METHOD FOR THE CULTURE OF PHOTOSYNTHETIC ORGANISMS USING A CO2 SOURCE

Abstract

Disclosed is a method for the culture of photosynthetic organisms selected from among microalgae, cyanobacteria and macroalgae using a continuous or discontinuous CO2 source.

Claims

1. Use of a first aqueous composition having a pH greater than pH.sub.H and of a second composition having a pH lower than pH.sub.B for the culture of photosynthetic organisms, selected from microalgae, cyanobacteria and macroalgae, in a culture system comprising a culture medium, in which: said first aqueous composition having a pH greater than pH.sub.H is obtained by contacting CO.sub.2 produced by a continuous or discontinuous CO.sub.2 source, a base, water and possibly all or some of the constituents of an algal culture medium; the second aqueous composition having a pH lower than pH.sub.B is obtained by dissolving CO.sub.2 produced by said source in water or an aqueous solution containing all some of the constituents of an algal culture medium; the pH of said culture medium being such that: when the pH of said culture medium reaches an upper limit, pH.sub.H, the second aqueous composition and/or CO.sub.2 produced by said source are/is added to said culture medium so as to lower the pH, preferably until the pH of said culture medium reaches a lower limit, pH.sub.B; when the pH of said culture medium reaches said lower limit, pH.sub.B, the first aqueous composition is added to said culture medium so as to increase the pH, preferably until the pH of said culture medium reaches an intermediate value, pH.sub.I, with pH.sub.B<pH.sub.I<pH.sub.H; and possibly, when the pH of said culture medium is lower than pH.sub.H, especially lower than pH.sub.I, the first aqueous composition is added to said culture medium so as to increase the pH, especially until the pH of said culture medium reaches the intermediate value pH.sub.I.

2. A method for the culture of photosynthetic organisms, selected from microalgae, cyanobacteria and macroalgae, using a continuous or discontinuous CO.sub.2 source, in which the CO.sub.2 is directed by means of pipes and valves controlled preferably by an automaton: in a culture system comprising a medium for the culture of photosynthetic organisms; and/or in water or an aqueous solution containing all or some of the constituents of an algal culture medium so as to obtain, in the presence of a base, a first aqueous composition having a pH greater than pH.sub.H; and/or in water or an aqueous solution containing all or some of the constituents of an algal culture medium so as to obtain a second aqueous composition having a pH lower than pH.sub.B, by dissolving CO.sub.2 produced by said source in water; said method being characterised in that, during the culture of photosynthetic organisms in said culture medium, in order to obtain a biomass of photosynthetic organisms using the CO.sub.2 originating from said source and/or the carbonate ions and the carbonic acid respectively contained in the first and second aqueous compositions: i. when the pH of said culture medium reaches an upper limit, pH.sub.H, the second aqueous composition and/or the CO.sub.2 produced by said source are added to said culture medium in order to lower the pH, preferably until the pH of said culture medium reaches a lower limit, pH.sub.B; ii. when the pH of said culture medium reaches said lower limit, pH.sub.B, the first aqueous composition is added to said culture medium so as to increase the pH, preferably until the pH of said culture medium reaches an intermediate value, pH.sub.I, with pH.sub.B<pH.sub.I<pH.sub.H; and iii. possibly, when the pH of said culture medium is lower than pH.sub.H, especially lower than pH.sub.I, the first aqueous composition is added to said culture medium so as to increase the pH, especially until the pH of said culture medium reaches the intermediate value pH.sub.I; said value of pH.sub.I being especially between 6 and 10 in the culture medium; said pH.sub.H being especially such that pH.sub.H=pH.sub.I+x in the culture medium, x being between 0.02 and 1.5, especially between 0.1 and 0.2; said pH.sub.B being especially such that pH.sub.B=pH.sub.Iy in the culture medium, y being between 0.02 and 1.5, especially between 0.1 and 0.2; said base being especially selected from the group composed of sodium hydroxide and potassium hydroxide; said culture medium being especially at a temperature between 15 C. and 35 C.

3. A method according to claim 2, wherein the photosynthetic organisms are selected from the group composed of: microalgae, especially microalgae of the genera Chlorella, Nannochloropsis, Chlamydomonas, Tetraselmis, Scendesmus, Parachlorella, Porphyridium, Botryococcus and Neochloris; cyanobacteria, especially of the genera Arthrospira, Aphazomenon and Synechocystis; and macroalgae, especially the macroalgae Ulva, Fucus, Palmaria.

4. A method according to claim 2, wherein the CO.sub.2 source is formed by industrial flue gases, said CO.sub.2 source being selected especially from the group formed by emissions from boilers, thermal power plants, cement plants, metallurgical plants, refineries, factories manufacturing ammonia, fermentation processes, and anaerobic digestion processes.

5. A method according to claim 2, wherein the CO.sub.2 source is discontinuous and the automaton acts on the various valves connecting a system for the culture of photosynthetic organisms comprising said culture medium, the first aqueous composition having a pH greater than pH.sub.H and the second composition having a pH lower than pH.sub.B, such that: when the CO.sub.2 source produces CO.sub.2: CO.sub.2 is directed into water or an aqueous solution containing all or some of the constituents of an algal culture medium so as to obtain, in the presence of a base, said first aqueous composition, and is directed into water or an aqueous solution containing all or some of the constituents of an algal culture medium so as to obtain said second aqueous composition by dissolving CO.sub.2 produced by said source in the water or the aqueous solution; (if desired) CO.sub.2 is directed directly into the culture system if the pH is such that pH.sub.B<pH<pH.sub.H; when the pH of said culture medium reaches an upper limit, pH.sub.H, CO.sub.2 produced by said source and possibly the second aqueous composition are added to said culture medium so as to lower the pH, preferably until the pH of said culture medium reaches a lower limit, pH.sub.B; when the pH of said culture medium reaches said lower limit, pH.sub.B, the CO.sub.2 produced by said source is no longer added to said culture medium, and, if desired, the first aqueous composition is added to said culture medium so as to raise the pH, preferably until the pH of said culture medium reaches an intermediate value, pH.sub.I, with pH.sub.B<pH.sub.I<pH.sub.H; when the CO.sub.2 source does not produce CO.sub.2: the first aqueous composition is added to the culture medium so as to supply dissolved carbon to said culture medium, resulting in an increase of the pH until preferably the pH of said culture medium reaches an intermediate value, pH.sub.I, with pH.sub.B<pH.sub.I<pH.sub.H; when the pH of said culture medium reaches an upper limit, pH.sub.H, the second aqueous composition is added to said culture medium so as to lower the pH, preferably until the pH of said culture medium reaches a lower limit, pH.sub.B.

6. A method according to claim 2, wherein the culture system is a closed system.

7. A method according to claim 2, wherein the culture system is an open system.

8. A device for the culture of photosynthetic organisms, selected from microalgae, cyanobacteria and macroalgae, using a continuous or discontinuous CO.sub.2 source, said device comprising the following elements: a means A for capturing CO.sub.2 produced by said source, said means comprising water or an aqueous solution containing all or some of the constituents of an algal culture medium, and a base, and making it possible to obtain a first aqueous composition having a pH greater than pH.sub.H; a means B for capturing CO.sub.2 produced by said source, said means comprising water or an aqueous solution containing all or some of the constituents of an algal culture medium and making it possible to obtain a second aqueous composition having a pH lower than pH.sub.B; a system for the culture of said photosynthetic organisms, equipped with means for measuring pH; pipes and valves connecting the CO.sub.2 source, the system for the culture of said photosynthetic organisms, and the means A and B; a system for controlling and regulating gaseous and liquid flows between the CO.sub.2 source, the system for the culture of said photosynthetic organisms, and the means A and B, preferably an automaton, characterised in that the control system is designed such that: the CO.sub.2 produced by said source is directed towards said culture system and/or said means A and B for capturing CO.sub.2; when the pH of said culture medium reaches an upper limit, pH.sub.H, the second aqueous composition originating from the means B and/or CO.sub.2 produced by said source are added to said culture medium so as to lower the pH, preferably until the pH of said culture medium reaches a lower limit, pH.sub.B; when the pH of said culture medium reaches said lower limit, pH.sub.B, the first aqueous composition originating from the means A is added to said culture medium so as to increase the pH, preferably until the pH of said culture medium reaches an intermediate value, pH.sub.I, with pH.sub.B<pH.sub.I<pH.sub.H; and possibly, when the pH of said culture medium is lower than pH.sub.H, especially lower than pH.sub.I, the first aqueous composition is added to said culture medium so as to increase the pH, especially until the pH of said culture medium reaches the intermediate value pH.sub.I, said means A being especially equipped with a pH and/or temperature probe; and/or said means A being especially equipped with a pressure sensor and a back-pressure regulator; and/or said means A being especially equipped with a system making it possible to form bubbles, especially bubbles of controlled size, more particularly bubbles with an average size between 10 m and 50 m, from the CO.sub.2 produced by the CO.sub.2 source; said means B being equipped with a system allowing the formation of bubbles, especially bubbles of controlled size, more particularly bubbles of an average size between 10 m and 50 m, from the CO.sub.2 produced by the CO.sub.2 source

9. A device according to claim 8, wherein the culture system is a closed system.

10. A device according to claim 8, wherein the culture system is an open system.

11. A device according to claim 8, wherein the means A and B are equipped with a liquid outlet and a gas outlet, said outlets being such that: the liquid outlets of the means A and B supply the culture system with first and second aqueous compositions, respectively; the gas outlet of the means A is connected to the means B; the gas outlet of the means B is connected to the culture system.

12. Device according to claim 8, wherein the CO.sub.2 source is discontinuous, and the automaton acts on the various valves connecting said culture system, the first aqueous composition having a pH greater than pH.sub.H and the second composition having a pH lower than pH.sub.B, such that: when the CO.sub.2 source produces CO.sub.2: CO.sub.2 is directed into the means A so as to obtain a first aqueous composition having a pH greater than pH.sub.H, and into the means B so as to obtain a second aqueous composition having a pH lower than pH.sub.B; (if desired) CO.sub.2 is directed directly into the culture system if the pH is such that pH.sub.B<pH<pH.sub.H; when the pH of said culture medium reaches an upper limit, pH.sub.H, CO.sub.2 produced by said source and possibly the second aqueous composition originating from the means B are added to said culture medium so as to lower the pH, preferably until the pH of said culture medium reaches a lower limit, pH.sub.B; when the pH of said culture medium reaches said lower limit, pH.sub.B, the first aqueous composition originating from the means A is added to said culture medium so as to raise the pH, preferably until the pH of said culture medium reaches an intermediate value, pH.sub.I, with pH.sub.B<pH.sub.I<pH.sub.H; when the CO.sub.2 source does not produce CO.sub.2: the first aqueous composition originating from the means A is added to said culture medium so as to supply dissolved carbon to said culture medium, resulting in an increase of the pH until preferably the pH of said culture medium reaches an intermediate value, pH.sub.I, with pH.sub.B<pH.sub.I<pH.sub.H; when the pH of said culture medium reaches an upper limit, pH.sub.H, the second aqueous composition originating from the means B is added to said culture medium so as to lower the pH, preferably until the pH of said culture medium reaches a lower limit, pH.sub.B.

Description

FIGURES

[0156] FIG. 1 shows a device according to the present invention.

[0157] The carbonation tank (2) is fed by a flue gas that is rich in CO.sub.2 (1). The gas-liquid transfer is assured either by simple contact between the gaseous environment and the liquid, or by a device allowing the generation of bubbles of small size in order to increase the transfer (21). The pressure within the vessel is a variable that makes it possible to adjust the partial pressure in the tank. In order to optimise the operation of the tank (2), said tank can be equipped with a pH/T probe (22), a pressure sensor (23), a back-pressure regulator (24), a relief valve (25) and a level sensor (26), which controls the intake of the liquid to be carbonated (27). A double jacket (28) can be added in order to assure the regulation of the temperature of the carbonation tank. The use of a centrifugal pump (29) connected to a basic solution makes it possible to produce a concentration of dissolved inorganic carbon in the carbonation solution in accordance with the setpoint pH value and the CO.sub.2 composition of the gas at the inlet.

[0158] The acidification tank is based on the same principle as the carbonation tank, with a gas-liquid transfer by simple contact, or improved transfer by a device allowing the generation of bubbles of small size (31). The tank can contain a relief valve (32) and a level sensor (33) controlling the intake of the liquid to be acidified (34). The tank is fed directly with gas by the flue gas (1) and/or by the gas outlet of the carbonation tank (2) in order to maximise the utilisation of the flue gas (1).

[0159] In addition to the elements necessary for conventional operation of a photobioreactor, the element (4) has inlets for gas (41) and carbonated liquid (42), a vent (43), and a relief valve (44) in the case of a closed system.

[0160] The carbonation tank (2) and acidification tank (3) are connected to the photobioreactor (4) by: [0161] a gas network making it possible to supply flue gas (1) independently to the elements (2), (3) and (4) of the process depending on the control parameters; [0162] a carbonated liquid network making it possible to supply acidic or basic solution to the photobioreactor (4) depending on the needs of the photobioreactor (4) by means of a centrifugal pump (11).

[0163] The automaton controls the operation of the solenoid valves depending on the pH value detected in the photobioreactor (4) and the availability of flue gas (1). The automation of the carbonation tank (2) is also assured by the automaton.

[0164] The carbonation tank and acidification tank are regulated via the automaton on the basis of the measurement of the pH in the culture system. In fact, the carbonation is favoured at basic pH, and the biological consumption of the carbon in the reactor also tends to basify the medium. The 2 tanks/liquid solutions are thus associated with a specific regulation method based on the measurement of the pH in the culture system so as to both provide the dissolved carbon in a quantity sufficient for growth and so as to maintain the pH optimum for growth. This is based on the determination of 2 pH setpoints (upper setpoint pH.sub.H and lower setpoint pH.sub.B) flanking the optimal value for growth (pH.sub.I). Ultimately, the following is thus given pH.sub.B<pH.sub.I<pH.sub.H.

[0165] Due to the fact that the consumption of the dissolved carbon by the photosynthetic growth results in a rise of the pH in the culture system, when the upper setpoint pH.sub.H is reached, the acidic solution is injected until the lower setpoint pH.sub.B is reached.

[0166] When the lower setpoint pH.sub.B is reached, the carbonated solution (basic, pH>pH.sub.I) is injected until the pH optimum for growth is reached.

[0167] The consumption of the dissolved carbon causes a basification of the medium until the upper setpoint pH.sub.H is reached, leading to a repetition of the cycle.

[0168] It should be noted that the setpoints pH.sub.B and pH.sub.H can be selected to be very close to pH.sub.I, ultimately making it possible to hold the pH at a level optimum for growth.

EXAMPLE

[0169] The CO.sub.2 source is an industrial flue gas comprising 9% CO.sub.2.

[0170] The first and second aqueous compositions in the carbonation and acidification tanks respectively, are at a temperature of 25 C.

[0171] In the carbonation tank, the pH and the concentration of DIC of the first aqueous composition are related as indicated in the following table:

TABLE-US-00002 pH DIC (mM) 7.5 46.7 8 141.2 8.5 444.1 9 1441.2

[0172] Thus, the addition of a base, especially a strong base, makes it possible to increase the concentration of DIC of the first aqueous composition, and therefore the amount of DIC stored in the carbonation tank.

[0173] In the acidification tank, the pH of the second aqueous composition, at equilibrium, is 4.42 and the concentration of DIC is 3 mM.