Patent Application
20070048848
The present invention relates to methods, compositions, apparatus and a system for growing and harvesting algae and/or other aquatic organisms. Certain embodiments concern methods, compositions, apparatus and a system for production of useful products from algae, such as biofuels (e.g., biodiesel, methanol, ethanol), bio-polymers, chemical precursors and/or animal or human food. Other embodiments concern use of such a system to remove carbon dioxide from sources such as power plant emissions.
In 1996 the National Renewable Energy Laboratory (NREL) in Golden, Colorado was forced to abandon its 10 year $25 million Aquatic Species Program that focused on extracting biodiesel from unusually productive species of algae. Before losing funding, the government scientists had demonstrated oil production rates 200 times greater per acre than achievable with fuel production from soybean farming. However, three fundamental problems limited the commercialization potential of algal culture.
The three problems were: [1] Oil prices were low in 1996 and hard to compete against. [2] The oil rich algae were difficult to protect from consumption or displacement by invading organisms as they were grown in ponds open to the environment. [3] Algae best produce oil within a narrow temperature band, yet night sky radiation and low temperatures and high temperature days and excessive solar IR radiation interfered with NREL's pond experiments by wildly varying the cultivation temperature.
A need exists in the field for technologies and methods to address these issues and provide a competitively priced, algal culture based biodiesel production in a biologically closed system, with better temperature control than the open pond model.
In certain embodiments, the methods, compositions, apparatus and system disclosed and claimed herein provide for biodiesel production from algal culture that is priced at or below diesel fuel costs from petroleum based production. The closed culture and harvesting system greatly reduces problems from contaminating algae, algae consuming microorganisms and/or other extraneous species. In more preferred embodiments, the apparatus is designed to be installed and operated in an outdoor environment, where it is exposed to environmental light, temperature and weather. The apparatus, system and methods provide for improved thermal regulation designed to maintain temperature within the range compatible with optimal growth and oil production. Another advantage of the system is that it may be constructed and operated on land that is marginal or useless for cultivation of standard agricultural crops, such as corn, wheat, soybeans, canola or rice.
The disclosed bioreactor technology stabilizes algae cultivation temperature with low energy usage, practical on any scale. By solving the problems of temperature and invading species at an affordable cost and adding a few other technologies, we have developed a system that is useful for creating a host of high value products from algae that is largely fed by industrial, agricultural, and municipal waste products. In some embodiments, the algal culture may be used directly to provide an animal or human food source, for example by culturing edible algae such as Spirulina. In other embodiments, the algal culture may be used to support growth of a secondary food source, such as shrimp or other aquatic species that feed on algae. Methods of shrimp farming and aquaculture of other edible species are known in the art and may utilize well-characterized species such as Penaeus japonicus, Penaeus duorarum, Penaeus aztecus, Penaeus setiferus, Penaeus occidentalis, Penaeus vannamei or other peneid species. The skilled artisan will realize that this disclosure is not limiting and other edible species that feed on algae may be grown and harvested.
One embodiment concerns methods, an apparatus and a system for producing biodiesel. High oil strains of algae are cultured in a closed system and harvested. Algae are completely or partially separated from the medium, which may be filtered, sterilized and reused. The oil is separated from the algal cells and processed into diesel using standard transesterification technologies such as the well-known Connemann process (see, e.g., U.S. Pat. No. 5,354,878, the entire text of which is incorporated herein by reference). However, it is contemplated that any known methods for converting algal oil products into biodiesel may be used.
In other embodiments, the system, apparatus and methods are of use for removing carbon dioxide pollution, for example from the exhaust gases generated by power plants, factories and/or other fixed source generators of carbon dioxide. The CO2 may be introduced into the closed system bioreactor, for example by bubbling through the aqueous medium. In a preferred embodiment, CO2 may be introduced by bubbling the gas through a perforated neoprene membrane, which produces small bubbles with a high surface to volume ratio for maximum exchange. In a more preferred embodiment, the gas bubbles may be introduced at the bottom of a water column in which the water flows in the opposite direction to bubble movement. This counterflow arrangement also maximizes gas exchange by increasing the time the bubbles are exposed to the aqueous medium. To further increase CO2 dissolution, the height of the water column may be increased to lengthen the time that bubbles are exposed to the medium. The CO2 dissolves in water to generate H2CO3, which may then be “fixed” by photosynthetic algae to produce organic compounds. It is estimated that the system and apparatus disclosed herein, installed over a surface area of about 60 square miles (4.5 mile radius), would fix sufficient CO2 to completely scrub the carbon exhaust of a 1 gigawatt power plant. At the same time, the carbon dioxide would provide an essential nutrient to support algal growth. Such an installation would produce algal lipid plus carbohydrate co-products that could generate about 14,000 gal/acre/year of total fuel output, absorbing 6 million tons/year of generated CO2 from the power plant. The value of the generated biodiesel plus methane produced by anarobically digesting the carbohydrate fraction of the algae plus potential carbon credits generated would produce a net profit of more than twice the value of the electrical energy generated by a typical coal or natural gas fired power plant.
Although there are thousands of species of known naturally occurring algae, any one of which may be used for biodiesel production and formation of other products, in certain embodiments the algae may be genetically engineered to further increase biodiesel feedstock production per unit acre. The genetic modification of algae for specific product outputs is relatively straight forward using techniques well known in the art. However, the low-cost methods for cultivation, harvesting, and product extraction disclosed herein may be used with either transgenic or non-transgenic algae. The skilled artisan will realize that different algal strains will exhibit different growth and oil productivity and that under different conditions, the system may contain a single strain of algae or a mixture of strains with different properties, or strains of algae plus symbotic bacteria. The algal species used may be optimized for geographic location, temperature sensitivity, light intensity, pH sensitivity, salinity, water quality, nutrient availability, seasonal differences in temperature or light, the desired end products to be obtained from the algae and a variety of other factors.
The disclosed closed bioreactor system and methods are scalable to any level of production desired, resulting in biodiesel feedstock production at well under current wholesale prices; even without factoring in government subsidies for biodiesel fuels.
Some embodiments may concern apparatus, methods and systems for temperature control of the algal culture. In one preferred embodiment, the closed bioreactor is comprised of flexible plastic tubes with an adjustable thermal barrier layer. The tubes and thermal barrier may be constructed of a variety of materials, such as polyethylene, polypropylene, polyurethane, polycarbonate, polyvinylpyrrolidone, polyvinylchloride, polystyrene, poly(ethylene terephthalate), poly(ethylene naphthalate), poly(1,4-cyclohexane dimethylene terephthalate), polyolefin, polybutylene, polyacrylate and polyvinlyidene chloride. In embodiments involving culture of photosynthetic algae or organisms that are fed on algae, the material of the thermal barrier preferably exhibits a transmission of visible light in the red and blue wavelengths of at least 50%, preferably over 60%, more preferably over 75%, more preferably over 90%, more preferably over 90%, most preferably about 100%. In other preferred embodiments, the material used for the top surface of the tubes exhibits a transmission of visible light of at least 90%, more preferably over 95%, more preferably over 98%, most preferably about 100%. In preferred embodiments polyethylene is used. Polyethylene transmits both long-wave black body radiation and red and blue visible light, allowing the temperature control system to radiate the inner heat of the water to the night sky and allowing the algae to receive visible light to support photosynthesis whether the medium is above or below the thermal barrier. Polyethylene exhibits increased transmittance of long wave infrared light associated with room temperature blackbody radiation, in comparison to certain alternative types of plastic. In various embodiments, thin layers of UV blocking materials may be applied to the surface of the tubes to reduce UV-degradation of the plastic. In other embodiments, fluorescent dyes that convert infrared (IR) or ultraviolet (UV) light to the visible (photosynthetic) light spectrum may be incorporated into the tube to increase efficiency of solar energy capture by photosynthetic organisms. Such dyes are known in the art, for example for coating the glass or plastic surfaces of greenhouses, or in fluorescent lighting systems that convert UV to visible light wavelengths. (See, e.g., Hemming et al., 2006, Eur. J. Hort. Sci. 71(3); Hemming et al., in International Conference on Sustainable Greenhouse Systems, (Straten et al., eds.) 2005.)
In embodiments employing a thermal barrier within the tubes, the aqueous medium containing the algae may be directed either above or below the thermal barrier. Under conditions of low temperature, the liquid may be directed above the thermal barrier, where it is exposed to increased solar irradiation including the infared wavelengths, resulting in temperature increase. Under high temperature conditions, the liquid may be directed below the thermal barrier, where it is partially shielded from solar irradiation and simultaneously may lose heat by contact with the underlying ground layer. In still other embodiments, the ground underlaying the closed bioreactor may be used as a heat sink and/or heat source, storing heat during the day and releasing it at night.
When the thermal barrier is up (at the top of the tube), the liquid in the tubes is isolated from both radiative and conductive heat transfer to the outside environment. However, it is in intimate thermal contact with the ground underneath. When the thermal barrier is down the liquid may easily gain or lose heat to the environment via both radiation and conduction. In effect, the thermal barrier acts as a thermal switch that can be used to take advantage of opportune environmental conditions like night, day, rain, clouds, etc. to gain or shed heat to control the temperature of the fluid. The ground beneath the apparatus has thermal mass whose temperature can also be modulated by close thermal contact when the thermal barrier is in the up position. The heat energy in this thermal mass may be used to further control the temperature of the fluid. If a cold night is anticipated, the fluid can be allowed to warm to slightly above optimum temperature during the day with the thermal barrier in the down position. Shift of the thermal barrier to the up position transfers this positive heat energy to the ground thermal mass. Several cycles of fluid warming and ground heating may occur. The heat transferred into the ground thermal mass may then be transferred back to the liquid during a cold night by keeping the thermal barrier is in the up position, to stabilize the water temperature in an optimal range.
Alternatively, when an excessively hot day is anticipated, the barrier may be placed in the down position at night until the mixture is slightly below the optimum temperature and then shifted to the upper position, where the cooled water is in contact with the ground, to pump down the temperature of the ground. This cycle may be repeated several times during the night. As the ensuing day heats up, the thermal barrier is raised, thereby connecting the fluid thermally to the ground to lengthen the time that the fluid stays at an acceptably low temperature.
Other embodiments may comprise apparatus and methods for liquid circulation within and extraction of oxygen or other gases from the closed bioreactor. In a preferred embodiment, large rollers may be arranged to roll over the surface of the closed tubes, pushing liquid along the bag. In addition to moving fluid, the rollers would function to collect bubbles of dissolved gases, such as oxygen that is generated by photosynthetic organisms, which may be removed from the system to reduce oxygen inhibition of algal growth. Because the roller compression does not extend all the way to the bottom of the tube, the roller movement creates a high-velocity localized “backwash” immediately under the roller that serves to scrub the lower tube surface to reduce attachment to and biofouling of the tube surface and to resuspend organisms that have settled to the bottom of the tube. Similarly, the movement of the accumulated gas bubble and gas/water interface in front of the roller at the top of the tube also scrubs the upper tube surface, reducing biofilm formation and increasing light transmission through the top surface. The roller system is a preferred method to move fluid through the tubes while minimizing hydrodynamic shear that would inhibit aquatic organism growth and division. Another benefit of the roller system is that when fluid is being diverted from below to above the thermal barrier, the roller provides a low-energy mechanism for moving a buoyant thermal barrier to the bottom of the tube, as the roller semi-seals the barrier to the tube bottom as it rolls along the tube.
Collection systems, such as sippers, may be arranged to siphon concentrated suspensions of oil-containing algae out of the system. In a more preferred embodiment, the hydrodynamic flow through the bioreactor is designed to produce a “whirlpool” effect, for example in a chamber at one end of the bags. The whirlpool results in a concentration of algae and partial separation from the liquid medium, allowing more efficient harvesting, or to remove undesired byproducts of metabolism like dead cells and mucilage containing bacteria. Other mechanisms for adding nutrients and/or removing waste products from the closed bioreactor may also be provided. One or more sipper tubes may be operably coupled to the whirlpool system to increase efficiency of harvesting from and/or nutrient input to the apparatus.
Certain embodiments may concern axial vortex inducers to provide for rotation of the algae suspension volume to within the top inch of the bioreactor which in a dense aquaculture may be the only volume that receives significant levels of photosynthetic light. The rotation of the water column within the tube results in the periodic movement of organisms between the light-rich environment at the top of the tube and dark regions at the bottom of the tube. In a preferred embodiment, the flexible tubes containing the algae are about 12 inches in height. At high algal density, sunlight will only penetrate approximately the top 1 inch layer of the suspension. Without a mechanism for rotation of the water column, aquatic organisms in the top inch would be overexposed to sunlight and aquatic organisms in the bottom 11 inches would be underexposed. In a preferred embodiment, the axial vortex inducers comprise internal flow deflectors (structured axial flow rotators) within the flexible plastic tubes, discussed below.
In an exemplary embodiment, the deflectors may comprise 6 inch wide by 12 inches long strips of flexible plastic tapered to 2 inches in the middle extending vertically through the tube, with a ninety degree twist from the top to bottom of the strip. In the exemplary illustration of
In some embodiments, the emissivity properties of the thermal barrier may be adjusted by incorporation of other materials of selected optical characteristics. For example, quartz sand from specific sources may have desirable optical properties and could be embedded within the upper surface of the thermal barrier. (See, e.g.,
Various embodiments may concern apparatus and methods for modeling algal production under environmental conditions. An example of a remote sensing bioreactor for condition optimization and algal strain selection is shown in
The following drawings form part of the present specification and are included to further demonstrate certain embodiments of the present invention. The embodiments may be better understood by reference to one or more of these drawings in combination with the detailed description of specific embodiments presented herein.
Terms that are not otherwise defined herein are used in accordance with their plain and ordinary meaning.
As used herein, “a” or “an” may mean one or more than one of an item.
As used herein, “about” means plus or minus ten percent. E.g., “about 100” refers to any number between 90 and 110.
Transgenic Algae for Enhanced Oil Production
In certain embodiments, algae of use to produce biodiesel may be genetically engineered (transgenic) to contain one or more isolated nucleic acid sequences that enhance oil production or provide other characteristics of use for algal culture, growth, harvesting or use. Methods of stably transforming algal species and compositions comprising isolated nucleic acids of use are well known in the art and any such methods and compositions may be used in the practice of the present invention. Exemplary transformation methods of use may include microprojectile bombardment, electroporation, protoplast fusion, PEG-mediated transformation, DNA-coated silicon carbide whiskers or use of viral mediated transformation (see, e.g., Sanford et al., 1993, Meth. Enzymol. 217:483-509; Dunahay et al., 1997, Meth. Molec. Biol. 62:503-9; U.S. Pat. Nos. 5,270,175; 5,661,017, incorporated herein by reference).
For example, U.S. Pat. No. 5,661,017 discloses methods for algal transformation of chlorophyll C-containing algae, such as the Bacillariophyceae, Chrysophyceae, Phaeophyceae, Xanthophyceae, Raphidophyceae, Prymnesiophyceae, Cryptophyceae, Cyclotella, Navicula, Cylindrotheca, Phaeodactylum, Amphora, Chaetoceros, Nitzschia or Thalassiosira. Compositions comprising nucleic acids of use, such as acetyl-CoA carboxylase, are also disclosed.
In various embodiments, a selectable marker may be incorporated into an isolated nucleic acid or vector to select for transformed algae. Selectable markers of use may include neomycin phosphotransferase, aminoglycoside phosphotransferase, aminoglycoside acetyltransferase, chloramphenicol acetyl transferase, hygromycin B phosphotransferase, bleomycin binding protein, phosphinothricin acetyltransferase, bromoxynil nitrilase, glyphosate-resistant 5-enolpyruvylshikimate-3-phosphate synthase, cryptopleurine-resistant ribosomal protein S14, emetine-resistant ribosomal protein S14, sulfonylurea-resistant acetolactate synthase, imidazolinone-resistant acetolactate synthase, streptomycin-resistant 16S ribosomal RNA, spectinomycin-resistant 16S ribosomal RNA, erythromycin-resistant 23S ribosomal RNA or methyl benzimidazole-resistant tubulin. Regulatory nucleic acid sequences to enhance expression of a transgene are known, such as C. cryptica acetyl-CoA carboxylase 5′-untranslated regulatory control sequence, a C. cryptica acetyl-CoA carboxylase 3′-untranslated regulatory control sequence, and combinations thereof.
Separation of Algae and Extraction of Oil
In various embodiments, algae may be separated from the medium and various algal components, such as oil, may be extracted using any method known in the art. For example, algae may be partially separated from the medium using a standing whirlpool circulation, harvesting vortex and/or sipper tubes, as discussed below. Alternatively, industrial scale commercial centrifuges of large volume capacity may be used to supplement or in place of other separation methods. Such centrifuges may be obtained from known commercial sources (e.g., Cimbria Sket or IBG Monforts, Germany; Alfa Laval A/S, Denmark). Centrifugation, sedimentation and/or filtering may also be of use to purify oil from other algal components. Separation of algae from the aqueous medium may be facilitated by addition of flocculants, such as clay (e.g., particle size less than 2 microns), aluminum sulfate or polyacrylamide. In the presence of flocculants, algae may be separated by simple gravitational settling, or may be more easily separated by centrifugation. Flocculent-based separation of algae is disclosed, for example, in U.S. Patent Appl. Publ. No. 20020079270, incorporated herein by reference.
The skilled artisan will realize that any method known in the art for separating cells, such as algae, from liquid medium may be utilized. For example, U.S. Patent Appl. Publ. No. 20040121447 and U.S. Pat. No. 6,524,486, each incorporated herein by reference, disclose a tangential flow filter device and apparatus for partially separating algae from an aqueous medium. Other methods for algal separation from medium have been disclosed in U.S. Pat. Nos. 5,910,254 and 6,524,486, each incorporated herein by reference. Other published methods for algal separation and/or extraction may also be used. (See, e.g., Rose et al., Water Science and Technology 1992, 25:319-327; Smith et al., Northwest Science, 1968, 42:165-171; Moulton et al., Hydrobiologia 1990, 204/205:401-408; Borowitzka et al., Bulletin of Marine Science, 1990, 47:244-252; Honeycutt, Biotechnology and Bioengineering Symp. 1983, 13:567-575).
In various embodiments, algae may be disrupted to facilitate separation of oil and other components. Any method known for cell disruption may be utilized, such as ultrasonication, French press, osmotic shock, mechanical shear force, cold press, thermal shock, rotor-stator disruptors, valve-type processors, fixed geometry processors, nitrogen decompression or any other known method. High capacity commercial cell disruptors may be purchased from known sources. (E.g., GEA Niro Inc., Columbia, Md.; Constant Systems Ltd., Daventry, England; Microfluidics, Newton, Mass.) Methods for rupturing microalgae in aqueous suspension are disclosed, for example, in U.S. Pat. No. 6,000,551, incorporated herein by reference.
Conversion of Algae into Biodiesel
A variety of methods for conversion of photosynthetic derived materials into biodiesel are known in the art and any such known method may be used in the practice of the instant invention. For example, the algae may be harvested, separated from the liquid medium, lysed and the oil content separated. The algal-produced oil will be rich in triglycerides. Such oils may be converted into biodiesel using well-known methods, such as the Connemann process (see, e.g., U.S. Pat. No. 5,354,878, incorporated herein by reference). Standard transesterification processes involve an alkaline catalyzed transesterification reaction between the triglyceride and an alcohol, typically methanol. The fatty acids of the triglyceride are transferred to methanol, producing alkyl esters (biodiesel) and releasing glycerol. The glycerol is removed and may be used for other purposes.
Preferred embodiments may involve the use of the Connemann process (U.S. Pat. No. 5,354,878). In contrast to batch reaction methods (e.g., J. Am. Oil Soc. 61:343, 1984), the Connemann process utilizes continuous flow of the reaction mixture through reactor columns, in which the flow rate is lower than the sinking rate of glycerine. This results in the continuous separation of glycerine from the biodiesel. The reaction mixture may be processed through further reactor columns to complete the transesterification process. Residual methanol, glycerine, free fatty acids and catalyst may be removed by aqueous extraction. The Connemann process is well-established for production of biodiesel from plant sources such as rapeseed oil and as of 2003 was used in Germany for production of about 1 million tons of biodiesel per year (Bockey, “Biodiesel production and marketing in Germany,”
www.projectbiobus.com/IOPD_E_RZ.pdf).
However, the skilled artisan will realize that any method known in the art for producing biodiesel from triglyceride containing oils may be utilized, for example as disclosed in U.S. Pat. Nos. 4,695,411; 5,338,471; 5,730,029; 6,538,146; 6,960,672, each incorporated herein by reference. Alternative methods that do not involve transesterification may also be used. For example, by pyrolysis, gasification, or thermochemical liquefaction (see, e.g., Dote, 1994, Fuel 73:12; Ginzburg, 1993, Renewable Energy 3:249-52; Benemann and Oswald, 1996, DOE/PC/93204-T5).
Other Algal Products
In certain embodiments, the disclosed methods, compositions and apparatus may be used for culture of animal or human-edible algae. For example, Spirulina is a planktonic blue-green algae that is rich in nutrients, such as protein, amino acids, vitamin B-12 and carotenoids. Human consumption of Spirulina grown in algae farms amounts to more than one thousand metric tons annually. The skilled artisan will realize that any type of free-living algae may be grown, harvested and utilized by the claimed system, including edible algae like Spirulina, Dunaliella or Tetraselmis (see U.S. Pat. Nos. 6,156,561 and 6,986,323, each incorporated herein by reference.)
Other algal-based products may also be produced using the claimed methods, apparatus and system. For example, U.S. Pat. No. 5,250,427, incorporated herein by reference, discloses methods for photoconversion of organic materials such as algae into biologically-degradable plastics. Any such known method for producing useful products by culture of either normal or transgenic algae may be used.
The methods, compositions, apparatus and system disclosed and claimed herein concern technology that supports large scale and low cost cultivation and harvesting of water born algal cultures. This technology may be used to support industrial manufacturing of the various products that different species of algae can provide. This technology may be of use to economically support the massive cultivation and harvesting of algae. The disclosed apparatus is generally referred to herein as a “bioreactor,” “photo-bioreactor,” “closed system bioreactor” and/or “bioreactor apparatus”. Other machinery, apparatus and/or technologies of use with the bioreactor may include sterilization technology, CO2 infusion technology, and/or extraction technology.
The products of the closed bioreactor system are not limited, but may include Biodiesel, Jet fuels, Spark ignition fuels, Methane, Bio-polymers (plastic), Human food products, Animal feed, Pharmaceuticals products such as vitamins and medicines, Oxygen, Waste stream mitigation (product removal), Waste gas mitigation (e.g. sequestering CO2).
Certain exemplary embodiments are illustrated in
Referring again to
As indicated in
The rollers form a kind of peristaltic pump but differ in two respects. First, the peristaltic filling force is provided by the leveling action of gravity on the fluid rather than the elastic return that is seen in many pumps. Second, the rollers only squeeze the tubes down about 85% rather than completely. This means the fluid pressure differential from front to back of the roller causes a relatively high speed reverse flow right under the roller, as discussed below. In some embodiments, the roller speed (and accordingly the fluid velocity) may be approximately 1 foot/sec.
In various embodiments, the aqueous medium may be used to culture photosynthetic algae. During photosynthesis, the algae absorb CO2 and release oxygen gas. As the roller moves along the upper surface of the bag, oxygen, other gases, fluid medium and algae are pushed ahead of the roller. This not only moves the algae through the bag but also provides a mixing action for the medium. The rollers may push a bubble of gas in front of them. This is a combination of gases released from the water, un-absorbed CO2, and oxygen generated by photosynthetic algae. The gas pocket in front of the rollers may be collected in end chambers and vented to the atmosphere or stored, to avoid oxygen inhibition of photosynthesis. In some embodiments stored oxygen may be reinjected into the apparatus at night to support algae metabolism during non-photosynthetic periods. Alternatively the collected oxygen may be piped to a power plant to increase the efficiency of its combustion processes. The rollers may also cause optical turnover of algae, which is desired to modulate its light input. Otherwise algae either become over-saturated with light or starved of light and the oil production goes down.
As illustrated in
A thermal barrier may be included within the bag, separating the liquid components into upper and lower layers for thermal control. Depending on how fluid movement is regulated, the liquid may be diverted primarily into the upper layer of the tube above the thermal barrier (FIG. 3D) or into the lower layer of the tube below the thermal barrier (
As shown in
The illustrative embodiment shows a research model that is only 65 feet long, with individual bioreactor bags that are 52 inches wide. In a preferred production scale embodiment each of the two bags would be about 300 feet long and 10 to 20 feet wide for a total photosynthesis area of 0.15 to 0.30 acre per bioreactor assembly. Each such bioreactor should grow about 7 to 14 gallons of biodiesel per day or more.
In some embodiments, a single tube may be formed to contain an upper layer, internal thermal barrier, and lower layer as shown in
In the exemplary embodiment of
A non-limiting example of bioreactor thermal control is illustrated in
The tube may be formed by side sealing two sheets (upper and lower) or three sheets (upper, thermal barrier, and lower) of flexible plastic, although other mechanisms may be utilized, such as providing a seamless tube by continuous extrusion or blowing of a cylindrical sheet of plastic. A ground sheet that is resistant to physical/mechanical disruption but is heat conductive may be placed between the ground and the tube. The ground may be treated or prepared to be relatively flat, smooth, heat conductive and plant resistant. Side walls may be provided to physically support the fluid-filled tube and/or provide additional thermal insulation from the sides of the tube and additionally to support and guide the roller carriages.
As shown in
In alternative embodiments, active thermal control with power plant water may be utilized. Heated water from a power plant's cooling towers may be pumped to a plastic mat placed under part of the bioreactor tubing. When it is cold this additional heat source may be utilized to prevent freezing and/or below optimum algal growth temperatures. The skilled artisan will realize that a variety of heat sources may be utilized, such as power plant exhaust, geothermal heat, stored solar heat or other alternatives. Additionally in hot seasons or locations of high solar flux, evaporative or other cooling systems that can be efficiently powered can be used to keep the algae from overheating.
In some embodiments, the emissivity properties of the thermal barrier may be adjusted by incorporation of other materials of selected optical characteristics, such as quartz sand (ee, e.g.,
The thermal control mechanism discussed above is highly effective at maintaining temperatures in a range for optimal algal growth.
An exemplary harvesting whirlpool of alternative design is illustrated at the right side of
As shown in
Another purpose of the whirlpool may be to serve as an alternative CO2 injection mechanism. This would happen on the bottom of the whirlpool where the fluid is spinning outward after leaving the control orifice. Gases like pure CO2, or alternatively CO2 rich flue gases obtained from a power plant, factory or other source, may be injected mid radius in the vortex or just below the opening of a central sipper tube. In this position the bubbles are prevented from seeking the center of the vortex because of the restriction caused by the sipper tube and the downward counter flow of the water. Yet because the force of buoyancy and downward flow are concurrently present, there is a dwell time until the bubble blows large enough from its source orifice. Its size constricts and speeds up the water flow around it so that the bubbles are sheered off the generating orifice as small bubbles that are carried in the slower flow. In preferred embodiments, much of the gas is absorbed into the fluid before the bubbles coalesce and rise to the top of the tube.
It may be possible for the bioreactor to aquire CO2 directly from the air either by bubbling up air through neoprene injectors or by direct permeation through the top skin of the bioreactor. In some embodiments, on the top inside of the tube there may be deposited 1 inch diameter pockets of sodium hydroxide mixture, sealed behind a gas permeable but water proof membrane, perhaps composed of a polystyrene membrane which has been shown to be very permeable to CO2. As these pockets are partially exposed to the outside atmosphere, they can selectively absorb the CO2 component of air. Then as the roller passes over the pockets they are physically compressed by the roller such that the top is sealed and the partial pressure of the CO2 is higher than in the water on the bottom side of the membrane and rapid transmembrane diffusion occurs into the liquid. In this construction the top sheet looks a bit like bubble wrap with the bubbles on top and filled with a sodium hydroxide mixture and both the bottom and top comprising CO2 permeable membranes. In an additional embodiment for direct CO2 acquisition, the top skin of the bioreactor is made of a composite of open-celled fabric as a strength component with the pores filled with a CO2 permeable and absorbing substance. This may be polystyrene microcapsules of sodium hydroxide. In operation the capsules would absorb CO2 from the air then either dispense the CO2 directly to the fluid through passive diffusion or through pressurized diffusion when the roller compresses the capsules on each sweep.
An exemplary model of a whirlpool device is shown in
The fluid mechanics of the whirlpool device are illustrated in
The purpose of the speed-up ramp and cone is to minimize turbulence as the fluid is speeded up for entry into the whirlpool, where it further speeds up in its spiral motion to provide centripetal force. It is estimated that the apparatus shown in
In certain embodiments, exhaust gases that are enriched in CO2 may be utilized to support photosynthetic carbon fixation, while simultaneously scrubbing the exhaust gases of their CO2 content to prevent further buildup of greenhouse gases. In this way huge amounts of, for example, power plant flue gases can be “mined” for their CO2 and the resulting gas piped to the algae farm.
Where long flexible tubes are used, it may be optimal to provide a supplemental CO2 injection mechanism at both ends of the tube. It is estimated that aquatic organisms flowing at 0.25 meter/second would require additional CO2 approximately every 7 minutes (105 meters). Supplemental CO2 could be provided in a variety of forms, such as gas bubbles, water pre-saturated with CO2, addition of solid forms of CO2 (e.g., NaHCO3, Na2CO3, etc.)
Ten to twenty foot long rollers must be accurately driven, against a background of reflected waves, misalignments, temperature differences, and varying friction in order to avoid skewing of the roller and diagonal wrinkling of the tube. In certain embodiments, the rollers may weigh thousands of pounds and may move along a track that can be 300 feet or greater in length. The exemplary system shown in
The velocity command of the upper master servo is derived from the controller by determining the difference between where the roller is and where it should be. By limiting the first and second derivatives of the resultant velocity command, the unstable water filled bioreactor bags are minimally excited. Wave action oscillation from any source is not magnified and does not induce out-of-phase feedback signals due to drivetrain compliance, because the velocity feedback sensors being directly attached to the drive motors are isolated from compliant elements. The bottom servo is slaved to match the same velocity as the upper main servo but with enhanced velocity following due to the dV/dt lead feed-forward network in its command. The slave velocity command is summed and offset by the skew strain sensor outputs on the kinematic carriage system. This actively drives the roller to a precise angular alignment referenced to the alignment rail. The exact angle of skew can be adjusted by the controller to compensate for roller directionally unique effects or to relieve detected wrinkle formation in the bioreactors. The controller can also use the fore-aft roller hydrostatic pressure difference sensed by the film (bioreactor tube) level sensors to control the roller velocity in order to maintain a specific pressure head. Battery or solar powered skew and level sensors with RF telemetry output require no power wires to be hooked to the roller. The carriage system is of kinematic mechanical design. This provides that changes in width between the roller rails or roller length changes due to expansion do not bind the carriage system. It also means that the roller perpenducularity is constrained by only one carriage end and therefore can accurately be measured by sensors on that end and the result used to differentially control the drive systems velocity on each end so as to zero out accumulated skew.
Technology for preventing or delaying bio-fouling of the inner plastic layers by algae adhering is important. This is because if the bags need to be replaced too often then it becomes an economic drain on the operation. There are a number of approaches to preventing biofouling under development worldwide although nano textured hydrophobic surfaces that are very pointy on a nano scale are one possibility. (See www.awi-bremerhaven.de/TT/antifouling/index-e.html). One way to make a non-fouling inner surface for the bioreactors at very low cost is to use flocking technology to electrostatically embed the ends of polyethylene fibers that are approximately 1-2 microns diameter by 10-20 microns long into the soft, still cooling, polyethylene plastic blown film “bubble” just as it leaves the blown film annular nozzle. (See e.g. www.bpf.co.uk/bpfindustry/process_plastics_blown_film.cfm to understand the blown film process. See e.g. www.swicofil.com/flock.html for details regarding flocking.) A non-limiting example of a flocking based substrate is illustrated in
The inner flocked surface on the inside of the bubble may be made hydrophobic by having the inside of the bubble pressurized with fluorine gas (rather than air) which reacts with the polyethylene to create a thin skin of hydrophobic polyfluoroethylene (which is similar to polytetrafluoroethylene, PTFE) on both the flock fiber's surface as well as the plastic film between the fiber bases.
In certain embodiments, the bag may be made completely black on at least one side of the two bag system. When algae goes into the darkness it consumes oxygen and when in the light it produces oxygen. There may be an oil productivity advantage if even during the day the algae mixture is channeled alternately through light and through darkness on some selectable duty cycle so as to consume some of the dissolved oxygen in the fluid and stimulate the energy converting photosynthesis reactions.
In various embodiments, the top surface of the tube may be patterned to maximize light absorption for photosynthesis during the winter months, particularly at higher latitudes. An exemplary Frenel pattern is shown in
Everything that goes into the bioreactors is preferably sterile except for the desired seed culture of the microorganism. In order to do this inexpensively on an industrial basis we may utilize a continuous flow autoclave (
An exemplary method and apparatus for oil extraction and/or centrifugation is illustrated in
An example of a remote sensing bioreactor for condition optimization and algal strain selection is shown in
In another exemplary, sensor-only based embodiment, one or more environmental monitoring stations may be located to monitor environmental conditions, such as temperature, ground thermal conductivity, ground thermal capacity, humidity, precipitation, solar irradiation, wind speed, etc. The detected conditions may be transmitted to a laboratory based test bioreactor apparatus, where the test site environmental conditions may be replicated in a controlled setting.
In either embodiment, various strains of aquatic organisms (e.g., algae) may be inoculated into the test bioreactor apparatus and their growth and productivity monitored. Strains selected for optimal growth and/or productivity at any desired production location may be determined at minimal expense and maximal efficiency.
A ⅕ scale model closed system bioreactor was constructed as shown in
Further details of the exemplary closed bioreactor apparatus are illustrated in
The exemplary closed system bioreactor that was constructed utilized a roller design as illustrated in
The bag (tube) may be stretched over a stiff sealing insert frame inserted into the end of the bag as shown in the drawings of
Algae are grown to maturity according to Example 11 and harvested for their oil content. A whirlpool device as described in Example 12 is used to partially separate algae from the medium. The algal cell walls are disrupted by passage through a high shear force mechanical device. Oil is separated from other algae contents by centrifugation in a commercial scale centrifuge. The oil is converted into biodiesel by alkaline catalyzed transesterification according to the Connemann process. The amount of biodiesel produced from one bioreactor incorporating two 20 foot×300 foot bioreactor tubes is 2,800 gallons per year.
In some embodiments, all aspects of bioreactor function may be controlled by a central processing unit, for example a computer controller. The controller may be operably coupled to various sensors and actuators on the bioreactor. The computer may integrate all functions of bioreactor operation, such as roller movement and alignment, fluid flow, whirlpool operation, harvesting of algae, nutrient and fluid input into the apparatus, gas removal, and CO2 injection. The computer may operate on a sensing and control program such as LabView made by National Instruments Corporation and may use interface cards and circuits well known in the art to connect with the sensors and actuators of the bioreactor system.
An exemplary operation cycle is illustrated in
At this point the circulation direction of the fluid is reversed. First flapper J is put in the down position so that counterclockwise water flow is directed first onto the top deck and flapper K is in the up position so that exiting lower deck water is expanded into the full height of the bioreactor tube. Roller I starts moving south in under control of the computer, pushing water ahead to start a counter-clockwise fluid movement. After it comes to rest at the end of tube S, roller H immediately starts moving north, to keep the pressure head on the whirlpool and full flow moving. For a short time after roller H comes to rest at the end of tube R, the fluid keeps moving under its own momentum until friction slows it down to near zero speed. Once this is achieved, the controller commands the clockwise motion sequence shown in
The CO2 injectors may be controlled so that only the bubble injector experiencing counter-current water flow is actuated to take advantage of the increased bubble dwell time and concurrent increased CO2 absorption (see
The septum valves for tube S are E and F. The septum valves for tube R are C and D. Each tube septum may be controlled independently of the other tube septum but each must be coordinated with its roller motion.
Before either roller leaves its rest position the controller must determine whether its associated septum should be placed in the up or down position. If the septum is decided to be in the up position, the septum valve at the roller start position must be in the up position such that water gets drawn under the septum during roller travel. The septum valve at the far end of the tube can be in either position during roller travel as long as the septum valve sealing method allows for expelling water from inside the tube regardless of position. When the roller has stopped however, the septum valve at the far end should be fixed into the upper position.
When the septum is desired to be in the down position, the septum valve at the roller start position must be in the down position so that water is drawn over the top of the septum by roller movement. The septum valve at the far end of the tube can be in either position as long as it is designed to allow the unimpeded expelling of water from either top or bottom tube chamber. When the roller stops however the septum must be fixed into the down position so that water is not allowed to seep under the septum which would allow it to float to the top.
“O” is a fluid temperature sensor interfaced to the computer, which compares the detected temperature with a set point of desired temperature for the algae. Depending on weather and time of day conditions, the computer decides to place the thermal septums in the up or down position and coordinates the actions of the septum valves with the roller movement accordingly. In some cases a sensor may be constructed to determine whether the fluid will gain or lose heat to the temperature and radiative environment. Such a sensor would be constructed by channeling a small amount of fluid (about 0.1 gallon per minute) through a plastic bag of about 3 feet square by 3 inches deep that is laying on ground substantially the same temperature as the ground the main bioreactors are sitting on. Differential temperature sensors with a resolution of 0.02 degree F. measure the temperature at both the intake and outlet of the sensor bag. If the temperature is calculated to be increasing as fluid passes through the bag then the computer positions the septums to expose the fluid to the environment if the fluid is too cold in the bags or to insulate the bags from the environment if the fluid is too warm. The converse logic would apply if the sensor bag indicates that environmental exposure would cool the fluid.
“P” is a pH sensor and is interfaced to the computer. The value of the fluid pH is compared with a desirable pH set point that is indicative of the proper concentration of dissolved CO2 in the water to support optimum growth or harvesting. When the pH is too high the computer opens valves to the appropriate CO2 bubbler to allow pure CO2 or flue gas containing CO2 to bubble through the water making it more acid with the formation of carbonic acid and lowering the pH.
All of the COMPOSITIONS, APPARATUS, SYSTEMS and METHODS disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods have been described in terms of preferred embodiments, it is apparent to those of skill in the art that variations maybe applied to the COMPOSITIONS, APPARATUS, SYSTEMS and METHODS and in the steps or in the sequence of steps of the methods described herein without departing from the concept, spirit and scope of the invention. More specifically, certain agents that are both chemically and physiologically related may be substituted for the agents described herein while the same or similar results would be achieved. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.
The present application claims priority under 35 U.S.C. 119(e) to Provisional U.S. Patent Application Ser. Nos. 60/711,316, filed Aug. 25, 2005; 60/733,569, filed Nov. 4, 2005; 60/740,855, filed Nov. 30, 2005; 60/757,587, filed Jan. 10, 2006; and 60/818,102, filed Jun. 30, 2006; each incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60711316 | Aug 2005 | US | |
| 60733569 | Nov 2005 | US | |
| 60740855 | Nov 2005 | US | |
| 60757587 | Jan 2006 | US | |
| 60818102 | Jun 2006 | US |
