Method for preparing humus by using urban solid waste

Abstract

The invention discloses a method for preparing humus by using urban solid waste. According to the method, a humus solution is obtained through separation and purification by means of citric acid solution soaking, microbial culture, chelating agent chelation and the like, then the humus solution and an amino acid solution are mixed for a hydrothermal reaction, then freeze drying is conducted, and the high-activity humus product is obtained. The humus product prepared by the method is high in purity and high in biological activity, urban solid waste is effectively utilized, an innovative solution is provided for resource utilization of dredged sediment and perishable solid waste, and the humus product has remarkable environmental benefits and economic benefits.

Description

Technical Field

[0001] The present invention relates to a method for preparing humus from municipal solid waste, belonging to the technical fields of solid waste treatment and environmental protection. Background Art

[0002] In recent years, with the acceleration of urbanization and the increasing attention to ecological environment protection, the demand for high-fertilizer green planting soil has been growing continuously. However, the limited natural soil resources and the ecological damage problems caused by over-exploitation make it an urgent problem to find sustainable green planting soil resources. At the same time, the large generation of dredged sediment and municipal perishable solid waste (such as kitchen waste, garden waste, etc.) not only occupies a large amount of land resources, but also poses a potential threat to the ecological environment.

[0003] There are many deficiencies in the existing methods for extracting and preparing humus from municipal solid waste. For example, the existing literature ("Pilot-scale aerobic composting of dredged sediment from black and odorous water bodies coupled with biomass materials", Song Chuxuan et al., Environmental Engineering, 2024, 42(3): 138-146) points out that the humus prepared by traditional composting methods has a high heavy metal content and insufficient humification degree, which limits its application scope. In addition, there is generally a lack of precise regulation of the humus structure in the existing technologies, resulting in its single function and difficulty in meeting the requirements of high-fertilizer green planting soil. Therefore, it is urgent to develop a more efficient method for preparing humus from municipal solid waste to improve the purity, stability and functionality of humus, so as to meet the needs of green agriculture and ecological environment restoration. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a method for preparing humus from municipal solid waste. The present invention greatly improves the utilization rate of municipal solid waste, and the prepared humus has high purity and activity, and can effectively promote the growth and metabolism of microorganisms.

[0005] To achieve the above technical purpose, the present invention provides a method for preparing humus from municipal solid waste. The method is as follows: Soak the soil containing organic matter with a citric acid solution and then perform solid-liquid separation to obtain a liquid phase containing humus. Then, add microbial strains to the liquid phase containing humus for microbial culture and then separate by centrifugation and membrane filtration to obtain a purified humus solution. The purified humus solution is concentrated after adding a chelating agent to obtain a humus solution; Mix the humus solution with an amino acid solution for hydrothermal reaction and then freeze-dry to obtain the product.

[0006] The present invention promotes the dissolution of humus by soaking in a citric acid solution, and then further increases the humus content through the microbial culture process by using ligninase and cellulase secreted by microorganisms. Fine impurity removal is carried out by centrifugation and membrane filtration, and then chelating agents are used to stabilize heavy metal ions therein to ensure the green safety of humus. Finally, amino acid modification is carried out to promote the reaction between amino acids and phenolic and aldehyde substances in humus to form a more stable and highly bioactive humus-amino acid complex. The introduction of amino acids can increase the content of nitrogen sources in humus and improve the activity of beneficial microorganisms during the use of humus.

[0007] As a preferred embodiment, the mass concentration of the humus solution is 10-50 g / L.

[0008] As a preferred embodiment, the molar concentration of the amino acid solution is 0.1-0.5 mol / L. The amino acids include glutamic acid, lysine, etc. Controlling the concentrations of the humus solution and the amino acid solution within a suitable range is beneficial to improving the product performance. Among them, if the concentration of the amino acid solution is too low (<0.1 mol / L), the reaction will be incomplete, reducing the stability and bioactivity of the complex, while if the concentration is too high (>0.5 mol / L), side reactions may be triggered and the purification difficulty will increase; if the concentration of the humus solution is too low (<10 g / L), the yield of the complex will be reduced, and if the concentration is too high (>50 g / L), the reaction may be uneven and subsequent treatment will be difficult. By controlling the concentration of the humus solution at 10-50 g / L and the concentration of the amino acid solution at 0.1-0.5 mol / L, the best balance of the reaction system can be achieved, ensuring the efficient formation of a high-purity and highly active humus-amino acid complex.

[0009] As a preferred embodiment, the volume ratio of the humus solution to the amino acid solution is 1:1. The influence of the amino acid addition amount on the product performance is mainly reflected in the reaction degree between it and humus, the stability and functional characteristics of the complex. When the amino acid addition amount is too small, phenolic and aldehyde substances in humus cannot react with enough amino acids, resulting in insufficient formation of the complex and reducing the stability and bioactivity of the product; while when the amino acid addition amount is too large, although the full reaction of humus can be ensured, excessive amino acids may remain in the product, increasing the subsequent purification difficulty and even triggering side reactions, affecting the purity and performance of the product. By controlling the volume ratio of the humus solution to the amino acid solution at 1:1, the best ratio of humus to amino acids in the reaction system can be achieved, ensuring the full reaction of both to form a stable humus-amino acid complex, while avoiding the negative impact caused by excessive amino acids, so as to obtain a high-purity and highly active product. This preferred embodiment not only ensures the reaction efficiency but also optimizes the functional characteristics of the product, making it show better stability and bioactivity in practical applications.

[0010] As a preferred embodiment, the conditions for the hydrothermal reaction are as follows: the temperature is 120 - 160°C, and the time is 30 - 60 min. The influence of the hydrothermal reaction conditions on the product performance is mainly reflected in the regulation of the reaction temperature and time on the structure, morphology, purity, and functional properties of the product. The change in temperature will significantly alter the reaction kinetics, product crystallinity, and chemical composition: at a lower temperature (120 - 130°C), the reaction rate is slower, which may lead to incomplete reactions, a lower degree of binding between humus and amino acids in the product, and affect the stability and activity of the complex; while at a higher temperature (140 - 160°C), the reaction rate increases, which can promote the full reaction of phenolic and aldehyde substances in humus with amino acids to form a stable humus - amino acid complex, but too high a temperature may cause partial degradation of amino acids or humus, affecting the purity and functional properties of the product. Too short a reaction time may lead to insufficient reactions, and too long a reaction time may trigger side reactions or over - polymerization of the product. Therefore, controlling the hydrothermal reaction temperature within 120 - 160°C and the time within 30 - 60 minutes can achieve the best balance between reaction efficiency and product performance, ensuring the formation of a high - purity and high - activity humus - amino acid complex.

[0011] As a preferred embodiment, the conditions for freeze - drying are as follows: the temperature is - 80 to - 50°C, and the time is 12 - 36 h.

[0012] As a preferred embodiment, the solid - liquid mass ratio of the soil containing organic matter to the citric acid solution is 1:8 - 10. Among them, the soil containing organic matter includes lake bottom mud, mature compost, humus soil, etc.

[0013] As a preferred embodiment, the mass concentration of the citric acid solution is 0.5% - 2.5%.

[0014] As a preferred embodiment, the soaking temperature is 25 - 40°C, and the soaking time is 10 - 12 h.

[0015] As a preferred embodiment, the soil containing organic matter is soaked in the citric acid solution, then subjected to ultrasonic treatment and solid - liquid separation. Ultrasonic waves can promote the dissolution of humus in the liquid.

[0016] As a preferred embodiment, the conditions for microorganism cultivation are as follows: the microorganism strain is Pseudomonas putida, the cultivation temperature is 25 - 30°C, and the time is 12 - 36 h.

[0017] As a preferred embodiment, the chelating agent is a chitosan derivative. Using green chelating agents such as chitosan derivatives can accurately chelate heavy metal ions, and the bioavailability of its residual state component (RES) is relatively low, without the need for secondary treatment.

[0018] As a preferred solution, the addition amount of the chelating agent is 0.5 - 2.0 wt% of the humus purification liquid. The dosage of the chelating agent can be adjusted according to the content of heavy metal ions in the humus purification liquid to ensure effective chelation and passivation of heavy metal impurities, while avoiding cost increase or introduction of new impurities caused by excessive addition.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] (1) Humus is purified by technologies such as ultrasonic intensification, microbial culture and green chelating agent, and at the same time, amino acids are used to further modify humus, significantly improving the functionality and biological activity of humus and enhancing its ability to promote the growth and metabolism of microorganisms;

[0021] (2) Effectively solve the problems of difficult urban solid waste treatment, environmental pollution, low utilization rate, etc., and realize the resource utilization of solid waste;

[0022] (3) The method is simple, highly operable and has good adaptability. Description of the Drawings

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0024] Figure 1 It is a process flow diagram of Embodiment 1 of the present invention. Detailed Embodiments

[0025] The following will clearly and completely describe the technical solutions of the present invention in combination with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0026] Embodiment 1

[0027] After the dredged sediment is transported to the solidification site through the sludge pipeline, it is preliminarily screened and filtered through a grille to form the initial dredged sediment. At the same time, perishable solid waste such as food waste is sorted and processed to remove impurities such as non-degradable substances such as metals, plastics, and glass. Then, the initial dredged sediment and perishable solid waste are fully mixed in equal mass and subjected to pre-anaerobic fermentation treatment for later use.

[0028] The solid after the above-mentioned fermentation treatment is crushed and screened to a particle size of less than 2 mm, and then immersed in a citric acid solution with a mass concentration of 0.5% for 12 hours to change the organic matter structure and form a liquid material. The liquid material is subjected to ultrasonic treatment (frequency of 40 kHz, 30 minutes), and the dissolution of humus is promoted at 45°C. The saprophytic Pseudomonas bacteria strain is added to the liquid material after ultrasonic treatment and cultured at 37°C for 24 hours. The liquid material after microbial culture is subjected to high-speed centrifugal separation (10,000 rpm, 10 minutes), and then finely filtered using a 0.22 μm polyethersulfone (PES) microfiltration membrane to remove impurities. A carboxymethyl chitosan chelating agent is added to the filtrate to chelate and passivate heavy metal ions (the addition amount of the chelating agent is 1 wt% of the filtrate), and then vacuum evaporation concentration is carried out (pressure: 0.05 MPa, temperature: 50°C), and finally a humus solution with a humus concentration of 20 g / L is obtained.

[0029] Glutamic acid is dissolved in deionized water to prepare a glutamic acid solution with a concentration of 0.2 mol / L. The above-mentioned purified humus solution and the glutamic acid solution are mixed at a volume ratio of 1:1 and placed in a hydrothermal reactor, heated to 130°C, and maintained for 40 minutes to promote the reaction between amino acids and phenolic and aldehyde substances in humus to form a stable humus-amino acid complex. The reaction solution after the hydrothermal reaction is freeze-dried at -50°C for 36 hours to obtain a high-purity and high-activity humus powder.

[0030] Example 2

[0031] The solid after the fermentation treatment to be carried out is crushed and screened to a particle size of less than 2 mm, and then immersed in a citric acid solution with a mass concentration of 0.5% for 12 hours to change the organic matter structure and form a liquid material. The liquid material is subjected to ultrasonic treatment (frequency of 40 kHz, 30 minutes), and the dissolution of humus is promoted at 40°C. The saprophytic Pseudomonas bacteria strain is added to the liquid material after ultrasonic treatment and cultured at 38°C for 24 hours. The liquid material after microbial culture is subjected to high-speed centrifugal separation (10,000 rpm, 10 minutes), and then finely filtered using a 0.22 μm polyethersulfone (PES) microfiltration membrane to remove impurities. The filtrate is concentrated by vacuum evaporation (pressure: 0.05 MPa, temperature: 50°C), and at the same time, a chitosan derivative (such as carboxymethyl chitosan) is added before concentration, and the addition amount is 1.0% of the mass of the humus solution, and finally a humus solution with a humus concentration of 40 g / L is obtained.

[0032] Dissolve glutamic acid in deionized water to prepare a glutamic acid solution with a concentration of 0.4 mol / L. Mix the purified humus solution and the glutamic acid solution prepared above in a volume ratio of 1:1, and place them in a hydrothermal reactor. Heat to 150 °C and maintain for 60 minutes to promote the reaction between amino acids and phenolic and aldehyde substances in humus to form a stable humus-amino acid complex. Freeze-dry the reaction solution after the hydrothermal reaction at -60 °C for 36 hours to obtain high-purity and high-activity humus powder.

[0033] Comparative Example 1

[0034] Prepare humus by the method of Example 1, except that the concentration of the amino acid solution is 0.05 mol / L.

[0035] Comparative Example 2

[0036] Prepare humus by the method of Example 1, except that the concentration of the amino acid solution is 1 mol / L.

[0037] The performance of the humus products prepared in the above examples and comparative examples is shown in Table 1.

[0038]

[0039] As can be seen from the table, the humus products prepared by the present invention have high purity, high cellulase activity, strong stability, and controlling the addition amount of amino acids within a suitable range can significantly improve the comprehensive performance of the humus products.

[0040] Various modifications to these embodiments will be apparent to those of ordinary skill in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing humus using urban solid waste, characterized in that: Soil containing organic matter is soaked in a citric acid solution and then separated into solid and liquid to obtain a liquid phase containing humus. Microbial strains are then added to the liquid phase containing humus for microbial cultivation and then separated by centrifugation and membrane filtration to obtain a humus purified liquid. A chelating agent is added to the humus purified liquid and then concentrated to obtain a humus solution. The humus solution is mixed with an amino acid solution for hydrothermal reaction and then freeze-dried to obtain the product.

2. The method for preparing humus from urban solid waste according to claim 1, characterized in that: The concentration of the humus solution is 10-50 g / L; The concentration of the amino acid solution is 0.1-0.5 mol / L.

3. The method for preparing humus from urban solid waste according to claim 2, characterized in that: The volume ratio of the humus solution to the amino acid solution is 1:

1.

4. A method for preparing humus from urban solid waste according to claim 1, 2 or 3, characterized in that: The conditions of the hydrothermal reaction are: temperature of 120-160° C. and time of 30-60 min.

5. The method for preparing humus from urban solid waste according to claim 1, characterized in that: The freeze-drying conditions are: temperature of -80 to -50°C and time of 12 to 36 hours.

6. The method for preparing humus from urban solid waste according to claim 1, characterized in that: The solid-liquid mass ratio of the organic-containing soil to the citric acid solution is 1:8-10; the soaking temperature is 25-40°C, and the soaking time is 10-12h.

7. A method for preparing humus from urban solid waste according to claim 1 or 6, characterized in that: The soil containing organic matter is soaked in a citric acid solution, then ultrasonically treated and solid-liquid separated.

8. The method for preparing humus from urban solid waste according to claim 1, characterized in that: The conditions for the microbial culture are as follows: the microbial species is saprophytic Pseudomonas, the culture temperature is 25-30° C., and the culture time is 12-36 hours.

9. The method for preparing humus from urban solid waste according to claim 1, characterized in that: The chelating agent is a chitosan derivative.

10. The method for preparing humus from urban solid waste according to claim 9, characterized in that: The addition amount of the chelating agent is 0.5-2.0wt% of the humus purification liquid.

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