Method for enhancing microalgae biofilm carbon sequestration and water purification based on metal organic framework material

Abstract

The invention belongs to the technical field of carbon capture and sewage treatment, and discloses a method for enhancing microalgae biofilm carbon sequestration and water purification based on a metal organic framework material, which comprises the following steps: adding MOF materials with different types and concentrations into a microalgae biofilm culture system; and carrying out microalgae biological membrane culture and sewage treatment under natural illumination or artificial light supplement. By utilizing the unique property that the MOF material can adsorb CO2, the enrichment of CO2 in a gas phase environment to a microalgae biological membrane system is accelerated; meanwhile, CO2 generated by respiration of microalgae and bacteria in the biological membrane is captured, a microalgae biological membrane growth condition with sufficient inorganic carbon supply is formed, and a micro-pore channel formed in the biological membrane due to addition of the MOF material can also improve the mass transfer condition in the biological membrane. The method is simple and easy and convenient to operate, a large amount of CO2 dissolved in water can be fixed, and pollution reduction and carbon reduction synergistic interaction is achieved while a large amount of microalgae biomass is obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of carbon capture and sewage treatment, and relates to a method for enhancing carbon fixation of microalgae biofilm and water purification based on metal organic framework materials. Background Art

[0002] The combustion of fossil fuels and the consumption of non-renewable energy sources have led to CO 2 Large-scale greenhouse gas emissions such as CO2 have led to rising sea levels and frequent severe weather events, posing a serious threat to the safety of life and property. 2 Capture and utilization are imminent. Microalgae, like most terrestrial plants, can fix CO through photosynthesis. 2 , whose photosynthesis efficiency is 10 to 50 times that of terrestrial plants and has great potential in capturing CO 2 Compared with the traditional suspended microalgae culture system, the biofilm culture of microalgae will further reduce the cost of microalgae biomass harvesting and help microalgae fix CO 2 However, pure CO 2 Providing bicarbonate to microalgae at a certain concentration or adding it as an inorganic carbon source to the microalgae culture medium will increase the total cost of microalgae cultivation. 2 The utilization of microalgae can save the addition of exogenous inorganic carbon sources, but CO 2 The algae have a short residence time in the liquid and are difficult to convert into soluble carbon sources, so it is necessary to increase the CO 2 The residence time in water is to promote the chemical equilibrium to move toward the soluble carbon source. Most solid adsorbents are in solution and have a low CO 2 The adsorption capacity of CO is poor. 2 The article "Adsorption and recovery from wet flue gas by using activated carbon" reported that activated carbon has a good adsorption capacity for CO under the condition of 100% relative humidity. 2 The adsorption capacity of zeolite 13X decreased by 23.37% compared with the gas environment with a relative humidity of 0%. Mark J. Purdue et al. reported in the article "Molecular simulation study of wet flue gas adsorption on zeolite 13X" that zeolite has a low adsorption capacity for CO at a relative humidity of 100%. 2Compared with traditional adsorbents such as metal oxides and zeolites, metal-organic frameworks (MOFs) have become the most promising CO adsorbents due to their unsaturated metal sites, high specific surface area, and adjustable pore channels. 2 It is one of the adsorbents and has the adsorption effect of heavy metals and dyes. For example, Zhao Lun et al. in "Application of ametal cobalt based on4,6-Bis(imidazol-1-yl)isophthalicacidMetal-Organic-Framework materialsin photocatalytic CO 2 Reduction, Antibacterial, and Dye Adsorption” reported that the removal rate of CR (Congo red dye) by MOF (Co) reached 83.42% at 60 min; Alejandro Zepeda et al. reported in the article “Synthesis of a new co Metal-Organic Framework assembledfrom5,10,15,20-Tetrakis((pyridin-4-yl)phenyl)porphyri “Co-MTPhPyP” and its application to the removal of heavy metal ions” that a synthetic Co-based porphyrin MOF (Co-MTPhPyP) had an adsorption capacity of up to 458.8 mg / g for Pb(II) after 30 minutes, and the Pb(II) adsorption capacity could still reach 383.4 mg / g after 2 hours. However, MOF (Co) has a poor adsorption capacity in the adsorption of CO 2 , heavy metals, dyes, etc., but cannot significantly promote the growth of microalgae. Although some trace elements are at low concentrations in water, they can significantly affect the growth of microalgae and are necessary components of key enzymes for microalgae photosynthesis. When MOF stays in the solution for a long time, metal ions may be dissolved, which can supplement certain trace elements required for the growth of microalgae and promote biochemical reactions such as photosynthesis as auxiliary factors, thereby promoting the growth of microalgae. The growth of microalgae is accompanied by the absorption of a large amount of nutrients such as nitrogen and phosphorus, thereby improving the removal of pollutants such as nitrogen and phosphorus in sewage. Summary of the invention

[0003] In order to solve the above problems, the present invention provides a method for enhancing carbon fixation and water purification of microalgae biofilm based on metal organic framework materials. Different metal element concentrations have different effects on the growth of microalgae. Different concentrations of MOF materials are added to control the concentration of metal elements in the microalgae biofilm culture system. The method provided by the present invention can achieve the production of CO by microorganisms in air and sewage. 2 The efficient utilization of algae, the efficient accumulation and transformation of high value-added components in biomass, and the efficient removal of nitrogen and phosphorus pollutants in sewage can achieve the synergistic effect of pollution reduction and carbon reduction in microalgae wastewater treatment technology.

[0004] The technical solution of the present invention:

[0005] A method for enhancing carbon fixation and water purification of microalgae biofilm based on metal organic framework materials, the steps are as follows:

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

[0007] The microalgae biofilm culture system is that microalgae 1 is inoculated on an attachment carrier 4 to form a microalgae biofilm 8, sewage 7 is used as a culture medium, and cultured under light 3 conditions;

[0008] (2) Adding different types and concentrations of MOF materials 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 ability to adsorb CO 2 5. The metal elements in the metal organic framework 2 are trace metal elements such as iron or magnesium that can promote the growth of microalgae.

[0010] Light 3 The culture conditions are natural light or artificial light, or natural light supplemented by artificial light.

[0011] The attachment carrier 4 is a carrier material that is conducive to the adhesion of microalgae and the formation of biofilm, such as polystyrene or polymethyl methacrylate with TC coating.

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

[0013] Metal-organic framework 2 is more susceptible to CO adsorption 2 Improved MOF. That is, in the process of synthesizing MOF, auxiliary ligands (tripyridine ligands, etc.) and inert metal ions (Cr(III), Rh(III), etc.) are introduced, or hydrophobic functional groups (such as carbon straight chain, isopropyl, butylene, etc.) are introduced 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 bacteria or non-controlled bacteria.

[0015] Beneficial effects of the invention: The invention provides a method for enhancing carbon fixation and water purification of microalgae biofilm based on metal organic framework materials, which has the advantages of simple operation and low cost. The invention uses the unique structural characteristics of MOF to extend the CO 2 Residence time in solution to achieve CO 2 The effective fixation of MOF increases the available carbon source for microalgae; the dissolution of metal ions in MOF materials provides the necessary trace elements for the growth of microalgae. The efficient growth of microalgae is accompanied by efficient water purification, with a total nitrogen removal efficiency of more than 97% and a total phosphorus removal efficiency of 95%. The large amount of microalgae biomass obtained can be used for further resource conversion. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0017] Figure 2 Schematic diagram of the results of Example 1, wherein (a) is a graph showing the change in dry weight of microalgae 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 Schematic diagram of the results of Example 2, wherein (a) is a graph showing the change in dry weight of microalgae biofilm under different MOF-74 (Mg) concentration modes; (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 It is a schematic diagram of the results of Comparative Example 1, wherein (a) is a graph showing the change in dry weight of microalgae biofilm under different MOF-74 (Co) concentration modes; (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 figure: 1 microalgae; 2 metal organic framework; 3 light; 4 attachment carrier; 5 CO 2 ; 6 Gas phase; 7 Wastewater; 8 Microalgae biofilm. DETAILED DESCRIPTION

[0021] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0022] Example 1

[0023] Chlorella in the logarithmic growth period was treated with 3-6 g / m 2The initial inoculum size was 0-20 mg / L MIL-101(Fe), sewage was added, and the cells were cultured in a TC-coated polystyrene six-well plate for 12 days. The culture conditions were a 16h / 8h light / dark cycle, a light intensity of 4000Lux, and a temperature controlled at 25±2℃.

[0024] In the first 4 days, the sewage above the microalgae biofilm was collected every day to determine the total nitrogen and total phosphorus concentrations. On the 4th day of inoculation, after the microalgae biofilm was formed, the total nitrogen and total phosphorus concentrations were determined every two days, and the biofilm was resuspended to determine the dry weight. The microalgae biofilm was collected every 4 days to analyze the carbon fixation of the microalgae. Figure 2 (a) The dry weight of the microalgae biofilm showed an upward trend over time. In the first 4 days, the microalgae did not adapt to the addition of MIL-101(Fe) and the dry weight accumulation was slow. In the next 8 days, the microalgae adapted to the environment and grew rapidly. On the 12th day, the dry weight accumulation of 10 mg / MIL-101(Fe) was as high as 15.8 g / m 2 . Figure 2 (b) is the composition of biomass. In the early stage of the experiment, the contents of protein, total sugar and total fat were similar. In the middle and late stages of the experiment, the sugar content was greater than the total fat content and greater than the protein content. When 10 mg / LMIL-101(Fe) was added, the total fat content accumulated the highest in the late stage of the experiment, reaching 37%. Figure 2 (c)2(d) are the removal of total nitrogen and total phosphorus. The concentration of nitrogen and phosphorus showed an overall downward trend. The total phosphorus reached a maximum removal rate of 95% when 10 mg / L MIL-101(Fe) was added. In the first 6 days, the total nitrogen concentration dropped rapidly. After the 6th day, the removal rate was slow and slightly recovered. This may be because the concentration of nitrogen, phosphorus and other nutrients for the growth of microalgae in the sewage was too low to be easily utilized in the later stage of the experiment. The total nitrogen reached a maximum removal rate of 97% on the 6th day when 10 mg / L MIL-101(Fe) was added. Fe is an essential trace element for the photosynthetic growth of microalgae. Studies have reported that the leaching rate of iron ions during long-term immersion in MIL-101(Fe) is about 30%. When the addition concentration of MIL-101(Fe) is low, the concentration of leached iron ions is low, and iron ions can promote the growth of microalgae as a trace element; when the addition concentration of MIL-101(Fe) is too high, the concentration of leached iron ions is too high, which will cause an effect similar to heavy metal poisoning on microalgae cells and inhibit the growth of microalgae. Taking 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 the growth of microalgae.

[0025] Example 2

[0026] Except for the following differences, the other aspects are the same as those of Example 1.

[0027] The added metal organic framework material is MOF-74(Mg). Figure 3 (a) shows the growth of dry weight of microalgae biofilms with different concentrations of MOF-74 (Mg). The dry weight accumulation of biofilms showed an overall upward trend. When the concentration was 15 mg / L, the maximum dry weight accumulation of biofilms was 16.2 g / m on the 12th day. 2 , while promoting the growth of microalgae, it removes a large amount of nitrogen and phosphorus. Figure 3 (b) is the composition of biomass. The total sugar content generally increased first and then decreased, the protein content generally increased, and the total fat content generally decreased. On the 12th day, the total fat content was about 10%. Figure 3 (c) 3(d) are the total nitrogen and total phosphorus removal. The total nitrogen and total phosphorus concentrations showed an overall downward trend. When the addition amount of 15 mg / L MOF-74 (Mg) was used, the total phosphorus reached a maximum removal rate of 94% on the 12th day. In the first 6 days, the total nitrogen concentration dropped rapidly. After the 6th day, the rate of decline was gentle and slightly recovered. The total nitrogen removal rate was the highest on the 12th day when the addition concentration of MOF-74 (Mg) was 15 mg / L, reaching 95%. Magnesium plays an important role in the synthesis and photosynthesis of microalgae chlorophyll. Appropriate concentrations of magnesium ions can promote the photosynthetic growth of microalgae. MOF-74 (Mg) is structurally unstable in solution. Existing studies have shown that the leaching rate of magnesium ions is about 44% during long-term immersion, and the process is accompanied by the diffusion of organic ligands in the solution. Studies have reported that the ligand 2,5-dihydroxyterephthalic acid of MOF-74 (Mg) promotes the growth of microalgae cells at low concentrations, but when the ligand concentration reaches 5 mg / L, the growth of microalgae cells is inhibited. At a dosage of 20 mg / L MOF-74 (Mg), the release of organic ligands was greater than 5 mg / L, which caused the ligands to inhibit the growth of microalgae cells, significantly offsetting the promotion effect of leached magnesium ions on the growth of microalgae. Therefore, 15 mg / L MOF-74 (Mg) was most conducive to the growth of microalgae.

[0028] It can be seen from the above examples that the metal organic framework material is MIL-101 (Fe) and the added concentration is 10 mg / L, which can achieve a higher total nitrogen and total phosphorus removal efficiency and obtain a large amount of biomass.

[0029] Comparative Example 1

[0030] Except for the following differences, the other aspects are the same as those of Example 1.

[0031] The added metal organic framework material is MOF-74(Co). Figure 4 (a) The dry weight growth of microalgae biofilms with different concentrations of MOF-74(Co) was shown. The dry weight of microalgae biofilms increased over time, but during the culture period, the dry weight of 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) is the biomass composition. On the 12th day, the total biomass of the experimental group was lower than that of the control group. Figure 4 (c)4(d) are the removal of total nitrogen and total phosphorus. The results show that different concentrations have a removal effect on total nitrogen and total phosphorus. The concentrations of total nitrogen and total phosphorus show a downward trend. The total nitrogen in the control group decreased significantly in the first 6 days, and the removal rate reached a maximum of 97% on the 6th day. The downward trend was relatively gentle in the next 6 days. The removal rate was still higher than that of the experimental group on the 12th day. The total phosphorus removal of the control group was better than that of the experimental group, reaching a maximum removal rate of 91% on the 12th day. In summary, the addition of MOF-74(Co) is not conducive to the growth of microalgae, which may be because Co in MOF 2+ The release of ions causes damage to the microalgae cells, thereby inhibiting the growth of microalgae.

[0032] The above description is only an embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements without departing from the principle of the present invention. These improvements should also be regarded as within the protection scope of the present invention.

Claims

1. A method for enhancing carbon fixation and water purification of microalgae biofilm based on metal organic framework materials, characterized in that: Here are the steps: (1) Construction of microalgae biofilm culture system The microalgae biofilm culture system comprises microalgae (1) inoculated on an attachment carrier (4) to form a microalgae biofilm (8), using sewage (7) as a culture medium and cultured under light (3) conditions; (2) Adding different types and concentrations of MOF materials to the microalgae biofilm culture system MOF materials of different types and concentrations 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) are trace metal elements that can promote the growth of microalgae.

2. The method according to claim 1, characterized in that The illumination (3) culture condition is natural illumination or artificial illumination, or natural illumination supplemented by artificial supplementary illumination.

3. The method according to claim 1, characterized in that: The attachment carrier (4) is a carrier material that is conducive to the adhesion of microalgae and the formation of biofilm, including polystyrene and polymethyl methacrylate containing TC coating.

4. The method according to claim 1, characterized in that: The ratio of the added concentration of the metal organic framework (2) to the total phosphorus concentration in the sewage (7) is (10-40):

9.

5. The method according to claim 1, characterized in that The metal organic framework (2) is a modified MOF, that is, auxiliary ligands and 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.

6. The method according to claim 5, characterized in that The auxiliary ligand is a tripyridine ligand.

7. The method according to claim 5, characterized in that The inert metal ion is Cr(III) or Rh(III).

8. The method according to claim 5, characterized in that The hydrophobic functional group is a carbon straight chain, isopropyl or butylene.

9. The method according to claim 1, characterized in that: The culture method is batch, semi-continuous or continuous culture, and the culture conditions are bacteria control or non-bacteria control.

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