WO2009087567A2

WO2009087567A2 - Photobioreactor for the culture of photosynthetic microorganisms

Info

Publication number: WO2009087567A2
Application number: PCT/IB2009/000034
Authority: WO
Inventors: Salvatore Arghiro
Original assignee: Algues Energy Systems Ag
Priority date: 2008-01-12
Filing date: 2009-01-10
Publication date: 2009-07-16
Also published as: WO2009087567A3

Abstract

The invention relates to a photobioreactor for the culture of photosynthetic microorganisms, in particular micro-algae, that comprises a housing containing photosynthetic microorganisms and a feeding medium, wherein the micro-organisms are in contact with the feeding medium and exposed to solar radiation. According to the invention, at least a portion of said housing is made of a flexible structure supported by the pressure of a gas contained inside said housing.

Description

Photobioreactor for the cultivation of photosynthetic microorganisms

Field of the invention

The present invention relates to a photobioreactor for the culture of photosynthetic microorganisms, in particular microalgae.

A known photobioreactor comprises an enclosure containing photosynthetic microorganisms and a nourishing medium. The microorganisms are in contact with the nourishing medium and are exposed to solar radiation.

State of the art

It is known that microalgae, especially unicellular algae of the plankton (phytoplankton) type, which are likely to be carried by freshwater or saltwater currents, are capable of converting carbon dioxide (CO ₂ ) into biomass and oxygen (O ₂ ) using solar radiation as a source of energy and water (H ₂ O), carbon dioxide (CO ₂ ) and sources of nitrogen (N), sulfur (S) and phosphorus (P) as a source of matter (photosynthesis process). At the cellular level, there is thus an increase in the number of unicellular microalgae.

This process is used to grow microalgae (aquaculture). In general, microalgae are cultivated in natural ponds or artificial basins built in the open air, for example culture basins and oxidation tanks for the treatment of wastewater. However, in "open" aquacultures for microalgae culture, there is a risk of contamination of the microalgae population by invading microorganisms, including bacteria, which may to unbalance or even destroy this population of microalgae in such an open photobioreactor.

To address this problem, closed aquaculture can be used with a hermetic barrier to protect microalgae from microorganisms in the atmosphere that could affect the microalgae population.

Unfortunately, constructions of this type are quite expensive, especially when trying to achieve photobioreactor structures covering areas of several tens of square meters, which is indispensable from a profitability point of view. In particular, the construction costs of such structures are very high and make it uneconomic to produce large-scale crops.

Description of the invention

The subject of the invention is a photobioreactor for the cultivation of photosynthetic microorganisms (phytoplankton), in particular microalgae, comprising an enclosure containing photosynthetic microorganisms and a nourishing medium, said microorganisms being in contact with said nourishing medium and exposed to solar radiation. According to the invention, at least a portion of said enclosure consists of a flexible structure supported by the pressure of a gas contained within said enclosure.

In this way, the invention makes it possible to suppress a phytoplankton invasion (population of photosynthetic microorganisms) by predacious zooplankton (non-photosynthetic microorganisms, for example bacteria), thus avoiding a proliferation of zooplankton at the expense of the phytoplankton populations. Stable populations of phytoplankton / microalgae are thus obtained.

Then, the invention allows an efficient enrichment of the nourishing medium carbon dioxide, essential for good productivity of phytoplankton / microalgae biomass. Preferably, this biomass is "harvested" continuously by ensuring that the concentration of the microorganism population remains substantially constant. Of course, this "harvest" of biomass can also be performed almost continuously, that is to say with samples of a certain quantity / portion of biomass at predetermined intervals and sufficiently short to avoid too large a difference between the instantaneous microorganism concentration and the desired concentration for optimal yield.

Then, the invention allows an effective control and control of the temperature of the nourishing medium, thus photosynthetic microorganisms, essential for a good yield of the photosynthetic process.

According to the invention, these advantages are obtained because at least a portion of said enclosure consists of a flexible structure supported by the pressure of a gas enclosed within said enclosure. This allows the construction of a photobioreactor at sufficiently low costs to make economic the production of large-scale crops.

Preferably, the nourishing medium comprises a nourishing solution in which said photosynthetic microorganisms are suspended. Advantageously, the solution is shallow in order to allow all the microorganisms, especially those in the deepest layers of the nourishing solution, to be exposed to the sun's rays.

Preferably, the enclosure is partially filled with a volume of liquid and partially filled with a volume of gas above said liquid, so that the pressure of said liquid supports a lower part and the pressure of said gas carries an upper part. of said enclosure. This also allows the support / swelling of the flexible enclosure, but because of the high density of the liquid with respect to the density of the gas, with the additional advantage of a lower center of gravity, thus more stability at bad weather, including storms.

In a variant, a lower part of the enclosure consists of a rigid structure while an upper part of the enclosure consists of a flexible structure. In particular, the lower part of the enclosure is filled with a liquid while the upper part of the enclosure is filled with a gas. Typically, the bottom and rigid the speaker is heavier than the top and flexible speaker. The result is an even lower center of gravity, so even more stability and storm resistance.

In an even more advantageous variant, the aforementioned liquid consists of the aforementioned suspension of microorganisms in a nourishing solution. Thus, the nourishing medium contributes not only to the supply of microorganisms food (N, P, S elements), but also to the stability of the structure of the enclosure.

In yet another more advantageous embodiment, the aforementioned gas comprises carbon dioxide. Thus, the gas contributes not only to the supply of microorganisms food (CO ₂ ), but also to the stability of the structure of the enclosure. Preferably, compressed air and / or enriched with carbon dioxide is used.

Preferably, the enclosure comprises at least one gas opening through which a gas can be introduced into said enclosure or withdrawn from it. Similarly, the enclosure may comprise at least one liquid opening through which a liquid can be introduced into said enclosure or withdrawn from it. Preferably, this gas opening and / or liquid opening is controllable. This allows the control of the flow rates of the photobioreactor according to the invention.

In another particularly advantageous variant, the photobioreactor comprises a movement device for the liquid inside the enclosure. Similarly, the photobioreactor comprises a movement device for the gas inside said enclosure. These movement devices make it possible to stir and / or propel respectively the aforementioned liquid and gas. In particular, agitation of the nourishing medium in the form of a liquid makes it possible, on the one hand, to homogenize the temperature and concentrations of nourishing substances in the enclosure and, on the other hand, to accelerate the exchanges of nourishing substances between the microorganisms and the body. nourishing liquid. This makes it possible to increase the speed of photosynthesis in the photobioreactor. Preferably, the enclosure comprises a basin in the form of a closed circuit in which the nourishing medium (liquid) and / or the gas is circulated.

In another particularly advantageous variant, the closed circuit is composed of a plurality of enclosure sections installed in series. Preferably, these enclosure sections are connected and communicated at their ends by a connection unit between two adjacent sections. Thus, it is possible to build large structures in a modular way.

In a compact and attractive version, the aforementioned basin comprises two substantially parallel channels or even a plurality of substantially parallel channels and in communication at their ends.

Preferably, the liquid movement device is arranged in a connection unit where two adjacent channels are in communication. Similarly, the gas movement device can be arranged in a connection unit where two adjacent channels or sections are in communication. This further increases the modular character of the photobioreactor according to the invention.

In another particularly advantageous variant, the aforementioned enclosure sections consist of said flexible structure supported by the pressure of a gas contained within said enclosure. This variant makes it possible to obtain a self-supporting enclosure structure without any additional element of support (rods) or suspension (rods and / or cables).

Preferably, the aforementioned sections are made of polymer material. Advantageously, the sections are formed by polymeric sheets connected and stretched between two connection units. This voltage of the sections through their connection to the connection units contributes to the stability of the self-supporting enclosure structure.

In a particularly advantageous variant for a controlled process in the photobioreactor according to the invention, at least one sensor is arranged in the connection unit. Preferably, the connection unit comprises one or more sensors selected from the following sensor types: temperature sensor, pressure sensor, pH sensor, photometer.

Brief description of the drawings

The invention will be better understood from the following description of an exemplary embodiment of the invention, given by way of non-limiting example, with reference to the appended drawings in which:

Fig. 1 is a top view (schematic plan) of an exemplary embodiment of the photobioreactor according to the invention;

Fig. 2 is a longitudinal sectional view along the line A-A in FIG. 1;

Fig. 3 is a view in more detail and also in longitudinal section along the line A-A in Ia Rg. 1;

Fig. 4 is a cross-sectional view along line B-B in FIG. 1; Fig. 5 is a cross-sectional view along line C-C in FIG. 1; and

Fig. 6 is a view in more detail and also in cross-section along line C-C in FIG. 5.

The figures schematically illustrate the essential parts as well as details of an exemplary embodiment of the present invention:

A structure forms two parallel channels of transparent material and contains a suspension containing a culture of microalgae and a nutrient solution (culture liquid e), arranged to be exposed to the sun's rays and at the same time kept out of direct contact with the air, so as to achieve a confined or relegated environment, which allows to pressurize the interior and to regulate air exchanges with the outside only through controllable special openings. An upper cover b closes hermetically and isolate the structure a. A space s2 formed between the structure a and the upper cover b is provided with an opening valve for the control of pressure and ventilation.

A ventilation pipe d is united with the structure a, which allows the entry of pressurized gas into a space if in the channel and above a culture liquid e.

A ventilation pipe c2 supplies air to the space s2 delimited by the roof or upper fabric b, thus producing a counter-current air flow with thermal regulation function for the space si.

A feed gas composed of a mixture of air + carbon dioxide under pressure is supplied to the space si.

Two vane mixers 2a and 2b for the displacement of the culture liquid e are installed at the ends of the channels. Each of the two mixers is driven by a motor 6.

A rigid support base 1 is provided and constitutes a support for the aforementioned elements forming the channels and enclosed in the latter.

Two end supports at the ends of the channels 3a and 3b are provided.

A fan 4 is provided beyond the end 3a to generate a pressure in the space si.

A fan 4 ¹ is provided beyond the end 3b to generate a pressure in the space s2.

Valves v1 and v2 are provided to adjust or limit the internal pressure in the spaces si and s2.

A pump 7 is provided to fill the channels with liquid by a valve 8 and for harvesting microalgae by a valve 9.

Tie rods are provided to stabilize the structures / ends 3a θt 3b. Detailed description of the exemplary embodiment of the present invention

The figures show, inside the two parallel channels, a shallow liquid phase arranged so that it is illuminated superiorly by the solar rays and swirled by the two mixers 2a and 2b which provide the connection between the two parallel channels. divided by a wall f, it also made of transparent material, for example the same material as for the structure a.

The characteristic shape, observable in section, is obtained by the simultaneous action of the weight of the mass of the culture liquid e on the one hand and the effect of the internal pressure in the space if generated by the fan 4. The upper cover b anchored at both ends 3a and 3b by profiles (which are not shown in the figures) constitutes the second cover with thermal adjustment function.

The air pressure in the space s2 generated by the fan 4 ¹ supports the upper cover b. This pressure is less than the air pressure in the space if generated by the fan 4. The regulation or limitation of the internal pressures in the spaces si and s2 is possible by means of the valves v1 and v2 calibrated to open at a requested or predetermined pressure.

As illustrated in the exemplary embodiment, the present invention makes possible the elimination of all intermediate support structures, allowing considerable constructive economy.

In the exemplary embodiment, the photobioreactor of the present invention uses a base 1 perfectly flat and leveled.

The filling of the channels is carried out by means of the pump 7 and the valve 8, while the harvest takes place by the opening of the valve 9.

The mixers 2a and 2b are actuated by the electric motors 6 rotating at a sufficient number of revolutions to induce a turbulent movement in the culture liquid. The structures 3a and 3b have solid or solid vertical parts which define on the two ends the space s2, while the tie rods t serve to reinforce the structure.

The gas mixture air + carbon dioxide d, pressurized by the fan 4, is introduced through the ventilation pipe d into the space if above the suspension of microalgae e.

By remaining in contact with the culture liquid, the difference in partial pressure pCU2 and pθ ₂ between the culture medium e (liquid phase) and the gaseous phase gas mixture allows the mutual exchange between the liquid phase and the gaseous phase. , carbon dioxide in a first direction to the suspension of the culture medium e on the one hand and oxygen, produced by photosynthesis in microalgae, in the opposite direction to the gaseous mixture d.

The speed of movement of the gas must be slow enough to allow the best exchange of the two gases. The ventilation pushes the gas, now exhausted, that is to say, low in CO ₂ and rich in O ₂ , to expel it outwards through the valve v2, when this one opens, in order to stabilize the internal pressure.

Mixers 2a and 2b are responsible for stirring the microalgae suspension so as to optimize exposure to light during the day and avoid sedimentation during the night.

The photobioreactor according to the present invention can also be used, beyond the production of microalgae, for cultures of other photosynthetic microorganisms for the fixation of CO ₂ and the production of biomass.

From an economic point of view, it is advantageous to combine the fixation of CO ₂ with the production of biodiesel and with the purification of urban or agricultural liquid waste. Industrial application

The important characteristics for the industrial application of the photobioreactor of the present invention are the following: a) parallel horizontal flow channels which contain the culture liquid and which can be illuminated by the sun's rays, isolated from the outside air by a surface (cover) made of transparent and flexible material, b) a second surface (cover) also made of transparent and flexible material, to create a transparent tunnel over the underlying channels, c) the channels and the tunnel assuming their shape because of the internal pressure, d) mixers inside the channels and intended to stir with their wheels (blades and / or blades) the culture liquid,

e) the channels and the tunnel, hermetically closed and provided with mechanisms of unloading of air, allowing an adjustment and / or an adjustment and / or a limitation of their internal pressures, f) the gaseous spaces above the liquid phase undergoing pressurization by a gas mixture comprising a variable part of CO ₂ (air enriched with CO ₂₎ and with nutritive function, g) the parallel channels that are placed in communication at their ends to create a continuity (closed circuit for the nutrient liquid),

h) the flow of air enriched with CO2 remaining relegated or confined inside and in constant contact with the culture medium during variable periods and adjustable as required, i) the air flow in closed spaces with function of thermal regulation by means of external fans, (j) spaces made for pressurisation which can be used as reservoirs for CO2-enriched gas mixtures, especially during night periods, and (k) a structure without rigid materials which could produce shade throughout their lengths.

The present invention allows the creation of low-cost modular installations, based on a covered "raceway" system that uses CO2 or agricultural or urban waste rich in nitrogen and phosphorus and which allows temperature stability and vigorous growth of biomass while minimizing external emissions.

The advantages deriving from the present invention make it possible

1) reduce the energy cost of agitation of the culture medium,

2) to thwart the proliferation of predacious zooplankton in the culture medium,

3) build an efficient system of carbon dioxide enrichment essential for good productivity,

4) to realize a closed system which makes it possible to control the thermal exchanges by making possible the management of the temperature of the culture medium,

5) use for the construction of materials, so transparent materials of low cost and easy availability,

6) to realize a system of closed photobioreactors at low cost of construction, which makes economically advantageous crop systems of large dimensions, developed according to criteria of modularity and for a production of biomass intended to be transformed into biofuels, biofuels, bioplastics, etc. .

Claims

claims

1. Photobioreactor for the cultivation of photosynthetic microorganisms, in particular microalgae, comprising an enclosure containing photosynthetic microorganisms and a nourishing medium, said microorganisms being in contact with said nourishing medium and exposed to solar radiation, characterized in that at least one part of said enclosure is constituted by a flexible structure supported by the pressure of a gas contained within said enclosure.

2. photobioreactor according to claim 1, characterized in that at least a portion of said enclosure is at least partially transparent to solar radiation.

3. Photobioreactor according to claim 1 or 2, characterized in that said nourishing medium comprises a nourishing solution in which said photosynthetic microorganisms are suspended.

4. Photobioreactor according to any one of claims 1 to 3, characterized in that substantially all of said enclosure consists of a flexible structure.

5. Photobioreactor according to claim 4, characterized in that said enclosure is filled and supported with a suspension of microorganisms in a nourishing solution.

6. Photobioreactor according to claim 4, characterized in that said enclosure is partially filled with a volume of liquid and partially filled with a volume of gas above said liquid, so that the pressure of said liquid carries a lower part and the pressure of said gas carries an upper portion of said enclosure.

7. photobioreactor according to any one of claims 1 to 3, characterized in that a lower portion of said enclosure consists of a rigid structure while an upper portion of said enclosure consists of a flexible structure.

8. Photobioreactor according to claim 7, characterized in that said lower part of the chamber is filled with a liquid while said upper part of the enclosure is filled with a gas.

9. Photobioreactor according to any one of claims 6 to 8, characterized in that said liquid consists of said suspension of microorganisms in a nourishing solution.

10. Photobioreactor according to any one of claims 6 to 8, characterized in that said gas comprises carbon dioxide.

11. Photobioreactor according to any one of claims 1 to 10, characterized in that said enclosure is in the form of pipe.

12. Photobioreactor according to claim 11, characterized in that said pipe comprises at least two separate boxes.

13. Photobioreactor according to any one of claims 1 to 12, characterized in that said enclosure comprises at least one gas opening through which a gas can be introduced into said enclosure or withdrawn from it.

14. Photobioreactor according to any one of claims 1 to 13, characterized in that said enclosure comprises at least one liquid opening through which a liquid can be introduced into said enclosure or withdrawn from it.

15. Photobioreactor according to claim 13 or 14, characterized in that said gas opening and / or said liquid opening is controllable.

The photobioreactor according to any one of claims 1 to 15, further comprising a movement device for the liquid inside said enclosure.

17. Photobioreactor according to any one of claims 1 to 16, further comprising a movement device for the gas inside said enclosure.

18. Photobioreactor according to any one of claims 1 to 17, characterized in that said enclosure comprises a basin in the form of a closed circuit in which is circulated said nourishing medium and / or said gas.

19. Photobioreactor according to claim 18, characterized in that said closed circuit is composed of a plurality of enclosure sections installed in series.

20. Photobioreactor according to claim 18, characterized in that said enclosure sections are connected and communicated at their ends by a connection unit between two adjacent sections.

21. Photobioreactor according to any one of claims 17 to 20, characterized in that said basin comprises two substantially parallel channels and in communication at their ends.

22. Photobioreactor according to any one of claims 17 to 20, characterized in that said basin comprises a plurality of substantially parallel channels and in communication at their ends.

23. Photobioreactor according to any one of claims 18 to 22, characterized in that said liquid movement device is arranged in a connection unit where two adjacent channels are in communication.

24. Photobioreactor according to any one of claims 18 to 23, characterized in that said gas movement device is arranged in a connection unit where two adjacent channels are in communication.

25. Photobioreactor according to any one of claims 19 to 23, characterized in that said enclosure sections consist of said flexible structure supported by the pressure of the enclosed gas inside said enclosure.

26. Photobioreactor according to claim 25, characterized in that said sections are made of polymeric material.

27. Photobioreactor according to claim 26, characterized in that said sections are formed by polymeric sheets connected and stretched between two connecting units.

28. Photobioreactor according to any one of claims 20 to 27, characterized in that at least one sensor is arranged in said connection unit.