Abstract: A mixing device, especially for a fermenter, capable of dispersing gas in a broth therein, in which a number of propeller mixers are provided on a vertically extending shaft. The lower propeller mixer is a gas dispersing mixer having a hollow hub and open channels on the blades extending from this hub and tapering outwardly. At least one intermediate propeller mixer has some blades shorter than others and of reverse flow direction, some blades having baffle bars on trail edges thereof. The upper propeller mixer has the longer blades without channels and flow modifying elements.

Abstract: The invention refers to a new microbial process for preparing .beta.,.delta.-dihydroxy-7-[1,2,6,7,8,8a-hexahydro-2.6-dimethyl-8-(2-methy l-butyryloxy)-naphthalen-1-yl]-heptanoic acid .delta.-lactone of formula (I) and .beta.,.delta.-dihydroxy-7-[1,2,6,7,8,8a-hexahydro-2.6-dimethyl-8-(2-methy lbutyryloxy)-naphtalen-1-yl]-heptanoic acid of formula (II), ##STR1## by the aerobic fermentation of the submerged culture of an imperfect fungus strain biosynthesizing the above compounds, in a nutrient medium containing utilizable carbon and nitrogen sources as well as mineral salts, and by isolating the product of formula (I), which comprises cultivating a strain of the new Aspergillus obscurus fungus species producing the above compound(s) of formulas (I) and/or (II), in a temperature range of 25.degree. to 30.degree. C. and, if desired, separating the product(s) formed from the fermentation broth, then isolating it in the lactone form of formula (I) and, if desired, purifying the same.

Abstract: Complex mixing system with stages consisting of propeller mixers of high diameter ratio, where the blades are provided with flow modifying elements, whereby the energy proportions spent on dispersion of the amount of gas injected into the reactor, homogenization of the multi-phase mixtures, suspension of solid particles, etc. and the properties corresponding to the rheological properties of the gas-liquid mixtures and to the special requirements of the processes can be ensured even in extreme cases. Open channels (5) opposite to the direction of rotation are on the blades (4) of the dispersing stage (2a) of the propeller mixers (2) fixed to a common shaft, where the channels (5) are interconnected with gas inlet (7). The angle of incidence of a certain part of the blades (4) of mixing stages (2b, 2d) used for homogenization and suspension is of opposite direction and the length is shorter and/or the angle of incidence is smaller than those of the other blades.