Environmental footprints of biological end-of-life strategies for residual post-consumer polylactic acid: A comparative life cycle assessment

• Comparative LCA of biological EoL options for rPC-PLA waste under ISO standards. • Anaerobic digestion outperformed other EoL routes due to efficient energy recovery. • Evaluates uncertainty propagation from data reliability and process variability. • Provides Australia’s key challenges in expanding biological treatment of PLA waste. • Offers policy insights to support sustainable and circular bioplastic management. Bioplastics are increasingly promoted as sustainable alternatives to conventional polymers, yet their environmental performance strongly depends on end-of-life (EoL) treatment. For polylactic acid (PLA), the most widely used biodegradable bioplastic, repeated recycling leads to progressive polymer degradation, leaving residual fractions that can no longer be recovered. These residual streams require biological disposal, but their climate implications remain poorly quantified and inconsistently compared. We present a comprehensive, process-based life cycle assessment of three biological EoL pathways for residual post-consumer PLA (rPC-PLA), such as industrial composting, anaerobic digestion (AD), and landfilling, conducted under ISO 14040/14044 standards and coupled with uncertainty modelling via Monte Carlo simulation and pedigree-matrix parameterization. AD demonstrates a net-negative climate impact (-134 kg CO 2 eq per tonne of rPC-PLA) through biogas recovery and fossil-energy substitution, whereas composting generates substantially higher emissions (1932 kg CO 2 eq per tonne) due to rapid biogenic CO 2 release and high aeration energy demand. Landfilling delivers moderate impacts in engineered facilities with optimized gas capture, but uncontrolled disposal leads to markedly higher emissions over a 100-year time horizon. These findings show that not all biodegradable waste pathways deliver environmental benefits and that AD uniquely converts unavoidable rPC-PLA into climate-beneficial energy. The work provides quantitative evidence to guide bioplastic waste policy and demonstrates that realizing the sustainability promise of PLA depends not only on its material design but on aligning waste infrastructure with circular bioeconomy goals.