Method and apparatus for CO2 sequestration

A method and apparatus for growing algae for sequestering carbon dioxide and then harvesting the algae includes a container for a suspension of algae in a liquid and a bioreactor having a translucent channel in fluid communication with the container to absorb CO2 and grow the algae. A monitor determines the growth of the algae in the channel. A separator separates the grown algae from the suspension and an extractor extracts biomaterials from the grown algae.

Not applicable.

BACKGROUND

1. Field of the Invention

This invention relates generally to the field of CO2sequestration and more specifically to apparatus and methods for sequestering CO2using algae.

2. Background of the Invention

Increasing global levels of carbon dioxide (CO2) has been a worldwide concern for some time. Measured in terms of volume, there were about 280 parts per million CO2in air at the beginning of the Industrial Revolution, and today there are 360 parts per million (ppm), a thirty percent increase. The annual increase is 2 ppm, and rising. If present trends continue, the concentration of CO2in the atmosphere will double to about 700 ppm in the latter half of the 21st century. Many scientists now believe that most of the global warming observed over the past 50 years can be attributed to this increase in carbon dioxide from human activities.

It is well known that green plants uptake CO2through photosynthesis. Photosynthesis converts the renewable energy of sunlight into energy that living creatures can use. In the presence of chlorophyll, plants use sunlight to convert CO2and water into carbohydrates that, directly or indirectly, supply almost all animal and human needs for food. Oxygen and some water are released as by-products of this process. The principal factors affecting the rate of photosynthesis are a favorable temperature, level of light intensity, and availability of carbon dioxide. Most green plants respond favorably to concentrations of CO2well above current atmospheric levels.

While there are a number of ways to increase carbon dioxide uptake in biological systems such as plants, it has proven difficult to do so cost effectively. Various strains of algae offer the fastest CO2uptake. Ocean based enrichment programs are invasive and may lead to more problems than they solve. Specifically they tend to grow weed and filamentous forms of algae and can damage or destroy entire ecosystems. Efficient methods of harvesting the algae produced by such means are not in advanced development.

Land-based algae systems are very effective in capturing CO2, but are limited by available land space and cost. In an open passive or batch system, it is only possible to produce approximately 150 metric tons of dry biomass from algae per hectare per year. Using these figures, it would require over 200 hectares (495 acres) of open land to capture the output from a 1000-megawatt gas turbine power plant, not even taking into consideration weather and water availability. Critical to the production of large amounts of algae is the presence of light. Algae use light to convert CO2into sugars, i.e. photosynthesis. Unfortunately, light only penetrates a few centimeters into an active culture of algae. As the algae organisms multiply and the culture density increases, the degree of light penetration decreases. Some researchers have used fiber optics as a light source but thus far this method has been prohibitively expensive and ineffective. Consequently, there is a need for apparatus and methods for sequestering CO2using algae, which exposes the algae to a sufficient amount of light in a cost-effective manner.

BRIEF SUMMARY

A method and apparatus for growing algae for sequestering carbon dioxide and then harvesting the algae includes a container for a suspension of algae in a liquid and a bioreactor having a translucent channel in fluid communication with the container to absorb CO2and grow the algae. A monitor determines the growth of the algae in the channel. A separator separates the grown algae from the suspension and an extractor extracts biomaterials from the grown algae.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and the claims to refer to particular system components. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ”.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1illustrates an embodiment of a system for sequestering CO2using algae. In this embodiment, the system10includes an apparatus100with a culture tank101, a pump122, and one or more bioreactors131. The culture tank101, pump122, and bioreactors131are in fluid communication with each other and are connected to each other via a plurality of conduits or lines.

The culture tank101is filled with a suspension of algae and water. In embodiments, the volume of the algae suspension is monitored by a volume meter174included in the culture tank101. Typically, culture tank101has a rectangular structure. However, culture tank101may be of any configuration, i.e. cylindrical, known to one of ordinary skill that is optimal for culturing algae. Culture tank101is made of materials that are resistant to corrosion, such as polymers or stainless steel. In a preferred embodiment, culture tank101is constructed out of plastic, plastic liner, treated metal, or combinations thereof. Culture tank101also comprises at least one gas jet103. According to another embodiment, culture tank101is closed to the atmosphere such that apparatus100is a closed system. Having a closed system prevents contamination of the algae suspension as well as evaporation of the water. Thus, the only gas entering culture tank101is through gas jets103. Moreover, all culture medium and fluids entering bioreactors131are preferably sterile to prevent contamination. That is, the suspension is flowed through the bioreactors131under sterile conditions. As used herein, sterile conditions may refer to conditions known to those of ordinary skill in the art sufficient to maintain an aseptic environment free of contaminating germs or microorganisms.

The gas jets103introduce a CO2-containing gas into culture tank101. Gas jets103may comprise any type of suitable inlets such as valves, nozzles, gas diffusers or membranes. In a preferred embodiment, the plurality of gas jets103comprises a plurality of gas diffusers. Gas diffusers break up the introduced gas into smaller, more soluble bubbles. According to another preferred embodiment, a plurality of gas jets103is located at the bottom of culture tank. In an embodiment, gas jets103are provided a CO2-containing gas from gas supply line107by a gas compressor194. Gas compressor194pressurizes the gas for introduction to the algae suspension in the tank101. Preferably, the gas is ambient air bubbled into the culture tank101where the CO2in the air is then dissolved in the algae suspension.

Generally, the algae suspension entering the feed conduit120has a predetermined CO2concentration. In an embodiment, the CO2level is no more than about 5,000 ppm, or alternatively preferably no more than about 2,500 ppm, or alternatively more preferably no more than about 1,000 ppm. CO2concentration beyond a certain level causes the algae suspension to become acidic, thereby stunting algae growth. The CO2-enriched algae suspension is pumped from the culture tank101through feed conduit120to inlet manifold151for bioreactors131. Feed conduit120extends from the culture tank101to the pump122and then from the pump122to the inlet manifold151. Pump122is any suitable device capable of pumping the suspension. Examples of suitable devices include without limitation, centrifugal pumps, impeller pumps, or rotary pumps. In one embodiment, feed conduit120additionally comprises an air inlet valve124allowing more CO2-containing gas to saturate the algae suspension. Air inlet valve124is a one-way valve that allows gas to enter the feed conduit120, but does not allow any of the algae suspension to escape. Thus, the algae suspension is constantly being supplied with carbon dioxide.

Referring now toFIG. 2, inlet manifold151distributes the CO2-enriched algae suspension to the inlets132of each bioreactor131. The inlet132of each bioreactor131is preferably located on the top of each bioreactor131such that the algae suspension flows downward through the bioreactor131to the outlet134. Generally, the outlet134is disposed on the same face and near the same edge of the bioreactor131as the inlet manifold151as illustrated inFIG. 7.

Referring again toFIG. 1, typically, outlets134are located at the bottom of each bioreactor and lead to an outlet manifold153. The outlet manifold153may comprise a conduit made of a flexible hose material, such as but not limited to neoprene, silicon, rubber or other materials as known to one skilled in the art. Outlet manifold153distributes the flow into an outlet conduit139. Outlet conduit139re-circulates the suspension with uncompleted growth algae back into culture tank101and/or separates the suspension with completed growth algae for extraction by separator171.

In additional embodiments, outlet manifold153may have one or more vents177to purge any excess oxygen present in the bioreactors131. The one or more vents may comprise one or more purge valves178. Furthermore, the one or more vents may vent excess oxygen in a manner such as to maintain sterile conditions in the bioreactors131.

Alternatively, each bioreactor131has an individual outlet conduit139coupled to each outlet134. In another embodiment, each bioreactor131has an outlet conduit, which flows directly into culture tank101. Further each bioreactor131may have an outlet conduit which directs the algae into the inlet of another bioreactor131before returning to the tank101.

Referring toFIG. 1, an artificial light source196may be provided. Although the light source preferably is natural sunlight, one or more artificial light sources196may also be utilized. Examples of suitable artificial light sources are fluorescent lamps, halogen lamps, or other artificial lighting well known to one skilled in the art. In a specific embodiment, a combination of metal halogen lights and a sodium vapor lights is utilized. The artificial light sources may be arranged around the one or more bioreactors131to provide light to the algae within each bioreactor131.

The one or more bioreactors131may be entirely covered by a protective shell181shown inFIG. 1. The function of the shell181is to prolong the life of bioreactors131and protect them from environmental elements such as wind, rain and direct sunlight. In an embodiment, the protective shell181is a Quonset-type shell. The Quonset-shell is preferably made of a weatherproof material that is permeable to light. Examples of suitable materials include without limitation, polyethylene, polycarbonate, polyvinylchloride, polypropylene, or glass. In a further embodiment, the protective shell181is a greenhouse-type enclosure. Furthermore, the protective shell may be directly affixed to the bioreactor rack159illustrated inFIGS. 9 through 12. In such embodiments, the heat produced within the greenhouse-type enclosure can be converted to electrical power for powering supplemental artificial light source196.

Algae cultures preferentially grow and sequester CO2within specific temperature ranges. In embodiments, the optimal temperature ranges for CO2sequestering algae may be between about 10° C. and about 50° C., and more preferred between about 20° C. and about 30° C. It can be appreciated that this range is exemplary, as different species and strains of algae have different optimal growth temperatures. In embodiments, cooling or heating steps are taken when the temperature approaches within about 3° C. to about 5° C. of the end points of the optimal range. Furthermore, the regulation of shading, cooling and heating may change as a function of culture maturity. For example, after introduction to the bioreactor system100, algae may be sensitive to increased light intensity and preferring shading while the algae acclimate. Light intensity, ambient temperature, and humidity are factors that have an affect on the culture temperatures. As a means to optimize CO2uptake, devices to control the amount of light, the temperature and the humidity surrounding the bioreactor131may be included in the protective shell181. A removable shade180, as shown inFIG. 1, may cover a portion, the top or all of a bioreactor131or shell181. The shade180shields the bioreactor131and the algae suspension flowing therein from intense light. Additionally, the bioreactors131need to be kept within a temperature range favorable for CO2uptake by the algae. In order to address this property, a temperature control system190may be used. The system190may include liquid misters, fans, air conditioning units or combinations thereof for maintaining a favorable temperature. In preferred embodiments a system for controlling the temperature within the protective shell181may comprise fans192directing air across the exterior surface of the bioreactors131. Additionally, the temperature control system190may include heaters198, without limitation, in order to maintain algae suspension temperature in optimal ranges. Differential control of the shading, cooling and heating may be done manually or under the control of an automated system.

In a further embodiment, various lines such as inlet conduit120or outlet conduit139may be run underground to cool the culture medium and algae. The ground may act as a natural heat sink or heat exchanger to absorb heat from the warmer fluid within the lines, such as lines120,139. Even during the hot summer months, the ground may remain cool enough to cool the culture medium and algae flowing through apparatus100. In another embodiment, culture tank101is located underground.

As illustrated inFIG. 13, the apparatus100may be constructed as a two level building, such that the bioreactors131are positioned at a level above culture tank101and algae harvester171. Thus, pump122pumps the algae suspension from underground culture tank101to the top of the bioreactors131through feed conduit120. This arrangement facilitates access to the devices for cleaning, maintenance, repair and supplementing material into the algae suspension. Alternatively, culture tank101may be elevated at the same height as the top of bioreactors131. In such embodiments, the algae suspension flows from culture tank into the inlet manifold151by gravity. Pump122can be envisioned to pump the algae suspension from outlet line139to culture tank101.

Wherein the apparatus100comprises more than one bioreactor131, algae may be circulated or cycled through each bioreactor131at least once to maximize exposure of the algae to light. Ultimately, the algae from the one or more bioreactors131eventually return to culture tank101and then are continuously re-circulated again and again through one or more bioreactors131. Thus, the advantage of the continuous process is that even if some algae do not receive sufficient light in one cycle, chances are that those algae eventually will be exposed to light because of the continuous re-distribution of the algae through the one or more bioreactors131.

Any suitable algae may be cultured in the tank101. In a preferred embodiment, the algae species,Chlorella, is used. Other examples of suitable algae species include, without limitation, red algae, brown algae,Spirulina, or combinations thereof. According to preferred embodiments, the algae species is preferably non-filamentous so as not to clog the apparatus. In an embodiment, the algae species is a single-cell algae species ranging from about 1 micron to about 15 microns.

Generally, water, i.e. tap water or distilled water, is used to culture the algae. In an embodiment, the water is sterile and free from all contaminants. Alternatively, saltwater may be used to culture saltwater species of algae. However, any appropriate culture mediums known to those of skill in the art may be used depending on the specific algae species.

In other embodiments, a plurality of fish may be maintained in culture tank101. The fish consume algae as well as produce nitrate in the form of feces. The fish feces are used to further nourish the algae. In further embodiments, culture tank101may include one or more feed inlets to introduce or provide additional nutrients to the algae. The one or more feed inlets may be coupled to one or more feed tanks filled with specific types of nutrients, minerals, mediums, or the like. In an embodiment, the one or more feed tanks may be disposed in series or in parallel to the culture tank101. Preferably, feed inlets and feed tanks are maintained under sterile conditions.

The bioreactors131are generally constructed from any transparent or translucent polymeric material. In other words, a polymeric material that is permeable to light. Furthermore, the polymeric material is preferably a flexible material. A flexible material allows the bioreactor to compensate for different and varying flow rates as well as being easier to handle. In some cases, the polymeric material may even possess elastic properties. Furthermore, the polymeric material is UV treated to withstand repeated and extended exposure to light. In alternative embodiments, it can be envisioned that the polymeric material is a rigid material. Examples of suitable materials include without limitation, polypropylene, polystyrene, polypropylene-polyethylene copolymers, polyurethane, or combinations thereof. In a preferred embodiment, the bioreactors131are made of polyethylene. Any type of polyethylene may be used including high-density polyethylene or low-density polyethylene. A rigid material resists pressure, weight and flow velocity based deformations. Additionally, a rigid material may increase laminar flow of the algae suspension through the bioreactor131.

The thickness of the polymeric material is in the range of about 3 mils (0.003 inches) to about 10 mils (0.010 inches), more preferably from about 4 mils (0.004 inches) to about 6 mils (0.006 inches). The polymeric material preferably has a tensile strength capable of withstanding the weight of the suspension flowing through the bioreactor, such as the weight of at least 50 gallons of suspension. The polymeric material is typically produced in the form of a tube and is heat sealable. The tubular polymeric material is folded forming adjacent sides that are heat sealed to close the upper and lower ends of the tubular polymeric material and to form internal flow channels133, hereinafter described in further detail. It should be appreciated that the bioreactors131may be made from two planar sheets of polymeric material that are heat sealed along their periphery, sealing the sheets to form bioreactors131. In embodiments, the bioreactors131may be made of a rigid material as previously described.

According to a preferred embodiment, bioreactors131are substantially planar in configuration. In an exemplary embodiment, each bioreactor is about 10 ft tall and about 2 ft wide, alternatively about 10 ft tall and about 4 ft wide, alternatively about 10 ft tall and about 10 ft wide. However, in other embodiments, each bioreactor may range from about 4 feet wide to about 30 feet wide and from about 5 feet tall to about 20 feet tall. Moreover, the height to width ratio of each bioreactor may be any ratio. In embodiments, the height to width ratio of each bioreactor may range from about 10:1 to about 1:1. In addition, each bioreactor131may have different heights and widths in order to optimize light exposure to the circulating algae.

Referring toFIGS. 1,2A and2B, flow channels133are formed by a plurality of baffles or partitions135. Baffles135serve to maximize the residence time of the algae in each flow channel133. The greater the residence time of the algae, the longer the algae in the bio-reactor131is exposed to light. In embodiments, the residence time of the algae in bioreactors131may range from about 1 minute to about 60 minutes, alternatively preferred from about 5 minutes to about 45 minutes, alternatively more preferred from about 10 minutes to about 15 minutes. In an embodiment, the baffles135may be created by heat-sealing, ultrasonic welding or other methods for joining the polymeric material at specific locations along adjacent sides of the material.

Baffles135define the flow channel133within each bioreactor131.FIG. 2Bshows a cross-section of channels133in one embodiment of a bioreactor131. InFIG. 2B, h refers to the height of each channel133(the space between each baffle135) and w refers to the maximum width of each channel133. Preferably, h is no more than about 3 inches. Additionally, in most embodiments, h is preferably no more than about 2 inches. The width, w, of each channel is set such that the algae flowing through each channel133receive sufficient light to survive and grow. The weight of the suspension flowing through the bioreactor stretches the non-rigid polymeric material causing the width w to be maintained at a minimum so as to allow the light passing through the polymeric material to reach all of the algae in the suspension flowing through the channels133. This weight prevents the channels133from ballooning so as to increase the width w and prevent the light from reaching the algae flowing through the center of the channel133.

In certain embodiments, baffles135are arranged in an alternating horizontal configuration to form generally horizontal channels139and return or end channels137. Each horizontal channel139has an open end141and a closed end143. End channel137is formed around the open end141of an upper baffle135together with a closed end143of an adjacent lower baffle135. Baffles135form a serpentine configuration of the channel133.

Channels133have configurations to minimize dead spaces in the channels. Dead spaces are fluid/air interfaces in the channels133where a pocket of air develops creating a dry pocket or area where there is no flow. These cause stagnant areas fostering contamination. The suspension tends to leave residue in the dead spaces such as polysaccharides forming secondary metabolites in the form of sugars and starches. This residue tends to stick to the walls of the channels133which then fosters the growth of bacteria that can harm the overall system. Therefore it is an objective to completely fill the channel and maintain fluid velocity as high as possible without buckling or pinching the walls of the bioreactor131.

In embodiments it is preferred to create turbulent flow at potential dead spaces to prevent stagnant flow and contamination. Bioreactors131made of a material that can deform, distend or inflate allows the dimension of the channels133to vary thus making it difficult to ensure flow through potential dead spaces because the wall of the channel133is not longer smooth and uniform. In embodiments, a rigid bioreactor may be used such as a thermal formed plastic. With a rigid bioreactor, the flow through the bioreactor may be substantially laminar. It is desired that the suspension completely fill the channels133such that there are no dead spaces as the suspension flows through the bioreactor131.

Each baffle end141, as shown inFIGS. 3 and 4, creates turbulence in the algae suspension as it flows downward through the bioreactor131. The turbulence creates vortexes at these ends141, which allow for better mixing of the algae suspension and prevention of dead spaces. As shown inFIG. 4Aadditional baffles may be configured in vertical orientations to the horizontally arranged baffles135to increase residence time of the culture suspension.

Referring now toFIG. 3, in an additional embodiment, baffles135may be angled upward to increase residence time of algae in bioreactor131. That is, each baffle135forms an upward acute angle155with the side157of bioreactor131toward the top of bioreactor131. A corner149or pocket is formed at the intersection of each baffle135and side157of bioreactor131. Corner149may cause the formation of vortexes in the circulating algae and culture medium. As algae flows through bioreactor131, the algae may circulate or swirl temporarily in the vortices or mixing zones formed at each corner149thus, altering laminar flow to turbulent flow and increasing exposure time of the algae in bioreactor131to light and preventing dead spaces. In some embodiments, baffles135may be angled downwardly as shown inFIG. 4D. Thus, it is envisioned that baffles135may be angled at any suitable angle from the side157of bioreactor131ranging from about 30° to about 160° from horizontal.

Referring now toFIGS. 4A-4D, in general, each baffle135is angled at the same angle. However, in other embodiments, each baffle135may be angled at different angles to each other.FIGS. 4A-Dillustrate various configurations of baffles135which may be incorporated into bioreactor131.FIG. 4Bshows an embodiment where baffles135are all upwardly angled.FIG. 4Cshows an embodiment where baffles135are configured in an alternating upward and downward angled parallel arrangement.FIG. 4Dshows an embodiment where baffles135are all downwardly angled. It is to be understood that the arrangement of baffles135is not limited by these preferred embodiments, but may comprise an unlimited number of configurations to increase the sequestration of CO2by the algae. For example the baffles may be angled in the same direction, but retain different angles of elevation from horizontal. In embodiments with a plurality of bioreactors131, each bioreactor may comprise a different baffle arrangement or configuration in order to optimize algae residence time.

Referring now toFIGS. 5A-5C, according to preferred embodiments, the plurality of transparent bioreactors131are suspended or hung vertically. Bioreactors131may be hung in any suitable configuration. However, it is desirable for bioreactors131to be hung such that each channel133is exposed to the maximum amount of light.FIGS. 5A-Cdepict a schematic top view of the different variations at which the bioreactors131may be hung or suspended from a top-down view.FIG. 5Ashows a typical embodiment in which the bioreactors are configured in a rectangular matrix formation. For example, inFIG. 5A, the matrix is two bioreactors wide and 6 bioreactors deep.FIG. 5Bshows yet another embodiment in which the matrix is 6 bioreactors wide and two bioreactors deep. In embodiments where bioreactors are arranged in a matrix formation, the bioreactors131preferably are no more than 6 inches apart.FIG. 5Cillustrates another embodiment in which the bioreactors are arranged in a polygonal configuration. Thus, the bioreactors provide nearly unlimited possibilities in configurations so as to maximize exposure of the culture medium to light.

In further embodiments illustrated inFIGS. 7 and 8, the bioreactor131may have flow means in the channel133to improve suspension flow within the baffles135. The flow means may include additional heat sealed areas136that prevent the suspension from becoming stagnant, immobile or settling. In exemplary embodiments, the bioreactors131include a sloped sealed area160in the baffle135immediately adjacent to the inlet132, such that suspension does not become trapped between the inlet132and the outer edge of the bioreactor131. Additionally, the bioreactor131includes a sloped bottom baffle162to maximize the flow of the algae suspension to the outlet134. In certain embodiments, the end channels137are formed to create a curved or radiused channel164for the flow of the culture suspension. The radiused channel164may comprise a smaller cross-sectional area than channel133. The smaller cross-sectional area acts to accelerate the flow through radiused channel164in a manner to induce additional turbulence in the following channel. Radiused channel164eliminates dead spaces, such as stagnant gas and fluid pockets, in bioreactor131that may permit contamination of algae suspension. Examples of contamination may include biofilms and degrading algae cells.

Referring toFIG. 8, the flow means formed by the baffle ends141may comprise alternative shapes such as but not limited to a triangle, a square, an ellipse, a circle or a teardrop such that the algae suspension flow increases turbulence about the baffle end141. In most preferred embodiments a teardrop shaped baffle end166is oriented with the thin tapered end168facing into the flow on top channel133a, while the blunted round end170faces the end channel137. This orientation creates a gentle slope for flow of the suspension around and over the baffle end141, before creating a sharper drop off into the end channel137. Further, the shape of baffle end141creates turbulence by directing the flow through the channel133upward slightly before entering the channel end137. The upward displacement of the liquid before cascading vertically through the channel end137to a lower channel133bcreates a vortex or turbulent swirl in the lower channel133bwithout excessive flow interference. The teardrop shaped baffle end166reduces the cross-sectional area of the end channel137to accelerate flow from the larger top channel133ainto the smaller cross-sectional area of end channel137. Fluid flow then passes into the larger cross-sectional area of lower channel133b. The velocity of the flow over the teardrop shaped baffle166in the upper channel133acreates a high pressure area due to Bernoulli's principle and/or a Venturi effect. As flow passes into the end channel136, there is a pressure drop into the lower channel133bcausing turbulence and mixing. The turbulent flow of the algae suspension prevents the algae from clinging or sticking to the inside surfaces of the walls of the bioreactor131. Furthermore, the baffle end141shapes may increase the durability of the bioreactor131by decreasing deformation, tearing, delaminating or other related plastic stress wear as understood by one skilled in the art.

In embodiments, the baffle end141is between about 0.25 inches and about 2 inches wide, preferably between about 0.25 inches and about 1 inch, and most preferably between about 0.5 inches and 0.75 inches wide. Other shapes of the baffle end141may alter flow through the channel so as to create vortices within the channel133prior to introduction to the channel end137. The created turbulent swirl mixes the algae solution and gases within the bioreactor131.

According to another embodiment, each bioreactor131includes a gas inlet163as seen inFIG. 2A. In an embodiment, a gas such as carbon dioxide is introduced (e.g. bubbled) in each bioreactor131through gas inlet163. Gas inlet163is typically disposed at the bottom or lower end of each bioreactor131. However, gas inlet163may be disposed at any portion of bioreactor131. Furthermore, gas inlet163may include a valve for adjusting the flow of gas into bioreactor131. The gas may be introduced from gas supply107or from another source such as ambient air. Any suitable gas may be introduced into bioreactor131through gas inlet. The gas introduced into bioreactor131may serve several purposes. For instance, the bubbling action of gas through the bioreactor131may facilitate further agitation and mixing of the algae and the culture medium within bioreactor131. Without being limited by theory, the introduction of gas also may serve to maintain the rate of photosynthesis by the algae as the photosynthetic reaction is dependent on CO2concentration. If the CO2concentration within the bioreactor131drops too low, the algae may cease its photosynthesis. Moreover, introduction of CO2-containing gas into bioreactor131via the gas inlet may provide a further means of absorbing or sequestering CO2from the ambient air.

Referring toFIGS. 9 and 10, in certain embodiments, bioreactors131are hung at different heights. In further embodiments, the reactors are hung from racks159. The racks159may be comprised of about four parallel vertical support members201that are positioned approximately at the corners of a rectangle. Vertical support members201have a first lower end201alocated at ground level and a second upper end201bvertically disposed from the first end201aat a height Hr. The vertical support members201are positioned at a width Wfapart in one dimension, such that Wfis larger than the width w of the bioreactor131. In another dimension, the vertical support members201are positioned at a length apart Ls. The vertically oriented support members201disposed thusly and connected by parallel beams207, with a length of Ls, and a height above ground of Hb, at the second end201b. The rack159for the support of at least one hanging member205is disposed between parallel beams207for hanging one or more bioreactors131. The bioreactor hanging racks159are spaced a distance Lbapart, such as no more than six inches. The height and width of the bioreactor hanging racks159is dependent on the dimensions of the bioreactors131. In alternative embodiments, the hanging racks159may have alternate dimensions to hang bioreactors131at different heights, orientations and configurations. Hanging bioreactors131at different heights, orientations and configurations changes the flow rate of the algae suspension through each bioreactor131. It is believed that differing flow rates for each bioreactor131provides improved distribution of light to each bioreactor131

Referring now toFIG. 6, in an additional embodiment, bioreactor131may include an agitating means having at least two cleaning members148to cause any algae settling or clinging to the interior of the bioreactor131to drop off and flow through the bioreactor131. In some embodiments, cleaning members148are elongate bars or rollers movably disposed horizontally on either face of bioreactor131. In other words, bioreactor131is disposed in between agitation members. In an embodiment, agitation members148are coupled to vertical tracks146disposed on both sides of bioreactor131. Agitation members148may compress bioreactor131between each member148and move vertically up or down the height of bioreactor131to unsettle any settled algae or to release any algae that has attached to the inner surface of bioreactor131. Furthermore, agitation members148may be coupled to vertical tracks146by movable screw arms such that agitation members148move up and down to compress and release each bioreactor131. Agitation members148may be operated by computer control or manually.

FIGS. 11 and 12illustrate alternative agitation means to agitate algae suspension flow within the bioreactors131and can be manipulated to temporarily alter, agitate or displace the flow within the bioreactors131. The agitation means may include an angling means for lifting one side of the bioreactor131and alter the angles of the channels133with respect to horizontal. The angling means may be any member that directionally displaces a bioreactor131, such as but not limited to a piston, an actuator, a pushrod or a cam. In embodiments the hanging member205has a first end205aand a second end205b. A pivot connection209pivotably connects end205aof the hanging member205to vertical support member201. The pivot connection209can be any structure or device commonly known, such as a ball joint, a cradle or a hinge. As illustrated, cradle172may be disposed on vertical support201, for receiving a pivot head174disposed on end205aof member205. The other end205bof hanging member205is a free articulating end. The free end205bhaving a first position, wherein the hanging member205remains substantially parallel with the ground, appreciably in contact with the rack159, and a second position wherein the free end205bis vertically displaced above the bioreactor131, such as between about 2 inches and about 24 inches, preferably between about 2 inches and about 12 inches, and most preferably between about 4 inches and 6 inched above the first position. Disposed at the second end205bmay be a lifting member217to mechanically mediate the translocation of the free end205b. The lifting member217is in mechanical interface with the lifting device211ofFIG. 11or cam213ofFIG. 12. The lifting member217may be a part of the parallel bar207, at the second end205bof individual hanging members205, at the ends of multiple hanging members or combinations thereof. The lifting member217can be envisioned as a pivot point, a ball joint or other mechanism to allow interaction or a linkage between the lifting member217and the lifting device211.

In embodiments the action of the lifting device211or the cam213vertically disposes the free end205bof the hanging member205for duration of time t. Time t maybe any suitable time to temporarily disrupt the flow of algae suspension through the bioreactor131. In embodiments t is between about 2 minutes and about 60 minutes, preferably about 2 minutes and about 10 minutes, and more preferably between about 2 minutes and about 5 minutes. The lifting of one side of the bioreactor131as shown in broken lines inFIGS. 11 and 12, varies the flow rate and angle of the channel133and pools an additional volume of the algae suspension in the opposing channel ends137. Upon lowering or replacing the raised end of the bioreactor131, the volume of water released to flow varies across the channel133. The rapid transfer of this volume across the channel133agitates, re-suspends and flushes sediment or settled algae from the channel133. In alternative embodiments, the free end205bmay be lifted and lowered rapidly at least once to agitate, re-suspend and flush the channel133. In preferred embodiments, the agitation means is activated periodically each day.

Referring toFIGS. 1 and 14, a plurality of sensors215monitor predetermined parameters of the algae suspension prior to introduction to the bioreactors131. The algae suspension then flows down through the circuitous channels133of bioreactors131via gravity flow. As the suspension flows down through the bioreactors131, the algae in the mixture are exposed to light, preferably natural sunlight. The algae uptakes or sequesters the CO2dissolved in the suspension and converts it into sugars and carbohydrates through the process of photosynthesis. In photosynthesis, a photon strikes a chloroplast within the organism. The chloroplast contains the compound chlorophyll. In the presence of chlorophyll and CO2, a chemical reaction takes place forming carbohydrates, sugars, and oxygen. Thus, through the natural process of photosynthesis, the algae suspension sequesters the CO2and converts it into other useful carbon compounds. The produced compounds are a source of nutrients for the algae allowing further growth and production of algae. When no light is available, the algae go through cellular respiration, converting the sugars into energy for the production of further algae. In an embodiment, about 1,000 to about 1,200 tons of CO2per hectare (2.5 acres) of land may be sequestered a year.

After the algae suspension has flowed through bioreactor131the same predetermined parameters of the algae suspension are measured by sensors216disposed at the exit of the bioreactor131. In embodiments, the sensors215,216relay information about the algae suspension parameters to a computer219for comparison of the information against predetermined ranges. Computer219controls a nutrient pump244to inject nutrients to maintain the preferred and/or predetermined parameters for optimized algae growth.

Conditions of the suspension may be monitored using any suitable type monitoring devices. Variables that may be tracked using monitors215and216include without limitation, pH, temperature, conductivity, turbidity, dissolved oxygen, chlorophyll concentration, as well as the concentration of nitrates, ammonia and chloride. These variables may be recorded through out the process or apparatus100.

In certain embodiments, the temperature of the algae suspension is monitored by temperature probes215aand216a, before and after the bioactors131respectively. As the suspension passes through bioreactor131as illustrated inFIG. 14, temperature is maintained between about 0° C. and about 50° C., preferably between 10° C. and about 40° C., and most preferably between about 15° C. and about 35° C. Regulation of the temperature of the culture is necessary to maximize the growth of the algae in bioreactors131. High temperatures may kill the culture and low temperatures may impede growth or damage cells within the culture.

Dissolved oxygen concentration in algae suspension by monitors215band216bis monitored to ensure the algae are continuing photosynthesis. Photosynthesis requires CO2and high concentrations of dissolved oxygen inhibits this process. The dissolved oxygen concentration is in a range of about 0 mg/L to about 50 mg/L, preferably about 0 mg/L to about 30 mg/L and most preferably between about 6 mg/L and about 8 mg/L. CO2and other gases may be bubbled into the algae suspension to decrease the dissolved oxygen concentration.

The turbidity of the solution is tracked by monitors215cand216cto maintain the suspension within a range of about 0 NTU to about 300 NTU, preferably between about 20 NTU and about 200 NTU and most preferably between about 150 NTU and about 200 NTU. Turbidity is a further measure of solids, particulate and microscopic matter suspended in a liquid. In the apparatus100, the turbidity data aids in determining cell density.

The flow rate of the algae suspension is dependent on the height of bioreactors131and other factors. The flow rate is tracked by monitors215dand216d. In general, the flow rate of the suspension flowing through each bioreactor may range from about 1 gallon/hr to about 100 gallons/hr, preferably from about 5 gallons/hr to about 75 gallons/hr, more preferably from about 10 gallons/hr to about 50 gallons/hr. Alternatively, the flow rate of the algae suspension through the bioreactors may range from about 1 cm/s to about 50 cm/s, preferably from about 3 cm/s to about 25 cm/s, more preferably from about 5 cm to about 15 cm/s.

Chlorophyll is the green pigment found in algae. The chlorophyll concentration is monitored by monitors215eand216ebefore and after flowing through bioreactors131. Chlorophyll concentration is maintained to be within the range of about 0.01 mg/L to about 8 mg/L. The concentration of chlorophyll in the algae suspension is one factor in determining the maturity of the algae in the suspension. Additionally, the concentration of the chlorophyll in the bioreactors131influences the light penetration into the media and the quantity of light reaching the interior of the bioreactor131.

The conductivity of the algae solution is an indicator of the quantity and types of nutrients and minerals in the suspension. Monitoring the conductivity within predetermined parameters at monitors215fand216fverifies the total dissolved solids within the suspension before and after the suspension flows through bioreactor131. The conductivity is maintained within the range of about 50 μS/cm to about 30,000 μS/cm, preferably between about 500 μS/cm and about 3,000 μS/cm and most preferable between about 500 μS/cm and about 1,500 μS/cm.

Nitrogen is a nutrient for the successful culturing of algae as it is a key component in the biosynthetic pathways to produce chlorophyll and proteins within the algae. In order to maintain an actively growing algae culture within the bioreactor131, a level of accessible nitrogen compounds, or nitrates, is maintained in the suspension. It is preferred to maintain a nitrate concentration between about 0 mg/L and about 200 mg/L in the suspension. Monitors215gbefore and216gafter the suspension passes through bioreactor131notify computer219if the nitrate concentration varies from the predetermined range. Ammonia may be an additional nitrogen source that is monitored in suspension and has monitors215iand216i. In embodiments, the ammonia concentration in the water is regulated to maintain a range of about 0 mg/l to about 50 mg/L.

In exemplary embodiments, the pH is maintained in a range of about 0.5 to about 13.5 dependent on the species of algae. In order to identify fluctuations in pH, it is monitored by monitors215hand216hbefore and after the bioreactors131. The pH is preferred between about 5.5 and about 8, and most preferably between 6.5 and 8. Acidic or basic environments are unfavorable to grow concentrations of algae. If the pH of the media changes, it may identify changes within the algae culture, or inhibit the growth of the culture. Additional gaseous CO2may be bubbled into algae suspension prior to introduction to bioreactor131by CO2jet221or by jet163to adjust the pH of the solution.

Ion chloride is beneficial to regulate the osmotic balance within the suspension of algae. The chloride content of the media is dependent on the natural environment of the algae; fresh water species require a lower salinity concentration. In embodiments, the range of chloride concentration is maintained at between about 0 mg/L and about 100 mg/L. Monitors may be included to monitor the ion chloride.

The algae suspension leaving the bioreactors131may pass through an algae growth monitor225. Algae growth or concentration in suspension may be monitored by measuring the light level, which penetrates each bioreactor131. For example, if the light level is less than about 250 foot-candles, algae growth has likely reached a saturation point or density in which light cannot penetrate the innermost areas of bioreactors. In another embodiment, algae growth or concentration may be measured using methods or devices known by those skilled in the art to measure cell density (i.e. cells/mL of culture solution). For example, devices and methods such as without limitation, a Coulter Counter® Micro-sizer 3 or centrifugation may be used to determine cell density. Upon reaching a predetermined cell growth or density, the algae may be harvested as hereinafter described.

The algae may now be directed to a collector tank220. The collector tank220collects the algae suspension from multiple bioreactors131. In certain embodiments, the collector tank220may include a means to introduce gases to the suspension, or alternatively to vent gases from the suspension. The collector tank220may be in fluid communication with a separator222. The separator222divides the algae suspension into separate process streams.

The separator222routes the algae suspension into the separate streams based on the measured parameters of the algae growth monitor225.FIG. 14illustrates the separator222that divides the algae suspension into two parts an uncompleted growth algae part222a, and/or a completed growth algae part222b.

In one embodiment, the uncompleted growth algae part222aof the algae suspension stream is returned to the algae tank101by conduit241. The algae suspension may have nutrients, algae cells or other biomaterials without limitation added to the suspension by an injection means244in conduit241before return to the algae tank101. The tank101includes an oxygen vent104and a compressed air inlet105receiving compressed air from a compressor106.

Once it is determined that algae growth has reached a predetermined cell density or other parameter, the suspension with completed growth algae is separated by separator222and is routed to a settler224by conduit167. The completed growth algae part222bof the algae suspension is then pumped through harvest conduit167to an algae harvester171.

Settler224initiates the process of harvesting by routing algae suspension to the harvester171. The settler224filters the algae from the suspension. Once the suspension ceases flowing and agitation, the algae will settle out of the liquid suspension. The liquid media may then be decanted or skimmed from the settled algae and recycled back into the algae tank101. Removal of excess media from the algae suspension by the settler224creates a high viscosity slurry of algae.

Alternatively, the algae may be kept in the settler224for a predetermined time period to starve the algae. In embodiments, starving the algae may act to stimulate, stress, or otherwise initiate the production of desirable biomaterials within the algae. Biomaterials may include, without limitation, proteins, carbohydrates, oils, fats, nucleic acids, or other biological materials known to one skilled in the art. Additionally, other chemicals may be added to the settler to increase production of the desired biomaterials. The algae slurry is pumped from the settler224by slurry pump226to harvesting system171. The rate at which the slurry is pumped to the harvesting system may be monitored by a monitor227at the pump226.

Generally, the algae harvester171is used to remove and recover algae so that it can be used for other purposes. In embodiments illustrated inFIGS. 1 and 14, conduit167runs from the separator222to algae harvester171. In alternative embodiments, the bioreactor outlet conduit139may run directly from the bioreactor131to the algae harvester171. Generally, algae harvester171comprises a filter, skimmer, centrifuge or other means to strain out algae from the algae suspension.

In embodiments, the algae may be isolated from the media suspension by centrifuging. The centrifuge230creates a paste, pellet or bolus of algae, with the media floating on top. Removal of the liquid media leaving an algae paste. In further embodiments, the remaining media may further be removed from the paste by spray drying the algae. From a spray dryer232the algae goes to a biomaterial extractor234.

In another embodiment, algae is filtered from the algae suspension and then deposited on a conveyer belt. The conveyor belt passes through a drying chamber or a heater to dry the algae. The dried algae are then collected for future use. In some embodiments, the dried algae are used to produce oil. The filtered water is returned to culture tank101through a recycle conduit165shown inFIG. 1.

In general, the disclosed methods and apparatus are capable of reducing the CO2level in an area by an amount ranging from about 100 ppm to about 1,900 ppm.

An algae extraction process is described in U.S. Patent Application No. 61/056,628, filed May 28, 2008, entitled Method and Apparatus for Algae Separation, hereby incorporated herein by reference. The algae separation apparatus228includes a micro-bubble flocculation column with an inlet and outlet, a micro-bubble generator, and an electrical charge generator. The micro-bubble generator generates micro-bubbles, preferably having a size less than 100 μm, with the electrical charge generator placing a charge on the micro-bubbles that is opposite to the charge of the algae. The algae enter through the inlet and are mixed with the charged micro-bubbles by the cavitations of the liquid in the column to form a froth. The resultant froth is comprised primarily of air. The micro-bubbles are sized to float the algae of a certain size, shape, and/density vertically up through the micro-bubble flocculation column. At a point where the algae reach its highest point in the column, the outlet in the column removes the algae and froth. In exemplary embodiments, the froth carries the algae within a certain size range to the outlet for isolation from the media. The algae are then withdrawn as a slurry at the outlet for extraction of the desired biomaterials from the algae. A negative pressure may be applied at the outlet to assist the removal of the algae from the column.

The algae slurry is than transported to extractor234where it is processed to extract certain biomaterials. Extraction may be conducted by any means known to one skilled in the art. In embodiments, the extraction method may be super critical fluid extraction, solvent extraction, or cold press expeller extraction, in preferred embodiments the extraction technique is super critical fluid extraction. Once the biomaterials are extracted, they may be transported to a separation system242. In embodiments oils are separated for processing independently from other biomaterials such as proteins, sugars or other biomaterial, without limitation.

The water and media suspension that is removed from harvester171is transported by return conduit175to a water reclamation device or recycler173. The water recycler173includes means to treat algae growth media. The media may require sterilization to remove any contaminating micro-organisms prior to return to tank101. Sterilization may be conducted by any means as known to one skilled in the art, including but not limited to boiling, steam, pressure or irradiation. The media and water are moved through a UV sterilizer240to kill any contaminant organisms. Additional nutrients, media and water may be added to the suspension to make up for the loss in the harvesting system by nutrient pump264.

Additionally, illustrated inFIG. 1, water vapor is pumped from culture tank101to water recycler173via the water recycle conduit161. In certain embodiments, the water recycler173includes a condenser, which condenses the water vapor. Furthermore, the water recycler173comprises a filtration system to purify the water and a make-up water/nutrients supply261before sending the recycled water back to the culture tank101. Alternatively, water recycler173may comprise any device known to those of skill in the art used to purify water.

Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations may be made herein without departing from the scope of the invention as defined by the appended claims. Likewise, the sequential recitation of steps in the claims is not intended to require that the steps be performed sequentially, or that a particular step be completed before commencement of another step.