Patent Application
20120115217
The disclosed devices and methods herein relate to apparatus for performing light dependent chemical reactions. In some advantageous embodiments, the apparatus is configured as a photobioreactor. The apparatus may be applied to photosynthetic cell cultures, as it is applied to production of biomass as well as carbon dioxide (CO2) recycling or sequestration and waste water mitigation.
Current human dependence on fossil or petroleum fuel as a limited resource has prompted development of alternative renewable energy sources. Carbon dioxide (CO2) emitted from the burning of fossil fuel, as a green house gas and primary cause of global warming, adds further urgency. The United States, it is estimated, consumes more than 43 billion gallons per year of diesel fuel for transportation plus a multiple of this amount for gasoline and other oil-based fuels. In effort to provide fuel using resources other than so called fossil or petroleum derived fuels, biodiesel is derived from vegetable oil and animal fats. Corn based ethanol is now blended with gasoline at higher percentages. Current development of biofuels such as ethanol from corn requires extensive amounts of land and water. The use of food stuff in generation of transportation fuel has caused pricing pressure on agricultural commodities.
Photosynthesis converts the solar electromagnetic energy into stored chemical energy in long carbon chains by assembling carbon from carbon dioxide. Microalgae are the most photosynthetically efficient organisms. Algae, as a source of biofuel, have long been studied. The last energy crisis in the 1970's fueled research in alternative energy sources. A substantial amount of knowledge has been amassed by the U.S. Department of Energy's Aquatic Species Program (ASP). Algae may be grown in impaired water. Algae are highly efficient in photosynthesis with amazing rates of replication. Some algae strains can double every 4 to 6 hours. Algae when grown in certain conditions such as nitrogen-deficient culture can synthesize and accumulate fatty acids to levels greater than half of its dry weight. The algal fatty acids or oils are capable of being and currently are refined into jet fuel for the U.S. Navy. However, cultivation systems allowing for scale up of algae culture from laboratory quantities to an industrial scale of production have heretofore been challenging. Conventionally, such algal cultivation systems can be separated into two categories: open vs. closed. Each conventional category has pros and cons.
The open cultivation systems are “open” to the environment and the most common current form can be described as large raceway ponds. Such open ponds are the least expensive to build and operate. As such, open ponds were advocated by the ASP to compete with fossil fuel. However, raceway ponds require high water use due to constant evaporation. Open ponds offer sub-optimal light intensity control. Open ponds are prone to contamination from wild type strains overwhelming the desired cultured strains being propagated. Additionally, this type of open culture, being unprotected, is subject to predators which feed on algae. Large culture ponds could be decimated in a few days by such predators. While large amount of resources are being funneled into designing or genetically modifying algae to improve yield and overcome the above-noted short comings of open ponds, it is unlikely that public opinion would allow the use of genetically altered mutant strains in open systems with the accompanying risk of uncontrollable environmental contamination even though such risk is very small. Geographic limitations such as temperature and solar irradiance as well as land requirement are additional limitations.
Closed systems or photobioreactors are designed to address all of these limitations and concerns of the open pond systems to varying degrees. However, one of the major challenges is efficient utilization of solar irradiance. Solar irradiance as experienced at the earth's surface is highly variable. The phenomenon of “self shading or self shadowing” further complicates the utilization of solar irradiance. As light penetrates an algal culture, photons are absorbed by chlorophyll, decreasing the light intensity. This “self shading” is exaggerated in high cell concentration culture with high chlorophyll concentration. In fact, light does not penetrate very far at all in ultra high cell concentration cultures, sometimes just a few millimeters. Optimal light intensity for algal photosynthesis has been demonstrated to be a small fraction of direct bright solar irradiance, in the range of 10%. An algal culture in an open pond commonly experiences a detrimental superficial culture layer in which the excessively high light intensity of direct solar beam causes photoinhibition, cell damage and possibly cell death. Through “self-shading”, the high “toxic” layer whereby a middle layer of culture experience “optimized” light intensity for algal photosynthesis. Any deeper layer of culture, as light intensity further attenuates, fails to receive sufficient light to drive algal photosynthesis.
Current art of culture systems, open and closed, rely on the strategy of cell movement in and out of the various light zones: 1) superficial toxic, 2) middle optimal and 3) deep deficient zones. Algal cells may move into the potential toxic superficial layer to absorb photons for only milliseconds to microseconds before leaving such zone so damaging radicals do not build up. Current art of open ponds utilize large paddles to create stirring and current flow and typical closed systems such as tubular systems utilize pumps. Much of the current flow is laminar flow, parallel to the conceptual light zones described above, instead of more efficient turbulent flow in moving cells perpendicular through the light zones. Furthermore, algal movement through the pumps may experience shear injury at higher velocities. Despite the efficiencies gained with current closed systems, in general, photobioreactors are not cost effective to compete with fossil fuels in normal market conditions. The least expensive of the current closed systems are simple plastic bags with little structure. As these batch type cultures grow and chlorophyll content increases, larger and larger proportions of the culture in the middle does not receive enough light for photosynthesis, limiting achievable cell concentrations.
One prior art example of a closed system is that of U.S. Pat. No. 6,509,188 (Trosch) which teaches a photobioreactor having a reactor chamber formed of transparent material and having recesses and projections adapted to increase the reactor surface area with tubular projections and extensions. However, the Trosh construction uses thick glass walls that would be especially required if the device were used in industrial production sizes where the enclosure would need to withstand the weight of a tall water column. The increased material needed to enclose the algae culture significantly increases the cost of such apparatus. There is also no strategy provided to address biofouling. The growth efficiency gained by such photobioreactor is unlikely to be cost affective in completing with fossil fuels.
As such, there exists an unmet need for algae culture systems which have a reasonable capital and operational cost to compete with crude oil under normal market conditions.
In one embodiment, an apparatus for containing a light dependent chemical process comprises an enclosure defining an inner chamber to hold a liquid medium. The shape of the inner chamber is structurally stabilized in part or in full by bridging elements. In some embodiments, the apparatus is configured as a photobioreactor. A photobioreactor may be formed of a thin film or sheet material that is structurally stabilized by the bridging elements, and these bridging elements may distribute light to an enlarged inner chamber surface area. In some embodiments the bridging elements serve as light guides. In some embodiments the bridging elements are tightly configured to increase the surface area to volume ratio of the inner chamber to provide light exposure to greater portions of the contained high cell density algae culture.
In one embodiment, a photobioreactor has a sufficiently large vertical height and sufficiently small horizontal cross sectional area to establish a nutrient gradient when a nutrient is applied in one end of the photobioreactor. Diffusion of a nutrient may be reduced by the presence of bridging elements in an inner chamber of the photobioreactor by further decreasing the cross sectional area in a simple planar enclosure. One nutrient that may be applied to the chamber to establish a gradient is Nitrogen.
In one embodiment, photobioreactors are deployed in a system comprising one or more supports along which a plurality of photobioreactors can independently translate. In this embodiment, the plurality of photobioreactors can translate from a configuration to allow access and maintenance, to a second configuration with more even spatial distribution to allow more solar energy collection. In some embodiments this system also allows rotation of the plurality of the photobioreactors to control the amount of solar energy exposed to the photobioreactors.
The device and method herein disclosed provides a novel means for the cultivation of algae. Possible application includes but not limited to the production of biomass for biofuels, feed stock, fertilizers, nutriceuticals, as well as water treatment and carbon dioxide sequestration.
It is one aspect of many embodiments of the invention that photobioreactor side walls may be constructed with thin plastic materials. These materials are usable in this environment even for large photobioreactor sizes because of bridging elements provided between opposed walls of the photobioreactor. With this design, cost effective photobioreactors or photopanels can be made with common inexpensive and preferably recyclable material like transparent plastics such as but not limited to Polyethylene Terephthalate (PET). The photopanels may be vertically disposed. The photopanels may provide containment of an algal culture with an expanded surface area exposed to light. Furthermore, the algal culture after taking on the shape of the inner chamber of the photopanel may have a high surface area to volume ratio to facilitate high cell concentration. The photopanel may be sufficiently thin and tall for the establishment of different functional zones for cell replication vs. fatty acid synthesis. This is better described as a limited cross sectional area relative to the volume of algae above or below by which the cross sectional area available for diffusion of nutrients, such as nitrogen, to subsequent levels is limited. In some embodiments, these objectives are all achieved by the application of a novel construct referred to herein as “hollow trabeculae.” Some examples of hollow trabeculae can be seen as the cones 14 of
The novel construct of “hollow trabeculae” is inspired by nature. Trabeculae are microbridges such as seen in animal cancellous bone. The trabeculae in cancellous bone stabilize the cortical bone outer surfaces with less bony material and increases the surface area (along the surface area of the trabeculae) for supporting red marrow cells. The idea of small bridges is applied to give structure to thin plastic membranes and sheets. One manifestation of the trabeculae may be interleaved cones or pyramids. The bridging elements (which may be hollow cones as stated) can be easily applied to plastic material by the process of thermoforming. Thin plastic sheets or membranes are heated and made to take on the shape of a mold by vacuum and/or positive pressure. The molded thin plastic membranes with studded, repetitive, multi-conal structure may then be fused in an interleaved pattern with an opposing similarly molded plastic membrane or to itself in a clam shape configuration. After the conal apexes are bonded or fused to the opposing side, the formed “hollow trabeculae” bridge the opposing sides, and resist the lateral forces exerted by the weight of the water column. This converts the weaker compression strength of current art to higher tensile strength of plastics. The “hollow trabeculae” are hollow because the cones represent negative space that may be occupied only with air. Climactic conditions and specific algal strain requirements may necessitate thermoregulation of the algae culture. An additional separate outer compartment may be incorporated as one additional layer of transparent material applied to one or both sides of the photopanel to serve as a water bath or jacket. In such case, the “hollow trabeculae” would be filled with circulating water, discontinuous from the algae culture medium. The water jacket could contain solution that further scatters light if desired. Alternatively, the photopanels may be submerged in a large pool of water. The new construct of “ hollow trabeculae” provides structural shape and strength, allowing utilization of thin plastic material such as recyclable thermoplastic membranes and sheets instead of thick plates and tubes of current art, substantially decreasing material cost.
Beyond the structural strength function in maintaining the shape of the inner chamber of the photopanel with high surface area to volume ratio by resisting the deformity from the weight of a water column, the “hollow trabeculae” may also serve to distribute light. The “hollow trabeculae” as transparent structures increase the area of the inner chamber potentially exposed to light. The intensity of scattered light may be decreased by distributing the amount of light over an enlarged surface area such as that provided by the “hollow trabeculae”. If light otherwise irradiates the circle area of a conal base is allowed to strike the larger surface area of the slanted side walls of the cone, that amount of light or number of photons are now distributed over a larger surface area, thereby effectively decreasing the light intensity. The ratio of surface area expansion is related to the ratio of conal height (H) to the radius (r) of the conal base. For example, a cone with a conal height (H) that equal the diameter of the conal base or twice the radius of the conal base (r), translates to approximately 2.2 times increase in surface area from the circular conal base to the slanted surface area of the conal walls. Similarly, conal height H that equal 3(r) represents expansion of surface area by approximately 3.2 times. Additional surface area expansion can be made with secondary structures on the “hollow trabeculae”. This may represent fine surface irregularities on the conal sides or as regular stair-steps. Conceptually, this could be likened to animal intestinal structure, by which increased surface area is desired for higher nutrient absorption rates. The “hollow trabecula” or cones, would be analogous to the primary villi, with the additional conal surface irregularity or stair-steps as secondary villi.
The cones as “hollow trabeculae” may further distribute light as a light guide. Portions of light entering the thin clear plastic material of the cones may be trapped due to total internal reflection. This is facilitated by the large difference in index of refraction between air and PET (1.0 vs 1.5 respectively). Stair steps along the conal sides may be designed to provide escape angles allowing light into the culture medium. This mechanism is especially useful in guiding spectral light beam striking the apex of the cone and adjacent area. With the optimal conal apex geometry, spectral solar beams may be captured despite shallow angle of incidence. Portions of the captured light may be guided to the photopanel side not directly exposed to the spectral solar beams. Portions of the incident spectral solar beams may be reflected and utilized as scattered light in other photopanels in the deployment system. Potential manipulation beyond the geometry of the conal apex may include application of reflective film and or sand blasting to enhance increased trapped and guided light as well as reflected and scattered light. Such manipulations may also be applied strategically in other sections of the photopanel.
The “hollow trabeculae” when placed in a tight configuration substantially increases the surface area to volume ratio of the inner chamber and cell culture. The increased light exposed surface area to volume ratio facilitates high cell density algae culture. Light penetration of the algae culture is inversely proportional the cell density due to “self shading” phenomenon. Due to limited light penetration of dense algae cultures by only a few millimeter, a tight “hollow trabeculae” configuration whereby the conal sidewalls are less than one centimeter apart, insures high portions of the cell culture would be exposed to sufficient light to drive photosynthesis, especially with agitation or cell movement.
A tight “hollow trabeculae” configuration also limits the cross section area to facilitate a more specific objective towards development of algal biofuel is accommodating the mutually exclusive needs for algal cell replication vs. algal fatty acid synthesis and accumulation. In nitrogen-rich culture medium, algal protein synthesis readily occurs. Excess energy is stored in more immediately available energy storage forms such as carbohydrates to drive processes of cell growth and cell replication. In the absence of nitrogen, protein synthesis is limited and cell growth and replication is inhibited. Excess energy from photosynthesis is instead driven towards long term storage in the form of fatty acids. In current production of algal biomass, the whole algal cell is harvested. Cell harvest necessitates cell replication to maintain a stable culture size or cell number. A system that could accommodate both nitrogen-rich environment for cell replication in log-rhythmic phase and nitrogen-depleted environment to drive fatty acid synthesis and accumulation would allow more efficient continuous culture as oppose to limited batch culture. The compartmentalization in relatively small individual photopanels benefits early isolation of problems that may arise such as contamination with viruses, fungi, and eukaryotic predators. The establishment of the two functionally different zones, nitrogen-rich vs. nitrogen-depleted zones is also facilitated by the construct of “hollow trabeculae” which further decrease the cross sectional area available for diffusion as well as providing the overall structural stability of a thin vertically disposed photopanel. A nutrient gradient and establishment of the two different functional zones is established by applying the nutrient only in one end of the photopanel further described under methods.
Another specific objectives to optimize photosynthetic utilization efficiency of available solar irradiance is sought by applying the dictum of the Hippocratic Oath, “First do no harm”. The high light intensity of direct spectral solar beam is toxic to algal cells causing photoinhibition, cell damage and possible death, all of which are energetically expensive, lowering the light use efficiency. The novel system seeks to limit direct solar irradiance by spectral sun beams and to more effectively utilize scattered light. Scattered light or indirect natural light is much closer to optimal light intensity for algal photosynthesis. This is largely achieved by simply orienting vertically disposed photopanels substantially parallel to the spectral solar beam during day hours, rotating the photopanels with the movement of the sun across the sky. This allows solar beams to evenly penetrate the algae farm to be scattered and reflected by surface treatment of the ground. The top portion of the vertically disposed photopanels would receive atmospherically scattered light and the bottom portion of the photopanels would receive ground scattered light. The atmospherically scattered light experienced by the upper portion of vertically oriented photopanel is surprisingly consistent within a smaller light intensity range, irregardless of sunny vs. cloudy days. The photopanels' exposure to the high intensity of direct spectral solar beam can be dialed up by angling the photopanels partially off parallel with the solar beam, to match the photosynthetic capacity of the algae culture. This application or strategy may seem simple, but not obvious, as it may be counter intuitive that less light may be more. These principles lead to the deployment strategy and system below. Increased algal culture surface area exposed to light, distribution and reduction of light intensity, as well as the structure to maintain a high culture surface area to volume ratio are all achieved by the application of a novel construct, “hollow trabeculae.”
High light conditions in which the scattered and redistributed light as well as limited direct spectral solar light is still above optimal algal photosynthetic light intensity, the strategy of cell movement through the various conceptual toxic, optimal and deficient light zones, as previously described are applicable. This mechanism is even optimized by high cell concentration culture because exaggerated “self-shading” causes less light penetration, effectively decreasing the thickness of the first two theoretical zones or layers of light conditions. Algal cells would therefore experience the different zones with little or short displacement. Algal cells could oscillate between light and dark conditions rapidly. The stirring of the cells may be achieved by bubbling, instead of more energy requiring large paddles as in open raceway ponds or fluid pumps in closed tubular systems. CO2-rich gases such as flue gas from combustion of natural gas or coal are administered through a sparger at the bottom of the photopanel as a primary nutrient. The gas bubbles serve an additional function of cell agitation as it rises. Since CO2 utilization for photosynthesis is proportional to available light, increased light source requires more CO2 delivery or higher bubbling rate, which translates to a higher rate of agitation. In another words, higher light condition could be titrated with higher bubbling rates delivering the higher requirement for CO2. The predominant turbulent flow caused by bubbling is much more efficient in moving cells perpendicular to the light zones.
For ease of manufacturing, the photopanel may be made as smaller photopanel component parts that could be assembled into the desired photopanel height. The smaller photopanel components may be manufactured with different surface area expansion ratios and assembled to optimize light intensity for algal photosynthesis relative to the location on the photopanel height as well as geophysical factors. Thinner enclosure materials may be used for upper components of the photopanel. Other manufacturing techniques such as injection molding may also be applied, especially if higher ratios of surface area expansion is desired. Application of “hollow trabeculae” as a disposable and recyclable liner supported by additional structure support may be especially beneficial in certain conditions. Such a flexible photopanel system may be highly adaptable to accommodate the diversity of photosynthetic organisms and organelles as well as geophysical conditions.
Elements of the photobioreactor such as sampling, and inlet and outlet ports are for basic utility. Their location may be variable, either inserted on the narrow sides on the panel or en-face with the face of the photopanel. The importance of the sparger as well as application of nutrients and supplemental artificial light source will be further discussed below.
The global objective to facilitate and to maintain high cell concentration in an efficient continuous system is achieved with the application of the new construct of “hollow trabeculae”. Such increased efficiency includes reducing the volume of cell culture medium and the material needed to enclose the medium. This represents further reduction of enclosure material cost afforded by the structural strength provided by “hollow trabeculae”. The higher the cell concentration, the higher solar intensity the algal culture could utilize with cell movement. Achieving high cell concentration will also lessen the cost of algal separation from the culture media at harvest.
The global objective of the disclosed novel deployment system for vertically disposed photobioreactors is to optimize the solar irradiance exposed to the algal culture to match the photosynthetic capacity of an algal culture. The disclosed deployment system seeks to optimize the following: 1) consistent and uniform distribution of solar energy among the multiple photosynthetic panels within an algae farm, 2) Control of light intensity, and 3) operational practicality. The available solar electromagnetic energy varies tremendously over the hours of the day, as well as with seasonal and atmospheric conditions. The emphasis is on limiting toxic high light intensities as damage to the algal photosynthetic apparatus as well as other cell damage and possible cell death, all energetically expensive. During bright sunny conditions, a control mechanism may be provided to limit the available light quantities exposed to the algal culture to match the maximum photosynthetic rate that the algal culture is capable of utilizing. Consistent uniform distribution of solar energy to the individual photopanels within a green house or algae farm allows monitoring of just a few representative photopanels. If every photopanel needed to be monitored for pH, nitrate, ammonia, oxygen and CO2, the instrumentation would be relatively expensive. With even distribution of solar energy, such that shading from adjacent photopanels is minimized, monitoring of the algae farm may be done with minimal sampling of the central vs. peripheral photopanels. The novel deployment strategy must also allow easy accessibility for maintenance, repair or replacement of the photopanels.
The novel deployment system for vertically disposed photobioreactors or photopanels organizes the photopanels in racks. The racks will have a mechanism to allow translation to improve uniform spatial distribution. The racks in the tight configuration form corridors and allow easy access to the individual photopanels. The limbs on which the photopanels are hung will have a pivot or rotational mechanism to control light intensity. With the broad face of the photopanel pivoted parallel to the direct spectral solar beams, high intensity solar irradiance is neutralized. By deviating slightly off parallel, algal culture exposure to direct solar beam irradiance could be increased as desired. In other words, light intensity from direct spectral solar beam irradiance could be dialed up by slight deviation from parallel, less than 30 degrees, thereby still limiting shading from adjacent photopanels. The solar beams still penetrate the algae farm uniformly, allowing sample monitoring of just a few photopanels. The solar beams that hit the ground treatment are scattered. Typical ground treatment with low absorption coefficient will potentiate the scattering and reflecting of the solar beams. Example of such ground treatment would include but not limited to white high gloss polyurethane on cement. The scattered light adds to the direct irradiance exposed to the algae culture.
Readily available coating technology may be applied to or in proximity to the physical structure or building that encloses the photopanels. UV-absorbing films may be applied to the physical structure or green house. Moveable light diffusion films may also be applied. Consideration for application of such film technology should consider the geophysical location of the algae farm installation. Diffusion films may not be necessary in the equatorial latitudes due to the increase in humidity that causes increased scatter. Similarly, latitudes greater than 40 Degrees also receive significant percentage of scattered light due to a long light path through the atmosphere.
General methods of culture to benefit the structural design offered by the novel construct of “hollow trabeculae” are described in broad conceptual terms to accommodate wide varying culture needs of the diversity of photosynthetic organisms and organelles not limited to eukaryotic microalgae or prokaryotic cyanobacteria. Described methods are meant to illustrate more common application scenarios and not meant to limit other creative applications.
Photosynthetic organisms in aqueous medium are contained within tall photopanels and arranged on sliding and pivoting racks as described above. Both autotrophic and heterotrophic, as well as mixed culture may be applied. Fresh culture medium containing nutrient such as nitrogen (N) and phosphorus (P) are delivered continuously from either the top or bottom ends of the photopanel. The rates of the nutrient delivery, in molar amounts as well as total liquid volume of the fresh medium, are dependent on the photosynthetic activity of the algae culture, the achievable cell concentration for the algal strain and desired rate of harvest. Carbon dioxide (CO2) rich gas is bubbled through the culture from a sparger positioned at the bottom of the panel. Continuous or semi-continuous algal harvest may be from either end of the photopanel, typically opposite end from the delivery of fresh culture media.
Sparger design and selection of bubble size and rate require careful selection. Delivery of CO2 rich gases into the photopanel serves multiple purposes. Beyond delivery of CO2 as a primary nutrient required by photosynthesis, CO2 also serves a pH buffer. Bubbling also serves in gas exchange of oxygen (O2). Oxygen as a by-product of photosynthesis will accumulate. At high levels, O2 inhibits photosynthesis. Gas exchange of CO2 and O2 are in opposite directions: CO2 out of the bubble and O2 into the bubble as the bubbles rise towards the top. Gas exchange rates are dictated by mass transfer functions. Gas exchange efficiency or rate relates to bubble size. The higher the surface area (SA) to volume ratio equates to the higher relative gas exchange rate. As such, smaller bubbles with higher SA to volume ratio have relative higher gas exchange rates. Long circular flow stream are to be avoided with a preference for localized turbulent flows. The bubble also serves to agitate the cell culture as described above, causing cells to be exposed to photons, especially in high light conditions with high cell concentrations. The larger the bubble size relates to greater algal cell displacement. Bubble size selection should take into consideration of these two polar benefits. Two separate spargers may be incorporated for better control. Constant agitation by bubbling will also help in limiting biofouling.
High cell concentration culture can be achieved by the structural characteristic of high culture surface area to volume ratio as offered by the tightly packed “hollow trabeculae” novel construct explained above. The high cell concentration culture needs night time support. Because oxygen is a by-product of photosynthesis and often a concern for excessive build up, frequently the need for oxygen in night time algal respiration is forgotten. In low cell concentration cultures or open culture systems, the amount of dissolved oxygen in the culture medium is sufficient for night time respiration of a few cells or there is constant gas exchange with the open environment. In a closed system with ultra-high cell concentration, dissolved oxygen without a constant replenishing source will cause culture collapse.
Night time or dark-hour artificial light may be applied to the bottom of the photopanel. The artificial light will drive photosynthesis in the irradiated portion as a replenishing source of oxygen for algae cells in levels above requiring oxygen for night time respiration. O2 from the photosynthetically active lower irradiated zone is transported by bubbling. Application of night time artificial light may generate two separate circadian rhythms within a continuous culture. Bubbling with O2 containing air may be an alternative to night time supplemental artificial light. Any energy efficient artificial light source may be utilized such as fluorescence, LED and OLED. LED, a currently available technology, offers substantial benefits. LED may be 5 times more efficient in generating white light. Furthermore, LED can generate only photosynthetically utilized wavelengths so every photon could be utilized. Additional energy saving may be achieved by reliance on red wavelength photons which require less energy to generate than any other color wavelength. LED lighting also has a longer lifespan, upwards of 60,000 hours. A side-lit light panel utilizing a clear material such as polycarbonate is easily incorporated into the photopanel, either in isolation or part of the containment for thermoregulating water bath or jacket. During day time hours when not in use, the side-lit LED light panels are essentially transparent to allow collection of natural scattered light off the ground, so artificial light sources do not have to be moved around daily.
High cell concentration culture helps establish a nutrient gradient within a tall and thin vertically disposed panel. Rate of diffusion is proportional to cross sectional area available between adjacent levels and concentration gradient. A tall and thin photopanel has a relatively small cross-section area at any level relative to the height, or more specifically the volume, above or below the reference level. The cross-sectional area in the novel photopanel design is further reduced by the tightly packed “hollow trabeculae” construct that also maintain the structure shape and dimension, of otherwise widening deformity by the weight of the high water column.
If nitrogen (N) is continuously administered to an algal culture at either end of the tall photopanels, there is a limited cross-sectional area for N to diffuse down a nutrient gradient towards N-depleted zones. Furthermore, N is being consumed by a large number of algal cells as it is diffused to adjacent levels. The higher the cell concentration the higher the number of algal cells consuming the nutrient. As a result, a nitrogen-rich zone at the end of nitrogen administration vs. a nitrogen-depleted zone at the opposite end is established. The transitional zone size is proportional by the cross sectional area and inversely proportional to the cell density concentration of the algal culture. The higher consumption rate from higher cell density culture helps to negate the stirring effect from bubbling. An N-rich zone is thereby established to optimize cell replication and an N-depleted zone is established to drive fatty acid synthesis.
In the scenario by which particular desired algal strain is expected to accumulate fatty acid content greater than 50% of its dry weight and the overall individual cell density becomes less than the density of the culture medium, the algal cells plump with fatty acids would slowly float towards the top of the photopanel, where lipid-rich cells would be continuously harvested. Nutrients including N would be administered at the bottom of the photopanel, where the bottom N-rich environment would potentiate cell replication and the top N-depleted environment would drive fatty acid synthesis. The reverse scenario by which fatty acid rich cells have individual cell density greater than the culture medium, the lipid-rich cells would settle to the bottom of the photopanel where harvesting occurs, and nutrients would be administered at the top of the photopanel. The first scenario is applicable for algal strains selected for or genetically engineered to secrete oil droplets into the culture medium. The secreted oil droplets would accumulate at the top of the photopanel to be easily harvested. This novel photopanel design could accommodate suspension cultures as described above as well as possible adherent cultures that some oil secreting strains may be.
Although constant stirring of the algal culture with bubbling may slow biodeposition on the photopanel, biofouling is inevitable, causing light transmission efficiency of the plastic membrane to deteriorate. The preference for a recyclable material such as PET offers the ultimate option of recycling and reforming. Before recycling, the biofilm remaining on an end-of-life photopanel may be utilized to feed concurrent aquacultures such as mollusks, shimp and fish. New coating technologies may also be applied to slow the rate of biofouling. Potentially, two, three, or four crops of different algal strains could be cultivated with optimized pairing of photopanel surface area characteristics and seasonal variability.
With respect to the above description, before explaining at least one preferred embodiment of the thermoformed vertically disposed system for algae growth herein in detail, it is to be understood that the invention is not limited in its application nor the arrangement of the components or steps set forth in the following description or illustrations in the drawings. The various methods of implementation and operation of the disclosed algae growth system and invention are capable of other embodiments and of being practiced and carried out in various ways which will be obvious to those skilled in the art once they review this disclosure. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.
Referring now to the drawings in
The photopanels 12 may be comprised of a plurality of segments 13 each having sidewalls 15 (such as shown in
The conal space of the “hollow trabeculae” may be only occupied by air. The inner chamber shape and volume containing the culture medium is limited to the space 21 between the sides of the cones 14 (
To further demonstrate the light distribution function of the new construct of “hollow trabeculae” as applied to photobioreactor design, a photon or light ray tracing diagram is included in
The thin plastic segments 13 formed of opposing sidewalls making up the individual photopanels 12, afford the photopanels 12 greatly enhanced structural integrity as well as increased area for algae propagation, by inclusion of these projections 14 (
With the hollow trabeculae (for example) as bridging elements, thin plastic sheets or even films can be used as the enclosure sidewalls. Advantageously, the thickness of the plastic enclosure walls may be less than 0.25 inches. Plastic walls of less than 0.1 inch thick have been found suitable in many implementations, sometimes less than 0.060 inches. In some embodiments, it is possible to use photobioreactor panel segments from plastic of different thicknesses. Near the top of the photopanel, the thinnest plastic can be used since the weight of the water column is the smallest. Progressively thicker materials can be used for portions of the panel that are closer to the bottom of the photobioreactor. If desired, very thin materials can be used for the photobioreactor enclosure if some structural support is also provided by an external relatively thick plastic or glass enclosure into which the plastic enclosure with the bridging elements is inserted. In this implementation, the photobioreactor may form a liner for a rectangular glass or plastic enclosure. Immersing the thin plastic photobioreactor enclosure in a water bath of similar height can perform the same function.
The shape of the projections 14 may be of any shape suitable to the installation or task, however a frusto-conical stepped configuration as shown in
The complete tall photopanel 12 may be assembled from one or a plurality of interlocking segments 13 to yield the desired height. Each segment 13 is configured with an upper engagement 18 fitting configured for a sealed engagement with a lower engagement 20 fitting of another segment 13 whereby they may be engaged and stacked to form the photopanel 12. The formed photopanel 12 is configured for sealed engagement with a water source to supply necessary fluid to the interior of all engaged segments 13.
The projections 14 or “hollow trabeculae” as conal structures may have different characteristics and may be formed in an infinite number of shapes a few of which are depicted in
While the sidewalls 15 may be formed in any process which yields the correct shapes, thermoforming is currently a favored mode of construction. Molds utilized in the thermoforming process may be built such that each mold may have differing conal height to conal base diameter ratios. The photopanel 12 can then be assembled with a highly customizable series of different trabeculae patterns to optimize light intensity and surface area as relative to available solar irradiance at a particular height. Furthermore the surface of the mold is made irregular with microprotrusions so that the surface of the “hollow trabeculae” provided by the projections 14 in contact with the algae culture is further expanded in terms of surface area in contact.
Specific components as depicted in
The liquid medium port 24, extrusion and drainage port 26 on the ends of the formed photopanel 12, may be interchangeable in part dependent upon culture method and particular culture requirements. The location of the sparger 22 at the bottom of the photopanel 12 is less flexible. These elements may be incorporated to the photopanel along the narrow sides of or en face to the photopanel.
Also shown in
The photopanel 12 formed in such a relatively inexpensive fashion with recyclable material is amicable to reforming and replacement approximately every 3 months. This ultimately solves biofouling and UV degradation of PET. This also allows crop rotation with selection of appropriate algal strain pairing with appropriate seasonal changes as well as optimized “hollow trabeculae” characteristics. Before reforming, the proteinaceous biofouling on old photopanels may be used as feed for simultaneous aquaculture.
The formation of the segments 13 in this fashion is inexpensive and allows them to be recycled and reformed when replacements are needed instead of attempting to clean and otherwise maintain segments 13 which have become dirty or where the plastic has clouded over time due to exposure to light. While other plastic material which will not cloud easily in sunlight might be employed, because the thermoforming allows for the plastic to be recycled, and because the engagement of the segments 13 affords an easy manner to form new photopanels 12 it may be much more cost effective to simply recycle the plastic from segments 13 which need maintenance and use newly formed segments 13.
As shown in
The most materially efficient and cost effective plastic membrane thickness may be selected. In considering the thickness of the sidewalls 15, consideration is made for the support they must provide, further thinning during thermoform of the projections 14 providing the trabeculae, as well as the tension placed on the segments 13 in the vertical orientation as related to weight of the formed photopanel 12 itself as well as the contained culture therein. The thickness of the sidewalls 15 should be able to adequately support the formed photopanel 12 and its contents and is calculable based on the strength of the plastic employed. Similarly, the thinness of the photopanel 12 is optimized with similar considerations, as the thinness is dictated by the height of the trabecular cones formed by the projections 14.
In addition, the thinness of the photopanel 12 as related to the height of the photopanel 12 may be such that a nutrient gradient can be easily established. The relative cross sectional area of the photopanel with the application of “hollow trabeculae” (
The deployment strategy with rack systems of
The deployment ability afforded by the rack system is shown in
The daytime configuration depicted in section “B” employs the provided means for translation of the photopanels 12, to position the photopanels 12 in alternating and/or angled positions to yield a more uniform distribution to each photopanel 12 of incoming light as shown. The translation and pivoting system thereby operates a means to maximize the positioning of the photopanels 12 for an optimum communication of incoming daylight. Employing the arms of the translating racks and a pivotal engagement provides a means to angle the photopanels to positions to maintain them substantially parallel to the incoming direct solar beams such as on bright sunny days (B).
Additionally shown in
There is shown in
For maximizing light transmission and positioning for maintenance, the photopanel 12 is operatively engaged upright to support 32 slidingly engaged to a rack 34 with a pivot 36 providing means to rotate the photopanel 12. Of course those skilled in the art will realize that the sparger and liquid medium port may be combined, and that other configurations might be employed for fluid and gas supplies to the photopanel 12 and such are anticipated within the scope of this application.
As shown in
In
The method and apparatus for the system herein, represents a new and improved system to scale up algae production into industrial quantities which employs novel vertically-oriented photosynthetic photobioreactors or photopanels and method of culture and deployment strategy.
The disclosed system optimizes the available solar energy for photosynthesis through the distribution of solar irradiance over a dramatically expanded surface area whereby the solar intensity is reduced toward or into optimal intensity range for algal photosynthesis. The disclosed photopanel device is highly adaptable to accommodate the diversity of algae strains, as well as geographic and seasonal variation utilizing common inexpensive and recyclable material. The disclosed photopanel design is especially adaptable for suspended as well as adherent algal cultures for the purpose of producing algal oil for use as biofuel. The new disclosed photopanel design addresses very specific nearly mutually exclusive culture needs for algal replication vs. algal fatty acid synthesis in the same continuous culture with ultra high cell concentrations.
Although the above described apparatus, methods, and features are advantageously applicable to the production of algal cultures in photobioreactors, the principles may be applied to other light dependent reactions as well. Such other applications may be biological in nature such as cell constituent or protein molecule processing or other biochemical reactions, or may involve organic or inorganic chemical reactions, such as compound synthesis.
While all the fundamental characteristics and features of the vertically disposed device and method for algae growth been shown and described herein, with reference to particular embodiments thereof, a latitude of modification, various changes and substitutions are intended in the foregoing disclosure and it will be apparent that in some instances, some features of the invention may be employed without a corresponding use of other features without departing from the scope of the invention as set forth. It should also be understood that various substitutions, modifications, and variations may be made by those skilled in the art without departing from the spirit or scope of the invention. Consequently, all such modifications and variations and substitutions are included within the scope of the invention as defined by the claims.
This application is a continuation-in-part of U.S. patent application Ser. No. 13/161,462, filed on Jun. 15, 2011, and also claims the benefit of U.S. Provisional Application Ser. No. 61/422,184 filed on Dec. 12, 2010 and U.S. Provisional Application Ser. No. 61/355,121 filed on Jun. 15, 2010. All of these prior filed applications are respectively incorporated herein in their respective entirety by reference thereto.
| Number | Date | Country | |
|---|---|---|---|
| 61422184 | Dec 2010 | US | |
| 61355121 | Jun 2010 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13161462 | Jun 2011 | US |
| Child | 13327686 | US |
