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

Abstract

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.