Introduction

Re-Distributed by http://www.tpub.com

National Renewable Energy Laboratory

Introduction

Photosynthetic organisms, including plants, algae, and some photosynthetic bacteria, efficiently

utilize the energy from the sun to convert water and CO2 from the air into biomass. The Aquatic

Species Program (ASP) at SERI1 was initiated as a long-term, basic research effort to produce

renewable fuels and chemicals from biomass. It emphasized the use of photosynthetic organisms

from aquatic environments, especially species that grow in environments unsuitable for crop

production. Early in the program, macroalgae, microalgae, and emergents were investigated for

their ability to make lipids (as a feedstock for liquid fuel or chemical production) or carbohydrates

(for fermentation into ethanol or anaerobic digestion for methane production). Macroalgae

(seaweeds) are fast-growing marine or freshwater plants that can reach considerable size; for

example, the giant brown kelp can grow a meter in 1 day and as long as 60 m. Emergents are

plants such as cattails or rushes that grow partially submerged in bogs or marshes. Macroalgae

and emergents were found to produce small amounts of lipid, which function mainly as structural

components of the cell membranes, and produce carbohydrate for use as their primary energy

storage compound. In contrast, many microalgae, (microscopic, photosynthetic organisms that

live in saline or freshwater environments), produce lipid as the primary storage molecule. By the

early 1980s, the decision was made to focus ASP research efforts on the use of microalgal lipids

for the production of fuels and other energy products. The studies on the growth and chemical

composition of macroalgae and emergents will not be discussed in this report. However,

interested readers are referred to reports by subcontractors J.D. Ryther, Harbor Branch

Foundation, Florida (seaweeds), and D. Pratt , from the University of Minnesota, St. Paul

(emergents) listed in the Bibliography.

Microalgae, like higher plants, produce storage lipids in the form of triacylglycerols (TAGs).

Although TAGs could be used to produce a wide variety of chemicals, work at SERI focused on

the production of fatty acid methyl esters (FAMEs), which can be used as a substitute for fossil-

derived diesel fuel. This fuel, known as biodiesel, can be synthesized from TAGs via a simple

transesterification reaction in the presence of acid or base and methanol. Biodiesel can be used

in unmodified diesel engines, and has advantages over conventional diesel fuel in that it is

renewable, biodegradable, and produces less SOX and particulate emissions when burned. The

technology is available to produce biodiesel from TAGs, and there are growing biodiesel

industries both in the United States and Europe that use soybean or rapeseed oil as the biodiesel

feedstock. However, the potential market for biodiesel far surpasses the availability of plant oils

not designated for other markets. Thus, there was significant interest in the development of

microalgal lipids for biodiesel production.

Microalgae exhibit properties that make them well suited for use in a commercial-scale biodiesel

production facility. Many species exhibit rapid growth and high productivity, and many

The Solar Energy Research Institute (SERI) became the National Renewable Energy Laboratory (NREL)

in 1990. In this report, the laboratory may be referred to as either SERI or NREL, depending on the time

period during which the work being described was performed.

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