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Investigating the Fate of Bio-based Plastics in Anaerobic Digestion
Summary
This study tested the breakdown of three types of bio-based food packaging plastics in anaerobic digesters over 26 weeks, assessing how well they degrade under conditions similar to industrial composting. Understanding whether bio-based plastics truly break down in real waste treatment settings is critical to evaluating their environmental claims.
The anaerobic digestibility of three bio-based after-market plastics used for food packaging applications was evaluated. These plastic samples were tested in a lab-scale solid-state digester, called Daisy, that was operated for 26 weeks. Daisy comprises 6 sequentially fed leach beds (~10 kg each) fed with a mixture of fibres and food waste, with each leach bed having a residence time of 6 weeks. The mass loss of polyhydroxyalkanoate straws, bamboo-fibre coffee cups, and polylactic acid clamshell containers was evaluated as a measure of anaerobic biodegradability. The PHA straws exhibited a mass loss of 55 % ± 17, the bamboo-fibre cups had a mass loss of 54% ± 15, and the PLA clamshell containers had no measurable mass loss. Scanning electron microscopy was conducted on samples of each bioplastic before and after digestion. These images revealed the formation of a biofilm and potentially the presence of methanogens on all bioplastic types.