Ethanol as the promising alternative fuel in Indonesia fights against cost competitiveness with fossil fuel due to low productivity using a conventional batch process. Therefore, the production of ethanol employing continuous fermentation process in which it acquires higher productivity was investigated. The investigation was done using uncontrolled continuous process in the integrated aerobic-anaerobic baffled reactor for 168-340h at 30? and medium pH of 4-5. The substrate of sugarcane molasses-water was varied in three concentrations, i.e. 20, 30, and 45% w/w. The productivity was indicated by ethanol concentration in the effluent stream and sugar to ethanol conversion (fermentation efficiency). The result showed that average ethanol concentration of 20, 30, and 45% molasses was 50.43, 62.70, and 57.17g/l, respectively. Further, the fermentation efficiencies were 87.2, 80.3, and 46.7% for each of the molasses concentrations. The productivity can be monitored as follows: 1.75g/l h (20% molasses), 2.31g/l h (30% molasses), and 2.01 (45% molasses). Additionally, the steadiness of the process for long process duration was observed, and the result showed that the ethanol productivity was raised from 2.31g/lh (168h) to 2.71g/lh (340h).
