Dilute-acid pretreatment of lignocellulosic biomass enhances the ability of enzymes to hydrolyze cellulose to glucose, but produces many toxic compounds that inhibit fermentation of sugars to ethanol. The objective of this study was to compare the effectiveness of treating hydrolysate liquor with Ca(OH)(2) and NH(4)OH for improving ethanol yields. Corn stover was pretreated in a pilot-scale reactor and then the liquor fraction (hydrolysate) was extracted and treated with various amounts of Ca(OH)(2) or NH(4)OH at several temperatures. Glucose and xylose in the treated liquor were fermented to ethanol using a glucose-xylose fermenting bacteria, Zymomonas mobilis 8b. Sugar losses up to 10% occurred during treatment with Ca(OH)(2), but these losses were two to fourfold lower with NH(4)OH treatment. Ethanol yields for NH(4)OH-treated hydrolysate were 33% greater than those achieved in Ca(OH)(2)-treated hydrolysate and pH adjustment to either 6.0 or 8.5 with NH(4)OH prior to fermentation produced equivalent ethanol yields. (C) 2010 Elsevier Ltd. All rights reserved.