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. A method for the culture of photosynthetic organisms, in which 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 is used, said method comprising: culturing the photosynthetic organisms in a culture system comprising a culture medium, wherein the photosynthetic organisms are selected from the group consisting of microalgae, cyanobacteria and macroalgae; obtaining said first aqueous composition having a pH greater than pH.sub.H by contacting CO.sub.2 produced by a continuous or discontinuous CO.sub.2 source, a base, and water; obtaining said second aqueous composition having a pH lower than pH.sub.B by dissolving CO.sub.2 produced by said source in water; wherein the pH of said culture medium is such that: when the pH of said culture medium reaches an upper limit, pH.sub.H, adding the second aqueous composition and/or CO.sub.2 produced by said source, to said culture medium so as to lower the pH, 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, adding the first aqueous composition to said culture medium so as to increase the pH, 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 pH of said culture medium is lower than pH.sub.H, and lower than pH.sub.I, optionally adding the first aqueous composition to said culture medium so as to increase the pH, until the pH of said culture medium reaches the intermediate value pH.sub.I, wherein in the first aqueous composition, the dissolved inorganic carbon (DIC) is predominantly in the form of carbonate ions and bicarbonate ions, said DIC is between 45 and 1450 mM, and wherein in the second aqueous composition, the dissolved inorganic carbon (DIC) is predominantly in the form of carbonic acid.

2. The method according to claim 1, wherein the first aqueous composition has a pH comprised between 7.5 and 9, and wherein the second composition has a pH comprised between 4 and 5.

3. A method according to claim 1, wherein the photosynthetic organisms are selected from the group consisting of: microalgae, selected from the group consisting of the genera Chlorella, Nannochloropsis, Chlamydomonas, Tetraselmis, Scendesmus, Parachlorella, Porphyridium, Botryococcus and Neochloris; cyanobacteria, selected from the group consisting of the genera Arthrospira, Aphazomenon and Synechocystis; and macroalgae, selected from the group consisting of Ulva, Fucus, and Palmaria.

4. A method according to claim 1, wherein the CO.sub.2 source is formed by industrial flue gases, said CO.sub.2 source being selected from the group consisting of 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 1, 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, said method comprising when the CO.sub.2 source produces CO.sub.2: obtaining in the presence of a base, said first aqueous composition, by directing CO.sub.2 into water or an aqueous solution containing all or some of the constituents of an algal culture medium, and obtaining said second aqueous composition by directing CO.sub.2 into water or an aqueous solution containing all or some of the constituents of an algal culture medium and by dissolving CO.sub.2 produced by said source in the water or the aqueous solution; directing CO.sub.2 directly into the culture system if the pH is such that pH.sub.B<pH<pH.sub.H; adding CO.sub.2 produced by said source and by the second aqueous composition when the pH of said culture medium reaches an upper limit, pH.sub.H, to said culture medium so as to lower the pH, until the pH of said culture medium reaches a lower limit, pH.sub.B; no longer adding the CO.sub.2 produced by said source to said culture medium when the pH of said culture medium reaches said lower limit, pH.sub.B, and adding the first aqueous composition to said culture medium so as to raise the pH, 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: adding the first aqueous composition to the culture medium so as to supply dissolved carbon to said culture medium, resulting in an increase of the pH until the pH of said culture medium reaches an intermediate value, pH.sub.I, with pH.sub.B<pH.sub.I<pH.sub.H; adding the second aqueous composition, when the pH of said culture medium reaches an upper limit, pH.sub.H, to said culture medium so as to lower the pH, until the pH of said culture medium reaches a lower limit, pH.sub.B.

6. A method according to claim 1, wherein the culture system is a closed system.

7. A method for the culture of photosynthetic organisms, using a continuous or discontinuous CO.sub.2 source, in which the CO.sub.2 is directed by means of pipes and valves controlled by an automaton: in a culture system comprising a medium for the culture of photosynthetic organisms; 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; 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 comprising culturing the photosynthetic organisms in a culture system comprising a culture medium, wherein the photosynthetic organisms are selected from the group consisting of microalgae, cyanobacteria and macroalgae, using the CO.sub.2 originating from said source and the carbonate ions and the carbonic acid respectively contained in the first and second aqueous compositions, obtaining a biomass of photosynthetic organisms, by culturing the photosynthetic organisms, and i. when the pH of said culture medium reaches an upper limit pH.sub.H, adding the second aqueous composition and/or the CO.sub.2 produced by said source to said culture medium in order to lower the pH, 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, adding the first aqueous composition to said culture medium so as to increase the pH, until the pH of said culture medium reaches an intermediate value, pH.sub.I, with pH.sub.B<pH.sub.I<pH.sub.H; iii. when the pH of said culture medium is lower than pH.sub.H, and lower than pH.sub.I, adding the first aqueous composition to said culture medium so as to increase the pH, until the pH of said culture medium reaches the intermediate value pH.sub.I; said value of pH.sub.I being between 6 and 10 in the culture medium; said pH.sub.H being such that pH.sub.H=pH.sub.I+x in the culture medium, x being between 0.02 and 1.5; said pH.sub.B being such that pH.sub.B=pH.sub.I−y in the culture medium, y being between 0.02 and 1.5; said base being selected from the group composed of sodium hydroxide and potassium hydroxide; said culture medium being at a temperature between 15° C. and 35° C., wherein in the first aqueous composition, the dissolved inorganic carbon (DIC) is predominantly in the form of carbonate ions and bicarbonate ions, said DIC is between 45 and 1450 mM, and wherein in the second aqueous composition, the dissolved inorganic carbon (DIC) is predominantly in the form of carbonic acid.

8. A method according to claim 7, wherein the photosynthetic organisms are selected from the group consisting of: microalgae, selected from the group consisting of the genera Chlorella, Nannochloropsis, Chlamydomonas, Tetraselmis, Scendesmus, Parachlorella, Porphyridium, Botryococcus and Neochloris; cyanobacteria, selected from the group consisting of the genera Arthrospira, Aphazomenon and Synechocystis; and macroalgae, selected from the group consisting of Ulva, Fucus, and Palmaria.

9. A method according to claim 7, wherein the CO.sub.2 source is formed by industrial flue gases, said CO.sub.2 source being selected from the group consisting of emissions from boilers, thermal power plants, cement plants, metallurgical plants, refineries, factories manufacturing ammonia, fermentation processes, and anaerobic digestion processes.

10. A method according to claim 7, 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, said method comprising when the CO.sub.2 source produces CO.sub.2: obtaining in the presence of a base, said first aqueous composition, by directing CO.sub.2 into water or an aqueous solution containing all or some of the constituents of an algal culture medium, and obtaining said second aqueous composition by directing CO.sub.2 into water or an aqueous solution containing all or some of the constituents of an algal culture medium and by dissolving CO.sub.2 produced by said source in the water or the aqueous solution; directing CO.sub.2 directly into the culture system if the pH is such that pH.sub.B<pH<pH.sub.H; adding CO.sub.2 produced by said source and by the second aqueous composition when the pH of said culture medium reaches an upper limit, pH.sub.H, to said culture medium so as to lower the pH, until the pH of said culture medium reaches a lower limit, pH.sub.B; no longer adding the CO.sub.2 produced by said source to said culture medium when the pH of said culture medium reaches said lower limit, pH.sub.B, and adding the first aqueous composition to said culture medium so as to raise the pH, 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: adding the first aqueous composition to the culture medium so as to supply dissolved carbon to said culture medium, resulting in an increase of the pH until the pH of said culture medium reaches an intermediate value, pH.sub.I, with pH.sub.B<pH.sub.I<pH.sub.H; adding the second aqueous composition, when the pH of said culture medium reaches an upper limit, pH.sub.H, to said culture medium so as to lower the pH, until the pH of said culture medium reaches a lower limit, pH.sub.B.

11. A method according to claim 7, wherein the culture system is a closed system.

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

Description

FIGURES

(1) FIG. 1 shows a device according to the present invention.

(2) 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.

(3) 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).

(4) 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.

(5) The carbonation tank (2) and acidification tank (3) are connected to the photobioreactor (4) by: 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; 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).

(6) 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.

(7) 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.

(8) 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.

(9) 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.

(10) 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.

(11) 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

(12) The CO.sub.2 source is an industrial flue gas comprising 9% CO.sub.2.

(13) The first and second aqueous compositions in the carbonation and acidification tanks respectively, are at a temperature of 25° C.

(14) In the carbonation tank, the pH and the concentration of DIC of the first aqueous composition are related as indicated in the following table:

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

(16) 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.

(17) In the acidification tank, the pH of the second aqueous composition, at equilibrium, is 4.42 and the concentration of DIC is 3 mM.