Abstract:
An algal production system that uses CO2 injections to promote the growth of algae. The system includes an algal growth medium within a floway for channeling water. A fluid diffuser also resides in the floway in proximity to the algal growth medium. The fluid diffuser injects CO2 into the water in the floway. The system further includes a detector for monitoring the pH levels of the water and a controller, which based on the measured pH levels, determines when and how much CO2 to inject into the water.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application 61/263,168, filed on Nov. 20, 2009, the subject matter of which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    The following described method and apparatus relates to the algal production technology which was conceived and developed over a period of about 30 years and patented as U.S. Pat. Nos. 4,333,263, issued Jun. 8, 1982; 4,966,096, issued Oct. 30, 1990; 5,097,795, issued Mar. 24, 1992; 5,851,398, issued Dec. 22, 1998; and 5,715,774, issued Feb. 10, 1998; the disclosures of which are incorporated herein by reference. Existing large-scale algal production systems marketed under the brand Algal Turf Scrubber®, or ATS systems include in-ground troughs or “floways.” Many small-scale algal production systems have been utilized for research and aquaria under the existing patents referenced above. 
         [0003]    As in most photosynthetic systems, algae require carbon to complete the chemical process of photosynthesis with production of organic material. The carbon is taken from carbon dioxide (CO2) and bicarbonate (HCO3) in the ambient water and is effectively a nutrient, the concentration of which will affect the rate of productivity or biomass building. 
         [0004]    In the modern era of concern about climate change and excess CO2 release into the atmosphere, there exists a need for disposal or reutilization of CO2 produced as a result of industrial operations, in particular electrical generation at coal and oil fired power plants. 
       SUMMARY 
       [0005]    This method and apparatus described herein provides an algal production system. The system may include a method and apparatus for introduction of CO2 to affect the production of algal biomass. The system may utilize carbon dioxide (CO2) from industrial operations to reduce release into the atmosphere. 
         [0006]    In one aspect, the system includes a floway for channeling water from a water source, an algal growth medium arranged within the floway, and a fluid diffuser arranged in proximity to the algal growth medium. The fluid diffuser is configured to diffuse fluid from a fluid source into the water to promote the growth of algae on the algal growth medium. The fluid source includes a gas source or a fluid source, such as, a gas dissolved in a liquid, such as, water. The fluid may include a nutrient which may be CO2 gas. 
         [0007]    In another aspect, the system includes a controller for controlling the fluid supplied by the fluid source and the water supplied from the water source. A detector is coupled to the controller, the detector measuring the pH level of the water and sending the measurements to the controller. The controller uses the pH level measurements to determine the amount of water supplied by the water source and the amount of fluid supplied by the gas source. pH should generally be maintained between about 7.5 to about 8.5 for some algae and growing conditions. 
         [0008]    In another aspect, the fluid diffuser of the system includes a plurality of tubes coupled to a mat. The floway has a plurality of ridges arranged in parallel along a surface with a space between each ridge, and at least one tube of the plurality of tubes is located in each space. 
         [0009]    In another aspect, the fluid diffuser of the system is located within a depression in the floway. The depression runs parallel to a length of the floway, or may run at an angle, such as perpendicular to a length of the floway. 
         [0010]    In another aspect, the floway of the system includes a plurality of segments connected together. The depression may be located at a connection of one segment to another. 
         [0011]    In another aspect, a method of producing algae includes the steps of providing a floway having an algal growth medium arranged within the floway, channeling water along the floway, and diffusing fluid into the water of the floway by use of a fluid diffuser arranged on the upper surface of the algal growth medium, configured to diffuse gas, such as CO2, from a fluid source into the water to promote the growth of algae on the algal growth medium. 
         [0012]    In another aspect, a method of producing algae includes the steps of providing a floway having an algal growth medium arranged within the floway, channeling water along the floway, and diffusing gas into the water of the floway by the addition of carbonated fluid at one or more points along the floway to promote the growth of algae on the algal growth medium. Carbonated water may be produced external to the system by injection of CO2 or stack gasses from a fluid source into water in a container or tubing, and then introduced via tubing to the floway. 
         [0013]    In another aspect, the method includes the step of controlling the flow of water into the floway and the flow of fluid into the water by use of a controller. The pH level of the water is measured and provided to the controller. The controller uses the pH level measurements to determine the amount of water supplied to the floway or the amount of fluid supplied to the water. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a schematic view of a system including a tube mat for introducing gas into water near algal growth of an algal production system according to a preferred embodiment. 
           [0015]      FIG. 2  is a bottom end view of the tube mat of  FIG. 1 . 
           [0016]      FIG. 3  is a manifold end view of the tube mat of  FIG. 1 . 
           [0017]      FIG. 4  is a cross section elevation view of the tube mat of  FIG. 1  arranged within a floway. 
           [0018]      FIG. 5  is a side view of gas tubes arranged within depressions of a floway of an algal production system according to another preferred embodiment. 
           [0019]      FIG. 6  is a plan view of a gas tube arranged within a junction between two floways of an algal production system according to another preferred embodiment. 
           [0020]      FIG. 7 . is a view taken along section line VII-VII of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0021]    Referring now to the drawings, where like reference numerals designate like elements, there is shown in  FIG. 1  an algal production system  110  according to a preferred embodiment. The system  110  provides a method and apparatus for introduction of gasses, of which CO2 is of primary interest in the illustrated embodiment, to the water adjacent to the cell walls of algal filaments via membrane systems located in proximity to algal growth screens on algal production systems such as Algal Turf Scrubber® systems. Introduction of other substances may also be desirable, such as gaseous or liquid phosphorus or nitrogen ion may also be accomplished with membranes, for example. These membranes are readily available on the market today for scientific and industrial uses, and exist in a variety of conformations related to use. 
         [0022]    Injection of CO2 and/or stack gasses into waters that will be treated by algal remediation satisfies the need for disposal of the CO2, while presenting the opportunity to increase production of algal biomass. 
         [0023]    Simple injection into passing water flow via a bubbler system and air stones could be utilized, provided that losses to the atmosphere are limited. Bubble walls do not present gasses to the algal cells in an effective manner, reducing uptake by the cells as the water passes. Surface area relative to volume is lower as bubble size increases, suggesting that smaller bubbles would be more effective in diffusing CO2 into solution. Bubblers producing extremely fine bubbles may be useful in introducing CO2 and other gasses to an algal growth medium, provided the bubblers are of sufficient length and of sufficiently small size to be maintained in close proximity to algal cells without undue loss of CO2 to the atmosphere. 
         [0024]    Membrane technology allows introduction of selected material on the atomic or molecular level, obviating the process of diffusion across the air/water boundary in the case of gas bubbles. Direct diffusion using submerged membranes will minimize losses of gasses to the atmosphere, and maximize availability to algal cells. Membranes exist on the market in a wide variety of physical conformations, and have designed chemical compositions for uses such as reverse osmosis and kidney dialysis, and can permit or prevent the passage of gasses or liquids in a range of sizes from atomic to large complex molecules. Membranes suited to the selective diffusion of CO2 could be used for application to algal cells, in tubular conformation, in a range of sizes suitable for the algal growth medium. Sheet membranes could be installed beneath algal growth media, fed by pressure connection through the bottom of the algal growth units, but would likely be harder to maintain. Testing has shown that gasses such as CO2 and stack gasses are easily introduced to water using membrane technology. While large pore sizes do diffuse the gasses into the water, there may be some loss to the atmosphere due to bubble formation. The preferred pore size would be less than one micron. For ideal algal uptake of the CO2 gas diffused into water, the pore size should be less than one tenth of a micron. Pore size would be larger for a liquid such as carbonated water or a nutrient solution such as nitrogen or phosphorus solutions. 
         [0025]    Since CO2 and HCO3 are part of the carbonate system in an aqueous environment, pH measurement may be used for controlling CO2 and/or water flow rates to control the rate of addition of carbon to the algal photosynthetic/productivity process. 
         [0026]    A preferred configuration illustrated in the FIGS. includes a number of small hollow membrane tubes  120  made of CO2 specific membrane material and laid in an enclosing mesh  130  such that they form a sheet mat  112  approximately forty-two inches wide and ten feet long. A gas supply manifold  140  joins all the membrane tubes  120  at one end, with a pressure hose connection  142  entering the manifold  140  at an appropriate location to suit application. CO2 gas is fed into the manifold  140  and distributed through the inside of the hollow membrane tubes  120 . The gas molecules inside the tubes migrate, driven by the pressure differential, through the wall of the tubes to outside the tubes to enter the water in proximity to the algal filaments on the algal growth screen  19 . This sheet  112  of membrane tubes  120  would be laid underneath or in proximity to the algal growth medium  19  within the floway  12  ( FIG. 4 ), and connection would be supplied via a conduit  143  from a source  144  of CO2. The source  144  provides the CO2 in gas form. The algal growth medium could be a plastic mesh available from netting suppliers. The plastic mesh should have a size range, depending upon the algae involved, on the order of from about one millimeter to about one centimeter. 
         [0027]    In an alternative embodiment, the source  144  may provide carbonated water that contains CO2. In this embodiment, the fluid flows into the membrane tubes  120  and is distributed by the membrane tubes  120  into the water in proximity to the algal filaments on the algal growth medium  19 . The carbonated water mixes with the water to provide the CO2 to the algal growth. 
         [0028]    This system can be applied in any algal production systems including ATS systems. An algal production system may include a trough or floway  12  having a floway bottom  15  and floway sides  14 . The floway  12  may be supported at an incline for water to flow down the incline. The water may be provided in surges from a bucket (not shown) that functions like a tipping bucket as described in U.S. Pat. No. 4,966,096. The floway  12  may be constructed from modular pieces or floway “trays” or “segments”  20  arranged end to end and supported by suitable supports  220 . As shown in the illustrated embodiment of  FIG. 6 , each of the floway segments  20  has an upper segment end  24  and a lower segment end  22 . Within the floway  12 , there are several ridges  114  on the floway bottom  15  integral to the fiberglass of the floway  12  and extending in a longitudinal direction. The ridges  114  preferably have a height  116  of approximately one quarter to one half inch above the top surface  115  of the tray bottom  15 . The sheet mat  112  for CO2 injection fits over these ridges  114  such that the membrane tubes  120  rest in the low areas between the ridges  114 , and the enclosing mesh  130  holds the membrane tubes  120  in position relative to each other between the ridges  114 , and positioned below the algal growth medium  19 . The membrane tubes  120  may or may not be attached to the mesh  130 . In another embodiment, the membrane tubes  120  may be woven into the mesh  130  to form the sheet  112 . In another embodiment, the membrane tubes  120  may be incorporated into the algal growth matrix itself, such as by gluing, welding, or weaving. 
         [0029]    The gas pressure fitting  142  on the manifold  140  is located at a ninety degree angle to the manifold  140  and penetrates through the bottom  15  of the floway  12  such that connection to the gas source can be accomplished beneath the floway  12 . Each of the membrane sheets  112  is about the same length as each floway tray segment  20  of the fiberglass floway  12  in the illustrated embodiment. Thus, there will be a maximum number of sheets  112  equal to the number of floway segments  20 . Not all floway segments  20  will necessarily need to have installed membrane sheets, and gas flow to each sheet can be adjusted to accomplish maximum algal growth enhancement, allowing adaptation to particular desired water and algal growth requirements. pH measurement will be used to control either water flow rate or CO2 input pressure, or both, to maximize algal productivity and nutrient removal relative to the typical need to allow pH elevation near the end of an ATS floway where zonal precipitation of phosphorus, heavy metals, and other minerals would occur (see U.S. Pat. No. 5,851,398). 
         [0030]    The pH detector  150  senses the pH level of the water from one or more locations in or downstream along the floway  12 . The pH information is communicated  155  to the controller  160 , which processes the pH information, communicates  165  to control the CO2 gas pressure via the source  144 , and communicates  167  to control the water flow via the water source  170 . The communications may be wired or wireless or other media and computers may be used to effect communications. 
         [0031]      FIG. 5  shows another embodiment of the system  110  with the membrane tubes  120  laid in one or more depressions  17  in the floway  12 . The depressions  17  are wells that are integrally manufactured along the bottom of the floway  12 . The depressions  17  may run parallel to the sides  14  of the floway  12  along the length of the floway  12 . Alternatively, the depressions  17  may run perpendicular to the sides  14  of the floway  12  along the width of the floway  12 . The depressions  17  have sufficient depth so that the membrane tubes  120 , when placed within the depressions  17  are substantially or wholly located below the top surface  115  of the floway bottom  15  and submerged beneath the algal growth medium  19  within the floway  12 . In another embodiment, the membrane tubes  120  within the depressions  17  may not be wholly below the top surface  115  of the floway bottom  15  but are still be located below the algal growth medium  19 . Locating the membrane tubes  120  within the depressions  17  keeps the membrane tubes  120  substantially below the plane of the top surface  115  of the floway bottom  15  so as to lessen any contact or interference with the growth medium  19  as the growth medium  19  is maintained, removed or serviced by an harvesting apparatus to harvest algal growth. 
         [0032]      FIGS. 6 and 7  show another embodiment of the system  110  with the membrane tubes  120  laid in a groove  18  between adjoining segments  20  that form the floway  12 . Each segment  20  has a flange  16  at one end that couples the segment  20  to the non-flanged end of an adjacent segment  20 . The groove  18  is formed in the bottom  15  of the floway  12  where the two segments  20  are coupled by the flange  16 . The membrane tube  120  is placed within the groove  18  to be located substantially wholly beneath the top surface  115  of the floway bottom  15  and beneath the algal growth membrane  19 . The membrane tube  120  within the groove  18  is perpendicular to the sides  14  of the floway  12  and to the direction of the water flow  172 . The membrane tube  120  is coupled to a supply line  145 , which is coupled to the conduit  143  and the CO2 source  144  ( FIG. 1 ). The supply line  145  of the illustrated embodiment runs inside the vertical groove in the floway sidewall  14  formed by the flange  16 , and then along the top or the side of the floway sidewalls  14  to the source  144  of gas. The supply line  145  may also serve as a supply line to additional membrane tubes  120  that may be positioned in the floway  12 . For example, multiple membrane tubes  120  running lengthwise within the floway  12  may connect to the supply line  145 . 
         [0033]    The membrane tubes  120  are placed in any number of flange grooves  18  or depressions  17  along the floway  12  to inject CO2 into the water in the floway  12  to suit the application and water chemistry. A single membrane tube  120  may be used in a single location or multiple locations along the floway  12 . Alternatively, multiple membrane tubes  120  may be used in a single location or multiple locations along the floway  12 . Additionally, the membrane tubes  120  may be located in one or more selected areas the floway  12 . The floway  12  may have the membrane tubes  120  located in the grooves  18  as shown in  FIGS. 6 and 7 , as well as having the membrane tubes  120  within the depressions  17  as shown in  FIG. 5 . 
         [0034]    The injection of CO2 affects the pH level and/or increases the available carbon in the water. The injection of CO2 into the water from the tubes  120  shown in  FIGS. 5-7  is controlled by the controller  160  based on information provided by the detector  150  as previously described. The controller  160  is able to maintain desired pH levels along the floway  12  within a range suitable for the prescribed water, algae species and production requirements. The pH level can be adjusted to control the type of algae that will grow within the floway  12 . For example, in the brackish waters of the Chesapeake Bay, a desired pH level for the growth of the algae including those in the genera Berkeleya and Melosira is preferably in the range of from about 7.0 to about 8.5. The desired range of pH level will depend on the specific species of algae and the composition of the water, such as the salinity of seawater, brackish water, and fresh water. 
         [0035]    Additionally, the pH level and/or the available carbon in the water may be controlled to obtain certain characteristics of the algal growth. For example, more than one species of algae may grow on the growth medium  19 . The pH level may be controlled to vary the relative proportions of the algae species. Additionally, the pH and/or the available carbon in the water may be controlled to vary characteristics of specific algae growing on the growth medium  19 . 
         [0036]    It should be apparent that many modifications and variations of the preferred embodiments as hereinbefore set forth may be made without departing from the spirit and scope of the present invention. The specific embodiments described are given by way of example only. The invention is limited only by the terms of the appended claims.