A method for changing reverse carbon sink into positive carbon sink and enhancing carbon sink efficiency based on reverse pumping of carbonate by alkaline cultivation tail water of microalgae

Abstract

The application discloses a method for changing the carbonate reverse pump into positive and enhancing the carbon sink efficiency based on microalgae alkaline cultivation tail water. The method comprises the following steps: cultivating microalgae, treating the microalgae alkaline cultivation tail water, and utilizing the tail water to enhance the carbon sink ability of the carbonate reverse pump. Compared with other carbon sink approaches, the method changes the carbonate reverse pump into positive, combines the biological carbon fixation of the microalgae, realizes the combined carbon fixation of the carbonate reverse pump and the biological carbon pump of the microalgae, and significantly improves the overall carbon sink efficiency of the technical approach. In addition, the application also co-produces high-value microalgae biomass, creates economic value, and realizes the resource utilization of the microalgae cultivation tail water, thereby providing an effective approach for solving the problems of microalgae cultivation resource waste and low carbon sink efficiency.

Description

Technical Field

[0001] This invention relates to the field of marine biotechnology, specifically to a method for converting the reverse carbonate pump to a positive one and enhancing carbon sequestration efficiency based on alkaline microalgae aquaculture wastewater. Background Technology

[0002] Carbonate counter pumps (CCPs) are an important carbon sink mechanism in the Earth's carbon cycle, capable of fixing CO2 into stable calcium carbonate, thus achieving long-term carbon sequestration. Through the formation and dissolution of carbonate minerals in marine and terrestrial ecosystems, CCPs help convert atmospheric CO2 into solid carbonates, reducing greenhouse gas concentrations. Although CCPs are carbon storage processes based on the formation and deposition of stable carbonates, the carbonate formation process also releases an equal amount of CO2 (Equation 1), which not only leads to water acidification but may even release this CO2 into the atmosphere. Therefore, CCPs are also known as "counter pumps" in academia, which is currently the biggest limitation and obstacle to their application in marine ecological conservation. Furthermore, given the urgent need to address rapid climate change, relying solely on natural processes for CCP carbon sinks is insufficient to slow the rate of climate change; a combination of human emission reduction measures and technological innovation is needed.

[0003]

[0004] In fact, pH is the key factor in determining whether a carbonate back pump is a carbon source or a carbon sink. For example... Figure 1 As shown, when the pH of freshwater and seawater exceeds 8.0, CO2 is almost non-existent in the solution, and the solution mainly contains HCO3. - and CO3 2- At pH values ​​above 10.0, the solution is almost entirely composed of CO3. 2- (Especially in seawater systems). Therefore, under high pH conditions (such as pH 8.92 in seawater), the CO2 released by the CCP will be rapidly absorbed and converted into HCO3. - and CO3 2- Furthermore, maintaining a high pH (e.g., through algal photosynthesis) can prevent the release of CO2 into the gas phase and avoid solution acidification, thus turning the CCP "inverse to positive." More importantly, under high pH conditions, because the partial pressure of CO2 in the solution is very low, CO2 from the air is transferred into the gas phase, which is a carbon sink process. In summary, maintaining high pH conditions for CCP occurrence has the potential to reduce or even completely eliminate the CCP back pump effect.

[0005] As a type of photosynthetic microorganism, microalgae possess advantages such as high photosynthetic efficiency, rapid growth rate, and high CO2 fixation efficiency. Therefore, microalgae carbon sequestration enhancement is considered a highly efficient and sustainable carbon sequestration technology. Furthermore, some microalgae (such as Chlorella and Coccolithophora) also have carbon concentration mechanisms, enabling them to efficiently utilize HCO3-. - And convert it into CO3 2- This simultaneously maintains the solution pH at a stable high level (pH 9.0-12.0). The aforementioned highly alkaline conditions and high CO3 levels... 2- High concentrations of algae can promote efficient CCP carbon fixation and storage, turning CCP from an adverse to a beneficial process. Because they simultaneously possess the ability to synthesize particulate organic and inorganic carbon through photosynthesis, calcified microalgae exhibit dual functions as a biological carbon pump (BCP) and CCP, maximizing the combined carbon storage of microalgae's CCP and BCP under highly alkaline conditions. Furthermore, microalgae contain high-value bioactive substances such as proteins, lipids, and pigments, possessing significant economic value. Therefore, utilizing microalgae cultivation for carbon sequestration can simultaneously achieve the dual goals of carbon sink management and economic development, demonstrating immense application potential in marine ecological protection.

[0006] In conclusion, it is of paramount importance to develop an environmentally friendly and economical method to turn the CCP from negative to positive and enhance carbon sequestration efficiency. Summary of the Invention

[0007] The purpose of this invention is to provide a method for converting the reverse carbonation pump (CCP) to a positive one based on the alkaline wastewater from microalgae aquaculture, simultaneously achieving combined carbon sequestration by both CCP and BCP. The method utilizes the highly alkaline wastewater from microalgae aquaculture to convert the reverse carbonation pump to a positive one, and combines this with microalgae biological carbon sequestration, achieving combined carbon sequestration by the carbonate reverse pump and the microalgae biological carbon pump, significantly enhancing carbon sequestration efficiency. Simultaneously, this method also co-produces high-value microalgae biomass, creating economic value and realizing the resource utilization of microalgae aquaculture wastewater. It solves the problems of resource waste and low carbon sequestration efficiency in microalgae aquaculture, providing an effective solution.

[0008] The technical solution adopted in this invention is:

[0009] A method is provided to enhance carbon sequestration efficiency by "turning negative CCP to positive" based on alkaline aquaculture effluent from microalgae, including the following specific steps:

[0010] S1. Microalgae are cultured in a photobioreactor using a culture medium containing an alkaline carbon source. The inoculum size is 0.01-10.0 g / L, the culture temperature is 15-45℃, and the culture is conducted under natural light or artificial light (where the light intensity of the artificial light source is maintained at 0-100000 μmol / m²). 2The microalgae were cultured under s) conditions and operated semi-continuously, that is, each time 10%-100% of the culture medium was taken and the same volume of new culture medium was added to carry out the next round of culture, so that the pH of the culture medium after culture was between 8.0 and 14.0.

[0011] S2. Collect the microalgae produced in the photobioreactor described in step S1, and obtain the microalgae biomass and the alkaline culture medium (i.e., alkaline culture wastewater) by separation and harvesting, and adjust the pH value of the culture wastewater to between 9.0 and 12.0.

[0012] S3. The alkaline aquaculture wastewater collected in step S2 is mixed with at least one Ca... 2+ or Mg 2+ Metal ions react at room temperature and at a pH between 9.0 and 12.0, with Ca... 2+ / Mg 2+ Concentration and CO3 2- When the concentrations react according to a certain molar ratio, it promotes the formation of carbonate precipitates.

[0013] Preferably, the alkaline carbon source in step S1 is one or more of the following: alkaline wastewater or natural alkaline water, waste solid alkaline substances, natural alkaline minerals, or artificially added alkaline materials.

[0014] Preferably, the alkaline materials added artificially in step S1 include, but are not limited to, one or more of bicarbonates, carbonates, and alkaline minerals such as olivine.

[0015] Preferably, the concentration of the alkaline carbon source in step S1 is from 0 to its saturation concentration.

[0016] Preferably, the method for adjusting the pH of the aquaculture wastewater in step S2 is to introduce one or more of the following into the microalgae aquaculture wastewater: air, artificially purified mixed gas containing 0%-100% CO2, flue gas, SO2, etc.

[0017] Preferably, Ca is provided in step S3. 2+ The material source can be one or more of the following: calcium oxide, calcium hydroxide, calcium-containing ore, seawater, and concentrated seawater.

[0018] Preferably, Mg is provided in step S3. 2+ The material source can be one or more of magnesium oxide, magnesium hydroxide, magnesium-containing ore, seawater, and concentrated seawater.

[0019] Preferably, in step S2, the aquaculture wastewater is recycled, and the recycling frequency is no less than once.

[0020] Preferably, the microalgae cultured in step S1 include, but are not limited to, one or more of Spirulina, Chlorella, Micrococcus pluvialis, Coccolithophora, Haematococcus pluvialis, Dunaliella salina, and Chrysophyta.

[0021] Preferably, photosynthetic bacteria can also be added to the culture medium in step S1, and inoculated into the microalgae culture medium at a ratio of 1-5% (v / v), stirred appropriately, and co-cultured to produce alkaline tailwater.

[0022] The effective effects of this invention are as follows:

[0023] 1. This invention innovatively utilizes highly alkaline microalgae aquaculture wastewater to "turn negative into positive" CCP and enhance its carbon sequestration efficiency, which is expected to promote the large-scale application of CCP in marine ecological protection;

[0024] 2. Based on CCP carbon fixation, this invention also combines microalgae culture carbon fixation, realizing synergistic carbon fixation of CCP and microalgae BCP, which is expected to maximize carbon fixation and carbon storage.

[0025] 3. This invention provides a method for the resource utilization of alkaline aquaculture wastewater and improves carbon sequestration efficiency, truly realizing "turning waste into treasure";

[0026] 4. The method of this invention, while increasing carbon sequestration, also co-produces high-value microalgae biomass, thus achieving carbon sequestration.

[0027] It serves the dual purpose of attracting foreign investment and developing the economy, and has great application potential. Attached Figure Description

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0029] Figure 1 This represents the proportions of different combined forms of carbonic acid at different pH levels in freshwater and seawater.

[0030] Figure 2 Figure showing the dry weight of microalgae biomass after 7 days of cultivation.

[0031] Figure 3 pH chart for microalgae cultured for 7 days.

[0032] Figure 4 This is a schematic diagram of a method to "turn the negative into the positive" of CCP and enhance carbon sequestration efficiency based on algae-based alkaline wastewater. Detailed Implementation

[0033] To better understand the present invention, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. However, those skilled in the art will understand that the following embodiments are not intended to limit the scope of protection of the present invention, and any changes and variations made on the basis of the present invention are within the scope of protection of the present invention.

[0034] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0035] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0036] Example 1

[0037] Carbonic acid exists in three different chemical states in water: molecular free carbonic acid (CO2 + H2CO3), bicarbonate (HCO3), and carbonic acid (HCO3). - and carbonates and carbonic acid CO3 2- The proportions of these substances in freshwater under different pH conditions are calculated as follows:

[0038] The equilibrium equation between molecular carbonic acid is:

[0039]

[0040] At equilibrium, the amount of H2CO3 is less than 1% of the amount of CO2. For ease of description, [CO2] represents the total amount of molecular free carbonic acid.

[0041] In summary, the CO2 dissolution equilibrium equation is shown in equation (3):

[0042]

[0043] Wherein, the first-order dissociation equilibrium constant is:

[0044]

[0045] Second-order dissociation equilibrium constant:

[0046]

[0047] If the total amount of carbon dioxide in the water is C t If we express this, then we have:

[0048] C t = [CO2] + [HCO3] - ]+[CO3 2- (6)

[0049] Set the total carbonic acid concentration (C) t Initial conditions such as temperature (T) and other conditions.

[0050] Calculate the distribution coefficients (a0, a1, a2) of each carbonate compound state based on the first and second dissociation equilibrium constants (K1 and K2).

[0051]

[0052] Calculate hydrogen ion concentration (H+) using pH value +).

[0053] The proportions of each carbonate compound at different pH values ​​were obtained using the above formulas (2)-(9), and plotted as follows: Figure 1 The calculation conditions for freshwater are: T = 25℃, first-order equilibrium constant of carbonic acid K1 = 0.000000445, and second-order equilibrium constant K2 = 4.69 * 10⁻⁶. -11 The calculation conditions for seawater are: S = 35℃, T = 25℃, and the first-order equilibrium constant K1 = 1.38038 * 10⁻⁶. -6 The second-order equilibrium constant K2 = 1.20226 * 10 -9 .

[0054] Figure 1 This visually illustrates the distribution of the three carbonate forms in the solution as pH changes. Details are as follows:

[0055] In the low pH range (4.0-5.0), inorganic carbon in both seawater and freshwater exists in the form of CO2, while HCO3- is present in other forms. - and CO3 2- The total percentage is less than 20%.

[0056] When the pH value rises to 7.0, the HCO3- in seawater and freshwater... - The proportions of all three increased significantly, while the proportion of CO2 approached zero. Additionally, the proportion of CO3 in seawater... 2- The proportion of CO3 in freshwater is also increasing, but there is almost no CO3 in freshwater. 2- .

[0057] As the pH value further increases to the range of 7.0-9.0, HCO3- - It is the main form of HCO3 in seawater and freshwater, of which HCO3 is present in both. - Their respective proportions are as high as 50%-93% and 80%-99%. In comparison, CO3... 2- The proportions are 0.0-50% and 0.0%-6.0% respectively, while CO2 is almost completely absent.

[0058] When the pH value reaches 9.0-12.0, inorganic carbon in both seawater and freshwater mainly exists in the form of HCO3-. - and CO3 2- CO3 exists in the form of both seawater and freshwater. 2- The proportions ranged from 50% to 100% and 6.0% to 99%, respectively. In comparison, the HCO3- in seawater... - The proportion of inorganic carbon in seawater becomes virtually non-existent as pH increases; at pH = 12.0, almost all inorganic carbon in seawater is CO3. 2- HCO3 exists in freshwater. -The proportion decreases from 95% to about 2% as pH increases. At pH = 12.0, inorganic carbon in freshwater, besides being metabolized by a large amount of CO3, is... 2- It exists in the form of HCO3, with a very small amount as HCO3. - It exists in the form of.

[0059] Through the Figure 1 Comprehensive analysis further verified that under high pH conditions (where freshwater pH > 8.0), the main component in the freshwater-seawater system is HCO3-. - and CO3 2- At pH 12.0, almost all inorganic carbon in the freshwater-seawater system is in the form of CO3. 2- The presence of this form indicates the presence of a large amount of CO3 in an alkaline environment. 2- This provides an important theoretical basis for improving the efficiency of CCP carbon sequestration and turning it from negative to positive.

[0060] Example 2

[0061] Spirulina was cultured in a thin-layer fountain photobioreactor using Zarrouk medium containing 0.3 mol / L sodium bicarbonate at a total culture volume of 5.15 L, maintaining an initial inoculum concentration of 0.2-0.3 g / L. The culture temperature was controlled within the range of 30-33℃, and the light intensity was 200 μmol / m². 2 •s, the culture period is 7 days. 3*20mL of Spirulina culture medium was sampled daily to measure pH and biomass dry weight, and the same volume of culture medium was added back after each sampling to maintain the liquid layer thickness.

[0062] like Figure 2 As shown, the pH of the culture medium increases with increasing culture time, reaching a maximum of 11.87, indicating that microalgae can efficiently utilize the alkaline carbon source of bicarbonate and produce alkaline aquaculture wastewater. Figure 3 As shown, the biomass of microalgae reached a final concentration of 3.3 g / L after 7 days of cultivation, with a maximum growth rate of 1.3 g / L / day. Based on the calculation that each 1 g of microalgal biomass fixes 1.8 g of CO2, the carbon fixation capacity and maximum carbon fixation efficiency of microalgae in this implementation case are 30.59 g CO2 and 2.34 g CO2 / L / day, respectively.

[0063] Example 3:

[0064] The alkaline wastewater (with high alkalinity and pH) generated in Example 2 was collected and reacted with 0.5 mol / L Ca at room temperature. 2+ The reaction. Because the microalgae culture environment in Example 2 was a bicarbonate system, the effluent contained not only a large amount of CO3... 2- It also contains HCO3 that is not utilized by microalgae. -Besides CO3 2- With Ca 2+ The reaction produces calcium carbonate, while the HCO3- that is not utilized by the microalgae... - Will and Ca 2+ The reaction produces calcium carbonate, but the CO2 released is rapidly converted into HCO3 under highly alkaline conditions. - and CO3 2- At the same time, a large amount of CaCO3 precipitate is generated.

[0065] Based on the calculations, 0.5 mol of Ca was added to the tailwater. 2+ The generated calcium carbonate was 42.5g, corresponding to a carbon fixation amount of 18.7g CO2. After adding the carbon fixation amount of microalgae, the total carbon fixation amount of the system based on CCP and BCP was 49.29g CO2, which is 61.13% higher than the carbon fixation capacity of microalgae alone in Example 2.

[0066] In summary, this patent transforms CCP from negative to positive through the resource utilization method of alkaline microalgae aquaculture wastewater, and simultaneously achieves joint carbon sequestration of BCP and CCP. This not only increases the overall carbon sequestration efficiency of this technical pathway, but also allows the high-yield microalgae biomass obtained to be used as livestock feed and agricultural fertilizer, creating significant economic value.

[0067] The above implementation plan is for reference only, and can be adjusted and optimized according to specific circumstances in actual operation. This invention effectively turns CCP (carbon sequestration) into positive and improves carbon sequestration efficiency by combining microalgae cultivation with alkaline aquaculture wastewater treatment, providing a new approach to increasing carbon sequestration.

[0068] While specific embodiments of the present invention have been described above, those skilled in the art should understand that the specific embodiments described are merely illustrative and not intended to limit the scope of the invention. Equivalent modifications and variations made by those skilled in the art in accordance with the spirit of the invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for converting a carbonate backflow into a positive flow and enhancing carbon sequestration efficiency based on alkaline microalgae aquaculture wastewater, characterized in that, The specific steps include the following: S1. Microalgae are cultured in a photobioreactor using a culture medium containing an alkaline carbon source. The inoculum size of the microalgae is 0.01-10.0 g / L, the culture temperature is 15-45 ℃, and the culture is conducted under natural light or artificial light. The light intensity of the artificial light source is maintained at 0-100000 μmol / m²·s. The next round of culture is carried out through semi-continuous operation to ensure that the pH of the culture medium after culture is between 8.0 and 11.

87. S2. Collect the microalgae produced by the photobioreactor described in step S1, and obtain the microalgae biomass and alkaline microalgae aquaculture wastewater by separation and harvesting methods, and adjust the pH value of the alkaline microalgae aquaculture wastewater to between 9.0 and 12.

0. S3. Mix the alkaline aquaculture wastewater collected in step S2 with Ca 2+ or Mg 2+ At least one of the metal ions reacts with each other, Ca 2+ / Mg 2+ Concentration and CO3 2- When the concentrations react according to a certain molar ratio, it promotes the formation of carbonate precipitates.

2. The method according to claim 1, characterized in that: The alkaline carbon source in step S1 is one or more of alkaline wastewater or natural alkaline water, natural alkaline minerals, bicarbonates or carbonates.

3. The method according to claim 1, characterized in that: The concentration of the alkaline carbon source in step S1 is from 0 to its saturation concentration.

4. The method according to claim 1, characterized in that: The method for adjusting the pH of the alkaline microalgae culture wastewater in step S2 is to introduce one or more of the following into the alkaline microalgae culture wastewater: air, artificially purified mixed gas containing 0%-100% CO2, flue gas, and SO2 gas.

5. The method according to claim 1, characterized in that: Ca is provided in step S3 2+ The material source is one or more of the following: calcium oxide, calcium hydroxide, calcium-containing ore, seawater, and concentrated seawater.

6. The method according to claim 1, characterized in that: Mg is provided in step S3 2+ The material source is one or more of magnesium oxide, magnesium hydroxide, magnesium-containing ore, seawater, and concentrated seawater.

7. The method according to claim 1, characterized in that: In step S2, the wastewater from the alkaline microalgae aquaculture is recycled, and the recycling frequency is no less than once.

8. The method according to claim 1, characterized in that: The microalgae species mentioned in step S1 include one or more of the following: Spirulina, Chlorella, Micrococcus pluvialis, Coccolithophora, Haematococcus pluvialis, Dunaliella salina, and Chrysophyta.

9. The method according to claim 1, characterized in that: In step S1, photosynthetic bacteria are also added to the culture medium for co-culture, and alkaline aquaculture wastewater containing microalgae is produced.

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