METHOD AND DEVICE FOR THE PRODUCTION OF MICROALGAE BIOMASS

Abstract

The invention relates to the production of microalgae biomass. The microalgae contained in a suspension of water and microalgae are continuously phototrophically or mixotrophically cultivated in a cultivation module (1), which is passed multiple times by the suspension and has a gas part and a liquid part with a liquid supply (3), by supplying light from at least one artificial light source (5) and nutrients. According to the turbidity established by sensors, volume fractions of the suspension are repeatedly discharged from the cultivation module (1) for the harvest of microalgae and removed by means of a centrifuge (7). The cultivation of the microalgae occurs in an climate chamber forming the cultivation module (1), which is operated using water. Alongside a regulating of the temperature of the suspension, there also occurs a regulating of its pH value via the controlled addition of buffer ions and a regulating of the redox potential of the suspension and thereby also of its microbial contamination by controlling the light and nutrient supply, as well of a metered addition of oxygen. In addition, after the removal of microalgae, the remaining suspension is irradiated with UV light in order to kill unwanted microbial contamination before being returned into the cultivation module (1).

Claims

1. A process for producing microalgae biomass, in which microalgae contained in a suspension of water and microalgae are phototrophically or mixotrophically cultivated in a continuous circulation in a cultivation module through which the suspension passes multiple times and which comprises a gas portion and a liquid portion having a liquid reservoir with supply of light from at least one artificial light source, which light evenly floods the entire gas portion of the cultivation module, and of nutrients, wherein volume fractions of the suspension are repeatedly discharged from the cultivation module for harvesting of microalgae and centrifuged by means of a centrifuge and the suspension remaining after centrifugation is supplied back to the cultivation module, characterized in that volume fractions of the suspension are discharged for harvesting of microalgae whenever the turbidity of the suspension, as established by means of optical sensors, exceeds a minimum value, and in that the microalgae are cultivated in a climatic chamber which forms the cultivation module and which is operated in a water-economical manner by not only regulating the temperature of the suspension, but also regulating the pH thereof by means of controlled addition of buffer ions and regulating the redox potential of the suspension and hence the microbial contamination thereof by means of control of the supply of light and nutrients and of metered addition of oxygen, and by irradiating the suspension remaining after centrifuging out the microalgae, before it is recycled into the cultivation module, with UV light to kill undesirable microbial contamination until a minimum redox potential measured in the suspension is reached.

2. The process as claimed in claim 1, characterized by the process steps which are passed through multiple times: a) spraying volume fractions of the suspension, which volume fractions contain microalgae to be cultivated and are taken from the liquid reservoir of the liquid portion, in the upper region of the gas portion of the cultivation module into which nutrients, including at least CO.sub.2 as gaseous nutrient, are introduced, b) retarding the gravitational downward movement of droplets of the suspension that arise upon spraying and contain the microalgae, by means of suitable structural elements arranged for this purpose in the gas portion of the cultivation module, c) exposing the microalgae contained in the droplets retarded in their downward movement to the light from LED light sources arranged in the gas portion of the cultivation module, which light is tailored to the species of the microalgae to be cultivated with respect to the wavelength thereof and the intensity thereof, and to the introduced CO.sub.2, d) recycling downwardly moving, microalgae-containing droplets into the liquid reservoir formed at the bottom of or in a container below the gas portion of the cultivation module after passage through the gas portion of the cultivation module, e) discharging volume fractions of suspension recycled for respraying in the gas portion of the cultivation module from the liquid reservoir and harvesting microalgae contained in the discharged volume fractions by centrifugation in a centrifuge if the turbidity of the volume fractions of the suspension that are supplied back to the gas portion of the cultivation module for respraying as per process step a), which turbidity is established by means of optical sensors, exceeds a minimum value, and also recycling the suspension remaining after centrifugation of the discharged volume fractions into the cultivation module after irradiation with UV light, wherein the pH of the suspension in the liquid portion is measured and is regulated by controlled metered addition of buffer ions and is thereby kept within a pH range between 7 and 8, preferably between 7 and 7.5, that promotes the growth of the microalgae, the microbial contamination of the suspension is regulated through monitoring of the redox potential thereof by increasing the supply of nutrients and the light intensity of the LED light sources if the redox potential exceeds an upper limit and reducing the supply of nutrients and the light intensity of the LED light sources and also increasing the metered addition of oxygen that takes place in the liquid portion of the cultivation module if the redox potential falls below a lower limit, wherein the light intensity of the LED light sources is additionally controlled depending on the turbidity of the suspension, which turbidity is determined as per process step e), such that it is adjusted proportionally to the turbidity.

3. The process as claimed in claim 2, characterized in that the surface temperature of the LED light sources arranged in the gas portion of the cultivation module is used for temperature control of the suspension, which surface temperature is regulated by reducing or increasing the volumetric flow rate of a cooling medium used for cooling of the LED light sources.

4. The process as claimed in claim 1, characterized in that calcium ions and/or magnesium ions are metered in as buffer ions for the carbonic acid equilibrium for regulation of the pH of the suspension in the liquid portion of the cultivation module.

5. The process as claimed in claim 1, characterized in that nitrogen, phosphorus and carbon are supplied as nutrients to the suspension in the liquid portion of the cultivation module.

6. The process as claimed in claim 1, characterized in that secondary ingredients are formed or enriched in the microalgae by supplying in a controlled quantity to the suspension in the liquid portion of the cultivation module substances or groups of substances that belong to at least one of the following categories: nutrients and microbiological contamination for formation of vitamins, nutrients for formation of omega-3 fatty acids, nutrients for formation of bioactive proteins/peptides, minerals to be bound by the microalgae, zinc or iron to be bound by the microalgae.

7. The process as claimed in claim 1, characterized in that volume fractions of the suspension in the order of magnitude of 15% to 50% of the volume of suspension present in the liquid portion of the cultivation module are discharged from the cultivation module if the minimum value defined for the turbidity of the suspension is exceeded.

8. An installation for production of microalgae biomass, wherein the installation comprises at least at least one cultivation module for phototrophic or mixotrophic cultivation of microalgae contained in a suspension with water, consisting of a gas portion and a liquid portion having a liquid reservoir and having at least one nozzle arranged in an upper region of the gas portion as application element for suspension, having at least one light source for emission of artificial light tailored to the species of the microalgae to be cultivated with respect to the wavelength thereof and the intensity thereof, which light source is arranged in the gas portion, and also having structural elements arranged in the gas portion for retardation of the gravitational downward movement of droplets that arise upon spraying the suspension, inlets and application elements for introduction of CO.sub.2, other nutrients and oxygen into the at least one cultivation module, at least one centrifuge for centrifugation of microalgae out of volume fractions of the suspension that are discharged from the at least one cultivation module and supplied to the centrifuge for the purpose of harvesting of the microalgae, a piping system having pumps for movement of the suspension between the aforementioned components and for supply of substances to be introduced, including nutrients and volume fractions of the suspension, into the cultivation module via the respective application elements, a control device for control of the at least one centrifuge and of the aforementioned pumps and application elements in accordance with the results of the evaluation of different sensor signals received from sensors which are arranged in the components of the installation and are operatively connected to the controller, characterized in that the at least one cultivation module is designed as a climatic chamber which is operated in a water-economical manner by not only regulating the temperature of the suspension by means of the control device on the basis of sensor signals of the sensors arranged in the at least one cultivation module, but also regulating the pH of the suspension by means of controlled addition of buffer ions into the liquid portion of the at least one cultivation module and regulating the redox potential of the suspension, which redox potential is measured repeatedly by means of sensors, by means of control device-controlled supply of the CO.sub.2, the other nutrients and oxygen into the at least one cultivation module and a control of the light intensity in the gas portion of the at least one cultivation module, and by irradiating suspension which remains upon centrifugation of the microalgae out of discharged volume fractions and which is resupplied to the at least one cultivation module, before it is reintroduced into the at least one cultivation module, with UV light in a controlled manner by means of the control device to kill undesirable microbial contamination until a minimum redox potential measured by sensor in the suspension to be recycled is reached.

9. The installation as claimed in claim 8, characterized in that the gas portion of the at least one cultivation module has reflective walls which are mirrored or high-gloss reflective on their inner surface.

10. The installation as claimed in claim 9, characterized in that the side walls and the ceiling of the gas portion of the at least one cultivation module are fully mirrored or fully high-gloss reflective on their inner surface.

11. The installation as claimed in claim 8, characterized in that the at least one light source arranged in the gas portion of the at least one cultivation module simultaneously acts as heating for temperature control of the suspension in said at least one cultivation module, wherein the waste heat caused by the surface temperature of said at least one light source is controlled by the control device by means of control of the volumetric flow rate of a liquid cooling medium used for active cooling of the at least one light source.

12. The installation as claimed in claim 8, characterized in that the at least one cultivation module has arranged on the side walls or on the side walls and the ceiling of the gas portion thereof one or more light strips composed of LEDs as light sources.

13. The installation as claimed in claim 8, characterized in that the structural elements for retardation of the downward movement of the droplets formed by spraying of the suspension, which structural elements are arranged in the gas portion of the at least one cultivation module, are horizontally arranged, tautly stretched planar elements composed of a textile nonwoven or of a textile fine-meshed mesh.

14. The installation as claimed in claim 8, characterized in that the installation comprises a plurality of cultivation modules which each comprise a gas portion and a liquid portion having a liquid reservoir, wherein a centrifuge for centrifugation of volume fractions of the suspension discharged for harvesting of microalgae is jointly assigned to multiple or all cultivation modules.

15. The installation as claimed in claim 14, characterized in that it comprises up to 40 cultivation modules having a base area of at least 250 m.sup.2 in each case.

Description

[0057] Some aspects of the invention shall be more particularly elucidated once again in what follows with reference to FIG. 1.

[0058] FIG. 1 shows, by way of example, a possible embodiment of a cultivation module of the installation according to the invention, including a centrifuge coupled thereto. The cultivation module forms a central component or the central component of the installation according to the invention for production of microalgae biomass, which component is ultimately also the focus of the invention, and so many other components of the installation (e.g., controller[s] and the like) are not depicted. Depending on the design of an installation configured according to the invention, it can comprise a relatively large number of such cultivation modules. In such a case, a plurality of said cultivation modules work together with one centrifuge (not depicted here) used for harvesting of the microalgae by centrifugation out of the suspension. In very large facilities, multiple centrifuges can optionally also be present, though typically not each cultivation module is separately assigned one centrifuge, but rather each of the centrifuges will work together with multiple cultivation modules.

[0059] The cultivation module 1 which is shown by way of example in FIG. 1 and which, as mentioned, may be present more than once in an installation designed according to the invention consists of the gas portion 2 and the liquid portion comprising a liquid reservoir 3 for accommodation of a supply of suspension consisting of water and the microalgae to be cultivated. As can be seen from FIG. 1, the liquid reservoir 3 is arranged at the bottom of the gas portion 2 of the cultivation module 1. In a process or cycle that is continuous apart from any changeover times, volume fractions of the suspension are fed from the liquid reservoir 3 to the gas portion 2 of the cultivation module 1 designed as a climatic chamber operated in a water-economical manner. This is done with the aid of the pump(s) 9 via pipes of a piping system, which pipes belong to the liquid portion of the cultivation module 1.

[0060] The suspension fed to the climatic chamber, i.e., to the cultivation module 1 climate-controlled in a water-economical mode of operation, is applied by spraying in the upper region of the gas portion 2—i.e., preferably directly below the ceiling—with the aid of multiple nozzles 4. Arranged in the gas portion 2 of the cultivation module 1 are multiple LED light sources 5—here, in the form of one or more light strips installed on the ceiling and the walls of the gas portion 2 of the cultivation module 1—which are controllable with regard to the wavelength and the intensity of the light emitted thereby. In addition, the cultivation module 1 has inlets for supply of nutrients, including CO.sub.2 as gaseous nutrient, and oxygen for the microalgae cultivated therein.

[0061] The volume fractions of the suspension that are sprayed in the gas portion 2 of the cultivation module 1 via nozzles 4 form, as a result of the spraying, a mist (aerosol) of droplets each containing microalgae. The droplets gradually move to the bottom of the gas portion 2 of the cultivation module 1 while they are floating, the gas portion 2 also having arranged therein structures 6 which are formed by textile meshes or textile nonwovens and which retard the gravitational downward movement of the droplets. The purpose of this measure is to prolong the residence time of the volume fractions of the suspension sprayed in the cultivation module 1, i.e., the droplets containing the microalgae, in the gas portion, so that they are exposed to the artificial light of the LED light sources 5 and to the CO.sub.2 introduced into the cultivation module 1 for as long as possible to promote algae growth and algae proliferation.

[0062] The suspension accumulating at the bottom of the gas portion 2 of the cultivation module 1 as a result of droplets admitted to the liquid reservoir 3 is refed from here to the gas portion 2 of the cultivation module 1. As the suspension circulates multiple times in this circuit, the turbidity of the suspension gradually increases owing to algae growth. The turbidity of the suspension repeatedly fed to the gas portion 2 of the cultivation module 1 is constantly determined by means of optical sensors 8 arranged in the pipelines. To this end, the installation according to the invention comprises a control device (not shown) operatively connected to the aforementioned sensors 8 and to further sensors.

[0063] The control device can be a central control unit or one due to multiple control units arranged in a decentralized manner and jointly forming the control device. Moreover, the control device is operatively connected to multiple actuators controlled thereby, such as application elements (these include the nozzles 4 in the gas portion 2 of the cultivation module 1) and controllable valves, in accordance with the results of the evaluation of sensor signals received from the sensors 8. If the turbidity of the volume fractions of the suspension repeatedly supplied to the gas portion 2 of the cultivation module 1 exceeds a minimum value defined in the control device by appropriate configuration, the control device causes a portion (volume fraction) of the suspension present in the liquid portion at that moment to be discharged from the cultivation module 1 and to be fed to the centrifuge 7.

[0064] In the centrifuge 7, the microalgae contained in the discharged volume fractions of the suspension are centrifuged out and supplied to subsequent processing operations which may no longer be carried out in the installation considered here. The suspension which remains upon centrifugation of the volume fractions discharged from the cultivation module 1 and which very predominantly consists of water is recycled back into the cultivation module 1, though it is treated beforehand by irradiation with UV light to eliminate microbial contamination. The latter takes place in a section of the pipe connection via which these volume fractions of the suspension predominantly consisting of water are resupplied to the cultivation module 1. In the pipe section equipped with an appropriate UV light source (not shown here), the residence time of the suspension remaining after centrifugation of the volume fractions discharged from the cultivation module 1 depends on the time required to kill any microbial contamination, with the suspension remaining in the region of UV light input until a minimum redox potential is reached, which redox potential is established by means of sensors (electrodes) (likewise not shown) within the pipe section between the output of the centrifuge 7 and the cultivation module 1.

[0065] To realize the water-economical mode of operation of the climatic chamber forming the cultivation module 1, yet further sensors 8 are arranged at least in the liquid portion of said climatic chamber, which sensors 8 are operatively connected to the control device (not shown). These are at least sensors 8—for example in the form of silver chloride electrodes—for determination of the pH of the suspension and sensors 8—likewise specific electrodes—for determination of the redox potential of the suspension. It is in accordance with the result from the continuous measurement of the pH of the suspension that the control device controls a metered addition of buffer ions, namely calcium ions and/or magnesium ions, by actuation of corresponding application elements (likewise not shown here in detail) arranged for this purpose in the liquid portion of the cultivation module 1.

[0066] The redox potential of the suspension is regulated in a controlled manner by means of the control device, in that, in the event of the redox potential falling below 100 mV, the supply of nutrients (nutrients introduced into the liquid portion and the gaseous nutrient CO.sub.2 ultimately applied in the gas portion 2 of the cultivation module 1) is stopped and the intensity of the light emitted by the LED light sources 5 in the gas portion 2 of the cultivation module 1 is reduced, with the input of oxygen being increased at the same time by actuation of corresponding application elements in the liquid zone. If the event of an excessively high redox potential, namely a redox potential of more than 300 mV, the light intensity in the gas portion 2 of the cultivation module 1 is increased and the input of nutrients, namely the CO.sub.2 introduced into the cultivation module 1 and other nutrients introduced, is increased.

[0067] In order to bring about a substantially constant input of energy throughout the cultivation cycle in the form of the light emitted by the LED light sources 5, the light intensity in the gas portion 2 of the cultivation module 1 is also increased as the turbidity of the suspension increases, which turbidity is established by sensor in the liquid portion of the cultivation module 1. To support the temperature control of the suspension, the controller, on the basis of the temperature of the suspension ascertained by means of at least one temperature sensor in the liquid portion of the cultivation module 1, can control the volumetric flow rate of a cooling medium conducted through active cooling elements for the LED light sources 5 and thereby control the surface temperature of the LED light sources 5 emitting not only light but also heat (as a by-product in a sense) into the cultivation module 1, it optionally also being possible for the temperature control of the suspension to be effected exclusively on the basis of such control.