Abstract:
The ethanol production in batch and fed-batch fermentations by Zymomonas mobilis TISTR 405 using broken rice grains as a C-source for fermentation were investigated in this research. The experiments firstly selected the best loog-pang for digest the broken rice grains and produce the highest total sugar. Look pang code Ubonratchathani 2 give a highest sugar concentration 400-420 gL-1, was used in investigation for optimal ethanol production by Z. moblis with 20% glucose in the rich culture medium. From factorial design experiments, and analysis by response surface methodology (RSM), the optimal conditions for ethanol production were 150 gL-1 glucose initial pH of 5.5, 30 0C and 48 h incubation. In 500 ml Erlenmeyer flask under the optimal conditions ethanol yield and productivity of 49.72 gL-1 and 1.03 gL-1h-1 were obtained. Scaling up to a 2 L bioreactor with the working volume of 1.0 L, the ethanol yield and productivity 59.73 gL-1 and 2.13 gL-1h-1,respectively. In fed-batch production, Initial sugar concentration of 150 gL-1. After the 24th h , sugar was almost depleted. Five hundred ml of the medium was taken out then one litre of the newly hydrolyzed broken rice grain was added to keep total sugar concentration close to 150 gL-1. The fermentation was a little bit slower than the previous experiments. The total sugar consumption rate and ethanol production rate were 4.83 gL-1h-1 and 2.41 gL-1h-1 respectively.