Life Cycle Assessment for Microalgae Oil Production

Abstract

Abstract

Microalgae oil production is the subject of intensive worldwide research and development, with several billion dollars invested in the past few years. Many different approaches and technologies are being investigated:

 (1) growing microalgae on sunlight and CO₂ in enclosed photobioreactors (tubes, bags, panels, etc.) or open ponds;

 (2) growing algae heterotrophically in the dark on sugar and starches;

 (3) hybrid systems using both sunlight and sugar or starches, and even

 (4) processes using artificial lights.

Generally, the microalgae strains used in the above systems are isolated from nature, superior strains are selected, and then these are genetically improved for high productivity of vegetable oils (triglycerides) or hydrocarbons. Genetic improvement can include genetic engineering to create microalgae strains that excrete fuel products, which can then be recovered without need to harvest or even produce large amounts of algal biomass. Many types of microalgae are being investigated, and several companies and projects are currently moving to pilot and even large demonstration projects.

Over a score of life cycle assessment (LCA) studies on microalgae oil and biofuels production have been recently published, with a majority, but not all, concluding that algae biofuels could substantially reduce greenhouse gas (GHG) emissions, compared to fossil fuels. However, with the exception of fermentation processes (using sugar or starch as inputs), essentially no algae oil is currently produced beyond small amounts for fuel testing. Thus, all LCA studies are based on extrapolations from laboratory experiments, small-scale outdoor studies, and, mainly, on assumptions and projections of future technological advances. A more crucial problem is that most studies have not been based on the detailed engineering designs and systems analyses required to derive energy inputs and mass balances.

A preliminary LCA of microalgae oil production using open ponds, based on a recent detailed engineering and economic cost study, is presented. It concludes that algae vegetable oil could be produced with essentially no fossil energy inputs or net GHG emissions, based on realistic productivity, scale, site, and operating assumptions. This LCA will be compared to others available in the open literature.