Microalgae have potential as a feedstock for biofuel production, but integrated production systems still need improvements to be economically viable at a large scale. Key research areas that could help microalgal biofuels attain economic reality include improving strain selection, cultivation techniques, and downstream processing methods. While microalgal biofuels show promise as a renewable alternative to controversial first generation biofuels, significant advances are still needed for the industry to develop and scale up successfully.

1. Feature Review
Future prospects of microalgal biofuel
production systems
Evan Stephens1, Ian L. Ross1, Jan H. Mussgnug2, Liam D. Wagner3,
Michael A. Borowitzka4, Clemens Posten5, Olaf Kruse2 and Ben Hankamer1
1 The University of Queensland, Institute for Molecular Bioscience, St. Lucia, Qld 4072, Australia
2 University of Bielefeld, Department of Biology, Algae Biotechnology & Bioenergy, Bielefeld, NRW D-33501, Germany
3 The University of Queensland, School of Economics, St. Lucia, Qld 4072, Australia
4 Murdoch University, School of Biological Sciences and Biotechnology, Algae R & D Center, Murdoch, WA 6150, Australia
5 University of Karlsruhe, Institute of Life Science Engineering, Bioprocess Engineering, Karlsruhe, BW D-76131, Germany
Climate change mitigation, economic growth and
stability, and the ongoing depletion of oil reserves are
all major drivers for the development of economically
rational, renewable energy technology platforms. Microalgae
have re-emerged as a popular feedstock for the
production of biofuels and other more valuable products.
Even though integrated microalgal production
systems have some clear advantages and present a
promising alternative to highly controversial first generation
biofuel systems, the associated hype has often
exceeded the boundaries of reality. With a growing
number of recent analyses demonstrating that despite
the hype, these systems are conceptually sound and
potentially sustainable given the available inputs, we
review the research areas that are key to attaining
economic reality and the future development of the
industry.
Politics of renewable energy technology development
The importance ofdevelopingCO2-neutralfuelsources has
been highlighted by thedetailed modelling ofclimate
change effects [1],its global[2] and nationaleconomic
impacts [3] and the increasing competition forfossilfuel
reserves [4,5](Figure 1). Of these,climate change appears to
be the most time-constrained driverofrenewable energy
technologydevelopment.This is because a reduction in CO2
emissions of25–40% by 2020 and 80–90% by 2050 is predicted
to be required to limit globaltemperature increases to
less than the 28C limit agreed at the 2009 Copenhagen
ClimateChangeSummit (see also [1–3]). Fossilfuel supplies
extend beyondthis time windowbut are by definition finite.
Consequently policy makers are underincreasingpressure
to develop and deployclean energy technologies,although
there is a heated debateoverthe most effective political
mechanisms forimplementation.This article reviews the
potentialand limitations ofmicroalgalbiofuel systems in
this context,which we hope will also provide an informed
guide to policy development.
The already apparent problemofreducing CO2 emissions
is compoundedby the predictionthatthe global
populationwill increase from6.6 billion in 2008 to 9.2
billion by 2050 [11] and by the fact that the resultant
increase in fuel use will be furtherexacerbated by the
increasing energy demands ofthe rapidly expanding economies
of China and India. Figure 1 shows the compounding

2. effects ofincreasing the globalpopulation andeconomic
growth (1.5–3% pa)on the depletion ofboth‘proven fossil
fuel reserves’(1P reserves:observed andmarketable
reserves ofoil,gas,coaland nuclear)and farless certain
and more costly ‘ultimately recoverable’reserves (the sum
of 1P; and the increasinglesscertain 2P,3P and 1C
reserves)[6].A 1% increase in energy efficiency peryear
is also included in these calculations.The importantconclusion
highlighted by Figure 1is that if we rely solely on
fossilfuels to supply globalenergy demandthenproven
reserves (1P)would be predicted be completely depleted
between 2069 and 2088. As the recent oilspill in the Gulf of
Mexico has shown,the extraction of1Preserves is already
technically challengingand likely to become increasingly
costly.Consequently reliance on 2P,3P and 1C reserves
must be regarded as increasingly insecure.However,current
data suggeststhat based purely on the estimated
reserves anda stable populationofnine billion people
beyond2050 even these reserveswould only secure fossil
fuel supply until2084–2112 at economic growth rates of
1.5–3% pa. A major transition to renewable energy before
2030 should therefore be supported to ensure an orderly
changeoverfromfinite reserves andto addressthe more
pressingconstraintsofclimate change [12].
A major problemfor policy makers and industry is how
best to facilitate the transition to a renewable energy
future [13] and what role biofuels should play in the energy
mix. Currently almost all renewable energytechnologies
(e.g. photovoltaic,solarthermal,geothermal,wind and
wave power)are designed to produce electricity,which
accounts foronly a third ofthe current globalenergy
market [14]. By contrast,biofuelsystems offerthe best
studied andclosest to market potentialrenewable solution
for supplyingthe globalliquid fueldemand,which makes
up two-thirds ofthe globalenergy market [14], by producing
biodieseloraviation fuel,methane,butanol,ethanol
or hydrogen.Although electricity hascertain advantages
Review
Corresponding author: Hankamer, B. (b.hankamer@imb.uq.edu.au).
5541360-1385/$ – see front matter . CrownCopyright_ 2010 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.tplants.2010.06.003 Trends in Plant Science,October
2010, Vol. 15,No. 10