The fiber chemical hydrolysis process can produce a large number of sugar degradation products which are known to inhibit bacteria and yeast and thus the conversion of fermentable sugars into bioethanol (Ban et al., 2008). The most important inhibitors are furfural, 5-hydroxymethylfurfural and acetic acid. After the acid hydrolysis, it is necessary to adjust the pH with alkalis in order to obtain the adequate conditions for the subsequent step of fermentation. Lime or calcium hydroxide is commonly added to increase the pH to 9­10. This alkali treatment precipitates inhibitors in the form of insoluble salts and therefore acts as detoxifying treatment (Kurian et al., 2010).