Method and system for preparing liquid slow-release organic fertilizer from kitchen waste

Abstract

The invention belongs to the technical field of kitchen waste recycling and liquid organic fertilizer preparation, and particularly relates to a method and system for preparing a liquid slow-release organic fertilizer from kitchen waste. The Maillard reaction is controlled and inhibited through the two-stage alkaline hydrolysis reaction, acid and alkali are produced on line through electrodialysis acid-alkali extraction, internal supply of the acid and the alkali is achieved, the slow release function is achieved by combining nanofiltration grading and the in-situ generated nano magnesium phosphate ammonium functional slow release suspension, and the method is suitable for large-scale industrial production. And a low-bacterium and low-odor liquid organic fertilizer finished product is obtained through pH value buffering and amino acid chelated trace element stabilization. According to the method, the additional agent is reduced by more than or equal to 30%, and the method has remarkable economical efficiency and engineering replicability.

Description

Technical Field

[0001] This invention belongs to the field of food waste resource utilization and liquid organic fertilizer preparation technology, specifically relating to a method and system for preparing liquid slow-release organic fertilizer from food waste. Background Technology

[0002] With the rapid development of urbanization and the catering industry, the amount of food waste generated continues to rise, and its efficient treatment and resource utilization have become a major challenge for urban environmental governance. Currently, the solid residue after oil extraction from food waste has a complex composition, characterized by high water content and rich organic matter, nitrogen, phosphorus, and potassium content. Improper treatment can easily lead to foul odors, leachate, and greenhouse gas emissions, becoming a prominent challenge in further reducing, recycling, and harmlessly managing food waste. Existing engineering projects mostly adopt treatment pathways such as feed production, anaerobic digestion, or conventional composting, but these have limitations in applicability, low product added value, and significant susceptibility to seasonal and raw material fluctuations.

[0003] In recent years, the process of producing liquid organic fertilizer from kitchen waste based on alkaline hydrolysis and neutralization has been gradually developed, proving that chemical alkaline hydrolysis can efficiently dissolve organic matter and nutrients, providing a new approach for integrated water and fertilizer utilization. However, it still faces bottlenecks such as high alkali and acid consumption, high system salinity, high color and viscosity, insufficient odor control, limited product stability, and difficulty in directly adapting to drip irrigation systems, which can easily cause equipment corrosion and pipeline blockage, thus restricting its large-scale promotion and application in facility agriculture. On the other hand, the reduction of chemical fertilizers and the control of agricultural non-point source pollution have placed comprehensive demands on new liquid organic fertilizers, requiring low salinity, low chlorine, adjustable nutrient ratios, and stable microbial communities. However, current liquid organic fertilizer processes from kitchen waste suffer from high alkali and acid consumption, high salinity, color, and viscosity, and poor odor and microbial stability. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a method and system for preparing liquid slow-release organic fertilizer from kitchen waste. This invention achieves efficient leaching and high-value utilization of kitchen waste through a two-stage alkaline hydrolysis reaction, electrodialysis acid-base closed loop, nanofiltration fractional enrichment, and in-situ generation of nano-magnesium ammonium phosphate slow-release suspension, thereby reducing the amount of acid and alkali used and obtaining a liquid organic fertilizer product with controllable salt content, adjustable formula, and stable odor and microbial community.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing liquid slow-release organic fertilizer from kitchen waste, comprising the following steps: The pretreated kitchen waste residue is mixed with alkaline solution and subjected to a two-stage alkaline hydrolysis reaction, followed by solid-liquid separation to obtain alkaline hydrolysis solution and alkaline hydrolysis residue, respectively. After adjusting the pH value to 5.5-8.5 by adding acid to the alkaline hydrolysate, electrodialysis acid-base extraction is performed. The resulting acid-base extraction mother liquor is then fractionated and enriched by nanofiltration to obtain permeate and concentrate, respectively. The concentrated solution and soluble magnesium salt are mixed, and the resulting mixture is neutralized. The pH value of the resulting neutralization reaction system is increased to carry out a precipitation reaction, thereby obtaining a nano-magnesium phosphate functional slow-release suspension. The mixture of the nano-magnesium ammonium phosphate functional slow-release suspension and the permeate was sequentially subjected to pH buffering and amino acid chelation trace element stabilization to obtain liquid slow-release organic fertilizer.

[0006] Preferably, the pretreated kitchen waste residue has a moisture content of ≤30wt% and an oil content of ≤30wt%.

[0007] Preferably, the alkaline solution includes one or more of potassium hydroxide solution, sodium hydroxide solution, calcium hydroxide solution, and ammonium hydroxide solution.

[0008] Preferably, the two-stage alkaline hydrolysis reaction includes sequentially performing a first-stage alkaline hydrolysis and a second-stage alkaline hydrolysis; The first stage of alkaline hydrolysis is carried out under moderate alkalinity and moderate temperature conditions; the moderate alkalinity is defined as a pH value of 9 to 10.5; and the hydrolysis temperature is defined as 50 to 80°C. The second stage of alkaline hydrolysis involves rapidly increasing the pH value and then performing high-temperature hydrolysis; the rapid pH increase means raising the pH value to 11.5-12.2 within 5-15 minutes; the high-temperature hydrolysis temperature is 80-95℃.

[0009] Preferably, the current density of the electrodialysis acid-base extraction is 100~200 A / m. 2 The method used for electrodialysis acid-base extraction is bipolar membrane electrodialysis; the two stages of the bipolar membrane electrodialysis produce alkaline solution and acid solution respectively, and the concentration of the alkaline solution produced by the bipolar membrane electrodialysis is 3~20wt%; the concentration of the acid solution produced by the bipolar membrane electrodialysis is 3~20wt%.

[0010] Preferably, the nanofiltration membrane used for nanofiltration fractionation and enrichment has a molecular weight cutoff of 300~800 Da.

[0011] Preferably, the molar ratio of Mg, N and P in the mixture is 1.05~1.25:1.0:1.0.

[0012] Preferably, the buffer used for the pH buffer is an organic acid and / or an organic acid salt; the organic acid includes one or more of citric acid, malic acid and acetic acid; the organic acid salt is potassium citrate and / or an amino acid salt.

[0013] Preferably, the liquid slow-release organic fertilizer meets the following requirements: total organic matter content ≥ 80 g / L, N content 1.5~5.0 g / L, P2O5 content 2.0~8.0 g / L, K2O content 8.0~25 g / L, and Cl content ≥ 80 g / L. - Content ≤2.0g / L, viscosity at 20℃ ≤50mPa·s, sediment volume fraction <0.2%.

[0014] The present invention also provides a system for implementing the method described in the above technical solution, comprising a two-stage alkaline hydrolysis reactor, a bipolar electrodialysis acid-base recovery device, a nanofiltration fractionation device, an in-situ magnesium ammonium phosphate functional slow-release suspension generation device, a formulation compounding device, and a buffer stabilization unit connected in sequence.

[0015] This invention provides a method for preparing liquid slow-release organic fertilizer from kitchen waste, comprising the following steps: Pretreated kitchen waste residue is mixed with alkaline solution and subjected to a two-stage alkaline hydrolysis reaction, followed by solid-liquid separation to obtain alkaline hydrolysis solution and alkaline hydrolysis residue. Acid is added to the alkaline hydrolysis solution to adjust the pH to 5.5-8.5, and then electrodialysis acid-base extraction is performed. The resulting acid-base extraction mother liquor is then subjected to nanofiltration fractionation and enrichment to obtain permeate and concentrate. The concentrate is mixed with soluble magnesium salt, and the resulting mixture is neutralized. The pH of the neutralization reaction system is then increased to induce precipitation, yielding a nano-magnesium phosphate functional slow-release suspension. The mixture of the nano-magnesium phosphate functional slow-release suspension and the permeate is sequentially subjected to pH buffering and amino acid chelation trace element stabilization to obtain a liquid slow-release organic fertilizer.

[0016] Compared with existing processes for producing liquid organic fertilizer from kitchen waste through alkaline hydrolysis and neutralization, this invention has the following advantages: (1) Through a two-stage alkaline hydrolysis reaction, the Maillard reaction and unnecessary condensation reaction are effectively suppressed while ensuring a high dissolution rate of organic matter, significantly reducing liquid color and viscosity and reducing amino nitrogen loss; (2) By using electrodialysis to extract acid and alkali, the electrochemical closed-loop supply of acid and alkali within the process is realized, which greatly reduces the amount of externally sourced acid and alkali solutions, reduces operating costs and reduces the amount of saline wastewater discharged. (3) By nanofiltration fractionation enrichment, the alkaline hydrolysate is separated into permeate rich in amino acids and oligopeptides and concentrate rich in oligosaccharides and humified organic matter. On the one hand, it realizes the directional distribution of organic components and inorganic salts, reduces total salinity and chloride ion content, and on the other hand, it provides a more flexible formula base liquid for different crops and different fertilization methods. (4) A nano-sized magnesium ammonium phosphate functional crystal suspension is generated in situ in the concentrate, and some phosphorus and ammonium nitrogen are solidified into struvite (calcium phosphate crystals) and magnesium ammonium phosphate crystals, so as to achieve slow-release supply of phosphorus and structural retention of nitrogen, and significantly reduce free NH4. +The conversion and volatilization loss between the nanocrystals and NH3 reduces the ammonia and amine odors of kitchen liquid fertilizer from the source. At the same time, the nanocrystals form a stable colloidal dispersion system under the coating of organic colloids, which is not easy to settle and clog the dripper. (5) Based on the existing alkaline hydrolysis-neutralization route, this invention further introduces units such as acid-base closed-loop, graded enrichment, and enhanced deodorization and sterilization to construct a new process for liquid organic fertilizer from kitchen waste with low reagent consumption, controllable salt content, and strong formula plasticity, so as to realize the high-value resource utilization of kitchen waste and green agricultural development. The method has a high degree of integration of the overall process flow, low reagent consumption (reduction of external reagents by ≥30%), and stable product quality, and has good engineering application prospects and promotion value. Detailed Implementation

[0017] This invention provides a method for preparing liquid slow-release organic fertilizer from kitchen waste, comprising the following steps: The pretreated kitchen waste residue is mixed with alkaline solution and subjected to a two-stage alkaline hydrolysis reaction, followed by solid-liquid separation to obtain alkaline hydrolysis solution and alkaline hydrolysis residue, respectively. After adjusting the pH value to 5.5-8.5 by adding acid to the alkaline hydrolysate, electrodialysis acid-base extraction is performed. The resulting acid-base extraction mother liquor is then fractionated and enriched by nanofiltration to obtain permeate and concentrate, respectively. The concentrated solution and soluble magnesium salt are mixed, and the resulting mixture is neutralized. The pH value of the resulting neutralization reaction system is increased to carry out a precipitation reaction, thereby obtaining a nano-magnesium phosphate functional slow-release suspension. The mixture of the nano-magnesium ammonium phosphate functional slow-release suspension and the permeate was sequentially subjected to pH buffering and amino acid chelation trace element stabilization to obtain liquid slow-release organic fertilizer.

[0018] Unless otherwise specified, the present invention does not have special requirements on the source of raw materials used, and commercially available products well known to those skilled in the art can be used.

[0019] This invention mixes pretreated kitchen waste residue with alkaline solution and performs a two-stage alkaline hydrolysis reaction, followed by solid-liquid separation to obtain alkaline hydrolysis solution and alkaline hydrolysis residue, respectively.

[0020] In one implementation, the pretreatment includes sequential sorting, crushing, and multi-stage centrifugal oil extraction; the moisture content of the kitchen waste residue is 60-85 wt%, specifically 65-71 wt% in this embodiment; the particle size after crushing is 2-20 mm, specifically 6-15 mm in this embodiment; the multi-stage centrifugal oil extraction involves 2-3 centrifugations, specifically 2 centrifugations, at a temperature of 50-80℃, specifically 60-80℃ in this embodiment, for each centrifugation session lasting 5-15 min, specifically 10 min in this embodiment, and at a speed of 3000-6000 rpm, specifically 4000-5000 rpm in this embodiment; the moisture content of the pretreated kitchen waste residue is ≤30 wt%, specifically 21 wt%, and the oil content is ≤30 wt%, specifically 17 wt% or 21 wt% in this embodiment.

[0021] In actual production, the kitchen waste collected contains many impurities such as plastic products (packaging bags, plastic bottles, tableware), metal items (metal cans, iron tableware), glass (glass bottles), large hard objects (bones, hard food residues), and other non-degradable or unprocessable impurities. This invention removes the above impurities by sorting.

[0022] The purpose of crushing is to break down large pieces of organic matter and solid waste in kitchen waste into particle sizes suitable for further processing, thereby improving the efficiency of subsequent oil extraction.

[0023] The purpose of multi-stage centrifugal oil extraction is to separate oil from kitchen waste using centrifugal force, reducing the content of water and solid impurities. Multi-stage centrifugal oil extraction first performs coarse separation, then fine separation, and finally refined extraction. Each round of centrifugation further separates more oil. The centrifugation temperature used in this invention helps improve the fluidity of the oil and increases extraction efficiency.

[0024] In one embodiment, the alkaline solution includes one or more of potassium hydroxide solution, sodium hydroxide solution, calcium hydroxide (Ca(OH)2) solution, and ammonium hydroxide (NH4OH) solution, with potassium hydroxide solution being used in a specific embodiment. The present invention does not have a specific limitation on the concentration of the alkaline solution, as long as the pH value can be adjusted to the desired value. The two-stage alkaline hydrolysis reaction includes sequentially performing a first-stage alkaline hydrolysis and a second-stage alkaline hydrolysis. The first-stage alkaline hydrolysis process is hydrolysis under moderate alkalinity and moderate temperature conditions. The first-stage alkaline hydrolysis is carried out under stirring conditions. The stirring speed is 40-80 rpm, with 50-60 rpm in a specific embodiment. The moderate alkalinity is a pH value of 9-10.5, with 10.0 in a specific embodiment. The hydrolysis temperature is 50-80℃, with 65℃ in a specific embodiment. The hydrolysis time is 50-70 min, with 20 min in a specific embodiment. The first-stage alkaline hydrolysis fully dissolves the kitchen solids.

[0025] In one implementation method, the second-stage alkaline hydrolysis process involves rapidly increasing the pH value and performing high-temperature hydrolysis. The rapid pH increase is achieved by raising the pH value to 11.5-12.2 within 5-15 minutes, specifically 11.8 in this embodiment. The high-temperature hydrolysis temperature is 80-95°C, specifically 90°C in this embodiment, and the time for maintaining the pH value and temperature is 10-40 minutes, specifically 35 minutes in this embodiment. The second-stage alkaline hydrolysis improves the solubility of organic matter by rapidly increasing the pH value and performing short-term chain scission under high alkalinity and high temperature conditions. At the same time, it inhibits Maillard reactions and unnecessary excessive condensation, thereby reducing liquid color and viscosity and minimizing amino nitrogen loss.

[0026] In one embodiment, the solid-liquid separation is sieving or centrifugation, specifically sieving in this embodiment; the sieve used for sieving has a mesh size of 80-100 mesh, specifically 90-100 mesh in this embodiment; the centrifugation temperature is 30-60℃, specifically 45-50℃ in this embodiment, the time is 5-20 min, specifically 10-15 min in this embodiment, and the rotation speed is 2000-400 rpm, specifically 3000-4000 rpm in this embodiment; the equipment used for centrifugation is a centrifuge.

[0027] After solid-liquid separation, the resulting alkaline hydrolysate is further de-oiled until the free oil mass fraction is no higher than 2%, specifically 1.2% in this embodiment. The de-oiling method includes flotation or membrane de-oiling. This invention reduces the risk of contamination in subsequent membrane separation and drip irrigation pipelines by removing oil.

[0028] In one implementation, the alkaline hydrolysis residue is returned to continue the two-stage alkaline hydrolysis reaction; during the process of returning the alkaline hydrolysis residue to continue the two-stage alkaline hydrolysis reaction, the amount of added alkali solution does not exceed 70% of the total amount of alkali solution used in the two-stage alkaline hydrolysis reaction.

[0029] After obtaining the alkaline hydrolysate, the present invention adds an acid solution to the alkaline hydrolysate to adjust the pH value to 5.5-8.5, and then performs electrodialysis acid-base extraction. The resulting acid-base extraction mother liquor is then subjected to nanofiltration fractionation and enrichment to obtain permeate and concentrate, respectively.

[0030] In one embodiment, the acid solution includes phosphoric acid, nitric acid, sulfuric acid, or citric acid; the pH value is adjusted to 5.5-8.5 by adding an external acid solution to the alkaline hydrolysis solution, specifically 7-7.5 in this embodiment; the current density of the electrodialysis acid-base extraction is 100-200 A / m. 2 In a specific embodiment, it is 147 A / m 2 Or 150A / m 2The electrodialysis acid-base extraction method used is bipolar membrane electrodialysis, and the equipment used is a bipolar membrane electrodialysis device. The two stages of the bipolar membrane electrodialysis produce alkaline and acid solutions respectively. The concentration of the alkaline solution produced by the bipolar membrane electrodialysis is 3~20wt%, and 10wt% in a specific embodiment. The concentration of the acid solution produced by the bipolar membrane electrodialysis is 3~20wt%, and 8wt% in a specific embodiment. The alkaline solution produced by the bipolar membrane electrodialysis is recycled for the two-stage alkaline hydrolysis reaction, and the acid solution produced by the bipolar membrane electrodialysis is used for neutralization reaction and / or pH adjustment. The alkaline solution produced by the bipolar membrane electrodialysis is the same as the alkaline solution used in the two-stage alkaline hydrolysis reaction, and the acid solution produced by the bipolar membrane electrodialysis is the same as the acid solution used to adjust the pH value of the alkaline hydrolysis solution, thereby realizing an electrochemical closed-loop supply of acid and base.

[0031] In one embodiment, the present invention does not have a special limitation on the amount of external acid added to the alkaline hydrolysis solution, as long as the pH value of the alkaline hydrolysis solution can be adjusted to 5.5~8.5.

[0032] In one implementation method, the power consumption during the electrodialysis acid-base extraction process is 0.8~2.5 kWh / kg-KOH equivalent, and in a specific embodiment it is 1~1.7 kWh / kg-KOH equivalent. The acid-base self-sufficiency rate is ≥40%, and in a specific embodiment it is 43% or 44%.

[0033] In one embodiment, the nanofiltration membrane used for nanofiltration fractionation and enrichment has a molecular weight cutoff of 300-800 Da, specifically 400-600 Da in this embodiment; the transmembrane pressure difference for nanofiltration fractionation and enrichment is 0.6-1.8 MPa, specifically 0.9 MPa or 1.19 MPa in this embodiment; the mass concentration of free amino acids in the permeate is ≥2.0 g / L, specifically 3.0 g / L or 4.5 g / L in this embodiment, and the mass concentration of oligopeptides is ≥4.0 g / L, specifically 5.0 g / L or 4.4 g / L in this embodiment; the mass concentration of soluble polysaccharides in the concentrate is ≥15 g / L, and the humification indicator (E4 / E6 value) is ≤7, specifically 18 g / L and the E4 / E6 value is 6 in this embodiment; the enrichment recovery rate of nanofiltration fractionation and enrichment is 60-85%, specifically 67% or 70% in this embodiment. This invention, through nanofiltration fractionation, can reduce total salinity and Cl-. - The content was determined, and two intermediate liquids with significantly different properties were obtained: a permeate rich in amino acids and oligopeptides and a concentrate rich in oligosaccharides and humified organic matter, providing greater freedom for subsequent formulation adjustments.

[0034] After obtaining the concentrated solution, the present invention mixes the concentrated solution with soluble magnesium salt, and after the resulting mixture undergoes a neutralization reaction, the pH value of the resulting neutralization reaction system is increased to carry out a precipitation reaction, thereby obtaining a nano-magnesium phosphate functional slow-release suspension.

[0035] In one embodiment, the soluble magnesium salt includes one or more of magnesium sulfate, magnesium aminophosphate, and magnesium chloride, with magnesium aminophosphate being used in a specific embodiment; the neutralization reaction is as follows: the pH of the resulting mixture is adjusted to neutral or weakly alkaline using an acid solution, with a pH of 6.8 to 7.4 being used in a specific embodiment; the acid solution is an acid solution produced by bipolar membrane electrodialysis; the pH of the resulting neutralization reaction system is raised to 8.5 to 9.2, with a pH of 8.9 being used in a specific embodiment; the reagent used to raise the pH of the resulting neutralization reaction system is one or more of potassium hydroxide, sodium hydroxide, and calcium hydroxide, with potassium hydroxide being used in a specific embodiment; the precipitation reaction time is 5 to 30 minutes, with a time of 30 minutes being used in a specific embodiment.

[0036] In one embodiment, the molar ratio of Mg, N, and P in the mixture is 1.05~1.25:1.0:1.0, and in a specific embodiment it is 1.15:1.0:1.0; the D of the nano-magnesium phosphate crystals in the nano-magnesium phosphate functional slow-release suspension is... 50 The particle size is 100~500nm, specifically 250nm in this embodiment; the nano-magnesium phosphate ammonium functional slow-release suspension also contains added seed crystals; the added seed crystals include struvite and / or magnesium phosphate ammonium, specifically magnesium phosphate ammonium; the concentration of the added seed crystals in the nano-magnesium phosphate ammonium functional slow-release suspension is 0~200mg / L, specifically 100~150mg / L in this embodiment. The crystal morphology, particle size distribution, and stability in the suspension are controlled by adding seed crystals.

[0037] In one embodiment, the mixture further includes a soluble calcium salt; the soluble calcium salt includes one or more of calcium sulfate, calcium carbonate, and calcium chloride, with calcium carbonate being the specific example; the molar ratio of Ca, N, and P in the mixture is 1.02~1.25:1.0:1.0, with 1.05:1.0:1.0 being the specific example. Adding a soluble calcium salt to the mixture allows the system to generate a small amount of calcium carbonate in addition to magnesium phosphate, which helps improve soil aggregate structure and regulate pH.

[0038] This invention utilizes the acid solution generated by electrodialysis to precisely control the pH value. After neutralization is completed in the neutral to weakly alkaline range, the pH value is locally increased to reduce the NH4 content in the system. + With PO4 3- Nanoscale magnesium ammonium phosphate functional crystals were generated in situ in the presence of magnesium ions to obtain a nano-magnesium ammonium phosphate functional sustained-release suspension.

[0039] After obtaining the nano-magnesium ammonium phosphate functional slow-release suspension, the present invention sequentially performs pH buffering and amino acid chelation trace element stabilization on the mixture of the nano-magnesium ammonium phosphate functional slow-release suspension and the permeate to obtain liquid slow-release organic fertilizer.

[0040] In one embodiment, the mass ratio of N, P and K in the mixture of the nano-magnesium ammonium phosphate functional slow-release suspension and the permeate is 1:1:1~2, and in a specific embodiment it is 1:1:2.

[0041] As one implementation method, before pH buffering, the process further includes: subjecting the mixture of the nano-magnesium phosphate functional slow-release suspension and the permeate to a triple inactivation and deodorization process; the triple inactivation and deodorization methods include pasteurization, UV-C irradiation, and ozone micro-nano bubble treatment. This invention does not specifically limit the specific operation of the triple inactivation and deodorization; operations well-known in the art can be used.

[0042] In one implementation method, the liquid slow-release organic fertilizer product prepared by triple inactivation and deodorization has a total coliform count of <3 MPN / mL, mold count of <10 CFU / mL, and a reduction of ammonia and volatile amine odor by ≥70%. This invention achieves deep control of miscellaneous bacteria and odor through triple inactivation and deodorization.

[0043] In one embodiment, the buffer used for the pH buffer is an organic acid and / or an organic acid salt; the organic acid includes one or more of citric acid (C6H8O7), malic acid (C4H6O5), and acetic acid (CH3COOH), with citric acid (C6H8O7) being used in a specific embodiment; the organic acid salt is potassium citrate and / or an amino acid salt; the amino acid salt is monosodium glutamate; the pH of the system after pH buffering is 6.5~7.0, with 6.8 being used in a specific embodiment.

[0044] Citric acid (C6H8O7): Commonly used in agriculture, it effectively regulates pH and has a buffering effect. Malic acid (C4H6O5): Has good buffering properties and is often used to adjust the pH of liquid fertilizers. Acetic acid (CH3COOH): Commonly used to adjust neutral or weakly acidic environments and does not significantly inhibit microorganisms. Amino acid salts: Such as monosodium glutamate (MSG), which not only provide buffering but also help stabilize micronutrients. Choose suitable organic acids or organic acid salts according to the needs of the liquid fertilizer. After adding the buffer, adjust the pH to the target range by monitoring the pH. The buffered pH is usually controlled within the range of 5-6.5 to maintain the stability of the liquid fertilizer and avoid excessive acidity or alkalinity affecting crop absorption.

[0045] In one embodiment, the amount of buffer used for pH buffering is 0.1-2% of the mass of the mixture of the nano-magnesium phosphate functional slow-release suspension and the permeate, specifically 0.5-1.8% in this embodiment; when the buffer used for pH buffering is an organic acid solution, the amount of buffer used for pH buffering is 0.5-1% of the mass of the mixture of the nano-magnesium phosphate functional slow-release suspension and the permeate, specifically 0.6-0.8% in this embodiment; when the buffer used for pH buffering is an organic acid salt solution, the amount of buffer used for pH buffering is 0.1-1% of the mass of the mixture of the nano-magnesium phosphate functional slow-release suspension and the permeate, specifically 0.6-0.8% in this embodiment; the specific amount added needs to be adjusted according to the initial pH of the liquid fertilizer and the required buffering effect.

[0046] In one embodiment, the amino acid used for the amino acid chelation trace element stabilization includes one or more of glycine, glutamic acid, and aspartic acid, with aspartic acid being used in a specific embodiment; the trace element stabilized in the amino acid chelation trace element stabilization includes Fe. 2+ Zn 2+ and Cu 2+ One or more of the following, specifically Fe in the embodiment. 2+ In each liter of the mixture of the nano-magnesium phosphate functional sustained-release suspension and the permeate, the amount of amino acid used for amino acid chelation and trace element stabilization is 0.1~1.5g, and in the specific embodiment it is 0.5~0.9g.

[0047] Trace elements (such as iron, zinc, and copper) are usually present in a dissolved state in liquid organic fertilizers (e.g., Fe). 2+ Zn 2+ Cu 2+ These substances are prone to precipitation or reaction with other components, leading to their inactivation. This invention addresses this by chelating trace elements with amino acids, allowing trace elements (such as Fe) to be released into the final product. 2+ Zn 2+ Cu 2+ Micronutrients combine with amino acids to form chelates. Chelated chelates are highly stable and can prevent micronutrients from precipitating or reacting with other substances, thereby improving the stability and bioavailability of these micronutrients. Adding chelated micronutrients to liquid fertilizers can improve fertilizer stability and crop absorption efficiency.

[0048] As one embodiment, the liquid slow-release organic fertilizer meets the following requirements: total organic matter content ≥80g / L, N content 1.5~5.0g / L, P2O5 content 2.0~8.0g / L (specifically 2.4~7.2g / L in this embodiment), K2O content 8.0~25g / L (specifically 9~18g / L in this embodiment), and Cl... -Content ≤2.0g / L, viscosity at 20℃ ≤50mPa·s, sediment volume fraction <0.2%.

[0049] In this embodiment of the invention, the liquid slow-release organic fertilizer has a total organic matter content of 132 g / L, a nitrogen content of 1.7 g / L, a p2O5 content of 2.4 g / L, a k2O content of 9.7 g / L, and a chloride content of 132 g / L. - The content is 1.4 g / L, the viscosity at 20℃ is 37 mPa·s, and the volume fraction of sludge is 0.2%; or the total organic matter content is 120 g / L, the N content is 3.0 g / L, the P2O5 content is 5.0 g / L, the K2O content is 18 g / L, and the Cl content is... - The content is 1.6 g / L, the viscosity at 20℃ is 35 mPa·s, and the volume fraction of sediment is 0.12%.

[0050] The present invention also provides a system for implementing the method described in the above technical solution, comprising a two-stage alkaline hydrolysis reactor, a bipolar electrodialysis acid-base recovery device, a nanofiltration fractionation device, an in-situ magnesium ammonium phosphate functional slow-release suspension generation device, a formulation compounding device, and a buffer stabilization unit connected in sequence.

[0051] In one embodiment, the system further includes a pretreatment unit located before the two-stage alkaline hydrolysis reactor.

[0052] In one embodiment, the system further includes a multi-stage inactivation unit located after the formulation compounding device.

[0053] As one implementation, the system further includes: a tail gas collection and acid absorption reflux system, used to absorb and treat ammonia and nitrogen-containing odorous gases generated during the alkaline hydrolysis and neutralization process and to partially reuse them.

[0054] In one implementation, the two-stage alkaline hydrolysis reactor is equipped with an online monitoring and rapid control system for pH and temperature, enabling alkalinity pulse control; the in-situ magnesium ammonium phosphate functional slow-release suspension generation device is a circulating shear-jet mixing reactor with a pH adjustment gradient zone and an adjustable residence time of 5-30 minutes; the nanofiltration stage is equipped with periodic permeate backwashing or cross-flow enhancement measures to mitigate membrane fouling and improve operational stability.

[0055] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments thereof, but they should not be construed as limiting the scope of protection of the present invention.

[0056] Example 1 Kitchen waste residue with a moisture content of 71 wt% was sequentially sorted, crushed, and subjected to multi-stage centrifugal oil extraction. The crushed particle size was 6 mm. The multi-stage centrifugal oil extraction process involved three centrifugation cycles at 80℃ for 10 minutes each, at a speed of 5000 rpm. The resulting pretreated kitchen waste (with metal and plastic impurities removed, a moisture content of 25 wt%, and an oil content of 21 wt%) was fed into a two-stage alkaline hydrolysis reactor. Potassium hydroxide solution was added for the two-stage alkaline hydrolysis reaction. The first stage was controlled at a pH of 10.0, a temperature of 65℃, a time of 20 minutes, and a stirring speed of 60 rpm. The first stage involves solid swelling and partial dissolution of organic matter. The second stage rapidly raises the pH to 11.8 within 10 minutes and increases the temperature to 90°C, maintaining this temperature for 35 minutes to improve the solubility of organic matter and inhibit the Maillard reaction. After alkaline hydrolysis, solid-liquid separation is achieved by centrifugation (45°C, 10 minutes, 4000 rpm), with the free oil mass fraction controlled below 1.2%, yielding alkaline hydrolysis solution and alkaline hydrolysis residue. The alkaline hydrolysis residue is returned to continue the two-stage alkaline hydrolysis reaction, with the amount of external alkali added not exceeding 70% of the total amount of alkali used in the two-stage alkaline hydrolysis reaction. The alkaline hydrolysis solution (containing salt-containing circulating mother liquor) enters the bipolar membrane electrodialysis device. After adjusting the pH of the alkaline hydrolysis solution to 8.1 with added acid (H3PO4 solution), the current density is 150 A / m. 2 Under normal operating conditions, the energy consumption is 1.7 kWh / kg-KOH equivalent, and the acid-base self-sufficiency rate is 43%. The system produces 10 wt% KOH solution and 8 wt% H3PO4 solution in two stages. The KOH solution is recycled for the two-stage alkaline hydrolysis reaction, while the H3PO4 solution is used for subsequent neutralization and pH fine-tuning. The resulting acid-base extraction mother liquor is fractionated and enriched using a nanofiltration membrane with a molecular weight cutoff of 600 Da. The transmembrane pressure difference is 1.19 MPa, yielding permeate and concentrate. Measurements show that the permeate contains 3.0 g / L of free amino acids and 5.0 g / L of oligopeptides, while the concentrate contains 18 g / L of soluble polysaccharides. The E4 / E6 ratio is 6, and the enrichment recovery rate of the nanofiltration fractionation is 70%. MgCl2 was added to the concentrated solution to make the molar ratio of Mg, N, and P 1.15:1.0:1.0. The resulting mixture was first neutralized by adjusting the pH to 7.0 with H3PO4 solution generated by bipolar membrane electrodialysis. Then, the pH was raised to 8.9 with potassium hydroxide and maintained for 30 minutes to induce precipitation, generating nano-magnesium phosphate functional crystals. The D-value was then determined. 50The nanoparticle size is 250 nm, forming a stable nano-magnesium phosphate functional slow-release suspension. 121 mg / L of external seed crystals (magnesium phosphate) are added. The nano-magnesium phosphate functional slow-release suspension is mixed with the permeate at a N:P:K mass ratio of 1:1:2, and then subjected to triple inactivation and deodorization through pasteurization, UV-C irradiation, and ozone micro-nano bubble treatment. The pH is then adjusted to 6.8 with citric acid and its potassium salt, and 0.9 g / L of amino acids are added to form Fe, Zn, B, and Mn amino acid chelates, ultimately obtaining a liquid slow-release organic fertilizer.

[0057] The test results show that the total organic matter content of the liquid slow-release organic fertilizer is 120 g / L, the nitrogen content is 3.0 g / L, the phosphorus pentoxide content is 5.0 g / L, the potassium oxide content is 18 g / L, the chloride ion content is 1.6 g / L, the viscosity at 20℃ is 35 mPa·s, and the sediment volume fraction is 0.12%.

[0058] Example 2 This embodiment adjusts the nanofiltration fractional enrichment and formulation ratio based on Example 1 to prepare a fast-acting liquid organic fertilizer: By replacing the nanofiltration membrane with one that has a molecular weight cutoff of 400 Da, the nanofiltration fractionation and enrichment recovery rate was increased to 80%, the permeate ratio was increased, and the free amino acid content in the permeate was increased to 4.5 g / L and the oligopeptide content was increased to 4.4 g / L. When generating magnesium ammonium phosphate functional crystal suspension in situ, the seed crystal dosage is increased to 150 mg / L to obtain nanocrystals with smaller particle size and narrower distribution, thereby improving rhizosphere availability. After adjustment, the mass concentration of phosphorus pentoxide in the finished fertilizer can reach 7.2 g / L, the mass concentration of potassium oxide is 16.4 g / L, and the proportion of ammonium nitrogen in nitrogen forms is increased, which is conducive to the rapid absorption of leafy vegetables.

[0059] Example 3: Liquid Organic Fertilizer for Fruit Tree Rhizosphere Repair and Soil Improvement This embodiment adjusts the nanofiltration grading and formulation to make the product more suitable for improving the rhizosphere environment of fruit trees and restoring soil aggregate structure: The molecular weight cutoff of the nanofiltration membrane was adjusted to appropriately reduce the nanofiltration recovery rate to 57%, and the proportion of concentrate was increased to increase the soluble polysaccharide content to 6.7 g / L and the humified organic matter content (E4 / E6 value) to 4.7. During the in-situ generation of magnesium ammonium phosphate functional crystal suspension, soluble Ca was introduced. 2+Calcium chloride participates in the reaction, with a Ca:N:P molar ratio of 1.07:1.0:1.0. This results in the formation of a small amount of calcium carbonate in the system, in addition to magnesium phosphate, which helps improve soil aggregate structure and regulate pH. After formula optimization, the total organic matter content of the finished liquid fertilizer can reach over 150 g / L, with a phosphorus pentoxide concentration of approximately 3.3 g / L and a potassium oxide concentration of approximately 12.7 g / L.

[0060] Comparative Example 1 The difference from Example 1 lies in changing the two-stage alkaline hydrolysis reaction to a one-step reaction. Kitchen waste residue is directly mixed with potassium hydroxide solution, and a single reaction condition is set, maintaining a temperature of 90°C, a pH of 11.8, and a reaction time of 35 minutes. This makes it difficult to effectively distinguish between the solid swelling and organic matter dissolution processes, and to precisely control the degree of reaction. Experimental results show that, under the simplified one-step reaction, the organic matter dissolution rate is less than 90%, which leads to a weakened effect of subsequent reactions, insufficient removal of sparingly soluble organic matter, and a liquid organic matter content below 15 g / L.

[0061] Comparative Example 2 The difference from Example 1 is that the bipolar membrane electrodialysis step used in Example 1 is removed. Instead, the alkaline solution and acid solution are directly mixed for neutralization and treated by other physical methods, resulting in a significant reduction in the recovery rates of potassium hydroxide and phosphoric acid. Removing the electrodialysis step necessitates the additional purchase of potassium hydroxide and phosphoric acid, significantly increasing raw material costs. The consumption of potassium hydroxide and phosphoric acid increases by approximately 20-30%, leading to an overall increase in energy consumption. Due to the lack of a recovery step, raw material costs increase by 15-20%.

[0062] Comparative Example 3 The difference from Example 1 is that hydrochloric acid or nitric acid was used for direct adjustment, resulting in larger pH fluctuations, ranging from ±1.5, which affected the stability of the reaction. The addition of strong acid may accelerate the degradation of organic matter, produce incomplete neutralization reactions, affect the quality of the final product, and concentrated acid can easily cause equipment corrosion, increasing maintenance costs.

[0063] Comparative Example 4 The difference from Example 1 is that the multi-stage centrifugal oil extraction step is removed, and the kitchen waste is sent directly or through a single oil extraction to the alkaline hydrolysis reaction. At this time, the oil concentration is greater than 35 wt%, which reacts with the organic matter in the alkaline hydrolysis solution, inhibiting the subsequent alkaline hydrolysis efficiency, and reducing the solubility of organic matter to below 75%.

[0064] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing liquid slow-release organic fertilizer from kitchen waste, characterized in that, Includes the following steps: The pretreated kitchen waste residue is mixed with alkaline solution and subjected to a two-stage alkaline hydrolysis reaction, followed by solid-liquid separation to obtain alkaline hydrolysis solution and alkaline hydrolysis residue, respectively. After adjusting the pH value to 5.5-8.5 by adding acid to the alkaline hydrolysate, electrodialysis acid-base extraction is performed. The resulting acid-base extraction mother liquor is then fractionated and enriched by nanofiltration to obtain permeate and concentrate, respectively. The concentrated solution and soluble magnesium salt are mixed, and the resulting mixture is neutralized. The pH value of the resulting neutralization reaction system is increased to carry out a precipitation reaction, thereby obtaining a nano-magnesium phosphate functional slow-release suspension. The mixture of the nano-magnesium ammonium phosphate functional slow-release suspension and the permeate was sequentially subjected to pH buffering and amino acid chelation trace element stabilization to obtain liquid slow-release organic fertilizer.

2. The method according to claim 1, characterized in that, The pretreated kitchen waste residue has a moisture content of ≤30wt% and an oil content of ≤30wt%.

3. The method according to claim 1, characterized in that, The alkaline solution includes one or more of potassium hydroxide solution, sodium hydroxide solution, calcium hydroxide solution, and ammonium hydroxide solution.

4. The method according to claim 1, characterized in that, The two-stage alkaline hydrolysis reaction includes sequentially performing a first-stage alkaline hydrolysis and a second-stage alkaline hydrolysis. The first stage of alkaline hydrolysis is carried out under moderate alkalinity and moderate temperature conditions; the moderate alkalinity is defined as a pH value of 9 to 10.5; and the hydrolysis temperature is defined as 50 to 80°C. The second stage of alkaline hydrolysis involves rapidly increasing the pH value and then performing high-temperature hydrolysis; the rapid pH increase means raising the pH value to 11.5-12.2 within 5-15 minutes; the high-temperature hydrolysis temperature is 80-95℃.

5. The method according to claim 1, characterized in that, The current density for the electrodialysis acid-base extraction is 100~200 A / m. 2 The method used for electrodialysis acid-base extraction is bipolar membrane electrodialysis; the two stages of the bipolar membrane electrodialysis produce alkaline solution and acid solution respectively, and the concentration of the alkaline solution produced by the bipolar membrane electrodialysis is 3~20wt%; the concentration of the acid solution produced by the bipolar membrane electrodialysis is 3~20wt%.

6. The method according to claim 1, characterized in that, The nanofiltration membrane used for the nanofiltration fractionation enrichment has a molecular weight cutoff of 300~800 Da.

7. The method according to claim 1, characterized in that, The molar ratio of Mg, N and P in the mixture is 1.05~1.25:1.0:1.

0.

8. The method according to claim 1, characterized in that, The buffer used for the pH buffer is an organic acid and / or an organic acid salt; the organic acid includes one or more of citric acid, malic acid and acetic acid; the organic acid salt is potassium citrate and / or an amino acid salt.

9. The method according to claim 1, characterized in that, The liquid slow-release organic fertilizer meets the following requirements: total organic matter content ≥ 80 g / L, N content 1.5~5.0 g / L, P2O5 content 2.0~8.0 g / L, K2O content 8.0~25 g / L, Cl... - Content ≤2.0g / L, viscosity at 20℃ ≤50mPa·s, sediment volume fraction <0.2%.

10. A system for implementing the method according to any one of claims 1 to 9, characterized in that, It includes a two-stage alkaline hydrolysis reactor, a bipolar electrodialysis acid-base recovery device, a nanofiltration classification device, an in-situ phosphorus magnesium ammonium functional slow-release suspension generation device, a formulation compounding device, and a buffer stabilization unit connected in sequence.