Classifications

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  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
  • C12M21/00—Bioreactors or fermenters specially adapted for specific uses
  • C12M21/02—Photobioreactors
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
  • C12N1/00—Microorganisms, e.g. protozoa; Compositions thereof; Processes of propagating, maintaining or preserving microorganisms or compositions thereof; Processes of preparing or isolating a composition containing a microorganism; Culture media therefor
  • C12N1/12—Unicellular algae; Culture media therefor
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  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
  • C12M23/00—Constructional details, e.g. recesses, hinges
  • C12M23/20—Material Coatings
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
  • C12M23/00—Constructional details, e.g. recesses, hinges
  • C12M23/22—Transparent or translucent parts
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
  • C12M29/00—Means for introduction, extraction or recirculation of materials, e.g. pumps
  • C12M29/02—Percolation
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
  • C12M29/00—Means for introduction, extraction or recirculation of materials, e.g. pumps
  • C12M29/06—Nozzles; Sprayers; Spargers; Diffusers
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
  • C12M3/00—Tissue, human, animal or plant cell, or virus culture apparatus
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
  • C12M31/00—Means for providing, directing, scattering or concentrating light
  • C12M31/08—Means for providing, directing, scattering or concentrating light by conducting or reflecting elements located inside the reactor or in its structure
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
  • C12M31/00—Means for providing, directing, scattering or concentrating light
  • C12M31/10—Means for providing, directing, scattering or concentrating light by light emitting elements located inside the reactor, e.g. LED or OLED
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
  • C12M41/00—Means for regulation, monitoring, measurement or control, e.g. flow regulation
  • C12M41/12—Means for regulation, monitoring, measurement or control, e.g. flow regulation of temperature

Definitions

• the invention relates to the intensive and continuous cultivation of photosynthetic microorganisms.
• Microalgae are plant photosynthetic organisms whose metabolism and growth require, among others, CO 2 , light and nutrients.
• the microalgae can be cultivated to value and purify the carbon dioxide, NOx and / or SOx discharges of certain plants (WO 2008042919).
• the oil extracted from microalgae can be used as biofuel (WO2008070281, WO2008055190, WO2008060571).
• Microalgae can be grown for their production of omega-3 and polyunsaturated fatty acids.
• Microalgae can also be grown to produce pigments.
• microalgae uses the sun as a source of light.
• microalgae are often placed in open basins ("raceways") with or without circulation (US2008178739).
• Tubular or plate photobioreactors made of translucent materials, are also passage of light rays in the culture medium and in which the microalgae circulate (FR2621323).
• Other three-dimensional transparent tube network systems improve the use of space (EP0874043).
• closed photobioreactors To reduce congestion and improve yield, closed photobioreactors have been developed. They use the availability of artificial lighting 24 hours a day, 7 days a week, this lighting can be interrupted according to sequences specific to the biological cycles of the algae concerned.
• microalgae the crucial factor in increasing the biomass of microalgae is light, both in terms of quantity and quality since, although absorbing all the photons of the visible spectrum, microalgae absorb particularly with minimal losses only certain wavelengths of white light.
• a photobioreactor is defined as a closed system within which there is production of biological material under the action of light energy, this production is also optimizable by controlling the culture conditions: nutrients, hydrodynamics of the medium, transfers gaseous, speed of circulation of the liquid, etc.
• the production depends directly on the quality of the lighting in the volume of the photobioreactor. It is necessary that all biological fluid is properly illuminated with optimum average energy. Therefore, the interface between the 'light sources' and the biological fluid must be as large as possible while maximizing the useful volume of the biological fluid.
• the volume of biological fluid concerned will be only 1/200 m 3 .
• the ideal reactor would be such that the illuminated volume is equal to the volume of the reactor.
• a first artificial lighting solution to solve this problem is to bring the light of a light source into the culture medium near the micro-algae using optical fibers (U S61 56561 and EP0935991).
• the optical fibers may be associated with other immersed light-guiding means within the enclosure (J P2001 1 78443 and DE29819259).
• This solution only achieves low yields (light output) / (light efficient). Indeed, the intensity is reduced because of the interfaces between the light sources and the waveguide and it is difficult to couple more than one light source on the same fiber.
• a problem arises when using several different wavelengths: Indeed, to get the light out of the optical fibers immersed in the culture medium, it is necessary to make a surface treatment (roughness), which will diffract or diffract a fraction of the guided light.
• the most effective solution is to burn a network at the periphery of the fiber with a pitch that is of the order of the wavelength of the light conveyed. This solution has a narrow bandwidth and is totally unsuitable when using several wavelengths.
• Another artificial lighting solution to solve this problem is to directly immerse light sources into the chamber of the photobioreactor, such as for example fluorescent lamps (US 5, 104,803) or LEDs (Light Emitting Diode) (DE202007013406 and WO2007047805). .
• This solution improves the energy efficiency of the lighting process because the light sources are closer and better coupled to the culture medium.
• the first is inherent to the emission geometry of the LEDs because their energy em ission diagram is directional and follows a Lambertian profile. Only the algae in the beam will be illuminated, the solid angle of the emission cone is typically 90 °, three quarters of the space around a LED will not be lit by the latter. Note that the situation will be substantially identical for lighting ends of submerged optical fibers.
• the emission beam of an LED being lambertian
• the algae passing through the emission beam will receive an inhomogeneous photon flux.
• the inventors have discovered a new, particularly efficient way of guiding and diffusing in the photobioreactor the light produced by external LEDs.
• the light sources no longer need to be placed inside the enclosure, which greatly facilitates thermal regulation.
• the diffusing light guide used also allows a particularly uniform and uniform light distribution, and adapts to all the wavelengths of interest for the culture of microalgae.
• the subject of the invention relates to a photobioreactor intended for the continuous cultivation, in particular, of photosynthetic microorganisms, preferably microalgae, comprising at least one less a culture chamber intended to contain the culture medium of the microorganisms, and at least one light source outside the culture chamber, characterized in that it further comprises at least one cylindrical or prismatic light diffusing element placed in the culture chamber, the light diffusing element being optically coupled to the light source so as to capture the photons emitted by the light source and restore them in the culture medium by its lateral surface.
• the light diffusing element is a solid element made of a non-absorbing transparent material at the end of which the light source is placed;
• the light diffusing element comprises inclusions made of a partially diffusing material
• the light diffusing element is a hollow element made of a transparent material, at the end of which the light source is placed;
• a semi-reflecting layer is disposed on the inner face of the light-diffusing element
• a semi-reflecting layer is disposed on the outer face of the diffuser element
• the one or more semi-reflective layers is made of a metallic material or a metal oxide, of optical index higher than the index of the material constituting the diffuser element, preferably aluminum;
• the thickness of the dimming semi-reflecting layer or layers away from the light source is the thickness of the dimming semi-reflecting layer or layers away from the light source
• the light diffusing element is made of polymethylmethacrylate
• the light source is a quasi-point source, and the light diffusing element is a diffuser tube;
• the light source is a linear source, and the light diffusing element is a diffuser parallelepiped;
• the light source is a (or a) set of electro-luminescent diode (s) (LEDs) which is quasi-point (s) or in ribbon, preferably one (or a set of) electroluminescent diode (s) (s) power (HPLED);
• LEDs electro-luminescent diode
• HPLED electroluminescent diode
• a convergent lens is placed at the interface between the LED and the light scattering element
• the end of the light diffusing element opposite to the light source is provided with a mirror
• the end of the light-canceling element opposite to the light source is cone-shaped or dome-shaped;
• the outer surface of the light diffusing element has a suitable roughness improving the diffusion of light
• the outer surface of the light diffusing element is encapsulated in a protective sheath
• the light diffusing element comprises a cleaning wiper surrounding the sheath
• the photobioreactor includes a cooling system of the light sources
• the photobioreactor comprises a system for generating bubbles at the base of the culture medium.
• the invention relates to the use of a photobioreactor according to the first aspect of the invention for cultivating photosynthetic micro-organisms, preferably microalgae.
• a third object of the invention relates to the use of a cylindrical or prismatic light diffusing element optically coupled to a light source so as to capture the photons emitted by the light source. and restore them by its lateral surface to illuminate the culture medium of a photobioreactor.
• FIGS. 1 a-d and 2 are diagrams of five embodiments of a light-diffusing element of the photobioreactor according to the invention.
• FIG. 3 is a perspective view of a particularly advantageous embodiment of a light-diffusing element of the photobioreactor according to the invention.
• FIG. 4 is a perspective view of a parallelepipedal embodiment of the photobioreactor according to the invention.
• FIG. 5 is a perspective view of a cylindrical embodiment of the photobioreactor according to the invention.
• FIG. 6 is a perspective view of another parallelepipedic embodiment of the photobioreactor according to the invention.
• LEDs of high power that is to say more than 10W electric, and emitting around the wavelength of absorption of chlorophyll (650 nm - 680nm). They have in particular optical yields which exceed 25%, on industrial products. In laboratories, there are even yields exceeding 35% and in some cases 50%.
• the applicant has developed light scattering elements, which can collect the light from a light source and in particular a quasi-point LED or bar, even placed outside of the culture chamber, and to diffuse it into a complete column of photobioreactor culture medium.
• the fact that the light sources are placed outside the culture chamber has many advantages, in particular, a facilitated heat dissipation, the absence of shadows caused by the sources themselves, the maintenance of the connections electric out of the biological environment, etc.
• Photobioreactor Architecture A simplified schema of a photobioreactor according to the invention is shown in Figure 1a.
• This photobioreactor intended for the continuous cultivation of photosynthetic microorganisms, preferably of micro-algae, comprises, as can be seen, at least one culture chamber 1 intended to contain the culture medium 3 of the microorganisms, and minus a light source 2 outside the culture chamber 1.
• the diffuser element 4 being optically coupled to the light source 2 so as to capture the photons emitted by the light source. 2 and return them to the culture medium 3 by its lateral surface.
• the light source 2 is a quasi-point source, for example a single LED (or a set of simple LEDs), of the case where the light source 4 is a linear (or even surface) source. for example, there are LEDs called “bar” or “ribbon” (see patent application FR1050015).
• LED quad-point or ribbon
• power that is to say an LED power greater than 1 W , or more than 10W power.
• HPLED quad-point or ribbon
• the remainder of the present description will therefore essentially refer to LED light sources, but it will be understood that the invention is in no way limited to this type of source.
• Those skilled in the art will be able to adapt the photobioreactor according to the invention to other known light sources 2, including laser sources, which have the advantage of being extremely directional, and whose price has dropped considerably.
• the light sources 2 can be both monochromatic and polychromatic, either naturally or by juxtaposition of monochromatic light sources emitting at different wavelengths. It will be noted that it is possible to directly obtain multi-spectral LEDs by stacking semiconductors of different gaps (including quantum well diodes).
• the emission symmetry of commercial quasi-point LEDs is a cylindrical symmetry (Lambertian emission), therefore the easiest coupling to achieve is with a tube, whether hollow or solid.
• a tube does not necessarily have a circular section, in other words is not necessarily a cylinder of revolution.
• the invention relates to any cylindrical or prismatic shape, in other words polyhedra having on the one hand a rectangular lateral surface, and on the other hand a constant section, this section advantageously having a central symmetry to respect the emitted Lambertian ission.
• sections of diffuser tubes 4 in regular or star-shaped polygons, which would make it possible in particular to increase the lateral surface, that is to say the contact surface with the culture medium 3 of the microorganisms.
• the invention is not limited to any geometry, and concerns any cylindrical or prismatic light diffuser element.
• the diffuser tube 4 is a hollow tube made of a transparent material, preferably glass or plexiglass, at the end of which the LED 2 is placed, oriented towards the diffuser tube 4 so that the latter receives the emitted photons by the LED 2.
• the propagation of light is here in the air, that is to say, there is no absorption.
• the angles of attack on the inner face of the diffuser tube 4 are multiple, the light comes out according to a classical law (Descartes law) related to the index difference with respect to the 'air.
• the index n of refraction of the air is indeed 1, and is well below the index n of glass or plexiglass which reaches 1, 5.
• a convergent lens 5 can be placed between the LED 2 and the diffuser tube 4.
• This lens 5 makes it possible to control the divergence of the beam coming from the LED 2.
• the diode is in the focal plane of the lens
• most of the lumen flux is guided. It is understood that by defocusing more or less the beam can modulate the light output from the diffuser tube 4.
• the penetration length of the light energy in the diffuser tube 4 can be adjusted to the length of the diffuser tubes. We will see the importance further from this point.
• the diffuser tube 4 is a solid tube made of a transparent material that does not absorb light, preferably polymethyl methacrylate (PMMA).
• PMMA index (1, 49) being the similarly, that of water and glass, there will be no light guiding a priori if it is immersed in water, but no loss of Fresnel at the interface LED / tube (glass spherical encapsulation).
• the LED 2 is introduced into a recess made in the diffuser tube 4 (of the size of the spherical encapsulation cap of the LED 2).
• the density of inclusions 6 varies over the height of the diffuser tube 4, and increases away from the LED 2 so as to compensate for the gradual loss of light.
• the invention is not limited to any diffuser tube size 4 in particular. These can be up to several meters long, there is no limit given, and have a diameter most often between a few millimeters and a few centimeters, The diameter is essentially determined by the choice of the concentration of microalgae in the reactor (continuous mode and / or chemostat) which conditions the penetration of the light, as well as the average power which one wants to apply to microalgae. These dimensions will be discussed later.
• tubular diffuser elements 4 to diffuse the light is not the only possible configuration. It is indeed possible to use linear light sources 2 such as ribbon LEDs. It is noted as already stated above that the ribbon LEDs can be composite (several wavelengths) or by polychromatic construction.
• the diffuser elements 4 are advantageously substantially parallelepipedal in order to take account of the emission geometry of an LED strip. We note that this is a special case of prismatic geometry.
• Such a parallelepiped diffuser 4 light is shown in Figure 2. It can be full, hollow, and can be the subject of the same embodiments as the tubular elements. We will speak later of "light scattering tubes", but it will be understood that all the possibilities that have been described and will be described in the present description (structures, treatments, materials ...) can be applied as well whatever the geometry of the diffuser element 4, tube or parallelepiped.
• another semi-reflecting layer 8 may be disposed on the outer face of the diffuser tube 4, including the hollow tubes replacing or in addition to an inner layer 7.
• a metallic material or a metal oxide of higher optical index than the index of the material constituting the diffuser tube 4, preferably aluminum.
• reflection is favored over transmission.
• the quality of the coating is essentially related to its absorption, which must be minimal.
• optical multilayers metal or oxides
• the fact of putting a semi-reflecting layer 8 outside the finger for a hollow tube is not a necessity, but simplifies the technique of depositing the semi-reflective material. It is possible, however, to proceed with the deposit by dipping in a bath, both on the outer face and inside the tube.
• the semi-reflecting layers 7, 8 may be deposited more generally by any chemical method (soaking), electrolytic, or sputtering (cathodic sputtering), CVD (vapor deposition), evaporation, etc.
• the materials envisaged go as explained by metals (Al, Ag, etc.) which make it possible to form semi-transparent layers of small thicknesses (from nanometers to a few microns), to transparent oxides (of indium doped or not, rare earths, etc. ) to perform this function.
• metals Al, Ag, etc.
• transparent oxides of indium doped or not, rare earths, etc.
• the intrinsic absorption of this layer should not exceed 10%.
• the thickness of the semi-reflective layer or layers 7, 8 decreases away from the LED 2, so as to compensate for the gradual loss of light.
• Those skilled in the art will be able to choose the variation profile of the thickness of the semi-reflecting layer (s) 7, 8 (as a function of the distance to the LED 2) to optimize (equalize) the energy This is the same concern that leads to having a variable density of inclusions 6 in the case of a diffuser tube 4 full (see above).
• an aluminum oxide layer whose thickness varies from 20 to 100 nm is interesting.
• the outer surface of the diffuser tube 4 has a high roughness 9 improving the diffusion of the light.
• suitable roughness is meant in particular a roughness at scales comparable to or greater than the wavelength of the light used.
• FIG. 1 shows a diffuser tube 4 in which roughness 9 and an internal semi-reflecting layer 7 are combined.
• the level of roughness can increase when one moves away from the LED 2 to compensate for the loss of luminous flux when one moves away from the source.
• the end of the diffuser tube 4 opposite the LED 2 is provided with a mirror 42.
• this moiroir can advantageously be inclined at a predetermined angle or even shaped, for example taking the conical shape (as seen in Figure 1a).
• Various examples of the mirror geometries 42 are also visible in FIGS. It is noted that the use of semi-reflective layers 7, 8 of variable thickness as a function of the distance to the LED 2 constitutes an additional degree of freedom to optimize the extraction of light.
• the end of the diffuser tube 4 opposite the LED 2 is preferably cone-shaped or dome-shaped to facilitate the flow of water or bubbles (in areas to be sparger), as we will see later. If a double-walled tube is used, it is the end of the tube that must be cone-shaped or dome-shaped.
• the outer surface of the diffuser tube 4 is encapsulated in a protective sheath 10.
• the essential object of the encapsulation is to protect in particular the semi-reflecting layer 8 of the culture medium 3 which by nature is corrosive.
• the outer surface of the diffuser tube 4 has an artificial roughness 9, it is noted that this promotes the attachment of the microalgae, which is why it is also desirable to encapsulate the diffuser tube 4.
• the protective sheath 10 must be made of a non-rough and transparent material (for example plastics such as PMMA again, polycarbonate, crystal polystyrene ...), and on which the attachment of the algae is the lowest possible.
• plastics such as PMMA again, polycarbonate, crystal polystyrene
• the invention will not be limited to any particular embodiment, and may be the subject of all possible combinations of semi-reflecting layers, roughness, on the outer face and / or on the inner face s' There is one. It is also possible to combine several materials in particular with different indices, and to assemble these different materials in concentric multilayers. Those skilled in the art will be able to adopt all these options according to the production characteristics chosen for the photobioreactor (concentration of algae, density of the diffuser tubes 4, desired yield, desired cost, etc.)
• sheath double tube or encapsulation
• HPLEDs preferably used have as explained a yield of about 25%, that is to say that 75% of the power supplied is dissipated in heat.
• the photobioreactor advantageously comprises a cooling system 12 of the LEDs 2.
• the LEDs 2 are for example mounted on a metal support of a few square centimeters which will be put in direct contact with this system 12, called "heat pipe", consisting of two metal plates between which will be circulated a high thermal conductivity liquid, pulsed air, water or other. It is also possible to provide individual radiators cooled by air or water, as can be seen in FIG. 3.
• the elements 1 21 and 1 22 respectively correspond to the inlet and the outlet of the heat transfer fluid. In case of individual radiators, it can be planned to mount them in series and / or in bypass. The flow rate of the coolant is controlled by measuring the em base temperature of the LEDs
• the LED 2 is here mounted on a base at the top of the diffuser tube 4, and is in contact with its heat pipe 12, its spherical em issive face is in contact with the light diffuser tube 4 (a spherical hole is provided if the diffuser tube is full, the hole being advantageously filled with optical grease).
• a lossless light guide (cylindrical mirror) a few centimeters long at the end of the diffuser tube 4.
• This guide can be for example a truncated cone whose inside is lined with a mirror.
• the diffuser tube 4 advantageously comprises a cleaning wiper 11 surrounding the sheath 10.
• the cleaning wiper 11 also visible in Figure 3, consists for example of a rubber O-ring surrounding the diffuser tube 4 in its upper part.
• the seal scrapes the algae deposits.
• the size of a culture chamber 1 of the photobioreactor can be very variable, and go from a few liters to hundreds of cubic meters.
• the general geometry of a culture chamber 1 is most often parallelepipedal (FIG. 4) or cylindrical (FIG. 5), but has little or no effect, except possibly with regard to edge effects and construction costs, resistance to pressure.
• the photobioreactor may furthermore comprise a single culture chamber 1 as well as several embodiments. The invention is not limited to any size or geometry.
• the culture chamber is preferably also parallelepipedic, as can be seen in FIG. 6.
• the light sources 2 and therefore the heat pipes 1 2 are placed on the flanks of the photobioreactor, this symmetrical configuration increases the flow of light in the guides, but is not necessarily necessary. On the other hand, it makes it easy to illuminate at two different wavelengths.
• a photobioreactor comprising a single cubic culture chamber 1 according to FIG. 4 with an overall volume of 1 m 3 (volume of the culture medium 3 plus volume of the diffuser tubes 4).
• light diffusing tubes 4 previously described, approximately 1 m long, are chosen so as to illuminate over the entire height of the culture chamber 1, and optimized to emit a flux. constant over their entire height. Had the light sources been lateral, the width of the growing chamber would have been considered.
• the arrangement of the diffuser tubes 4 in the volume of the culture chamber 1 is intended to optimize the overall homogenization of the light flux emitted in the culture medium 3.
• the parameter dimensioning to have a "bath” of quasi-homogeneous light Intensity is the "effective penetration length" of light ( eff ).
• the Calvin cycle is indeed a series of biochemical reactions that take place in the chloroplasts of organisms when they carry out photosynthesis.
• This triggering threshold expressed in moles of photons per m 2 per second, corresponds to the minimum luminous flux level to initiate the production of biomass by the microorganisms. Typically, 50 mole.m- 2 .s- 1 " of" red “photons (wavelength around 650 nm) are present for microalgae (eg, of the genus Nannochloris).
• X eff is defined as the distance beyond which the luminous flux falls below the threshold i eff .
• X eff is inversely proportional to the concentration of microalgae, and at fixed concentration it is determined by the species of microalgae. It is considered that a point located at a distance from a light source beyond X eff does not receive enough photons to produce organic matter. In other words this means that each point of the culture medium 3 must be on average at a distance less than X eff of a tube 4. This means that two tubes are advantageously of the order of 2 rpm .
• the dynamic operation of the photobioreactor also supposes that it is advantageously injected at its base with a gas under pressure (possibly with nutrients).
• This injection in particular through a device called “sparger”, leads to the creation of a flow of bubbles that induces the rise of the biological fluid.
• the photobioreactor therefore advantageously comprises a bubble generation system 13 disposed at the base of the culture medium 3.
• FIGS. 4 and 5 show different geometries of a sparger bubble generation system 1 3 capable of injecting these bubbles in a controlled manner at the base of the culture medium 3.
• Reactors operating according to this conventional principle are called "air-lift".
• the main liquid flow although oriented in the direction of the rise (then in the direction of the descent) leads the microalgae to "diffuse" transversely between the diffuser tubes 4.
• the microalgae moving thus capture a variable light, since in this direction the decay profile of the light is exponential when one deviates from the diffuser tubes 4.
• the microalgae thus receive a mean power in the length A eff.
• the effectiveness condition of this "averaging" of the quantity of light received by each microalgae is that the diffusion time of a microalga between two diffuser tubes 4 is very short compared to the life cycle of an alga, and preferably at the time of rise (or descent) of a microalga in the culture chamber 1.
• Operation air-type ift generally assumes an upward flow of the culture medium 3 and obviously a downward flow.
• the fluid injection is done at the base of the rising part.
• Optimizing the configuration of the liquid flows can lead to other partitions of a culture chamber 1 of the photobioreactor in N upstanding blocks, M falling blocks, or to the use of nozzles arranged at the base of the enclosure of culture 1 and placed between the diffuser tubes 4.
• the stacking of the culture chambers 1 is easier in the parallelepipedic case and makes it possible to optimize the space.
• the hydrodynamics of the upstream and downstream flows, which are associated with concentric spargers 13 is more difficult to manage.
• the extension of the interface between the flows and against flow does not exceed the interval between two planes of diffuser tubes 4. This interface is established naturally to the limit of sparger areas.
• the photobioreactor operates in
• the photobioreactor may in fact comprise various control systems.
• the latter having to operate continuously for a given geometry, in particular related to the spacing of the diffusing elements, one must control the optimal density of algae in stationary regime. This measurement will be made by measuring the optical density of the biological medium.
• the invention relates to the use of a photobioreactor according to the first aspect of the invention for cultivating photosynthetic micro-organisms, preferably microalgae.
• Another aspect of the invention relates, as previously explained, to the use of a cylindrical or prismatic light diffusing element 4 optically coupled to a light source 2 so as to capture the photons emitted by the light source 2 and to restore them by its surface. lateral to illuminate the culture medium of a photobioreactor.
• the light diffusing element 4 may be the subject of all the embodiments previously written.
• Penetration length characteristic of light 1 3.8 mm (concentration of 10 8 cells / mL);
• the square arrangement described above provides a gap of 2 rms between two successive diffuser tubes 4, so it is possible to place up to 1369 (37x37) diffuser tubes 4 in the cubic chamber 1.
• the total illumination area is then 43m 2 , and the instantaneous power consumption of the LEDs 2 is then 13.7 kW, of which 10.28kWth to dissipate.
• the volume of culture medium 3 in the culture chamber 1 corresponds to the total volume of 1 m 3 minus the volume of the 1369 diffuser tubes 4. It is 0.89 m 3 .

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