Chemistry: molecular biology and microbiology – Apparatus – Bioreactor
Reexamination Certificate
2000-02-17
2002-02-19
Beisner, William H. (Department: 1744)
Chemistry: molecular biology and microbiology
Apparatus
Bioreactor
C435S296100, C047S001400, C261S121100, C239S229000, C239S231000
Reexamination Certificate
active
06348347
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a culture device of a domed shape, a conical shape, or a cylindrical shape used in culture of photosynthetic organisms such as microalgae or the like, a gas discharge device disposed so as to be movable in the culture device and functioning to supply gas necessary for the culture into a culture solution and agitate the culture solution, or a culture system as a combination of the culture device with the gas discharge device.
BACKGROUND ART
In order to produce useful substances such as vitamins, amino acids, pigments, proteins, polysaccharides, fatty acids, and so on or in order to dispose of carbon dioxide which is considered to be one of causes of global warming, extensive research has been conducted heretofore on mass culture of microorganisms including microalgae such as Chlorella, Spirulina, or the like, and products of cultures based on the result of research are commercially available.
Most of the algae among these microorganisms absorb carbon dioxide to biosynthesize the useful substances by photosynthesis. In this case, because it is important to effect the culture of algae efficiently, a culture apparatus for making the algae efficiently perform the photosynthesis is necessary. Therefore, improvement in the conventional culture apparatus and development of new culture apparatus are under way.
The conventional algae culture apparatus commonly known include, for example, culture ponds, raceway culture devices, tubular culture devices, liquid membrane forming culture devices, and so on. The artificial culture ponds are of a type in which a culture pool or a culture tank is constructed, for example, of concrete outdoors, the culture solution is poured into the pool to form a culture pond, and the microalgae such as Chlorella or the like are cultured in the solution by making use of the sunlight. However, the systems of this type necessitate the surface area of the pool, for example, of 3000 M
2
and are thus normally huge.
In addition, when the microalgae are cultured in the system of this type, concentrations of the microalgae increase in the culture solution with progress of culture, so as to turn the solution into deep green and thus inhibit the sunlight from reaching the bottom part of the culture pond. From this phenomenon, there will arise a problem that the overall efficiency of photosynthesis of algae is decreased, unless the culture concentrations of the microalgae are lowered.
For this reason, the depth of the solution has to be kept below 15 cm and broad areas are necessary for the volume culture of microalgae. Since the concentrations of the culture solution cannot be high, there arises a problem that, for collecting the cultures from the solution, the cultures must be collected from an enormous amount of the culture solution with low concentration.
On the other hand, the culture ponds have to be agitated to facilitate the photosynthesis of the microalgae, but a lot of energy is necessary for agitating the huge amount of the solution of low concentration. Further, because the culture ponds are set outdoors and are open to the air, impurities of dirt, dust, etc. are mixed readily into the solution, and microorganisms and other algae floating in the air are mixed into the ponds to propagate; these pose another problem that the cultures cannot be obtained in high purity and with high quality.
Since the culture ponds are set outdoors, the temperature varies with variations in climate and it is thus very difficult to keep the temperature of the ponds constant. Particularly, the culture ponds have such a drawback that the temperature becomes too low in the winter season, depending upon regions.
For these reasons, the culture of algae making use of the culture ponds has such a drawback that it cannot be applied to the algae except for those such as Chlorella, Spirulina, and Dunaliella which can grow even under such a special condition as high pH or high salinity.
The raceway culture apparatus is constructed in such structure that the inside of a culture tank is partitioned with straightening plates to form a circuit path of the culture solution and the algae are cultivated by a method for circulating the culture solution in the circuit path by circulating means. This method is an improvement in the method of the culture ponds, but it also fails to utilize the light efficiently, because rates of photosynthesis of algae are lowered with progress of the culture, as in the case of the culture method with the culture ponds. This also raises a problem of low utilization efficiency of carbonic acid gas. For accomplishing efficient utilization of light, there is also a suggestion of guiding the sunlight through optical fibers into the solution. (Japanese Laid-open Utility Model Application No. 5-43900)
However, since the solution is circulated by mechanical agitation in the case of the culture of algae by this method, this method will encounter such an inevitable drawback that cells of algae are subject to breakage or shear stress (a phenomenon in which the algae are cut by shearing stress to degrade the activity of cells and thus make growth rates slower).
The tubular culture apparatus is an apparatus for culturing the microalgae etc. by use of the culture tank constructed of a light-transmitting tube. When the algae are cultured by use of this apparatus, there is no contamination of the culture solution due to various germs or the like and the culture concentrations can also be high; therefore, this is an extremely advantageous method for separating the algae from the culture solution and collecting the useful substances produced by the algae.
However, after long-term culture of algae, the algae attach to the internal wall of the tube, so as to considerably decrease the quantity of light transmitted by the tube. This phenomenon makes the efficient culture of microalgae difficult and it is not easy to remove the algae attaching to the internal wall of the tube.
For solving this problem, there is a suggestion about a method for putting cleaning balls in the tube and always circulating these balls with the culture solution, thereby cleaning the internal wall of the tube (Japanese Laid-open Patent Application No. 6-90739). This method, however, has many problems; it is not possible to continuously remove the dirt and the attachment of algae on the internal wall of the tube well, the balls have to be collected and cleaned, the balls always have to be circulated in the tube, and so on. A further problem of the culture of algae according to this method is that oxygen gas resulting from the photosynthesis of algae stays inside the tube because of the culture inside the tube and this oxygen acts to inhibit the photosynthesis of algae conversely (inhibition of photosynthesis). There is thus another suggestion about an idea of a device for suppressing the adverse effect on the culture due to the oxygen evolving in the photosynthesis. (Japanese Laid-open Patent Application No. 9-121835)
The liquid film forming culture apparatus is one constructed in such structure that a light-transmitting domed lid is placed on the culture tank, the culture solution is sprayed from below toward the internal surface at the top of the domed lid to form a liquid film of the culture solution on the internal surface of the lid, and this liquid film is exposed to the light. (Japanese Laid-open Patent Application No. 8-38159)
This suggested method, however, has problems that it requires a circulating pump for continuously forming the liquid film, that it is not suitable for the mass culture, that the sunlight cannot be utilized, and so on.
Since the microalgae accumulate the useful substances in their body through the photosynthesis, a significant challenge is to make the microalgae conduct the photosynthesis at as high efficiency as possible. Conceivable factors for the efficient photosynthesis are enlargement of the light-receiving area of the culture apparatus, efficient agitation of the culture solution, adjustment of the thickness or the depth of the cu
Hirabayashi Seishiro
Prilutsky Alexander
Sadamatsu Hisato
Beisner William H.
Micro Gaia Co., Ltd.
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