Transforming waste wood into pure L-(+)-lactic acid: Efficient use of mixed sugar media through cell-recycled continuous fermentation

Lignocellulosic media, containing diverse sugars and growth inhibitor compounds, pose great challenges to fermentation processes. This study tested thermophile Heyndrickxia coagulans strains for the production of L-(+)-lactic acid from waste wood hydrolysate. H. coagulans A166 reached high titers of up to 94.6 g·L^-1 lactic acid in batch studies, tolerating furfuralic compounds, however, productivity was affected by carbon catabolite repression. Within cell-recycled continuous fermentation studies, this limitation was overcome by determining optimal initial dilution rates: complete and concurrent utilization of mixed sugars was realized at 7.6 g·L^-1·h^-1 productivity - an increase by factor 4.5-5.8 compared to batch studies. Work on synthetic media enabled process durations of up to 188 h, providing further insights into the process behavior and offering cues for further optimization. Employing inhibitor compound tolerant H. coagulans A166 at optimal initial dilution rate, cell-recycled continuous fermentation is a promising approach to enhance lactic acid production from lignocellulose media.