Saccharomyces cerevisiae is commonly used for the production of ethanol from glucose via fermentation. Typical kinetic parameters for this organism performing this process are:

Y = 0.1 gVSS/g glucose

mmax = 0.46 h^-1

Ks = 100 mg glucose/L

b = 0.05 day-1

If ethanol is continuously produced in a chemostat (a reactor in which the hydraulic retention time is equal to the solids retention time) with a hydraulic retention time of 5 hours, and the influent glucose concentration is 25 g glucose/L, estimate Effluent ethanol concentration (in g ethanol/L). Useful assumption: The S. cerevisiae biomass can be represented by the chemical formula C5H7O2N.

A good approximate answer can be obtained by considering only the energy reaction to determine the moles of ethanol produced per mole of glucose. Answering more accurately will require you to back calculate an fso value from the yield coefficient and then estimate the stoichiometry when some of the glucose is also used for cell synthesis (i.e., combining half-reaction equations). However, note that in a fermentation reaction there is no external electron acceptor, so you need to be careful on the construction of an appropriate energy reaction