WO2025085952A1

WO2025085952A1 - Photobioreactor

Info

Publication number: WO2025085952A1
Application number: PCT/AU2024/051106
Authority: WO
Inventors: Nicholas John Gerard Hazell
Original assignee: Algenie Pty Ltd
Current assignee: Algenie Pty Ltd
Priority date: 2023-10-27
Filing date: 2024-10-22
Publication date: 2025-05-01
Anticipated expiration: 2026-04-27

Abstract

A photobioreactor (100) to cultivate a phototrophic or mixotrophic organism for production of biomass, the photobioreactor including a channel (102) providing a flow path (104) for conveying a culture medium (106) containing the organism to be cultivated, with the channel providing a length that revolves around an axis and having a cross-sectional profile transverse to the flow path configured to cause the culture medium to flow in a thin layer flow regime.

Description

PHOTOBIOREACTOR

Field

[0001] The present invention relates generally to a biomass manufacturing system. More particularly, the invention relates to a photobioreactor to cultivate a phototrophic or mixotrophic organism, in particular algae and cyanobacteria, for production of biomass. However, while some embodiments will be described herein with particular reference to that application, it will be appreciated that the invention is not limited to such a field of use, and is applicable in broader contexts.

Background

[0002] Algae and cyanobacteria represent an interesting biotechnology opportunity because of their ability to sequester carbon and produce complex chemistry, with light and CO2 as the dominant ingredients. However, many potential applications, particularly in the low-cost petrochemical industry, have been prevented because of the relatively high economic cost of growing algae in photobioreactors. This cost is related to both capital and operational costs per kilogram of biomass. While many of these costs and problems are similar to other biotechnology platforms such as yeast and bacterial systems, phototrophic algae have a particular problem related to its reliance on energy from light (photons) to grow and multiply. At high densities of algal cells in grams per litre, the algae blocks out light for its neighbours, making the useable concentrations productivity of such systems stall at around a gram of algal cells (by dried weight) per litre of water. With such dilute algal concentrations, the productivity is unable to exceed around a gram per litre per day in scale systems. In laboratory systems where small amounts of algae are grown at a millilitre scale it is possible to have higher gram per litre per day productivity, because the pathway for photons in a well of less than a millilitre is only 1 or 2 mm in distance. However, this productivity at small scale has not been scalable to factory production where larger channels, tubes or vessels mean much more dilute concentrations are needed to enable all cells to receive the necessary photons for growth. The more successful or faster the algae or cyanobacteria grow, the quicker the growth is limited because of the algae growth blocking the light for other cells to receive the photons they require. [0003] Typical phototrophic bioreactor designs attempt to overcome the above challenges with mixing strategies, such as turbulence of gas bubbles to move the algae out of the shadows and into the light. However, such designs are necessarily inefficient, do not enable sufficient scale productivities and/or still do not provide adequate light accessibility for the microorganism to grow. Thin Layer cascades (TLCs) have been worked on where the depth of the algae can be as low as 0.5 to 1 cm and productivity increases greater than 2 g per litre have been observed, but such TLCs tend to be expensive to construct or cover large areas of land.

[0004] For algae (or cyanobacteria) to be a significant solution to the problem of producing biomass to replace unsustainable coal, oil or gas-based petrochemicals, hundreds of millions of tonnes of capacity are needed at an economic cost equivalent to the price of fossil fuels. No existing methods are within an order of magnitude of this result.

Summary of Invention

[0005] It is an object of the present invention to substantially overcome, or at least ameliorate, one or more drawbacks of present arrangements, or to provide a useful alternative.

[0006] In one aspect, the invention provides a photobioreactor to cultivate a phototrophic or mixotrophic organism for production of biomass, the photobioreactor including a channel providing a flow path for conveying a culture medium containing the organism to be cultivated, with the channel providing a length that revolves around an axis and having a cross-sectional profile transverse to the flow path configured to cause the culture medium to flow in a thin layer flow regime.

[0007] In some embodiments, the axis is a helical axis and wherein the length of the channel helically extends along the helical axis between an upstream end portion and a downstream end portion.

[0008] In some embodiments, the cross-sectional profile of the channel is generally rectilinear in configuration.

[0009] In some embodiments, the channel includes a pair of sidewalls and a floor extending between each of the sidewalls to define a width of the channel, with each of the sidewalls projecting perpendicularly or obliquely from the floor to define a depth of the channel. [0010] In some embodiments, a ratio of the depth of the channel to the width of the channel is from about 0.01 to 0.5.

[0011] In some embodiments, the helical length of the channel defines a pitch such that each of the sidewalls is separated from itself along the length of the channel.

[0012] In some embodiments, the photobioreactor further includes a seal between adjacent lengths of each of the sidewalls along each helical turn.

[0013] In some embodiments, the helical length of the channel defines a pitch such that each of the sidewalls adjoins with itself along the length of the channel.

[0014] In some embodiments, each of the sidewalls is configured for interlocking engagement with itself.

[0015] In some embodiments, the helical length of the channel forms a column having a geometric form approximating an annular cylinder.

[0016] In some embodiments, the floor is sloped at an outer radius of the annular cylinder to define a first angle, and wherein the floor is sloped at an inner radius of the annular cylinder to define a second angle which is greater than the first angle.

[0017] In some embodiments, the photobioreactor further includes optical diffusing or dispersing particles embedded into the channel to at least aid in distributing photon energy along the flow path of the channel.

[0018] In some embodiments, the channel has an optical surface geometry to at least aid in distributing photon energy towards the culture medium.

[0019] In some embodiments, the photobioreactor further includes a light source positioned adjacent to the channel such that at least a portion of light emitted from the light source is dispersed by the optical diffusing or dispersing particles or the optical surface geometry of the channel.

[0020] In some embodiments, the channel is formed of extruded material. [0021] In some embodiments, the material is transparent to enable light to illuminate the culture medium along the flow path.

Brief Description of Drawings

[0022] Exemplary embodiments of the present disclosure will now be described, by way of examples only, with reference to the accompanying description and drawings in which:

[0023] FIG. 1 is a simplified three-dimensional model of a photobioreactor according to an embodiment;

[0024] FIG. 2 is a simplified schematic representation of a transverse cross-sectional profile of a channel of the photobioreactor of FIG. 1, showing the channel adjoined with itself along helical turns; and

[0025] FIG. 3 is a simplified schematic plan view of a portion of the channel of the photobioreactor of FIG. 1.

Description of Embodiments

[0026] Referring to FIG. 1 of the drawings, a photobioreactor 100 according to an embodiment is depicted. The photobioreactor 100 is primarily configured as a closed system for use in cultivating phototrophic and mixotrophic microorganisms for production of biomass. In a primary application, the photobioreactor 100 is configured to cultivate algae or cyanobacteria. In other applications, the photobioreactor may be configured to cultivate other organisms, such as aquatic plants (duckweeds, for example) or macroalgae.

[0027] With particular reference to FIGs. 1 and 2, the photobioreactor 100 includes a channel 102 providing a flow path 104 along which a culture medium 106 containing the algae to be cultivated is to be conveyed. In substantially any cross-sectional plane extending transversely to the flow path 104 through the channel 102 (as best depicted in the cross-sectional view of FIG. 2), the channel 102 has a generally “U-shaped” rectilinear profile which is formed by a floor 108 having a constant thickness and a symmetrical pair of sidewalls 110a, 110b projecting perpendicularly from the floor 108. In use, the floor 108 extends close to horizontally whilst the pair of sidewalls 110a, 110b are upstanding or extend generally vertically or obliquely from the floor 108. In some embodiments, the intersection between each of the sidewalls 110a, 110b with the floor 108 may be filleted.

[0028] The floor 108 extends in a widthwise direction, separating the sidewalls 110a, 110b to define a width W of the channel 102. In a similar manner, each of the sidewalls 110a, 110b extend heightwise of the floor 108 to define a height or depth D of the channel 102. In the embodiment depicted, the channel 102 has an aspect ratio, that is, the ratio of the depth D to the width W of the channel 102, less than 1 and more preferably in the range of 0.01 to 0.5. In other words, the width W of the channel 102 is greater, preferably orders of magnitude greater, than the depth D of the channel 102. In this way, the channel 102 is configured as a shallow “traylike” channel 102 to convey a thin layer (such as a layer having a thickness < 5 cm, preferably in the range of about 0.2 to 1 cm) of the culture medium 106. As shown in FIG. 2, the level of the culture medium 106 may only rise to a portion of the depth D of the channel 102 so as to leave an optional gap or head space 112 occupying the remaining depth D of the channel 102. Together, the floor 108, the pair of sidewalls 110a, 110b and the head space 112 enclose the flow path 104 provided by the channel 102.

[0029] As shown in FIG. 1, the rectilinear profile of the channel 102 is revolved around an axis X to form a length of the channel 102. In the embodiment depicted, the axis is a screw or helical axis X such that the length of the channel 102 forms a generally uniform spiral, helical, helicoid or involute arrangement or configuration. In the embodiment depicted, the helical length of the channel 102 has a constant pitch which is minimised such that the pair of sidewalls 110a, 110b extending along a given turn of the helical length abut their respective self along the adjoining (that is, upper and lower) turns of the length (apart from the uppermost and lowermost turns). In this way, the length of the channel 102 helically extends between an upstream end portion 114 and a downstream end portion (not shown) of the channel 102 to form a column 116 having a geometric form which approximates an annular cylinder. The helical length may comprise 50 to 200 turns to create a 2 m high column 116, although the number of turns and/or pitch may be varied to vary the height of the column 116. In other embodiments, the helical length of the channel 102 may define a pitch such that each of the sidewalls 110a, 110b is separated from itself along the length of the channel 102 to permit gas flow across the channel 102. In some embodiments, the separation of adjacent lengths of each of the sidewalls 110a, 110b between each revolution or helical turn of the helical length of the channel 102 may be sealed. [0030] In the embodiment depicted, the pair of sidewalls 110a, 110b define an inner sidewall 110a and an outer sidewall 110b, respectively. Each of the inner and outer sidewalls 110a, 110b has an external sidewall surface 118a, 118b which is located outside of the flow path 104, and an internal sidewall surface 120a, 120b which borders the flow path 104. The external and internal sidewall surfaces 118a, 118b, 120a, 120b are separated by a nominal thickness having a sufficient breadth to define an upper ledge 122 and a lower base 124 of each of the inner and outer sidewalls 110a, 110b. The external sidewall surface 118b of the outer sidewall 110b, when continuous with itself along adjoined turns of the helical length, defines the curved surface area of the periphery of the column 116. In a similar manner, the external sidewall surface 118a of the inner sidewall 110a, when continuous with itself along adjoining turns of the helical length, defines an internal wall which surrounds a central hole 126 of the column 116. The rectilinear profile and/or helical length of the channel 102 may be dimensioned or configured so that the volume of the central hole 126 is about 5 to 75% of the effective total volume of the column 116. As shown in FIG. 3, an inner radius Ri of the column 116 is defined as the radial distance from the helical axis X to the internal sidewall surface 120a of the inner sidewall 110a, whereas an outer radius R2 of the column 116 is defined as the radial distance from the helical axis X to the internal sidewall surface 120b of the outer sidewall 110b.

[0031] Each of the inner and outer sidewalls 110a, 110b are configured for interlocking engagement with their respective self to hermetically seal the channel 102, specifically the flow path 104, from the exterior of the column 116 thereby effectively creating a closed system. In addition, the interlocking engagement may also contribute to the mechanical integrity of the column 116, negating the need for a dedicated support frame. In one form, the interlocking engagement may be provided by way of cooperating male and female components, such as a complementary-shaped tongue 128 and groove 130 arrangement, formed on the upper ledge 122 and the lower base 124, respectively, of each of the inner and outer sidewalls 110a, 110b. In some embodiments, the tongue 128 may be provided by way of a sealing elastomer (or other sealing compound) positioned or otherwise secured along the upper ledge 122 (or, alternatively, lower base 124) of each of the inner and outer sidewalls 110a, 110b for sealing engagement with the complementary groove 130 formed through the lower base 124 (or, alternatively, upper ledge 122) of each of the inner and outer sidewalls 110a, 110b.

[0032] In the embodiment depicted, the channel 102 is formed of a transparent material to enable light to pass therethrough and illuminate the culture medium 106 as the culture medium 106 is conveyed along the flow path 104. In one embodiment, the transparent material comprises a synthetic polymer, such as polycarbonate or poly(methyl methacrylate). In this way, the channel 102 may be formed by helically extruding the homogenous rectilinear profile of the channel 102 via a plastic extrusion process, permitting continuous manufacture of the column 116 in one piece from an extruder and die set up. Other embodiments are contemplated in which discrete sections of the channel 102 are extruded and subsequently joined to form the column 116. In an alternative embodiment, the column 116 may be fabricated via an additive manufacturing technique.

[0033] In some embodiments, the channel 102 may be embedded with optical diffusing particles such as light dispersing and/or scattering particles to achieve uniform distribution of photon energy throughout the column 116, and particularly orthogonally through the floor 108 of the channel 102 throughout each turn of the helical length. In one form, the optical diffusing particles may be comprised of titanium dioxide. The density of the optical diffusing particles may be optimised to ensure that light flux at the inner radius Ri is similar to the outer radius R2. The flux density across the channel 102 can further be varied to optimise algal growth by varying the thickness of the floor 108 of the channel 102, effectively increasing the numbers of the light reflecting particles available to reflect the light upwards or downwards. In addition, the inner sidewall 110a may be silvered or mirrored to reflect any photons that reach the inner sidewall 110a to at least aid in achieving constant light flux across the channel 102. In other embodiments, the photobioreactor 100 may include a light-dispersing layer (such as a diffractive transparent plastic film) affixed to the floor 108 or integrally formed therewith. In other embodiments, the floor 108 may be formed of a material having a refractive index, or may include a surface grating or other surface discontinuity, to at least aid in reflecting or distributing photon energy towards the culture medium 106. Any one or more of the light-scattering particles, the light-dispersing layer, the refractive index of the floor 108 or the surface grating may configure the floor 108 to provide an illumination surface or a “glow surface” along the flow path 104 provided by the channel 102.

[0034] In some embodiments, the light-scattering particles may include luminophores that emit photons at an emission wavelength after excitation. The luminophores may include fluorophores, phosphors or quantum dots with appropriate decay times. In another embodiment, the light-dispersing layer may be in fluid form, with a secondary transparent substrate placed on top such as to provide a fluid light-dispersing layer between two panes (the floor 108 and the secondary transparent substrate). The fluid may include gas or liquid, and the fluid may have properties which affect the light and diffuse, disperse or scatter the light upwards and downwards through the secondary transparent substrate so as to provide uniform distribution of light throughout the column 116.

[0035] In the embodiment depicted, the photobioreactor 100 further includes a light source 132 mounted to the channel 102 to illuminate the culture medium 106 as the culture medium 106 is conveyed along the flow path 104. The light source 132 is positioned adjacent or affixed to the external sidewall surface 118b of the outer sidewall 110b and is generally aligned with the floor 108 to emit light toward the floor 108 such that at least a portion of the emitted light is dispersed by the light-scattering particles or the light-dispersing layer through the floor 108. Light waves are directed generally horizontally through the floor 108 and subsequently diffracted vertically by the light-scattering particles or the light-dispersing layer to form a continuously illuminated floor 108 throughout the column 116. In this way, light is able to diffract uniformly and directly to the thin layer of the culture medium 106 to cultivate the algae, thereby achieving a ratio of cultivation surface over volume which is substantially higher (up to 100 times more) than traditional photobioreactor systems.

[0036] In some embodiments, the light source 132 may include a light-emitting element (LEE). The light emitting element may be any device that emits electromagnetic radiation at a defined wavelength to maximise yield for the particular algae species. For example, the emitted light may be in the visible, infrared or ultraviolet wavelengths. The light emitting elements may be activated by passing a current through the element or applying a potential difference across the element. The light-emitting elements may include a semiconductor device. The light-emitting element may include, but is not limited to, solid-state, organic, polymer, phosphor-coated or high-flux light emitting diodes (LEDs), and/or laser diodes. A combination of two or more different wavelengths may serve to create higher productivities or create different, more advantageous compositions of the algae.

[0037] The light source 132 may be of any appropriate size to suit the photobioreactor 100 and may include an array of light-emitting elements. In the embodiment depicted, the light source 132 is a light-emitting element in the form of a strip or ribbon of a plurality of LEDs. The plurality of LEDs 132 is arranged along at least a majority of the external sidewall surface 118b of the outer sidewall 110b. The plurality of LEDs 132 may be mounted on the photobioreactor 100 by using an adhesive, an adhesive intermediate material, a separate mount which is attachable to the outer sidewall 110b, or any other suitable means of mounting the light source 132. Each of the LEDs may be “flickered” with a frequency and duty cycle designed to match the natural photochemical pathways in the algae and maximise production of biomass while minimising the energy usage.

[0038] The photobioreactor 100 may further include a gas stream fluidly communicable with the head space 112 to enable gas exchange with the culture medium 106. The gas stream is configured to supply or administer carbon dioxide (CO2) into the channel 102 to maintain an abundant level of CO2 so as not to limit availability of CO2 for growth of the algae. The flow rate of the gas may be adjusted to ensure the necessary gas exchange to optimise CO2 availability for the algae throughout the photobioreactor 100. In other embodiments, the gas supply may include a mixture of air and CO2 or air with environmental CO2. The flow of gas may also be regulated to provide an evaporative cooling effect on the column 116.

[0039] Oxygen which is released by the algae during photosynthesis is able to enter the gas stream for extraction out of the channel 102 so as to minimise the negative effect of an oxygenrich environment. The rate of flow of gas and relative size of the gas stream may be optimised along with the depth of the channel 102 and algal density.

[0040] In some embodiments, the column 116 may include multiple ports for permitting gas to be injected or ejected therethrough, particularly if the degree of evaporative cooling, CO2 supply, or oxygen removal needed for optimal productivity is not possible in one pass from end to end of the column 116.

[0041] In the embodiment depicted, the floor 108 is pitched or sloped at an optimal angle to convey the culture medium 106 downward under gravity in a flow regime which minimises stagnation and biofouling of the algae along the channel 102. In some embodiments, the floor 108 may be sloped at the outer radius R2 by an angle in the range of about 0.5 to 1.5 degrees, and at the inner radius Ri in the range of about 1.5 to 3 degrees. In this way, the channel 102 may be dimensioned and arranged to cause the culture medium 106 to flow in a fully developed laminar flow regime thereby minimising changes in momentum, ensuring relatively smooth and consistent flow. In an alternative embodiment, the channel 102 may be dimensioned and arranged to cause the culture medium 106 to flow in a turbulent flow regime. With reference to FIG. 3, the culture medium 106 is conveyed along the channel 102 at a first velocity adjacent the outer sidewall 110b, and at a second velocity adjacent the inner sidewall 110a. The second velocity may be proportional to the first velocity by a ratio of the inner radius Ri to the outer radius R2. The floor 108 may be coated or otherwise smoothened to facilitate constant motion of the algae along the flow path 104. In addition, the gas stream may be supplied at a velocity that interacts with the flow of the culture medium 106, either encouraging the flow in the downstream direction, or at higher velocities to cause the culture medium 106 to flow against gravity in the upstream direction thereby negating the need for pumping. The interaction between the gas stream and the culture medium 106 may also be controlled to cause the culture medium 106 to flow in the turbulent flow regime.

[0042] A plurality of the photobioreactors 100 may be arranged in a stacked or other close- packed configuration to form an assembly which is readily scalable for high-throughput synchronous cultivation of algae. In this configuration, each of the photobioreactors 100 may be “fed” from a common manifold and may be designed to be modular to permit removal from the assembly for cleaning or for replacement with a new photobioreactor 100, thereby enabling continuous biomass production even if one or more of the photobioreactors 100 becomes defective. The assembly may be arranged within a container (such as a 20 ft or 40 ft shipping container) for ease of manufacture and transportation. Alternatively, the assembly may be arranged within a factory space.

[0043] In the stacked configuration, the assembly may contain a number of the photobioreactors 100 joined end-to-end to provide a flow path 104 of sufficient distance or journey to permit cultivation of algae from a seed stage to a harvest stage. Such a complete flow path 104 may also be provided by one of the photobioreactors 100. For example, to double the density of the algae from the start of the flow path 104 to the end of the flow path 104 with the culture medium 106 having a flow rate of 1 cm/sec and a specific growth of 4, the column may be dimensioned so that the outer radius R2 is 18 cm with approximately 350 revolutions of the helical length. If the depth D of the channel 102 is made to be 2 cm, the column 116 or stack of photobioreactors 100 will be approximately 7 m in height, and effectively means minimal or no pumping is required, which is particularly desirable for sensitive algal varieties.

[0044] The photobioreactor 100 provides a cost-efficient thin layer system which can be operated continuously and which reduces the optical pathway to 1-20 mm, maximising density of the algae in cells per litre without reducing optimal access to photons (light) and to nutrients and CO2. The helical arrangement of the channel 102 provides a continuous flow path with no joins or disruptions which can be manufactured with significant cost reduction via a plastic extrusion process in one single extrusion, enabling relatively cheap mass production analogous to large-scale extrusion of guttering and edging profiles. By the economical nature of continuous plastic extrusion processes, the channel 102 can be manufactured with a relatively high productive surface area at low depths without incurring significant additional manufacturing costs. In this way, much higher densities of algae can be achieved using very thin layers, without reducing the volume of liquid in the photobioreactor 100. This enables higher grams per liter per day and orders of magnitude higher production per cubic meter of the photobioreactor 100 compared with existing photobioreactor systems. In combination with the regulated gas flow through the sealed channel 102, the photobioreactor 100 enables very high density (cells/ml) whilst still providing adequate light penetration from the light source 132 via optimal light penetration throughout the column 116. Some embodiments of the present disclosure may enable depths as low as 1-5 mm to cultivate algal concentrations of 1-50 grams per litre whilst still providing adequate access to photon energy. This would represent a 30-50 times increase in the productivity per litre compared to existing photobioreactor systems. Technoeconomic modelling indicates that the capital cost per tonne of algae capacity of the photobioreactor 100 could be 5-10 times lower than existing designs.

[0045] The helical arrangement of the channel 102 also permits sealing between revolutions along the column 116. Advantageously, this arrangement minimises contamination of the algae from environmental bacteria, yeast, or other contaminations and permits production of food, and pharmaceuticals in the photobioreactor 100, whilst enabling continuous production, negating the need to shut down the photobioreactor 100 to sterilise the photobioreactor 100, for example. The helical arrangement also facilitates thermal insulation of the algal mass from the light source 132, by positioning the light source 132 on the periphery of the column 116 external to the channel 102. Also, the regulation of the speed of the gas stream in the head space 112 can advantageously minimise blockages and permit evaporative cooling to keep the algae at an optimal temperature for maximising productivity. Reference Numeral List

100 Photobioreactor

102 Channel

104 Flow path

106 Culture medium

108 Floor

110a,b Sidewalls (inner and outer sidewall)

W Width of channel

D Depth of channel

112 Head space

X Helical axis

114 Upstream end portion

116 Column

118a,b External sidewall surface

120a,b Internal sidewall surface

122 Upper ledge

124 Lower base

126 Hole

Ri Inner radius

R₂ Outer radius

128 Tongue

130 Groove

132 Light source

Claims

CLAIM

1. A photobioreactor to cultivate a phototrophic or mixotrophic organism for production of biomass, the photobioreactor including a channel providing a flow path for conveying a culture medium containing the organism to be cultivated, with the channel providing a length that revolves around an axis and having a cross-sectional profile transverse to the flow path configured to cause the culture medium to flow in a thin layer flow regime.

2. The photobioreactor of claim 1, wherein the axis is a helical axis and wherein the length of the channel helically extends along the helical axis between an upstream end portion and a downstream end portion.

3. The photobioreactor of claim 2, wherein the cross-sectional profile of the channel is generally rectilinear in configuration.

4. The photobioreactor of claim 2 or 3, wherein the channel includes a pair of sidewalls and a floor extending between each of the sidewalls to define a width of the channel, with each of the sidewalls projecting perpendicularly or obliquely from the floor to define a depth of the channel.

5. The photobioreactor of claim 4, wherein a ratio of the depth of the channel to the width of the channel is from about 0.01 to 0.5.

6. The photobioreactor of claim 4 or 5, wherein the helical length of the channel defines a pitch such that each of the sidewalls is separated from itself along the length of the channel.

7. The photobioreactor of claim 6 further including a seal between adjacent lengths of each of the sidewalls along each helical turn.

8. The photobioreactor of claim 4 or 5, wherein the helical length of the channel defines a pitch such that each of the sidewalls adjoins with itself along the length of the channel.

9. The photobioreactor of claim 8, wherein each of the sidewalls is configured for interlocking engagement with itself.

10. The photobioreactor of claim 8 or 9, wherein the helical length of the channel forms a column having a geometric form approximating an annular cylinder.

11. The photobioreactor of claim 10, wherein the floor is sloped at an outer radius of the annular cylinder to define a first angle, and wherein the floor is sloped at an inner radius of the annular cylinder to define a second angle which is greater than the first angle.

12. The photobioreactor of any one of the preceding claims further including optical diffusing or dispersing particles embedded into the channel to at least aid in distributing photon energy along the flow path of the channel.

13. The photobioreactor of any one of the preceding claims, wherein the channel has an optical surface geometry to at least aid in distributing photon energy towards the culture medium.

14. The photobioreactor of claim 12 or 13 further including a light source positioned adjacent to the channel such that at least a portion of light emitted from the light source is dispersed by the optical diffusing or dispersing particles or the optical surface geometry of the channel.

15. The photobioreactor of any one of the preceding claims, wherein the channel is formed of extruded material.

16. The photobioreactor of claim 15, wherein the material is transparent to enable light to illuminate the culture medium along the flow path.