Cell adhesion device for culturing microalgae

Abstract

The present invention relates to an adhesion device (1) for culturing microalgae that increases the density of microalgae cultures and their biomass productivity. The device comprises a body (2) with an upper opening that contains a culture medium (3), which occupies half of its volume; a plurality of rotary discs (4) as a supporting surface on which the microalgae cells (5) adhere, promoting their growth to form a biofilm, said plurality of discs (4) being fixed to a horizontal rotation shaft (6), which passes through the body (2), and being equally spaced apart, the location of the rotation shaft (6) inside the body (2) being such that said discs remain semi-submerged in the culture medium (3); gas-liquid diffusers for gas transfer and bubbling in the culture medium (3); at least one moisture sensor and at least one temperature sensor for monitoring the moisture and temperature, respectively, of the gas phase inside the body (2) of the device (1); at least one temperature sensor for monitoring the temperature of the culture medium (3); an upper cover (7) on the upper opening of the body (2), which prevents the culture medium (3) and microalgae cells (5) from being exposed to the outside environment; a lighting board (8) arranged between each pair of discs (4) of the plurality of discs (4), being located on the rotation shaft (6) and arranged in slots (71) in the cover (7) so that said lighting boards (8) are not in contact with the inside of the body (2); and an electric motor to provide slow and accurate rotation of the rotation shaft (6), wherein the body (2) and the cover (7) are made of a transparent or translucent material that allows sunlight or artificial light to pass through.

Description

[0001] Device for microalgae cultivation based on cell adhesion

[0002] DESCRIPTIVE MEMORY

[0003] FIELD OF INVENTION

[0004] The present invention is developed in the field of technologies for the cultivation of microalgae, specifically, it refers to a high biomass productivity device for the cultivation of microalgae at very high density based on cell adhesion with an integrated lighting system.

[0005] BACKGROUND OF THE INVENTION

[0006] Microalgae are photosynthetic unicellular organisms that can grow autotrophically or heterotrophically, and are generally efficient at fixing CO2 and using solar energy to produce biomass.

[0007] The biomass produced by microalgae can correspond to different types of resources, such as proteins, fatty acids, polysaccharides, vitamins, antioxidant pigments, biofertilizers, among others, which can be applied in various industrial sectors such as food, aquaculture, agriculture, medicine, water purification, biofuels, etc., there being an interest in the research and use of microalgae for various purposes.

[0008] Because of the above, there is interest in developing microalgae cultures that allow obtaining biomass for different applications.

[0009] Currently, a cultivation system commonly used for industrial purposes is an open pond with a configuration called race-ponds or race-track due to its characteristic racetrack shape. This system allows cell densities of up to 3 g / L to be achieved, with surface productivity that can reach, in optimized systems, 100 tons / ha / year (27.7 g / m 2 According to NREL (National Research Energy Laboratory), dry microalgae biomass is produced. These types of systems are preferably built on land with no agricultural value, using seawater, but also freshwater, depending on the microalgae being cultivated, and in areas with high solar irradiation.

[0010] Another alternative is the use of a photobioreactor, which is a closed cultivation unit or one with little exposure to the atmosphere. It is configured to allow the physical and chemical variables of a culture to be controlled, depending on the microalgae that are to be cultivated to obtain a particular product.

[0011] In both cases, the cultivation mode is typically in suspension, where the microalgae cells are dispersed in water, obtaining low cell densities, requiring energetically demanding processes for their separation / concentration or the use of external substances to facilitate phase separation to achieve an adequate microalgae harvest.

[0012] The yield of a microalgae culture will depend both on the cell concentration in the culture and on the appropriate physical and / or chemical conditions for the cells to develop properly. Factors that affect the production of a microalgae culture include temperature, light intensity, salinity, nutrients, aeration, pH, and others.

[0013] Another alternative that has been investigated is cell adhesion-based culture, where microalgae cells adhere to the surface of a support material to grow. Comparatively, harvesting the biomass produced in this type of culture is simpler than in suspension culture, so the collection cost is lower. However, this type of culture also presents problems or disadvantages related to growth rate, efficiency, and / or operational control.

[0014] Therefore, there is a need for culture systems that can improve productivity in order to obtain higher cell densities.

[0015] State-of-the-art solutions have been developed that seek to improve the productivity and operation of microalgae cultivation.

[0016] In this regard, mention may be made of document WO2017 / 190504, which describes a method for recovering and harvesting nutrients from a liquid stream by incorporating them into microorganisms cultured in a rotating photobioreactor, comprising a reactor main body containing a culture liquid, a horizontal rotating shaft extending along the main body, at least one rotating disc fixed vertically to the rotating shaft made of a material whose adhesion allows microalgae cells to attach and the formation of a biofilm, a drive motor, a transmission system and a vent tube at the bottom of the body for injecting carbon dioxide and ventilating the reactor, where the at least one rotating disc is partially immersed in the culture liquid and partially exposed to air.A motor drives the rotating disk to rotate slowly so that the microalgae cells attached to the disk alternately enter the liquid phase and the gas phase, the main body of the reactor is made of a transparent material to promote photosynthesis and the photobioreactor is arranged in a location where it is exposed to natural light or under an artificial light source.

[0017] Another document that may be considered corresponds to document CN210620778, which describes a rotary-type microalgae cultivation device comprising a cultivation pond containing contaminated water or any nutrient solution containing nitrogen and phosphorus; a rotating shaft that can rotate inside the cultivation pond, circular discs, for cultivating microalgae, evenly distributed on the rotating shaft to be driven by the rotating shaft to be placed alternately in contaminated water or in the air; a microalgae collection mechanism;and a light source arranged on the rotating shaft to provide illumination for the growth of microalgae, being arranged on the outer surface or on the inside of the rotating shaft when a transparent material is used, wherein the rotating shaft comprises a cavity through which steam or hot water is introduced to heat the apparatus in order to regulate the temperature that allows the growth of microalgae.;

[0018] Another precedent that can be mentioned corresponds to the ALGADISK project aimed at a modular, scalable and automatic biofilm reactor for the production of algal biomass, which comprises a horizontally arranged axis with a series of vertical circular plates mounted with a porous substrate on which a biofilm grows, a motor connected to an axis to rotate the plates, an open reservoir of nutrient medium for each plate, where they are partially submerged, so that when the plates rotate, nutrients are extracted from the reservoirs, being diffused into the porous substrate due to gravity and capillarity, and aeration means connected to each reservoir.Based on the prior art disclosures, a packaged photobioreactor has been developed that features a particular configuration of its elements that allows for a high cell density of the biomass produced and a surface and volumetric productivity of the culture far superior to that of existing culture devices.

[0019] DESCRIPTION OF THE INVENTION

[0020] The invention relates to a device for cultivating microalgae based on cell adhesion with vertical rotating discs where the microalgae adhere and an arrangement of vertical illumination plates intercalated with said vertical rotating discs that allow increasing the density of microalgae cultures and increasing their surface and volumetric biomass productivity.

[0021] Another objective of the invention is to provide a packaged cultivation device that allows large quantities of microalgae to be produced in small surfaces that facilitate the harvesting of biomass with reduced energy consumption.

[0022] The proposed device for cultivating microalgae corresponds to a photobioreactor based on microalgae adhesion or bioadherence photobioreactor, formed by a body containing a culture medium; a plurality of rotating discs for the microbial adhesion cultivation of microalgae fixed to a horizontal rotation axis, said discs being arranged equidistant from each other and semi-submerged in the culture medium; gas-liquid diffusers for gas transfer and bubbling in the culture medium; humidity and temperature sensors to monitor the temperature of the culture medium and the environment and the humidity of the environment; lighting plates located between the discs and in the upper area of ​​the rotation axis; a low-consumption electric motor with a reduction group to provide slow and precise rotation of the rotation axis.

[0023] The plurality of rotating discs are made of a material that has an adhesive capacity suitable for the selected microalgae culture so as to promote biomass production.

[0024] In operation, the plurality of discs rotate, coming into contact with the culture medium when they pass through the lower part and taking said culture medium and receiving light at the appropriate intensity and wavelengths according to the microalgae in culture, which they need when they pass through the upper part, eliminating oxygen producing an exchange of CO2-0oxygen gases.

[0025] DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are included to provide a greater understanding of the invention and constitute part of this description and also illustrate a preferred embodiment of the invention, where it can be seen that:

[0027] Figure 1 shows the device for microalgae cultivation based on cell adhesion, according to an embodiment of the invention.

[0028] Figure 2 shows a cover of the device for cultivating microalgae, according to an embodiment of the invention.

[0029] Figure 3A shows the biomass generated for the microalga Spirulina subsalsa on device discs made of PMMA, glass, stainless steel, colorless PVC, PET, and recycled PET. Figure 3B shows the biomass generated for the microalga Chlorella vulgaris on device discs made of PMMA, glass, stainless steel, colorless PVC, PET, and recycled PET.

[0030] Figure 3C shows the biomass generated for the microalga Dunaliella tertiolecta on device discs made of PMMA, Glass, Stainless Steel, Colorless PVC, PET, recycled PET.

[0031] Figure 4A shows the attached biomass as a function of time for the microalga Spirulina subsalsa on PMMA discs.

[0032] Figure 4B shows the attached biomass as a function of time for the microalga Chlorella vulgaris on PMMA discs.

[0033] Figure 4C shows the attached biomass as a function of time for the microalga Dunaliella tertiolecta on glass discs.

[0034] Figure 5 shows the biomass generated in each of the discs of the device for the microalga Chlorella vulgaris using PMMA discs.

[0035] DETAILED DESCRIPTION OF THE INVENTION

[0036] The device (1 ) for the cultivation of microalgae that allows to increase the density of microalgae cultures and their superficial and volumetric biomass productivity, corresponds to a photobioreactor based on microalgae adhesion or bioadherence photobioreactor, comprising: a body (2) with an upper opening containing a culture medium (3); a plurality of rotating discs (4) as a support surface on which the microalgae cells (5) adhere, favoring their growth for the formation of a biofilm, said plurality of discs (4) being fixed to a horizontal rotation axis (6), which passes through the body (2), and arranged equidistant from each other, wherein the location of the rotation axis (6) inside the body (2) is such that said discs are semi-submerged in the culture medium (3); gas-liquid diffusers for gas transfer and bubbling in the culture medium (3);at least one humidity sensor and at least one temperature sensor for monitoring, respectively, the humidity and temperature of the gas phase inside the body (2) of the device (1); at least one temperature sensor for monitoring the temperature of the culture medium (3); an upper cover (7) in the upper opening of the body (2), for its closure, which prevents exposure of the culture medium (3) and microalgae cells (5) to the outside environment; an illumination plate (8) arranged between each pair of discs (4) of the plurality of discs (4), being located on the axis of rotation (6) and arranged in slots (71) in the cover (7) such that said illumination plates (8) are not in contact with the interior of the body (2); a low consumption electric motor with a reduction group to provide a slow and precise rotation of the axis of rotation (6);

[0037] In one embodiment, the axis of rotation rotates at a speed between 0.1 to 10 RPM.

[0038] In one embodiment, the body (2) is a parallelepiped-shaped container, where half of its volume is occupied by the culture medium (3). The body (2) comprises an inlet (21) that allows the entry of the culture medium (3) and an outlet to extract the culture medium. The culture medium (3) can correspond to a fixed volume inside the body (2), circulate continuously inside the body (2), maintaining a constant occupied volume.The culture medium (3) can be replaced after each production / harvest cycle or the device (1) may further comprise a system for reusing the culture medium (3) to reuse it each time the microalgae are harvested from the plurality of discs (4), comprising instant pasteurization means and devices for measuring pH, redox potential (Eh), nutrients and level to determine the state of the culture medium (3) to define and adjust the initial conditions of the culture medium (3) through the dilution of salts, nutrients, pH adjustment, filtration. By virtue of the culture state (3) obtained with the reuse system, it will also be possible to choose to define its discard and replacement.

[0039] The cover (7) comprises slots (71 ) that correspond to equidistant depressions that define depressions where the illumination plates (8) are placed. The distance between the slots (71 ) corresponds to the separation of the discs (4) such that each slot (71 ) is between a pair of discs (4). The slots (71 ) have an extension towards the interior of the body (2) such that their edge or bottom is near the top of the axis of rotation. In one embodiment, said edge or bottom of the slots (71 ) is approximately 1 mm from the top of the axis of rotation (6) such that the illumination plates (8) continue to continuously and directly illuminate the part of the discs (4) that is not submerged in the culture medium (3), such that the surface of the adhesion discs and the surface of the illumination plates are parallel.The arrangement and configuration of the lighting plates (8) ensures that the microalgae on the discs (4) receive the required artificial light directly and orthogonally in the portion that is not submerged in the culture medium (3), allowing to favor and increase the density of microalgae cultures and to increase their superficial and volumetric biomass productivity, with minimum energy consumption due to the close position and parallel configuration of the lighting plates (8) with respect to the discs (4). The cover (7) also comprises holes for the installation of instrumentation and sensors inside the body (2).

[0040] The body (2) and the cover (7) are made of a transparent or translucent material that allows the passage of sunlight or artificial light, and may be polymethyl methacrylate (PMMA).

[0041] The rotation axis (6) is supported on bearings arranged on opposite sides of the body (2) allowing its precise, stable rotation with minimal friction. In one embodiment, the rotation axis (6) comprises an internal stainless steel reinforcement and a 10 mm diameter PMMA mantle.

[0042] The plurality of rotating discs (4) can be manufactured in transparent, translucent or opaque materials such as PMMA, Polycarbonate PC, Polystyrene terephthalate PET, High or low density polyethylene HPDE or LPDE, Polypropylene PP, Lexan, stainless steel, glass or other smooth, rough or porous natural materials with an adhesion capacity for the cultivation of microalgae. In one embodiment, the plurality of rotating discs (4) are made of a material that has an adhesion capacity for the cultivation of microalgae that favors the production of biomass, it being investigated and evidenced that discs (4) manufactured PMMA favor the adhesion of microalgae cells (5) and their biomass productivity, in particular, of the microalga Chlorella vulgaris. In one embodiment, the discs (4) are removably fixed to the rotation axis (6).The discs (4) can be manufactured with microdesigns to generate a relief on their surface, to improve the adherence and thickness of the biofilm obtained.

[0043] Gas-liquid diffusers correspond to perforated devices for the transfer of gases and bubbling in the culture medium (3) to promote the mixing of the volume occupied by said culture medium (3) and the transfer of gases (elimination of O2 and incorporation of CO2). In one embodiment, the perforating devices correspond to microperforated diffuser hoses, arranged at the bottom of the body (2), being connected to an air pump.

[0044] For monitoring the operation of the device (1), the humidity and temperature sensors of the device (2) have remote data transmission capacity for online sending of the measurements taken to a suitable electronic device. In one embodiment, the device (1) also comprises sensors for monitoring pH, conductivity and nutrients (nitrogen and phosphorus) via samplers.

[0045] In one embodiment, the lighting plates (8) correspond to rectangular plates that are inserted into each slot (71) of the cover (7), comprising a plurality of LED lights (81) arranged horizontally, parallel and equidistant from each other along each rectangular plate, said LED lights (81) being adhered to the edges by means of fixing means (82). The LED lights (81) can be of the SMD LED type of wavelengths specific to microalgae to produce photosynthetic activity in them. The range varies for each type of microalgae, being between 400 and 700 nm, being classified as photosynthetically active radiation, known as PAR, for its acronym in English. This device has the capacity to use both a specific wavelength of light in the indicated range, a specific sub-range of light within the indicated range or a full range or spectrum of photosynthetically active light or PAR.In one embodiment, the lighting plates (8) are powered by a 12V DC power source. The lighting plates (8) may be connected to a fan (9) that constitutes an air ventilation cooling system for said lighting plates (8), forcing air circulation in the slots (71) of the cover (7), regulating the temperature.

[0046] The biomass produced is mechanically harvested, in each production cycle, with "Wiper Washer" type systems, detaching them from the discs (4), saving on centrifugation and drying, allowing the device (1 ) to continue functioning during the harvest. Alternatively, there is the possibility of maintaining the biofilm that forms on the discs (4) until it reaches a density such that the shear stresses due to gravity cause it to detach itself for a continuous harvest or before, by means of vibrations or mechanical pulses to the axis of rotation. In one embodiment, the production cycle of the device (1 ), that is, until the detachment or extraction of the biomass, is approximately 9 days, which corresponds to when the maximum amount of generated biomass is obtained.

[0047] EXPERIMENTAL RESULTS:

[0048] To test the operation of the developed device (1 ), tests and trials were carried out using different microalgae, in order to determine a relationship between the disc material and microalgae that allows optimizing biomass production. The device (1 ) implemented for the tests carried out presents the characteristics described previously, considering the following particular implementations:

[0049] Table 1: Characteristics of the device (1) implemented for carrying out tests and experiments.

[0050] For the tests carried out, the device (1) was operated using the microalgae Spirulina subsalsa, Chlorella vulgaris and Dunaliella tertiolecta, using discs made of PMMA, glass, stainless steel, PVC, PET and recycled PET.

[0051] A first experiment corresponds to testing the microalgae with discs of different materials to test their adherence, operating the device (1 ) for 14 days. For each microalga and each disc, the generated biomass is extracted, which is shown in figures 3A, 3B and 3C. For the microalgae Spirulina subsalsa and Chlorella vulgaris, it is obtained that the PMMA discs generate a greater amount of Biomass, being, respectively, 4.34 and 8.21 g dry / m 2 . For the microalga Dunaliella tertiolecta, the materials that generate the greatest biomass correspond to glass discs (4.80 g dry / m 2 ) and PMMA (4.03 g dry / m 2 ).

[0052] A second experiment consists of studying the adhesion over time, using discs made of the material with which the highest amount of biomass was obtained for each microalga in the first experiment, in particular, the microalga - disc material pairs considered were the following: Spirulina subsalsa - PMMA, Chlorella vulgaris - PMMA and Dunaliella tertiolecta - Glass. For this experiment, the device (1 ) was operated for 18 days. The results obtained are shown in Figures 4A, 4B and 4C. The microalgae Spirulina subsalsa and Chlorella vulgaris, studied on discs of the same material, show a similar behavior, showing an increasing adhered biomass up to a maximum obtained during day 9, and then decreasing in the following days due to a semi-detachment of the biomass.In the case of the microalga Dunaliella tertiolecta, where glass discs are used, the growth of attached biomass increases in a staggered manner, with partial semi-detachments observed approximately every 3 days. Based on the results obtained, a recommended production cycle of 9 days can be established to harvest the generated biomass and prevent unwanted detachment of the biofilm into the culture medium. Additionally, it is verified that the microalga Chlorella vulgaris records the highest value for attached biomass.

[0053] A third experiment consists of studying the reactor operation by quantifying the biomass generated on the surface of the discs, using the microalga for which the best performance in biomass production was obtained, so this experiment considered the use of the microalga Chlorella vulgaris with PMMA discs. For this experiment, the device (1) was operated for 14 days. The results obtained are shown in Figure 5. It is observed that the biomass adhered to each disc is similar, where it is obtained that the central disc (No. 3) has a slightly lower amount of adhered biomass than the rest of the discs.

[0054] Finally, design parameters of the proposed device (1) were quantified with respect to other film or biofilm photobioreactors on the market, as shown in Table 2, including:

[0055] • Productivity

[0056] Significant differences are obtained in productivity and degree of packing of adhesion surface by physical surface of photo bioreactor and the relation adhesion surface by volume of photo bioreactor, which would allow the device (1) to be designed with smaller dimensions than those used in the market.

[0057] Table 2: Device design parameters (1 ) and film or biofilm photobioreactors on the market.

Claims

CLAIMS 1. A device (1) based on adhesion for the cultivation of microalgae that allows to increase the density of microalgae cultures and their biomass productivity, CHARACTERIZED in that it comprises: a body (2) with an upper opening containing a culture medium (3), which occupies half of its volume; a plurality of rotating discs (4), made of PMMA, as a support surface on which the microalgae cells (5) adhere, favoring their growth for the formation of a biofilm, said plurality of discs (4) being fixed to a horizontal rotation axis (6), which passes through the body (2), and arranged equidistant from each other, wherein the location of the rotation axis (6) inside the body (2) is such that said discs are semi-submerged in the culture medium (3); gas-liquid diffusers for gas transfer and bubbling in the culture medium (3);at least one humidity sensor and at least one temperature sensor for monitoring, respectively, the humidity and temperature of the gas phase inside the body (2) of the device (1); at least one temperature sensor for monitoring the temperature of the culture medium (3); an upper cover (7) in the upper opening of the body (2), for closing it, which prevents exposure of the culture medium (3) and microalgae cells (5) to the outside environment; a lighting plate (8) arranged between each pair of discs (4) of the plurality of discs (4), being located on the axis of rotation (6) and arranged in slots (71) in the cover (7) such that said lighting plates (8) are not in contact with the interior of the body (2); and a low consumption electric motor with a reduction group to provide a slow and precise rotation of the axis of rotation (6), wherein the body (2) and the cover (7) are made of a transparent or translucent material that allows the passage of sunlight or artificial light.

2. The device (1) according to claim 1, CHARACTERIZED in that the cover (7) comprises slots (71) that correspond to equidistant depressions that define depressions where the lighting plates (8) are placed and holes for the installation of instrumentation and sensors inside the body (2).

3. The device (1 ) according to claims 1 or 2, CHARACTERIZED in that the lighting plates (8) correspond to rectangular plates that are inserted into each slot (71 ) of the cover (7), comprising a plurality of LED lights (81 ) arranged equidistantly from each other along each rectangular plate, said LED lights (81 ) being adhered to the edges by means of fixing means (82).

4. The device (1) according to claim 3, CHARACTERIZED in that the LED lights (81) can be of the SMD LED type of wavelengths that produce photosynthetic activity in the microalgae.

5. The device (1) according to claim 4, CHARACTERIZED in that the LED lights (81) of the SMD LED type have wavelengths between 400 to 700 nm.

6. The device (1) according to claims 1 to 5, CHARACTERIZED in that the lighting plates (8) can be connected to a fan (9) constituting an air ventilation cooling system for said lighting plates (8), forcing air circulation in the slots (71) of the cover (7), regulating the temperature.

7. The device (1) according to claims 1 to 6, CHARACTERIZED in that the plurality of rotating discs (4) can be manufactured in transparent, translucent or opaque materials such as PMMA, Polycarbonate PC, Polystyrene terephthalate PET, High or low density polyethylene HPDE or LPDE, Polypropylene PP, Lexan, stainless steel, glass or other smooth, rough or porous natural materials with an adhesion capacity for the cultivation of microalgae.

8. The device (1) according to claims 1 to 7, CHARACTERIZED in that the plurality of rotating discs (4) rotate at a speed between 0.1 to 10 RPM.

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