Comparative analysis of mixing distribution in aerobic stirred bioreactor for simulated yeasts and fungus broths

Abstract

The study on mixing distribution for an aerobic stirred bioreactor and simulated (solutions of carboxymethylcellulose sodium salt), yeasts (S. cerevisiae) and fungus (P. chrysogenum pellets and free mycelia) broths indicated the significant variation of mixing time on the bioreactor height. The experiments suggested the possibility to reach a uniform mixing in whole bulk of the real broths for a certain value of rotation speed or biomass concentration domain. For S. cerevisiae broths the optimum rotation speed increased to 500 rpm with the biomass accumulation from 40 to 150 g/l d.w. Irrespective of their morphology, for fungus cultures the existence of optimum rotation speed (500 rpm) has been recorded only for biomass concentration below 24 g/l d.w. The influence of aeration rate depends on the apparent viscosity/biomass concentration and on the impellers and sparger positions. By increasing the apparent viscosity for simulated broths, or biomass amount for real broths, the shape of the curves describing the mixing time variation is significantly changed for all the considered positions. The intensification of the aeration induced the increase of mixing time, which reached a maximum value, decreasing then, due to the flooding phenomena. This variation became more pronounced at higher viscosities for simulated broths, at higher yeasts concentration, and at lower pellets or filamentous fungus concentration, respectively. By means of the experimental data and using MATLAB software, some mathematical correlations for mixing time have been proposed for each broth and considered position inside the bioreactor. These equations offer a good agreement with the experiment, the maximum deviation being +/-7.3% for S. cerevisiae broths.

Volumetric Oxygen Mass Transfer Coefficient and Surface Tension in Simulated Salt Bioremediation Media

“…This parameter is influenced by a number of factors such as agitation intensity, aeration, type and features of the bioreactor, composition of culture media, and type and concentration of microorganism [10][11][12][13][14]. In turn, oxygen mass transfer plays a fundamental role in the control of oxygen available for the metabolism of aerobic microorganisms in the bioreactor.…”

“…The volumetric oxygen mass transfer coefficient (k L a) 1) is the most important parameter in all the aerobic bioprocesses [9], which is influenced by a number of factors, among which are the agitation intensity, aeration, bioreactor features, media composition, biomass concentration, and microbial species [10][11][12][13][14]. However, above all, it plays a key role in bioreactors, where it influences the level of oxygen available to aerobic metabolism; k L a may then be used as an indicator of performance of aerobic wastewater treatments as well as of bioremediation processes [15].…”

Comparative analysis of oxygen transfer rate distribution in stirred bioreactor for simulated and real fermentation broths

“…The decisive influence of media circulation on the oxygen transfer rate is underlined by results previously obtained for the mixing time distribution in fermentation broths [5]. The cited study indicated that maximum mixing efficiency is achieved for specific power input values close to those corresponding to maximum k l a, and that the mixing intensity distribution is similar to that of the oxygen transfer rate.…”

“…The lower stirrer was placed 64 mm from the bottom of the bioreactor. The upper stirrer was placed on the shaft at the optimum distance from the lower one according to the type of broth studied, namely at 128 mm for simulated broths and at 64 mm for the real broths, as demonstrated in previous work [5]. The rotation speed was maintained below 600 rpm.…”

Kinetic Studies on Alcoholic Fermentation Under Substrate Inhibition Conditions Using a Bioreactor with Stirred Bed of Immobilized Yeast Cells

“…The experiments have been carried out in 5 l (4 l working volume) laboratory bioreactor (Biostat A, B. Braun Biotech International), with computer-controlled and recorded parameters [18].…”