Cornell University research on algae biofuel. (Photo: Cornell University)

New research on algae-to-biofuel schemes quantifies uncertainty

UNITED STATES
Friday, January 04, 2013, 22:50 (GMT + 9)

A Cornell University team has used the Monte Carlo approach to quantify the role of uncertainty associated with process parameters in life cycle analysis (LCA) of algae-to-biofuel schemes for determining metrics such as Energy Return on (Energy) Invested (EROI) and global warming potential (GWP). 

The results, reported in a paper on the ACS journal Environmental Science & Technology, show that uncertainties exist at all stages of biofuel production from microalgae, from cultivation to dewatering to conversion processes and production of coproducts.

This indicates, the researchers suggest, that the values reported in earlier studies are not incorrect, but, rather each represent a specific case. These cases should not be used solely to conclude whether algal biofuels are expected to be energetically viable or environmentally sustainable, the authors say. 

Instead, LCA results, especially those associated with developing technologies such as algal biofuel, should be reported as ranges of expected values to provide decision makers with reliable results, they conclude.

The results of the study are generally in agreement with previous studies highlighting the role of critical processing steps in algae biofuel production—such as the need to develop viable wet lipid extraction technologies, incorporate high-energy coproducts, and reduce energy consumption of algae cultivation. However, the new study extends previous LCA studies with the Monte Carlo approach.

"Despite algae’s potential as a renewable energy feedstock, it is not yet clear if algal biofuels can be produced economically in an environmentally sustainable manner. […]

...Our work was motivated by the lack of comprehensive uncertainty analysis in earlier LCA studies. To obtain a better understanding of the expected performance of proposed algae to biofuel processes, LCA models should include an uncertainty analysis that quantifies the effect of simultaneously varying all model parameters on results. Such an improvement would more reliably inform industry and policy makers on expected EROI values and environmental sustainability of algal biofuels." —Sills et al.

For their study, the Cornell team assumed that marine algae were cultivated at a coastal location in a 1210-ha production facility with access to seawater. The functional unit for the study is 1 MJ of liquid biofuel: biodiesel (fatty acid for their study). The model comprises five unit processes:

• cultivation;
• harvesting and dewatering;
• lipid extraction;
• lipid conversion to a liquid transportation fuel; and
• coproduct production from defatted algae.

Alternative technologies were modeled for each of the five stages. Each process stage was analyzed separately and assembled with the other stages to create six alternative case studies.

A base case analysis, performed to emphasize the importance of the uncertainty analysis, found—as other studies have—that processes with high nonrenewable energy demands were associated with high GWP values (e.g., thermal drying and algal cultivation).

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