Initial Life Cycle Assessment Results for Bio-Jet Fuel From Algal Feedstocks

Initial Life Cycle Assessment Results for Bio-Jet Fuel From Algal Feedstocks

Of the potential feedstocks for renewable fuel production, algae have been investigated for more than two decades due to their high lipid content, rapid growth rate, and ability to sequester atmospheric or waste CO₂ from coal-fired power plants. Unlike other biofuel feedstocks (i.e., corn and soy), algae do not compete with existing food commodities, can grow on marginal lands not suitable for conventional agriculture, and do not require large volumes of fresh water – factors that limit the economic and environmental benefits of terrestrial crop feedstocks. Algae can grow in nutrient-rich wastewaters; alternatively, some species of algae can grow in saline waters, utilizing saline aquifers as a water source instead of fresh water. Algal production has been estimated to yield from 3,200 to 14,600 gallons of oil/acre/year – a 130-fold increase over soybean. However, these estimates have generally been calculated from lab-scale cultures; in contrast, all mass culture efforts reported to date have yielded 10-20 times less oil than expected. For the production and conversion of algae to biofuels to be viable at full-scale, life cycle analyses must be conducted using field-level data for the productivity assumptions.

Recently, there have been several “cradle to tailpipe” life cycle assessments (LCA) of biodiesel from microalgae in ponds. Most of these assumed that algal ponds would be supplemented with chemical fertilizer to meet the necessary nitrogen and phosphorus requirements, which provides an immense upstream burden to the LCA. Clarens et al. concluded that algal biodiesel would actually generate greenhouse gas emissions, although the authors acknowledged that most of the environmental burdens associated with algae would be offset if wastewater were used as a nutrient source. Others have concluded that fertilizer consumption must be decreased before microalgae production can be economically viable.

Algal feedstocks are also being investigated for bio-jet fuel, which differs from biodiesel in its chemical composition of C8-C16 carbon chain lengths and added aromatics. Algal feedstocks, in addition to others, have been used in Continental and Japan Airlines test flights. The first commercial flights powered by bio-jet fuel are scheduled to begin this year through a six-month trial of a 50-50 mix of traditional kerosene and biofuel on Lufthansa flights between the cities of Hamburg and Frankfurt.[1] The International Air Transport Association (IATA) aspires to a blend of 6% biofuels to be used in aircraft by 2020.[2] With a consumption of nearly 17.3 billion gallons in 2010 by US passenger and cargo airlines alone,[3] this goal demands a substantial amount of bio-jet fuels and requires the development of large biofuel production operations. At these early stages in the adoption of algal bio-jet fuel by the international aviation industry, an LCA is critically needed before commercial production is proposed to ensure that bio-jet fuel produced from algal feedstocks is environmentally sustainable regarding water use, greenhouse gas emissions, and other potential impacts.

Initial results for an LCA of algal-based bio-jet fuel will be presented. The LCA is conducted following the ISO 14040 and 14044 guidelines as outlined in Guinée's “Handbook on Life Cycle Assessment.”[4] The functional unit chosen is 1 GJ obtained from the combustion of algae-derived bio-jet fuel in a commercial aircraft engine. This functional unit takes into account the difference in energy content between bio-jet fuel and conventional types of jet fuel.[5] The system consists of algal production in wastewater pond reactors, harvesting of algae through flocculation and sedimentation, dewatering, lipid extraction using ethyl acetate, deoxygenation of the algal lipids, catalytic cracking of the hydrocarbon chains, conversion to bio-jet fuel, transportation and distribution of the fuel, and combustion in an airplane engine.

Inputs for the life cycle inventory are largely obtained from peer-reviewed literature and the US Life-Cycle Inventory database by the National Renewable Energy Laboratory. Information for this LCA is also obtained from the pilot-scale study in algal production in wastewater effluent conducted at the University of Kansas. A sensitivity analysis is performed to examine the effects of different algal lipid contents and biomass growth rates, as well as the effects of different technologies used in the production process. The life cycle impact assessment (LCIA) is performed using the Tool for the Reduction and Assessment of Chemical and other environmental Impacts (TRACI) developed by the US EPA. The LCA results are compared against other published life cycle assessments for bio-jet fuels derived from Jatropha curcas[6] and camelina,[7] as well as conventional jet fuel.

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[1] Lufthansa, 2010. World premiere: Lufthansa first airline to use biofuel on commercial flights. <http://presse.lufthansa.com/en/news-releases/singleview/archive/2010/november/29/article/1828.html>

[2] IATA. A Global Approach to Reducing Aviation Emissions; International Air Transport Association: Geneva, October 2009; p 5.

[3] Air Transportation Association, 2011. ATA monthly jet fuel cost and consumption report. <http://www.airlines.org/Energy/FuelCost/Pages/MonthlyJetFuelCostandConsumptionReport.aspx>

[4] Guinée, J.B., 2002. Handbook on Life Cycle Assessment: Operational Guide to the ISO Standards, Springer, New York.

[5] Hileman, J.I., Stratton, R.W., & Donohoo, P.E. , 2010. Energy content and alternative jet fuel viability. Journal of Propulsion and Power 26, 1184-1195.

[6] Bailis, R.E., and Baka, J.E., 2010. Greenhouse Gas Emissions and Land Use Change from Jatropha curcas-Based Jet Fuel in Brazil. Environmental Science & Technology, 44, 8684-8691.

[7] Shonnard, D.R., Williams, L., and Kalnes, T.N., 2010. Camelina-Derived Jet Fuel and Diesel: Sustainable Advanced Biofuels. Environmental Progress & Sustainable Energy, 29, 382-391.