Self-circulation system and method for low-carbon enrichment and degradation of micro-plastics

Abstract

The invention discloses a self-circulation system and method for micro-plastic low-carbon enrichment and degradation, and relates to the field of water governance, micro-plastic adsorption and water body micro-plastic adsorbent regeneration are integrated, a closed-loop treatment system of enrichment, preheating, precise pyrolysis and cyclic reuse is constructed, and the micro-plastic adsorption and water body micro-plastic adsorbent regeneration are integrated. The solar photo-thermal pretreatment device is adopted to preheat the water body micro-plastic adsorbent, the water content is effectively reduced, the initial temperature is increased, and therefore the energy consumption requirement of the follow-up pyrolysis link is remarkably reduced. Meanwhile, the adsorption bin is combined with the crawler belt transmission mechanism, so that the underwater coverage area is enlarged, and the enrichment efficiency of the micro-plastics is further improved. In addition, a variable-pitch spiral heating pipe structure is adopted in the pyrolyzing furnace, so that the pyrolyzing furnace can adapt to temperature gradient distribution in the furnace, heat transfer and material pyrolyzing processes are enhanced, and the overall pyrolyzing efficiency is remarkably improved. Long-acting removal of the water body micro-plastics, recycling of adsorption materials, in-situ enrichment and degradation are integrated, and efficient treatment of the water body micro-plastics and sustainable utilization of resources are achieved.

Description

Technical Field

[0001] This invention relates to the field of water treatment, specifically to a self-circulating system and method for the low-carbon enrichment and degradation of microplastics. Background Technology

[0002] Plastics are man-made polymers widely used due to their ductility, versatility, low cost, durability, excellent oxygen resistance, lightweight, and bioinsensitivity. In the production and consumption of tires, cosmetics, coatings, and other large plastic products, as well as in the environment, plastics continuously break down into tiny particles during breakage, wear, and degradation. Plastic fragments and particles with a diameter of less than 5 mm are defined as microplastics. Because of their strong pollutant loading capacity and direct ingestion by plants and animals, microplastics pose a serious threat to the ecological environment and human health, and are an emerging pollutant of widespread international concern.

[0003] Currently, microplastics are mainly removed from wastewater through a combination of physical, chemical, and / or biological treatments. However, these methods have some limitations. First, traditional wastewater treatment processes have limited efficiency in removing microplastics. The limited removal efficiency of existing wastewater treatment systems for microplastics stems primarily from two challenges: First, microplastics are highly similar in particle size and density to organic matter and suspended solids in water, making it difficult for traditional physical, chemical, and biological treatment processes to achieve efficient separation. Second, the diverse morphology and size of microplastics mean that a single treatment technology cannot cover the removal needs of the entire spectrum and wide range of microplastics, ultimately affecting the overall treatment efficiency.

[0004] To achieve simultaneous enrichment of microplastics of various sizes across a full cross-section of water, Chinese invention patent "A Device and Method for Simultaneous Enrichment of Microplastics of Various Sizes Across a Small River" (CN202210880416.1) introduces a device and method for simultaneously enriching microplastics of various sizes at different horizontal positions and vertical depths across a cross-section through the synergistic action of a filtration and collection unit, a sample point positioning unit, and a sampling opening and closing unit. This device is easy to operate and ensures the reliability of the sampling data. However, this device only focuses on the enrichment and collection of microplastics and does not involve subsequent degradation treatment, still requiring separate treatment equipment. Furthermore, in terms of treatment technology, physical filtration methods mostly rely on disposable filter materials, which suffer from problems such as easy clogging, frequent replacement, and high costs, making it difficult to achieve long-term, continuous microplastic removal. In addition, most devices cannot achieve integrated in-situ enrichment and degradation of microplastics, requiring the transfer of microplastics from the water body before treatment, increasing operational complexity and labor costs.

[0005] In view of the above situation, it is urgent to develop a low-carbon self-circulating system and method that can achieve long-term removal of microplastics in water, recycle adsorption materials, and integrate in-situ enrichment and degradation. Summary of the Invention

[0006] To address the aforementioned shortcomings of existing technologies, this invention provides a self-circulating system and method for low-carbon enrichment and degradation of microplastics, which integrates long-term removal of microplastics from water, recyclability of adsorbent materials, and in-situ enrichment and degradation.

[0007] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: A self-circulating system for the low-carbon enrichment and degradation of microplastics is provided, comprising a tracked adsorption chamber assembly. The tracked adsorption chamber assembly includes a track composed of several adsorption chambers connected in sequence, and a pulley for driving the track. The upper part of the track is located above the water surface, and the lower part of the track is located below the water surface. The adsorption chambers are loaded with water-based microplastic adsorbents. A collection port and a pyrolysis furnace are respectively provided at both ends of the track. When the adsorption chambers are driven by the pulley to run above the water surface, the adsorption chambers overturn, allowing the water-based microplastic adsorbents to fall into the collection port. A screw feeder is installed between the collection port and the pyrolysis furnace. The screw feeder is used to convey the water microplastic adsorbent falling into the collection port to the feed hopper of the pyrolysis furnace. The discharge hopper of the pyrolysis furnace is equipped with a feeding device. The feeding device is used to load the pyrolyzed water microplastic adsorbent into the adsorption hopper at the end away from the collection port. The water microplastic adsorbent includes, but is not limited to, metal-modified activated carbon loaded with metal oxides and metal hydroxides by impregnation.

[0008] Furthermore, the water microplastic adsorbent is Mg-magnetic activated carbon, prepared by the following method: S1: Mix Mg(NO3)2·6H2O, Fe(NO3)3·9H2O and activated carbon in a mass ratio of 2:3:2; after mixing, add deionized water in a solid-liquid mass ratio of 2:5 and stir at 150~200r / min for 12h. S2: After stirring, dry at 105℃. Then, heat the dried activated carbon to 550℃ at a heating rate of 5℃ / min under an inert atmosphere and maintain the temperature for 2 hours. S3: After heat treatment, the carbon is naturally cooled to room temperature, washed three times with deionized water, and then dried at 105℃ to obtain Mg-magnetic activated carbon.

[0009] Furthermore, a low-mesh filter with a pore size larger than that of the microplastic adsorbent in the water is installed on the side of the adsorption chamber closest to the center of the track, while a high-mesh filter with a pore size smaller than that of the microplastic adsorbent in the water is installed on the side of the adsorption chamber furthest from the low-mesh filter. High-mesh filters are also installed on the front and rear ends of the adsorption chamber along the water flow direction.

[0010] Furthermore, a baffle extends from the side of the adsorption chamber, which is used to push floating debris that has been collected in front of the high-mesh filter by the water flow to the rear.

[0011] Furthermore, the collection port is equipped with a toothed plate, which is used to actuate the low-mesh filter screen of the adsorption chamber, so that the microplastic adsorbent in the water falls through the low-mesh filter screen to the collection port.

[0012] Furthermore, it also includes a pyrolysis recovery preheating component, which comprises a cold molten salt storage tank, a solar collector area, a hot molten salt storage tank, and a water microplastic adsorbent preheating pipeline connected in sequence. The water microplastic adsorbent preheating pipeline is located at the axis of the screw feeder. The low-temperature molten salt in the cold molten salt storage tank is heated by the solar collector area and then transported to the hot molten salt storage tank. The high-temperature molten salt in the hot molten salt storage tank preheats the water microplastic adsorbent in the screw feeder via the water microplastic adsorbent preheating pipeline. The movement direction of the high-temperature molten salt in the water microplastic adsorbent preheating pipeline is opposite to the transmission direction of the screw feeder. After the high-temperature molten salt transfers heat to the water microplastic adsorbent, it becomes low-temperature molten salt again and is transported to the cold molten salt storage tank through the pipeline. The low-temperature molten salt is a ternary nitrate molten salt, which is composed of 53% KNO3, 40% NaNO2, and 7% NaNO3.

[0013] Furthermore, the feed hopper of the pyrolysis furnace includes a temporary storage hopper and a transition hopper. The temporary storage hopper is located above the transition hopper and is used to temporarily store the water microplastic adsorbent transported by the screw feeder. A first valve is installed between the transition hopper and the temporary storage hopper, and a second valve is installed between the transition hopper and the feed inlet of the pyrolysis furnace. A nitrogen inlet and a first nitrogen outlet are respectively installed on both sides of the transition hopper. When the first valve and the second valve are closed, the water microplastic adsorbent is purged with nitrogen through the nitrogen inlet and the first nitrogen outlet to ensure that the oxygen content in the transition hopper is ≤1%.

[0014] Furthermore, a third valve is installed at the discharge hopper of the pyrolysis furnace, and a second nitrogen outlet is installed on the side of the third valve away from the discharge hopper. When the pyrolysis furnace is pyrolyzing, the first valve, the third valve and the first nitrogen outlet are closed, while the second valve and the second nitrogen outlet are opened, so that the oxygen content in the pyrolysis furnace is ≤1% through the nitrogen inlet and the second nitrogen outlet.

[0015] Furthermore, the pyrolysis furnace is equipped with a coaxial two-stage screw feeder. The two ends of the two-stage screw feeder are long-pitch screw sections, and the middle of the two-stage screw feeder is a short-pitch screw section; the length ratio of any long-pitch screw section to the short-pitch screw section is 2:5.

[0016] The present invention also provides a method for the low-carbon enrichment and degradation of microplastics in water using the above-mentioned self-circulating system, comprising the following steps: S1: The adsorption chamber is filled with water microplastic adsorbent by the feeding device, and the drive wheel is controlled to move the adsorption chamber filled with water microplastic adsorbent below the water surface. The water microplastic adsorbent captures microplastics in the water. S2: Under the action of the drive wheel, the adsorption chamber moves along the track and overturns at the end away from the pyrolysis furnace. When overturning, the water microplastic adsorbent containing microplastics in the adsorption chamber passes through the low mesh filter and falls to the collection port, and continues to slide down to the feed port of the screw feeder. S3: The screw feeder transports the microplastic-adsorbent in the water to the pyrolysis furnace. Simultaneously, the pyrolysis recovery preheating component operates, and the microplastic-adsorbent preheating pipeline preheats the transported microplastic-adsorbent to 120~130℃, reducing its moisture content to below 8%. The preheated microplastic-adsorbent falls into the feed hopper of the pyrolysis furnace. The low-temperature molten salt in the microplastic-adsorbent preheating pipeline has a velocity of 30g / s. After heat exchange between the low-temperature molten salt and the microplastic-adsorbent, the molten salt returns to the cold molten salt storage tank and is reheated by the solar collector area. S4: The microplastic adsorbent in the water body with microplastics is purged with nitrogen in the feed hopper to reduce its oxygen content to ≤1%, and then pyrolyzed in an anaerobic pyrolysis furnace. S5; The pyrolyzed water microplastic adsorbent is cooled to below 120°C in the discharge hopper and then refilled into the adsorption hopper via the feeding device.

[0017] The beneficial effects of this invention are as follows: This invention integrates microplastic adsorption and water microplastic adsorbent regeneration to construct a closed-loop treatment system of "enrichment—preheating—precise pyrolysis—recycling and reuse." A solar thermal pretreatment device is used to preheat the water microplastic adsorbent, effectively reducing its water content and increasing the initial temperature, thereby significantly reducing the energy consumption of the subsequent pyrolysis stage. Simultaneously, the adsorption chamber is combined with a tracked drive mechanism to expand the underwater coverage area, further improving the microplastic enrichment efficiency. Furthermore, the pyrolysis furnace employs a variable-pitch spiral heating tube structure, which can adapt to the temperature gradient distribution within the furnace, enhancing heat transfer and the material pyrolysis process, thus significantly improving the overall pyrolysis efficiency. This system integrates long-term removal of water microplastics, recyclable adsorbent materials, and in-situ enrichment and degradation, achieving efficient treatment and sustainable resource utilization of water microplastics. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the hidden pyrolysis recovery preheating component of the present invention; Figure 2 This is a schematic diagram of the internal structure of a pyrolysis furnace; Figure 3 This is a schematic diagram of the three-dimensional structure of the adsorption chamber; Figure 4 A cross-sectional schematic diagram of an adsorption chamber filled with microplastic adsorbent for water. Figure 5 A schematic diagram of the structure of the pyrolysis recovery preheating component; The components include: 1. Feed hopper; 2. Pyrolysis furnace; 3. Discharge hopper; 4. Feeding device; 5. Track; 6. Adsorption hopper; 7. Collection port; 8. Screw feeder; 101. First valve; 102. First nitrogen outlet; 103. Nitrogen inlet; 104. Second valve; 105. Temporary storage hopper; 106. Transition hopper; 201. Secondary screw feeder; 202. Short-pitch screw section; 203. Long-pitch screw section; 301. Second nitrogen outlet; 302. Third valve; 501. Pulley; 601. High-mesh filter screen; 602. Water microplastic adsorbent; 603. Low-mesh filter screen; 604. Baffle; 901. Hot molten salt storage tank; 902. Solar collector area; 903. Cold molten salt storage tank; 904. Water microplastic adsorbent preheating pipeline. Detailed Implementation

[0019] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0020] like Figures 1-4 As shown, a self-circulating system for low-carbon enrichment and degradation of microplastics includes a track 5 and an adsorption chamber 6 assembly. The track 5 and adsorption chamber 6 assembly includes a track 5 composed of several adsorption chambers 6 connected in sequence by track links, and a pulley 501 for driving the track 5. The upper part of the track 5 is above the water surface, and the lower part of the track 5 is below the water surface. The adsorption chamber 6 is loaded with a water microplastic adsorbent 602. Water microplastic adsorbent 602 is Mg-magnetic activated carbon, prepared by the following method: S1: Mix Mg(NO3)2·6H2O, Fe(NO3)3·9H2O and activated carbon in a mass ratio of 2:3:2; after mixing, add deionized water in a solid-liquid mass ratio of 2:5 and stir at 150~200 r / min for 12 h; the activated carbon used is 80~100 mesh activated carbon. S2: After stirring, dry at 105℃. Then, heat the dried activated carbon to 550℃ at a heating rate of 5℃ / min under an inert atmosphere and maintain the temperature for 2 hours. S3: After heat treatment, the mixture is naturally cooled to room temperature, washed three times with deionized water, and dried at 105°C to obtain Mg-magnetic activated carbon. In this embodiment, Mg-magnetic activated carbon with a particle size of 0.5~0.8 mm was screened and used as water microplastic adsorbent 602.

[0021] The two ends of the track 5 are respectively provided with a collection port 7 and a pyrolysis furnace 2. When the adsorption chamber 6 is driven by the pulley 501 to run above the water surface, the adsorption chamber 6 overturns, causing the water microplastic adsorbent 602 to fall into the collection port 7. A screw feeder 8 is installed between the collection port 7 and the pyrolysis furnace 2. The screw feeder 8 is used to convey the water-based microplastic adsorbent 602 falling into the collection port 7 to the feed hopper 1 of the pyrolysis furnace 2. The discharge hopper 3 of the pyrolysis furnace 2 is equipped with a feeding device 4, which is used to load the pyrolyzed water-based microplastic adsorbent 602 into the adsorption hopper 6 at the end away from the collection port 7. The screw feeder 8 has a diameter of 0.4 m, an inclination angle of 25°, and a blade rotation speed of 20 r / min.

[0022] A low-mesh filter 603 with a pore size larger than that of the microplastic adsorbent in the water is provided on the side of the adsorption chamber 6 closest to the center of the track 5. A high-mesh filter 601 with a pore size smaller than that of the microplastic adsorbent in the water is provided on the side of the adsorption chamber 6 furthest from the low-mesh filter 603. High-mesh filters 601 are also provided at the front and rear ends of the adsorption chamber 6 along the water flow direction. In this embodiment, the high-mesh filter 601 is 250 mesh, and the low-mesh filter 603 is 16 mesh. A baffle 604 extends from the side of the adsorption chamber 6. The baffle 604 is used to push the floating garbage on the water surface that is gathered in front of the high mesh filter 601 with the water flow to the rear side.

[0023] The collection port 7 is equipped with a toothed plate, which is used to actuate the low-mesh filter 603 of the adsorption chamber 6, causing the water microplastic adsorbent 602 to fall through the low-mesh filter 603 into the collection port 7. After adsorption is complete, the adsorption chamber 6 is moved to the surface area, with the high-mesh filter 601 facing upwards and the low-mesh filter 603 facing downwards. When the adsorption chamber 6 passes through the collection port 7, it collides with the toothed plate on the collection port 7, causing it to vibrate up and down. Under the action of gravity, the water microplastic adsorbent 602 falls through the collection port 7 into the screw feeder 8. The entire underwater adsorption process lasts for about 0.5 hours.

[0024] It also includes a pyrolysis recovery preheating component, which comprises a cold molten salt storage tank 903, a solar collector zone 902, a hot molten salt storage tank 901, and a water microplastic adsorbent preheating pipeline 904 connected in sequence. The water microplastic adsorbent preheating pipeline 904 is located at the axis of the screw feeder 8. The low-temperature molten salt in the cold molten salt storage tank 903 is heated by the solar collector zone 902 and then transported to the hot molten salt storage tank. The high-temperature molten salt in the hot molten salt storage tank 901 is heated by the water microplastic adsorbent... The preheating pipeline 904 preheats the water microplastic adsorbent 602 in the screw feeder 8. The high-temperature molten salt moves in the water microplastic adsorbent preheating pipeline 904 in the opposite direction to the transmission direction of the screw feeder 8. After the high-temperature molten salt transfers heat to the water microplastic adsorbent 602, it becomes low-temperature molten salt again and is transported to the cold molten salt storage tank 903 through the pipeline. The low-temperature molten salt is a ternary nitrate molten salt, which is composed of 53% KNO3, 40% NaNO2 and 7% NaNO3.

[0025] The feed bin 1 of the pyrolysis furnace 2 includes a temporary storage bin 105 and a transition bin 106. The temporary storage bin 105 is located above the transition bin 106 and is used to temporarily store the water microplastic adsorbent 602 conveyed by the screw feeder 8. A first valve 101 is provided between the transition bin 106 and the temporary storage bin 105, and a second valve 104 is provided between the transition bin 106 and the feed inlet of the pyrolysis furnace 2. A nitrogen inlet 103 and a first nitrogen outlet 102 are respectively provided on both sides of the transition bin 106. When the first valve 101 and the second valve 104 are closed, the water microplastic adsorbent 602 is purged with nitrogen through the nitrogen inlet 103 and the first nitrogen outlet 102 to make the oxygen content in the transition bin 106 ≤1%.

[0026] A third valve 302 is also installed at the discharge hopper 3 of the pyrolysis furnace 2, and a second nitrogen outlet 301 is installed on the side of the third valve 302 away from the discharge hopper 3. When the pyrolysis furnace 2 is pyrolyzing, the first valve 101, the third valve 302 and the first nitrogen outlet 102 are closed, while the second valve 104 and the second nitrogen outlet 301 are opened. The oxygen content in the pyrolysis furnace 2 is kept ≤1% through the nitrogen inlet 103 and the second nitrogen outlet 301. The entire pyrolysis process lasts for about 20 minutes.

[0027] The pyrolysis furnace 2 is equipped with a coaxial two-stage screw feeder 201. The two ends of the two-stage screw feeder 201 are long-pitch screw sections 203, and the middle of the two-stage screw feeder 201 is a short-pitch screw section 202; the length ratio of any long-pitch screw section 203 to short-pitch screw section 202 is 2:5. The rotational speed of the two-stage screw feeder 201 is 2 r / min. The water microplastic adsorbent 602 is fed sequentially through the front, middle and rear sections of the pyrolysis furnace 2 via a two-stage screw feeder 201. It undergoes three processes: rapid heating, full pyrolysis, and cooling. The microplastics are thermally degraded into harmless small molecule gases, which are then treated by the exhaust gas purification device to meet emission standards. The pyrolyzed water microplastic adsorbent 602 is temporarily stored in the discharge hopper 3, which has a volume of 10L. When the pyrolyzed water microplastic adsorbent 602 is cooled to below 120°C in the hopper, the third valve 302 is opened, and the water microplastic adsorbent 602 enters the feeding device 4 under the action of gravity.

[0028] The specific steps of the water microplastic low-carbon enrichment and degradation method using the above-mentioned self-circulating system are as follows: S1: The water microplastic adsorbent 602 is filled into the adsorption chamber 6 by the feeding device 4, and the transmission wheel is controlled to work so that the adsorption chamber 6 filled with water microplastic adsorbent 602 moves below the water surface, and the water microplastic adsorbent 602 captures microplastics in the water. S2: Under the action of the drive wheel, the adsorption chamber 6 moves along the track 5 and overturns at the end away from the pyrolysis furnace 2. When overturning, the water microplastic adsorbent 602 with microplastic adsorbent adsorbed in the adsorption chamber 6 passes through the low mesh filter screen 603 and falls to the collection port 7, and continues to slide down to the feed port of the screw feeder 8. S3: The screw feeder 8 transports the microplastic adsorbent 602 containing microplastics to the pyrolysis furnace 2. Simultaneously, the pyrolysis recovery preheating component operates, and the microplastic adsorbent 602 preheating pipeline preheats the microplastic adsorbent 602 in the transport to 120~130℃, reducing the moisture content of the microplastic adsorbent 602 to below 8%. The preheated microplastic adsorbent 602 falls into the feed hopper 1 of the pyrolysis furnace 2. The low-temperature molten salt in the microplastic adsorbent 602 preheating pipeline has a velocity of 30g / s. After heat exchange between the low-temperature molten salt and the microplastic adsorbent 602, it returns to the cold molten salt storage tank 903 and is reheated by the solar collector area 902. S4: The microplastic adsorbent 602 in the water body containing microplastics is purged with nitrogen in the feed hopper 1 to reduce its oxygen content to ≤1%, and then undergoes anaerobic pyrolysis in the pyrolysis furnace 2. S5; The pyrolyzed water microplastic adsorbent 602 is cooled to below 120°C in the discharge hopper 3 and then refilled into the adsorption hopper 6 via the feeding device 4.

Claims

1. A self-circulating system for the low-carbon enrichment and degradation of microplastics, characterized in that, The device includes a tracked adsorption chamber assembly, which comprises a track consisting of several adsorption chambers connected in sequence, and a pulley for driving the track. The upper part of the track is above the water surface, and the lower part of the track is below the water surface. The adsorption chambers are filled with water microplastic adsorbent. A collection port and a pyrolysis furnace are respectively provided at both ends of the track. When the adsorption chamber is driven by the pulley to run above the water surface, the adsorption chamber overturns, allowing the water microplastic adsorbent to fall into the collection port. A screw feeder is installed between the collection port and the pyrolysis furnace. The screw feeder is used to convey the water microplastic adsorbent falling into the collection port to the feed hopper of the pyrolysis furnace. The discharge hopper of the pyrolysis furnace is equipped with a feeding device. The feeding device is used to load the pyrolyzed water microplastic adsorbent into the adsorption hopper at the end away from the collection port. The water microplastic adsorbent includes, but is not limited to, metal-modified activated carbon loaded with metal oxides and metal hydroxides by impregnation.

2. The self-circulating system for low-carbon enrichment and degradation of microplastics according to claim 1, characterized in that, The water microplastic adsorbent is Mg-magnetic activated carbon, prepared by the following method: S1: Mix Mg(NO3)2·6H2O, Fe(NO3)3·9H2O and activated carbon in a mass ratio of 2:3:2; after mixing, add deionized water in a solid-liquid mass ratio of 2:5 and stir at 150~200r / min for 12h. S2: After stirring, dry at 105℃. Then, heat the dried activated carbon to 550℃ at a heating rate of 5℃ / min under an inert atmosphere and maintain the temperature for 2 hours. S3: After heat treatment, the carbon is naturally cooled to room temperature, washed three times with deionized water, and then dried at 105℃ to obtain Mg-magnetic activated carbon.

3. The self-circulating system for low-carbon enrichment and degradation of microplastics according to claim 1, characterized in that, The adsorption chamber is equipped with a low-mesh filter screen with a pore size larger than that of the microplastic adsorbent in the water on the side closest to the center of the track, and a high-mesh filter screen with a pore size smaller than that of the microplastic adsorbent in the water on the side of the adsorption chamber away from the low-mesh filter screen. The adsorption chambers at the front and rear ends along the water flow direction are also equipped with high-mesh filters.

4. The self-circulating system for low-carbon enrichment and degradation of microplastics according to claim 3, characterized in that, A baffle extends from the side of the adsorption chamber, which is used to push floating debris that has been collected in front of the high-mesh filter screen by the water flow to the rear.

5. The self-circulating system for low-carbon enrichment and degradation of microplastics according to claim 4, characterized in that, The collection port is equipped with a toothed plate, which is used to actuate the low-mesh filter screen of the adsorption chamber, so that the microplastic adsorbent in the water falls through the low-mesh filter screen to the collection port.

6. The self-circulating system for low-carbon enrichment and degradation of microplastics according to claim 5, characterized in that, It also includes a pyrolysis recovery preheating component, which comprises a cold molten salt storage tank, a solar collector area, a hot molten salt storage tank, and a water microplastic adsorbent preheating pipeline connected in sequence. The water microplastic adsorbent preheating pipeline is located at the axis of the screw feeder. The low-temperature molten salt in the cold molten salt storage tank is heated by the solar collector area and then transported to the hot molten salt storage tank. The high-temperature molten salt in the hot molten salt storage tank preheats the water microplastic adsorbent in the screw feeder via the water microplastic adsorbent preheating pipeline. The movement direction of the high-temperature molten salt in the water microplastic adsorbent preheating pipeline is opposite to the transmission direction of the screw feeder. After the high-temperature molten salt transfers heat to the water microplastic adsorbent, it becomes low-temperature molten salt again and is transported to the cold molten salt storage tank through the pipeline. The low-temperature molten salt is a ternary nitrate molten salt, which is composed of 53% KNO3, 40% NaNO2, and 7% NaNO3.

7. The self-circulating system for low-carbon enrichment and degradation of microplastics according to any one of claims 1 to 6, characterized in that, The feed hopper of the pyrolysis furnace includes a temporary storage hopper and a transition hopper. The temporary storage hopper is located above the transition hopper and is used to temporarily store the water microplastic adsorbent transported by the screw feeder. A first valve is provided between the transition hopper and the temporary storage hopper, and a second valve is provided between the transition hopper and the feed inlet of the pyrolysis furnace. A nitrogen inlet and a first nitrogen outlet are respectively provided on both sides of the transition hopper. When the first valve and the second valve are closed, the water microplastic adsorbent is purged with nitrogen through the nitrogen inlet and the first nitrogen outlet to ensure that the oxygen content in the transition hopper is ≤1%.

8. The self-circulating system for low-carbon enrichment and degradation of microplastics according to claim 7, characterized in that, A third valve is also installed at the discharge hopper of the pyrolysis furnace, and a second nitrogen outlet is installed on the side of the third valve away from the discharge hopper. When the pyrolysis furnace is pyrolyzing, the first valve, the third valve and the first nitrogen outlet are closed, while the second valve and the second nitrogen outlet are opened. The oxygen content in the pyrolysis furnace is kept ≤1% through the nitrogen inlet and the second nitrogen outlet.

9. The self-circulating system for low-carbon enrichment and degradation of microplastics according to claim 8, characterized in that, The pyrolysis furnace is equipped with a coaxial two-stage spiral feeder. The two ends of the two-stage spiral feeder are long-pitch spiral sections, and the middle of the two-stage spiral feeder is a short-pitch spiral section. The length ratio of any long-pitch spiral section to the short-pitch spiral section is 2:

5.

10. A method for the low-carbon enrichment and degradation of microplastics in water using a self-circulating system for low-carbon enrichment and degradation of microplastics as described in claim 9, characterized in that, The following steps are used: S1: The adsorption chamber is filled with water microplastic adsorbent by the feeding device, and the drive wheel is controlled to move the adsorption chamber filled with water microplastic adsorbent below the water surface. The water microplastic adsorbent captures microplastics in the water. S2: Under the action of the drive wheel, the adsorption chamber moves along the track and overturns at the end away from the pyrolysis furnace. When overturning, the water microplastic adsorbent containing microplastics in the adsorption chamber passes through the low mesh filter and falls to the collection port, and continues to slide down to the feed port of the screw feeder. S3: The screw feeder transports the microplastic-adsorbent in the water to the pyrolysis furnace. Simultaneously, the pyrolysis recovery preheating component operates, and the microplastic-adsorbent preheating pipeline preheats the transported microplastic-adsorbent to 120~130℃, reducing its moisture content to below 8%. The preheated microplastic-adsorbent falls into the feed hopper of the pyrolysis furnace. The low-temperature molten salt in the microplastic-adsorbent preheating pipeline has a velocity of 30g / s. After heat exchange between the low-temperature molten salt and the microplastic-adsorbent, the molten salt returns to the cold molten salt storage tank and is reheated by the solar collector area. S4: The microplastic adsorbent in the water body with microplastics is purged with nitrogen in the feed hopper to reduce its oxygen content to ≤1%, and then pyrolyzed in an anaerobic pyrolysis furnace. S5; The pyrolyzed water microplastic adsorbent is cooled to below 120°C in the discharge hopper and then refilled into the adsorption hopper via the feeding device.

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