Adsorptive removal of inhibitors from paddy straw hydrolysate using surfactant-modified bentonite clay for fermentative xylitol production

Thermal acid hydrolysis of paddy straw is one of the most widely used pre-treatment methods to deal with its recalcitrant nature as well as utilize its abundant accessibility. However, the presence of inhibitory compounds (acetic acid, phenolics, and furan derivatives) in hemicellulose enriched spent liquor, produced during paddy straw hydrolysis, adversely affects its utilization for downstream xylitol production. Various detoxifying agents such as paddy straw biochar, lignite, activated charcoal, sodium bentonite (SB), and surfactant-modified organobentonite (CTAB@SB) were assessed for removal of inhibitors from the spent liquor. CTAB@SB performed as the best detoxifying adsorbent while retaining the maximum amount of xylose (16.23 gL−1). Concentration of acetic acid reduced from 4.95 gL−1 in concentrated and neutralized hydrolysate (control) to 0.023 gL−1 in CTAB@SB-detoxified hydrolysate. The furfural and hydroxymethylfurfural contents (with initial concentrations of 0.711 and 0.236 gL−1, respectively) were undetectable in the hydrolysate after CTAB@SB-assisted detoxification. Successful intercalation of bentonite layers with CTAB was confirmed using FTIR and XRD analysis. Specific surface area and pore size (31.73 m2 g−1, 4.45 nm, respectively) of CTAB@SB were revealed using BET analysis. The detoxified hydrolysate was subjected to fermentation using Candida tropicalis MTCC 6192 where xylitol yield and productivity were 0.59 g g−1 and 0.81 gL−1 h−1 , respectively. Thus, CTAB@SB-assisted detoxification was successfully established for inhibitor removal and integrated into paddy straw pre-treatment for downstream xylitol production.