Biotech Updates

Microalgae-to-Biodiesel Life Cycle Energy and CO2 Emissions Analysis

April 20, 2011
(complete access to journal article may require payment or subscription) http://dx.doi.org/10.1016/j.biortech.2011.02.055

Researchers from the Institute of Chemical and Engineering Sciences (IECS, Singapore) report the preliminary results on the life cycle energy and life cycle carbon dioxide analysis of a microalge-to-biodiesel process. They conducted energy and mass balances for a microalgae-to-biodiesel production system consisting of four subcomponents: (1) microalgae cultivation using raceway ponds for main cultivation and photobioreactors for algal mass build-up, (2) harvesting by coagulation/flocculation, settling and centrifugation, (3) Extraction of lipids from micoalgal biomass by use of hexane/methanol, and (4) Transesterification of extracted lipids by the addition of methanol to produce the biofuels.

The microalgae used was Nannochloropsis sp. in saline medium, with an assumed oil content of 25%. Results showed that 85% of the total energy demand for the process was due to the lipid extraction process, while 13% was attributed to biomass cultivation. Only 2% of the total energy demand was attributed to the biodiesel production component.

Sensitivity analysis showed that substantial decreases in life cycle energy can be achieved by lowering the energy requirement for lipid extraction. For a "base case" only a 25% life cycle energy efficiency can be obtained; however, under an "optimistic case" (presumably a case where substantial improvements are made in reducing energy requirement for lipid extraction), the lifecycle energy efficiency increases to 60%. The complete results of the study are published in the journal, Bioresource Technology (URL above).

Related information:
Microalgae: http://www.fao.org/DOCREP/003/W3732E/w3732e03.htm
Microalgae cultivation: (photobioreactors and algal raceway ponds) http://www.fao.org/DOCREP/003/W3732E/w3732e06.htm
http://www.greentechmedia.com/green-light/post/open-pond-vs.-closed-bioreactors-4012/ http://en.phyco.org/wiki/Photobioreactor
Life Cycle Analysis: http://www.rsc.org/ScienceAndTechnology/Policy/EHSC/EHSCnotesonLifeCycleAssessment.asp http://www.its.ucdavis.edu/publications/2006/UCD-ITS-RR-06-08.pdf.