The study aims to investigate a cost-effective approach to convert non-pretreated rice straw hydrolysate into biobutanol. The influences of the initial cell concentration and incubation temperature on biobutanol production were evaluated under both sterile and non-sterile conditions. Results indicate that 100% glucose utilization could be achieved for initial cell concentrations greater than 2100 mg/L under both sterile and non-sterile conditions. Regression analyses resolve that under the sterile condition, the maximum butanol productivity of 1.45 g/L/d was projected at 1.96 g/L of cells and 32.3 degrees C, while the maximum butanol yield of 0.22 g/g was predicted at 2.01 g/L of cells and 26.3 degrees C. These two maximum values could not be projected by the regression analyses for the non-sterile condition. However, this study confirms that a high initial cell concentration of Clostridium saccharoperbutylacetonicum N1-4 can minimize interference from other microbes so that non-sterile biobutanol production is comparable to sterile biobutanol production. (C) 2012 Elsevier Ltd. All rights reserved.