Application of ZIF-8 in inducing microalgae growth, carbon fixation and lipid accumulation in phosphorus-containing wastewater

Abstract

This invention discloses the application of ZIF-8 in inducing microalgal growth, carbon fixation, and lipid accumulation in phosphorus-containing wastewater, belonging to the field of bioengineering technology. The method includes the following steps: inoculating *Monochorhynchus* in a culture medium to cultivate a seed culture, and then inoculating the seed culture into phosphorus-containing wastewater containing ZIF-8 for wastewater treatment. The method significantly improves the overall performance of microalgae. Under optimal conditions (ZIF-8 concentration of 2.5 mg / L), the carbon dioxide fixation efficiency of microalgae reaches 0.82 g CO2 / L / d, the biomass reaches 4.40 g / L, and the lipid yield reaches 207.69 mg / L / d. This invention has a simple and easy-to-operate process, effectively reducing the cost of microalgae cultivation and significantly improving the economic feasibility of microalgae cultivation, providing a new technical approach for the industrialization of microalgae cultivation.

Description

Technical Field

[0001] This invention relates to the field of bioengineering technology, specifically the application of ZIF-8 in inducing microalgae growth, carbon fixation, and oil accumulation in phosphorus-containing wastewater. Background Technology

[0002] In recent years, my country's overall water environment quality has shown an improving trend, but pollution problems in some river basins and regions remain prominent, and water environment governance and ecological restoration still face severe challenges. With the accelerated pace of global industrialization and urbanization, large amounts of industrial wastewater, domestic sewage, and agricultural non-point source pollution are discharged into natural water bodies, triggering a serious water environment crisis. Excessive nitrogen, phosphorus, heavy metals, and toxic substances in water bodies accumulate through the food chain, posing a toxic risk to organisms at the upper levels of the food chain and severely damaging the stability and biodiversity of aquatic ecosystems. Phosphorus is a key factor leading to eutrophication, and the treatment of phosphorus-containing wastewater is a key focus of water pollution prevention and control. Phosphorus-containing wastewater has a wide range of sources, mainly including agricultural non-point source pollution. The sources of phosphorus loss include phosphorus from domestic sewage, the discharge of phosphorus-containing detergents, and high-phosphorus wastewater from the chemical industry. Overall, wastewater discharge exhibits characteristics of excessive total phosphorus concentration and complex phosphorus forms. Discharge of high-phosphorus wastewater into natural water bodies leads to a significant increase in phosphorus content, easily inducing eutrophication and promoting rapid algal and phytoplankton proliferation, resulting in algal blooms. Existing wastewater treatment processes suffer from drawbacks such as high operating costs, large sludge production, and the risk of secondary pollution, with low resource recovery rates. Furthermore, microalgae cultivation technology is limited by high cultivation costs and low oil yield, and its stability in treating highly polluted wastewater is insufficient. Because microalgae have limited tolerance to pollutants, the treatment effect is easily affected by fluctuations in environmental factors.

[0003] Exploring green wastewater treatment processes is of practical significance. Microalgae treatment technology has significant advantages, as it can simultaneously remove nitrogen and phosphorus and realize biomass resource utilization, thereby achieving a balance between environmental and economic benefits and promoting the advancement of water environment restoration projects. Existing research has shown that adding appropriate exogenous substances to the microalgae culture system can promote microalgae growth and enhance the microalgae's tolerance to pollutants and its decontamination capabilities. Summary of the Invention

[0004] To solve or partially solve the problems existing in related technologies, the primary objective of this invention is to provide the application of ZIF-8 in inducing microalgae growth, carbon fixation, and oil accumulation in phosphorus-containing wastewater.

[0005] The specific operation of the application described in this invention is as follows: (1) Inoculate the mononechoalveolar algae into the culture medium and culture the seed culture.

[0006] (2) Inoculate the seed solution into phosphorus-containing wastewater and add ZIF-8 to culture the algae solution.

[0007] Preferably, in step (1) of the present invention, the culture medium is BG-11 culture medium with added glucose, wherein the glucose concentration is 10 g / L.

[0008] Preferably, the concentration of ZIF-8 in the phosphorus-containing wastewater in step (2) of the present invention is 1.25~5 mg / L.

[0009] As a further preferred embodiment of the present invention, the concentration of ZIF-8 in the phosphorus-containing wastewater in step (2) of the present invention is 2.5 mg / L.

[0010] Preferably, the culture conditions of the algal solution in step (2) of the present invention are a temperature of 25°C and a light intensity of 7000~8000 lux.

[0011] The step (1) described in this invention is a dual-culture module for algae, which is mainly for the dual-culture of algae to rapidly grow a large number of algal cells.

[0012] Step (2) of the present invention is a ZIF-8 and phosphorus-containing wastewater cultivation module, which is mainly for cultivating microalgae in phosphorus-containing wastewater and ZIF-8 to further promote the growth of microalgae and oil accumulation, and simultaneously remove nitrogen and phosphorus from the water.

[0013] This invention also measures the OD of algal cells in algal solution using an ultraviolet spectrophotometer. 750 The algal culture obtained after cultivation in a column-type photobioreactor was collected, algal cells were collected by centrifugation and then freeze-dried. The dry weight of the freeze-dried algal cells was weighed, and the biomass, biomass yield, specific growth rate, and carbon dioxide fixation efficiency of the algal cells were calculated. Lipids in microalgae were extracted using organic solvents, and the lipid content and lipid yield of algal cells were determined by gravimetric method. The total nitrogen content was determined by potassium persulfate digestion-hydrazine sulfate reduction method (EPA-METHOD), and the total phosphorus content was determined by potassium persulfate digestion-molybdenum antimony method (GB11893-1989).

[0014] Another object of the present invention is to provide the application of the method in promoting microalgae growth, carbon fixation and lipid accumulation.

[0015] The beneficial effects of this invention are: (1) The present invention adopts a two-stage cultivation mode of omphalotrophic-photoautotrophic and combines it with ZIF-8 material, which significantly improves the comprehensive performance of microalgae. Under optimal conditions (ZIF-8 concentration of 2.5 mg / L), the carbon dioxide fixation efficiency of microalgae reaches 0.82 g CO2 / L / d, the biomass reaches 4.40 g / L, and the lipid yield reaches 207.69 mg / L / d, which are significantly improved by 74.50%, 64.08% and 121.15% compared with the comparative example.

[0016] (2) In the photoautotrophic stage, phosphorus-containing wastewater is used as the basic culture medium. Microalgae can efficiently remove nitrogen and phosphorus while growing. After cultivation, the remaining nitrogen content in the culture medium is 105.50 mg / L (removal rate 57.33%), and the remaining phosphorus content is only 0.47 mg / L (removal rate 97.48%), thus realizing the organic combination of wastewater treatment and biomass production.

[0017] (3) The process of this invention is simple and easy to operate. By using wastewater as a culture medium, the cost of microalgae cultivation is effectively reduced, while the oil yield is increased. This significantly improves the economic feasibility of microalgae cultivation and provides a new technical approach for the industrialization of microalgae cultivation.

[0018] (4) This invention comprehensively improves the growth rate and oil accumulation capacity of microalgae through the synergistic effect of multiple mechanisms, such as glucose dual-trophic rapid biomass accumulation, ZIF-8 enhancing the antioxidant capacity and pollutant tolerance of microalgae, photobioreactor providing sufficient light and CO2, and organic solvent efficient oil extraction. Furthermore, by establishing a complete total nitrogen and total phosphorus detection system, the stability and repeatability of the process are ensured. Attached Figure Description

[0019] Figure 1 The ZIF-8 method for promoting mononephrite algae production provided in this embodiment of the invention... Monoraphidium Flowchart for phosphorus removal, carbon fixation, and oil accumulation in sp. QLZ-3.

[0020] Figure 2 The embodiments of this invention provide different concentrations of ZIF-8 on microalgae OD 750 Schematic diagram of the impact; Figure 3 This is a graph showing the effect of different concentrations of ZIF-8 on microalgal biomass and biomass yield, provided in the embodiments of the present invention. Figure 4 This is a graph showing the effect of different concentrations of ZIF-8 on the specific growth rate of microalgae, provided in the embodiments of the present invention. Figure 5 This is a graph showing the effect of different concentrations of ZIF-8 on the carbon dioxide fixation efficiency of microalgae, provided in the embodiments of the present invention. Figure 6 This is a schematic diagram illustrating the effect of different concentrations of ZIF-8 on oil content and oil yield, provided in an embodiment of the present invention. Figure 7 This is a schematic diagram illustrating the effect of different concentrations of ZIF-8 on the residual total nitrogen content in the culture medium, provided in this embodiment of the invention. Figure 8 This is a schematic diagram illustrating the effect of different concentrations of ZIF-8 on the remaining total phosphorus content in the culture medium, as provided in the embodiments of the present invention. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings, but the scope of protection of the present invention is not limited to the content described therein; unless otherwise specified, all reagents used in the present invention are commercially available analytical grade reagents, and all raw materials used in the present invention can be purchased through conventional commercial channels.

[0022] The culture medium used in this embodiment: BG-11 medium with added glucose: 10 g / L glucose, 1.7 g / L standard BG-11 powder.

[0023] The phosphorus-containing wastewater used in this invention is an artificial high-phosphorus wastewater culture medium, specifically prepared as follows: 1.7 g / L standard BG-11, 50 mg / L dipotassium hydrogen phosphate: K2HPO4.

[0024] Mononephrite algae used in this invention Monoraphidium sp. QLZ-3 was isolated and screened from Qilu Lake, a freshwater lake on the plateau, and is preserved at Kunming University of Science and Technology in Yunnan Province.

[0025] Example 1 ZIF-8 promotes mononephrite algae Monoraphidium The process flow diagram for the QLZ-3 method of phosphorus removal, carbon fixation, and oil accumulation is as follows: Figure 1 As shown, the specific steps are as follows: (1) Cultivation and collection of seed culture: Add 250 mL of BG-11 medium supplemented with glucose to a 500 mL Erlenmeyer flask and inoculate with *Syngonium moniliforme*. Monoraphidium sp. QLZ-3 was cultured as a mononephrite algae in a shaker at 25℃, 150 r / min, and 4000 lux of light. Monoraphidium sp. QLZ-3, up to mononephrite algae Monoraphidium sp. QLZ-3 was grown to the late logarithmic growth phase; the cultured algal solution was left to stand on an indoor operating table for 48 hours, and then the upper supernatant was removed in a clean bench. The lower layer of algal cells was mixed evenly with the residual culture medium to form the seed culture.

[0026] (2) Mix 1.7g of standard BG-11 powder with 50mg of dipotassium hydrogen phosphate, and dilute with water to 1L to prepare artificial high-phosphorus wastewater. At the same time, add ZIF-8 to the artificial high-phosphorus wastewater at a dosage of 2.5mg / L. Transfer the artificial high-phosphorus wastewater with added ZIF-8 to a column photobioreactor and add the seed liquid obtained in step (1) to ensure that the concentration of microalgae in the artificial high-phosphorus wastewater is 0.36g / L.

[0027] A 3% CO2 mixed gas was continuously introduced into a column-type photobioreactor and cultured in an environment with a temperature of 25°C and a light intensity of 7500 lux to obtain the final algal solution.

[0028] (3) Biomass determination: In step (2), after 1, 3, 5, 7, and 9 days of cultivation, the algal solution was collected, and the growth trend of algal cells at different cultivation days was measured using a UV spectrophotometer at 750 nm. The results are as follows. Figure 2 As shown.

[0029] Immediately after inoculating the seed culture in step (2), the algal culture was collected and its OD value was measured. 750 The result was that the initial inoculation OD 750 On day 9 of culture, 100 mL of the algal solution obtained in step (2) was taken, and algal cells were collected by centrifugation at 5000 r / min for 5 min. The cells were transferred to a 50 mL centrifuge tube, washed twice with PBS solution, placed at -80℃ overnight (14 h), and then freeze-dried to constant weight to obtain dry algal powder. The biomass was obtained by weighing the dry algal powder and calculating the biomass yield. The calculation formula is as follows: Initial biomass (g / L) = Initial inoculation OD 750 ×0.2(1-1) (1-2) The results are as follows Figure 3 As shown, the addition of 2.5 mg / L ZIF-8 resulted in a biomass of 4.40 g / L and a biomass yield of 448.37 mg / L / d for *Syngonium moniliforme* after 9 days of culture.

[0030] Simultaneously, the specific growth rate of *Single-needle Algae* was calculated using the following formula: (1-3) The results are as follows Figure 4 As shown, the specific growth rate of *Synapticulata* is 0.28 d. -1 .

[0031] Simultaneously, the carbon dioxide fixation efficiency of *Algae moniliformis* was calculated using the following formula: (1-4) The results are as follows Figure 5 As shown, the carbon dioxide fixation efficiency of *Synystoma moniliforme* is 0.82 g CO2 / L / d.

[0032] (4) Determination of oil content: Weigh 0.15g of the dried algae powder obtained in step (3), grind and mix it with 0.3g of quartz sand, collect the algae sample obtained from grinding into a 10mL EP tube, wash the algae sample remaining on the mortar into the EP tube with 5mL of chloroform-methanol solution (chloroform to methanol volume ratio of 2:1), shake and mix, centrifuge, transfer the upper organic phase to a 50mL centrifuge tube, continue to add 3mL of chloroform-methanol solution to the lower precipitate, repeat the extraction 3 times until the algae turn white; dry the obtained upper organic phase in an oven at 37℃ to constant weight, the difference between the mass of the 50mL centrifuge tube itself and the mass of the 50mL centrifuge tube after drying is the oil mass, calculate the oil content and oil yield using the following formula: (1-5) (1-6) The results are as follows Figure 6 As shown, the oil content in the dried algae powder is 46.31%, and the oil yield is 207.69 mg / L / d.

[0033] (5) Determination of total nitrogen and total phosphorus content: The total nitrogen content in the seed culture at different time points was determined according to the potassium persulfate digestion-hydrazine sulfate reduction method (EPA-METHOD): Algal culture was collected at 1, 3, 5, 7, and 9 days after culture in step (2). The culture was centrifuged at 7000 r / min for 5 min, and the supernatant was collected. 0.5 mL of the supernatant was transferred to a 25 mL stoppered graduated tube and diluted to 10 mL with pure water. Additionally, 10 mL of pure water was used as a blank control. 5 mL of alkaline potassium persulfate was added to each tube, and the tubes were placed in an autoclave at 120℃ and a pressure of 1.1-1.4 kg / cm². 2 Digestion was performed for 30 minutes; 1 mL of 10% hydrochloric acid solution was added uniformly, and water was added to bring the volume to 25 mL; the results were obtained using a fully automated discrete chemical analyzer. Figure 7 As shown, the total nitrogen content in the seed culture was 105.50 mg / L on day 9 of cultivation. Compared with the original total nitrogen content in the artificial high-phosphorus wastewater, the total nitrogen removal rate was 57.33% on day 9 of cultivation.

[0034] The total phosphorus content in seed culture at different time points was determined according to the potassium persulfate digestion-molybdenum antimony method (GB11893-1989): 0.5 mL of supernatant was transferred to a 50 mL stoppered graduated tube, and the volume was adjusted to 25 mL with water. Additionally, 10 mL of pure water was used as a blank control. 4 mL of potassium persulfate solution was added to each tube, and after mixing, the tube was capped and placed in an autoclave at 120°C and a pressure of 1.1-1.4 kg / cm². 2 The solution was boiled for 30 minutes, cooled to room temperature, and diluted to 50 mL with pure water. The solution was then analyzed using an automated discrete chemical analyzer. The results are as follows: Figure 8As shown, the total phosphorus content in the seed culture was 0.47 mg / L on day 9 of cultivation. Compared with the original total phosphorus content in the artificial high-phosphorus wastewater, the total phosphorus removal rate was 97.48% on day 9 of cultivation.

[0035] In the 2.5 mg / L ZIF-8 treatment group, the nitrogen removal rate continuously increased during the first seven days of culture, reaching a maximum of 69.26% on the seventh day, at which point the remaining nitrogen content in the culture medium was at its lowest value of 76.00 mg / L. On the ninth day of culture, the remaining nitrogen content in the culture medium was 105.50 mg / L, representing a nitrogen removal rate of 57.33%. The 2.5 mg / L ZIF-8 treatment group showed significant phosphorus removal effect from the first day of culture, with a phosphorus removal rate of 96.41%, and reaching a maximum of 99.82% on the third day, demonstrating a significant phosphorus removal effect. By the ninth day of culture, the remaining phosphorus content in the culture medium was 0.47 mg / L, representing a phosphorus removal rate of 97.48%.

[0036] Comparative Example 1 The difference between this comparative example and Example 1 is that no external ZIF-8 was applied in step (2), and it was set as the CK group. All other steps are the same as in Example 1.

[0037] The biomass of *Synapticola* obtained in this comparative example was measured to be 2.68 g / L, with a biomass yield of 256.95 mg / L / d and a specific growth rate of 0.22 d. -1 The carbon dioxide fixation efficiency was 0.47 g CO2 / L / d; the oil content was 36.56%, and the oil yield was 93.91 mg / L / d. After the culture was completed, the remaining contents of total nitrogen and total phosphorus in the culture medium were 82.17 mg / L and 0.48 mg / L, respectively, with a total nitrogen removal rate of 66.77% and a total phosphorus removal rate of 97.44%.

[0038] Compared with Example 1, Comparative Example 1 showed a significant decrease in biomass, biomass yield, specific growth rate, carbon dioxide fixation efficiency, oil content, and oil yield when using Monophylla alone.

[0039] Example 2 ZIF-8 promotes mononephrite algae Monoraphidium The specific steps for using sp. QLZ-3 to remove phosphorus, fix carbon, and eliminate accumulated grease are as follows: (1) Cultivation and collection of seed culture: Add 250 mL of BG-11 medium to a 500 mL Erlenmeyer flask and inoculate with *Syngonium moniliforme*. Monoraphidium sp. QLZ-3 was cultured as a mononephrite algae in a shaker at 25℃, 150 r / min, and 4000 lux of light. Monoraphidium sp. QLZ-3, up to mononephrite algae Monoraphidiumsp. QLZ-3 was grown to the late logarithmic growth phase; the cultured algal solution was left to stand on an indoor operating table for 48 hours, and then the upper supernatant was removed in a clean bench. The lower layer of algal cells was mixed evenly with the residual culture medium to form the seed culture.

[0040] (2) Mix 1.7g of standard BG-11 powder with 50mg of dipotassium hydrogen phosphate, and dilute with water to 1L to prepare artificial high-phosphorus wastewater. At the same time, add ZIF-8 to the artificial high-phosphorus wastewater at a dosage of 1.25mg / L. Transfer the artificial high-phosphorus wastewater with added ZIF-8 to a column photobioreactor and add the seed liquid obtained in step (1) to ensure that the concentration of microalgae in the artificial high-phosphorus wastewater is 0.36g / L.

[0041] A 3% CO2 mixed gas was continuously introduced into a column-type photobioreactor and cultured in an environment with a temperature of 25°C and a light intensity of 7500 lux to obtain the final algal solution.

[0042] (3) Biomass determination: In step (2), after 1, 3, 5, 7, and 9 days of cultivation, the algal solution was collected, and the growth trend of algal cells at different cultivation days was measured using a UV spectrophotometer at 750 nm. The results are as follows. Figure 2 As shown.

[0043] On day 9 of culture, take 100 mL of the algal solution obtained in step (2), centrifuge at 5000 r / min for 5 min to collect algal cells, transfer to a 50 mL centrifuge tube, wash twice with PBS solution, place at -80℃ overnight (14 h), and freeze dry to constant weight to obtain dry algal powder. Weigh the dry algal powder to obtain biomass and calculate the biomass yield. The calculation formula is shown in Equations 1-1 and 1-2 of Example 1.

[0044] The results are as follows Figure 3 As shown, the addition of 1.25 mg / L ZIF-8 resulted in a biomass of 3.41 g / L and a biomass yield of 338.51 mg / L / d for *Syngonium moniliforme* after 9 days of culture.

[0045] Simultaneously, the specific growth rate of *Synapticulata* was calculated using the formulas shown in Equations 1-3 of Example 1, and the results are as follows: Figure 4 As shown, the specific growth rate of *Synapticulata* is 0.25 d. -1 .

[0046] The formula for calculating carbon dioxide fixation efficiency is shown in Equations 1-4 of Example 1, and the results are as follows: Figure 5 As shown, the carbon dioxide fixation efficiency of *Synystoma moniliforme* is 0.62 g CO2 / L / d.

[0047] (4) Determination of oil content: Weigh 0.15g of the dry algae powder obtained in step (3), grind and mix it with 0.3g of quartz sand, collect the algae sample obtained from grinding into an EP tube with a volume of 10mL, wash the algae sample remaining on the mortar into the EP tube with 5mL of chloroform-methanol solution (the volume ratio of chloroform to methanol is 2:1), shake and mix, centrifuge, transfer the upper organic phase to a 50mL centrifuge tube, continue to add 3mL of chloroform-methanol solution to the lower precipitate, repeat the extraction 3 times until the algae turn white; dry the obtained upper organic phase in an oven at 37℃ to constant weight, the difference between the mass of the 50mL centrifuge tube itself and the mass of the 50mL centrifuge tube after drying is the oil content, the formula for calculating the oil content is shown in Formula 1-5 of Example 1, and the formula for calculating the oil yield is shown in Formula 1-6 of Example 1.

[0048] The results are as follows Figure 6 As shown, the oil content in the dried algae powder is 34.80%, and the oil yield is 117.77 mg / L / d.

[0049] (5) Determination of total nitrogen and total phosphorus content: The total nitrogen content in the seed culture at different time points was determined according to the potassium persulfate digestion-hydrazine sulfate reduction method (EPA-METHOD): Algal culture was collected at 1, 3, 5, 7, and 9 days after culture in step (2). The culture was centrifuged at 7000 r / min for 5 min, and the supernatant was collected. 0.5 mL of the supernatant was transferred to a 25 mL stoppered graduated tube and diluted to 10 mL with water. Additionally, 10 mL of pure water was used as a blank control. 5 mL of alkaline potassium persulfate was added to each tube, and the mixture was placed in an autoclave at 120℃ and a pressure of 1.1-1.4 kg / cm². 2 Digestion was performed for 30 minutes; 1 mL of 10% hydrochloric acid solution was added uniformly, and water was added to bring the volume to 25 mL; the results were obtained using a fully automated discrete chemical analyzer. Figure 7 As shown, the total nitrogen content in the seed culture was 139.83 mg / L on day 9 of cultivation. Compared with the original total nitrogen content in the artificial high-phosphorus wastewater, the total nitrogen removal rate was 43.44% on day 9 of cultivation.

[0050] The total phosphorus content in seed culture at different time points was determined according to the potassium persulfate digestion-molybdenum antimony method (GB11893-1989): 0.5 mL of supernatant was transferred to a 50 mL stoppered graduated tube, and the volume was adjusted to 25 mL with water. Additionally, 10 mL of pure water was used as a blank control. 4 mL of potassium persulfate solution was added to each tube, and after mixing, the tube was capped and placed in an autoclave at 120°C and a pressure of 1.1-1.4 kg / cm². 2 The solution was boiled for 30 minutes, cooled to room temperature, and diluted to 50 mL with pure water. The solution was then analyzed using an automated discrete chemical analyzer. The results are as follows: Figure 8As shown, the total phosphorus content in the seed culture was 0.44 mg / L on day 9 of cultivation. Compared with the original total phosphorus content in the artificial high-phosphorus wastewater, the total phosphorus removal rate on day 9 of cultivation was 97.65%.

[0051] Example 3 ZIF-8 promotes mononephrite algae Monoraphidium The specific steps for using sp. QLZ-3 to remove phosphorus, fix carbon, and eliminate accumulated grease are as follows: (1) Cultivation and collection of seed culture: Add 250 mL of BG-11 medium to a 500 mL Erlenmeyer flask and inoculate with *Syngonium moniliforme*. Monoraphidium sp. QLZ-3 was cultured as a mononephrite algae in a shaker at 25℃, 150 r / min, and 4000 lux of light. Monoraphidium sp. QLZ-3, up to mononephrite algae Monoraphidium sp. QLZ-3 was grown to the late logarithmic growth phase; the cultured algal solution was left to stand on an indoor operating table for 48 hours, and then the upper supernatant was removed in a clean bench. The lower layer of algal cells was mixed evenly with the residual culture medium to form the seed culture.

[0052] (2) Mix 1.7g of standard BG-11 powder with 50mg of dipotassium hydrogen phosphate, and dilute with water to 1L to prepare artificial high-phosphorus wastewater. At the same time, add ZIF-8 to the artificial high-phosphorus wastewater at a dosage of 5.0mg / L. Transfer the artificial high-phosphorus wastewater with added ZIF-8 to a column photobioreactor and add the seed liquid obtained in step (1) to ensure that the concentration of microalgae in the artificial high-phosphorus wastewater is 0.36g / L.

[0053] A 3% CO2 mixed gas was continuously introduced into a column-type photobioreactor and cultured in an environment with a temperature of 25°C and a light intensity of 7500 lux to obtain the final algal solution.

[0054] (3) Biomass determination: In step (2), after 1, 3, 5, 7, and 9 days of cultivation, the algal solution was collected, and the growth trend of algal cells at different cultivation days was measured using a UV spectrophotometer at 750 nm. The results are as follows. Figure 2 As shown.

[0055] On day 9 of culture, take 100 mL of the algal solution obtained in step (2), centrifuge at 5000 r / min for 5 min to collect algal cells, transfer to a 50 mL centrifuge tube, wash twice with PBS solution, place at -80℃ overnight (14 h), and freeze dry to constant weight to obtain dry algal powder. Weigh the dry algal powder to obtain biomass and calculate the biomass yield. The calculation formula is shown in Equations 1-1 and 1-2 of Example 1.

[0056] The results are as follows Figure 3 As shown, the addition of 5.0 mg / L ZIF-8 resulted in a biomass of 2.90 g / L and a biomass yield of 282.09 mg / L / d for *Syngonium moniliforme* after 9 days of culture.

[0057] Simultaneously, the specific growth rate of *Synapticus simulans* was calculated using the formulas shown in Equations 1-3 of Example 1, and the results are as follows: Figure 4 As shown, the specific growth rate of *Synapticus monophylla* was 0.23 d. -1 .

[0058] The formula for calculating the carbon dioxide fixation efficiency is shown in Equations 1-4 of Example 1, and the results are as follows: Figure 5 As shown, the carbon dioxide fixation efficiency of *Synystoma moniliforme* is 0.52 g CO2 / L / d.

[0059] (4) Determination of oil content: Weigh 0.15g of the dry algae powder obtained in step (3), grind and mix it with 0.3g of quartz sand, collect the algae sample obtained from grinding into an EP tube with a volume of 10mL, wash the algae sample remaining on the mortar into the EP tube with 5mL of chloroform-methanol solution (the volume ratio of chloroform to methanol is 2:1), shake and mix, centrifuge, transfer the upper organic phase to a 50mL centrifuge tube, continue to add 3mL of chloroform-methanol solution to the lower precipitate, repeat the extraction 3 times until the algae turn white; dry the obtained upper organic phase in an oven at 37℃ to constant weight, the difference between the mass of the 50mL centrifuge tube itself and the mass of the 50mL centrifuge tube after drying is the oil content, the formula for calculating the oil content is shown in Formula 1-5 of Example 1, and the formula for calculating the oil yield is shown in Formula 1-6 of Example 1.

[0060] The results are as follows Figure 6 As shown, the oil content in the dried algae powder is 38.72%, and the oil yield is 109.22 mg / L / d.

[0061] (5) Determination of total nitrogen and total phosphorus content: The total nitrogen content in the seed culture at different time points was determined according to the potassium persulfate digestion-hydrazine sulfate reduction method (EPA-METHOD): Algal culture was collected at 1, 3, 5, 7, and 9 days after culture in step (2). The culture was centrifuged at 7000 r / min for 5 min, and the supernatant was collected. 0.5 mL of the supernatant was transferred to a 25 mL stoppered graduated tube and diluted to 10 mL with water. Additionally, 10 mL of pure water was used as a blank control. 5 mL of alkaline potassium persulfate was added to each tube, and the mixture was placed in an autoclave at 120℃ and a pressure of 1.1-1.4 kg / cm². 2 Digestion was performed for 30 minutes; 1 mL of 10% hydrochloric acid solution was added uniformly, and water was added to bring the volume to 25 mL; the results were obtained using a fully automated discrete chemical analyzer. Figure 7As shown, the total nitrogen content in the seed culture was 88.67 mg / L on day 9 of cultivation. Compared with the original total nitrogen content in the artificial high-phosphorus wastewater, the total nitrogen removal rate was 64.14% on day 9 of cultivation.

[0062] The total phosphorus content in seed culture at different time points was determined according to the potassium persulfate digestion-molybdenum antimony method (GB11893-1989): 0.5 mL of supernatant was transferred to a 50 mL stoppered graduated tube, and the volume was adjusted to 25 mL with water. Additionally, 10 mL of pure water was used as a blank control. 4 mL of potassium persulfate solution was added to each tube, and after mixing, the tube was capped and placed in an autoclave at 120°C and a pressure of 1.1-1.4 kg / cm². 2 The solution was boiled for 30 minutes, cooled to room temperature, and diluted to 50 mL with pure water. The solution was then analyzed using an automated discrete chemical analyzer. The results are as follows: Figure 8 As shown, the total phosphorus content in the seed culture was 0.11 mg / L on day 9 of cultivation. Compared with the original total phosphorus content in the artificial high-phosphorus wastewater, the total phosphorus removal rate was 99.40% on day 9 of cultivation.

[0063] In summary, when cultured to day 9, the OD of *Synapticulata* in the 2.5 mg / L ZIF-8 treatment group was... 750 The value was 14.99, which was significantly higher than the control group by 50.11%, significantly higher than the 1.25 mg / L ZIF-8 treatment group by 16.43%, and significantly higher than the 5.0 mg / L ZIF-8 treatment group by 57.72%.

[0064] The biomass of *Neurophyta* in the 2.5 mg / L ZIF-8 treatment group was 4.40 g / L, which was significantly higher than that of the control group by 64.08%, significantly higher than that of the 1.25 mg / L ZIF-8 treatment group by 29.00%, and significantly higher than that of the 5.0 mg / L ZIF-8 treatment group by 51.67%. The biomass yield of *Neurophyta* in the 2.5 mg / L ZIF-8 treatment group was 448.37 mg / L / d, which was significantly higher than that of the control group by 74.50%, significantly higher than that of the 1.25 mg / L ZIF-8 treatment group by 32.45%, and significantly higher than that of the 5.0 mg / L ZIF-8 treatment group by 58.94%.

[0065] The specific growth rate of *Synapticulata* in the 2.5 mg / L ZIF-8 treatment group was 0.28 d. -1 Compared with the control group, it was significantly improved by 25.70%, compared with the 1.25 mg / L ZIF-8 treatment group by 11.40%, and compared with the 5.0 mg / L ZIF-8 treatment group by 19.81%.

[0066] The carbon dioxide fixation efficiency of *Synapticulata* in the 2.5 mg / L ZIF-8 treatment group was 0.82 g CO2 / L / d, which was significantly higher than that of the control group by 74.50%, significantly higher than that of the 1.25 mg / L ZIF-8 treatment group by 32.45%, and significantly higher than that of the 5.0 mg / L ZIF-8 treatment group by 58.94%.

[0067] The lipid content of *Synechocera monophylla* in the 2.5 mg / L ZIF-8 treatment group was 46.31%, which was significantly higher than that of the control group by 26.66%, significantly higher than that of the 1.25 mg / L ZIF-8 treatment group by 33.07%, and significantly higher than that of the 5.0 mg / L ZIF-8 treatment group by 19.60%. The lipid yield of *Synechocera monophylla* in the 2.5 mg / L ZIF-8 treatment group was 207.69 mg / L / d, which was significantly higher than that of the control group by 121.15%, significantly higher than that of the 1.25 mg / L ZIF-8 treatment group by 76.35%, and significantly higher than that of the 5.0 mg / L ZIF-8 treatment group by 90.15%.

[0068] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. Application of ZIF-8 in inducing microalgae growth, carbon fixation, and oil accumulation in phosphorus-containing wastewater.

2. The application according to claim 1, characterized in that, The specific operation of its application is as follows: (1) Inoculate the mononechoalveolar algae into the culture medium and cultivate the seed culture; (2) Inoculate the seed solution into phosphorus-containing wastewater and add ZIF-8 to culture the algae solution.

3. The method according to claim 2, characterized in that, In step (2), the concentration of ZIF-8 in the phosphorus-containing wastewater is 1.25~5 mg / L.

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