Process Optimization for the Adsorption of Inhibitors in Corn Stover Prehydrolysate by Cow Manure Biochar for Lactic Acid Fermentation

The pretreatment of lignocellulosic biomass generates inhibitory compounds that severely limit the efficiency of subsequent enzymatic biocatalytic conversions during fermentation. Biochar can be used for inhibitor removal by adsorption, but its efficiency depends on tailored process conditions. In this study, the cow manure biochar (CMB) was applied in the detoxification of prehydrolysate generated from dilute acid pretreatment of corn stover, and the detoxification process was optimized by the response surface method (RSM). At the optimal detoxification condition (53 °C, 118 min, and the biochar loading of 4.5% w/v), the detoxified prehydrolysate achieved a lactic acid (LA) production of 42.89 g/L with an 85.67% yield, while a removal efficiency of 46.47% was obtained for the major inhibitors in the prehydrolysate. The reusability of CMB was investigated by water-washing, thermal, and NaOH regenerations. All methods obtained over 80% regeneration performance, and the lactic acid yield remained above 35 g/L after two regeneration cycles. CMB regenerated by water washing maintained 81.86% of its initial adsorption capacity after two cycles, achieving a lactic acid concentration of 36.83 g/L. These results suggested that water washing could serve as a simple and potentially sustainable regeneration approach for maintaining biochar performance in biocatalytic systems.