Study no 1
In study no 1, recycling, landfill and incineration with energy recovery are compared for PE and PET. For
depletion of natural resources and energy demand, landfill appears as the least preferable option for both
products. However, for climate change, landfill performs better than incineration with energy recovery. Indeed,
the contribution to global warming is assessed over a 100-year period while plastic is assumed not to decompose
over this time period, thus there are no emissions of gases contributing to climate change. Recycling appears as
the best option for all three indicators.
Study no 2
This study compares a range of mechanical recycling technologies, two technologies for pyrolysis, landfill and
incineration with energy recovery for domestic mixed plastic wastes (PE, PET, PP, PS, PVC). Some of the
technologies assessed are operated on a large scale while some others still at the pilot stage. This study
compares nine different recycling scenarios that differed in terms of sorting and recycling technologies are
compared. Depending on the scenario, the sorting technology is either near-infrared (NIR) sorting or density
separation. The recycling technologies are similar in all scenarios since the plastic is always first shredded and
then extruded to form recycled granulate. As a consequence of these similarities between the various recycling
scenarios, the results are of a similar magnitude. To reflect the range of values, it has been decided to use the
highest and lowest results for each indicator.
Regarding pyrolysis, the two technologies assessed are feedstock recycling (leading to products substituting
naphtha, paraffin and refinery gas) and conversion to diesel. Feedstock recycling and conversion to diesel is
suitable for polyolefins^2 (i.e. PE and PP) and polystyrene. PET and nylon have also been processed through
feedstock recycling on a semi-commercial basis. It should be also be noted that pyrolysis is not yet considered as
a mature technology and that relatively poor data is available on pyrolysis technologies. Thus, the two pyrolysis
scenarios assessed are not sufficient to draw general conclusions on the overall environmental performance of
pyrolysis.
The results from this study show that recycling performs better than the other alternatives for the impacts on
depletion of natural resources and climate change while pyrolysis is the preferred alternative for energy demand.
This can be explained by the fact that the avoided impacts associated with displacing production of fuels exceed
the credits gained by avoiding the use of gas to produce electricity. The least favourable alternative is landfill for
depletion of natural resources and energy demand but landfill performs better than incineration regarding climate
change. As for the previous study, the explanation lays in the choice of a 100-year time horizon to assess the
global warming potential.
Study no 3
In study no 3, recycling, incineration with energy recovery and landfill are compared over a large range of
plastics: PE, PP, PS, PET and PVC. The study highlights that recycling is the preferred alternative for all types of
plastics for climate change, energy demand and depletion of natural resources. Landfill is the worst alternative for
all materials for those three indicators including climate change. This result thus differs from both previous
studies but can be explained by the choice of the time period. In this study, the authors have chosen a
hypothetical infinite time period when inventorying emissions which implies that complete degradation of
landfilled material is assumed.
Study no 4
This study assesses the environmental performances of recycling, incineration with energy recovery, landfill and
pyrolysis for a mix of PE and PET. For the pyrolysis scenario, low-temperature pyrolysis is applied to the
polyolefins fraction while the PET fraction not suitable for pyrolysis goes to mechanical recycling.
Unlike the previously mentioned studies, contribution to depletion of natural resources is not analysed but water
consumption is. Recycling appears as the preferred alternative for the three indicators. Landfill is the worst option
regarding energy demand and water consumption but performs better than incineration regarding climate
change. The limited impacts on climate change from landfills are again explained by the choice of a time period
of 100 years during which very little degradation takes place.
(^2) A polyolefin is a polymer produced from a simple olefin as a monomer. For example, polyethylene is the polyolefin produced
by polymerizing the olefin ethylene. Polypropylene is another common polyolefin which is made from the olefin propylene.