Enzymatic Saccharification and Ethanol Fermentation of Hazelnut Shells with Low Temperature Alkali Pretreatment

Abstract

In this study, the effect of alkali catalyzed, low temperature chemical pretreatment on the enzymatic hydrolysis of hazelnut shells and ethanol yields were investigated. Low temperature treatment of hazelnut shells was performed in a water bath at 30°C for 1 to 4 day with NaOH (2.25%-10%, w/v) and at different solid:liquid ratios (1:5-1:10-1:20-1:40). The pretreated solid was used as the substrate for enzymatic hydrolysis. Supernatants from enzymatic hydrolysis were used for ethanol fermentation. For this purpose, Saccharomyces cerevisiae strain was used as yeast. This study showed that pretreatment time at 30°C was effective in improving the overall process efficiency (OPE, mg ethanol/g dried biomass) for ethanol production. Maximum process efficiency after 3 days pretreatment was 34.35 mg/g. With increasing total alkali loading from 2.25 to 6% at the same temperature, and pretreatment time (30°C, 3 days) OPE increased significantly. Solid to liquid ratio had a little effect on the product efficiency. Maximum OPE was obtained at the pretreatment conditions of 6% NaOH, 1:10 solid to liquid ratio, 30°C and for 3 days. At these conditions, theoretical ethanol yield (ethanol produced/potential glucose in biomass) was 40.71%, overall process efficiency was 37.73 mg/g, ethanol productivity, and fermentation efficiency were 0.12 (g/L h) and 96.68%, respectively.