Page 93 - Advances in bioenergy (2016)

the establishment of ‘system boundaries’ and usually the definition of a ‘functional unit’. A
functional unit is a quantitative description of the service performance of products. It may for
instance be: 1 GJ (GigaJoule) of biofuel (measured as lower heating value). This allows for
comparing different products providing the same service.

In the goal and scope definition stage, system boundaries are drawn between technological
systems and the environment, between significant and insignificant processes, and between
technological systems. For instance, in dealing with microalgal biofuel production, one has to
decide whether, when applicable, water management facilities serving algal cultivation and
wastewater treatment of effluents from bioreactors or ponds and harvesting facilities (cf. Table
3.1) should be included. It would seem proper to do so. When algal cultivation includes the
use of wastes as inputs in the production of microalgae, the extent to which the generation and
treatment of such wastes should be included in LCA has to be decided upon. Also when

considering the emission of greenhouse gases, in establishing new algal cultivation facilities,
one should consider the inclusion of land use references, reflecting what would otherwise have
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happened with the land used for the biofuel production studied. When algal cultivation for
biofuels replaces algal cultivation for food and greenhouse gas emissions are considered, the
indirect effect on land use linked to the inelasticity of demand for food should be considered
for inclusion in LCA. 80-82 The choice of system boundaries may have a substantial effect on the

outcomes of LCAs. 27, 83, 84
The inventory analysis gathers the necessary data for all processes involved in the product life

cycle and the impact assessment stage deals with estimating impacts of the life cycle.

When dealing with the environmental impacts of microalgal products in these stages of LCA,
the problem arises that the conversion of microalgae into biodiesel may have more than one
output (e.g., Refs 27 and 39). For instance, processing Chlorella biomass into biodiesel not
only may lead to the output oil (lipids), which may be used for biodiesel production, but also
to algal cake, which may be used as (animal) feed ingredient, and to the output glycerol (cf.
Table 3.1). Also, biorefineries that may process microalgal biomass can produce a variety of
product outputs. 29,50,51 Biofuel production processes may generate wastes (nonproduct outputs)
27 and nonproduct outputs of other processes (such as flue gases and waste water) may be used
as inputs for the production of microalgae.

In the case of multi-output processes, extractions of resources and emissions have to be
allocated to the different outputs. There are several ways to do so. Major ways to allocate are
based on physical units (e.g., energy content or weight of outputs) or on monetary value
(price). There may also be allocation on the basis of substitution. In the latter case, the
environmental burden of a coproduct is established on the basis of another, similar product.
Occasionally, there is disagreement about the question whether there should be allocation to
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any biofuel coproduct at all. There is often, although not always, no allocation to ‘wastes’, 27
but this can change when the nonproduct output is found to be useful as an input in a production
process. In the latter case, ‘wastes’ might be considered coproducts. On the other hand,
coproducts may be ‘overproduced’ to such an extent that they are handled as ‘wastes’. This has
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for instance happened with glycerol, a coproduct of biodiesel production. Changes of