Waste-Derived Lactic Acid for Polylactic Acid Production: Processes, Challenges, and Prospects

Global plastic production is expected to continue rising in the next few decades, with packaging accounting for roughly one quarter of the total volume of plastic and intensifying interest in biodegradable alternatives such as polylactic acid (PLA). One approach towards bioplastic production is lactic acid fermentation. Lactic acid (LA) can be produced from waste and by-products, such as food and agricultural waste, and then polymerised into PLA. This review provides an overview of LA production from waste-derived feedstocks, covering substrate composition, pretreatment and hydrolysis strategies, fermentation modes, and downstream operations, and highlights key performance indicators (yield, final LA concentration, and volumetric productivity). This review examines technological bottlenecks associated with waste heterogeneity, mixed sugar utilisation, inhibitor formation, pH and temperature control, contamination risks, high cost, and complexity of LA recovery and purification. Recent advances in pre-treatment, robust or engineered microbial strains, mixed microbial cultures, process integration, and intensified downstream schemes are also discussed to increase productivity and purity while reducing energy and chemical inputs. Finally, techno-economic assessment studies on waste-based PLA are synthesised, showing that both economic and environmental performance depend on feedstock logistics, process configuration, and end-of-life options for PLA products.