A multi-stage resource treatment method for kitchen waste and its application

Abstract

The present invention provides a multi-stage resource recovery method for food waste, comprising: subjecting the food waste to a solid-liquid separation to obtain a first solid phase and a leachate discharged from the bottom; separating and removing inorganic heavy components and ferrous metal impurities from the first solid phase, while retaining organic solid phase components; crushing the organic solid phase components and slurrying them together with the lower layer of the leachate after standing and stratifying, separating light fine residues and removing heavy residues such as inorganic sand to obtain a slurry, mixing the slurry with the supernatant of the leachate, and performing three-phase separation and quality control and multi-stage resource recovery; wherein the organic solid phase components include long fruit and vegetable fibers, paper towels, wooden chopsticks, and plastics, and the inorganic heavy components include stones, glass, and ceramics. The multi-stage resource recovery method for food waste provided by the present invention has a low residue rate, easily controllable biochar product quality, and high calorific value. The multi-stage resource recovery not only improves resource utilization but also reduces wastewater treatment costs.

Description

Technical Field

[0001] The present invention relates to the technical field of solid waste treatment, in particular to converting solid waste into useful substances, and specifically to a multi-stage resource treatment method for kitchen waste and its application. Background Art

[0002] Food waste primarily refers to organic waste generated by catering businesses and food production, sales, processing, residential life, and consumption. Besides water, its primary components are carbohydrates, fats, proteins, cellulose, and small amounts of inorganic salts and lignin. Depending on the level of classification, it may also contain inorganic impurities such as silt, glass, ceramics, and metals. The water content of food waste is typically around 70%-90%, and this high moisture content somewhat impacts its treatment. While its high moisture content makes it susceptible to spoilage, its composition reveals that it contains significant amounts of organic matter, such as carbohydrates, proteins, and fats. This rich organic content gives it considerable potential for resource utilization, high biodegradability, and high energy potential, making it a promising biomass energy source.

[0003] To reduce the harmful effects of food waste, it must be properly handled. Food waste treatment technologies primarily include traditional treatment technologies and resource-based treatment technologies. Traditional treatment technologies primarily include landfill and incineration. Landfill not only occupies a significant amount of valuable land resources, but also leachate easily seeps into the ground. Limited collection methods also lead to large amounts of landfill gas being released into the open air, causing a series of environmental pollution problems. Incineration, on the other hand, consumes significant energy during the drying and evaporation phases of food waste due to its high water content, which also impacts the efficiency of other waste components used for power generation. Furthermore, neither landfill nor incineration methods effectively utilize food waste as a resource, running counter to the demands of energy conservation, emission reduction, and the development of a circular economy. Resource-based treatment technologies primarily include anaerobic fermentation, aerobic composting, feed conversion, and thermal dehydration and drying. Anaerobic fermentation involves the use of anaerobic bacteria to degrade organic matter in food waste into biogas and inorganic compounds. The primary outputs are methane and biogas residue and liquid biogas. The residue and liquid biogas are then subsequently treated and used for land use. Aerobic composting uses aerobic bacteria to oxidize and decompose food waste, ultimately producing organic compound fertilizer and soil conditioner. However, aerobic composting requires a long fermentation cycle and large floor space. Furthermore, due to the high moisture content of food waste, a large amount of auxiliary materials must be added to regulate its moisture. High oil and salt content in food waste also produces wastewater and odor pollution, affecting fertilizer quality. On-site aerobic composting machines have a shorter fermentation cycle, but incomplete fermentation prevents direct fertilizer use. Feed conversion primarily involves insect farming or direct drying. Insect farming feed conversion requires a high level of environmental and automated feeding equipment, and the organic matter undergoes incomplete reaction after passing through the stomach, posing safety risks. Direct drying feed conversion consumes significant amounts of heat energy and is less widely used due to the safety risk of homologous contamination. Thermal dehydration and drying technology primarily uses high-temperature, high-pressure hydrolysis to break down large organic molecules in food waste into smaller ones. During this process, the moisture in the food waste is released, reducing the viscosity of the material, reducing the difficulty of subsequent mechanical dehydration and enabling rapid dehydration and drying. Furthermore, thermal hydrolysis kills bacteria and pathogens in the food waste, rendering it harmless. However, the fundamental purpose of thermal dehydration and drying is waste reduction and disposal. It does not achieve the resource utilization of organic matter, product desalination, or the stabilization of heavy metals in solid and liquid products. This makes it suitable only for small-scale food waste treatment and easy co-processing with waste incineration plants, but not for large-scale centralized food waste treatment and disposal. How can we rationally utilize the high organic matter, moisture content, and organic matter content of food waste, fully explore the resource utilization pathways for food waste, and maximize the energy potential of this biomass?

[0004] Existing methods for converting food waste into energy, besides anaerobic fermentation to produce biogas and oil extraction for biodiesel, primarily involve hydrothermal carbonization. This involves subjecting the organic slurry of finely separated and impurity-removed food waste to a hydrothermal reaction under high temperature and pressure. This reaction then proceeds through solid-liquid separation to produce biochar as an energy conversion product. The hydrothermal fluid then enters the sewage treatment system for treatment. Existing food waste pretreatment technologies, in addition to removing inorganic impurities such as glass, ceramics, and sand and gravel, and metals, typically include a fine separation process to remove long fruit and vegetable fibers, plastics, wooden chopsticks, and paper. This typically results in a residue rate of 15% to 25%. These recalcitrant organic impurities have the potential to be converted into biochar at high hydrothermal reaction intensities and contribute a high calorific value. This pretreatment fine separation not only results in high disposal costs due to the high residue rate, but also wastes resources. Furthermore, existing food waste hydrothermal carbonization technologies still have several drawbacks. First, hydrothermal process parameters primarily include reaction temperature, heating rate, reaction time, operating pressure, pH value, and solid-liquid ratio. Different parameter settings and material characteristics determine the energy consumption of the hydrothermal reaction and the degree of product gasification, liquefaction, and carbonization. The goal of the hydrothermal carbonization of food waste is to convert as much organic components as possible into solid biochar, avoiding excessive conversion of organic components to liquid or even gaseous phases due to excessive temperature, pressure, and reaction time. The complexity of food waste composition leads to uncertainty in the setting of hydrothermal carbonization process parameters, which is one of the main reasons why hydrothermal carbonization was initially applied to sewage sludge rather than food waste. For example, hydrothermal carbonization can be carried out within three main temperature ranges: generally, hydrothermal carbonization can be carried out at low temperatures (170–220°C), moderate temperatures (220–260°C), or high temperatures (>260°C). For example, carbohydrates and sugars, which are easily decomposed, require lower reaction temperatures, while proteins and fats require higher reaction temperatures. Biochar produced from hemicellulose, cellulose, and lignin requires more intense hydrothermal heat treatment. At the same time, under different reaction condition intensities, the biochar yield and calorific value vary greatly, and it is necessary to select appropriate reaction conditions based on the characteristics of the raw materials, operating costs, and product benefits. Therefore, the more complex the material components, the more difficult it is to control the reaction conditions, and the product quality cannot be guaranteed. In addition, the material composition fluctuates in different seasons and regions, resulting in the control of hydrothermal carbonization process parameters becoming a key difficulty limiting the application of this technology. In addition, the hydrothermal liquid after the hydrothermal carbonization reaction has the characteristics of humification, low carbon-nitrogen ratio, and high salinity. If water treatment is carried out directly, it will not only cause waste of resources, but also require the addition of carbon sources depending on the water quality, which increases the subsequent treatment costs and reduces the overall benefits of the project. Summary of the Invention

[0005] The present invention aims to at least partially solve one of the technical problems in the prior art. To this end, one object of the present invention is to provide a multi-stage resource recovery method for food waste, comprising: subjecting the food waste to a solid-liquid separation to obtain a first solid phase, discharging the first liquid phase from the bottom as leachate, and allowing the first liquid phase to stand for stratification; separating and removing inorganic heavy components and ferrous metal impurities from the first solid phase, while retaining organic solid phase components; crushing the organic solid phase components and slurrying them together with the lower layer of the leachate to separate light fine residue and remove heavy residue such as inorganic sand to obtain a slurry, mixing the slurry with the supernatant of the leachate, subjecting the slurry to a three-phase separation and fractionation treatment to extract oil and fat, and obtaining a second solid phase and a second liquid phase, which are then recycled in multiple stages; wherein the organic solid phase components include long fruit and vegetable fibers, paper towels, wooden chopsticks, and plastic, and the inorganic heavy components include stones, glass, ceramics, etc. Among them, crushing and pulping, using an extrusion shear crusher to coarsely crush the organic solid phase components, then mixing them with the lower layer liquid of the leachate and sending them to a pulping machine for pulping, and after pulping, sending them to a hydrocyclone desander to remove heavy residues such as inorganic sand.

[0006] The multi-resource treatment method for kitchen waste provided by the present invention has a low residue rate and a high calorific value of the product. In the pretreatment stage, only inorganic impurities such as sand and gravel, glass, ceramics, and scrap metal need to be removed. Impurities such as plastics, wooden chopsticks, and paper towels can be crushed and pulped together. Impurities that cannot be crushed are separated as light fine residues to avoid affecting the three-phase separation and oil extraction process, and directly enter the hydrothermal carbonization process for carbonization reaction. The overall residue rate can be reduced from 15% to 25% to within 8%. On the one hand, inorganic impurities are removed, and at the same time, components such as long fibers of fruits and vegetables, plastics, wooden chopsticks, and paper towels that contribute to the calorific value in the carbonization process can be retained to the maximum extent.

[0007] In some embodiments, the multi-stage resource utilization includes: secondary resource utilization: saccharifying the second liquid phase obtained by the three-phase separation and fractionation treatment, and then performing hydrolysis and acidification treatment to produce a lactic acid product and extracting the lactic acid using a membrane separation method.

[0008] Preferably, during the saccharification treatment, 100,000-300,000 U / ton of saccharifying enzyme is added based on the weight of the second liquid phase; the treatment temperature is 40-60° C., and the pH is 4-6.

[0009] In some embodiments, the multi-stage resource utilization further includes a tertiary resource utilization step: combining the waste liquid after the hydrolysis and acidification treatment with the second solid phase obtained from the three-phase separation and fractionation treatment and the light fine residue, and subjecting the mixture to hydrothermal carbonization. A first solid-liquid separation is performed to produce a biochar product and a hydrothermal fluid. The light fine residue includes long fiber from fruits and vegetables, plastic, chopsticks, paper, and other refractory organic matter.

[0010] Preferably, the temperature of the hydrothermal carbonization treatment is 220-260°C.

[0011] In some embodiments, the multi-stage resource utilization further includes: fourth-stage resource utilization: after the hydrothermal carbonization treatment, alkaline heat treatment is performed to extract humic acid, and acid is added to precipitate the humic acid, and humic acid and hydrothermal residual liquid are obtained through a second solid-liquid separation.

[0012] Preferably, the temperature of the alkali thermal reaction is 150-200° C., and the reaction time is 1-2 h.

[0013] Preferably, the alkali is at least one of sodium hydroxide or potassium hydroxide, and the addition amount thereof is 1.5% to 2.5%.

[0014] In some embodiments, the multi-stage resource utilization further includes: fifth-stage resource utilization: desalting and denitrifying the hydrothermal residual liquid, and recovering salt.

[0015] Preferably, the desalination and nitrogen removal adopts electrodialysis technology, and industrial sodium chloride and industrial potassium chloride are recovered by applying a direct current electric field.

[0016] Preferably, during electrodialysis, the current density of the DC electric field is 10-30 mA / cm 2 , single pair voltage is 1.5~3V, reaction time is 60~150 min, and flow rate on the membrane surface is 1-3cm / s;

[0017] Preferably, when performing electrodialysis, 2-4 stages of electrodialysis are used in series.

[0018] In some embodiments, the hydrothermal carbonization uses a tubular reaction device, a medium-pressure pipeline, connected in series / parallel, a reaction pressure of 2.5-4 MPa, a heating rate of 1-3°C / min, and a residence time of 2 hours.

[0019] In some embodiments, the organic solid phase components are crushed to a size of less than 5-10 mm. The particle size of the material entering the three-phase separation is controlled to be less than 5 mm.

[0020] Secondly, the application of the treatment method in environmental engineering, the treatment and reuse of biomass such as kitchen waste, livestock and poultry manure and straw, and garden waste, and energy engineering is provided.

[0021] The present invention has at least the following technical effects:

[0022] 1. Low residue rate: This technical solution only needs to remove sand and gravel, glass, ceramics, scrap metal and other inorganic impurities in the pretreatment stage. Fruit and vegetable fibers, plastics, wooden chopsticks, paper towels and other impurities can be crushed and pulped together or enter the hydrothermal carbonization stage in the form of light fine residue for carbonization reaction. The residue rate can be reduced from 15% to 25% to less than 8%.

[0023] 2. High calorific value of the product: This technical solution can retain calorific components to the greatest extent possible. On the one hand, it removes inorganic impurities and retains components that contribute to calorific value during the carbonization process, such as fruit and vegetable fibers, plastics, wooden chopsticks, and paper towels. On the other hand, the liquid phase of the three-phase separation and fractionation treatment undergoes saccharification, hydrolysis, and acidification to produce lactic acid, prioritizing the recycling of most easily soluble and degradable carbohydrates such as starch and sugars. The heating rate, reaction temperature, residence time, pressure, and other process parameters can be set according to the requirements of the remaining protein and fat, lignin, cellulose, plastic, and other difficult-to-degrade organic substances. The setting range is relatively concentrated, reducing the difficulty of quality control of the biochar product and achieving a high calorific value. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the present invention or the prior art, a brief introduction is given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 This is one of the flow charts of the multi-stage resource processing method for garbage provided by the present invention. DETAILED DESCRIPTION

[0026] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work shall fall within the scope of protection of the present invention.

[0027] In a first aspect, the present invention proposes a multi-stage resource treatment method for kitchen waste, comprising the following steps.

[0028] (1) Coarse solid-liquid separation and organic-inorganic separation: The kitchen waste is subjected to a solid-liquid separation to obtain a first solid phase and a layered leachate; inorganic heavy components such as stones, glass, ceramics and iron metal debris are separated and removed from the first solid phase, food residues are separated, and organic solid phase components containing impurities such as plastics, wooden chopsticks, and paper are retained; in some embodiments, the first solid phase is separated and crushed to pulp light organic matter such as plastics, wooden chopsticks, and paper that is difficult to degrade, and the fine residue before entering the three-phase separation and fractionation treatment directly enters the hydrothermal carbonization to participate in the hydrothermal reaction.

[0029] The primary separation is performed in a temporary food waste storage silo, achieving a simple solid-liquid separation. In some embodiments, the inorganic heavy components are removed by bag breaking using a star screen. In some embodiments, the ferrous metal impurities are removed using an electromagnetic self-unloading iron remover.

[0030] (2) Crushing and pulping: The organic solid phase components are crushed and pulped together with the lower layer of the leachate to separate the light fine slag and remove heavy slag such as inorganic sand to obtain slurry; during crushing and pulping, an extrusion shear crusher is used to crush the organic solid phase components to less than 5-10 mm, and the mixture is mixed with the lower layer of the leachate and sent to a pulping machine for pulping. After pulping, the pulping is sent to a hydrocyclone desanding tank to remove heavy slag such as inorganic sand.

[0031] In some embodiments, the particle size of the material entering the three-phase separation is controlled to be below 5 mm, and light fine slag is separated.

[0032] (3) Three-phase separation and fractionation: The slurry from which heavy residues such as inorganic sand have been removed is mixed with the supernatant of the leachate and then subjected to a three-phase separation and fractionation process. After the three-phase separation and fractionation process, an upper surface layer of grease, an intermediate layer of slurry (referred to as the second liquid phase in this invention, having a lower solid content), and a lower layer of slurry (referred to as the second solid phase in this invention, having a higher solid content) are obtained.

[0033] (4) Multi-stage resource utilization: Through three-phase separation, oil is extracted as biodiesel and / or aviation fuel raw materials (primary resource utilization), and a second solid phase and a second liquid phase are obtained. The second liquid phase is saccharified and then hydrolyzed and acidified, and easily degradable organic matter such as carbohydrates and sugars are converted into organic acids such as lactic acid. Products such as lactic acid are extracted by membrane separation (secondary resource utilization); the residual liquid after extracting lactic acid is mixed with the second solid phase and the light fine residue and heated and then hydrothermally carbonized. In the hydrothermal carbonization process section, protein, fat, cellulose, plastic, lignin, etc. Part of the intermediate products produced by hydrolysis and acidification undergo polymerization and condensation reactions to generate biochar. An alkali catalyst is added to the mixed slurry after the reaction, and the residual heat of the hydrothermal reaction is used to generate an alkali thermal reaction, which provides a basis for the subsequent extraction of humic acid from the liquid phase product. After a second solid-liquid separation, a biochar product (tertiary resource utilization) and a hydrothermal liquid are obtained. Acid is added to the hydrothermal liquid, and after a third solid-liquid separation, a humic acid product (quaternary resource utilization) and a hydrothermal residual liquid are obtained. The hydrothermal residual liquid is desalinated and denitrified, and the salt is recovered (fifth-level resource utilization).

[0034] In some embodiments, during the saccharification treatment, 100,000-300,000 U / ton of saccharifying enzyme is added based on the weight of the second liquid phase; the treatment temperature is 40-60°C, and the pH is 4-6. The treatment temperature can be 40°C, 42°C, 45°C, 50°C, 55°C, 60°C, or other temperature values ​​or ranges thereof, such as 40-55°C, 45-60°C, 45-55°C, 40-50°C, etc.; the pH value can be 4, 4.5, 5, 5.5, 6, or other pH values ​​or ranges thereof, such as 4-5.5, 4.5-5.5, 5-6, 4.5-6, etc.

[0035] The liquid phase of the three-phase separation and fractionation treatment is saccharified and hydrolyzed to produce lactic acid, and most of the easily soluble and degradable carbohydrates such as starch and sugars are prioritized for resource utilization. The remaining proteins and fats, lignin, cellulose, plastics and other difficult-to-degrade substances are subjected to medium- and high-temperature hydrothermal carbonization treatment. The process parameter setting range is relatively concentrated, the difficulty of quality control of biochar products is reduced, and the calorific value of biochar is high.

[0036] In some embodiments, the temperature of the hydrothermal carbonization treatment is 220-260°C, and a shell-and-tube reaction device and a medium-pressure pipeline are used, which are connected in series / parallel. The reaction pressure is 2.5-4MPa, the heating rate is 1-3°C / min, and the residence time is 2h. The temperature of the hydrothermal carbonization treatment can be 220°C, 230°C, 240°C, 250°C, 260°C, or other temperatures or ranges consisting of these temperature values, such as 230-260°C, 220-250°C, 240-260°C, 220-240°C, etc. The reaction pressure can be 2.5MPa, 2.8MPa, 3MPa, 3.2MPa, 3.5MPa, 3.8MPa, 4MPa, or other pressure values ​​or these pressure values. The range of the composition is as follows: 2.5-3.5MPa, 3-4MPa, 2.5-3MPa, etc. The heating rate can be 1°C / min, 1.2°C / min, 1.5°C / min, 1.8°C / min, 2°C / min, 2.5°C / min, 3°C / min, or other rates or ranges composed of these rate values, such as 1.2-2.5°C / min, 2-3°C / min, 1.5-2.5°C / min, 1-2°C / min, etc.

[0037] In some embodiments, the temperature of the alkali thermal reaction is 150-200°C, and the reaction time is 1-2 hours. The reaction temperature can be 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, or other temperatures or ranges thereof, such as 150-180°C, 160-200°C, 180-200°C, etc. The reaction time can be 1 hour, 1.2 hours, 1.5 hours, 1.8 hours, 2 hours, or other times or ranges thereof, such as 1-1.5 hours, 1.5-2 hours, 1.2-1.8 hours, etc.

[0038] During the alkaline thermal reaction, a base and a catalyst are added, the base is at least one of sodium hydroxide or potassium hydroxide, and the addition amount is 1.5% to 2.5% (the addition amount can be 1.5%, 1.8%, 2%, 2.5%, or other addition amounts or ranges composed of these point values, such as 1.8-2.5%, 1.5-2%, 1.8-2%, etc.); the acid is usually hydrochloric acid, especially a dilute acid solution with higher purity, generally with a mass fraction of 1% to 5%.

[0039] Resource utilization of hydrothermal fluids can effectively reduce subsequent water treatment costs. Because a significant portion of the carbon in hydrothermal fluids is converted to biochar in the solid phase during the initial hydrothermal carbonization reaction, the fluids have a low carbon-to-nitrogen ratio, requiring additional carbon source supplementation for direct water treatment. During the hydrothermal carbonization process, organic matter in food waste (such as proteins, carbohydrates, and lignin) undergoes complex decomposition reactions under high temperature, high pressure, and water. Some large organic molecules are broken down into small organic acids, phenols, and other compounds. Under certain conditions, these small compounds can form humic acid through reactions such as condensation and polymerization. For example, phenols produced by lignin decomposition can react with nitrogen-containing compounds, providing the raw materials for humic acid formation. Therefore, extracting humic acid using an alkaline-thermal reaction followed by a catalyst after the hydrothermal reaction improves resource utilization and reduces subsequent water treatment costs.

[0040] In some embodiments, the desalination and nitrogen removal uses electrodialysis technology, and industrial sodium chloride and industrial potassium chloride are recovered by applying a direct current electric field.

[0041] In some embodiments, when performing electrodialysis denitrification and desalination, the current density of the DC electric field is 10-30 mA / cm 2 The single pair voltage is 1.5~3V, the reaction time is 60~150 min, the flow rate on the membrane surface is 1-3cm / s; 2-4 stages of electrodialysis are connected in series. Among them, the current density can be 10mA / cm 2 , 15mA / cm 2 , 20mA / cm 2 , 25mA / cm 2 、30mA / cm 2 Or other current densities, or a range of these point values, such as 15-25 mA / cm 2 , 10-20mA / cm 2 , 20-30mA / cm 2 etc., which are not listed here one by one; the voltage can be 1.5V, 2V, 2.5V, 3V, or other voltage values, or a voltage range composed of these point values, such as 2-3V, 1.5-2.5V, etc.; the reaction time can be 60min, 80min, 100min, 120min, 150min, or other time or range composed of these time point values, such as 60-120min, 80-150min, 80-120min, etc.; the flow rate on the membrane surface can be 1cm / s, 1.5cm / s, 2cm / s, 2.5cm / s, 3cm / s, or other flow rates or ranges composed of these flow rates, such as 1.5-2.5cm / s, 2-3cm / s, 1-2cm / s, etc., which are not listed here one by one.

[0042] After the hydrothermal residual liquid is salted and then fed into the water treatment process, it can fully utilize the liquid product as a resource and reduce subsequent water treatment costs. The hydrothermal residual liquid is desalinated through electrodialysis, using cation exchange membranes and anion exchange membranes. The cation exchange membrane only allows the passage of cations, while the anion exchange membrane only allows the passage of anions. For example, when the hydrothermal residual liquid enters the desalination chamber of the electrodialysis unit, sodium ions, migrating toward the cathode, can smoothly pass through the cation exchange membrane into the adjacent concentrating chamber. Chloride ions, migrating toward the anode, can pass through the anion exchange membrane into the adjacent concentrating chamber. This directional migration of ions gradually reduces the salt concentration in the desalination chamber, while the sodium and chloride ion concentrations in the concentrating chamber increase, resulting in the concentration of sodium chloride in the concentrating chamber.

[0043] In practice, because the hydrothermal residual solution contains a variety of salts, primarily sodium chloride and potassium chloride, and the migration rates of sodium and potassium ions are different, with sodium ions migrating faster than potassium ions, the separation and recovery of sodium chloride and potassium chloride can be improved by adjusting the current density, voltage, and liquid flow rate of the electrodialysis unit or by using a multi-stage electrodialysis system in series. The multi-stage series electrodialysis desalination system installs intermediate storage tanks between each stage of the electrodialysis unit to detect and analyze the intermediate products. The operating parameters of subsequent electrodialysis, such as current density and flow rate, are adjusted based on changes in the concentrations of sodium and chloride ions to achieve better separation results.

[0044] In some embodiments, after the alkaline thermal reaction is completed, waste heat is recovered through a heat exchanger, which can effectively realize energy recovery and avoid energy waste.

[0045] In some embodiments, the temperature during the three-phase separation and fractionation treatment is 40-45°C, such as 40°C, 42°C, 45°C or other temperatures and their respective temperature ranges.

[0046] After the above treatment, the remaining waste liquid is treated as sewage.

[0047] Secondly, the application of the treatment method in environmental engineering, the treatment and reuse of biomass such as kitchen waste, livestock and poultry manure and straw, and garden waste, and energy engineering is provided.

[0048] When this treatment method is applied to the treatment and reuse of biomass such as kitchen waste, livestock and poultry manure, straw, and garden waste, there is no need for initial solid-liquid separation or three-phase separation for oil extraction, and direct crushing and pulping for hydrothermal carbonization can be performed. The reaction conditions for hydrothermal carbonization of biomass containing a high proportion of refractory organic matter, such as straw and garden waste, are set at the higher end of the range.

[0049] The present invention adopts different process sections to treat restaurant kitchen waste in a graded and quality-based manner, thereby improving the resource utilization of restaurant kitchen waste and the energy conversion efficiency; rationally planning the connection sequence of process sections, reducing the impact of material component fluctuations on process parameter design; and recovering the effective components in the hydrothermal liquid and the hydrothermal residual liquid, making subsequent sewage treatment more targeted, reducing treatment costs, and avoiding the waste of available components.

[0050] If specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in the field or the product instructions were used. Reagents or instruments used without manufacturer's indication are commercially available conventional products, and the reagent amounts used are the amounts of the active ingredients.

[0051] It is worth noting that the first, second, third, fourth and fifth levels, the first and second, the first, second and third times, etc., the first, second and third times, etc. involved in the present invention are merely names for distinction, have no substantive meaning, and do not represent level priority and implementation order, etc.

[0052] The present invention is described below with reference to specific examples. It should be noted that these examples are merely illustrative and do not limit the present invention in any way. Example 1

[0053] This embodiment provides a multi-stage resource processing method for kitchen waste, the process is as follows Figure 1 As shown, the following steps are included.

[0054] Step 1: First, the food waste is dumped into a temporary storage silo, where gravity allows for a simple, initial solid-liquid separation, yielding a first solid phase and a layered leachate. The separated solid phase (first solid phase) is conveyed to a sieve, where a rotating spherical structure breaks down the solid waste, effectively removing heavy inorganic components such as stone, glass, and ceramic. After the sieve, the solid waste passes through an electromagnetic self-unloading iron remover to remove ferrous metal debris. While recalcitrant organic solid components such as fruit and vegetable fibers, paper towels, chopsticks, and plastic bags are retained, providing a relatively pure organic material base for subsequent processing.

[0055] Step 2: The pre-treated and impurity-removed food waste is fed into an extrusion and shearing shredder. The shredder's powerful squeezing and shearing forces crush the organic solids in the food waste to less than 5-10 mm and initially mix them evenly. The crushed organic solids in the food waste are then mixed with the lower layer of the leachate to a moisture content of approximately 70%-80%. The mixed material is then conveyed to a pulper. High-speed rotating blades within the pulper thoroughly agitate and grind the material, creating a uniform and fine slurry. This separates light, fine residues, such as insoluble organic matter and light materials, from fruit and vegetable fibers, wood, paper, and plastic. The resulting slurry is then conveyed to a hydrocyclone desander. Centrifugal force in the hydrocyclone pulls heavy residues, such as inorganic sand, toward the tank walls and out the bottom, effectively removing these heavy residues and producing a relatively pure organic slurry. The residue rate (as a percentage of the total slurry mass) is 5.8%.

[0056] Step 3: After removing heavy residues such as inorganic sand, the slurry is mixed with the leachate supernatant and heated to 45°C using a heating device. The heated slurry is then fed into a three-phase separation and fractionation process, producing an upper oil layer, an intermediate slurry layer (referred to herein as the second liquid phase, with a lower solids content), and a lower slurry layer (referred to herein as the second solid phase, with a higher solids content). The separated oil is extracted through a dedicated collection pipeline and, due to its high energy value, is recycled as biodiesel (primary resource utilization). The second liquid phase components are then transferred to a saccharification tank, where an appropriate amount of saccharifying enzyme (200,000 U per ton of second liquid phase) is added. Saccharification proceeds at a temperature of 55°C and a pH of 5. The saccharified liquid phase is then fed into a hydrolysis and acidification system, where microbial activity completes the hydrolysis and acidification reaction, and lactic acid is extracted using a membrane separation process. The hydrolysis and acidification wastewater after lactic acid extraction is mixed with the light fine slag and the second solid phase obtained from the three-phase separation and fractionation process. The mixture is then transported to a hydrothermal carbonization tubular reactor. Medium-pressure pipelines are connected in series and parallel. Within the reactor, the mixture is heated to 225°C at a heating rate of 2.5°C / min for hydrothermal carbonization. The pressure within the tubular reactor is maintained at 2.8 MPa for 2 hours. After the hydrothermal carbonization reaction, the temperature in the discharge buffer tank is lowered to approximately 195-200°C. Sodium hydroxide solution (1.5% by mass) is added and allowed to react for one hour. A heat exchanger is then used to recover waste heat, which is then used for three-phase separation and fractionation, saving energy and reducing costs. The recovered waste heat undergoes a second solid-liquid separation to produce a biochar product and a hydrothermal fluid. Acid is added to the hydrothermal fluid to separate and precipitate humic acid from other substances. A third solid-liquid separation is then performed to produce humic acid and a hydrothermal residual fluid.

[0057] Step 4: The hydrothermal residual liquid is transported to the electrodialysis device and desalination and nitrogen removal are performed using electrodialysis technology. During the electrodialysis process, a DC electric field (current density of 25 mA / cm 2, single-pair voltage of 1.5V, and liquid flow rate of 2cm / s), causing sodium and potassium ions in the solution to migrate toward the cathode, while chloride and nitrate ions migrate toward the anode. Electrodialysis units utilize cation exchange membranes and anion exchange membranes. The cation exchange membrane allows only cations to pass through, while the anion exchange membrane allows only anions to pass through. For example, when the hydrothermal residual solution enters the dilute water compartment of the electrodialysis unit, sodium ions migrate toward the cathode and can smoothly pass through the cation exchange membrane into the adjacent concentrating compartment. Chloride ions, on the other hand, migrate toward the anode and can pass through the anion exchange membrane into the adjacent concentrating compartment. This directional migration of ions gradually decreases the salt concentration in the dilute water compartment, while the sodium and chloride ion concentrations in the concentrating compartment increase, resulting in the enrichment of sodium chloride in the concentrating compartment. Due to the different migration rates of sodium and potassium ions (sodium ions migrate faster than potassium ions), sodium chloride and potassium chloride can be separated and recovered by adjusting the current density, single-pair voltage, and liquid flow rate of the electrodialysis unit, using a three-stage electrodialysis system in series. An intermediate storage tank is set between each level of electrodialysis equipment to detect and analyze the intermediate products, and the operating parameters are adjusted according to the changes in the concentration of sodium ions and chloride ions to achieve better separation effects.

[0058] Electrodialysis technology is a technology well known in the art. In this embodiment, only electrodialysis technology is used to recover sodium chloride and potassium chloride, and no improvement is made to the electrodialysis technology, so no further explanation is given here.

[0059] The remaining waste liquid after electrodialysis treatment is transported to the sewage treatment system and treated according to conventional sewage treatment processes so that it meets the emission standards before being discharged.

[0060] Through the operation process of the above embodiment, the resource utilization of all components of food waste can be effectively achieved, and the oils, sugars, solid organic matter, etc. in the food waste can be converted into valuable products such as biodiesel, lactic acid, biochar, humic acid, etc. At the same time, the humic acid and waste salt in the hydrothermal fluid are recycled and reused, which reduces the pollution of food waste to the environment, improves the recycling rate of resources, and has significant economic and environmental benefits.

[0061] The multi-stage resource treatment method for food waste provided in this embodiment can effectively solve the problem of low biomass energy conversion efficiency, especially improve the efficiency of the food waste treatment industry and the energy utilization rate of food waste, reduce the operating costs of food waste resource projects, improve production efficiency, and help promote the development of food waste and biomass energy industries. Secondly, the effective components in food waste can be more accurately graded and differentiated, retaining the carbon elements of fruit and vegetable fibers, plastics, paper, wooden chopsticks, etc. in food waste, reducing product calorific value losses, reducing residue rates and sewage treatment difficulties. Grading and differentiation can achieve resource utilization of food waste and diversify products, meet the current social needs for environmental protection and carbon reduction, have broad market prospects, and can be applied to environmental engineering, treatment and reuse of organic waste and biomass, energy engineering and other application fields. Comparative Example 1

[0062] This comparative example provides a method for treating kitchen waste, which is basically the same as Example 1, except that in the bag breaking and impurity removal and crushing and pulping steps, the separated organic impurities such as fruit and vegetable fibers, plastics, wooden chopsticks, and paper are transported out for disposal as residues and do not enter the hydrothermal carbonization step. Comparative Example 2

[0063] This comparative example provides a method for treating kitchen waste, which is basically the same as Example 1, except that the second liquid phase obtained by three-phase separation is directly subjected to hydrothermal carbonization treatment to obtain a biochar product, that is, there is no saccharification and hydrolysis acidification step to prepare and extract lactic acid. Comparative Example 3

[0064] This comparative example provides a method for treating kitchen waste, which is basically the same as Example 1, except that after hydrothermal carbonization and recovery of the biochar product, water treatment is directly performed. That is, in Comparative Example 3, the hydrothermal liquid is not subjected to alkaline thermal catalysis and acid extraction of humic acid and electrodialysis to recover salt, and biochar is only separated from the solid and liquid after hydrothermal carbonization.

[0065] Test Example 1 Calorific value of biochar

[0066] Test objects: Biochar obtained by the treatment methods of Example 1 and Comparative Example 1, samples were sent for testing.

[0067] Test items and methods:

[0068] Elemental analysis: "Methods for elemental analysis of coal" (GB / T476-2001);

[0069] Industrial analysis: in accordance with "Industrial Analysis Methods of Coal" (GB / T212-2008);

[0070] High calorific value and low calorific value: "Determination of calorific value of coal" (GB / T213-2008);

[0071] Biochar yield: biochar product mass / raw material mass × 100%.

[0072] Test results: The results are shown in Table 1.

[0073] Table 1

[0074]

[0075] As can be seen from Table 1, in the elemental analysis of Example 1, the C element, fixed carbon content, biochar yield, higher calorific value and lower calorific value of the biochar are significantly higher than those of Comparative Example 1, indicating that in the present application, retaining organic impurities such as fruit and vegetable fibers, plastics, wooden chopsticks, and paper into the hydrothermal carbonization process can significantly increase the calorific value of the biochar. This is because under the subcritical conditions of high temperature and high pressure of hydrothermal carbonization, difficult-to-degrade organic matter such as cellulose, lignin and plastics can also undergo carbonization reactions, contributing to the calorific value of the biochar, reducing the generation of residues and the cost of external transportation and disposal.

[0076] Test Example 2 Yield of hydrolysis acidification and hydrothermal carbonization products

[0077] Test objects: The yield and calorific value of biochar and the yield and purity of lactic acid in the hydrothermal carbonization and hydrolysis acid processes in Example 1 and Comparative Example 2 were tested, and the COD of the hydrothermal fluid was tested.

[0078] Test items and methods:

[0079] Calorific value and yield of biochar: The calorific value test standard is "Method for Determination of Calorific Value of Coal" (GB / T213-2008); the biochar yield is calculated as: biochar product mass / raw material mass × 100%;

[0080] Lactic acid yield and purity: lactic acid product mass / raw material mass × 100%; measured using the enzyme electrode method and biosensor analyzer M-100;

[0081] COD of hydrothermal carbonization liquid: the detection method standard is GB11914-89.

[0082] Test results: See Table 2.

[0083] Table 2

[0084]

[0085] Table 2 shows that although Comparative Example 2 lacks hydrolysis and acidification to extract lactic acid, the entire slurry after three-phase separation undergoes hydrothermal carbonization. The yield and calorific value of the biochar product are still slightly lower than those of Example 1, while the COD value of the hydrothermal liquid is higher than that of Example 1. This indicates that under the same reaction conditions, more readily degradable organic matter reacts and is converted into the liquid product. In contrast, Example 1 produces more high-quality biochar and a smaller amount of lactic acid.

[0086] Experimental Example 3 Effects of Electrodialysis Desalination and Nitrogen Removal and Humic Acid Extraction and Recovery on Water Quality

[0087] Test subjects: Example 1 and Comparative Example 3 were finally subjected to water quality analysis of wastewater treatment.

[0088] Test items and methods:

[0089] pH value: pH meter;

[0090] Conductivity: Conductivity benchtop meter, model: Orion Star A212 Star A210;

[0091] Total dissolved solids (TDS): Gravimetric method. A certain volume of water sample is dried at 103-105°C to a constant weight, and the TDS is calculated by weighing the remaining solids. The calculation formula is:

[0092]

[0093] Where m1 is the mass of the evaporating dish, m2 is the total mass of the evaporating dish and the dried solid, and V is the volume of the water sample;

[0094] Chemical oxygen demand (CODcr): The detection method standard is GB11914-89;

[0095] Biochemical oxygen demand (BOD5): The detection method standard is HJ505-2009;

[0096] Ammonia nitrogen (NH3-N): The detection method standard is HJ537-2009;

[0097] Total nitrogen (TN): The detection method standard is HJ636-2012;

[0098] Volatile fatty acids (VFAs): The detection method standard is Q / YZJ10-03-02-2000.

[0099] Test results: The test results are shown in Table 3.

[0100] Table 3

[0101]

[0102] As can be seen from Table 3, after the hydrothermal residual liquid is treated with humic acid and electrodialysis for desalination and nitrogen removal, the water quality indicators such as conductivity and TDS are significantly improved, the difficulty of water treatment is reduced, and it helps to reduce the subsequent sewage treatment costs while recycling resources.

[0103] In summary, the present invention can effectively reduce the residue rate of the pulp by first separating inorganic recombinant graded iron metal impurities such as stones, glass, and ceramics, and then pulping them; retaining organic solid phase components such as fruit and vegetable fibers, paper towels, wooden chopsticks, and plastics can increase the calorific value of biochar; the second liquid phase obtained by three-phase separation and fractionation treatment is first subjected to saccharification treatment to produce lactic acid, which not only improves resource utilization but also makes the control range of process parameters more accurate; the hydrothermal liquid after hydrothermal carbonization treatment is subjected to alkaline heat treatment to extract humic acid and further recover the salt in the hydrothermal residual liquid, and at the same time, while electrodialysis desalination is carried out, ammonia nitrogen is also removed, which not only improves resource utilization but also reduces water treatment costs.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A multi-stage resource treatment method for kitchen waste, characterized in that: include: The garbage is subjected to a solid-liquid separation to obtain a first solid phase, and the first liquid phase is discharged from the bottom as leachate, which is allowed to stand and stratify; Separating and removing inorganic heavy components and iron metal impurities from the first solid phase, retaining organic solid phase components; crushing the organic solid phase components and slurrying them together with the lower layer of the leachate, separating the light fine residue and removing the heavy residue to obtain a slurry, mixing it with the supernatant of the leachate, and subjecting it to three-phase separation and fractionation to extract oil to obtain a second solid phase and a second liquid phase, which are then subjected to multi-stage resource utilization; wherein the organic solid phase components include long fruit and vegetable fibers, paper towels, wooden chopsticks, and plastics, and the inorganic heavy components include stones, glass, and ceramics; The multi-stage resource utilization includes: secondary resource utilization: saccharifying the second liquid phase obtained by the three-phase separation and fractionation, and then performing hydrolysis and acidification treatment, and extracting lactic acid from the fermentation liquid through membrane separation; The multi-stage resource utilization also includes: tertiary resource utilization: mixing the waste liquid after the hydrolysis and acidification treatment with the second solid phase obtained by the three-phase separation and fractionation treatment and the light fine slag, performing hydrothermal carbonization treatment, and obtaining a biochar product and hydrothermal liquid through the first solid-liquid separation; The temperature of the hydrothermal carbonization treatment is 220-260°C.

2. The processing method according to claim 1, characterized in that: During the saccharification treatment, 100,000-300,000 U / ton of saccharifying enzyme is added based on the weight of the second liquid phase; the treatment temperature is 40-60° C., and the pH is 4-6.

3. The processing method according to claim 2, characterized in that: The light fine residue includes insoluble organic light matter in long fiber of fruits and vegetables, plastic, wooden chopsticks and paper.

4. The processing method according to claim 3, characterized in that: The multi-stage resource utilization also includes: fourth-stage resource utilization: the hydrothermal carbonization treatment is followed by alkaline heat treatment to extract humic acid, and acid is added to precipitate the humic acid, and the second solid-liquid separation is performed to obtain humic acid and hydrothermal residual liquid.

5. The processing method according to claim 4, characterized in that: The temperature of the alkali heat treatment is 150-200°C, and the reaction time is 1-2h; The alkali is at least one of sodium hydroxide or potassium hydroxide, and the addition amount thereof is 1.5% to 2.5%.

6. The processing method according to claim 5, characterized in that: The multi-stage resource utilization also includes: fifth-stage resource utilization: desalting and denitrifying the hydrothermal residual liquid, and recovering salt.

7. The processing method according to claim 6, characterized in that: The desalination and nitrogen removal adopts electrodialysis technology and recovers industrial sodium chloride and industrial potassium chloride by applying a direct current electric field; During electrodialysis, the current density of the DC electric field is 10-30 mA / cm 2 , single pair voltage is 1.5~3V, reaction time is 60~150 min, and flow rate on the membrane surface is 1-3cm / s; When performing electrodialysis, 2-4 stages of electrodialysis are used in series.

8. The processing method according to claim 1, characterized in that: The hydrothermal carbonization reaction pressure is 2.5-4 MPa, the heating rate is 1-3°C / min, and the residence time is 2 hours.

9. The processing method according to claim 8, characterized in that: The particle size of the material entering the three-phase separation is controlled below 5mm.

10. Application of the treatment method according to any one of claims 1 to 9 in environmental engineering or energy engineering.

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