EMPIRICAL-MODELS FOR OXYGEN MASS-TRANSFER - A COMPARISON BETWEEN SHAKE FLASK AND LAB-SCALE FERMENTER AND APPLICATION TO MANGANIFEROUS ORE BIOLEACHING

An investigation on oxygen mass transfer in shake flasks and in a lab- scale bioreactor is reported. An analysis of the main factors influenc ing oxygen mass transfer in shake flasks has been carried out using fu ll and fractional factorial designs. The factors investigated were: mi xing conditions (rpm); temperature (degrees C); weight of closure (g); liquid hold-up (ml); and geometry of shake flasks. The ANOVA (analysi s of variance) showed the importance of the investigated factors on th e oxygen mass transfer coefficient. An empirical model with dimensionl ess parameters has been proposed in order to predict the oxygen mass t ransfer in several experimental conditions. An investigation has also been performed on the oxygen mass transfer in a lab-scale bioreactor, considering stirring, air flow rate and temperature as factors. Parame ters of an usual empirical model for oxygen transfer coefficient have been estimated. The relationships proposed have been obtained in a wid e range of experimental conditions, and they can be used both to deter mine if oxygen limiting conditions occur during biological tests in th e shake-flask scale or in the lab-scale bioreactor, and in the phase o f translation of experimental data to a bigger scale. Using this model the bioleaching of manganiferous minerals by heterotrophic microorgan isms is judged to take place just in microaerobic conditions, i.e. in oxygen limiting conditions. (C) 1998 Elsevier Science Ltd. All rights reserved.