Method for reducing phosphorus loss from agricultural biomass waste by hydrotalcite-assisted hydrothermal carbonization

Abstract

The present invention belongs to the field of resource and environmental technology, and discloses a method for reducing phosphorus loss from agricultural biomass waste by hydrothermal carbonization assisted by hydrotalcite. The method mainly adds hydrotalcite and improves the hydrothermal carbonization process on the basis of hydrothermal carbonization treatment of agricultural biomass waste, thereby increasing the aggregation of phosphorus elements to solid hydrothermal carbon. The present invention first utilizes thermal hydrolysis of an acidic solution to promote the release and conversion of phosphorus, and then utilizes carbonization polymerization of hydrotalcite to enhance phosphorus enrichment in hydrothermal carbon, thereby reducing the risk of phosphorus loss with hydrothermal fluid, and can provide an effective reference for improving hydrothermal carbonization treatment of agricultural biomass waste and reducing phosphorus loss.

Description

Technical Field

[0001] The invention belongs to the field of resource and environmental technology, and in particular to a method for reducing phosphorus loss in agricultural biomass waste by hydrotalcite-assisted hydrothermal carbonization. Background Art

[0002] A large amount of waste is generated during agricultural production, and agricultural biomass waste is a rich source of carbon, nitrogen and phosphorus. However, there is a lack of feasible and effective methods to recycle these waste resources, which has caused serious pollution. The second national pollution source census bulletin shows that the total phosphorus emissions from the national planting industry are 76,200 tons, and the total phosphorus emissions from the national livestock and poultry breeding industry are 119,700 tons, accounting for 37.95% of the total phosphorus emissions of national water pollutants, which is far more than the total phosphorus emissions of industrial sewage sludge. High concentrations of phosphorus emissions will lead to eutrophication of water bodies and cause environmental problems such as algal blooms. Hydrothermal carbonization has received increasing attention due to its potential in reduction, harmless treatment and nutrient recovery.

[0003] It is difficult to recover all phosphorus from agricultural biomass wastes due to the complex existence of phosphorus, mainly including phosphorus bound to extracellular polymeric substances (orthophosphate, DNA, polyphosphate) and metal phosphates as well as inorganic phosphorus. Although hydrothermal carbonization of agricultural biomass wastes has been widely adopted, a considerable proportion (about 49%) of residual phosphorus is still lost in the hydrothermal fluid. At present, most studies focus on converting organic phosphates and pyrophosphates in agricultural biomass wastes into easily recoverable orthophosphates through acid / alkali pretreatment, hydrothermal pretreatment or anaerobic digestion, but there is still a lack of methods for further recovery of phosphorus. In the treatment of agricultural biomass wastes by hydrothermal carbonization, phosphorus is usually recovered by producing hydrothermal charcoal, so it is urgent to develop methods for effectively enriching phosphorus into hydrothermal charcoal. Summary of the invention

[0004] The purpose of the present invention is to provide a method for reducing phosphorus loss from agricultural biomass waste by hydrotalcite-assisted hydrothermal carbonization.

[0005] In order to achieve the purpose of the present invention, in a first aspect, the present invention provides a method for reducing phosphorus loss from agricultural biomass waste by hydrothermal carbonization assisted by hydrotalcite, using agricultural biomass waste as raw materials, adopting hydrothermal carbonization processing technology, improving the process and adding hydrotalcite to assist in enhancing phosphorus recovery during the hydrothermal carbonization process, comprising the following steps:

[0006] S1, thermal hydrolysis stage: typical agricultural biomass waste is introduced into a hydrothermal reactor, an acidic solution is added, and the reaction temperature of the reactor is adjusted to perform a thermal hydrolysis reaction at a shorter residence time;

[0007] S2, carbonization polymerization stage: adding hydrotalcite to the reactor after the reaction in step S1, setting the reaction temperature to carry out hydrothermal carbonization polymerization at a longer residence time to generate hydrothermal char.

[0008] In the present invention, the typical agricultural biomass waste is livestock and poultry manure and crop residues. The livestock and poultry manure includes manure produced by breeding livestock and poultry such as pigs, cattle, chickens, and ducks, and the crop residues include corn stalks, wheat stalks, rice straw, rice husks, fruit peels, sawdust, etc.

[0009] The hydrotalcite is a layered metal hydroxide having acid and base sites, and specifically may be magnesium-iron hydrotalcite, copper-iron hydrotalcite or magnesium-iron-copper hydrotalcite.

[0010] The agricultural biomass waste can be directly placed in the hydrothermal reactor without pretreatment such as solid-liquid separation and drying, and the moisture content is adjusted to 70% to 95%.

[0011] In step S1, the acidic solution is the acidic hydrothermal liquid obtained after hydrothermal carbonization of crop residues in the typical agricultural biomass waste, and is used to adjust the initial pH of the raw materials in the reactor to 3-6 before the reaction.

[0012] In a specific embodiment of the present invention, the acidic solution is a hydrothermal liquid obtained by hydrothermal carbonization of crop residues sawdust and rice husks, and the preparation method is as follows: a material prepared by mixing rice husks and sawdust in a dry matter mass ratio of 2:1 is put into a hydrothermal reactor, and the solid content is adjusted to 4%, and the hydrothermal liquid is obtained by hydrothermal carbonization reaction at a temperature of 240°C for 180 minutes.

[0013] Furthermore, the agricultural biomass waste is mixed with the acidic solution at a solid-liquid ratio of 1-3 g:9 mL.

[0014] In step S1, the temperature of the reactor is adjusted to 120° C. to 260° C., and the residence time is 0.5 h to 2 h.

[0015] In step S2, the magnesium-iron hydrotalcite is prepared by a co-precipitation method, comprising:

[0016] Prepare a mixture of Fe(NO3)3 and Mg(NO3)2, which is based on the metal cation Fe 3+ Mg 2+=1:2 molar ratio to prepare a mixed solution with a concentration of 30.56 mg / mL (the Fe(NO3)3 and Mg(NO3)2 used are both analytically pure, AR>99%), and then the mixed solution is dropped into a Na2CO3 solution with a concentration of 5.3 mg / mL, the volume ratio of the mixed solution to the Na2CO3 solution is (2-3):1, the dropping rate is 1-2s / d and accompanied by stirring at a speed of 50-300r / min; then, the pH value is adjusted to 10.5±0.2 by adding NaOH solution, and the mixture is stirred for 2-3 hours and then allowed to stand for 16-18 hours, and the bottom layer of the sediment is collected and dried in an oven at 65°C-105°C for 6-12 hours to obtain magnesium-iron hydrotalcite.

[0017] The copper-iron hydrotalcite is prepared by a co-precipitation method, comprising:

[0018] Prepare a mixture of Fe(NO3)3 and Cu(NO3)2, which is based on the metal cation Fe 3+ :Cu 2+ =1:2 molar ratio to prepare a mixed solution with a concentration of 29.57 mg / mL (the Fe(NO3)3 and Cu(NO3)2 used are both analytically pure, AR>99%), and then the mixed solution is dropped into a Na2CO3 solution with a concentration of 5.3 mg / mL, the volume ratio of the mixed solution to the Na2CO3 solution is (2-3):1, the dropping rate is 1-2s / d and accompanied by stirring at a speed of 50-300r / min; then, the pH value is adjusted to 10.5±0.2 by adding NaOH solution, and the mixture is stirred for 2-3 hours and then allowed to stand for 16-18 hours, and the bottom layer of the sediment is collected and dried in an oven at 65°C-105°C for 6-12 hours to obtain iron-copper hydrotalcite.

[0019] The magnesium-iron-copper hydrotalcite is prepared by a co-precipitation method, comprising:

[0020] A mixture of Fe(NO3)3, Mg(NO3)2 and Cu(NO3)2 was prepared according to the metal cation Fe 3+ Mg 2+ :Cu 2+ =1:1:1 molar ratio to prepare a mixed solution with a concentration of 30.07 mg / mL (the Fe(NO3)3, Mg(NO3)2 and Cu(NO3)2 used are all analytically pure, AR>99%), and then the mixed solution is dropped into a Na2CO3 solution with a concentration of 5.3 mg / mL, the volume ratio of the mixed solution to the Na2CO3 solution is (2-3):1, the dropping rate is 1-2s / d and accompanied by stirring at a speed of 50-300r / min; then, the pH value is adjusted to 10.5±0.2 by adding NaOH solution, and the mixture is stirred for 2-3 hours and then allowed to stand for 16-18 hours, and the bottom layer of the sediment is collected and dried in an oven at 65°C-105°C for 6-12 hours to obtain magnesium-iron-copper hydrotalcite.

[0021] In step S2, the dry matter mass ratio of the hydrotalcite to the agricultural biomass waste is (0.5-1):10.

[0022] In step S2, the reaction temperature is set to 200°C~280°C, and the residence time is 2h~4h.

[0023] In a second aspect, the present invention provides application of the method in promoting the enrichment of phosphorus into hydrothermal carbon.

[0024] In a third aspect, the present invention provides phosphorus-rich hydrothermal charcoal prepared according to the method.

[0025] In a fourth aspect, the present invention provides the application of the phosphorus-rich hydrothermal charcoal in agricultural fertilizer and industrial fields.

[0026] By means of the above technical solution, the present invention has at least the following advantages and beneficial effects:

[0027] The present invention aims at the problem of loss of most of the phosphorus remaining in the hydrothermal liquid in the hydrothermal carbonization treatment of agricultural biomass waste. Hydrotalcite is used to improve the hydrothermal carbonization process. The agricultural biomass waste is firstly thermally hydrolyzed in an acidic solution to enhance the release and conversion of phosphorus, and then hydrotalcite is added for hydrothermal carbonization polymerization to promote phosphorus enrichment and recovery in the hydrothermal charcoal, thereby providing an effective reference for improving the hydrothermal carbonization treatment of agricultural biomass waste and reducing phosphorus loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a characterization diagram of the magnesium-iron hydrotalcite prepared for assisting hydrothermal carbonization to recover phosphorus in the present invention.

[0029] Figure 2 This is a characterization diagram of the copper-iron hydrotalcite prepared for assisting hydrothermal carbonization to recover phosphorus in the present invention.

[0030] Figure 3 This is a characterization diagram of the magnesium-iron-copper hydrotalcite prepared for assisting hydrothermal carbonization to recover phosphorus in the present invention.

[0031] Figure 4 The residual phosphorus content in the hydrothermal solution after treatment in the examples of the present invention and the comparative examples. In the figure, different lowercase letters between the treatment groups indicate significant differences ( P <0.05). DETAILED DESCRIPTION

[0032] The present invention aims to provide a method for treating agricultural biomass waste and recovering phosphorus therein for resource utilization. The method utilizes hydrothermal carbonization to improve the process, overcomes the problem of phosphorus release from refractory substances and conversion of organic phosphorus, and combines hydrotalcite catalytic adsorption technology to solve the problem of phosphorus loss in the liquid phase and low recovery efficiency.

[0033] The present invention adopts the following technical solution:

[0034] The present invention provides a method for reducing phosphorus loss from agricultural biomass waste by hydrotalcite-assisted hydrothermal carbonization, comprising the following steps:

[0035] (1) Thermal hydrolysis stage: agricultural biomass waste is introduced into a hydrothermal reactor, an acidic solution is added, and the reaction temperature of the reactor is adjusted to carry out thermal hydrolysis reaction at a short residence time;

[0036] (2) Carbonization polymerization stage: Add magnesium-iron-copper hydrotalcite to the reactor after the reaction in step (1) is completed, and the reaction temperature is set to a longer residence time to perform hydrothermal carbonization polymerization to generate hydrothermal carbon.

[0037] In the above method, in step (1), the moisture content of the agricultural biomass waste is adjusted to 70% to 95% after entering the reactor, specifically 80% to 90%, in order to ensure a certain amount of water solvent required for the hydrothermal carbonization reaction and to process as much organic matter in the agricultural biomass waste as possible.

[0038] The addition of the acidic solution is mainly used to adjust the initial pH of the solution in the reactor to 3-6. The acidic solution can be an acidic hydrothermal liquid after hydrothermal carbonization of agricultural biomass waste. During the hydrothermal carbonization process, high-concentration hydrothermal liquid wastewater rich in organic acids will be produced simultaneously as a by-product. Generally, the hydrothermal liquid prepared by hydrothermal pretreatment of manure has a higher concentration of organic acid content (4.3g / L ~15.6g / L); in particular, the hydrothermal liquid of rice husks, sawdust, straw, etc. after hydrothermal carbonization has lower acidity, and the lowest pH can reach 3.5, which can be used as a natural acidic solvent.

[0039] The agricultural biomass waste is mixed with the acidic solution at a solid-liquid ratio of 1-3 g:9 mL.

[0040] The method is to carry out a hydrothermal carbonization reaction in two steps. In step (1), the temperature of the reactor is first adjusted to 120°C to 260°C, and the residence time is 0.5h to 2h to fully hydrolyze the manure, so that phosphorus is released to achieve organic phosphorus conversion. The acid catalytic decomposition can be appropriately carried out at low energy consumption, and the reaction temperature can be specifically 150°C, 180°C, 200°C, 220°C, 240°C and 260°C, and the residence time can be specifically 0.5h, 1h and 2h.

[0041] In step (2), the magnesium-iron-copper hydrotalcite is a layered metal hydroxide having acid and base sites and is prepared by a coprecipitation method, that is, according to M 3+ :M 2+=1:2 molar ratio of metal cations, Fe(NO3)3·9H2O, Mg(NO3)2·6H2O and Cu(NO3)2·3H2O are combined in pairs or mixed into a solution, and then the mixed solution is dropped into a Na2CO3 solution with a concentration of 5.3 mg / mL, the volume ratio is (2-3):1, the dropping rate is 1-2s / d and accompanied by stirring at a speed of 300r / min; then, the pH value is stabilized at 10.5±0.2 by adding NaOH solution, stirred for 3 hours and then allowed to stand for 18 hours, and the bottom layer of the sediment is collected and dried in an oven at 65°C for 12 hours to obtain various types of hydrotalcite.

[0042] In the scanning electron microscope (SEM) images of various hydrotalcites, MgFe hydrotalcite has a flaky structure, the surface structure of CuFe hydrotalcite contains many small flocculent grains, and the surface structure of MgFeCu hydrotalcite shows both flaky and flocculent grains attached, all showing a good crystalline state. The signal intensity and mass ratio of the surface elements of each hydrotalcite are reflected by the energy dispersive spectrometer (EDS). The mass ratio of Cu element in MgFe hydrotalcite is 0wt%, and the mass of Mg element is relatively high; while the mass ratio of Mg element in CuFe hydrotalcite is 0wt%, and the mass of Cu element is relatively high, both of which are typical hydrotalcite target products.

[0043] The characterization diagrams of the three types of hydrotalcite are shown in Figure 1~Figure 3 ,in, Figure 1 The scanning electron microscope and energy spectrum characterization diagram of magnesium-iron hydrotalcite. Figure 2 The scanning electron microscope and energy spectrum characterization diagram of copper-iron hydrotalcite. Figure 3 These are the scanning electron microscope and energy spectrum characterization images of magnesium-iron-copper hydrotalcite.

[0044] The mass ratio of the added amount of the hydrotalcite to the dry matter of the agricultural biomass waste is (0.5-1):10, specifically 0.5:10 or 1:10.

[0045] In the method, the reaction temperature set in step (2) is 200°C to 280°C, and the residence time is 2h to 4h, mainly to further realize the polymerization of carbonized materials. Compared with step (1), the reaction temperature and residence time should be longer, but considering the maximization of solid phase yield, the temperature should not be too high to avoid excessive liquefaction or gasification. The specific reaction temperature can be 220°C, 240°C and 260°C, and the residence time can be 2h, 3h and 4h.

[0046] Furthermore, the hydrothermal fluid and hydrothermal charcoal are collected by vacuum filtration, the hydrotalcite can be reused through roasting and ion exchange, and the phosphorus-rich hydrothermal charcoal has great potential in agricultural and industrial applications.

[0047] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art, and the raw materials used are all commercially available products.

[0048] In the following examples and comparative examples, the raw materials used are duck manure with high phosphorus content and sawdust and rice husk with high lignocellulose content. After removing obvious impurities, they are placed in an oven and dried at 105° C. until the moisture content no longer changes. After grinding, they are passed through a 40-mesh steel sieve for later use.

[0049] Example 1 Efficient recovery of phosphorus from agricultural biomass waste

[0050] This embodiment includes the following steps:

[0051] (1) Duck manure, rice husk and sawdust were first mixed. The dry weight of the three materials was 3.2 g. They were mixed with 60 mL of acidic solution in a 150 mL reactor. The heating temperature was set to 240 °C and the residence time was 1 h for hydrothermal carbonization reaction.

[0052] The acid solution was a mixture of 1.6 g rice husk and 0.8 g sawdust, added to 60 mL water, and then hydrothermally carbonized at 240 °C for 180 min.

[0053] (2) Mix 3mmol Fe(NO3)3·9H2O and 6mmol Mg(NO3)2·6H2O in 90mL water, and drop the mixture into 40mL water containing 2mmol Na2CO3 at a dropping rate of 2s / d and a stirring rate of 300r / min. Then, add NaOH solution to stabilize the pH value at 10.5±0.2. Stir for 3 hours and let stand for 18 hours. Collect the bottom layer and dry it in an oven at 65°C for 12 hours to obtain ferromagnesian hydrotalcite.

[0054] After the reaction in step (1) is completed, the reactor is taken out and 0.9 g of magnesium iron hydrotalcite is added and mixed, and the heating temperature is continued to be 240° C. for a residence time of 2 h to carry out a hydrothermal carbonization reaction.

[0055] (3) After the reactor was cooled to room temperature, the hydrothermal liquid and hydrothermal charcoal samples of each treatment group were collected by vacuum filtration.

[0056] After the agricultural biomass waste was subjected to hydrothermal carbonization treatment in this embodiment, the residual phosphorus content in the hydrothermal liquid was detected to be 70.60±6.32 mg / L, which reduced the phosphorus loss in the hydrothermal liquid by 84.63%.

[0057] Example 2 Efficient recovery of phosphorus from agricultural biomass waste

[0058] This embodiment includes the following steps:

[0059] (1) Duck manure, rice husk and sawdust were first mixed. The dry weight of the three materials was 3.2 g. They were mixed with 60 mL of acidic solution in a 150 mL reactor. The heating temperature was set to 240 °C and the residence time was 1 h for hydrothermal carbonization reaction.

[0060] The acid solution was a mixture of 1.6 g rice husk and 0.8 g sawdust, added to 60 mL water, and then hydrothermally carbonized at 240 °C for 180 min.

[0061] (2) Mix 3mmol Fe(NO3)3·9H2O and 6mmol Cu(NO3)2·3H2O in 90mL water, and drop the mixture into 40mL water containing 2mmol Na2CO3 at a dropping rate of 2s / d and a stirring rate of 300r / min. Then, add NaOH solution to stabilize the pH value at 10.5±0.2. Stir for 3 hours and let stand for 18 hours. Collect the bottom layer and dry it in an oven at 65°C for 12 hours to obtain copper-iron hydrotalcite.

[0062] After the reaction in step (1) is completed, the reactor is taken out and 0.9 g of copper-iron hydrotalcite is added and mixed, and the heating temperature is continued to be 240° C. for a residence time of 2 h to carry out a hydrothermal carbonization reaction.

[0063] (3) After the reactor was cooled to room temperature, the hydrothermal liquid and hydrothermal charcoal samples of each treatment group were collected by vacuum filtration.

[0064] After the agricultural biomass waste was subjected to hydrothermal carbonization treatment in this embodiment, the residual phosphorus content in the hydrothermal liquid was detected to be 33.72±4.48 mg / L, reducing the phosphorus loss in the hydrothermal liquid by 92.66%.

[0065] Example 3 Efficient recovery of phosphorus from agricultural biomass waste

[0066] This embodiment includes the following steps:

[0067] (1) Duck manure, rice husk and sawdust were first mixed. The dry weight of the three materials was 3.2 g. They were mixed with 60 mL of acidic solution in a 150 mL reactor. The heating temperature was set to 240 °C and the residence time was 1 h for hydrothermal carbonization reaction.

[0068] The acid solution was a mixture of 1.6 g rice husk and 0.8 g sawdust, added to 60 mL water, and then hydrothermally carbonized at 240 °C for 180 min.

[0069] (2) Combine 3mmol Fe(NO3)3·9H2O, 3mmol Mg(NO3)2 ·6H2O and 3mmol Cu(NO3)2·3H2O were mixed in 90mL water, and the mixture was dropped into 40mL water containing 2mmol Na2CO3 at a dropping rate of 2s / d and accompanied by a stirring speed of 300r / min; then, NaOH solution was added dropwise to stabilize the pH value at 10.5±0.2, and the mixture was stirred for 3 hours and allowed to stand for 18 hours. The bottom layer was collected and dried in an oven at 65°C for 12 hours to obtain magnesium-iron-copper hydrotalcite.

[0070] After the reaction in step (1) is completed, the reactor is taken out and 0.9 g of magnesium iron copper hydrotalcite is added and mixed, and the heating temperature is continued to be 240° C. for a residence time of 2 h to carry out a hydrothermal carbonization reaction.

[0071] (3) After the reactor was cooled to room temperature, the hydrothermal liquid and hydrothermal charcoal samples of each treatment group were collected by vacuum filtration.

[0072] After the agricultural biomass waste was subjected to hydrothermal carbonization treatment in this embodiment, the residual phosphorus content in the hydrothermal liquid was detected to be 39.58±1.84 mg / L, reducing the phosphorus loss in the hydrothermal liquid by 91.39%.

[0073] Comparative Example 1

[0074] This comparative example comprises the following steps:

[0075] (1) Duck manure, rice husk and sawdust were mixed, and the dry weight of the three materials was 3.2 g. They were mixed with 60 mL of acidic solution and 0.9 g of ferromagnesium hydrotalcite, wherein the acidic solution was a hydrothermal solution of rice husk with a solid content of 4% and sawdust with a ratio of 2:1. The hydrothermal solution was carbonized at 240°C for 180 min. The preparation method of ferromagnesium hydrotalcite was the same as that in Example 1. The heating temperature was set at 240°C in a 150 mL reactor, and the residence time was 3 h for hydrothermal carbonization reaction.

[0076] (2) After the reactor is cooled to room temperature, the hydrothermal liquid and hydrothermal carbon products of each treatment group are collected by vacuum filtration.

[0077] After the agricultural biomass waste was subjected to hydrothermal carbonization treatment in this embodiment, the residual phosphorus content in the hydrothermal liquid was detected to be 193.72±16.14 mg / L, which only reduced the phosphorus loss in the hydrothermal liquid by 57.84%.

[0078] Comparative Example 2

[0079] This comparative example comprises the following steps:

[0080] (1) Duck manure, rice husk and sawdust were mixed, and the dry weight of the three materials was 3.2 g. They were mixed with 60 mL of acidic solution and 0.9 g of copper-iron hydrotalcite, wherein the acidic solution was a hydrothermal solution of rice husk with a solid content of 4% and sawdust with a ratio of 2:1. The hydrothermal solution was kept at a temperature of 240°C for 180 min after hydrothermal carbonization. The preparation method of copper-iron hydrotalcite was the same as that in Example 2. The heating temperature was set at 240°C in a 150 mL reactor, and the residence time was 3 h for hydrothermal carbonization reaction.

[0081] (2) After the reactor is cooled to room temperature, the hydrothermal liquid and hydrothermal carbon products of each treatment group are collected by vacuum filtration.

[0082] After the agricultural biomass waste was subjected to hydrothermal carbonization treatment in this embodiment, the residual phosphorus content in the hydrothermal liquid was detected to be 107.74±22.97 mg / L, which only reduced the phosphorus loss in the hydrothermal liquid by 76.55%.

[0083] Comparative Example 3

[0084] This comparative example comprises the following steps:

[0085] (1) Duck manure, rice husk and sawdust were mixed, and the dry weight of the three materials was 3.2 g. They were mixed with 60 mL of acidic solution and 0.9 g of magnesium iron copper hydrotalcite, wherein the acidic solution was a hydrothermal solution of rice husk with a solid content of 4% and sawdust with a ratio of 2:1, and the material was kept at a temperature of 240°C for 180 min for hydrothermal carbonization. The preparation method of magnesium iron copper hydrotalcite was the same as that in Example 3. The heating temperature was set at 240°C in a 150 mL reactor, and the residence time was 3 h for hydrothermal carbonization reaction.

[0086] (2) After the reactor is cooled to room temperature, the hydrothermal liquid and hydrothermal carbon products of each treatment group are collected by vacuum filtration.

[0087] After the agricultural biomass waste was subjected to hydrothermal carbonization treatment in this embodiment, the residual phosphorus content in the hydrothermal liquid was detected to be 75.73±8.43 mg / L, which only reduced the phosphorus loss in the hydrothermal liquid by 83.52%.

[0088] Comparative Example 4

[0089] This comparative example comprises the following steps:

[0090] (1) Duck manure, rice husk and sawdust were mixed. The dry weight of the three materials was 3.2 g. They were mixed with 60 mL of an acidic solution. The acidic solution was a 2:1 ratio of rice husk and sawdust with a solid content of 4%. The materials were retained at 240 °C for 180 min. The hydrothermal liquid after hydrothermal carbonization was set at 240 °C in a 150 mL reactor for 3 h for hydrothermal carbonization reaction.

[0091] (2) After the reactor was cooled to room temperature, the hydrothermal fluid and hydrothermal char samples of each treatment group were collected by vacuum filtration. The residual phosphorus content in the hydrothermal fluid was detected to be as high as 468.54±29.10 mg / L. The acidic solution environment promoted the conversion of more organic phosphorus into easily recyclable inorganic phosphorus and released into the solution.

[0092] Comparative Example 5

[0093] This comparative example comprises the following steps:

[0094] (1) Duck manure, rice husk and sawdust were mixed. The dry weight of the three materials was 3.2 g. They were mixed with 60 mL of deionized water and placed in a 150 mL reactor at a heating temperature of 240 °C for a residence time of 3 h for hydrothermal carbonization reaction.

[0095] (2) After the reactor was cooled to room temperature, the hydrothermal fluid and hydrothermal charcoal samples from each treatment group were collected by vacuum filtration. The residual phosphorus content in the hydrothermal fluid was detected to be as high as 459.50±9.28 mg / L.

[0096] The residual phosphorus content in the hydrothermal solution after treatment in each embodiment and comparative example is shown in Figure 4 .

[0097] In summary, the present invention provides a method for treating agricultural biomass waste by adding hydrotalcite to assist hydrothermal carbonization and reduce phosphorus loss. The method is mainly to solve the problem that agricultural biomass waste is difficult to treat and causes a large amount of phosphorus loss. On the basis of hydrothermal carbonization treatment of agricultural biomass waste, hydrotalcite is added and the process is improved to strengthen the aggregation of phosphorus elements to solid hydrothermal carbon. It includes the following steps: 1) Thermal hydrolysis stage: introducing agricultural biomass waste into a hydrothermal reactor, adding an acidic solution, and regulating the reaction temperature of the reactor to perform a thermal hydrolysis reaction at a shorter residence time; 2) Carbonization polymerization stage: adding magnesium-iron-copper hydrotalcite to the reactor after the reaction in step 1), setting the reaction temperature to perform a hydrothermal carbonization reaction at a longer residence time to polymerize and generate hydrothermal carbon. The present invention first uses the acidic solution thermal hydrolysis to promote the release and conversion of phosphorus, and then uses hydrotalcite to enhance phosphorus enrichment in hydrothermal carbon that can be used as a multifunctional slow-release fertilizer, thereby reducing phosphorus loss.

[0098] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A method for reducing phosphorus loss from agricultural biomass waste by hydrotalcite-assisted hydrothermal carbonization, characterized in that: Using agricultural biomass waste as raw materials, using hydrothermal carbonization processing technology, improving the process and adding hydrotalcite to assist in enhancing the recovery of phosphorus during the hydrothermal carbonization process, including the following steps: S1, thermal hydrolysis stage: typical agricultural biomass waste is introduced into a hydrothermal reactor, an acidic solution is added, and the reaction temperature of the reactor is adjusted to perform a thermal hydrolysis reaction at a shorter residence time; S2, carbonization polymerization stage: adding hydrotalcite to the reactor after the reaction in step S1, setting the reaction temperature to carry out hydrothermal carbonization polymerization at a longer residence time to generate hydrothermal charcoal; The typical agricultural biomass wastes are livestock and poultry manure and crop residues. The livestock and poultry manure includes manure from pigs, cattle, chickens and ducks, and the crop residues include corn stalks, wheat stalks, rice straw, rice husks, fruit peels and sawdust. The hydrotalcite is a layered metal hydroxide having acid and base sites, specifically magnesium-iron hydrotalcite, copper-iron hydrotalcite or magnesium-iron-copper hydrotalcite; In step S2, the dry matter mass ratio of the hydrotalcite to the agricultural biomass waste is (0.5-1):10; In step S2, the reaction temperature is set to 200°C to 280°C, and the residence time is 2 h to 4 h; In step S2, the magnesium-iron hydrotalcite is prepared by a co-precipitation method, comprising: Prepare a mixture of Fe(NO3)3 and Mg(NO3)2, which is based on the metal cation Fe 3+ Mg 2+ =1:2 in a molar ratio to prepare a mixed solution with a concentration of 30.56 mg / mL, and then dripping the mixed solution into a Na2CO3 solution with a concentration of 5.3 mg / mL, the volume ratio of the mixed solution to the Na2CO3 solution is (2-3):1, the dripping rate is 1-2 s / d and accompanied by stirring at a speed of 50-300 r / min; then, the pH value is adjusted to 10.5±0.2 by adding NaOH solution, stirring for 2-3 hours and then standing for 16-18 hours, collecting the bottom layer and drying it in an oven at 65°C-105°C for 6-12 hours to obtain magnesium-iron hydrotalcite; The copper-iron hydrotalcite is prepared by a co-precipitation method, comprising: Prepare a mixture of Fe(NO3)3 and Cu(NO3)2, which is based on the metal cation Fe 3+ :Cu 2+ =1:2 molar ratio to prepare a mixed solution with a concentration of 29.57 mg / mL, then dripping the mixed solution into a Na2CO3 solution with a concentration of 5.3 mg / mL, the volume ratio of the mixed solution to the Na2CO3 solution is (2-3):1, the dripping rate is 1-2 s / d and accompanied by stirring at a speed of 50-300 r / min; then, the pH value is adjusted to 10.5±0.2 by adding NaOH solution, stirring for 2-3 hours and then standing for 16-18 hours, collecting the bottom layer and drying it in an oven at 65°C-105°C for 6-12 hours to obtain iron-copper hydrotalcite; The magnesium-iron-copper hydrotalcite is prepared by a co-precipitation method, comprising: A mixture of Fe(NO3)3, Mg(NO3)2 and Cu(NO3)2 was prepared according to the metal cation Fe 3+ Mg 2+ :Cu 2+ =1:1:1 molar ratio to prepare a mixed solution with a concentration of 30.07 mg / mL, and then drop the mixed solution into a Na2CO3 solution with a concentration of 5.3 mg / mL, the volume ratio of the mixed solution to the Na2CO3 solution is (2-3):1, the dropping rate is 1-2 s / d and accompanied by stirring at a speed of 50-300 r / min; then, the pH value is adjusted to 10.5±0.2 by adding NaOH solution, and the mixture is stirred for 2-3 hours and then allowed to stand for 16-18 hours, and the bottom layer of the sediment is collected and dried in an oven at 65°C-105°C for 6-12 hours to obtain magnesium-iron-copper hydrotalcite.

2. The method according to claim 1, characterized in that The agricultural biomass waste is directly placed into the hydrothermal reactor without solid-liquid separation and drying pretreatment, and the moisture content is adjusted to 70% to 95%.

3. The method according to claim 1, characterized in that In step S1, the acidic solution is an acidic hydrothermal solution obtained by hydrothermal carbonization of crop residues in the typical agricultural biomass waste, and is used to adjust the initial pH of the raw materials in the reactor to 3-6 before the reaction; The agricultural biomass waste is mixed with the acidic solution at a solid-liquid ratio of 1-3 g:9 mL.

4. The method according to claim 1, characterized in that: In step S1, the temperature of the reactor is regulated to be 120° C. to 260° C., and the residence time is 0.5 h to 2 h.

5. Application of the method according to any one of claims 1 to 4 in promoting the enrichment of phosphorus into hydrothermal charcoal.

Images