A method for anaerobic digestion and gas production of high-sodium food waste

Abstract

This invention belongs to the field of waste treatment technology, specifically relating to a method for anaerobic digestion and gas production from high-sodium kitchen waste. The method includes the following steps: (1) loading inoculated sludge into a reaction bottle in an anaerobic workstation, adding basic nutrient solution, running for 3-5 days without adding NaCl, then adding NaCl daily to increase the sodium ion concentration to 5-5.5 g / L, and continuing stable operation for 7-9 days to obtain acclimated inoculated sludge; (2) collecting kitchen waste, removing large debris such as bones, plastics, and chopsticks, crushing it to obtain cleaned kitchen waste, adding betaine to the cleaned kitchen waste, and stirring evenly; (3) adding the acclimated inoculated sludge from step (1) and the cleaned kitchen waste from step (2) into a reactor for mesophilic anaerobic digestion. This invention addresses the problem of low gas production efficiency in anaerobic digestion of high-sodium kitchen waste by acclimation, further improving gas production efficiency.

Description

Technical Field

[0001] This invention belongs to the field of waste treatment technology, specifically relating to a method for anaerobic digestion and gas production from high-sodium kitchen waste. Background Technology

[0002] With the acceleration of urbanization, the amount of urban domestic waste has increased dramatically, and food waste is one of the main components of urban domestic waste. Food waste refers to food scraps and waste generated during the production and operation of catering services and collective meal services, as well as by residents in their daily lives. Because food waste has a high water content and is easily perishable, improper disposal can cause significant harm to the atmosphere, soil, water bodies, and public health. Anaerobic digestion for biogas production is an effective technical approach for the resource utilization of food waste and is also a major treatment technology for food waste in my country. Anaerobic digestion is a process that uses anaerobic and facultative microorganisms under anaerobic conditions to convert biodegradable organic components into methane and carbon dioxide, thus stabilizing organic waste. For example, CN101250554B discloses a method for increasing the hydrogen production rate of anaerobic digestion of food waste.

[0003] Sodium chloride is an essential condiment in Chinese cuisine, inevitably accumulating in large quantities in food waste. However, during anaerobic digestion, high concentrations of sodium ions can cause osmotic pressure imbalances, cell membrane disturbances, and inhibit cell division and expansion in anaerobic microorganisms, negatively impacting microbial metabolism and enzyme function. While washing can reduce sodium ion content in food waste, it is costly and inefficient, and the wastewater generated requires further treatment. Therefore, high sodium ion concentrations significantly inhibit the production of biogas from anaerobic digestion.

[0004] Anaerobic digestion is a complex biochemical process. The stability and efficiency of anaerobic systems are influenced by the microbial community structure. Through acclimatization, the microbial community can gradually adapt to a high-sodium environment, thereby improving the gas production efficiency of anaerobic digestion. Many plants and other organisms synthesize compounds called osmotic regulators, whose main function is to maintain the osmotic pressure inside and outside the cell. They maintain a dynamic balance by regulating the concentration of inorganic salts between the cytoplasm and vacuoles. Betaine, also known as trimethylhydantoin (C5H... 11 NO2·H2O is an osmotic regulator with water-absorbing and water-retaining properties. It plays an irreplaceable role in the metabolic processes of biological cells, regulating the osmotic pressure of cell sap and increasing stress resistance. However, current technologies only add betaine during the acclimation process, which is not ideal for anaerobic digestion and gas production of high-sodium food waste, especially food waste with a sodium ion content of ≥5g / L. Summary of the Invention

[0005] The purpose of this invention is to provide a method for anaerobic digestion and gas production of high-sodium food waste. Addressing the problem of low gas production efficiency in anaerobic digestion of high-sodium food waste, this invention enhances the adaptability of microbial strains to high-sodium environments through acclimatization, and further improves gas production efficiency by adding an osmotic regulator to maintain the osmotic pressure inside and outside the cells of the functional microbial strains.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for anaerobic digestion and gas production from high-sodium food waste includes the following steps: (1) Load the inoculated sludge into the reaction bottle in the anaerobic workstation, add basic nutrient solution, run without adding NaCl for 3-5 days, then add NaCl every day to increase the sodium ion concentration to 5-5.5 g / L, and continue to run stably for 7-9 days to obtain the acclimated inoculated sludge. (2) Collect kitchen waste, remove large pieces of debris such as bones, plastics, and chopsticks, crush it to obtain kitchen waste after impurity removal, add betaine to the kitchen waste after impurity removal, and stir evenly; (3) Add the inoculated sludge after acclimatization in step (1) and the kitchen waste after impurity removal in step (2) to the reactor for mesophilic anaerobic digestion.

[0007] Preferably, the basic nutrient solution includes water, glucose, NH4Cl, yeast extract, KH2PO4, NaHCO3, betaine, trehalose, tetrahydropyrimidine, and trace element solution.

[0008] Preferably, NaCl is added daily to increase the sodium ion concentration by 0.3-0.4 g / L per day, eventually reaching 5-5.5 g / L.

[0009] Preferably, during the acclimatization period in step (1), the nutrient solution is changed every 3 days, the supernatant is discarded after standing, and fresh nutrient solution and corresponding NaCl are added to keep the volume of the mixture in the reaction flask constant.

[0010] Preferably, the basic nutrient solution comprises: 2064-2080 mg / L glucose, 0.12-0.20 g / L NH4Cl, 0.1-0.2 g / L yeast extract, 16.4-17 mg / L KH2PO4, 2-3 g / L NaHCO3, 0.5-1 g / L betaine, 0.5-1.0 g / L trehalose, 85-100 mg / L tetrahydropyrimidine, and 1.0-1.4 mL / L trace element solution per liter of water.

[0011] In existing anaerobic digestion of high-sodium food waste, only a single osmotic regulator, betaine, is typically added. However, a single substance cannot simultaneously address multiple inhibitory targets under high sodium stress: osmotic pressure imbalance, decreased cell membrane fluidity, and inactivation of key enzymes, resulting in a long salt tolerance acclimatization period and slow recovery of methanogenic activity. This invention uses a specific basal nutrient solution formula containing a ternary combination of 0.5–1.0 g / L betaine, 0.5–1.0 g / L trehalose, and 85–100 mg / L tetrahydropyrimidine. This improves the methanogenic activity of food waste under anaerobic digestion conditions with a sodium ion concentration of 5–8 g / L. The reason for this is that betaine, as the most effective compatible solute, directly participates in intracellular osmotic pressure balance without consuming additional energy; trehalose stabilizes the cell membrane phospholipid bilayer and the natural structure of proteins, preventing protein denaturation caused by high salt; and tetrahydropyrimidine specifically protects DNA and enzyme active sites and promotes the expression of heat shock proteins. The three elements complement each other in their target areas and work synergistically to form a three-in-one defense network of osmotic pressure balance, membrane structure protection, and enzyme activity maintenance, enabling functional bacteria to quickly adapt to high-sodium environments.

[0012] Preferably, the formulation of the trace element solution includes: per liter of water: FeCl2·4H2O 2.0-2.4g, CoCl2·6H2O 0.5-1.0g, MnCl2·4H2O 0.3-0.5g, AlCl3 0.5-0.8g, H3BO3 0.5-0.6g, ZnCl2 0.4-0.6g, (NH4)6Mo7O 24 ·4H2O0.5-0.7g, CuCl2·2H2O0.3-0.5g.

[0013] This invention ensures that the activity of various metalloenzymes in the methanogenic metabolic pathway is not restricted in a high-sodium environment by using the synergistic supply of trace elements with a specific composition, forming a comprehensive protection with the osmotic regulator: the osmotic regulator maintains the intracellular environment, and the trace elements ensure better metabolic function.

[0014] Preferably, betaine is added to the cleaned kitchen waste, and the amount added is weighed at 1-1.2 g / L of betaine per liter of kitchen waste.

[0015] Traditional acclimatization methods often involve increasing the sodium ion gradient by approximately 0.5 g / L daily, but this approach is not ideal in the method described in this invention. The specific parameters used in this invention involve daily addition of NaCl to gradually increase the sodium ion concentration from an initial low salt level, stabilizing at a final concentration. This improves the rate and stability of the microbial community's tolerance to high sodium. Analysis shows that this rate provides sufficient time for microorganisms to synthesize endogenous compatible solutes through gene expression upregulation, while also forming a dual osmotic protection system with exogenously added betaine, trehalose, and tetrahydropyrimidine: the exogenous protectant directly alleviates acute stress, while the gradual gradient induces the microbial community to initiate long-term adaptive mechanisms. The synergistic result is that the acclimatized microbial community not only remains stable under static high sodium conditions but also maintains metabolic activity during dynamic salt increases, thereby significantly increasing the cumulative methane production during subsequent anaerobic digestion of food waste.

[0016] Preferred mesophilic anaerobic digestion conditions: temperature 30-35℃, shaking speed 120-150rpm.

[0017] Preferably, based on volatile solids, the inoculated sludge after acclimatization in step (1) and the kitchen waste after impurity removal in step (2) are added to the reactor at a mass ratio of (2-4):1.

[0018] Preferably, the volume of the nutrient solution is 15-20% of the sludge volume.

[0019] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: 1. The specific basic nutrient solution formula used in this invention contains a ternary compound combination of betaine, trehalose, and tetrahydropyrimidine at specific concentrations. This improves the methanogenic activity of food waste undergoing anaerobic digestion under sodium ion concentrations of 5-8 g / L.

[0020] 2. This invention ensures that the activity of various metalloenzymes in the methanogenic metabolic pathway is not restricted in a high-sodium environment by using the synergistic supply of trace elements with specific composition, forming a comprehensive protection with the osmotic regulator: the osmotic regulator maintains the intracellular environment, and the trace elements ensure better metabolic operation.

[0021] 3. Specific parameters used in this invention: NaCl is added daily to increase the sodium ion concentration by a specific amount each day, gradually increasing it from an initial low salt level and stabilizing it at the final concentration, thereby improving the rate and stability of the bacterial community's tolerance to high sodium. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] All raw materials used in the following embodiments of the present invention are commercially available products.

[0024] Example 1 This embodiment provides a method for anaerobic digestion and gas production from high-sodium food waste, including the following steps: (1) Take the digested sludge from the anaerobic digester of the municipal wastewater treatment plant as the inoculum sludge. The volatile suspended solids (VSS) concentration of the inoculum sludge is 15 g / L. Use an anaerobic workstation and keep the temperature stable at 35℃. Preparation of basic nutrient solution: The basic nutrient solution includes: 2069 mg / L glucose, 0.16 g / L NH4Cl, 0.14 g / L yeast extract, 16.8 mg / L KH2PO4, 2.3 g / L NaHCO3, 0.5 g / L betaine, 0.5 g / L trehalose, 90 mg / L tetrahydropyrimidine, and 1.2 mL / L trace element solution per liter of water. The formula for the trace element solution includes: per liter of water: FeCl2·4H2O 2.2g, CoCl2·6H2O 0.6g, MnCl2·4H2O 0.4g, AlCl3 0.7g, H3BO3 0.55g, ZnCl2 0.49g, (NH4)6Mo7O 24 ·4H2O0.6g, CuCl2·2H2O0.4g.

[0025] The inoculated sludge was placed into the reaction flask in the anaerobic workstation, and a basic nutrient solution was added, with the volume of the nutrient solution being 20% ​​of the sludge volume. The system was run for 3 days initially. After 3 days, solid NaCl was added daily to increase the sodium ion concentration by 0.35 g / L per day, eventually reaching 5 g / L. Once the concentration reached 5 g / L, the system continued to operate stably for 7 days. During the acclimation period, the nutrient solution was changed every 3 days. After settling, the supernatant was discarded, and fresh nutrient solution and the corresponding amount of NaCl were added to maintain a constant volume of the mixture in the reaction flask.

[0026] (2) Collect kitchen waste, remove large pieces of debris such as bones, plastics, and chopsticks, and crush it to a particle size ≤5mm using a food processor to obtain the cleaned kitchen waste. Measure its total solids (TS), volatile solids (VS), and pH. In this example, TS=23.54%, VS / TS=92.8% (i.e., VS=21.85%), and pH=5.74. Add betaine by weighing 1g / L of anhydrous betaine into the kitchen waste and stirring thoroughly. (3) Based on volatile solids, the inoculated sludge after acclimatization in step (1) and the kitchen waste in step (2) are added to the reactor at a mass ratio of 3:1. The mesophilic anaerobic digestion conditions are: temperature 35℃, shaking speed 120rpm, and digestion cycle 20 days.

[0027] Example 2 This embodiment provides a method for anaerobic digestion and gas production from high-sodium food waste, including the following steps: (1) The digested sludge from the anaerobic digester of the municipal wastewater treatment plant was used as inoculum sludge, and the volatile suspended solids (VSS) concentration of the inoculum sludge was 15 g / L. An anaerobic workstation was used, and the temperature was stably controlled at 35℃. Preparation of basic nutrient solution: The basic nutrient solution consisted of the following: 2064 mg / L glucose, 0.12 g / L NH4Cl, 0.2 g / L yeast extract, 16.4 mg / L KH2PO4, 3 g / L NaHCO3, 0.5 g / L betaine, 1.0 g / L trehalose, 85 mg / L tetrahydropyrimidine, and 1.4 mL / L trace element solution per liter of water. The formula for the trace element solution includes: per liter of water: FeCl2·4H2O 2.0g, CoCl2·6H2O 1.0g, MnCl2·4H2O 0.3g, AlCl3 0.8g, H3BO3 0.5g, ZnCl2 0.6g, (NH4)6Mo7O 24 ·4H2O0.5g, CuCl2·2H2O0.5g.

[0028] The inoculated sludge was placed into the reaction flask within the anaerobic workstation, and a basic nutrient solution was added, with the nutrient solution volume being 20% ​​of the sludge volume. The system was run for 3 days initially. After 3 days, solid NaCl was added daily to increase the sodium ion concentration by 0.4 g / L per day, eventually reaching 5 g / L. Once the concentration reached 5 g / L, the system continued to operate stably for 7 days. During the acclimation period, the nutrient solution was changed every 3 days. After settling, the supernatant was discarded, and fresh nutrient solution and the corresponding amount of NaCl were added to maintain a constant volume of the mixture in the reaction flask.

[0029] (2) Collect kitchen waste, remove large pieces of debris such as bones, plastics, and chopsticks, and crush it to a particle size ≤5mm using a food processor to obtain the cleaned kitchen waste. Measure its total solids (TS), volatile solids (VS), and pH. In this example, TS=23.54%, VS / TS=92.8% (i.e., VS=21.85%), and pH=5.74. Add betaine by weighing 1g / L of anhydrous betaine into the kitchen waste and stirring thoroughly. (3) Based on volatile solids, the inoculated sludge after acclimatization in step (1) and the kitchen waste in step (2) are added to the reactor at a mass ratio of 3:1. The mesophilic anaerobic digestion conditions are: temperature 35℃, shaking speed 120rpm, and digestion cycle 20 days.

[0030] Comparative Example 1 The difference between this comparative example and Example 1 is that the basic nutrient solution includes: 2069 mg / L glucose, 0.16 g / L NH4Cl, 0.14 g / L yeast extract, 16.8 mg / L KH2PO4, 2.3 g / L NaHCO3, 1.0 g / L betaine, 90 mg / L tetrahydropyrimidine and 1.2 mL / L trace element solution added per liter of water.

[0031] Comparative Example 2 The difference between this comparative example and Example 1 is that trehalose is replaced with mannitol.

[0032] Comparative Example 3 The difference between this comparative example and Example 1 is that trehalose is replaced with proline.

[0033] Comparative Example 4 The difference between this comparative example and Example 1 is that the trace element solution formulation is as follows: 1.5g FeCl2·4H2O, 0.2g NiCl2·6H2O, 0.1g CoCl2·6H2O, 0.05g Na2SeO3, 0.05g Na2WO4·2H2O, 0.2g MnCl2·4H2O, 0.1g ZnCl2, and (NH4)6Mo7O are added per liter of water. 24 0.1g of 4H2O, 0.05g of H3BO3, and 0.05g of CuCl2·2H2O, without adding AlCl3.

[0034] Comparative Example 5 The difference between this comparative example and Example 1 is that the daily sodium ion increase rate is 0.2 g / L.

[0035] Comparative Example 6 The difference between this comparative example and Example 1 is that the daily sodium ion increase rate is 0.5 g / L.

[0036] Blank group A method for anaerobic digestion and gas production from high-sodium food waste includes the following steps: (1) Collect kitchen waste, remove large pieces of debris such as bones, plastics, and chopsticks, and crush it to a particle size ≤5mm using a food processor. Measure its total solids (TS), volatile solids (VS), and pH. TS = 23.54%, VS / TS = 92.8% (i.e., VS = 21.85%), pH = 5.74, obtaining the purified kitchen waste; (3) Based on volatile solids, the inoculated sludge and the cleaned kitchen waste were added to the reactor at a mass ratio of 3:1. The mesophilic anaerobic digestion conditions were: temperature 35℃, shaking speed 120rpm, and digestion cycle 20 days.

[0037] Performance testing Using the same batch of inoculated sludge, the following high-sodium food waste was treated according to the methods of Examples 1-2 and Comparative Examples 1-6: (1) Kitchen waste with a sodium ion content of 5 g / L: solid content is 23.54%, volatile solid content is 21.85%, and pH is 5.74; (2) Kitchen waste with a sodium ion content of 8 g / L: solid content of 23.54%, volatile solid content of 21.85%, pH of 5.74; The cumulative methane production over 20 days was calculated, including the number of milliliters of methane produced per gram of volatile solids. The results are shown in Table 1.

[0038] Table 1 Test Results

[0039] As shown in Table 1, the methods in Examples 1-2 significantly increased methane production when treating kitchen waste with high sodium content.

[0040] In Comparative Example 1, trehalose was not added to the basic nutrient solution formula, and betaine was used instead of trehalose. The cumulative methane production over 20 days decreased. This indicates that adding trehalose to the basic nutrient solution to form a ternary complex with betaine and tetrahydropyrimidine plays a crucial role in increasing the gas production from the anaerobic digestion of high-sodium food waste.

[0041] In Comparative Example 2, replacing trehalose with mannitol resulted in a decrease in the cumulative methane production over 20 days. This indicates that although mannitol is a polyhydroxy compound osmotic protectant that can regulate osmotic pressure, its mechanism of action is fundamentally different from that of trehalose. Mannitol cannot replace the function of trehalose. Trehalose stabilizes cell membrane structure through a unique water substitution mechanism and is an indispensable component in ternary compound formulations.

[0042] In Comparative Example 3, when trehalose was replaced with proline, the cumulative methane production over 20 days was still lower than in Example 1. This indicates that although proline can act as a permeation protectant, its function overlaps with that of betaine and cannot compensate for the unique role of trehalose in membrane protection.

[0043] In Comparative Example 4, a traditional trace element formula was used, and its cumulative methane production over 20 days was lower than that in Example 1. This indicates that the trace element formula containing Al, B, and sufficient amounts of Fe, Co, Mn, Zn, Mo, and Cu used in this invention can provide more comprehensive nutritional support and shock resistance in complex systems of high-sodium food waste, while commercially available formulas cannot achieve the same effect.

[0044] In Comparative Example 5, the daily sodium ion increase rate was only 0.2 g / L, and its cumulative methane production over 20 days was lower than that in Example 1. This indicates that while a slow salt increase rate can alleviate osmotic stress, the prolonged acclimatization period prevents the microorganisms from fully inducing endogenous protective mechanisms within a limited time. In contrast, the present invention can balance adaptation efficiency and metabolic activity.

[0045] In Comparative Example 6, the daily sodium ion increase rate was 0.5 g / L, and its cumulative methane production over 20 days was lower than that in Example 1. This indicates that the gradient selected in this invention is the optimal range for balancing acclimatization efficiency and microbial survival.

[0046] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for anaerobic digestion of high-sodium kitchen waste to produce gas, characterized in that, The method comprises the following steps: (1) inoculating sludge into a reaction bottle in an anaerobic workstation, adding a basic nutrient solution, not adding NaCl first, operating for 3-5 days, then adding NaCl daily, increasing the concentration of sodium ions by 0.3-0.4 g / L per day, and operating stably for 7-9 days after reaching 5-5.5 g / L, to obtain inoculated sludge after domestication; (2) collecting kitchen waste, removing large impurities such as bones, plastics and chopsticks, crushing, obtaining kitchen waste after impurity removal, and adding betaine to the kitchen waste after impurity removal and stirring uniformly; (3) adding the inoculated sludge after domestication in step (1) and the kitchen waste after impurity removal in step (2) into a reactor for mesophilic anaerobic digestion.

2. The method for anaerobic digestion of high-sodium-content kitchen waste to produce gas according to claim 1, characterized in that, The basic nutrient solution comprises water, glucose, NH4Cl, yeast extract, KH2PO4, NaHCO3, betaine, trehalose, tetrahydroprimidine and a trace element solution.

3. The method for anaerobic digestion of high-sodium-content kitchen waste to produce gas according to claim 1, characterized in that, NaCl is added daily, the concentration of sodium ions is increased by 0.3-0.4 g / L per day, and finally reaches 5-5.5 g / L.

4. The method for anaerobic digestion of high-sodium-content kitchen waste to produce gas according to claim 1, characterized in that, The nutrient solution is replaced every 3 days during domestication in step (1), the supernatant is discarded after standing, and fresh nutrient solution and corresponding NaCl are added to keep the volume of the mixed solution in the reaction bottle constant.

5. The method for anaerobic digestion of high-sodium-content kitchen waste to produce gas according to claim 1, characterized in that, Betaine is added to the kitchen waste after impurity removal, and the addition amount is 1-1.2 g / L of kitchen waste.

6. The method for anaerobic digestion of high-sodium-content kitchen waste to produce gas according to claim 2, characterized in that, The formula of the trace element solution comprises: FeCl2*4H2O 2.0-2.4 g, CoCl2*6H2O 0.5-1.0 g, MnCl2*4H2O 0.3-0.5 g, AlCl3 0.5-0.8 g, H3BO3 0.5-0.6 g, ZnCl2 0.4-0.6 g, (NH4)6Mo7O 24 24H2O 0.5-0.7 g, CuCl2*2H2O 0.3-0.5 g per liter of water.

7. The method for biogas production from high-sodium kitchen waste anaerobic digestion according to claim 2, characterized in that, The basic nutrient solution comprises: 2064-2080 mg / L of glucose, 0.12-0.20 g / L of NH4Cl, 0.1-0.2 g / L of yeast extract, 16.4-17 mg / L of KH2PO4, 2-3 g / L of NaHCO3, 0.5-1 g / L of betaine, 0.5-1.0 g / L of trehalose, 85-100 mg / L of tetrahydroprimidine and 1.0-1.4 mL / L of a trace element solution per liter of water. 8.The method of claim 1, wherein the high-sodium kitchen waste is characterized in that, The mesophilic anaerobic digestion conditions are: temperature 30-35℃, and shaking speed 120-150 rpm. 9.The method of claim 1, wherein the high-sodium kitchen waste is characterized in that, The inoculated sludge after domestication in step (1) and the kitchen waste after impurity removal in step (2) are added into the reactor at a mass ratio of (2-4):1, calculated by volatile solids.

10. The method for biogas production from high-sodium kitchen waste anaerobic digestion according to claim 1, characterized in that, The volume of the nutrient solution is 15-20% of the volume of the sludge.

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