Method for preparing slow-release gel soil conditioner by converting biogas residue and biogas slurry through hydrothermal and cross-linking reaction

Abstract

The invention discloses a method for preparing a slow-release gel soil conditioner by converting biogas residues and biogas slurry through hydrothermal and cross-linking reaction. Biogas residues and biogas slurry are subjected to hydrolysis, dehydration, decarboxylation, condensation polymerization and other reactions through a hydrothermal reaction, humic acid, fulvic acid and other humus are rapidly formed, and meanwhile nitrogen, phosphorus and other soluble nutrients are reserved. Then polyvinyl alcohol and the like are added, a coupling cross-linking reaction is carried out to rapidly convert the soil into a slow-release gel soil conditioner rich in humic acid, fulvic acid and nitrogen and phosphorus nutrient elements, the slow-release, water-retaining and nutrient transfer characteristics of the soil conditioner are fully utilized, and the humic acid-based slow-release soil conditioner is prepared by taking anaerobic fermentation biogas residues and biogas slurry as raw materials through a one-pot method. The additional value of the anaerobic fermentation biogas residue and biogas slurry is increased, the preparation time is short, and the problems of serious loss of nutrients such as nitrogen and phosphorus, easy non-point source pollution and the like caused by direct returning of the biogas residue and the biogas slurry to the field are avoided.

Description

Technical field:

[0001] The invention relates to the technical field of deep utilization of biogas residue, and in particular to a method for preparing a slow-release gel soil conditioner by converting biogas residue and liquid through hydrothermal and cross-linking reactions. Background technology:

[0002] Anaerobic fermentation is an important means of resource utilization of organic waste. With the increasing demand for green development in society, anaerobic fermentation projects are growing rapidly. Biogas residue / liquid is a by-product of anaerobic fermentation of organic solid waste, and its production is also increasing. If biogas residue and liquid are not used properly, it will also cause secondary pollution, thus affecting the operation of anaerobic fermentation projects. At the same time, biogas residue and liquid contain organic matter such as carbohydrates and proteins, as well as nutrients such as nitrogen, phosphorus, and potassium, and have a high potential for fertilizer utilization.

[0003] At present, biogas residue is mainly treated by incineration and composting, while biogas liquid is mainly returned to the field and discharged in compliance with standards. Composting can transform biogas residue into fertilizer, effectively utilize nutrients and realize the purpose of material circulation. However, traditional composting technology has problems such as long treatment cycle and unstable microbial efficiency. Hydrothermal treatment is an efficient thermochemical conversion process. Organic matter such as biogas residue undergoes hydrolysis, dehydration, decarboxylation and condensation polymerization under specific temperature and pressure, which can quickly form nutrients such as humus and release other soluble nutrients such as nitrogen and phosphorus. Although the solid part of biogas residue after hydrothermal treatment can be used directly as fertilizer, the liquid part of the hydrothermal process is usually difficult to use, which easily causes nutrient waste and secondary pollution.

[0004] Therefore, there is an urgent need for a method for efficient recovery and high-value utilization of anaerobic fermentation residues and liquids with a short treatment time. Summary of the invention:

[0005] The purpose of the present invention is to provide a method for preparing a slow-release gel soil conditioner by converting biogas residue and liquid through hydrothermal and cross-linking reactions, which solves the problems of long biogas residue utilization time and loss of nutrients in the prior art.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for preparing a slow-release gel soil conditioner by converting biogas residue and liquid through hydrothermal and cross-linking reactions, the method comprising the following steps:

[0008] (1) adding urea and / or amino acids to the biogas slurry to make the concentration of urea reach 0.5-1 mol / L or the concentration of amino acids reach 0.4-0.8 mol / L, and adjusting the pH of the biogas slurry to 10-14 with potassium hydroxide to obtain alkaline biogas slurry;

[0009] (2) adding the biogas residue to the alkaline biogas slurry obtained in step (1) at a solid-liquid ratio of 3:1-8:1, and mixing to obtain a mixed slurry;

[0010] (3) pouring the slurry obtained in step (2) into a stainless steel reactor, stirring and reacting at 30° C.-110° C., preferably 60-90° C., for 0.5-1 hour in a sealed state, adding polyvinyl alcohol (PVA), adding konjac flour and / or alkali lignin, stirring and reacting for 4-8 hours in a sealed state, then letting it stand to room temperature, and freeze-drying to obtain a gel-type soil conditioner with a sustained release function; the amount of polyvinyl alcohol added is 5%-30% of the total mass of the slurry, preferably 15%-30%, and the amounts of konjac flour and alkali lignin added are 2%-5% and 0.5%-5% of the mass of the polyvinyl alcohol, respectively.

[0011] Preferably, the amino acid in step (1) is one of glycine, alanine and serine.

[0012] Preferably, the biogas residue in step (2) is fermentation residue produced by a biogas project using livestock and poultry manure, straw, kitchen waste and other organic waste raw materials.

[0013] Preferably, the stirring speed in step (3) is 300 rpm-500 rpm.

[0014] The beneficial effects of the present invention are:

[0015] 1) The present invention utilizes hydrothermal reaction to subject biogas residue and biogas liquid to hydrolysis, dehydration, decarboxylation and condensation polymerization, so as to rapidly form humic substances such as humic acid and fulvic acid, while retaining other soluble nutrients such as nitrogen and phosphorus, and then adds polyvinyl alcohol and other coupling cross-linking reactions to rapidly convert the biogas residue and biogas liquid into a slow-release gel soil conditioner rich in humic acid, fulvic acid, and nitrogen and phosphorus nutrients, making full use of its slow-release, water-retaining and nutrient transfer characteristics, realizing a one-pot method for preparing a humic acid-based slow-release soil conditioner using anaerobic fermentation biogas residue and biogas liquid as raw materials, thereby increasing the added value of anaerobic fermentation biogas residue and biogas liquid.

[0016] 2) The preparation time of the present invention is short, and the whole process only takes 4.5-9 hours, which saves a lot of production time compared with the preparation time of more than 10 days of the traditional method (see CN116514611 B A method for the coordinated production of fulvic acid fertilizer from agricultural waste). At the same time, the slow-release gel is synthesized through cross-linking reaction, which avoids the serious loss of nutrients such as nitrogen and phosphorus caused by the direct return of biogas residues and biogas slurry to the field, and easily causes non-point source pollution. Description of the drawings:

[0017] Figure 1 It is a process flow chart of the present invention. Specific implementation method:

[0018] The following is a further description of the present invention, rather than a limitation of the present invention.

[0019] Embodiment 1:

[0020] (1) Using the biogas residue and slurry from the livestock and poultry manure biogas project of Ganzhou Ruiyuan Biotechnology Co., Ltd. as raw materials, urea was added to the slurry to make its concentration reach 0.5 mol / L, and potassium hydroxide was used to adjust the pH of the slurry to 10 to obtain alkaline slurry.

[0021] (2) The alkaline biogas slurry obtained in step (1) is mixed with biogas residue at a solid-liquid ratio of 6:1, and the mixture is added to the alkaline biogas slurry to obtain a mixed slurry.

[0022] (3) pouring the slurry obtained in step (2) into a stainless steel reactor, setting the reaction temperature to 90° C., stirring at 300 rpm, and reacting in a closed state for 1 hour; adding polyvinyl alcohol (PVA) at 15% of the mass of the slurry, and adding konjac flour (SA) and alkali lignin at 5% of the mass of the added polyvinyl alcohol, respectively, and continuing the closed reaction for 6 hours.

[0023] (4) The gel obtained after the reaction in step (3) is allowed to stand at room temperature, and then freeze-dried to obtain a gel-type soil conditioner with a sustained release function.

[0024] Through relevant tests, the humus content reached 23.42%, the nitrogen content reached 1.15%, the water absorption capacity was 38.36g / g, and the total phosphorus release rate after immersion in static water at 25°C for 7 days was <20%.

[0025] Example 2

[0026] (1) Using the biogas residue and biogas slurry from the straw biogas project of Hebei Zhuolu Dahua Zhiyuan Agricultural Development Co., Ltd. as raw materials, glycine and urea were added to the biogas slurry to make their concentrations reach 0.4 mol / L and 1 mol / L respectively, and potassium hydroxide was used to adjust the pH of the biogas slurry to 14 to obtain alkaline biogas slurry.

[0027] (2) The alkaline biogas slurry obtained in step (1) is mixed with biogas residue at a solid-liquid ratio of 8:1, and the mixture is added to the alkaline biogas slurry to obtain a mixed slurry.

[0028] (3) pouring the slurry obtained in step (2) into a stainless steel reactor, setting the reaction temperature to 80° C., stirring at 500 rpm, and reacting for 1 hour in a closed state; adding polyvinyl alcohol (PVA) at 30% of the mass of the slurry, adding konjac flour (SA) at 5% of the mass of the polyvinyl alcohol, and continuing the closed reaction for 8 hours.

[0029] (4) The gel obtained after the reaction in step (3) is allowed to stand at room temperature, and then freeze-dried to obtain a gel-type soil conditioner with a sustained release function.

[0030] Through relevant tests, the humus content reached 28.88%, the nitrogen content reached 1.49%, the water absorption capacity was 32.36g / g, and the total phosphorus release rate after immersion in static water at 25°C for 7 days was <18%.

[0031] Example 3

[0032] (1) Using the biogas residue and slurry from the food waste biogas project of Guangdong Zhaoqing Lvhong Environmental Protection Technology Co., Ltd. as raw materials, alanine and urea were added to the slurry to make their concentrations reach 0.4 mol / L and 0.5 mol / L, respectively. The pH value of the slurry was adjusted to 12 with potassium hydroxide to obtain alkaline slurry.

[0033] (2) The alkaline biogas slurry obtained in step (1) is mixed with biogas residue at a solid-liquid ratio of 4:1, and the mixture is added to the alkaline biogas slurry to obtain a mixed slurry.

[0034] (3) pouring the slurry obtained in step (2) into a stainless steel reactor, setting the reaction temperature to 60° C. and the stirring speed to 500 rpm for reaction in a closed state for 0.5 hour; adding polyvinyl alcohol (PVA) at 20% of the mass of the slurry, and adding 3% and 3% of konjac flour (SA) and alkali lignin at the mass of the polyvinyl alcohol, respectively, and continuing the closed reaction for 4 hours.

[0035] (4) The gel obtained after the reaction in step (3) is allowed to stand at room temperature, and then freeze-dried to obtain a gel-type soil conditioner with a sustained release function.

[0036] Through relevant tests, the humus content reached 24.05%, the nitrogen content reached 1.82%, the water absorption capacity was 11.10g / g, and the total phosphorus release rate after immersion in static water at 25°C for 7 days was <15%.

[0037] Example 4

[0038] Refer to Example 2, except that alanine is used instead of glycine to achieve a concentration of 0.6 mol / L.

[0039] Example 5

[0040] Refer to Example 2, except that serine is used instead of glycine to achieve a concentration of 0.8 mol / L.

[0041] Example 6

[0042] Refer to Example 3, the difference is that 5% of the mass of polyvinyl alcohol is added to alkali lignin in step (3), and no konjac flour is added.

[0043] The above-described embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or changes made by those skilled in the art based on the present invention are within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A method for preparing a slow-release gel soil conditioner by converting biogas residue and liquid through hydrothermal and cross-linking reactions, characterized in that: The method comprises the following steps: (1) adding urea and / or amino acids to the biogas slurry to make the concentration of urea reach 0.5-1 mol / L or the concentration of amino acids reach 0.4-0.8 mol / L, and adjusting the pH of the biogas slurry to 10-14 with potassium hydroxide to obtain alkaline biogas slurry; (2) adding the biogas residue to the alkaline biogas slurry obtained in step (1) at a solid-liquid ratio of 3:1-8:1, and mixing to obtain a mixed slurry; (3) pouring the slurry obtained in step (2) into a stainless steel reactor, stirring and reacting at 30° C.-110° C. in a closed state for 0.5-1 hour, adding polyvinyl alcohol, adding konjac flour and / or alkali lignin, stirring and reacting in a closed state for 4-8 hours, then letting it stand to room temperature, and freeze-drying to obtain a gel-type soil conditioner with a sustained release function; the amount of polyvinyl alcohol added is 5%-30% of the total mass of the slurry, and the amounts of konjac flour and alkali lignin added are 2%-5% and 0.5%-5% of the mass of the polyvinyl alcohol, respectively.

2. The method according to claim 1, characterized in that The added amount of polyvinyl alcohol is 15%-30% of the total mass of the slurry.

3. The method according to claim 1, characterized in that The amino acid in step (1) is one of glycine, alanine and serine.

4. The method according to claim 1, characterized in that: The biogas residue in step (2) is the fermentation residue produced by the biogas project of livestock and poultry manure, straw, and kitchen waste.

5. The method according to claim 1, characterized in that: The stirring speed in step (3) is 300 rpm-500 rpm.

6. The method according to claim 1, characterized in that The reaction temperature of step (3) is 60-90°C.

Images