coarse coal gasification slag and fine coal gasification slag in a mass ratio of 1:3. (4) The improved material is applied to the desert soil at a mass ratio of 1:1.

[0008] Preferably, the agricultural and forestry waste includes at least one of wine lees, corn stalks, mushroom residue, and fruit tree branches.

[0009] Preferably, the livestock and poultry manure includes at least one of cow manure and sheep manure.

[0010] Preferably, the improved material is applied to desert soil and then used to plant nitrogen-fixing / sand-fixing plants, including sweet clover, alfalfa, or sheepgrass.

[0011] Preferably, after the improved material is applied to desert soil, the sand content of the soil is reduced to below 80%, and the proportion of aggregates is increased to 45-60%, thereby transforming the soil texture from sandy soil to sandy loam.

[0012] Preferably, the agricultural and forestry waste needs to be pretreated with microwaves before carbonization. The microwave power is 800W and the time is 5-10 minutes to destroy the lignocellulose structure and increase the porosity to ≥70%.

[0013] Preferably, the agricultural and forestry waste needs to be pretreated with microwaves before carbonization. The microwave power is 800W and the time is 5-10 minutes to destroy the lignocellulose structure and increase the porosity to ≥70%.

[0014] Preferably, the compound microbial agent includes Bacillus subtilis, Aspergillus niger, and Actinomycetes in a mass ratio of 1:1:1, and the inoculation amount is 1‰-2‰ of the total weight of the fermentation substrate.

[0015] Preferably, the plants are inoculated with rhizobium at the same time, with an inoculation amount of 0.5-2% of the seed weight.

[0016] The method provided by this invention has the following beneficial effects: (1) This invention uses agricultural and forestry waste, livestock and poultry manure and coal gasification slag as raw materials, takes ecological safety as the core, and simultaneously achieves the dual goals of desert soil structure improvement and solid waste resource utilization, breaking through the dual predicament of "barren sandy soil" and "solid waste surrounding the city".

[0017] (2) The present invention further optimizes the physical and chemical properties of soil by combining coal gasification slag with agricultural and forestry waste. Compared with the treatment of adding coal gasification slag alone (CK), the improvement of desert soil by coal gasification slag combined with agricultural and forestry waste reduces the sand content to below 80% and increases the clay content by 8-12%, realizing the transformation of soil texture from sand to sandy loam. The soil bulk density is reduced by about 10%, and the fermented organic substrate promotes the formation of soil aggregates, increasing the proportion of aggregates by more than 40%. In comparison with Example 5, nitrogen (nitrate nitrogen, ammonium nitrogen, alkaline nitrogen), phosphorus (available phosphorus), potassium (total potassium), and organic matter are increased by at least 130%, 230%, 6%, and 150%, respectively. The porous structure of coal gasification slag, the microporous structure of biochar, and the fermented organic substrate work together to increase the saturated moisture content by 80-200% compared with the CK group.

[0018] (3) Compared with CK, the present invention increases the average survival rate of plants by more than 120% and the average fresh weight by more than 60%.

[0019] (4) The heavy metal content of the soil after the improvement of this invention meets the standard of GB15618-2018 "Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard (Trial)", and the heavy metal content of each part of the plant roots, stems and leaves meets the standard of GB13078-2017 "Feed Hygiene Standard". The potential ecological risk index (RI) is less than 90 (low risk). Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly described below.

[0021] The accompanying drawings described below are only related to some embodiments of the invention and are not intended to limit the invention.

[0022] In the attached diagram: Figure 1 The diagram shows a triangular coordinate diagram of soil texture classification using coal gasification slag coupled with agricultural and forestry waste in an embodiment of the present invention. Figure 1 SS represents desert soil, CGCS represents coarse coal gasification slag, CGFS represents fine coal gasification slag, PT represents wine lees used as biomass to improve desert soil (Example 1); JZ represents mushroom residue used as biomass to improve desert soil (Example 2); JG represents corn stalks used as biomass to improve desert soil (Example 3); and CK represents coal gasification slag used alone to improve desert soil (Example 5). Detailed Implementation

[0023] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0024] Example 1 (Acid Pickling Enhancement): The coal gasification slag (physicochemical values ​​are shown in Table 1, CGCS:CGFS=1:3) was soaked in hydrochloric acid with pH=4 for 3 hours, washed with water until neutral, dried and pulverized to 100 mesh; a portion of the wine lees was pulverized to ≤2 mesh. mm, after pretreatment by microwave at 800W for 5-10 minutes, carbonized at 550℃ for 2 hours under limited oxygen conditions to obtain biochar; separately, the remaining wine lees and sheep manure were mixed, and a C / N ratio of 25 and a moisture content of 55% were added, along with 2‰ compound microbial agent (Bacillus subtilis: Aspergillus niger: Actinomycetes = 1:1:1) for 35 days to obtain fermentation substrate; the components of coal gasification slag, biochar, and fermentation substrate were mixed according to the ratio A, B, C (A, B, C represent the mass ratio of coal gasification slag, biochar, and fermentation substrate. A is 1:0.23:0.31 [65:15:20], B is 1:0.25:0.42 [60:15:25], C is 1:0.4:0.6 [50:20:30]), and matured for 20 days to obtain improved material. A suitable amount of improved material was mixed with sand at a 1:1 mass ratio for pot experiments. Rhizobium was added simultaneously during planting, and the inoculation was 2% of the seed weight. The sweet osmanthus was planted for 90 days. Specific values ​​are shown in Tables 3 and 4.

[0025] Comparative Example 1 The process involves no acid washing of coal gasification slag; the remaining steps are the same as in Example 1.

[0026] Compared to Comparative Example 1, most indicators in Example 1 increased significantly, with potassium decreasing significantly. This is mainly because the acid washing process dissolves and removes most of the soluble salts from the gasification slag, resulting in a significant decrease in EC. Furthermore, ammonium nitrogen increased significantly. The cation exchange capacity of the gasification slag increased significantly after acid washing, enhancing its adsorption and fixation capacity for ammonium nitrogen, making it less prone to volatilization and loss. The increase in available phosphorus is mainly due to the removal of phosphorus-fixing metal ions (such as Ca) from the gasification slag during acid washing. 2+ Fe 3+ Al 3+ This greatly alleviates the fixation of phosphorus in the soil, thus significantly improving the availability of phosphorus from the fermentation substrate and the soil itself.

[0027] Example 2 (Enhanced with Compound Microbial Agent) The biomass (wine lees) used in Example 1 was replaced with yeast bran, and the remaining steps were the same as in Example 1. The fermentation time was 40 days to obtain the fermentation substrate; the maturation time after mixing was 20 days.

[0028] Comparative Example 2 No compound microbial agent was added during the fermentation process; the remaining steps were the same as in Example 2.

[0029] Compared to Comparative Example 2, the fermentation and maturation process took 85 days (55 days of fermentation + 30 days of maturation). In Comparative Example 2, the fermentation and maturation time was shortened to 60 days (40 + 20). The odor during the fermentation process was significantly reduced, most nutrient indicators were significantly improved, organic matter was basically the same, and ammonium nitrogen was reduced. Due to the promotion of nitrogen conversion by the microbial agent, more nitrogen was converted into available nitrogen, which increased the nutrients that plants could directly utilize. The plant growth indicators were significantly higher than those in Comparative Example 2.

[0030] Example 3 (Rhizobium Enhancement) The biomass (wine lees) used in Example 1 was replaced with corn stalks, and the remaining steps were the same as in Example 1.

[0031] Comparative Example 3 The planting process did not involve the addition of rhizobium; the remaining steps were the same as in Example 3.

[0032] Compared to Comparative Example 3, Example 3 showed a significant improvement in nitrogen levels, while potassium levels remained largely unchanged. This is likely due to the inoculant promoting nitrogen fixation, resulting in an overall increase in nitrogen content and improved soil microbial environment. Simultaneously, rhizobia stimulated plant secretion of organic acids, and the enriched microbial community participated in phosphate mineralization, enhancing phosphatase activity and increasing available phosphorus content in the soil. This nutrient advantage further promoted plant growth, and higher biomass resulted in less heavy metal stress on plants, which was more conducive to plant growth, leading to a significant improvement in plant growth indicators.

[0033] Example 4 (Process Intensification) The biomass (wine lees) used in Example 1 was replaced with grapevines, and the remaining steps were the same as in Example 1.

[0034] Comparative Example 4 The biomass used is not carbonized, and the biomass and sheep manure are directly mixed without fermentation and decomposition. The remaining steps are the same as in Example 4.

[0035] Compared to Comparative Example 4, Example 4 showed a significant increase in the content of each nutrient. This is because microbial mineralization significantly enhances the availability of nitrogen and phosphorus, fermentation and maturation accelerate the decomposition of organic matter, biochar reduces nutrient loss, field water holding capacity increases by 106%, resulting in a significant increase in plant survival rate and significant improvement in other growth indicators.

[0036] Example 5 (CK) The coal gasification slag was simply mixed with sand at a 1:1 mass ratio, without the addition of biochar, fermentation substrate, or microorganisms.

[0037] Table 1 Basic Physicochemical Properties of Raw Materials Used

[0038] Supplement: The organic matter content of biomass materials wine lees (PT), shiitake mushroom residue (JZ), corn stalks (JG), and fruit tree branches (ZT) was 289, 320, 428, and 461 g / kg, respectively.

[0039] The potential ecological risk assessment of heavy metals in the soils of Examples 1-4 was carried out. The assessment method was as follows: based on the toxicity response coefficient of heavy metals, the hazard coefficient of individual heavy metals was calculated, and then the comprehensive ecological hazard index of multiple heavy metals was calculated. E This refers to the individual hazard coefficient; T This represents the toxicity response coefficient of a certain heavy metal. C The reference values ​​are for heavy metals; the toxicity response coefficients for Cd, As, Pb, Cu, and Cr are 30, 10, 5, 5, and 2, respectively; RI is the comprehensive ecological hazard index for multiple heavy metals in the soil. C for Measured heavy metal concentration (mg / kg); C This is a reference value for the background of heavy metals.

[0040]

[0041] The results are shown in Table 2. The application of the soil amendment material, through microbial activation and heavy metal passivation mechanisms, enabled acid washing, compound microbial agents, and rhizobia to effectively reduce the comprehensive ecological hazard index of multiple heavy metals in the soil. The potential ecological risks of the amendment material ratios A, B, and C in Examples 1-4 were all lower than those in Example 5. Therefore, the amendment material of this invention can reduce the potential ecological risks of heavy metals in soil, and the overall risk is only minor.

[0042] Table 2. Assessment of Potential Ecological Risks from Heavy Metals in Soil

[0043] Table 3. Specific numerical values ​​for each soil example.

[0044] Table 4. Numerical values ​​for each potted plant.

[0045] Example 6 In the implementation, agricultural and forestry waste is crushed and mixed with livestock and poultry manure. Agricultural and forestry waste is not limited to wine lees, corn stalks, mushroom compost, or fruit tree branches; livestock and poultry manure is not limited to cow dung or sheep dung. Similarly, after the improved material is applied to the desert soil, the nitrogen-fixing / sand-fixing plants used for planting are not limited to sweet clover, alfalfa, or sheepgrass; any suitable plant can be used. The C / N ratio should be adjusted to within the range of 20-25, and in specific embodiments, it can be 20 or 25. The moisture content should be adjusted to within the range of 50-60%, not limited to 55%, and in specific embodiments, it can be 50 or 60%. The fermentation time for adding compound microbial agents is adjusted according to the raw materials, generally 30-40 days to basically meet the fermentation requirements of all agricultural and forestry wastes. During the fermentation process, the pile should be turned every 2-5 days, depending on the actual situation. Furthermore, the fermentation temperature should be controlled within the range of 45-65℃, generally with a stable temperature of 55±2℃ being ideal.

[0046] Except for Comparative Examples 1 and 5, the coal gasification slag needs to be acid-washed before use. The pH of the acid washing solution should be in the range of 3-5, and in specific examples it can be 3, 4 or 5. The soaking time should be 2-4 hours, and in specific examples it can be 2, 3 or 4 hours. After that, it is dried and pulverized to 100-200 mesh, and in specific examples it can be 100, 150 or 200 mesh, to remove soluble salts and free heavy metals from the surface. In specific examples, the ratio of CGCS to CGFS can be 1:1, 1:2 or 1:3.

[0047] Except for Comparative Examples 2 and 5, the inoculation amount of the compound microbial agent is 1‰-2‰ of the total weight of the fermentation substrate, and in specific examples it can be 1‰, 1.5‰ or 2‰.

[0048] Except for Comparative Examples 3 and 5, the amount of rhizobium inoculated is 0.5-2% of the seed weight, and in specific examples it can be 0.5%, 1%, 1.5% or 2%.

[0049] Except for comparative examples 4 and 5, the carbonization temperature of biomass char is not limited to 550℃. Generally, biomass char prepared by carbonization at 500-650℃ under oxygen-limited conditions can meet the requirements. The temperature can be adjusted appropriately according to the preparation conditions. In specific examples, it can be 500℃ or 650℃. Biomass char prepared under these conditions has a porosity ≥60% and a specific surface area ≥150m². 2 / g. If microwave pretreatment is performed before carbonization, the microwave power is set to 800W for 5-10 minutes to destroy the lignocellulose structure, which can increase the porosity to ≥70%. The mixing ratio of gasification slag, biochar, and fermentation substrate is not limited to the three ratios A, B, and C in the examples. The mass ratio of gasification slag, biochar, and fermentation substrate can be mixed in the range of 20-70%:10-40%:10-40%, and the maturation time can be 20-30 days. The compost should be turned over every 7-10 days, depending on the actual situation.

[0050] like Figure 1 Experimental data show that when coal gasification slag is used in conjunction with agricultural and forestry waste to improve desert soil, compared with the treatment of adding coal gasification slag alone (CK), the soil texture changes from sandy soil to sandy loam, the soil bulk density decreases by about 10%, and the proportion of aggregates increases by more than 40%.

[0051] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for improving desert soil using coal gasification slag in conjunction with agricultural and forestry waste, characterized in that, Includes the following steps: (1) Take a portion of agricultural and forestry waste and carbonize it at 500-650℃ under oxygen-limited conditions to obtain biochar. The porosity of the biochar is ≥60% and the specific surface area is ≥120m². 2 / g; (2) Take the remaining agricultural and forestry waste, crush it and mix it with livestock and poultry manure, adjust the C / N ratio to 20-25, the moisture content to 50-60%, add compound microbial agent, ferment it at 45-65℃ for 30-40 days, turn the pile every 2-5 days to obtain fermentation base material; (3) The acid-washed coal gasification slag, the biochar obtained in step (1), and the fermentation substrate obtained in step (2) are mixed in a mass ratio of 20-70%: 10-40%: 10-40%, and matured for 20-30 days. The mixture is turned over every 7-10 days to obtain the improved material. The coal gasification slag is composed of coarse coal gasification slag and fine coal gasification slag in a mass ratio of 1:

3. (4) The improved material is applied to the desert soil at a mass ratio of 1:

1.

2. The method according to claim 1, characterized in that: The agricultural and forestry waste includes at least one of wine lees, corn stalks, mushroom residue, and fruit tree branches.

3. The method according to claim 1, characterized in that: The livestock and poultry manure includes at least one of cow manure and sheep manure.

4. The method according to claim 1, characterized in that: After the improved material is applied to the desert soil, it is used to plant nitrogen-fixing / sand-fixing plants, including sweet clover, alfalfa, or sheepgrass.

5. The method according to claim 1, characterized in that: After the improved material is applied to the desert soil, the sand content of the soil drops to below 80%, and the proportion of aggregates increases to 45-60%, thus transforming the soil texture from sandy soil to sandy loam.

6. The method according to claim 1, characterized in that: Before carbonization, the agricultural and forestry waste needs to be pretreated with microwaves at a power of 800W for 5-10 minutes to destroy the lignocellulose structure and increase the porosity to ≥70%.

7. The method according to claim 1, characterized in that: The acid washing solution for the coal gasification slag acid washing treatment has a pH of 3-5 and a soaking time of 2-4 hours. After that, it is dried and pulverized to 100-200 mesh to remove soluble salts and free heavy metals from the surface.

8. The method according to claim 1, characterized in that: The compound microbial agent includes Bacillus subtilis, Aspergillus niger, and Actinomycetes in a mass ratio of 1:1:1, and the inoculation amount is 1‰-2‰ of the total weight of the fermentation substrate.

9. The method according to claim 4, characterized in that: When planting plants, inoculate them with rhizobia simultaneously, with an inoculation amount of 0.5-2% of the seed weight.

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