Method for anaerobic digestion of kitchen waste and biological enzyme modified starch-containing bioplastic

Abstract

The invention relates to a method for anaerobic digestion of starch-containing bioplastics modified by kitchen waste and bio-enzyme, and belongs to the field of solid waste treatment and recycling. The bioplastic is modified by protease K, and the effect of starch in the composite material is combined, so that the degradation rate and biogas yield of the bioplastic in the anaerobic digestion process are greatly improved. According to the method disclosed by the invention, the degradation rate of the bioplastic is increased from 5.38% to 20.21% under the medium-temperature condition, and meanwhile, the methane yield is remarkably increased by about 34.75%. The method effectively promotes synchronous degradation of the kitchen waste and the bioplastics, and provides a new way for optimization of a waste management strategy.

Description

Technical Field

[0001] The invention belongs to the field of solid waste treatment and resource utilization, and specifically relates to a method for anaerobic digestion of kitchen waste and bio-enzyme-modified starch-containing bioplastic. Background Art

[0002] With the improvement of global environmental awareness and the advancement of sustainable development goals, the problem of plastic pollution has attracted widespread attention. Traditional plastics have caused tremendous pressure on the environment due to their difficult-to-degrade characteristics. Therefore, biodegradable plastics have gradually become a research hotspot in the plastics industry, especially in the fields of food packaging, agricultural films and disposable tableware. However, although bioplastics can be degraded under certain conditions, their actual degradation rate is still slow, especially in the absence of a suitable environment, resulting in their degradation efficiency in nature being much lower than expected. In the field of waste treatment, food waste, as an important component of organic waste, has a high moisture content and organic matter content, and is an ideal raw material for resource utilization through anaerobic digestion technology. However, in the actual treatment of food waste, mixed bioplastics often become obstacles in the degradation process. The degradation time of bioplastics is much longer than that of food waste, resulting in a long retention time in the anaerobic reactor, which reduces the overall treatment efficiency. Summary of the invention

[0003] In order to overcome the shortcomings of the existing technology in the synergistic degradation of bioplastics with food waste, the present invention combines the unique role of bioenzyme modification technology and starch components, and achieves a more efficient degradation process and energy recovery by synergistic anaerobic digestion of commercial bioplastics and food waste. This method is not only significantly superior to traditional processes in terms of degradation rate and methane production, but also has high environmental friendliness and economic feasibility, providing a new solution for solid waste management and resource utilization.

[0004] A method for anaerobic digestion of kitchen waste and bio-enzyme-modified starch-containing bioplastics, comprising the following steps:

[0005] Step 1, pre-treatment of kitchen waste: sorting the kitchen waste to remove hard debris, and then crushing it for standby use; the kitchen waste includes one or more components of starch, oil and protein;

[0006] Step 2, pretreatment of starch-containing bioplastics: preparing the starch-containing bioplastics granules modified by bio-enzymes for later use; the starch-containing bioplastics include polylactic acid PLA, polybutylene adipate PBAT and starch;

[0007] Step 3, anaerobic degradation: The pretreated food waste, anaerobic activated sludge and bioplastics are mixed and placed in an anaerobic reactor, and anaerobic fermentation is carried out in a constant temperature water bath at 35°C for 40 days.

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

[0009] The natural structure of starch provides a direct carbon source and energy for microorganisms, which can promote microbial activity and thus accelerate the hydrolysis reaction of polylactic acid (PLA) and PBAT in the composite material. The addition of starch also changes the surface microstructure of the plastic, increases the porosity of the material, makes it easier for hydrolases to enter, enhances the biodegradability of the plastic, and further increases the degradation rate.

[0010] The hydrolyzate of starch provides sufficient substrate for acidogens and methanogens, thereby increasing the relative abundance of key bacterial groups (such as Clostridium and Methanothrix), which play a core role in methane metabolism and the decomposition of complex organic matter, and optimizing the microbial community structure.

[0011] Furthermore, the content of starch in the degradable plastic is 50%.

[0012] Furthermore, the biological enzyme includes proteinase K and lipase, preferably proteinase K.

[0013] As a highly efficient enzyme, proteinase K can significantly increase the degradation rate of bioplastics by hydrolyzing the polymer chain structure in plastics. Bioplastics treated with proteinase K show better biodegradation properties during anaerobic digestion and can be decomposed into small molecular compounds more quickly, thereby accelerating their transformation process under anaerobic conditions.

[0014] Furthermore, the method is specifically as follows:

[0015] Step 1, pretreatment of food waste: manually sort the food waste to remove hard debris, such as chopsticks, paper towels, bamboo sticks, stones, metals and other non-degradable substances, and then use an experimental wall-breaking machine to simulate engineering equipment to break the food waste into particles with a size of less than 5 mm to improve its degradation efficiency in anaerobic reaction;

[0016] Step 2, pretreatment of starch-containing bioplastics: using proteinase K to modify the bioplastics (PLA / PBAT / starch composites), and cutting the plastic bags into 5×5 mm particles to improve their degradability in an anaerobic environment;

[0017] Step 3, anaerobic degradation process: the treated food waste, anaerobic activated sludge and proteinase K modified bioplastic are mixed in an anaerobic reactor and placed in a 35°C constant temperature water bath for anaerobic fermentation for 40 days to achieve the best degradation effect.

[0018] Furthermore, analysis was performed after the reaction: Scanning electron microscopy (SEM) and Fourier transform infrared spectrometer (FTIR) were used to observe the morphological structure and chemical bond functional group changes of the bioplastics to evaluate the degradation effect and its synergistic effect with food waste.

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

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

[0021] Furthermore, the physicochemical properties of the anaerobic activated sludge used in step 3 are: total solid (TS) content of 10-11%, volatile solid (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 does not exceed half of its total volume.

[0023] Furthermore, in step 3, a water bath thermostat 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 has a scanning magnification of 20,000 times in order 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 sticks, stones, metals and other materials, so as to ensure that the anaerobic digestion process is not interfered with by foreign objects.

[0026] Furthermore, the food waste is broken into particles with a size of less than 5 mm by a wall-breaking machine; commercial bioplastic bags are cut into a size of 5×5 mm for subsequent anaerobic treatment.

[0027] Beneficial effects:

[0028] (1) Synergistic effect of starch:

[0029] This application not only uses bio-enzyme modification technology, but also introduces starch to further improve the efficiency of anaerobic co-digestion. Starch forms VFA through rapid hydrolysis, which not only increases methane production, but also shortens the lag period of anaerobic co-digestion, effectively accelerates the degradation of bioplastics, and realizes the synchronous anaerobic digestion of bioplastics and kitchen waste.

[0030] (2) Microbial community regulation:

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

[0032] (3) Economical and operable:

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

[0034] (4) Application potential:

[0035] The technology proposed in the patent is not only applicable to PLA and PBAT, but also provides a new direction for the industrial degradation of commercially available bioplastics, especially when garbage sorting is incomplete. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0037] Figure 2 SEM images of anaerobic degradation of food waste and different types of bioplastics at 35°C;

[0038] Figure 3 Fourier transform infrared spectra of food waste and different types of bioplastics after anaerobic degradation at 35°C. DETAILED DESCRIPTION

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

[0040] A method for degrading commercially available bioplastics using kitchen waste and activated sludge, the specific steps are as follows:

[0041] (1) Preliminary treatment of food waste: This process mainly includes starch, protein, oil and other components. Plastic, chopsticks, paper towels, bamboo sticks, bones, stones and metals that are not suitable for anaerobic treatment are removed by manual screening. Then, these processed food wastes are mixed and ground into a paste with particles less than 5 mm using a cooking homogenizer, and then 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 left to stand at 4°C for 24 hours, the supernatant was manually separated, and the lower sludge was extracted and gravity concentrated before storage. The sludge was acclimatized at a mesophilic temperature of 35°C for one week, and the treated sludge was finally stored for later use.

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

[0044] (4) Anaerobic decomposition process: A headspace bottle with a volume of 200 ml was used as the reaction container to ensure that its effective volume did not exceed one-half of the total volume. N2 (purity 99.99%) was passed into the reactor for no less than 5 minutes to ensure an anaerobic environment. The reactor was sealed with a butyl rubber stopper and an aluminum cap, and the gas production was measured daily by a glass syringe. The experiment used a water bath thermostat oscillator to control the reaction temperature. The fermentation lasted for 40 days, and the oscillator speed was set to 120 rpm to ensure that the substrate and the inoculum were fully mixed.

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

[0046] Comparative Example 1

[0047] After manual screening and sorting of the food waste, it was ground into a paste with a particle size of less 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 was added, and 5 g of anaerobic activated sludge was added for methanogenesis. No degradable plastics were introduced, and only food waste and sludge were anaerobically co-digested. The initial pH value was set to 7, while ensuring that the effective working volume of the reactor remained below 100 ml. Nitrogen was introduced into the inoculated serum bottle for 5 minutes to maintain the anaerobic state before anaerobic fermentation. The temperature of the entire fermentation process was controlled at 35°C and lasted for 40 days. The volume of gas produced was measured every day using a glass syringe, and the methane content was analyzed by gas chromatography. The final methane production in the biogas was 103 ml / VS added .

[0048] Comparative Example 2

[0049] After manually sorting the food waste to remove non-degradable impurities, the food waste was crushed into a paste with a particle size of less than 5 mm using a crusher; PLA / PBAT / starch degradable plastic was cut into small pieces of 5 mm × 5 mm, and a 200 ml serum bottle was used as an anaerobic reaction container. 10.02 g of the crushed food waste paste was added, and 5 g of anaerobic activated sludge was inoculated, and 0.2 g of PLA / PBAT / starch degradable plastic CPB was added at the same time, with a starch ratio of 50%. The initial pH was set to 7, and the effective working volume of the reactor was kept less than 100 ml. Nitrogen was passed into the inoculated serum bottle for 5 minutes to ensure the anaerobic environment in the bottle and then anaerobic fermentation began. The fermentation temperature was controlled at 35°C and the duration was 40 days.

[0050] The gas volume was measured daily by glass syringe and the methane content was analyzed by gas chromatography. The final methane production in the biogas was 130 ml / VS added , which is 26.21% higher than that of comparative example 1; after 40 days of medium-temperature anaerobic decomposition, electron microscope scanning showed that some irregular small holes appeared on the surface, and the overall structure became looser; the chemical bond vibration absorption peak of Fourier infrared spectrum was weakened.

[0051] Comparative Example 3

[0052] After manually sorting the food waste to remove non-degradable impurities, the food waste was crushed into a paste with a particle size of less than 5 mm using a crusher; the PLA / PBAT degradable plastic modified by the in-situ impregnation method of proteinase K was cut into small pieces of 5 mm × 5 mm, and a 200 ml serum bottle was used as an anaerobic reaction container. 10.02 g of the crushed food waste paste was added, and 5 g of anaerobic activated sludge was inoculated, and 0.2 g of PLA / PBAT degradable plastic PLPB was added. The initial pH was set to 7, and the effective working volume of the reactor was kept less than 100 ml. Nitrogen was passed into the inoculated serum bottle for 5 minutes to ensure the anaerobic environment in the bottle and then anaerobic fermentation began. The fermentation temperature was controlled at 35°C and the duration was 40 days.

[0053] The gas volume was measured daily by glass syringe and the methane content was analyzed by gas chromatography. The final methane production in the biogas was 165 ml / VS added , which is 60.2% higher than that of comparative example 1; after 40 days of medium-temperature anaerobic decomposition, electron microscope scanning showed that some irregular small holes appeared on the surface, and the overall structure became looser; the chemical bond vibration absorption peak of Fourier infrared spectrum was weakened.

[0054] Example 1

[0055] After manually sorting the food waste to remove non-degradable impurities, the food waste was crushed into a paste with a particle size of less than 5 mm using a crusher; PLA / PBAT / starch modified by proteinase K in situ impregnation, with a starch content of 50% biodegradable plastic cut into 5 mm × 5 mm small pieces, a 200 ml serum bottle was used as an anaerobic reaction container, 10.02 g of the crushed food waste paste was added, and 5 g of anaerobic activated sludge was inoculated, and 0.2 g of PLA / PBAT / starch biodegradable plastic PKPB was added. The initial pH was set to 7, and the effective working volume of the reactor was kept less than 100 ml. Nitrogen was passed into the inoculated serum bottle for 5 minutes to ensure the anaerobic environment in the bottle and then anaerobic fermentation began. The fermentation temperature was controlled at 35 ° C and the duration was 40 days.

[0056] The gas volume was measured daily by glass syringe and the methane content was analyzed by gas chromatography. The final methane production in the biogas was 176 ml / VS added , which is 70.87% higher than that of comparative example 1; after 40 days of medium-temperature anaerobic decomposition, electron microscope scanning showed that some irregular small holes appeared on the surface, and the overall structure became looser; the chemical bond vibration absorption peak of Fourier infrared spectrum was weakened.

[0057] like Figure 1 As shown in the figure, the cumulative methane production curve of co-digestion of different plastics and food waste changes over time under 35°C conditions.

[0058] FW: Only anaerobic digestion of food waste

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

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

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

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

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

[0064] FW+PLPB group: Food waste was co-digested with proteinase K-modified PLA / PBAT plastic, and the methane production was significantly increased to 165ml / VSadded, an increase of 60.2% over the control group.

[0065] FW+PKPB group: kitchen waste was co-digested with proteinase K-modified PLA / PBAT / starch plastics, and the methane production was the highest, reaching 176ml / VSadded, which was 70.87% higher than the control group.

[0066] In summary, the results showed that proteinase K modification significantly improved the anaerobic degradation ability of plastics, while the starch component of PLA / PBAT / starch plastics further enhanced the degradation efficiency and methane production, giving it a significant advantage in anaerobic co-digestion.

[0067] like Figure 2 Shown are SEM images of co-digestion of different plastic films and food waste at 35°C.

[0068] CPB: SEM images of unmodified PLA / PBAT / starch plastics

[0069] PLPB: SEM image of PLA / PBAT modified plastic

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

[0071] After 40 days, the unmodified plastic (CPB) showed only a few cracks and slight pits, indicating that its degradation was limited; the PLA / PBAT modified plastic (PLPB) showed a significant increase in surface cracks and pits, indicating that enzyme modification significantly enhanced the degradation ability; the PLA / PBAT / starch modified plastic (PKPB) showed the most serious surface damage, with densely distributed cracks and obvious depth, indicating that the addition of starch further promoted the degradation effect of enzyme-modified plastics. These results show that the synergistic effect of proteinase K and starch can greatly improve the degradation efficiency of plastics.

[0072] like Figure 3 As shown, FTIR images of co-digestion of different plastic films and food waste at 35°C, 10 represents 10 days and 40 represents 40 days

[0073] CPB: FTIR images of unmodified PLA / PBAT / starch plastics

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

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

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

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

Claims

1. A method for anaerobic digestion of food waste and bio-enzyme-modified starch-containing bioplastics, characterized in that: The method comprises the following steps: Step 1, pre-treatment of kitchen waste: sorting the kitchen waste to remove hard debris, and then crushing it for standby use; the kitchen waste includes one or more components of starch, oil and protein; Step 2, pretreatment of starch-containing bioplastics: preparing the starch-containing bioplastics granules modified by bio-enzymes for later use; the starch-containing bioplastics include polylactic acid PLA, polybutylene adipate PBAT and starch; Step 3, anaerobic degradation: The pretreated food waste, anaerobic activated sludge and bioplastics are mixed and placed in an anaerobic reactor, and anaerobic fermentation is carried out in a constant temperature water bath at 35°C for 40 days.

2. The method for anaerobic digestion of food waste and enzyme-modified starch-containing bioplastics according to claim 1, characterized in that: The starch content in starchy bioplastics is 50%.

3. The method for anaerobic digestion of food waste and enzyme-modified starch-containing bioplastics according to claim 1, characterized in that: The biological enzyme includes proteinase K and lipase, preferably proteinase K.

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

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

6. The method for anaerobic digestion of food waste and 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: total solid TS content of 10-11%, volatile solid VS content of 8-9%, VS / TS ratio of 80-82%, and moisture content of 89-90%.

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

8. The method for anaerobic digestion of food waste and enzyme-modified starch-containing bioplastics according to claim 1, characterized in that: The reaction temperature of anaerobic digestion was controlled at 35°C and the fermentation time was 40 days.

9. The method for anaerobic digestion of food waste and bio-enzyme-modified starch-containing bioplastic according to claim 1, characterized in that: The kitchen waste sorting process includes removing debris that cannot be anaerobically digested, specifically including chopsticks, paper towels, bamboo sticks, stones or metals.

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