Analysis of Three Delignification Treatments of Corncob Residues for High Cellulosic Ethanol Production

Three delignification treatments of corncob residues (CCR), including NaOH, formic acid, and sulfite treatments, were compared at the respective optimized condition and in light of chemical compositions, sugar recovery, and ethanol production. NaOH and sulfite treatment can remove lignin in the CCR efficiently. Though NaOH treatment showed a superior ability of delignification, its solid cellulose recovery is lower than that of sulfite treatment. The sulfite treatment has the highest selectivity between delignification and cellulose conservation. The formic acid-treated CCR still had high lignin contents because formic acid also accelerated the solvation of cellulose. In fed-batch simultaneous saccharification and fermentation (SSF) with 25% substrate loading, the highest 77.1 ± 2.33 g/L ethanol was from NaOH-treated CCR, corresponding to a CCR-to-ethanol yield of 0.208 ± 0.0021 g/g. However, the sulfite pretreated CCR also produced 68.2 ± 2.22 g/L ethanol, with a higher CCR-to-ethanol yield of 0.219 ± 0.0012 g/g. The high substrate dosage is beneficial to ethanol concentration but not beneficial to CCR-to-ethanol yield. The optimal substrate dosage required for ethanol production depends on the targeted aim (ethanol concentration or CCR-to-ethanol yield).