Kitchen waste treatment method, carbon source and application thereof

Abstract

The invention relates to the technical field of waste treatment, in particular to a kitchen waste treatment method, a carbon source and application thereof. The kitchen waste treatment method comprises the following steps: performing directional fermentation treatment on kitchen waste in an acid environment to obtain a fermentation mixture; filtering the fermentation mixture to obtain filtrate; the filtrate is sequentially subjected to distillation treatment and condensation treatment, volatile organic compounds are collected, and condensate containing volatile fatty acid and low-molecular alcohol is obtained. According to the kitchen waste treatment method, directional fermentation treatment is carried out, and a fermentation mixture is rich in volatile organic compounds including volatile fatty acids (VFAs) such as propionic acid, butyric acid and acetic acid and low-molecular alcohols such as propyl alcohol and ethyl alcohol. And carrying out filtration treatment to reduce the nitrogen content and the suspended matter value in the filtrate. After distillation treatment, the small-molecular organic matters in the filtrate are evaporated, less water is evaporated, and the nitrogen-containing components in the filtrate are almost not evaporated. And the prepared condensate is high in COD value, high in content of micromolecular organic matters and extremely low in nitrogen content.

Description

Technical Field

[0001] The present application relates to the technical field of waste treatment, and in particular to a method for treating kitchen waste, a carbon source and applications thereof. Background Art

[0002] In the field of sewage treatment, it is often necessary to add an external carbon source to improve the denitrification effect and effluent quality. The carbon source needs to have the characteristics of high chemical oxygen demand (COD value) and low nitrogen content. Common external carbon sources include traditional carbon sources, new solid carbon sources, and new liquid carbon sources. Traditional carbon sources are generally low molecular organic matter and sugars, such as methanol, ethanol, acetic acid, sodium acetate, glucose, sucrose, fructose, and maltose. New liquid carbon sources generally come from high-concentration organic wastewater containing fat, sugar, protein and other organic matter produced by food factories, beverage factories and agricultural and sideline product processing factories during production and processing. This type of organic wastewater has small toxic side effects and high biodegradability. Kitchen waste has the characteristics of large output and high organic content. The products after anaerobic fermentation are mainly volatile fatty acids (VFAs) that are easily biodegradable. At present, directional fermentation technology is generally used to hydrolyze and acidify the organic matter in kitchen waste, convert it into a single component, and then extract and concentrate it to obtain a new liquid carbon source.

[0003] The existing kitchen waste directional fermentation treatment technology is mainly directional fermentation into two directions: lactic acid and ethanol. The lactic acid production process includes hydrolysis, saccharification, fermentation, separation and purification, etc. The macromolecular organic matter in the kitchen waste is converted into small molecular organic matter that can be used by lactic acid bacteria (LAB) through hydrolysis and saccharification. During the hydrolysis and saccharification process, the accumulation of sugars and acids in the product will reduce the enzyme activity, resulting in a decrease in lactic acid production. The main methods for separating and extracting lactic acid from the fermentation broth include crystallization separation technology, esterification hydrolysis method, extraction method, molecular distillation method, membrane separation method, adsorption method, chromatographic separation technology, etc. However, these methods have their own advantages and disadvantages, such as cost, yield, time, etc. The lack of extraction technology limits the application of kitchen waste lactic acid fermentation. Especially when treated by distillation, lactic acid has a high boiling point and will be distilled out together with water, diluting the proportion of organic matter. The new liquid carbon source finally obtained often has a low COD value and a high nitrogen content.

[0004] The ethanol production process generally goes through the steps of "pretreatment-hydrolysis-fermentation-distillation-dehydration". The pretreatment process destroys the structure of polysaccharides such as starch and cellulose, and the hydrolysis process converts large molecular polysaccharides into smaller reducing sugars. The reducing sugars are converted into crude ethanol through microbial fermentation, and finally high-purity ethanol products are obtained through distillation and dehydration. However, kitchen waste has been acidified during storage and collection, and polysaccharides such as starch and cellulose have been decomposed into small molecular acids. The yield of ethanol is very low, and the COD value of the new liquid carbon source is low. In addition, the kitchen waste needs to be sterilized before adding yeast, which is a complex process with low efficiency. Summary of the invention

[0005] The purpose of the present 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 the liquid carbon source produced by the kitchen waste directional fermentation technology in the prior art.

[0006] In order to achieve the above application purpose, the technical solution adopted in this application is as follows:

[0007] In a first aspect, the present application provides a method for treating food waste, comprising the following steps:

[0008] fermenting the kitchen waste in an acidic environment to obtain a fermentation mixture;

[0009] filtering the fermentation mixture to obtain a filtrate;

[0010] The filtrate is sequentially subjected to distillation treatment and condensation treatment, and volatile organic matter is collected to obtain a condensate containing volatile fatty acids (VFAs) and low molecular alcohols.

[0011] The kitchen waste treatment method of the present application changes the existing technical routes of lactic acid directional fermentation and ethanol directional fermentation to VFAs directional fermentation treatment, and the obtained fermentation mixture is rich in volatile fatty acids (VFAs) (propionic acid, butyric acid, acetic acid) and low molecular alcohols (propanol, ethanol). Then filter treatment is carried out to separate solid residue and filtrate, and there are many nitrogen residues in the solid residue, so that the filtration treatment is conducive to reducing the nitrogen content and suspended matter value in the filtrate. After the filtrate is further distilled, volatile organic substances such as VFAs and low molecular alcohols in the filtrate will evaporate. During the distillation process, pressure, temperature and other conditions can be controlled to make these volatile or low-boiling components in the filtrate evaporate more, and less water evaporates, and the nitrogen-containing components in the filtrate are almost not evaporated, thereby increasing the organic content in the condensate. Therefore, the obtained condensate is a refined carbon source with high COD value, high content of small molecule organic matter and extremely low nitrogen content.

[0012] In a second aspect, the present application provides a condensate collected by the food waste treatment method of the above application.

[0013] The carbon source of the present application includes the condensate collected by the above-mentioned kitchen waste treatment method. Therefore, the COD value in the carbon source is high, the nitrogen content is low, and the main components are volatile fatty acids (VFAs) such as propionic acid / butyric acid / acetic acid and low molecular weight alcohols such as propanol / ethanol and other small molecular weight organic substances with small molecular weight and short carbon chain.

[0014] In a third aspect, the present application provides the use of the carbon source of the above-mentioned application in any one of denitrification and denitrification, sludge acclimation, and restoration of sludge activity in sewage treatment.

[0015] The application of this application is the application of the carbon source of the above application. Since the carbon source has a high COD value, low nitrogen content, and its main components are small molecular organics such as volatile fatty acids (VFAs) and low molecular alcohols, with small molecular weight and short carbon chain, it is easier to be used by microorganisms in the fields of sewage treatment. As a biological denitrification carbon source, it has good effects on sewage denitrification and phosphorus removal, which is conducive to improving the quality of effluent. The carbon source can also be used as a chemical raw material. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 is a process flow chart of the method for treating kitchen waste according to Example 1 of the present application;

[0018] Figure 2 is a schematic diagram of a ceramic flat membrane filtration system in step S2 of Example 1 of the present application;

[0019] Figure 3 is a flow chart of the MVR distillation system in step S3 of Example 1 of the present application;

[0020] Figure 4 The filtrate obtained in step S2 of Example 1 of the present application;

[0021] Figure 5 It is the condensate obtained in step S3 of Example 1 of the present application. DETAILED DESCRIPTION

[0022] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0023] In this application, the term "and / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

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

[0025] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and 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 the present application.

[0026] The weight of the relevant components mentioned in the embodiment description of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the embodiment description of the present application, it is within the scope disclosed in the embodiment description of the present application. Specifically, the mass in the embodiment description of the present application can be μg, mg, g, kg and other mass units known in the chemical industry.

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

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

[0029] Reducing lactic acid production: The problems of the technical route of directional fermentation of lactic acid have been introduced in the background technology. Lactic acid in the fermentation product is difficult to extract and separate, especially when it is treated by distillation. Lactic acid has a high boiling point and will be distilled out together with water, diluting the proportion of organic matter. The new liquid carbon source finally obtained often has a low COD value and a high nitrogen content. The technical route of the present application is a technical route for directional fermentation of VFAs and low-molecular alcohols. In addition to the above-mentioned problems, it is of course even more undesirable to produce lactic acid, thereby affecting the production of small molecule organic matter such as the required VFAs and low-molecular alcohols.

[0030] Low molecular alcohols: In the field of organic chemistry and chemical engineering, alcohols with a carbon number of less than 4 are low molecular alcohols, including methanol, ethanol and propanol, and alcohols with a carbon number of equal to or greater than 4, i.e., butanol and above, are high molecular alcohols, which is recognized by those skilled in the art. Therefore, the word "low" in low molecular alcohols will not cause unclear issues in the meaning of the patent.

[0031] A first aspect of an embodiment of the present application provides a method for processing kitchen waste, comprising the following steps:

[0032] S10: performing directed fermentation treatment on the kitchen waste in an acidic environment to obtain a fermentation mixture;

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

[0034] S30: The filtrate is sequentially subjected to distillation treatment and condensation treatment, and volatile organic matter is collected to obtain a condensate containing volatile fatty acids and low molecular alcohols.

[0035] The kitchen waste treatment method of the present application embodiment changes the existing technical route of lactic acid directional fermentation and ethanol directional fermentation, and changes to a directional fermentation process with volatile fatty acids (VFAs) and low molecular alcohols as products, reduces the generation of lactic acid, and the obtained fermentation mixture is rich in volatile organic matter, including small molecular organic matter such as volatile fatty acids (VFAs) and low molecular alcohols, and the main small molecular organic matter is propionic acid, butyric acid, acetic acid, propanol, and ethanol. The fermentation mixture also contains a variety of solid and liquid by-products, and then filtered to separate solid residues and filtrate. There are many nitrogen residues in the solid residue, so the filtration process is conducive to reducing the nitrogen content and suspended matter value in the filtrate. The filtrate is actually a crude carbon source, and can also be used as a carbon source in fields such as sewage treatment, but the filtrate has a high water content, a low chemical oxygen demand (COD value), and a high nitrogen content, so it does not meet the standard of a high-quality liquid carbon source. After the filtrate is further treated by distillation, volatile organic compounds such as volatile fatty acids (VFAs) and low molecular alcohols in the filtrate will evaporate, so that the condensate after condensation treatment is rich in volatile organic compounds such as volatile fatty acids (VFAs) and low molecular alcohols. In the distillation process, the pressure, temperature and other conditions can be controlled to make more of these volatile or low-boiling components in the filtrate evaporate, and less water evaporates, and the nitrogen-containing components in the filtrate hardly evaporate, thereby increasing the organic content in the condensate. Therefore, the obtained condensate is a refined carbon source with a high COD value, a high content of small molecular organic matter, and an extremely low nitrogen content. The organic matter therein has a small molecular weight and a short carbon chain, and is more easily utilized by microorganisms in fields such as sewage treatment, and has a good effect of denitrification and phosphorus removal in sewage. Therefore, kitchen waste can be used to produce a high-quality carbon source through the above-mentioned treatment method.

[0036] [Step S10]

[0037] This step is a step of conducting directed fermentation to produce volatile fatty acids (VFAs) and low molecular alcohols. Before conducting directed fermentation treatment, the kitchen waste can also be pretreated, such as crushing, deoiling, and deslagging steps, including using a three-phase centrifuge to separate the kitchen waste into a solid phase, an oil phase, and a liquid phase, and then conducting directed fermentation treatment on the three-phase centrifuge. The liquid phase here is a commonly used term in the industry, and is a parallel term with the oil phase, and does not include the oil phase. After the three-phase separation treatment of kitchen waste pretreatment in the prior art, it is inevitable that the liquid phase still contains organic matter, rather than an inorganic solution mixture. This is a consensus in the industry. Therefore, the liquid phase and the oil phase are terms within the industry and within the industry, rather than the liquid phase and the oil phase distinguished from the perspective of chemical disciplines. Compared with directly fermenting with kitchen waste, this method of first pretreating the kitchen waste and then conducting subsequent directed fermentation treatment on the three-phase centrifuge is conducive to the directional production of volatile fatty acids (VFAs) and low molecular alcohols, and is also conducive to reducing the impurity content in the fermentation mixture.

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

[0039] In some embodiments, the bacteria species of the directional fermentation treatment include Propionibacterium, Clostridium butyricum, yeast and Lactobacillus, that is, a mixed strain of at least the above bacteria species. Different bacteria species become dominant bacteria species under different control conditions; the temperature of the directional fermentation treatment is 38-40°C, which may include but is not limited to any value of 38°C, 39°C, 40°C or a range between any two values, and the pH value of the acidic environment is 4.5-6.0, which may include but is not limited to any value of 4.5, 5, 5.5, 6.0 or a range between any two values. The acidic environment of these temperatures and pH values ​​is more conducive to the fermentation of the above bacteria species, and improves the treatment effect of the directional fermentation treatment for the directional production of volatile fatty acids (VFAs) and low-molecular alcohols.

[0040] Directed fermentation treatment has different dominant bacteria at different pH values, and the composition of the final product also changes. Among them, the pH value of the acidic environment is 4.5-5, and the dominant bacteria in the directed fermentation treatment are lactobacillus and yeast, and the content of acetic acid and ethanol in the product is relatively high.

[0041] In some embodiments, the pH value of the acidic environment is 5.0-5.5, and the dominant bacteria in the directional fermentation treatment is Propionibacterium, and the content of propionic acid and propanol in the product is relatively high.

[0042] In some embodiments, the pH value of the acidic environment is 5.5-6.0, and the dominant bacteria in the directional fermentation treatment is Clostridium butyricum, and the butyric acid content in the product is relatively high.

[0043] In some embodiments, the directed fermentation treatment lasts for 2 to 3 days to allow the directed fermentation treatment to proceed fully, thereby increasing the yield of small molecular organic matter such as volatile fatty acids (VFAs) and low molecular alcohols, while reducing lactic acid output.

[0044] The ingredients required in the fermentation mixture mainly include VFAs such as propionic acid, butyric acid, and acetic acid, as well as a certain amount of low molecular alcohols represented by propanol and ethanol, and a trace amount of lactic acid, etc. The specific product types and the yields of various products are affected by many factors such as the carbon-nitrogen ratio of the kitchen waste substrate, pH, temperature, etc. After testing, the obtained fermentation mixture contains propionic acid, butyric acid, acetic acid, propanol, and ethanol, and the mass ratio is (1.5-3): (0.8-1.5): (1.5-2.5): (1.1-1.5): 1. In the exemplary example, it can include but is not limited to (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 any ratio or the range between any two ratios.

[0045] The fermentation mixture also contains other organic matter. After testing, the chemical oxygen demand (COD value) of the fermentation mixture is 60000-80000 mg / L. The total nitrogen content of the fermentation mixture is 2000-4000 mg / L. It can be seen that the COD value of the fermentation mixture is low, the total nitrogen content is high, and in addition, it contains solid components that need to be removed.

[0046] [Step S20]

[0047] Step S20 is a step of filtering. The filtering is mainly to remove the solid components in the fermentation mixture. These solid components contain a large amount of nitrogen-containing substances, which leads to a high total nitrogen content in the fermentation mixture, which is not conducive to the preparation of a condensate with a low nitrogen content. At the same time, these solid components themselves are also impurities and cannot be used in subsequent condensates. Therefore, the obtained fermentation mixture needs to be filtered to separate the solid residue and the filtrate, and the filtrate is collected for subsequent processing to further prepare a carbon source.

[0048] The filtration treatment can be performed by at least one of ceramic membrane filtration, medium filtration, and flocculation centrifugation. In some embodiments, the filtration treatment includes the step of filtering through a ceramic membrane, and the pore size of the ceramic flat membrane is 0.05 to 0.2 microns, and can be optionally 0.1 microns.

[0049] After the above filtration treatment, the filtrate is mostly a light yellow liquid, which also contains ammonia nitrogen components. After testing, the suspended matter value (SS value) of the filtrate is 10-100 mg / L. The chemical oxygen demand (COD value) of the filtrate is 40000-60000 mg / L. The total nitrogen content of the filtrate is 500-1500 mg / L, indicating that the solid suspended impurities in the filtrate are less, and the total nitrogen content is significantly lower than that of the fermentation mixture, but there is still a certain total nitrogen content. At the same time, the filtrate also has a certain level of COD value. Therefore, the filtrate at this time can be used as a crude carbon source in fields such as sewage treatment.

[0050] [Step S30]

[0051] Step S30 is a step of performing distillation and condensation, collecting volatile organic matter, and obtaining a condensate containing volatile fatty acids (VFAs) and low-molecular alcohols. The effect of distillation is to distill out the volatile organic matter in the filtrate, such as acetic acid, ethanol, propanol and other volatile small-molecule organic matter. Due to the directional production of volatile fatty acids (VFAs) and low-molecular alcohols in the directional fermentation process, lactic acid production (high boiling point and not volatile) is suppressed at the same time, therefore, distillation can be carried out at a lower temperature, and these volatile fatty acids (VFAs) and low-molecular alcohols and other small-molecule organic matter can be distilled normally, and the lower distillation temperature can reduce the evaporation of moisture and lactic acid in the filtrate, and reduce energy consumption at the same time, so that the mass proportion of small-molecule organic matter in the distillation steam is much higher than the proportion in the filtrate. It is conducive to the subsequent condensate to increase the organic content and improve the COD value.

[0052] The gas obtained by distillation mainly contains the required volatile fatty acids (VFAs) and small molecular organic substances such as low molecular alcohols, as well as other components such as water vapor. The small amount of nitrogen-containing components in the filtrate will hardly evaporate, so the total nitrogen content of the condensate obtained by condensing the distilled gas and liquefying it will also be very low. In summary, the COD value of the condensate obtained is high and the total nitrogen content is low.

[0053] In some embodiments, the temperature of the distillation treatment can be 70 to 95°C. In the exemplary embodiment, it can include but is not limited to any value of 70°C, 80°C, 90°C, 95°C or the range between any two values. The parameters are in accordance with vacuum distillation, the vacuum degree is -80 to -10kpa; the distillation time is 5 to 30min; the distillation treatment at these temperatures belongs to low-temperature distillation treatment, mainly because the small molecular organic substances such as acetic acid, ethanol, propanol required in the filtrate will be distilled into gaseous state. Compared with the high-temperature distillation method, the distillation treatment at these temperatures can significantly reduce the evaporation of water, reduce the content of water vapor in the distilled gas, and also reduce the evaporation of nitrogen-containing substances. The final evaporation ratio (yield) can reach 10% to 30%. Therefore, the gas obtained by distillation treatment has a high content of the above-mentioned small molecular organic substances and water vapor, but the nitrogen content is extremely low.

[0054] The distillation treatment can be carried out by mechanical vapor recompression (MVR) technology. The filtrate is passed into the MVR evaporator and the above parameters are set for distillation treatment. The MVR technology not only has a stable distillation effect, but also saves energy.

[0055] After the above-mentioned distillation and condensation treatment, the condensate is obtained. After testing, the chemical oxygen demand (COD value) of the condensate is 100000-150000 mg / L, the total nitrogen content of the condensate is 0-50 mg / L; the solid content of the condensate is 0%-1%; the suspended solids value (SS) of the condensate is 0-1 mg / L. It can be seen that compared with the crude carbon source such as the filtrate, the COD value of the condensate obtained after further distillation and condensation treatment is significantly increased, and the total nitrogen content is significantly reduced, which is almost negligible. Therefore, this condensate can be used as a refined carbon source to meet the requirements of a new liquid carbon source required in the fields of sewage treatment and the like.

[0056] Moreover, the distillation treatment and condensation treatment in step S30 still ensure a relatively high COD yield. According to calculation, the COD yield of the condensate obtained by the entire preparation method can reach 15% to 30% (calculated based on the original solution). The calculation method of the COD yield is exemplified as follows: the filtrate yield of the filtration treatment is 60%, and the condensate yield of the distillation treatment is 20%, that is, 100 cubic meters of raw materials (fermentation mixture) are filtered to obtain 60 cubic meters of filtrate, and 12 cubic meters of condensate are evaporated from the 60 cubic meters of filtrate, the COD equivalent of the condensate is 100,000, and the COD equivalent of the original solution is 60,000, 12*10 / 100*6=20%, and the above data are all intermediate values.

[0057] The main components of the condensate are volatile fatty acids (VFAs) and low molecular alcohol solutions, which can be directly stored as acid solution or preserved through alkali absorption. The COD value can be further increased through membrane concentration, distillation, reverse osmosis, etc., or evaporated and crystallized to produce solid carbon sources to meet specific needs in technical fields such as sewage treatment.

[0058] In summary, the kitchen waste treatment method of the present application embodiment generates a fermentation mixture through a directional fermentation process, which contains the required volatile organic compounds, including volatile fatty acids (VFAs) and low molecular alcohols and other volatile small molecule organic compounds, and the fermentation process also inhibits the generation of lactic acid. Then the solid residue is removed by filtration, the nitrogen content and suspended matter value of the filtrate are reduced, and finally the filtrate is subjected to distillation and condensation treatment. The distillation treatment can be a low-temperature distillation treatment, and the small molecule organic compounds such as acetic acid will evaporate, and the small amount of nitrogen-containing substances in the filtrate will hardly evaporate into a gaseous state, and the amount of water evaporation is also small. The gas distilled out at last is liquefied to obtain a condensate, which contains volatile organic compounds such as acetic acid, and the water content in the condensate is lower than that in the filtrate, that is, the COD value is high, and the total nitrogen content is also significantly reduced, which belongs to a high-quality refined carbon source. The kitchen waste treatment method converts kitchen waste into high value-added products, while reducing environmental pollution and waste of resources.

[0059] A second aspect of an embodiment of the present application provides a condensate collected by the kitchen waste treatment method of the above embodiment of the present application.

[0060] The carbon source in the embodiment of the present application includes the condensate collected by the above-mentioned kitchen waste treatment method. Therefore, the COD value in the carbon source is high, the nitrogen content is low, and the main components are volatile organic compounds such as acetic acid and other small molecular organic compounds with small molecular weight and short carbon chain.

[0061] The third aspect of the embodiments of the present application provides the use of the carbon source of the embodiments of the present application in any one of denitrification and denitrification, sludge acclimation, and restoration of sludge activity in sewage treatment.

[0062] Because the carbon source has a high COD value, low nitrogen content, and its main components are small molecular organic matter such as volatile fatty acids (VFAs) and low molecular weight alcohols, with small molecular weight and short carbon chain, it is more easily utilized by microorganisms in fields such as sewage treatment. As a biological denitrification carbon source, it has a good effect on sewage denitrification and is beneficial to improving the effluent quality.

[0063] Acetic acid, ethanol, propanol, etc. in carbon sources are all important chemical raw materials, so carbon sources can be widely used in the chemical field, such as in the preparation of chemical products such as sodium acetate.

[0064] In addition, carbon sources can also be used for sludge domestication, restoration of sludge activity, regulation of microbial activity in sludge, and adaptation of microorganisms to sewage quality.

[0065] The following describes the invention in conjunction with specific embodiments.

[0066] Example 1

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

[0068] S1: 1 ton of collected urban kitchen waste is sorted, pulped, extruded, and pre-processed by three-phase centrifugation, and the obtained three-phase centrifuge liquid is collected.

[0069] The three-phase centrifuge liquid is put into a directional fermentation tank, and mixed bacteria are added. The mixed bacteria are acidobacillus, clostridium, yeast and lactobacillus. The weight ratio of the three-phase centrifuge liquid and the microorganisms is 10:1. The pH is set to 5.0, the temperature is 38.5°C, and the stirring speed is 50 rpm. The directional fermentation treatment is carried out for 2 days, and the fermentation mixture obtained by the fermentation treatment is collected.

[0070] S2: Figure 2 As shown, the fermentation mixture is filtered through a ceramic flat membrane device, and the pore size of the ceramic flat membrane is 0.1 micron, so that high nitrogen substances such as fine residues can be filtered out, and the filtrate collected is a crude carbon source, such as Figure 4 shown.

[0071] S3: Figure 3 As shown, the filtrate is put into the MVR evaporator, and the parameters are set as evaporation temperature of 90°C, vacuum degree of 20kPa, and distillation time of 10min. The distilled gas is collected and condensed to obtain condensate, i.e., carbon source, such as Figure 5 shown.

[0072] Example 2

[0073] This embodiment provides a method for treating kitchen waste and a prepared carbon source. The only difference from Embodiment A1 is that the pH value of the fermentation treatment in Step S1 is changed to 5.5, and the rest is the same.

[0074] Example 3

[0075] This embodiment provides a method for treating kitchen waste and a prepared carbon source. The only difference from Embodiment A1 is that the pH value of the fermentation treatment in Step S1 is changed to 4.5, and the rest is the same.

[0076] Example 4

[0077] This embodiment provides a method for treating kitchen waste and a prepared carbon source. The only difference from Embodiment A1 is that the filtering treatment method in step S2 is changed to medium filtration, and the rest is the same.

[0078] Example 5

[0079] This embodiment provides a method for treating kitchen waste and a prepared carbon source. The only difference from Embodiment A1 is that the filtering treatment method in step S2 is changed to flocculation centrifugation, and the rest is the same.

[0080] Example 6

[0081] This embodiment provides a method for treating kitchen waste and a prepared carbon source. The only difference from Embodiment A1 is that the distillation treatment method in step S3 is changed to reduced pressure low temperature evaporation, the vacuum degree is 90 kPa, and the evaporation temperature is 75° C., and the rest are the same.

[0082] Comparative Example 1

[0083] This example provides a method for treating kitchen waste and a carbon source obtained. This comparative example is a process route for directional fermentation of lactic acid, including the following steps S1 to S5 of 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 1‰ mass fraction of mixed hydrolase (protease, lipase, amylase, cellulase, etc.) was added. The temperature was controlled at 50°C, the pH value was 5.0, and the reaction time was 4h.

[0086] S2: Fermentation

[0087] 5% by mass of activated lactic acid bacteria was added to the fermentation tank, the temperature was adjusted to 38°C, the pH value was 6.0, and the fermentation was carried out for 48 hours.

[0088] S3: Filtering

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

[0090] S4: Esterification

[0091] The lactic acid content in the filtrate was detected, n-butanol was added in a molar ratio of 3:1 between alcohol and acid, and 1.5% by mass of concentrated sulfuric acid was added to the filtrate as a catalyst. The temperature was controlled at 120° C. and the reaction was carried out for 6 hours.

[0092] S5: Distillation

[0093] The esterified liquid is added to a distillation device, distilled under a vacuum degree of 95 kPa, and the distillate is collected as a lactic acid ester product.

[0094] Comparative Example 2

[0095] This embodiment provides a method for treating kitchen waste and a prepared carbon source. The difference from Comparative Example 1 is that the strain added in step S2 is yeast, there are no steps 4 and 5, and the filtrate is treated by the reduced pressure and low temperature evaporation method described in Example 6.

[0096] Related performance tests and result analysis

[0097] 1. Suspended solids (SS) test

[0098] The carbon sources prepared in the above-mentioned Examples 1 to 6, Comparative Example 1 and Comparative Example 2 were tested for suspended matter value.

[0099] The test standard refers to the "Determination of suspended solids in water by gravimetric method (GB 11901-89)", and the instruments used are a suction filtration device, a 0.45μm filter membrane, and an oven. The test steps are as follows:

[0100] After drying the filter membrane to a constant weight, weigh the filter membrane weight m1; weigh 100mL of water sample and filter it with a suction filtration device; after the filtration is completed, put the filter membrane in an oven and dry it at 100-105℃ to a constant weight, and weigh the filter membrane weight m2. The suspended matter calculation formula is: C = (m2-m1) / 100, where: C - suspended matter concentration, in mg / L; m1, m2: filter membrane weight, filter membrane + suspended matter weight, in g.

[0101] 2. Chemical oxygen demand (COD value) test

[0102] The intermediate products of Examples 1 to 9, Comparative Example 1, Comparative Example 2 and the finally prepared carbon source were subjected to chemical oxygen demand tests.

[0103] The test standard refers to the "Determination of Chemical Oxygen Demand in Water - Dichromate Method (HJ828-2017)". The instruments used are digestion device, acid burette, 25mL digestion tube, 150mL conical flask, 250mL beaker. The test steps are as follows:

[0104] (1) Digestion

[0105] Accurately draw 3.00mL of uniform water sample (two blanks need to be made at the same time of testing, and 3.00mL of distilled water is directly measured for the blanks) and place it in the digestion tube, add 1.00mL of masking agent, 3.00mL of digestion solution (the amount added needs to be accurately measured), 5.00mL of catalyst, and shake well. Tighten the sealing cap, insert the digestion tube into the device that has reached 160℃ in turn, and digest for 25 minutes.

[0106] (2) Titration

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

[0108] (3) Calculation

[0109]

[0110] Where:

[0111] V0—blank consumption of ammonium ferrous sulfate standard solution (mL);

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

[0113] V2—water sample volume (mL);

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

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

[0116] 3. Total nitrogen content test

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

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

[0119] The test steps are:

[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 for testing.

[0122] (2) Sample determination

[0123] Dilute the sample 1000 times, take 10.00mL of the sample into a 25mL stoppered ground glass colorimetric tube, add water to the 10mL mark, (blank is synchronized with the following method) and then add 5.00mL of alkaline potassium persulfate solution, plug the tube tightly, and tie the tube tightly with gauze and string to prevent it from popping out. Place the colorimetric tube in a high-pressure steam sterilizer, heat until the top pressure valve blows, close the valve, continue to heat to 120℃ and start timing, and keep the temperature between 120 and 124℃ for 30min. Cool naturally, open the valve to release air, remove the outer cover, take out the colorimetric tube and cool it to room temperature, press the tube stopper to mix the liquid in the colorimetric tube upside down 2 to 3 times. Add 1.0mL of hydrochloric acid solution to each colorimetric tube, dilute with water to the 25mL mark, cover and mix. Use a 10mm quartz cuvette on a UV spectrophotometer, with water as a reference, and measure the absorbance at wavelengths of 220nm and 275nm respectively.

[0124] (3) Blank experiment

[0125] Substitute 10.00 mL of water for the sample and perform the measurement according to the sample measurement procedure.

[0126] (4) Calculation

[0127]

[0128] Where:

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

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

[0131] a—intercept of the calibration curve;

[0132] f—dilution factor;

[0133] b—slope of the calibration curve;

[0134] V—sample volume (mL).

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

[0136] Table 1

[0137]

[0138]

[0139] It can be seen from Table 1 that Examples 1 to 6 all adopt directional fermentation treatment, followed by filtration treatment, and finally the filtrate is subjected to distillation treatment and condensation treatment to obtain condensate as a carbon source, which has a high COD value, low total nitrogen content, and low SS value, and is a high-quality carbon source. In contrast, the directional fermentation of lactic acid in Comparative Example 1 is difficult to separate and purify lactic acid, especially during evaporation treatment, because lactic acid is not volatile and has a high boiling point, so water will evaporate when evaporating, resulting in a high water content in the obtained carbon source and a low COD value. In Comparative Example 2, directional fermentation of ethanol, because the kitchen waste has been acidified during storage and collection, polysaccharides such as starch and cellulose have been decomposed into small molecular acids, and the yield of ethanol is very low.

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

[0141] The COD value of the condensate obtained in Examples 1 to 3 is high, indicating that setting a suitable pH range is conducive to the fermentation of the bacteria in the composite bacteria. There are different dominant bacteria under different fermentation conditions. The adaptation of reaction conditions and bacteria can improve the fermentation effect.

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

Claims

1. A method for treating food waste, characterized in that: The steps include: The kitchen waste is subjected to a directed fermentation treatment in an acidic environment to obtain a fermentation mixture; filtering the fermentation mixture to obtain a filtrate; The filtrate is sequentially subjected to distillation treatment and condensation treatment, and volatile organic matter is collected to obtain a condensate containing volatile fatty acids and low molecular alcohols.

2. The method for treating food waste according to claim 1, characterized in that: The bacteria species subjected to the directed fermentation treatment include Propionibacterium, Clostridium, Saccharomyces and Lactobacillus; And / or, 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 bacteria strain is (5-10):

1.

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

4. The method for treating food waste according to claim 1 or 2, characterized in that: The time of the directional fermentation treatment is 2 to 3 days.

5. The method for treating food 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 food 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 the propionic acid, the butyric acid, the acetic acid, the propanol and the ethanol is (1.5-3): (0.8-1.5): (1.5-2.5): (1.1-1.5): 1; And / or, the temperature of the distillation treatment is 70-95°C.

7. The method for treating food waste according to claim 1 or 2, characterized in that: The filtration treatment includes the step of filtering through a ceramic flat membrane, wherein the pore size of the ceramic flat membrane is 0.05 to 0.2 microns; and / or, the suspended matter value of the filtrate is 10 to 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 food waste according to claim 1 or 2, characterized in that: The chemical oxygen demand of the condensate is 100000-150000 mg / L; and / or, the total nitrogen content of the condensate is 0 to 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 method for treating kitchen waste according to any one of claims 1 to 8.

10. Use of the carbon source according to claim 9 in any one of denitrification and denitrification, sludge acclimatization, and restoration of sludge activity in sewage treatment.

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