Hydrothermal processing of polylactic acid: Analysis of intermediate products and toxicity evaluation of anaerobically digestated residues

Polylactic acid (PLA) plastic is increasingly recognized as a sustainable alternative to petroleum-based plastics. However, its biodegradability remains a challenge, requiring substantial improvements to its biodegradation efficiency. This study explored the use of combined hydrothermal treatment (HTT) (160°C–240°C) and anaerobic digestion (AD) to improve methane yield from PLA. HTT enhanced significant structural changes in PLA, yielding 2-hydroxypropanoic acid, 1-decanol, 1-tetradecanol, pentan-2-one, and butyl 2-hydroxypropanoate, which facilitated PLA degradation. The methane yield from AD of hydrothermal-treated PLA (HTT-PLA) products at 180°C was 493 NmL/g-volatile solid, a 21.4-fold increased compared to untreated PLA. Genomic and proteomic analyses identified key genes and proteins involved in HTT-PLA products biodegradation, elucidating pathway for HTT-PLA products transformation in biodegradation process. The residues from AD of HTT-PLA products at 180°C exhibited rapeseeds germination index of approximately 90% and maintain stability locomotion and vitality in Caenorhabditis elegans , indicating their suitability for land application. Enhanced methane production offers a renewable energy source, and reduces PLA’s environmental footprint, providing significant practical implications for bioplastic waste management and sustainability.