Life-Cycle Assumptions of Landfilled Polylactic Acid Underpredict Methane Generation

The life-cycle assessment (LCA) tool, Waste Reduction Model, currently applies no methane generation to landfilled polylactic acid (PLA), considering the carbon sequestered. A selection of PLA products were analyzed by the biochemical methane potential (BMP) assay, and the results were compared to LCA model values. BMPs were performed at 35 and 55 °C on a variety of single-use products that would be disposed alongside food scraps. No biodegradation was observed for any product after incubation at 35 °C for 60 days. PLA products generated 185–372 mL of CH4/g of volatile solids at 55 °C after 60 days, some approaching the theoretical methane potential. The results here indicate that PLA may generate significant quantities of methane in an anaerobic landfill environment, which can reach thermophilic temperatures, and the current assumption of PLA as an absolute carbon sink in landfills is incorrect.