WO2010103154A2

WO2010103154A2 - Method for the culture of microorganisms and photobioreactor used in same

Info

Publication number: WO2010103154A2
Application number: PCT/ES2010/070132
Authority: WO
Inventors: Carlos DÍAZ GARCÍA; Eduardo Romero Palazón; Guillermo GARCÍA-BLAIRSY REINA
Original assignee: Repsol Ypf, S. A.
Priority date: 2009-03-09
Filing date: 2010-03-09
Publication date: 2010-09-16
Also published as: ES2351566A1; ES2351566B1; WO2010103154A3

Abstract

The invention comprises a transparent cylindrical vertical body (1) and a base (2) supporting the body (1) and having an outlet in the lower part thereof, which outlet is connected to an outlet pipe (3) that opens into a recirculation pipe (4) connected to an upper inlet (6) in the upper part of the body (1). According to the invention, injection means (5) inject air and optionally CO₂into the recirculation pipe (4), producing a vortex (11) inside the body (1). In addition, the invention relates to a method for obtaining biomass from microalgae using this photobioreactor.

Description

METHOD OF CROP OF MICROORGANISMS AND PHOTOBIOR REACTOR

EMPLOYEE IN SUCH METHOD

The present invention can be included within the field of cultivation of microorganisms in reactors, in particular it describes a method for obtaining biomass from algae and a high performance vertical reactor employed in said method.

BACKGROUND OF THE INVENTION

Microalgae are unicellular beings very varied in size and shape that exist in almost all known habitats. Most of them are aquatic habitats, both marine and freshwater, although some live on land.

The seas and oceans contain huge amounts of planktonic algae, with an estimated 90% of the Earth's total photosynthesis being performed by these aquatic plants.

Currently, this microalgal biomass can be used for applications as biofertilizers, in the purification of wastewater, as soil conditioners and as food. Likewise, the potential of microalgae for the production of a wide variety of substances, such as fatty acids, pigments, vitamins, antibiotics, pharmaceuticals and other chemical products of interest, as well as hydrogen, hydrocarbons and other biological fuels has been revealed.

In order to carry out the production of phototropic microorganisms, the so-called photobioreactors can be used. It is essential, for said production, to properly select the design of the reactor to be used, as well as a series of parameters depending on the microorganism to be used, such as optimal growth conditions and resistance to environmental variations. In this way, the design of reactors that allow to achieve high productivity at minimum costs is one of the most important lines of work. important in the field of biotechnology, and without whose progress a worldwide expansion of this industry will be impossible.

Thus, in the Mexican patent application MX PA05007801A the design of a transparent cylindrical photobioreactor (glass), conical in its lower part, with air-driven circulation (airlift) is described. This photobioreactor is used for the production of astaxanthin.

DESCRIPTION OF THE INVENTION

The present invention provides a method for the cultivation of oil-generating microalgae for use as fuels, as well as a reactor employed in said method.

In some closed systems, for marine cultures, an aqueous solution is available with microalgae that grow by photosynthesis due to the combined effect of sunlight and injection of both air and eventually CO2. The cultivation of algae requires, therefore, these two basic conditions; The entry of light that allows the simultaneous existence of illuminated and shaded areas to provide the cycle of photosynthesis and agitation of the culture liquid that promotes the exchange of algae between both areas.

In order for both of the above conditions to be met, the present invention provides a high efficiency advanced vertical photobioreactor (hereinafter FBR) for algae culture, in a cylindrical shape, with a bottom that can be conical or flat, of transparent material and with an external recirculation duct, in which a vortex effect is generated in the upper part of the aqueous medium that allows a greater entry of light energy into the system and a more efficient agitation of the medium, which allows to increase the production of biomass cultivated by unit of volume and surface. Said vortex or swirl is generated by the effect of the tangential entry into the system of the culture medium itself, which is driven from the lower part of the reactor to the upper part by a gas injection system located in the recirculation duct.

In addition, it must be taken into account that the optimal design of the system, dimensions and / or materials for the manufacture of a reactor for the generation of biomass is determined by the following parameters:

• Maximize the volume while maintaining a proportion of illuminated volume - shadow and so that a global vortex or vortex is obtained that guarantees adequate resistance time to the photosynthesis cycle.

• Avoid areas of low agitation.

Therefore, a first aspect of the present invention refers to a reactor for the cultivation of microorganisms, or FBR photobioreactor, which comprises a transparent cylindrical body, a bottom located next to the cylindrical body and an outlet conduit connected to an outlet located at the bottom, characterized in that it additionally comprises: a recirculation duct whose inlet is located next to the outlet duct and which flows into the upper part of the cylindrical body, and injection means, located in the vicinity of the inlet of the duct inlet. recirculation, which introduce gases.

The reactor of the invention is a cylindrical reactor, made of a transparent material, which may be included, but not limited to, the group comprising glass fiber, low density polyethylene (LDPE), polycarbonate (PC), polymethylmethacrylate (PMMA) or any other material that meets the optimal light transmission conditions PAR (photosynthetically active radiation, from English Photosynthetically Active Radiation). In addition to the side walls, the upper surface of the container is transparent or open to the atmosphere so that it also allows the passage of light. The bottom of the reactor can be conical or flat, preferably flat.

The height of the reactor can be between 1 and 5 meters and the diameter can vary between 15 and 100 cm.

The reactor of the invention contains an aqueous solution that in turn contains microalgae that grow by photosynthesis by combined effect of sunlight and air, more preferably CO2, injected.

A second aspect of the present invention relates to a process for producing biomass from a culture of microorganisms using the reactor of the invention.

The conditions that this algae culture procedure requires, in addition to the use of a reactor like the one described above, are: light input with illuminated areas and in shaded areas to allow photosynthesis; and a stirring of the culture liquid that promotes the exchange of algae between the lighted areas and the shaded areas.

Said reactor is subjected to adequate lighting to provide illuminated areas and shaded areas, and to agitation of the culture liquid by means of a biphasic current self-propelled by the injection of gases.

The agitation in the reactor of the invention is achieved by means of a biphasic liquid-gas stream self-propelled by means of gas injection and its subsequent rise in buoyancy bubbles. Said current is ejected tangentially in the plane formed by the free surface of the culture liquid with the aim of obtaining a swirl sufficiently intense to generate a conical free surface whose vertex is located in the vicinity of the outlet duct. The additional effect of free surface increase It increases the area of the illuminated area and can increase the capacity of the system to capture light from the environment and transform it into plant matter (biomass).

As just indicated, the eddy is obtained by introducing gas into the recirculation duct ("riser"), in the vicinity of the outlet duct. The air rises bubbling through the recirculation duct to the height of the free surface of the culture liquid. The entrainment of liquid due to the continuous injection of gas, called the "holdup" effect, must provide the necessary impulse to generate rotation.

Since the light is absorbed by the medium, there is a length of light penetration that determines the volume of illuminated liquid.

In a preferred embodiment of the process of the present invention, the microorganisms are microalgae that can be selected from the list comprising, but not limited to, the following genera: Spirulina, Chlorella, Chlorococcum, Neochloris Isochrysis ,, Tetraselmis, Oocytis Ettlia, Porphyridium , Nannochloris Synechocystis, Crucigenia, Muriellopsis, Haematococcus, Clamidomonas, Synechococcus, Phaeodactylum,

Platymonas, Amphora, Auxenochlorella, Ankistrademus, Nanochloropsis, Navícula, Boekelovia, Scenedesmus or Rhodopseudomonas.

In a more preferred embodiment, the microalgae can be selected from the following species: Phaeodactylum trichornutum, Platymonas sp., Amphora sp., Boekelovia sp., Swedish Tetraselmis, Navícula sp. Synechococcus sp., Scenedesmus quadricuada, Rhodopseudomonas palustres, Muriellopsis sp. Chlorella sorokiniana, Spirulina platensis, Chlorella sp., Neochloris oleoabundans, Scenedesmus sp., Auxenochlorella protothecoides, Synechocystis sp., Chlorococcum sp., Isochrysis galbana, Oocytis sp., Ettlia carotinosa, Porphyridnois ouent. Crucigenia tetrapedia, Haematococcus pluviales, Clamidomonas sp., Ankistrademus, sp., Nanochloropsis occulata or Nanochloropsis gaditana.

The main advantages of the reactor of the present invention over others already known are: a) Compared to conventional vertical systems. It improves the dissolution of nutrients and ensures the light-dark periods of the microalgae in crops with high densities. b) Against open systems (Race-Ways): better agitation of the culture medium and better control of the culture conditions (pH, Temperature, dissolution of nutrients in a homogeneous way) as well as avoiding the entry into the environment of contaminants that may affect to the yield of biomass production. c) Against helical tubular systems with small tubes: ease of operation (control of crop conditions such as pH,

Temperature, nutrient dissolution in a homogeneous way) as well as the possibility of using materials and construction systems with much lower costs while maintaining production levels.

Another aspect of the present invention relates to the biomass obtainable by the process of the invention.

Another aspect of the present invention relates to the use of the biomass of the invention for the manufacture of fuel, preferably this fuel is biodiesel although it can also be used for other energy uses, such as gasification.

Throughout the description and the claims the word "comprises" and its variants are not intended to exclude other technical characteristics, elements, components or steps. For those skilled in the art, other objects, advantages and characteristics of the invention will emerge partly from the description and partly from the practice of the invention. The following examples and drawings are accompany the present description to better understand the characteristics of the invention, as an integral part thereof and by way of illustration, not intended to be limiting of the present invention.

DESCRIPTION OF THE DRAWINGS

To complement the description that is being made and in order to help a better understanding of the characteristics of the invention, according to a preferred example of practical implementation thereof, a set of drawings is attached as an integral part of said description. where, for the purposes of illustration and not limitation, the following has been represented:

Figure 1.- Represents a diagram of an FBR reactor of the invention.

Figure 2.- Represents an operating scheme of an FBR reactor of the invention with the non-return valve closed.

Figure 3.- Represents an operating scheme of an FBR reactor of the invention with the non-return valve open.

PREFERRED EMBODIMENT OF THE INVENTION

For a better understanding of the invention, the detailed description of some of the modalities thereof will be shown, shown in the drawings which, for illustrative but non-limiting purposes, are attached to this description.

As can be seen in Figure 1, the FBR reactor of the invention is composed of the following elements: a) A vertical body (1) of cylindrical shape, with a height between 1 and 5 meters, and a diameter between 15 and 100 cm, built in a transparent material, which can be both rigid and flexible, such as the group comprising fiberglass, low density polyethylene (LDPE), polycarbonate (PC), polymethylmethacrylate (PMMA) or any other material that meets the optimal conditions of PAR light transmission. The upper part of the body (1) is provided with a cover that is not necessarily airtight that allows the aeration of said reactor and the placement of different crop control systems (thermocouples, pH meters, salinity, O2 concentration, etc.). The lower part of the body rests on a bottom (2) described below in point b). b) A bottom (2) on which the body (1) rests, which can be conical or flat, of material that can be opaque, such as for example steel, aluminum, polyvinyl chloride (PVC), or transparent according to materials similar to those described for the body (1). On the upper part of the bottom (2) the body (1) rests by means of a hermetic seal that ensures the tightness of the union between the body (1) and the bottom (2). In the lower part of the bottom (2) there is an outlet, connected to an outlet duct (3), with a diameter between 2 cm and 15 cm, which in turn connects with a recirculation duct (4) described below in the next point. The bottom (2) is provided with a stable, strong and safe system to support the entire weight of the reactor on the ground. c) An external recirculation conduit (4), which connects the lower part and the upper part of the reactor by means of upper (6) and lower (not shown) sealed connections, respectively. The material of the circulation duct (4) can be opaque, such as steel, aluminum, polyvinyl chloride (PVC), or transparent, according to materials similar to those described for the body (1). Additionally, the upper connection (6) is located so that the culture medium accesses the reactor tangentially to the surface of said reactor. The recirculation duct (4) incorporates, in the vicinity of the outlet duct (3), a third connection (8) to which an injector (5) is connected, which injects air or air + CO2 mixture into the reactor.

The reactor of the invention comprises a non-return valve (12) located in the outlet duct (3). As can be seen in figures 2 and 3, when said non-return valve (12) is open and the air rises bubbling through the recirculation duct (4) up to the height of the free surface of the culture liquid, thanks to the "hold up" effect of the generated air bubbles, a recirculating movement of the culture medium is created which generates a vortex effect in the part upper of the aqueous medium that allows a greater entry of light energy into the reactor and a more efficient agitation of the medium. The recirculation duct (4), in its lower section is provided with a purge duct (9) to facilitate the emptying of the reactor. Additionally, the recirculation system is provided with a diverting duct (10) that allows the recirculation of the culture medium to be diverted to any other element such as a second reactor, a harvesting tank or a drain.

Once all the elements of the reactor have been assembled as described above, said reactor must be filled to a pre-established maximum level with an aqueous solution that will act as a culture medium for the microalgae. In addition, a sufficient inoculum of individual individuals will be incorporated into this medium to initiate the growth phase. After this first filling stage, the start-up stage of the recirculation begins. For this, air is injected through the injection means (5), with a flow rate of 20-150 l / min. The "hold up" effect of the bubbles created will propel the culture medium upwards through the recirculation system to the upper entrance (6) of the body (1), generating a circular movement on the surface that will eventually become a vortex (11). At this time we can consider that the reactor of the invention has been started. After the period of growth set according to the species of microalgae that is cultivated, the harvesting process will be carried out using either the purge duct (9) or the diversion duct (10), located in the recirculation duct ( 4).

Next, in table 1, the following production values are detailed, in cultures of different microalgae, carried out by means of the procedure described. Table 1

Where: "PSSC max." is the maximum dry weight without ashes, "PSSC Range" is the optimum harvest range, "g" is the generation time in days, "μ" is the growth rate, P vol. It is the average volumetric production for the different species tested abroad (E) and in the greenhouse (I) in FFBR.

( ^* ) The cultivation of Spirulina plantensis was carried out throughout the year, testing different harvest ranges in order to determine the most suitable for achieving a sustained production over time. Table 2 shows the average production values for the different harvest ranges used.

BNA are the codes of microalgae deposited in the National Algae Bank located in Las Palmas de Gran Canaria (Spain).

The PSSC values were calculated from the relationship between the optical density of the culture at 680 nm and the dry weight without ashes for each species / strain.

Table 2

Claims

1. Photobioreactor for the cultivation of microorganisms comprising:

- a transparent cylindrical vertical body (1), - a bottom (2) located next to the body (1), on which said body (1) rests, and

- an outlet duct (3) connected to an outlet located in the lower part of the bottom (2), characterized in that it additionally comprises: - a recirculation duct (4) connected to the outlet duct (3) and to the upper inlet (6 ) of the body (1),

- injection means (5) located in the circulation duct (4), in the vicinity of the outlet duct (3), which inject gases, which produce a vortex (11) that increases biomass production, - a duct purge (9), located in the lower section of the recirculation duct (4), to facilitate emptying, and

- a diverting duct (10), located in the recirculation duct (4), used to extract the culture outwards.

2. Photobioreactor according to claim 1, characterized in that the bottom (2) has a flat shape.

3. Photobioreactor according to claim 1, characterized in that the bottom (2) has a conical shape.

4. Photobioreactor according to claim 1, characterized in that the injection means (5) are adapted for the circulation of gases comprising air and / or CO ₂ .

5. Photobioreactor according to claim 1, characterized in that the body is made of a material selected from:

- fiberglass, - low density polyethylene (LDPE),

- polycarbonate (PC), and

- polymethyl methacrylate (PMMA).

6. Photobioreactor according to claim 1, characterized in that the upper part of the body (1) comprises a transparent cover.

7. Photobioreactor according to claim 1, characterized in that the upper part of the body is open.

8. Method for producing biomass from microorganisms comprising: lighting the reactor, according to any of claims 1 to 7, which contains a culture of microorganisms, and stirring the liquid of said culture of microorganisms by means of gas injection.

9. Method according to claim 8, wherein the microorganisms are microalgae.

10. Method according to claim 9, wherein the microalgae are selected from the list comprising Spirulina, Chlorella, Chlorococcum, Neochloris Isochrysis ,, Tetraselmis, Oocytis Ettlia, Porphyridium, Nannochloris Synechocystis, Crucigenia, Muriellopsis, Haematococcus, Clamidomonasdachoachocdane, Chlamydum Platymonas, Amphora, Auxenochlorella, Ankistrademus, Nanochloropsis, Navícula, Boekelovia, Scenedesmus or Rhodopseudomonas.

11. Method according to claim 10, wherein the microalgae are selected from the list comprising Phaeodactylum trichornutum, Platymonas sp., Amphora sp., Boekelovia sp., Swedish Tetraselmis, Navícula sp. Synechococcus sp., Scenedesmus quadricuada, Rhodopseudomonas palustres, Muriellopsis sp. Chlorella sorokiniana, Spirulina platensis, Chlorella sp., Neochloris oleoabundans, Scenedesmus sp., Auxenochlorella protothecoides, Synechocystis sp., Chlorococcum sp., Isochrysis galbana, Oocytis sp., Ettlia carotinosa, Porphyridnois ouentum. Crucigenia tetrapedia, Haematococcus pluviales, Clamidomonas sp., Ankistrademus, sp., Nanochloropsis occulata or Nanochloropsis gaditana.

12. Biomass obtainable by the method according to any of claims 8 to 11.

13. Use of the biomass according to claim 12, for the manufacture of biodiesel.