Abstract
Steam explosion conditions were evaluated as pretreatment for unbleached pulp waste to prepare fermentable sugars with xylose fermenting yeast, Candida intermedia 4-6-4T2. The hydrolysates pretreated under low or moderate severity conditions (severity factor (Ro) = 3.53 or 4.12) did not contain known inhibitors to fermentation such as organic acids, furans and lignin-derived aromatic compounds in the LC-Mass (LC-MS) and HPLC analyses. C. intermedia 4-6-4T2 simultaneously converted both xylose and glucose in these hydrolysates to ethanol within 24 h. The ethanol yield was 0.40 (g/g) or 0.41 (g/g), respectively. In contrast, hydrolysates pretreated under high severity conditions (Ro = 4.71) contained thirteen lignin-derived aromatic compounds, of which eleven were quantified by HPLC analyses. The concentrations of furans or lignin-derived aromatic compounds in the hydrolysate were less than 0.2 g/L or 0.02 g/L, respectively. The ethanol yield was 0.21 (g/g) after 24 h fermentation. C. intermedia 4-6-4T2 did not completely convert xylose and glucose to ethanol even during longer fermentation periods (48 h). Model sugar solutions containing higher concentrations of furans and lignin-derived aromatic compounds in 0.1 M KH2PO4 containing 3 g/L of acetic acid adjusted to pH 6 with KOH than in the high severity hydrolysate did not affect the fermentation of C. intermedia 4-6-4T2. Therefore, the inhibitory effect on the hydrolysate pretreated under high severity conditions (Ro = 4.71) was not induced by previously identified compounds such as furfural, HMF and lignin-derived aromatic compounds, but may be induced by other unidentified compounds.
