A biochar-biogas slurry-microalgae composite material based on nano-CO2 bubble regulation and its application in promoting soil biocrust formation.

Abstract

This invention relates to a biochar-biogas slurry-microalgae composite material based on nano-CO2 bubble regulation and its application in promoting soil biocrust formation. This method achieves precise pH regulation and CO2 enrichment through two nano-CO2 bubble injections: the first injection is used for acidification and carbon enrichment of the biochar-biogas slurry mixture; the second injection is used for material activation and pH fine-tuning before spraying, lowering the system pH to below 7 and enhancing microalgae activity and EPS secretion capacity. This invention achieves rapid soil crust formation, enhanced wind erosion resistance, evaporation inhibition, and carbon sequestration in arid and cold regions through a four-pronged synergistic mechanism of "nano-CO2 bubble regulation, biochar framework support, biogas slurry nutrient supply, and microalgae EPS bonding."

Description

Technical Field

[0001] This invention relates to the field of ecological restoration and carbon sequestration technology, specifically to a biochar-biogas slurry-microalgae composite material based on nano-CO2 bubble regulation and its application in promoting soil biocrust formation. Background Technology

[0002] Biocrusts, an important component of ecosystems in cold and arid regions, are formed by cyanobacteria, algae, and other cryptogams through their binding with surface soil particles. They possess key ecological functions such as sand fixation and erosion resistance, promotion of carbon and nitrogen cycling, water regulation, soil improvement, and maintenance of biodiversity.

[0003] Related studies have shown that biocrusts can reduce wind erosion by more than 95% and soil moisture evaporation by 50%–90%. However, the formation rate of biocrusts under natural conditions is extremely slow, usually requiring several years or even decades, which is difficult to meet the current practical needs of rapid ecological restoration. Although existing artificial induction techniques can shorten the formation time to 1-2 years, they are costly, and the resulting biocrusts have low mechanical strength and are easily damaged by wind erosion and trampling, requiring a long initial maintenance period.

[0004] Based on this, the present invention proposes a high-value coupling CO2 capture technology using biochar-biogas slurry-microalgae composite materials. Through a four-fold synergistic mechanism of "nano-CO2 bubble regulation, biochar framework support, biogas slurry nutrient supply, and microalgae EPS bonding", it achieves efficient and rapid crust formation. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a biochar-biogas slurry-microalgae composite material based on nano-CO2 bubble regulation and a method for promoting soil biocrust formation in cold and arid regions.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a biochar-biogas slurry-microalgae composite material based on nano-CO2 bubble regulation includes the following steps: Step 1: Mix biochar and biogas slurry to prepare a biochar-biogas slurry mixture; Step 2: Inject CO2 into the mixture of biochar and biogas slurry prepared in the previous step to acidify and enrich the carbon in the mixture; Step 3: Cultivate microalgae in the mixture after the previous step to obtain a mixture of CO2-rich biogas slurry and microalgae. Step 4: Mix biochar with CO2-rich biogas slurry and microalgae to prepare a biochar-biogas slurry-microalgae composite spray solution with a biochar concentration of 1%-20%. The concentration is adjusted according to the target soil moisture content.

[0007] Furthermore, in step 2, the CO2 is nano-CO2 bubbles.

[0008] Furthermore, step 3 is performed in the following manner: After solid-liquid separation of the biochar and biogas slurry mixture, the biogas slurry was diluted with water at a ratio of 1:10 and used as a microalgae culture medium. Cold-resistant and drought-resistant algae species were cultured in the microalgae culture medium until OD ≥ 2 and the volume of microalgae accounted for more than 10% of the total volume of the material. Alternatively, steps 1 and 2 can be omitted, and microalgae can be cultured directly in the biogas slurry infused with nano CO2 bubbles until OD = 2 and the volume of microalgae accounts for more than 10% of the total volume of the material.

[0009] Furthermore, the cold- and drought-resistant algae species is Chlorella or Spirulina.

[0010] A biochar-biogas slurry-microalgae composite material based on nano-CO2 bubble regulation was prepared by the above method.

[0011] The application of the above-mentioned biochar-biogas slurry-microalgae composite material based on nano-CO2 bubble regulation in promoting soil biocrust formation includes the following steps: Furthermore, this includes the following steps: Bubble CO2 bubbles into the spray solution until the pH of the spray solution drops below 7, then spray it onto the target soil surface.

[0012] The beneficial effects of this invention are as follows: This method achieves precise pH control and CO2 enrichment through two rounds of nano-CO2 bubble injection: the first injection is used for acidification and carbon enrichment of the biochar-biogas slurry mixture; the second injection is used for activation of the material before spraying and pH fine-tuning, lowering the system pH to below 7 and enhancing microalgae activity and EPS secretion capacity. This invention achieves rapid surface crusting, enhanced wind erosion resistance, evaporation inhibition, and carbon sequestration in arid and cold regions through a four-pronged synergistic mechanism of "nano-CO2 bubble control, biochar framework support, biogas slurry nutrient supply, and microalgae EPS bonding."

[0013] This invention has the following significant advantages: the materials are simple and readily available, and the operation is simple. This method solves the technical problems of high cost of traditional biological crust cultivation and low resource utilization rate of carbon-rich biogas slurry through the synergistic effect of biochar, biogas slurry and microalgae, and realizes the synergy of carbon fixation and ecological restoration.

[0014] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. Attached Figure Description

[0015] Figure 1 This is a diagram of the microstructure of the surface of biological soil crust; Figure 2 Map showing the thickness of biological soil crust; Figure 3The diagram illustrates the effect of different treatments on soil moisture evaporation by the formation of crusts. Detailed Implementation

[0016] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0017] 1. Materials and Equipment Materials: Biochar, biogas slurry, cold- and drought-resistant algae (Chlorella, Spirulina, etc.) Equipment: Micro / nano bubble generator, spraying equipment 2. Preparation method of biochar-biogas slurry-microalgae composite material Step 1: Preparation of biochar and biogas slurry mixture Biochar is a solid aromatic fluorocarbon complex produced by the thermal decomposition or gasification of biomass. It contains abundant porous structures and oxygen-containing functional groups, exhibiting a high adsorption capacity for nutrient ions such as nitrates and phosphates. This enhances the supply of essential nutrients to microorganisms, thereby effectively improving their proliferation tolerance and survival rate.

[0018] Biogas slurry is a bright brown liquid produced by the anaerobic fermentation of organic waste. It is weakly alkaline (pH 7-8), rich in nitrogen, phosphorus, and other essential elements for microalgae growth, but lacks a carbon source. It has the functions of efficient fertilization, antibacterial and insecticidal effects, soil improvement, and ecological recycling. It can be used as a renewable absorbent that integrates CO2 absorption and CO2 storage.

[0019] In this invention, sufficient biochar and biogas slurry materials are prepared according to the spraying area, and mixed at a mass ratio of biochar:biogas slurry = 16:100, and stirred evenly.

[0020] Step 2: Acidification and carbon enrichment of the biochar and biogas slurry mixture Acidification refers to the process by which the concentration of hydrogen ions (H⁺) in a system increases and the pH value decreases, resulting in acidity or enhanced acidity, through the addition of acidic substances, chemical reactions, or environmental changes.

[0021] In this invention, the biogas slurry is weakly alkaline, while the mixture of biochar and biogas slurry is alkaline. A micro / nano bubble generator is used to bubble CO2 into the mixture. This process acidifies the entire system to a neutral or weakly acidic state, while simultaneously enriching CO2 within the pores of the biochar. The amount of CO2 bubbled in is determined to lower the system's pH to 6.0-7.0.

[0022] Carbon enrichment refers to the process by which the concentration / storage of carbon in a specific system, sphere, or medium exceeds the background level, resulting in directional accumulation and deposition. Carbon enrichment can be used to restore acidified, desertified, and infertile degraded soils and restore soil productivity.

[0023] Step 3: Microalgae cultivation Microalgae cultivation is the entire process of separating, purifying, propagating, and preserving pure / mixed strains of microalgae and macroalgae under a controlled artificial environment.

[0024] Spirulina and Chlorella were selected in this invention because Spirulina is adapted to high-alkaline, high-salt, and high-temperature environments, grows rapidly, and has strong pollution resistance; Chlorella has strong temperature tolerance (20~30℃), light intensity of 3000~5000 lx, can be cultured autotrophically / heterotrophically, grows rapidly, is easy to propagate, and has strong pollution resistance.

[0025] The goal is to obtain algal strains with high purity, strong activity, and stable growth. Microalgae and other microorganisms are artificially cultured, and their efficient photosynthesis is used to fix CO2, thereby enriching carbon in the microbial biomass.

[0026] The mixture of biochar and biogas slurry was subjected to solid-liquid separation, and the treated biogas slurry was collected; it was then diluted with water at a ratio of 1:10 to serve as a microalgae culture medium.

[0027] Cultivate cold- and drought-resistant algal species such as Chlorella and Spirulina to: A. OD = 2; (In algal culture, the OD value generally refers to the wavelength of 680 nm. OD = 2 indicates the late stage of the logarithmic growth phase of microalgae, when the algal cells are highly active and have stable density, making it the optimal concentration for experimental / application sampling.) B. The volume of microalgae accounts for ≥10% of the final material volume; (Microalgae volume percentage = pure algal liquid volume (OD=2) ÷ total final material volume × 100%. The final material can be culture medium, buffer solution, reaction system, etc. Unless otherwise specified, supplement with blank culture medium corresponding to the original algal species.) Alternatively, steps 1 and 2 can be omitted, and microalgae can be directly cultured in biogas slurry infused with nano-CO2 bubbles until OD = 2 and the microalgae volume accounts for more than 10% of the total material volume. Step 4: Preparation of biochar-biogas slurry-microalgae composite material Biochar, CO2-rich biogas slurry, and microalgae are mixed in a certain proportion to prepare a spray solution with a biochar concentration of 1%-20%, and the concentration is adjusted according to the target soil moisture content.

[0028] Step 5: Activation of biochar-biogas slurry-microalgae composite material The activation of the biochar-biogas slurry-microalgae composite material involves inflating nano-CO2 bubbles into the composite material again before spraying, which lowers the pH of the material to below 7. At the same time, the added CO2 alleviates carbon limitation, enhances the photosynthetic efficiency of microalgae, and promotes the growth and nutrient absorption of microalgae. The secretion of microalgae EPS and the material's bonding ability can also serve as a material or energy raw material, forming a closed loop.

[0029] 3. Promote soil biocrust formation in cold and arid regions Methods for promoting soil biocrust formation in cold and arid regions using the aforementioned composite materials include: Step 1: Spraying composite material Control the amount of biochar applied according to standards to ensure the desired crusting effect is achieved; Application rate ≥63 g / m²: Primary crust forms on the ground surface.

[0030] Application rate ≥250 g / m²: Stable crust forms on the ground surface.

[0031] During operation, maintain a uniform distance between the spraying equipment and the ground surface, move at a steady speed, and ensure that the composite material fully covers the construction area without any omissions or accumulations.

[0032] Step 2: Post-construction management The critical maintenance period is within 3 days after spraying. During this period, it is necessary to pay close attention to the weather forecast. If it rains during this period, it is necessary to check the adhesion of the composite material on the ground surface in time and determine whether to re-spray. The amount of re-spray should be in accordance with the original standard.

[0033] After the initial spraying or in the absence of rainfall, water should be replenished periodically for maintenance, with a frequency of once every 7 days. When replenishing water, the amount of water should be controlled to keep the surface moist, avoiding excessive water flow that could wash away the composite material.

[0034] After normal spraying is completed, monitoring records should be kept of the crust formation process, and maintenance measures should be adjusted in a timely manner according to the crust status: Under normal conditions, the sprayed area will form a primary crust within 7-15 days; and a stable crust will form within 30-45 days.

[0035] This invention has the following significant advantages: the materials are simple and readily available, and the operation is simple. This method solves the technical problems of high cost of traditional biological crust cultivation and low resource utilization rate of carbon-rich biogas slurry through the synergistic effect of biochar, biogas slurry and microalgae, and realizes the synergy of carbon fixation and ecological restoration.

[0036] Application Case: Construction Project of Surface Biocrust in Cold and Arid Mining Areas In a cold and arid mining area, an exposed surface was selected as the experimental area. First, the surface was lightly leveled and large stones were removed. Then, one ton of material was mixed with biochar at a ratio of 16:100. CO2 was bubbled into the mixture using a micro-nano bubble generator to lower the pH of the system to 6.5. After solid-liquid separation, the treated biochar was diluted 1:10 and used to cultivate Chlorella until the OD = 2, with microalgae comprising 10% of the volume.

[0037] Biochar, CO2-rich biogas slurry, and microalgae were mixed to form a 5% biochar concentration spray solution. Before spraying, nano-CO2 bubbles were bubbled in again to lower the pH of the material to 6.8. The solution was then evenly sprayed onto the ground surface at a rate of 3–5 L / m² using a spraying device, achieving a biochar application rate of 250 g / m².

[0038] Avoid rainfall for 3 days after spraying, and water once during the first 7 days. Figure 1 and Figure 2 As shown, a primary crust forms on day 10, and a stable crust forms on day 35. Monitoring results show that the surface's resistance to wind erosion increased by 45%, evaporation inhibition rate increased by 22%, soil water holding capacity increased by 28%, and soil carbon pool increased by 17%.

[0039] This engineering case verifies the feasibility and significant effect of the materials and methods of this invention in the ecological restoration of mines in cold and arid regions.

[0040] like Figure 3 As shown, the soil moisture content of different treatment groups decreased over time: the Chlorella treatment group (a mixture of Chlorella, biochar, and biogas slurry) and the Spirulina treatment group (a mixture of Spirulina, biochar, and biogas slurry) saw their moisture content decrease from approximately 95% on day 6 to approximately 65%-70% on day 11, with a relatively gradual decrease, stronger water retention, and the best water retention effect; followed by the biochar treatment group (biochar + biogas slurry); then the compound fertilizer treatment group; the clean water control group saw the largest decrease from approximately 60% on day 6 to approximately 38% on day 11, with the worst water retention capacity.

[0041] The above description provides examples of the preferred embodiments of the present invention. Parts not detailed herein are common knowledge to those skilled in the art. The scope of protection of the present invention is determined by the claims. Any equivalent modifications based on the technical teachings of the present invention are also within the scope of protection of the present invention.

Claims

1. A method for preparing a biochar-biogas slurry-microalgae composite material based on nano-CO2 bubble regulation, characterized in that, Includes the following steps: Step 1: Mix biochar and biogas slurry to prepare a biochar-biogas slurry mixture; Step 2: Inject CO2 into the mixture of biochar and biogas slurry prepared in the previous step to acidify and enrich the carbon in the mixture; Step 3: Cultivate microalgae in the mixture after the previous step to obtain a mixture of CO2-rich biogas slurry and microalgae. Step 4: Mix biochar with CO2-rich biogas slurry and microalgae to prepare a biochar-biogas slurry-microalgae composite spray solution with a biochar concentration of 1%-20%. The concentration is adjusted according to the target soil moisture content.

2. The preparation method of biochar-biogas slurry-microalgae composite material based on nano-CO2 bubble regulation according to claim 1, characterized in that, In step 2, the CO2 is nano CO2 bubbles.

3. The preparation method of biochar-biogas slurry-microalgae composite material based on nano-CO2 bubble regulation according to claim 1, characterized in that, Step 3 is performed in the following manner: After solid-liquid separation of the biochar and biogas slurry mixture, the biogas slurry was diluted with water at a ratio of 1:10 and used as a microalgae culture medium. Cold-resistant and drought-resistant algae species were cultured in the microalgae culture medium until OD ≥ 2 and the volume of microalgae accounted for more than 10% of the total volume of the material.

4. The preparation method of biochar-biogas slurry-microalgae composite material based on nano-CO2 bubble regulation according to claim 3, characterized in that, The cold- and drought-resistant algae species are Chlorella or Spirulina.

5. A biochar-biogas slurry-microalgae composite material based on nano-CO2 bubble regulation, characterized in that, The biochar-biogas slurry-microalgae composite material prepared by any one of claims 1-4 based on the preparation method of nano-CO2 bubble-regulated biochar-biogas slurry-microalgae composite material is obtained.

6. The application of the biochar-biogas slurry-microalgae composite material based on nano-CO2 bubble regulation as described in claim 5 in promoting soil biocrust formation, characterized in that, Includes the following steps: Bubble CO2 bubbles into the spray solution until the pH of the spray solution drops below 7, then spray it onto the target soil surface.

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