Method for improving ocean negative emission efficiency based on alkaline cultivation of microalgae

Abstract

This invention relates to a method for improving marine negative emission efficiency based on algae algae aquaculture wastewater, comprising the following steps: S1. Cultivating microalgae in a photobioreactor using a culture medium containing an alkaline carbon source, ensuring the pH of the culture medium is between 8.0 and 14.0; S2. Collecting the microalgae produced in the photobioreactor as described in step S1, and obtaining microalgae biomass and alkaline aquaculture culture medium (i.e., alkaline aquaculture wastewater) separately through a separation and harvesting method, and adjusting the pH of the wastewater to between 8.0 and 12.0; S3. Discharging the treated alkaline aquaculture wastewater from step S2 into the sea. This method can effectively reduce the partial pressure of CO2 in seawater, thereby increasing the efficiency of seawater in absorbing atmospheric CO2, aiming to improve marine negative emissions by enhancing the carbon sequestration capacity of the solubility pump.

Description

Technical Field

[0001] This invention relates to the field of carbon capture technology, specifically to a method for improving marine negative emission efficiency based on microalgae alkaline aquaculture wastewater. Background Technology

[0002] Due to the increasing concentration of CO2 in the atmosphere, the Earth is facing increasingly severe environmental crises, such as global warming and ocean acidification. While reducing carbon emissions, efficient and cost-effective anthropogenic CO2 sequestration strategies have gained increasing attention. In recent years, ocean carbon emission reduction based on Ocean Alkalinity Enhancement (OAE) has been considered a relatively rapid and efficient approach. This involves adding alkaline substances to reduce the partial pressure of carbon dioxide (pCO2) in the ocean surface, promoting negative atmospheric carbon dioxide emissions into the ocean, where it is sequestered as carbonates. However, directly adding alkaline substances to natural seawater leads to the precipitation of large amounts of associated carbonate minerals (such as CaCO3), resulting in low utilization efficiency of alkaline materials and reduced CO2 absorption efficiency. Furthermore, since the current ocean is already supersaturated with CaCO3, it is not suitable to increase ocean alkalinity by dissolving alkaline silicate raw materials such as olivine into seawater.

[0003] To address the limitations of traditional OAE (Oil-Off Effluent) methods, Academician Jiao Nianzhi of Xiamen University proposed a new OAE paradigm in 2022: increasing the alkalinity of wastewater treatment plant effluent and discharging it into the ocean. This involves raising the alkalinity of wastewater during treatment and releasing the alkalized effluent into the ocean to achieve safe, economical, and long-term CO2 sequestration from the atmosphere. Because wastewater has characteristics such as low pH, high pCO2, and high organic acid concentration, it can effectively absorb strong alkalis and avoid secondary carbonate precipitation. It can also efficiently dissolve olivine and carbonate minerals under low pH conditions. Due to these advantages, the OAE scheme based on alkalized wastewater treatment plant effluent holds promise as a feasible and efficient new paradigm for negative ocean emissions.

[0004] However, the alkaline materials currently used in the OAE process are typically low-cost minerals such as olivine and calcite, but their solubility in water is very low (e.g., olivine's solubility in seawater is approximately 0.1 kg / ton). This leads to increased demand for ore, raising operating costs, and the alkalization effect on seawater is minimal. While ultrafine grinding can reduce mineral particle size and improve ore solubility in seawater, this also significantly increases treatment costs and the risk of environmental pollution. Therefore, obtaining low-cost, highly soluble alkaline materials is of great significance for the OAE process based on wastewater treatment plant effluent transportation. Summary of the Invention

[0005] To promote the application of ocean algae emissions (OAEs) and enhance their economic value, this invention proposes a method for improving marine negative emission efficiency based on algae alkaline aquaculture wastewater. This method utilizes the characteristic that microalgae consume alkaline carbon sources, causing the pH of the culture medium to rise while maintaining stable alkalinity. This alkaline solution is then discharged into the sea to increase ocean alkalinity, thereby achieving efficient and safe marine negative emissions. This technology not only increases the absorption and sequestration of atmospheric CO2 by the ocean, but the use of algae alkaline aquaculture wastewater also significantly reduces the cost of seawater alkalization. Furthermore, the microalgae biomass obtained from cultivation has significant economic value, making it crucial for promoting the large-scale application of OAEs.

[0006] To achieve the above process, the present invention is implemented through the following technical solution:

[0007] 1. A method for improving marine negative discharge efficiency based on microalgae alkaline aquaculture wastewater, comprising the following steps:

[0008] 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 temperature is 15-45℃, and the environment is under natural light or with a light intensity maintained at 0-100000 μmol / m². 2 The microalgae were cultured under artificial light conditions and operated semi-continuously, that is, 10%-100% of the culture medium was taken each time, 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 cultivation was between 8.0 and 14.0.

[0009] S2. Collect the microalgae produced by 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 methods, and adjust the pH value of the culture wastewater to between 8.0 and 12.0.

[0010] S3. Discharge the treated alkaline aquaculture wastewater from step S2 into the sea.

[0011] Preferably, the alkaline carbon source in step S1 is one or more of alkaline wastewater, waste solid alkaline substances, or artificially added alkaline materials.

[0012] Preferably, the artificially added alkaline material includes, but is not limited to, one or more of bicarbonates, carbonates, hydroxides, olivine, and clay.

[0013] Preferably, the concentration of alkaline carbon source in the microalgae culture medium is from 0 to its saturation concentration.

[0014] Preferably, the pH value of the aquaculture wastewater in step S2 is adjusted to between 8.0 and 9.0.

[0015] Preferably, the method for adjusting the pH of the tailwater in step S2 is to introduce one or more acidic gases such as CO2 and SO2 or other acidic substances into the alkaline tailwater of microalgae cultivation.

[0016] Preferably, the alkaline aquaculture wastewater in step S3 includes, but is not limited to, direct discharge into the ocean, or mixing with wastewater from sewage treatment plants and river water before discharge into the ocean.

[0017] Preferably, the photobioreactor in step S1 is either closed or open. It can be, but is not limited to, closed types such as flat plate photobioreactors, column photobioreactors, pipeline photobioreactors, fountain thin-layer photobioreactors, etc., or open types such as racetrack pools, membrane photobioreactors, etc.

[0018] Preferably, the microalgae species mentioned in step S1 include, but are not limited to, one or more of Spirulina, Chlorella, Dunaliella salina, Haematococcus pluvialis, Micrococcus pluvialis, and Chlorella.

[0019] Preferably, photosynthetic bacteria can be added to the culture medium in step S1 for co-culture, and alkaline tail water can be produced.

[0020] The effective effects of this invention are as follows:

[0021] 1. The alkaline wastewater from microalgae aquaculture can serve as a cheap or even free source of alkalinity for the OAE pathway;

[0022] 2. The alkaline aquaculture wastewater of microalgae not only has a higher solubility in water than solid alkaline substances, but also avoids the formation of associated carbonates in a high pH environment compared to active alkaline particles.

[0023] 3. The wastewater from alkaline microalgae cultivation can be repeatedly recycled by absorbing waste gas or mixing wastewater, further reducing the discharge of waste gas and wastewater;

[0024] 4. In addition to providing alkaline aquaculture wastewater, microalgae cultivation can also efficiently fix carbon, contributing to the achievement of carbon neutrality goals. At the same time, it can also produce high-value-added microalgae products and carry out commercial processing, significantly improving economic benefits.

[0025] 5. By mixing alkaline aquaculture wastewater from microalgae production with wastewater from sewage treatment plants, the risk of CO2 emissions from the ocean to the atmosphere is reduced due to direct discharge of high-pCO2 water. Furthermore, the mixed alkaline wastewater can react with CO2 in seawater, reducing seawater pCO2. This not only reduces near-shore CO2 emissions but also increases the ocean's absorption of atmospheric CO2, thereby increasing the efficiency of the ocean's solubility pump.

[0026] 6. The alkaline carbon source in step S1 can significantly increase the pH of the water body after microalgae cultivation and maintain stable alkalinity. The selected microalgae can grow in an alkaline environment and utilize the HCO3- in the water. 3- Alternatively, CO2 can be used to raise the pH of the water, maintain alkalinity, and generate high-value-added products. Meanwhile, the efficiency of microalgae cultivation in the photobioreactor in step S1 is 10-100 g / m³. 2 / day, enabling large-scale commercial production. In step S2, the pH of the microalgae is controlled between 8 and 12 to prevent the formation of calcium carbonate precipitation due to excessive alkalinity and to ensure that the water meets discharge standards. Attached Figure Description

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0028] Figure 1 This is a flowchart of a method to improve marine negative discharge efficiency based on microalgae alkaline aquaculture wastewater. Detailed Implementation

[0029] 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.

[0030] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0031] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0032] Example 1

[0033] The present invention discloses a method for improving marine negative discharge efficiency based on alkaline microalgae aquaculture wastewater, which includes the following steps:

[0034] Step S1: Cultivate microalgae in a photobioreactor using a culture medium containing an alkaline carbon source, and ensure that the pH of the culture medium is between 8.0 and 14.0.

[0035] Microalgae can grow efficiently in environments with a pH of 7-14 and can utilize HCO3 in the water. -Alternatively, CO2 can be used to increase the pH of the water body, maintain the alkalinity, and produce high-value-added products. Microalgae include, but are not limited to, Chlorella, Spirulina, Dunaliella salina, Haematococcus pluvialis, Phaeodactylum tricornutum, Euglena, and Micrococcus microcarpa, etc. These microalgae can be cultivated under alkaline conditions and have economic value. These microalgae can produce high-value-added products for further processing in the food, medicine, feed, energy and other industries, realizing the commercial value of microalgae.

[0036] Microalgae culture media can provide the carbon source, nitrogen source, inorganic salts, growth hormones, and water required for microalgae growth. Production can be achieved using culture media based on a 0.01-200 g / L bicarbonate system to provide carbon, enabling efficient carbon fixation by microalgae. To further achieve green production, components in the microalgae culture media can also be derived from factory emissions of waste gas or wastewater. All of the aforementioned microalgae culture media can be recycled until the microalgae can no longer grow in them.

[0037] Photobioreactors are devices used for the culture of photosynthetic microorganisms and their photosynthetic tissues or cells. These photobioreactors can be closed systems such as flat-plate, column, tubular, and fountain-type thin-layer photobioreactors, or open systems such as raceway ponds and membrane photobioreactors. The efficiency of microalgae culture in photobioreactors is 10-100 g / m³. 2 / day, capable of achieving 1-10000m 2 Large-scale production.

[0038] Alkaline carbon sources can be alkaline aquaculture wastewater and waste solid alkaline substances or artificially added alkaline materials. Artificially added alkaline materials include, but are not limited to, one or more of bicarbonates, carbonates, hydroxides, olivine, and clay.

[0039] The concentration of alkaline carbon source in the microalgae culture medium is from 0 to its saturation concentration.

[0040] Step S2: Collect the alkaline aquaculture wastewater produced by the photobioreactor in step S1 after the microalgae are produced, and adjust the pH value of the wastewater to between 8.0 and 12.0.

[0041] The alkaline aquaculture wastewater mentioned above is recycled.

[0042] The pH of the microalgae aquaculture wastewater can be adjusted by introducing acidic gases such as CO2 and SO2 or by adding other acidic substances.

[0043] This invention utilizes the alkaline wastewater generated during microalgae production, adjusting its pH to serve as a low-cost or even free source of alkaline substances in the OAE (Overseas Alkali-Acid) method. Furthermore, as a highly soluble liquid material, its solubility in water is almost negligible, enabling large-scale application. Before discharge into the sea, the wastewater needs pH adjustment. This step can be done by mixing it with acidic wastewater from sewage treatment plants or acidic waste gas from chemical plants. After adjusting the pH to 8-12, the wastewater is discharged into the sea, reducing seawater pCO2, increasing the ocean's ability to absorb atmospheric CO2, enhancing the ocean's carbon sequestration effect, and achieving negative ocean emissions. In addition, microalgae can accumulate high-value products such as proteins, lipids, and pigments, possessing significant commercial value. This method allows for the simultaneous development of carbon neutrality and economic growth.

[0044] The alkaline microalgae aquaculture effluent typically features high pH, ​​high alkalinity, and low pCO2. High alkalinity and low pCO2 are beneficial for achieving negative ocean discharge, while high pH, ​​especially above 9, requires pH adjustment to maintain between 8 and 9 to prevent carbonate precipitation upon discharge into the sea. Therefore, a low-cost adjustment method can be achieved by mixing acidic wastewater from sewage treatment plants to obtain a mixed solution with a pH between 8 and 9 before discharge into the sea. Alternatively, pH can be adjusted by receiving factory exhaust gas containing CO2. If the obtained alkaline microalgae aquaculture effluent has a pH between 8 and 9, no pH adjustment is necessary before direct discharge into the sea.

[0045] Step S3: Discharge the treated alkaline aquaculture wastewater from step S2 into the sea.

[0046] It can be discharged directly into the ocean, or mixed with sewage before being discharged into the ocean.

[0047] When wastewater from algae algae aquaculture is discharged into the sea, dissolved CO2 in the ocean reacts with it to produce HCO3. - This reduces seawater pCO2, disrupts the CO2 dissolution balance between the seawater surface and the atmosphere, allowing atmospheric CO2 to continuously dissolve in seawater, thus enhancing the ocean's ability to absorb atmospheric CO2 and increasing the ocean's carbon sequestration effect.

[0048] The method for enhancing negative emissions in the ocean based on alkaline microalgae aquaculture wastewater, as described in this invention, can theoretically significantly improve the ocean's carbon sequestration capacity. To evaluate the marine carbon sequestration effect of this method, wastewater treatment plant wastewater, alkaline microalgae aquaculture wastewater, or a mixture of both, was mixed in natural seawater, and the change in dissolved inorganic carbon (DIC) content in the seawater was measured after a certain period of time.

[0049] Specifically, the wastewater generated during the Spirulina cultivation process is used as the source of the alkaline microalgae culture tailwater in this method. The specific components of the Spirulina culture medium are: 25.2 g / L sodium bicarbonate, 0.50 g / L dipotassium hydrogen phosphate, 2.50 g / L sodium nitrate, 1.00 g / L potassium sulfate, 0.20 g / L magnesium sulfate heptahydrate, 0.03 g / L anhydrous calcium chloride, 0.01 g / L ferrous sulfate heptahydrate, and 1 ml of A5 trace elements.

[0050] After dissolving the above-mentioned microalgae culture medium components in distilled water according to the specified proportions, the culture medium required for the growth of Spirulina is obtained. The microalgae are cultured in a fountain thin-layer photobioreactor to a concentration of more than 3 g / L and the pH of the culture medium exceeds 11. The algal solution is then filtered, and 100% CO2 gas is introduced into the resulting alkaline microalgae filtrate to adjust the pH to pH=9.0. In addition, treated wastewater (pH=7.6) from a sewage treatment plant is collected for the experiment.

[0051] The experiment was conducted in a 100L eco-bucket, and the specific experimental group settings are as follows:

[0052] Experimental group 1: 100L natural seawater

[0053] Experimental Group 2: 10L of wastewater from the wastewater treatment plant + 90L of natural seawater

[0054] Experimental Group 3: 10L of treated alkaline microalgae culture wastewater + 90L of natural seawater

[0055] Experimental Group 4: 5L of wastewater from the wastewater treatment plant + 5L of treated algae algae aquaculture effluent + 90L of natural seawater

[0056] After all experimental groups were set up, the pH and total dissolved inorganic carbon (DIC) in the seawater were measured, and measured again after one week. All experimental groups were equipped with water pumps to simulate ocean waves. The experimental results are as follows:

[0057] Experimental group 1 Experimental group 2 Experimental group 3 Experimental group 4 Start pH 8.32 8.09 8.62 8.46 Terminate pH 8.24 8.04 8.09 8.07 Start DIC (mg / L) 22.83 23.32 27.21 26.76 Termination of DIC (mg / L) 23.04 23.47 30.32 30.63 DIC changes (mg / L) 0.21 0.15 3.11 3.87

[0058] Results Analysis: During the experiment, the DIC content in natural seawater increased by 0.21 mg / L. The DIC increase in other experimental groups exceeded that in the natural seawater group. Experimental group 2, due to the slightly acidic nature of the reclaimed water and the low pH fluctuation range, had even lower carbon dioxide solubility. Experimental group 4, which combined reclaimed water and tailwater, showed approximately 17 times higher carbon sequestration compared to natural seawater. This was mainly due to the increased alkalinity in the mixed system, which enhanced the absorption of atmospheric CO2 by the seawater. However, the carbon sequestration in experimental group 3 was lower than that in experimental group 4. This may be because the rapid increase in pH in the seawater system caused some marine organisms to die, making it impossible for them to adapt to the environment. Furthermore, the bicarbonate generated after the seawater absorbed CO2 could not be utilized in time, thus inhibiting CO2 dissolution.

[0059] Conclusion: Adding alkaline microalgae aquaculture wastewater to seawater can greatly increase the efficiency of the marine solubility pump. Moreover, after being combined with the slightly acidic reclaimed water from the sewage treatment plant, it has a small impact on marine organisms in the short term and is more efficient than adding highly alkaline microalgae aquaculture wastewater directly.

[0060] In summary, the method of this invention utilizes the characteristic of microalgae to increase the pH of the culture medium while maintaining stable alkalinity after consuming alkaline carbon sources. This alkaline solution is then discharged into the sea to increase ocean alkalinity, thereby achieving efficient and safe negative ocean emissions. This method not only increases the absorption and sequestration of atmospheric CO2 by the ocean, but the use of alkaline microalgae culture wastewater can also significantly reduce the cost of seawater alkalization. Furthermore, the microalgae biomass obtained from the cultivation has significant economic value and is of great importance in promoting the large-scale application of their ocean alkaline emissions (OAE).

[0061] 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 present invention. Equivalent modifications and variations made by those skilled in the art in accordance with the spirit of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for improving marine negative discharge efficiency based on microalgae alkaline aquaculture wastewater, characterized in that, Includes the following steps: 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 temperature is 15-45℃, and the environment is under natural light or with a light intensity maintained at 0-100000 μmol / m². 2 The microalgae were cultured under artificial light conditions and operated semi-continuously, that is, 10%-100% of the culture medium was taken each time, 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 cultivation was between 8.0 and 14.

0. S2. Collect the microalgae produced by 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 methods, and adjust the pH value of the culture wastewater to between 8.0 and 9.

0. S3. Discharge the treated alkaline aquaculture wastewater from step S2 into the sea.

2. The method for improving marine negative discharge efficiency based on microalgae algae aquaculture wastewater according to claim 1, characterized in that: The alkaline carbon source mentioned in step S1 is one or more of alkaline wastewater, bicarbonate, carbonate, hydroxide, olivine, and clay.

3. The method for improving marine negative discharge efficiency based on microalgae alkaline aquaculture wastewater according to claim 1, characterized in that: The method for adjusting the pH of the aquaculture wastewater in step S2 is to introduce CO2 and / or SO2 acidic gases into the alkaline aquaculture wastewater.

4. The method for improving marine negative discharge efficiency based on microalgae alkaline aquaculture wastewater according to claim 1, characterized in that: The wastewater from the alkaline microalgae aquaculture described in step S3 is either directly discharged into the ocean or mixed with wastewater from sewage treatment plants and river water before being discharged into the ocean.

5. The method for improving marine negative discharge efficiency based on microalgae alkaline aquaculture wastewater according to claim 1, characterized in that: The photobioreactor mentioned in step S1 is either a closed photobioreactor or an open photobioreactor.

6. The method for improving marine negative discharge efficiency based on microalgae alkaline aquaculture wastewater according to claim 5, characterized in that: The closed photobioreactor is one or more of the following: flat plate photobioreactor, column photobioreactor, pipeline photobioreactor, or fountain thin-layer photobioreactor.

7. The method for improving marine negative discharge efficiency based on microalgae algae aquaculture wastewater according to claim 5, characterized in that: The open photobioreactor is one or more of a raceway pool or a membrane photobioreactor.

8. The method for improving marine negative discharge efficiency based on microalgae alkaline aquaculture wastewater according to claim 1, characterized in that: The microalgae species mentioned in step S1 include, but are not limited to, one or more of Spirulina, Chlorella, Dunaliella salina, Haematococcus pluvialis, Micrococcus pluvialis, and Chlorella.

9. The method for improving marine negative discharge efficiency based on microalgae algae aquaculture wastewater according to claim 1, characterized in that: In step S1, photosynthetic bacteria are added to the culture medium for co-culture, and alkaline tail water is produced.

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