WO2006120278A1

WO2006120278A1 - Method of fixing carbon dioxide using a culture of cyanobacteria

Info

Publication number: WO2006120278A1
Application number: PCT/ES2006/070056
Authority: WO
Inventors: Miguel GARCÍA GUERRERO; José MORENO FÉRNANDEZ; Mercedes GARCÍA GONZÁLEZ; Antonio MARTÍNEZ BLANCO; Francisco Gabriel ACIÉN FERNÁNDEZ; Emilio Molina Grima
Original assignee: Consejo Superior De Investigaciones Científicas; Universidad De Sevilla; Universidad De Almeria
Priority date: 2005-05-11
Filing date: 2006-05-11
Publication date: 2006-11-16
Also published as: ES2262432A1; ES2262432B1

Abstract

The invention relates to a method of fixing carbon dioxide (CO2) by cultivating any halotolerant nitrogen-fixing cyanobacterium which can produce an exopolysaccharide that is excreted to the medium. The inventive method can be used to reduce or eliminate CO2 emissions from industrial processes, such as from electrical power plants. The invention also relates to the biofuel use of an exopolysaccharide that is produced from the cultivation of cyanobacterium Anabaena which has a high calorific value. By using the aforementioned exopolysaccharide as a biofuel, it is possible to reduce fossil fuel consumption in industrial processes that use same.

Description

TITLE

PROCEDURE FOR FIXING CARBON DIOXIDE THROUGH THE

USE OF A CIANOBACTERIA CULTURE

SECTOR OF THE TECHNIQUE

Environment. The object of the present invention is a process for fixing and eliminating carbon dioxide (CO2), from industrial process emissions, by cultivating a nitrogen-fixing cyanobacterium, halotolerant and capable of producing an exopolysaccharide (EPS).

STATE OF THE TECHNIQUE

Carbon dioxide or carbon dioxide (CO ₂ ), despite being a minor gas in the Earth's atmosphere (0.03%, v / v), is one of its most important components, since it is a substrate in photosynthesis, on the one hand, and the main product of the respiration of living beings and the combustion of energy products on the other. Currently there is an increase in the level of CO ₂ in the atmosphere, which is responsible for the increase in the use of fossil fuels (coal, oil, natural gas), which can lead to overheating of the earth's surface (greenhouse effect). A major problem affecting the economic development of many countries is the high level of _CO2 emissions, which can put them in a precarious situation in the future emissions market.

To solve these problems it becomes necessary to develop and deploy new technologies to generate energy with lower _CO2 emission and other needed to eliminate CO _2, reducing its level in the exhaust gases generated industrially. The first aspect involves a technological substitution difficult to address in the short term by many countries.

Regarding the second aspect, various studies are being carried out that consider from the fixation of CO ₂ by forest masses to its retention in the sea, gas bags or petrocalcic soils, with special emphasis on various alternatives for taking advantage of the photosynthetic fixation of the CO ₂ . In fact, among the different options based on favoring natural CO ₂ sinks, the photosynthetic fixation of CO ₂ through the cultivation of microalgae and cyanobacteria is, in principle, the most promising alternative, since these microorganisms are the most effective fixative agents of CO2 of the planet, with yields more than five times higher than corn plantations, also constituting one of the most versatile groups in the biosphere. Likewise, the nature hydraulic crop facilitates handling and the installation thereof contiguous to Ia own radio source of CO _2, whereas, in general, other natural sinks proposed only carbon CO2 fixation of the released Ia atmosphere, constituting diffuse pollution.

The culture of photosynthetic microorganisms uses CO2 as a source of carbon, converting it into organic carbon fixed in the form of the different organic compounds that constitute the biomass, as well as other photosynthetic products that can release cells, such as polysaccharides. A possible option for the use of biomass and / or other photosynthetic products generated through CO2 fixation, is its use as a source of energy, being materials with considerable energy content or heat of combustion. This reuse as a fuel for photosynthetic products involves carbon recycling and leads to a parallel reduction in fossil fuel consumption.

The efficiency and success of the use of photosynthetic microorganism cultures for the fixation of CO ₂ depend largely on the selected microorganism (species, strain, etc.), as well as the production system used and the optimization of the parameters of culture. Additionally, the properties of the generated photosynthetic products and the possibilities of their subsequent use must be considered. The emissions of CO ₂ into the atmosphere constitute a global problem. It would be desirable to develop a system that eliminates or at least reduces the emissions of CO ₂ emission sources of the pollutant own, efficiently, inexpensive, simple and versatile, achieving high rates of fixation of CO2, and at the same time generating photosynthetic products with applications of interest.

Using the green algae Chlorococcum littorale it has been possible to fix about 1 g of CO ₂ per liter and day in containers of 20 I capacity (Kurano N, lkemoto H, Miyashita H, Hasegawa T, Hata H and Miyachi S (1995). Fixation and utilization of carbon dioxide by microalgal photosynthesis. Energy Convers. Management 36 (6-9), 689-692). With the technology proposed here, CO ₂ fixation values between 2 and 6 g CO2 per liter and day can be achieved.

US patent WO0205932 "Photosynthetic carbon dioxide mitigation" uses thermophilic cyanobacteria (Cyanidium caldarium) immobilized on membranes, using a hybrid energy system for lighting (converting sunlight into electricity using photovoltaic panels and supply 400-700 nm light wavelength to the cells). The fixation product of CO ₂ is biomass, without considering the production of other compounds. The biomass produced must be regularly removed from the membranes through a complex cleaning system, which negatively results in the economy and performance of the process, making it difficult to scale.

In the present invention, the main product of the fixation of CO ₂ is a polysaccharide that the cells excrete in the medium. Said exopolysaccharide (EPS) possesses properties that confer practical interest for a variety of industrial applications (Bender J, Rodríguez-Eaton S, Ekanemesang UM and Phillips P (1994). Characterization of metal-binding bioflocculants produced by the cyanobacterial component of mixed microbial mats. Appl Environ Microbiol 60, 2311-2315); From Philippis R and Vicenzini M (1998). Exocellular polysaccharides from cyanobacteria and their possible applications. FEMS Microbiology Reviews 22, 151-175; Flaibani A, Olsen Y and Painter TJ (1989). Polysaccharides in desert reclamation: Compositions of exocellular proteoglycan complexes produced by filamentous blue-green edaphic algae. Carbohydr Res 190, 235-248; Sutherland IW (1996). Extracellular polysaccharides In: Biotechnology, VCH, Weinheim (Rehm, HJ and Reed, G eds.) Vol 6, 615-657). This system uses direct sunlight for developing the fixation of CO ₂ and permits easy scaling.

BRIEF DESCRIPTION OF THE INVENTION

As previously mentioned, it would be convenient to have a CO ₂ fixation procedure capable of reducing the concentration of this gas in the atmosphere, coupled with the generation of an organic product that can be used. The present invention describes a method for fixing CO ₂ by means of the use of a culture of photosynthetic microorganisms coupled to the production of an exopolysaccharide, which has considerable heat of combustion and other properties that confer practical interest.

Therefore, in one aspect, the invention relates to said method for fixing CO ₂ comprising the following steps: a- cultivating a photosynthetic microorganism in a suitable system. b- supply CO ₂ or another inorganic form of carbon derived from it, such as bicarbonate (HCO ₃ ) and / or CCO ₃ carbonate), at high concentrations, and c- collect the products of CO ₂ fixation and other forms of inorganic carbon derived from it (bicarbonate, carbonate), generated by said culture.

The cultured microorganism is a N ₂ fixing cyanobacterium, halotolerant, that photosynthesizes an exopolysaccharide that excretes in the environment. This cyanobacterium can be grown in open or closed systems. The supply of CO ₂ (in high concentrations, and always higher than natural atmospheric) can be carried out directly in the form of gas or after its solubilization in a liquid (such as CO ₂ , such as bicarbonate or carbonate) that would be used as a culture medium . CO ₂ in high concentration can come from power generation plants, cement plants or industrial plants that develop CO ₂ generating processes. As one of the majority photosynthetic products of the fixation of inorganic carbon (CO ₂ , bicarbonate, carbonate) through the cultivation of these cyanobacteria, an exopolysaccharide (EPS) is obtained that is released into the environment.

Said polysaccharide, given its energy properties, can be used as a biofuel, either in the plant itself that generated the polluting CO ₂ or in other facilities.

In a particular embodiment, the Anabaena species is used, and preferably the Anabaena sp. ATCC 33047, which produces an EPS that has a heat of combustion similar to that of coal or wood, of at least 14 kJ / g.

The process of the present invention has a high rate of fixation of CO ₂ and production of exopolysaccharide, being able, in the case of Anabaena, to generate at least 1.3 g of polysaccharide in addition to at least 0.4 g of biomass per liter and day and fix 1, 6 kg of CO ₂ for each kg of polysaccharide produced.

In another aspect, the invention is therefore related to the use of said method to reduce or eliminate CO ₂ emissions produced by power generation plants and a variety of industrial processes, but also, on the other hand, the use of their products As a biofuel it is possible to reduce the consumption of fossil fuels.

The invention also relates to the use of the polysaccharide generated from the fixation of CO ₂ by Anabaena, as an emulsifying, stabilizing or thickening agent in the food, textile, paint, paper, cosmetic and pharmaceutical industries.

Said polysaccharide can also be used for adsorption, concentration, or elimination of (heavy) metals in wastewater of diverse origin (urban, heavy industry, mining, etc.), as well as for the conditioning and recovery of soils for agricultural use. Similarly, EPS can be used as an antiviral agent, or as a substrate for fermentation processes.

DETAILED DESCRIPTION OF THE INVENTION

In one aspect, the invention relates to a method for fixing CO2 by using a culture of photosynthetic microorganisms, hereinafter the method of the invention, which comprises the following steps: a) cultivating said microorganism in a suitable system b) supplying the CO2 culture or other inorganic form of carbon derived from it, such as bicarbonate (HCO ₃ ) and / or carbonate CCO ₃ ), at high concentrations, and c) collecting the products of the fixation of CO ₂ and other forms of inorganic carbon of he derivatives (bicarbonate, carbonate), generated by said culture, the cultured microorganism being any nitrogen fixing cyanobacterium, halotolerant, and capable of producing an exopolysaccharide (EPS) that is excreted in the medium.

The process of the invention contemplates that the culture of the selected microorganism can be carried out both in open and closed systems. The cultivation of microorganisms in the open system is more economical, but in counterpart it allows little control of important parameters for the adequate progress of the process. Closed cropping systems allow a better and stricter control of the operating conditions of the crop, which results in higher productivity and higher quality products, but these are more sophisticated and more expensive systems. In a particular embodiment of the invention, a closed culture system was used, specifically a closed tubular photobioreactor, placed outdoors. In another particular embodiment of the invention, the viability of the crop, outdoors, in open ponds with a surface area of 1 and 10 m ² was observed. The contribution of inorganic carbon at high concentrations mentioned in point b) of the process of the invention is carried out either directly in the form of CO ₂ gas or after its solubilization in a liquid (such as CO ₂ , bicarbonate and / or carbonate) that subsequently it is used as a culture medium for the microorganism. The concentration of initial CO ₂ supplied to the crop, in all cases is higher than atmospheric, 0.03% (v / v). The emitting source of said CO ₂ can be selected from an electricity generation plant, a cement plant, or an industrial process plant, among others. In a particular embodiment of the invention, CO ₂ is supplied in the form of a gas, which is injected into a closed tubular photobioreactor through its gas inlet valves. In another particular embodiment of the invention it would be possible to supply the CO ₂ fixed in seawater that would be used later as a culture medium. The use of seawater would not negatively affect the growth of the microorganism since it is a halotolerant strain.

Through the process of the invention and as a consequence of the fixation of CO ₂ , various photosynthetic products are obtained, of which at least one is an exopolysaccharide (EPS), this EPS being able to constitute the majority photosynthetic product.

In a particular embodiment of the invention, the cultured microorganism belongs to the Anabaena species, specifically the Anabaena sp. ATCC 33047. This lineage, Anabaena sp. ATCC 33047, has a high growth rate, even at high population density, tolerates wide ranges of pH, temperature, irradiance and concentration of salts, has the ability to fix nitrogen (so it does not need nitrogen fertilizer and reduces the risk of contamination), high productivity and high efficiency for the fixation of CO ₂ , being easy to collect (Moreno J, Vargas MA, Olivares H, Rivas J and Guerrero MG (1998). Exopolysaccharide production by the cyanobacterium Anabaena sp. ATCC 33047 in batch and continuous culture J Biotechnol 60, 175-182; Moreno J, Vargas MA, Madiedo JM, Muñoz J, Rivas J and Guerrero MG (2000) Chemical and rheological properties of an extracellular polysaccharide produced by the cyanobacterium Anabaena sp. ATCC 33047. Biotechnol Bioeng 67, 283-290). Especially noteworthy is its high rate of EPS generation, which is even higher under stress conditions, reaching an EPS productivity at least 3 times higher than that of biomass generation. These characteristics make this cyanobacteria an ideal candidate for use in the effective biofixation of CO ₂ present in exhaust gases or in other polluting sources emitting this gas.

Said EPS produced by Anabaena species has a heat of combustion similar to that of wood or coal. In a particular embodiment of the invention, the heat of combustion of said EPS is at least 14 kJ / g.

The method of the invention provides an effective and efficient mechanism for fixing CO _2, coupled to the production of a susceptible EPS be exploited. In a particular embodiment of the invention, at least 1.3 g per liter and day of polysaccharide were obtained in addition to at least 0.4 g of biomass per liter and day. In another particular embodiment, the fixation of 1.6 kg of CO ₂ was verified for each kg of polysaccharide produced. In another particular embodiment of this procedure, between 2 and 6 g of CO ₂ were fixed per liter and day.

In another aspect, the invention relates to the use of the process to reduce or eliminate CO ₂ emissions that come from industrial processes, preferably from power generation plants, and to reduce the consumption of fossil fuels in those industrial processes that They used, by replacing products CO ₂ fixation obtained in said process.

Both the biomass or cellular material, and the EPS generated by this process, using Anabaena species crops, such as the mixture of biomass and EPS, can be used for various purposes, being one of its possible applications its combustion for heat generation or electricity, since both biomass and EPS have considerable heat of combustion (equal to or greater than 14 kJ / g). Therefore, in another aspect, the invention relates to the use of the EPS obtained, as a biofuel. In a Particular embodiment of the invention, the EPS obtained could be used as biofuel in the same plant that generates the CO ₂ pollutant emissions.

The EPS produced by the microorganisms can have applications in the agri-food and / or pharmaceutical industry (Sutherland IW (1996) Extracellular polysaccharides. In: Biotechnology VCH, Weinheim (Rehm HJ and Reed G. eds.), Vol 6, 615-657). Anionic polysaccharides are useful for the detection, adsorption, concentration and / or elimination of metal ions from wastewater (Bender J, Rodríguez-Eaton S, Ekanemesang UM and Phillips P (1994). Characterization of metal-binding bioflocculants produced by the cyanobacterial component of mixed microbial mats. Appl Environ Microbiol 60, 2311-2315; Bertocchi C, Navarini L and Cesara A (1990). Polysaccharides from cyanobacteria. Carbohydr Polym 12, 127-153). Similarly, EPS can be used to induce flocculation of solid particles in the treatment of urban wastewater, as well as in the conditioning and recovery of soils for agricultural use (Flaibani A, Olsen Y and Painter TJ (1989). Polysaccharides in desert reclamation : Compositions of exocellular proteoglycan complexes produced by filamentous blue-green edaphic algae. Carbohydr Res 190, 235-248). Some microorganism polysaccharides, especially those of the photoautotrophic type have antiviral activity (Yim JH, Kim SJ, Ahn SH, Lee ChK, Rhie KT and Lee HK (2004). Antiviral Effects of Sulphated Exopolysaccharide from the Marine Microalga Gyrodinium impudicum Strain KG03. Mar Biotechnol 6, 17-25). Therefore, another aspect of the invention relates to the use of EPS generated from the Anabaena species as an emulsifying, stabilizing or thickening agent in the food, textile, paint, paper, cosmetic and / or pharmaceutical industry, as well as as its use for the concentration and / or elimination of metals in wastewater of diverse origin (urban, heavy industry, mining, etc.). Likewise, the invention relates to the use of this EPS in the conditioning and recovery of soils for agricultural use, as a potential antiviral agent and as a substrate for fermentation processes. The following example serves to illustrate the invention and should not be considered for limiting purposes thereof.

EXAMPLE OF EMBODIMENT OF THE INVENTION

CROP OF Anabaena sp. IN CLOSED TUBULAR PHOTOBIOR REACTOR

In this particular embodiment of the invention the fixing cyanobacterium of N ₂ Anabaena sp. ATCC 33047, taking into account its special characteristics of CO ₂ fixing efficiency and its high productivity.

The cultivation of Anabaena sp. ATCC 33047 was carried out outdoors in a closed tubular photobioreactor, the light source being sunlight. Said system consists of a solar light collection module consisting of tubes of transparent material (rigid plexiglass) of 24 mm internal diameter and 30 mm external diameter and a total length of 90 m, located horizontally in parallel and connected to each other by half of pieces in the form of "u" of the same material, with a photosynthetically active surface of 2.2 m ² and 55 I of useful volume. Two rubber balls with a diameter slightly smaller than the inside diameter of the tubes circulate to prevent the deposit of cells in their walls. These tubes are submerged in water, which acts as a thermostatting element of the crop, in a bath of dimensions 1, 8x6.0x0.15 m, equipped with a closed circulation circuit with heating and cooling elements. In this culture system, the cell suspension is stirred and circulated through the tubes by the delivery of sterile air under pressure generated by a compressor (air-lift). The tubular system ends in a 52 cm high by 26 cm external diameter cylinder, located 2.8 m high from the horizontal of the reactor. In the cover of this cylinder there are several holes for: gas outlet (protected by a 0.22 μm filter), input for rapid filling of the reactor, fresh medium input to operate in continuous culture and level sensor. In the lower part of the cylinder are also the pH and temperature probes. These probes are connected to a control unit.

The introduction into the culture system of a cell suspension of Anabaena sp. ATCC 33047 with a concentration of chlorophyll between 5 and 10 mg per liter of culture. Said suspension was kept in circulation at a speed between 0.2 and 0.4 ms ^"1 for a period of 72 hours, during which the culture is maintained in a watertight regime, with temperature control, maximum of 35 ° C during the day and 18 ° C overnight, and subjected to solar irradiance After 72 hours, the culture is subjected to continuous regime, with continued addition of fresh culture medium (which covers all the nutritional requirements of the microorganism) during the period of light The cell suspension is kept circulating in the tubes for 45 days.

During the process, the pH value is maintained between 8.0 and 8.5 by means of the injection of CO2 through a solenoid valve regulated by a pH controller. The CO2 is injected into the horizontal zone of the return tube of the cell suspension towards the light collection module. The photosynthetic consumption of CO ₂ by the cells of the cyanobacteria causes an increase in the pH of the medium, which, upon exceeding the value of 8.5, triggers the injection of a stream of CO ₂ pure gas, with which the medium is acidified, stopping The injection of CO ₂ once the pH 8.0 is recovered.

Maintaining the culture in the system and conditions indicated above, the concentration of exopolysaccharide in the medium reached values of up to 8 g per liter, with an EPS productivity of up to 4 g per liter per day. The collection of the suspension enriched with the EPS generated and the accompanying biomass is carried out continuously during the light period at a flow of approximately 2 liters per hour.

Claims

1.- Procedure for fixing CO2 by means of the use of a culture of photosynthetic microorganisms comprising the following steps: a) cultivating said microorganism in a suitable system, b) supplying the CO2 culture or other inorganic form of carbon derived therefrom, such as bicarbonate (HCO ₃ ) and / or CCO ₃ carbonate, at high concentrations, and c) collect the products of the fixation of CO2 and other forms of inorganic carbon derived from it (bicarbonate, carbonate), generated by said crop, characterized in that The microorganism grown in a) is any nitrogen-fixing cyanobacterium, halotolerant and capable of producing an exopolysaccharide that is excreted in the medium.

2. Method for fixing CO ₂ according to claim 1, characterized in that said microorganism culture is carried out in a closed system, preferably in a closed tubular photobioreactor.

3. Method for fixing CO ₂ according to claim 1 characterized in that said culture of microorganisms is carried out in an open system.

4. Method for _CO2 set according any of claims 1 to Ia 3 Ia wherein the CO ₂ at high concentration is supplied to the culture in gaseous form, preferably by supplying said gas directly from Ia source emitting _CO2.

5. Method for fixing CO ₂ according to any of claims 1 to 3, characterized in that the CO ₂ in high concentrations is supplied to the fixed culture in liquid medium, said liquid medium being subsequently used as the microorganism culture medium.

6. Method for fixing CO2 according to claim 5, characterized in that said liquid medium where CO ₂ is fixed and the microorganism is grown, is salt water, preferably seawater

7. Method for fixing CO ₂ according to any of claims 4, 5 and 6 characterized in that the emitting source of CO ₂ is a power generation plant, a cement plant, or an industrial process plant.

8. Method for fixing CO ₂ according to any of claims 4 to 7, characterized in that the concentration of CO ₂ supplied is greater than 0.03% (v / v).

9. Method for fixing CO ₂ according to any of claims 1 to 8, characterized in that the majority product of the fixation of CO ₂ generated by the culture of the microorganism, is a polysaccharide that is released into the medium.

10. Method for fixing CO ₂ according to any of claims 1 to 9, characterized in that said culture of microorganisms is a culture of the Anabaena species, preferably the Anabaena sp. ATCC 33047.

11. Method for fixing CO ₂ according to claim 10, characterized in that it fixes at least 1.6 kg of CO ₂ for each kg of polysaccharide produced.

12. Method for fixing CO ₂ according to claim 10, characterized in that, by means of the cultivation of microorganisms, it produces at least 1.3 g of polysaccharide and 0.4 g of biomass per liter and day.

13.- Procedure for fixing CO ₂ according to claim 10 characterized in that by means of the culture of microorganisms it fixes between 2 and 6 g of CO ₂ per liter and day.

14.- Use of a method according to any of claims 1 to 13, to reduce or eliminate CO ₂ emissions that come from industrial processes, preferably from power generation plants.

15.- Use of a process according to any of claims 1 to 13 to reduce the consumption of fossil fuels in those industrial processes that use them, by replacing them with CO2 fixation products obtained in said process.

16.- Use of a polysaccharide (alone or mixed with biomass) obtained according to the method described in claim 10, as biofuel.

17. Use of a polysaccharide (alone or mixed with biomass) according to claim 16 as biofuel Ia same gas generating plant with high CO ₂ content.

18.- Use of a polysaccharide obtained according to the method described in claim 10, as an emulsifying, stabilizing or thickening agent in the food, textile, paint, paper, cosmetic and pharmaceutical industry.

19.- Use of a polysaccharide obtained according to the procedure described in claim 10, for the concentration or elimination of metals in wastewater of diverse origin (urban, heavy industry, mining, etc.)

20.- Use of a polysaccharide obtained according to the method described in claim 10, for the conditioning and recovery of soils for agricultural use.

21.- Use of a polysaccharide obtained according to the method described in claim 10, as an antiviral agent.

22.- Use of a polysaccharide obtained according to the procedure described in claim 10, alone or in combination with the biomass, as a substrate for fermentation processes.