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Three pilot-scale continuous mix reactors of 5-L volume each were used to study the effects of retention time (18-42 hours) and initial substrate concentration (50-150 g / L ) on the cell yield, lactose consumption, and maximum ethanol concentration during continuous fermentation of cheese whey using the yeast Candida psuedotropicalis. A microaeration rate of 480 mL/min and a nutrient supplement (yeast extract) concentration of 0.1% uol/uol were used. The results indicated that the dissolued oxygen concentration, temperafure, cell concentration, lactose utilization rate, and ethanol concentration were affected by hydraulic retention time and initial substrate concentration. The highest cell concentration of 5.46 g / L and the highest ethanol concentration of 57.96 g / L (with a maximum ethanol yield of 99.6% from the theoretical yield) were achieued at the 42-hour hydraulic retention time and the I50 g / L initial substrate concentration, whereas the highest ceN yield was obserued at the 50 g / L initial substrate concenfration and the 36-hour hydraulic retention time. Lactose utilizations of 98, 91, and 83% were obtained with 50, 100, and 150 g / L initial substrate concentrations at the 42-hour hydraulic retention time. A pH control system was found unnecessary.

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