Effect of dilution rate on growth characteristics of Candida utilis in multistage culture systems with different interstage mixing

The effect of dilution rate on important process parameters of biomass production in two multistage culture systems with different interstage mixing has been examined. Experiments were performed in a multistage tower fermenter and in a cascade of fermenters. Measurements were made at steady-state of continuous culture under constant and identical values of ethanol concentration of 50 gl^?1 in the feed, temperature, OTR and pH in both culture systems used. The microorganism used was Candida utilis. Ethanol inhibition influenced cell growth rate due to the complete dissimilation of the restricted quantity of acetate to H₂O and CO₂, leading to insufficient energy generation. The value of ethanol concentration at which ethanol started to inhibit cell growth was a combined function of OTR, S_R and D. The presence of the interstage mixing resulted in more efficient ethanol conversion to biomass in the whole range of dilution rates and significantly lowered the risk of washing-out at high values of both S_R and D.