Comparative Energy Balance of Algal Biofuel Production Using Dry and Wet Routes

Researchers from the University of Twente (the Netherlands) compared the energy balances for two routes of biodiesel production (the "wet" and "dry" routes) from the microalgae, Chlorella vulgaris. The comparative energy balance would contribute toward a more comprehensive Life Cycle Analysis (LCA) for algal biodiesel production. In the "dry route" the cultivated algae are concentrated, mechanically dewatered, and  then thermally dried. The dried algae are cell-disrupted to release the oil, and the oil is converted to biodiesel by reaction called "transesterification".

In the wet process, the cultivated algae are concentrated and initially dewatered. Then the wet extraction process (usually involving the use of water under subcritical conditions) is conducted to extract the lipids from the oil. The lipids undergo a process called "hydrotreatment" to produce "green diesel".

Results showed that both routes gave "significantly positive" energy balances. The drying process in the dry route consumed large amounts of energy, while in the wet process, it was the wet oil extraction part (involving supercritical fluids) which was most energy consuming. "By applying more efficient dryer/extraction process or coupling waste heat from a nearby power plant to the process, the energy balance can be improved". In the short term, the dry route was found to be "more interesting", because it had a higher FER (fossil energy ratio). However, in the long term, the wet route is said to have "more potential" due to its capability to produce higher-value biofuels.

The complete paper is published in the journal, Bioresource Technology (URL above).  Related information on the Wet Process for Algal Biodiesel
http://www.oilgae.com/blog/2010/09/wet-extraction-of-algal-biomass-to-biodiesel.html
http://www.oilgae.com/club/users/Richard/blogs/631