A PULSING DEVICE FOR PACKED-BED BIOREACTORS .2. APPLICATION TO ALCOHOLIC FERMENTATION

When the immobilized cells are employed in packed-bed bioreactors seve ral problems appear. To overcome these drawbacks, a new bioreactor bas ed on the use of pulsed systems was developed [1]. In this work, we st udy the glucose fermentation by immobilized Saccharomyces cerevisiae i n a packed-bed bioreactor. A comparative study was then carried out fo r continuous fermentation in two packed-bed bioreactors, one of them w ith pulsed flow. The determination of the axial dispersion coefficient s indicates that by introducing the pulsation, the hydraulic behaviour is closer to the plug flow model. In both cases, the residence time t ested varied from 0.8 to 2.6 h. A higher ethanol concentration and pro ductivity (increases up to 16%) were achieved with the pulsated reacto rs. The volumes occupied by the CO2 were 5.22% and 9.45% for fermentat ion with/without pulsation respectively. An activity test of the parti cles from the different sections revealed that the concentration and v iability of bioparticles from the two bioreactors are similar. From th e results we conclude that the improvements of the process are attribu table to a mechanical effect rather than to physiological changes of m icroorganisms.