DE102011002763A1 - Photobioreactor with illumination by means of light fittings - Google Patents

Abstract

The invention relates to a photobioreactor with lighting by means of molded luminous parts which are arranged in the interior of the photobioreactor, in the interior of which the cultivation medium is mixed, the luminous molded parts being arranged at a distance from one another and at a distance from at least one of the walls of the photobioreactor. characterized in that the surface / volume ratio O / V of the surface of the illuminated molded parts to the volume of the cultivation medium O / V is> 10 m2 / m3 and when the photobioreactor is in operation, a mixing quality of> 95% after a mixing time of 20 to 200 s is set.

Description

The invention relates to photobioreactors with illumination by means of luminous moldings in the form of LED moldings or light-conducting moldings.

Phototrophic microorganisms, for example microalgae such as Spirulina, or Chlorella, are able, with the aid of light energy, convert it into biomass in the presence of appropriate nutrient elements, CO ₂ and water. Instead of gaseous CO ₂ , it is also possible to use organic or inorganic carbon sources in nutrient media as carbon source. An overview of common closed cultivation technologies Eriksen NT, Biotechnol. Lett., Vol. 30, No. 9, 1525-1536 (2008) , Algal biomass can be used, for example, for the production of valuable substances or active substances, for example pharmaceuticals.

The economic cultivation of phototrophic microorganisms on an industrial scale has not yet been solved due to the problems of the light supply, the monoseptic culture and the scale-up. A universal standard system for the cultivation of phototrophic microorganisms on a large scale is not available until now. Of tens of thousands of phototrophic microorganisms, only a few dozen are currently cultivated in larger quantities, mostly in open, non-contaminated systems. The cultivation conditions of phototrophic microorganisms, which are processed on a pilot scale in closed reactors, can not be kept constant until now over a longer period of time. Problems arise here, especially with regard to the optimal light supply, and the susceptibility to contamination of conventional systems. In addition, the flow conditions in the reactor are adversely affected by additional fixtures such as lighting elements.

From the WO 92/00380 A1 For example, a closed photobioreactor of cubic or cylindrical shape is known. The illumination of the reactor is carried out by means of LEDs, transparent, light-emitting bodies made of acrylic, glass or other transparent materials. In the photobioreactors, these luminous bodies are arranged at a distance from each other and alternately attached to the lid or bottom of the reactor. The filament moldings are shorter than the reactor length, so that between the free ends of the filament and the bottom or lid of the reactor each room remains for the flow of the reactor medium. The disadvantage here is the uneven illumination and uneven material distribution.

A similar arrangement is in the WO 2009/069967 described. In a cubic reactor, plates populated with LEDs are used as light sources. The plates are alternately attached to the lid or bottom of the reactor at a distance from each other. Again, the flow of the medium is ensured by the fact that the length of the plates is shorter in each case than the distance from bottom to top. Unsatisfactory here is the uneven material distribution in the culture medium, in particular the increasing concentration gradient for the photosynthetically formed oxygen between the inlet and outlet of the reactor.

In the utility model DE 298 19 259 U1 a cylindrical photobioreactor is described, the illumination of which takes place with a cylindrical lighting body with a ring light segment, which is arranged at a distance from the walls of the reactor. As the materials for the luminaire glass for the lighting fixture, and silicone, casting resin or glass fiber for the ring light segment are specified.

The DE 10 2005 012 515 B4 describes a lighting device for a photobioreactor, which is composed of a plurality of LEDs on a flat illumination carrier to a lighting matrix. This illumination matrix can be attached to the jacket of the bioreactor. The disadvantage here is the uneven illumination of the culture medium.

In the WO 2007/047805 describes a method for CO ₂ degradation in a photobioreactor system equipped with LEDs, which is charged with an aqueous algae culture and CO ₂ -containing exhaust gas. The photobioreactor system is equipped with a large number of reactor compartments, with transparent lid and bottom part, in which LED strips are embedded. The disadvantage here is the completely inadequate substance distribution.

The WO 2008/145719 describes photobioreactors with LED plastic moldings, in particular LED silicone moldings, for illuminating the reactor. These LED plastic moldings are used as tubes, hoses or plates and are spaced inside the reactor. Luminaire silicone moldings, in particular for the illumination of bioreactors are from the WO 2008/145718 A1 known. A uniform illumination and uniform distribution of the components in the culture medium is not discussed here.

In the DE 44 16 069 A1 A method for illuminating media for culturing phototrophic organisms by means of light guides is described. The light source is external, ie the Light source with which the light is coupled into the optical waveguide is positioned outside the reactor. This results in problems regarding the bundling of the light on a relatively small area for coupling into the light guide; and concomitantly a high heat load at the coupling points. The scalability is very difficult or not given.

The invention had the object of providing a closed photobioreactor for the production of phototrophic microorganisms in a constant and reproducible product quality available.

The invention relates to a photobioreactor with illumination by means of luminous molded parts, which are arranged in the interior of the photobioreactor, in the interior of which the culture medium is mixed, wherein the luminous moldings are arranged at a distance from each other and at a distance to at least one of the walls of the photobioreactor, characterized in that the surface / volume ratio O / V of the surface of the luminous moldings to the volume of the culture medium O / V> 10 m ² / m ³ and the operation of the photobioreactor a mixing quality of> 95% after a mixing time of 20 is set to 200 s.

Suitable photobioreactors are made with a pressure-bearing, possibly temperature-resistant jacket, for example made of steel, stainless steel, plastic or enamel, or ceramic. Transparent and non-transparent materials can be used; non-transparent materials are preferred in the case of closed reactors. Preferably, the photobioreactor is equipped with an antifouling silicone coating as in the DE 10 2009 028338 is recommended, and the details of which are intended to be part of this application and are hereby incorporated by reference. Particularly preferred are reactors made of electropolished stainless steel, since this material only a small fouling occurs and the cleaning is facilitated by appropriate standard devices.

The reactor volumes can be chosen arbitrarily. Due to the pressure-bearing materials, in contrast to reactors, which are made of glass, a high, space-saving design for mass production is possible. Next can be carried out at elevated pressure, preferably in a range of 0.1 to 5 bar overpressure.

The photobioreactor is preferably equipped for filling and nutrient supply with feed lines and for product separation and discharge with discharges. For a continuous procedure, it may be advisable to equip it with an external loop in which phase separation devices or modules for dialysis, reverse osmosis and micro- or nanofiltration are arranged. For heat removal and heating, the photobioreactor can optionally be equipped with a double jacket, half-pipe coils on the reactor walls or internal heat exchangers. Furthermore, the reactor may still contain agitators and pumps for mixing. Preferably, the mixing is carried out by gassing with the feed gas analogously in a bubble column according to the airlift principle, without additional mechanical energy. Preferably, the photobioreactor is equipped with a steam sterilization unit.

For lighting, luminous moldings which contain one or more LED filaments, or a light-conducting material (light guide), enclosed in one or more transparent matrices, are used, or moldings which consist of light-conducting materials (light guides) are used.

Suitable materials for the matrix of luminous moldings are transparent materials, for example made of glass or of thermoplastic or thermosetting plastics such as acrylic glass, polyethylene, polypropylene, PVC, polyamides, polyesters such as PET. Preferred are silicones. Suitable silicones are in the WO 2008/145719 A1 whose disclosures are intended to be part of this application and are hereby incorporated by reference. Transparent materials are those in which the transmission in the range of a wavelength of 400-700 nm is> 50%. Particularly preferred is a transmission of> 80% in this wavelength range.

Suitable LED filaments are radiation-emitting semiconductor components of organic (OLED) or inorganic semiconductors, so-called LEDs. The LEDs may be already encapsulated with plastic diodes or unencapsulated diodes. The LEDs can radiate in the infrared range, in the visible range or in the UV range. The choice depends on the intended applications. For photosynthesis in photobioreactors, LEDs are preferred which emit in the visible range, in particular red light. The embedded in the transparent molded body LEDs can emit at the same wavelength. However, LEDs with different radiation characteristics can also be combined with one another. In general, a plurality of LEDs are conductively connected to one another in the LED molded part, connected in series and / or in parallel. The LED array may be connected to sensors as well as to measurement / control devices. The LED luminaires can be continuous or pulsed operate. The number of LEDs and their arrangement depends on their application.

Suitable light-conducting materials are optical fibers of a transparent material, usually glass or plastic. Examples of light guides are optical waveguides, glass fibers, polymeric optical fibers or other light-conducting components made of plastic and fiber optic components. Also suitable are phosphorescent light guides, which can store light for many hours, and can absorb the daytime sunlight during the night. The light guides are equipped so that the light is emitted evenly over the entire extent of the light guide. Optionally, the optical fibers may be equipped with a lens, such as a Fresnel lens, to focus and amplify the light prior to being introduced into the optical fiber.

In the light guides, those based on thermoplastic silicone elastomers (TPSE) are preferred. Thermoplastic silicone elastomers contain an organopolymer moiety, for example polyurethane or polyvinyl ester, and a silicone moiety, mostly based on polydialkylsiloxane-based of the abovementioned specification. Suitable thermoplastic silicone elastomers are commercially available, for example the corresponding Geniomer ^R types from Wacker Chemie.

In general, the luminous moldings are equipped with LEDs or equipped with light guides in such a way that the luminous moldings have a surface irradiance of 1 to 5 × 10 ⁴ .mu.mol photons / m ² / s. In continuous operation, the surface irradiance is preferably 1 to <1 x 10 ³ μmol photons / m ² / s. In pulsed mode, the surface irradiance may also be preferably 10 to 5 × 10 ⁴ μmol photons / m ² / s, more preferably 1 × 10 ³ to 5 × 10 ⁴ μmol photons / m ² / s. In the case of luminous molded parts equipped with LEDs, it is preferred that the LEDs be distributed as uniformly as possible over the entire surface of the molded part.

The above areas for the surface irradiance can be achieved by using luminous moldings having a surface irradiance within said ranges, or also obtained by combining luminous moldings which partly have a surface irradiance outside of said ranges, but on average the given values for the surface irradiance.

The arrangement of the luminous molded parts is designed so that a uniform illumination due to a high surface-to-volume ratio (O / V) is ensured with respect to the irradiation, ensuring a stirred tank characteristic with complete backmixing and low mixing times. This ensures effective heat exchange, effective gas exchange and homogeneous reaction conditions and prevents gradients in terms of relevant process parameters. As a prerequisite, this is particularly relevant for ensuring high and special metabolic performances that are very sensitive to the environmental conditions. One example is the production of secondary metabolites. In addition to the light supply, relevant process parameters are, for example, pH value, nutrient concentrations, partial pressure of oxygen and temperature.

The surface / volume ratio O / V, that is, the ratio of the surface O of the luminous moldings to the volume V of the culture medium is generally O / V ≥ 10 m ² / m ³ , preferably, the O / V is from 10 to 100 m ² / m ³ , in particular from 30 to 80 m ² / m ³ . Under the surface O is the part of the total surface of an LED molded part to understand, which is covered with LEDs. For example, in the case of a cylindrical LED molded part, which is only covered on the outside of the cylinder with one or many LEDs, only the surface of the outside surface O. When using light-conducting materials, the surface O is defined so that this surface includes over which the light guide emits light. The volume V of the culture medium is to be understood as the volume which is taken up by the culture medium in the reactor.

The luminescent shaped parts are preferably arranged such that a volumetric irradiation intensity of 1 × 10 ² to 5 × 10 ⁵ μmol photons / m ³ / s results via the reactor volume filled with the culture medium, preferably 5 × 10 ³ to 5 × 10 ⁴ μmol photons / m ³ / s.

It is also essential for the photobioreactor that during operation a stirred tank characteristic is maintained, which is achieved by the corresponding arrangement of the luminous moldings. Rührkesselcharakteristik means procedurally a thorough mixing of the culture medium over the entire filled reactor space. Rührkesselcharakteristik means in the case of the present invention, a mixing grade of ≥ 95 The mixing quality is to be obtained within a mixing time of 20 to 200 s.

The statistical parameter mixing quality is used to characterize the mixing state. It allows a quantitative statement of the complete mixing process resulting from diffusive and convective mass transfer. At a Deviation of 5 from the final value of the concentration is the mixing quality 95%, that is, when measuring the concentration of the mixture, in any volume fraction of the mixture, the final value of the concentration is reached with a deviation of + 5%. The mixing quality can be determined in a manner known to the person skilled in the art, for example using the marking method used in the example.

Mixing time refers to the time required to completely mix a trace substance fed to the reaction mass. The state of ideal homogeneity of a mixture occurs after the addition of the miscible substance only after an infinite time. Therefore, in practice, the mixing time is defined as the time to reach a maximum deviation of + 5% from the end value of the concentration measurement, ie a mixing grade of> 95%, for the miscible substance.

The luminous moldings are mounted freely in volume and without extensive contact of the luminous moldings to the bottom or lid of the reaction vessel. For example, over existing suspension points on the reactor vessel side wall, which are in the case of using stirred tank fermenters, for example, tabs for the attachment of flow breakers.

The luminous moldings can also be attached by means of ropes or rods to the reactor wall, including the lid and bottom. The luminous moldings can also be located in special brackets that can be connected to said suspension points. Alternatively, a positioning of the luminous moldings can be carried out by simply placing the holders containing the luminous moldings in the reactor. The internals are not connected to the floor or lid in the way that a spatial separation arises. Rather, there is a cross-exchange of the culture medium over the reactor cross section.

The luminous moldings can have any desired shape. In general, the photobioreactors are cylindrical. The shape shape of the luminous molded parts is therefore preferably derived from the cylinder. The luminous moldings may accordingly have the shape of a cylinder or the shape of cylinder segments such as cylinder half-shell. Examples of the shape of the luminous moldings are also curved plate, rings or helix and also flat plate. Luminous moldings in the form of flat plates may be circular (disk-shaped) or also polygonal, such as triangle, quadrangle, hexagon, octagon, etc.

Also suitable are light-shaped bodies in the form of hollow bodies with polyhedral base.

It can also be plugged into each other several lighting moldings, preferably with gaps. For example, a plurality of cylindrical luminous moldings can be arranged concentrically with one another.

The photobioreactors according to the invention with illumination by means of luminous moldings are suitable for the cultivation of phototrophic microorganisms. Preferred for the cultivation of phototrophic microalgae.

The invention is in 1 and the examples 1 and 2 exemplified:

Fig. 1: LED moldings in Rührkesselfermenter

The photobioreactor unit is a stirred tank fermenter in the form of a reactor housing 1 and lids 2 and arranged in the reactor housing LED installation, which evenly illuminates the reactor interior, composed.

The LED installation includes the bracket 3a in which the individual LED moldings 3b are arranged. The LED moldings 3b are configured in a cylindrical shape, wherein the cylinders are arranged concentrically to each other and in height offset from each other and in the holder 3a are bordered. The holder 3a is at suitable suspension points 4 For example, tabs which are provided for the attachment of flow breakers and the circumference of the inner wall of the reactor vessel 1 are arranged, attached.

The circulation, mixing and suspension in the reactor housing 1 contained phototrophic cells via introduction and distribution of gas bubbles through the gassing 5 and optionally by a stirring element in the central axis 6 is arranged.

Example 1: Cultivation with demanding O / V ratio and irradiance

• (1) Höhe 350 mm, mittlerer Durchmesser 40 mm, 420 LED's
• (2) Höhe 350 mm, mittlerer Durchmesser 86 mm, 1020 LED's
• (3) Höhe 350 mm, mittlerer Durchmesser 132 mm, 1560 LED's
• (4) Höhe 350 mm, mittlerer Durchmesser 178 mm, 2160 LED's Damit resultierte eine Gesamtanzahl von 5160 LED's bei einem O/V von 39 m²/m³.

A reactor analogous to that in 1 was filled with an algal suspension volume of 24 l. Four LED moldings in the shape of cylinders were positioned inside the reactor. The 4 cylinders had the following geometric dimensions and the following number of LEDs:

• (1) height 350 mm, average diameter 40 mm, 420 LED's
• (2) height 350 mm, average diameter 86 mm, 1020 LED's
• (3) height 350 mm, average diameter 132 mm, 1560 LED's
• (4) height 350 mm, average diameter 178 mm, 2160 LED's This resulted in a total of 5160 LED's with an O / V of 39 m ² / m ³ .

The LED molded parts consisted of a stainless steel foil in the core, on which individual LED emitters of a wavelength of 620-625 nm and the power of 83 mW were arranged and interconnected / wired. The resulting LED boards were sealed with an epoxy resin layer and encapsulated by silicone potting. The installed total power was 430 W.

Measurement of irradiance at maximum load gave maximum values of 1 × 10 ³ to 2 × 10 ³ μE / m ² / s for the surface irradiance and correspondingly 42 × 10 ³ to 84 × 10 ³ μE / m ³ / s for the volumetric irradiance. The irradiation intensities could be reduced by dimming the LEDs.

Cultivation was carried out with the organism Porphyridium purpureum in artificial seawater medium (ASW medium) and a reaction volume of 22 l. The described LED molded parts (1) to (4) were arranged concentrically to each other in the reactor volume. The operation of the LEDs was pulsed at a frequency of 500 Hz with an effective power of 100W. The further reaction conditions were: a cultivation temperature of 25 ° C, a pH of 7, which was controlled by the supply of CO ₂ , a stirrer speed of 200 rpm (axial stirrer) and a gassing rate of 1 vvm (volume / volume / minute) , The cultivation was carried out in batch mode. This resulted in a maximum specific growth rate of 0.75 d ^-1 .

Example 2

Measurement of the flow characteristic in a reactor according to Example 1 (without culture medium)

On the basis of the measurement of the residence time, knowledge about the flow pattern and the backmixing in the 25 liter stirred tank fermenter were obtained. This was done by means of an impact marking with potassium chloride and subsequent measurement of the conductivity. The reactor was filled with 24 liters of H ₂ O. For impact marking, 10 ml of a 3 molar potassium chloride solution was used. This was introduced by means of a syringe between the outermost cylinder and vessel wall about 8 cm below the liquid level in the reactor. The conductivity was measured 10 cm below the liquid level in the central axis of the reactor by means of a conductivity probe. The solution was gassed from below via a ring. In addition, the reactor contents were mixed below the cylinder by means of a propeller stirrer.

The time evolution of the conductivity was recorded until a nearly constant value was reached, starting with the injection of the KCl solution. In order to assess the state of backmixing in the reactor, the time after injection was indicated, at which the conductivity did not deviate more than 5% from the constant value (complete backmixing). To influence the flow conditions in the reactor, the stirrer speed of 100-300 l / min and the gassing rate to 0.5 and 1 vvm (gas volume / liquid volume / minute) was varied.

The measurements were made with 3 different positions of the LED installation.

In one position, the cylinders were offset in shape so that the top of the innermost cylinder was 3 cm below the liquid surface and the top edges of the other two cylinders were 6.5 cm below the liquid surface.

In the second position, the upper edges of the innermost and second smallest cylinders were each 6.5 cm below the liquid surface and the upper edges of the other two cylinders were each 3 cm below the liquid surface.

In the third position, the upper edges of the four cylinders were each 3 cm below the liquid surface.

For all positions, the mixing quality of 95% in the settings for the gassing of 0, 0.5 and 1 vvm and for the stirrer speed of 0, 100, 200 300 revolutions per minute within a mixing time of 20-100 s was obtained.

Measurement of the illumination characteristic in Example 1:
The irradiation characteristic in the reactor interior with LED installation was made by measuring the photon flux density distributed at a representative number of points in the reactor volume and then averaged over the radiating surface, taking into account the O / V ratio or the reactor volume.

The photon flux density was measured in the area or spherically with the Universal Light Meter ULM-500 from Heinz Walz GmbH. The photon count of the photosynthetically active light in the range of 400-700 nm wavelengths was detected integrated.

With the inventive combination of defined surface / volume ratio and defined mixing quality for the arrangement of the luminous molded parts in the reactor, both the light and the components of the cultivation medium are distributed uniformly in the reactor.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 92/00380 A1 [0004]
• WO 2009/069967 [0005]
• DE 29819259 U1 [0006]
• DE 102005012515 B4 [0007]
• WO 2007/047805 [0008]
• WO 2008/145719 [0009]
• WO 2008/145718 A1 [0009]
• DE 4416069 A1 [0010]
• DE 102009028338 [0013]
• WO 2008/145719 A1 [0017]

Cited non-patent literature

• Eriksen NT, Biotechnol. Lett., Vol. 30, No. 9, 1525-1536 (2008) [0002]

Claims (9)

Photobioreactor with illumination by means of luminous moldings, which are arranged in the interior of the photobioreactor, in the interior of which the culture medium is mixed, wherein the luminous moldings are arranged at a distance from each other and at a distance from at least one of the walls of the photobioreactor, characterized in that the Surface / volume ratio O / V of the surface of the luminous moldings to the volume of the culture medium O / V> 10 m ² / m ³ and when mixing the photobioreactor, a mixing quality of> 95% after a mixing time of 20 to 200 s is set , Photobioreactor according to claim 1, characterized in that the luminous molded parts are LED molded parts, in which a plurality of LED filaments are enclosed in a transparent matrix. Photobioreactor according to claim 1, characterized in that the luminous molded parts are optical waveguide molded parts. Photobioreactor according to claim 1 to 3, characterized in that the luminous molded parts have a surface irradiance of 1 to 5 × 10 ⁴ .mu.mol photons / m ² / s. Photobioreactor according to claim 4, characterized in that in continuous operation with respect to the irradiation, the luminous-shaped parts have a surface irradiance of 1 to <1 × 10 ³ .mu.mol photons / m ² / s. Photobioreactor according to claim 4, characterized in that in pulsed operation with respect to the irradiation, the luminous-shaped parts have a surface irradiance of 10 to 5 × 10 ⁴ .mu.mol photons / m ² / s. Photobioreactor according to claim 1 to 6, characterized in that the luminous moldings are arranged so that a volumetric irradiance of 1 × 10 ² to 5 × 10 ⁵ μmol photons / m ³ / s results over the filled with the culture medium reactor volume. Use of photobioreactors according to claim 1 to 7 for the cultivation of phototrophic microorganisms. Use according to claim 8 for the cultivation of phototrophic microalgae.

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