Method for microalgae to fix carbon dioxide in high mineral high temperature environment

Abstract

This invention provides a method for microalgae to fix carbon dioxide under high-mineralization and high-temperature environments, belonging to the field of microalgae cultivation and carbon neutrality technology. The carbon dioxide fixation method includes the following steps: S1: Constructing a carbon fixation culture system using ammonium sulfate as the sole nitrogen source; S2: Introducing microalgae into the carbon fixation culture system for cultivation at a temperature of 20-43℃; S3: Passing carbon dioxide-containing flue gas into the carbon fixation culture solution, and collecting the microalgae biomass after cultivation to fix carbon dioxide. This invention can improve the stress resistance and carbon fixation performance of microalgae under high-mineralization and high-temperature environments, is suitable for the synergistic treatment of high-mineralization water bodies and high-carbon dioxide concentration flue gas in power plants, and has low treatment costs, is easy to operate, and has broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of microalgae cultivation and carbon neutrality technology, specifically to a method for microalgae to fix carbon dioxide under high mineral and high temperature conditions. Background Technology

[0002] Coal-fired power plants are one of the major sources of carbon dioxide emissions. Typically, the volume fraction of carbon dioxide in the flue gas emitted by coal-fired power plants is 10% to 15%. Therefore, how to effectively capture and convert this portion of carbon dioxide is of great significance for achieving the goal of carbon neutrality.

[0003] Currently, using microalgae photosynthetic carbon fixation technology to treat power plant flue gas and convert carbon dioxide into economically valuable biomass resources is considered a highly promising biological carbon fixation pathway.

[0004] However, large-scale cultivation of microalgae requires significant water resources. Given the increasing scarcity of freshwater, coal-fired power plants typically use highly mineralized water sources such as groundwater, mine drainage water, and seawater to replace freshwater in water-intensive processes like ash removal, flue gas desulfurization, and circulating cooling. Therefore, applying microalgae carbon fixation technology to coal-fired power plants, utilizing highly mineralized water for microalgae cultivation, can reduce water costs and freshwater consumption, demonstrating significant application value.

[0005] However, highly mineralized water environments exert a significant stress on microalgae growth. Furthermore, the water bodies and flue gas associated with coal-fired power plants typically exhibit high temperatures. If microalgae are used to treat flue gas from coal-fired power plants, the microalgae are often subjected to a combined stress of high mineralization and high temperature during cultivation. Under these combined stress conditions, microalgae cells are prone to osmotic imbalance, damage to the photosynthetic system, and cellular structural damage, thus adversely affecting their growth and carbon fixation processes. This severely restricts the stable operation of microalgae carbon fixation processes.

[0006] In summary, existing microalgae carbon fixation technologies struggle to overcome the metabolic burden posed by high-mineralization, high-temperature environments, and are not directly applicable to the existing water and exhaust systems of coal-fired power plants. Therefore, developing a cost-effective carbon fixation method that can significantly reduce the metabolic burden of microalgae under high-mineralization, high-temperature conditions, and achieve synergistic treatment of highly mineralized water and flue gas from power plants, has become a pressing technical challenge in this field. Summary of the Invention

[0007] The technical problem to be solved by this invention is: how to achieve efficient carbon fixation of microalgae under high mineral and high temperature conditions.

[0008] To address the aforementioned technical problems, the first aspect of this invention provides a method for microalgae to fix carbon dioxide under high mineral and high temperature conditions, comprising the following steps: S1: Construct a carbon fixation culture system, wherein ammonium sulfate is the sole nitrogen source and seashell particles are added, and the concentration of ammonium sulfate in the carbon fixation culture system is 377~2121 mg / L; S2: Microalgae are placed into the carbon fixation culture system described in step S1 for culture, wherein the culture temperature is 20~43℃, and a carbon fixation culture solution is obtained. S3: Passing carbon dioxide-containing flue gas into the carbon fixation culture medium, and collecting microalgal biomass after the culture is completed, thereby fixing carbon dioxide.

[0009] In the cultivation of microalgae, nitrogen source is a key nutrient affecting their stress resistance. Traditional microalgae culture media, such as BG-11 medium, often use sodium nitrate as the nitrogen source. However, the assimilation pathway of sodium nitrate is complex, requiring a large amount of ATP and NADPH to be reduced to ammonia nitrogen before it can be utilized. Under high mineral and high temperature stress, microalgae cells already face energy and reducing power shortages. The high-energy-consuming assimilation pathway of sodium nitrate further exacerbates the metabolic burden on microalgae, thus limiting their stress resistance and carbon fixation capabilities. In the technical solution provided by this invention, ammonium sulfate, a byproduct of power plant flue gas treatment, is used as the sole nitrogen source. The ammonia nitrogen provided by ammonium sulfate can be directly assimilated via the glutamine synthase-glutamate synthase pathway. This nitrogen assimilation pathway is short and energy-efficient, saving microalgae more energy and reducing power for stress response and photosynthetic carbon fixation.

[0010] Preferably, the microalgae are selected from any one or more of Chlorella proteoglycans, Chlorella kappa, Chlorella obliquee, Chlorella sorokinensis, Chlorella ehrlich, and Chlorella ellipsoides.

[0011] Preferably, the carbon fixation culture system contains sodium chloride, and the concentration of sodium chloride is 8~12 g / L.

[0012] As a preferred option, in actual industrialization, the carbon fixation culture system can be prepared using sodium chloride and water, or it can be obtained directly from surface saline water, mine water, or seawater after salt supplementation or dilution.

[0013] Preferably, the shell particles are oyster shell particles with a particle size of 8-12 mesh and a content of 1-5 g / L in the carbon fixation culture system.

[0014] In the technical solution provided by this invention, the role of shell particles is to work synergistically with ammonium sulfate. By controlling the amount of shell particles and ammonium sulfate added, the pH value of the carbon fixation culture system can be stabilized between 6.7 and 8, thereby achieving the substitution of buffer salts and making the carbon fixation culture system simpler and cheaper.

[0015] Preferably, the carbon fixation culture system further includes the following components: dipotassium hydrogen phosphate trihydrate, magnesium sulfate heptahydrate, calcium chloride, sodium carbonate, citric acid monohydrate, disodium magnesium EDTA, boric acid, manganese chloride tetrahydrate, zinc sulfate heptahydrate, cobalt chloride hexahydrate, copper sulfate pentahydrate, and sodium molybdate dihydrate.

[0016] Preferably, the concentrations of the following are specified: dipotassium hydrogen phosphate trihydrate is 0.02-0.05 g / L; magnesium sulfate heptahydrate is 0.05-0.09 g / L; calcium chloride is 0.02-0.03 g / L; sodium carbonate is 0.015-0.03 g / L; citric acid monohydrate is 0.005-0.007 g / L; and magnesium disodium EDTA is 0.00 g / L. The concentrations of the following components are as follows: 1~0.002 g / L, boric acid 2.5~3 mg / L, manganese chloride tetrahydrate 2.5~3 mg / L, zinc sulfate heptahydrate 0.2~0.25 mg / L, cobalt chloride hexahydrate 0.04~0.06 mg / L, copper sulfate pentahydrate 0.07~0.09 mg / L, and sodium molybdate dihydrate 0.3~0.5 mg / L.

[0017] Preferably, the volume fraction of carbon dioxide in the flue gas is 10% to 15%.

[0018] Preferably, in step S3, the aeration rate of the flue gas is 0.15~0.3vvm.

[0019] Preferably, in step S2, the culture temperature is 35~43℃.

[0020] Furthermore, a second aspect of the present invention provides a method for treating power plant flue gas, wherein the method employs the microalgae carbon dioxide fixation method described in the first aspect under high mineral and high temperature conditions to treat power plant flue gas.

[0021] Compared with the prior art, the present invention has the following beneficial effects: 1. In industrial scenarios where high temperature and high mineralization coexist, this invention uses ammonium sulfate as the sole nitrogen source to construct a carbon fixation culture system. By utilizing the energy-saving assimilation advantage of ammonium nitrogen, and by regulating the distribution of photosynthetic energy, it enhances the activity of antioxidant enzymes (SOD) and reduces the level of membrane lipid peroxidation (MDA), thereby effectively alleviating oxidative damage under complex stress and significantly improving the carbon fixation performance of microalgae. 2. In the method for microalgae to fix carbon dioxide under high mineral and high temperature environment provided by the present invention, the only nitrogen source is ammonium sulfate, a by-product of power plant flue gas treatment; pH control is achieved by using aquatic waste shell particles, eliminating the need for chemical buffers to control pH, resulting in lower raw material costs and simpler operation, making it suitable for large-scale open ponds or pipeline reactors, with broad prospects for industrial application. 3. The carbon fixation method provided by this invention can directly utilize highly mineralized water such as surface saline water, mine water, and seawater to prepare a carbon fixation culture system without the need for additional freshwater consumption. At the same time, it can adapt to high-temperature environments in summer without the need for additional cooling equipment, which can significantly reduce operating energy consumption. Attached Figure Description

[0022] Figure 1 This is a graph showing the pH change of each group of microalgae in the test examples of this invention; Figure 2 This is a statistical chart of intracellular SOD activity in each group of microalgae in the test examples of this invention; Figure 3 This is a statistical chart of the intracellular MDA content of microalgae in each group of test examples of the present invention; Figure 4 This is a statistical chart showing the changes in the dry weight of microalgal biomass in each group of test examples in this invention; Figure 5 This is a comparison chart of the average carbon fixation rates of microalgae in each group in the test examples of this invention. Detailed Implementation

[0023] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0024] It should be noted that the endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0025] As described in the background section, during the operation of power plants, especially coal-fired power plants, flue gas treatment byproducts include ammonium sulfate, and the flue gas also contains high concentrations of carbon dioxide. Simultaneously, power plants may use high-mineralized water in circulating cooling and other water usage processes, resulting in power plant wastewater typically characterized by high mineral content and high temperature. Therefore, achieving the synergistic treatment of high-mineralized, high-temperature water and high-carbon dioxide waste gas is crucial for reducing treatment costs and improving resource utilization efficiency. Although microalgae carbon fixation technology is relatively mature, the optimal growth temperature for microalgae is typically 26–30°C, and the optimal sodium chloride salinity for growth is usually below 100 mM. Therefore, the combined effect of high mineralization and high temperature significantly inhibits microalgae growth, easily leading to a decrease in microalgae carbon fixation efficiency. Thus, providing a method to improve the carbon fixation performance of microalgae under high mineral and high-temperature stress has significant application value.

[0026] In view of this, a specific embodiment of the present invention provides a method for microalgae to fix carbon dioxide under high mineral and high temperature conditions, comprising the following steps: S1: Construct a carbon fixation culture system, wherein ammonium sulfate is the sole nitrogen source and seashell particles are added, and the concentration of ammonium sulfate in the carbon fixation culture system is 377~2121 mg / L; S2: Microalgae are placed into the carbon fixation culture system described in step S1 for culture, wherein the culture temperature is 20~43℃, and a carbon fixation culture solution is obtained. S3: Passing carbon dioxide-containing flue gas into the carbon fixation culture medium, and collecting microalgal biomass after the culture is completed, thereby fixing carbon dioxide.

[0027] In some specific implementations, the preferred cultivation temperature is 35~43℃, at which temperature the stress resistance of microalgae is significantly enhanced.

[0028] In some specific embodiments, the microalgae are selected from any one or more of Chlorella pyrenoidosa, Chlorella kJK, Tetracyclis obliqueis, Chlorella sorokinosa, Chlorella ehrlich, and Chlorella ellipsoidis. Among them, Chlorella pyrenoidosa is the most preferred microalgae.

[0029] In some specific embodiments, the carbon fixation culture system contains sodium chloride, and the concentration of sodium chloride is 8~12 g / L.

[0030] Those skilled in the art should understand that the aforementioned carbon fixation culture system can be prepared using water and sodium chloride, or it can be obtained by supplementing or diluting surface saline water, mine water, seawater, or power plant cooling water with salt, so that the mineralization of the culture system is within the range suitable for the specific embodiments of the present invention.

[0031] In some specific embodiments, the shell particles are oyster shell particles with a particle size of 8-12 mesh, and the content of the shell particles in the carbon fixation culture system is 1-5 g / L.

[0032] When shell particles are used in combination with ammonium sulfate, the pH value of the system can be maintained at 6.7-8.0 during the cultivation process by controlling the amount of both added, thereby reducing or avoiding the need for additional chemical buffers.

[0033] More specifically, the preparation method of the shell particles is as follows: After removing impurities, washing, and drying the shells, they are crushed and sieved to select shell particles with a particle size of 8-12 mesh. These particles are used to neutralize the hydrogen ions released during the assimilation of ammonium nitrogen in situ during microalgae cultivation, maintain the pH stability of the culture medium, and maintain good buffering performance, especially under high temperature and high salt conditions.

[0034] In some specific implementations, seashell particles can be added during the preparation of the carbon fixation culture system or during the microalgae culture process to stabilize the microalgae growth environment.

[0035] In some specific embodiments, the carbon fixation culture system further includes the following components: dipotassium hydrogen phosphate trihydrate, magnesium sulfate heptahydrate, calcium chloride, sodium carbonate, citric acid monohydrate, disodium magnesium EDTA, boric acid, manganese chloride tetrahydrate, zinc sulfate heptahydrate, cobalt chloride hexahydrate, copper sulfate pentahydrate, and sodium molybdate dihydrate.

[0036] In some specific embodiments, the concentrations of dipotassium hydrogen phosphate trihydrate, magnesium sulfate heptahydrate, calcium chloride, sodium carbonate, citric acid monohydrate, disodium magnesium EDTA, boric acid, manganese chloride, zinc sulfate heptahydrate, cobalt chloride hexahydrate, copper sulfate pentahydrate, and sodium molybdate dihydrate are 0.02-0.05 g / L, 0.05-0.09 g / L, 0.02-0.03 g / L, sodium carbonate, 0.015-0.03 g / L, 0.005-0.007 g / L, 0.001-0.002 g / L, boric acid, manganese chloride tetrahydrate, zinc sulfate heptahydrate, cobalt chloride hexahydrate, copper sulfate pentahydrate, and sodium molybdate dihydrate are 0.3-0.5 mg / L.

[0037] In some specific implementations, the volume fraction of carbon dioxide in the flue gas is 10% to 15%.

[0038] In some specific implementations, the aeration rate of the flue gas is 0.15~0.3vvm.

[0039] In some specific implementations, the cultivation process may employ natural light or simulated natural light.

[0040] In some specific embodiments, the method for microalgae to fix carbon dioxide under high mineral and high temperature conditions further includes a scaling-up cultivation step. This scaling-up cultivation step is performed before step S2, i.e., the microalgae are pre-cultured to scale up, using algal solution in the exponential growth phase as the inoculum for step S2. The specific inoculation method can be adjusted according to the cultivation device and the state of the algae. Those skilled in the art can determine the appropriate inoculation amount based on actual needs.

[0041] In some specific implementations, the microalgal biomass can be collected by centrifugation, flocculation, or filtration. The collected microalgal biomass can be further dried, pulverized, or utilized for resource recovery according to actual needs.

[0042] The technical solution of the present invention is further described below through specific embodiments. Unless otherwise defined, all terms, symbols, and other scientific terms used herein are intended to have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In some cases, terms having a conventional meaning are defined herein for clarification or ease of reference, and such definitions should not be construed as indicating a significant difference from the conventional understanding in the art. The technical methods described or referenced herein are generally well understood by those skilled in the art and have been employed by conventional methods. Unless otherwise stated, the use of commercially available kits, reagents, and instruments shall be performed according to the manufacturer's instructions and parameters.

[0043] Example 1

[0044] Experiment on carbon dioxide fixation by microalgae under high mineral and high temperature conditions Take 1L of deionized water and add the following substances: 10g sodium chloride, 0.04g dipotassium hydrogen phosphate trihydrate, 0.075g magnesium sulfate heptahydrate, 0.027g calcium chloride, 0.02g sodium carbonate, 0.006g citric acid monohydrate, 0.0019g disodium magnesium EDTA, 2.86mg boric acid, 2.86mg manganese chloride tetrahydrate, 0.222mg zinc sulfate heptahydrate, 0.049mg cobalt chloride hexahydrate, 0.079mg copper sulfate pentahydrate, and 0.391mg sodium molybdate dihydrate. After high-temperature and high-pressure steam sterilization, allow it to cool naturally to room temperature to obtain the culture medium.

[0045] Add Chlorella working stock solution to the culture medium at an inoculation volume ratio of 1:10, mix well, and then transfer to a column-type photobioreactor; then add ammonium sulfate as the sole nitrogen source to the reactor, with a concentration of 377 mg / L, and add 2 g / L of shell particles with a particle size of 8-12 mesh to construct a carbon fixation culture system.

[0046] Flue gas from a coal-fired power plant containing carbon dioxide was introduced into a vertical photobioreactor. The volume fraction of CO2 in the flue gas was 12%. The culture temperature was controlled at 42℃, and the aeration rate was 0.2 vvm.

[0047] Taking a cylindrical photobioreactor made of glass with a diameter of 65 mm and a height of 145 mm as an example, during the 7-day culture of Chlorella proteoglycans, the effect of ammonium sulfate on promoting carbon fixation of microalgae under abiotic stress was observed by simulating outdoor natural irradiation with a 12-hour light-12-hour dark light cycle.

[0048] Example 2

[0049] Experiment on carbon dioxide fixation by microalgae under high mineral and high temperature conditions Take 1L of deionized water and add the following substances: 10g sodium chloride, 0.04g dipotassium hydrogen phosphate trihydrate, 0.075g magnesium sulfate heptahydrate, 0.027g calcium chloride, 0.02g sodium carbonate, 0.006g citric acid monohydrate, 0.0019g disodium magnesium EDTA, 2.86mg boric acid, 2.86mg manganese chloride tetrahydrate, 0.222mg zinc sulfate heptahydrate, 0.049mg cobalt chloride hexahydrate, 0.079mg copper sulfate pentahydrate, and 0.391mg sodium molybdate dihydrate. After high-temperature and high-pressure steam sterilization, allow it to cool naturally to room temperature to obtain the culture medium.

[0050] Add Chlorella working stock solution to the culture medium at an inoculation volume ratio of 1:10, mix well, and then transfer to a column-type photobioreactor; then add ammonium sulfate as the sole nitrogen source to the reactor, with a concentration of 943 mg / L, and add 2 g / L of shell particles with a particle size of 8-12 mesh to construct a carbon fixation culture system.

[0051] Flue gas from a coal-fired power plant containing carbon dioxide was introduced into a vertical photobioreactor. The volume fraction of CO2 in the flue gas was 12%. The culture temperature was controlled at 42℃, and the aeration rate was 0.2 vvm.

[0052] Taking a cylindrical photobioreactor made of glass with a diameter of 65 mm and a height of 145 mm as an example, during the 7-day culture of Chlorella proteoglycans, the effect of ammonium sulfate on promoting carbon fixation of microalgae under abiotic stress was observed by simulating outdoor natural irradiation with a 12-hour light-12-hour dark light cycle.

[0053] Example 3

[0054] Experiment on carbon dioxide fixation by microalgae under high mineral and high temperature conditions Take 1L of deionized water and add the following substances: 10g sodium chloride, 0.04g dipotassium hydrogen phosphate trihydrate, 0.075g magnesium sulfate heptahydrate, 0.027g calcium chloride, 0.02g sodium carbonate, 0.006g citric acid monohydrate, 0.0019g disodium magnesium EDTA, 2.86mg boric acid, 2.86mg manganese chloride tetrahydrate, 0.222mg zinc sulfate heptahydrate, 0.049mg cobalt chloride hexahydrate, 0.079mg copper sulfate pentahydrate, and 0.391mg sodium molybdate dihydrate. After high-temperature and high-pressure steam sterilization, allow it to cool naturally to room temperature to obtain the culture medium.

[0055] Add Chlorella working stock solution to the culture medium at an inoculation volume ratio of 1:10, mix well, and then transfer to a column-type photobioreactor; then add ammonium sulfate as the sole nitrogen source to the reactor, with a concentration of 1509 mg / L, and add 2 g / L of shell particles with a particle size of 8-12 mesh to construct a carbon fixation culture system.

[0056] Flue gas from a coal-fired power plant containing carbon dioxide was introduced into a vertical photobioreactor. The volume fraction of CO2 in the flue gas was 12%. The culture temperature was controlled at 42℃, and the aeration rate was 0.2 vvm.

[0057] Taking a cylindrical photobioreactor made of glass with a diameter of 65 mm and a height of 145 mm as an example, during the 7-day culture of Chlorella proteoglycans, the effect of ammonium sulfate on promoting carbon fixation of microalgae under abiotic stress was observed by simulating outdoor natural irradiation with a 12-hour light-12-hour dark light cycle.

[0058] Example 4

[0059] Experiment on carbon dioxide fixation by microalgae under high mineral and high temperature conditions Take 1L of deionized water and add the following substances: 10g sodium chloride, 0.04g dipotassium hydrogen phosphate trihydrate, 0.075g magnesium sulfate heptahydrate, 0.027g calcium chloride, 0.02g sodium carbonate, 0.006g citric acid monohydrate, 0.0019g disodium magnesium EDTA, 2.86mg boric acid, 2.86mg manganese chloride tetrahydrate, 0.222mg zinc sulfate heptahydrate, 0.049mg cobalt chloride hexahydrate, 0.079mg copper sulfate pentahydrate, and 0.391mg sodium molybdate dihydrate. After high-temperature and high-pressure steam sterilization, allow it to cool naturally to room temperature to obtain the culture medium.

[0060] Add Chlorella working stock solution to the culture medium at an inoculation volume ratio of 1:10, mix well, and then transfer to a column-type photobioreactor; then add ammonium sulfate as the sole nitrogen source to the reactor, with a concentration of 2121 mg / L, and add 2 g / L of shell particles with a particle size of 8-12 mesh to construct a carbon fixation culture system.

[0061] Flue gas from a coal-fired power plant containing carbon dioxide was introduced into a vertical photobioreactor. The volume fraction of CO2 in the flue gas was 12%. The culture temperature was controlled at 42℃, and the aeration rate was 0.2 vvm.

[0062] Taking a cylindrical photobioreactor made of glass with a diameter of 65 mm and a height of 145 mm as an example, during the 7-day culture of Chlorella proteoglycans, the effect of ammonium sulfate on promoting carbon fixation of microalgae under abiotic stress was observed by simulating outdoor natural irradiation with a 12-hour light-12-hour dark light cycle.

[0063] Comparative Example 1 Experiment on carbon dioxide fixation by microalgae under high mineral and high temperature conditions In this comparative example, the traditional BG11 medium containing sodium nitrate was used, and its preparation method was based on (Feng Lingchong. Three-dimensional structural analysis and environmental adaptation mechanism of microalgae converting and utilizing CO2 from power plant flue gas [D]. Zhejiang University). The specific medium preparation method was as follows: 1.5g sodium nitrate, 0.04g dipotassium hydrogen phosphate trihydrate, 0.075g magnesium sulfate heptahydrate, 0.027g calcium chloride, 0.02g sodium carbonate, 0.006g citric acid monohydrate, 0.0019g disodium magnesium EDTA, 2.86mg boric acid, 2.86mg manganese chloride tetrahydrate, 0.222mg zinc sulfate heptahydrate, 0.049mg cobalt chloride hexahydrate, 0.079mg copper sulfate pentahydrate, and 0.391mg sodium molybdate dihydrate were added to 1L of deionized water. After high-temperature and high-pressure steam sterilization, the medium was naturally cooled to room temperature before adding NaCl to a final concentration of 10g / L as the comparative medium.

[0064] Add Chlorella working stock solution to the culture medium at an inoculation volume ratio of 1:10, mix well, and then transfer to a column-type photobioreactor to construct a carbon fixation culture system.

[0065] Flue gas from a coal-fired power plant containing carbon dioxide was introduced into a vertical photobioreactor. The volume fraction of CO2 in the flue gas was 12%. The culture temperature was controlled at 42℃, and the aeration rate was 0.2 vvm.

[0066] Taking a cylindrical photobioreactor made of glass with a diameter of 65 mm and a height of 145 mm as an example, during the 7-day culture of Chlorella proteoglycans, the effect of ammonium sulfate on promoting carbon fixation of microalgae under abiotic stress was observed by simulating outdoor natural irradiation with a 12-hour light-12-hour dark light cycle.

[0067] Test case First, convert the ammonium nitrogen (NH4) in Examples 1-4. + -N) and nitrate nitrogen (NO3) in the comparative example - The amount of -N) added is shown in Table 1.

[0068] Table 1

[0069] The pH of the culture system was measured daily, and the results were as follows: Figure 1 As shown. By Figure 1 It is evident that under the dual abiotic stress of 42℃ and 10 g / L mineralization, the shell-based buffering system still exhibits strong pH buffering capacity, successfully controlling the pH of the culture medium within the suitable range of 6.7–8.0. The relatively higher pH in the comparative group is because this experimental group used nitrate nitrogen as the nitrogen source for microalgae, and the assimilation of nitrate nitrogen requires the consumption of a large amount of H₂O. + Cells expel large amounts of OH- -To maintain internal pH stability, the pH of the culture medium is relatively higher under these conditions.

[0070] After 7 days of culture, the activity of superoxide dismutase (SOD) in microalgae was measured in each group, and the results are as follows: Figure 2 As shown in the figure. Simultaneously, the malondialdehyde (MDA) content of each group of microalgae was measured, and the results are as follows. Figure 3 As shown. Malondialdehyde (MDA) is a lipid peroxidation product of microalgae, and its content can be used to indirectly characterize the degree of lipid peroxidation in algal cells and the degree of damage to microalgae caused by environmental stress. To scavenge reactive oxygen species, superoxide dismutase (SOD), as the first line of defense in the microalgal antioxidant defense system, catalyzes the scavenging of superoxide anions (O2). - SOD (superoxide dismutase) is converted into hydrogen peroxide (H2O2) and oxygen. H2O2 is then decomposed into H2O and O2 via CAT catalysis, thus enabling cell self-repair. Therefore, SOD activity is also considered to be the cell's ability to scavenge reactive oxygen species. Figure 2 and Figure 3 It is evident that under dual abiotic stress, the SOD activity of microalgae first increases and then decreases with increasing ammonium nitrogen concentration. When the ammonium nitrogen concentration is too low, the nitrogen source supply in the nitrogen assimilation mechanism of microalgae is insufficient, limiting the synthesis of microalgal proteins and enzymes, thereby inhibiting the catalytic activity of SOD enzyme. When the ammonium nitrogen concentration is increased to 200 mg / L, under the conditions of sufficient nitrogen source supply and photosynthetic energy allocation induced by the ammonium nitrogen short-path assimilation mechanism, SOD enzyme can be synthesized normally, and under a higher intensity of photosynthetic energy supply, its catalytic activity is also increased to 96.62 U / mgprot, which is 56.9% higher than that of the nitrate nitrogen control group. Therefore, under this condition, the degree of lipid peroxidation in algal cells is the lowest, and the MDA content is reduced to 11.21 nmol / mgprot, which is the lowest value among all experimental groups, only 33.8% of that of the control group. At higher ammonium nitrogen concentrations, excess ammonium nitrogen damages the oxygen evolution complex (OEC) in the photosynthetic system, inhibits photosynthetic electron transfer, and thus reduces the photosynthetic energy supply of the SOD antioxidant mechanism. This reduces SOD activity, leading to severe oxidative damage to algal cells. Therefore, MDA content tends to decrease first and then increase with increasing ammonium nitrogen concentration.

[0071] The dry weight of microalgal biomass in each group was measured daily, and the results are as follows: Figure 4 As shown. After 7 days of cultivation, the average carbon fixation rate of microalgae in each group was calculated, and the results are as follows. Figure 5 As shown. By Figure 4 and Figure 5It is evident that under stable pH conditions, the assimilation and absorption of ammonium nitrogen by microalgae can effectively promote growth and carbon fixation under dual abiotic stress. With increasing ammonium nitrogen concentration, the damage to the microalgal photosynthetic system caused by excess intracellular ammonium nitrogen intensifies. Therefore, in the early stages of cultivation, the biomass dry weight of microalgae tends to decrease with increasing ammonium nitrogen concentration. At the lowest ammonium nitrogen concentration of 80 mg / L, the biomass dry weight of microalgae is consistently higher than in other examples. However, starting from day 4, the biomass dry weight of the 80 mg / L example gradually decreases compared to other experimental groups. This is because after all the ammonium nitrogen in the culture medium is consumed, the lack of nitrogen source inhibits the photosynthetic carbon fixation of microalgae. Furthermore, the short-path assimilation mechanism of ammonium nitrogen by microalgae is not altered by dual abiotic stress. Compared to the comparative nitrate nitrogen condition, more photosynthetic energy is used for the Calvin carbon fixation cycle and activation of antioxidant protection mechanisms. Therefore, after 7 days of cultivation, under the optimal condition of 200 mg / L nitrogen source, the biomass dry weight of microalgae was 1.27 g / L, and the average carbon fixation rate was as high as 0.32 g / L / d, representing increases of 38% and 45% respectively compared to the control group. Even under the condition of 450 mg / L, where ammonium nitrogen damage was most severe, the biomass dry weight was still as high as 1.16 g / L, although it was 8.6% lower than the optimal condition, it was still 26% higher than the nitrate nitrogen control group. Therefore, ammonium nitrogen can effectively promote the growth and carbon fixation of microalgae under adverse conditions, but it is necessary to avoid the inhibition of microalgae growth by nitrogen limitation and nitrogen excess.

[0072] As can be seen from the results of all the above embodiments, the carbon fixation method provided by the present invention is feasible in high-temperature and high-mineral environments. By using ammonium sulfate as the sole nitrogen source and combining it with seashell particles to construct a carbon fixation culture system, carbon dioxide fixation by microalgae can be achieved, and the culture stability and carbon fixation performance of microalgae under combined stress conditions can be improved. The above embodiments also demonstrate that the method of the present invention has good applicability within the defined parameter range.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for microalgae to fix carbon dioxide under high mineral and high temperature conditions, characterized in that, Includes the following steps: S1: Construct a carbon fixation culture system, wherein ammonium sulfate is the sole nitrogen source and seashell particles are added, and the concentration of ammonium sulfate in the carbon fixation culture system is 377~2121 mg / L; S2: Microalgae are placed into the carbon fixation culture system described in step S1 for culture, wherein the culture temperature is 20~43℃, and a carbon fixation culture solution is obtained. S3: Passing carbon dioxide-containing flue gas into the carbon fixation culture medium, and collecting microalgal biomass after the culture is completed, thereby fixing carbon dioxide.

2. The method as described in claim 1, characterized in that, The microalgae are selected from any one or more of Chlorella proteoglycans, Chlorella kappa, Chlorella tetracyclis, Chlorella sorokinensis, Chlorella ehrlich, and Chlorella ellipsoides.

3. The method as described in claim 1, characterized in that, The carbon fixation culture system contains sodium chloride, and the concentration of sodium chloride is 8~12 g / L.

4. The method as described in claim 1, characterized in that, The shell particles are oyster shell particles with a particle size of 8-12 mesh and a content of 1-5 g / L in the carbon fixation culture system.

5. The method as described in claim 1, characterized in that, The carbon fixation culture system also includes the following components: dipotassium hydrogen phosphate trihydrate, magnesium sulfate heptahydrate, calcium chloride, sodium carbonate, citric acid monohydrate, disodium magnesium EDTA, boric acid, manganese chloride tetrahydrate, zinc sulfate heptahydrate, cobalt chloride hexahydrate, copper sulfate pentahydrate, and sodium molybdate dihydrate.

6. The method as described in claim 5, characterized in that, The concentrations of the following are specified: dipotassium hydrogen phosphate trihydrate (0.02-0.05 g / L), magnesium sulfate heptahydrate (0.05-0.09 g / L), calcium chloride (0.02-0.03 g / L), sodium carbonate (0.015-0.03 g / L), citric acid monohydrate (0.005-0.007 g / L), and disodium magnesium EDTA (0.001-0.007 g / L). The concentrations of the following components are specified: 0.002 g / L, boric acid 2.5-3 mg / L, manganese chloride tetrahydrate 2.5-3 mg / L, zinc sulfate heptahydrate 0.2-0.25 mg / L, cobalt chloride hexahydrate 0.04-0.06 mg / L, copper sulfate pentahydrate 0.07-0.09 mg / L, and sodium molybdate dihydrate 0.3-0.5 mg / L.

7. The method as described in claim 1, characterized in that, The volume fraction of carbon dioxide in the flue gas is 10% to 15%.

8. The method as described in claim 1, characterized in that, In step S3, the aeration rate of the flue gas is 0.15~0.3vvm.

9. The method as described in claim 1, characterized in that, In step S2, the culture temperature is 35~43℃.

10. A method for treating flue gas from a power plant, characterized in that, The method for fixing carbon dioxide by microalgae under high mineral and high temperature conditions as described in any one of claims 1 to 9 is used to treat power plant flue gas.

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