Patent Publication Number: US-2012028346-A1

Title: Microalgae Photobioreactor

Description:
FIELD OF THE INVENTION 
     The present invention pertains generally to photobioreactors. More particularly, the present invention pertains to photobioreactors that circulate a fluid medium for growing microalgae. The present invention is particularly, but not exclusively, useful as a bioreactor that includes a fluid medium circulation channel formed by sealing two plastic sheets together at selected locations. 
     BACKGROUND OF THE INVENTION 
     The growth rate of selected microalgae in a liquid environment is dependent on several disparate factors. For one, it is known that the fluid medium in which the selected microalgae grows (i.e. liquid environment) must be circulated to provide for mixing and exposure of the selected microalgae to light for photosynthesis. For another, the selected microalgae may require protection from competition with contaminants such as other algae, bacteria, and viruses. Also, loss of fluid medium through evaporation should be minimized or compensated for. Due to their success in confronting these issues, closed systems, such as photobioreactors, are frequently used to effectively grow microalgae. 
     However, closed photobioreactors are typically complicated devices that include multiple connections, high pressure drops, expensive materials, and vertical supports. As a result, typical closed photobioreactors are expensive to construct, maintain and operate. 
     In light of the above, it is an object of the present invention to provide a closed photobioreactor that minimizes required connections. Another object of the present invention is to provide a photobioreactor having a channel formed by selectively sealing two transparent plastic sheets together. Still another object of the present invention is to provide a photobioreactor for promoting microalgae growth that relies on gravity as the primary force for moving a fluid medium through the photobioreactor. Yet another object of the present invention is to provide a photobioreactor that is relatively simple to manufacture, is easy to use, and is comparatively cost effective. 
     SUMMARY OF THE INVENTION 
     A bioreactor that is used to circulate a fluid medium for the purpose of growing algae includes a substantially U-shaped channel having a first and second opening. Further, the channel is interconnected with a conduit formed in a transfer section. Specifically, the transfer section includes a collection trough connected to the second opening and an elevated distribution trough connected to the first opening. Between the collection trough and the distribution trough, a pump or other flow device is positioned to drive the fluid medium from the collection trough to the distribution trough. 
     Importantly, the U-shaped channel is formed from two transparent plastic sheets. Structurally, each sheet has a proximal end, a distal end, and side edges extending between the ends. For purposes of the present invention, the sheets are bonded to one another at an outer seal along their respective side edges and distal ends. Further, the sheets are bonded to one another at an inner seal along a longitudinally-extending median located between the opposite side edges. Because the inner seal does not intersect the outer seal, the U-shaped channel is formed between the two sheets. Further, the first and second openings of the channel are positioned adjacent one another along the proximal end of the sheets. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which: 
         FIG. 1  is a schematic of a bioreactor in accordance with the present invention; 
         FIG. 2  is a perspective view of the sheets used to form the channel of the bioreactor shown in  FIG. 1 ; 
         FIG. 3A  is an overhead view of the sheets of  FIG. 2  during formation of the channel; 
         FIG. 3B  is an overhead view of an alternate formation of the channel from the sheets; and 
         FIG. 4  is a perspective view of the bioreactor, illustrating the function of the transfer section in accordance with the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring initially to  FIG. 1 , a bioreactor is shown, and is generally designated  10 . As shown in  FIG. 1 , the bioreactor  10  forms a U-shaped channel  12  which holds a fluid medium (arrow  14 ). For purposes of the present invention, the channel  12  has a first opening  16  and a second opening  18 . As shown, a transfer section  20  forming a conduit  22  interconnects the first opening  16  and the second opening  18 . Structurally, the transfer section  20  includes a collection trough  24  for receiving the fluid medium  14  from the second opening  18 . Further, the transfer section  20  includes a distribution trough  26  for feeding the fluid medium  14  to the first opening  16 . Interconnected between the collection trough  24  and the distribution trough  26  is a device  28  for flowing the fluid medium  14 . 
     Referring now to  FIG. 2 , the construction of the U-shaped channel  12  may be understood. As shown, the channel  12  is formed from two transparent plastic sheets  30 . Each sheet  30  has a proximal end  32 , a distal end  34 , a first edge  36  and a second edge  38 . Further, the sheets  30  define a longitudinal axis  40  and have a length “I” that may be between 0.5 and 2.0 kilometers. Cross-referencing  FIG. 2  with  FIG. 3A , it can be seen that the sheets  30  are bonded to one another by a seal  42  along the first edges  36 , the distal ends  34 , and the second edges  38 . Further, the sheets  30  are bonded together by an axially-extending seal  44  that is distanced between the first and second edges  36 ,  38 . As a result, the seal  42  forms an outer boundary  46  and the seal  44  forms an inner boundary  48  for the U-shaped channel  12 . In  FIG. 3B , an alternate embodiment is shown in which the inner boundary  48  itself is U-shaped. As a result, the parallel legs  50   a ,  50   b  of the channel  12  are separated from one another by a void  52 . As a result, increased sunlight may enter each leg  50   a ,  50   b.    
     As illustrated in  FIG. 4 , the channel  12  is substantially circular, though it may be flat-bottomed, or rectangular. Further, it can be seen that the channel  12  has a height “h” which is less than 15 centimeters, and preferably about 7.5 centimeters. As shown in  FIG. 4 , the flow device  28  is an Archimedes pump that elevates the fluid medium  14  from the collection trough  24  to the distribution trough  26 . Alternatively, the flow device  28  may be a conveyor, a bucket lift, a paddle wheel, a sealed paddle wheel, an electro-mechanical pump, or a similar device for moving fluid. As further shown in  FIG. 4 , the bioreactor  10  includes a disentrainment section  54  for removing gas such as oxygen from the fluid medium  14 . The gas may be captured as a product or released. 
     While in  FIGS. 1 ,  3 A,  3 B and  4 , the bioreactor  10  is illustrated to include a single seal  44 , it is noted that multiple seals  44  can be used to establish a longer channel  12 . Despite the length of the channel  12 , the present bioreactor  10  utilizes only two connections, from the distribution trough  26  to the first opening  16  and from the second opening  18  to the collection trough  24 . Therefore, the costs associated with manufacturing and maintaining interconnections are reduced. Further, the present bioreactor  10  relies on a single flow device  28  which can supply acres of fluid medium flow. 
     For use of the bioreactor  10 , the collection trough  24  is connected to the second opening  18  and the distribution trough  26  is connected to the first opening  16 . Then, the flow device  28  is activated and pumps the fluid medium  14  from the collection trough  24  to the distribution trough  26 . As gravity pulls the fluid medium  14  from the distribution trough  26  to the first opening  16 , circulation of the fluid medium  14  through the channel  12  and conduit  22  is established. 
     While the particular Microalgae Photobioreactor as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.