OPTIMIZATION OF THE START-UP OF A PASSIVELY IMMOBILIZED ZYMOMONAS-MOBILIS SYSTEM FOR CONTINUOUS ETHANOL-PRODUCTION

The start-up of a mixed system, with passively immobilized Zymomonas m obilis in a fibrous matrix and suspended flocs) has been optimized for continuous ethanol production. Reactor inoculation with a flocculent variant of Z. mobilis ZM4 allowed the incubation periods previous to t he continuous feeding be suppressed The flocculent characteristics of the bacterium together with the features of the system resulted in an increase of the retained biomass as dilution rate was increased. In or der to obtain a high biomass concentration in the reactor in a short t ime, rather than operating the system at a fixed dilution rate for lon g periods of time, it is proposed to increase the dilution rate stepwi se with short time intervals.