Method for injecting co2 in the absence of light, in spirulina culture

Abstract

The present invention relates to equipment for supplying, to a facility for culturing microalgae and in particular for culturing spirulina, water in which a specified CO 2 content has been dissolved, characterized in that the equipment makes it possible for the CO 2 to be dissolved (1, 8, 4, ...) under light-obscuring conditions, the equipment being located outside of, and adjacent to, the culture facility.

Description

CO2 injection process in the absence of light, in spirulina culture

[0001] The present invention relates to the cultivation of microalgae and is particularly interested in the cultivation of spirulina.

[0002] If we consider the case of spirulina, it is a micro-algae cultivated for its nutritional benefits. It is rich in proteins, carotenoids, iron, unsaturated fatty acids, and is also rich in phycocyanin. It is sold on the food supplement market mainly in its dry state, in the form of capsules or even in powder form.

[0003] For example, 40 to 50 tonnes are produced and consumed in France annually, and it is considered that around 3,000 tonnes are consumed per year worldwide.

[0004] It should also be mentioned that, in addition to its nutritional qualities, which offer an extremely valuable solution for certain populations worldwide, the cultivation of spirulina (and more generally of micro-algae) represents a major contribution to resolving the problem of reducing greenhouse gases, since it specifically allows CO2 to be sequestered.

[0005] In fact, it has been shown that on average, each year, spirulina absorbs 50 tonnes of CO2 per hectare, compared to 4 tonnes for forests, so it is a capture of carbon dioxide 10 times higher than what is achieved by the traditional solution of tree forests.

[0006] We can therefore see that everything that can be proposed to improve the cultivation conditions and yield of micro-algae cultures, and in particular spirulina, is of enormous interest to the population.

[0007] Spirulina comes in the form of filaments made up of juxtaposed cells. Spirulina reproduces asexually by dividing the filaments.

[0008] To cultivate spirulina, it is necessary to artificially reproduce its living environment and create the conditions necessary for its development: greenhouse basins for heat, water at 37°C, agitation systems using paddle wheels or pumps, alkalinity, pH between 8 and 10, etc.

[0009] It is generally considered that its cultivation requires ten times less water than any other crop.

[0010] Very rich in protein, it offers a protein yield per hectare (30 to 50 tons) fifteen times higher than soy (2.5 tons). Its yield per hectare is very high. A great producer of oxygen, the crop does not emit greenhouse gases.

[0011] It is known that there are different cultivation systems currently in practice, which are adapted to the species of microalgae cultivated and the target molecules of interest: Open ponds: the method is undoubtedly the simplest and least expensive. It consists of cultivating spirulina in open ponds, exposed directly to sunlight. This method is particularly commonly used in hot and sunny regions where spirulina grows naturally.

[0012] However, this method is not without its drawbacks, linked to contamination by other micro-organisms, or even to pollution phenomena by heavy metals or other pollutants.

[0013] andClosed photo-bioreactors: this method involves cultivating spirulina in closed systems, "in a greenhouse", thus controlling all the cultivation conditions much better, including temperature, light, water quality and culture density. This method is obviously more expensive but it has several advantages, linked in particular to the purity of the spirulina produced, and the possibility of cultivating all year round.

[0014] In France, spirulina is mainly grown in freshwater ponds under greenhouse conditions. The quality of the water used in these farms is very important and therefore highly controlled. To get as close as possible to spirulina's natural habitat, French aquaculture farms add various elements such as sea salt, sodium bicarbonate, and various mineral salts (nitrogen, phosphorus, potassium, magnesium, iron, trace elements, etc.) to the water used. These elements constitute the food of spirulina.

[0015] Each element is provided in a quantity proportional to what the spirulina consumes and therefore to its productivity. All elements are consumed by the spirulina and transformed into proteins, carbohydrates and other elements.

[0016] No phytosanitary products are necessary for the cultivation of spirulina, no pesticides, herbicides, fungicides, GMOs or others are used for the cultivation of spirulina in France.

[0017] The main food of spirulina, however, is carbon, whose normal source is carbon dioxide. The simplest cultivation method, where the carbon food comes from the air, which contains carbon dioxide, but in extremely diluted proportions, has a modest productivity, but which, expressed in proteins, remains much higher than that of the best agricultural or horticultural crops, and which, expressed in food calories, is equivalent to them, and this without consuming more water, or even significantly less. The absorption of atmospheric CO2 occurs night and day, independently of daily variations in the weather, which therefore does not affect the average productivity of these crops; the latter is also not affected by an exaggerated temperature at night (the pH drops due to nocturnal respiration, but without loss of CO2, which will be used later).

[0018] In these cultures, the pH is traditionally maintained at around 10.6 or less by varying the shade, and the intensity of agitation is not critical.

[0019] It is generally considered that the factors that can promote lipid production are: Increased light intensity; A drop in the temperature of the pond water; An increase in the CO2 content injected into the water of the pond(s); A deficiency in nitrogen or phosphorus.

[0020] It should also be noted that the composition of lipids (particularly the fatty acid composition) also depends on culture conditions.

[0021] Once mature, the spirulina is harvested, dried, and packaged, most often following the following steps: Using a pump in the pond, the water is drawn into a harvester shaped like a rotating cylinder equipped with a 35 µm food filter. The filtrate is recycled and returned to the pond. Harvesting takes place in the early morning because this is the time of day when the algae are richest in protein. Spirulina then resembles fresh cheese, with the added chlorophyll color. Pressing removes the culture medium contained in the harvested biomass, which is 90% water. This is done with a press equipped with an air vacuum pump. At this stage, the spirulina resembles modeling clay. Fresh, it can be eaten on toast with fresh cheese, for example, or applied to the face as a beauty mask.Using a stainless steel sausage stuffer, the spirulina is placed in spaghetti on drying racks. It is important to form regular spaghetti to avoid clumps, which slows down the drying process. The algae are then dried for approximately ten hours in a ventilated dark room at 35°C. This technique allows the spirulina to retain all its nutritional properties (proteins, vitamins, trace elements, etc.). After drying, the spirulina is reduced to flakes. It is generally analyzed and packaged in food bags. These bags protect the spirulina from light and oxidation. Dried spirulina can be stored in flakes for approximately two years or reduced to powder or tablets depending on the consumption method.

[0022] It is also possible to increase the productivity of spirulina in good weather, for example to 12 or 15, or even 20 g / day / m², if there is sufficient agitation, by injecting pure carbon dioxide directly into the culture to lower its pH to 10 or less. The CO2 consumption is around 2 kg CO2 / kg of spirulina.

[0023] One possible way to inject the gas is to introduce it into a venturi at the outlet of a pump and to make the emulsion travel through several meters of pipe.

[0024] The problem with these previous processes lies in the competition between photosynthesis and the injection of CO2 into the pond water to regulate the pH.

[0025] It is also known that a better CO2 absorption efficiency is obtained at night due to the absence of oxygen release in the culture medium.

[0026] The present invention then seeks to propose conditions making it possible to improve the results obtained in such a culture of micro-algae and in particular spirulina.

[0027] As will be seen in more detail below, the present invention proposes conditions based on an injection of CO2 in the absence of light, allowing 24 / 7 use including for installations equipped with industrial lighting.

[0028] The present invention also makes it possible to improve gas / liquid transfers by acting on the following parameters: contact time for dissolution without light. gas velocity. liquid velocity: according to the invention, to dissolve a gas in a liquid, it is preferred to carry out this operation in a circuit which mixes the gas and the liquid with a velocity of at least 2m / s. gas pressure and depression (CO2): to have an adequate velocity the circuit increases in pressure, by the use of a pump, the pressurization and the pressure reduction generating gas exchanges, conducive to removing dissolved gases present in the water which are not CO2. circuit pressure at discharge (liquid): this pressure is directly linked to the characteristics of the pump used and the mixing circuit which generates a pressure difference. volume to be treated: this volume is dependent on the needs of the micro-algae producing site.the volume to be bypassed: the volume to be bypassed is preferably between 5 and 25%, and more preferably around 10%. degassing: degassing is the operation which allows the removal of unwanted gases dissolved in the treated water and improves the transfer of CO2 into the liquid. Knowing that approximately 90% of the water turns "into a duck", the water increases in pressure then in depression to carry out this degassing. the pH the temperature (which can be regulated in particular by injecting CO2 in its gaseous form or in its liquid form).

[0029] The fact that CO2 is dissolved in the absence of light promotes absorption efficiency, close to 100%, due to the absence of oxygen release.

[0030] And thus, in order not to be limited to an injection of CO2 at night, in order to carry out the dissolution in the absence of light, the present invention proposes to carry out the dissolution of the CO2 under conditions of opacity to light, in particular using dissolution equipment, external, adjacent to the culture installation, comprising a tank and a gas / liquid contactor which are opaque to light.

[0031] Dissolution therefore takes place without in any way competing with photosynthesis, promoting, as we have seen, an extremely high absorption yield, whether day or night.

[0032] According to an advantageous embodiment of the invention, the dissolution equipment comprises: a pump, which makes it possible to achieve a fluid speed preferably greater than 2 m / s; a gas / liquid contactor, for example, a coil, which makes it possible to achieve a contact time between the CO2 and the liquid preferably of at least 10 seconds, and even more preferably of at least 20 seconds; an atmospheric pressure tank making it possible in particular to degas the oxygen and nitrogen naturally present in the culture medium.

[0033] The appended document presents a partial schematic view of an installation for dissolving CO2 in water taken from a culture basin and returned to this basin once the dissolution has been carried out, allowing the implementation of the invention.

[0034] The presence of the following elements can be noted in this figure: an injector 1, for example of the Venturi type, allowing a gas to be injected into water; a water inlet line and a gas inlet line ("GAS") arrive at this injector, a gas line here connected in its upstream part to a CO2 storage (represented by a bottle), or a gas mixture comprising CO2; a pressure reducer 2; a control valve 3 (gas control valve allowing, due to its calibration, to inject a chosen quantity of gas into the injector); a contactor 4, for example like here a coil (device for making contact between the water and the CO2), the length of the coil allows a chosen gas / water contact time, preferably greater than or equal to 10 seconds; a water circulation pump 5, the water pump allows high water speeds to be reached in the coil, for example a speed greater than 2 m / s ;a spillway 6;a float valve 7;a tank of water at atmospheric pressure (8); line 9 is the line bringing the water from the basin to be treated; line 10 is the line which brings back to the basin culture water in which CO2 has been dissolved.;

[0035] The tank (opaque like the contactor) provides a recycling buffer volume, and it is the overflow which allows part of the water to be sent to the crop and another part according to recycling needs.

[0036] If this is an example of an installation allowing the invention to be implemented, one could also consider implementing the invention with what the industry calls a "smoke scrubber", by replacing the air with CO2.

[0037] The present invention then relates to equipment for supplying, to a micro-algae cultivation installation and in particular spirulina cultivation, water in which a given content of CO2 has been dissolved, characterized in that the equipment allows the CO2 to be dissolved in conditions of opacity to light, equipment which is located in an external position, adjacent to the cultivation installation.

[0038] According to one embodiment of the invention, the equipment comprises: a tank at atmospheric pressure, capable of constituting a recycling buffer volume, capable of receiving water to be treated from said microalgae culture; a pump, capable of supplying the tank with water from said culture, a pump which makes it possible to achieve a fluid speed preferably greater than 2 m / s; a gas injector in a liquid, for example of the Venturi type, injector on which arrive a water inlet line from the tank and a gas inlet line connected in its upstream part to a storage of CO2 or a gas mixture comprising CO2; a gas / liquid contactor, for example a coil, which makes it possible to achieve a contact time between the CO2 and the water to be treated, preferably of at least 10 seconds, and even more preferably of at least 20 seconds; a pipe for supplying water from said culture, into the tank;a water return pipe, from the tank to said crop, water in which said given CO2 content has been dissolved; a discharger receiving treated water from the contactor and capable of sending, according to the needs of the cultivation site, all or part of the water received to the crop and / or to the tank;

[0039] the tray and the contactor being opaque to light.

Claims

Equipment for supplying, to a microalgae cultivation facility and in particular spirulina cultivation, water in which a given CO2 content has been dissolved, characterized in that: the equipment is located in an external position, adjacent to the cultivation facility; and in that the equipment allows the CO2 to be dissolved in conditions of opacity to light, by the fact that it comprises: a tank (8) at atmospheric pressure, capable of constituting a recycling buffer volume, capable of receiving water (9) to be treated from said microalgae cultivation; a pump (5), capable of supplying the tank with water from said cultivation, a pump which makes it possible to achieve a fluid speed preferably greater than 2m / s;a gas injector (1) in a liquid, for example of the Venturi type, injector on which arrive a water inlet line from the tank and a gas inlet line (2, 3) connected in its upstream part to a storage of CO2 or a gas mixture comprising CO2; a gas / liquid contactor (4), for example a coil, which makes it possible to achieve a contact time between the CO2 and the water to be treated, preferably of at least 10 seconds, and even more preferably of at least 20 seconds; a pipe (9) for supplying water from said culture, into the tank; a pipe (10) for returning water, from the tank to said culture, water in which said given content of CO2 has been dissolved; a discharger (6) receiving treated water from the contactor and capable of sending, according to the needs of the culture site, all or part of the water it receives to the culture and / or to the tray; where the tray and the contactor are opaque to light.;

Images