Hydroxyl-phosphorus-rich cyanobacteria biochar as well as preparation method and application thereof

Abstract

The invention relates to hydroxyl-phosphorus-rich cyanobacteria biochar as well as a preparation method and application thereof. The preparation method comprises the following steps: dehydrating and drying obtained cyanobacteria, grinding and crushing, and screening to obtain cyanobacteria powder; the method comprises the following steps: uniformly mixing blue-green algae powder and a magnesium-based additive to obtain a mixed sample, putting the mixed sample into a pyrolytic reaction system, and setting a pyrolytic target temperature to be 400-800 DEG C; when the pyrolysis temperature reaches a pyrolysis target temperature, immediately adding the mixed sample, carrying out rapid pyrolysis, and collecting pyrolysis gas generated by a pyrolysis reaction system; and circulating and pumping pyrolysis gas collected in the pyrolysis process back to the pyrolysis reaction system for continuous calcination, and cooling to obtain the hydroxyl-phosphorus-rich cyanobacteria charcoal. The magnesium-based additive is used as a phosphorus fixing agent, and generation of hydroxyl phosphorus in the pyrolysis process is effectively promoted; and the volatile phosphorus-containing component is re-deposited in a reaction system through gas-phase circulation operation and is returned to a solid product, so that the total phosphorus retention rate in the final product biochar is remarkably improved through cooperation.

Description

Technical Field

[0001] This invention belongs to the field of organic waste treatment and bioenergy technology, specifically relating to a hydroxyl phosphorus-rich cyanobacterial biochar, its preparation method, and its application. Background Technology

[0002] With the acceleration of global industrialization and urbanization, large amounts of nitrogen- and phosphorus-rich nutrients are discharged into rivers, lakes, and seas through agricultural runoff, domestic sewage, and industrial wastewater, leading to increasingly severe eutrophication problems. Against this backdrop, cyanobacteria and other algae proliferate wildly in water bodies, forming large-scale algal blooms. Cyanobacterial blooms not only disrupt the balance of aquatic ecosystems, causing water hypoxia and a decline in biodiversity, but some of the toxins they produce also directly threaten drinking water safety and public health. How to effectively control cyanobacterial blooms has become an urgent environmental problem to be solved globally. Traditionally, common methods for treating cyanobacteria harvested from land, such as landfilling, composting, or simple incineration, not only occupy a large amount of land resources but may also cause secondary pollution, failing to achieve the effective utilization of phosphorus resources in cyanobacteria. Therefore, treating cyanobacteria, a typical "waste biomass," as a potential resource and carrying out efficient recycling and utilization to turn waste into treasure is an important research direction in the field of environmental engineering and resource recycling.

[0003] Thermochemical conversion technology, especially pyrolysis (heating under anaerobic conditions), is an effective means of converting biomass into high-value-added products (such as bio-oil, pyrolysis gas, and biochar). For cyanobacteria treatment, pyrolysis technology has advantages such as thorough volume reduction, fast processing speed, and degradation of algal toxins. Converting cyanobacteria into biochar through pyrolysis is considered a promising disposal route. However, the core challenge in the pyrolysis conversion process of cyanobacteria lies in how to effectively prevent the volatilization and loss of phosphorus, thereby achieving its efficient enrichment in the solid product (biochar), i.e., obtaining a high phosphorus retention rate. Conventional pyrolysis technology generally results in low phosphorus retention rates because phosphorus is easily converted into gaseous products and lost at high temperatures. Hydroxyphosphorus, as an extremely stable phosphorus mineral, has a crystal structure that is a major component of natural phosphate rock, providing an ideal form for long-term phosphorus fixation. This phosphorus-rich cyanobacteria biochar can be directly returned to the field as a slow-release phosphate fertilizer, improving soil fertility, promoting plant growth, and thus safely reintroducing phosphorus from the water into the agricultural ecological cycle. However, there is currently limited research on the preparation of hydroxyl-enriched cyanobacterial biochar. Therefore, this invention provides a method for preparing hydroxyl-enriched cyanobacterial biochar and its applications. Summary of the Invention

[0004] The purpose of this invention is to provide a hydroxyl-rich cyanobacterial biochar, its preparation method, and its application in order to solve the above-mentioned problems.

[0005] The present invention achieves the above objectives through the following technical solutions: This invention provides a method for preparing hydroxyphosphorus-rich cyanobacterial biochar, comprising the following steps: (1) The obtained cyanobacteria are dehydrated, dried, ground, pulverized, and sieved to obtain cyanobacteria powder; (2) Place the mixed sample obtained by uniformly mixing cyanobacteria powder and magnesium-based additives into a pyrolysis reaction system and set the target pyrolysis temperature; (3) When the pyrolysis temperature reaches the target pyrolysis temperature, immediately add the mixed sample, pyrolyze rapidly, and collect the pyrolysis gas generated by the pyrolysis reaction system; (4) The pyrolysis gas collected during the pyrolysis process is pumped back to the pyrolysis reaction system for further calcination. After cooling, hydroxyl-rich phosphorus blue algae biochar is obtained.

[0006] This invention introduces magnesium-based additives (such as magnesium oxide) to guide the conversion of organic phosphorus released by cyanobacteria into hydroxyl phosphorus during pyrolysis, and fixes the phosphorus firmly through chemical bonding. This is the key chemical basis for achieving high phosphorus retention.

[0007] However, when dealing with high-temperature pyrolysis environments, a single magnesium-based additive strategy may still result in some phosphorus escaping in gaseous form during the initial stage of pyrolysis. To overcome this limitation, a novel gas-phase circulating deposition technology was introduced. This technology reintroduces the volatile phosphorus-containing gas generated during the initial stage of pyrolysis into the reaction system, allowing it to re-contact and react with the metal additives in the solid residue. This process recaptures and fixes the phosphorus that is about to be lost. The resulting hydroxyl phosphorus not only achieves stable phosphorus fixation but also has high resource value.

[0008] As a further optimization of the present invention, in step (1), the sieving is performed using a 100-mesh standard sieve.

[0009] As a further optimization of the present invention, in step (2), the magnesium-based additive is MgO, and the number of moles of magnesium in MgO is 10%-20% of the number of moles of phosphorus in the cyanobacteria powder.

[0010] As a further optimization of the present invention, in step (2), the target pyrolysis temperature is 400-800℃.

[0011] As a further optimization of the present invention, in step (2), the pyrolysis reaction system includes a sample injection basket, a pyrolysis zone, and a condensation zone connected in sequence. The condensation zone is connected to a pyrolysis gas collection bag and a gas circulation pump. The output end of the gas circulation pump is connected to the sample injection basket. The mixed sample is placed in the sample injection basket.

[0012] As a further optimization of the present invention, in step (3), the rapid pyrolysis time is 2-10 min.

[0013] As a further optimization of the present invention, in step (4), the calcination time is 50-75 min.

[0014] The present invention also provides a hydroxyl-rich phosphorus cyanobacterial biochar, which is prepared by the preparation method described above.

[0015] The present invention also provides an application of hydroxyl-enriched cyanobacterial biochar in the preparation of slow-release phosphate fertilizer, wherein the hydroxyl-enriched cyanobacterial biochar is used directly as slow-release phosphate fertilizer.

[0016] The beneficial effects of this invention are as follows: 1) This invention uses magnesium-based additive (MgO) as a phosphorus fixative, which effectively promotes the formation of stable phosphorus compounds (such as hydroxyl phosphorus) during pyrolysis. At the same time, the gas-phase circulation operation allows volatile phosphorus-containing components to redeposit in the reaction system and return to the solid product. The two work synergistically to significantly improve the phosphorus retention rate in the final product biochar. Experiments have shown that this method achieves a total phosphorus retention rate of 93.05%, and the proportion of hydroxyl phosphorus in biochar reaches 42.09%. This realizes the transformation from algal biomass to high value-added products. Moreover, the process is simple and provides an efficient and reliable technical path for algal bloom control and phosphorus resource recycling. 2) This invention achieves efficient recovery and fixation of phosphorus in waste cyanobacterial biomass during pyrolysis through the synergistic effect of magnesium-based additives and gas-phase circulating deposition technology. This strategy not only provides an innovative solution for the control and resource-based disposal of cyanobacterial blooms, but also contributes a promising technical approach to addressing the global phosphorus resource shortage challenge. It fully embodies the concept of circular economy and has significant environmental and potential economic benefits. 3) This invention completes phosphorus fixation and biochar preparation in a single pyrolysis process, which simplifies the traditional multi-step phosphorus recovery process and makes the operation more convenient. Moreover, the hydroxyl phosphorus in the prepared hydroxyl phosphorus-rich cyanobacterial biochar is highly stable, which allows the hydroxyl phosphorus-rich cyanobacterial biochar to be used directly as a slow-release fertilizer, making the resource utilization path more direct. 4) This invention opens up a new way for the treatment of lake cyanobacteria, shifting from simple consumption-based treatment to resource utilization. It organically combines the treatment of algal blooms with the recovery of phosphorus resources, forming a closed-loop model of "treating waste with waste and turning waste into treasure". Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the pyrolysis apparatus of the present invention.

[0018] Figure 2 This is a comparison chart showing the total phosphorus retention rate of the hydroxylphosphocyanin biochar from Examples 1-3 of the present invention.

[0019] Figure 3This is an XRD analysis result diagram of the hydroxyl-enriched phosphorus cyanobacterial biochar of Example 3 of the present invention.

[0020] Figure 4 This is a comparison chart showing the total phosphorus retention rate of the phosphorus-blue algae biochar of Comparative Examples 1-3 of the present invention.

[0021] Figure 5 This is a comparison chart showing the proportion of hydroxyl phosphorus in the phosphorus cyanobacteria biochar of Example 3 and Comparative Examples 1-2 of the present invention. Detailed Implementation

[0022] The present application will now be described in further detail with reference to the accompanying drawings. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0023] I. Materials 1. Cyanobacteria: Cyanobacteria samples with a water content of 80-85% were collected from Chaohu Lake in Hefei, Anhui, China. After filtration and dehydration, the cyanobacteria samples were dried in an oven at 105℃ for 24 hours. Then, the dried cyanobacteria samples were crushed with a pulverizer and sieved through a 100-mesh sieve to collect cyanobacteria samples for the experiment. The total phosphorus (TP) content in the cyanobacteria powder used in the experiment was 690.88 mg / kg.

[0024] Unless otherwise specified, all methods used in this application are conventional methods known to those skilled in the art, and all reagents and materials used are commercially available products unless otherwise specified.

[0025] II. Methods 2.1 Preparation of hydroxyl-enriched cyanobacterial biochar This invention provides a method for preparing hydroxyphosphorus-rich cyanobacterial biochar, comprising the following steps: (1) The obtained cyanobacteria were dehydrated, dried, ground and pulverized, and then sieved using a 100-mesh standard sieve to obtain cyanobacteria powder; (2) The mixed sample obtained by uniformly mixing cyanobacterial powder with magnesium oxide (MgO, based on the molar number of phosphorus in cyanobacterial powder, the molar number of magnesium in MgO is 15% of the phosphorus) is placed in the reaction basket of the pyrolysis reaction system (pyrolysis device), and the target pyrolysis temperature is 400-800℃. Pyrolysis apparatus such as Figure 1 As shown, it includes a sample inlet basket, a pyrolysis zone, and a condensation zone connected in sequence. The condensation zone is connected to a pyrolysis gas collection bag and a gas circulation pump. The output end of the gas circulation pump is connected to the sample inlet basket.

[0026] (3) When the pyrolysis temperature reaches the target pyrolysis temperature, immediately and quickly add the mixed sample, pyrolyze rapidly for 5 minutes, and collect the pyrolysis gas generated by the pyrolysis reaction system with a gas bag; (4) The pyrolysis gas collected during the pyrolysis process is pumped back to the pyrolysis reaction system for calcination for 1 hour. After cooling, hydroxyl-rich phosphorus blue algae biochar is obtained.

[0027] To investigate the effects of different pyrolysis target temperatures on the total phosphorus retention rate and hydroxyl phosphorus ratio of hydroxyl phosphorus-rich cyanobacterial biochar, this application, based on the above preparation method, designed and obtained the experimental schemes shown in Examples 1-3 below by only changing the pyrolysis target temperature (Example 1: pyrolysis target temperature 400℃; Example 2: pyrolysis target temperature 600℃; Example 3: pyrolysis target temperature 800℃). The methods for detecting total phosphorus and hydroxyl phosphorus in the cyanobacterial biochar are as follows: Retention rate of total phosphorus: The method for determining total phosphorus is ultraviolet-visible spectrophotometry, specifically according to the national standard HJ631-2011 "Determination of total phosphorus in soil by alkaline fusion-molybdenum antimony spectrophotometric method". Potassium dihydrogen phosphate (KH2PO4) is used as the standard substance to plot the standard curve, and the total phosphorus content of each sample is calculated accordingly. Hydroxyphosphorus content: Utilization 31 Quantitative determination was performed using nuclear magnetic resonance (NMR) technology to qualitatively and quantitatively analyze the phosphorus speciation and content of phosphorus-containing compounds such as hydroxyphosphorus in the hydroxyphosphorus-rich cyanobacterial biochar of Examples 1-3 below. Specific test data are as follows: Figure 2 , 3 As shown in 5 and Table 1: Table 1. Experimental data recording table of hydroxylphosphocyanin biochar at different pyrolysis target temperatures. project Target pyrolysis temperature (°C) Total phosphorus retention rate (%) Percentage of hydroxyphosphorus compounds (%) Example 1 400 86.01% 6.15% Example 2 600 82.08% 27.36% Example 3 800 93.05% 42.09% Experimental conclusion: Figure 3 The image shows the XRD analysis results of the hydroxyphosphorus-enriched cyanobacterial biochar prepared in Example 3. The analysis revealed typical Mg2PO4(OH) diffraction peaks, thus proving that the hydroxyphosphorus-enriched cyanobacterial biochar prepared by the present invention was successfully prepared. The total phosphorus retention rate of the hydroxyphosphorus-enriched cyanobacterial biochar prepared by the method in Example 3 of the present invention is 93.05%, and the proportion of hydroxyphosphorus forms reaches 42.09%. The process of the present invention is highly efficient and provides an innovative approach for the resource utilization of cyanobacteria and phosphorus recovery.

[0028] To investigate the effects of gas circulation process and the addition of magnesium-based additives (MgO) on the total phosphorus retention rate and hydroxyl phosphorus ratio of cyanobacterial biochar enriched with hydroxyl phosphorus, based on Example 3 above, the present invention designed the experimental schemes of Comparative Examples 1-3 as shown below, specifically as follows: Comparative Example 1 This comparative example provides a method for preparing cyanobacterial biochar, comprising the following steps: (1) The obtained cyanobacteria were dehydrated, dried, ground and pulverized, and then sieved using a 100-mesh standard sieve to obtain cyanobacteria powder; (2) Place the cyanobacteria powder directly into the reaction basket of the pyrolysis reaction system (pyrolysis device), with a target pyrolysis temperature of 800℃; (3) When the pyrolysis temperature reaches 800℃, pure cyanobacteria powder is immediately added for pyrolysis. The pyrolysis time is 65 min. After cooling, cyanobacteria biochar without magnesium-based additives and without gas circulation is obtained.

[0029] Comparative Example 2 This comparative example provides a method for preparing cyanobacterial biochar, comprising the following steps: (1) The obtained cyanobacteria were dehydrated, dried, ground and pulverized, and then sieved using a 100-mesh standard sieve to obtain cyanobacteria powder; (2) The mixed sample obtained by uniformly mixing cyanobacterial powder and magnesium oxide (MgO, based on the molar number of phosphorus in cyanobacterial powder, the molar number of magnesium in MgO is 15% of the phosphorus) is placed in the reaction basket of the pyrolysis reaction system (pyrolysis device), and the target pyrolysis temperature is 800℃. (3) When the pyrolysis temperature reaches 800℃, the mixed sample is immediately and quickly added for pyrolysis. The pyrolysis time is 65 min. After cooling, cyanobacterial biochar without gas circulation is obtained.

[0030] Comparative Example 3 This comparative example provides a method for preparing cyanobacterial biochar, comprising the following steps: (1) The obtained cyanobacteria were dehydrated, dried, ground and pulverized, and then sieved using a 100-mesh standard sieve to obtain cyanobacteria powder; (2) Place the cyanobacteria powder directly into the reaction basket of the pyrolysis reaction system (pyrolysis device), with a target pyrolysis temperature of 800℃; (3) When the pyrolysis temperature reaches 800℃, immediately add pure blue algae powder, pyrolyze rapidly for 5 minutes, and collect the pyrolysis gas generated by the system using a gas bag; (4) The pyrolysis gas collected during the pyrolysis process is pumped back to the pyrolysis reaction system for calcination for 1 hour. After cooling, cyanobacterial biochar without magnesium-based additive phosphorus is obtained.

[0031] The test data is as follows: Figure 3 , 5 As shown in Table 2: Table 2. Experimental data record of phosphorus cyanobacteria biochar prepared in Example 3 and Comparative Examples 1-3 project Total phosphorus retention rate (%) Percentage of hydroxyphosphorus compounds (%) Example 3 93.05% 42.09% Comparative Example 1 65.04% 16.95% Comparative Example 2 70.30% 21.74% Comparative Example 3 66.87% 20.16% Experimental conclusions: Experimental verification shows that the magnesium-based additive used in this invention as a phosphorus fixative effectively promotes the generation of hydroxyl phosphorus during pyrolysis; and the gas-phase circulation operation allows volatile phosphorus-containing components to redeposit within the reaction system (gas-phase circulation deposition technology), returning them to the solid product, which synergistically and significantly improves the total phosphorus retention rate and the proportion of hydroxyl phosphorus in the final product biochar, providing an efficient and reliable technical path for algal bloom control and phosphorus resource recycling.

[0032] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for the preparation of a hydroxyl group rich blue-green algae biochar, characterized by: The method comprises the following steps: (1) drying, grinding and screening the obtained blue-green algae to obtain blue-green algae powder; (2) uniformly mixing the blue-green algae powder with a magnesium-based additive to obtain a mixed sample, and placing the mixed sample in a pyrolysis reaction system and setting a pyrolysis target temperature; (3) when the pyrolysis temperature reaches the pyrolysis target temperature, immediately adding the mixed sample, rapidly pyrolyzing, and collecting pyrolysis gas generated by the pyrolysis reaction system; (4) circulating the collected pyrolysis gas back to the pyrolysis reaction system for calcination, and obtaining a hydroxyl-rich phosphorus blue-green algae biochar after cooling.

2. The method of claim 1, wherein the method is characterized by: In step (1), the screening is performed using a 100-mesh standard sieve.

3. The method of claim 1, wherein the method is characterized by: In step (2), the magnesium-based additive is MgO, and the number of moles of magnesium in the MgO is 10%-20% of the number of moles of phosphorus in the blue-green algae powder.

4. The method of claim 1, wherein the method is characterized by: In step (2), the pyrolysis target temperature is 400-800℃.

5. The method of claim 1, wherein the method is characterized by: In step (2), the pyrolysis reaction system comprises a sample basket, a pyrolysis zone and a condensation zone connected in sequence, the condensation zone is connected with a pyrolysis gas collection bag and a gas circulation pump, the output end of the gas circulation pump is connected with the sample basket, and the mixed sample is placed in the sample basket.

6. The method of claim 1, wherein the method is characterized by: In step (3), the rapid pyrolysis time is 2-10 min.

7. The method of claim 1, wherein the method is characterized by: In step (4), the calcination time is 50-75 min.

8. A hydroxyl group-rich blue-green algae biochar, characterized by: The method is prepared by any one of claims 1-7.

9. Use of the hydroxyl group-rich blue-green algae biochar as claimed in claim 8 for the preparation of slow-release phosphorus fertilizer, characterized by, The hydroxyl-rich phosphorus blue-green algae biochar is directly used as a slow-release phosphorus fertilizer.

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