PHOTOBIOREACTOR

Abstract

Photobioreactor for culturing a photosynthetic microorganism, comprising: an enclosure comprising a light-collecting wall and defining a culture chamber for containing a culture medium containing at least the photosynthetic microorganism, the light-collecting wall being transparent to infrared radiation and to visible radiation, and an optical filter for filtering irradiation radiation directed toward the culture chamber,
the optical filter being transparent to radiation in the visible and containing a thermochromic compound, the optical filter being transparent to infrared radiation at a temperature at least 10 C. below the transition temperature of the thermochromic compound and having an optical transmittance to infrared radiation of 20% or less at a temperature at least 10 C. above the transition temperature of the thermochromic compound.

Claims

1. Photobioreactor for culturing a photosynthetic microorganism, the photobioreactor comprising: an enclosure having a light-collecting wall and defining a culture chamber for containing a culture medium containing at least the photosynthetic microorganism, the light-collecting wall being transparent to infrared and visible radiation, and an optical filter for filtering radiation directed toward the culture chamber, the optical filter being transparent to radiation in the visible and containing at least one thermochromic compound, the optical filter being transparent to infrared radiation at a temperature at least 10 C. below the transition temperature of the thermochromic compound and having an optical transmittance to infrared radiation of 20% or less at a temperature at least 10 C. above the transition temperature of the thermochromic compound.

2. Photobioreactor according to claim 1, wherein the transition temperature is greater than or equal to 30 C.

3. Photobioreactor according to claim 1, wherein the thermochromic compound is an optionally doped thermochromic oxide selected from the group consisting of VO.sub.2, BiVO.sub.4, NbO.sub.2 and mixtures thereof.

4. Photobioreactor according to claim 1, wherein the optical filter has an optical transmittance to infrared radiation greater than or equal to 80%, or even greater than or equal to 90%, respectively less than or equal to 20%, or even less than or equal to 10%, at a temperature at least 5 C. below, respectively at least 5 C. above the transition temperature of the thermochromic compound.

5. Photobioreactor according to claim 1, wherein the optical filter is disposed on the light-collecting wall.

6. Photobioreactor according to claim 1, wherein the optical fitter is formed by a coating covering at least partially or completely one side of the light-collecting wall.

7. Photobioreactor according to claim 6, wherein the coating has outer and inner surfaces, the inner surface being in contact with the light-collecting wall, the outer surface being opposite the inner surface and having a rough texture in the form of a network formed by a regular succession of a relief pattern.

8. Photobioreactor according to claim 1, wherein the optical filter is disposed so that the visible portion of the irradiation radiation transmitted by the optical filter and by the light-collecting wall reaches the culture chamber, when the photobioreactor is exposed to visible radiation.

9. Photobioreactor according to claim 1, wherein the light-collecting wall is disposed between the culture chamber and the optical filter.

10. Photobioreactor according to claim 1, wherein the light-collecting wall has an outer side facing the culture chamber and an inner side opposite the outer side and in contact with the optical filter, the outer side or the inner side of the light-collecting wall having a rough texture.

11. Photobioreactor according to claim 1, wherein the texturing ratio of the inner side of the light-collecting wall is between 1.30 and 2.00.

12. Photobioreactor according to claim 1, wherein the culture chamber contains the culture medium, the photosynthetic microorganism being selected from a photosynthetic bacterium, a photosynthetic cyanobacterfum, and an especially eukaryotic microalga.

13. Photobioreactor according to claim 1, wherein the outer side of the light-collecting wall has a rough texture whose average pitch is less than the size of the photosynthetic microorganism.

14. Process for culturing a photosynthetic microorganism, wherein a photobioreactor according to claim 1 is exposed to irradiation radiation comprising components in the visible and infrared, the culture chamber of the photobioreactor containing a culture medium comprising a photosynthetic microorganism.

15. Process according to claim 14, wherein the irradiation radiation is solar radiation.

16. Photobioreactor according to claim 1, wherein the transition temperature is greater than or equal to 35 C. or less than or equal to 55 C.

17. Photobioreactor according to claim 1, wherein the transition temperature is less than or equal to 50 C.

18. Photobioreactor according to claim 1, wherein the transition temperature is less than or equal to 45 C.

19. Photobioreactor according to claim 3, wherein the thermochromic compound is tungsten-doped vanadium oxide VO.sub.2:W.

20. Photobioreactor according to claim 10, wherein the outer side or the inner side of the light-collecting wall has a rough texture in the form of a network formed by a regular succession of a relief pattern.

21. Photobioreactor according to claim 11, wherein the texturing ratio of the inner side of the light-collecting wall is between 1.50 and 1.90.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0065] Other aspects of the invention will appear more clearly when reading the detailed description below and the drawings in which:

[0066] FIG. 1 shows, schematically and in cross section, an example of a photobioreactor according to the invention;

[0067] FIG. 2 is an enlargement of a part of the photobioreactor of FIG. 1;

[0068] FIG. 3 a) to c) are photographs, taken by scanning electron microscopy, of the rough texture of the inner side of the light-collecting wall of different examples of photobioreactors according to the invention.

[0069] FIG. 4 illustrates the variation, as a function of the wavelength of the incident radiation, of the optical transmittance of the light-collecting walls shown of FIGS. 3a to 3c; and

[0070] FIG. 5 illustrates the variation, as a function of the wavelength of the incident radiation, of the haze ratio of the light-collecting walls shown in FIGS. 3a to 3c;

[0071] FIG. 6 illustrates the variation, as a function of the wavelength of the incident radiation, of the total reflection weighted by the spectral response of the eye of the light-collecting walls shown in FIGS. 3a to 3c; and

[0072] FIG. 7 illustrates another example of a photobioreactor according to the invention.

[0073] For reasons of clarity, the different elements of the figures are represented with a free scale, the actual dimensions of the different parts not necessarily being respected. In particular, the dimensions of the patterns of the rough textures may be exaggerated compared to the dimensions of the other components of the photobioreactor.

[0074] Hereinafter, the terms between . . . and . . . , from . . . to . . . and varying from . . . to . . . are equivalent and mean that the boundaries are included, unless otherwise stated.

DETAILED DESCRIPTION

[0075] FIG. 1 shows an example of a photobioreactor 5 according to the invention. The photobioreactor has a chamber 10 and an optical filter 15 disposed in contact with the chamber.

[0076] The enclosure comprises a tank 20, with a bottom 25 and at least one side wall 30 extending from the bottom in a direction of extension E. The direction of extension may be vertical, although other orientations may be considered. The tank defines an upper tank opening 35.

[0077] The enclosure also has a cover 40, in the form of a plate, placed on the tank and completely covering the upper tank opening, so as to close the enclosure. The tank and cover thus define a culture chamber 45, which contains a culture medium 50 containing the photosynthetic microorganism 55. The culture medium contains an aqueous solvent 60 containing elements essential for the growth of the photosynthetic microorganism. The culture chamber can be hermetically sealed from the outside 65, for example by means of seals, not shown, sandwiched between the tank and the cover.

[0078] In the example of FIG. 1, the light-collecting wall 70 is defined by the cover 40. The light-collecting wall is transparent to sunlight and is made of glass, for example. The bottom and side walls of the tank can be made of a material that is opaque to visible radiation. In a variant, the bottom wall and the bottom side wall of the tank can be light-collecting walls.

[0079] The light-collecting wall has an outer side 75 facing the culture chamber and an inner side 80, opposite the outer side and separated by the thickness e.sub.p of the light-collecting wall. The optical filter 15 is in contact with and covers the inner side 80 of the light-collecting wall. In a variant, the optical filter can cover the outer side of the wall.

[0080] The optical filter is formed by a coating 85 made of a thermochromic material, for example tungsten-doped vanadium oxide, with a transition temperature between 38 C. and 42 C. The coating preferably has a thickness e.sub.r between 50 nm and 800 nm. It has an inner surface 90 in contact with the inner side of the light-collecting wall and an outer surface 95 located opposite said inner surface.

[0081] In addition, as shown in FIG. 2, the outer surface 95 of the optical filter and the inner side 80 of the light-collecting wall each have a rough texture to increase the optical transmittance to visible radiation of the light-collecting wall and the optical filter. The rough texture is formed by the regular repetition of a pattern of triangular cross section. The texture has a pitch P between two patterns and a pattern height H.

[0082] In addition, the outer side 75 of the light-collecting wall has a rough texture, which is also formed by the regular repetition of a pattern such as the outer surface of the optical filter. However, the average pitch of the rough texture of the outer side of the light-collecting wall is less than the size of the microorganism, in order to limit the formation of an opaque biofilm comprising the photosynthetic microorganism on the light-collecting wall.

[0083] The photobioreactor may also include means, not shown, for renewing the aqueous solvent and/or supplying nutrients to the culture medium, such as a source of potassium or a gas such as carbon dioxide. It may include means for extracting the products of the growth of the photosynthetic microorganism, for example a gas such as dioxygen generated by photosynthetic activity.

[0084] FIGS. 3a to 3c are scanning microscopy photographs of the rough texture of the inner side of the light-collecting wall of three photobioreactors, hereinafter referred to as Examples 1 to 3. The light-collecting wall shown in these figures is an aluminoborosilicate glass plate.

[0085] The rough textures shown in FIGS. 3a to 3c were obtained by vacuum plasma treatment of the light-collecting wall using dry etching equipment. The dry etching process was carried out using a gas mixture of trifluoromethane CHF.sub.3 and dioxygen O.sub.2 with a CHF.sub.3/O.sub.2 ratio between 10 and 15, at a working pressure between 50 mTorr and 200 mTorr, with a power density between 1.65 W/cm.sup.2 and 3.56 W/cm.sup.2 (RF), and during a treatment time between 10 minutes and 30 minutes.

[0086] As can be seen in FIGS. 3a to 3c, the rough texture has a substantially regular structure formed by the repetition, depending on the width and length of the coating, of a pattern with a pyramidal shape.

[0087] The variation in working pressures, power density and processing time results in variation in the average pitch and height of the texture.

[0088] FIG. 4 illustrates the changes 110, 111 and 112 as a function of the wavelength , expressed in nm, of the optical transmittance, expressed in percent, of the light-collecting walls of Examples 1 to 3, respectively. The collecting walls of Examples 1 to 3 are transparent to visible and infrared radiation with a wavelength of less than 1100 nm.

[0089] FIG. 5 illustrates the changes 115, 116 and 117 as a function of the wavelength , expressed in nm, of the total reflection R.sub.tot, expressed in percent, of the light-collecting walls of Examples 1 to 3, respectively. The presence of a rough texture on the inner side of the collecting walls of Examples 1 to 3, although not essential to the invention, limits the total reflection of incident radiation. The total reflection, shown in FIG. 5, is always less than 6% regardless of the wavelength of the incident radiation between 350 nm and 1100 nm for Examples 1 to 3. The total response weighted by the spectral response of the eye is at most 2.16% for Example 1, as shown in Table 1. It is of the order of 8% for a collecting wall formed from the same material but not having a rough texture.

[0090] FIG. 5 illustrates the changes 120, 121 and 122 as a function of the wavelength , expressed in nm, of the haze ratio Ha of the light-collecting walls of Examples 1 to 3, respectively. Weighted by the spectral response of the eye, the haze ratio is at least 22.0% (Example 3). The collecting wall of the example not treated with plasma, not having a rough texture, has a haze ratio of less than 1.0%.

[0091] The presence of a rough texture, although not essential to the invention, therefore improves the optical transmittance of the assembly formed by the optical filter and the light-collecting wall.

TABLE-US-00001 TABLE 1 Without plasma Example 1 2 3 treatment Total reflection (TR) 2.16 1.23 1.59 8 weighted by the spectral response of the eye (%) Minimum total reflection 1.28 1.16 1.11 8 over the wavelength range 400 nm to 800 nm (%) Wavelength for which the 785 610 330 Not applicable total reflection is minimal (nm) Diffuse reflection (DR) 1.84 0.66 0.35 <0.5 weighted by the spectral response of the eye (%) Haze ratio = DR/TR (%) 85.2 53.7 22.0 <1.0

[0092] FIG. 7 illustrates another example of a photobioreactor according to the invention.

[0093] The photobioreactor 5 of FIG. 7 differs from the photobioreactor shown in FIG. 1 in that the enclosure 10 consists of the light-collecting wall, the outer side of which 130 is defined by the outer surface side of the tube, and is covered by the optical filter 15 as a coating formed of the thermochromic compound. The enclosure has a general tubular shape of revolution and has inlet openings 135 and outlet openings 140 through which the culture medium 45 flows into and out of the enclosure, respectively. The circulation V of the culture medium is carried out in a closed loop. A pump 145 draws the culture medium leaving the chamber through the outlet opening 140 and reinjects it through the inlet opening 135. As is apparent from the reading the description, the photobioreactor according to the invention ensures a passive regulation of the temperature of the culture medium, thus promoting culture, at low cost with a high yield of the photosynthetic microorganism.

[0094] Of course, the invention is not limited to the exemplary embodiments of the device and of implementation of the process described above.