Continuous ethanol production and cell growth in an immobilized-cell bioreactor employing Zymomonas mobilis

Ethanol‐producing bioreactors employing cells of Zymomonas mobilis attached to glass‐fiber pads were operated continuously for as long as 28 days. Ethanol production, which is related to bed‐associated biomass levels, was found to occur in three distinct phases: an exponential phase, a linear phase, and a “steady‐state” phase. After prolonged operation, a bacterial floc developed in the reactor. The maximum effluent ethanol concentration and the maximum volumetric productivity were 6.4% and 152 g L−1 h−1, respectively, and both were attained at a liquid residence time of from 10–15 min. Both maxima occurred after the development of the bacterial floc. The flocculant bacterium has been isolated and tentatively identified as a flocculant strain of Z. mobilis.