An internal light source coupled nano-carbon supply reinforced microalgae plastic waste carbon fixation system and method

Abstract

The application provides an inner light source coupling micro-nano carbon supply reinforced microalgae plastic removal and carbon fixation system and method, which comprises a light reinforcement module, a micro-nano gas oscillation carbon supply module, a photobioreactor main body and an algae plastic collection and resource utilization module; the light reinforcement module, the micro-nano gas oscillation carbon supply module and the algae plastic collection and resource utilization module are connected with the photobioreactor main body respectively; the light reinforcement module adds carbon quantum dots and plant hormone IAA into the photobioreactor main body, and realizes composite illumination in cooperation with illumination; the micro-nano gas oscillation carbon supply module transports micro-nano dispersed CO2 into the photobioreactor main body, and makes the deagglomeration of microplastics in water; the algae plastic collection and resource utilization module collects, processes and realizes resource utilization of the microalgae mixture adsorbing microplastics in the photobioreactor main body. The application aims to realize efficient removal of microplastics, efficient fixation of CO2 and resource utilization of biomass.

Description

Technical Field

[0001] This invention belongs to the field of water microplastic pollution control and carbon dioxide fixation technology, specifically involving an internal light source coupled with nano-micro carbon supply to enhance microalgae plastic removal and carbon fixation system and method. Background Technology

[0002] Over the past two decades, global plastic production has continued to climb. Microplastics (particle size <5mm), formed from the physical, chemical, and biological degradation of plastic waste, have become one of the major pollutants in the water environment. The detection rate of microplastics in drinking water sources has exceeded 80%, seriously threatening water supply security. Microplastics can adsorb pollutants such as heavy metals and pharmaceutical compounds, forming complex pollution. Existing water purification processes lack dedicated microplastic removal units, making treatment extremely difficult.

[0003] Microalgae, due to their strong environmental adaptability, high metabolic capacity, and good pollution tolerance, have become a preferred material for the bioremediation of microplastics in water bodies. Their extracellular polymeric substances (EPS) are the core substances for adsorbing microplastics, and model algae species such as *Chlorella* and *Scenedesmus* exhibit excellent adsorption capacity for micron-sized microplastics. Simultaneously, microalgae can fix CO2 through photosynthesis, making them an ideal carrier for achieving synergistic "pollution control and carbon sequestration." However, existing microalgae-based microplastic remediation and carbon sequestration technologies face three major bottlenecks:

[0004] The problem of light limitation is prominent: Traditional microalgae cultivation uses a single external light source for illumination, which leads to severe light attenuation and self-shading in the deep layers of the algal solution. This results in low light energy utilization, which cannot support the stable synthesis of EPS and limits the biomass production rate of microalgae.

[0005] Inefficient carbon source supply: Traditional aeration-type CO2 supply mode has the problem of high emission rate, which cannot match the vigorous carbon demand of microalgae after photoenhanced, thus restricting EPS synthesis and microplastic adsorption efficiency.

[0006] The separation between governance and resource utilization: Existing technologies only focus on the adsorption and removal of microplastics or the separate fixation of CO2, without constructing a complete closed-loop chain of "adsorption-harvesting-resource utilization-carbon sequestration". As a result, the resource utilization rate is low and it is impossible to achieve a win-win situation for ecological and economic benefits.

[0007] To address these issues, existing research has attempted to optimize the lighting conditions or CO2 mass transfer methods for microalgae cultivation, such as using multi-faceted light sources and increasing aeration intensity. However, these efforts have not fundamentally solved the problem of light shading, and blindly increasing aeration intensity increases energy consumption. Furthermore, they have failed to address the issue of low adsorption efficiency caused by microplastic aggregation. Other studies have prepared biochar from microalgae, but have not achieved the targeted resource utilization of microplastics after adsorption by microalgae, resulting in a break in the technology chain. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a light source coupled with nano-micro carbon supply to enhance microalgae plastic removal and carbon fixation system and method, aiming to achieve efficient removal of microplastics, efficient CO2 fixation, and biomass resource utilization.

[0009] The present invention achieves the above-mentioned technical objectives through the following technical means.

[0010] An internal light source coupled with nano-micro carbon supply to enhance microalgae plastic removal and carbon fixation system includes a light enhancement module, a nano-micro gas oscillation carbon supply module, a photobioreactor body, and an algae plastic harvesting and resource utilization module.

[0011] The light enhancement module, the nano-micro gas oscillation carbon supply module, and the algae plastic harvesting and resource utilization module are respectively connected to the main body of the photobioreactor.

[0012] The light enhancement module adds carbon quantum dots and plant hormone IAA to the main body of the photobioreactor, and achieves composite lighting in conjunction with illumination; the nano-micro gas oscillation carbon supply module delivers micro-nano dispersed CO2 to the main body of the photobioreactor, while simultaneously causing the deagglomeration of microplastics in the water; the algae plastic harvesting and resource utilization module harvests, processes and utilizes the microalgae mixture that adsorbs microplastics in the main body of the photobioreactor.

[0013] The above solution also includes a photovoltaic energy storage power supply module;

[0014] The photovoltaic energy storage and power supply module includes a natural light collection panel, a photovoltaic energy storage battery, a light timing controller, and LED supplemental lighting. The output end of the natural light collection panel is electrically connected to the input end of the photovoltaic energy storage battery. The output end of the photovoltaic energy storage battery is electrically connected to the light timing controller, the light enhancement module, the nano-micro gas oscillation carbon supply module, and the algae plastic harvesting and resource utilization module, respectively, to provide power to each module. The signal output end of the light timing controller is electrically connected to the control end of the LED supplemental lighting. The light timing controller adjusts the on / off state and light intensity of the LED supplemental lighting according to the natural light intensity. The LED supplemental lighting is set outside the main body of the photobioreactor and works with the light enhancement module to achieve all-weather composite lighting.

[0015] In the above scheme, the light enhancement module includes a Ulva prolifera-based U-CQDs storage bin, a metering pump, an IAA storage tank, a dosage pump, an algal cell activity sensor, and an oxidative stress probe;

[0016] The outlet of the U-CQDs storage silo is connected to the inlet of the quantitative dosing pump, and the outlet of the quantitative dosing pump is connected to the dosing port of the photobioreactor body for adding U-CQDs into the photobioreactor body; the outlet of the IAA storage tank is connected to the inlet of the dosage dosing pump, and the outlet of the dosage dosing pump is connected to the dosing port of the photobioreactor body for adding plant hormone IAA into the photobioreactor body; the algal activity sensor and the oxidative stress probe are installed inside the photobioreactor body and are used to detect microalgal activity and reactive oxygen species content, respectively.

[0017] In the above scheme, the nano-micro gas oscillation carbon supply module includes a fan, a nano-micro gas oscillator, a flow meter, and a smart valve; the outlet of the fan is connected to the inlet of the smart valve, the outlet of the smart valve is connected to the inlet of the flow meter, the outlet of the flow meter is connected to the inlet of the nano-micro gas oscillator, and the outlet of the nano-micro gas oscillator is connected to the inlet at the bottom of the photobioreactor body; the smart valve is electrically connected to the flow meter and is used to regulate the CO2 delivery rate.

[0018] The nano-micro gas oscillator comprises, from top to bottom, an air inlet unit, a turbulent oscillation cavity unit, a gradually expanding flow guide unit, and a tripod air outlet support unit. The air inlet unit is located at the top of the nano-micro gas oscillator and serves as the sole inlet for CO2 gas. The turbulent oscillation cavity unit comprises a cylindrical section and a gradually expanding conical section, with its inner wall forming a continuous concave arc-shaped turbulent cavity structure, used to generate self-excited high-frequency oscillations in the CO2 gas. The gradually expanding flow guide unit is a downwardly expanding conical structure, with its upper end smoothly transitioning to the lower end of the turbulent oscillation cavity unit, used to guide the oscillated airflow to the tripod air outlet support unit. The tripod air outlet support unit comprises three air outlet pipes, with the middle outlet pipe pointing vertically downwards, adjacent outlet pipes spaced 30° apart, the upper end of the tripod air outlet support unit connecting to the bottom of the gradually expanding flow guide unit at their intersection point, and the lower end of the tripod air outlet support unit serving as an outlet for exporting nano-micro bubbles and supporting the device.

[0019] The nano-micro gas oscillator relies on self-excited fluid oscillation and cavitation backflow effect without moving parts to break up CO2 into nano-micro bubbles, while breaking up the aggregation of microplastics in the water.

[0020] In the above scheme, the algae plastic harvesting and resource utilization module includes a microporous filter, a centrifuge, and a pyrolysis carbonization device. The inlet of the microporous filter is connected to the outlet of the main body of the photobioreactor, and is used to perform preliminary solid-liquid separation on the microalgae mixture that has adsorbed microplastics. The outlet of the microporous filter is connected to the inlet of the centrifuge, and the centrifuge is used to perform secondary solid-liquid separation on the microalgae mixture after preliminary separation to obtain microalgae mud. The solid outlet of the centrifuge is connected to the inlet of the pyrolysis carbonization device, and the pyrolysis carbonization device is used to pyrolyze and carbonize the microalgae mud to prepare modified biochar. The microporous filter, centrifuge, and pyrolysis carbonization device are all located outside the main body of the photobioreactor and are connected in series through pipelines.

[0021] A method for microalgae plastic removal and carbon fixation in a microalgae-enhanced carbon fixation system using an internal light source coupled with nano-micro carbon supply includes the following steps:

[0022] Algal culture: Common Chlorella was inoculated into BG-11 medium and placed inside the main body of the photobioreactor. The culture temperature was controlled at 25~30℃ to complete the initial culture of microalgae.

[0023] Light enhancement regulation: By adding U-CQDs based on *Ulva prolifera* and plant hormone IAA into the main body of the photobioreactor through the light enhancement module, composite light is achieved in conjunction with light irradiation;

[0024] Nano-micro carbon supply: CO2 is supplied to the main body of the photobioreactor through the nano-micro gas oscillation carbon supply module. It is then broken down into nano-micro bubbles by the nano-micro gas oscillator, realizing the micro-nano dispersion of CO2 and the de-aggregation of microplastics in the water, thereby increasing the contact probability between microalgae and carbon source and microplastics.

[0025] Photo-carbon synergistic plastic removal and carbon fixation: Through the synergistic effect of photo-enhancing module and nano-micro gas oscillation carbon supply module, the synthesis and secretion of extracellular polymers of microalgae are enhanced. Microalgae adsorb microplastics in water through extracellular polymers, and at the same time fix CO2 through photosynthesis.

[0026] Algae-plastic mixture harvesting: The microporous filter and centrifuge of the algae-plastic harvesting and resource utilization module are used to separate the microalgae mixture that adsorbs microplastics in the main body of the photobioreactor into solid and liquid, and the microalgae mud is harvested.

[0027] Resource utilization: The harvested microalgae mud is placed in a pyrolysis carbonization device for pyrolysis carbonization to prepare modified biochar.

[0028] In the above scheme, the U-CQDs in the light enhancement regulation step are Ulva prolifera-based carbon quantum dots, the quantitative dosing pump adds 1~10 mg·L⁻¹ to the U-CQDs, and the dosage dosing pump adds 1~5 mg·L⁻¹ to the plant hormone IAA;

[0029] In the above scheme, the operating parameters of the nano-gas oscillator in the nano-carbon supply step are: oscillation frequency 500Hz~5kHz, CO2 inlet gauge pressure 0.2~1.0MPa, outlet gauge pressure 0.01~0.05MPa, and the generated bubble particle size D 90 ≤500nm.

[0030] In the above scheme, the pore size of the microporous filter in the algae-plastic mixture harvesting step is 2~10μm, the speed of the centrifuge is 3000~5000r / min, the pyrolysis temperature of the pyrolysis carbonization device is 300~500℃, and the pyrolysis time is 2~8h.

[0031] Furthermore, the concentration of the *Ulva prolifera*-based U-CQDs is 1 mg·L⁻¹, and the concentration of the plant hormone IAA is 5 mg·L⁻¹; the reactive oxygen species (ROS) content is detected by an oxidative stress probe, and when the ROS content exceeds a preset value, the plant hormone IAA is added to alleviate the oxidative damage to the microalgae.

[0032] The nano-gas oscillator has an oscillation frequency of 800 Hz, an inlet gauge pressure of 0.3 MPa for CO2, an outlet gauge pressure of 0.02 MPa, and a generated bubble particle size D. 90 ≤500nm;

[0033] In the photo-carbon synergistic plastic removal and carbon fixation step, the cultivation period is 13 days; in step S5, the recovery rate of the microalgae sludge is 80%.

[0034] The microporous filter has a pore size of 5 μm, the centrifuge has a rotation speed of 4000 r / min, the pyrolysis temperature of the pyrolysis carbonization device is 500 ℃, and the pyrolysis time is 4 h.

[0035] Compared with the prior art, the beneficial effects of the present invention are:

[0036] 1. Overcoming light limitations and significantly improving photosynthetic efficiency and microalgal biomass: The Ulva prolifera-based U-CQDs and IAA synergistic internal light source system constructed in this invention achieves full-domain luminescence within the algal solution, increasing the microalgal light energy utilization rate to a maximum of 16.69%, nearly 30% higher than the traditional external light source system; the microalgal biomass reaches 2.17 g·L⁻¹, 30.01% higher than the control group, fundamentally solving the light shading problem in high-density microalgal cultivation and providing sufficient EPS material basis for microplastic adsorption;

[0037] 2. Precise carbon supply and de-agglomeration, significantly improving the adsorption and carbon fixation efficiency of microplastics: The nano-micro gas oscillator of this invention achieves the dual effects of CO2 micro-nano dispersion and microplastic de-agglomeration, significantly improving CO2 mass transfer efficiency and the contact probability between microalgae and microplastics. The daily carbon fixation capacity of microalgae per unit volume reaches 537 mg / L, which is about 40% higher than that of traditional non-coupled systems.

[0038] 3. Modular design, strong adaptability, and easy engineering application: The system of this invention adopts a modular design, and each functional module can be independently controlled and flexibly combined to adapt to different water volumes and different microplastic pollution concentrations. It can be directly integrated into the front-end pretreatment process of existing water purification plants without the need for large-scale modification of existing processes. It solves the technical bottleneck of traditional water purification processes lacking a dedicated microplastic removal unit and has broad market application prospects. Attached Figure Description

[0039] Figure 1 : An overall schematic diagram of the microalgae carbon fixation and plastic removal system of the present invention, which is coupled with an internal light source to provide carbon to nano-microorganisms.

[0040] Figure 2 : A schematic diagram of the composition of the carbon quantum dot-IAA synergistic light enhancement module of the present invention;

[0041] Figure 3 : A schematic cross-sectional view of the nano-micro gas oscillator of this invention;

[0042] Figure 4 This invention provides a schematic diagram of the entire process of microalgae plastic removal, carbon fixation, and resource utilization.

[0043] Figure 5 Flowchart of the U-CQDs synthesis method of this invention;

[0044] In the diagram, 1-photovoltaic energy storage module; 2-photomagnetic enhancement module; 3-nano-micro gas oscillation carbon supply module; 31-air inlet unit; 32-turbulent oscillation cavity unit; 33-gradually expanding flow guiding unit; 34-tripod air outlet support unit; 4-photobioreactor main body; 5-harvesting and resource utilization module. Detailed Implementation

[0045] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0046] The present invention will be further described in detail below with reference to specific embodiments. Experimental conditions not specified in the following embodiments are all carried out in accordance with conventional conditions in the field or conditions recommended by the manufacturer. The equipment and reagents involved in the present invention are all commercially available conventional products.

[0047] This invention addresses the three major bottlenecks of existing microalgae plastic removal and carbon fixation technologies by providing an enhanced microalgae plastic removal and carbon fixation system and method that couples an internal light source with nano-micro carbon supply. It overcomes light shading through a carbon quantum dot-IAA synergistic internal light source system, achieves precise CO2 carbon supply and microplastic deagglomeration using a nano-micro gas oscillator, and enhances microalgae EPS synthesis through photo-carbon synergistic regulation. Ultimately, it constructs a closed-loop chain of "microplastic removal - carbon fixation - biomass resource utilization," achieving the triple goals of efficient microplastic removal, CO2 fixation, and resource utilization. This provides a feasible synergistic solution for ensuring drinking water safety and realizing the "dual carbon" goals.

[0048] This invention is applicable to microplastic removal and carbon fixation in drinking water sources and pretreatment of water purification plants, and can also be applied to microplastic treatment and ecological restoration of landscape water and sewage treatment plant effluent.

[0049] like Figure 1 As shown, the microalgae plastic removal and carbon fixation system with internal light source coupled with nano-micro carbon supply and enhanced microalgae plastic removal and enhanced carbon supply according to the present invention includes a light enhancement module 2, a nano-micro gas oscillation carbon supply module 3, a photobioreactor body 4, and an algae plastic harvesting and resource utilization module 5.

[0050] The light enhancement module 2, the nano-micro gas oscillation carbon supply module 3, and the algae plastic harvesting and resource utilization module 5 are respectively connected to the main body of the photobioreactor 4. The integrated and coordinated operation of each module realizes the whole process of microalgae plastic removal and carbon fixation.

[0051] The light enhancement module 2 adds carbon quantum dots and plant hormone IAA to the main body 4 of the photobioreactor, and achieves composite lighting in conjunction with light irradiation; the nano-micro gas oscillation carbon supply module 3 delivers micro-nano dispersed CO2 to the main body 4 of the photobioreactor, while simultaneously causing the deagglomeration of microplastics in the water; the algae plastic harvesting and resource utilization module 5 harvests, processes and utilizes the microalgae mixture that adsorbs microplastics in the main body 4 of the photobioreactor.

[0052] The internal light source coupled with nano-micro carbon supply to enhance microalgae plastic removal and carbon fixation system further includes a photovoltaic energy storage module 1. The photovoltaic energy storage module 1 includes a natural light harvesting panel, a photovoltaic energy storage battery, a light timing controller, and LED supplemental lighting. The output end of the natural light harvesting panel is electrically connected to the input end of the photovoltaic energy storage battery. The output end of the photovoltaic energy storage battery is electrically connected to the light timing controller, the light enhancement module 2, the nano-micro gas oscillation carbon supply module 3, and the algae plastic harvesting and resource utilization module 5, respectively, to provide power to each module. The signal output end of the light timing controller is electrically connected to the control end of the LED supplemental lighting. The light timing controller adjusts the on / off state and light intensity of the LED supplemental lighting according to the natural light intensity. The LED supplemental lighting is located outside the main body 4 of the photobioreactor, working in conjunction with the light enhancement module 2 to achieve all-weather composite lighting. The photovoltaic energy storage module 1 realizes the harvesting, storage, and intelligent control of light energy, providing clean power to the entire system, while simultaneously achieving all-weather composite lighting based on natural light intensity, breaking the limitations of day and night rhythms.

[0053] like Figure 2 As shown, the light enhancement module 2 includes a U-CQDs storage bin for *Ulva prolifera*, a metering pump, an IAA storage tank, a dosage pump, an algal cell activity sensor, and an oxidative stress probe. The outlet of the U-CQDs storage bin is connected to the inlet of the metering pump, and the outlet of the metering pump is connected to the dosing port of the photobioreactor body 4, for adding U-CQDs into the photobioreactor body 4. The outlet of the IAA storage tank is connected to the inlet of the dosage pump, and the outlet of the dosage pump is connected to the dosing port of the photobioreactor body 4, for adding the plant hormone IAA into the photobioreactor body 4. The algal cell activity sensor and the oxidative stress probe are located inside the photobioreactor body 4 and are used to detect microalgal activity and reactive oxygen species content, respectively. The light enhancement module 2 is a carbon quantum dot-IAA synergistic light enhancement module. Through the synergistic effect of U-CQDs and IAA, an internal light source system with full-domain luminescence inside the algal liquid is constructed. U-CQDs convert ultraviolet / weak light into orange-red light that is easily absorbed by microalgae, while IAA removes excess reactive oxygen species to alleviate oxidative damage to algae and solves the problem of light shading.

[0054] like Figure 3As shown, the nano-micro gas oscillation carbon supply module 3 includes a fan, a nano-micro gas oscillator, a flow meter, and a smart valve; the outlet of the fan is connected to the inlet of the smart valve, the outlet of the smart valve is connected to the inlet of the flow meter, the outlet of the flow meter is connected to the inlet of the nano-micro gas oscillator, and the outlet of the nano-micro gas oscillator is connected to the inlet at the bottom of the photobioreactor body 4; the smart valve is electrically connected to the flow meter and is used to regulate the CO2 delivery rate according to the microalgae growth stage; the nano-micro gas oscillator includes, from top to bottom, an inlet unit 31, a turbulent oscillation chamber unit 32, a gradually expanding flow guide unit 33, and a tripod outlet support unit 34; the inlet unit 31 is located at the top of the nano-micro gas oscillator and is the only inlet for CO2 gas; the turbulent oscillation chamber unit 32 includes a circular... The column section and the gradually expanding conical section have a continuous concave arc-shaped turbulent cavity structure on their inner walls, which is used to generate self-excited high-frequency oscillation of CO2 gas. The gradually expanding flow guiding unit 33 is a downwardly expanding conical structure. The upper end of the gradually expanding flow guiding unit 33 is smoothly connected to the lower end of the turbulent oscillation cavity unit 32, which is used to guide the oscillating airflow to the tripod air outlet support unit 34. The tripod air outlet support unit 34 includes three air outlet pipes, which are evenly distributed in a 120° circle. The upper end of the tripod air outlet support unit 34 is connected to the bottom intersection point of the gradually expanding flow guiding unit 33. The lower end of the tripod air outlet support unit 34 is the air outlet, which is used to export the nano-micro bubbles and support the device. The nano-micro gas oscillator relies on the self-excited fluid oscillation and cavitation backflow effect without moving parts to break up CO2 into nano-micro bubbles, while breaking up the agglomeration of microplastics in the water.

[0055] The specific dimensions of the nano-micro gas oscillator are adapted to the laboratory testing instruments as follows:

[0056] The nano-gas oscillator is a vertical, three-legged, integrated structure used to break CO2 gas into nano-scale bubbles through oscillation and cavitation. It is suitable for scenarios such as microalgae carbon fixation and wastewater treatment.

[0057] The intake unit 31 is a vertical cylindrical intake pipe at the top, which is the only inlet for CO2 gas. The inner wall is smooth to reduce intake resistance. The intake unit 31 has an inner diameter of 16mm, an outer diameter of 20mm, and a length of 30mm.

[0058] The turbulent oscillation cavity unit 32 includes a cylindrical section and a gradually expanding conical section. The inner wall is a continuous concave arc shape, forming a turbulent cavity structure that induces a vortex street, causing the gas to generate self-excited high-frequency oscillations. After the CO2 gas enters, due to the cross-sectional change and the induction of the arc-shaped wall, high-speed turbulence and Karman vortex street are formed, generating periodic high-frequency pressure pulsations. Combined with the cavitation backflow effect, the oscillation is enhanced, providing energy for CO2 breakup.

[0059] The cylindrical section is the upper half of the oscillation cavity: the inner diameter is 66mm, the outer diameter is 70mm, the wall thickness is 2mm, and the height is 45mm.

[0060] The gradually expanding conical section is the lower half of the oscillation cavity and the guide section: the upper inner diameter is 60mm, the lower inner diameter is 80mm, the height is 100mm, and the wall thickness is 2mm.

[0061] The gradually expanding flow guiding unit 33, which is the conical section of the oscillation cavity, is a downwardly expanding conical structure with a smooth arc transition between the inner wall and the cylindrical section. It uniformly guides the high-speed airflow after oscillation to the three air outlet pipes. At the same time, the gradually expanding structure reduces the airflow velocity, enhances the cavitation effect, and improves the bubble breaking efficiency.

[0062] The tripod air outlet support unit 34 includes three air outlet pipes extending from the bottom intersection of the conical section. One pipe extends vertically downwards, while the two side air outlet pipes are symmetrically arranged at an angle α of 30° between adjacent pipes. This allows air bubbles to be more evenly distributed into the entire algal solution through the three pipes, serving as both a support device and an air outlet channel. It can export CO2 gas after vibration and breakup while providing stable support. The dimensions of a single air outlet pipe are: inner diameter 12mm, outer diameter 16mm, wall thickness 2mm, and length 240mm. The maximum width when the tripod is extended, i.e., the horizontal distance between the ends of the two inclined pipes, is 280mm.

[0063] The nano-gas oscillator employs a self-excited fluid oscillation source without moving parts. It requires no external ultrasonic transducers, solenoid valves, or other active driving components, relying entirely on the device's own fluid dynamics structure to achieve oscillation triggering and maintenance. Its core working mechanism is as follows: after CO2 gas enters the arc-shaped turbulent cavity, it forms periodic vortex shedding and jet deflection under the constraint of the cavity walls. Combined with the backflow cavitation effect of the gradually expanding conical structure, a stable self-excited oscillating flow field is formed, thereby breaking down CO2 into nano- and micro-scale bubbles.

[0064] The nano-micro gas oscillation carbon supply module 3 adopts the design of "oscillation cavity + flared flow guide structure". Relying on high-frequency oscillation and cavitation backflow effect, CO2 is broken into nano-micro bubbles, realizing the dual effect of CO2 micro-nano dispersion and micro-plastic de-agglomeration. The intelligent valve and flow meter work together to precisely control the CO2 delivery rate according to the microalgae growth stage, which is conducive to achieving precise carbon supply in stages.

[0065] The main body 4 of the photobioreactor is a vertical tubular reactor, which is suitable for high-density cultivation of microalgae. The inner wall of the reactor is coated with an anti-bioadhesion coating. The bottom is connected to a nano-micro gas oscillator, the top is connected to a harvesting module, and the side is provided with a light enhancement module injection port and a photovoltaic lighting interface.

[0066] The algae plastic harvesting and resource utilization module 5 includes a microporous filter, a centrifuge, and a pyrolysis carbonization device. The inlet of the microporous filter is connected to the outlet of the photobioreactor body 4, and is used for preliminary solid-liquid separation of the microalgae mixture that has adsorbed microplastics. The outlet of the microporous filter is connected to the inlet of the centrifuge, and the centrifuge is used for secondary solid-liquid separation of the microalgae mixture after preliminary separation to obtain microalgae mud. The solid outlet of the centrifuge is connected to the inlet of the pyrolysis carbonization device, and the pyrolysis carbonization device is used for pyrolysis carbonization of the microalgae mud to prepare modified biochar. The microporous filter, centrifuge, and pyrolysis carbonization device are all located outside the photobioreactor body 4 and are connected in series via pipelines.

[0067] Algae plastic harvesting and resource utilization module 5 includes a microporous filter, a high-speed centrifuge, and a pyrolysis carbonization device to achieve efficient solid-liquid separation of the microalgae mixture that adsorbs microplastics, and to prepare modified biochar by pyrolysis of algae mud to achieve resource utilization and carbon sequestration.

[0068] like Figure 4 As shown, a method for microalgae plastic removal and carbon fixation in a microalgae-enhanced carbon fixation system using the internal light source coupled with nano-micro carbon supply includes the following steps:

[0069] Algal culture: Common Chlorella was inoculated into BG-11 medium and placed in the main body 4 of the photobioreactor. The culture temperature was controlled at 25~30℃ to complete the initial culture of microalgae.

[0070] Light enhancement regulation: By adding U-CQDs based on *Ulva prolifera* and plant hormone IAA into the main body of the photobioreactor 4 through the light enhancement module 2, combined with light irradiation, a composite light irradiation is achieved, which solves the light shading problem in high-density microalgae cultivation;

[0071] Nano-micro carbon supply: CO2 is supplied to the main body of the photobioreactor 4 through the nano-micro gas oscillation carbon supply module 3. The CO2 is broken down into nano-micro bubbles by the nano-micro gas oscillator, realizing the micro-nano dispersion of CO2 and the de-aggregation of microplastics in the water, thereby increasing the contact probability between microalgae and carbon source and microplastics.

[0072] Photo-carbon synergistic plastic removal and carbon fixation: Through the synergistic effect of photo-enhancing module 2 and nano-micro gas oscillation carbon supply module 3, the synthesis and secretion of extracellular polymers of microalgae are enhanced. Microalgae adsorb microplastics in water through extracellular polymers, and at the same time fix CO2 through photosynthesis.

[0073] Algae-plastic mixture harvesting: The microporous filter and centrifuge in the algae-plastic harvesting and resource utilization module 5 are used to perform solid-liquid separation on the microalgae mixture that adsorbs microplastics in the main body 4 of the photobioreactor to harvest the microalgae mud.

[0074] Resource utilization: The harvested microalgae mud is placed in a pyrolysis carbonization device for pyrolysis carbonization to prepare modified biochar, which can be used for wastewater pollutant adsorption or soil improvement.

[0075] In the light enhancement regulation step, U-CQDs are Ulva prolifera-based carbon quantum dots. The quantitative dosing pump adds U-CQDs at a concentration of 1~10 mg·L⁻¹, and the dosage dosing pump adds plant hormone IAA at a concentration of 1~5 mg·L⁻¹.

[0076] The operating parameters of the nano-gas oscillator in the nano-carbon supply step are: oscillation frequency 500Hz~5kHz, CO2 inlet gauge pressure 0.2~1.0MPa, outlet gauge pressure 0.01~0.05MPa, and the generated bubble particle size D. 90 ≤500nm.

[0077] In the algae-plastic mixture harvesting step, the pore size of the microporous filter is 2~10μm, the speed of the centrifuge is 3000~5000r / min, the pyrolysis temperature of the pyrolysis carbonization device is 300~500℃, and the pyrolysis time is 2~8h.

[0078] Preferably, the concentration of the *Ulva prolifera*-based U-CQDs is 1 mg·L⁻¹, and the concentration of the plant hormone IAA is 5 mg·L⁻¹. The reactive oxygen species (ROS) content is detected by an oxidative stress probe; when the ROS content exceeds a preset value, the plant hormone IAA is added to alleviate oxidative damage to the microalgae. The oscillation frequency of the nano-micro gas oscillator is 800 Hz, the CO2 inlet gauge pressure is 0.3 MPa, the outlet gauge pressure is 0.02 MPa, and the generated bubble particle size D... 90 ≤500nm; in the photo-carbon synergistic plastic removal and carbon fixation step, the cultivation period is 13 days; in step S5, the harvest ratio of the microalgae mud is 80%; the pore size of the microporous filter is 5μm, the speed of the centrifuge is 4000 r / min, the pyrolysis temperature of the pyrolysis carbonization device is 500 ℃, and the pyrolysis time is 4 h.

[0079] In one specific embodiment of the present invention, Chlorella vulgaris FACHB-2723 is used as the test algae species, and BG-11 is used as the culture medium. Typical microplastics in water bodies of 50-100 μm are targeted for treatment. Through the synergistic regulation of photoenhancing and nano-micro carbon supply, the synthesis of EPS by microalgae is enhanced, and microplastic adsorption and CO2 fixation are achieved. Finally, the algae-plastic mixture is pyrolyzed to prepare modified biochar, forming a resource utilization closed loop. The specific steps include initial algae culture, photoenhancing regulation, precise nano-micro carbon supply, photo-carbon synergistic removal of plastics and fixation, harvesting of algae-plastic mixture, preparation of modified biochar and resource utilization.

[0080] Specifically, the following steps are included:

[0081] Algal culture: Common Chlorella was inoculated into BG-11 medium and placed in the main body 4 of the photobioreactor. The culture temperature was controlled at 25~30℃ to complete the initial culture of microalgae.

[0082] Light enhancement regulation: By adding an appropriate concentration of Ulva prolifera-based U-CQDs and IAA into the reactor through the light enhancement module 2, and relying on the photovoltaic energy storage module 1, all-weather composite lighting of natural light and LED supplementary lighting is achieved, and the light intensity is regulated to 3000 Lux, thus solving the light shading problem in high-density microalgae cultivation.

[0083] Nano-micro carbon supply: CO2 is supplied to the reactor through the nano-micro gas oscillation carbon supply module 3. The CO2 is broken down into nano-micro bubbles by the nano-micro gas oscillator, realizing the micro-nano dispersion of CO2, which greatly increases the solubility of CO2 in water, and at the same time de-aggregates 50-100μm microplastics in water.

[0084] Photosynergistic carbon fixation and plastic removal: Through the synergistic effect of photoenhancing and nano-micro carbon supply, the synthesis and secretion of extracellular polymeric substances (EPS) by microalgae are enhanced. Microalgae adsorb microplastics in the water through EPS, and fix CO2 through photosynthesis. The culture period is 13 days. After the culture, the microalgal biomass reached 2.17 g·L⁻¹, which is 30.01% higher than that of the control group.

[0085] Algae-plastic mixture harvesting: The microporous filter and centrifuge of the algae-plastic harvesting and resource utilization module 5 are used to separate the microalgae mixture that adsorbs microplastics into solid and liquid, and harvest the microalgae mud, with a harvesting ratio of 80%.

[0086] Resource utilization: The harvested microalgae mud is placed in a pyrolysis carbonization device and pyrolyzed at 300~500℃ for 2~8h to prepare modified biochar. The modified biochar can adsorb nitrogen, phosphorus and residual microplastics in wastewater. As a bio-fertilizer, it can realize soil water and fertilizer retention and carbon sequestration, forming a closed loop of microplastic removal-carbon fixation-biomass resource utilization.

[0087] The nano-gas oscillator is an integrated cavity structure with a single gas input pipe at the top and three symmetrical gas output pipes at the bottom. Within the core area of ​​the cavity, an arc-shaped turbulent oscillation cavity and a gradually expanding conical flared flow guide structure are sequentially arranged, connecting the input and output pipes respectively. The device has no moving mechanical parts, relying on the synergistic effect of fluid self-excited oscillation and cavitation backflow to achieve CO2 nano-scale decomposition. This embodiment employs a self-excited fluid oscillation source without external drive, relying on the wall constraint of the arc-shaped turbulent cavity, jet adhesion to the wall, and vortex feedback mechanism to form periodic oscillations. The oscillation frequency is determined by the cavity size, inlet and outlet pressure difference, and CO2 property coupling, requiring no external drive components. During operation, CO2 enters the arc-shaped turbulent oscillation cavity through the input pipe, forming a high-speed swirling turbulent flow field. After initial breakage by jet deflection, vortex shedding, and cavitation backflow effects, it enters the gradually expanding conical flow guide structure for deceleration and pressure stabilization, further shearing and breaking down, ultimately forming stable nano-scale CO2 bubbles, which are discharged into the microalgae carbon fixation reaction system through the three bottom output pipes.

[0088] Experimental operating parameters: oscillation frequency 800Hz, CO2 inlet gauge pressure 0.3MPa, outlet gauge pressure 0.02MPa, maintaining a stable pressure difference to ensure continuous oscillation; under these parameters, the bubble particle size D... 90 With a wavelength of ≤500nm and a liquid phase residence time of ≥4h, microalgae can enhance carbon fixation and simultaneously adsorb microplastics.

[0089] The inlet and outlet pressures can be adjusted to suit different scenarios: for laboratory pilot tests, the inlet gauge pressure is 0.2~0.4MPa and the oscillation frequency is 500Hz~1.2kHz; for pilot-scale and large-scale applications, the inlet gauge pressure is 0.6~1.0MPa and the oscillation frequency is 1.2kHz~5kHz, to enhance the bubble refinement effect. The structure and parameters of this embodiment have been verified under operating conditions, demonstrating stable operation and maintenance-free operation, and can meet the continuous operation requirements of the coupled microalgae carbon fixation and microplastic removal system for a long period of time.

[0090] Carbon dot preparation and characterization:

[0091] like Figure 5 As shown, in this embodiment, CQDs are synthesized using a hydrothermal synthesis method, which has advantages such as being pollution-free and having low toxicity. It also allows for easy adjustment of the precursor composition to synthesize various functionalized CQDs. Preferably, the aqueous phase after the hydrothermal reaction of *Ulva prolifera* is used as the carbon source for the CQDs. The specific synthesis method is as follows:

[0092] Weigh 3 g of *Ulva prolifera* powder and mix it with 30 mL of deionized water. Place the mixture into a 50 mL stainless steel high-pressure hydrothermal reactor. To stabilize the hydrothermal reaction conditions, nitrogen gas was introduced into the reactor before the reaction, with a pressure of 4 MPa. The stainless steel high-pressure hydrothermal reactor was heated to 300 °C and held at that temperature for 1 h. After the reactor cooled, the aqueous and oil phase products were collected by vacuum filtration, and the aqueous phase product was separated by a separatory funnel. The aqueous phase product was placed in a 50 mL hydrothermal synthesis reactor and reacted at 180 °C for 8 h. After the reactor cooled to room temperature, the product was filtered through a 0.22 μm microporous membrane to remove larger aggregated particles. The filtrate was dialyzed for 24 h using a dialysis bag (molecular weight cutoff: 1000 Da). Finally, the liquid in the dialysis bag was dried in a vacuum freeze dryer. The dried powdered product is U-CQDs. The morphology and particle size of U-CQDs were observed using transmission electron microscopy (TEM, FEI TalosF200X G2); the chemical structure and composition were analyzed using X-ray diffraction (XRD, PANalytical X'Pert3) and X-ray photoelectron spectroscopy (XPS, X-ray (1486.6 eV)); fluorescence excitation and emission spectra were determined using a fluorescence spectrophotometer (F97, Lengguang Tech, China) equipped with a 450 W xenon lamp and a dual-grating monochromator. Surface functional group information was recorded using Fourier transform infrared spectroscopy (FTIR, Perkin Elmer Frontier).

[0093] U-CQDs synergistically regulate Chlorella growth with plant hormones:

[0094] In the synergistic regulation of Chlorella growth by U-CQDs and plant hormone IAA, a 15% CO2 concentration was used as the gas source for Chlorella culture, and the total ventilation rate of the air pump and CO2 mixture was 0.18 L·min. -1 The LED light source in the photobioreactor had an intensity of 3000 Lux; a light-to-dark ratio of 12:12; and a temperature control of 20 °C. The concentrations of U-CQDs in the algal solution were 0, 1, 5, and 10 mg·L⁻¹. -1 The dosage of exogenous plant hormone IAA is 0.5 mg / L. -1 During the initial culture phase (days 2–3) after Chlorella inoculation, IAA or U-CQDs were added to the culture medium simultaneously. The final concentration gradient of IAA in the culture medium was 1–5 mg·L⁻¹, and the final concentration gradient of U-CQDs was 1–10 mg·L⁻¹. After addition, the algae were cultured under the above standard culture conditions until the growth stabilized.

[0095] Under the condition of exogenous plant hormones, 5 mg·L -1 Under IAA, different concentration gradients of U-CQDs (0, 1, 5, 10 mg·L⁻¹) -1 The effects of U-CQDs on Chlorella biomass accumulation were studied. Experimental data showed that when the U-CQDs concentration was 1 mg·L⁻¹, the biomass accumulation of Chlorella was significantly reduced. -1 The effect of this method on Chlorella biomass accumulation was most significant: Chlorella biomass accumulated rapidly from day 6 to 10, and by day 13, after the culture was completed, the accumulated biomass of Chlorella reached 2.17 mg·L⁻¹. -1 Compared with the control group (1.67 mg·L), -1 The effect was increased by 30.01% compared to no exogenous plant hormones, 1 mg·L -1 Under U-CQDs conditions, the biomass accumulation of Chlorella increased by 19.89%, indicating that appropriate amounts of exogenous plant hormones IAA and U-CQDs can synergistically increase the biomass accumulation of Chlorella. This synergistic effect occurs because U-CQDs absorb ultraviolet light and convert it into visible light, working with IAA to regulate the photoreceptor protein (such as phytosalicylate) signaling pathway in Chlorella, stimulating photomorphogenesis. Furthermore, IAA can mitigate oxidative damage in Chlorella and maintain cell membrane integrity, thereby further ensuring the photosynthetic activity of Chlorella. When the U-CQDs concentration increased to 5 mg·L⁻¹, the biomass accumulation of Chlorella increased further. -1 At that time, the biomass accumulation on day 13 was 1.90 mg·L⁻¹. -1 The effect was 13.81% higher than that of the control group. (At 10 mg / L...) -1 Under U-CQDs conditions, the biomass accumulation of Chlorella was 1.87 mg·L⁻¹ on day 13. -1 The level was increased by 12% compared to the control group. At 5 mg·L⁻¹ -1 After the addition of exogenous plant hormone IAA, 10 mg·L -1 U-CQDs promoted the biomass accumulation of Chlorella. The application of 5 ppm IAA scavenged some ROS, alleviated the oxidative stress induced by high concentrations of U-CQDs on Chlorella, and enhanced its environmental tolerance. The results indicate that appropriate amounts of U-CQDs and the exogenous plant hormone IAA can synergistically increase the biomass accumulation of Chlorella, and the addition of IAA can mitigate the oxidative stress induced by high concentrations of U-CQDs on Chlorella. Under the condition of 5 ppm IAA addition, the U-CQDs dosage was 1 mg·L⁻¹. -1 At that time, the biomass energy of Chlorella reached a peak of 23.43 kJ under the synergistic effect of IAA and U-CQDs, which was 8.01% higher than that under the condition without exogenous hormones.

[0096] This invention addresses the technical bottlenecks in existing microalgae plastic removal and carbon fixation technologies, such as light limitation and the disconnect between treatment and resource utilization, by providing an internal light source coupled with nano-micro carbon supply to enhance microalgae plastic removal and carbon fixation. The system includes a photobioreactor body, and connected to the body are a carbon quantum dot-IAA synergistic light enhancement module 2, a nano-micro gas oscillation carbon supply module 3, an algae plastic harvesting and resource utilization module 5, and a photovoltaic energy storage module 1. The method uses *Chlorella vulgaris* as the algae species. It constructs an internal light source system by regulating 1-10 mg·L⁻¹ of *Ulva prolifera*-based carbon quantum dots (U-CQDs) coupled with 1-5 mg·L⁻¹ of IAA to overcome light obstruction. A nano-micro gas oscillator is used to achieve CO₂ micro-nano dispersion and microplastic deagglomeration. Combined with photo-carbon synergistic regulation to enhance microalgae EPS synthesis, the algae-plastic mixture is finally pyrolyzed to prepare modified biochar, forming a closed-loop resource utilization system.

[0097] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0098] The detailed descriptions listed above are merely specific illustrations of feasible embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A system for enhancing microalgae plastic removal and carbon fixation by coupling an internal light source with nano-micro carbon supply, characterized in that, It includes a light enhancement module (2), a nano-micro gas oscillation carbon supply module (3), a photobioreactor body (4), and an algae plastic harvesting and resource utilization module (5). The light enhancement module (2), the nano-micro gas oscillation carbon supply module (3), and the algae plastic harvesting and resource utilization module (5) are respectively connected to the main body (4) of the photobioreactor; The light enhancement module (2) adds carbon quantum dots and plant hormone IAA to the main body (4) of the photobioreactor and achieves composite lighting in conjunction with light irradiation; the nano-micro gas oscillation carbon supply module (3) delivers micro-nano dispersed CO2 to the main body (4) of the photobioreactor, while causing the microplastics in the water to disaggregate; the algae plastic harvesting and resource utilization module (5) harvests, processes and utilizes the microalgae mixture that adsorbs microplastics in the main body (4) of the photobioreactor.

2. The internal light source coupled with nano-micro carbon supply to enhance microalgae plastic removal and carbon fixation system according to claim 1, characterized in that, It also includes a photovoltaic energy storage power supply module (1); The photovoltaic energy storage power supply module (1) includes a natural light collection board, a photovoltaic energy storage battery, a light timing controller, and an LED supplementary light. The output end of the natural light collection board is electrically connected to the input end of the photovoltaic energy storage battery. The output end of the photovoltaic energy storage battery is electrically connected to the light timing controller, the light enhancement module (2), the nano-micro gas oscillation carbon supply module (3), and the algae plastic harvesting and resource utilization module (5), respectively, to provide power to each module. The signal output end of the light timing controller is electrically connected to the control end of the LED supplementary light. The light timing controller adjusts the opening and light intensity of the LED supplementary light according to the natural light intensity. The LED supplementary light is set outside the main body (4) of the photobioreactor and works with the light enhancement module (2) to achieve all-weather composite lighting.

3. The internal light source coupled with nano-micro carbon supply to enhance microalgae plastic removal and carbon fixation system according to claim 1, characterized in that, The light enhancement module (2) includes a Ulva prolifera-based U-CQDs storage bin, a quantitative dosing pump, an IAA storage tank, a dosage dosing pump, an algal cell activity sensor, and an oxidative stress probe; The outlet of the U-CQDs storage silo is connected to the inlet of the quantitative dosing pump, and the outlet of the quantitative dosing pump is connected to the dosing port of the photobioreactor body (4) for adding U-CQDs into the photobioreactor body (4); the outlet of the IAA storage tank is connected to the inlet of the dosage dosing pump, and the outlet of the dosage dosing pump is connected to the dosing port of the photobioreactor body (4) for adding plant hormone IAA into the photobioreactor body (4); the algal activity sensor and the oxidative stress probe are set inside the photobioreactor body (4) for detecting microalgal activity and reactive oxygen content, respectively.

4. The internal light source coupled with nano-micro carbon supply to enhance microalgae plastic removal and carbon fixation system according to claim 1, characterized in that, The nano-micro gas oscillation carbon supply module (3) includes a fan, a nano-micro gas oscillator, a flow meter, and a smart valve; the outlet of the fan is connected to the inlet of the smart valve, the outlet of the smart valve is connected to the inlet of the flow meter, the outlet of the flow meter is connected to the inlet of the nano-micro gas oscillator, and the outlet of the nano-micro gas oscillator is connected to the inlet at the bottom of the photobioreactor body (4); the smart valve is electrically connected to the flow meter and is used to regulate the CO2 delivery rate. The nano-micro gas oscillator includes, from top to bottom, an air inlet unit (31), a turbulent oscillation cavity unit (32), a gradually expanding flow guide unit (33), and a tripod outlet support unit (34). The air inlet unit (31) is located at the top of the nano-micro gas oscillator and serves as the sole inlet for CO2 gas. The turbulent oscillation cavity unit (32) includes a cylindrical section and a gradually expanding conical section, with its inner wall being a continuous concave arc-shaped turbulent cavity structure used to generate self-excited high-frequency oscillations in the CO2 gas. The gradually expanding flow guide unit (33) is a downwardly expanding conical structure. The upper end of the flow guiding unit (33) is smoothly connected to the lower end of the turbulent oscillation cavity unit (32) to guide the oscillating airflow to the tripod air outlet support unit (34); the tripod air outlet support unit (34) includes three air outlet pipes, wherein the middle air outlet pipe is vertically downward, and the air outlet pipes on both sides are symmetrically arranged at an angle α between adjacent air outlet pipes with an interval of 30°. The upper end of the tripod air outlet support unit (34) is connected to the bottom intersection point of the gradually expanding flow guiding unit (33), and the lower end of the tripod air outlet support unit (34) is an air outlet to export nano-micro bubbles and support the device. The nano-micro gas oscillator relies on self-excited fluid oscillation and cavitation backflow effect without moving parts to break up CO2 into nano-micro bubbles, while breaking up the aggregation of microplastics in the water.

5. The internal light source coupled with nano-micro carbon supply to enhance microalgae plastic removal and carbon fixation system according to claim 1, characterized in that, The algae plastic harvesting and resource utilization module (5) includes a microporous filter, a centrifuge, and a pyrolysis carbonization device; the inlet of the microporous filter is connected to the outlet of the photobioreactor body (4) for preliminary solid-liquid separation of the microalgae mixture adsorbed with microplastics; the outlet of the microporous filter is connected to the inlet of the centrifuge, which is used for secondary solid-liquid separation of the microalgae mixture after preliminary separation to obtain microalgae mud; the solid outlet of the centrifuge is connected to the inlet of the pyrolysis carbonization device, which is used for pyrolysis carbonization of the microalgae mud to prepare modified biochar; the microporous filter, centrifuge, and pyrolysis carbonization device are all located outside the photobioreactor body (4) and are connected in series through pipelines.

6. A method for microalgae plastic removal and carbon fixation using an internal light source coupled with nano-micro carbon supply to enhance microalgae plastic removal and carbon fixation system as described in any one of claims 1-5, characterized in that, Includes the following steps: Algal culture: Common Chlorella was inoculated into BG-11 medium and placed in the main body of the photobioreactor (4). The culture temperature was controlled at 25~30℃ to complete the initial culture of microalgae. Photointensification regulation: Ulva-based U-CQDs and plant hormone IAA are added into the main body (4) of the photobioreactor through the photointensification module (2) to achieve composite light in conjunction with light irradiation; Nano-micro carbon supply: CO2 is supplied to the main body (4) of the photobioreactor through the nano-micro gas oscillation carbon supply module (3), and is broken into nano-micro bubbles by the nano-micro gas oscillator, so as to realize the micro-nano dispersion of CO2 and the deagglomeration of microplastics in the water, thereby increasing the contact probability between microalgae and carbon source and microplastics. Photo-carbon synergistic plastic removal and carbon fixation: Through the synergistic effect of photo-enhancing module (2) and nano-micro gas oscillation carbon supply module (3), the synthesis and secretion of extracellular polymers of microalgae are enhanced. Microalgae adsorb microplastics in water through extracellular polymers, and at the same time fix CO2 through photosynthesis. Algae-plastic mixture harvesting: The micro-algae mixture adsorbed with microplastics in the main body (4) of the photobioreactor is separated into solid and liquid by the microporous filter and centrifuge of the algae-plastic harvesting and resource utilization module (5) to harvest the microalgae mud. Resource utilization: The harvested microalgae mud is placed in a pyrolysis carbonization device for pyrolysis carbonization to prepare modified biochar.

7. The microalgae plastic removal and carbon fixation method of the internal light source coupled with nano-micro carbon supply to enhance microalgae plastic removal and carbon fixation system according to claim 6, characterized in that, In the light enhancement regulation step, U-CQDs are Ulva prolifera-based carbon quantum dots. The quantitative dosing pump adds U-CQDs at a concentration of 1~10 mg·L⁻¹, and the dosage dosing pump adds the plant hormone IAA at a concentration of 1~5 mg·L⁻¹.

8. The microalgae plastic removal and carbon fixation method of the microalgae plastic removal and carbon fixation system coupled with internal light source and nano-micro carbon supply to enhance microalgae plastic removal and carbon fixation according to claim 7, characterized in that, The operating parameters of the nano-gas oscillator in the nano-carbon supply step are: oscillation frequency 500Hz~5kHz, CO2 inlet gauge pressure 0.2~1.0MPa, outlet gauge pressure 0.01~0.05MPa, and the generated bubble particle size D. 90 ≤500nm.

9. The microalgae plastic removal and carbon fixation method of the microalgae plastic removal and carbon fixation system coupled with internal light source and nano-micro carbon supply to enhance microalgae plastic removal and carbon fixation according to claim 6, characterized in that, In the algae-plastic mixture harvesting step, the pore size of the microporous filter is 2~10μm, the speed of the centrifuge is 3000~5000r / min, the pyrolysis temperature of the pyrolysis carbonization device is 300~500℃, and the pyrolysis time is 2~8h.

10. The microalgae plastic removal and carbon fixation method of the internal light source coupled with nano-micro carbon supply to enhance microalgae plastic removal and carbon fixation system according to claim 6, characterized in that, The concentration of the *Ulva prolifera*-based U-CQDs added is 1 mg·L⁻¹, and the concentration of the plant hormone IAA added is 5 mg·L⁻¹. The reactive oxygen species (ROS) content is detected by an oxidative stress probe. When the ROS content exceeds the preset value, the plant hormone IAA is added to alleviate the oxidative damage to the microalgae. The nano-gas oscillator has an oscillation frequency of 800 Hz, an inlet gauge pressure of 0.3 MPa for CO2, an outlet gauge pressure of 0.02 MPa, and a generated bubble particle size D. 90 ≤500nm; In the photo-carbon synergistic plastic removal and carbon fixation step, the cultivation period is 13 days; in step S5, the recovery rate of the microalgae sludge is 80%. The microporous filter has a pore size of 5 μm, the centrifuge has a rotation speed of 4000 r / min, the pyrolysis temperature of the pyrolysis carbonization device is 500 ℃, and the pyrolysis time is 4 h.

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