Study reveals compostables biodegrade ‘quickly enough’ in Dutch composting sites

A new study has revealed that compostable plastics biodegrade sufficiently quickly in Dutch composting facilities, though conventional plastics remain a problem.

In a report published last Wednesday (12 February), researchers from the Wageningen Food & Biobased Research unit at Wageningen University and Research in the Netherlands investigated how compostable plastics behaved in the processing of food and garden waste (GFT).

Front cover of the Wageningen Food & Biobased Research unit study.The researchers followed compostable variants, such as those made with PLA (polyactic acid), of plastic products, including tea bags and plastic bags and thicker products such as plant pots, supplied by Holland Bioplastics through the regular composting process.

To obtain usable compost at the end of the regular composting cycle – around 11 days in the Netherlands – the not-yet-biodegraded GFT residues were sieved, along with contaminants including 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 (10-40 mm), about 70 per cent of what came out of the composting reactor, consisted of slowly biodegradable GFT such as remnants of branches, leaves, peelings and paper, which is then 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 40 mm), which represented approximately nine per cent of what came out of the composting reactor, also consisted mainly of slowly biodegradable GFT.

Conventional plastics were found in this fraction, as well as some remnants of biodegradable plastic bags, but the biodegradable plastics were expected to completely break down while the conventional plastics were expected to accumulate.

It was striking that the compostable products made from 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 thin tea bags, but also to the thicker plant pots.

A spokesperson for Wageningen Food and Biobased Research said: “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 GFT is a real problem for GFT waste processing and will have to be solved.”

‘Dispels the myth’

The study seeks to ease doubts over whether compostable plastics are suitable for the industrial facilities for which they are destined.

Issues frequently identified include packaging that is labelled as compostable or biodegradable but not conforming to the EU’s EN13432 standard, which states that to be deemed compostable or biodegradable an item must be able to biodegrade in an industrial composting facility, and public confusion leading to conventional plastics ending up in the organic waste stream.

In the UK, the Waste and Resources Action Programme (WRAP) recently released new guidance to provide clarity on the use of compostable packaging, explaining what counts as compostable packaging, what applications it should be used in, how it should be labelled and how it should be treated.

Commenting on the Wageningen research, David Newman, Managing Director of the Bio-based and Biodegradable Industries Association (BBIA), said: “In the Netherlands, the waste industry has traditionally taken a position opposed to the use of compostable plastics, apart from compostable bags for food waste collections, teabags and other items strictly related to food waste purity. Partly the reason for this is that they have claimed that their short-cycle compost systems (sometimes as short as two weeks) mean that compostable plastics do not break down in time and therefore go on to contaminate the compost.

“The Wangingen study dispels this myth, showing the materials are generally compatible even with short process systems. Even thicker plastics such as PLA break down. But above all Wangingen shows how food waste and compost in compost plants in the Netherlands are contaminated by traditional plastics, something common across the EU and an increasing concern as mandated food waste collections will be implemented across the whole continent in 2023. Just how many tens of thousands of tonnes of plastic fragments will we put to soil with these massive amounts of food waste going into treatment from 2023 if we allow plastics in the collection systems?

“Compostable plastics are compatible with Dutch composting processes and indeed reduce the contamination of traditional plastics going to soil, something we have been preaching for a decade. This is indeed the whole point of using compostable materials in the first place.”

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