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This paper approaches the problem of oxygen mass transfer. This transfer is in antibiotic biosynthesis liquids produced by microorganisms belonging to the actinomycete and fungi classes, which exhibit a shear thinning non-Newtonian rheological behaviour. The volumetric oxygen mass transfer coefficients in these liquids (kLab) change during biosynthesis processes. The change is mainly due to rheological parameter modifications, such as increasing the consistency index (K) and decreasing the flow behaviour index (n). The values of kLab were 3.0-6.5 times lower than those recorded in water, and their decreasing depended on the kLa values obtained without biological liquid and on the nature of fermentation broths, as well.Starting from experimental data, two correlations were established between kLab and P / V , ySG and P/ V , vSG, N , respectively. These correlations contain a dimensionless factor (qa,,,/qg)a6, which takes into account the rheological properties of the liquid phase and offers the possibility for a fast and sufficiently accurate estimation of kLab. The empirical correlations developed in the paper correspond reasonably well with the relatively wide variety of experimental data, as in the model proposed by PEREZ and SANDALL, and allow for the comparison of the fermentation batches of the same or different microorganisms; also, they may be applied to the workings of design, scaleup, control and monitoring of bioreactors.

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The data presented here with respect to the behaviour of industrial scale stirred tank bioreactors equipped with modified RUSHTON turbine agitators in the biosynthesis processes of antibiotics are valid for that case that the power consumption is the same as it is in standard RUSHTON turbine agitators. Each modified RUSHTON turbine agitator was obtained through the variation of the blade surface by adding perforations so that the ratio between the perforation surface area and the full surface area (or the surface fraction of the perforations) is 0.36. In the fermentations of Streptomyces aureofaciens, Streptomyces rimosus and Penicillium chrysogenum producing tetracycline, oxytetracyline and penicillin, respectively, in bioreactors equipped with modified RUSHTON turbine agitators, the relative antibiotic production is increased by more than 30% compared to standard bioreactors.

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