Microalgal biomass production pathways: evaluation of life cycle environmental impacts.

George G Zaimes,Vikas Khanna

doi:10.1186/1754-6834-6-88

Abstract

BackgroundMicroalgae are touted as an attractive alternative to traditional forms of biomass for biofuel production, due to high productivity, ability to be cultivated on marginal lands, and potential to utilize carbon dioxide (CO2) from industrial flue gas. This work examines the fossil energy return on investment (EROIfossil), greenhouse gas (GHG) emissions, and direct Water Demands (WD) of producing dried algal biomass through the cultivation of microalgae in Open Raceway Ponds (ORP) for 21 geographic locations in the contiguous United States (U.S.). For each location, comprehensive life cycle assessment (LCA) is performed for multiple microalgal biomass production pathways, consisting of a combination of cultivation and harvesting options.ResultsResults indicate that the EROIfossil for microalgae biomass vary from 0.38 to 1.08 with life cycle GHG emissions of −46.2 to 48.9 (g CO2 eq/MJ-biomass) and direct WDs of 20.8 to 38.8 (Liters/MJ-biomass) over the range of scenarios analyzed. Further anaylsis reveals that the EROIfossil for production pathways is relatively location invariant, and that algae’s life cycle energy balance and GHG impacts are highly dependent on cultivation and harvesting parameters. Contrarily, algae’s direct water demands were found to be highly sensitive to geographic location, and thus may be a constraining factor in sustainable algal-derived biofuel production. Additionally, scenarios with promising EROIfossil and GHG emissions profiles are plagued with high technological uncertainty.ConclusionsGiven the high variability in microalgae’s energy and environmental performance, careful evaluation of the algae-to-fuel supply chain is necessary to ensure the long-term sustainability of emerging algal biofuel systems. Alternative production scenarios and technologies may have the potential to reduce the critical demands of biomass production, and should be considered to make algae a viable and more efficient biofuel alternative.

Highlights

Microalgae are touted as an attractive alternative to traditional forms of biomass for biofuel production, due to high productivity, ability to be cultivated on marginal lands, and potential to utilize carbon dioxide (CO2) from industrial flue gas
Microalgae’s promising characteristics, such as: high productivity [2], ability to be cultivated on marginal lands [3], semi-continuous to continuous harvesting, high lipid content, and potential to utilize carbon dioxide (CO2) from industrial flue gas make it an attractive feedstock for biofuel production [4,5,6,7,8]
Extraction and subsequent upgrading of microalgal biomass feedstock may provide both a liquid fuel that has the potential to be compatible with current transportation fuel infrastructure, and satisfy the Energy Independence and Security Act (EISA) mandate

Summary

Introduction

Microalgae are touted as an attractive alternative to traditional forms of biomass for biofuel production, due to high productivity, ability to be cultivated on marginal lands, and potential to utilize carbon dioxide (CO2) from industrial flue gas. Researchers have examined various biomass feedstocks such as corn, soybean, canola, and lignocellulosic crops for their bioenergy potential Major drawbacks to these first and second generation biofuels including land use, water footprint, and influence in global food markets of microalgal biomass feedstock may provide both a liquid fuel that has the potential to be compatible with current transportation fuel infrastructure, and satisfy the EISA mandate. Evaluation of the life cycle greenhouse gas (GHG) emissions, fossil energy consumption, and water demands for multiple biomass production pathways within the framework of one study can provide insight into the potential tradeoffs, environmental impacts, and technical feasibility of these pathways. Holistic evaluation of emerging algae-to-fuel systems that considers the resource consumption, emissions, and their impact across the entire life cycle is critical to assess the environmental sustainability of emerging algae-based energy systems

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