PROCESS AND DEVICE FOR CULTIVATING MICROALGAE IN A CLOSED CIRCUIT

Abstract: A process for carrying out on an industrial level the cultivation of microalgae is implemented in a hydraulic closed circuit: by causing a liquid containing the algae to circulate; by keeping thetemperature of the liquid between two preset values; by introducing into the liquid the amounts of carbon dioxide and nutrients necessary for the algae's metabolism; by exposing the circulating liquid to the sun's rays in a specific transparent part of the closed circuit, so as to allow the algae to conduct chlorophyllic photosynthesis; by extracting the oxygen that is produced during the course of said process; by periodically separating from the circulating liquid the algae that are produced; finally, by extracting said algae from said hydraulic closed circuit.

Description: Process and Device for Cultivating Microalcrae in a Closed Circuit This invention relates to the field of biology, and particularly to the cultivation of microalgae for industrial purposes in order to extract from them substances that can be used for a wide variety of purposes. People have long been aware of, for example, the importance of some types of algae as food for humans, and these algae have been and are still being cultivated in open-air tanks that contain the substances in which the algae reproduce. Other kinds of algae are cultivated in a similar fashion in order to extract substances that have applications in the field of pharmaceuticals or that are used as fertilizer in agriculture, or as fodder for animals, and so on. Various species of microalgae are used for the purposes described above, and these are well known to the specialist in the field: of them, let us mention a few by way of example: anabaena, which contains fertilizer-type substances, dunaliella, which contains chemicals that can be used in the fields of chemistry and pharmaceuticals, chlorella and spirulina, which mainly contain substances with a high protein value, etc. The concentration of the active elements or of the desired substances in the organisms of the algae is very high, and in addition each alga contains numerous substances that are useful for a particular purpose. To give an idea of the importance of this phenomenon, we present below a more detailed description of the above-mentioned alga spirulina, but it should be noted that a similar description could also be given for other kinds or species of algae. Spirulina is a single cell of the planktoid type with the characteristic that protein comprises such a large portion of i composition that it is a preferred food for those who suffer fr endemic nutritional deficiencies and a source of active substances and protein for the pharmaceutical industry. The cultivation of this alga, even with extremely rudimentary means of production, has long been done in places where the environmental conditions make it possible to do so in the open air. The titer of protein, which is equal to 60-70%, is not the only property that the alga possesses. As a matter of fact, being a living phototropic cell, it also contains unsaturated fatty acids, vitamins (particularly B 12 , the high content of which, between 3 and 9 g/kg, cause it to be considered a sourc for vitamin extraction) , and dyes. Because of these characteristics of the alga, its exploitation is of interest to various industrial sectors for appropriate production, such as: - the food industry, particularly for the production of alternative food lines, without any dietary deficiency and with absolutely no cholesterol; - the pharmaceutical industry, which can, by hydrolysis, produce a vast array of amino acids, sterols, vitamins, and fat acids, as well as providing a food substitute for patients with severe or chronic illnesses, as nutrition to be given enterally or parenterally; - the dye industry, for use as feedstock for the production of natural vegetable dyes (green, blue, and orange) , in strict conformity with the applicable international regulations; - the fodder industry, with appropriate production, in view of the alga's high biological value, as artificial milk for calves, fish food, highly digestible foods for the early weaning of young animals, and in all cases where high breeding productivity is desired. The cultivation of any species of microalgae may, as is still being done today, be carried out in open-air tanks, as already mentioned, i.e., with a fairly high pH, provided, however, that the cultivation is done in regions that do not experience excessively high thermal excursions and have temperatures which, even in the winter months, do not drop so low as to block the growth and reproduction of the microalgae or directly lead to their death. The open-air tanks also carry the risk of intrusion by other types of algae or other anaerobic organisms that can develop in the culture, stealing nutrients and often impairing both the reproduction of the microalgae under cultivation and the composition and quantity of extractable substances. This latter problem, combined with the necessity of keeping the temperature of the culture liquid within a preset temperature range if the results of the culture itself are to be optimized in terms of quality and quantity, has caused the inventor of this invention to come up with a process and a device for implement said process that make it possible to cultivate industrial-typ microalgae with a yield, optimum in weight, of algae produced volume of culture liquid per unit of time. To accomplish this, the inventor has developed a process that is suitable for cultivating microalgae in a hydraulic clo circuit in which it is possible to constantly monitor the valu of the temperature of the culture liquid, as well as the other physico-chemical variables (for example, pH and the content of mineral salts) associated therewith that can affect the growth and reproduction of the algae. The process was developed taking into account the results the studies carried out by the Center for Microorganism Studie of the C.N.R. [Italian National Research Council] in Florence microalgae and, in particular, on the alga spirulina, and the object of the invention consists of a process for implementing industrially the cultivation of the microalgae; said process i characterized by the fact that said cultivation is carried out a hydraulic closed circuit: - y causing a liquid containing the algae to circulate; - by keeping the temperature of the liquid between two preset values; - by introducing into the liquid the amounts of carbon dioxide and nutrients necessary for the algae's metabolism; - by exposing the circulating liquid to the sun's rays in specific transparent part of the closed circuit, so as to allo the algae to carry out chlorophyllic photosynthesis; - by extracting the oxygen that is produced during the course of said process; - by periodically separating from the circulating liquid the algae that are produced; - finally, by extracting said algae from said hydraulic closed circuit. Another object of the invention is also a particular type of device that makes it possible for said process to be carried out. The attached figure shows only the outline of one possible embodiment of the device, which is intended to be neither restrictive nor limiting with regard to other embodiments that are based on the same concepts as are set forth in the attached claims. The above-described process is effectively carried out in the device shown, in which it is possible to cultivate any species of microalgae by appropriately varying, by means of the instruments described below, the maximum and minimum temperature values of the liquid, the kinds of mineral salts used as nutrients, the pH of the liquid, etc. The liquid that is generally used is simply water in which the concentration of microalgae by weight can generally range around 2-4%. In closed circuit 1 of the device, the liquid is circulated by a pump 2, for example a membrane pump, and flows through a heat exchanger 10 located in a cooling tower 8, which will be further described below. Thus, the passage of the liquid through said exchanger 10, which by its very nature has a considerable surface area for exchange with the ambient air, usually has the effect of reducing the temperature of the liquid to a certain extent, even if cooling tower 8 is not in operation; in the eve that this temperature is below a reference value (e.g., 25°C, i the case of the alga spirulina) , it is good for the liquid not circulate, for which reason said membrane pump 2 is equipped wi electronic controls 2a, 2c, which start it and keep it in operation only at times when the temperature of the liquid of t device exceeds said reference value. The temperature of the liquid may also reach elevated values, beyond the threshold of optimum physiological compatibility of the alga under cultivation (in the case of the alga spirulina: 35-37°C) . In this case the liquid that is discharged from said membrane pump 2 passes through exchanger 1 onto which spraying device 9 sprays more or less nebulized wate which, by evaporating, removes heat from the circulating liquid Said spraying device 9 is also equipped with a pump 9a which starts and remains in operation only when the temperature of th liquid, as sensed by a probe 9b, reaches a first value that is greater than the reference value of said membrane pump 2 (in th case of the alga spirulina, 36°C) . The process of evaporation the cooling water may also be accelerated by the action of the ventilation that is produced by an appropriate device 11, which is started and kept in operation as a function of the time duri which the temperature sensed from the circulating liquid exceed a preset second value which, in turn, is greater than said firs value (in the case of the alga spirulina, said second value is 37°C) . With the devices described up to this point, it is possible to precisely regulate the temperature of the circulating liquid, keeping it within a range of values (35-37°C for the alga spirulina) that are optimum for the biological cycle of the microalgae under cultivation. During the cold seasons, when the temperature of the circulating liquid has a tendency to drop below the preset boundary value, the inventor has made provision for supplying heat to it by causing it to circulate in another appropriate exchanger, which is not shown in the figure but which can readily be imagined and implemented according to the state of the art by a specialist in the field, or more simply by heating the water that is supplied by spraying device 9 in order to cause it to perform both a heating as well as a cooling function. The life cycle of the algae in question includes the well known process of chlorophyllic photosynthesis, during the course of which, as is known, there occur chemical reactions which, in simplified terms, involve a decrease in the amount of carbon dioxide and an increase in the amount of oxygen that are contained in the environment in which the algae live. This is an environment which, in the present case being a closed circuit 1 with no communication with the ambient air, requires that the necessary amount of carbon dioxide be continuously added when the alkalinity of the liquid increases and, in turn, the relative pH consequently rises above a preset threshold (e.g., 9-10 for the alga spirulina) . In the device that is adapted for implementing the process according to the invention, the gaseous carbon dioxide that is introduced into the circulating liquid comes from a pressurized tank 4, of a known type, and is delivered via an inlet valve 4a that is controlled by an electronic control device as a functio of the pH that is sensed by the latter control device by means an appropriate probe 6b. In order for said process of photosynthesis to be able to occur, as we know, it is necessary that the algae, like any oth plant organism, be exposed to the sun's rays for an appropriate length of time. In the device in question, this is accomplishe by means of a segment of circuit 3 that is composed of a batter of tubes or coils that are made of a material, synthetic or glass-like, which is transparent to the sun's rays. Into the tubes or coils are inserted sheets which are helical in shape and which, as they move, serve to ensure that the liquid containing the algae also follows a helical path, th exposing all of the algae to the sun's rays completely and uniformly. Owing to the development of the process of photosynthesis, as mentioned, the formation of oxygen takes place in closed circuit 1 of the device; said oxygen remains dissolved in the gaseous state in the circulating liquid and is therefore continuously extracted therefrom as it is formed. To accomplis this, the inventor has made provision for installing in said closed circuit 1 a holding tank 5 which has a large enough capacity to ensure that the liquid passes through it at a slow enough speed to allow the oxygen to be separated by flotation from the liquid that is carrying it, allowing it to float towar upper part 5a of tank 5, which is kept free of the liquid. From this area the oxygen is extracted by the action of an appropriate suction pump 6 that can generate a preset underpressure. The assembly consisting of pump 6 and holding tank 5 can then be defined as a deoxygenation unit. Suction pump 6 in question is electronically controlled by a probe 6a which measures the pressure prevailing inside the closed circuit, in order to keep the latter within a preset range of values. The quantities of mineral salts that are necessary to feed the algae in their biological cycle are introduced into a subsequent tank 8, which will be called a filtering tank, or at other points in the device. In filtering tank 8, finally, is located a mechanical filter 7 that is able to hold up the algae when the circulating liquid carrying the algae pass through it, and said tank 8 is connected to the circuit with a bypass system, according to known methods and with the aid of known interception means, in order to allow the circulating liquid to pass through it only when it is felt that the amount of algae contained in the latter is such as to allow or require their extraction. Once the algae, which constitute a plastic, fairly viscous mass, are extracted, filter 7 is reinstalled inside filtering tank 8, and the flow of circulating liquid is shifted toward the normal circulation path without filtration. The inventor has made provision for placing the components of the device that are more susceptible to damage caused by adverse weather, in practice all of them except for cooling tower 8 and segment 3 that is transparent to the sun's rays, in a box 12 or some other kind of structure that is aerated by appropria means 14, 14a and whose size is made appropriate to the size of the device. With the process and the device of this invention, the goa that the inventor set himself is readily achieved, i.e., that o cultivating microalgae on an industrial scale, with a level of productivity that is high and almost constant over time. Both the process and the device for implementing it that have been described up to this point may be modified by specialists in the field, but different embodiments that are based on the concepts set forth in the attached claims still fa within the framework of the protection conferred by this patent

Claims: Claims 1. Process for carrying out on an industrial level the cultivation of microalgae, characterized in that said cultivation is carried out in a hydraulic closed circuit: - by causing a liquid containing the algae to circulate; - by keeping the temperature of the liquid between two preset values; - by introducing into the liquid the amounts of carbon dioxide and nutrients necessary for the algae's metabolism; - by exposing the circulating liquid to the sun's rays in a specific transparent part of the closed circuit, so as to allow the algae to conduct chlorophyllic photosynthesis; - by extracting the oxygen that is produced during the course of said process; - by periodically separating the algae from the circulating liquid that are produced; - finally, by extracting said algae from said hydraulic closed circuit. 2. Device suitable for carrying out on an industrial level the cultivation of microalgae, characterized in that it comprises: a) a closed hydraulic circulation circuit (l) inside of which is a liquid that is suitable for holding the algae; b) pumping means (2) to circulate said liquid containing the algae through said closed circuit; c) means (8, 9, 10, 11) for monitoring and keeping the temperature of said liquid within a preset range of values; d) a segment of circuit (3) that is made of a material tha is transparent to the sun's rays and has inside of it a helical sheet that makes it possible for the process of chlorophyllic photosynthesis of the algae to take place within it; e) a device (4) that can introduce preset quantities of carbon dioxide into the circulating liquid; f) a device (5, 6) that can, by extracting oxygen from sai circuit (1) , sense the oxygen that is formed in the execution o chlorophyllic photosynthesis; g) means (7) that can mechanically separate the algae from the liquid and extract them from closed circuit (l) . 3. Device according to claim 2, which comprises: - a closed circulation circuit (1) inside of which is a liquid containing the algae; - a membrane-type circulation pump (2); - a cooling tower (8) that is composed of a heat exchanger (10) through which flows the liquid containing the algae, a spraying device (9) that can spray heat exchanger (10) with water, and a ventilation device (11) that is arranged in such a way as to allow air to circulate through said exchanger (10) in order to accelerate the evaporation of the water with which it sprayed; - a tank (4) containing pressurized carbon dioxide that is connected to said circuit (1) in such a way as to introduce int it preset amounts of carbon dioxide in the gaseous state via an inlet valve (4a) ; - a deoxygenation unit (5, 6) that comprises a holding tank (5) and a suction pump (6) ; said pump is able to generate a preset underpressure inside of said tank in order to remove the oxygen that is dissolved in the circulating liquid; - a filtering tank (8), inside of which is a filter (7) that can mechanically separate the algae from the circulating liquid by holding them up inside of it and that can be reversibly removed from filtering tank (8) itself; - a tube battery (3) that is made of a material that is transparent to the sun's rays and has a preset length. 4. Device according to claim 3, in which said introduction of gaseous carbon dioxide into the circuit is regulated by means of an electronic control device which can vary the rate of flow of the gas that passes through said inlet valve (4a) as a function of the pH value of the circulating liquid, as sensed by an appropriate probe (6b) . 5. Device according to either of claims 3 or 4, in which said membrane-type circulation pump (2) is equipped with an electronic control device (2a) which starts it and keeps it in operation only when the temperature of the liquid contained in closed circuit (1) exceeds a preset reference value, whereby said temperature is sensed by an appropriate probe (2c) . 6. Device according to any of claims 3, 4, or 5, in which said suction pump (6) is electronically controlled by a probe (6a) that measures pressure in order to generate a preset underpressure inside of holding tank (5) . 7. Device according to any of claims 3, 4, 5, or 6, in which said spraying device (9) is equipped with a pump (9a) tha is automatically started and is kept in operation only when the temperature of the circulating liquid, as sensed by a probe (13 exceeds a first preset value which is greater that the referenc value of said membrane pump (2), while said ventilation device (11) of cooling tower (8) is automatically started and is kept operation only when the above-mentioned temperature exceeds a second preset value which, in turn, is higher than the first value mentioned above.

Inventors: CURTI PAOLO, PEDRETTI MAURO, CURTI, PAOLO, PEDRETTI, MAURO
Applicants: ALGA DEV N V, CURTI PAOLO, PEDRETTI MAURO, ALGA DEVELOPMENT N.V., CURTI, PAOLO, PEDRETTI, MAURO
Application year: 1995
Main classification: C12M1
IPC codes: C12M1, C12N1