ALGAE PRODUCTION SYSTEMS
What is Algae?
Algae are microscopic plants and are found in all aquatic environments, including marine, freshwater and brackish water. Green algae (singular: green alga) are the large group of algae from which the embryophytes (higher plants) emerged. As such, they form a paraphyletic group, variously included among the Plantae or with the Protista. The green algae include unicellular and colonial flagellates, usually but not always with two flagella per cell, as well as various colonial, coccoid, and filamentous forms. In the Charales, the closest relatives of higher plants, full differentiation of tissues occurs. There are about 6000 species of green algae. Many species live most of their lives as single-cells, other species form colonies or long filaments.
The seminal work on algae-to-biodiesel was performed in the wake of our nation's first energy crisis (mid 70's to mid 90's) by the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) in Golden, Colorado, whose original mission for the algae project was carbon dioxide mitigation (Sheehan 1998).
During the early years of their program they discovered that some of the algae species were capable of producing 50% or more of their weight in lipids, under the proper growth conditions, and the program therefore transitioned from carbon dioxide mitigation to algae-to-biodiesel. The program included laboratory and field work to identify the most promising species and to optimize growth conditions for maximizing lipid yield per acre. Their key findings, over 30 years ago, were that it was possible to produce 30 grams of algae per square meter per day, at 30% lipids (Soy Beans are typically 20% lipids) content which would yield 4,000 gallons of biodiesel fuel per acre annually.
Current bio-engineered strains of algae are capable achieving up to 80% lipid content, and to double their mass in less than 24 hours, with some strains capable of doubling every 8 hours. Production of 50,000 gallons per acre is currently being achieved, with production rates of over 100,000 gallons per acre per year considered to be fully achievable using closed photo bio reactor systems.
In any algae oil production system the algae is harvested from the growing process as algae paste. It is then de-watered either by heat drying or de-watering presses. Centrifuges are also another way in which the algae past can be de-watered. The oil is then separated from the paste wither by a chemical process or by pressing in a high pressure device such as a screw press. The finished product is algae oil in a form that is then suitable for use in the transesterification process to make biodiesel fuel.