The Sustainability of Biofuels Produced from Microalgae

Fossil fuels are not sustainable due to their worldwide depletion and greenhouse gas (GHG) emissions. Transportation biofuels produced from microalgae are sustainable if GHG emissions are lower than fossil fuels and the sources for materials used during production are sustainable. Four areas were evaluated to address these concerns. First, a study of peer reviewed life-cycle analyses (LCAs) was performed. The purpose of this evaluation was to determine which processing choices during cultivation have the most impacts. Data from nine authors was converted to similar units, and a new LCA was performed to evaluate the impacts. Overall GHG emissions per kg of algae cultivation ranged from 0.1 - 4.4 kg CO₂ eq. / kg algae, with the most of the emissions coming from fertilizer contributions. The second topic evaluated was the GHG emissions from experimental dewatering technologies. The five experimental technology emissions, for acoustic harvesting, membrane filtration, flocculation, electrocoagulation and flocculation plus belt filtration, were compared to a modeled dissolved air flotation technology and a fossil fuel source. For a functional unit of one MJ of renewable diesel (RD), membrane filtration had the lowest GHG emissions at 40.8 g CO₂(eq)/MJ RD. Dissolved air flotation was the highest scenario at 51.9 g CO₂(eq)/MJ RD. All technologies were lower than gasoline at 90.7 g CO₂(eq)/MJ gasoline. The third topic evaluated was the GHG emissions from the materials used for plant construction. A LCA was performed for the infrastructure materials and compared to results from the fuel-cycle. Plastic from pond liners had the largest contribution to GHG emissions for the baseline case. Increasing productivity and lipid content both decreased infrastructure emissions. The final topic evaluated was the sustainability of nitrogen, phosphorus and potassium used for microalgae growth. Results show that the surplus of world fertilizers cannot sustain large scale algae production in the United States. Technology choices that can recycle nutrients lower the overall requirement. Alternative sources of nutrients, like concentrated animal feeding operations, can provide enough nutrients for large scale production of algae.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Graduate College

Grantor dc:publisher

The University of Arizona.

Year dc:date.issued

2013

Author dc:creator

• Canter, Christina Elizabeth

Advisor dc:contributor.advisor

• Blowers, Paul

Committee members dc:contributor.committeemember

• Ogden, Kimberly
• Guzman, Roberto
• Deymier, Pierre
• Blowers, Paul

• Dewatering Technologies
• LCA
• Microalgae
• Nutrients
• Sustainability
• Chemical Engineering
• Biofuels

Statement dc:rights

• Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.

Language dc:language.iso

en

Handle dc:identifier.uri

http://hdl.handle.net/10150/293419

OAI identifier oai:identifier

oai:repository.arizona.edu:10150/293419