Hybrid process for carbon fixation from combustion gases and / or fermentation to obtain biomass of cyanobacteria or microalgae

Description

DESCRIPTIVE REPORT Hybrid process for carbon fixation from combustion gases and / or fermentation to obtain cyanobacteria or microalgae biomass. Field of Invention

[001] The present invention belongs to the area of ​​environmental biotechnology with emphasis on bioprocesses, referring to a hybrid process for carbon fixation from gases using a chemical reactor and a photobioreactor with the cyanobacterium Spirulina sp.

[002] This method consists of an integrated process to optimize carbon dioxide (CO2) fixation using a bubble column reactor with sodium hydroxide (NaOH) solution and a bubble column photobioreactor for biological carbon fixation.

[003] The process proposed in this invention provided a fixation of over 70% of CO2 and a notable increase in Spirulina biomass of 43.78% compared to the control group and a protein content of 57% (mm-1). Fundamentals of the Invention and State of the Art

[004] Population growth and increasingly evident climate change due to the growing carbon footprint have been widely discussed by international bodies, with a continuous search for the development and implementation of new carbon-negative emission technologies. This is because over the years there has been a growing increase in greenhouse gas (GHG) emissions resulting from human and industrial activities, with 72% coming from energy generation using fossil fuels (Center for Climate and Energy Solutions. Global Emissions, 2021). In 2023, atmospheric CO2 levels reached a concentration of 424 parts per million (ppm), 50% higher than at the beginning of the industrial era (NOAA. Broken record: Atmospheric carbon Petition 870250009089, dated 04 / 02 / 2025, page 7 / 26 2 / 12 dioxide levels jump again. National Oceanic and Atmospheric Administration, 2023).

[005] Gases emitted during power generation generally come from the combustion of coal, natural gas, diesel, or woody biomass (among others) and have a predominant composition of CO2 (3 to 25% vv-1) (Scapini et al., Microalgae-mediated biofixation as an innovative technology for flue gases towards carbon neutrality: A comprehensive review. Journal of Environmental Management 363, 121329, 2024), this being the most predominant GHG in anthropogenic emissions (76%) (Center for Climate and Energy Solutions. Global Emissions, 2021). In addition, sulfur oxides (SOx), nitrogen oxides (NOx), and particulates are also present in industrial combustion gases.

[006] International targets for net-zero emissions and carbon neutrality between 2030 and 2050 have been pursued by more than 100 countries, representing 80.7% of global GHG emissions, including China, the United States, India, Brazil and South Africa (Climatewatch. Net-zero Tracker, 2024).

[007] Considering this context, gas capture in power plants or industrial emission sources can be a strategy to effectively reduce carbon emissions from point sources. This post-combustion capture strategy is of interest since it avoids modifications to industrial processes and offers operational flexibility. Technologies with technical, economic and sustainable viability are urgently needed to minimize CO2 emissions from industrial sources (Fu et al., Techno-economic and life cycle assessment of membrane separation in post-combustion carbon capture: A review. Gas Science and Engineering 129, 205401, 2024).

[008] As a strategy, technologies such as carbon capture and utilization (CCU) have been recognized as promising by relevant international bodies, such as the International Energy Agency (IEA). This technology involves capturing CO2 from Petition 870250009089, dated 04 / 02 / 2025, page 8 / 26 3 / 12 combustion gases and subsequent direct (i.e., not chemically modified) or indirect (i.e., transformed) use in production processes, contributing to a circular economy. For example, in the production of fertilizers, fuels, chemicals and construction aggregates (IEA. CO2 capture and utilisation, 2024).

[009] CO2 can be captured by processes such as chemical and / or physical absorption, membrane separation, electrochemical separation, etc., transformed into value-added products such as fuels and chemicals, directly contributing to the reduction of GHG emissions (Kerner et al., Efficient supply with carbon dioxide from flue gas during large scale production of microalgae: A novel approach for bioenergy facades. Bioresource Technology 391, 129917, 2024).

[010] An example of chemical capture is the commercially available Belfield™ Process, developed by UOP LLC (Universal Oil Products), patent US2886405A. This process is based on an absorption tower where a gas stream containing CO2 and hydrogen sulfide (H2S) comes into contact with a potassium carbonate (K2CO3) solution to form potassium bicarbonate (KHCO3) and bisulfite (KHS), which is regenerated to carbonate by heating and recirculated in the absorption tower. While CO2 is captured and stored and / or used in industrial processes. Still, it faces a number of challenges, mainly with limitations regarding the initial concentration of CO2 in the gas stream, since concentrations lower than 20% can present high capture and transport costs, storage difficulties, and gas losses to the atmosphere.

[011] To address this problem, a process is proposed in which CO2 is captured as bicarbonate (HCO3-) in a bubble column reactor and used as an inorganic carbon source (further coupling the chemically unabsorbed gas stream) for algae cultures, as in a closed loop, avoiding carbonate regeneration and gas transport. Petition 870250009089, dated 04 / 02 / 2025, page 9 / 26 4 / 12

[012] The CO2 capture process in a bubble column involves injecting a gas stream (combustion gas or gas resulting from biological processes, e.g., fermentation) rich in CO2 into an aqueous solution containing carbonate chemical compounds or hydroxides. When CO2 comes into contact with this solution, it reacts chemically, forming bicarbonate (HCO3-) or other carbonate ions (e.g., CO32-). This method is especially efficient for capturing CO2 from less concentrated streams (below 20%), as the chemical reaction occurs effectively even with lower CO2 concentrations compared to the Belfield™ Process, allowing the gas to be sequestered directly in the solution and used as a source of inorganic carbon for other processes, such as the cultivation of microalgae and / or cyanobacteria.

[013] The integration of this CO2 capture process with microalgae cultivation is recognized as an important CCU technology for transitioning to a circular economy and for mitigating GHG emissions (IEA. Bio-CCS and Bio-CCUS in climate change mitigation, tks 41, 2018). Also called Bio-CCU, it has significant technical and economic relevance and occurs through the use of microalgae and / or cyanobacteria that are able to use the bicarbonate generated in chemical fixation as a source of inorganic carbon, facilitating assimilation through photosynthesis and promoting efficient cell growth (Scapini et al., Microalgae-mediated biofixation as an innovative technology for flue gases towards carbon neutrality: A comprehensive review. Journal of Environmental Management 363, 121-329, 2024).

[014] This chemical and biological coupling – also called a CO2 absorption and microalgae conversion (CAMC) system – results in a closed-loop system in which captured CO2 is removed from the gas stream directly or indirectly and converted into high-value biomass. The algal biomass generated can be further processed for the production of biofuels, chemicals or other byproducts (e.g., pigments). Petition 870250009089, dated 04 / 02 / 2025, page 10 / 26 5 / 12 adding an economic value dimension to the carbon capture process (Abraham et al., Integrating biological and chemical CO2 sequestration using green microalgae for bioproducts generation. Frontiers in Climate 4, 2023).

[015] In this scenario, microalgae and cyanobacteria fix carbon from gases through photosynthesis, where CO2 is incorporated into metabolic cycles to obtain organic carbon, resulting in microalgal growth, using solar energy and releasing oxygen into the atmosphere.

[016] Furthermore, some of these microorganisms have increased enzyme activity such as carbonic anhydrase, and consequently exhibit greater efficiency in metabolizing bicarbonate (HCO3-). In this sense, it is worth highlighting the cyanobacterium Spirulina sp. (Arthrospira sp.), efficient due to its high growth rate in highly alkaline media (pH > 8.0), which makes contamination difficult in open or large-scale cultivation; and due to its commercial relevance because of the characteristics of its biomass rich in protein (> 50% mm-1) and pigments of high added value (de Jesus et al., Outdoor pilot-scale cultivation of Spirulina sp. LEB-18 in different geographic locations for evaluating its growth and chemical composition. Bioresource Technology 256, 86-94, 2018).

[017] Spirulina sp. is a filamentous, photosynthetic cyanobacterium, with media reported in the literature that predominantly use sodium bicarbonate (NaHCO3) as a carbon source (da Rosa et al., Spirulina cultivation with a CO2 absorbent: Influence on growth parameters and macromolecule production. Bioresource Technology 200, 528-534, 2016). This cyanobacterium is widely used on an industrial scale due to its high protein and nutraceutical content (e.g., antioxidants, anti-inflammatories, neuroprotectors), as well as having applications as biofuels and in the production of biomolecules (Wan et al., Spirulina. Nutraceuticals 2, 959-974, 2021).

[018] This cyanobacterium is also targeted for the development of Bio-CCU technologies. However, a gap in growth and carbon biofixation studies is the limitation of the CO2 residence time in liquid, Petition 870250009089, dated 04 / 02 / 2025, page 11 / 26 6 / 12 which is insufficient for it to be efficiently retained in photobioreactors (Scapini et al., Microalgae-mediated biofixation as an innovative technology for flue gases towards carbon neutrality: A comprehensive review. Journal of Environmental Management 363, 121329, 2024).

[019] This gap is filled by the solution proposed in this document, where the gas stream is retained in the chemical absorbent in the liquid medium, converting to bicarbonate rapidly and allowing supplementation in the cultivation of cyanobacteria, with gains in carbon biofixation and biomass productivity, and the possibility of obtaining bioproducts such as protein and pigments.

[020] In view of the foregoing, the present invention proposes a method for carbon fixation from combustion and fermentation gases rich in CO2 using a chemical system with conversion to HCOf and subsequent cultivation of microalgae and / or cyanobacteria, such as Spirulina sp., in a bubble column photobioreactor.

[021] Several patents were collected and analyzed to recognize the state of the art in the field of study, as shown in Table 1. Table 1 - Patents and scientific articles related to the subject of this patent application. Patent / Article Country Microalgae or cyanobacteria Chemical absorbent CN109609383 China Chlorella sp. LAMB38 Ammonium hydroxide KR101841917B1 South Korea Nannochloropsis, Porphyridium and Spirulina Sodium hydroxide 0.2 N US20240209297 United States of America Filamentous algae, microalgae and / or cyanobacteria Porous membrane immersed in carbonate solution Petition 870250009089, dated 04 / 02 / 2025, page 12 / 26 7 / 12 CN114790424 JP1998057745 Botryococcus, Dunaliella, Chlorella, China Scenedesmus, Chamydomonas reinhardtii, Cryptomonas, Cylindrotheca, Pavlova, Diethanolamine (DEA) Japan Tetraselmis, Phaeodactylum, Isochrysis, Spirulina, Nannochloropsis, Euglena Spirulina, Dunaniella and Polyphyllidium Calcium hydroxide, Magnesium hydroxide and Sodium hydroxide Song et al., Concept of regeneration and use of romance using chemically rich absorption solvent as a carbon source for microalgae biomass production. Industrial & Engineering Chemical Research 58, 11720-27, 2019 China Chlorella sp. L38 Potassium carbonate and ammonium carbonate Zhang et al., Effects of different bicarbonates in Spirulina on CO2 absorption and hybrid microalgae conversion system. Frontiers in Bioengineering and Biotechnology 10, 2023 China Spirulina platensis Sodium carbonate and potassium carbonate Source: The Author (2024)

[022] In the patent literature and scientific articles, several records can be cited, both nationally and internationally, related to processes and products from cyanobacteria and / or microalgae with objectives such as obtaining biomass (BR1020180118463), food products (BR1020220032190), pharmaceuticals (BR1320200177000E2), biofuels Petition 870250009089, dated 04 / 02 / 2025, page 13 / 26 8 / 12 (CN107523423), wastewater treatment (BR1020220135380A2), among others.

[023] In comparison with the present invention, for example, invention KR101841917B1 entitled “The method of cultivating microalgae by fixation of carbon dioxide using strong base” refers to a process for pretreating the microalgae culture medium using 0.2 N sodium hydroxide to reduce the bacterial count, reducing sterilization costs while converting to inorganic carbon (sodium bicarbonate) for the growth of microalgae and cyanobacteria. This invention differs from the present invention in that it provides for the coupling of chemical and biological reactors at different stages, allowing for different routes for obtaining microalgae and bicarbonate.

[024] The invention JP1998057745 entitled “Recovering and fixing method of carbon dioxide” refers to the fixation process using bases such as sodium, magnesium and calcium hydroxides, which, after fixation, is introduced into an algae cultivation tank. Although both inventions deal with chemical fixation followed by biological fixation, the present invention differs because the patent application proposes an integrated system where there is liquid and gaseous transfer between the reactors. Furthermore, it presents a divergence in the concentrations of sodium hydroxide used.

[025] The invention KR1020200016503, entitled “Device for measuring carbon dioxide absorption rate in green algae culture”, refers to a process in which microalgae are cultivated in carbonated water supplied by a generator and gas injection is conducted for simultaneous fixation in the same reactor. This system differs from the present patent application, since the medium described in this invention uses strong bases (NaOH or others) that chemically fix and provide a bicarbonate-rich culture medium for the cultivation of microalgae and / or cyanobacteria.

[026] In this context, the present invention proposes to use chemical and biological reactors as a means of carbon fixation from combustion and / or fermentation gases or other gases rich in CO2, aiming at the recovery of Petition 870250009089, dated 04 / 02 / 2025, p. 14 / 26 9 / 12 Value-added bioproducts, addressing the context of a circular economy and low carbon footprint. Description of the approach to the technical problem

[027] The process development in the present invention proposes the biofixation of CO2 from combustion and / or fermentation gases or other CO2-rich gases in a bubble column reactor filled with an alkaline solution (e.g., NaOH), with transfer of the liquid (rich in HCO3-) and excess gas to a photobioreactor with microalgae or cyanobacteria culture.

[028] The process of the present invention stands out as a technological solution to increase CO2 fixation in gases, overcoming the technical bottleneck of low gas dissolution in liquid medium and coupling a biological system with microalgae, with evident gains in productivity and biofixation.

[029] In summary, the process developed presents a series of innovative advantages, such as: a. High efficiency in CO2 fixation from industrial combustion or fermentation gases using a bubble column reactor; b. Integration of chemical and biological fixation, where chemical CO2 capture is followed by biological conversion into high-value-added biomass, creating a closed system that maximizes the use of captured carbon; c. The process shows a notable increase in cyanobacteria biomass production of 29%, demonstrating a clear gain in biological productivity; d. This is a simplified process, with the possibility of extracting multiple products; Petition 870250009089, dated 04 / 02 / 2025, page 15 / 26 10 / 12 e. The process is designed for post-combustion or fermentation gases, requiring no major modifications to existing industrial processes.

[030] Thus, the objective of the present invention is to offer a technological solution for CO2 biofixation and the production of microalgal and / or cyanobacterial biomass which, consequently, generates high value-added products for different industrial sectors. List of figures [0 31] Figure 1. Flowchart of a method to maximize the biofixation of industrial combustion and / or fermentation gases using a hybrid process.

[032] Figure 2. Chemical reaction between NaOH and CO2-rich gas. Detailed description of the invention.

[033] The process for fixing CO2-rich gases from industrial combustion and / or fermentation gases, according to the present invention, consists of the following steps (Figure 1): a. Preparation of an alkaline solution, such as sodium hydroxide (NaOH), in a bubble column reactor; b. Injection of a gas stream (rich in CO2) into the alkaline solution, where the CO2 is chemically converted into bicarbonate (HCO3-); c. Transfer of liquid (HCOi) and non-chemically absorbed gas to a photobioreactor where microalgae and / or cyanobacteria will be cultivated; d. Inoculation of microalgae and / or cyanobacteria, such as Spirulina sp., into the photobioreactor; e. Cultivation and carbon biofixation through the cultivation of microalgae and / or cyanobacteria in a photobioreactor; f. Harvesting the biomass produced; g. Drying of the biomass produced. Petition 870250009089, dated 04 / 02 / 2025, page 16 / 26 11 / 12

[034] The carbon biofixation process using a hybrid system (chemical and biological), as described in the present invention, involves integrated reactors that combine chemical capture of CO2 in a bubble column reactor with the subsequent cultivation of cyanobacteria and / or microalgae in a photobioreactor, with biomass recovery.

[035] Step “a” consists of the chemical fixation medium, for example NaOH (0.05 to 2.2 N), which has the ability to capture CO2 from the gas stream originating from industrial sources (combustion and / or fermentation gases).

[036] Step “b” consists of injecting a gas stream into the bubble column reactor, at a CO2 concentration of 0.04% to 15% (vv-1). The gas stream is introduced into the solution at a controlled flow rate of 1 to 8.5 vvm. The reaction of CO2 in the alkaline solution forms bicarbonate (HCO3-), in order to obtain a liquid rich in carbon source for the cultivation of microalgae and / or cyanobacteria.

[037] An example of carrying out step “b” is reported below: an alkaline NaOH solution at a concentration of 1.35 N is introduced into a reactor with a working volume of 800 mL. A gas stream containing 12% (vv-1) CO2 is injected into the reactor at a flow rate of 5.45 vvm. During the process, the CO2 present in the gas stream reacts with the NaOH, forming bicarbonate (HCO3-) and a CO2 fixation of 70% in 10 minutes of reaction (Figure 2).

[038] Step “c” consists of transferring the liquid enriched with bicarbonate, along with the excess gas, to a bubble column photobioreactor.

[039] Step “d” of the process consists of inoculating the cyanobacteria or microalga, preferably Spirulina sp., at a cell concentration of 0.1 to 0.4 gL-1.

[040] Step “e” consists of cultivating cyanobacteria and / or microalgae in a bubble column photobioreactor using bicarbonate and CO2 as a carbon source for microbial growth under controlled light conditions (50 to Petition 870250009089, dated 04 / 02 / 2025, page 17 / 26 12 / 12 150 μmol.m-2.s-1) and temperature (25 to 35°C) and with a growth time of 4 to 14 days.

[041] An example of carrying out step “e” involves using a bubble column photobioreactor with a working volume of 1.6 L of Zarrouk medium with a sodium bicarbonate concentration of 30 gL-1 from chemical fixation and inoculating it with a 0.2 gL-1 culture of Spirulina sp. The system is then incubated at room temperature, which can vary from 25°C to 32°C, for 14 days with a 12:12 photoperiod and illumination of 100 μmol.m-2.s-1. During cultivation, the CO2 concentration should be 1.5 to 2.5% (vv-1) for 4 hours in a light photoperiod. Cell growth reaches 280 mg.L-1 in 4 days and 542 mg.L-1 in 14 days, with an average carbon biofixation of 93 mg.L-1.d-1 and biomass productivity of 50.95 mg.L-1.d-1, demonstrating an increase of 43.78% compared to the control, with standard Zarrouk and without CO2 addition.

[042] Step “f” consists of the process of harvesting the biomass produced, carried out by centrifugation at 3,000 rpm for 10 to 30 minutes.

[043] Stage “g” is characterized by the drying of the biomass, and is carried out at temperatures up to 50°C until it reaches a moisture content between 5 and 15% (mm-1).

[044] The present invention also contemplates a cellular composition characterized by a protein content greater than 55% (mm-1). And with recovery of excess bicarbonate and precipitate during chemical fixation.

Claims

1. HYBRID PROCESS FOR CARBON FIXATION FROM COMBUSTION GASES AND / OR FERMENTATION TO OBTAIN CYANOBACTERIA OR MICROALGAE BIOMASS, characterized by the use comprising the following steps: a. Preparation of an alkaline solution in a bubble column reactor; b. Injection of a gas stream (rich in CO2) into the alkaline solution, forming bicarbonate (HCO3-); c. Transfer of liquid (HCO3-) and non-chemically absorbed gas to a photobioreactor where the microalgae or cyanobacteria will be cultivated; d. Inoculation of the microalgae or cyanobacteria into the photobioreactor; e. Cultivation and carbon biofixation by cultivating microalgae and / or cyanobacteria in the photobioreactor; f. Harvesting of the biomass produced; g. Drying of the biomass produced.

2. PROCESS, according to claim 1, characterized by carrying out step “a” using more specifically sodium hydroxide (NaOH) in concentrations of 0.05 to 2.2 N.

3. PROCESS, according to claim 1, characterized by carrying out step “b” with the injection of a gas stream rich in CO2 at a concentration of 0.04 to 15% (vv-1), with a controlled flow rate of 1 to 8.5 vvm.

4. PROCESS, according to claim 1, characterized by carrying out step “c” with the transfer of liquid (HCO3-) and chemically unabsorbed gas to a photobioreactor where the cultivation of microalgae or cyanobacteria will occur. Petition 870250009089, dated 04 / 02 / 2025, page 21 / 26 2 / 2 5. PROCESS, according to claim 1, characterized by carrying out step “d” by inoculating microalgae or cyanobacteria, preferably Spirulina sp., at a cell inoculum concentration of 0.1 to 0.4 gL-1.

6. PROCESS, according to claim 1, characterized by carrying out step “e” by conducting the cultivation of cyanobacteria and / or microalgae in a bubble column photobioreactor, with injection of CO2-rich gases from 0.04 to 5% (vv-1), temperature from 25 to 35°C, with a photoperiod of 12h:12h (light:dark), light intensity from 50 to 150 μmol.m-2.s-1 for 4 to 14 days.

7. PROCESS, according to claim 1, characterized by carrying out steps “f” and “g”, respectively, at a rotation speed of 3,000 to 5,000 rpm and a drying temperature of 25 to 50°C.

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