generates energy credits. However, as mentioned earlier, to maximise benefits both electricity and heat should be
generated and valorised.
Future potential for recycling
The study highlighted that recycling, together with incineration, are the most beneficial alternatives regarding
depletion of abiotic resources, energy demand and acidification.
However, some detail needs to be provided regarding the type of recycling that was included in the reviewed
study. Two of the selected studies evaluated mechanical recycling for PLA and Mater-Bi. However, these were
prospective scenarios since this technology is not yet in place. These scenarios have thus been evaluated
extrapolating data from fossil-based plastics recycling processes. In both cases, the results indicated that
mechanical recycling was the best option.
Another recycling option for biopolymers is chemical recycling. Chemical recycling has been assessed in study no
3 for PLA, based on the process used to recover PLA production waste. The biopolymer is first hydrolysed and
then repolymerised into similar or other products. Chemical recycling appeared to perform better that composting
and anaerobic digestion regarding all the indicators assessed. As for mechanical recycling, sufficient amounts of
source-separated collected wastes are needed in order to be able to develop this recycling option.
The last type of recycling investigated in the studies was feedstock recycling, in which biopolymer waste is used
as a reducing agent in blast furnaces or converted to methanol. The advantage of this option is that there is no
need for specific infrastructures and the biopolymer waste can be treated together with mixed plastics. This
option was assessed in two scenarios and the results showed that this option does not bring additional benefits
compared to incineration or anaerobic digestion. This option thus brings fewer environmental benefits than the
other forms of recycling.
Based on these findings, mechanical and chemical recycling of biopolymers seem promising but further research
is needed to assess the real potential of these options depending on the biopolymer type. Councils and recycling
authorities will then need to develop the logistics associated with mass disposal of biopolymers (WRAP, 2009 (c)).
Following biowastes routes
In the case they are degradable, biopolymers can also follow the waste routes designed for biowastes such as
food waste. The main options are thus composting and anaerobic digestion. The study has highlighted that
anaerobic digestion, when assessed, performs better than composting. Anaerobic digestion has the advantage of
generating energy that can replace electricity and heat from the grid. This finding goes along with the UK waste
strategy which promotes anaerobic digestion. For instance, anaerobic digestion benefits from the Renewables
Obligations scheme. Nevertheless, it should be noted that anaerobic digestion has only been assessed in two
studies for PLA and maize starch and that there is to date little knowledge about the behaviour of biopolymers
during anaerobic digestion. Further research would thus be needed to confirm the benefits of anaerobic digestion.
Regarding composting, it should first be noted that degradable biopolymers are not necessarily compostable.
Compostable packaging should comply with the standard EN 13432 which defines the characteristics of
compostable materials. Composting was found to perform quite poorly, due to the fact that composting does not
bring any energy credit, compared to anaerobic digestion or incineration, and the composition of biopolymers is
such that they offer no nutrient replacement value in compost. However, the degradation rate of the materials
has been found to be of key importance when assessing composting performances, especially for the climate
change issue. This degradation rate depends on the type of biopolymer. For biopolymers with a low degradation
rate, composting can be more advantageous than incineration with energy recovery. More knowledge about
degradation behaviour is thus needed to further discuss the potential for composting. Composting also presents
some advantages regarding eutrophication since LCA studies generally assume that the compost is used as a
replacement for fertilisers. In order to optimise the environmental performances of composting it would thus be
interesting to develop technologies for gas emission recovery. Composting could then allow combining material
(via compost production) and energy recovery.