WO2024068658A1

WO2024068658A1 - Photobioreactor and method for growing microalgal-type biological organisms

Info

Publication number: WO2024068658A1
Application number: PCT/EP2023/076585
Authority: WO
Inventors: Vincent LALANNE; Yoan FORGET
Original assignee: Idpoc
Priority date: 2022-09-27
Filing date: 2023-09-26
Publication date: 2024-04-04
Also published as: FR3140092A1

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 THE GROWTH OF MICROALGAE TYPE BIOLOGICAL ORGANISMS

FIELD OF INVENTION

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

[02] More precisely, 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 contribution from light.

TECHNOLOGY BACKGROUND

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

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

[05] Autotrophy requires, in addition to mineral nutrients, to provide energy. This is generally light in order to carry out photosynthesis. The source of light to achieve this contribution can be natural, that is to say 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 substrate rich in nutrients, in an aqueous medium, which is placed in the reactor. The reactor of this type of culture is then called a photobioreactor. Among autotrophic organisms, we know chlorella.

[06] Natural light has the advantage of being easily available and free. However, it has many disadvantages: in particular it is difficult to control, its intensity is subject to climatic hazards and it is not available at all times, particularly at night. Thus, the production of the targeted organisms is not optimal. For example, in order to maximize the light intensity received, it It is known to use so-called open reactors, that is to say with a surface in the open air, preferably very large, in which the organisms develop. Such reactors involve the use of large surface areas, which is restrictive for example depending on the nature of the terrain in which these tanks are installed. Furthermore, the introduction of foreign bodies into the reactors is not controlled at all.

[07] It is also known to use closed reactors, that is to say in which there is no open air surface. Typically, the organisms are suspended in an aqueous medium, which forms the liquid substrate, and are circulated in a reactor. The reactor is placed to receive sunlight to achieve photosynthesis.

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

[09] Artificial light is more easily controllable than natural light. However, it is more expensive, and therefore requires to be perfectly optimized to ensure sufficient profitability. Several reactor designs were then developed. These designs must mainly meet two requirements: a sufficient circulation length for the organisms to develop and a supply of light optimized as much as possible. However, the supply of light must also take into account technological limitations, particularly in terms of available power and the problem of overheating of biological organisms.

[10] The work presented in the thesis of A. Souliès, Contribution to the hydrodynamic study and modeling of photobioreactors with high volume productivity, 2014, highlights in particular the sensitivity of chlorella to light for their growth in a photobioreactor . Light is characterized by the flux density of photons impacting an optical face of the photobioreactor, in a given wavelength range. This photon flux density is directly linked to the surface productivity of a photobioreactor. The volume 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.

[11] 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 the others 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 presents, among other things, the disadvantage of having a significant bulk, since it depends on the number of rectilinear sections: the greater the number of rectilinear sections, the longer the journey of the organisms in the reactor, and the more the bulk is disadvantageously high. It is also necessary that the dimensions of the lighting systems follow the dimensions of the reactor, which again increases the bulk.

[12] 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 make it possible to maximize the light supply at all points of the pipes. In fact, some 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 involves installations of large dimensions to accommodate the pipes with sufficient length.

[13] The 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 distinct outlets, and between which a system of lighting in the form of fluorescent tubes is arranged; the fluorescent tubes are stacked vertically, and are in contact with one wall of each tank. According to this design, only one surface of each tank receives light, so the specific surface area is not optimized. In addition, the path of the organisms between an entrance and an exit is rectilinear, so that to lengthen the path, it is necessary to lengthen the reservoirs, posing problems of construction and size. [14] Finally, in these photobioreactor designs, the sensitivity to light of the cultured organisms can cause accumulations on the transparent walls of the reactor pipes, and thus ultimately create dark zones harmful to productivity. Cleaning reactor walls can be tedious.

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

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

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

[18] A third aspect of the invention is to propose a new photobioreactor whose bulk is limited.

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

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

[21] A sixth aspect of the invention is to propose a new photobioreactor which can be easily cleaned.

[22] SUMMARY OF THE INVENTION

[23] Thus, according to a first aspect, the invention relates to a photobioreactor for the growth of biological organisms of 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, has no or almost no influence. undetectable on the growth of organisms. In the photobioreactor, organisms grow in a nutrient-rich liquid substrate 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 part of the upper optical surface and a second lighting section illuminating at least part of the lower optical surface of the transparent conduit.

[24] The photobioreactor, of the closed type, thus makes it possible to have a path length in the spiral conduit which is maximized for a reduced footprint, while offering 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. The performance is improved.

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

[26] 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 over the surface of the panel so as to illuminate at least part of the upper or lower optical surface of the transparent spiral conduit.

[27] The lighting section can thus easily be manufactured and adjusted to adapt to the organisms in question.

[28] For example, the diodes in each lighting section can emit light composed exclusively of two colors. In other words, the light emitted by the diodes is composed for part of light of a first color and for another part 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.

[29] The use of light-emitting diodes also makes it possible to adjust the distribution and ratio between the different colors. For example, in the case of a green colored organism, such as Chlorella, the ratio of 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 organisms and increase yield.

[30] According to one embodiment, the photobioreactor may comprise at least a first transparent conduit and a second transparent conduit. The first transparent spiral conduit is offset in a vertical direction from the second transparent conduit, also spiral. The two transparent spiral conduits are in fluid connection so as to ensure the circulation of the substrate. Furthermore, 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 fluidly connected to each other, so as to lengthen the path in the photobioreactor depending on the needs, while maintaining an optimized specific surface area.

[31] 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.

[32] 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.

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

[34] 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 a set intended to be handled individually as a block. This makes handling an illuminated cell easier.

[35] 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 then repair or replacement is facilitated, reducing the downtime of the photobioreactor.

[36] 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.

[37] According to a particular embodiment, the frame comprises three housings to receive three illuminated cells superimposed in the vertical direction. The number of accommodations can however be adapted according to needs. [38] Thus, particularly in the case where the illuminated cells comprise 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 replacing it or putting it back in place, for example for maintenance, is also particularly easy.

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

[40] According to one example, the biological organism is of the genus Chlorella, which is a microalgae rich in vitamins and edible, which can be used as a food supplement for example.

BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[44] [Fig. 3] schematically represents an example of an illuminated cell.

[45] [Fig. 4a] represents a first example of producing a transparent conduit in the shape of a spiral of the photobioreactor of Figure 1 in top view.

[46] [Fig. 4b] represents a second embodiment of a transparent conduit in the shape of a spiral of the photobioreactor of Figure 1 in top view.

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

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

[49] [Fig. 7] represents a top view of a lighting section of the photobioreactor of Figure 1.

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

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

[52] [Fig. 10] represents a detailed view of Figure 9 along the circle X.

[53] [Fig. 11] represents a side view of an alternative embodiment of a lighting section.

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

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

[56] [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.

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

[58] In the drawings, identical references designate identical or similar objects.

DETAILED DESCRIPTION

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

[60] For the growth of chlorella, typically, a strain is, first, inoculated into a column in order to obtain a larger volume of chlorella. Then, the chlorella are suspended in a liquid culture medium, in particular 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 in order to maintain a determined nutrient concentration. The culture medium containing the chlorella in suspension is referred to in the following as being a fluid.

[61] Light is supplied to the chlorella in the photobioreactor. In the context of the present invention, the light provided is essentially, if not exclusively, artificial, that is to say that the growth of chlorella in the photobioreactor is obtained thanks to the supply of artificial light. By artificial light, we mean here light provided by a lighting device manufactured and controlled by humans, 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 in an almost unmeasurable way, on the growth of chlorella. In other words, the specific surface area is almost not impacted by sunlight.

[62] 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 includes a zone for harvesting organisms , not shown in the figures. It may for example be a harvesting tank mounted on frame 2, or carried by a separate frame, which is specific to it, the harvesting column being in fluid connection with the illuminated cell.

[63] The frame 2 is made of rigid material, for example metallic such as steel. It notably comprises feet 4, for example four feet, intended to rest directly or indirectly, for example via 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. [64] In the following, for purposes of clarity, we will use the terms horizontal, vertical, lower, upper, above, below, top, bottom and their variant according to the natural orientation of Figure 1, on which it is considered that the feet 4 rest on the ground, the posts 5 extending substantially vertically.

[65] Four substantially vertical faces are then defined on frame 2. A first vertical face is called front face 6. The front face 6 is defined between two so-called front posts 5. A second vertical face is called rear face 7 and is defined between two so-called rear posts 5. The two other 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 end 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 sleepers 9 in order to reinforce the frame of the sleepers 9. The posts 5 are not arranged exactly at the four corners of the frame formed by the sleepers 9. Indeed, for reasons which will be explained further, 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 a 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's thus formed are distributed vertically between the upper and lower ends of the posts 5. Reinforcement beams 12 can be placed between two intermediate crosspieces 11 so as to extend between the two lateral faces 8, close to the feet 4. The Reinforcement beams 12 thus allow better support for the weight of the illuminated cells 3 when they are mounted on the frame 2.

[66] 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 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 side 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 for example 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 removable type, that is to say that it allows rapid assembly and disassembly between the frame 2 and an illuminated cell 3, by simple sliding on the angles 15 according to the example, without tedious assembly and assembly operation. dismantling or destruction, like shelving.

[67] The assembly device 14 can then include a locking system 17 between the frame 2 and the cell 3 illuminated in the housing 13. For example, it can be a hook 18 mounted in rotation on a post 5 front 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 cell 3 is illuminated in place in a housing 13 by sliding, the hook 18 is simply engaged with the dedicated element of cell 3 by rotation. Likewise, by rotating hook 18 in the other direction, cell 3 can be slid out of the housing of frame 2.

[68] The frame 2 thus forms housings 13 superimposed vertically, three in number according to the example of Figures 1 and 2, but which can be adapted according to needs, without increasing the footprint.

[69] 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.

[70] An example of producing a lighting cell 3 will now be described.

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

[72] By transparent, we designate here the property according to which the walls of the conduit allow light to pass through them. Growth being based on autotrophy, 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.

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

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

[75] 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.

[76] A first embodiment of the spiral conduit is illustrated in Figures 4a and 5 to 7, in which it is defined by convention that the second end 23 is closer to the fixed point of the spiral described by the conduit 21 than the first end 22, which is located at the outer periphery of the spiral. It is formed for example by assembling portions of substantially rectilinear tubes 21a with portions of tubes 21b bent at substantially 90°, so that the contour of the spiral conduit 21, when seen in a plane parallel to the average plane M, describes a substantially rectangular or square shape, with rounded corners. This form has several advantages. In particular, it makes it possible to manufacture the conduit 21 in a spiral by watertight assembly of portions of straight tubes 21a and bent tubes 21b, easily available. The rectilinear 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. Portions 21a, 21b are for example assembled by gluing. More precisely, the rectilinear tube portions 21a are for example fitted and glued to 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 frame 2 of cell 3, as well as the possible replacement of a portion 21a, 21b. Finally, this shape ensures an optimized specific surface area.

[77] More precisely, a so-called upper optical surface 24 is defined on the conduit 21 as being the entire portion of free exterior surface of the wall of the conduit 21 located on an upper side of the average plane M and a surface 25 called lower optics as being the entire free exterior surface portion of the wall of the conduit located on a lower side of the average plane M. By free surface, we designate here 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 presented on the figures, the conduit 21 has a section substantially circular, so that an upper or lower optical surface 24, 25 is formed by all the portions of semi-cylindrical exterior surfaces with a circular base. The adjacent turns may or may not be in contact with each other. 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.

[78] Variant embodiments of the conduit 21 in a substantially flat spiral are possible. A second example of embodiment in particular is illustrated in Figure 4b, in which the first end 22 and the second end 23 are both at the outer periphery of the plane spiral, for example but not necessarily substantially at the same distance from the fixed point center of the spiral. Without describing again the elements common with the first embodiment, the conduit 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 the first direction and which comprises the second end 23. According to the second example, the center of the spiral comprises a connection portion 21c ensuring the connection between the first spiral 22a and the second spiral 23a. The connection portion 21c is for example S-shaped, formed by rectilinear 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 possible to facilitate the connection of conduits 21 together, as will be seen later, by leaving the ends 22 and 23 accessible at the outer periphery of the spiral conduit 2. In addition, the length of the fluid path in the conduit 21 between the two ends 22, 23 is increased in particular by the connection portion 21c.

[79] 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 part 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 part 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 average plane M of the conduit 21. In other words still, 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.

[80] The sum of the optical surfaces 24, 25 thus corresponds to the specific surface 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 conduit 21 makes it possible to match the specific surface almost to the total exterior surface of the walls of conduit 21.

[81] 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 a source of electrical energy, not shown in the figures. The panel 27 extends over two dimensions so as to preferably completely, or almost, cover the optical surfaces 24, 25 of the conduit 21. Thus, it is substantially of generally rectangular or square shape, so as to follow the shape of the spiral described by conduit 21. It has been demonstrated that the wavelengths of light provided exert an influence on the growth of biological organisms in a photobioreactor. Thus, in the case of chlorella, red light, that is to say for a wavelength between 600 and 780 nm (nanometers) and blue light, that is to say for a length of The wave between 400 to 500 nm, were determined to be those which are absorbed by chlorella, with an absorption peak by chlorella around 660 nm and 450 nm. The ratio and distribution between colors also has an influence on growth. For chlorella, 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 the photobioreactor 1, to the exclusion of any other color. This distribution and the choice of colors can vary depending on the organism in the photobioreactor 1. For example, for a red-colored microorganism, the 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 can include light-emitting diodes (LEDs) which allow you to choose the colors and their distribution.

[82] 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 light intensity substantially constant 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 panel 27.

[83] 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 on the panel 27 for example using a screw/nut system, by gluing, or any other equivalent system. Preferably, the attachment 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. Managing the power supply of the LEDs can be carried out by considering all of the LEDs on panel 27, or by considering each group of LEDs on a plate 29 independently of the LEDs on the other plates 29.

[84] 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.

[85] For reasons which will be explained later, the panel 27 can 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, on one dimension per example less than half of the total dimension between the two free edges.

[86] 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 clutter. 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, spiral conduits 21, superimposed vertically, each associated with two lighting sections 26. As previously, for a transparent conduit 21, two lighting sections 26 are therefore arranged 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.

[87] The conduits 21 of the illuminated cell 3 are in fluidic connection with each other. We describe here the case when the conduits 21 conform to the first exemplary 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. Even more precisely, 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 central connection, which is for example a portion bent for example at 90°, is fluidly connected to the two second ends 23 of the two conduits 21. The first end 22 of the second conduit 21 is then fluidly 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 the level of 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 lateral connection, which is a portion for example bent at 180°, then ensures the fluid connection between the two first ends 22. Likewise between the first conduit 21 and the second conduit 21, the second end 23 of the third conduit is connected fluidly to the second end 23 of a fourth conduit 21 using a central connection portion 31. The connections between 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 needs.

[88] When the conduits 21 conform to 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. [89] 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 device 34 for fixing between the panels 27 in order to form a unitary block. The fixing device 34 is for example of the screw or glue type. It can make it possible to maintain a space between the two panels 29 in order to accommodate, for example, electronic components which may 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 device 34 for fixing between the two panels 27 can also be confused with the system for fixing 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.

[90] This double panel design 29 also makes it possible to stiffen the panels 29. This is why, preferably, the panel 29 of a lower lighting section 26 associated with the first conduit 21 so as to illuminate its surface 25 lower optical, or 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 which does not form the support for a light source. This also makes it possible to standardize the manufacturing methods of lighting sections 26, and therefore to reduce costs.

[91] 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, up 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 from cell 3.

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

[93] According to an exemplary embodiment, the sub-frame 37 comprises a frame 38, for example formed from a metal sheet folded in a U, that is to say comprising two substantially parallel side branches defining an opening , and which are connected by a back wall. Two support systems are then fixed on 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.

[94] 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 one wall side 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 of support of the conduits 21 may further comprise a set 42 of reinforcement bars which is fixed between two angles 41 aligned horizontally, either directly on the angles or on the side walls of the frame 38. This set 42 of reinforcement forms for example a crossed X or more generally a “spider” whose number of legs can vary. Thus, a conduit 21 placed on the angles 41 of the conduit support system 39 21 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 bend, causing a downward deformation arrow. Thanks to the reinforcement assembly 42 placed under the conduit 21, the deflection is reduced, or even eliminated. The support assembly 42 is also designed to limit the shadow areas in the transparent conduits 21, so as to limit its impact on the specific surface. Thus the barred only with the bent portions of tubes 21b of conduits 21.

[95] The system 40 for supporting the lighting sections 26, for example, also comprises angles 43 fixed to the side walls of the frame 38 in a manner similar 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.

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

[97] The illuminated cell 3 may include 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 include a screw/nut type fixing system for 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 easily allow them to be put in place and removed with a simple sliding movement.

[98] 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, if necessary, to insert the connection portions 31 central in the openings 30 of the panels 27 of lighting sections 26. A system for locking the conduits and/or lighting sections 26 on the sub-frame 27 can be implemented. To disassemble the illuminated cell 3, the locking system can be deactivated if necessary, then the lighting sections 26, 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 photobioreactor 1 is reduced, and maintenance costs are reduced.

[99] 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 on 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 on a fixing plate 45 itself fixed between two vertically successive angles 43 and which are fixed on the same lateral branch of the frame 38. The two handles 44 are preferably opposite each other one from the other, aligned substantially horizontally, so that an operator can grasp each handle in one of his hands. At least one of the plates 45 for fixing 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.

[100] Cell 3 thus forms an assembly which can thus be manipulated as a single physical object, a unitary block, to be assembled on frame 2. More precisely, illuminated cell 3 can be mounted by sliding the sub-frame 37 on frame 2 on the front side 6. For this purpose, the photobioreactor 1 can include a sliding assembly system 46 facilitating the sliding of the cell on the frame 2. For example, the sliding device 46 may comprise casters 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 position. contact on the lugs 16 of the frame 2. Alternatively, the sliding device 46 may comprise elements of the pad 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 recessed allows the lateral connection portions 32 to protrude out of the frame 2, beyond said post 5.

[101] The frame 2 can thus receive several illuminated cells 3, for example three illuminated cells 3 as described above. 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.

[102] In order to maintain the organisms in the photobioreactor 1 at a given temperature, favorable to their growth, the photobioreactor can include a temperature regulation system. In particular, the light sources tend to provide heat to the fluid circulating in the conduits 21 which can be harmful to the growth of organisms, and may themselves need 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 include a ventilation device making it possible to dissipate heat by ensuring air circulation between the ducts 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 cells 3 and openings 20 on plate 19 of the rear face of frame 2 allowing air to escape from photobioreactor 1 and thus ensuring effective ventilation.

[103] The photobioreactor 1 thus described makes it possible to limit the bulk, 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 area, determining for the performance of the photobioreactor 1, is optimized. For example, for a conduit 21 of a length between 20 and 40 linear m (meter) 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).

[104] 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 process comprises emptying the conduits 21 and circulating a cleaning device in the conduits, for example in the form of a ball made of material allowing the internal walls to be cleaned, and of diameter substantially equal to, or slightly greater than, the diameter of the conduits 21. The cleaning device is for example put into circulation using a blower.

Claims

[Claim 1] Photobioreactor (1) for the growth of biological organisms of microalgae type, the growth being based on autotrophy in essentially artificial light, in which the organisms develop 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 a 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 sections (23) d lighting 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 the 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).

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

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

[Claim 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.

[Claim 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 one direction vertical of 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).

[Claim 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 the lower lighting section (23) associated with the second transparent conduit (21) is formed.

[Claim 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 conduits (21) spiral transparencies.

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

[Claim 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 sections (26) of lighting are assembled on either side of each transparent conduit (21) in a spiral, so that each illuminated cell (3) forms an assembly intended to be handled individually as a block.

[Claim 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).

[Claim 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.

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

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

[Claim 14] Process for growing a biological organism of the microalgae type, the growth being based on autotrophy in essentially artificial light, in which the organisms develop in a liquid substrate rich in nutrients circulating in a photobioreactor (1) according to any one of the preceding claims.

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