Researchers from ETH Zurich and the Swiss Federal Institute of Hydrosphere and Technology Sciences (Eawag) conducted an interdisciplinary study to demonstrate that soil microorganisms metabolically convert carbon contained in a PBAT polymer both to energy production and to create microbial biomass.

The researchers used a biodegradable polymer PBAT (polybutylene adipate terephthalate) labeled with a carbon isotope. This isotope label has allowed scientists to track carbon derived from the polymer through various biodegradation pathways in the soil. It turned out that the carbon from PBAT was not only converted to carbon dioxide (CO2) as a result of microbial respiration, but also included in the biomass of microorganisms colonizing the polymer surface.

The researchers were the first to successfully demonstrate where the polymer carbon ends and that the plastic material effectively biodegrades in soils. “This shows that after biodegradation there is nothing left but water, CO2 and biomass,” says Hasso von Pogrell, managing director of the European Bioplastics Association European Bioplastics e.V. “In this study, the two problems that constantly arise with respect to biodegradable plastics have been disproved – doubts that microorganisms completely metabolize certified biodegradable plastics, and concern that part of the polymer based on petroleum products will not completely degrade.”

The tested PBAT polymer is a biodegradable polymer based on fossil materials, which is used, among others, for the production of biodegradable certified, recyclable bags for biological waste (in accordance with EN 13432) or biodegradable biodegradable soil mulching films (in accordance with EN 17033).

“The results of this study will undoubtedly allow municipalities and waste management managers in the EU member states to recognize the advantages and functionality of certified compostable plastic bags for separate collection of organic waste, and in the agricultural context, an alternative in the form of biodegradable mulching films in the soil,” concluded Hasso von Pogrell.