Introduction (cont)

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National Renewable Energy Laboratory

(oil-producing) microalgae. Work performed by several ASP subcontractors was designed to

understand the mechanism of lipid accumulation. In particular, these researchers tried to

determine whether there is a specific "lipid trigger" that is induced by factors such as nitrogen (N)

starvation. Subcontractors also studied ultrastructural changes induced in microalgae during lipid

accumulation. They also initiated efforts to produce improved algae strains by looking for genetic

variability between algal isolates, attempting to use flow cytometry to screen for naturally-

occurring high lipid individuals, and exploring algal viruses as potential genetic vectors. The

work performed by ASP subcontractors is described in Section II.B.1.

Although some efforts of the in-house SERI researchers were also directed toward understanding

the lipid trigger induced by N starvation, they showed that silica (Si) depletion in diatoms also

induced lipid accumulation. Unlike N, Si is not a major component of cellular molecules;

therefore, it was thought that the Si effect on lipid production might be less complex than the N

effect, and thus easier to understand. This initiated a major research effort at SERI to understand

the biochemistry and molecular biology of lipid accumulation in Si-depleted diatoms. This work

led to the isolation and characterization of several enzymes involved in lipid and carbohydrate

synthesis pathways, as well as the cloning of the genes that code for these enzymes. One goal was

to genetically manipulate these genes to optimize lipid accumulation in the algae. Therefore,

research was performed simultaneously to develop a genetic transformation system for oleaginous

microalgal strains. The successful development of a method to genetically engineer diatoms was

used in attempts to manipulate microalgal lipid levels by overexpressing or down-regulating key

genes in the lipid or carbohydrate synthetic pathways. Unfortunately, program funding was

discontinued before these experiments could be carried out beyond the preliminary stages.

Cost-effective production of biodiesel requires not only the development of microalgal strains with

optimal properties of growth and lipid production, but also an optimized pond design and a clear

understanding of the available resources (land, water, power, etc.) required. Section III reviews

the R&D on outdoor microalgae mass culture for production of biodiesel, as well as supporting

engineering, economic, and resource analyses, carried out and supported by ASP during the 1980s

and early 1990s. It also covers work supported by DOE and its predecessor agency, the Energy

Research and Development Administration (ERDA), during the 1970s and some recent work on

utilization of CO2 from power plant flue gases.

From 1976 to 1979, researchers at the University of California-Berkeley used shallow, paddle

wheel mixed, raceway-type (high-rate) ponds to demonstrate a process for the simultaneous

treatment of wastewater and production of energy (specifically methane). Starting in 1980, the

ASP supported outdoor microalgal cultivation projects in Hawaii and California, using fresh and

seawater supplies, respectively, in conjunction with agricultural fertilizers and CO2. The two

projects differed in the types of algae cultivated and the design of the mass culture system, with

the project in California continuing to develop the high-rate pond design, and the Hawaii project

studying an (initially) enclosed and intensively mixed system. From 1987 to 1990, an AOutdoor

Test Facility@ was designed, constructed, and operated in Roswell, New Mexico, including two

1,000 m2 high-rate ponds. This last project represented the culmination of ASP R&D in

large-scale algal mass culture R&D. These studies are described in Section III.A. Some

supporting laboratory studies and development of an "Algal Pond Model" (APM) are also

A Look Back at the Aquatic Species Program--Technical Review