Classifications

• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
  • C12N1/00—Microorganisms, e.g. protozoa; Compositions thereof; Processes of propagating, maintaining or preserving microorganisms or compositions thereof; Processes of preparing or isolating a composition containing a microorganism; Culture media therefor
  • C12N1/12—Unicellular algae; Culture media therefor
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
  • C12M23/00—Constructional details, e.g. recesses, hinges
  • C12M23/58—Reaction vessels connected in series or in parallel
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
  • C12M47/00—Means for after-treatment of the produced biomass or of the fermentation or metabolic products, e.g. storage of biomass
  • C12M47/02—Separating microorganisms from the culture medium; Concentration of biomass

Definitions

• the present invention relates to a method for harvesting microalgae and to a device for implementing such a method.
• Microalgae and cyanobacteria are aquatic organisms ranging in size from micron to 100 microns in size and use light as a source of energy to fix carbon dioxide (C0 2 ). Like terrestrial plants, microalgae and cyanobacteria can accumulate the carbon absorbed in the form of lipids, which makes it possible to consider using them to produce biofuels. Such a use is all the more promising as microalgae and cyanobacteria exhibit a very high photosynthetic yield and cell growth rate (one to several tens of times higher than those of terrestrial oilseeds such as rapeseed, sunflower, etc.). and that the fraction of directly usable biomass is maximal (conversely, the terrestrial plants release a part of the carbon absorbed towards lignocellulosic molecules, more difficult or even impossible to valorize).
• culture media are obtained in which there are microalgae with a concentration of a few grams of dry matter per liter of culture medium.
• microalgae and use them for example for the production of biofuels, or other products (food, cosmetics, ...), it is necessary to obtain a medium with a much higher concentration.
• Techniques of the prior art for concentrating the dry matter content are based for example on centrifugation of the culture medium. These techniques are generally used after a sedimentation step to increase the efficiency of the centrifugation.
• a device such as that shown in Figures 2 and 3 of EP-1 671 704 is for example used to extract water from a concentrate of microalgae obtained after a first preconcentration step by sedimentation.
• US2009 / 0162919 discloses a method of concentrating an aqueous environment in microalgae, which process comprises: contacting microalgae with a mineral flocculant at a concentration of less than 10% solids, and extraction by separation of microalgae flakes obtained out of the aqueous environment, thereby concentrating the microalgae into a sludge having a biomass density of at least 1%.
• the proposed method is limited to unicellular microalgae having an average diameter of less than 20 ⁇ m.
• the addition to the culture medium of a foreign product may limit the possibilities of use of the mud obtained (it is known for example that the application on the skin of cosmetic products containing aluminum presents risks) and strike the cost of the process.
• the use of the recommended flocculants (flocculants based on aluminum or iron in particular) is not environmentally neutral.
• the object of the present invention is therefore to provide a new process making it possible to obtain a large concentration of microalgae in a culture medium, without adding solid matter foreign to the culture medium, and preferably with as little energy consumption as possible.
• Another object of the invention is to provide a concentration and harvesting process in which the microalgae (living organisms) do not undergo any shock or lethal treatment. This process will more advantageously provide a concentrated microalgae medium in a continuous manner.
• the concentration obtained will advantageously allow a direct exploitation for the production biofuels or other products obtained from microalgae.
• the present invention provides a method for harvesting microalgae in a culture medium.
• this method is characterized in that:
• the culture medium passes through a set of successive reservoirs, called concentrators, thus defining a succession of upstream and downstream concentrators,
• each concentrator has, on the one hand, an envelope defining an interior space and, on the other hand, a passive filter unit separating said interior space into an upper volume and a lower volume,
• the upper volume comprises an inlet allowing the introduction of a culture medium into said upper volume and an outlet placed in a low position with respect to the inlet making it possible to extract a culture medium more concentrated in microalgae out of the upper volume,
• the lower volume comprises an outlet making it possible to extract a liquid from the lower volume
• each concentrator has, on the one hand an input, and on the other hand two outputs separated by a passive filter unit; the presence of two outputs allows the force of gravity to act by two resultants; the culture medium that enters a concentrator is thus divided within it;
• the inlet of the upper volume of a downstream concentrator is connected to the output of the upper volume of the upstream concentrator
• a concentrated culture medium is harvested at the outlet of the upper volume of a concentrator.
• the harvest is performed at the exit of the last (the most downstream) concentrator of the set.
• the harvest may however occur further upstream.
• each concentrator (with the exception of the first and the last concentrator of the assembly) can be qualified in turn as a downstream concentrator or an upstream concentrator. depending on whether we observe the pair of concentrators formed by the concentrator and the preceding or the following in the succession of concentrators (following the direction of circulation of the medium of culture).
• the inlet of the upper volume of an upstream concentrator is advantageously at an altitude greater than the inlet of the upper volume of the downstream concentrator.
• carbon dioxide can be injected into the lower volume of the concentrator concerned (and preferably at the level of each concentrator).
• the third advantage of carbon dioxide injection is that it prevents clogging of the passive filter unit and any sedimentation of microalgae in the upper volume of the concentrator.
• the present invention also relates to a device for harvesting microalgae, characterized in that it comprises a set of tanks, said concentrators, successive defining a succession of upstream and downstream concentrators, in that each concentrator has, on the one hand , an envelope defining an interior space and, on the other hand, a passive filter unit separating said interior space into an upper volume and a lower volume, in that the upper volume comprises an inlet allowing the introduction of a culture medium in said upper volume and an outlet disposed in a low position relative to the inlet for extracting a culture medium more concentrated microalgae out of the upper volume, in that the lower volume has an outlet for extracting a liquid from the lower volume, and in that the inlet of the upper volume of a downstream concentrator is connected to the output of the upper volume upstream concentrator.
• a device for harvesting microalgae characterized in that it comprises a set of tanks, said concentrators, successive defining a succession of upstream and downstream concentrators, in that each concentrator
• the input of the upper volume of an upstream concentrator is advantageously at an altitude greater than the input of the upper volume of the downstream concentrator.
• the lower volume of at least one concentrator preferably comprises means for injecting a gas under pressure into said lower volume.
• all concentrators are placed on the same plane. However, it would for example be possible to plan successive steps to receive the successive concentrators of a device according to the invention.
• all the passive filter units of the device are arranged at the same height, that is to say at the same height relative to said plane on which are the hubs.
• a device according to the present invention is preferably hermetic to avoid contaminating the algal medium.
• the upper volume of at least one concentrator advantageously has in its upper part a semi-permeable membrane with oxygen, allowing oxygen to leave the concentrator. It is also possible, in a variant or in combination, to provide a hydrogen-permeable membrane at the top of the concentrator, if the equivalent medium discharges hydrogen.
• the present invention also provides an original passive filter unit which can be advantageously used in a concentrator according to the present invention or in other applications.
• a passive filter unit comprises two metal sheets between which there are filtering membranes whose porosity is decreasing from a wire mesh towards the center of the passive filter unit.
• FIG. 1 represents an embodiment of a concentrator that can be used in a microalgae harvesting device according to the present invention
• FIG. 2 represents a microalgae harvesting device according to the present invention implementing seven concentrators represented in FIG. 1, and
• Figure 3 illustrates a passive filter unit used in a concentrator of a harvesting device according to the present invention.
• FIG. 1 illustrates a concentrator 2 used for the implementation of the present invention. As illustrated in FIG. 2, several concentrators 2 of the type of that shown in Figure 1 are combined with each other to obtain a microalgae harvesting device and be able to implement a microalgae harvesting method according to the present invention.
• the concentrator 2 of FIG. 1 has a circular cylindrical overall shape corresponding to a preferred embodiment of the present invention. It has an outer casing with a side wall 4, a bottom 6 and a cover 8.
• the side wall 4 is circular cylindrical.
• the bottom 6 and the cover 8 are in turn disk-shaped, the radius of the disk corresponding to the radius of the circular cylinder of the side wall 4.
• the side wall 4 and the bottom 6 are for example made of steel, preferably stainless . It is clear that other materials and other forms can be considered here.
• a transparent side wall 4 may advantageously be provided so that the microalgae in the culture medium can benefit from the light and develop.
• the concentrator 2 is intended to be placed on a flat horizontal floor, the bottom 6 then coming into contact with the ground. The following description assumes that each concentrator 2 is in such a position when up / down, lower / upper orientations are mentioned.
• the passive filter unit 0 has an overall shape of a disk and is arranged in the concentrator 2, parallel to the bottom 6 and the cover 8, between these, so as to define in the hub envelope a separation defining a lower volume 12 and higher volume 14.
• a side wall 4 in two parts: a lower part extending from the bottom 6 to the passive filter unit 10 and an upper part extending from the passive filter unit 10 to 8.
• the passive filter unit 10 then rests for example on a base (not shown) machined in the upper edge of the lower part of the side wall 4 to receive the passive filter unit 10.
• the upper part of the wall Lateral side 4 can then for example come to maintain the passive filter unit 10 by resting on the lower part of the side wall 4.
• the side wall 4 can also be made in one piece and means can then be provided inside. of it to accommodate the passive filter unit 10. In all cases, it is expected to preferably have a tight connection between the passive filter unit 10 and the side wall 4, or between the side wall 4 and a support provided to receive and house the passive filter unit 10.
• the passive filter unit 10 can be subjected to large forces, depending in particular on the pressure exerted on it by the culture medium in the upper volume 14 and also on the surface of the passive filter unit 10, it is possible to provide various means to support this passive filter unit 10, and not only at its periphery. Braces can support the passive filter unit 10 or can also provide a support which is based on the bottom 6 of the concentrator to maintain the passive filter unit 10. Many solutions can be envisaged here for maintaining this filter unit passive. Those skilled in the art will be able to choose a solution adapted to the mechanical stresses to which the passive filter unit 10 will be subjected.
• the upper volume 14 has an inlet 16.
• the latter is disposed near the lid 8. It is intended to feed, for example using a pipe, the upper volume 14 with a culture medium containing microalgae and is preferably as far away as possible from the passive filter unit 10.
• the distance between the inlet 16 and the passive filter unit defines a height called useful height and referenced HU in FIG.
• the distance between the cover 8 and the center of the inlet 16 is for example about 10 to 20 cm.
• the upper volume 14 also has an outlet 18.
• the latter is disposed near the passive filter unit 10, preferably as close as possible to this passive filter unit 10. In any case, it is at an altitude lower than that of the entrance 16.
• the distance between the passive filter unit 10 and the center of the outlet 18 is, for example, approximately 5 to 15 cm.
• a pipe 20 having two elbows is connected to the outlet 18 of the upper volume 14 of the concentrator 2.
• This pipe 20 has, in its mounted position illustrated in the figures, a first horizontal section 22 connected to the outlet 18, a vertical section 24 connected to the first horizontal section 22 by a first elbow 26 and a second horizontal section 28 by a second elbow 30.
• the position of the second horizontal section 28 relative to the passive filter unit 10 defines a height called output height and referenced HS in Figure 1. For each concentrator 2 the output height is less than the useful height HU.
• the lid 8 closes the upper volume 14. It is for example formed by a semi-permeable membrane oxygen (0 2 ) and is mounted so that oxygen can escape out of the upper volume 14. In Alternatively, the membrane (which is optional) can take place in the cover 8 so as to be at the highest point of the concentrator 2.
• the lower volume 12 has an outlet 32 preferably disposed in the lower part of the concentrator 2, close to the bottom 6. This outlet 32 is connected to a discharge pipe 34 preferably provided with a solenoid valve 36.
• the lower volume 12 is intended to collect the filtrate obtained when a culture medium is introduced into the upper volume 14. This filtrate is most often pure water. As illustrated in the figures, the filtrate does not fill all the lower volume 12, but only a part of it thus defining a level referenced N.
• the presence of the solenoid valve 36 (and a level sensor not shown) allows maintain in the lower volume 12 a level N substantially constant in time.
• the space between the filtrate and the passive filtering unit 10 is preferably occupied by carbon dioxide (CO 2 ) which is introduced into the lower volume 12 via an injector 38. This is for example above the level filtrate, for example three-quarters of the overall height of the lower volume 12.
• CO 2 carbon dioxide
• FIG. 1 thus illustrates a concentrator 2 having an inlet 16 of culture medium and two outlets 18 and 32 separated by a passive filter unit 10, the two outlets thus enabling the force of gravity to act by two resultants and to obtain at outlet 18 a culture medium whose concentration of microalgae is greater than that of the culture medium introduced at the inlet 16.
• FIG 2 illustrates the combination of several concentrators 2 each corresponding to a concentrator as illustrated in Figure 1 and described above.
• concentrators 2 are arranged next to one another on a horizontal plane surface.
• the concentrators may be aligned as shown in Figure 2 or may be arranged on a circle, form an L, etc.
• each concentrator 2 has a distinct diameter and a total overall height.
• all the passive filtering units 10 can be arranged at the same altitude or height (that is to say at the same distance from the ground on which the concentrators 2 are based). It can then be expected that all the outputs 32 corresponding to the lower volumes 12 of the concentrators are themselves at the same altitude or height. The same is true for the outlets 18 of the upper volumes of the concentrators 2 as well as for the injectors 38.
• the concentrators 2 are interconnected so that the second horizontal section 28 of each pipe 20 connected to an outlet 18 of a concentrator 2, said upstream concentrator, is connected to the inlet 16 of a concentrator 2, said concentrator downstream.
• the first concentrator, or concentrator furthest upstream, is fed at its inlet 16 directly into the culture medium from, for example, a photobioreactor, or another means of production (culture) of microalgae.
• the downstream concentrator 2 may comprise a pipe 20 as illustrated in FIG. 2, but this latter is not connected to a concentrator.
• the concentrators 2 are designed and arranged relative to each other so that the inlet 16 of an upstream concentrator 2 is at an altitude (distance from the ground on which it rests in the case where all the concentrators are arranged on a same horizontal plane or otherwise distance relative to a common horizontal reference plane) greater than that of the input of the corresponding downstream concentrator 2.
• an altitude distance from the ground on which it rests in the case where all the concentrators are arranged on a same horizontal plane or otherwise distance relative to a common horizontal reference plane
• FIG. 3 illustrates a passive filter unit 10 in exploded perspective.
• This passive filter unit 10 comprises in the preferred embodiment represented here eight layers arranged symmetrically with respect to the center of said passive filter unit 10.
• each layer of the passive filter unit has the shape of a disk.
• the porosity of the filter membranes is given solely by way of non-limiting example. This porosity is varied according to the size of the microorganisms in the culture medium.
• the passive filter unit described has eight layers. Depending on the concentration to be achieved and the nature of the microorganisms, the number and / or the nature and / or the thickness of the layers can also be adapted.
• the structure of the metal fabrics can also be adapted to the medium treated.
• This original structure for a passive filter unit is particularly well suited to the present invention but could also be used in other applications within a concentration device.
• Such a passive filter unit 10 makes it possible in particular to have fine C0 2 bubbles after passing through the passive filter unit 10, preventing any sedimentation of microalgae (or other organisms) in the upper volume of the concentrator. In addition, to clean such a passive filter unit 10, it is sufficient to turn it over and can thus achieve a self-cleaning operation of the passive filter unit.
• the different layers of the passive filter unit 10 are for example surrounded by a not shown circular seal made in a elastic material. This seal could also furthermore coat the outer face of each of the metal fabrics 40 to maintain coherence between the layers of the passive filter unit before it is mounted in a concentrator 2.
• microalgae harvesting device as shown in Figure 2 can then operate as explained below. This device is intended to operate continuously and by gravity.
• a culture medium from a photobioreactor is introduced into the first concentrator, the one upstream.
• the concentration of algae in the culture medium is 4 g / l of dry matter.
• the height of the inlet 16 of the first concentrator 2 is for example placed about 5 m from the ground on which the concentrator 2 (and the following) rests.
• the upper volume 14 of the first concentrator 2, and the following, is completely filled by the culture medium.
• the culture medium exerts pressure on the passive filter unit 10, the latter allowing the force of gravity to act by two resultants (outputs of the upper and lower volumes). Since each concentrator may have a diameter different from that of the other concentrators, the passive filtering units 10, which all preferably have the same structure, nevertheless have adequate dimensions (area) each time for the concentrator 2 which contains them.
• the culture medium is then concentrated and pure water (or at least without microalgae) through the passive filter unit 10 to arrive in the lower volume 12 of the concentrator.
• the water level N is kept constant in each concentrator 2, thanks in particular to the presence of a solenoid valve 36 on each discharge pipe 34.
• each concentrator 2 makes it possible to maintain a constant pressure in the lower volume 12.
• Slow diffusion of the carbon dioxide through the passive filtration unit 10 makes it possible to slowly drain the microalgae in the upper volume 14 to the corresponding outlet 18 and prevent sedimentation of microalgae in the upper volume 14.
• each concentrator 2 there is an input flow DE1 of the culture medium, an output flow DS1 of pure water through the discharge pipe 34 and an outlet flow DS2 of culture medium through the pipe 20.
• Solenoid valves may also be used at the hoses 20 to better manage the concentration process of microalgae.
• concentration of microalgae in the downstream concentrator which is twice that of the culture medium in the upstream concentrator.
• the concentration of microalgae therefore doubles from an upstream concentrator to a downstream concentrator.
• the dimensions of the pipe 20, in particular the inside diameter thereof and the radius of curvature of the bends 26, 30 will advantageously be adapted to each stage of the harvesting device according to the invention.
• the input flow of the system (with seven concentrators 2) is 10,000 l / h (ie 10 m 3 / h) with a concentration of algal medium of 4 g / l
• the output flow at the level of the pipe 20 furthest downstream will be 78 l / h with a concentration of 512 g / l of dry matter.
• 9922 I of pure water will be available. This water can be recycled to supply water photobioreactors (requires pumping) or for other uses.
• the concentration of microalgae is here only by gravity and continuously.
• the system is preferably perfectly hermetic so as to avoid any contamination of the algal medium during the concentration process.
• concentrators without cover. Such system is then more difficult to manage because of the risks of overflows.

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• 2011
  • 2011-05-02 FR FR1101349A patent/FR2974813B1/fr not_active Expired - Fee Related
• 2012
  • 2012-03-27 EP EP12717395.3A patent/EP2705132A1/de not_active Withdrawn
  • 2012-03-27 WO PCT/FR2012/050640 patent/WO2012150390A1/fr active Application Filing
  • 2012-03-27 CN CN201280028444.5A patent/CN103597066A/zh active Pending
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