Photobioreactor and method for growing microalgal-type biological organisms

Abstract

The invention relates to a photobioreactor (1) for growing microalgal-type biological organisms, the growth being based on autotrophy under light that is essentially, or even exclusively, artificial, wherein the organisms grow in a nutrient-rich liquid substrate circulating in the photobioreactor, the photobioreactor comprising at least one cell (3) referred to as an illuminated cell, the photobioreactor (1) being characterized in that the illuminated cell (3) comprises at least one spiral-shaped transparent pipe and in that the illuminated cell (3) comprises at least two sections referred to as lighting sections which are associated with the transparent pipe and arranged on either side of the transparent pipe.

Description

DESCRIPTION PHOTOBIOREACTOR AND METHOD FOR GROWING MICROALGAE-TYPE BIOLOGICAL ORGANISMS FIELD OF THE INVENTION

[0001] The present invention relates to the field of the culture of biological organisms, in particular of the microalgae type, and for example to the culture of chlorella.

[0002] More specifically, the invention relates to a photobioreactor type reactor, that is to say in which the growth of biological organisms suspended in an aqueous medium is based on photosynthesis, and therefore involves a supply of light. TECHNOLOGICAL BACKGROUND

[0003] The development of biological organisms is generally carried out in a reactor, in which the organism to be developed is circulated and fed to cultivate it. Three types of culture are generally implemented.

[0004] The first type is called heterotrophy: organisms grow by feeding on organic matter. The second type is called autotrophy: organisms grow by feeding on mineral matter. The third type is called mixotrophy: organisms grow by both autotrophy and heterotrophy.

[0005] Autotrophy requires, in addition to mineral nutrients, the supply of energy. This is generally light in order to carry out photosynthesis. The light source for this supply can be natural, i.e. the Sun, or artificial, or both. Thus, the higher the quantity of light provided, the better the production yield, while remaining below a maximum limit so as not to damage the organisms. Thus, in general, biological organisms are suspended in a nutrient-rich substrate, in an aqueous medium, which is placed in the reactor. The reactor for this type of culture is then called a photobioreactor. Among the autotrophic organisms, chlorella is known.

[0006] Natural light has the advantage of being readily available and free. However, it has many disadvantages: in particular, it is difficult to direct, its intensity is subject to climatic hazards, and it is not available at all times, especially at night. As a result, the production of the target organisms is not optimal. For example, in order to maximize the light intensity received, it is It is known to use so-called open reactors, i.e. with a surface area in the open air, preferably very large, in which the organisms develop. Such reactors involve the use of large ground surfaces, which is restrictive, for example, depending on the nature of the terrain where these tanks are implemented. In addition, the introduction of foreign bodies into the reactors is not controlled at all.

[0007] It is also known to use closed reactors, i.e., ones in which there is no surface exposed to the open air. Typically, the organisms are suspended in an aqueous medium, which forms the liquid substrate, and are circulated in a reactor. The reactor is positioned so as to receive sunlight to obtain photosynthesis.

[0008] Document US2015 / 0230420 describes an example of a reactor formed from a system of transparent pipes and placed in a building that allows daylight to enter. In order to provide an additional light source and limit shadow areas in the pipes, light strips can be positioned at different locations around the pipes. However, such a solution is not entirely satisfactory, since it remains dependent on natural light.

[0009] Artificial light is more easily controlled than natural light. However, it is more expensive and therefore requires careful optimization to ensure sufficient profitability. Several reactor designs have been developed. These designs must meet two main requirements: sufficient circulation length for organisms to develop and light input optimized as much as possible. However, the light input must also take into account technological limitations, particularly in terms of available power and the problem of overheating of biological organisms.

[0010] The work presented in A. Souliès' thesis, Contribution to the hydrodynamic study and modeling of high volumetric productivity photobioreactors, 2014, highlights in particular the sensitivity of chlorella to light for their growth in a photobioreactor. Light is characterized by the photon flux density impacting an optical face of the photobioreactor, in a given wavelength range. This photon flux density is directly related to the surface productivity of a photobioreactor. The volumetric productivity of a photobioreactor, which is a widely used indicator to characterize the performance of photobioreactors, is obtained by multiplying the surface productivity with what is called the specific surface area. The specific surface area of ​​a photobioreactor is the total illuminated surface area of ​​the photobioreactor per illuminated volume of fluid that is in the photobioreactor at a given time.The performance of a photobioreactor is therefore directly and strongly dependent on the surface area. specific. However, the specific surface area depends in particular on the geometry of the photobioreactor.

[0011] Document LIS2014 / 004600 describes a reactor for the cultivation of living organisms such as algae, comprising a conduit with a serpentine geometry, that is to say it is formed of a conduit comprising substantially rectilinear sections, of the same length, parallel to each other and connected two by two by bent sections. According to one embodiment, a lighting system is placed on both sides of the conduit to saturate the conduit with light. However, such a geometry has, among other things, the disadvantage of having a significant footprint, since it depends on the number of rectilinear sections: the greater the number of rectilinear sections, the longer the path of the organisms in the reactor is advantageously, and the greater the footprint is disadvantageously high. In addition, the dimensions of the lighting systems must follow the dimensions of the reactor, which again increases the footprint.

[0012] Another known reactor geometry is called helical. This is a reactor comprising substantially horizontal turns of transparent pipes, superimposed substantially vertically. Document US10,876,087 describes an example of such a helical photobioreactor, in which the turns are elongated horizontally. Artificial light sources are placed on vertical panels, arranged on either side of the photobioreactor, in the direction of elongation of the turns. However, such a design does not allow for maximizing the light input at all points of the pipes. Indeed, points of the pipes are further from the panels than others, which can result in a drastic drop in production for the most sensitive organisms. In addition, this design requires large installations to accommodate the pipes with sufficient length.

[0013] Document KR20030018197 describes another type of photobioreactor in the form of two flat tanks parallel to each other, made of transparent material, the two tanks having common inlets but separate outlets, and between which a lighting system in the form of fluorescent tubes is arranged; the fluorescent tubes are stacked vertically, and are in contact with a wall of each tank. According to this design, only one surface of each tank receives light, so that the specific surface is not optimized. In addition, the path of the organisms between an inlet and an outlet is rectilinear, so that to lengthen the path, the tanks must be lengthened, posing problems of realization and size.

[0014] Finally, in these photobioreactor designs, the light sensitivity of the cultured organisms can cause accumulations on the transparent walls of the reactor pipes, ultimately creating shadow areas that are detrimental to productivity. Cleaning the reactor walls can be tedious.

[0015] There is therefore a need for a new type of reactor, and more precisely a photobioreactor, overcoming in particular the aforementioned drawbacks.

[0016] A first aspect of the invention is to propose a new photobioreactor in which only an artificial light source is used, and optimizing the supply of light.

[0017] A second aspect of the invention is to propose a new photobioreactor whose specific surface area is maximized.

[0018] A third aspect of the invention is to propose a new photobioreactor with limited space requirements.

[0019] A fourth aspect of the invention is to propose a new photobioreactor in which maintenance is facilitated.

[0020] A fifth aspect of the invention is to propose a new photobioreactor particularly suited to the cultivation of chlorella.

[0021] A sixth aspect of the invention is to provide a novel photobioreactor that can be easily cleaned.

[0022] SUMMARY OF THE INVENTION

[0023] Thus, according to a first aspect, the invention relates to a photobioreactor for the growth of biological organisms of the microalgae type. More specifically, the photobioreactor of the invention is dedicated to organisms whose growth is based on autotrophy in essentially artificial light, that is to say that natural light, from the Sun, does not influence or has an almost undetectable influence on the growth of the organisms. In the photobioreactor, the organisms grow in a liquid substrate rich in nutrients circulating in the photobioreactor. The photobioreactor then comprises at least one so-called illuminated cell. The illuminated cell comprises at least one transparent conduit of substantially planar spiral shape having an upper optical surface and a lower optical surface. In addition, the illuminated cell comprises at least two so-called lighting sections associated with the transparent conduit.The lighting sections are arranged on either side of said transparent conduit so as to each illuminate an optical surface of the transparent conduit, namely a first lighting section illuminating at least a portion of the upper optical surface and a. second lighting section illuminating at least a portion of the lower optical surface of the transparent conduit.

[0024] The closed-type photobioreactor thus allows for a path length in the spiral conduit that is maximized for reduced space requirements, while providing a high specific surface area over the entire path. The artificial light provided by the lighting sections is directed specifically and exclusively to each side of the transparent conduit. The specific surface area is then equal to the sum of the two optical surfaces of the transparent conduit. This improves efficiency.

[0025] Depending on different aspects, it is possible to provide one and / or the other of the characteristics below taken alone or in combination.

[0026] According to one embodiment, at least one lighting section comprises a panel extending opposite a lower or upper optical surface of the transparent spiral conduit. In addition, it may comprise a plurality of light-emitting diodes distributed on the surface of the panel so as to illuminate at least a portion of the upper or lower optical surface of the transparent spiral conduit.

[0027] The lighting section can thus easily be manufactured and developed to suit the organisms in question.

[0028] For example, the diodes of each lighting section can emit light composed exclusively of two colors. In other words, the light emitted by the diodes is composed partly of light of a first color and partly of light of a second color, different from the first color, to the exclusion of any other color, so that the wavelengths emitted by the lighting sections correspond substantially to the absorption peaks of the organisms growing in the photobioreactor.

[0029] The use of light-emitting diodes also allows the distribution and ratio between the different colors to be adjusted. For example, in the case of a green organism, such as Chlorella, the ratio of the diodes is between 60% and 80% for the first color, which is red, and between 40% and 20% for the second color, which is blue. Light absorption is then maximized, to optimize the growth of the organisms and increase yield.

[0030] According to one embodiment, the photobioreactor may comprise at least a first transparent conduit and a second transparent conduit. The first transparent conduit, in a spiral, is offset in a vertical direction from the second transparent conduit, also in a spiral. The two transparent spiral conduits are in fluid connection so as to ensure the circulation of the substrate. In addition, two lighting sections are associated with each of the first transparent conduit and the second transparent conduit. A third transparent conduit also associated with two lighting sections arranged on either side, then a fourth, etc. can thus be fluidically connected to each other, so as to lengthen the path in the photobioreactor according to needs, while maintaining an optimized specific surface.

[0031] According to one embodiment, the photobioreactor comprises at least one lighting support interposed between the two superimposed transparent conduits. The lighting support has a lower surface on which the upper lighting section associated with the first transparent conduit is formed and an upper surface on which the lower lighting section associated with the second transparent conduit is formed.

[0032] Thus, according to a particular embodiment, the photobioreactor can comprise six transparent spiral conduits, in fluidic connection with each other so that the substrate can circulate successively in the six transparent spiral conduits.

[0033] According to one embodiment, the transparent spiral conduit has a substantially circular section, so as to limit turbulence in the circulating fluid.

[0034] According to one embodiment, each illuminated cell may comprise a sub-frame on which each transparent spiral conduit is assembled and on which the lighting sections are assembled on either side of each transparent spiral conduit, so that each illuminated cell forms an assembly intended to be handled as a unit. The handling of an illuminated cell is thus facilitated.

[0035] According to one embodiment, at least one illuminated cell comprises a removable assembly system between at least one lighting section and the sub-frame. Thus, in the event of failure of a lighting section, its removal and then its repair or replacement are facilitated, reducing the downtime of the photobioreactor.

[0036] According to one embodiment, the photobioreactor may comprise a frame intended to rest on the ground. The frame comprises at least one housing equipped with an assembly device with at least one illuminated cell. For example, the assembly device with an illuminated cell is of the removable type. It is thus possible to easily assemble an illuminated cell on the frame, by placing it in its housing.

[0037] According to a particular embodiment, the frame comprises three housings for receiving three illuminated cells superimposed in the vertical direction. The number of housings can however be adapted according to needs.

[0038] Thus, particularly in the case where the illuminated cells include a sub-frame, assembly on the frame is particularly easy: the illuminated cell as a block is simply mounted on the frame. Dismantling an illuminated cell, then positioning or replacing it, for example for maintenance, is also particularly easy.

[0039] According to a second aspect, the invention also provides a method for growing a biological organism of the microalgae type. The growth is based on autotrophy in essentially artificial light. The organisms develop in a nutrient-rich liquid substrate circulating in a photobioreactor as presented below. The yield of such a method is then high enough to satisfy industrial-scale production.

[0040] In one example, the biological organism is of the genus Chlorella, which is a vitamin-rich and edible microalgae that can be used as a food supplement, for example. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Embodiments of the invention will be described below with reference to the drawings, briefly described below:

[0042] [Fig. 1] represents a part of a photobioreactor according to an embodiment of the invention, comprising a frame and an illuminated cell.

[0043] [Fig. 2] represents a frame of the photobioreactor of Figure 1.

[0044] [Fig. 3] schematically represents an example of the construction of an illuminated cell.

[0045] [Fig. 4a] represents a first example of the realization of a transparent spiral-shaped conduit of the photobioreactor of figure 1 in top view.

[0046] [Fig. 4b] represents a second example of the embodiment of a transparent spiral-shaped conduit of the photobioreactor of Figure 1 in top view.

[0047] [Fig. 5] represents the conduit of figure 4a in three-quarter view.

[0048] [Fig. 6] represents a sectional view along line VI-VI of Figure 4a.

[0049] [Fig. 7] represents a top view of an illumination section of the photobioreactor of Figure 1.

[0050] [Fig. 8] represents the lighting section of Figure 7 in three-quarter view.

[0051] [Fig. 9] shows the lighting section of Figure 7 in side view.

[0052] [Fig. 10] represents a detail view of figure 9 along circle X.

[0053] [Fig. 11] shows a side view of an alternative embodiment of a lighting section.

[0054] [Fig. 12] represents a front view of an illuminated cell according to one embodiment.

[0055] [Fig. 13] shows a side view of a sub-frame of the illuminated cell of Figure 12.

[0056] [Fig. 14] represents a three-quarter view of a set of bars of a reinforcement system for the illuminated cell of figures 12 and 13.

[0057] [Fig.15] represents a three-quarter view of the illuminated cell of Figure 12.

[0058] In the drawings, like references designate identical or similar objects. DETAILED DESCRIPTION

[0059] The figures illustrate an embodiment of a photobioreactor and its various components that is particularly suited to the development of biological organisms by autotrophy. Several organisms develop by autotrophy, including Chlorella. Chlorella is a genus of microalgae, chlorella, whose The nutritional properties make its production particularly attractive. It is one of only ten algae authorized in the Codex Alimentarius, along with spirulina. Thus, the present invention relates in particular to the cultivation of chlorella, but not limited to this, the photobioreactor being able to be used for the cultivation of other organisms, and in particular other microalgae, by autotrophy.

[0060] For chlorella growth, typically, a strain is first inoculated into a column to obtain a larger volume of chlorella. Then, the chlorella are suspended in a liquid culture medium, particularly aqueous, rich in inorganic nutrients, and finally they are circulated, with the culture medium, in the photobioreactor, in order to grow. Nutrients can also be injected into the photobioreactor to maintain a determined nutrient concentration. The culture medium containing the suspended chlorella is referred to below as a fluid.

[0061] Light is supplied to the chlorella in the photobioreactor. In the context of the present invention, the light supplied is essentially, or even exclusively, artificial, that is to say that the growth of the chlorella in the photobioreactor is obtained thanks to the supply of artificial light. By artificial light, we mean here a light supplied by a lighting device manufactured and controlled by Man, as opposed to so-called natural light which is that of the Sun. Of course, the photobioreactor can be placed in sunlight, but this natural light then has no influence, or only in a virtually immeasurable manner, on the growth of the chlorella. In other words, the specific surface area is almost not impacted by sunlight.

[0062] In Figure 1, a part of the photobioreactor 1 is shown. The photobioreactor 1 thus comprises a frame 2 and at least one so-called illuminated cell 3 mounted on the frame 2. The photobioreactor 1 also comprises an organism harvesting zone, not shown in the figures. This may be, for example, a harvesting tank mounted on the frame 2, or carried by a separate frame, which is specific to it, the harvesting column being in fluid connection with the illuminated cell.

[0063] The frame 2 is made of rigid material, for example metal such as steel. It comprises in particular feet 4, for example four feet, intended to rest directly or indirectly, for example by means of pads which limit the transmission of vibrations, on the ground. More precisely, each foot 4 is for example formed at a lower end of a substantially vertical post 5, the frame 2 then comprising four posts 5, substantially identical, arranged for example at the vertices of a quadrilateral.

[0064] In the following, for the sake of clarity, the terms horizontal, vertical, lower, upper, above, below, high, low and their variant will be used according to the natural orientation of Figure 1, in which it is considered that the feet 4 rest on the ground, the posts 5 extending substantially vertically.

[0065] Four substantially vertical faces are then defined on the frame 2. A first vertical face is called the front face 6. The front face 6 is defined between two so-called front posts 5. A second vertical face is called the rear face 7 and is defined between two so-called rear posts 5. The other two vertical faces are called lateral faces 8, are parallel to each other, and are each defined between a front post and a rear post 5. The so-called upper extreme portions, that is to say on the side opposite the feet 4, of the posts 5 are connected by crosspieces 9 forming a substantially square or rectangular horizontal frame. A reinforcing bar 10 can be placed between two parallel crosspieces 9 in order to reinforce the frame of the crosspieces 9. The posts 5 are not arranged exactly at the four corners of the frame formed by the crosspieces 9.Indeed, for reasons which will be explained later, a front post 5 is set back, towards the rear face 7, relative to the other post 5 of the front face. Thus, two rear posts 5 and one front post 5 are each arranged at a corner of the frame, and the last post 5 is arranged on a crosspiece 9 of the frame. In order to make the assembly between the posts 5 rigid, intermediate crosspieces 11 are arranged in threes in the same substantially horizontal plane, so as to form an open U between the front posts 5. The U thus formed are distributed vertically between the upper and lower ends of the posts 5. Reinforcing beams 12 can be placed between two intermediate crosspieces 11 so as to extend between the two lateral faces 8, near the feet 4. The reinforcing beams 12 thus allow better support of the weight of the illuminated cells 3 when they are mounted on the frame 2.

[0066] The frame 2 forms at least one housing 13 for at least one illuminated cell 3. According to the embodiment of the figures, the frame 2 forms for example three housings 13, each housing 13 being intended to receive an illuminated cell 3. A housing 13 is defined for example between two U-shaped sections formed by the intermediate crosspieces 11. Each housing 13 comprises an assembly device 14 with at least one illuminated cell 3. More precisely, according to the example of the figures, an assembly device 14 comprises two L-shaped angles 15 facing each other, each extending substantially horizontally on a lateral face 8. For example, for a housing 13, each angle 15 is rigidly fixed on an intermediate crosspiece 11 which extends between a front post 5 and a rear post 5, for the same U. The third intermediate crosspiece 11 of this same U is by example provided with studs 16 projecting horizontally towards the front face 6. Thus, as will be explained later, a lighting cell can be assembled to the frame 2 by resting under the effect of its weight on two angles 15 and the studs 16 of a housing 13. The assembly device 14 is thus of the removable type, that is to say that it allows assembly and disassembly between the frame 2 and a rapid illuminated cell 3, by simple sliding on the angles 15 according to the example, without tedious assembly and disassembly operations or destruction, in the manner of shelving.

[0067] The assembly device 14 may then comprise a locking system 17 between the frame 2 and the illuminated cell 3 in the housing 13. For example, it may be a hook 18 mounted in rotation on a front post 5 of the frame and which makes it possible to engage a dedicated element of the cell 3 in position in a housing 13 of the frame 2. Thus, once the illuminated cell 3 is in place in a housing 13 by sliding, the hook 18 is simply engaged with the dedicated element of the cell 3 by rotation. Similarly, by pivoting the hook 18 in the other direction, the cell 3 can be slid out of the housing of the frame 2.

[0068] The frame 2 thus forms vertically superimposed housings 13, three in number according to the example in figures 1 and 2, but which can be adapted according to needs, without increasing the floor space.

[0069] The rear face 7 of the frame 2 of the photobioreactor can be closed by a plate 19 provided with openings 20 distributed over the surface of the plate 19 and which ensure air circulation as will be explained later.

[0070] An example of the embodiment of a lighting cell 3 will now be described.

[0071] The illuminated cell 3 comprises at least one transparent conduit 21, in which the fluid comprising the chlorella suspended in their substrate is in circulation.

[0072] By transparency here is meant the property that the walls of the conduit allow light to pass through them. Since growth is based on autotrophy, the conduit 21 is here as transparent as possible in order to allow as much light as possible to pass through the walls. The conduit 21 is for example made of PMMA (poly(methyl methacrylate)) or glass.

[0073] According to the invention, the conduit 21 is shaped as a spiral, or snail, which is substantially flat. By spiral, we mean here the shape in which the conduit 21 describes curves, or turns, around a central fixed point. By plane, we mean here the fact that the turns of the conduit 21 are substantially aligned on the same mean plane M which intersects each turn and on which the central point is located. In other words terms, the turns of the conduit 21 are substantially coplanar. The average plane M is substantially horizontal.

[0074] The terms upper, lower, vertical, horizontal, above, below, top, bottom, and their variants, used in connection with the illuminated cell 3, must be understood as before, in reference to the orientation of the cell 23 when assembled on the frame 2.

[0075] The conduit 21 comprises several substantially coplanar turns, at least three, and for example nine, and extends between a first end 22 and a second end 23.

[0076] A first example of embodiment of the spiral duct is illustrated in Figures 4a and 5 to 7, in which it is conventionally defined that the second end 23 is closer to the fixed point of the spiral described by the duct 21 than the first end 22, which is located at the outer periphery of the spiral. It is formed for example by assembling substantially rectilinear tube portions 21a with tube portions 21b bent at substantially 90°, so that the outline of the spiral duct 21, when seen in a plane parallel to the mean plane M, describes a substantially rectangular or square shape, with rounded corners. This shape has several advantages. In particular, it makes it possible to manufacture the spiral duct 21 by tightly assembling the straight tube portions 21a and bent tubes 21b, which are readily available.The straight tube portions 21a can be cut to the desired lengths to form the spiral, so that the dimensions of the spiral and the number of turns can be easily adjusted. The portions 21a, 21b are for example assembled by gluing. More precisely, the straight tube portions 21a are for example fitted and glued onto the bent tube portions 21b. This shape is also compact while maximizing the path of the chlorella in the photobioreactor 1. It limits turbulence during the circulation of the fluid. It also facilitates assembly on the frame 2 of the cell 3, as well as the possible replacement of a portion 21a, 21b. Finally, this shape ensures an optimized specific surface area.

[0077] More precisely, a surface 24 called the upper optical surface is defined on the conduit 21 as being the entire portion of the free external surface of the wall of the conduit 21 located on an upper side of the mean plane M and a surface 25 called the lower optical surface as being the entire portion of the free external surface of the wall of the conduit located on a lower side of the mean plane M. By free surface, here is meant a surface which is not in contact with a surface of another element, and which can therefore receive light from a light source external to the conduit 21. According to the embodiment shown in the figures, the conduit 21 has a cross-section substantially circular, so that an upper or lower optical surface 24, 25 is formed by all of the portions of semi-cylindrical outer surfaces with a circular base. The adjacent turns may be in contact with each other, or not. However, in order to maximize the total length of a conduit 21, that is to say the length of the path of the fluid passing through the conduit 21, two adjacent turns are as close as possible to each other. The choice of the circular section of the conduit 21 makes it possible, in particular, to limit the appearance of turbulence during the circulation of the fluid.

[0078] Alternative embodiments of the duct 21 in a substantially planar spiral are possible. A second exemplary embodiment in particular is illustrated in FIG. 4b, in which the first end 22 and the second end 23 are both at the outer periphery of the planar spiral, for example but not necessarily at substantially the same distance from the central fixed point of the spiral. Without describing again the elements common to the first exemplary embodiment, the duct 21 according to the second example is also formed for example by assembling portions of substantially rectilinear tubes 21a with portions of tubes 21b bent at substantially 90°.More precisely, the spiral conduit 21 of the second example can be explained as formed by two half-spirals whose turns are alternating: a first turn 22a in which the fluid circulates in a first direction and which comprises the first end 22 and a turn 23a in which the fluid circulates in a second direction opposite to the first direction and which comprises the second end 23. According to the second example, the center of the spiral comprises a connecting portion 21c ensuring the connection between the first spiral 22a and the second spiral 23a. The connecting portion 21c is for example S-shaped, formed by straight portions and bent portions like the rest of the spiral conduit 21. As before, the adjacent turns are preferably as close as possible to each other.This second example makes it easier to connect the conduits 21 to each other, as will be seen later, by leaving the ends 22 and 23 accessible at the outer periphery of the spiral conduit 2. Furthermore, the length of the path of the fluid in the conduit 21 between the two ends 22, 23 is increased in particular by the connection portion 21c.

[0079] The cell 13 further comprises at least two so-called lighting sections 26, which form two sources of artificial light. The two lighting sections 26 are associated with the transparent conduit 21, in order to provide light to the organisms circulating inside. More precisely, the two lighting sections 26 are arranged on either side of the transparent conduit 21 in a spiral so as to each illuminate an optical surface 24, 25 of the transparent conduit 21. A first so-called upper section 26 is placed above the conduit 21 so as to illuminate at least at least a portion of the upper optical surface 24, and the second, so-called lower, section 26 is placed below the conduit 21 so as to illuminate at least a portion of the lower optical surface 25 of the conduit 21. In other words, the lighting sections 26 are each arranged on one side of the mean plane M of the conduit 21. In other words, the light rays coming from the upper section 26 are intended to be incident on the upper optical surface 24 before any other surface, and the light rays coming from the lower section 26 are intended to be incident on the lower optical surface 25 before any other surface.

[0080] The sum of the optical surfaces 24, 25 thus corresponds to the specific surface area of ​​the photobioreactor 1. By maximizing these two optical surfaces 24, 25, the efficiency of the photobioreactor 1 is also maximized. However, the spiral shape of the conduit 21 makes it possible to make the specific surface area correspond almost to the total external surface area of ​​the walls of the conduit 21.

[0081] According to one embodiment which is that of the figures, a lighting section 26 is in the form of a panel 27 which serves as a support for a light-emitting device 28 connected to an electrical energy source, not shown in the figures. The panel 27 extends over two dimensions so as to preferably completely, or almost completely, cover the optical surfaces 24, 25 of the conduit 21. Thus, it is substantially of rectangular or square general shape, so as to follow the shape of the spiral described by the conduit 21. It has been demonstrated that the wavelengths of the light supplied exert an influence on the growth of biological organisms in a photobioreactor.Thus, in the case of chlorella, red light, i.e. for a wavelength between 600 and 780 nm (nanometers) and blue light, i.e. for a wavelength between 400 and 500 nm, were determined to be those absorbed by chlorella, with an absorption peak by chlorella around 660 nm and 450 nm. The ratio and distribution between the colors also exerts an influence on growth. For chlorella, which is green in color, it was determined that the ratio between 60% and 80%, with a preferred value around 70% for red light and between 40% and 20%, with a preferred value around 30% for blue light, provides the best yield in photobioreactor 1, to the exclusion of any other color. This distribution and choice of colors may vary depending on the organism in photobioreactor 1.For example, for a red-colored microorganism, blue and green colors will be favored in the light provided by the lighting sections 26. Thus, the light-emitting device 28 preferably comprises a plurality of discrete sources making it possible to choose the distribution of the. colors. For example, it may include light-emitting diodes (LEDs) that allow you to choose the colors and their distribution.

[0082] The distance between a lighting section 26 and the associated optical surface 24, 25 is chosen so that the entire associated optical surface 24, 25 is illuminated, without shadow points, with a substantially constant light intensity over the entire optical surface 24, 25. For example, in the case of LEDs, this distance is established in correlation with the opening angle of each LED and the distribution of the LEDs on the panel 27.

[0083] A more detailed embodiment of a lighting section 26 will be described with reference to Figures 7 and 8. The panel 27 serves as a support for plates 29 for the LEDs 28. For example, the plates 29 are four in number, although the number of plates 29 can be any. On each plate 29, the LEDs 28 are for example connected in series, and the plates 29 are for example connected in parallel. The plates 29 are fixed to the panel 27 for example using a screw / nut system, by gluing, or any other equivalent system. Preferably, the fixing between the plates 29 and the panel 27 can be removed without damaging the panel 29. Thus, in the event of failure of LEDs on a plate 29, only the plate 29 concerned can be changed, facilitating the maintenance of the photobioreactor 1 and reducing costs.The power supply management of the LEDs can be carried out by considering all the LEDs of the panel 27, or by considering each group of LEDs on a plate 29 independently of the LEDs of the other plates 29.

[0084] The conduit 21 is thus illuminated on its two optical surfaces 24, 25, so that the illumination of the chlorella which circulates in the conduit 21 is optimized over its entire path.

[0085] For reasons which will be explained later, the panel 27 may be provided with an opening 30 extending between two plates 29, horizontally from a free edge of the panel 27 towards the opposite free edge, over a dimension for example less than half of the total dimension between the two free edges.

[0086] Advantageously, in order to obtain an adequate path length for the organisms in the photobioreactor 1, the illuminated cell comprises at least two transparent conduits 21, superimposed vertically, and preferably aligned along a single vertical axis in order to limit the size. In other words, the fixed points of the spirals described by each of the conduits 21 of the same illuminated cell 3 are aligned along this same vertical axis. According to a particular embodiment, the illuminated cell 3 comprises six transparent conduits 21, in a spiral, superimposed vertically, each associated with two lighting sections 26. As previously, for a transparent conduit 21, two lighting sections 26 are therefore arranged on either side of the average plane M of the transparent conduit 21 in question. Thus, incidentally, the lighting sections 26 are also superimposed vertically, aligned along the same vertical axis.

[0087] The conduits 21 of the illuminated cell 3 are in fluid connection with each other. The case is described here when the conduits 21 are in accordance with the first embodiment. More precisely, between two superimposed conduits 21, either the second end 23 of a first conduit 21 is in fluid connection with the second end 23 of the second conduit 21, or the first end 22 of a first conduit 21 is in fluid connection with the first end 22 of the second conduit 21. More precisely still, considering a succession of several superimposed conduits 21, from top to bottom, the first end 22 of a first conduit 21 forms a fluid inlet. The second end 23 of the first conduit 21 is then in fluid connection with the second end 23 of a second conduit 21 which is immediately above the first conduit 21.For this purpose, a portion 31 of pipe called the central connection, which is for example a portion bent for example at 90°, is fluidically connected to the two second ends 23 of the two conduits 21. The first end 22 of the second conduit 21 is then fluidically connected to the first end 22 of a third conduit 21 which is immediately above the second conduit 21. The bent portion 31 then passes through the panels 27 at their opening 30 of the two lighting sections 26 interposed between the second conduit 21 and the third conduit 21. A portion 32 of pipe called the lateral connection, which is for example a portion bent at 180°, then ensures the fluidic connection between the two first ends 22. As between the first conduit 21 and the second conduit 21, the second end 23 of the third conduit is fluidically connected to the second end 23 of a fourth conduit 21 at using a central connection portion 31.The connections between the successive conduits 21 are thus made using central connection portions 31 and lateral connection portions 32 and make it possible to easily adjust the number of conduits 21 per cell 3 according to requirements.

[0088] When the conduits 21 are in accordance with the second embodiment, the design of a cell 3 can be simplified, in particular by removing the central connection portions 31: thanks to the position on the outer periphery of the ends 22 and 23 of each conduit 21, each connection between the superimposed conduits 21 can be made by a portion similar to the lateral connection portion 32 described above. The opening 30 in the panels 27 also becomes superfluous, further simplifying the design of a cell 3.

[0089] According to one embodiment, which is that of the figures, the lighting sections 26 between two successive conduits 21 of the same lighting cell 3 can be formed on the same lighting support 33. More precisely, each lighting section 26 can comprise, as previously, a panel 27 provided with plates 29 supporting the LEDs. The lighting support 33 then comprises two panels 29 and a fixing device 34 between the panels 27 in order to form a unitary block. The fixing device 34 is for example of the screw or adhesive type. It can make it possible to maintain a space between the two panels 29 in order to house, for example, electronic components which can be common, at least in part, to the LEDs 28 of each of the panels 27. The openings 30 of the two panels 29 are aligned vertically.The fixing device 34 between the two panels 27 can also be combined with the fixing system of the plates 29 on the panels 27, in particular so as to limit manufacturing costs. Two lighting sections 26 are thus formed on two opposite faces of a single block which can be handled individually.

[0090] This double panel 29 design further allows the panels 29 to be stiffened. This is why, preferably, the panel 29 of a lower lighting section 26 associated with the first conduit 21 so as to illuminate its lower optical surface 25, or of an upper lighting section 26 associated with the last conduit 21 so as to illuminate its upper optical surface 24 can also be assembled, using a fixing device 34, to a bare panel 29', that is to say one which does not form the support for a light source. This also makes it possible to standardize the manufacturing methods of the lighting sections 26, and therefore to reduce costs.

[0091] Thus, in an illuminated cell 3, the fluid containing the chlorella circulates from the first end 22 of the first conduit 21, this first end 22 forming a fluid inlet 35 of the cell 3, to, in the example with six conduits, the first end 22 of the last conduit 21, this first end 22 forming a fluid outlet 36 of the cell 3.

[0092] In order to facilitate the handling of the cell 3, its assembly and its disassembly on the frame 2, a sub-frame 37 of the cell 3 is produced in order to fix the conduits 21 and the lighting sections 26 there.

[0093] According to an exemplary embodiment, the sub-frame 37 comprises a frame 38, for example formed from a U-shaped folded metal sheet, i.e. comprising two substantially parallel lateral branches defining an opening, and which are connected by a bottom wall. Two support systems are then fixed to the frame 38: a first support system 39 dedicated to the conduits 21 and a second support system 40 dedicated to the lighting sections 26.

[0094] The system 39 for supporting the conduits 21 comprises, for example, angles 41, rigidly fixed, for example, by a screw / nut system, to the two side walls of the frame 38. The angles 41 extend substantially horizontally, and on a side wall of the frame 38, they are superimposed vertically. Finally, each angle 41 of a side wall of the frame is aligned substantially horizontally with another angle 41 of the other wall of the frame 38, the two aligned angles 41 thus forming a substantially horizontal support for a conduit 21. The system 39 for supporting the conduits 21 may further comprise a set 42 of reinforcing bars which is fixed between two horizontally aligned angles 41, either directly on the angles or on the side walls of the frame 38. This set 42 of reinforcement forms, for example, a barred X or more generally a “spider” whose number of legs may vary.Thus, a conduit 21 placed on the angles 41 of the conduit 21 support system 39 has its weight which is also supported by the reinforcement assembly 42 in order to limit bending deformations. Indeed, under the weight of the circulating fluid, the conduit 21 can flex, causing a downward deformation arrow. Thanks to the reinforcement assembly 42 placed under the conduit 21, the arrow is reduced, or even eliminated. The support assembly 42 is further designed to limit the shadow zones in the transparent conduits 21, so as to limit its impact on the specific surface. Thus the barred X shape, but also the dimension of the bars of the assembly 42, make it possible to limit direct contacts between the assembly 42 and the conduits 21. More precisely, the crossed bars of the barred X shape come into contact only with the bent tube portions 21b of the conduits 21.

[0095] The system 40 for supporting the lighting sections 26 also comprises, for example, angles 43 fixed to the side walls of the frame 38 in a similar manner to the angles 41 of the system 39 for supporting the conduits, so that two angles 43 are aligned horizontally and form a support for a lighting section 26.

[0096] The bottom of the frame 38 of the sub-frame 37 may be provided with openings promoting air circulation between the lighting sections 26 and the conduits 21.

[0097] The illuminated cell 3 may comprise an assembly system between the lighting sections 23 and the sub-frame 37. Preferably, this assembly system is of the removable type, that is to say that the lighting sections 23 can be easily assembled and disassembled on the sub-frame 37 without damaging the sub-frame 37 or the lighting sections 23. For example, the assembly system may comprise a screw / nut type fixing system of the lighting sections 26 on their system 40 support. However, preferably, the lighting sections 26 are simply placed on the angles 43 of the support system 40, so as to allow them to be easily put in place and removed with a simple sliding movement.

[0098] Thus, to assemble an illuminated cell 3, for example, the conduits 21 are first inserted by sliding in a horizontal direction on the angles 41. Optionally, the conduits 21 can be fixed to the sub-frame 37, for example by a screw / nut system. The connection portions 31, 32 between the conduits can be connected prior to the installation of the conduits 21 on the sub-frame 37, or once the conduits 21 are installed on the sub-frame 37. The lighting sections 26 are then in turn installed on the sub-frame 37, for example one by one by substantially horizontal sliding on the angles 43 of their dedicated support system 40, taking care, where appropriate, to insert the central connection portions 31 into the openings 30 of the panels 27 of lighting sections 26. A system for locking the conduits and / or lighting sections 26 to the sub-frame 27 may be implemented.To disassemble the illuminated cell 3, the locking system can be deactivated if necessary, then the lighting sections 26, and then possibly the conduits 21, can be removed from their support system 39, 40 by sliding. In particular, in the event of intervention on a lighting section 26, only the lighting section 26 can be removed, and for example quickly replaced. Thus, the downtime of the photobioreactor 1 is reduced, and maintenance costs are reduced.

[0099] According to one embodiment, the illuminated cell 3 is equipped with at least one handle 44. According to one embodiment, the illuminated cell 3 is equipped with two handles, fixed to the frame 38. For example, each handle 44 is fixed between two angles 43 of the system 40 for supporting the lighting sections. More precisely, each handle 44 is fixed to a fixing plate 45 itself fixed between two successive angles 43 vertically and which are fixed to the same lateral branch of the frame 38. The two handles 44 are preferably opposite each other, aligned substantially horizontally, so that an operator can grasp each handle in one of his hands. At least one of the fixing plates 45 of the handles 44 comprises a lug 46 on which the hook 18 of the locking system 17 between the frame 2 and the cell 3 engages.

[0100] The cell 3 thus forms an assembly which can thus be manipulated as a single physical object, a unitary block, to be assembled on the frame 2. More precisely, the illuminated cell 3 can be mounted by sliding the sub-frame 37 onto the frame 2 on the side of the front face 6. For this purpose, the photobioreactor 1 can comprise a sliding assembly system 46 facilitating the sliding of the cell onto the frame 2. For example, the sliding device 46 may comprise rollers 47 fixed to the sub-frame 37 of the cell 3 and which roll along the angles 15 of the frame 2 until the sub-frame 37 comes into contact with the lugs 16 of the frame 2. Alternatively, the sliding device 46 may comprise elements of the skate type sliding on the angles, or of the rail type cooperating with complementary elements of the frame, in the manner of a drawer. The post 5 of the frame 2 which is set back allows the lateral connection portions 32 to protrude outside the frame 2, beyond said post 5.

[0101] The frame 2 can thus receive several illuminated cells 3, for example three illuminated cells 3 as described previously. Each illuminated cell 3 is mounted in a housing 13 of the frame, and the outlet 36 of each cell 3 is in fluid connection with the harvesting tank. Each illuminated cell 3 thus provides an illuminated path of several meters for the growth of biological organisms such as chlorella, with an optimized specific surface area. The handles 44 and the sliding device 46 facilitate the assembly and disassembly of the cells 3 on the frame, for example in the event of maintenance on a cell 3.

[0102] In order to maintain the organisms in the photobioreactor 1 at a given temperature, favorable to their growth, the photobioreactor may comprise a temperature regulation system. In particular, the light sources tend to bring heat to the fluid circulating in the conduits 21 which can be harmful to the growth of the organisms, and may themselves require regulation of their temperature. For example, in the case of chlorella, the temperature of the culture medium must be maintained in a temperature range between 21°C and 24°C (degrees Celsius). For this purpose, the temperature regulation system may comprise a ventilation device for dissipating the heat by ensuring air circulation between the conduits 21 and the panels 29 of lighting sections 26.According to an exemplary embodiment, the ventilation system comprises for example a blower arranged so as to generate an air flow in the direction of the front face 6 of the frame 2 towards the rear face 7, the openings in the bottom of the frame 38 of the sub-frame 37 of the cells 3 and the openings 20 on the plate 19 of the rear face of the frame 2 allowing the air to exit the photobioreactor 1 and thus ensuring effective ventilation.

[0103] The photobioreactor 1 thus described makes it possible to limit the footprint, on the ground and also vertically, while maximizing a path with a supply of light. Thanks in particular to the spiral shape of the conduits 21 in which the organisms circulate, the specific surface, determining for the performances of the photobioreactor 1, is optimized. For example, for a conduit 21 of a length between 20 and 40 linear m (meters) and with a section between 705 and 2825 mm 2(square millimeter) the specific surface area reached is of the order of 100 m -1 (per meter).

[0104] The spiral shape of the conduits 21 also makes maintenance easier. Indeed, it may be necessary to clean the internal walls of the conduits 21. For this purpose, a cleaning method comprises emptying the conduits 21 and circulating in the conduits a cleaning device, for example in the form of a ball made of a material allowing the internal walls to be cleaned, and of a diameter substantially equal to, or slightly greater than, the diameter of the conduits 21. The cleaning device is for example circulated using a blower.

Claims

CLAIMS

1. Photobioreactor (1) for the growth of biological organisms of the microalgae type, the growth being based on autotrophy in essentially artificial light, in which the organisms grow in a liquid substrate rich in nutrients circulating in the photobioreactor, the photobioreactor (1) comprising at least one so-called illuminated cell (3), the photobioreactor (1) being characterized in that the illuminated cell (3) comprises at least one transparent conduit (21) of substantially planar spiral shape having an upper optical surface (24) and a lower optical surface (25) and in that the illuminated cell (3) comprises at least two so-called lighting sections (23) associated with the transparent conduit (21), the lighting sections (23) being arranged on either side of said transparent conduit (21) so as to each illuminate a so-called optical surface (24, 25) of the transparent conduit (21),namely a first lighting section (26) illuminating at least a portion of the upper optical surface (24) and a second lighting section (23) illuminating at least a portion of the lower optical surface (25) of the transparent conduit (21).,

2. Photobioreactor (1) according to claim 1, wherein at least one lighting section (23) comprises a panel (27) extending opposite a lower or upper optical surface (24, 25) of the transparent spiral conduit (21) and comprises a plurality of light-emitting diodes (28) distributed on the surface of the panel (27) so as to illuminate at least a portion of the upper or lower optical surface (24, 25) of the transparent spiral conduit (21).

3. Photobioreactor (1) according to the preceding claim, in which the diodes (28) emit light composed exclusively of two different colors.

4. Photobioreactor (1) according to the preceding claim, in which the ratio of the diodes is between 60% and 80% for the first color which is red and between 40% and 20% for the second color which is blue.

5. Photobioreactor (1) according to any one of the preceding claims, comprising at least a first transparent conduit (21) and a second transparent conduit (21), the first transparent spiral conduit (21) being offset in a vertical direction from the second transparent conduit (21), the two transparent spiral conduits (21) being in fluid connection so as to ensure the circulation of the substrate, two lighting sections (23) being associated with each of the first transparent conduit (21) and the second transparent conduit (21).

6. Photobioreactor (1) according to the preceding claim, comprising at least one lighting support (33) interposed between the two superimposed transparent conduits (21), the lighting support (33) having a lower surface on which is formed the upper lighting section (23) associated with the first transparent conduit (21) and an upper surface on which is formed the lower lighting section (23) associated with the second transparent conduit (21).

7. Photobioreactor (1) according to claim 5 or claim 6, comprising six transparent spiral conduits (21), in fluid connection with each other so that the substrate can circulate successively in the six transparent spiral conduits (21).

8. Photobioreactor (1) according to any one of the preceding claims, in which the transparent spiral conduit (21) is of substantially circular section.

9. Photobioreactor (1) according to any one of the preceding claims, in which each illuminated cell (3) comprises a sub-frame (37) on which each transparent spiral conduit (21) is assembled and on which the lighting sections (26) are assembled on either side of each transparent spiral conduit (21), so that each illuminated cell (3) forms an assembly intended to be handled as a unit.

10. Photobioreactor (1) according to the preceding claim, in which at least one illuminated cell (3) comprises a removable assembly system between at least one lighting section (26) and the sub-frame (37).

11. Photobioreactor (1) according to any one of the preceding claims, comprising a frame (2) intended to rest on the ground, the frame (2) comprising at least one housing (13) equipped with an assembly device (14) with at least one illuminated cell.

12. Photobioreactor (1) according to the preceding claim, in which the assembly device (14) with an illuminated cell (3) is of the removable type.

13. Photobioreactor (1) according to claim 11 or claim 12, wherein the frame (2) comprises three housings (13) for receiving three illuminated cells (3) superimposed in the vertical direction.

14. A method of growing a biological organism of the microalgae type, the growth being based on autotrophy in essentially artificial light, in which the organisms grow in a nutrient-rich liquid substrate circulating in a photobioreactor (1) according to any one of the preceding claims.

15. Method according to the preceding claim, in which the biological organism is of the genus Chlorella.

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