Method for rapidly denitrifying high-turbidity biogas slurry by using carbon quantum dot-assisted microorganisms and application of carbon quantum dot-assisted microorganisms

Abstract

The invention belongs to the technical field of wastewater purification, and particularly relates to a method for rapidly denitrifying high-turbidity biogas slurry by using carbon quantum dot-assisted microorganisms and application of the method. The method comprises the following steps: inoculating microalgae into biogas slurry, adding carbon quantum dots, and uniformly mixing to construct a purification system; the purification system is subjected to continuous visible light irradiation, meanwhile, mixed gas of carbon dioxide and air is introduced, and photosynthetic denitrification purification treatment is conducted on the biogas slurry. According to the invention, the technical problems of inhibition of photosynthesis of microalgae, slow electron transfer of microorganisms, difficulty in recovery of nano materials and the like in existing wastewater (especially biogas slurry) purification are solved.

Description

Technical Field

[0001] This invention belongs to the field of wastewater purification technology, and more specifically relates to a method and application of carbon quantum dot-assisted microorganisms for rapid denitrification in high-turbidity biogas slurry. Background Technology

[0002] The rapid development of animal husbandry has resulted in a large amount of livestock and poultry manure. Biogas projects can realize the resource utilization of waste and are one of the effective ways to solve this problem. However, the biogas slurry produced during biogas production causes environmental hazards that urgently need to be treated. Common wastewater purification mainly uses physicochemical methods, but these usually have problems such as high cost and high energy consumption. Anaerobic digestion biogas slurry has the characteristics of low carbon-nitrogen ratio and high nutrient concentration, making biological methods for purifying this type of wastewater a promising prospect. Among them, microalgae, with their advantages of low energy consumption and high pollutant removal efficiency, have shown great application potential in the field of biogas slurry purification. However, the high ammonia nitrogen characteristics of biogas slurry inhibit microalgal photosynthesis, the large amount of suspended solids in biogas slurry leads to light attenuation, and the high turbidity characteristics greatly limit the utilization of light by microalgae, reducing their photosynthetic autotrophic growth capacity and thus reducing the purification efficiency of biogas slurry.

[0003] Reducing the content of organic suspended solids in biogas slurry can decrease turbidity and alleviate light attenuation. While bacteria naturally present in biogas slurry can degrade organic suspended solids into smaller molecules for microbial use, the slow electron transfer rate of microorganisms is a core bottleneck limiting the efficiency of this process. Electron transfer, as a key process in microbial purification of biogas slurry, directly affects the energy metabolism and material conversion rate of the microbial community. Nanomaterials, due to their excellent photoelectric properties, can not only promote electron transfer in microorganisms but also participate in energy metabolism to improve biodegradation efficiency and accelerate the conversion and utilization of waste resources. However, existing nanomaterials generally suffer from difficulties in recycling, high costs, and low subsequent utilization efficiency, limiting their large-scale application in biogas slurry treatment. Summary of the Invention

[0004] To address the technical challenges in wastewater (especially biogas slurry) purification, such as inhibited photosynthesis of microalgae, slow electron transfer in microorganisms, and difficulties in recovering nanomaterials, this invention provides a method and application for rapid denitrification of biogas slurry with carbon quantum dots assisted by microorganisms. This method is particularly suitable for the purification of biogas slurry with high ammonia nitrogen and high suspended solids content.

[0005] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of this invention is to provide a method for rapid denitrification of biogas slurry by carbon quantum dot-assisted microorganisms, comprising the following steps: Microalgae were inoculated into biogas slurry, and carbon quantum dots were added and mixed evenly to construct a purification system. The purification system is continuously irradiated with visible light while gas is introduced to perform photosynthetic denitrification purification of the biogas slurry.

[0006] Furthermore, the inoculum amount of the microalgae is 0.01-1 g / L, preferably 0.1 g / L.

[0007] Furthermore, the microalgae include at least one of Chlorella, Chlamydomonas, and Scenedesmus, preferably Chlorella.

[0008] Furthermore, the amount of carbon quantum dots added is 0-1 g / L, and not 0, preferably 0.03 g / L.

[0009] Furthermore, the preparation steps of the carbon quantum dots include: The carbon quantum dots are obtained by uniformly mixing biomass powder and ethanol aqueous solution, followed by hydrothermal reaction, centrifugation, dialysis, filtration and drying.

[0010] Optionally, the mass-to-volume ratio of the biomass powder to the ethanol aqueous solution is 1g:(10-200)mL, preferably 1g:60mL.

[0011] Optionally, the volume fraction of the ethanol aqueous solution is 0-100%.

[0012] Optionally, the hydrothermal reaction is carried out at a temperature of 120-300 °C for a duration of 4-24 h.

[0013] Preferably, the hydrothermal reaction is carried out at a temperature of 180 °C for 6 h.

[0014] Optionally, the dialysis is performed in water using a 3500 Da dialysis bag for 3 days, with the water changed every 7 hours.

[0015] Optionally, the filtration is performed using a 0.22 μm filter membrane.

[0016] Optionally, the biomass includes at least one of agricultural and forestry waste (straw), food processing waste (fruit peel), and microalgae recovered after purification of biogas slurry.

[0017] Furthermore, the light intensity during continuous visible light irradiation is 0-1000 μmol·m⁻¹. -2 ・s -1 And not 0, preferably 150 μmol·m -2 ・s -1 .

[0018] Furthermore, the gas is carbon dioxide and air in a volume ratio of 0-60:40-100, with the preferred volume ratio being 5:95.

[0019] Furthermore, the ventilation rate of the carbon dioxide and air mixture is 0-0.5 vvm, and not 0, preferably 0.1 vvm.

[0020] Furthermore, it also includes: after photosynthetic denitrification and purification treatment, microalgae are recovered, dried to constant weight, and ground into algal powder for use in the preparation of carbon quantum dots.

[0021] The second technical solution of the present invention provides an application of carbon quantum dots in a suspended microalgae purification biogas slurry system, wherein the amount of carbon quantum dots added is 0-1 g / L, and the amount added is not 0.

[0022] Optionally, the suspended microalgae purification system for biogas slurry is a technical system that utilizes microalgae to treat biogas slurry with high ammonia nitrogen and high suspended solids content.

[0023] This invention achieves efficient removal of ammonia nitrogen from biogas slurry with high ammonia nitrogen and high suspended solids content by promoting electron transfer between indigenous microorganisms and inoculated microalgae in biogas slurry and mitigating light attenuation in the biogas slurry system.

[0024] The present invention discloses the following technical effects: Carbon quantum dots, as excellent electron mediators, improve the electron transfer efficiency of microorganisms. This invention utilizes the synergistic effect of carbon quantum dots with common microorganisms and microalgae in wastewater to significantly accelerate the electron transfer efficiency of microorganisms and promote the efficient degradation of organic suspended matter—that is, reducing the turbidity of the biogas slurry to reduce light attenuation, allowing more light to be captured and utilized by microalgae. The degradation products can also serve as an organic carbon source to assist the heterotrophic growth of microalgae. Through a hybrid cultivation mode of photosynthetic autotrophy and heterotrophic synergy, rapid proliferation of microalgae in biogas slurry is achieved, thereby efficiently removing ammonia nitrogen from the biogas slurry (especially suitable for biogas slurry).

[0025] The carbon quantum dot-assisted microbial denitrification method of this invention features simple process steps, requires no wastewater pretreatment, uses microalgae cultured in wastewater as raw material, achieving "waste-to-waste treatment," and allows for the recycling of carbon quantum dots, resulting in low preparation and operating costs. Simultaneously, this method boasts high ammonia nitrogen removal efficiency and rapid microalgae growth rate, effectively purifying biogas slurry with high ammonia nitrogen and high suspended solids content. This invention constructs a closed-loop, high-value utilization system suitable for large-scale engineering treatment of high-ammonia nitrogen wastewater such as anaerobic digestion biogas slurry from livestock and poultry farming, and has broad industrial application prospects in the field of wastewater purification. Attached Figure Description

[0026] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a flowchart of the carbon quantum dot preparation process in this invention.

[0027] Figure 2 The graph shows the change in ammonia nitrogen concentration over time in the biogas slurry of Example 1 and Comparative Examples 1-3.

[0028] Figure 3 The graph shows the concentration change of suspended solids in the biogas slurry of Example 1 and Comparative Examples 1-3 over time. Detailed Implementation

[0029] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0030] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0031] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0032] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0033] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0034] Unless otherwise specified, all raw materials and reagents involved in the specific embodiments of this invention are commercially available products.

[0035] The microalgae used in the specific embodiments of this invention is Chlorella proteoglycans. Chlorella pyrenoidosa Number FACHB-9.

[0036] In a specific embodiment of the present invention, the precursor of the carbon quantum dots prepared is Chlorella proteoglycans, which is prepared hydrothermally after drying and grinding.

[0037] In the specific embodiments of the present invention, the biogas slurry involved is a biogas slurry with a suspended solids concentration of 0-10 g / L (not 0) and an ammonia nitrogen concentration of 50-1000 mg / L that has not undergone any pretreatment.

[0038] In a specific embodiment of this invention, the biogas slurry is untreated anaerobic digestion biogas slurry from a pigsty, sourced from an anaerobic digestion plant in Guang'an, Sichuan Province, with the following parameters: The concentrations of ammonia nitrogen, total phosphorus, COD, and suspended solids were 513 mg / L, 10.17 mg / L, 539.4 mg / L, and 8.1 g / L (5.8 g / L of volatile suspended solids). The main indigenous microbial phyla were Bacillus, Pseudomonas, and Bacteroides.

[0039] Unless otherwise specified, room temperature and normal temperature in the specific embodiments of this invention refer to 20-30℃.

[0040] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0041] Figure 1 This is a flowchart of the carbon quantum dot preparation process in this invention.

[0042] In some specific embodiments, the present invention provides a method for rapid denitrification of biogas slurry by carbon quantum dot-assisted microorganisms, the steps of which include: S1. Weigh 0.01-1.0 g of dried and ground biomass (including at least one of the following multi-source biomass resources: microalgae and other microbial biomass, agricultural and forestry waste such as straw, and food processing waste such as fruit peels), add it to the polytetrafluoroethylene liner of a hydrothermal reactor, and then add 60 mL of a 0-100% mixed solution to the liner; cover with the liner and sonicate for 30 min to ensure the algae powder is evenly dispersed in the solvent; place the liner into the hydrothermal reactor and tighten it, then place it in an oven at 120-300 ℃ for 4-24 h; after the reaction is complete and cooled to room temperature, centrifuge the reaction substrate at 10000 rpm for 10 min; then transfer the supernatant to a 3500 Da dialysis bag and dialyze in deionized water for 3 days, changing the deionized water every 7 h; finally, centrifuge the dialysate again at 10000 rpm for 10 min, and take the supernatant through a 0.22 mL aspirate filter. μm filter membrane, the filtrate is freeze-dried under vacuum, and the collected solid powder is carbon quantum dots grown from biogas slurry; S2. Inoculate microalgae (at least one of Chlorella, Chlamydomonas and Scenedesmus) into the biogas slurry at an inoculation amount of 0.1 g / L (dry weight), and simultaneously add carbon quantum dots prepared in step S1 at an amount of 0-1 g / L (not 0). Mix the system evenly by mechanical stirring to obtain the purification system. S3. Continuous LED visible light irradiation is used, with a light intensity of 0-1000 μmol·m⁻¹. -2 ・s -1 (Not 0); A mixture of carbon dioxide and air (0-60% carbon dioxide + 40-100% air) is introduced into the system by bubbling at a rate of 0-0.5 vvm (not 0) to perform photosynthetic denitrification purification of the biogas slurry.

[0043] After the biogas slurry is purified, the microalgae and carbon quantum dots in the system are recovered together. The recovered products are dried and ground, and then directly used as precursors for the preparation of high-value compounds such as carbon quantum dots for recycling, thus solving the problem of the difficulty in separating carbon quantum dots.

[0044] The carbon quantum dots used in this invention are zero-dimensional carbon nanomaterials with excellent water solubility, biocompatibility, and photoelectric properties. To realize the large-scale application of carbon quantum dots in wastewater purification, this invention uses biomass (microalgae used for wastewater purification) after biogas slurry purification as a precursor to prepare carbon quantum dots, which can significantly reduce costs. At the same time, the prepared carbon quantum dots can enhance the electron transfer capacity of microorganisms in biogas slurry, accelerate the degradation of macromolecular organic matter, reduce the turbidity of biogas slurry, and promote the heterotrophic and photosynthetic autotrophic processes of microalgae. Ultimately, it achieves the biological purification of high-turbidity biogas slurry (rapidly removing ammonia nitrogen from biogas slurry through the synergistic effect between microorganisms and carbon quantum dots), providing a new method for overcoming the obstacle of high turbidity to microalgal photosynthesis in wastewater purification.

[0045] For carbon quantum dots: Carbon quantum dots are prepared by using microalgae cultured and recovered from biogas slurry, achieving "waste treatment with waste", with sustainable raw material sources and significantly reducing the cost of carbon quantum dot preparation; Carbon quantum dots can efficiently promote electron transfer in microorganisms and accelerate the degradation of organic suspended matter. They can alleviate the inhibition of microalgal photosynthesis by light decay, and their degradation products can provide organic carbon sources for microalgae. Through the synergistic mode of photosynthetic autotrophy and heterotrophy, they can significantly improve the ammonia nitrogen removal efficiency of biogas slurry and the growth rate of microalgae. The carbon quantum dots contained in the harvested microalgae do not require additional separation and purification. They can be directly dried and recycled as precursors for the next batch of carbon quantum dots, completely solving the problems of high difficulty and high cost in recycling traditional nanomaterials. A closed-loop system of "microalgae cultivation and purification of biogas slurry - microalgae recovery - carbon quantum dot preparation - cyclical assisted purification" is constructed to realize the high-value transformation of microalgae, which has significant environmental and economic benefits.

[0046] This invention involves inoculating microalgae and adding carbon quantum dots into biogas slurry containing a large amount of organic suspended solids and high ammonia nitrogen concentration. The carbon quantum dots promote electron transfer between the microorganisms in the biogas slurry and the inoculated microalgae cells, and alleviate light attenuation caused by high turbidity, thereby improving the photosynthetic decontamination of microalgae and achieving efficient removal of ammonia nitrogen by microorganisms in biogas slurry.

[0047] Example 1 The steps involved in the rapid denitrification of biogas slurry by carbon quantum dot-assisted microorganisms include: S1. Weigh 1.0 g of dried and ground algal powder (Chlorella proteoglycans), add it to the polytetrafluoroethylene liner of the hydrothermal reactor, and then add a mixed solution of 60 mL ethanol (50 mL) and water (10 mL) to the liner; cover with the liner and sonicate for 30 min to disperse the algal powder evenly in the solvent; put the liner into the hydrothermal reactor and tighten it, and place it in an oven at 180 ℃ for 6 h; after the reaction is completed and cooled to room temperature, centrifuge the reaction substrate at 10000 rpm for 10 min; then transfer the supernatant to a 3500 Da dialysis bag and dialyze in deionized water for 3 days, changing the deionized water every 7 h; finally, centrifuge the dialysate again at 10000 rpm for 10 min, take the supernatant and filter it through a 0.22 μm filter membrane, freeze-dry the filtrate under vacuum, and collect the solid powder, which is the carbon quantum dots grown based on biogas slurry; S2. Inoculate microalgae (Chlorella proteoglycans) into the biogas slurry at an inoculation amount of 0.1 g / L (dry weight), and simultaneously add carbon quantum dots prepared in step S1 at an inoculation amount of 0.03 g / L. Mix the system evenly by mechanical stirring to obtain the purification system. S3. Continuous LED visible light irradiation is used, with a light intensity of 150 μmol·m⁻¹. -2 ・s -1 A mixture of carbon dioxide and air (5 vol% carbon dioxide + 95 vol% air) is introduced into the system by bubbling at a rate of 0.1 vvm to perform photosynthetic denitrification purification of the biogas slurry.

[0048] Comparative Example 1 Compared to Example 1, the difference lies in that microalgae are not inoculated in the purification system and no carbon quantum dots are added. The specific steps include: The biogas slurry was continuously irradiated with LED visible light at an intensity of 150 μmol·m⁻¹. -2 ・s -1 A mixture of carbon dioxide and air (5 vol% carbon dioxide + 95 vol% air) is introduced into the system by bubbling at a rate of 0.1 vvm to remove nitrogen from the biogas slurry.

[0049] Comparative Example 2 The difference from Example 1 is that microalgae are not inoculated in the purification system. The specific steps include: S1. Weigh 1.0 g of dried and ground algal powder (Chlorella proteoglycans), add it to the polytetrafluoroethylene liner of the hydrothermal reactor, and then add a mixed solution of 60 mL ethanol (50 mL) and water (10 mL) to the liner; cover with the liner and sonicate for 30 min to disperse the algal powder evenly in the solvent; put the liner into the hydrothermal reactor and tighten it, and place it in an oven at 180 ℃ for 6 h; after the reaction is completed and cooled to room temperature, centrifuge the reaction substrate at 10000 rpm for 10 min; then transfer the supernatant to a 3500 Da dialysis bag and dialyze in deionized water for 3 days, changing the deionized water every 7 h; finally, centrifuge the dialysate again at 10000 rpm for 10 min, take the supernatant and filter it through a 0.22 μm filter membrane, freeze-dry the filtrate under vacuum, and collect the solid powder, which is the carbon quantum dots grown based on biogas slurry; S2. Add the carbon quantum dots prepared in step S1 to the biogas slurry at a concentration of 0.03 g / L. Mix the system evenly by mechanical stirring to obtain the purification system. S3. Continuous LED visible light irradiation is used, with a light intensity of 150 μmol·m⁻¹. -2 ・s -1 A mixture of carbon dioxide and air (5 vol% carbon dioxide + 95 vol% air) is introduced into the system by bubbling at a rate of 0.1 vvm to remove nitrogen from the biogas slurry.

[0050] Comparative Example 3 Compared to Example 1, the difference lies in that no carbon quantum dots are added to the purification system, and the specific steps include: S1. Inoculate microalgae (Chlorella proteoglycans) into biogas slurry at an inoculation rate of 0.1 g / L (dry weight), and mix the system evenly by mechanical stirring to obtain a purification system; S2. Continuous LED visible light irradiation is used, with a light intensity of 150 μmol·m⁻¹. -2 ・s -1 A mixture of carbon dioxide and air (5 vol% carbon dioxide + 95 vol% air) is introduced into the system by bubbling at a rate of 0.1 vvm to remove nitrogen from the biogas slurry.

[0051] Test case The biogas slurry was purified using the methods of the examples and comparative examples. Samples were taken daily at regular intervals to continuously monitor the ammonia nitrogen concentration and suspended solids concentration. The test methods are as follows: Every 24 hours, 8 mL of the system suspension was taken and centrifuged at 8000 rpm for 10 min. The supernatant was collected, and the ammonia nitrogen concentration was determined by salicylic acid spectrophotometry. The ammonia nitrogen removal rate was recorded, and the results are as follows: Figure 2 As shown; The precipitate was transferred to a dried weighing bottle, dried in an oven at 105 °C for 24 h, cooled to room temperature, and then weighed. The concentration of suspended solids was calculated, and the results are as follows: Figure 3 As shown.

[0052] Figure 2 The graph shows the change in ammonia nitrogen concentration over time in the biogas slurry of Example 1 and Comparative Examples 1-3.

[0053] Figure 3 The graph shows the concentration change of suspended solids in the biogas slurry of Example 1 and Comparative Examples 1-3 over time.

[0054] Figure 2 and Figure 3 In this example, DPW+Microalgae+CQDs is Example 1, DPW is Comparative Example 1, DPW+CQDs is Comparative Example 2, and DPW+Microalgae is Comparative Example 3.

[0055] Figure 2 and Figure 3 The results showed that in the anaerobic digestion slurry system of the pigsty in Example 1, the ammonia nitrogen removal rate was significantly higher than that in Comparative Examples 1-3, and the suspended solids concentration decreased the fastest. Comparative Example 3, which only inoculated microalgae without adding carbon quantum dots, had a lower ammonia nitrogen removal rate than Example 1, indicating that carbon quantum dots can effectively promote ammonia nitrogen removal. Comparative Example 2, which only added carbon quantum dots without inoculating microalgae, had a much lower denitrification efficiency than Example 1, indicating that the synergistic effect of microalgae and carbon quantum dots is key to efficient denitrification. Meanwhile, the suspended solids concentration degradation in Example 1 was significantly higher than in Comparative Example 3, indicating that carbon quantum dots promoted the decomposition of organic suspended solids by microorganisms, alleviated the inhibition of microalgal photosynthesis by light attenuation, and provided an organic carbon source for microalgae through the degradation products of suspended solids, achieving synergistic growth of microalgae.

[0056] In this invention, after wastewater purification, microalgae and carbon quantum dots from the system of Example 1 are recovered together. The recovery steps are as follows: the purified wastewater is centrifuged at 4000 rpm, and the supernatant is the purified wastewater. The collected solid components are placed in a 60 ℃ oven for drying. After drying and grinding, the carbon quantum dots are used as raw materials to prepare carbon quantum dots again. The recycled carbon quantum dots still have excellent electron transfer promoting effects, and the carbon quantum dots of this invention can be recycled.

[0057] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0058] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for rapid denitrification of biogas slurry by carbon quantum dot-assisted microorganisms, characterized in that the steps include... include: Microalgae were inoculated into biogas slurry, and carbon quantum dots were added and mixed evenly to construct a purification system. The purification system is continuously irradiated with visible light while gas is introduced to perform photosynthetic denitrification purification of the biogas slurry.

2. The method as described in claim 1, characterized in that, The inoculum amount of the microalgae is 0.01-1 g / L; And / or, the microalgae include at least one of Chlorella, Chlamydomonas, and Scenedesmus; And / or, the amount of carbon quantum dots added is 0-1 g / L, and not 0.

3. The method as described in claim 1, characterized in that, The preparation steps of the carbon quantum dots include: The carbon quantum dots are obtained by uniformly mixing biomass powder and ethanol aqueous solution, followed by hydrothermal reaction, centrifugation, dialysis, filtration and drying.

4. The method as described in claim 3, characterized in that, The mass-to-volume ratio of the biomass powder to the ethanol aqueous solution is 1g:(10-200)mL; And / or, the volume fraction of the ethanol aqueous solution is 0-100%; And / or, the hydrothermal reaction is carried out at a temperature of 120-300 °C for a time of 4-24 h; And / or, the dialysis is performed in water using a 3500 Da dialysis bag for 3 days, with the water changed every 7 hours; And / or, the filtration is through a 0.22 μm filter membrane; And / or, the biomass includes at least one of agricultural and forestry waste, food processing waste, and microalgae recovered after purification of biogas slurry.

5. The method as described in claim 1, characterized in that, The light intensity during continuous visible light irradiation is 0-1000 μmol·m⁻¹. -2 ・s -1 And it is not 0.

6. The method as described in claim 1, characterized in that, The gas is carbon dioxide and air in a volume ratio of 0-60:40-100.

7. The method as described in claim 1, characterized in that, The ventilation rate of the mixture of carbon dioxide and air is 0-0.5 vvm, and is not 0.

8. The method as described in claim 1, characterized in that, Also includes: After photosynthetic denitrification and purification, microalgae are recovered, dried to constant weight, and then ground into algal powder for the preparation of carbon quantum dots.

9. An application of carbon quantum dots in a suspended microalgae purification system for biogas slurry, characterized in that, The amount of carbon quantum dots added is 0-1 g / L, and the amount added is not 0.

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