Continuous ethanol fermentation of cheese whey powder solution: effects of hydraulic residence time.

Continuous ethanol fermentation of cheese whey powder solution was realized using pure culture of Kluyveromyces marxianus (DSMZ 7239) at hydraulic residence times (HRT) between 12.5 and 60 h. Sugar utilization, ethanol and biomass formation were investigated as functions of HRT. Effluent sugar concentration decreased, but percent sugar utilization, ethanol and biomass concentrations increased with HRT. Ethanol productivity was maximum (0.745 gE l(-1)h(-1)) at an HRT of 43.2 h where the biomass productivity was almost minimum (0.18 gX l(-1) h(-1)). The ethanol yield coefficient was almost constant at 0.4 gE g(-1)S up to HRT of 43.2 h and the growth yield coefficient was minimum at HRT of 43.2 h. Kinetic models were developed and the constants were determined by using the experimental data.