<p>The valorization of wood waste is critical for advancing a circular bioeconomy. This study investigated the conversion of white oak sawdust into lactic acid through chemical and hydrothermal pretreatment routes using a yogurt-derived microbial consortium as a practical fermentation screening model. Hydrothermal pretreatment demonstrated superior process robustness, yielding relatively consistent lignin contents (14–16% cysteine-assisted sulfuric acid lignin, CASA_<i>L</i>) while maintaining hydrolysate fermentability. Fermentation experiments were conducted both in the presence and absence of nutrient supplementation to differentiate hydrolysate-related effects from substrate accessibility and nutrient limitations. Hydrothermally derived hydrolysates supported rapid and sustained lactic acid production, reaching 19.90&#xa0;mg/mL by spectrophotometric analysis and 16.49&#xa0;mg/mL by HPLC-RID after 168&#xa0;h. In contrast, chemically derived hydrolysates exhibited delayed fermentation behavior and benefited substantially from nutrient supplementation, indicating that extensive delignification alone did not translate into improved fermentation performance. HPLC profiling further revealed more efficient sugar utilization and a fermentation pattern more closely associated with homolactic metabolism in hydrothermal systems, whereas chemically pretreated substrates showed greater accumulation of secondary metabolites associated with mixed-acid responses. Analytical greenness assessment and laboratory-scale reagent cost analysis favored the hydrothermal route, which achieved a higher AGREE score (0.66 versus 0.34) together with substantially lower reagent-related costs under the conditions investigated. The results demonstrate that pretreatment selectivity may be more important than delignification severity for mixed-culture valorization of hardwood waste, supporting hydrothermal processing as a promising strategy for sustainable lactic acid production.</p> Graphical abstract <p></p>