one fuel source only which is carbon intensive, the benefits for the system are great. If an average mix is
assumed to produce the substituted energy, the benefits depend on the average contribution of the mix to
climate change.
An example that depicts the influence of the substituted energy mix is the examination of the incineration results
for climate change. The studies that assume an exclusive fossil-based mix replaced by energy recovery produce
net negative results (studies 2 and 5). On the other hand, the studies that include some percentage of renewable
energy sources (study no 4 substitutes partly forest residues for heat and study no 6 Scandinavian and
Norwegian mixes) attribute worse results to incineration. This observation is illustrated in the Table 80.
Table 80 Analysis of the influence of the electricity mix on the performances of incineration regarding the climate change potential. A negative %
means that incineration is more beneficial than composting. A positive value means that composting is more beneficial than incineration.Study
number
Substituted energy Type of mix
Impacts of incineration
compared to composting
regarding climate change
(% difference)
(^2) Coal Fossil From ‐1320% to ‐400%
(^5) Fossil Fossil 0%
(^4) Hard coal/forest residues Partly renewable 22%
(^6) Norwegian/Scandinavian mix Partly CO2 neutral 150%
Issues around carbon sequestration and biogenic CO 2
As for other degradable materials, the issue of the inclusion or exclusion of biogenic CO 2 is of importance for food
and garden waste. As explained above, the problem is in deciding how to deal with the emissions of the CO 2 that
occur during degradation and that counterbalance the CO 2 absorption during the growth of the plants or trees.
The question is thus whether the emissions of biogenic CO 2 should be counted as contributing to climate change.
There is some controversy among experts about this issue. According to the Joint Research Center, biogenic and
non biogenic CO 2 emissions should both be inventoried, but there is still debate about how to deal with this issue
in the calculations. Indeed the method of accounting biogenic CO 2 has a major influence on the results since if
biogenic CO 2 emissions are disregarded, it means that burning organic waste in the case of incineration does not
contribute to climate change. In study no 4, it is argued that the exclusion of biogenic CO2 can lead to erroneous
results by creating unfair advantages for one of the compared options. For example, when comparing landfill to
incineration, biogenic CO 2 from incineration would be disregarded, while methane from landfill counts. Moreover,
combustion leads to immediate release of CO 2 while there is some trapped CO 2 in the landfill, emitted later. This
difference cannot be registered based on the biogenic exclusion assumption.
Other issues that arise around the fate of the carbon content during composting are carbon storage and carbon
binding. Carbon storage refers to the carbon part of the material being composted that is not degraded and that
remains stored in the compost after a certain amount of time (usually 100 years), thus avoiding some biogenic
CO 2 and methane emissions. The issue of carbon binding arises during compost utilisation. Indeed, compost
utilisation stimulates additional carbon storage in soils through a variety of processes, such as better soil humus
formation and better retention of carbon in the soil from plant residues, leading to increased plant primary
productivity. Carbon storage and binding are thus both linked with climate change mitigation. Table 81 below
illustrates the studies’ assumptions regarding carbon binding or storage. All studies have addressed these issues
but only four have decided to take them into account. They all agree, however, that the dynamics of the carbon
binding/storage are quite complex and, given the great amount of time necessary for these functions to unfold,
the uncertainty is rather high. Moreover, the numbers used for each study’s calculations are presented in such a
way that a comparison of the level of carbon binding/storage across studies is impossible (the reference quantity
changes from one study to another). In all studies that consider carbon binding/storage, the benefits of
composting manage to overcome the burdens, except for study no 1. Studies 3 and 4 which do not take into
account either of the two carbon phenomena, present higher burdens than benefits. Study no 1 has a high value
of benefits due to carbon binding, but the results show higher burdens. The reason behind this observation could
be that study no 1 is the only one that includes biogenic carbon dioxide emissions in the results.