Systems, methods, and applications for mild alkaline thermal pretreatment to enhance biodegradable plastic composting degradation

Abstract

The application discloses a system and method for enhancing biodegradable plastic composting degradation by mild alkali heat pretreatment, and belongs to the field of organic solid waste treatment and disposal. The method comprises the following steps: biodegradable plastics are crushed by a plastic crushing unit to reduce the size; pretreatment is performed in an alkali heat treatment unit and solid-liquid separation is performed; after being mixed with organic solid waste in a material mixing unit, controlled composting or natural composting is performed in a composting unit; a heat exchange unit is additionally arranged to recycle heat; and liquid phase treatment is performed after pretreatment in a liquid phase treatment unit. The method provided by the application can simply and quickly enhance the composting degradation performance of biodegradable plastics; when applied to controlled composting, the degradation and mineralization of biodegradable plastics can be accelerated; when applied to natural composting, the plastic residues can be reduced, the adverse effects of biodegradable plastics on composting can be reduced, the risk of secondary pollution can be reduced, and the composting can better meet the standards of maturity and harmlessness.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of organic solid waste treatment and disposal, and relates to a system, a method and an application for mild alkali-thermal pretreatment for enhancing biodegradable plastic compost degradation. BACKGROUND

[0002] According to the Opinions on Further Strengthening Plastic Pollution Control, the production, sale and use of some plastic products such as non-degradable plastic bags are to be orderly banned or limited. The demand and application of biodegradable plastics as substitutes for traditional plastics are rapidly growing. The total production of biodegradable plastics in China in 2022 was about 795,000 tons, and the main types include thermoplastic starch (TPS), polylactic acid (PLA), polybutylene adipate / terephthalate (PBAT), etc. Biodegradable plastic products are usually certified under controlled composting conditions, while actual composting often uses natural heating methods. Due to the complexity of the composting system and the differences in material properties, biodegradable plastics may be difficult to degrade and have a lag phase, and the time to reach the standard degradation rate (≥90%) is much longer than the operation period of the composting system. In addition, biodegradable plastics may also affect composting maturity, reduce the fertility of compost, and cause secondary pollution, etc.

[0003] Alkali-thermal pretreatment is commonly used to enhance the anaerobic digestion performance of biodegradable plastics. Biodegradable plastics will undergo ester bond hydrolysis under alkaline conditions, resulting in a decrease in molecular weight and the generation of hydroxyl groups and other hydrophilic groups. When the temperature exceeds the glass transition temperature, the molecular chain can be expanded, accelerating the hydrolysis process. In addition, alkali-thermal pretreatment can increase the surface area and porosity of plastics through surface erosion, increasing biological affinity. The combined action of the above mechanisms can accelerate the degradation of biodegradable plastics. The current problems include: (1) The current application scenarios are mostly aimed at single polymer particles in the form of particles or powders, rather than mixed biodegradable plastic products which are more commonly used. (2) Alkali-thermal pretreatment using high temperature (>100℃) and / or long time (>1h) and / or high alkali concentration (>0.1mol / L) can dissolve more organic matter in biodegradable plastics into the liquid phase for subsequent anaerobic digestion, but it is not suitable for simply and quickly enhancing the composting degradation performance of biodegradable plastics, and high-alkali-concentration liquid-phase biological treatment is more difficult. Therefore, it is necessary to find a mild and effective alkali-thermal pretreatment condition.

[0004] The patent document with the publication number CN109593638A discloses a system and method for promoting degradation of polylactic acid plastic by hydrothermal pretreatment and methanation, which comprises a material mixing unit, a crushing and impurity removing unit, a heat exchange device, a hydrothermal treatment reactor, an anaerobic fermentation reactor, a dehydration device and a biogas combustion system, and a method for modifying polylactic acid plastic by water / alkali heat, which can shorten the degradation time from more than 100 days to within 30 days. However, the pretreatment temperature in the invention is 120-200 DEG C, which needs to be pressurized, and a corresponding system is needed in actual application, which has high cost, and only targets single polylactic acid plastic, while in actual biodegradable plastics, polybutylene adipate terephthalate (PBAT) is mixed, which is considered to be difficult to degrade in anaerobic digestion. Therefore, the technology lacks universality. In addition, whether the alkali heat pretreatment can strengthen the compost degradation of biodegradable plastics, the optimal conditions of pretreatment, whether it can weaken the adverse effects on the compost system, and the control of secondary pollution are also worth exploring. SUMMARY

[0005] In order to solve the problems in the prior art, the present application provides a system and method for mild alkali heat pretreatment to strengthen the compost degradation of biodegradable plastics, and application, which applies mild alkali heat pretreatment conditions to biodegradable plastics, softens the molecular chain under conditions higher than the glass transition temperature, promotes the non-biological hydrolysis of polymers, reduces the crystallinity and molecular weight, and improves the biological affinity, which is more conducive to the subsequent microbial enzymolysis. The present application focuses on the mild alkali heat pretreatment to strengthen the compost degradation performance of biodegradable plastics, rather than the extreme conditions to promote anaerobic methanation by dissolving a large amount of organic matter, which has relatively mild conditions, less organic matter dissolution, short time consumption and low cost. The biodegradable plastics after pretreatment are applied to controlled composting or natural composting, which can accelerate the degradation and mineralization of biodegradable plastics, reduce the adverse effects on composting, reduce the risk of secondary pollution, improve the reliability and safety of the application of compost products, and have important environmental significance and economic benefits.

[0006] To achieve the above object, the present application adopts the following technical solutions:

[0007] The present application provides a system for mild alkali heat pretreatment to strengthen the compost degradation of biodegradable plastics, which comprises a plastic crushing unit, an alkali heat treatment unit, a heat exchange unit, a solid-liquid separation unit, a liquid phase treatment unit, a material mixing unit and a composting unit. The plastic crushing unit, the alkali heat treatment unit, the solid-liquid separation unit, the material mixing unit and the composting unit are connected in sequence to pretreat the biodegradable plastics and then degrade them by composting. The heat exchange unit is connected to the alkali heat treatment unit and the solid-liquid separation unit for heat recycling, and is connected to the liquid phase treatment unit for treating the separated liquid phase.

[0008] The technical difficulties / technical difficulties overcome by the present application are how to improve the degradation performance of biodegradable plastics through mild alkali heat pretreatment under the conditions of controlling the proportion, time and cost of organic matter dissolution, promote the degradation of biodegradable plastics in the aerobic composting process, reduce the environmental risk of residual microplastics and the adverse effects on the resource utilization of organic solid waste.

[0009] The present application also provides a method for enhancing the compost degradation of biodegradable plastics through mild alkali heat pretreatment, and the steps are as follows:

[0010] Step one, crushing the biodegradable plastics to reduce the size;

[0011] Step two, pretreating the biodegradable plastics crushed in step one under mild alkali heat conditions and solid-liquid separation;

[0012] Step three, degrading the biodegradable plastics pretreated in step two through controlled composting or natural composting.

[0013] In the present application, the biodegradable plastics refer to a kind of biodegradable plastic products that can ultimately degrade into carbon dioxide or / and methane, water, mineral inorganic salt of elements contained therein and new biomass under various environmental conditions, and the biodegradable plastics use one or more of polybutylene adipate terephthalate (PBAT), polylactic acid (PLA), starch, inorganic filler, etc. as raw materials, and meet the requirements of GB / T 41010-2021 "Biodegradable plastics and products degradation performance and identification requirements"; the crushing and alkali heat pretreatment method is used to enhance the compost degradation performance of biodegradable plastics, and the pretreated biodegradable plastics are applied to controlled composting and / or natural composting.

[0014] In step one, the biodegradable plastics are crushed by mechanical crushing such as rotary cutting, tearing and crushing, or other suitable methods, and the area of the crushed biodegradable plastics is 1-100 cm 2 ; preferably 1-25 cm 2 ; more preferably 1-4 cm 2 .

[0015] In step two, the pretreatment temperature is controlled at 60-100℃; preferably 100℃.

[0016] In step two, the pretreatment is carried out under normal pressure.

[0017] In step two, the alkali includes one or more of NaOH, KOH, Ca(OH)2, etc.; preferably NaOH.

[0018] In step two, the concentration of the alkali is 0-0.1 mol / L in terms of NaOH; preferably 0.1 mol / L.

[0019] In step two, the pretreatment time is 10-60 min; preferably 40 min.

[0020] In step two, the solid-liquid separation is performed by plate-and-frame filter pressing, centrifugation or suction filtration, etc. to recover the liquid phase components for preheating the alkali solution, thereby achieving heat recycling.

[0021] In step two, the mass ratio of the biodegradable plastic to the volume of the alkali solution is 1:1-1:10; preferably 1:10, in g / mL.

[0022] In step two, the biodegradable plastic is hydrolyzed after the alkali heat pretreatment, and after the hydrolysis is completed, the pH of the liquid phase components is 7.0-12.5, the total organic carbon concentration dissolved from the biodegradable plastic is 0.1-3 g / L, and the mass of the total organic carbon dissolved from the biodegradable plastic accounts for less than 5% of the original total organic carbon mass.

[0023] In step two, after the alkali heat pretreatment, the solid phase components, i.e. the biodegradable plastic after the pretreatment, have a water contact angle reduced by 5%-25% and a molecular weight reduced by 3%-30%.

[0024] In step three, the controlled composting is performed for 30-60 days at a temperature of 50-60℃ and a material ratio of 1 g of the biodegradable plastic to (20-100) g of the composting substrate; preferably, the controlled composting is performed for 60 days at a temperature of 58℃ and a material ratio of 1 g of the biodegradable plastic to 100 g of the composting substrate; the mineralization rate of the biodegradable plastic after the alkali heat pretreatment is 80%-90%, and the molecular weight is reduced by 40%-60%.

[0025] In step three, the natural composting is performed for 30-40 days at a temperature in the range of 25-70℃ and a material ratio of 1 g of the biodegradable plastic to (10-150) g of the composting substrate; preferably, the natural composting is performed for 40 days at a temperature in the range of 40-70℃ and a material ratio of 1 g of the biodegradable plastic to 150 g of the composting substrate; the mineralization rate of the biodegradable plastic after the alkali heat pretreatment is 60%-80%, the molecular weight is reduced by 50%-60%, and the seed germination index of the composting reaches more than 85%.

[0026] The application also provides the use of the system or the method as described above in the alkali heat pretreatment and / or composting degradation of biodegradable plastics.

[0027] Compared with the prior art, the present application has the following advantages: the present application proposes a simple and rapid mild alkali-thermal pretreatment method to solve the problem that biodegradable plastics degrade slowly and may be harmful to compost maturation in aerobic composting. When applied to mixed biodegradable plastic products, the pretreatment can reduce the molecular weight by 3% to 30% and the water contact angle by 5% to 25% within 10 to 60 minutes, improve the compost degradation performance, and the reaction temperature is not higher than 100 DEG C, the conditions are mild, the reaction can be carried out under normal pressure, and the time is relatively short. The total organic carbon dissolved accounts for less than 5% of the total organic carbon of the original, which is lower than 10% to 90% in the prior art, and the loss of organic matter is less, which will not affect the subsequent compost degradation. After the pretreatment, the biodegradable plastics applied to controlled composting can accelerate the degradation and mineralization. According to the method of the present application, the mineralization rate of biodegradable plastics can reach 80% to 90% and the molecular weight can be reduced by 40% to 60% after 30 to 60 days of controlled composting. In the prior art, the mineralization rate is 40% to 70% and the molecular weight is reduced by only 30% to 40%. When applied to natural composting, the method can reduce the plastic residues and reduce the adverse effects of biodegradable plastics on composting, so that the composting can better meet the maturation and harmless standards. According to the method of the present application, the mineralization rate of biodegradable plastics is 60% to 80% and the molecular weight is reduced by 50% to 60% after 30 to 40 days of natural composting, and the seed germination index of composting reaches more than 85%. In the prior art, the mineralization rate of biodegradable plastics is 30% to 50%, the molecular weight is reduced by 30% to 40%, and the seed germination index is about 70%. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0029] Figure 1 is a system schematic diagram of the present application.

[0030] Figure 2 is the pH, total organic carbon and terephthalic acid concentration of the liquid phase component of the biodegradable plastics after low-concentration alkali-thermal pretreatment of the present application.

[0031] Figure 3 is the molecular weight change of the biodegradable plastics after low-concentration alkali-thermal pretreatment of the present application.

[0032] Figure 4 is the pH, total organic carbon and terephthalic acid concentration of the liquid phase component of the biodegradable plastics after different time alkali-thermal pretreatment of the present application.

[0033] Figure 5The pH, total organic carbon and terephthalic acid concentration of the liquid phase component after alkali-thermal pretreatment of the biodegradable plastic of the present application.

[0034] Figure 6 The surface micro-morphology and water contact angle after pretreatment of the biodegradable plastic of the present application.

[0035] Figure 7 The molecular weight change after pretreatment of the biodegradable plastic of the present application.

[0036] Figure 8 The appearance change after controlled composting of the biodegradable plastic of the present application.

[0037] Figure 9 The residue condition after natural composting of the biodegradable plastic of the present application.

[0038] Figure 10 The molecular weight change after natural composting of the biodegradable plastic of the present application.

[0039] Figure 11 The thermal property change after natural composting of the biodegradable plastic of the present application.

[0040] Figure 12 The Hu-Fubai change after natural composting of the biodegradable plastic of the present application.

[0041] Figure 13 The seed germination index change after natural composting of the biodegradable plastic of the present application. DETAILED DESCRIPTION

[0042] The present application will be further described with reference to the following specific examples and drawings. The process, conditions, experimental methods, etc. for implementing the present application are all common knowledge and common practice in the art, and the present application does not have special limitations.

[0043] It is apparent that the described embodiments are only a part of the embodiments of the present application, and are not all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative, and by no means as any limitation on the present application and its applications or uses. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present application.

[0044] In all examples shown and discussed herein, any specific value should be interpreted as merely exemplary, and not as a limitation. Thus, other examples of the exemplary embodiments can have different values.

[0045] The test materials used in the examples are all conventional biochemical reagents, unless otherwise specified.

[0046] The application provides a system and method for enhancing biodegradable plastic compost degradation by mild alkaline thermal pretreatment, and belongs to the field of organic solid waste treatment and disposal. Figure 1 The system schematic diagram of the application is shown in the accompanying drawings, and the method comprises the following steps: crushing biodegradable plastics to reduce the size; pretreating under mild alkaline thermal conditions and solid-liquid separation; and performing controlled composting or natural composting.

[0047] Example 1: Low-concentration alkaline thermal pretreatment of mixed biodegradable plastic products

[0048] The mixed biodegradable plastic products in the form of common films with PBAT, PLA, starch and inorganic fillers as raw materials are reduced in size to 1-4 cm 2 , mixed with an alkaline solution at a ratio of 1:10 (g / mL), and subjected to alkaline thermal pretreatment under constant temperature and normal pressure conditions. The solid-liquid separation is performed by suction filtration, and the liquid phase components are recovered for preheating the alkaline solution to realize heat recycling. The 60℃, 40min, 0.01mol / L NaOH condition group is denoted as BDP-2, the 80℃, 20min, 0.01mol / L NaOH condition group is denoted as BDP-4, and the 100℃, 60min, 0.01mol / L NaOH condition group is denoted as BDP-9.

[0049] As shown in Figure 2 , the pH of the liquid phase components of BDP-2 and BDP-9 after alkaline thermal pretreatment is reduced to 11.7, and the pH of the liquid phase components of BDP-9 is reduced to 9.8. Therefore, BDP-9 is more fully hydrolyzed than the other two groups, indicating that high temperature and long time conditions are more conducive to the hydrolysis of biodegradable plastics. The total organic carbon concentration of BDP-9 is also the highest, which is 674mg / L. Since the PBAT component is hydrolyzed to produce terephthalic acid monomers, the terephthalic acid concentration can also reflect the degree of hydrolysis, and the concentration of BDP-9 is the highest, which is 79mg / L.

[0050] As shown in Figure 3 , the number average molecular weight (Mn) and the weight average molecular weight (Mw) of each group after alkaline thermal pretreatment are reduced by 1%-3% and 3%-12% respectively for BDP-2, BDP-4 and BDP-9, indicating that the biodegradable plastics have undergone preliminary hydrolysis, which is more conducive to subsequent biodegradation. The polymer dispersity index PDI (Mw / Mn) decreases significantly, and the decrease of BDP-9 is the largest, from 2.26 to 2.06, indicating that both macromolecules and small molecules are hydrolyzed during the degradation process, and the molecular weight distribution tends to be concentrated and uniform.

[0051] Therefore, a ratio of 1:10 (g / mL) between biodegradable plastic and alkaline solution, a pretreatment temperature of 100℃, normal pressure, an alkaline concentration of 0.01 mol / L (NaOH), and a treatment time of 60 min are more conducive to the hydrolysis of the mixed biodegradable plastic product.

[0052] Example 2: Alkali-thermal pretreatment of mixed biodegradable plastic products at different times

[0053] The same biodegradable plastic was subjected to alkali-thermal pretreatment according to the alkali-thermal pretreatment method of Example 1 of the present invention. The pretreatment was carried out at 100°C and 0.1 mol / L NaOH, with other conditions being the same, and the pretreatment time was 10, 20, 40, 60, 90 and 120 min respectively.

[0054] like Figure 4 As shown, with the increase of alkaline heat pretreatment time, the pH showed a decreasing trend, decreasing from 12.5 to 10.0, indicating that the biodegradable plastic continued to hydrolyze. The total organic carbon concentration and terephthalic acid concentration of the liquid phase components showed an increasing trend, with a more significant increase within 10–40 min, followed by a slowdown in the increase, which is related to the preferential hydrolysis of the amorphous region of the biodegradable plastic, indicating that the pretreatment time does not need to be too long. Therefore, the optimal pretreatment conditions for this mixed biodegradable plastic product are a ratio of biodegradable plastic to alkaline solution of 1:10 (in g / mL), a pretreatment temperature of 100℃, atmospheric pressure, an alkaline concentration of 0.1 mol / L (NaOH), and a treatment time of 40 min.

[0055] Example 3: Mild alkaline-thermal pretreatment of mixed biodegradable plastic products

[0056] The same biodegradable plastic was subjected to alkali-thermal pretreatment according to the alkali-thermal pretreatment method of Example 1 of this invention. The group with 80℃, 40min, and 0.1mol / L NaOH conditions was designated as BDP-5, the group with 100℃, 20min, and 0.1mol / L NaOH conditions was designated as BDP-7, the group with 100℃, 40min, and 0.1mol / L NaOH conditions was designated as BDP-10, and the control group without pretreatment was designated as BDP.

[0057] like Figure 5 As shown, after alkaline heat pretreatment, the pH of the liquid phase components was 12.0–12.5. The total organic carbon concentration of BDP-10 was the highest, at 2731 mg / L, and the mass of dissolved total organic carbon was less than 5% of the original total organic carbon mass. Among them, the PBAT component hydrolyzed to produce terephthalic acid monomer, and the BDP-10 concentration was the highest, at 408 mg / L. The results indicate that the BDP-10 group hydrolyzed most fully within the reasonable range of organic matter dissolution, and the pretreatment effect was the best.

[0058] like Figure 6As shown in Fig. 2, a large number of hole structures appeared on the surface of the biodegradable plastic bag after alkali-thermal pretreatment, and the surface roughness and surface area increased significantly, which was more conducive to microbial adhesion. The water contact angle decreased by 8% to 22% compared to the initial value, and the plastic surface changed from hydrophobic to hydrophilic, which was more conducive to hydrolysis and biodegradation.

[0059] As shown in Fig. 2, a large number of hole structures appeared on the surface of the biodegradable plastic bag after alkali-thermal pretreatment, and the surface roughness and surface area increased significantly, which was more conducive to microbial adhesion. The water contact angle decreased by 8% to 22% compared to the initial value, and the plastic surface changed from hydrophobic to hydrophilic, which was more conducive to hydrolysis and biodegradation. Figure 7 As shown in Fig. 3, the Mn and Mw of the biodegradable plastic decreased by 4% to 16% and 13% to 26%, respectively, after alkali-thermal pretreatment with BDP-5, BDP-7, and BDP-10. The PDI of BDP-9 decreased from 2.26 to 1.99, and the molecular weight distribution tended to be concentrated and uniform.

[0060] Therefore, according to the above results, the ratio of biodegradable plastic to alkali solution is 1:10 (unit: g / mL), the pretreatment temperature is 100°C, the pressure is atmospheric pressure, the alkali concentration is 0.1 mol / L of NaOH, and the treatment time is 40 min, which are the optimal pretreatment conditions for the mixed biodegradable plastic products.

[0061] Example 4: Controlled composting of biodegradable plastics after mild alkali-thermal pretreatment

[0062] The same biodegradable plastics were subjected to alkali-thermal pretreatment according to the alkali-thermal pretreatment method of Example 1 of the present application, and the group settings were the same as in Example 3 of the present application. The activated vermiculite prepared using the mature compost under controlled conditions at 50°C was used for controlled composting, and the material ratio was 1 g of biodegradable plastic: 25 g of pumice: 50 g of activated vermiculite. Sampling, turning, and supplementing the mature compost inoculum (1 mL / 10 g of activated vermiculite) were performed every 7 days to maintain microbial activity. As shown in Fig. 4, traces of microbial adhesion appeared on the surface of the biodegradable plastic at 7 days, and the optimal pretreatment condition group was BDP-10, i.e., the ratio of biodegradable plastic to alkali solution was 1:10, the unit was g / mL, the pretreatment temperature was 100°C, the pressure was atmospheric pressure, the alkali concentration was 0.1 mol / L of NaOH, and the treatment time was 40 min. The surface showed obvious damage; at 60 days, the mineralization rate of the optimal pretreatment condition group BDP-10 reached 90%, which was 100% higher than that of the control group, and the mineralization rates of the other treatment groups also exceeded 60%. Under the optimal pretreatment conditions, the biodegradable plastic reached a degradation rate of 90% or more within 180 days, which was one-third of the time required by the biodegradable plastic arbitration standard. Figure 8 Example 5: Natural composting of biodegradable plastics after mild alkali-thermal pretreatment

[0063]

[0064] ​The same biodegradable plastic was subjected to alkaline heat pretreatment according to the alkaline heat pretreatment method of Example 1 of this invention. The conditions were the same as those of the optimal treatment group BDP-10, i.e., the ratio of biodegradable plastic to alkaline solution was 1:10 (unit: g / mL). The pretreatment temperature was 100℃, atmospheric pressure, and the alkaline concentration was 0.1mol / L (NaOH). The treatment time was 40min. After pretreatment, the biodegradable plastic was mixed with organic solid waste such as kitchen waste and straw for natural composting. The material ratio was 1g biodegradable plastic: 25g straw: 100g kitchen waste. A pretreatment group (TF) was set up, and a control group without pretreatment (NF) and a blank group without added biodegradable plastic (CK) were also set up. The compost was placed in a composting container and naturally heated in a temperature range of 25-70℃. The compost was turned over every 3 days. After the composting was completed, the degradation of biodegradable plastic and the degree of compost maturity were analyzed.

[0065] like Figure 9 As shown, after composting, the amount of plastic residue in the TF group was lower than that in the NF group in the 1-2mm, 2-5mm, and >5mm size ranges. In particular, in the >5mm size range, the amount of plastic residue in the TF group was only 40% of that in the NF group. This indicates that the pre-treated biodegradable plastics degraded more effectively and had fewer residual microplastics (by mass). Alkali-heat pretreatment promoted the degradation of biodegradable plastics in composting while reducing plastic residues and improving the safety of compost products.

[0066] like Figure 10 As shown, the molecular weight of the TF group decreased by 14.06% (Mn) and 11.69% (Mw) compared to the NF group after pretreatment. During composting, as the biodegradable plastic degraded, the overall Mn and Mw of each group showed a decreasing trend, with a more significant decrease in the early stage of composting. At the end of composting, the molecular weight of the TF group was 14467 g / mol (Mn) and 30744 g / mol (Mw), which were 45% (Mn) and 42% (Mw) lower than those of the NF group, respectively. Since the decrease in Mn was slightly greater than that in Mw, the PDI of each group increased slightly compared to the initial value, indicating that the long chains of the biodegradable plastic molecules were broken during the degradation process, resulting in a mixture of long and short chains and a wider molecular weight distribution.

[0067] like Figure 11 As shown, due to factors such as the decrease in molecular weight caused by hydrolysis after pretreatment, the initial decomposition temperature of the TF group (the temperature corresponding to a 10% mass loss, denoted as T) is... d ) and the temperature of maximum decomposition rate (the temperature at which the thermal decomposition rate is fastest, denoted as T). max Compared to the NF group, the temperatures decreased by 8.68℃ and 4.24℃, respectively. During composting, the temperatures of each group (T) decreased. d and T max All values ​​continuously increase, and thermal stability also improves accordingly. As the easily degradable portion decomposes through composting, the thermal stability of the remaining biodegradable plastic increases, with the TF group reaching its highest value at the end of composting. d and Tmax Both groups surpassed the NF group, indirectly reflecting that the TF group underwent more degradation. Furthermore, the percentage of thermal decomposition residue in the NF group was 24.35%, higher than that in the NF group (22.46%), confirming the above results.

[0068] The ratio of fulvic acid to humic acid, known as the humic-to-fulvic acid ratio (HFU / FMR), can be used to assess the degree of compost maturity. A higher HFU / FMR indicates a higher degree of maturity. Figure 12 As shown, the Hu-F-ratio decreased slightly in the early stage of composting, and continued to increase after reaching the high temperature period. At the end of composting, the TF group was significantly higher than the NF group and slightly higher than the CK group, indicating that the addition of biodegradable plastics is not conducive to composting maturity, while pretreatment can reduce its adverse effects and promote the composting humification process.

[0069] Seed germination index is also an important indicator for evaluating compost maturity, such as Figure 13 As shown, at the end of composting, the GI of all groups exceeded 70%, meeting the standards for organic fertilizers, indicating that the compost was fully decomposed. The TF and CK groups were similar, both exceeding 85%, significantly higher than the NF group, which is consistent with the Hufby results, indicating that pretreatment can reduce the adverse effects of biodegradable plastic bags on compost maturity and improve the quality of compost products.

[0070] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0071] As used in this invention, the term "comprising" is an open-ended expression, meaning it includes the contents specified in this invention but does not exclude other aspects.

[0072] As used in this invention, the term "and / or" includes any one or more of the related listed items and all combinations thereof.

[0073] The scope of protection of this invention is not limited to the above embodiments. Any variations and advantages that can be conceived by those skilled in the art without departing from the spirit and scope of this invention are included in this invention and are protected by the appended claims.

Claims

1. A method for enhancing the composting degradation of a mildly alkaline thermally pretreated biodegradable plastic, characterized in that, The biodegradable plastics refer to a kind of biodegradable plastic products that can ultimately degrade into carbon dioxide or / and methane, water, mineral inorganic salt of elements contained therein and new biomass under various environmental conditions, with one or more of polybutylene adipate terephthalate, polylactic acid, starch and inorganic filler as raw materials, in accordance with GB / T 41010-2021 "Biodegradable Plastics and Products Degradation Performance and Identification Requirements", and the method comprises the following steps: Step one, crushing biodegradable plastics to reduce size; in the step one, the biodegradable plastics are crushed by mechanical crushing of rotary cutting, tearing and crushing, the area of the biodegradable plastics after crushing is 1-100 cm 2 ; Step two, the biodegradable plastics crushed in step one are pretreated under mild alkali heat conditions and solid-liquid separation is performed; In step two, the pretreatment temperature is controlled at 60-100 DEG C; the pretreatment is performed under normal pressure; the alkali is selected from one or more of NaOH, KOH and Ca(OH)2; the alkali concentration in the alkali solution is 0-0.1 mol / L in terms of NaOH; the solid-liquid separation is performed by plate and frame filter pressing, centrifugation or suction filtration, and the liquid phase components are recovered for preheating the alkali solution, so as to realize heat recovery and utilization; Step three, the biodegradable plastics pretreated in step two are degraded by controlled composting or natural composting.

2. The method of claim 1, wherein, In step two, the pretreatment time is 10-60 min.

3. The method of claim 1, wherein, In step two, the mass of the biodegradable plastics to the volume of the alkali solution is 1:1-1:10, in g / mL.

4. The method of claim 1, wherein, In step two, the biodegradable plastics are hydrolyzed after alkali heat pretreatment, the pH of the liquid phase components after hydrolysis is 7.0-12.5, the total organic carbon concentration dissolved from the biodegradable plastics is 0.1-3 g / L, and the mass of the organic carbon dissolved from the biodegradable plastics accounts for less than 5% of the total mass of the original organic carbon.

5. The method of claim 1, wherein, The water contact angle of the biodegradable plastics after alkali heat pretreatment is reduced by 5%-25%, and the molecular weight is reduced by 3%-30%.

6. The method of claim 1, wherein, In step three, the controlled composting is performed for 30-60 days, the temperature range is 50-60 DEG C, and the material ratio is 1 g of the biodegradable plastics to (20-100) g of composting substrate; The mineralization rate of the biodegradable plastics after alkali heat pretreatment is 80%-90%, and the molecular weight is reduced by 40%-60%.

7. The method of claim 1, wherein, In step three, the natural composting is performed for 30-40 days, the temperature range is 25-70 DEG C, the material ratio is 1 g of the biodegradable plastics to (10-150) g of composting substrate, the mineralization rate of the biodegradable plastics after alkali heat pretreatment is 60%-80%, the molecular weight is reduced by 50%-60%, and the seed germination index of the composting reaches more than 85%.

8. A system for enhancing the biodegradation of composting of a mildly alkaline thermally pretreated biodegradable plastic, characterized by, The system adopts the method according to any one of claims 1-7, and the system comprises a plastic crushing unit, an alkali heat treatment unit, a heat exchange unit, a solid-liquid separation unit, a liquid phase treatment unit, a material mixing unit and a composting unit; wherein, The plastic crushing unit, the alkali heat treatment unit, the solid-liquid separation unit, the material mixing unit and the composting unit are connected in sequence, and the biodegradable plastic is pretreated and degraded by composting; the heat exchange unit is connected with the alkali heat treatment unit and the solid-liquid separation unit for heat recycling, and is connected with the liquid phase treatment unit for treating the separated liquid phase.

9. Use of the system according to claim 8, or the method according to any one of claims 1-7, in alkali heat pretreatment and composting degradation of biodegradable plastic.

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