(384c) 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.