Multi-stage resourceful treatment method for kitchen waste and application of multi-stage resourceful treatment method

Abstract

The invention provides a multistage resourceful treatment method for kitchen waste, which comprises the following steps: performing primary solid-liquid separation on the kitchen waste to obtain a first solid phase and leachate discharged from the bottom; inorganic heavy components and iron metal impurities are separated and removed from the first solid phase, and organic solid phase components are reserved; crushing the organic solid-phase component, pulping together with subnatant obtained by standing and layering the leachate, separating light fine slag, removing heavy slag such as inorganic sand and the like to obtain slurry, mixing the slurry with supernate of the leachate, and performing three-phase separation quality-divided treatment and multi-stage resource utilization; wherein the organic solid-phase components comprise fruit and vegetable long fibers, tissues, wooden chopsticks and plastics, and the inorganic heavy components comprise stones, glass and ceramics. According to the multi-stage resourceful treatment method for the kitchen waste, the residue rate is low, the quality of a biochar product is easy to control, the calorific value of biochar is high, and due to multi-stage resourceful utilization, the resource utilization degree is improved, and the wastewater treatment cost is reduced.

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] Restaurant waste mainly refers to organic waste generated by catering enterprises and food production, sales, processing, residents' lives, consumption and other links. In addition to water, its components are mainly carbohydrates, fats, proteins, cellulose and a small amount of inorganic salts and lignin. Depending on the degree of refinement of classification, it may be mixed with inorganic impurities such as mud, glass, ceramics, and metals. The water content of restaurant waste is usually around 70%-90%, and the high water content affects its treatment method to a certain extent. Restaurant waste has a high water content and is easy to rot and deteriorate, but in terms of composition, restaurant waste contains a large amount of organic matter, such as carbohydrates, proteins, fats, etc. The rich organic matter content makes it have considerable resource utilization potential, high biodegradability and energy potential, and is a good biomass energy source.

[0003] In order to reduce the harm of food waste, it needs to be properly treated. Food waste treatment technologies mainly include traditional treatment technologies and resource-based treatment technologies. Traditional treatment technologies mainly include landfill and incineration. Landfill treatment not only occupies a large amount of valuable land resources, but also the leachate of garbage can easily penetrate into the ground. Due to limited collection methods, a large amount of landfill gas is directly discharged in the open air, which causes a series of environmental pollution problems. In incineration treatment, due to the high water content of food waste itself, a large amount of energy is consumed in the water drying and evaporation stage, which will also affect the efficiency of incineration power generation of other garbage components. In addition, whether it is landfill or incineration, these two traditional treatment methods have failed to effectively utilize food waste as a resource, which runs counter to the requirements of energy conservation, emission reduction, carbon reduction and the development of circular economy. Resource-based treatment technologies mainly include anaerobic fermentation, aerobic composting, feed treatment, thermal dehydration and drying, etc. Anaerobic fermentation refers to the use of anaerobic bacteria to degrade organic matter in food waste into biogas and inorganic matter. The main outputs are methane and biogas residue and biogas liquid. The biogas residue and biogas liquid are subsequently treated and then used for land. Aerobic composting uses aerobic bacteria to oxidize and decompose food waste, and finally produces organic compound fertilizer and soil conditioner. However, aerobic composting has a long fermentation cycle and occupies a large area. Because the food waste has a high moisture content, a large amount of auxiliary materials need to be added for moisture conditioning. The high oil and salt content in the food waste will also produce sewage and odor pollution, affecting the quality of fertilizer. The fermentation cycle of the aerobic composting machine for on-site treatment is short, but the fermentation is not thorough and cannot be directly used as fertilizer. There are two main ways to make feed: insect breeding or direct drying. Among them, the insect breeding feed technology has high requirements for the breeding environment and breeding automation equipment. The organic matter does not react completely after passing through the stomach, and there is a risk of safe application. Direct drying feed requires a lot of heat energy and is rarely used because of the safety risk of homologous pollution. Thermal dehydration and drying technology mainly decomposes the macromolecular organic matter in food waste into small molecular organic matter through high temperature and high pressure thermal hydrolysis reaction. In this process, the moisture in the food waste is released, the viscosity of the material decreases, and the difficulty of subsequent mechanical dehydration is reduced, which can achieve rapid dehydration and drying. At the same time, the thermal hydrolysis reaction can also kill bacteria and pathogens in the food waste and achieve harmless treatment. However, the fundamental purpose of thermal dehydration and drying is to reduce and dispose of it, and it does not achieve the resource utilization of organic matter, product desalination, and stabilization of heavy metals in solid and liquid phase products. It is only suitable for small-scale food waste treatment and easy to coordinate with waste incineration plants. It is not suitable for large-scale centralized treatment and disposal of food waste. How to reasonably utilize the characteristics of high organic matter, high moisture, and high organic matter in food waste, fully explore the resource utilization path of food waste, and maximize the energy potential of food waste as biomass, is more in line with the strategic development requirements of energy conservation, environmental protection and new energy encouraged by the country, and has more significant environmental value-added benefits.

[0004] The existing methods of energy utilization of food waste include anaerobic fermentation to produce biogas and oil extraction of biodiesel, mainly through hydrothermal carbonization, which is to hydrothermally react the organic pulp of food waste after fine separation and impurity removal under high temperature and high pressure conditions, and then obtain biochar as an energy conversion product through solid-liquid separation, and the hydrothermal liquid enters the sewage treatment system for treatment. In addition to removing inorganic impurities and metals such as glass, ceramics, sand and gravel, the existing food waste pretreatment technology usually sets up a fine separation process section to remove long fibers of fruits and vegetables, plastics, wooden chopsticks, paper, etc. The residue rate is generally 15%~25%, and these difficult-to-degrade organic impurities have the potential to be converted into biochar at a high hydrothermal reaction intensity, and contribute a high calorific value. The pretreatment fine separation not only leads to high disposal costs due to the high residue rate, but also leads to waste of resources. In addition, there are still some problems with the existing food waste hydrothermal carbonization technology. First of all, the hydrothermal process parameters mainly include reaction temperature, heating rate, reaction time, working pressure, pH value, solid-liquid ratio, etc. Different parameter settings and material characteristics determine the energy consumption of the hydrothermal reaction and the degree of gasification, liquefaction and carbonization of the product. The goal of the hydrothermal carbonization reaction of food waste is to convert organic components into solid biochar products as much as possible, and avoid excessive organic components from being converted to liquid or even gas phases due to excessive temperature and pressure and too long time. The complexity of the composition of food waste determines the uncertainty of the setting of hydrothermal carbonization process parameters, which is also one of the main reasons why the hydrothermal carbonization process was initially applied to sludge rather than food waste. Taking temperature conditions as an example, the temperature range of hydrothermal carbonization reaction is mainly divided into three types: Generally speaking, the hydrothermal carbonization reaction can be carried out in the temperature range of low temperature (170~220℃), medium temperature (220~260℃) or high temperature (>260℃). For example, the reaction temperature conditions required for the components of carbohydrates and sugars that are easy to decompose are lower, the reaction temperature of proteins and fats is higher, and the hydrothermal intensity required to prepare biochar with hemicellulose, cellulose and lignin as raw materials is more intense. 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, which makes the control of hydrothermal carbonization process parameters a key difficulty that limits 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 processing costs and reduces the overall benefits of the project. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems in the prior art to a certain extent. To this end, one object of the present invention is to propose a multi-stage resource treatment method for food waste, comprising: performing a solid-liquid separation on the food waste to obtain a first solid phase, discharging the first liquid phase from the bottom as a leachate, and standing to separate; separating and removing inorganic heavy components and iron metal impurities from the first solid phase, and retaining organic solid phase components; crushing the organic solid phase components and pulping them together with the lower layer of the leachate, separating light fine slag and removing heavy slag materials such as inorganic sand to obtain slurry, mixing with the supernatant of the leachate, and extracting oil by three-phase separation and quality treatment to obtain a second solid phase and a second liquid phase, and then 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, ceramics, etc. Among them, crushing and pulping, the organic solid phase components are roughly crushed by an extrusion shearing crusher, and then mixed with the lower layer liquid of the leachate and sent to a pulping machine for pulping. After pulping, it is sent to a hydraulic cyclone desanding tank to remove heavy slag 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 product calorific value. In the pretreatment stage, only inorganic impurities such as sandstone, glass, ceramics, and scrap metal need to be removed. Impurities such as plastics, wooden chopsticks, and paper towels can be crushed and pulped together. Those that cannot be crushed are separated in the form of 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 less than 8%. On the one hand, inorganic impurities are removed, and at the same time, components such as long fiber of fruits and vegetables, plastics, wooden chopsticks, and paper towels that contribute to 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, and then hydrolyzing and acidifying it to produce a lactic acid product and extracting lactic acid by membrane separation.

[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: 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 residue, and performing hydrothermal carbonization treatment, and obtaining a biochar product and hydrothermal liquid after the first solid-liquid separation. The light fine residue includes light organic matter that is difficult to degrade in long fiber of fruits and vegetables, plastics, wooden chopsticks, paper, etc.

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

[0011] In some embodiments, the multi-stage resource utilization also 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 humic acid, and humic acid and hydrothermal residual liquid are obtained through a second solid-liquid separation.

[0012] Preferably, the temperature of the alkaline 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 the 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, flow rate on membrane surface is 1-3cm / s; Preferably, when performing electrodialysis, 2-4 stages of electrodialysis are used in series.

[0017] In some embodiments, the alkaline heat treatment is performed immediately after the hydrothermal carbonization treatment, and the first solid-liquid separation and the second solid-liquid separation are performed after waste heat recovery.

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

[0019] In some embodiments, the organic solid phase components are crushed to 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] The second aspect provides 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.

[0021] The present invention has at least the following technical effects: 1. Low residue rate: This technical solution only needs to remove sand, stone, 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%~25% to less than 8%.

[0022] 2. High calorific value of products: This technical solution can retain calorific value components to the maximum extent. On the one hand, inorganic impurities are removed, and components such as fruit and vegetable fibers, plastics, wooden chopsticks, and paper towels that contribute to calorific value in the carbonization process are retained; on the other hand, the liquid phase of the three-phase separation and fractionation treatment is saccharified, hydrolyzed, and acidified to produce lactic acid, and most of the easily soluble and degradable carbohydrates such as starch and sugar substances are prioritized for resource utilization. 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, the difficulty of quality control of biochar products is reduced, and the calorific value of biochar is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces 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 creative work.

[0024] Figure 1 This is one of the flow charts of the multi-level resource processing method for garbage provided by the present invention. DETAILED DESCRIPTION

[0025] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making any creative work shall fall within the scope of protection of the present invention.

[0026] In a first aspect, the present invention proposes a multi-stage resource treatment method for kitchen waste, comprising the following steps.

[0027] (1) Rough 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, and ceramics and iron metal debris are separated and removed from the first solid phase, and food residues are separated, while 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 the plastics, wooden chopsticks, paper, and other refractory organic light matter and the fine residue before entering the three-phase separation and fractionation treatment directly enters the hydrothermal carbonization to participate in the hydrothermal reaction.

[0028] The first separation is in a temporary storage bin for food waste, and a simple solid-liquid separation is achieved. In some embodiments, the inorganic heavy components are removed by breaking the bag through a star screen. In some embodiments, the iron metal impurities are removed by an electromagnetic self-unloading iron remover.

[0029] (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 then sent to a pulping machine for pulping. After pulping, the pulping is sent to a hydraulic cyclone desanding tank to remove heavy slag such as inorganic sand.

[0030] 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.

[0031] (3) Three-phase separation and quality separation: After the slurry from which heavy slag such as inorganic sand is removed is mixed with the supernatant of the leachate, a three-phase separation and quality separation is performed. After the three-phase separation and quality separation, an upper surface layer of grease, an intermediate layer of slurry (referred to as the second liquid phase in the present invention, having a lower solid content) and a lower layer of slurry (referred to as the second solid phase in the present invention, having a higher solid content) are obtained.

[0032] (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. Degradable organic matter such as carbohydrates and sugars are converted into organic acids such as lactic acid. Products such as lactic acid are extracted through membrane separation (secondary resource utilization); the residual liquid after lactic acid extraction is mixed with the second solid phase and the light fine residue and heated and then hydrothermally carbonized. In the hydrothermal carbonization process, protein, fat, cellulose, plastic, lignin, etc. are removed. And some intermediate products produced by hydrolysis and acidification are polymerized and condensed to generate biochar, and an alkali catalyst is added to the mixed slurry after the reaction to utilize the residual heat of the hydrothermal reaction to cause an alkali thermal reaction to provide a basis for the subsequent extraction of humic acid from the liquid phase product, and a biochar product (tertiary resource utilization) and hydrothermal liquid are obtained through a second solid-liquid separation; acid is added to the hydrothermal liquid, and a humic acid product (quaternary resource utilization) and hydrothermal residual liquid are obtained through a third solid-liquid separation; the hydrothermal residual liquid is desalted and denitrified, and the salt is recovered (fifth-level resource utilization).

[0033] In some embodiments, during the saccharification treatment, 100,000-300,000 U / ton of saccharifying enzyme is added according to 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 of these temperature values, 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 of these pH values, such as 4-5.5, 4.5-5.5, 5-6, 4.5-6, etc.

[0034] The liquid phase of the three-phase separation and quality 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 setting range of process parameters is relatively concentrated, the difficulty of quality control of biochar products is reduced, and the calorific value of biochar is high.

[0035] In some embodiments, the temperature of the hydrothermal carbonization treatment is 220-260°C, and a tube-in-tube reaction device and a medium-pressure pipeline are used, which are connected in series / parallel, with a reaction pressure of 2.5-4MPa, a heating rate of 1-3°C / min, and a residence time of 2h. Among them, the temperature of the hydrothermal carbonization treatment can be 220°C, 230°C, 240°C, 250°C, 260°C, or other temperatures or ranges composed 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 composition can be 2.5-3.5MPa, 3-4MPa, 2.5-3MPa, etc. The heating rate can be 1℃ / min, 1.2℃ / min, 1.5℃ / min, 1.8℃ / min, 2℃ / min, 2.5℃ / min, 3℃ / min, or other rates or ranges of these rate values, such as 1.2-2.5℃ / min, 2-3℃ / min, 1.5-2.5℃ / min, 1-2℃ / min, etc.

[0036] In some embodiments, the temperature of the alkali thermal reaction is 150-200°C, and the reaction time is 1-2h. The reaction temperature can be 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, or other temperatures or ranges of these temperature values, such as 150-180°C, 160-200°C, 180-200°C, etc. The reaction time can be 1h, 1.2h, 1.5h, 1.8h, 2h, or other times or ranges of these time values, such as 1-1.5h, 1.5-2h, 1.2-1.8h, etc.

[0037] 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%.

[0038] The resource utilization of hydrothermal fluid can effectively reduce the subsequent water treatment costs. Due to the early hydrothermal carbonization reaction, a considerable part of the carbon elements in the hydrothermal fluid are converted into biochar and enter the solid phase product. The hydrothermal fluid has a low carbon-nitrogen ratio, and direct water treatment requires additional carbon source supplementation. During the hydrothermal carbonization process, the organic matter in the kitchen waste (such as protein, carbohydrates, lignin, etc.) undergoes complex decomposition reactions under high temperature, high pressure and water. Among them, some macromolecular organic matter is decomposed into small molecular organic acids, phenols and other compounds. Under certain conditions, these small molecular compounds can form humic acid through condensation, polymerization and other reactions. For example, phenolic substances produced by the decomposition of lignin can react with nitrogen-containing compounds to provide raw materials for the formation of humic acid. Therefore, after the hydrothermal reaction, a catalyst is added to extract humic acid under alkaline heat reaction to improve the degree of resource utilization and reduce the subsequent water treatment costs.

[0039] In some embodiments, 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.

[0040] In some embodiments, when performing electrodialysis denitrification and desalination, 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, flow rate on 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 / cm2 Or other current densities, or a range of these point values, such as 15-25mA / cm 2 , 10-20mA / cm 2 , 20-30mA / cm 2 etc., which are not listed one by one here; 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 one by one here.

[0041] After the hydrothermal residual liquid is salted, it enters the water treatment link, which can fully realize the resource utilization of liquid products and reduce the subsequent water treatment costs. The hydrothermal residual liquid is desalinated by electrodialysis, and cation exchange membranes and anion exchange membranes are used in the electrodialysis device. The cation exchange membrane only allows cations to pass through, and the anion exchange membrane only allows anions to pass through. Take sodium chloride as an example: when the hydrothermal residual liquid enters the desalination chamber of the electrodialysis device, the sodium ions can smoothly pass through the cation exchange membrane to enter the adjacent concentration chamber during the process of moving to the cathode; while the chloride ions can pass through the anion exchange membrane to enter another adjacent concentration chamber when moving to the anode. In this way, with the directional migration of ions, the salt concentration in the desalination chamber gradually decreases, while the concentration of sodium ions and chloride ions in the concentration chamber continues to increase, so that they are enriched in the concentration chamber to form sodium chloride.

[0042] In fact, since the hydrothermal residual liquid contains a variety of salts, mainly sodium chloride and potassium chloride, the migration rates of sodium ions and potassium ions are different, and the migration rate of sodium ions is higher than that of potassium ions. The separation and recovery of sodium chloride and potassium chloride can be achieved and improved by adjusting the current density, voltage, and liquid flow rate of the electrodialysis device or using multi-stage electrodialysis in series. The multi-stage series electrodialysis desalination system sets intermediate storage tanks between each stage of electrodialysis devices, detects and analyzes the intermediate products, and adjusts the operating parameters of subsequent electrodialysis, such as current density, flow rate, etc., according to the changes in the concentration of sodium ions and chloride ions, to achieve better separation effects.

[0043] 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.

[0044] 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 compositional temperature ranges.

[0045] After the above treatment, the remaining waste liquid is treated as sewage.

[0046] The second aspect provides 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.

[0047] When the 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 to perform the first solid-liquid separation, three-phase separation and oil extraction, and the crushing and pulping can be directly performed for hydrothermal carbonization. The reaction conditions for hydrothermal carbonization of biomass such as straw and garden waste containing a high proportion of refractory organic matter are taken as the higher value within the range.

[0048] The present invention adopts different process sections to grade and treat restaurant kitchen waste according to its quality, thereby improving the resource utilization degree and energy conversion efficiency of restaurant kitchen waste; rationally plans the connection sequence of process sections, and reduces the influence of material component fluctuation on process parameter design; recovers effective components in hydrothermal liquid and hydrothermal residual liquid, thereby making subsequent sewage treatment more targeted, reducing treatment costs, and avoiding waste of available components.

[0049] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased commercially, and the amount of the reagents used is the amount of the active ingredient therein.

[0050] It is worth noting that the first, second, third, fourth and fifth levels, first and second, first, second, third, etc., first, second, third, 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.

[0051] The present invention is described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present invention in any way.

[0052] Example 1 This embodiment provides a multi-level resource treatment method for kitchen waste, the process is as follows Figure 1 As shown, the following steps are included.

[0053] Step 1: First, pour the kitchen waste into the temporary storage silo, and use gravity to simply achieve preliminary solid-liquid separation in the temporary storage silo to obtain the first solid phase and layered leachate. The separated solid phase (first solid phase) is transported to the star screen, which breaks the bags of solid waste through a rotating star structure to effectively remove inorganic heavy components such as stones, glass, and ceramics. The solid waste treated by the star screen continues to be adsorbed by an electromagnetic self-unloading iron remover to remove iron metal debris, while the difficult-to-degrade organic solid components such as fruit and vegetable fibers, paper towels, wooden chopsticks, and plastic bags are retained, providing a relatively pure organic material basis for subsequent treatment.

[0054] Step 2: Put the pre-treated and impurity-removed food waste into an extrusion shearing crusher, which crushes the organic solid phase components in the food waste to less than 5-10 mm through its powerful extrusion and shearing force and preliminarily mixes them evenly. Then, the organic solid phase components in the crushed food waste are mixed with the lower layer of the leachate to a water content of about 70%-80%, and the mixed materials are transported to a pulping machine. The high-speed rotating blades inside the pulping machine fully stir and grind the materials to make them into a uniform and fine slurry. Light fine residues such as insoluble organic light substances in fruit and vegetable fibers, wood blocks, paper, plastics, etc. are separated and the prepared slurry is then sent to a hydrocyclone desanding tank. In the hydrocyclone desanding tank, heavy residues such as inorganic sand are thrown to the tank wall and discharged from the bottom by centrifugal force, thereby achieving effective removal of inorganic sand and heavy residues in the slurry and obtaining a relatively pure organic slurry. The residue rate (percentage of the total mass of the slurry) is 5.8%.

[0055] Step 3: After the slurry from which heavy slag such as inorganic sand is removed is mixed with the supernatant of the leachate, the mixed slurry is heated to 45°C by a heating device. Then, the heated mixed slurry is sent to a three-phase separation and quality treatment equipment for three-phase separation and quality treatment to obtain an upper layer of oil, an intermediate layer of slurry (referred to as the second liquid phase in the present invention, with a lower solid content) and a lower layer of slurry (referred to as the second solid phase in the present invention, with a higher solid content). The separated oil is extracted through a special collection pipeline, and because of its high energy value, it is used as a biodiesel for resource utilization (primary resource utilization). The second liquid phase component is transported to a saccharification tank, and an appropriate amount of saccharifying enzyme is added to the saccharification tank (addition ratio: 200,000 U per ton of the second liquid phase), and a saccharification reaction is carried out under reaction conditions of a temperature of 55°C and a pH value of 5. The liquid phase after saccharification treatment is sent to a hydrolysis and acidification system, in which the hydrolysis and acidification reaction is completed by the action of microorganisms, and lactic acid is extracted by a membrane separation process. The hydrolysis acidification waste liquid after the extraction of lactic acid is mixed with the light fine slag and the second solid phase obtained by the three-phase separation and fractionation treatment, and is transported to the hydrothermal carbonization tube reactor. The medium-pressure pipeline is connected in series / parallel. The mixed material is heated to 225°C at a heating rate of 2.5°C / min in the device for hydrothermal carbonization reaction, and the pressure in the tube reactor is maintained at 2.8MPa for 2h. After the hydrothermal carbonization reaction is completed, the temperature in the discharge buffer tank drops to about 195-200°C, and sodium hydroxide solution (1.5% by mass fraction) is added to react for 1 hour. The heat exchanger is used to recover the waste heat, and the recovered waste heat is used for three-phase separation and fractionation treatment, which can achieve energy saving and help reduce costs. The material after waste heat recovery undergoes a second solid-liquid separation operation to obtain biochar products and hydrothermal liquid; acid is added to the hydrothermal liquid to separate and precipitate humic acid from other substances in the hydrothermal liquid, and humic acid and hydrothermal residual liquid are obtained after the third solid-liquid separation.

[0056] Step 4: The hydrothermal residual liquid is transported to the electrodialysis device, and the electrodialysis technology is used for desalination and nitrogen removal. During the electrodialysis process, a DC electric field (current density of 25 mA / cm 2, single pair voltage is 1.5V, liquid flow rate is 2cm / s), so that the sodium ions and potassium ions in the solution move to the cathode, and the chloride ions and nitrate ions move to the anode. Cation exchange membranes and anion exchange membranes are used in electrodialysis devices. Cation exchange membranes only allow cations to pass through, and anion exchange membranes only allow anions to pass through. Take sodium chloride as an example: when the hydrothermal residual liquid enters the fresh water chamber of the electrodialysis device, in the process of sodium ions moving to the cathode, they can smoothly pass through the cation exchange membrane to enter the adjacent concentration chamber; while chloride ions can pass through the anion exchange membrane to enter another adjacent concentration chamber when they move to the anode. In this way, with the directional migration of ions, the salt concentration in the fresh water chamber gradually decreases, while the concentration of sodium ions and chloride ions in the concentration chamber continues to increase, so that they are enriched in the concentration chamber to form sodium chloride. According to the different migration rates of sodium ions and potassium ions, the migration speed of sodium ions is higher than that of potassium ions. By adjusting the current density, single pair voltage, and liquid flow rate of the electrodialysis device, and adopting a three-stage electrodialysis series method, the separation and recovery of sodium chloride and potassium chloride can be achieved. An intermediate storage tank is set between each stage 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.

[0057] 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.

[0058] 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.

[0059] Through the operation process of the above embodiment, the resource utilization of all components of food waste can be effectively realized, 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., and the humic acid and waste salt in the hydrothermal fluid can be recycled, thereby reducing the pollution of food waste to the environment, improving the recycling rate of resources, and having significant economic and environmental benefits.

[0060] The multi-level resource treatment method for kitchen waste provided in this embodiment can effectively solve the problem of low biomass energy conversion efficiency, especially improve the benefits of the kitchen waste treatment industry and the energy utilization rate of kitchen waste, reduce the operating costs of kitchen waste resource projects, improve production efficiency, and help promote the development of kitchen waste and biomass energy industries. Secondly, the effective components in kitchen waste can be more accurately graded and differentiated, retaining the carbon elements of fruit and vegetable fibers, plastics, paper, wooden chopsticks, etc. in kitchen waste, reducing product calorific value losses, reducing residue rates and sewage treatment difficulties. Grading and differentiation realize the resource utilization of kitchen waste, and the product diversification meets the current social demand for environmental protection and carbon reduction, has broad market prospects, and can be applied to environmental engineering, organic waste and biomass processing and reuse, energy engineering and other application fields.

[0061] Comparative Example 1 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 stages, 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 stage.

[0062] Comparative Example 2 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 for preparing and extracting lactic acid.

[0063] Comparative Example 3 This comparative example provides a method for treating kitchen waste, which is basically the same as Example 1, except that after hydrothermal carbonization treatment 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.

[0064] Test Example 1 Calorific value of biochar Test object: biochar obtained by the treatment methods of Example 1 and Comparative Example 1, samples were sent for testing.

[0065] Test items and methods: Element analysis: "Element analysis method of coal" (GB / T476-2001); Industrial analysis: Based on "Industrial Analysis Methods for Coal" (GB / T212-2008); High calorific value and low calorific value: "Method for determination of calorific value of coal" (GB / T213-2008); Biochar yield: biochar product mass / raw material mass × 100%.

[0066] Test results: The results are shown in Table 1.

[0067] 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 improve 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 and reducing the generation of residues and the cost of external disposal.

[0068] Test Example 2 Yield of Hydrolysis Acidification and Hydrothermal Carbonization Products 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 liquid was tested.

[0069] Test items and methods: Calorific value and yield of biochar: The calorific value test standard is "Method for Determination of Calorific Value of Coal" (GB / T213-2008); The yield of biochar is calculated as follows: biochar product mass / raw material mass × 100%; Lactic acid yield and purity: lactic acid product mass / raw material mass × 100%; measured by enzyme electrode method using biosensor analyzer M-100; COD of hydrothermal carbonization liquid: The detection method standard is GB11914-89.

[0070] Test results: See Table 2.

[0071] As can be seen from Table 2, although Comparative Example 2 did not undergo hydrolysis and acidification to extract lactic acid, the entire slurry after three-phase separation was subjected to hydrothermal carbonization, and the yield and calorific value of its biochar product were still slightly lower than those of Example 1, while the COD value of the hydrothermal liquid was higher than that of Example 1, indicating that under the same reaction conditions, more easily degradable organic matter reacted and converted into liquid products. In contrast, Example 1 can obtain more high-quality biochar and a small amount of lactic acid products.

[0072] Experimental Example 3 Effects of Electrodialysis Desalination and Nitrogen Removal and Humic Acid Extraction and Recovery on Water Quality Test object: Example 1 and Comparative Example 3 were finally subjected to water quality analysis of wastewater treatment.

[0073] Test items and methods: pH value: pH meter; Conductivity: Conductivity benchtop meter, model: Orion Star A212 Star A210; Total dissolved solids (TDS): Gravimetric method. Dry a certain volume of water sample at 103-105°C to constant weight, and calculate TDS by weighing the remaining solids. The calculation formula is: 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; Chemical oxygen demand (CODcr): The detection method standard is GB11914-89; Biochemical oxygen demand (BOD5): The detection method standard is HJ505-2009; Ammonia nitrogen (NH3-N): The detection method standard is HJ537-2009; Total nitrogen (TN): The detection method standard is HJ636-2012; Volatile fatty acids (VFAs): The detection method standard is Q / YZJ10-03-02-2000.

[0074] Test results: The test results are shown in Table 3.

[0075] Table 3

[0076] As can be seen from Table 3, after the hydrothermal residual liquid is desalted and denitrified by humic acid and electrodialysis, 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.

[0077] 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; 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 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 performed, ammonia nitrogen is also removed, which not only improves resource utilization but also reduces water treatment costs.

[0078] 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 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 for stratification; The inorganic heavy components and iron metal impurities are separated and removed from the first solid phase, and the organic solid phase components are retained; the organic solid phase components are crushed and pulped together with the lower layer of the leachate, the light fine residue is separated and the heavy residue is removed to obtain a slurry, which is mixed with the supernatant of the leachate, and the second solid phase and the second liquid phase are obtained after three-phase separation and fractionation to extract the oil, and then multi-stage resource utilization is carried out; wherein the organic solid phase components include long fiber of fruits and vegetables, paper towels, wooden chopsticks, and plastics, and the inorganic heavy components include stones, glass, and ceramics.

2. The processing method according to claim 1, characterized in that: The multi-stage resource utilization includes: secondary resource utilization: saccharifying the second liquid phase obtained by the three-phase separation and fractionation, and then hydrolyzing and acidifying it, and extracting lactic acid from the fermentation liquid through membrane separation; 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.

3. The processing method according to claim 2, characterized in that: 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, and performing hydrothermal carbonization treatment to obtain a biochar product and hydrothermal liquid through the first solid-liquid separation; Preferably, the light fine residue includes insoluble organic light matter in long fiber of fruits and vegetables, plastic, wooden chopsticks, and paper; Preferably, the temperature of the hydrothermal carbonization treatment is 220-260°C.

4. The processing method according to claim 3, characterized in that: The multi-stage resource utilization also 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 humic acid, and humic acid and hydrothermal residual liquid are obtained through a second solid-liquid separation; Preferably, the temperature of the alkaline thermal reaction is 150-200°C and the reaction time is 1-2h; Preferably, the alkali is at least one of sodium hydroxide or potassium hydroxide, and the addition amount thereof is 1.5% to 2.5%.

5. The processing method according to claim 4, characterized in that: The multi-stage resource utilization also includes: fifth-stage resource utilization: desalting and denitrifying the hydrothermal residual liquid, and recovering salt; 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; 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, flow rate on membrane surface is 1-3cm / s; Preferably, when performing electrodialysis, 2-4 stages of electrodialysis are used in series.

6. The processing method according to any one of claims 3 to 5, characterized in that: The alkaline heat treatment is immediately performed after the hydrothermal carbonization treatment, and the first solid-liquid separation and the second solid-liquid separation are performed after the waste heat is recovered.

7. The processing method according to any one of claims 3 to 6, 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 2h.

8. The processing method according to any one of claims 3 to 7, characterized in that: The hydrothermal carbonization adopts a tube-in-tube reaction device and a medium-pressure pipeline connected in series or parallel.

9. The processing method according to any one of claims 1 to 8, characterized in that: The organic solid phase components are crushed to less than 5-10 mm; Preferably, the particle size of the material entering the three-phase separation is controlled below 5 mm.

10. Application of the treatment method according to any one of claims 1 to 9 in environmental engineering, treatment and reuse of biomass such as kitchen waste, livestock and poultry manure and straw, garden waste, and energy engineering.

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