Enhancing the biodegradation of PBS, PBAT, and their biocomposites under decentralized mesophilic composting conditions through bioaugmentation

The limited biodegradability of polyester-based bioplastics under mesophilic conditions remains a major constraint for decentralized end-of-life pathways, including home and community-scale composting. This study assesses whether bioaugmentation can improve the mesophilic compostability of two biodegradable polyesters, poly (butylene succinate) (PBS) and poly (butylene adipate-co-terephthalate) (PBAT), as well as their biocomposites containing 10% agro-industrial fillers (orange peel and brewer’s spent grain). Two bacterial consortia were isolated through selective enrichment in minimal medium using compost extracts incubated with the target materials for 200 days at 28 °C. Biodegradation assays were conducted in closed respirometric chambers following an adapted NF T51-800 / ISO 14855-1 protocol. Vermiculite activated with compost extract served as the substrate, with or without the enriched consortia, and the tested materials were the only carbon sources. Mineralization kinetics were monitored for 133 days at 28 °C. Structural changes were evaluated using DSC, FTIR, and macroscopic and SEM imaging, while microbial dynamics were characterized by CFU enumeration and Community-Level Physiological Profiling (Biolog EcoPlates™). Bioaugmentation substantially enhanced PBS biodegradation, increasing final mineralization by +68.3% relative to the control (43.6%) and reaching 72.4%, a value approaching the 90% threshold defined for home-compostability. No improvement was observed for PBS/OP. PBAT exhibited very limited biodegradation under mesophilic conditions, with no detectable effect of bioaugmentation. Hydrolysis was confirmed as the dominant degradation mechanism. Overall, bioaugmentation appears to be a promising strategy to accelerate the mesophilic biodegradation of PBS, although its effectiveness depends strongly on polymer–filler interactions and material formulation. • Bioaugmentation increases PBS mineralization by +68.3% • PBS/OP shows +83.2% higher mineralization than PBS with only 10% filler • Crystallinity unchanged as degradation targets both amorphous and crystalline parts • FTIR shows hydrolysis as the dominant degradation mechanism