One of the statements of the LCA methodology is to link every economic and environmen­tal flow to the reference flow of the FU. However, several processes implied in the production of the FU can lead to the production of several products. Two approaches are possible to han­dle the multifunctionality of the system: allocation or substitution. The allocation approach consists of distributing the environmental burden of the upstream between all the coproducts of the multi-output process. This distribution should be based on the most sensitive criterion, e. g., mass, economic value, or energy content of the products. The perimeter expansion (or sub­stitution) option consists of adding the coproduct to the FU. The ISO norm for LCA stipulates that perimeter expansion should be preferred when possible. When substitution is not pos­sible, energy allocation should be preferred for processes leading to the production of energy.

Among the 15 publications, 3 publications (Kadam, 2002; Clarens et al., 2010; Jorquera et al., 2010) analyze systems without coproducts. Table 13.8 presents the various coproducts and the choices between allocation and substitution. Several processes can lead to coproducts:

• The oil extraction process leads to the production of an extraction residue (oilcake); only Lardon et al. (2009) chose to use an energy-based allocation at this level. Other authors (Stephenson et al., 2010; Brentner et al., 2011; Campbell et al., 2011; Clarens et al., 2011) chose to directly treat the oilcake by anaerobic digestion. Oilcakes can also replace other products: aquaculture or livestock food, carbohydrates’ source for bioethanol production.

• Oil esterification produces methylester and glycerol; here economic and energy allocation are often used. In case of substitution, glycerol is mainly used as a source of heat.

• Anaerobic digestion produces biogas and solid and liquid digestates; these digestates can be considered waste (and hence cannot support a part of the environmental burden of the process), fertilizer, or soil conditioner. The liquid digestate can be recirculated to the culturing device and hence substituted to a fraction of the mineral fertilizer required for the algae. The produced biogas is transformed into heat used on site to heat the digesters and/ or converted into electricity. Electricity is also consumed on site, and the surplus is injected into the network (Stephenson et al., 2010; Clarens et al., 2011).