Biochemical treatment method for promoting plastic degradation

Abstract

The invention discloses a biochemical treatment method for promoting plastic degradation, which comprises the following steps: digging out soil containing plastic on the surface layer by 15-20cm, then mixing the soil with a surface layer plastic accelerator, then spreading a bottom layer plastic degradation agent into a pit after digging out the soil, sprinkling water, then backfilling the soil mixed with the surface layer plastic accelerator into the pit, and finally, covering the surface layer plastic degradation agent with the surface layer plastic accelerator. Spraying water to enable the soil humidity to reach 20-30%, and completing the biochemical treatment; according to the method, crushing and degradation of the micro-plastics on the surface layer of the soil can be promoted, degradation of the crushed and settled micro-plastics with smaller diameters can also be promoted, the implementation mode is simple, the manual labor is less, special equipment and repeated soil treatment are not needed, the treatment time is saved, and the applicability is high.

Description

Technical Field

[0001] The invention belongs to the technical field of organic solid waste treatment, and in particular relates to a biochemical treatment method for promoting plastic degradation. Background Art

[0002] Plastic is one of the most commonly used synthetic materials because it is durable, lightweight and cost-effective. In 2015, global plastic production reached 6.3 billion tons. However, only 21% of plastics are recycled or incinerated, and the rest are weathered and broken down into tiny fragments, forming "microplastics" with a diameter of less than 5 mm; currently, microplastics have spread all over the world and polluted rivers, lakes, farmland, etc. Plastic pollution has become a global problem, and how to promote plastic degradation needs to be solved urgently.

[0003] Patent CN115889423A discloses a method for enhancing the biodegradation performance of microplastics through biochar. Biochar increases the abundance of microorganisms, provides a suitable habitat for soil microorganisms, increases the content of microorganisms in the soil, and improves the decomposition efficiency of microplastics. However, since microplastics of different diameters are distributed at different depths in the soil, this solution is more dependent on the distribution degree and sedimentation capacity of biochar in the soil, and is more dependent on the types and activity of microorganisms in the soil, and has poor applicability.

[0004] Patent CN116060435A discloses a method for rapid degradation of microplastics in a soil environment. By preparing a degradation agent containing plastic-degrading bacteria, the purpose of rapidly degrading microplastics through high-temperature continuous fermentation of the bacteria is achieved. This solution requires 1-2 days of high-temperature fermentation treatment with a covering film, which requires a lot of manpower and energy and has low practicality.

[0005] Therefore, a biochemical treatment method is needed to promote the degradation of plastics, which can promote the degradation of microplastics on the soil surface and smaller microplastics below the soil surface to meet the plastic degradation needs in the corresponding fields. Summary of the invention

[0006] The purpose of the present invention is to solve the problem of how to promote the degradation of microplastics on the soil surface and microplastics with smaller diameters in deep soil layers.

[0007] The present invention assists in the crushing and degradation of microplastics on the soil surface by containing a promoter for promoting the crushing of microplastics and a biological agent on the surface, and applies a microbial agent in the soil below the surface to assist in the degradation of microplastics and small-diameter microplastics settled on the surface.

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

[0009] A biochemical treatment method for promoting plastic degradation comprises the following steps:

[0010] Step 1: Dig out the soil with plastic on the surface layer by 15 - 20 cm, and mix the surface plastic promoter with the dug - out soil at a mixing amount of 300 - 400 g / m 3 .

[0011] Step 2: Spread the bottom - layer plastic degrading agent at a spreading amount of 150 - 200 g / m 2 in the pit after digging out the soil, and sprinkle water to make the surface of the bottom - layer plastic degrading agent turn black;

[0012] Step 3: Backfill the soil mixed with the surface plastic promoter into the pit, sprinkle water at 50 - 60 °C to make the soil humidity reach 20 - 30%, and the biochemical treatment is completed.

[0013] The surface plastic promoter is prepared through the following steps:

[0014] Mix the starch - bacterium agent microspheres and the promoter carrier at a mass ratio of 1 - 2:20, stir while sprinkling water until the surface humidity of the promoter carrier reaches 10 - 20%, then conduct vacuum drying, crushing, and screening through a 40 - mesh sieve at 40 - 50 °C to obtain the surface plastic promoter;

[0015] The bottom - layer plastic degrading agent is prepared through the following steps:

[0016] Mix the starch - bacterium agent and the biochar at a mass ratio of 1 - 2:20, stir while sprinkling water until the surface humidity of the biochar reaches 10 - 20%, then conduct vacuum drying, crushing, and screening through a 40 - mesh sieve at 40 - 50 °C to obtain the bottom - layer plastic degrading agent.

[0017] Furthermore, the promoter carrier is prepared through the following steps:

[0018] Dissolve zinc chloride in dilute hydrochloric acid with a pH value of 4 - 5 in a reaction kettle, add biochar and stir for 12 - 16 h, then add sodium carbonate, stir at 100 - 200 r / min for 15 - 20 min, and conduct hydrothermal reaction at 130 - 140 °C for 12 - 14 h. Wash the obtained precipitate and dry it to obtain the promoter carrier.

[0019] Furthermore, the dosage ratio of zinc chloride, dilute hydrochloric acid, biochar, and sodium carbonate is: 0.2 - 0.3 g: 60 mL - 80 mL: 25 - 30 g: 15 - 20 g.

[0020] Furthermore, the starch - bacterium agent microspheres are prepared through the following steps:

[0021] Mix the fermentation broth after the enlarged cultivation of the biodegradable plastic strains with a 10-12 wt% propionylated starch emulsion and oscillate for 10-15 min to obtain a starch-bacteria liquid. Then add sodium alginate accounting for 2-3% of the mass of the starch-bacteria liquid, stir and mix until dissolved, and then dropwise add a 6-8 wt% calcium chloride solution. After stirring at 200-300 r / min for 1.5-2 h, centrifuge, wash the precipitate, and dry to obtain starch-bacteria agent microspheres.

[0022] Further, the starch-bacteria agent is prepared by the following steps:

[0023] Mix the fermentation broth after the enlarged cultivation of the biodegradable plastic strains with a 10-12 wt% propionylated starch emulsion at a constant temperature of 50-60 °C and oscillate for 10-15 min, and then spray dry to obtain the starch-bacteria agent.

[0024] Further, the biodegradable plastic strains include Pseudomonas aeruginosa, Chryseobacterium, Bacillus subtilis, and Alkanivorax.

[0025] Further, the volume ratio of the fermentation broth to the 10-12 wt% propionylated starch emulsion is 1-2:100.

[0026] Further, the propionylated starch emulsion is obtained by stirring and mixing propionylated starch with deionized water.

[0027] Further, the propionylated starch is prepared by the following steps: Mix dry starch with propionic anhydride in a reaction kettle, add p-toluenesulfonic acid, stir and react, then wash, dry, and grind to obtain propionylated starch.

[0028] Advantages of the present invention:

[0029] (1) The method of the present invention can not only promote the fragmentation and degradation of microplastics on the soil surface, but also promote the degradation of smaller-diameter microplastics after fragmentation and sedimentation. The implementation method is simple, with less manual labor, no special equipment is required, and the soil does not need to be repeatedly treated, saving treatment time and having high applicability.

[0030] (2) The method of the present invention promotes the degradation and fragmentation of microplastics by preparing a surface plastic promoter and a bottom plastic degrader and mixing them with the plastic-containing soil on the surface layer and the bottom soil respectively. The surface plastic promoter promotes the degradation and fragmentation of microplastics, and the bottom plastic degrader promotes the degradation of the microplastics sedimented on the surface layer and the microplastics in the soil by microorganisms and agents, improving the plastic degradation ability in the soil.

[0031] (3) The method of the present invention prepares a promoter carrier by compounding zinc oxide on the surface of biochar. While the biochar adsorbs microplastics, zinc oxide also adheres to the surface of microplastics, enabling zinc oxide to promote the degradation and fragmentation of microplastics under the conditions of oxygen and light. At the same time, the surface plastic promoter in the present invention contains starch bacteria agent microspheres, which can form a film on the plastic surface after watering in the method of the present invention. The water in the film is conducive to the formation and transmission of hydroxyl radicals, which is beneficial to the degradation of microplastics.

[0032] (4) The method of the present invention prepares a starch bacteria agent by mixing a bacteria agent for degradable plastics and propionylated starch. While propionylated starch protects the bacteria agent, it also increases the adsorption capacity of the bacteria species of degradable plastics. When the bacteria agent adsorbs with propionylated starch to microplastics, the bacteria species of degradable plastics also adsorb on the surface of microplastics, improving the microplastic degradation ability of the bacteria species. Detailed implementation mode

[0033] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0034] Example 1

[0035] A biochemical treatment method for promoting plastic degradation includes the following steps:

[0036] Step 1: Dig out 15 cm of soil with plastic on the surface layer, and mix the surface plastic promoter with the dug-out soil at a mixing amount of 300 g / m 3 ;

[0037] During the mixing process, the looseness of the soil is increased, the oxygen content of the soil is increased, and the surface plastic promoter is also more likely to move downward with gravity in the soil;

[0038] Step 2: Spread the bottom plastic degrading agent at a spreading amount of 150 g / m 2 in the pit after the soil is dug out, and sprinkle water to make the surface of the bottom plastic degrading agent turn black;

[0039] The content of microplastics that have been degraded in the bottom of the pit for many years is relatively high, and after the surface microplastics are degraded, they will settle to the bottom soil. Mix the bottom plastic degrading agent with the soil at the bottom of the pit. The starch bacteria agent in the bottom plastic degrading agent flows out from the pores of the biochar under the action of water flow impact and dissolution and mixes with the soil at the bottom of the pit. The propionylated starch has enhanced hydrophobicity, making it easier for the starch bacteria agent to bind to the microplastics in the bottom soil, promoting the degradation of microplastics. Starch also provides a carbon source for the bacteria agent, making the bacteria agent more rapidly activated. The rich porous surface area of the biochar also provides a habitat for the microorganisms in the soil, increasing the abundance of microorganisms in the soil and improving the degradation efficiency;

[0040] Step 3: Backfill the soil mixed with the surface plastic promoter into the soil pit, sprinkle water at 50 °C to make the soil humidity reach 20%, and the biochemical treatment is completed.

[0041] The promoter carrier of the surface plastic promoter has a porous surface area and is more likely to adsorb on the surface of microplastics in the soil. The surface of the promoter carrier contains zinc oxide. Under high humidity, zinc oxide will generate reactive oxygen species such as hydroxyl radicals and superoxide radicals under the irradiation of ultraviolet and visible light. These reactive oxygen species will damage the polymer chains of microplastics, generate more free radicals, cause an increase in the Young's modulus of microplastics, increase the brittleness of microplastics, promote plastic fragmentation, increase the contact area, and improve the degradation ability.

[0042] Preparation of the promoter carrier:

[0043] Dissolve 0.2 g of zinc chloride in 60 mL of dilute hydrochloric acid with a pH value of 4 in a reaction kettle, add 25 g of biochar and stir for 12 h, then add 15 g of sodium carbonate. After stirring at 100 r / min for 15 min, hydrothermally react the solution at 130 °C for 12 h; wash the precipitate obtained at the bottom of the reaction kettle with deionized water and absolute ethanol until the washing solution is close to neutral, and then put the washed product into a blast drying oven and dry it at 60 °C for 8 h to obtain the promoter carrier.

[0044] The biochar is obtained by high-temperature pyrolysis of straw in a muffle furnace and passing through a 60-mesh sieve.

[0045] By mixing zinc chloride with biochar and performing hydrothermal reaction, zinc oxide is formed in the pores on the surface of the biochar.

[0046] Preparation of the starch bacteria agent

[0047] Expand the culture of the degradable plastic bacteria species to obtain a number of bacteria species greater than 8x10 8The fermentation broth at cfu / mL was then added to the sterilized 10 wt% propionylated starch emulsion at a volume ratio of 1:100. After mixing in a constant temperature oscillator at 50 °C for 10 min, it was dried in a spray dryer under the conditions of an inlet air temperature of 90 °C and an outlet temperature of 45 °C to obtain the starch microbial agent.

[0048] Preparation of starch microbial agent microspheres:

[0049] The biodegradable plastic strains were expanded and cultured to obtain a fermentation broth with a strain number greater than 8x10 8 cfu / mL. Then, propionylated starch was mixed with deionized water at 50 °C and stirred to prepare a 10 wt% propionylated starch emulsion. The fermentation broth was added to the sterilized propionylated starch emulsion at a volume ratio of 1:100, and mixed in a constant temperature oscillator at 50 °C for 10 min to obtain a starch microbial solution. Then, sodium alginate was mixed with the starch microbial solution to prepare a starch microbial solution with a sodium alginate content of 2 wt%, and stirred at a rotation speed of 200 r / min for 10 min. Then, a 6 wt% calcium chloride solution was added dropwise to the starch microbial solution containing sodium alginate, and stirring was continued for 1.5 h. Then, it was centrifuged at 3000 r / min for 5 min, and the lower precipitate was washed with isopropanol, petroleum ether, and absolute ethanol respectively. The microspheres were collected and dried at 50 °C to obtain the starch microbial agent microspheres.

[0050] The strains of biodegradable plastics are: Pseudomonas aeruginosa, Chryseobacterium;

[0051] The freeze-dried powder of the strains was purchased from Beijing BioWin Biotechnology Co., Ltd.

[0052] The microspheres formed by sodium alginate and the starch microbial agent have good water absorption and water retention capabilities, and also have good adhesion capabilities. After binding with water, a film can be formed on the plastic surface. The water in the film is beneficial to the formation of free hydroxyl radicals, thereby promoting the degradation of microplastics. And the film will generate adsorption stress on the microplastics. After continuous sunlight irradiation, the film will gradually dry and break, and the desorption stress generated will act on the microplastic surface, further promoting the fragmentation of the plastic. The fragmented microplastics provide more contact area, improve the degradation ability of the microbial agent, and increase the degradation speed.

[0053] The preparation method of propionylated starch is:

[0054] 10 g of dry starch was mixed with 30 mL of propionic anhydride in a reaction kettle, 0.5 g of p-toluenesulfonic acid was added, and the mixture was stirred and reacted for 4 h. After the reaction was completed, when the solution was cooled to room temperature, ice distilled water at 2 °C was added for sufficient washing to remove the unreacted propionic anhydride and p-toluenesulfonic acid, and the solid product was separated by vacuum filtration through a Buchner funnel. The solid product was dried in an oven at 45 °C for 24 h, ground, and passed through a 100-mesh sieve to obtain propionylated starch.

[0055] The hydrophobic ester carbonyl group of propionylated starch is connected to the starch molecule by substituting some hydrophilic hydroxyl groups, enhancing the hydrophobicity of propionylated starch; and the acylation reaction increases the roughness of the starch surface, enhancing the adsorption property of the starch.

[0056] Prepare the surface plastic promoter:

[0057] Mix the starch bacterium agent microspheres and the promoter carrier in a mass ratio of 1:20, sprinkle water while stirring until the surface humidity of the promoter carrier reaches 10%, then dry in vacuum at 40°C, pulverize, and pass through a 40-mesh sieve to obtain the surface plastic promoter.

[0058] Sprinkle water on the surface of the promoter carrier to promote the fixation of the starch bacterium agent in the pores on the surface of the promoter carrier.

[0059] Prepare the bottom plastic degrader:

[0060] Mix the starch bacterium agent and biochar in a mass ratio of 1:20, sprinkle water while stirring until the surface humidity of the biochar reaches 10%, then dry in vacuum at 40°C, pulverize, and pass through a 40-mesh sieve to obtain the bottom plastic degrader.

[0061] Sprinkle water on the surface of the biochar to promote the fixation of the starch bacterium agent in the pores of the biochar carrier.

[0062] Example 2

[0063] A biochemical treatment method for promoting plastic degradation includes the following steps:

[0064] Step 1: Dig out the soil with plastic on the surface layer by 17.5 cm, and mix the surface plastic promoter with the dug-out soil at a mixing amount of 350 g / m 3 ;

[0065] Step 2: Spread the bottom plastic degrader in the pit after digging out the soil at a spreading amount of 175 g / m 2 , and sprinkle water to make the surface of the bottom plastic degrader turn black;

[0066] Step 3: Backfill the soil mixed with the surface plastic promoter into the pit, sprinkle water at 55°C to make the soil humidity reach 25%, and the biochemical treatment is completed.

[0067] Prepare the promoter carrier:

[0068] Dissolve 0.25 g of zinc chloride in 70 mL of dilute hydrochloric acid with a pH of 4.5 in a reaction kettle, add 27.5 g of biochar and stir for 14 h, then add 17.5 g of sodium carbonate. After stirring at 150 r / min for 17 min, place the solution in the reaction kettle and carry out a hydrothermal reaction at 135 °C for 13 h. Wash the precipitate obtained at the bottom of the reaction kettle with deionized water and absolute ethanol until the washing liquid is close to neutral, and then put the washed product into a blast drying oven and dry it at 65 °C for 10 h to obtain the promoter carrier.

[0069] The biochar is obtained by high-temperature pyrolysis of agricultural wastes such as straw and rice husks in a muffle furnace and passing through a 60-mesh sieve.

[0070] Prepare the starch bacterium agent:

[0071] Expand the culture of the biodegradable plastic bacteria to obtain a fermentation broth with a bacterial count greater than 8x10 8 cfu / mL, and then add the fermentation broth to the sterilized 11 wt% propionylated starch emulsion at a volume ratio of 1.5:100. Mix it in a constant temperature oscillator at 55 °C for 12.5 min, and then dry it through a spray dryer under the conditions of an inlet air temperature of 95 °C and an outlet temperature of 47.5 °C to obtain the starch bacterium agent.

[0072] Prepare the starch bacterium agent microspheres:

[0073] Expand the culture of the biodegradable plastic bacteria to obtain a fermentation broth with a bacterial count greater than 8x10 8 cfu / mL, then mix propionylated starch with deionized water at 55 °C and stir to prepare an 11 wt% propionylated starch emulsion. Add the fermentation broth to the sterilized propionylated starch emulsion at a volume ratio of 1.5:100, mix it in a constant temperature oscillator at 55 °C for 12.5 min to obtain the starch bacterium liquid. Then mix sodium alginate with the starch bacterium liquid to prepare a starch bacterium liquid with a sodium alginate content of 2.5 wt%, and stir it at a speed of 200 r / min for 12 min. Then, gradually add a 7 wt% calcium chloride solution dropwise to the starch bacterium liquid containing sodium alginate and continuously stir for 1.8 h. Then centrifuge at 3000 r / min for 6.5 min, wash the lower precipitate with isopropanol, petroleum ether, and absolute ethanol respectively, collect the microspheres, and dry them at 55 °C to obtain the starch bacterium agent microspheres.

[0074] The strains of biodegradable plastics are: Chryseobacterium and Bacillus subtilis;

[0075] The freeze-dried powder of the strains is purchased from Beijing BioWin Biotechnology Co., Ltd.

[0076] The preparation method of propionylated starch is:

[0077] Mix 12.5 g of dry starch with 40 mL of propionic anhydride in a reaction kettle, add 0.65 g of p-toluenesulfonic acid, stir and react for 5 h. After the reaction is completed, wait for the solution to cool to room temperature, add ice-distilled water at 3 °C and wash thoroughly to remove unreacted propionic anhydride and p-toluenesulfonic acid, and separate the solid product by vacuum filtration through a Buchner funnel. Dry the solid product in an oven at 47.5 °C for 26 h, grind it, and pass it through a 100-mesh sieve to obtain propionylated starch.

[0078] Prepare the surface plastic promoter:

[0079] Mix the starch bacterium agent microspheres and the promoter carrier in a mass ratio of 1.5:20, sprinkle water while stirring until the surface humidity of the promoter carrier reaches 15%, then dry and crush it under vacuum at 45 °C, and pass it through a 40-mesh sieve to obtain the surface plastic promoter.

[0080] Prepare the bottom plastic degrader:

[0081] Mix the starch bacterium agent and biochar in a mass ratio of 1.5:20, sprinkle water while stirring until the surface humidity of the biochar reaches 15%, then dry and crush it under vacuum at 45 °C, and pass it through a 40-mesh sieve to obtain the bottom plastic degrader.

[0082] Example 3

[0083] A biochemical treatment method for promoting plastic degradation, comprising the following steps:

[0084] Step 1: Dig out 20 cm of the soil with plastic on the surface, and mix the surface plastic promoter with the dug-out soil in a mixing amount of 400 g / m 3 ;

[0085] Step 2: Spread the bottom plastic degrader in the pit after digging out the soil at a spreading amount of 200 g / m 2 , and sprinkle water to make the surface of the bottom plastic degrader turn black;

[0086] Step 3: Backfill the soil mixed with the surface plastic promoter into the pit, sprinkle water at 60 °C to make the soil humidity reach 30%, and the biochemical treatment is completed.

[0087] Prepare the promoter carrier:

[0088] Dissolve 0.3 g of zinc chloride in 80 mL of dilute hydrochloric acid with a pH value of 5 in a reaction kettle, add 30 g of biochar and stir for 16 h, then add 20 g of sodium carbonate, stir at 200 r / min for 20 min, and then subject the solution to hydrothermal reaction at 140 °C for 14 h; wash the precipitate obtained at the bottom of the reaction kettle with deionized water and absolute ethanol until the washing liquid is close to neutral, and then put the washed product into a blast drying oven and dry it at 70 °C for 12 h to obtain the promoter carrier.

[0089] Biochar was obtained by pyrolyzing agricultural wastes such as straw and rice husk at high temperature in a muffle furnace and then passing through a 60-mesh sieve.

[0090] Preparation of starch inoculant

[0091] The degradable plastic strains were enlarged and cultured to obtain a fermentation broth with a strain number greater than 8x10 8 cfu / mL, and then the fermentation broth was added to the sterilized 12 wt% propionylated starch emulsion at a volume ratio of 2:100. After mixing for 15 min in a constant temperature oscillator at 60 °C, it was dried by a spray dryer under the conditions of an inlet air temperature of 100 °C and an outlet temperature of 50 °C to obtain the starch inoculant.

[0092] Preparation of starch inoculant microspheres:

[0093] The degradable plastic strains were enlarged and cultured to obtain a fermentation broth with a strain number greater than 8x10 8 cfu / mL, and then propionylated starch was mixed with deionized water at 60 °C and stirred to prepare a 12 wt% propionylated starch emulsion. The fermentation broth was added to the sterilized propionylated starch emulsion at a volume ratio of 2:100 and mixed for 15 min in a constant temperature oscillator at 60 °C to obtain a starch bacterial solution. Then sodium alginate was mixed with the starch bacterial solution to prepare a starch bacterial solution with a sodium alginate content of 3 wt%, and stirred at a speed of 300 r / min for 15 min; then an 8 wt% calcium chloride solution was added dropwise to the starch bacterial solution containing sodium alginate and continuously stirred for 2 h, and then centrifuged at 3000 r / min for 8 min. The lower layer precipitate was washed with isopropanol, petroleum ether, and absolute ethanol respectively, and the microspheres were collected and dried at 60 °C to obtain the starch inoculant microspheres.

[0094] The strains of degradable plastics are: Bacillus subtilis, Alkanivorax;

[0095] The freeze-dried powder of the strains was purchased from Beijing BioWin Biotechnology Co., Ltd.

[0096] The preparation method of propionylated starch is:

[0097] 15 g of dry starch was mixed with 45 mL of propionic anhydride in a reaction kettle, 0.75 g of p-toluenesulfonic acid was added, and the mixture was stirred and reacted for 6 h. After the reaction was completed, the solution was cooled to room temperature, and ice-distilled water at 4 °C was added for sufficient washing to remove unreacted propionic anhydride and p-toluenesulfonic acid, and the solid product was separated by vacuum filtration through a Buchner funnel. The solid product was dried in an oven at 50 °C for 28 h, ground, and passed through a 100-mesh sieve to obtain propionylated starch.

[0098] Preparation of surface plastic promoter:

[0099] Mix the starch bacterium agent microspheres and the promoter carrier in a mass ratio of 2:20, sprinkle water while stirring until the surface humidity of the promoter carrier reaches 20%, then dry in vacuum at 50°C, crush, and pass through a 40-mesh sieve to obtain the surface plastic promoter.

[0100] Prepare the bottom plastic degrading agent:

[0101] Mix the starch bacterium agent and biochar in a mass ratio of 2:20, sprinkle water while stirring until the surface humidity of the biochar reaches 20%, then dry in vacuum at 50°C, crush, and pass through a 40-mesh sieve to obtain the bottom plastic degrading agent.

[0102] Comparative Example 1

[0103] Step 1: Dig out the top 15 cm of the soil layer containing plastic, and mix the biochar with the dug-out soil at a mixing amount of 300 g / m 3 ;

[0104] Step 2: Spread the biochar at a spreading amount of 150 g / m 2 in the pit after digging out the soil, and sprinkle water to make the surface of the bottom plastic degrading agent turn black;

[0105] Step 3: Backfill the soil mixed with biochar into the pit, sprinkle water to make the soil humidity reach 30%, and the biochemical treatment is completed.

[0106] Comparative Example 2

[0107] The difference from Example 1 is that:

[0108] Step 1: Dig out the top 15 cm of the soil layer containing plastic, and mix the plastic promoter with the dug-out soil at 300 g / m 3 ;

[0109] Step 2: Backfill the soil mixed with the plastic promoter into the pit, and sprinkle water to make the soil humidity reach 20%.

[0110] Prepare the plastic promoter:

[0111] Mix the promoter carrier and the starch bacterium agent in a mass ratio of 1:20, sprinkle water while stirring until the surface humidity of the promoter carrier reaches 10%, then dry in vacuum at 40°C, crush, and pass through a 40-mesh sieve to obtain the plastic promoter.

[0112] The plastic decomposition ability tests were carried out on Examples 1 - 3 and Comparative Examples 1 - 2. The test method was as follows: Examples 1 - 3 and Comparative Examples 1 - 2 were used to treat 10 kg of soil with the same plastic content respectively. The plastic types were a mixture of polyethylene, polypropylene and polyester crushed into plastic flakes of 5 mm × 5 mm. The microplastic mass in the soil after 18 weeks in the natural environment was detected respectively. The plastic fragments in the soil were separated and collected by the flotation separation method, the plastic mass after treatment was measured, and the degradation rate was calculated. The calculation results are shown in Table 1:

[0113] Table 1

[0114] Project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Degradation rate 41.4％ 42.1％ 42.8％ 18.2％ 26.8％

[0115] It can be seen from the data in Table 1 that the degradation rates of Examples 1 - 3 are all higher than 50%. Compared with Comparative Example 1 that only uses biochar, the plastic degradation ability is greatly improved; the plastic degradation rate of Comparative Example 2 is much lower than that of Examples 1 - 3, indicating that the bottom plastic degrading agent prepared by the present invention can degrade the microplastics settling from the surface soil. In Comparative Example 2, since only the plastic promoter is mixed in the surface soil, after the microplastics in the surface soil are degraded, the volume becomes smaller and sinks downward, separating from the plastic promoter, resulting in a low degradation rate. The biochemical treatment method of the present invention effectively degrades the microplastics on the soil surface and the microplastics sinking from the surface, with a high degradation rate.

[0116] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non - exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device.

[0117] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principle and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A biochemical treatment method for promoting plastic degradation, characterized in that, It includes the following steps: Step 1: Dig out the soil with plastic on the surface layer by 15 - 20 cm, and mix the surface plastic promoter with the dug-out soil at a mixing amount of 300 - 400 g / m 3 ; Step 2: Spread the bottom plastic degrading agent in the pit after the soil is dug out at a spreading rate of 150 - 200 g / m 2 , and sprinkle water to make the surface of the bottom plastic degrading agent turn black; Step 3: Backfill the soil mixed with the surface plastic promoter into the soil pit, sprinkle water at 50 - 60 °C to make the soil humidity reach 20 - 30%, and the biochemical treatment is completed; The surface plastic promoter is prepared through the following steps: Mix the starch bacterium agent microspheres and the promoter carrier at a mass ratio of 1 - 2:20, stir while sprinkling water until the surface humidity of the promoter carrier reaches 10 - 20%, then vacuum dry, pulverize, and pass through a 40 - mesh sieve at 40 - 50 °C to obtain the surface plastic promoter; The bottom plastic degrading agent is prepared through the following steps: Mix the starch bacterium agent and biochar at a mass ratio of 1 - 2:20, stir while sprinkling water until the surface humidity of the biochar reaches 10 - 20%, then vacuum dry, pulverize, and pass through a 40 - mesh sieve at 40 - 50 °C to obtain the bottom plastic degrading agent.

2. The biochemical treatment method for promoting plastic degradation according to claim 1, characterized in that The promoter carrier is prepared through the following steps: Dissolve zinc chloride in dilute hydrochloric acid with a pH value of 4 - 5 in a reaction kettle, add biochar and stir for 12 - 16 h, then add sodium carbonate, stir at 100 - 200 r / min for 15 - 20 min, and then carry out a hydrothermal reaction at 130 - 140 °C for 12 - 14 h. Wash the obtained precipitate and dry it to obtain the promoter carrier.

3. The biochemical treatment method for promoting plastic degradation according to claim 2, wherein, The dosage ratio of the zinc chloride, dilute hydrochloric acid, biochar, and sodium carbonate is: 0.2 - 0.3 g: 60 mL - 80 mL: 25 - 30 g: 15 - 20 g.

4. A biochemical treatment method for promoting plastic degradation according to claim 1, characterized in that, The starch bacterium agent microspheres are prepared through the following steps: Mix the fermentation broth after the expand culture of the biodegradable plastic bacteria species with a 10 - 12 wt% propionylated starch emulsion and oscillate for 10 - 15 min to obtain a starch bacterium liquid. Then add sodium alginate accounting for 2 - 3% of the mass of the starch bacterium liquid, stir and mix until dissolved, and then dropwise add a 6 - 8 wt% calcium chloride solution. Stir at 200 - 300 r / min for 1.5 - 2 h, then centrifuge, wash the precipitate, and dry it to obtain the starch bacterium agent microspheres.

5. A biochemical treatment method for promoting plastic degradation according to claim 1, characterized in that, The starch bacterium agent is prepared through the following steps: Mix the fermentation broth after the expand culture of the biodegradable plastic bacteria species with a 10 - 12 wt% propionylated starch emulsion at 50 - 60 °C and oscillate and mix for 10 - 15 min, and then spray dry to obtain the starch bacterium agent.

6. The biochemical treatment method for promoting plastic degradation according to claim 4 or 5, characterized in that, The biodegradable plastic bacteria species include Pseudomonas aeruginosa, Chryseobacterium, Bacillus subtilis, and Alkanivorax.

7. A biochemical treatment method for promoting plastic degradation according to claim 4 or 5, characterized in that The volume ratio of the fermentation broth and the 10 - 12 wt% propionylated starch emulsion is 1 - 2:

100.

8. A biochemical treatment method for promoting plastic degradation according to claim 4, characterized in that, The propionylated starch emulsion is obtained by stirring and mixing propionylated starch and deionized water.

9. The biochemical treatment method for promoting plastic degradation according to claim 8, characterized in that, The propionylated starch is prepared through the following steps: Mix dry starch and propionic anhydride in a reaction kettle, add p - toluenesulfonic acid, stir and react, then wash, dry, and grind to obtain propionylated starch.