Mesophilic Anaerobic Digestion as a Pre-Treatment to Enhance the Composting Biodegradation of PLA-Based Compostable Packaging

The limited biodegradation of many commercially available compostable polymer formulations under mesophilic anaerobic digestion (AD) currently represents one of the main barriers to their acceptance in integrated organic recycling systems. This study evaluated whether mesophilic anaerobic digestion, followed by industrial composting, can improve the subsequent biodegradation of these materials. Compostable coffee capsules made of polylactic acid (PLA), poly(hydroxybutyrate-co-valerate) (PHBV), poly(butylene adipate-co-terephthalate) (PBAT), and poly(butylene succinate) (PBS) were used as model materials to evaluate physicochemical and morphological changes induced by AD. Mesophilic AD significantly altered the supramolecular structure of PLA-, PHBV-, and PBAT-based capsules, whereas PBS-rich formulations showed limited macroscopic changes. AD promoted PLA hydrolysis, induced chain scission, reduced polymer molecular weight, and triggered material fragmentation. These structural modifications markedly accelerated the subsequent biodegradation of PLA-based capsules under industrial composting conditions, reducing the half-time by a factor of 2.3–3.7. Integrating mesophilic AD with composting therefore appears to be a promising strategy for treating biowaste containing industrially compostable packaging. These results demonstrate that the response of commercial compostable formulations to anaerobic digestion is formulation-dependent and governed by polymer-specific structural changes. The study highlights the importance of polymer formulation in determining biodegradation pathways under integrated organic recycling conditions.