BACKGROUNDRapeseed straw is an agricultural residue increasingly produced in recent years due to a growing interest in biodiesel production. In the present study, rapeseed straw pretreated by liquid hot water was tested as a substrate to optimize ethanol production by simultaneous saccharification and fermentation (SSF). Temperature, time, substrate loading and cellulase charge were selected as operation variables and modified according to a three-level four-variable experimental design. Ethanol concentration, ethanol yield and volumetric productivity were monitored and adjusted to a quadratic model using response surface methodology. RESULTSOptimal SSF conditions, based on the mathematical model in terms of ethanol yield and concentration, were found to be 40 degrees C, 71 h, 10% substrate loading, and 40 FPU g(-1) substrate. The resulting ethanol concentration was 23 g L-1, which corresponds to 69% ethanol yield. CONCLUSIONLiquid hot water is an effective pretreatment that increased the cellulose concentration of rapeseed straw, making it a good substrate for SSF, with a maximum yield of 0.12 g ethanol g(-1) dry straw. The novel combination of hydrothermal pretreatment and SSF configuration results in yields comparable yields with those previously reported, and has additional advantages, e.g. no chemicals use and high solid concentration operation. (c) 2013 Society of Chemical Industry