Possibilities and limitations of biotechnological plastic degradation and recycling
Considerable research achievements were made to address the plastic crisis by biotechnology, e.g. for PET. In our Comment article we clarify important aspects related to myths and realities about plastic biodegradation and we suggest distinct strategies for a biobased circular plastic economy.
The plastic crisis experienced around the whole world asks for sophisticated solutions – some must be rather rapid, for instance reduced plastic use and improved waste logistics, while others require medium- and long-term solutions to ensure a transition to a circular plastic economy. Importantly, such a transition is not only driven by the (partially) failed end-of-life use of valuable plastic products, but also by the much needed zero net carbon footprint of the plastic industry. Both, the production as well as the end-of-life scenarios and therefore the envisaged circular plastic economy open up many opportunities for biotechnology. Meanwhile, recent relevant publications in high-impact journals have attracted extensive attention both in the scientific and public discourses. For the widely used polyester PET (polyethylene terephthalate) enzymes have indeed been discovered1,2 and engineered3 to enable its efficient degradation to its monomers and therefore PET-recycling.
Along with these exciting scientific breakthroughs, notable misconceptions – such as plastic eating insects/microbes as solution of the plastic crisis – have been widespread among different readerships, causing meaningless follow-up research activities, unnecessarily raising obscuring hope for industry and end-users of plastic products. Therefore, in our Comment article4, we share our thoughts and opinions on the state-of-art of biotechnological researches, as well as realistic opportunities to tackle the plastic crisis. Our contribution first explains that the chemical bond in plastics dictates whether a bio-recyclability – using biocatalysis/biotechnology – is possible at all. In addition to degradation of plastics to their then recyclable monomers, we also highlight the importance of upcycling. That is the use of degradation products as growth sources for microorganisms to make other valuable products. This ‘plastic waste to plastic value’ concept is also the central theme of our ongoing EU Horizon 2020 project MIX-UP (www.mix-up.eu), which aims to valorise mixed plastic fractions, e.g. collected from ocean plastic or households using biotechnology.
Finally, for plastic ending up in the environment, we point out in our Comment that we require two extremely different timelines for biodegradation: plastic that is purposefully put into the environment like agricultural foils and textiles with biodegradation rates in the range of weeks or months, while all other plastics require an emergency biodegradation strategy – preferentially in the range of years and not centuries – to circumvent plastic accumulation by ‘wear and tear and littering’.
Overall, we envision a better plastic future built on the ‘6 R’ principles (rethink, refuse, reduce, reuse, recycle, replace) and look forward to a lively discussion on how to achieve a circular plastic economy.
- Yoshida, S. et al. Science 351, 1196-1199 (2016).
- Bornscheuer, U. T. Science 351, 1154-1155 (2016).
- Tournier, V. et al. Nature 580, 216-219 (2020).
- Wei et al., Nature Catalysis, DOI: https://www.nature.com/articles/s41929-020-00521-w (2020).