Page 88 - Advances in bioenergy (2016)

3

Lipid-Based Liquid Biofuels from Autotrophic

Microalgae: Energetic and Environmental Performance

Lucas Reijnders *
Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam,
the Netherlands

INTRODUCTION

Growing microalgae on a commercial scale for food production has a substantial tradition,
dating back to the 1950s (Refs 1–4 and references therein). For this purpose, autotrophic
1
microalgae such as Spirulina and Chlorella are grown, usually in open ponds. Omega-3
polyunsaturated fatty acids extracted from such microalgae, which are considered to be

important for ‘healthy diets’, are commercially available. 3-6

Autotrophic microalgae, which convert solar energy into biomass by photosynthesis, have also
been proposed as a source of biofuels, especially as a source of lipids (fatty acids, oil) for
1
biodiesel. Table 3.1 outlines the main stages in an autotrophic microalgal biodiesel life cycle
and the energetic inputs and co-outputs linked to this life cycle.

Proposals for lipid-based biofuels from autotrophic microalgae were firstly triggered by the
3
oil crisis of the 1970s. Substantial research and development work was done in the 1970s and
3
Goldman concluded at the end of this decade that autotrophic microalgae had little to offer as
even a partial solution to national and worldwide energy needs. Since then, substantial
research and development work on autotrophic microalgal biofuels has continued, but there is
as yet no commercial production of lipid-based autotrophic microalgal biofuels and there is no
proof that near-term commercial production would be financially competitive if compared
with other sources of energy. 1,7-19 Estimated near-term costs for lipid-based autotrophic
microalgal biofuels produced with currently available technologies are much, usually many
times, higher than current fossil fuel prices, even if for inputs there is heavy reliance on
wastes. 7,8,14,16,17,19 Estimates for near-term costs of autotrophic microalgal lipids from
17
bioreactors exceed those of lipids from cultivation in ponds typically by a factor 4–7. Also,
near-term costs of autotrophic microalgal lipids originating from ponds have been estimated to
be a factor 3 to 4 higher than near-term costs of competing lignocellulosic (bio)fuels, which in
turn are higher than near-term costs of biofuels from edible parts of food crops including
19
terrestrial oil crops. Nor is there consensus about the future commercial viability of
microalgal biofuels. Some hold that lipid-based autotrophic microalgal biofuels will become
commercially viable and will outperform biofuels from terrestrial plants, whereas others feel

that the prospects for commercial algal biofuels are very bleak. 13,17,20-22 In view of the many