CULTURE TANK

Abstract

A photobioreactor for culturing light-sensitive microbes is provided, the reactor comprising a body comprising at least one floor panel and at least one wall extending upwardly around the periphery of the floor panel to define a body, wherein the at least one floor panel comprises at least one graded segment so as to define a trough along the bottom of the body towards which debris within the body flows, at least one illumination panel within the body so that there is free flow of liquid along the sides and floor panel of the body, at least one gas inlet within the trough in the floor panel, for providing an upward stream of gas into the body so as to generate air lift of the light sensitive microbes within the body. Also provided is a method for growing light-sensitive microbes.

Claims

1. A photobioreactor, in particular for culturing light sensitive microbes, the photobioreactor comprising a. a body comprising at least one floor panel and at least one wall extending upwardly around the periphery of the at least one floor panel to define a body for receiving and holding liquids; wherein the at least one floor panel comprises at least one graded segment so as to define a trough along the bottom of the body towards which debris within the body flows; b. at least one illumination panel, the at least one illumination panel comprising illumination means adapted to emit light that is suitable for sustaining growth of the light sensitive microbes within the photobioreactor, wherein the at least illumination panel is disposed within the body so that there is free flow of fluid along the sides and floor panel of the body; and c. at least one gas inlet disposed in the at least one floor panel, within the trough in the at least one floor panel, for providing an upward stream of gas into the body so as to generate air lift of the light sensitive microbes within the body; so that, during incubation of a liquid culture of microbes in the photobioreactor, microbe circulation and growth in the photobioreactor is stimulated through concomitant exposure to light emitted by the at least one illumination panel and circulation of microbes within the body that is facilitated by an upward air lift generated by the stream of gas into the body.

2. The photobioreactor of claim 1, wherein the at least illumination panel is disposed within the body so that there is at least one gap between the at least one panel and the at least one wall and/or the floor panel of the photobioreactor.

3. The photobioreactor of claim 1, wherein the illumination panel is provided in the form of at least one flat panel that is disposed within the body.

4. The photobioreactor of claim 3, wherein the angle between the illumination panel and the side walls is in the range of 45 to 90.

5. The photobioreactor of claim 1, wherein the body comprises an elongate structure comprising at least two side walls and at least two end walls, and wherein the trough extends longitudinally along the floor panel of the body.

6. The photobioreactor of claim 5, wherein the trough extends longitudinally along the middle of the floor panel.

7. (canceled)

8. (canceled)

9. The photobioreactor of claim 1, wherein the floor panel comprises a continuously downwardly convex structure, so that debris can flow towards the lowermost part of the floor panel.

10. (canceled)

11. (canceled)

12. The photobioreactor of claim 1, wherein the at least one gas inlet is disposed in the floor panel.

13. The photobioreactor of claim 12, wherein the at least one gas inlet comprises delivery spout that extends no more than 10 mm into the body of the photobioreactor.

14. The photobioreactor claim 1, wherein the at least one gas inlet is disposed in the floor panel of the body, below the at least one illumination panel.

15. The photobioreactor of claim 1, wherein the at least one gas inlet comprises a plurality of gas inlets that are provided in a lowermost section of the floor panel.

16. (canceled)

17. (canceled)

18. (canceled)

19. (canceled)

20. The photobioreactor of claim 1, wherein the at least one illumination panel comprises a parallel arrangement of a plurality of illumination panels and wherein a plurality of gas inlets are arranged in the floor panel, between the illumination panels.

21. The photobioreactor of claim 1, wherein the floor panel comprises a continuous convex structure of generally half-cylindrical shape, and wherein the at least one gas inlet comprises a first row of gas inlets that is arranged along the bottom of the half-cylindrical surface, and at least one further row of gas inlets that is arranged in the photobioreactor floor panel along its longitudinal axis, upwardly from and parallel to the first row of gas inlets.

22. (canceled)

23. The photobioreactor of claim 1, wherein the illumination means is embedded within the illumination panel, so that a water-tight seal separates the illumination means from their surroundings.

24. (canceled)

25. (canceled)

26. (canceled)

27. (canceled)

28. The photobioreactor of claim 23, wherein the body comprises a generally elongate structure, and wherein the illumination panel provides illumination along the longitudinal axis of the body.

29. The photobioreactor of claim 1, wherein the illumination panels comprise illumination means that are adapted to deliver light with a photon flux in the range of 20-1200 mol/m.sup.2s.

30. (canceled)

31. (canceled)

32. (canceled)

33. (canceled)

34. The photobioreactor of claim 1, wherein the illumination panel has a height that is in the range of about 80% to about 99% of the body height from its lowermost point in the floor panel.

35. The photobioreactor of claim 1, wherein the illumination panels are disposed within the body so that there is a gap between the illumination panels and the side walls and floor panel of the body that is in the range of about 2-20 cm.

36. (canceled)

37. (canceled)

38. (canceled)

39. (canceled)

40. (canceled)

41. (canceled)

42. (canceled)

43. The photobioreactor of claim 1, wherein the body has an internal volume that is in the range of about 200 L to about 40,000 L.

44. The photobioreactor of claim 1, wherein the side walls have a length in the range of about 1-10 m.

45. The photobioreactor of claim 1, wherein the end walls have a length in the range of about 0.5-3 m.

46. The photobioreactor of claim 1, further comprising at least one water inlet, for delivering water into the photobioreactor, and at least one water outlet, for draining water from the photobioreactor.

47. The photobioreactor of claim 1, further comprising a thermal jacket, wherein the thermal jacket comprises a hollow structure that encapsules at least a portion of the body.

48. The photobioreactor of claim 47, wherein the thermal jacket comprises at least one inlet and at least one outlet, for introducing and releasing water from the hollow structure, respectively.

49. The photobioreactor of claim 5, wherein the body is enclosed within a frame structure comprising outer side walls that are disposed outwardly from at least the side walls of the body so as to enclose the body.

50. (canceled)

51. The photobioreactor of claim 1, further comprising at least one CO.sub.2 recirculation loop that is fluidly connected to the body via at least one recirculation loop tank outlet and at least one recirculation loop tank inlet, and at least one pump, for pumping culture through the CO.sub.2 recirculation loop, the CO.sub.2 recirculation loop further comprising at least one CO.sub.2 inlet that is provided downstream of the at least recirculation pump, with respect to the direction of liquid flow in the CO.sub.2 recirculation loop.

52. The photobioreactor of claim 51, wherein the at least one recirculation loop tank outlet and the at least one recirculation loop tank inlet are provided in the lower half of the body, with respect to the volume of the body.

53. (canceled)

54. The photobioreactor of claim 1, the photobioreactor further comprising at least one of: a. one or more pH meter to provide a measure of pH of liquid in the body; b. one or more gas inlet for delivering a stream of carbon dioxide enriched gas into the body; c. one or more temperature probe; d. one or more chemical probe for detecting inorganic matter such as nitrate; and e. one or more optical density and/or light density meter.

55. The photobioreactor of claim 1, further comprising at least one controller, for controlling at least one of: illumination, water temperature, pH and air flow in the photobioreactor.

56. The photobioreactor of claim 55, wherein the controller is adapted to adjust at least one or more parameter selected from light intensity, temperature and pH, in response to measurements of microbe density within the body, as determined by optical density and/or light density measurements.

57. A method of growing light sensitive microbes, the method comprising: a. providing a photobioreactor, the photobioreactor comprising i. a body comprising a floor panel and at least one wall extending upwardly around the periphery of the floor panel to define a body for receiving and holding an aqueous solution comprising microbes; wherein the floor panel comprises at least one graded segment so as to define a trough along the bottom of the body towards which the microbes can flow; ii. at least one illumination panel that is disposed within the body, the illumination panel comprising illumination means adapted to emit light that is suitable for sustaining growth of the light sensitive microbes within the body, wherein the at least one illumination panel is disposed within the body so that there is free flow of water along the at least one wall and/or floor panel; and iii. at least one gas inlet disposed in the trough in the floor panel, for providing an upward stream of gas in the body so as to generate air lift of the light sensitive microbes within the body; b. providing an aqueous culture of light-sensitive microbes into the body so that the illumination panels are at least partially submerged; c. delivering gas into the aqueous culture in the body through the at least one gas inlet, thereby generating air-lift in the body that provides an upwardly flow of microbes from the at least gas inlet and a downwardly gravitational flow of microbes at least along and down the at least one side wall, towards the trough in the floor, d. providing illumination in the body by means of the at least one illumination panel; whereby microbe growth is stimulated through the airlift-driven circulation of the microbes within the body and exposure to light emitted by the at least one illumination panel.

58. (canceled)

59. The method of claim 57, wherein gas is delivered into the photobioreactor through the at least one gas inlet at a combined total flow rate into the body per minute that is in the range of 10% to about 30% of the volume of the body.

60. (canceled)

61. (canceled)

62. (canceled)

63. (canceled)

64. (canceled)

65. The method of claim 57, further comprising delivering at least one source of nutrients into the body for sustaining growth of the microbes in the photobioreactor.

66. The method of claim 57, wherein gas is delivered into the body of the photobioreactor so as to generate a vertical airlift from the trough in the floor of the body, and simultaneously allowing down-flow of microbes along and down the side walls and the floor, towards the trough in the floor.

67. (canceled)

Description

BRIEF DESCRIPTION OF THE FIGURES

[0120] The skilled person will understand that the figures, described below, are for illustration purposes only. The figures are not intended to limit the scope of the present teachings in any way.

[0121] FIG. 1 depicts a photobioreactor in accordance with the invention that is enclosed by an outer frame.

[0122] FIG. 2 shows a cross-sectional view of the photobioreactor shown in FIG. 1, showing the internal body and panels within the body.

[0123] FIG. 3 shows a longitudinal cross-sectional view of the photobioreactor shown in FIG. 1, showing internal panels along the body of the container, as well as air inlets in the floor panel of the body.

[0124] FIG. 4 shows a perspective view of a modified photobioreactor according to the invention.

[0125] FIG. 5 shows a longitudinal cross-sectional view of the photobioreactor depicted in FIG. 4

[0126] FIG. 6 shows a cross section of a photobioreactor as illustrated in FIG. 4, showing internal panels and a cross-section view of drivers disposed on the outer side walls of the reactor.

[0127] FIG. 7 show in (A) and (B) show respectively two alternate photobioreactors in accordance with the present invention.

[0128] FIG. 8 shows another photobioreactor in accordance with the invention having a tubular shape.

[0129] FIG. 9 shows how CO.sub.2 diffusers can be arranged in the floor panel of the photobioreactor tank.

[0130] FIG. 10 shows a photobioreactor comprising a manifold assembly for disposing suspended CO.sub.2 diffusers into the photobioreactor tank.

[0131] FIG. 11 shows how a schematic illustration of the circulation within the photobioreactor tank that is generated by gas delivery into the bottom of the tank floor.

[0132] FIG. 12 shows an illumination panel in accordance with the invention.

[0133] FIG. 13 shows an alternative illumination panel in accordance with the invention.

[0134] FIG. 14 shows an exemplary thermal jacket that can be provided on the outer surface of the photobioreactor tank.

[0135] FIG. 15 shows a CO.sub.2 recirculation loop that can be connected to the photobioreactor tank.

[0136] FIG. 16 shows a photobioreactor with a two-part lid arranged thereon, to close the photobioreactor tank.

[0137] FIG. 17 shows an alternative lid arrangements, where six lid units, each having a slanted upper surface, can be used to close the photobioreactor tank.

DESCRIPTION

[0138] In the following, exemplary embodiments of the invention will be described, referring to the figures. These examples are provided to provide further understanding of the invention, without limiting its scope.

[0139] In the following description, a series of steps are described. The skilled person will appreciate that unless required by the context, the order of steps is not critical for the resulting configuration and its effect. Further, it will be apparent to the skilled person that irrespective of the order of steps, the presence or absence of time delay between steps, can be present between some or all of the described steps.

[0140] As used herein, including in the claims, singular forms of terms are to be construed as also including the plural form and vice versa, unless the context indicates otherwise. Thus, it should be noted that as used herein, the singular forms a, an, and the include plural references unless the context clearly dictates otherwise. The present invention provides a productive, sustainable and resource-efficient (energy, space and water) production system, allowing for mass culture and exploitation of valuable micro-algae derived bioactive compounds. The system provides for not only a low, but a negative carbon footprint production chain, as the algae culture consumes CO.sub.2 and delivers back oxygen. The photobioreactor is furthermore designed for integrated pest management to considerably reduce product losses and waste on algae farms. Present culturing techniques are expensive, and producers indicate to lose of their harvest because of pests, usually unwanted microalgae species that take over the production systems.

[0141] Thus, the system and method is expected to play a crucial role in unlocking the cost-efficiency of microalgae cultivation systems so that microalgae cultivation can eventually be efficiently used for production of food and bio-based products, even in unfavourable climates.

[0142] There is a general unmet demand on the market for industrial sized tanks for algae culturing. Current solutions utilize tubular glass reactors, including those offered by Varicon Aqua Solutions. Small non-industrial sized tanks are offered by two companies, Algae Food & Fuel (1000 L tank-based PhotoBioReactor for laboratory use) and Industrial plankton in Canada (1250 L tank-based PhotoBioReactor). Both these systems are small and unpractical for farmers; furthermore, Industrial Plankton's solution is very expensive.

[0143] The present invention has been made with an aim of solving problems of limited and uneven access of light-sensitive microbes, such as certain algae, to light in photobioreactors and of problems with cleaning and disinfection of photobioreactors to avoid contamination, both problems having a negative influence on yield. The invention provides tanks having particular structure comprising immersed illumination elements or panels that are mounted in the tank at certain intervals. One advantage of the invention is that the lighting elements can easily be removed for cleaning, if needed. The photobioreactor can be scaled up by serial connection of tanks in a modular way. Furthermore, tank sizes can be varied as needed, increasing the flexibility of the solution.

[0144] Nevertheless, the skilled person will appreciate that an important practical advantage is that the photobioreactor described herein is a stand-alone system, in that it does not require additional functionalities, supply tanks, harvesting tanks or external components for its use. Moreover, the photobioreactor can be operated in a continuous fashion without having to remove any components during or in between culturing cycles. If so desired, the photobioreactor can in fact be kept closed at all times, with no requirement for opening the tank in between cycles, for draining, cleaning or other reasons.

[0145] The photobioreactor according to the invention is based on an inverted panel configuration, where the light panels are enclosed and disposed within a tank for culturing e.g. light sensitive microbes, delivering light into the tank at regular intervals within the tank. This is an inverse configuration compared with prior art solutions, where the panel encloses the algal culture and the light source is positioned outside the panel. The unique configuration of the invention significantly enhances the operational efficiency of the culturing system by allowing operation and service of large culture volumes in a single unit while still receiving light from numerous light panels which in turn simplifies and speeds up the culturing process. This is made possible by using flat panels that are arranged at an angle to the side walls of the tank. The flat panels can in particular be disposed within a tank having a floor that is sloping, or has at least one sloping section, so that culture within the tank flows toward the bottom of the floor, which will be in the shape of a trough in the floor (or floor panel). By providing airlift from the trough in the floor panel, efficient aeration and circulation of microbes in the tank is provided which, when combined with the high density lighting capabilities, provides a photobioreactor that has significant advantages over prior art solutions.

[0146] An inverted layout of the flat-panel principle is thus a new technical approach where the light source is positioned in thin panels submerged into and surrounded by a culturing liquid receiving photosynthetic active irradiation from the source for driving growth. The culture is enclosed by a tank with a sloping floor (preferably U-shaped, or having a U-shaped lower portion) and the culture is mixed and circulated in the tank by air injected through sparges located in in the bottom of the tank.

[0147] The present invention solves i.a. the problem of uneven exposure of light-sensitive culture to light by applying a combination of tank shape, nozzle arrangement and/or orifice direction and defined illumination panel structure and illumination panel intervals to manage the fluid dynamics in the tank and create flow characteristics that ensure even light exposure to all subvolumes of the liquid culture. The present invention at the same time solves the problem of cleaning and disinfection by creating easy access to all exposed surfaces, tank surfaces as well as light panel surfaces. The interior of the tank, including all internal surfaces can thus be easily cleaned, without removing any components of the tank for cleaning. The internal surfaces of the tank are thus smooth and easily accessible for cleaning.

[0148] Turning to FIG. 1, there is depicted a photobioreactor 10, comprising an inner body 5 (not seen except from above in this view) enclosed by a rectangular outer frame structure consisting of side walls 18 and end walls 11. The end walls can be separate from, and disposed outwardly from, the end walls of the body 5 of the photobioreactor, such that the entire body is enclosed within the outer frame structure. Alternatively, the end walls 11 may also serve as end walls of the internal body 5, such that the end walls also represent a portion of the outer frame structure. The frame structure is in such embodiments completed by side walls 18, which may be in the form of side panels 18 that are arranged on a common frame. Legs 15 extend downwardly from the side walls 18, providing support to the outer frame structure.

[0149] A plurality of illumination panels 17 is disposed within the body 5. The illumination panels are arranged in parallel so as to be suspended via supports 16 that sit on upper rims on a frame structure 19 disposed on the upper rim of side walls of the body 5 or side walls of the photobioreactor 10. In the embodiment shown, there are eight sets of illumination panels 17 shown, each set containing six illumination panels that are arranged in tandem within a section of the frame structure 19. Four such sets of tandem arrangements are provided along each sidewall 18 of the photobioreactor, so that overall there are in total 48 illumination panels 17 in the reactor. The illumination panels 17 are removable from the frame structure 19. Thus, each panel can be removed as needed, e.g. for maintenance or cleaning purposes. Furthermore, the density of illumination panels 17 can be modified in accordance with the particular culturing needs. Thus, either fewer or more illumination panels can be arranged on the frame structure 19.

[0150] Valves 12, 13, 14 are arranged on lines extending from the body 5 and through the end wall 11. On each such line, there is a valve 12,13,14 provided, to control flow through line, to deliver fluid into the body 5, or to drain fluid from the body 5. Lowermost outlet 14 and/or outlet 13 can conveniently be used for draining the body 5, and fluid (e.g. water, nutrients and/or liquid culture) can be added through upper valve 12. However, as should be appreciated, fluid (water, nutrients, culture) can also, or alternatively, be added to the tank via the lower lines into the tank, regulated by valves 13,14.

[0151] A cross-sectional view of the photobioreactor in FIG. 1 is shown in FIG. 2. The body 5 can be seen to be defined by side walls 20 and floor panel 30. The floor panel has 30 a generally half-tubular shape, i.e. the floor panel has a semi-circular cross section such that the cross section is in the shape of a half circle. Trough 35 is formed by the lowermost portion of the floor panel. Due to the shape of the floor panel, debris of solid particles within the tank will flow towards and accumulate within the trough 35.

[0152] At the bottom of the trough 35 there are gas inlets 40 arranged along the trough. The gas inlets 40 are arranged at regular intervals along the trough 35. When the tank is filled with a liquid culture, gas (e.g., air) that is pumped into the body 5 via the gas inlets 40 will generate air lift in the tank, driving microbes being grown in the tank towards the liquid surface within the body. Natural flow of such airlift is toward the sides, thus driving the culture towards the side walls 20 of the body 5. Once the microbes reach the side walls, they will gravitate downwards, in the direction of trough 35 in the bottom of the body 5. Naturally, there will also be gravitational and random (Brownian) motion of liquid in the tank such that there will be a downward flow not only along the side walls, but also throughout the body, away from the side walls and floor panel. However, the overall effect of the airlift generated through air pumped through gas inlets along the middle of the floor panel of the body and the gravitational flow along the side walls towards the trough 35 will be that of circulation and mixing of culture within the tank, as further illustrated.

[0153] Circulation within the body is aided by liquid flow along the sides and bottom panel of the tank. Thus, in the shown embodiment, illumination panels 17 can be seen to not reach the side walls 20 or floor panel 30 of the body 5. Thereby, there is unrestricted (free) flow of liquid culture along the sides and the floor panel of the body 5, aiding in the unrestricted flow and circulation within the body.

[0154] The illumination panels 17 are provided by internal light sources (LED lights), provided by four LED panels 22 arranged within each illumination panel 17. Circulating culture within the tank will therefore come into contact with light emitted by the illumination panels. The degree and timing of illumination can be adjusted by both the degree of circulation (driven by air pumped into the tank via gas inlets 40) and the strength and wavelength of light emitted by the illumination panels, as well as the density of panels (distance between panels) in the body 5. Light intensity can also, or alternatively, be adjusted during growth, as light transmittance is significantly decreased with increased culture density.

[0155] Circulating light sensitive cultures in the tank (e.g. H. pluvialis) will thus experience high intensity light (high light exposure) when in close distance to the illumination panels 17, while when further away from the light (low light exposure), the culture will not experience such conditions. In other words, there will be a constant shift in exposure from low to high light exposure. In the case of H. pluvialis, high light exposure triggers biosynthetic pathways leading to astaxanthin formation in the cells. During conditions of astaxanthin formation (red phase) it can therefore be advantageous to grow H. pluvialis at high density of light panels and/or high light intensity, while other microbes may require less light exposure.

[0156] If desired, the wavelength of the light can be adjusted during culturing, so as to promote selective growth during the red and/or green phase of the culturing.

[0157] In FIG. 3, there is shown a longitudinal cross-sectional view of the tank 10. A plurality of gas inlets 40 can be seen to be disposed along and through the lowermost portion of the trough 35 in the floor panel 30. The gas inlets thus extend along the lowermost section of the tank, so as to provide an airlift from the bottom of the tank. This regular arrangement of gas inlets provides for uniform airlift along the longitudinal axis of the tank.

[0158] As an advantage of the uniform airlift in the tank is that the culture within the tank is well and uniformly mixed at all times. Following the addition of a solution (for example a starter culture) to one end of an otherwise filled tank, the solution within the tank reaches a homogeneous composition within about 15 minutes, a consequence of the rapid and thorough mixing provided by the airlift of the gas (e.g., air) delivered into the tank via the gas inlets 40 in the floor of the tank.

[0159] Three support members 50 provide support to the photobioreactor when placed on a flat surface. Additional support members can be provided as required, depending on the load on each tank, which depends on its length and height.

[0160] The photobioreactor also comprises one or more CO.sub.2 inlets (not shown in this view), for supplying a stream of CO.sub.2 gas into the tank, which serves to provide a source of carbon and adjust the pH in the tank. There can further be controllers arranged on the tank, to control growth parameters in the tank, including for example pH, temperature, inorganic salt levels, and illumination conditions.

[0161] In FIG. 4, there is shown a perspective view of an alternative photobioreactor in accordance with the invention. Referring to this figure, there is a control box 50, containing electronic controllers for controlling valves, illumination panels, pH, temperature and/or other parameters in the tank. The controllers can be manual or automatic, or a mixture thereof. For example, there can be controllers that are adapted to automatically respond to certain parameters, for example measurements of temperature or pH, and adjust conditions in the tank accordingly, depending on preset parameters.

[0162] The tank in the photobioreactor can be double walled, to define an open space (thermal jacket) surrounding the tank that can be filled with a fluid such as water, for controlling temperature in the tank. The outer surface of the double wall of the tank 56 can be seen. A series of inlets 53 are arranged in the outer wall of the tank. Water line 54 leads into these openings, for delivering water into the thermal jacket (line 54 and inlet 53 are shown disconnected in this view). Water exits the thermal jacket through exit openings 51, which can be connected to exit water line 52 (the exit openings and exit water line are depicted to be disconnected in this view).

[0163] The depicted tank has three entry openings and three exit openings, for delivering water into and out of the thermal jacket, respectively. However, it will be appreciated that fewer or additional such openings can be accommodated as desirable, depending on the dimensions and configuration of each tank. The electronic controller 55 can receive information about temperature in the tank from a temperature probe that can for example be suspended into the tank. The controller can compare measurements of the actual temperature to a set temperature, and adjust the temperature and/or water flow through the thermal jacket as needed, to bring the measured temperature in the tank to that of the preset temperature. If the temperature in the tank is too low, warmer water can be circulated through the thermal jacket. Alternatively, the controller may adjust flow through the thermal jacket to a higher setting, so as to bring fluid in the tank more quickly to the desired temperature.

[0164] Boxes 50 on the side of the photobioreactor structure contain power supplies to drive illumination in the illumination panels. The boxes 50 furthermore contain electrical switches for the lights in the illumination panels.

[0165] The photobioreactor can have dimensions so that its internal volume (the volume of the body) is about 7500 L. Each illumination panel in the photobioreactor provides illumination over an area of about 2.9 m.sup.2. The reactor has 25 illumination panels, for an overall area of illumination of about 73.2 m.sup.2. This means that overall, the illumination are per unit volume is 0.00976 m.sup.2/L or 97.6 cm.sup.2/L.

[0166] A longitudinal cross-section of the tank in FIG. 4 is shown in FIG. 5, illustrating the relative position of illumination panels 17 and gas inlets 40 along the trough in the tank floor. In this view, it can also be seen how frame member 57 provides support to the tank, and legs 15 extending downwardly from frame members 57.

[0167] In the cross-sectional view shown in FIG. 6, there are additional gas inlets 45, 46 shown, in addition to gas inlets 40. Air flow through gas inlets 40 can be supplemented by additional air flow through gas inlets 45, 46, thereby providing additional airlift in the tank. Also shown in FIG. 6 is a side view of illumination panels 17, with a plurality of LED lights 21 being disposed within each of the illumination panels. The LED lights are powered by power supplies (drivers) within boxes 50, and controlled by controller 55.

[0168] Alternative designs of photobioreactors in accordance with the invention can be seen in FIG. 7 and FIG. 8, respectively. Thus in FIG. 7 there are shown in (A) and (B) two alternative photobioreactor designs, each showing relatively small photobioreactors utilizing the same overall concept, i.e. each photobioreactor comprises a tank that contains illumination panels in an inverse configuration in that the panels are disposed within the tank. Thus, the photobioreactor shown in (A) contains illumination panels 17 suspended within a tank 10 in an analogous fashion to the reactor shown in FIG. 1. A wider configuration of a photobioreactor is shown in (B), where a series of illumination panels are controlled by means of controllers arranged within a control box 55.

[0169] Yet another design, shown in FIG. 8, shows a photobioreactor 10 comprising a round tank structure, where the outer side wall 18 surrounds the body of the photobioreactor. Illumination panels 17 can be seen to be suspended into the tank, in an analogous fashion to that shown for other embodiments in accordance with the invention.

[0170] Inlets for delivering carbon dioxide (CO.sub.2) can be provided in the photobioreactor, for controlling pH within the photobioreactor tank. In FIG. 9 it is shown how gas lines for delivery of CO.sub.2 can be provided in the tanks. A stream of CO.sub.2 is delivered through gas lines 60, and delivered into the photobioreactor via gas inlets 62. The gas inlets are preferably provided as a diffuser, that has very small pores (typically about 20 M) so that CO.sub.2 gas is dispersed by very small air bubbles into culture in the tank. This is important so that the introduced gas dissolves in the aqueous culture in the tank.

[0171] In the top view of FIG. 9 it can be seen that CO.sub.2 inlets 62 are provided in the floor of the container, close to gas inlets 45,46 that provide airlift in the tank. The stream of CO.sub.2 gas provides additional and supplementary agitation and airlift in the tank. A series of gas inlets 40,45,46, for providing airlift in the tank are shown to be provided in between illumination panels 17 in the tank.

[0172] Alternatively, CO.sub.2 can be delivered into liquid culture in the tank via diffusers that are suspended into the tank from above. An example of such a configuration is shown in FIG. 10, where a plurality of diffusers 61 are indicated to be suspended into the tank via CO.sub.2 gas line 60 that is disposed above the body of the photobioreactor.

[0173] By providing CO.sub.2 into the tank from above via suspended diffusers, the position (height) of the diffusers in the tank can be adjusted as needed.

[0174] Irrespective of the configuration of CO.sub.2 delivery into the photobioreactor, the number of CO.sub.2 diffusers can be altered and/or the stream of CO.sub.2 into the tank adjusted so as to provide an appropriate adjustment of dissolved CO.sub.2 (resulting in control of pH) in the tank. The stream of CO.sub.2 can be automatically controlled by controller 55, which receives input about pH in the tank (obtained either manually or automatically), and adjusts the stream of CO.sub.2 into the tank based on such measurements. Alternatively, there can be manual adjustment of the stream of CO.sub.2 into the tank based on pH measurements of the culture within the tank.

[0175] A schematic illustration of the airlift generated in the photobioreactors in accordance with the present invention is shown in FIG. 11. A series of gas inlets 40,45,46 are shown in this cross-sectional view. As illustrated in FIGS. 9 and 10, such inlets can be provided at regular intervals in the tank, for example in between each illumination panel 17 in the tank.

[0176] The stream of gas (e.g. air) into the trough 35 in the floor section of the tank through inlets 40,45,46 drives water in the tank, and thereby also culture that is suspended in the tank, towards the culture surface in the tank. When the air-lift generated flow reaches the surface, the flow will be forced towards the side walls 20 of the tank, and from there the flow will naturally occur along the internal side walls and downwardly in the tank. The circulation is further driven by gravitational forces, that pull culture in the tank downwardly along the side walls and floor 30 of the tank, towards the trough 35 in the floor 30, where circulation is completed by the airlift provided by the gas inlets 40,45,46. A critical feature of the airlift is that it is driven from the lowermost portion of the floor in the tank. This is to ensure that culture that settles at the bottom of the tank is lifted from the bottom, and thereby there is constant recirculation of culture in the tank, with minimal or no dead space in the tank (dead space meaning space through which there is little or no circulation of culture).

[0177] In FIG. 12, there is shown a closeup view of a rectangular illumination panel 17 in accordance with the invention. The illumination panel 17 contains a total of eight LED panels 22, arranged side by side within the panel so as to be in approximately the same plane. The illumination panel contains support 16 that can be used to suspend the panel from a frame structure within the photobioreactor (not shown).

[0178] An alternative illumination panel 17 is illustrated in FIG. 13. Here, the panel contains a total of four LED panels 22. The panel has a pentagonal structure that can be suitable for use in a photobioreactor with curved side walls and/or floor panel, such as the photobioreactor shown in FIG. 2.

[0179] An embodiment of the thermal jacket is shown in FIG. 14. In (A), a side external (i.e., away from the interior of the tank, facing the outside) view of a thermal jacket is shown. The thermal jacket is provided by a continuous series of regularly arranged channels, interspersed by depressions that meet the underlying photobioreactor tank. In (B), a side view along the dotted line in (A) is shown. In this cross-sectional plane the thermal jacket forms a corregated structure, with free flow of liquid within each channel. In reality, the channels are interconnected, as is apparent from the side view in (A). The thermal jacket is provided in the outer surface (side panels and/or floor panel) of the photobioreactor tank, such that there is free flow of culture within the tank (upper half of figure in (B)) and a separate free flow of thermal fluid within the thermal jacket (lower half of (B)). Thus, the thermal jacket can be integral to the side and/or floor panels in the tank, as illustrated by the configuration shown in FIG. 14. The arrow across the two channels in (B) indicates thermal transfer across the photobioreactor tank wall, through which the temperature within the tank can be controlled by controlling the temperature of the thermal liquid circulating in the thermal jacket. Connectors 70,71 represent inlets and outlets, for delivering flow of thermal liquid (such as water) into or out from the thermal jacket. The temperature of the thermal liquid can be controlled by a separate temperature control unit (not shown), if so desired.

[0180] The skilled person will appreciate that the thermal jacket can be adapted in a variety of alternate manners consistent with the jacket allowing for circulation of fluid through the jacket, and the jacket being provided on the outer surface of the photobioreactor tank, so that there is thermal flow between tank and the thermal jacket.

[0181] In FIG. 15, an embodiment showing delivery of CO.sub.2 into the tank via a CO.sub.2 injection loop in the photobioreactor is depicted. Culture from the tank is circulated through the CO.sub.2 injection loope via a photobioreactor outlet (PBR outlet) by means of a circulation pump. Downstream of the pump there is a high-pressure zone due to the pumping of liquid against the mass of liquid in the tank. A CO.sub.2 inlet is provided into this high-pressure zone, on which is provided a suitable CO.sub.2 diffuser or sparger. The CO.sub.2 injection loop finally connects with the photobioreactor tank via a PBR inlet, through which the culture, now rich in dissolved CO.sub.2, reenters the tank. As a consequence of the delivery of CO.sub.2 into a high-pressure environment, the dissolution of CO.sub.2 in the water is maximized. As a consequence, there is a high conversion of CO.sub.2 to biomass in the system.

[0182] The placement of the PBR inlets and outlets are in principle irrelevant, which means that the inlet and outlet can be placed anywhere within the tank. It may however be convenient to place the PBR outlet near one end of an elongated tank, and the PBR inlet near the opposite end of the tank. This way, the CO.sub.2 injection (recirculation) loop can extend along the tank, from one end (or close to one end) to the other end (or close to the other end).

[0183] This configuration results in improved solvation of CO.sub.2, and as a consequence, improved conversion of CO.sub.2 to biomass in the reactor. Thus, by comparison with a normal (tank only) design, the recirculation loop can result in an increase in CO.sub.2 to biomass conversion from about 0.14 to about 0.27.

[0184] In FIG. 16, a closed photobioreactor in accordance with the invention is shown. The tank is closed in this embodiment by two lid units 80, each of which is essentially flat. On each lid units there are a number of sprinkler inlets 90. These inlets allow sprinkling solutions, such as detergent solutions or water to be sprinkled into the tank. Tubing and/or pipes (not shown) are connected to the sprinklers, and desired detergent and/or rinsing solutions pumped into the tank as desired. It should be appreciated that the lid units can alternatively be provided without sprinkler inlets, if so desired.

[0185] It is thus possible to clean the tank without opening the tank, by delivering cleaning solutions through the sprinkler inlets 90. Culture in the tank (e.g., algae culture) can be drained from the tank, the tank and its interior components including light panels subsequently rinsed with water and/or cleaned by means of one or more detergent or disinfectant solutions by delivering these solutions through sprinklers 90 in the lid. As a consequence, the system is a closed, self-contained system that can be kept closed at all times. This way, contamination is minimized, as is evaporation from the tank during growth. The culturing also becomes more economical, and the downtime of the tank is kept to a minimum.

[0186] An alternative embodiments of a lid structure is shown in FIG. 17. In this embodiment, the tank can be closed by six lid units (only two are shown in this figure). Each of the units 80 has a sloping upper surface, so that any liquid that accumulates on the lid will flow off the lide. Sprinklers 90 are arranged on each of the lid units 80, for the delivery of washing and/or rinsing solutions.

[0187] There can be one or more supply tanks (not shown) from which detergent and/or rinsing solutions are pumped via the sprinklers 90 into the tank for cleaning purposes. Thus, the photobioreactor may comprise one or more detergent stock solution container, at least one pump, and tubes or piping for connecting to sprinklers installed in the lid of the photobioreactor, so as to ensure effective cleaning of the interior of the photobioreactor tank, including its interior light panels.

[0188] It will be appreciated that other configurations of the lid structure is possible and within scope of the invention. Thus, the tank can be closed off by a single lid unit if so desired. Alternate shapes and numbers of lid units that in combination cover the tank than shown here are also possible.

[0189] In summary, the circulation path within the tank can thus be described as being (i) vertical from the trough in the tank, towards the surface of liquid culture in the tank, (ii) horizontal, towards the internal walls of the tank, and (iii) vertical along the internal side walls in the tank, followed by a combination of vertical and horizontal movement towards the trough in the floor of the tank.

[0190] As will be appreciated from the foregoing description, the position of illumination in the tank that is parallel to the horizontal movement in this circulation path means that the illumination panels do not impede the circulation within the tank. Since the illumination panels also do not restrict flow along the side walls of the tank, there will also be unrestricted flow along the side walls and floor of the tank, towards its bottom (trough).

[0191] As will also be appreciated that the photobioreactor design described herein is geared to ensure stability and feasibility in the biomass production of e.g. microalgae. Ensuring stable production, free of contamination and other growth problems, has been a problem with prior art tank design. The photobioreactor described herein circumvents or prevents such problems, ensuring constant, secure cultivation of microalgae for the production of e.g. proteins and biomaterials such as asthaxanthin.

[0192] The present invention thereby provides a system and method for the growth of photosensitive organisms, driven by airlift that provides efficient circulation in the tank and at the same time adjustable and efficient illumination provided by the submerged illumination panels in the tank.

[0193] The present invention thus provides a number of advantages over prior art photobioreactors: [0194] User-friendly, highly adaptable and industrial sized photobioreactors [0195] High volumetric productivity [0196] High aerial productivityhigh culture volume per ground footprint [0197] High biomass production per ground footprint compared with other cultivation methods [0198] Safe harvesting and pest avoidance using an integrated photobioreactor [0199] Internal panel illumination that can be regulated and adapted, resulting in high photosynthetic efficiency [0200] Highly cost-effective production of biomass, due to high production per ground footprint [0201] Environmentally friendly production, involving minimal use of CO.sub.2, water and energy, resulting in high productivity of the tank

[0202] Throughout the description and claims, the terms comprise, including, having, and contain and their variations should be understood as meaning including but not limited to, and are not intended to exclude other components.

[0203] The present invention also covers the exact terms, features, values and ranges etc. in case these terms, features, values and ranges etc. are used in conjunction with terms such as about, around, generally, substantially, essentially, at least etc. (i.e., about 3 shall also cover exactly 3 or substantially constant shall also cover exactly constant).

[0204] The term at least one should be understood as meaning one or more, and therefore includes both embodiments that include one or multiple components. Furthermore, dependent claims that refer to independent claims that describe features with at least one have the same meaning, both when the feature is referred to as the and the at least one.

[0205] Embodiments of the present invention include: [0206] 1. A photobioreactor, in particular for culturing light sensitive microbes, the photobioreactor comprising [0207] a. a body comprising at least one floor panel and at least one wall extending upwardly around the periphery of the at least one floor panel to define a body for receiving and holding liquids; wherein the at least one floor panel comprises at least one graded segment so as to define a trough along the bottom of the body towards which debris within the body flows; [0208] b. at least one illumination panel, the at least one illumination panel comprising illumination means adapted to emit light that is suitable for sustaining growth of the light sensitive microbes within the photobioreactor, wherein the at least illumination panel is disposed within the body so that there is free flow of fluid along the sides and floor panel of the body; and [0209] c. at least one gas inlet disposed within the trough in the at least one floor panel, for providing an upward stream of gas into the body so as to generate air lift of the light sensitive microbes within the body; so that, during incubation of a liquid culture of microbes in the photobioreactor, microbe circulation and growth in the photobioreactor is stimulated through concomitant exposure to light emitted by the at least one illumination panel and circulation of microbes within the body that is facilitated by an upward air lift generated by the stream of gas into the body. [0210] 2. The photobioreactor of embodiment 1, wherein the at least illumination panel is disposed within the body so that there is at least one gap between the at least one panel and the at least one wall and/or the floor panel of the photobioreactor. [0211] 3. The photobioreactor of embodiment 1 or embodiment 2, wherein the illumination panel is provided in the form of at least one flat panel that is disposed within the body. [0212] 4. The photobioreactor of embodiment 3, wherein the angle between the illumination panel and the side walls is in the range of 45 to 90, preferably in the range of 60 to 90, more preferably in the range of 70 to 90, more preferably in the range of 80 to 90, more preferably in the range of 85 to 90, even more preferably in the range of about 90. [0213] 5. The photobioreactor of any one of the preceding embodiments, wherein the body comprises an elongate structure comprising at least two side walls and at least two end walls, and wherein the trough extends longitudinally along the floor panel of the body. [0214] 6. The photobioreactor of embodiment 5, wherein the trough extends longitudinally along the middle of the floor panel. [0215] 7. The photobioreactor of embodiment 5 or embodiment 6, wherein the side walls of the body have a rectangular structure. [0216] 8. The photobioreactor of any one of the preceding embodiments, wherein the floor panel comprises at least one downwardly convex segment. [0217] 9. The photobioreactor of any one of the preceding embodiments, wherein the floor panel comprises a continuously downwardly convex structure, so that debris can flow towards the lowermost part of the floor panel. [0218] 10. The photobioreactor of any one of the preceding embodiments, wherein the floor panel comprises a downwardly convex structure that merges into a flat strip at its lowermost point that stretches along the middle of the floor panel. [0219] 11. The photobioreactor of any one of the preceding embodiments, wherein the floor panel comprises a half-cylindrical structure having a semicircular cross-section, when viewed along the longitudinal axis of the body. [0220] 12. The photobioreactor of any one of the preceding embodiments, wherein the at least one gas inlet is disposed in the floor panel. [0221] 13. The photobioreactor of the preceding embodiment, wherein the at least one gas inlet comprises delivery spout that extends no more than 10mm into the body of the photobioreactor, preferably no more than 5 mm, even more preferably no more than 3 mm. [0222] 14. The photobioreactor of any one of the preceding embodiments, wherein the at least one gas inlet is disposed in the floor panel of the body, below the at least one illumination panel. [0223] 15. The photobioreactor of any one of the preceding embodiments, wherein the at least one gas inlet comprises a plurality of gas inlets that are provided in the lowermost section of the floor panel. [0224] 16. The photobioreactor of any one of the preceding embodiments, wherein the at least one gas inlet comprises a plurality of gas inlets that are provided along the trough in the floor panel. [0225] 17. The photobioreactor of any one of the preceding embodiments, wherein the at least one gas inlet comprises a plurality of gas inlets that are intermittently arranged along the trough in the floor panel. [0226] 18. The photobioreactor of any one of the preceding embodiments, wherein the at least one gas inlet comprises a plurality of gas inlets that are arranged at regular intervals along the trough in the floor panel. [0227] 19. The photobioreactor of any one of the preceding embodiments, wherein the at least one illumination panel comprises a parallel arrangement of a plurality of illumination panels and wherein a plurality of gas inlets are arranged in the floor panel, below each of the illumination panels. [0228] 20. The photobioreactor of any one of the preceding embodiments, wherein the at least one illumination panel comprises a parallel arrangement of a plurality of illumination panels and wherein a plurality of gas inlets are arranged in the floor panel, between the illumination panels. [0229] 21. The photobioreactor of any one of the preceding embodiments, wherein the floor panel comprises a continuous convex structure of generally half-cylindrical shape, and wherein the at least one gas inlet comprises a first row of gas inlets that is arranged along the bottom of the half-cylindrical surface, and at least one further row of gas inlets that is arranged in the photobioreactor floor panel along its longitudinal axis, upwardly from and parallel to the first row of gas inlets. [0230] 22. The photobioreactor of any one of the preceding embodiments, wherein the gas inlets have an internal diameter in the range of about 1-10 mm, preferably in the range of about 2-8 mm, more preferably in the range of about 2-6 mm, more preferably in the range of about 3-5 mm. [0231] 23. The photobioreactor of any one of the preceding embodiments, wherein the illumination means is embedded within the illumination panel, so that a water-tight seal separates the illumination means from their surroundings. [0232] 24. The photobioreactor of any one of the preceding embodiments, wherein the illumination panel comprises illumination means that provide illumination away from both sides of the panel along their entire surface. [0233] 25. The photobioreactor of embodiment 16, wherein the illumination panel comprises a plurality of light sources that provide approximately uniform illumination away from both sides of the illumination panel along substantially its entire surface. [0234] 26. The photobioreactor of any one of the preceding embodiments, wherein the illumination panel comprises a plurality of light sources that are disposed so as to provide illumination away from both sides of the illumination panel, into the body of the photobioreactor. [0235] 27. The photobioreactor of any one of the preceding embodiments, wherein the illumination means is provided as a plurality of LED light sources that are embedded in a light-transparent material, preferably light-transparent plastic material. [0236] 28. The photobioreactor of any one of the embodiments 23 to 27, wherein the body comprises a generally elongate structure, and wherein the illumination panel provides illumination along the longitudinal axis of the body. [0237] 29. The photobioreactor of any one of the preceding embodiments, wherein the illumination panels comprise illumination means that are adapted to deliver light with a photon flux in the range of 20-1200 mol/m.sup.2s, preferably 50-800 mol/m.sup.2s, more preferably- 120-500 mol/m.sup.2s. [0238] 30. The photobioreactor of any one of the preceding embodiments, wherein the illumination panel comprises a rectangular structure of approximately uniform thickness that is in the range of about 0.5% to about 5% of the panel width. [0239] 31. The photobioreactor of any one of the preceding embodiments, wherein the illumination panel comprises a rectangular structure of approximately uniform thickness that is in the range of about 0.5 cm to about 5 cm. [0240] 32. The photobioreactor of any one of the preceding embodiments, wherein the illumination panel comprises material that transmits visible light. [0241] 33. The photobioreactor of any one of the preceding embodiments, wherein the illumination panel has a width that is in the range of about 80% to about 99% of the width of the body of the photobioreactor. [0242] 34. The photobioreactor of any one of the preceding embodiments, wherein the illumination panel has a height that is in the range of about 80% to about 99% of the body height from its lowermost point in the floor panel. [0243] 35. The photobioreactor of any one of the preceding embodiments, wherein the illumination panels are disposed within the body so that there is a gap between the illumination panels and the side walls and floor panel of the body that is in the range of about 2-20 cm, preferably in the range of about 5-15 cm. [0244] 36. The photobioreactor of any one of the preceding embodiments, wherein the illumination panel comprises a water-proof housing comprising light-transmitting material, and one or more light board that is disposed within the housing. [0245] 37. The photobioreactor of the preceding embodiment, wherein the one or more light comprises a plurality of rectangular, linear and/or linear light boards. [0246] 38. The photobioreactor of any one of the embodiments 1-35, wherein the illumination panel consists of a water-proof light board comprising a plurality of light sources. [0247] 39. The photobioreactor of any one of the preceding embodiments, wherein the gas inlets are adapted to provide a combined volume of gas into the body of the photobioreactor per minute that is in the range of 10% to about 30% of the volume of the body. [0248] 40. The photobioreactor of any one of the preceding embodiments, wherein the upright side walls and the upright end walls are approximately vertical. [0249] 41. The photobioreactor of any one of the preceding embodiments, wherein the body of the photobioreactor has a rectangular shape when viewed from above, and wherein the ratio of the length of the side walls to the width of end walls is in the range of about 1:1 to about 5:1. [0250] 42. The photobioreactor of any one of the preceding embodiments, wherein the body of the photobioreactor has a ratio of width, at its widest point, to height, that is in the range of about 0.5:1 to about 2:1, preferably 0.8:1 to about 1.5:1, more preferably about 1:1. [0251] 43. The photobioreactor of any one of the preceding embodiments, wherein the body has an internal volume that is in the range of about 200 L to about 40,000 L. [0252] 44. The photobioreactor of any one of the preceding embodiments, wherein the side walls have a length in the range of about 1-10 m, preferably in the range of about 2-8 m, more preferably in the range of about 3-7 m. [0253] 45. The photobioreactor of any one of the preceding embodiments, wherein the end walls have a length in the range of about 0.5-3 m, preferably in the range of about 1-3 m, more preferably in the range of about 2-3 m. [0254] 46. The photobioreactor of any one of the preceding embodiments, further comprising at least one water inlet, for delivering water into the photobioreactor, and at least one water outlet, for draining water from the photobioreactor. [0255] 47. The photobioreactor of any one of the preceding embodiments, further comprising a thermal jacket, wherein the thermal jacket comprises a hollow structure that encapsules at least a portion of the body. [0256] 48. The photobioreactor of the preceding embodiment, wherein the thermal jacket comprises at least one inlet and at least one outlet, for introducing and releasing water from the hollow structure, respectively. [0257] 49. The photobioreactor of any one of the preceding embodiments 5 to 43, wherein the body is enclosed within a frame structure comprising outer side walls that are disposed outwardly from at least the side walls of the body so as to enclose the body. [0258] 50. The photobioreactor of any one of the preceding embodiments, the photobioreactor further comprising at least one support member that extends downwardly from the floor panel and/or end walls of the body so as to provide support to the photobioreactor when placed on a flat surface. [0259] 51. The photobioreactor of any one of the preceding embodiments, the photobioreactor further comprising at least one of: [0260] a. one or more pH meter to provide a measure of pH of liquid in the body; [0261] b. one or more gas inlet for delivering a stream of carbon dioxide enriched gas into the body; [0262] c. one or more temperature probe; [0263] d. one or more chemical probe for detecting inorganic matter such as nitrate; and [0264] e. one or more optical density and/or light density meter. [0265] 52. The photobioreactor of any one of the preceding embodiments, further comprising at least one controller, for controlling at least one of: illumination, water temperature, pH and air flow in the photobioreactor. [0266] 53. The photobioreactor of the preceding embodiment, wherein the controller is adapted to adjust at least one or more parameter selected from light intensity, temperature and pH, in response to measurements of microbe density within the body, as determined by optical density and/or light density measurements. [0267] 54. A method of growing light sensitive microbes, the method comprising: [0268] a. providing a photobioreactor, the photobioreactor comprising [0269] i. a body comprising a floor panel and at least one wall extending upwardly around the periphery of the floor panel to define a body for receiving and holding an aqueous solution comprising microbes; wherein the floor panel comprises at least one graded segment so as to define a trough along the bottom of the body towards which the microbes can flow; [0270] ii. at least one illumination panel that is disposed within the body, the illumination panel comprising illumination means adapted to emit light that is suitable for sustaining growth of the light sensitive microbes within the body, wherein the at least one illumination panel is disposed within the body so that there is free flow of water along the at least one wall and/or floor panel; and [0271] iii. at least one gas inlet disposed in the trough in the floor panel, for providing an upward stream of gas in the body so as to generate air lift of the light sensitive microbes within the body; [0272] b. providing an aqueous culture of light-sensitive microbes into the body so that the illumination panels are at least partially submerged; [0273] c. delivering gas into the aqueous culture in the body through the at least one gas inlet, thereby generating air-lift in the body that provides an upwardly flow of microbes from the at least gas inlet and a downwardly gravitational flow of microbes at least along and down the at least one side wall, towards the trough in the floor, [0274] d. providing illumination in the body by means of the at least one illumination panel; whereby microbe growth is stimulated through the airlift-driven circulation of the microbes within the body and exposure to light emitted by the at least one illumination panel. [0275] 55. The method of the previous embodiment, wherein gas is delivered into the aqueous culture through the at least one gas inlet at a pressure that is in the range of about 0.1-0.5 bar, preferably about 0.2-0.4 bar. [0276] 56. The method of any one of the previous embodiments 54 or 550, wherein gas is delivered into the photobioreactor through the at least one gas inlet at a combined total flow rate into the body per minute that is in the range of 10% to about 30% of the volume of the body. [0277] 57. The method of any one of the previous embodiments 54-56, wherein the photobioreactor comprises at least pH probe and/or at least one temperature probe, and wherein during growth, at least one of pH, temperature, illumination, inorganic matter such as nitrides, optical and/or ligh density and gas flow is selectively controlled. [0278] 58. The method of embodiment 57, wherein the controlling is achieved by at least one electronic controller. [0279] 59. The method of any one of the previous embodiments 54-58, wherein the gas is ambient air, optionally mixed with carbon dioxide. [0280] 60. The method of any one of the previous embodiments 54-59, wherein the gas is delivered into the tank at a total volume per volume of culture in the tank, that is in the range of about 50 to about 500 L/m.sup.3/min, preferably about 100 to about 400 L/m.sup.3/min, more preferably in the range of about 200 to about 300 L/m.sup.3/min. [0281] 61. The method of any one of the previous embodiments 54-60, wherein the body further comprises at least one inlet for delivering carbon dioxide gas into the body, and wherein during growth, pH of the microbe culture is controlled by adjusting the rate of carbon dioxide gas flow through the at least inlet into the body. [0282] 62. The method of any one of the previous embodiments 54-61, further comprising delivering at least one source of nutrients into the body for sustaining growth of the microbes in the photobioreactor. [0283] 63. The method of any one of the previous embodiments 54-62, wherein gas is delivered into the body of the photobioreactor so as to generate a vertical airlift from the trough in the floor of the body, and simultaneously allowing down-flow of microbes along and down the side walls and the floor, towards the trough in the floor. [0284] 64. The method of any one of the previous embodiments 54-63, wherein the method is performed using a photobioreactor as set forth in any one of the embodiments 1-53.

[0285] The invention will now be illustrated by the following non-limiting examples.

EXAMPLE 1

Cultivation of Haematococcus pluvialis

[0286] For the autotrophic production of biomass of the algae Haematococcus pluvialis for astaxanthin production in a photobioreactor (e.g. a photobioreactor as described herein) in a batch cultivation mode, the culturing is performed over 14 days, 7 days of green vegetative growth followed by 7 days of a astaxanthin formation period.

[0287] The vegetative growth is characterized by green cell-growth in size and active cell division and multiplication. The red phase is a process of cell encystment, characterized by plasmatic accumulation of astaxanthin and build-up of thick and sturdy for cell-wall for protection and survival of the cell.

[0288] Prior to cultivation the internal surfaces of the tank and light panels are cleaned. The tank is subsequently filled with water, the water is chlorinated as needed and heated typically from 7 C. to 25 C. by heating up the tank jacket for temperature regulation overnight. Then the water is dechlorinated by means of sodium thiosulphate and active aeration by injection of air through air-sparges located in the bottom of the tank. The aeration is continued for air-lift purpose, to keep the algae in suspension.

[0289] Inoculum of H. pluvialis is produced through step-up culturing in flasks from multiple 1 liter flasks to multiple 5 liter flasks under aseptic conditions using Kuhl-medium (Kuhl, A. & Lorenzen, H. (1964) Handling and culturing of Chlorella. In: D. M. Prescott, ed., Methods in cell physiology. Vol. 1, pp. 152-187, Academic Press, New York and London, 1964). Five liters flask cultures are then applied to inoculate a 1000 L inoculum photobioreactor which is propagated until the cell density has reached optical density around 1.5 absorbance units at 750 nm.

[0290] A 1000 L inoculum photobioreactor (PBR) is filled up with water and nutrients added in the form of Kristalon, a all-in-one formula in an appropriate concentration. After the water has reached 25 C. the flask inoculum cultures are added to the tank making up an optical density of approximately 0.3 absorbance units at 750 nm. The PBR inoculation culture is propagated until the cell density has reached approximately 1.5-2.5 absorbance units at 750 nm. Then the inoculation culture from the inoculation tank is transferred to production PBR which has at that point been filled up to around 80% of the tank volume with tap water, heated up to 25 C. and amended with Kristalon nutrient blend. The production tank is subsequently filled up with water. The production culture is then monitored in terms of growth of the alga, nutrient depletion and morphological changes of the algal cells. Depletion of potassium nitrate as the principal nutrient component is important to enhance astaxanthin formation. At the end of period of vegetative growth the biomass level has reached typically 3-3.5 g/L.

[0291] As the green vegetative growth phase is terminated the red phase starts; astaxanthin induction is triggered by creating a stress effect upon the alga which reacts by producing astaxanthin as a stress relief, principally comprising quenching of oxidative stress. A high intensity illumination is an effective stress factor. At the beginning of the red phase the illumination level is raised from approximately 250 to 700 mol/m.sup.2/s by turning on extra light units mounted on the light panels. In addition, the algae is also stressed by raising the salinity through adding sodium chloride typically creating salinity of 0.8-1.0%. After 7 days of red phase the cell mass contains typically 3.5-4% astaxanthin on a dry weight basis. Eventually the biomass is harvested and processed for astaxanthin down-streaming.

EXAMPLE 2

Cultivation of Marine Algae

[0292] Marine algae can in general be cultivated using the photobioreactors in accordance with the present invention. Culturing can in general terms follow the culturing described in the above under Example 1.

[0293] In the case of culturing marine microalgae such as Nannochloropsis oculata in the tank for oil production, in a similar way the up-scaling of inoculum from flask cultures involves step-up culturing of the alga in liters of seawater or seawater equivalent to tenths of liters under aseptic conditions supplied with an appropriate nutrient solution such as f/2 medium (Andersen, R. A., Morton, S. L., and Sexton, J. P. 1997. Provasoli-Guillard National Center for Culture of Marine Phytoplankton 1997 list of strains. J. Phycol. 33 (suppl.):1-75). The flask cultures are transferred to an inoculum PBR and cultivated for about one week until the desired cell density is achieved. The inoculum is then transferred to the production tank managed in a similar way as described above in case of Haematococcus pluvialis. When the vegetative growth phase is terminated, principal nutrient elements should be depleted which will trigger the synthesis of cytoplasmic oil.