A study by Wageningen Food & Biobased Research has found that compostable plastics break down sufficiently and quickly enough in Dutch composting facilities.
In a representative full-scale composting test conducted at an organic waste site in the Netherlands, no remains of compostables plastics were found in the compost produced by the organics waste processing, though conventional plastics remained.
At the end of the regular composting cycle (around 11 days), the not-yet-biodegraded organic waste residues are sieved to remove contaminants such as metals, glass, stones and plastics.
About 21 per cent of what came out of the composting reactor after 11 days was sufficiently small to be considered as compost. The largest sieve fraction (10-40mm), about 70 per cent of what came out of the composting reactor, consisted of slowly biodegradable organic waste such as remnants of branches, leaves, peelings, paper and the like, which is usually reintroduced into the composting process.
Approximately one per cent of this sieve fraction was plastic, that almost exclusively consisted of conventional fossil plastic. The coarser sieve fraction (larger than 40mm), which represented approximately nine per cent of what came out of the composting reactor, also consisted mainly of slowly biodegradable organic waste. The plastics found in this fraction were also mainly conventional fossil plastics, although remains of compostable organic waste collection bags were also found. It is likely that the fossil plastics will accumulate further in the residue while the compostable plastics will further completely break down if these sieved fractions are brought back into a subsequent composting cycle as usual.
A surprising finding from the study was that compostable products made from polylactic acid (PLA) were found to break
down faster than, for example, paper and orange peels, and could not be found even after one composting cycle of 11 days. This not only applied to the thin tea bags, but also to the thicker plant pots.
Based on all the findings, the researchers conclude that compostable plastics that meet the European standard EN13432 break down quickly enough in Dutch organic waste processing plants. However, the presence of conventional fossil plastics in organic waste is a real problem for organic waste processing and will have to be solved.
You can view the report in full here.