Method for preparing denitrification composite carbon source from kitchen waste

Abstract

The invention discloses a method for preparing a denitrification composite carbon source by using kitchen waste, and relates to the technical field of kitchen waste resourceful treatment, and the method comprises the following specific steps: pretreatment, oil removal, hydrolytic acidification, solid-liquid separation, biochar preparation and carbon source compounding. Wherein the yield of volatile fatty acid (VFAs) can be remarkably improved by performing damp-heat pretreatment on fermentation, the biochar provides an adsorption carrier and a microorganism attachment site for the VFAs, the release period of a carbon source is prolonged, and a carbon source-carrier-catalyst ternary system is formed by the biochar, the VFAs and divalent metal cations, so that the denitrification rate is improved. The cost of the denitrification composite carbon source is obviously lower than that of a traditional commercial carbon source, and deep resource utilization of the kitchen waste is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of resource processing of restaurant and kitchen waste, and in particular to a method for preparing a denitrification composite carbon source by utilizing restaurant and kitchen waste. Background Art

[0002] With the growth of urban populations and improvements in living standards, the amount of food waste generated has been increasing annually. As a significant component of municipal solid waste, its treatment has always been a challenge in environmental management. Traditional methods for food waste disposal include landfill, incineration, and composting. However, these methods are often associated with secondary pollution, resource waste, and long recycling times.

[0003] Carbon sources are key substances in biological processes such as denitrification and denitrification in the wastewater treatment industry. Currently, the industry primarily relies on commercial carbon sources such as sodium acetate and glucose. These are expensive, placing significant financial pressure on wastewater treatment plants. Furthermore, commercial carbon sources are limited in functionality, lacking the slow-release properties and synergistic effects on microbial growth.

[0004] The composition of restaurant kitchen waste is complex, containing high concentrations of grease, salt and various impurities, and the efficiency of direct fermentation is low. At present, restaurant kitchen waste can be fermented by microorganisms to produce liquid chemicals, which are used as carbon sources for sewage treatment. In CN111333179B, lactic acid fermentation of restaurant kitchen waste is used to produce a carbon source for denitrification of wastewater, and in CN103243125B, volatile fatty acids (VFAs) are produced by anaerobic fermentation of restaurant kitchen waste to prepare a carbon source. Although the carbon sources prepared by the above methods can be used for sewage treatment and can achieve the reduction, resource utilization and harmlessness of restaurant kitchen waste, the carbon source components and functions prepared by this method using restaurant kitchen waste are single, do not have a synergistic effect, and fail to achieve the maximum resource utilization of restaurant kitchen waste. Therefore, it is necessary to develop a carbon source that maximizes the resource utilization of restaurant kitchen waste, is more affordable and highly efficient and composite. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing a denitrification composite carbon source using food waste, thereby solving the following technical problems:

[0006] 1. Commercial carbon sources are expensive, which increases the cost of sewage treatment.

[0007] 2. Conventional carbon sources have a single function and lack the slow-release properties and synergistic promotion effect on microorganisms.

[0008] The purpose of the present invention can be achieved through the following technical solutions:

[0009] The present invention provides a method for preparing a denitrification composite carbon source using food waste, comprising the following steps:

[0010] S1. Pretreatment: The kitchen waste is crushed and magnetically separated to remove metal impurities, and then the material is put into a high-temperature cooking tank for wet heat treatment;

[0011] S2. Oil removal: Cool the material after wet heat treatment to 60-70℃ and perform centrifugal oil extraction;

[0012] S3, hydrolysis and acidification: cooling the oil-extracted material, adjusting the pH, and then inoculating lactic acid bacteria and Bacillus for fermentation;

[0013] S4, solid-liquid separation: separating the fermentation broth to obtain liquid-phase volatile fatty acids and solid-phase residue;

[0014] S5. Biochar preparation: The solid residue is pyrolyzed to generate biochar, which is then activated by acid washing and ground to nanoscale;

[0015] S6. Carbon source composite: Volatile fatty acids are mixed with biochar, 1‰ divalent cations are added, ultrasonic dispersion is performed, and then drying and granulation are performed to prepare a denitrification composite carbon source.

[0016] More preferably, in step S1, the food waste specifically includes food leftovers from restaurants, hotels, company canteens, etc. and waste generated from the processing of fruits, vegetables, meat, oil, pastries, etc. in the back kitchen.

[0017] More preferably, in step S1, the food waste is in any one of a solid mixture and a solid-liquid mixture.

[0018] More preferably, in step S1, the chemical components of the food waste include proteins, lipids, polysaccharides, trace inorganic salts and short-chain fatty acids.

[0019] More preferably, in step S1, the temperature of the high-temperature cooking tank is 100-120°C, the pressure is 0.2-0.5 MPa, and the time of the wet heat treatment is 30-60 minutes.

[0020] More preferably, in step S3, the temperature of hydrolysis and acidification is 35-45° C., the pH value is 5.0-6.0, and the fermentation is anaerobic fermentation for 24-48 hours.

[0021] More preferably, in step S5, the biochar is produced by pyrolysis of the solid residue at 500-700°C in the absence of oxygen.

[0022] More preferably, in step S5, the particle size of the ground biochar is ≤100 nm.

[0023] More preferably, in step S6, the mass ratio of volatile fatty acids to biochar is (3-8):1.

[0024] More preferably, in step S6, the divalent metal cation is Fe 2+ and Mg 2+ .

[0025] Beneficial effects of the present invention:

[0026] 1. Treat waste with waste: Use food waste as raw material to develop a cheap sewage denitrification composite carbon source. After the food waste is treated, the liquid part is used to prepare the carbon source, and the solid residue is prepared into biochar, thereby loading the carbon source and maximizing the resource utilization of food waste.

[0027] 2. Process advantages: The fermentation is subjected to moist heat pretreatment, which increases the yield of volatile fatty acids by at least 40% compared with conventional fermentation.

[0028] 3. Synergistic Effects: Pyrolysis of solid residues produces biochar, which not only provides a carbon source but also serves as a carrier for volatile fatty acids and a site for microbial attachment, thereby extending the carbon source release cycle. Biochar is loaded with volatile fatty acids and divalent metal cations, forming a "carbon source-carrier-catalyst" ternary system that enhances denitrification rates. With a carbon source TCOD equivalent of ≥570 mg / g, the denitrification rate is 30%-50% higher than that of the commercial carbon source, sodium acetate. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 : Schematic diagram of the process of the present invention;

[0030] Figure 2 : Microstructure diagram of composite carbon source. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0032] Unless otherwise specified, the experimental methods in the following examples are conventional methods and were performed according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials and reagents used in the following examples, unless otherwise specified, were all commercially available.

[0033] Example 1

[0034] S1. Take one ton of food waste, containing approximately 10%-30% protein, 5%-25% lipids, 20%-60% polysaccharides, and 0.1%-5% short-chain fatty acids. This food waste is crushed and pre-treated by magnetic separation to remove metal impurities, yielding a slurry containing 80% organic matter. This slurry is then placed in a high-temperature cooking tank at 100°C and 0.3 MPa for 45 minutes.

[0035] S2. Cool the material after the wet heat treatment in step S1 to 65°C for centrifugal oil extraction at a rotation speed of 2800 rpm and a centrifugal time of 6 minutes.

[0036] S3. Cool the oil-extracted material to 40°C, adjust the pH to 5.5, inoculate lactic acid bacteria and Bacillus, and perform anaerobic fermentation for 36 hours to complete hydrolysis and acidification, and measure the concentration of volatile fatty acids in the material.

[0037] Example 2

[0038] S1. Take one ton of food waste, containing approximately 10%-30% protein, 5%-25% lipids, 20%-60% polysaccharides, and 0.1%-5% short-chain fatty acids. This food waste is crushed and pre-treated by magnetic separation to remove metal impurities, resulting in a slurry containing 80% organic matter. This slurry is then placed in a high-temperature cooking tank at 110°C and 0.3 MPa for 45 minutes.

[0039] S2. Cool the material after the wet heat treatment in step S1 to 65°C for centrifugal oil extraction at a rotation speed of 2800 rpm and a centrifugal time of 6 minutes.

[0040] S3. Cool the oil-extracted material to 40°C, adjust the pH to 5.5, inoculate lactic acid bacteria and Bacillus, and perform anaerobic fermentation for 36 hours to complete hydrolysis and acidification, and measure the concentration of volatile fatty acids in the material.

[0041] Example 3

[0042] S1. Take one ton of food waste, containing approximately 10%-30% protein, 5%-25% lipids, 20%-60% polysaccharides, and 0.1%-5% short-chain fatty acids. This food waste is crushed and pre-treated by magnetic separation to remove metal impurities, resulting in a slurry containing 80% organic matter. This slurry is then placed in a high-temperature cooking tank at 120°C and 0.3 MPa for 45 minutes.

[0043] S2. Cool the material after the wet heat treatment in step S1 to 65°C for centrifugal oil extraction at a rotation speed of 2800 rpm and a centrifugal time of 6 minutes.

[0044] S3. Cool the oil-extracted material to 40°C, adjust the pH to 5.5, inoculate lactic acid bacteria and Bacillus, and perform anaerobic fermentation for 36 hours to complete hydrolysis and acidification, and measure the concentration of volatile fatty acids in the material.

[0045] Example 4

[0046] S1. Preprocessing

[0047] S1. Take one ton of food waste, containing approximately 15%-25% protein, 10%-20% lipids, 40%-55% polysaccharides, and 0.1%-3% short-chain fatty acids. This food waste is pre-treated by crushing and magnetic separation to remove metal impurities, yielding a slurry with an organic matter content of 80%. This slurry is then placed in a high-temperature cooking tank at 110°C and 0.3 MPa for 45 minutes.

[0048] S2. Degreasing

[0049] The material after the wet heat treatment in step S1 was cooled to 65°C for centrifugal oil extraction at a rotation speed of 2800 rpm and a centrifugal time of 6 minutes.

[0050] S3. Hydrolysis and acidification

[0051] The oil-extracted material was cooled to 40°C, the pH was adjusted to 5.5, lactic acid bacteria and Bacillus were inoculated, and hydrolysis and acidification were completed through anaerobic fermentation for 36 hours.

[0052] S4. Solid-liquid separation: The fermentation broth is separated into liquid VFAs and solid residue by filtration.

[0053] S5. Biochar preparation

[0054] The solid residue is pyrolyzed at 600°C and the volume fraction of oxygen content is less than 6% to generate biochar, which is activated by pickling with dilute hydrochloric acid and then ground into nanoscale.

[0055] S6, Carbon source complex

[0056] Liquid VFAs and biochar were mixed at a mass ratio of 3:1, and 1‰ Fe 2+ and Mg 2+ , ultrasonically dispersed and then dried and granulated to obtain a denitrification composite carbon source.

[0057] Example 5

[0058] S1. Preprocessing

[0059] S1. Take one ton of food waste, containing approximately 15%-25% protein, 10%-20% lipids, 40%-55% polysaccharides, and 0.1%-3% short-chain fatty acids. This food waste is pre-treated by crushing and magnetic separation to remove metal impurities, yielding a slurry with an organic matter content of 80%. This slurry is then placed in a high-temperature cooking tank at 110°C and 0.3 MPa for 45 minutes.

[0060] S2. Degreasing

[0061] The material after the wet heat treatment in step S1 was cooled to 65°C for centrifugal oil extraction at a rotation speed of 2800 rpm and a centrifugal time of 6 minutes.

[0062] S3. Hydrolysis and acidification

[0063] The oil-extracted material was cooled to 40°C, the pH was adjusted to 5.5, lactic acid bacteria and Bacillus were inoculated, and hydrolysis and acidification were completed through anaerobic fermentation for 36 hours.

[0064] S4. Solid-liquid separation: The fermentation broth is separated into liquid VFAs and solid residue by filtration.

[0065] S5. Biochar preparation

[0066] The solid residue is pyrolyzed at 600°C and the volume fraction of oxygen content is less than 6% to generate biochar, which is activated by pickling with dilute hydrochloric acid and then ground into nanoscale.

[0067] S6, Carbon source complex

[0068] Liquid VFAs and biochar were mixed at a mass ratio of 5:1, and 1‰ of metal elements (Fe 2+ Mg2 + ), ultrasonically dispersed and then dried and granulated to obtain a denitrification composite carbon source.

[0069] The specific surface area of ​​the biochar prepared in Example 5 is 600 m 2 / g, which can provide sufficient sites for VFAs adsorption. The microstructure of the prepared denitrification composite carbon source was observed by scanning electron microscopy (SEM). Figure 2 As shown in Figure 3), it can be seen that the pores of biochar provide adsorption sites for VFAs, thereby extending the carbon source release cycle.

[0070] Example 6

[0071] S1. Preprocessing

[0072] S1. Take one ton of food waste, containing approximately 15%-25% protein, 10%-20% lipids, 40%-55% polysaccharides, and 0.1%-3% short-chain fatty acids. This food waste is pre-treated by crushing and magnetic separation to remove metal impurities, yielding a slurry with an organic matter content of 80%. This slurry is then placed in a high-temperature cooking tank at 110°C and 0.3 MPa for 45 minutes.

[0073] S2. Degreasing

[0074] The material after the wet heat treatment in step S1 was cooled to 65°C for centrifugal oil extraction at a rotation speed of 2800 rpm and a centrifugal time of 6 minutes.

[0075] S3. Hydrolysis and acidification

[0076] The oil-extracted material was cooled to 40°C, the pH was adjusted to 5.5, lactic acid bacteria and Bacillus were inoculated, and hydrolysis and acidification were completed through anaerobic fermentation for 36 hours.

[0077] S4. Solid-liquid separation: The fermentation broth is separated into liquid VFAs and solid residue by filtration.

[0078] S5. Biochar preparation

[0079] The solid residue is pyrolyzed at 600°C and the volume fraction of oxygen content is less than 6% to generate biochar, which is activated by pickling with dilute hydrochloric acid and then ground into nanoscale.

[0080] S6, Carbon source complex

[0081] Liquid VFAs and biochar were mixed at a mass ratio of 8:1, and 1‰ Fe 2+ and Mg 2+ , ultrasonically dispersed and then dried and granulated to obtain a denitrification composite carbon source.

[0082] Comparative Example 1

[0083] Compared with Example 2, the only difference is that the slurry obtained in step S1 is not subjected to wet heat treatment, but is directly subjected to step S2 centrifugal oil extraction and subsequent steps.

[0084] Comparative Example 2

[0085] Compared with Example 6, the only difference is that in step S6, no divalent metal cations are added when preparing the composite carbon source.

[0086] Comparative Example 3

[0087] Compared with Example 5, the only difference is that in step S6, when preparing the composite carbon source, the mass ratio of VFAs to biochar is 10:1.

[0088] Comparative Example 4

[0089] The commercial carbon source sodium acetate was used for carbon source TCOD and denitrification rate calculations.

[0090] The VFA concentrations of Examples 1-3 and Comparative Example 1 were calculated using the following test method: Referring to CJ / T-2005:5 Determination of Fatty Acids. The VFA concentration results are listed in Table 1.

[0091] Table 1

[0092]

[0093] Analysis of the data in Table 1 shows that, compared with the conventional fermentation in Comparative Example 1, Examples 1-3 subjected the kitchen waste to wet heat treatment. As a result, the VFAs concentration in Example 1 was 17.2 g / L, and the VFAs concentration in Example 3 was 31 g / L, while the VFAs concentration without wet heat treatment was only 12 g / L. The wet heat treatment can increase the VFAs concentration by 43%-158%, indicating that wet heat pretreatment can significantly increase the VFAs concentration.

[0094] Carbon source TCOD equivalents were calculated for Examples 4-5 and Comparative Examples 2-4 using the following test method: The TCOD equivalent of a carbon source is the milligrams of oxygen required to oxidize a unit mass of the carbon source. This is an important indicator of oxygen consumption during carbon source oxidation. The measurement method follows HJ828-2017. The results of the carbon source TCOD equivalents are listed in Table 2.

[0095] Table 2

[0096]

[0097]

[0098] From the analysis of the data in Table 2, it can be seen that in Examples 4-6, the denitrification composite carbon source prepared by the method of the present invention is as follows: when the mass ratio of VFAs to biochar is 3:1, Fe 2+ and Mg 2+ When the addition amount is 1‰, the TCOD equivalent of the denitrifying composite carbon source is 860mg / g, while the TCOD equivalent of the commercial carbon source sodium acetate is only 630mg / g. The TCOD equivalent of the denitrifying composite carbon source of the present invention is significantly higher than the TCOD equivalent of the traditional commercial carbon source sodium acetate. After VFA is compounded with biochar, VFA is adsorbed on the surface of biochar. The high-efficiency composite carbon source prepared with a high proportion of biochar has a high TCOD. As can be seen from Comparative Example 2, Fe 2+ and Mg 2+ It has no effect on the TCOD equivalent of the carbon source.

[0099] Denitrification rates were calculated for Example 6 and Comparative Examples 2 and 4 using the following test method: A wastewater volume of 50 L and an initial nitrate-nitrogen concentration of 239 mg / L were used. Commercial sodium acetate and the high-efficiency composite carbon source prepared in Example 6 were dissolved in water to obtain an aqueous solution with a SCOD of 40,000 mg / L. The commercial sodium acetate carbon source and the prepared high-efficiency composite carbon source aqueous solution were then added to control the C / N ratio (based on SCOD) to be 7. The initial nitrate-nitrogen concentration in the mixed solution was measured, and the nitrate-nitrogen concentration in the mixed solution was measured at regular intervals. A nitrate-nitrogen curve was generated based on the measurement results. The denitrification rate was then calculated using the slope of the curve and the MLVSS value of the mixed solution. The denitrification rate results are listed in Table 3.

[0100] Table 3

[0101]

[0102] By analyzing the data in Table 3, it can be seen from Example 6 and Comparative Example 4 that the carbon source TCOD equivalent is ≥570 mg / g, and the denitrification rate of the composite carbon source prepared by the present invention is increased by 45% compared with the commercial carbon source sodium acetate. 2+ and Mg 2+ The denitrification rate increased by 15% compared with the composite carbon source without addition. The above results show that biochar loaded VFAs and divalent metal cations to form a "carbon source-carrier-catalyst" ternary system, which increased the denitrification rate and saved carbon source costs.

[0103] The above demonstrates that the disclosed method for preparing a composite carbon source for denitrification from food waste, leveraging process advantages such as wet heat treatment during fermentation, biochar support, and the addition of divalent metal cations to form a "carbon source-support-catalyst" ternary system, can effectively increase the denitrification rate. This method not only addresses the secondary pollution and resource waste associated with traditional food waste treatment methods, but also offers significant economic and environmental benefits.

[0104] The above is a detailed description of an embodiment of the present invention. However, the content described is only a preferred embodiment of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A method for preparing a denitrification composite carbon source using food waste, characterized in that: The method comprises the following steps: S1. Pretreatment: The kitchen waste is crushed and magnetically separated to remove metal impurities, and then the material is put into a high-temperature cooking tank for wet heat treatment; S2. Oil removal: Cool the material after wet heat treatment to 60-70℃ and perform centrifugal oil extraction; S3, hydrolysis and acidification: cooling the oil-extracted material, adjusting the pH, and then inoculating lactic acid bacteria and Bacillus for fermentation; S4, solid-liquid separation: separating the fermentation broth to obtain liquid-phase volatile fatty acids and solid-phase residue; S5. Biochar preparation: The solid residue is pyrolyzed to generate biochar, which is then activated by acid washing and ground to nanoscale; S6. Carbon source composite: Volatile fatty acids are mixed with biochar, 1‰ divalent cations are added, ultrasonic dispersion is performed, and then drying and granulation are performed to prepare a denitrification composite carbon source.

2. The method for preparing a denitrification composite carbon source from kitchen waste according to claim 1, wherein: In step S1, the food waste specifically includes food leftovers from restaurants, hotels, company canteens, etc. and waste generated during the processing of fruits, vegetables, meat, oil, pastries, etc. in the kitchen.

3. The method for preparing a denitrification composite carbon source from kitchen waste according to claim 1, wherein: In step S1, the food waste is in any one of a solid mixture and a solid-liquid mixture state.

4. The method for preparing a denitrification composite carbon source from food waste according to claim 1, wherein: In step S1, the chemical components of the food waste include proteins, lipids, polysaccharides, trace inorganic salts and short-chain fatty acids.

5. The method for preparing a denitrification composite carbon source from food waste according to claim 1, wherein: In step S1, the temperature of the high-temperature cooking tank is 100-120° C., the pressure is 0.2-0.5 MPa, and the time of the wet heat treatment is 30-60 minutes.

6. The method for preparing a denitrification composite carbon source from food waste according to claim 1, characterized in that: In step S3, the hydrolysis and acidification temperature is 35-45° C., the pH value is 5.0-6.0, and the fermentation is anaerobic fermentation for 24-48 hours.

7. The method for preparing a denitrification composite carbon source from kitchen waste according to claim 1, characterized in that: In step S5, the biochar is prepared by pyrolysis of solid residue at 500-700°C in the absence of oxygen.

8. The method for preparing a denitrification composite carbon source from food waste according to claim 1, characterized in that: In step S5, the particle size of the ground biochar is ≤100 nm.

9. The method for preparing a denitrification composite carbon source from food waste according to claim 1, characterized in that: In step S6, the mass ratio of the volatile fatty acids to the biochar is (3-8):

1.

10. The method for preparing a denitrification composite carbon source from food waste according to claim 1, characterized in that: In step S6, the divalent metal cation is Fe 2+ and Mg 2+ .

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