Page 89 - Advances in bioenergy (2016)

uncertainties regarding future production technologies, future costs of liquid autotrophic
microalgal biofuels are highly uncertain. 22,23 It has been argued that a successful strategy to
lower the prices of future microalgal biofuel is to use microalgal biomass as an input for
biorefineries, which produce, apart from liquid biofuel, a variety of high-value substances as
coproducts.23-26 A problem with this strategy is that to make a substantial contribution to
future energy supply, the production volume of biofuels should be large. This may easily lead

to an oversupply of current high-value substances. This has already happened to glycerol,
which is produced as a coproduct of biodiesel. The price thereof has dropped dramatically. 27

Table 3.1 Main Stages in an Autotrophic Microalgal Biodiesel Life Cycle and the Energetic
Aspects of Inputs and Co-Outputs

Stages 1–6: cradle-to-gate; stages 1–7: cradle-to-pump; all stages: cradle-to-wheel.

There is also no consensus on the energetic desirability of lipid-based autotrophic microalgal
biofuels. Whereas some hold that energetic inputs in commercial autotrophic microalgal
biofuel production will be much smaller than the energetic output embodied in those
biofuels, 12,13,28 others hold that energetic outputs of microalgal biofuel production are and/or

will be lower than, or not much exceed, inputs. 22,27 There is also disagreement about