Food waste treatment methods, carbon sources and their applications

Abstract

This application relates to the field of waste treatment technology, and particularly to a method for treating kitchen waste, a carbon source, and its application. The kitchen waste treatment method includes the following steps: directional fermentation of kitchen waste in an acidic environment to obtain a fermentation mixture; filtration of the fermentation mixture to obtain a filtrate; and sequential distillation and condensation of the filtrate to collect volatile organic compounds, resulting in a condensate containing volatile fatty acids and low-molecular-weight alcohols. The method in this application involves directional fermentation, resulting in a fermentation mixture rich in volatile organic compounds, including volatile fatty acids (VFAs) such as propionic acid, butyric acid, and acetic acid, and low-molecular-weight alcohols such as propanol and ethanol. Filtration further reduces the nitrogen content and suspended solids value of the filtrate. Distillation causes these small-molecule organic compounds in the filtrate to evaporate, while water evaporates minimally, and the nitrogen content in the filtrate hardly evaporates. The resulting condensate has a high COD value, a high content of small-molecule organic compounds, and an extremely low nitrogen content.

Description

Technical Field

[0001] This application relates to the field of waste treatment technology, and in particular to methods for treating kitchen waste, carbon sources and their applications. Background Technology

[0002] In wastewater treatment and other fields, it is often necessary to add external carbon sources to improve denitrification and effluent quality. These carbon sources need to have high chemical oxygen demand (COD) and low nitrogen content. Common external carbon sources include traditional carbon sources and novel solid and liquid carbon sources. Traditional carbon sources are generally low-molecular-weight organic matter and sugars, such as methanol, ethanol, acetic acid, sodium acetate, glucose, sucrose, fructose, and maltose. Novel liquid carbon sources generally originate from high-concentration organic wastewater containing fats, sugars, proteins, and other organic matter generated during the production and processing of food factories, beverage factories, and agricultural and sideline product processing plants. This type of organic wastewater has low toxicity and high biodegradability. Kitchen waste is characterized by large output and high organic matter content. The products of anaerobic fermentation are mainly easily biodegradable volatile fatty acids (VFAs). Currently, directional fermentation technology is generally used to hydrolyze and acidify the organic matter in kitchen waste, converting it into single components, which are then extracted and concentrated to obtain novel liquid carbon sources.

[0003] Existing targeted fermentation technologies for kitchen waste primarily focus on two directions: lactic acid and ethanol production. Lactic acid production processes include hydrolysis, saccharification, fermentation, and separation / purification. Large organic molecules in kitchen waste are converted into smaller organic molecules that can be utilized by lactic acid bacteria (LAB) through hydrolysis and saccharification. During hydrolysis and saccharification, the accumulation of sugars and acids in the products reduces enzyme activity, leading to a decrease in lactic acid yield. The main methods for separating and extracting lactic acid from fermentation broth include crystallization separation, esterification hydrolysis, extraction, molecular distillation, membrane separation, adsorption, and chromatographic separation. However, each method has its advantages and disadvantages, such as cost, yield, and time constraints. The limitations of extraction techniques restrict the application of kitchen waste lactic acid fermentation. Especially during distillation, the high boiling point of lactic acid causes water to be distilled out, diluting the proportion of organic matter. The resulting novel liquid carbon source often has a low COD value and a high nitrogen content.

[0004] Ethanol production typically involves pretreatment, hydrolysis, fermentation, distillation, and dehydration. Pretreatment breaks down the structure of polysaccharides like starch and cellulose. Hydrolysis converts large polysaccharides into smaller reducing sugars, which are then fermented by microorganisms to produce crude ethanol. Finally, distillation and dehydration yield high-purity ethanol. However, kitchen waste undergoes acidification during storage and transportation, breaking down polysaccharides like starch and cellulose into small-molecule acids, resulting in low ethanol yield and a low COD value for the novel liquid carbon source. Furthermore, sterilization of the kitchen waste is required before adding yeast, making the process complex and inefficient. Summary of the Invention

[0005] The purpose of this application is to provide a method for treating kitchen waste, a carbon source and its application, aiming to solve the technical problems of low chemical oxygen demand and high nitrogen content in liquid carbon sources obtained by directional fermentation technology of kitchen waste in the prior art.

[0006] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0007] Firstly, this application provides a method for treating kitchen waste, comprising the following steps:

[0008] Kitchen waste is fermented in an acidic environment to obtain a fermented mixture;

[0009] The fermentation mixture was filtered to obtain the filtrate;

[0010] The filtrate was subjected to distillation and condensation in sequence to collect volatile organic compounds, resulting in a condensate containing volatile fatty acids (VFAs) and low-molecular-weight alcohols.

[0011] This application's food waste treatment method departs from existing lactic acid-directed fermentation and ethanol-directed fermentation techniques, instead employing VFAs-directed fermentation. The resulting fermentation mixture is rich in volatile fatty acids (VFAs) (propionic acid, butyric acid, acetic acid) and low-molecular-weight alcohols (propanol, ethanol). Filtration separates the solid residue and filtrate. The solid residue contains a high amount of nitrogenous residue, thus filtration helps reduce the nitrogen content and suspended solids value in the filtrate. Further distillation of the filtrate causes the VFAs and low-molecular-weight alcohols to evaporate. During distillation, pressure and temperature can be controlled to maximize the evaporation of these volatile or low-boiling-point components while minimizing water evaporation. Nitrogenous components in the filtrate are almost entirely preserved, thereby increasing the organic matter content in the condensate. Therefore, the resulting condensate is a refined carbon source with a high COD value, high content of small-molecule organic matter, and extremely low nitrogen content.

[0012] Secondly, this application provides a condensate collected by the food waste treatment method described in the above application.

[0013] The carbon source in this application includes the condensate collected by the above-mentioned food waste treatment method. Therefore, the carbon source has a high COD value, low nitrogen content, and its main components are volatile fatty acids (VFAs) such as propionic acid / butyric acid / acetic acid and low molecular weight alcohols such as propanol / ethanol, which are small molecule organic compounds with small molecular weight and short carbon chains.

[0014] Thirdly, this application provides the application of the carbon source described above in any one of the following: denitrification in wastewater treatment, sludge acclimation, and sludge activity restoration.

[0015] The application of this application is the same as the application of the carbon source in the previous application. Because the carbon source has a high COD value, low nitrogen content, and its main components are volatile fatty acids (VFAs) and low-molecular-weight alcohols, etc., with small molecular weight and short carbon chains, it is more easily utilized by microorganisms in wastewater treatment and other fields. As a carbon source for biological denitrification, it has a good effect on nitrogen and phosphorus removal from wastewater, which is beneficial to improving effluent quality. The carbon source can also be used as a chemical raw material. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a process flow diagram of the kitchen waste treatment method in Embodiment 1 of this application;

[0018] Figure 2 This is a schematic diagram of the ceramic flat sheet membrane filtration system in step S2 of Embodiment 1 of this application;

[0019] Figure 3 This is a flowchart of the MVR distillation system in step S3 of Embodiment 1 of this application;

[0020] Figure 4 It is the filtrate obtained in step S2 of Example 1 of this application;

[0021] Figure 5 It is the condensate obtained in step S3 of Embodiment 1 of this application. Detailed Implementation

[0022] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0023] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0024] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items.

[0025] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0026] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass in the embodiments of this application can be a well-known unit of mass in the chemical industry, such as μg, mg, g, or kg.

[0027] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0028] Definition of terms: Kitchen waste: In this application, kitchen waste refers to garbage and kitchen scraps generated in daily life and food processing, catering services, and unit catering activities, including discarded vegetable leaves, leftover food, leftover rice, fruit peels, eggshells, tea dregs, bones (chicken bones, fish bones, etc.), etc. Its main sources are family kitchens, restaurants, hotels, canteens, markets and other industries related to food processing.

[0029] Reducing lactic acid production: The background section has already discussed the problems with the directional fermentation technology for lactic acid. Lactic acid in the fermentation products is difficult to extract and separate, especially during distillation. Lactic acid has a high boiling point, and water is often distilled out along with it, diluting the proportion of organic matter. The resulting novel liquid carbon source often has a low COD value and a high nitrogen content. This application uses a directional fermentation technology for VFAs and low-molecular-weight alcohols. In addition to the aforementioned problems, it is naturally undesirable to produce lactic acid, which would affect the yield of the desired VFAs and low-molecular-weight alcohols.

[0030] Low molecular weight alcohols: In the fields of organic chemistry and chemical engineering, alcohols with 4 or fewer carbon atoms are considered low molecular weight alcohols, including methanol, ethanol, and propanol. Alcohols with 4 or more carbon atoms, i.e., butanol and above, are considered high molecular weight alcohols. This is generally accepted by those skilled in the art. Therefore, the word "low" in "low molecular weight alcohols" will not cause any ambiguity in the patent's meaning.

[0031] The first aspect of this application provides a method for treating kitchen waste, including the following steps:

[0032] S10: Kitchen waste is subjected to directional fermentation in an acidic environment to obtain a fermentation mixture;

[0033] S20: Filter the fermentation mixture to obtain filtrate;

[0034] S30: The filtrate is subjected to distillation and condensation treatment in sequence to collect volatile organic compounds, resulting in a condensate containing volatile fatty acids and low molecular weight alcohols.

[0035] This application's kitchen waste treatment method departs from existing lactic acid-directed fermentation and ethanol-directed fermentation techniques. Instead, it employs a directed fermentation process using volatile fatty acids (VFAs) and low-molecular-weight alcohols as products, reducing lactic acid production. The resulting fermentation mixture is rich in volatile organic compounds, including VFAs and low-molecular-weight alcohols, primarily propionic acid, butyric acid, acetic acid, propanol, and ethanol. The fermentation mixture also contains various solid-liquid byproducts, which are then filtered to separate solid residue and filtrate. The solid residue contains a high amount of nitrogenous residue, thus filtration helps reduce the nitrogen content and suspended solids value in the filtrate. While the filtrate is essentially a crude carbon source and can be used in wastewater treatment, its high water content, low chemical oxygen demand (COD), and still relatively high nitrogen content prevent it from meeting the standards for a high-quality liquid carbon source. Further distillation of the filtrate causes the volatile organic compounds (VFAs) and low-molecular-weight alcohols to evaporate, resulting in a condensate rich in these compounds. During distillation, pressure and temperature can be controlled to maximize the evaporation of these volatile or low-boiling-point components while minimizing water loss. Nitrogenous components in the filtrate are almost entirely preserved, thus increasing the organic matter content of the condensate. Therefore, the resulting condensate is a refined carbon source with a high COD value, high content of small-molecule organic matter, and extremely low nitrogen content. Furthermore, the small molecular weight and short carbon chains of the organic matter make it more readily utilized by microorganisms in wastewater treatment and other applications, resulting in effective nitrogen and phosphorus removal. Thus, high-quality carbon sources can be obtained from kitchen waste using the above treatment method.

[0036] [Step S10]

[0037] This step involves directional fermentation to produce volatile fatty acids (VFAs) and low-molecular-weight alcohols. Before directional fermentation, the kitchen waste can be pre-treated, such as by crushing, degreasing, and removing slag. This includes using a three-phase centrifuge to separate the kitchen waste into solid, oil, and liquid phases, followed by directional fermentation of the three-phase centrifuged liquid. Here, "liquid phase" is a commonly used industry term, parallel to "oil phase," but does not include the oil phase. In existing technologies, after three-phase separation during kitchen waste pretreatment, the liquid phase inevitably still contains organic matter, rather than being an inorganic solution mixture—this is an industry consensus. Therefore, "liquid phase" and "oil phase" are industry-specific terms, not distinctions made from a chemical perspective. Compared to directly fermenting kitchen waste, this method of pre-treating the kitchen waste before directional fermentation of the three-phase centrifuged liquid is more conducive to the directional production of volatile fatty acids (VFAs) and low-molecular-weight alcohols, and also helps reduce the impurity content in the fermentation mixture.

[0038] In some embodiments, the mass ratio of kitchen waste to microbial inoculum is (5-10):1. In exemplary cases, it may include, but is not limited to, any ratio or any two ratios between 5:1, 7:1, 8:1, and 10:1. These mass ratios are conducive to the full interaction between microbial inoculum and kitchen waste, thereby improving the treatment effect of directional fermentation to produce volatile fatty acids and low molecular weight alcohols.

[0039] In some embodiments, the microorganisms used in the directional fermentation treatment include Propionibacterium acnes, Clostridium butyricum, yeast, and Lactobacillus, i.e., a mixed strain containing at least the above-mentioned microorganisms. Different microorganisms become dominant under different controlled conditions; the temperature of the directional fermentation treatment is 38–40°C, and may include, but is not limited to, any value or any two of 38°C, 39°C, and 40°C; the pH of the acidic environment is 4.5–6.0, and may include, but is not limited to, any value or any two of 4.5, 5, 5.5, and 6.0. These acidic environments at these temperatures and pH values ​​are more conducive to the fermentation of the above-mentioned microorganisms, improving the treatment effect of directional fermentation for the production of volatile fatty acids (VFAs) and low-molecular-weight alcohols.

[0040] Directed fermentation exhibits different dominant microbial species at different pH values, resulting in variations in the composition of the final product. Specifically, in acidic environments with a pH of 4.5–5, the dominant microbial species in directed fermentation are Lactobacillus and yeast, leading to higher levels of acetic acid and ethanol in the product.

[0041] In some embodiments, the pH of the acidic environment is 5.0 to 5.5, and the dominant strain in the directional fermentation treatment is Propionibacterium acnes, with high contents of propionic acid and propanol in the product.

[0042] In some embodiments, the pH of the acidic environment is 5.5 to 6.0, and the dominant strain in the directional fermentation treatment is Clostridium butyricum, resulting in a high butyric acid content in the product.

[0043] In some embodiments, the directional fermentation process is carried out for 2 to 3 days to allow the directional fermentation process to proceed fully, increase the yield of small molecule organic compounds such as volatile fatty acids (VFAs) and low molecular weight alcohols, and at the same time reduce lactic acid production.

[0044] The main components required in the fermentation mixture include propionic acid, butyric acid, acetic acid, and other VFAs, as well as a certain amount of low-molecular-weight alcohols, represented by propanol and ethanol, and trace amounts of lactic acid, etc. The specific product types and yields of various products are affected by factors such as the carbon-to-nitrogen ratio of the kitchen waste substrate, pH, and temperature. Testing revealed that the fermentation mixture contained propionic acid, butyric acid, acetic acid, propanol, and ethanol in a mass ratio of (1.5–3):(0.8–1.5):(1.5–2.5):(1.1–1.5):1. In the example, this ratio may include, but is not limited to, any ratio or any two ratios within the range of (1.5 or 2 or 2.5 or 3):(0.8 or 1.0 or 1.2 or 1.5):(1.5 or 2 or 2.5):(1.1 or 1.2 or 1.5):1.

[0045] The fermentation mixture also contains other organic matter. Testing showed that the chemical oxygen demand (COD) of the fermentation mixture was 60,000–80,000 mg / L. The total nitrogen content of the fermentation mixture was 2,000–4,000 mg / L. It can be seen that the COD value of the fermentation mixture is relatively low, the total nitrogen content is relatively high, and it also contains solid components that need to be removed.

[0046] [Step S20]

[0047] Step S20 involves filtration, which primarily removes solid components from the fermentation mixture. These solids contain a large amount of nitrogenous substances, resulting in a high total nitrogen content in the fermentation mixture, which is detrimental to obtaining a low-nitrogen condensate. Furthermore, these solids themselves are impurities and cannot be used in the subsequent condensate production. Therefore, the obtained fermentation mixture needs to be filtered to separate the solid residue and filtrate. The filtrate is then collected for further processing to prepare a carbon source.

[0048] The filtration process can be carried out by at least one of ceramic membrane filtration, media filtration, and flocculation centrifugation. In some embodiments, the filtration process includes a step of filtration through a ceramic membrane, wherein the pore size of the ceramic flat sheet membrane is 0.05 to 0.2 micrometers, and optionally 0.1 micrometers.

[0049] After the above filtration process, the filtrate is mostly a pale yellow liquid, containing ammonia nitrogen components. Testing showed that the suspended solids (SS) value of the filtrate was 10–100 mg / L. The chemical oxygen demand (COD) value was 40,000–60,000 mg / L. The total nitrogen content was 500–1500 mg / L, indicating that the filtrate contained few suspended solids and that the total nitrogen content was significantly lower than that of the fermentation mixture, although a certain level of total nitrogen was still present. Simultaneously, the filtrate also had a certain level of COD. Therefore, this filtrate can be used as a crude carbon source in fields such as wastewater treatment.

[0050] [Step S30]

[0051] Step S30 involves distillation and condensation to collect volatile organic compounds, resulting in a condensate containing volatile fatty acids (VFAs) and low-molecular-weight alcohols. The distillation process removes easily volatile small-molecule organic compounds such as acetic acid, ethanol, and propanol from the filtrate. Because the directed fermentation process selectively produces volatile fatty acids (VFAs) and low-molecular-weight alcohols while inhibiting lactic acid production (which is high-boiling and not easily volatile), distillation can be carried out at a lower temperature. This allows for the normal distillation of these small-molecule organic compounds, while also reducing the evaporation of water and lactic acid from the filtrate, thus lowering energy consumption. Consequently, the mass percentage of small-molecule organic compounds in the distillation vapor is significantly higher than their percentage in the filtrate. This results in a higher organic content and COD value in the subsequent condensate.

[0052] The gas obtained from distillation mainly consists of the desired volatile fatty acids (VFAs) and low-molecular-weight alcohols, as well as other components such as water vapor. The small amount of nitrogen-containing components in the filtrate hardly evaporates, resulting in a very low total nitrogen content in the condensate obtained after condensation of the distilled gas. In summary, the resulting condensate has a high COD value and a low total nitrogen content.

[0053] In some embodiments, the distillation temperature can be 70–95°C. In exemplary cases, it can include, but is not limited to, any value or a range between two of 70°C, 80°C, 90°C, and 95°C. The parameters are based on vacuum distillation, with a vacuum degree of -80 to -10 kPa; the distillation time is 5–30 min. This distillation at these temperatures is a low-temperature distillation process, primarily because the small-molecule organic compounds such as acetic acid, ethanol, and propanol in the filtrate are distilled into gaseous states. Compared to high-temperature distillation, this method significantly reduces water evaporation, decreases the water vapor content in the distilled gas, and also reduces the evaporation of nitrogenous substances. The final evaporation ratio (yield) can reach 10%–30%. Therefore, the gas obtained from the distillation process has a high content of the aforementioned small-molecule organic compounds and water vapor, but an extremely low nitrogen content.

[0054] Distillation can be carried out using mechanical vapor recompression (MVR) technology. The filtrate is passed into an MVR evaporator and the above parameters are set for distillation. MVR technology not only provides stable distillation results but also saves energy.

[0055] After the above distillation and condensation treatments, the resulting condensate was tested and found to have a chemical oxygen demand (COD) of 100,000–150,000 mg / L, a total nitrogen content of 0–50 mg / L, a solids content of 0%–1%, and a suspended solids (SS) content of 0–1 mg / L. It can be seen that compared to the filtrate, a crude carbon source, the condensate obtained after further distillation and condensation treatment has a significantly higher COD and a significantly lower, almost negligible, total nitrogen content. Therefore, this condensate, as a refined carbon source, can meet the requirements for novel liquid carbon sources in wastewater treatment and other fields.

[0056] Furthermore, the distillation and condensation processes in step S30 still ensure a high COD yield. Calculations show that the COD yield of the condensate obtained by the entire preparation method can reach 15% to 30% (calculated from the original liquid). For example, the calculation method for this COD yield is as follows: filtration treatment yields 60% of the filtrate, and distillation treatment yields 20% of the condensate. That is, 100 cubic meters of raw material (fermentation mixture) is filtered to obtain 60 cubic meters of filtrate, and 60 cubic meters of filtrate is evaporated to produce 12 cubic meters of condensate. The COD equivalent of the condensate is 100,000, and the COD equivalent of the original liquid is 60,000. 12*10 / 100*6 = 20%. All the above data are taken as intermediate values.

[0057] The condensate is mainly composed of volatile fatty acids (VFAs) and low-molecular-weight alcohol solutions. It can be stored directly as an acid solution or through alkali absorption. It can also be further improved by membrane concentration, distillation, reverse osmosis, etc., or evaporated and crystallized to obtain a solid carbon source to meet the specific needs of technologies such as wastewater treatment.

[0058] In summary, the food waste treatment method of this application generates a fermentation mixture through directional fermentation, containing the desired volatile organic compounds, including volatile fatty acids (VFAs) and low-molecular-weight alcohols, which are easily volatile small-molecule organic compounds. Simultaneously, the fermentation process inhibits the formation of lactic acid. After filtration to remove solid residue and reduce the nitrogen content and suspended solids value of the filtrate, the filtrate undergoes distillation and condensation. The distillation can be performed at low temperature, causing small-molecule organic compounds such as acetic acid to evaporate, while the small amount of nitrogenous substances in the filtrate hardly evaporates into a gaseous state, and the amount of water evaporated is also minimal. The distilled gas is liquefied to obtain a condensate containing volatile organic compounds such as acetic acid. The condensate has a lower water content than the filtrate, resulting in a higher COD value, while the total nitrogen content is also significantly reduced, making it a high-quality refined carbon source. This food waste treatment method transforms food waste into high-value-added products while reducing environmental pollution and resource waste.

[0059] The second aspect of this application provides a condensate collected by the food waste treatment method of the above-described application embodiments.

[0060] The carbon source in this application embodiment includes the condensate collected by the above-described food waste treatment method. Therefore, the carbon source has a high COD value, low nitrogen content, and its main components are volatile organic compounds such as acetic acid and other small molecule organic compounds with small molecular weight and short carbon chains.

[0061] The third aspect of this application provides the application of the carbon source described in the above-described application embodiments in any one of denitrification, sludge acclimation, and sludge activity restoration in wastewater treatment.

[0062] Because carbon sources have high COD values, low nitrogen content, and are mainly composed of small-molecule organic compounds such as volatile fatty acids (VFAs) and low-molecular-weight alcohols, with small molecular weight and short carbon chains, they are more easily utilized by microorganisms in wastewater treatment and other fields. As a carbon source for biological denitrification, they have a good effect on denitrification of wastewater and are conducive to improving effluent quality.

[0063] Acetic acid, ethanol, propanol, and other carbon sources are important chemical raw materials. Therefore, carbon sources can be widely used in the chemical industry, such as for the preparation of chemical products like sodium acetate.

[0064] In addition, carbon sources can also be used for sludge acclimatization, restoring sludge activity, regulating the activity of microorganisms in sludge, and enabling microorganisms to adapt to wastewater quality.

[0065] The following description is based on specific embodiments.

[0066] Example 1

[0067] This embodiment provides a method for treating kitchen waste and the resulting condensate. For example... Figure 1 As shown, the preparation method includes the following steps S1 to S4:

[0068] S1: The collected 1 ton of urban kitchen waste is pretreated by sorting, pulping, pressing, and three-phase centrifugation to obtain the three-phase centrifuged liquid.

[0069] The three-phase centrifuged liquid was put into a directional fermentation tank, and a mixed bacterial culture was added. The mixed bacterial culture consisted of Acidobacterium, Clostridium, yeast and Lactobacillus. The weight ratio of the three-phase centrifuged liquid to the microorganisms was 10:1. The pH was set to 5.0, the temperature to 38.5℃, and the stirring speed to 50 rpm. Directional fermentation was carried out for 2 days, and the fermentation mixture obtained from the fermentation process was collected.

[0070] S2: As Figure 2 As shown, the fermentation mixture is filtered through a ceramic flat-plate membrane device. The pore size of the ceramic flat-plate membrane is 0.1 micrometers, which can filter out fine residues and other high-nitrogen substances. The collected filtrate serves as a crude carbon source. Figure 4 As shown.

[0071] S3: As Figure 3 As shown, the filtrate was fed into an MVR evaporator, with the parameters set as follows: evaporation temperature 90℃, vacuum degree 20kPa, and distillation time 10min. The distilled gas was collected and condensed to obtain the condensate, which is the carbon source. Figure 5 As shown.

[0072] Example 2

[0073] This embodiment provides a method for treating kitchen waste and the carbon source obtained therefrom. The only difference from Embodiment A1 is that the pH value of the fermentation treatment in step S1 is changed to 5.5; all other aspects are the same.

[0074] Example 3

[0075] This embodiment provides a method for treating kitchen waste and the carbon source obtained therefrom. The only difference from Embodiment A1 is that the pH value of the fermentation treatment in step S1 is changed to 4.5; all other aspects are the same.

[0076] Example 4

[0077] This embodiment provides a method for treating kitchen waste and the resulting carbon source. The only difference from Embodiment A1 is that the filtration method in step S2 is changed to media filtration; all other aspects are the same.

[0078] Example 5

[0079] This embodiment provides a method for treating kitchen waste and the carbon source obtained therefrom. The only difference from Embodiment A1 is that the filtration process in step S2 is changed to flocculation and centrifugation; all other aspects are the same.

[0080] Example 6

[0081] This embodiment provides a method for treating kitchen waste and the carbon source obtained therefrom. The only difference from Embodiment A1 is that the distillation method in step S3 is changed to low-pressure low-temperature evaporation, with a vacuum degree of 90 kPa and an evaporation temperature of 75°C; all other aspects are the same.

[0082] Comparative Example 1

[0083] This embodiment provides a method for treating kitchen waste and the carbon source obtained therefrom. This comparative example illustrates a process route for lactic acid directed fermentation, including the following steps S1 to S5: hydrolysis, saccharification, fermentation, separation, esterification, and hydrolysis:

[0084] S1: Hydrolysis, Saccharification

[0085] One ton of collected urban kitchen waste was placed in a fermentation tank, and a mixed hydrolytic enzyme (protease, lipase, amylase, cellulase, etc.) with a mass fraction of 1‰ was added. The temperature was controlled at 50℃, the pH value at 5.0, and the reaction time was 4 hours.

[0086] S2: Fermentation

[0087] Add 5% by mass of activated lactic acid bacteria to the fermenter, adjust the temperature to 38℃ and the pH value to 6.0, and ferment for 48 hours.

[0088] S3: Filtering

[0089] The fermentation mixture was filtered through a ceramic flat plate membrane device with a pore size of 0.1 micrometers, and the resulting filtrate was collected.

[0090] S4: Esterification

[0091] To determine the lactic acid content in the filtrate, n-butanol was added at a molar ratio of 3:1 (alcohol to acid). Concentrated sulfuric acid at a mass ratio of 1.5% of the filtrate was added as a catalyst, and the temperature was controlled at 120℃ for 6 hours.

[0092] S5: Distillation

[0093] The esterified liquid was added to a distillation apparatus and distilled under a vacuum of 95 kPa. The distillate was collected as a lactic acid ester product.

[0094] Comparative Example 2

[0095] This embodiment provides a method for treating kitchen waste and the carbon source obtained therefrom. The difference from Comparative Example 1 is that the bacteria added in step S2 are yeast, steps 4 and 5 are omitted, and the filtrate is treated using the reduced pressure low temperature evaporation method described in Example 6.

[0096] Relevant performance tests and results analysis

[0097] 1. Suspended solids (SS) test

[0098] The carbon sources obtained in Examples 1 to 6, Comparative Example 1, and Comparative Example 2 were subjected to suspension solids value testing.

[0099] The testing standard referenced "Determination of Suspended Solids in Water - Gravimetric Method (GB 11901-89)". The instruments used were a vacuum filtration device, a 0.45μm filter membrane, and an oven. The testing procedure was as follows:

[0100] After drying the filter membrane to equilibrium, weigh the filter membrane (m1). Weigh 100 mL of water sample and filter it using a vacuum filtration device. After filtration, place the filter membrane in an oven and dry it at 100–105 °C to equilibrium, then weigh the filter membrane (m2). The formula for calculating suspended solids is: C = (m2 - m1) / 100, where: C—suspended solids concentration, in mg / L; m1, m2: filter membrane weight, filter membrane weight + suspended solids weight, in g.

[0101] 2. Chemical Oxygen Demand (COD) Test

[0102] The intermediate products of Examples 1 to 9, Comparative Examples 1 and 2, and the final carbon source were subjected to chemical oxygen demand (COD) testing.

[0103] The testing standard references the "Determination of Chemical Oxygen Demand in Water - Dichromate Method (HJ828—2017)". The instruments used include a digestion apparatus, acid burette, 25mL digestion tube, 150mL Erlenmeyer flask, and 250mL beaker. The testing procedure is as follows:

[0104] (1) Disintegration

[0105] Accurately pipette 3.00 mL of a homogeneous water sample (two blanks should be prepared simultaneously; the blank should be 3.00 mL of distilled water) into a digestion tube. Add 1.00 mL of masking agent, 3.00 mL of digestion solution (the amount added must be accurately measured), and 5.00 mL of catalyst. Shake well. Tighten the sealing cap and insert the digestion tube into the apparatus preheated to 160°C. Digest for 25 minutes.

[0106] (2) Titration

[0107] Transfer the sample solution to a 150 mL Erlenmeyer flask, rinse the digestion tube three times with 20 mL of distilled water, and combine the rinsing solution into the Erlenmeyer flask. Add 2-3 drops of ferrous ammonium sulfate standard solution to the ferrous indicator and back titrate. The endpoint is reached when the solution color changes from yellow through blue-green to reddish-brown. Record the amount of ferrous ammonium sulfate standard solution used.

[0108] (3) Calculation

[0109]

[0110] In the formula:

[0111] V0—Volume of ferrous ammonium sulfate standard solution consumed in the blank (mL);

[0112] V1—Volume (mL) of ferrous ammonium sulfate standard solution consumed in the water sample;

[0113] V2—Water sample volume (mL);

[0114] C—Ferrous ammonium sulfate standard solution concentration (mol / L);

[0115] The molar mass of 8000—1 / 4O2 is converted in mg / L.

[0116] 3. Total nitrogen content test

[0117] The total nitrogen content of the intermediate products of Examples 1 to 9, Comparative Examples 1 and 2 and the final carbon source were tested.

[0118] The test standard refers to "Determination of Total Nitrogen in Water by Alkaline Potassium Persulfate Digestion Ultraviolet Spectrophotometry (HJ 636—2012)" and the instruments used are ultraviolet spectrophotometer, 10mm cuvette, autoclave, 25mL colorimetric tube, and 250mL beaker.

[0119] The testing steps are as follows:

[0120] (1) Sample preparation

[0121] Take an appropriate amount of sample and adjust the pH value to 5-9 with sodium hydroxide solution or sulfuric acid solution, then test.

[0122] (2) Sample determination

[0123] Dilute the sample 1000 times. Take 10.00 mL of the sample into a 25 mL stoppered ground glass colorimetric tube, add water to the 10 mL mark (the blank is added simultaneously with the following method), then add 5.00 mL of alkaline potassium persulfate solution. Tightly stopper the tube and secure it with gauze and string to prevent it from popping out. Place the colorimetric tube in an autoclave, heat until the pressure valve is blown out, close the valve, continue heating to 120°C and start timing, maintaining the temperature between 120 and 124°C for 30 minutes. Allow it to cool naturally, open the valve to release the gas, remove the outer cap, remove the colorimetric tube and cool it to room temperature. Hold the stopper and invert the tube 2-3 times to mix the liquid. Add 1.0 mL of hydrochloric acid solution to each colorimetric tube, dilute with water to the 25 mL mark, stopper and mix well. Using a 10 mm quartz cuvette, measure the absorbance at wavelengths of 220 nm and 275 nm on a UV spectrophotometer, using water as a reference.

[0124] (3) Blank experiment

[0125] Replace the sample with 10.00 mL of water and perform the determination according to the sample determination procedure.

[0126] (4) Calculation

[0127]

[0128] In the formula:

[0129] ρ—The mass concentration of total nitrogen in the water sample (as N) (mg / L);

[0130] Ar—The difference between the corrected absorbance of the sample and the corrected absorbance of the blank test;

[0131] a—The intercept of the calibration curve;

[0132] f—dilution factor;

[0133] b—the slope of the calibration curve;

[0134] V — Sample volume (mL).

[0135] The test results are summarized in Table 1 below. In Table 1, the units for COD values ​​are mg / L, the units for total nitrogen content are mg / L, and the units for SS values ​​(suspended solids) are mg / L.

[0136] Table 1

[0137]

[0138]

[0139] As shown in Table 1, Examples 1 to 6 all employed directional fermentation followed by filtration, and finally, distillation and condensation of the filtrate to obtain a condensate as a carbon source. This condensate exhibited high COD, low total nitrogen content, and low SS, making it a high-quality carbon source. In contrast, Comparative Example 1, with its lactic acid directional fermentation, suffered from difficulties in lactic acid separation and purification, especially during evaporation due to the low volatility and high boiling point of lactic acid, resulting in water evaporation and a high water content in the carbon source, leading to a low COD. Comparative Example 2, with its ethanol directional fermentation, experienced a very low ethanol yield because the kitchen waste had already undergone acidification during storage and transportation, with starch, cellulose, and other polysaccharides decomposing into small-molecule acids.

[0140] Furthermore, the suspended solids values ​​of the filtrates from Examples 1 to 3 of this application are significantly lower than those from Examples 4 and 5, indicating that ceramic flat-plate membrane filtration is more conducive to separating fine residues from the fermentation mixture. The COD values ​​of the filtrates from Examples 1 to 3 are similar to those of Example 6, but the COD value of the condensate is significantly higher than that of Example 6, indicating that MVR evaporation and condensation, along with setting reasonable parameters, are more conducive to obtaining condensates with high COD values.

[0141] The high COD values ​​of the condensates obtained in Examples 1 to 3 indicate that setting a suitable pH range is beneficial for the fermentation of the microorganisms in the compound culture. Different dominant microorganisms exist under different fermentation conditions, and matching the reaction conditions with the microorganisms can improve the fermentation effect.

[0142] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for treating kitchen waste, characterized in that, Includes the following steps: Kitchen waste is subjected to directional fermentation in an acidic environment to obtain a fermentation mixture; The fermentation mixture was filtered to obtain a filtrate; The filtrate was subjected to distillation and condensation in sequence to collect volatile organic compounds, resulting in a condensate containing volatile fatty acids and low-molecular-weight alcohols. The strains used in the directional fermentation treatment include Propionibacterium, Clostridium, yeast, and Lactobacillus; The distillation process is carried out at a temperature of 70–95°C.

2. The kitchen waste treatment method according to claim 1, characterized in that: The temperature of the directional fermentation treatment is 38–40°C, and the pH value of the acidic environment is 4.5–6.0; And / or, the mass ratio of the kitchen waste to the bacterial strain is (5-10):

1.

3. The method for treating kitchen waste according to claim 1 or 2, characterized in that: The acidic environment has a pH of 4.5 to 5, and the dominant microorganisms in the directional fermentation treatment are yeast and lactobacillus. And / or, the pH value of the acidic environment is 5.0 to 5.5, and the dominant microbial species in the directional fermentation treatment is Propionibacterium acnes; And / or, the pH value of the acidic environment is 5.5 to 6.0, and the dominant microbial species in the directional fermentation treatment is Clostridium butyricum.

4. The method for treating kitchen waste according to claim 1 or 2, characterized in that: The directional fermentation process takes 2 to 3 days.

5. The method for treating kitchen waste according to claim 1 or 2, characterized in that: The chemical oxygen demand of the fermentation mixture is 60,000 to 80,000 mg / L; And / or, the total nitrogen content of the fermentation mixture is 2000-4000 mg / L.

6. The method for treating kitchen waste according to claim 1 or 2, characterized in that: The fermentation mixture contains propionic acid, butyric acid, acetic acid, propanol and ethanol, and the mass ratio of propionic acid, butyric acid, acetic acid, propanol and ethanol is (1.5-3):(0.8-1.5):(1.5-2.5):(1.1-1.5):

1.

7. The method for treating kitchen waste according to claim 1 or 2, characterized in that: The filtration process includes a step of filtration through a ceramic flat sheet membrane, wherein the pore size of the ceramic flat sheet membrane is 0.05 to 0.2 micrometers; And / or, the suspended solids value of the filtrate is 10–100 mg / L; And / or, the chemical oxygen demand of the filtrate is 40,000 to 60,000 mg / L; And / or, the total nitrogen content of the filtrate is 500–1500 mg / L.

8. The method for treating kitchen waste according to claim 1 or 2, characterized in that: The chemical oxygen demand of the condensate is 100,000 to 150,000 mg / L; And / or, the total nitrogen content of the condensate is 0–50 mg / L; And / or, the solid content of the condensate is 0% to 1%.

9. A carbon source, characterized in that: The carbon source includes the condensate collected by the food waste treatment method according to any one of claims 1 to 8.

10. The application of the carbon source as described in claim 9 in any one of the following: denitrification in wastewater treatment, sludge acclimation, and sludge activity restoration.

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