Method for the culture of photosynthetic organisms using a co2 source

A method for the culture of photosynthetic organisms, selected from microalgae, cyanobacteria and macroalgae, using a continuous or discontinuous CO2 source, in which the CO2 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 pHH;
• 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 pHB, by dissolving CO2 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 CO2 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, pHH, the second aqueous composition and/or the CO2 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, pHB;
• ii. when the pH of said culture medium reaches said lower limit, pHB, 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, pHI, with pHB<pHI<pHH;
• and
• iii. possibly, when the pH of said culture medium is lower than pHH, especially lower than pHI, 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 pHI;
• said value of pHI being especially between 6 and 10 in the culture medium;
• said pHH being especially such that pHH=pHI+x in the culture medium, x being between 0.02 and 1.5, especially between 0.1 and 0.2;
• said pHB being especially such that pHB=pHI−y 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.

A device for the culture of photosynthetic organisms, selected from microalgae, cyanobacteria and macroalgae, using a continuous or discontinuous CO2 source, said device comprising the following elements:

• a means A for capturing CO2 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 pHH;
• a means B for capturing CO2 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 pHB;
• a system for the culture of said photosynthetic organisms, equipped with means for measuring pH;
• pipes and valves connecting the CO2 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 CO2 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 CO2 produced by said source is directed towards said culture system and/or said means A and B for capturing CO2;
• when the pH of said culture medium reaches an upper limit, pHH, the second aqueous composition originating from the means B and/or CO2 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, pHB;
• when the pH of said culture medium reaches said lower limit, pHB, 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, pHI, with pHB<pHI<pHH;
• and
• possibly, when the pH of said culture medium is lower than pHH, especially lower than pHI, 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 pHI,
• 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 μm and 50 μm, from the CO2 produced by the CO2 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 μm and 50 μm, from the CO2 produced by the CO2 source