Energy recovery
In the case where some energy is recovered during the waste management stage, the production of energy from
other sources is avoided and these benefits are included in the system boundaries. The extent of the credits that
can be attributed depends on the type of energy that is replaced. The electricity produced is usually assumed to
be average national grid electricity. Although the electricity mix varies from one country to another, the electricity
production is still based mainly on fossil fuel resources; thus the credits for avoiding energy use significantly
improve the environmental performances.
Energy recovery is very often associated with incineration, which explains why incineration with
energy recovery often performs better than composting and landfill. The biogas from landfill can also be
collected to produce electricity, as in study no 2. For Biolice and Mater-Bi, landfill then emerges as a better
alternative than incineration with energy recovery. The explanation may lie in the fact that the degradation of the
material in methane releases more energy than the incineration process. The other studies assessing landfill
disposal (studies 1, 4 and 5) do not assume energy recovery from landfill. Therefore, the influence of this
parameter cannot be analysed further.
Some biogas is also produced in the case of anaerobic digestion in studies n°3 and 7 and the assumptions around
the recovery of the biogas are presented in the Table 62. The two studies differ in terms of biogas production
rate and type of energy recovery. It is also interesting to note that both studies take place in Germany and follow
an attributional approach, thus assuming that the energy produced replaces average grid energy.
Table 62 Overview of the assumptions regarding anaerobic digestion in the selected studies for biopolymersStudy
number
Material Biogas production Biogas valorisation
3 PLA 0.84 m
3/kg PLA electricity only
7 Maize starch 0.4 m^3 /kg organic matter 33% electricity/56% heat
The assumptions around energy recovery for incineration (See Table 63) also explain why in studies no 2 and 4
composting performs better than incineration for climate change as illustrated on Figure 32. Indeed, study no 2 is
a French study and the electricity is thus mainly comes from nuclear power which is CO 2 free. Thus the energy
generated by incineration does not give any credit to the system regarding GHG emissions. In study no 4, no
energy recovery is associated with incineration or landfill and composting thus results in a better option. The type
of energy recovered and the efficiencies assumed for incineration in the selected studies are shown in Table 63.
Table 63 Overview of the incinerator efficiencies assumed in the selected studies for biopolymers. The efficiency figures are based on gross
calorific values (GCV) or net calorific values (NCV). When it is not clear whether the figure is based on GCV or NCV a question mark is inserted.