European Bioplastics has criticised a recent US study by North Carolina State University for focussing on the green performance of some biodegradable plastics rather than taking a wider look at the whole bioplastics market.
The association, which represents the interests of Europe’s bioplastics industry, said the study “Is Biodegradability a Desirable Attribute for Discarded Solid Waste?” is misleading as it refers to just one grade of bioplastics from the branch of (biodegradable) polyhydroxyalkanoates (PHAs).
These are known to be biodegradable under a wide range of conditions including anaerobic ones such as is found in bioreactors for biogasification, said European Bioplastics. However, PHAs constitute just one class within the large family of bioplastics and it is therefore misleading to generalise from one material to the entire range.
There are bio-based, non-biodegradable bioplastics such as PET, PE, polyamides and many more that do not at all produce methane (also referred to as biogas or landfill gas) because they are not biodegradable, explained the association. They, however, constitute a significant proportion of the current bioplastics production.
In addition, biodegradable and bio-based materials do not all behave the same way under landfill conditions, explained European Bioplastics. Their biodegradation profiles strongly depend on the actual conditions in a specific environment, such as landfill. As well as the inherent anaerobic biodegradability, the moisture content is an important parameter. In sanitary landfill the moisture level is low and not conducive for biodegradation as shown by some studies.
Generalising statements about the potential of methane emissions from bioplastics in landfill do not reflect the heterogeneity and the variety of the material class and they also do not take into account the variety of landfill types, the quality of the landfill gas management and the fact that, compared with other waste going to landfills and potentially emitting methane, bioplastics only enter landfill in very low amounts, especially in Europe.
The European Landfill Directive 1999/31/EC prescribes the reduction of the amounts of biodegradable wastes going to landfill and determines that only treated, i.e. stabilised and biologically inactive, waste is allowed as input.
Source: PRW.com, 2011-06-28.