Photobioreactor for photosynthetic microorganism production

Abstract

A photobioreactor system includes at least two culture plates disposed within an outer casing and being parallel to each other and spaced apart by a gap defining a culture volume. The culture plates have two opposed surfaces, spaced apart from each other by a plate thickness. The culture volume receives a culture of photosynthetic microorganisms and culture media. First and second inlets are in communication with the culture volume for, respectively, injecting the culture of photosynthetic microorganisms and culture media, and injecting gas into the culture volume. First and second outlets are in communication with the culture volume for, respectively, extracting the photosynthetic microorganisms and extracting the liquid overflow and outlet gases. A light emitting device is positioned along an edge of each of the culture plates to emit light therein. The two opposed surfaces diffuse light outwards from within the culture plates into the culture volume.

Description

PHOTOBIOREACTOR FOR PHOTOSYNTHETIC MICROORGANISM PRODUCTIONCROSS-REFERENCE TO A RELATED APPLICATION

[0001] This application claims priority on U.S. patent application number 63 / 702,386 filed on October 2, 2024, the entirety of which is incorporated herein by reference.TECHNICAL FIELD

[0002] This disclosure relates to photobioreactors for the culture and production of photosynthetic microorganisms such as microalgae and cyanobacteria.BACKGROUND

[0003] Research into microalgae has seen growing interest worldwide, due to their vast application potential. These organisms are renewable, sustainable and cost-effective sources of biofuels, bioactive medicinal products and food ingredients. Their use has been explored in various industrial sectors, including renewable energies, biopharmaceuticals and dietary supplements.

[0004] Although microalgae can be cultivated under highly controlled laboratory conditions, it is increasingly difficult to ensure high microalgal productivity in large-scale production that is economical viable. An ideal microalgae culture system should have at least some of the following characteristics: substantially uniform distribution of light within growing systems (bioreactors) to convert this energy into biomass; effective transfer of matter across the liquid-gas barrier and culture system; effective control of culture temperature, carbon dioxide taming and oxygen removal; minimization of cellular / hydrodynamic stress-related damage to photosynthetic organisms; minimized risk of fouling and biofilm formation; and / or reduced construction, operation and maintenance costs for commercial units.

[0005] For economic reasons, open basins are traditionally used, but it is difficult to control culture growth conditions in open basins and they do not allow axenic cultures. Horizontal and vertical tubular photobioreactors were designed to attempt to solve the problems of open basins. However, they are generally not economically viable and have higher operating costs compared to open basins due to their energy requirements.

[0006] Accordingly, improvements are still desired in the industrial culture of photosynthetic microorganisms such as microalgae to overcome the limitations of open basins while still reducing or not significantly increasing the operation cost.SUMMARY

[0007] In one aspect, there is provided a photobioreactor system comprising: at least two culture plates disposed within an outer casing, the at least two culture plates being parallel to each other and spaced apart by a gap defining a culture volume, each of the at least two plates comprising two opposed surfaces spaced apart from each other by a plate thickness, the culture volume receiving a culture of photosynthetic microorganisms and culture media; a first inlet in communication with the culture volume for injecting the culture of photosynthetic microorganisms and culture media, and a second inlet in communication with the culture volume for injecting gas into the culture volume; a first outlet in communication with the culture volume for extracting the photosynthetic microorganisms, and a second outlet in communication with the culture volume for extracting liquid overflow and outlet gases; and a light emitting device positioned along an edge of each of the at least two culture plates, the light emitting device emitting light into the at least two culture plates, wherein the two opposed surfaces diffuse light from within the at least two culture plates outwards into the culture volume.

[0008] In certain embodiments the photobioreactor system as defined above and described herein further includes, in whole or in part, and in any combination, one or more of the following features.

[0009] In some embodiments, the two opposed surfaces have a diffusion gradient that is diffusive in a direction away from the light emitting device. Preferably, the diffusion gradient on the two opposed surfaces is defined by a surface defect causing light diffusion that is more concentrated in a direction away from the light emitting device. In some embodiments, the diffusion gradient on the two opposed surfaces is defined by linear etching, and wherein a distance between each linear etch decreases in a direction away from the light emitting device.

[0010] In some embodiments, the light emitting device is a light emitting diode.

[0011] In some embodiments, the system further comprises a second light emitting device positioned along a second edge of each of the at least two culture plates. Preferably, thesecond edge is opposite the edge. In some embodiments, the two opposed surfaces have a second diffusion gradient on a second portion of their surface, separate from the at least one portion, wherein the second diffusion gradient is more and more diffusive (i.e. gradually more diffusive) in a direction away from the second light emitting device. In some embodiments, the diffusion gradient on the two opposed surfaces is defined by a surface defect causing diffusion that is more and more concentrated in a direction away from the light emitting device. In some embodiments, the diffusion gradient on the two opposed surfaces is defined as a vertical etching and wherein the distance between each vertical etch is decreasing in a direction away from the light emitting device.

[0012] In some embodiments, a ratio of a surface area of the at least two culture plates to the culture volume is at least 200 m2 / m3.

[0013] In some embodiments, a width of the light emitting device is smaller than a width of the culture plate.

[0014] In some embodiments, the photosynthetic microorganisms are cyanobacteria or microalgae.

[0015] In some embodiments, the culture volume is one of multiple cultural volumes disposed between adjacent ones of the at least two culture plates, wherein the multiple culture volumes are in fluid communication with each other.

[0016] In some embodiments, the at least two culture plates each have a separation that is opaque, semi-transparent or transparent.

[0017] In some embodiments, the at least two culture plates each have one oblique surface.

[0018] In a further aspect, there is provided a method of culturing photosynthetic microorganisms: seeding a culture of the photosynthetic microorganisms in a culture volume defined between two culture plates within a photobioreactor, the at least two culture plates being parallel to each other and spaced apart to define the culture volume; diffusing light outwardly from each of the two culture plates into the culture volume; and providing nutrients and carbon dioxide to the culture.

[0019] Many further features and combinations thereof concerning the present improvements will appear to those skilled in the art following a reading of the instant disclosure.DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 is a schematic side elevation view of a photobioreactor system according to an exemplary embodiment of the present disclosure.

[0021] FIG. 2 is a schematic perspective elevation view of a photobioreactor system according to an exemplary embodiment of the present disclosure.

[0022] FIG. 3 is a front perspective view of a photobioreactor system according to an exemplary embodiment of the present disclosure.

[0023] FIG. 4 is a cross-section view of a photobioreactor system according to an exemplary embodiment of the present disclosure.

[0024] FIG. 5 is a schematic of a light-diffusing culture plate in the photobioreactor system according to an exemplary embodiment of the present disclosure.

[0025] FIG. 6 is a schematic showing an exploded view of a photobioreactor system according to an exemplary embodiment of the present disclosure.

[0026] FIG. 7 is a schematic showing a diffusion gradient on a surface of a light-diffusing culture plate according to an exemplary embodiment of the present disclosure.

[0027] FIG. 8 is an exploded view showing a plurality of light-diffusing culture plates in the photobioreactor system according to an exemplary embodiment of the present disclosure.

[0028] FIG. 9 is a schematic front view of a photobioreactor system according to an exemplary embodiment of the present disclosure.

[0029] FIG. 10 is a schematic showing a light-diffusing culture plate with a wall separation in the culture volume area according to an exemplary embodiment of the present disclosure.

[0030] FIG. 11A is a schematic showing a light-diffusing culture plate with light emitting devices on either side according to an exemplary embodiment of the present disclosure.

[0031] FIG. 11 B is a schematic showing a light-diffusing culture plate with light emitting devices on either side and a separation in the middle according to an exemplary embodiment of the present disclosure.

[0032] FIG. 11C is a schematic showing a light-diffusing culture plate with light emitting devices on either side and a light diffusing separation in the middle according to an exemplary embodiment of the present disclosure.

[0033] FIG. 11 D is a schematic showing a light-diffusing culture plate with light emitting devices on either side and a separation in the middle where the culture plate has a gradually decreasing from each end to the separation thickness according to an exemplary embodiment of the present disclosure.

[0034] FIG. 12 is a graph showing the concentration of photo-microorganisms in culture (diamond) and the productivity (square) in function of time.

[0035] FIG. 13A is an image of a culture plate having an indentation gradient.

[0036] FIG. 13B is a graph showing the gray value of light as a function of distance from the light emitting diode (LED), with the culture plate of Fig. 13A.

[0037] FIG. 14A is an image of a culture plate having one oblique surface and one parallel surface.

[0038] FIG. 14B is a graph showing the gray value of light as a function of distance from the light emitting diode (LED), with the culture plate of Fig .14A.

[0039] FIG. 15A is an image of a culture plate with a semi-transparent separation at the end.

[0040] FIG. 15B is a graph showing the gray value of light as a function of distance from the light emitting diode (LED) with the culture plate of Fig. 15A.DETAILED DESCRIPTION

[0041] The main problem to solve when designing a photobioreactor is how to introduce light in an efficient manner that distributes throughout the culture area. Open basins achieve this by having large surfaces. However, as previously explained, there are many limitationswith open basins, notably contamination risks. When considering a closed system, a tubular vessel has been traditionally used because they provide a good ratio of surface- to-volume ratio (SA / ), where the volume refers to the culture volume behind that surface. To improve the ratio of luminosity the thickness of the tubes is reduced and light emitting devices are positioned around the tubes. Unfortunately, this configuration leads to a waste of space to incorporate light sources at the surface of the tubes.

[0042] The present photobioreactor system overcomes the limitations of open basin cultures and tubular cultures by performing a vertical culture in a closed system. By virtue of being a closed system, the contamination risks are significantly reduced and can be, in fact, avoided. The problem with a traditional vertical culture is how to provide sufficient illumination on the entire culture. Oversaturating the culture with too much light can be detrimental to culture growth. Indeed, beyond a certain luminosity intensity each photo-microorganism will have a decline or a reduced growth. On the other hand, not providing sufficient light will slow or stop the growth of the culture. Providing sufficient light evenly throughout the surface can be difficult. It is therefore important to control the luminosity that the culture is exposed to.

[0043] The present photobioreactor has at least two light-diffusing culture plates (also simply referred to herein as “culture plates”) disposed within an outer casing, the at least two light-diffusing culture plates being parallel to each other and spaced apart by a gap defining a culture volume. Each of the at least two culture plates have two opposed surfaces spaced apart from each other by a plate thickness. In some embodiments, a ratio of a surface area of the at least two culture plates to the culture volume is at least 100, 150, or 200 m2 / m3based on the culture volume defined therebetween or from 100 to 300 m2 / m3or from 150 to 250 m2 / m3.

[0044] The connection that forms the gap between the opposed surfaces can be a separate element or can be part of one of the culture plates. The connection can have any suitable shape as long as a volume is delimited therein. Although the figures described below show a connection that is rectangular with triangular top and bottom sides, any other shape can be considered. The utility of having a triangular shape at the top and bottom is to reduce or eliminate the regions in which flow is low, and diffusion does not properly reach, particularly at the inlet and outlet zones where accumulation could occur. This shape is in no way limitative, however.

[0045] In order to sufficiently illuminate the culture volume, a light emitting device is positioned along an edge of each of the at least two culture plates for emitting light into the at least two culture plates. The light is then distributed within the culture volume by the diffusive surface of the two opposed surfaces. The two opposed surfaces may have on at least one portion of their surface a diffusion gradient that is gradually more diffusive in a direction away from the light emitting device. Stated differently, the density of the striations formed in the two opposed surfaces changes (becomes less dense) in a direction away from the light emitting device. This diffusion gradient, caused by the gradually lower density of the striations in the surface as the light moves away from light source, allows the luminosity to increase as a distance away from the light emitting device increases, to thereby better concentrate the light farther from the light emitting device. This helps to provide a luminosity that is substantially uniform, i.e., that is distributed substantially homogenously, on the culture volume because the light intensity would otherwise taper off as the distance from the light emitting device increases. In some embodiments, the uniform luminosity (e.g. measured in lux) may be defined as a variation between two points of the culture volume being less than 33%, less than 30% or less than 25%. The two points may be selected anywhere in the culture volume but in some embodiments, one of the points is in proximity of the light emitting device and the other is in proximity or at the opposite end of the culture plate. The photobioreactor system is particularly adapted for scaled up processes where a photobioreactor system contains a plurality of photobioreactors that are stacked parallel to each other. The diffusive properties of each of the culture plate surface causes a distribution of light that is more uniform on the culture. Indeed, because of the diffusion of light in that manner, the overall luminosity is increased and better distributed despite a compact arrangement of stacked culture plates. To increase the production volume of the system additional photobioreactors can simply be added in series to create additional culture volumes. Thanks to the diffusive properties of the surfaces that scatter light into the culture volume, there is no limitation of size with regards to the overall number of culture plates for the photobioreactor system.

[0046] The present system thus offers the following advantages: a high biomass productivity, a minimal environmental footprint, an agitation system and vertical orientation suitable for most strains of microalgae and cyanobacteria strains, an easy access to system components for efficient scale-up and maintenance, a stacked and modular system for easy scale-up, an adaptation and scalability of culture volumes (by increasing the number of photobioreactors within the same system) and a reduced risk of contamination compared toopen basin setups. The simplicity of the design also makes the system easier to operate and maintain. The present system makes it possible to: (1) optimize the exchange surface between light and culture volume, (2) increase reactor volume by increasing the number of plates (scaling), (3) maintain homogeneity of scattered light in the culture volume, and (4) maximize useful growth zone and productivity of the microorganisms. The present spacesaving, dismountable system with easy access to individual parts and easy cleaning is a clear improvement over traditional tubular cultures and open basins.

[0047] The present photobioreactor and system are suitable for any photosynthetic microorganisms such as microalgae and cyanobacteria, including but not limited to spirulina, chlorella, Scenedesmus, Tisochrysis lutea, Tetraselmis, Haematococcus pluvialis, Dunaliella, Nannochloropsis, Porphyridium, Phaeodactylum tricornutum, Isochrysis galbana, Skeletonema costatum, Synechococcus, Anabaena, Chlamydomonas reinhardtii, and Botryococcus braunii.

[0048] Now making reference to Figs. 1 -4, a photobioreactor system 100 is illustrated with culture plates 15 having opposed surfaces. The culture plates 15 are parallel to each other and spaced apart by a connection which creates a gap that defines a culture volume 20 between each of the culture plates 15. A chamber 22 may be provided on a top plate 23 for seeding the photosynthetic microorganisms and providing culture media or can be provided from an inlet at the bottom of the culture plate. The top plate 23 also provides a space for placing monitoring probes. An outer casing 5 covers the culture plates 15 to encase the photobioreactor system 100.

[0049] As shown in Figs. 1-4, the photobioreactor system 100 can have a plurality of culture plates 15 that are stacked in series, parallel to each other. In preferred embodiments, as shown in Fig. 5, the system has fluid communication 29 between adjacent photobioreactors which allows to provide a single chamber 22 for the photobioreactor system 100. Certain inlets can also be shared in this embodiment, for example the nutrients and culture media inlets. However, it is important that each culture volume be provided with a gas inlet and outlet to provide a carbon dioxide feed and an oxygen removal. For example, a bubbler in the form of a perforated rod, or other form of gas diffuser, allowing the formation of bubbles in each culture volume is provided. The photobioreactor system 100 has a configuration that allows the bubbler to be easily removed for cleaning or replacement. The temperature can for examplebe regulated with a heat exchange tube immersed in the culture volume (for example positioned at 29 see Fig. 10).

[0050] As shown in Fig. 6, each culture plate 15 is spaced apart from other culture plates 15 by a spacer 17. The spacer 17 keeps each culture plate 15 apart and creates a gap to allow the creation of the culture volumes. This gap can be adapted based on the microorganism and light intensity and can be optimized such that a uniform intensity of light is provided throughout the culture volumes. The distance can for example vary between 0.5 cm to 1.5 cm however this value is dependent on the type of microorganism and also the overall size of the culture plate and optical properties of the surface of the culture plates 15. Each microorganism requires different light intensities and has different absorbent properties. Some microorganisms absorb more light than others and / or tend to have a denser culture. The distance between the culture plates can thus be adapted to suit each specific photosynthetic microorganism. If the culture plates 15 are positioned too close to each other, there can be difficulties in obtaining a uniform luminosity as there may not be sufficient distance for the light to diffuse and scatter and could instead remain concentrated and not properly distributed into the culture volume.

[0051] A clamping system can be used for compressing the culture plates 15 against each other by threaded rods 18 passing through the culture plates 15. Other means of securing the culture plates together are also possible, and this is only an exemplary embodiment.

[0052] The diffusive properties of the opposed surfaces of the culture plates can be imparted therein by creating surface defects. The surface defects can be of any kind and can for example be produced by sanding the surface. The diffusive properties can also be a property of the material (e.g. acrylic) rather than a physical defect on the surface. The diffusive properties can also be caused by the introduction of angles on the surface to modify the surface such that it is not flat. In one embodiment, the surface defect is a ridge. In some embodiment, when a gradient is provided on the surface, the surface is engraved with streaks that are spaced apart gradually less in a direction away from the light emitting device. This is for example shown in Fig. 7 with the direction of light 26 showing the direction of the gradients 27, 28 being streaks. The gradient 27 is also shown in an exploded view of the photobioreactor system 100 in Fig. 8.

[0053] As shown in Fig. 8, the light emitting device 10 is positioned along an edge of each of the culture plates 15. In the embodiment illustrated in Fig. 8, there is provided two light emitting devices 10 for each of the culture plates 15. Accordingly, the surfaces of the culture plates can have two diffusive gradients for each of the light emitting devices as illustrated in Fig. 7.

[0054] In a preferred embodiment, the light emitting device is a light emitting diode (LED) illumination system. The LEDs can be affixed along the side edges of the culture plate 15 to force the light emitted by the LEDs into the culture plates and diffuse it into the system via the surfaces of the culture plates. The LED system can be fitted with a heat sink if required to diffuse the heat to the environment. An advantage of the present system however is that the incidental heating caused by the light emitting device is not within the culture volume and does not directly affect the culture volume’s temperature. In other words, the lateral illumination means that the indirect heating is separate from (i.e. outside of) the culture volume and can be managed without affecting the culture temperature.

[0055] As shown in Fig. 9, the photobioreactor system 100 has a first inlet 32 for receiving a culture of photosynthetic microorganisms and culture media, a second inlet 34 for injecting gas bubbles in the culture volume, a first outlet 36 for extracting the photosynthetic microorganisms and a second outlet 38 for liquid overflow and outlet gases. The culture media can be selected among many suitable culture mediums and can include different minerals (nitrogen, phosphate, etc.) which can be issued from the mining industry. There is also optionally provided a chamber 22 for providing additional microorganisms during continuous production. The photobioreactor system 100 can be equipped with at least one monitoring equipment 24, which can be a thermometer, a pH meter or an oximeter for example.

[0056] In some embodiments, the culture volume is separated into two areas by a separation 19 as shown in Fig. 10, which is optional. This separation 19, when present, is used when two gradients 27 and 28 are provided on each side of the separation 19 for better control of the diffusion of light and for preventing a concentration of light in the middle of the culture volume. The separation 19 also eliminates pressure differentials between the two volumes it separates due to inhomogeneous bubbling and also allows liquid circulation. Fig. 10 also shows the joint 30 which can be used to connect culture plates 15 together.

[0057] Fig. 11A illustrates an exemplary embodiment where a light emitting device 10 is provided on both ends of the culture plate. The light emitting device provides a light beam 11 which diffuses 12 when it comes into contact with a surface of the culture plate. A single light beam is illustrated for clarity and simplicity however it should be understood that a LED provides a large number of light beams 11. As indicated above, the separation 19 is optional and is not present in the embodiment of Fig. 11A but can be provided as shown in Fig. 11 B. The separation 19 can be made of an opaque material, a semi-transparent material or a transparent material. Fig. 11C illustrates an exemplary embodiment where the separation 19 is made of a semi-transparent material and diffuses the light. In many of the embodiments described herein the culture plate 15 is shown with two parallel surfaces, however, other configurations are contemplated such as one parallel surface and one oblique surface as shown in the exemplary embodiment of Fig. 11D. The oblique surface can have a surface defect gradient and / or can have a geometry that enhances the diffusion away from the light emitting device. The oblique surface in Fig. 11 D is shown with a separation 19 but this is a non-limitative illustration as the oblique surface can also be used without the separation 19, with both surfaces being oblique, and / or with a semi-transparent separation 19 as shown in Fig. 11C.

[0058] The cultivation by inoculum and production in photobioreactors, the microalgae harvested can be used for multiple purposes. The microalgae paste obtained can be either subjected to cell disruption or drying. Drying can be freeze drying or spray drying. The dry microalgae can then be used in the production of nutritional supplements. Cell disruption can be performed in a number of ways, such as ball milling, high pressure homogenization, enzymatic lysis, acid or alkaline treatment, pulsed electric field, etc. The contents of the cells are thus released and these include high value compound, proteins, lipids, and polysaccharides. They can be used to produce cosmetics, chemicals, food, feed, biodiesel, and bioethanol. The residual biomass of the microalgae can also be used to produce biofuel or biogas. At least a portion of the biogas could be revalorized and recycled as feed for the culture of microalgae.

[0059] The culture system transforms carbon dioxide and can be useful to help control the emissions of certain industries. For example, the photobioreactor can be used to reduce the carbon dioxide emission in mining operations, manufacturing plants, the transport industry, the energy sector (particularly when utilizing fossil fuels or natural gas), and pipeline transportations.

[0060] The culture system can also be used as means of mass producing of microalgae. The dry biomass obtained from the mass production is useful for the production of dietary supplements (animal or human consumption), or for other industries to produce other products.EXAMPLE 1

[0061] A culture of spirulina was performed using the photobioreactor system described herein, the details of which are presented in the table below.Table 1 : characteristic of each unit of the photobioreactor

[0062] The system demonstrated a high specific illuminated surface area that reaches up to 200 m2 / m3, a biomass productivity reaches of up to 2.4 g / L / day, and a maximum concentration of spirulina of 15 g / L (see Fig. 12).EXAMPLE 2

[0063] Three culture plate configurations were tested for their capacity to uniformly distribute light across their length. In each case, the LED was positioned on the left side of the culture plate (i.e. at the start of the indentation gradient where the distance between indentations is the greatest). Fig. 13A shows a configuration in which the culture plate has two parallel surfaces that have a gradient of indentation. Fig. 13B demonstrates the uniform distribution of the light emitted throughout its surface. Fig. 14A shows a configuration in which the culture plate has a parallel surface and an oblique surface and the parallel surface with indentations. Fig. 14B demonstrates the uniform distribution of the light emitted throughout its surface. Fig. 15A shows a configuration in which the culture plate has parallel surfaces with indentations but also a semi-transparent separation at the opposite end of the LED. Fig. 15B demonstrates the uniform distribution of the light emitted throughout its surface.

[0064] As used herein, the terms “comprises”, “comprising”, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. As used herein, the term “about” is intended to allow for a 10% variation of the associated numerical values.

[0065] No element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims.

[0066] While various aspects of the present disclosure have been disclosed, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the present disclosure. For example, the present disclosure as described herein includes several aspects and embodiments that include particular features. Although these particular features may be described individually, it is within the scope of the present disclosure that some or all of these features may be combined with any one of the aspects and remain within the scope of the present disclosure. References to “various embodiments,” “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particularfeature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. The use of the indefinite article “a” as used herein with reference to a particular element is intended to encompass “one or more” such elements, and similarly the use of the definite article “the” in reference to a particular element is not intended to exclude the possibility that multiple of such elements may be present.

[0067] The embodiments described in this document provide non-limiting examples of possible implementations of the present technology. Upon review of the present disclosure, a person of ordinary skill in the art will recognize that changes may be made to the embodiments described herein without departing from the scope of the present technology. Other applications would be recognized by the person of ordinary skill in the art and are considered to be within the scope of the present disclosure. Yet further modifications could be implemented by a person of ordinary skill in the art in view of the present disclosure, which modifications would be within the scope of the present technology.

Claims

WHAT IS CLAIMED IS:

1. A photobioreactor system comprising: at least two culture plates disposed within an outer casing, the at least two culture plates being parallel to each other and spaced apart by a gap defining a culture volume, each of the at least two culture plates comprising two opposed surfaces spaced apart from each other by a plate thickness, the culture volume receiving a culture of photosynthetic microorganisms and culture media; a first inlet in communication with the culture volume for injecting the culture of photosynthetic microorganisms and culture media, and a second inlet in communication with the culture volume for injecting gas into the culture volume; a first outlet in communication with the culture volume for extracting the photosynthetic microorganisms, and a second outlet in communication with the culture volume for extracting liquid overflow and outlet gases; and a light emitting device positioned along an edge of each of the at least two culture plates, the light emitting device emitting light into the at least two culture plates, wherein the two opposed surfaces diffuse light outwards from within the at least two culture plates into the culture volume.

2. The photobioreactor system of claim 1 , wherein the two opposed surfaces have a diffusion gradient that is diffusive in a direction away from the light emitting device.

3. The photobioreactor system of claim 2, wherein the diffusion gradient on the two opposed surfaces is defined by a surface defect causing light diffusion that is more concentrated in a direction away from the light emitting device.

4. The photobioreactor system of claim 2 or 3, wherein the diffusion gradient on the two opposed surfaces is defined by linear etching, and wherein a distance between each linear etch decreases in a direction away from the light emitting device.

5. The photobioreactor system of any one of claims 1 to 4, wherein the light emitting device is a light emitting diode.

6. The photobioreactor system of any one of claims 1 to 5, further comprising a second light emitting device positioned along a second edge of each of the at least two culture plates.

7. The photobioreactor system of claim 6, wherein the second edge is opposite the edge.

8. The photobioreactor system of claim 6 or 7, wherein the two opposed surfaces have a second diffusion gradient on a second portion of their surface, wherein the second diffusion gradient is more and more diffusive in a direction away from the second light emitting device.

9. The photobioreactor system of claim 8, wherein the second diffusion gradient on the two opposed surfaces is defined by a surface defect causing diffusion that is more and more concentrated in a direction away from the light emitting device.

10. The photobioreactor system of claim 7 or 8, wherein the second diffusion gradient on the two opposed surfaces is defined as a vertical etching and wherein a distance between each vertical etch decreases in a direction away from the light emitting device.11 . The photobioreactor system of any one of claims 1 to 10, wherein a ratio of a surface area of the at least two culture plates to the culture volume is at least 200 m2 / m3.

12. The photobioreactor system of any one of claims 1 to 11 , wherein a width of the light emitting device is smaller than a width of each of the at least two culture plates.

13. The photobioreactor system of any one of claims 1 to 12, wherein the photosynthetic microorganisms are cyanobacteria or microalgae.

14. The photobioreactor system of any one of claims 1 to 13, wherein the culture volume is one of multiple culture volumes disposed between adjacent ones of the at least two culture plates, wherein the multiple culture volumes are in fluid communication with each other.

15. The photobioreactor system of any one of claims 1 to 14, wherein the at least two culture plates each have a separation that is opaque, semi-transparent or transparent.

16. The photobioreactor system of any one of claims 1 to 15, wherein the at least two culture plates each have one oblique surface.

17. A method of culturing photosynthetic microorganisms: seeding a culture of the photosynthetic microorganisms in a culture volume defined between two culture plates within a photobioreactor, the two culture plates being parallel to each other and spaced apart to define the culture volume; diffusing light outwardly from each of the two culture plates into the culture volume; and providing nutrients and carbon dioxide to the culture.

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