A method for anaerobic digestion of food waste and enzyme-modified starch-containing bioplastics

Abstract

This invention relates to a method for the anaerobic digestion of food waste and enzyme-modified starch-containing bioplastics, belonging to the field of solid waste treatment and resource utilization. By modifying bioplastics with proteinase K and combining the role of starch in the composite material, the degradation rate and biogas production of bioplastics during anaerobic digestion are significantly improved. The method of this invention increases the degradation rate of bioplastics from 5.38% to 20.21% under mesophilic conditions, while significantly increasing methane production by approximately 34.75%. This method effectively promotes the simultaneous degradation of food waste and bioplastics, providing a new approach for optimizing waste management strategies.

Description

Technical Field

[0001] This invention belongs to the field of solid waste treatment and resource utilization, specifically relating to a method for anaerobic digestion of kitchen waste and bio-enzyme-modified starch-containing bioplastics. Background Technology

[0002] With the increasing global awareness of environmental protection and the advancement of sustainable development goals, plastic pollution has attracted widespread attention. Traditional plastics, due to their slow degradation, place enormous pressure on the environment. Therefore, biodegradable plastics have gradually become a research hotspot in the plastics industry, especially in the areas of food packaging, agricultural films, and disposable tableware, where their applications are rapidly expanding. However, although bioplastics can degrade under specific conditions, their actual degradation rate remains slow, particularly in the absence of suitable environments, resulting in a degradation efficiency in nature that is far lower than expected. In the field of waste management, food waste, as a significant component of organic waste, has a high moisture content and organic matter content, making it an ideal raw material for resource utilization through anaerobic digestion technology. However, in the actual treatment of food waste, mixed bioplastics often become obstacles to the degradation process. The degradation time of bioplastics far exceeds that of food waste, leading to excessively long residence times in anaerobic reactors and reducing overall treatment efficiency. Summary of the Invention

[0003] To overcome the shortcomings of existing technologies in the co-degradation of bioplastics with food waste, this invention combines bio-enzyme modification technology with the unique role of starch components. Through synergistic anaerobic digestion of commercial bioplastics and food waste, a more efficient degradation process and energy recovery are achieved. This method not only significantly outperforms traditional processes in terms of degradation rate and methane production, but also possesses high environmental friendliness and economic feasibility, providing a new solution for solid waste management and resource utilization.

[0004] A method for anaerobic digestion of food waste and enzyme-modified starch-containing bioplastics includes the following steps:

[0005] Step 1, Pre-treatment of kitchen waste: After sorting and removing hard debris, the kitchen waste is crushed for later use; the kitchen waste includes one or more components of starch, oil and protein;

[0006] Step 2, Pretreatment of starch-containing bioplastics: Prepare enzyme-modified starch-containing bioplastic granules for later use; the components of starch-containing bioplastics include polylactic acid (PLA), butylene adipate (PBAT), and starch;

[0007] Step 3, Anaerobic Degradation: The pretreated kitchen waste, anaerobic activated sludge and bioplastics are mixed and placed in an anaerobic reactor, and then anaerobic fermentation is carried out in a 35℃ constant temperature water bath for 40 days.

[0008] Starch, a natural polysaccharide, is easily broken down by microorganisms into volatile fatty acids (VFAs), such as acetic acid, propionic acid, and butyric acid, which are key intermediates in the anaerobic methanogenesis stage. Adding starch to PLA / PBAT / starch composite materials can significantly increase methane production during anaerobic co-digestion and promote anaerobic degradation efficiency.

[0009] The natural structure of starch provides microorganisms with a direct carbon and energy source, promoting their activity and thus accelerating the hydrolysis of polylactic acid (PLA) and PBAT in the composite material. The addition of starch also alters the surface microstructure of the plastic, increasing its porosity, making it easier for hydrolytic enzymes to enter, enhancing the plastic's biodegradability, and further increasing the degradation rate.

[0010] The hydrolysis products of starch provide ample substrates for acid-producing and methanogenic bacteria, thereby increasing the relative abundance of key bacterial groups (such as Clostridium and Methanothrix), which play a central role in methane metabolism and the decomposition of complex organic matter, thus optimizing the microbial community structure.

[0011] Furthermore, the starch content in biodegradable plastics is 50%.

[0012] Furthermore, the biological enzymes include proteinase K and lipase, preferably proteinase K.

[0013] Proteinase K, as a highly efficient enzyme, can significantly improve the degradation rate of bioplastics by hydrolyzing the polymer chain structure in plastics. Bioplastics treated with proteinase K exhibit better biodegradability during anaerobic digestion, breaking down into smaller molecule compounds more quickly, thereby accelerating their transformation process under anaerobic conditions.

[0014] Furthermore, the method specifically includes:

[0015] Step 1, Pre-treatment of kitchen waste: The kitchen waste is manually sorted to remove hard debris such as chopsticks, paper towels, bamboo skewers, stones and metals, which are non-degradable. Then, an experimental blender is used to simulate engineering equipment to crush the kitchen waste into particles with a diameter of less than 5mm in order to improve its degradation efficiency in anaerobic reaction.

[0016] Step 2, Pretreatment of starch-containing bioplastics: Bioplastics (PLA / PBAT / starch composite material) are modified using proteinase K, and the plastic bags are cut into 5×5mm granules to improve their biodegradability in anaerobic environments.

[0017] Step 3, Anaerobic Degradation Process: The treated kitchen waste, anaerobic activated sludge, and proteinase K modified bioplastics are mixed in an anaerobic reactor and placed in a 35℃ constant temperature water bath for anaerobic fermentation for 40 days to achieve the best degradation effect.

[0018] Further analysis was conducted after the reaction was completed: the morphology, structure, and changes in chemical bonds and functional groups of the bioplastics were observed using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) to assess the degradation effect and its synergistic effect with food waste.

[0019] Furthermore, the physicochemical properties of the food waste in step 1 are as follows: total solids (TS) content is 11-12%, volatile solids (VS) content is 9-10%, VS / TS ratio is 82-83%, and moisture content is 88-89%.

[0020] Furthermore, the main components of the biodegradable commercial plastic in step 2 are polylactic acid (PLA), butylene adipate (PBAT), and starch.

[0021] Furthermore, the physicochemical properties of the anaerobic activated sludge used in step 3 are as follows: total solids (TS) content of 10-11%, volatile solids (VS) content of 8-9%, VS / TS ratio of 80-82%, and moisture content of 89-90%.

[0022] Furthermore, in step 3, in order to ensure an anaerobic environment, the effective working volume of the reactor shall not exceed half of its total volume.

[0023] Furthermore, in step 3, a water bath constant temperature oscillator is used to control the internal temperature of the reactor at 35°C to ensure the stability of the reaction process.

[0024] Furthermore, in step 4, the electron microscope used is at a magnification of 20,000 to observe the microscopic morphological changes of the bioplastic.

[0025] Furthermore, the non-degradable debris removed during the sorting process of kitchen waste includes chopsticks, paper towels, bamboo skewers, stones, and metals, to ensure that the anaerobic digestion process is not disturbed by foreign objects.

[0026] Furthermore, the kitchen waste is crushed into particles smaller than 5mm using a high-speed blender; the commercial bioplastic bags are cut into 5×5mm sizes to facilitate subsequent anaerobic treatment.

[0027] Beneficial effects:

[0028] (1) Synergistic effect of starch:

[0029] This application not only utilizes bio-enzyme modification technology but also introduces starch to further improve the efficiency of anaerobic co-digestion. Starch rapidly hydrolyzes to form VFA, which not only increases methane production but also shortens the lag period of anaerobic co-digestion, effectively accelerating the degradation of bioplastics and achieving simultaneous anaerobic digestion with food waste.

[0030] (2) Microbial community regulation:

[0031] Starch promotes the activity of specific microbial communities (such as methanogens like Methanothrix and cellulose-degrading bacteria like Clostridium), thereby optimizing metabolic pathways within the anaerobic reactor and improving system stability and gas production.

[0032] (3) Economic efficiency and operability:

[0033] Adding starch not only reduces the cost of plastic production but also improves the efficiency of anaerobic co-digestion. Compared to modification strategies that rely solely on biological enzymes, it is lower in cost and more feasible.

[0034] (4) Application potential:

[0035] The patented technology is not only applicable to PLA and PBAT, but also provides a new direction for the industrial degradation of commercially available bioplastics, especially in situations where waste sorting is not thorough. Attached Figure Description

[0036] Figure 1 Daily methane accumulation from anaerobic degradation of food waste and different types of bioplastics at a mesophilic temperature of 35°C;

[0037] Figure 2 Scanning electron microscope images of anaerobic degradation of food waste and different types of bioplastics at a mesophilic temperature of 35°C;

[0038] Figure 3 Fourier transform infrared spectra of kitchen waste and different types of bioplastics after anaerobic degradation at 35°C. Detailed Implementation

[0039] The present invention will be explained in detail below with reference to illustrations and specific examples. This embodiment is based on the technical framework of the present invention and provides specific operating steps and detailed implementation methods. However, the scope of protection of the present invention is not limited to the examples described.

[0040] A method for degrading commercially available bioplastics using food waste and activated sludge, comprising the following steps:

[0041] (1) Pre-treatment of kitchen waste: This process mainly includes components such as starch, protein and oil. Impurities such as plastic, chopsticks, paper towels, bamboo skewers, bones, stones and metals that are not suitable for anaerobic treatment are removed by manual screening. Then, these treated kitchen wastes are mixed and ground into a paste with particles smaller than 5 mm using a food homogenizer, and placed in a refrigerated environment at 4°C for later use.

[0042] (2) Cultivation and acclimatization of anaerobic activated sludge: After the mesophilic sludge was allowed to stand at 4℃ for 24 hours, the supernatant was manually separated, the lower sludge was extracted and concentrated by gravity and then stored. The sludge was acclimatized at a mesophilic temperature of 35℃ for one week, and finally the treated sludge was stored for later use.

[0043] (3) Pretreatment of starch-containing bioplastics: The starch-containing biodegradable plastic bags are cut and crushed to a size of 5×5 mm using engineering equipment.

[0044] (4) Anaerobic decomposition process: A 200 mL headspace vial was used as the reaction vessel, ensuring that its effective volume did not exceed half of the total volume. N2 (99.99% purity) was introduced into the reactor for at least 5 minutes to ensure an anaerobic environment. The reactor was sealed with a butyl rubber stopper and an aluminum cap. Gas production was measured daily using a glass syringe. A water bath constant-temperature shaker was used to control the reaction temperature. Fermentation was continued for 40 days, with the shaker speed set at 120 rpm to ensure thorough mixing of the substrate and inoculum.

[0045] (5) The generated gas components were analyzed using a GC8860 gas chromatograph. The chromatographic column used was an HP-PLOT / Q capillary column (30 m × 0.530 mm × 40 μm). The injection port and column temperature were maintained at 60℃, the detector temperature was set to 200℃, and the injection volume was 0.2 mL.

[0046] Comparative Example 1

[0047] After manual sorting and screening, the food waste was ground into a paste with particles smaller than 5 mm using a crushing device. A 200 ml serum bottle was used as an anaerobic reactor, into which 10.02 g of crushed food waste and 5 g of anaerobic activated sludge were added for methanogenesis. No biodegradable plastics were introduced; only food waste and sludge were anaerobic co-digested. The initial pH was set to 7, while ensuring the effective working volume of the reactor remained below 100 ml. Nitrogen gas was purged into the inoculated serum bottle for 5 minutes to maintain an anaerobic state before anaerobic fermentation. The temperature was controlled at 35°C throughout the fermentation process for 40 days. The volume of gas produced was measured daily using a glass syringe, and the methane content was analyzed by gas chromatography. The final measured methane yield in the biogas was 103 ml / VS. added .

[0048] Comparative Example 2

[0049] After manually sorting and removing non-degradable impurities from food waste, it was pulverized into a paste with a particle size of less than 5 mm using a crusher. PLA / PBAT / starch-degradable plastic was cut into 5 mm × 5 mm pieces. Using a 200 ml serum bottle as the anaerobic reactor, 10.02 g of the pulverized food waste paste was added, along with 5 g of anaerobic activated sludge and 0.2 g of PLA / PBAT / starch-degradable plastic (CPB), with a starch ratio of 50%. The initial pH was set to 7, and the effective working volume of the reactor was maintained at less than 100 ml. Nitrogen gas was purged into the inoculated serum bottle for 5 minutes to ensure an anaerobic environment before initiating anaerobic fermentation. The fermentation temperature was controlled at 35°C, and the fermentation period was 40 days.

[0050] The gas volume was measured daily using a glass syringe, and the methane content was analyzed by gas chromatography. The final measured methane yield in the biogas was 130 ml / VS. added Compared with Comparative Example 1, it increased by 26.21%; after 40 days of mesophilic anaerobic decomposition, electron microscopy showed that some irregular small pores appeared on the surface, and the overall structure became more porous; the chemical bond vibration absorption peak of Fourier transform infrared spectroscopy was weakened.

[0051] Comparative Example 3

[0052] After manually sorting and removing non-degradable impurities from food waste, it was pulverized into a paste with a particle size of less than 5 mm using a crusher. PLA / PBAT biodegradable plastic modified by in-situ proteinase K impregnation was cut into 5 mm × 5 mm pieces. Using a 200 ml serum bottle as the anaerobic reaction vessel, 10.02 g of the pulverized food waste paste was added, along with 5 g of anaerobic activated sludge and 0.2 g of PLA / PBAT biodegradable plastic (PLPB). The initial pH was set to 7, and the effective working volume of the reactor was maintained at less than 100 ml. Nitrogen gas was purged into the inoculated serum bottle for 5 minutes to ensure an anaerobic environment before initiating anaerobic fermentation. The fermentation temperature was controlled at 35°C, and the fermentation period was 40 days.

[0053] The gas volume was measured daily using a glass syringe, and the methane content was analyzed by gas chromatography. The final measured methane yield in the biogas was 165 ml / VS. added Compared with Comparative Example 1, it increased by 60.2%; after 40 days of mesophilic anaerobic decomposition, electron microscopy showed that some irregular small pores appeared on the surface, and the overall structure became more porous; the chemical bond vibration absorption peaks in Fourier transform infrared spectroscopy were weakened.

[0054] Example 1

[0055] After manually sorting and removing non-degradable impurities, food waste was pulverized into a paste with a particle size of less than 5 mm using a crusher. PLA / PBAT / starch modified by in-situ impregnation with proteinase K, along with 50% starch-content biodegradable plastic, was cut into 5 mm × 5 mm pieces. Using a 200 mL serum bottle as the anaerobic reactor, 10.02 g of the pulverized food waste paste was added, followed by inoculation with 5 g of anaerobic activated sludge and 0.2 g of PLA / PBAT / starch biodegradable plastic PKPB. The initial pH was set to 7, and the effective working volume of the reactor was maintained at less than 100 mL. Nitrogen gas was purged into the inoculated serum bottle for 5 minutes to ensure an anaerobic environment before initiating anaerobic fermentation. The fermentation temperature was controlled at 35°C, and the fermentation period was 40 days.

[0056] The gas volume was measured daily using a glass syringe, and the methane content was analyzed by gas chromatography. The final measured methane yield in the biogas was 176 ml / VS. added Compared with control example 1, it increased by 70.87%; after 40 days of mesophilic anaerobic decomposition, electron microscopy showed that some irregular small pores appeared on the surface, and the overall structure became more porous; the chemical bond vibration absorption peak of Fourier transform infrared spectroscopy was weakened.

[0057] like Figure 1 The curves shown represent the cumulative methane production over time when different plastics are co-digested with kitchen waste at 35℃.

[0058] FW: Only anaerobic digestion of food waste

[0059] FW+CPB: Anaerobic co-digestion of food waste and PLA / PBAT / starch-modified plastics.

[0060] FW+PLPB: Anaerobic co-digestion of food waste and modified PLA / PBAT plastics.

[0061] FW+PKPB: Anaerobic co-digestion of food waste and plastics containing PLA / PBAT / starch.

[0062] FW group (control group): Food waste was co-digested with anaerobic sludge alone. The methane production was measured to be 103 ml / VS added within 40 days, providing a benchmark reference for subsequent groups.

[0063] FW+CPB group: Food waste was co-digested with unmodified PLA / PBAT / starch plastic, and the final methane yield was 130 ml / VSadded, which was 26.21% higher than the control group.

[0064] FW+PLPB group: Co-digestion of food waste with proteinase K-modified PLA / PBAT plastic significantly increased methane production to 165 ml / VSadded, which was 60.2% higher than the control group.

[0065] FW+PKPB group: Co-digestion of food waste with proteinase K-modified PLA / PBAT / starch plastic resulted in the highest methane production, reaching 176 ml / VSadded, which was 70.87% higher than the control group.

[0066] In summary, the results show that proteinase K modification significantly improves the anaerobic degradation capacity of plastics, while the starch content of PLA / PBAT / starch plastics further enhances degradation efficiency and methane production, giving it a significant advantage in anaerobic co-digestion.

[0067] like Figure 2 As shown, SEM images of different plastic films co-digested with kitchen waste at 35℃.

[0068] CPB: SEM image of PLA / PBAT / starch unmodified plastic

[0069] PLPB: SEM images of PLA / PBAT modified plastics

[0070] PKPB: SEM images of PLA / PBAT / starch modified plastics

[0071] Unmodified plastic (CPB) showed only a few cracks and slight pits after 40 days, indicating limited degradation. PLA / PBAT modified plastic (PLPB) showed a significant increase in surface cracks and pits, demonstrating that enzyme modification significantly enhanced degradation capacity. PLA / PBAT / starch modified plastic (PKPB) exhibited the most severe surface damage, with densely distributed and deep cracks, indicating that the addition of starch further promoted the degradation effect of the enzyme-modified plastic. These results demonstrate that the synergistic effect of proteinase K and starch can significantly improve the degradation efficiency of plastics.

[0072] like Figure 3 As shown, FTIR images of co-digestion of different plastic films with kitchen waste at 35℃ are presented. 10 represents 10 days, and 40 represents 40 days.

[0073] CPB: PLA / PBAT / starch unmodified plastic FTIR graph

[0074] PLPB: FTIR diagram of PLA / PBAT modified plastics

[0075] PKPB: FTIR diagram of PLA / PBAT / starch modified plastics

[0076] The results showed that the chemical structures of the plastics underwent significant changes after 10 and 40 days. The unmodified plastic (CPB) showed only slight changes in the CH bond and C=O carbonyl peaks, indicating minimal degradation chemical reactions. PLA / PBAT modified plastic (PLPB) showed a significant decrease in absorption peaks, particularly in the carbonyl and alkyl regions, indicating that enzyme modification effectively promoted chemical degradation. PLA / PBAT / starch modified plastic (PKPB) showed the greatest decrease in absorption peaks, especially in the C=O carbonyl peak, indicating that the addition of starch accelerated polymer structure breakage and enhanced chemical degradation. Overall, FTIR analysis further demonstrated the crucial role of the synergistic effect of starch and enzyme modification in plastic degradation.

[0077] The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to these specific methods. Any obvious improvements, substitutions, or modifications that can be made by those skilled in the art without departing from the core content of the present invention should be considered to fall within the protection scope of the present invention.

Claims

1. A method for anaerobic digestion of kitchen waste and enzyme-modified starch-containing bioplastics, characterized in that, The method includes the following steps: Step 1, Pre-treatment of kitchen waste: After sorting and removing hard debris, the kitchen waste is crushed for later use; the kitchen waste includes one or more components of starch, oil and protein; Step 2, Pretreatment of starch-containing bioplastics: Prepare enzyme-modified starch-containing bioplastic granules; the starch-containing bioplastics include polylactic acid (PLA), butylene adipate (PBAT), and starch; the starch content in the starch-containing bioplastics is 50%; the enzymes include proteinase K and lipase; Step 3, Anaerobic Degradation: The pretreated kitchen waste, anaerobic activated sludge and bioplastics are mixed and placed in an anaerobic reactor, and then anaerobic fermentation is carried out in a 35℃ constant temperature water bath for 40 days.

2. The method for anaerobic digestion of kitchen waste and bio-enzyme-modified starch-containing bioplastics according to claim 1, characterized in that, The enzyme in question is proteinase K.

3. The method for anaerobic digestion of kitchen waste and bio-enzyme-modified starch-containing bioplastics according to claim 1, characterized in that, The method for bio-enzyme modification is in-situ impregnation.

4. The method for anaerobic digestion of kitchen waste and bio-enzyme-modified starch-containing bioplastics according to claim 1, characterized in that, The physical and chemical properties of the kitchen waste in step 1 are as follows: total solids (TS) content is 11-12%, volatile solids (VS) content is 9-10%, VS / TS ratio is 82-83%, and moisture content is 88-89%.

5. The method for anaerobic digestion of kitchen waste and bio-enzyme-modified starch-containing bioplastics according to claim 1, characterized in that, The physicochemical properties of the anaerobic activated sludge used in step 3 are as follows: total solids (TS) content is 10-11%, volatile solids (VS) content is 8-9%, VS / TS ratio is 80-82%, and moisture content is 89-90%.

6. The method for anaerobic digestion of kitchen waste and enzyme-modified starch-containing bioplastics according to claim 1, characterized in that, In step 3, starch-containing bioplastics, kitchen waste, and anaerobic activated sludge are mixed, and the initial pH value is adjusted to between 6 and 8.

7. The method for anaerobic digestion of kitchen waste and bio-enzyme-modified starch-containing bioplastics according to claim 1, characterized in that, The anaerobic digestion reaction temperature was controlled at 35℃, and the fermentation time was 40 days.

8. The method for anaerobic digestion of kitchen waste and enzyme-modified starch-containing bioplastics according to claim 1, characterized in that, The process of sorting kitchen waste includes removing non-anaerobic digestible debris, specifically chopsticks, paper towels, bamboo skewers, stones, or metal.

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