A method for enhancing carbon sequestration and water purification of microalgae biofilm based on metal organic framework material

Abstract

The present application belongs to the technical field of carbon capture and sewage treatment, and discloses a method for carbon fixation and water purification based on metal organic framework material enhanced microalgae biofilm, which comprises the following steps: adding different types and concentrations of MOF materials to the microalgae biofilm culture system, and carrying out microalgae biofilm culture and sewage treatment under natural light or artificial light supplement. The present application utilizes the unique property of MOF materials that can adsorb CO2 to accelerate the enrichment of CO2 in the gaseous environment to the microalgae biofilm system; at the same time, CO2 produced by the respiration of microalgae and bacteria in the biofilm is captured to form a microalgae biofilm growth condition with sufficient inorganic carbon supply; and the microporous channels formed in the biofilm due to the addition of MOF materials can improve the mass transfer conditions inside the biofilm. The method is simple and easy to operate, can fix a large amount of dissolved CO2 in water, and can obtain a large amount of microalgae biomass while realizing the synergistic effect of pollution reduction and carbon reduction.

Description

Technical Field

[0001] This invention belongs to the field of carbon capture and wastewater treatment technology, and relates to a method for carbon fixation and water purification based on metal-organic framework materials to enhance microalgal biofilms. Background Technology

[0002] The burning of fossil fuels and the consumption of non-renewable energy sources lead to massive emissions of greenhouse gases such as CO2, causing sea-level rise and frequent severe weather events, posing a serious threat to life and property. CO2 capture and utilization are urgently needed. Like most terrestrial plants, microalgae can fix CO2 through photosynthesis, with a photosynthetic efficiency 10 to 50 times higher than that of terrestrial plants. They have great potential in CO2 capture and possess advantages such as short lifespan and strong environmental adaptability. Cultivating microalgae in biofilm form, compared to traditional suspended microalgae culture systems, will further reduce the cost of microalgae biomass harvesting and help improve the quality and efficiency of CO2 fixation by microalgae. However, providing pure CO2 at a certain concentration to microalgae or adding bicarbonate as an inorganic carbon source to the microalgae culture medium will increase the total cost of microalgae cultivation. If microalgae can utilize CO2 produced by domestic sewage and bacterial respiration, the addition of exogenous inorganic carbon sources can be saved. However, CO2 has a short residence time in algal solutions, making it difficult to convert into soluble carbon sources. Therefore, it is necessary to increase the residence time of CO2 in water to promote a shift in chemical equilibrium towards soluble carbon sources. Most solid adsorbents have poor CO2 adsorption capacity in solution. Liu Xiangjun et al. reported in "Modeling of CO2 adsorption and recovery from wet flue gas by using activated carbon" that activated carbon's CO2 adsorption capacity decreased by 23.37% at 100% relative humidity compared to a gas environment with 0% relative humidity. Mark J. Purdue et al. reported in "Molecular simulation study of wet flue gas adsorption on zeolite 13X" that zeolite's CO2 adsorption capacity decreased by 99.99% at 100% relative humidity compared to a gas environment with 0% relative humidity. Compared with traditional adsorbents such as metal oxides and zeolites, metal-organic frameworks (MOFs) are among the most promising CO2 adsorbents due to their unsaturated metal sites, high specific surface area and adjustable pore channels, and also have the adsorption effect on heavy metals, dyes and other adsorbents.For example, Zhao Lun et al. reported in their article "Application of ametal cobalt based on 4,6-Bis(imidazol-1-yl)isophthalic acid Metal-Organic-Framework materials in photocatalytic CO2 Reduction, Antibacterial, and Dye Adsorption" that MOF (Co) achieved a removal rate of 83.42% for CR (Congo Red dye) after 60 min; Alejandro Zepeda et al. reported in their article "Synthesis of a new co-Metal-Organic Framework assembled from 5,10,15,20-Tetrakis((pyridin-4-yl)phenyl)porphyri“Co-MTPhPyP” and its application to the removal of heavy metals The article "ions" reports that a synthetic Co-based porphyrin MOF (Co-MTPhPyP) exhibits a Pb(II) adsorption capacity of up to 458.8 mg / g after 30 minutes, and still reaches 383.4 mg / g after 2 hours. However, while adsorbing CO2, heavy metals, and dyes, the MOF (Co) does not significantly promote microalgal growth. Some trace elements, although present in low concentrations in water, can significantly influence microalgal growth and are essential components of key enzymes in microalgal photosynthesis. When MOFs remain in solution for extended periods, metal ions may dissolve, which can replenish certain trace elements needed for microalgal growth, acting as cofactors to promote photosynthesis and other biochemical reactions, thereby promoting microalgal growth. Simultaneously, microalgal growth is accompanied by the absorption of large amounts of nutrients such as nitrogen and phosphorus, thus enhancing the removal efficiency of pollutants like nitrogen and phosphorus from wastewater. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a method for enhancing carbon sequestration and water purification in microalgal biofilms based on metal-organic framework (MOF) materials. Different concentrations of metal elements have varying effects on microalgal growth; adding different concentrations of MOF materials controls the metal element concentration in the microalgal biofilm culture system. The method provided by this invention enables efficient utilization of CO2 generated by microorganisms in air and wastewater, efficient accumulation and conversion of high-value-added components in biomass, and efficient removal of nitrogen and phosphorus pollutants from wastewater, achieving a synergistic effect of pollution reduction and carbon reduction in microalgal wastewater treatment technology.

[0004] The technical solution of the present invention:

[0005] A method for enhancing carbon sequestration and water purification in microalgal biofilms based on metal-organic framework materials, comprising the following steps:

[0006] (1) Establishing a microalgae biofilm culture system;

[0007] The microalgae biofilm culture system is formed by inoculating microalgae 1 onto attachment carrier 4 to form microalgae biofilm 8, using wastewater 7 as the culture medium, and culturing under light 3.

[0008] (2) Different types and concentrations of MOF materials were added to the microalgae biofilm culture system.

[0009] Different types and concentrations of MOF materials were added to the microalgae biofilm culture system. Among them, metal-organic framework 2 has the function of adsorbing CO25, and the metal elements in metal-organic framework 2 are trace metal elements such as iron or magnesium that can promote the growth of microalgae.

[0010] The culture conditions for light 3 are natural light or artificial light, or natural light supplemented with artificial light.

[0011] The attachment carrier 4 is a carrier material that facilitates the adhesion of microalgae and the formation of biofilms, such as polystyrene with TC coating, polymethyl methacrylate, etc.

[0012] The ratio of the concentration of metal-organic framework 2 to the total phosphorus concentration in wastewater 7 is (10-40):9.

[0013] Metal-organic frameworks (MOFs) are modified MOFs that are more prone to CO2 adsorption. This is achieved by introducing auxiliary ligands (such as tripyridine ligands) or inert metal ions (such as Cr(III) or Rh(III)) during the synthesis of MOFs, or by introducing hydrophobic functional groups (such as carbon straight chains, isopropyl groups, butylene groups, etc.) after synthesis to improve the water resistance and alkali resistance of the structure.

[0014] The culture method is batch, semi-continuous, or continuous culture, and the culture conditions are controlled or uncontrolled bacteria.

[0015] The beneficial effects of this invention are as follows: This invention provides a method for enhancing carbon fixation and water purification in microalgal biofilms based on metal-organic frameworks (MOFs). This method is simple to operate and low in cost. By utilizing the unique structural characteristics of MOFs, this invention prolongs the residence time of CO2 in solution, achieving effective CO2 fixation and increasing the available carbon source for microalgae. Furthermore, the dissolution of metal ions from the MOF material provides essential trace elements for microalgal growth. High-efficiency microalgal growth is accompanied by high-efficiency water purification, with total nitrogen removal efficiency reaching over 97% and total phosphorus removal efficiency reaching 95%. The large amount of microalgal biomass obtained can be used for further resource conversion. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a microalgae biofilm culture system;

[0017] Figure 2 The diagram below shows the results of Example 1, where (a) is a graph showing the change in dry weight of microalgal biofilm under different concentrations of MIL-101 (Fe); (b) is a graph showing the change in biomass composition; (c) is a graph showing the change in total nitrogen pollutant removal; and (d) is a graph showing the change in total phosphorus pollutant removal.

[0018] Figure 3 The diagram below shows the results of Example 2, where (a) is a graph showing the change in dry weight of microalgal biofilm under different concentrations of MOF-74 (Mg); (b) is a graph showing the change in biomass composition; (c) is a graph showing the change in total nitrogen pollutant removal; and (d) is a graph showing the change in total phosphorus pollutant removal.

[0019] Figure 4 The diagram below shows the results of Comparative Example 1, where (a) is a graph showing the change in dry weight of microalgal biofilm under different concentrations of MOF-74(Co); (b) is a graph showing the change in biomass composition; (c) is a graph showing the change in total nitrogen pollutant removal; and (d) is a graph showing the change in total phosphorus pollutant removal.

[0020] In the diagram: 1. Microalgae; 2. Metal-organic framework; 3. Light; 4. Attachment carrier; 5. CO2; 6. Gas phase; 7. Wastewater; 8. Microalgae biofilm. Detailed Implementation

[0021] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0022] Example 1

[0023] Chlorella in its logarithmic growth phase was treated at 3–6 g / m³. 2 The initial inoculum was increased by adding 0-20 mg / L of MIL-101 (Fe), and wastewater was added. The mixture was cultured for 12 days in a TC-coated polystyrene six-well plate under the following conditions: a light-dark cycle of 16 h / 8 h, a light intensity of 4000 Lux, and a temperature of 25 ± 2 ℃.

[0024] For the first four days, wastewater was collected daily from above the microalgal biofilm to measure total nitrogen and total phosphorus concentrations. After the microalgal biofilm formed on the fourth day following inoculation, total nitrogen and total phosphorus concentrations were measured every two days, and the biofilm was resuspended to determine its dry weight. Microalgal biofilm was collected every four days to analyze the carbon fixation status of the microalgae. Figure 2 (a) The dry weight of the microalgal biofilm generally increased over time. In the first 4 days, the microalgae had not adapted to the addition of MIL-101(Fe), and the dry weight accumulation was relatively slow. In the following 8 days, the microalgae adapted to the environment and grew rapidly. At 10 mg / MIL-101(Fe), the maximum dry weight accumulation was 15.8 g / m³ on day 12. 2 . Figure 2 (b) shows the composition of biomass. In the early stage of the experiment, the contents of protein, total sugar and total lipid were similar. In the middle and later stages of the experiment, the sugar content was greater than the total lipid content, which was greater than the protein content. At the addition of 10 mg / LMIL-101(Fe), the total lipid content accumulated to the highest level in the later stage of the experiment, reaching 37%. Figure 2 (c)2(d) shows the removal of total nitrogen and total phosphorus. The overall nitrogen and phosphorus concentrations showed a decreasing trend. At a concentration of 10 mg / L MIL-101(Fe), the total phosphorus removal rate reached a maximum of 95%. In the first 6 days, the total nitrogen concentration decreased rapidly. After the 6th day, the removal rate leveled off and slightly increased, possibly because the concentrations of nitrogen, phosphorus, and other nutrients for microalgae growth in the wastewater were too low to be utilized in the later stages of the experiment. At a concentration of 10 mg / L MIL-101(Fe), the total nitrogen removal rate reached a maximum of 97% on the 6th day. Fe is an essential trace element for the photosynthetic growth of microalgae. Previous studies have reported that the leaching rate of iron ions during long-term soaking with MIL-101(Fe) is approximately 30%. When the concentration of MIL-101(Fe) is low, the concentration of leached iron ions is low, and iron ions can promote microalgae growth as a trace element. When the concentration of MIL-101(Fe) is too high, the concentration of leached iron ions is too high, which can have an effect similar to heavy metal toxicity on microalgae cells, inhibiting microalgae growth. Taking a 10 mg / L MIL-101 (Fe) addition as an example, the leached iron ion concentration is about 0.7 mg / L, which is close to the iron ion concentration of 0.9 mg / L in the conventional microalgae culture medium BBM medium. Therefore, this addition dosage is most conducive to microalgae growth.

[0025] Example 2

[0026] Except for the following differences, everything else is the same as in Example 1.

[0027] The metal-organic framework material added is MOF-74(Mg). Figure 3 (a) The dry weight growth of microalgal biofilms with different concentrations of MOF-74(Mg) is shown. The overall dry weight accumulation of the biofilm showed an upward trend, with the highest accumulation of 16.2 g / m³ on day 12 at a concentration of 15 mg / L. 2 It promotes the growth of microalgae while removing large amounts of nitrogen and phosphorus. Figure 3 (b) shows the composition of biomass. The total sugar content generally showed an upward trend followed by a downward trend, the protein content generally showed an upward trend, and the total lipid content generally showed a downward trend. On day 12, the total lipid content was around 10%. Figure 3(c)3(d) shows the removal of total nitrogen and total phosphorus. The overall concentrations of total nitrogen and total phosphorus showed a decreasing trend. With a MOF-74(Mg) addition concentration of 15 mg / L, the total phosphorus removal rate reached its maximum of 94% on day 12. In the first 6 days, the total nitrogen concentration decreased rapidly; after day 6, the rate of decrease slowed and slightly increased. The highest total nitrogen removal rate, reaching 95%, was achieved on day 12 with a MOF-74(Mg) addition concentration of 15 mg / L. Magnesium plays an important role in chlorophyll synthesis and photosynthesis in microalgae, and appropriate concentrations of magnesium ions can promote photosynthetic growth. MOF-74(Mg) is structurally unstable in solution. Existing studies have shown that the leaching rate of magnesium ions during long-term immersion is approximately 44%, and this process is accompanied by the diffusion of organic ligands in the solution. Previous studies have reported that the MOF-74(Mg) ligand 2,5-dihydroxyterephthalic acid promotes microalgal cell growth at low concentrations, but when the ligand concentration reaches 5 mg / L, microalgal cell growth is inhibited. At a dosage of 20 mg / L MOF-74(Mg), the release of organic ligands exceeded 5 mg / L, resulting in the inhibition of microalgal cell growth by the ligands and significantly offsetting the growth-promoting effect of leached magnesium ions. Therefore, 15 mg / L MOF-74(Mg) is most beneficial for microalgal growth.

[0028] As can be seen from the above examples, the metal-organic framework material MIL-101(Fe) with an addition concentration of 10 mg / L can achieve a high total nitrogen and total phosphorus removal efficiency and obtain a large amount of biomass.

[0029] Comparative Example 1

[0030] Except for the following differences, everything else is the same as in Example 1.

[0031] The metal-organic framework material added is MOF-74(Co). Figure 4 (a) The dry weight of microalgal biofilms with different concentrations of MOF-74(Co) increased over time. However, during the cultivation stage, the dry weight of the biofilms in the experimental group was lower than that in the control group. The results showed that the addition of MOF-74(Co) inhibited the growth of microalgae. Figure 4 (b) shows the biomass composition. On day 12, the total amount of biomass in the experimental group was lower than that in the control group. Figure 4 (c)4(d) shows the removal of total nitrogen and total phosphorus. The results indicate that different concentrations have a removal effect on both total nitrogen and total phosphorus. The overall concentrations of total nitrogen and total phosphorus show a decreasing trend. In the control group, the total nitrogen concentration decreased significantly in the first 6 days, reaching a maximum removal rate of 97% on the 6th day. The decreasing trend was relatively gradual in the following 6 days, and the removal rate was still higher than that of the experimental group on the 12th day. The removal of total phosphorus in the control group was better than that in the experimental group, reaching a maximum removal rate of 91% on the 12th day. In conclusion, the addition of MOF-74(Co) is not conducive to the growth of microalgae, possibly because Co in MOF is not readily available. 2+Ion release damages microalgal cells, thereby inhibiting microalgal growth.

[0032] The above description is merely an embodiment of the present invention. It should be noted that those skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A method for enhancing carbon sequestration and water purification by microalgae biofilm based on metal-organic framework material, characterized in that, The steps are as follows: (1) Build a microalgae biofilm culture system The microalgae biofilm culture system is that microalgae (1) are inoculated on an attached carrier (4) to form a microalgae biofilm (8), wastewater (7) is used as a culture medium, and culture is carried out under light (3) conditions; (2) Add different types and concentrations of MOF materials to the microalgae biofilm culture system Different types and concentrations of MOF materials are added to the microalgae biofilm culture system, wherein the metal organic framework (2) has the function of adsorbing CO2 (5), and the metal elements in the metal organic framework (2) can promote trace metal elements for microalgae growth; the metal elements are Fe and Mg; The ratio of the addition concentration of the metal organic framework (2) to the total phosphorus concentration in the wastewater (7) is (10-40):9; The metal organic framework (2) is a modified MOF, that is, auxiliary ligands, inert metal ions are introduced during the synthesis of MOF, or hydrophobic functional groups are introduced after synthesis to improve the water resistance and alkali resistance of the structure; The auxiliary ligand is a tripyridine ligand; The inert metal ion is Cr(III) or Rh(III); The hydrophobic functional group is a carbon straight chain, isopropyl, or butylene; The attached carrier (4) is a carrier material that is conducive to microalgae adhesion and biofilm formation, including TC-coated polystyrene and polymethyl methacrylate.

2. The method of claim 1, wherein, The light (3) culture conditions are natural light or artificial light, or natural light supplemented with artificial light.

3. The method of claim 1, wherein, The culture is carried out in a batch, semi-continuous, or continuous manner, and the culture conditions are controlled or uncontrolled.

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