addition, the credibility of an LCA report increases if the same technological advancement is assumed for the
different treatment options.
This problem is encountered when anaerobic digestion is a part of an LCA comparison. In all studies that
examined anaerobic digestion, the recovery efficiencies and the conversion to electricity efficiencies are quite
high. Therefore, this mode of treatment acquires an a priori advantage over the other alternatives.
The recovery and energy conversion (to electricity or heat) efficiencies assumed, especially in energy recovery
processes, are decisive for the amount of crediting for the system. The recovered energy is a major source for
indirect emissions in a waste system because of the avoided production of primary energy. The efficiencies play
an important part for the overall LCA since they determine the factor with which these indirect emissions are
multiplied before being included in the emissions inventory. Unfortunately, the assumed efficiency is not always
clearly stated in the studies, as illustrated in the Table 83.
Table 83 Overview of the incinerator efficiencies in the selected studies.
Study
number
Energy produced
with incinerator
Efficiency
(^2) electricity + heat n.a.
(^4) electricity + heat n.a.
(^5) electricity n.a.
(^6) electricity + heat n.a.
(^7) electricity + heat 80%
3.5.4 Conclusion..............................................................................................................
The overview of the selected reports can lead to important conclusions about the fate of organic municipal waste.
Although the analysed treatment technologies include the traditional methods (landfill, incineration and
composting) and anaerobic digestion, the impact assessment for each method is well documented and sufficient
in order to draw conclusions regarding their relative classification.
A first observation from the life cycle impact assessment results is that there is no technology that is generally
superior to the others. Some options prevail in some categories while they are considered as the worst for other
indicators. Therefore, the compilation of a weighting classification of impacts depends on the scope of the study.
In this review, four indicators are considered to be most important: depletion of natural resources, global
warming, energy demand and water consumption. Anaerobic digestion seems to be the best option even if it is
not included in many studies (only three out of the seven selected studies include this option). Incineration with
energy recovery also presents good results and it is never classified as the worst option for these four indicators,
even though food waste has a relatively low heating value. Landfill, on the contrary, generally should be placed
last in the list of preferable options.
The seven selected studies examine four different types of organic municipal waste. This general fraction includes
garden waste and food waste, but some studies concentrate only on only one of the two sub-fractions, as has
already been explained. The results for different materials should be interpreted with respect to different
properties of these materials. However, no safe conclusions can be drawn as the results of the review of the life
cycle assessments did not locate any consistency among results for the same type of material. The differences in
key parameters influence the results so much that comparisons across studies are impossible.
Another important issue relates to specialised technologies targeting only part of the organic municipal waste.
Besides obvious statements (incineration is more suitable for garden waste because of its higher heating value,
as garden waste includes branches and some wood), the selected studies did not compare treatment options for
different types of organic waste. Moreover, no study stated in its scope any specific interest in applying a specific
technology to garden or food waste, namely to differentiate the treatment according to the type of food or
garden waste.
The scarcity of credible studies and the fact that many studies examine site-specific issues, which is an intrinsic
problem of LCAs, do not allow a proper and comprehensive review in an international context. However, the
selected studies provide an overview of the more traditional treatment options for the organic fraction of the