Field of the invention

[0001] The field of the present invention relates to bioreactors for light-sensitive biological processes and a method for illuminating such bioreactors. In particular, the field of the present invention relates to a bioreactor for the growth of phototropic organisms and to a method for illuminating, and controlling the illumination of, the phototropic organisms in such a bioreactor.

Background of the invention

[0002] Many biological processes require light. The efficiency of many of these photosensitive or photosynthetic biological processes strongly depends on the intensity and the appropriate wavelength of the available light. While nature uses natural sunlight in most cases, artificial light sources may be used in bioreactors to control and enhance the growth of photosynthetic organisms.

[0003] Given optimal nutrient supply, temperature and pH, the limiting factor for growth of these photosynthetic organisms remains the amount and/or the intensity of the light. These photosynthetic organisms are often grown in ponds or other crude bioreactors making use of natural light or traditional illumination systems. The traditional illumination systems often comprise one or more lamps or other artificial light sources that are arranged outside the bioreactor. The bioreactors have windows or openings in the walls of the bioreactor allowing an illumination from the outside. These windows or openings, or the bulk of the entire container have to be made from a transparent material such as glass or plastics. The need for such materials limits the construction of large-scale bioreactors and are easily damaged. Furthermore, the surfaces of these transparent materials must be cleaned or the transparent materials must be replaced regularly to ensure sufficient light transmission. [0004] In some instances, a light source may also be arranged inside the bioreactor. In this instance the light source is placed in a vertical orientation centrally, suspended from the top of the bioreactor. All of these light sources provide a unidirectional illumination of the photosynthetic organism and result in an inhomogeneous light distribution inside the bioreactor.

[0005] For example, photosynthetic organisms in closer proximity to a light source will receive more light and consequently, all else being equal, grow faster than those photosynthetic organisms located more remotely from the light source. With the ongoing growth of the photosynthetic organisms more and more light is absorbed or shadowed by the biomass of the photosynthetic organisms leaving some areas of the bioreactor with little or no light making further growth inside the bioreactor less efficient.

[0006] Strong light sources with high light intensities may be used to provide illumination in larger bioreactors. However, the strong light sources can damage the photosynthetic organisms either by strong light intensities or by the heat developed by many traditional light sources. Furthermore the use of the strong light sources for illuminating dense suspensions of cells leads to high light intensities in the proximity of the light source and much weaker light intensities at a distance from the light source, again leading to inhomogeneous light distributions throughout the bioreactor.

[0007] Further, efficient use of energy is becoming increasingly important with the bioreactors. Heat developed by traditional light sources and the use of high light intensities is a waste of energy making those bioreactors less efficient. Excess heat elevates reactor temperature leading to cell death and evaporation of water.

[0008] In addition, traditional illumination systems provide a gradient of light intensity towards the light source causing the phototropic organisms to grow, and where possible to migrate, towards the light source. This results in a directed growth of the phototropic organism inside the bioreactor limiting the growth direction and thereby the efficiency of the bioreactor. Summary of the invention

[0009] The present disclosure relates to a bioreactor for photo- sensitive biological processes, comprising a container having a volume for acceptance of a liquid with biological material and a plurality of light arrays arranged inside the volume of the container, wherein the plurality of light arrays are arranged such that the biological material can be substantially homogeneously illuminated. Homogeneous illumination may be achieved in a self-regulatory system.

[0010] A photo-sensitive biological process may be any biological process requiring or using light. Examples of such photo- sensitive biological processes are photosynthetic processes in photosynthetic organisms or other biological material. Examples are the growth of phototropic organisms, such as planktonic microorganisms or algae, i.e. microalgae. In use, the container of the bioreactor may be filled with a liquid, such as an aqueous solution of freshwater or saline characteristic, containing the biological material. The arrangement of the light arrays inside the volume and thus, in use inside the liquid, enables a homogenous distribution of a light-field throughout the liquid, i.e. throughout a suspension comprising the biological material, such as cells and/or other microorganisms.

[0011] The use of the plurality of light arrays, positioned equidistance from each other, enables full scalability of the bioreactor. The number of light arrays can be increased with increasing volume maintaining a homogenous light distribution throughout any volume size. The bioreactor described herein is thus fully scalable and ensures a reproducibility of organism growth independent of the size of the container of the bioreactor.

[0012] Each one of the plurality of light arrays may further comprise one or more light sources such as, for example, light emitting diodes (LED). The one or more light sources may have an emission wave length or wave lengths spectrum adapted to the need of the biological material. Different light sources with different emission spectra may be used in parallel or alternately to enable several different biological processes in the same bioreactor. The spectrum of wavelength may be advantageously selected by the use of appropriate LEDs. [0013] While other light sources may by used, the use of LEDs as light source enables low power consumption, low heat production, with predictable and controllable illumination of the biological material and thus high energy efficiency. Furthermore, the LEDs are long-lived, easy to handle and operate and are plant safe and health safe to use.

[0014] At least one of the plurality of light arrays may comprise a tube-like structure, and a plurality of the light sources may be arranged inside the tube-like structure. The plurality of light sources may be linearly arranged along the tube-like structure. The light sources may be equally spaced from each other along the light array.

[0015] The container may comprise openings or passages in a wall as access ports through which the light arrays can be accessed or inserted into the container. The openings or passages may comprise a bio-secure seal. The openings or passages may also provide chemical or physical cleaning facilities. The openings or passages allow for easy and fast arrangement of the light arrays inside the container and reduce maintenance costs. In case of tubular light array, the openings or passages may have the shape of a circular hole.

[0016] The container of the bioreactor may further have opaque or non-transparent walls, because no openings or windows are necessary due to the light arrays arranged inside the container volume. Hence, the container walls can be of any material allowing the construction of any container size without any restrictions on physical strength and chemical resistance due to transparency. The container surfaces facing towards the inside, which come into contact with the liquid and the biological material, can be coated with any suitable material, such as silver-pigmented PTFE (poly-tetrafluoroethene).

[0017] The plurality of light arrays may be arranged in a geometric pattern of equi- distance between each one of the plurality of light arrays. The plurality of light arrays may be arranged at approximately half the distance between the peripheral arrays and the reactor wall. Thus an organism will be at a distance less than half the inter-array distance from a light source at any location within the reactor volume. [0018] A method for illuminating biological material in a bioreactor is also described, the method comprising illuminating the biological material in a liquid with a plurality of light arrays arranged at least partially inside the liquid, such that the biological material is substantially homogeneously illuminated. The arrangement of light arrays inside the liquid advantageously allows a substantially equal or homogeneous light distribution throughout the volume of the liquid, independent of its size. Thus any size or scale of bioreactor can be designed without substantially altering the light-intensity and light-intensity distribution throughout the liquid volume.

[0019] The illumination may be by means of one or more light sources, such as but not limited to LEDs.

[0020] The one or more light sources may be individually controlled or switched by a controller. Specific ones of the one or more light sources or a portion of the one or more light sources may be switched off and on individually in order to adjust the light emission or light intensity distribution inside the liquid volume according to the requirements of the biological material.

[0021] The light intensity of a particular one of the one or more light sources may be individually adjusted by operating the light source in flickering modus, i.e. by rapid switching frequency between on and off intervals. In this way, illumination of the biological material and the organisms can be optimised in terms of photon flux density, light density for a specific organism that is grown inside the bioreactor. Under- saturation or over- saturation of phototropic activity or photo synthetic activity can be advantageously prevented and growth of the organism or product synthesis can be optimised while energy consumption is minimised. This illumination method is particularly useful with the application of the LEDs as the light sources.

[0022] When one of the plurality of light sources is switched off, the light intensity from an adjacent one of the plurality of light sources may be determined or measured with a light sensor. In this way the actual light intensity can be measured inside the liquid containing biological material at any time during the growth or product synthesis process and the light intensity can be adjusted accordingly using the controller. For example the on-off frequency or intervals may be adjusted to compensate for the increasing amount of light that is absorbed by and/or shadowed by the growing amount of biological material within the reactor.

[0023] The measurement of the light intensity from an adjacent one of the plurality of light sources may also be used to determine a turbidity of the liquid or another parameter such as, for example, chlorophyll concentration. The measured light intensity can be compared to an expected light intensity known for a given electrical power applied to the adjacent one of the plurality of light sources. The expected light intensity may be known, for example, from calibration in clean liquid. The concentration of biomass inside the liquid can be determined from the measured turbidity or other parameter related to organism biomass or physiological status.

[0024] The addition of nutrients and or fresh medium to the reactor may be controlled based on the determined concentration of biomass. This is then used to operate the whole bioreactor as a turbidostat.

[0025] The bioreactor may further comprise in-situ cleaning means such as UV (ultra violet) emission light sources or other high energy illumination. The in-situ cleaning means may be arranged in or at the light arrays. The in-situ cleaning means may be used to discourage surface growth, for example by discouragement of organism settlement or killing of organisms, in order to decrease the growth of microbiological films that would otherwise adversely affect the bioreactor efficiency.

[0026] The bioreactor may be used for continuous or discontinuous cultures of biological material.

Short description of the figures

Fig. 1 shows a bioreactor according to the present invention. Fig. 2a and 2b show examples of a light tube according to the present invention in a side view and in a cross section, respectively

Fig. 3 illustrates the vertical distribution of light tubes according to the present invention.

Detailed description of an example

[0027] The following description of a detailed example is not intended to limit the scope of protection as defined by the appended claims. It will be noted that features of one aspect of the invention can be combined with features of another aspect of the invention.

[0028] Fig 1 shows a bioreactor 1. A plurality of light arrays 20a to 20f is arranged inside the volume of a container or growth chamber 10. The growth chamber 10 may be closed or sealed. The growth chamber 10 has a rectangular shape in this example, but any shape of the container may be used. Walls of the growth chamber 10 are illustrated as transparent walls for illustrative purposes only. The growth chamber 10 itself could be made of any material required and can be opaque. There is no need for a transparent wall for the growth chamber 10 as the light is provided internally from the light arrays 20a to 20f. A highly polished, smooth, reflective grow chamber surface is used in one aspect of the invention. This growth chamber surface minimises wall growth of biological material and maximises internal light reflection. A silver-pigmented PTFE (poly-tetrafluoroethene) coating may be ideal. Aeration and hence a degree of culture stirring would be provided either directly into the growth chamber 10 by specialised ports or by passage of gas down hollow-section light tubes as described below.

[0029] The light arrays 20a to 20f are positioned equi-distantly with respect to each other to provide a substantially homogeneous illumination of the volume inside the container 10.

[0030] Each of the light arrays 20a to 20f is connected to a computer control and power supply 60 that via electrical wiring 36. [0031] An aspect of this invention is the design of the light arrays 20a to 2Of as light tubes 20, having, for example a substantially cylindrical shape.

[0032] The transparent tubes 22 would be in one aspect of the invention of circular cross- section, entering the growth chamber through sealing 80, for example O-rings, that are disposed in proximity of top end 28 of the transparent tubes 22, thus facilitating the wiping of the surface to remove any surface attachments (mucus, wall growth, bacteria), and providing a seal. The top end 28 of the light tube 20 may extend to the exterior of the growth chamber 10. The growth chamber 10 may have corresponding openings in a wall 12 allowing the insertion of the light tube 20 into the volume of the growth chamber 10. The sealing 80 may seal the opening when a light tube 20 is inserted. Access to the inside of the light tube 20 from the exterior of the container 10 is provided through the top end 28 of the light tube 20.

[0033] The light tubes 20 may be arranged vertically inside the growth chamber as illustrated in Fig. 1. This allows easy access, removal, cleaning, and/or maintenance of the light tubes from the top side the container. However, the invention is not limited to this example and the light tubes 20 may be arranged horizontally or in any other position inside the growth chamber.

[0034] Examples of the light tubes 20 are shown in more detail in Fig. 2a and 2b. The light tubes 20 provide compact, self-adjusting, power-saving illumination for fully scalable light fields.

[0035] The light tube 20 shown in Fig. 2a comprises a transparent tube 22, made for example of visible light and UV-transparent glass or plastic. The transparent tube 22 has a sealed bottom end 24 so that that the inside of the transparent tube 22 remains dry, if the light tube 20 is immersed in a liquid. The transparent tubes 22 are of sufficient length to match the depth of the volume of the container 10 (the growth chamber). The transparent tubes 22 would be supported at intervals as required to at least minimise, if not prevent, lateral movement due to water turbulence. The tube diameter can be chosen to suit individual requirements but would typically be as small as possible, advantageously allowing for flexing of the light tube 20 inside the growth chamber 10. As an example, the tube diameter may be about 1 to 5 cm.

[0036] A plurality of (in the example shown four, but any number may be used) light emitting diodes (LEDs) 30 of appropriate wavelength (400-700nm) is arranged inside the transparent tube 22. The LEDs 30 may be distributed over the length of the transparent tube 22 as illustrated in Fig. 2a. The LEDs 30 may be equi-distantly spaced within the transparent tube 22.

[0037] In addition, a light sensor 40 is placed within this transparent tube 22. The light sensor 40 is for monitoring light sources from adjacent ones of the light arrays, as will be explained in detail with respect to Fig. 3.

[0038] High-energy UV LEDs 32 can be substituted for visible light emitting diodes 30 or placed in addition inside the transparent tube 22. The high energy UV LEDs as the UV light sources would be used to repel microalgal attachment to a tube surface of the transparent tubes 22. These high energy UV LEDs would be used infrequently, as experience dictated.

[0039] The transparent tube 22 could be hollow, allowing the passage of coolant or to facilitate gas exchange into or out of the liquid. A gas transportation device such as a motorised spindle attached to an impeller may be used to aid mixing, thus removing the need for additional tubes serving these purposes.

[0040] The transparent tube 22 could also comprise a hollow core 70 allowing the passage of coolant or to facilitate gas exchange into or out of the liquid. An example of this aspect is illustrated in Fig 2b in a cross sectional view. LEDs 30, 32 and sensors 40 and further electronic components may be arranged around the hollow core 70 of the transparent tube 22 and are thus not exposed to the liquid.

[0041] Aeration gases can provide nutrient (for example dissolved inorganic carbon, CO ₂ for photosynthesis) to the liquid inside the growth chamber 10. Gases may act to stir a suspension of biological material. The gases may also remove excess oxygen form the growth chamber 10. A gas transportation device such as, for example, a motorised spindle could also be passed through the hollow core 70, with an impeller on the lower end as an aid to suspension mixing (not shown).

[0042] An example of vertical distribution of light tubes 20 is shown Fig. 3. In this example nine light tubes 20 are shown and may be a section of a pattern of light tubes 20. The pattern is repeated as often as required throughout the growth chamber 10 resulting in an equi-distance arrangement of the light tubes 20 throughout the volume of the growth chamber 10. The inter tube distance would be established to suit individual requirements, but would typically be in the order of about 0.1 to I m separation between the adjacent light tubes 20.

[0043] Power and control wires 36 from each of the transparent light tubes 20 may be feed back to a computer control system 60 that regulates the power supplied to each one of the light tubes 20, i.e. to each one of the light sources 30 in order to maintain the required light field, for example with respect to photon flux density and colour (wavelength). The computer control system 60 changes the frequency of power supply to an individual tube 20 or an individual light source 30 so that - a) power supply is matched with light requirement, b) the light sources 30 in a specific one 20i of the light tubes 20 are off (for example for a short (ms) period) when the light sources in the adjacent ones 20a of the specific light tube 20i are on so that the light transmission between the light tubes can be determined to enable light requirements to be met, c) the frequency of light flicker from the light sources can be adjusted to attain an enhanced algal production (there being evidence in the literature that non-continuous illumination can be beneficial for some species of algae).

[0044] In other words, on command from the computer control system 60, the LEDs 30 of the specific one 20i of the light tubes 20 are switched off and the sensors 40 in that specific one 20i of the light tubes 20 monitor the light received from adjoining illuminated light tubes 20. The response is used to regulate to power provided to each light tube 20 or to each LED 30, to optimise power consumption, maximises biomass production, and minimise photodamage.