Lactic Acid Production from Green Microalgal Biomass Hydrolysates via Dilute Acid Pretreatment and Fermentation

Abstract

This study explored the feasibility of using green microalgae (Chlorella vulgaris) as a renewable feedstock for bio-based lactic acid production. Microalgal biomass was subjected to dilute sulfuric acid hydrolysis under various conditions to optimize fermentable sugar recovery. The optimal hydrolysis condition consisted of 2% sulfuric acid, heating at 121 °C for 20 min, and a 10% solid-to-liquid ratio. This treatment yielded 12.1 g/L glucose and 2.1 g/L xylose. The hydrolysate was then used as the sole carbon source for fermentation by Lactobacillus casei, which completely consumed the sugars and produced 10.7 g/L lactic acid within 24 h. The overall sugar-to-lactic acid conversion efficiency reached 98% without any observable inhibition, and the product consisted exclusively of L-lactic acid with no detectable D-isomer. These findings demonstrate the effectiveness of microalgal hydrolysis and confirm the potential for integrating cultivation, pretreatment, and fermentation into a sustainable, carbon-neutral biorefinery process.