Page 94 - Advances in bioenergy (2016)

coproduct into nonproduct output vice versa may lead to changes in allocation. Different kinds
of allocation may lead to different outcomes of LCA. 27,81,82

The interpretation stage of LCA connects the outcome of the assessment done to the real
world. In this stage, uncertainties in outcome can be considered and conclusions can be drawn.

RESULTS OF LCAs RELEVANT TO THE EROI OF

AUTOTROPHIC MICROALGAL LIPID-BASED BIOFUELS

A number of attributional and consequential LCAs of biomass, lipids, biodiesel, and other
biofuels derived from autotrophic microalgae are available (Refs 13, 19, 22, 27, 29, 36, 38,
40, 68, 85–102, and references therein). This is a large increase if compared with an earlier
review of the energetic performance of microalgal biofuels, which appeared in 2009. 61
Available LCAs tend to vary much in their quality, system boundaries, ways of allocation,
assumptions about inputs and outputs and outcomes. Table 3.2 summarizes the EROIs and key
assumptions of peer-reviewed LCAs of biodiesel from autotrophic microalgae, as they have
appeared in the 2009–2011 period.

From the available LCAs, several generalizing conclusions may be drawn regarding their

energetic implications.
It is noteworthy that several energetically relevant aspects of the life cycle tend to be outside
system boundaries of LCAs as they have been done so far (see also Table 3.2).

The first aspect which is rather often absent is (waste) water treatment, although there are
90
exceptions such as the LCAs of Clarens et al. 38,68 and Lardon et al. To the extent that waste
water is discharged, loading of waste water with nutrients and, in the case of ponds, with
substances conducive to achieving extreme conditions would seem such that waste water
treatment is warranted. To the extent that water is recycled, the removal of inhibitory waste
products and pathogens is necessary, which may require substantial energy inputs, as suggested
by water recycling in aquaculture and horticultural irrigation water for greenhouses. 103-105
Energy inputs into water supply management preceding algal cultivation is also often outside

the system boundaries. An exception is for instance the study of Murphy and Allen. 29

Another aspect that tends to be absent in LCA is the treatment of microalgal lipids to obtain
purified and/or upgraded biodiesel, beyond the transesterification step of the extracted
microalgal lipids. Purified and/or upgraded biodiesel is needed for a wide range of
3-6
applications. 9, 106-108 Because microalgal lipids as yet tend to be polyunsaturated, upgrading
by, e.g., hydrogenation is needed when biodiesel for the internal combustion engine is
produced. 8,27,108 Both upgrading and purification require substantial energetic inputs. 19,27,30,107-
109 It may be noted, although, that algal strain selection may focus on increased levels of

saturated fatty acids. 30

Available LCAs which include inputs in hardware (ponds and photobioreactors) suggest that,
per functional unit, open ponds are more energy efficient than current photobioreactors in spite