The production of sophorose lipids increased with increasing concentrations of both safflower oil and glucose, and was profoundly influenced by the concentration of yeast extract. A high concentration of sophorose llpids {about 135 g/L) was obtained (in a 1-L Bellco stirred reactor) when the medium consisted of 10% glucose, 10.5% safflower oil, 0.1% urea, and 0.25-0.3% yeast extract. A similar yield of sophorose llpids also was obtained in a 20-L bioreactor. About 50% of the apolar sophorose lipid l',4"-lactone 6',6"

Strains of Chlorella sp., Scenedesmus obliquus and Spirulina maxima were tested for degradation of some phenolic compounds listed by U.S. EPA as priority pollutants. Toxins were dissolved in a medium (pH 7 -7.2) without carbon source (except for testing Spirulina, in which case sodium bicarbonate was part of the medium at pH 9 -9.2) and algae prepared by batch cultivation were added. Phenol was found to be degraded easily by all tested algae at a concentration about 1000 mg 1 -1 . 2,4-dimethylphenol was found to be converted by Chlorella (even at a concentration of about 1000 mg1 -1 ) to an isomer of dimethylbenzenediol that was in some cases accumulated in the medium. Depending upon biomass and toxin concentration the rate of degradation changed and an optimum of toxin concentration which induces degradation might exist. Complete degradation could be reached with biomass concentrations higher than 4 g 1 -1 . 2,4-dinitrophenol at a concentration of about 190 mg 1 -1 was degraded by Scenedesmus quickly after an adaptation period of 5 days. 2-chlorophenol at a concentration about 200 mg 1 -1 was degraded and partly dechlorinated by Chlorella. Biodegradation of 2,4-dichlorophenol was not proven but the condition under which algae can survive a higher concentration of toxin could be found. All algae tested have a mechanism for degradation of phenolic compounds.

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Three methods, the dynamic one, the balance one, and the biological one, were used for K.a estimation in the culture of Aspergillus niger. Big differences between the values obtained by the dynamic and the other two methods were observed. The mathematical model including the diffusion of o• into the pellets can offer an explanation. INTROOUCTIONThe volumetric coefficient of oxygen transfer, K a, represents an important parameter of aerobic microbial pro~esses both from the point of view of function of the aeration system used and of their scaling up. A number of methods have been worked out for K.a estimation (Sobotka et al., 1982). When choosing a method, several factors must be taken into account, mainly the fermenter construction, the aeration and homogenization system used, the type of microorganism and its morphology, and the composition of the fermentation medium. In case of the viscous cultures of filamentous or pellet-fcrming streptomycetes and fungi, the situation is particularly complex and the results obtained by use of diverse methods ofte;~ differ substantially (Tuffile and Pinho, 1970).The aim of our work was to compare several methods currently used for the estimation of K.a in a growing culture of Aspergillus niger that produces glu~onic acid. Employing the two typical examples, the balance and the dynamic method, we tried to explain the differences found in the experiment by use of a simulation based on a mode]_ including the diffusion of oxygen into the pellets of the microorganism. THEORETICALThe concentration of dissolved oxygen in a suspension of respiring microorganisms generally depends on the rate of oxygen transfer from the ~as phase to the liquid, on the rate at which oxygen is transported to the site of utilization, and on the rate of its consumption by the microorganism. If oxygen is assumed to take part in an enzyme reaction, the saturation kinetics of Monod type can be used to describe the reaction rate. The transfer of oxygen from the gas to the liquid phase and ~ts transport inside the pellet can be described by diffusion rate equations. In the model, an ideally-stirred liquid phase, a hom:~geno,Js spherical pellet and the same diffusivity coef-243

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