Patent Publication Number: US-2011076747-A1

Title: Algae Producing Trough System

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit and is a continuation-in-part of co-pending U.S. patent application Ser. No. 12/436,583, filed May 6, 2009, which is a continuation-in-part of co-pending U.S. patent application Ser. No. 12/156,506, filed Jun. 2, 2008, which claims the benefit of provisional application No. 60/932,674, filed May 31, 2007, and Ser. No. 12/436,583 also claims the benefit of provisional application number 61/126,701, filed May 6, 2008. 
    
    
     FIELD OF INVENTION 
     This application relates to mechanical aeration of a biomass. This application relates particularly to a method and apparatus for simultaneously aerating and circulating a biomass while providing nutrients to the biomass to stimulate chemical changes therein. 
     BACKGROUND 
     Microscopic algae are unicellular organisms which produce oxygen by photosynthesis. Microscopic algae, referred to herein as algae, include flagellates, diatoms and blue-green algae; over 100,000 species are known. Algae are used for a wide variety of purposes, including the production of vitamins, pharmaceuticals, and natural dyes; as a source of fatty acids, proteins and other biochemicals in health food products; as an animal feed supplement with nutritional value equivalent to that of soybean meal; for biological control of agricultural pests; as soil conditioners and biofertilizers in agriculture; the production of oxygen and removal of nitrogen, phosphorus and toxic substances in sewage treatment; in biodegradation of plastics; as a renewable biomass source for the production of a diesel fuel substitute (biodiesel) and other biofuels such as ethanol, methane gas and hydrogen; to scrub CO 2 , NO x , VO x  from gases released during the production of fossil fuel; and as animal feed. With so many uses, it would be desirable to mass produce algae in a low-cost, high-yield manner. 
     Algae use a photosynthetic process similar to that of higher-developed plants, with certain advantages not found in traditional crops such as rapeseed, wheat or corn. Algae have a high growth rate; it is possible to complete an entire harvest in hours. Further, algae are tolerant to varying environmental conditions, for example, growing in saline waters that are unsuitable for agriculture. Because of this tolerance, algae are responsible for about one-third of the net photosynthetic activity worldwide. Cultivation of algae in a liquid environment instead of dirt allows them better access to resources: water, CO 2 , and minerals. It is for this reason that the algae are capable, according to scientists at the National Renewable Energy Laboratory (“NREL”), “of synthesizing 30 times more oil per hectare than the terrestrial plants used for the fabrication of biofuels.” (John Sheehan, et al.) The measurement per hectare is used because the important factor in the algae&#39;s cultivation is not the volume of the basin where they are grown, but the surface exposed to the sun. Productivity is measured in terms of biomass per day and by surface unit. Thus, comparisons with terrestrial plants are possible. Professor Michael Briggs at the University of New Hampshire estimates that the cultivation of these algae over a surface of 38,500 km 2 , and situated in a zone of high sun-exposure such as the Sonoran Desert, would make it possible to replace the totality of petroleum consumed in the United States. Interest in the biotechnology is therefore immense. Arid zones are ideal for the cultivation of algae because sun exposure is optimal while human activity is virtually absent. These algae can be nourished on recycled sources such animal manures. Presently, research is being done on algae that are rich in oils and whose yield per hectare is considerably higher than other oilseed crops such as corn and rapeseed. NREL and the Department of Energy are working to produce a commercial-grade fuel from triglyceride-rich micro-algae. NREL has selected 300 species of algae, both fresh water and salt water algae, including diatoms and green algae, for further development. 
     Yield can be limited by the limited wavelength range of light energy capable of driving photosynthesis, between about 400-700 nm, which is only about half of the total solar energy. Other factors, such as respiration requirements during dark periods, efficiency of absorbing sunlight, and other growth conditions can affect photosynthetic efficiencies in algal bioreactors. The net result is an overall photosynthetic efficiency that has been too low for economical large scale production. The need exists for a large scale production system that provides the user a cost-effective means of installation, operation and maintenance relative to production yields. It is desirable that such a system also increase photosynthesis to maximize production yield. 
     In order to produce optimal yields, algae need to have CO 2  in large quantities in the basins or bioreactors where they grow. However, known systems employ inefficient processes of aerating the algae with CO 2 . Typical open-pond or basin systems have a single injection point for the CO 2 , which is expect to diffuse throughout the biomass. The pond or basin is very large, however, and even if the CO 2  successfully diffuses throughout the biomass, it takes a very long time to do so. Another solution is the raceway system, wherein a paddle wheel pushes the biomass around a track. Again, a single point of injection, typically near the paddle wheel, “loads” the biomass with CO 2 . The CO 2  is consumed long before the algae again reach the injection point, resulting in a period of time when the algae is not growing as fast as it could be. Closed bioreactor systems employ similar CO 2  loading techniques, where one or multiple injection points load CO 2  that is completely consumed by the biomass before it reaches the next injection point. It would be advantageous to maximize contact between the CO 2  gas and the developing algae by providing continuous aerating of the algae biomass. 
     In addition to CO 2 , the growth rate of algae may benefit from exposure to other nutrients that are common in known plant fertilizers. These nutrients include nitrogen, phosphorus, potassium, and other micronutrients. Known systems that provide such nutrients to the algae biomass do so at a single point of injection, loading the algae as described above. The same drawback is experienced, wherein the nutrients are fully consumed long before the nutrients are resupplied. Additionally, the high concentrations needed for single-point injection may be hazardous to algae, as too much of certain nutrients may be poisonous or otherwise debilitating to algae growth. An algae growth system that provides continuous dosing of low concentrations of nutrients is needed. 
     One proposal for a large-scale bioreactor system uses a series of rigid pipes elevated over an earthen bed. This system suffers some disadvantages, however, because the rigid pipes are expensive to transport and difficult to install and maintain. Another approach uses polyethylene tubes coupled to a rigid roller structure. The flexible bioreactor tubes are made of two layers of 10 mil thick polyethylene, and lay between the two sets of guard rails. Rollers traverse the tubes to peristaltically move the algae through the bags. In one attempt to avoid an outdoor facility, the Japanese government has launched a research program to investigate the development of reactors which would use fiber optic lighting which would reduce the surface area necessary for algae production and ensure better protection against variety contamination. Unfortunately, all these approaches suffer the same significant disadvantage: they require a framework or other rigid structure be built to operate the system. It would be advantageous to avoid having to build a structure or framework, or at least minimize the amount of building required, in order to minimize capital cost, and reduce the difficulty in erecting and maintaining an algae system. 
     Another disadvantage of rigid systems is that the accumulation of gases resulting from algae production may restrict the flow of the biomass through the system. Algae consume CO 2  and produce O 2  and water vapor. A rigid system cannot expand in response to the increasing volume of gas within the system; as the pressure increases, the gases restrict the flow through the system and affect harvesting. Further, the system may eventually exceed a maximum pressure and rupture, resulting in repair and downtime costs. Simply installing pressure release valves would negate the potential benefits of collecting the gases, such as measuring the efficiency of CO 2  absorption and harvesting pure oxygen for burning or other uses. A system that accommodates the expanding gas volume and allows for maximum collection of the gases is desired. 
     Therefore, it is an object of this invention to provide a large-scale algae production system. It is another object to provide an algae production system that has a lower capital cost than elevated rigid piping and other existing systems. It is another object to simplify installation and maintenance of an algae system. It is another object to increase efficiency of an algae production system by exposing more algae to light and CO 2 . It is a further object to provide a consistent and favorable concentration of nutrients to further encourage algae growth. It is another object to facilitate collection of gases in the system without restricting biomass flow. 
     SUMMARY OF THE INVENTION 
     The invention is a trough system for aerating a biomass, such as one containing algae. The system comprises a trough lining assembly that conforms to the shape of a trough dug into the ground. A reinforced polymer liner lies on the trough walls and may be attached to the trough or held in place by the weight of the biomass. An aerator releases aerating gas into the biomass, churning and aerating the biomass. A nutrient line releases nutrients into the biomass at regular intervals to promote biomass growth. The aerator and nutrient line may be retained at the bottom of the trough by adhesion to the liner or attachment to the liner by heat seal during the manufacturing process, but preferably a retaining strip is attached to the liner and the aerator and nutrient line are retained in the envelope between the liner and the retaining strip. The retaining strip may have a pattern of apertures disposed through it to allow CO 2  and nutrient solution to pass through it. A self-luminescent material may be applied to the liner or the envelope to provide growth-inducing light continuously. A solar cover may be laid above the trough for control of temperature, moisture and light exposure. The solar cover may be expandable to accommodate the accumulation of gases inside the lined trough. 
     In a multiple-trough system, the trough lining assemblies are connected to a common inlet and outlet line, a circulation pump, control valves, and a gas injector. A biomass is deposited into the trough assemblies. Aerating gas is injected under pressure into the trough assemblies, so that the aerating gas is released through the aerator, preferably in the form of microbubbles. As the biomass is circulated through the trough lining assemblies, the aerating gas continuously aerates the biomass while causing a motive force that churns the biomass. Where the biomass contains algae, the continuous churning increases the amount of algae that is exposed to sunlight and the aerating gas. By exposure to sunlight, the algae photosynthesize, consuming CO 2  and supplied nutrients, producing O 2 , and reproducing. Once the algae biomass is concentrated enough to harvest, the biomass is gradually diverted into a harvesting system to extract the algae from the biomass. The O 2  produced during photosynthesis may be collected through gas collection valves. Where the system is connected to a power plant or other production facility, the collected gas can be analyzed to determine reduction of CO 2  emissions and reintroduced into the facility to increase efficiency of combustion machinery. The algae may be dried onsite using an integrated dryer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a cross-section schematic of the preferred embodiment of a trough lining assembly in a trough containing biomass, also showing a tractor in a service position. 
         FIG. 1B  is a cross-section schematic of a portion of the preferred embodiment of a trough lining assembly in a trough, as in  FIG. 1   a , with a solar cover laid on the surface of the biomass. 
         FIG. 2  is a front perspective cross-sectional view of a nutrient line. 
         FIG. 3  is a bottom schematic view of a reducer for the nutrient line of  FIG. 3A . 
         FIG. 4A  is a top-view schematic of a portion of the preferred embodiment of a trough lining assembly in a trough, not containing biomass, showing a pattern of apertures in the envelope. 
         FIG. 4B  is a top view of an envelope with a pattern of slits as apertures. 
         FIG. 4C  is a top view of an envelope with a pattern of rounded rectangles as apertures. 
         FIG. 4D  is a top view of an envelope with a pattern of squares as apertures. 
         FIG. 4E  is a top view of an envelope with a pattern of circles as apertures. 
         FIG. 5  is a cross-section schematic of a portion of the preferred embodiment of a trough lining assembly in a trough containing biomass, showing the motive force imparted by rising aerating gas. 
         FIG. 6  is a side view of the preferred embodiment of a trough lining assembly rolled onto a deploying spool. 
         FIG. 7  is a top view of the preferred embodiment of a field. 
         FIG. 8A  is a top view of an alternate embodiment of a field. 
         FIG. 8B  is a top view of three troughs in the field of  FIG. 7   a.    
         FIG. 9  is a top view of an on-site algae dryer. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     This invention uses a trough liner assembly that lies within a trough. The trough liner assembly aerates and circulates a biomass deposited therein, and also provides a nutrient solution into the biomass to promote growth. The biomass may be any biomass that receives a chemical benefit from aeration, fertilization, and circulation. For example, the invention serves as an aerobic digester for the treatment of wastewater, and stimulates growth of algae, shrimp, fish, and other water-based biological products. Algae and other plants may benefit the most from the invention, as the invention promotes exposure of the biomass to light, aerating gas, and common fertilizing nutrients. Multiple troughs are arranged side-by-side to form a bed. One or more beds form a facility of sufficient capacity to meet the local needs when the sunlight is at its most limited, and excess capacity with greater sunlight. 
     Beds 
     A trough  23  is formed by either digging into the ground or by shaping loose dirt into berms  20  that form the trough sides  24 . See  FIG. 1  a. The berms  20  are preferably 100 inches apart, measured from center to center of each berm  20 . A trough  23  is preferably over 350 feet long, most preferably 1250 feet long, and v-shaped, having two substantially planar sides  24  which converge to a point at the bottom, and an open top. In the preferred embodiment, the depth of the trough  23  is at least 24 inches, measured as the vertical distance from the bottom of the trough  23  to the horizontal line stretched between the tops of the berms  20  that form the trough sides  24 . The width of the trough  23  is the distance between the trough sides  24  measured at the top of the berms  20  that form the trough sides  24 . Preferably, the width is 70 inches. In a trough  23  having the preferred dimensions, the biomass in the trough will preferably have a depth of 18 inches and a width at fill level of 60 inches. The depth and width of the trough  23  may vary depending on the amount of expected rainfall in the region, the composition of the biomass, and the desired effect of the aeration. For example, the preferred dimensions are known to stimulate growth in  Chlorella  and  Nanochloropsis varities  of algae, but the trough  23  should be substantially wider to grow fish or shrimp, and may be narrower and deeper to treat wastewater. The trough  23  may alternatively be any other shape that facilitates aeration of a biomass, including but not limited to u-shaped, concave, rectangular, or asymmetrical. 
     A berm  20  separates two troughs  23  and may have a substantially flat or slightly concave top forming a tractor path  42  wide enough for a tractor  28  to drive over. Preferably, the top of the berm  20  is slightly concave to allow rainwater to collect and flow away from the troughs  23  instead of into them. The tractor  28  requires two tractor paths  42 , one on each side of the trough  23 , so that it straddles the trough  23  to service it. Preferably, the tractor path  42  is 30 inches wide. A bed is created by forming troughs  23  side-by-side with a tractor path  42  between each trough  23 , covering a field  1 . Each trough  23  contains a trough lining assembly which transports the biomass through the system. 
     Trough Lining Assembly 
     Referring to  FIGs. 1   a - 1   b , a trough lining assembly has a single sheet of a thin-walled, waterproof liner  32  along the sides of the trough  23 . Preferably the liner  32  is made of reinforced polyethylene that is at least  10  mil thick, but more preferably is at least  12 . 5  mil thick. The liner  32  may be held in place by the weight of the biomass introduced into the trough lining assembly, or the liner  32  may be retained against the trough sides  24  by other means. In the preferred embodiment, the liner  32  extends up the trough sides and the ends of the liner  32  are covered by the berms  20  to a distance sufficient for the weight of the berm  20  to hold the liner  32  in place. The portion of the liner  32  that is above the level of the biomass, referred to herein as the “hip”  34 , may suffer quicker degradation than the rest of the liner  32  due to its exposure to the sun. The hip  34  may be treated with a protective material, such as a layer of reflective paint or self-luminescent material that is introduced into the liner  32  during the manufacturing process or applied to the liner  32  once it is laid in place in the trough  23 . Preferably, the self-luminescent material comprises Litroenergy™ self-luminescent micro particles, manufactured by MPK Co. Litroenergy™ particles are non-toxic and crush-resistant up to 5000 lbs., and provide continuous light for a half-life of 12 years without exposure to sunlight. In addition to the hip  34 , some or all of the remaining surface of the liner  32  may contain or be covered by the self-luminescent material, in order to stimulate algae growth when sunlight is diminished or absent. For example, horizontal stripes of Litroenergy™-infused paint may be applied to the liner  32  so that the stripes sit below the level of the biomass once the trough lining assembly is in place in the trough  23 . 
     The trough lining assembly has an aerator  17  that emits aerating gas injected into the assembly. The aerator  17  cooperates with the liner  32  to aerate and churn the biomass in the trough, as described below. The aerator  17  may be perforated or porous, so that the aerating gas passes through it into the biomass. Preferably, the aerator  17  is a porous material made of spun polyethylene fiber, such as Tyvek®. The pores in such a material are so small that the aerating gas will not pass through it until a certain air pressure is reached, at which point the aerating gas is released in the form of microbubbles. Generally, no more than 2 psi of air pressure is required to produce microbubbles. Where algae or other plants are present in the biomass, the aerator  17  preferably releases the aerating gas at a rate that allows substantially all of the gas to be absorbed within the biomass before it reaches the top of the trough  23 . The rate of release through the aerator  17  can be limited by using different porosities of Tyvek® or other materials, or by coating the aerator  17  with varying thicknesses of porous or non-porous material. In the preferred embodiment, shown in  FIGS. 1   a ,  1   b , and  4   a , the aerator  17  is a pressurizable Tyvek® tube that lies flat when it is not pressurized. 
     The trough lining assembly may further have a nutrient line  18  that emits a nutrient solution into the biomass in the trough. The nutrient line  18  may be perforated or porous, so that the nutrient solution passes through it into the biomass. Preferably, the nutrient line  18  is a perforated, non-porous tube made of thin-walled polyethylene or another plastic material. The nutrient line  18  receives a flow of nutrient solution under a pressure of about 10 psi at the proximal end of the nutrient line  18 . The distal end of the nutrient line  18  is preferably capped to allow the nutrient line  18  to be pressurized by the nutrient solution. Preferably, the nutrient line  18  lies flat when it is not pressurized. A series of emitters  19  are disposed in a substantially straight line along the length of the nutrient line  18 . An emitter  19  is preferably a puncture, such as a slit or hole cut through the nutrient line  18  material. Alternatively, an emitter  19  may be an emitting device now known or later developed for drip irrigation. The emitters  19  may be spaced longitudinally at regular or irregular intervals. Preferably, the emitters  19  are spaced uniformly at a range of 4 inches to 36 inches, most preferably 12 inches, apart. The emitters  19  may be uniformly sized or have different sizes according to the amount of nutrient solution to be released through each emitter  19 . The nutrient line  18  may be custom-made for the implementation, or may be a retail or wholesale product such as AQUATRAXX® premium drip tape made by Toro Ag. 
     Referring to  FIGS. 2 and 3 , inside the nutrient line  18 , a pressure reducer  21  is attached to the interior surface, covering and running parallel with the series of emitters  19 . The reducer  21  is a small plastic strip into which a channel  26  is formed. The channel  26  extends between one or more inlets  25  and one or more outlets  27 . Inlets  25  are disposed on the surface of the reducer  21  that faces the interior of the nutrient line  18 , and are in fluid communication with the nutrient line  18  such that the nutrient solution may pass through the inlet  25  into the channel  26 . Outlets  27  provide fluid communication with the emitters  19 , such that each emitter  19  is paired with an outlet  27 . The reducer  21  thereby draws the nutrient solution in the nutrient line  18  through the inlets  25  into the channel  26 . The reducer  21  further delivers the nutrient solution to the outlets  27 , where the solution passes through the emitters  19  into the biomass. The channel  26  may be formed in a pattern that imparts a turbulent flow on the nutrient solution as it travels from the inlet  25  to the outlet  27 . The pattern may be any nonlinear, tortuous pattern that causes a turbulent flow, but is preferably a zigzag pattern such as that shown in  FIG. 3 . The turbulent flow reduces the fluid pressure of the nutrient solution in the reducer  21 , which in the preferred embodiment is a drop from 10 psi at the inlet  25  to 1 psi at the outlet  27 . 
     The aerator  17  and nutrient line  18  may each be positioned at or near the bottom of the trough  23  so that the released aerating gas and nutrient solution rise through and are diffused within the biomass. Because the aerator  17  may be buoyant with respect to the biomass, particularly when it is pressurized with aerating gas, a retention mechanism may be used to retain the aerator  17  at or near the bottom of the trough  23 . Similarly, the nutrient line  18  may be buoyant with respect to the biomass, due to the material used or the weight of the nutrient solution, and may need to be retained by the same or a second retention mechanism. The retention mechanism may be any mechanism that retains the aerator  17  and nutrient line  18  at or near the bottom of the trough  23 , without damaging the liner  32 , aerator  17 , nutrient line  18 , or biomass. For example, the retention mechanism may be a series of weights attached to one or both of the aerator  17  and nutrient line  18 ; a series of fibrous loops surrounding the aerator  17  and nutrient line  18 , together or separately, and attached to the liner  32 ; or a retaining strip positioned above the aerator  17 . In the preferred embodiment, shown in  FIGS. 1   a ,  1   b , and  4   a , a retaining strip  35  forms an envelope  36  for retaining the aerator  17  and nutrient line  18  between the liner  32  and the retaining strip  35 . The retaining strip  35  is preferably the same material as the liner  32 , but may alternatively be a high- or low-density polymer or another waterproof material that can be attached to the liner  32 . The retaining strip  35  may further comprise self-luminescent material, such as Litroenergy™ particles. 
     The retaining strip  35  may be manufactured in a number of ways. The retaining strip  35  may be adhered to the liner  32 , forming an envelope  36  at the bottom of the trough  23 , between the liner  32  and the retaining strip  35 . The retaining strip  35  may be adhered to the liner  32  by heat seal during the manufacturing process, or by application of an adhesive after the manufacturing process. The retaining strip  35  may alternatively be extruded integrally with the liner  32 , such as when the retaining strip  35  and liner  32  are made of the same material or co-extrudable materials. 
     When the trough lining assembly is in place in the trough  23 , the retaining strip  35  may be substantially parallel to the top of the trough  23 , or may be concave with respect to the top of the trough  23 , as shown in  FIGS. 1   a - b . The aerator  17  and nutrient line  18  are retained in the envelope  36 , at or near the bottom of the trough  23 , so that they do not float to the top of the trough  23 . To facilitate release of the aerating gas and nutrient solution into the biomass, the retaining strip  35  may have apertures  37  cut into it, as shown in  FIG. 4   a . The apertures  37  may be slits or shapes, as shown in  FIGS. 4   a -e, and may be randomized or follow a pattern. The amount of aerating gas released into the biomass at certain points along the trough  23  may be controlled using a predetermined pattern of apertures  37 . For example, fewer apertures  37  at the proximal end of the trough  23 , where the biomass is deposited, will release less aerating gas, and apertures  37  are gradually added or enlarged, releasing an increasing volume of aerating gas into the biomass as it travels to the distal end of the trough  23 . In an alternate embodiment, the aerator  17  and nutrient line  18  may be attached to the liner  32  by an adhesive. 
     The aerator  17  and nutrient line  18  preferably run the entire length of the trough  23 , so that the aerating gas and nutrient solution are released substantially continuously along the length of the trough  23 . The substantially continuous release of aerating gas induces a “churning” motive force in the biomass, shown in  FIG. 5 . The churning exposes more of the biomass to sunlight, the nutrient solution, and the aerating gas. The substantially continuous release also provides consistent sources of aerating gas and nutrients that are absorbed or diffused within the biomass. For growth of algae, shrimp, or other organic material, the substantially continuous release provides the amount of aerating gas and nutrients needed to maximize the growth benefits at all points in the trough. Further, for growth of organic material, as the biomass proceeds along the trough it will increase in concentration of organic material. The higher concentration will require more aerating gas and possibly more nutrients. It is contemplated that the volume of aerating gas released may continuously or periodically increase from the proximal end of the trough  23 , where the biomass is deposited, to the distal end of the trough  23 , where the biomass is harvested as explained below. In one embodiment, the aerating substrate  17  may have an increasing porosity from the proximal end to the distal end. In another embodiment, the aerating substrate  17  may be coated in a non-porous material that is gradually eliminated along the length of the aerating substrate  17 . 
     The aerating gas may be injected before the trough is filled with biomass or after. The aerating gas may be atmospheric air, CO 2 , or any combination of gases that facilitates the chemical reactions desired in the biomass. For the growth of algae or other plants, the aerating gas is preferably a mixture of CO 2 -enriched air and NO x  gas. 
     Referring to  FIG. 6 , the trough lining assembly is flat before deployment and can be rolled, fully assembled and without damage, onto a deploying spool  49 . To install the trough lining assembly, a loaded deploying spool  49  may be mounted in a truck bed or other installation implement having a wheel base that straddles the trough  23 . The trough lining assembly is then rolled off the deploying spool  49  and laid in the trough  23 . In the preferred embodiment, one or more gas injectors is attached to the pressurizable, tubular aerator  17  at the proximal or distal end, or both ends. A solution supply line (not shown) is attached to the nutrient line  18  at the proximal or distal end. An outlet line may be installed at the distal end of the trough, either onto or through the liner  32 . The ends of the liner  32  are covered by dirt from the berms  20  once the trough lining assembly is in place. 
     The aerator  17  may have a shorter operating life than the liner  32 . In the preferred embodiment, the aerator  17  may be replaced by simply attaching a new aerator to one end of the old aerator  17  and pulling the old aerator  17  out of the envelope  36  from the opposite end, simultaneously pulling the new aerator into place. The old aerator  17  may then be detached and discarded. 
     Once the trough lining assembly is laid in the trough  23 , a solar cover  33  may be laid over the top as shown in  FIG. 1   b . The solar cover  33  is transparent or substantially translucent to allow sufficient sunlight to enter the biomass. Preferably, the solar cover  33  is made of 1-2 mil thick extruded polyethylene, which is substantially elastic and capable of floating freely on the surface of the biomass. The solar cover  33  may alternatively be held in place over the trough  23  by covering the ends of the solar cover  33  with dirt from the berms  20 . The solar cover  33  may cover one or more troughs  23 . In the preferred embodiment, the solar cover  33  covers a single trough  23 . See  FIG. 1   b . In an alternate embodiment, the solar cover may cover a plurality of troughs  23 . 
     The solar cover  33  initially lays flat over the troughs  23 . As gas  40  collects within the trough lining assembly, the solar cover  33  is expandable to contain the volume of gas  40 . The volume  40  does not interfere with the progression of the biomass through the system. If the ends of the solar cover are secured, such as by insertion into the berms  20 , the volume of gas  40  may be easily collected with a gas collection system. 
     During winter months, a second solar cover can be installed over the first solar cover. The second solar cover creates an environment where temperature can be maintained. The parasitic temperature loss of the biomass during winter months can be managed by the greenhouse effect where the biomass temperature would serve to heat the air, along with sunlight, between the upper and lower solar covers. One or both solar covers can be replaced seasonally to relieve excess heat during the summer months. The edges of the solar cover are covered with dirt using mulch-laying equipment. Tractors  28  can straddle each bioreactor bed to travel up and down the rows for periodic maintenance, repair of leaks, and replacement of the first or second solar cover. Alternatively, over-the-row tunnels or miniature greenhouses can be used for temperature control and durability during changing weather conditions. 
     Maintenance 
     The surfaces of a trough assembly that come in contact with the biomass may gradually accumulate film, which decreases efficiency of the system by obscuring sunlight and restricting flow. The system design anticipates this potential loss in efficiency by using a long, wide trough  23 . The trough  23  dimensions ensure a sufficient surface area to prevent accumulation of film from affecting biomass flow or exposure to sunlight. The present trough assemblies may be implemented in lengths up to the preferred length of 1250 feet while maintaining system performance in all operating conditions over the operating life of the trough assembly. If it becomes necessary to remove accumulated film from the surfaces of the liner  32  and solar cover  33 , the solar cover  33  may be retrieved by tractor or other implement, after which the liner  32  is scrubbed with a tractor-powered scrubbing implement, and fresh mulch  33  is laid. Alternatively, the liner  32  may be scrubbed by depositing floating, textured balls, such as brushy balls, into each trough  23  at the proximal end. The balls loosen accumulated film on the liner  32  before they are retrieved at the distal end of the trough  23 . 
     Algae Production Facility 
     Referring to  FIG. 7 , an algae production facility includes at least one field  100  of beds comprising parallel troughs  23  separated by berms  20 . The number and size of fields  100  are limited by the land available, cost and other factors. For large scale algae production, a series of fields  100  will be interconnected into a common algae collection point for ease of processing. A field  100  is supplied by a harvest sump  50 , circulation pump  51 , inoculation sump  47 , settling tank  56 , and aerating gas injection system  55 . Each field  100  is designed to provide an adequate dwell time for the algae to convert the injected aerating gas into O 2  through the photosynthesis process by exposing the algae to sunlight. 
     The troughs  23  are subjected to a “dead-leveling” procedure which ensures that the troughs  23  are uniform in dimension and parallel or identically graded with respect to the ground, so that a consistent biomass level may be maintained across all trough lining assemblies. Once the troughs  23  are substantially uniform and parallel, a tractor  28 , pickup truck, or other installation implement lays the preferred trough lining assemblies into the troughs  23 . The tractor  28  also lays the solar cover  33  over the troughs  23  if the temperature maintenance, weather protection, or gas collection benefits of the solar cover  33  are desired. 
     The trough lining assemblies are connected to a common inlet line  45  and outlet line  46 , a circulation pump  51 , control valves (not shown), one or more aerating gas injection pumps  55 , a nutrient solution pumping unit  44 , and a solution supply line  59 . Biomass is introduced to the facility at the circulation pump  51 , which pumps the biomass through the system. From the circulation pump  51 , the biomass travels through the inlet line  45 , into the inlet header line  43 , which connects to each trough. The biomass is deposited into the trough lining assemblies in the growout troughs  52  through an inlet valve  54  in each trough. Aerating gas is injected under pressure into the aerator  17 , which pressurizes into its tubular shape. Once pressurized, the aerator  17  gradually releases aerating gas into the biomass stream through the apertures  37  in the retaining strip  35 . A nutrient solution is delivered through the pumping unit  44  to solution supply line  59 , and into the nutrient line  18  under sufficient pressure, preferably about 10 psi, to open the nutrient line  18  into its tubular shape. Once the nutrient line  18  is pressurized, it gradually releases the nutrient solution into the biomass stream as described above. The pumping unit  44  may comprise a pump and a prefilter for removing any matter in the nutrient solution that may clog the nutrient line  18 . 
     The aerating gas also agitates the biomass, keeping the aerating gas in suspension for a higher conversion rate of CO 2  to O 2  and churning the biomass to increase algal exposure to the nutrients and sunlight. As the biomass travels the length of the trough assembly, the algae concentration increases, as does CO 2  and nutrient intake and O 2  output. The increasing volume of O 2  and water vapor may expand the solar cover  33 , if present, and the O 2  may be collected through a gas collection valve at or near the end of the trough assembly. At the distal end of the trough, the biomass passes through an outlet valve  58  into the output line  46  and is either diverted to the harvest sump  50  or continues to the circulation pump  51  for recirculation, as described below. 
     As shown in  FIG. 7 , the preferred embodiment of a field  100  of 40 gross acres (1320 ft×1320 ft) has 121 1250 ft-long growout troughs  52 ; 15 inoculation troughs  53 ; 36 net acres of trough beds (1250 ft×1250 ft); over 19 net acres of biomass surface area (1250 ft×60 in.×135); a capacity of approximately 4.8 million gallons; a flow rate of about 3300 gpm/field or about 24 gpm/trough; and algae dwell time of 24 hours. At this dwell time, the biomass travels through the trough at a velocity of 0.808 feet per minute. The inoculation troughs  53  are fed by an inoculation line  48  connected to the inoculation sump  47 . The desired dominant species of algae is grown in the inoculation troughs, which are operated independently of the growout troughs  52 . Inoculated biomass is circulated through the inoculation sump  47  and diverted to the circulation pump  51  as needed to maintain dominance of the preferred species of algae in the growout troughs  52 . 
     In some environments, a higher flow velocity may be desirable to add motive force to the algae, preventing it from accumulating on the trough lining assembly  31 . The alternate embodiment of a field  100  shown in  FIG. 8   a  has the same trough  23  dimensions as the preferred embodiment, but provides an increased flow velocity in the growout troughs  52  by connecting adjacent troughs and allowing the biomass to flow through multiple troughs before passing into the output line  46 . The connection between adjacent troughs  23  allows the biomass to flow in alternating directions. In the example shown in  FIG. 8   b , the biomass enters a drain  70  that passes through the liner  32  and into the ground at the distal end of one trough  23 . The biomass travels through a siphon  71  and is deposited at the proximal end of the next trough  23 . The connection between troughs  23  may also be facilitated by mechanical pumps. After a predetermined number of troughs  23 , the biomass is let into the output line  46  through an outlet valve  58 . Any number of troughs may be connected to each other between an inlet valve  54  and an outlet valve  58 . Preferably, the biomass travels the length of six troughs before release, which results in a flow velocity of 5.2 feet per minute at a dwell time of 24 hours. 
     Algae Production Cycle 
     In the algae production cycle, the facility is initialized with biomass and growth is encouraged by maintaining proper algae, CO 2 , and fertilizer concentrations, as well as sunlight and temperature. The harvest process begins when the biomass reaches sufficient concentration, referred to herein as “harvest concentration.” To harvest algae from the field  100 , a partial diversion of the biomass is initiated. Between 20% and 80% of the biomass, depending on the present concentration, may be diverted daily for harvesting algae. The diverted biomass is delivered to a harvest sump  50  while the remaining biomass, called the bypass biomass, continues through the facility to the circulation sump  51 . In the harvest sump  50  a flocculant may be added to the diverted biomass to facilitate settling of the algae. The flocculant may be any known agent that will encourage flocculation without killing or harming the algae. Preferably, the flocculant is a commercially produced polyacrylamide or a natural product such as chitosan. 
     The diverted biomass is then delivered to a settling tank  56 . The settling tank  56  is preferably a weir tank, which will facilitate settling of the algae. Once the algae settles, it is collected by a harvest pump  57 . The water remaining in the settling tank  56  is delivered to the circulation pump  51 , where it is mixed with the bypass biomass to dilute the biomass that is reentering the field  100 . This recirculated water contains byproducts of the previous algae growth process, such as salt and fertilizer, that are beneficial to subsequent growth processes. The biomass will therefore be comprised of recirculated water in amounts necessary to optimize algae production and maintain the biomass at an ideal range of concentration. The solids content percentage in the biomass is measured periodically to make sure it is not exceeding a pre-determined limit. Excess concentration is easily controlled with the introduction of chlorine or simple dilution. While the harvest cycle is continuous, the total volume will vary throughout the seasons of the year. 
     The harvest pump  57  may have a filter to create an algae cake for easy harvest and transportation. After the algae is harvested, it is further processed for its desired use. For example, the wet algae may be subjected to processing methods which efficiently extract algae oil. The efficiency is created when the algae can be processed on-site without the need to dry and transport the material. However, in another example, the algae it may be dried, on-site, into a product which facilitates storage and shipping, so that the dry algae may be sold to customers who will process it according to their needs. 
     In one embodiment of an on-site dryer  60 , shown in  FIG. 9 , the harvested algae is deposited onto a conveyor  61  that slowly transports the algae through a drying tunnel  62 . Hot air is injected at a high velocity opposite the direction of the conveyor  61 , so that the algae is dry by the time it has traveled the length of the drying tunnel  62 . The hot air for drying is supplied by a propane furnace  63 . To increase the efficiency of the facility, CO 2  and NO x  gases generated by combustion within the propane furnace  63  are vented over a heat exchanger into the aerating gas injection pump  55 , enriching the atmospheric air to be injected into the aerator  17 . Since a standard propane furnace  63  can only increase the temperature of atmospheric air a limited amount, the efficiency of the dryer  60  can be further increased by supplying preheated air to the propane furnace  63 . The preheated air is obtained from an air trough  64  and covered by a solar cover  33 , creating a greenhouse effect that heats the air before it is delivered to the propane furnace  63 . The air trough  64  may have the same dimensions as a trough  23  so that it may be created and maintained with the same implements used to create and maintain the troughs  23 . The air trough  64  and dryer  60  may be in-line with the troughs  23  in a field  100  to maintain continuity of the field design. 
     The gas  40  produced by the algae is primarily O 2 . The gas  40  may be collected and processed depending on the overall configuration of the system. In one embodiment, the facility is placed in proximity and connected to a factory that burns oxygen during production and expels CO 2  and other gases. The factory provides the system with CO 2 , which is pressurized and injected into the trough assemblies. The collected gases  40  then represent the amount of CO 2  emission from the factory that has been scrubbed of carbon. This amount can be tested and the data used by the factory to show reduction of polluting emissions. After testing, the O 2  may supply the factory&#39;s burners to increase production efficiency. In another embodiment, livestock manure and food waste can be recycled to produce CO 2  for injection into the system. 
     Production is affected primarily by the number of daylight hours. To overcome seasonality of the production system and provide a constant supply of biomass for processing 24 hour 7 day per week, the number of fields  100  required is determined by the output on the day with shortest daylight hours of the year. As the volume increases with longer daylight hours, unnecessary fields can be idled. 
     While there has been illustrated and described what is at present considered to be the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made and equivalents may be substituted for elements thereof without departing from the true scope of the invention. Therefore, it is intended that this invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.