Excess turbulence caused by high-intensity stirring inhibited microbial growth and metabolism. In stirred tank bioreactors, the growth rate and lysine biosynthesis decreased in Brevibacterium flavum beyond 900 rpm, the growth rate of Trichoderma reesei on wheat straw beyond 150 rpm, and the growth rate of Saccharomyces cerevisae beyond 800 rprn. The term turbohypobiosis was introduced to describe this inhibition. Turbohypobiosis was characterized by a stress factor Fstr, expressing the interaction of medium flow with microbial cells in local turbulent zones, dependent on the energy distribution of the stirring regime. Lysine synthesis was inhibited at significantly lower F,,, values than the growth of B. flavum. The main reason for the inhibition was shear effects causing decreased adenosine triphosphate (ATP) generation, lower O2 uptake, and lower specific growth rate of bacteria.

The influence of two mixing geometries (at the same scale) with different flow energy distributions on the performance of the gibberellic acid fermentation and on the morphology of the producing fungus Fusarium moniliforme was investigated. Fermentations were performed using a turbine mixing system (TMS) and a counterflow mixing system (CMS), which were high and low power number mixing systems, respectively. Different agitator speed rate profiles were maintained to obtain equal specific power inputs to both mixing systems. Substantial differences in morphology and productivity of F. moniliforme were found. To investigate the causes of these differences, local values and spectra of the kinetic energy of flow fluctuations were measured during the fermentations using a stirring intensity measuring device (SIMD) and a frequency spectrum analyzer. Biomass and gibberellic acid concentrations were found to be higher in the TMS, where the energy distribution was less even, and Vi/here the main part of the energy was at small frequencies (large eddies). An automated image analysis method was used for quantitative characterization of F. moniliforme freely dispersed mycelia and clump morphology. A higher proportion of clumped mycelia with clumps of larger area, perimeter, and roughness was observed in the TMS. A correlation between the morphology and productivity was found, and TMS favored the development of more productive mycelia with longer and thinner hyphae. Introduced power was not a good parameter to characterize different impellers, even at a given scale.

There are many factors that can affect microalgae growth. In this research, four different groups of experiments were set up in order to determine the influence of different mixing conditions, CO 2 concentration and light intensities on Desmodesmus communis growth. The range of CO 2 concentration in the air-CO 2 mixture was 0-16 v/v%, light intensities ranged between 100 µmol m-2 s-1 and 300 µmol m-2 s-1. The best biomass productivity and biomass yield of 0.54 g d-1 and 3.53 g l-1 respectively were achieved when mixing was provided by using shaker as well as gas bubbling with air-CO 2 mixture of 96:4 v/v% and light intensity of 300 µmol m-2 s-1 .

Distribution data of local values of specific kinetic energy of medium flow in the bioreactor volume made it possible to determine some integral criteria. The relationship of these criteria, microorganism growth and biosynthesis characteristics was studied in 5–5,000‐L bioreactors. Energy‐efficient stirring systems that ensure a minimum damage of cells have been also studied.

Crypthecodinium cohnii is a marine heterotrophic dinoflagellate that can accumulate high amounts of omega-3 polyunsaturated fatty acids (PUFAs), and thus has the potential to replace conventional PUFAs production with eco-friendlier technology. So far, C. cohnii cultivation has been mainly carried out with the use of yeast extract (YE) as a nitrogen source. In the present study, alternative carbon and nitrogen sources were studied: the extraction ethanol (EE), remaining after lipid extraction, as a carbon source, and dinoflagellate extract (DE) from recycled algae biomass C. cohnii as a source of carbon, nitrogen, and vitamins. In mediums with glucose and DE, the highest specific biomass growth rate reached a maximum of 1.012 h−1, while the biomass yield from substrate reached 0.601 g·g−1. EE as the carbon source, in comparison to pure ethanol, showed good results in terms of stimulating the biomass growth rate (an 18.5% increase in specific biomass growth rate was observed). DE supplement to the EE-based mediums promoted both the biomass growth (the specific growth rate reached 0.701 h−1) and yield from the substrate (0.234 g·g−1). The FTIR spectroscopy data showed that mediums supplemented with EE or DE promoted the accumulation of PUFAs/docosahexaenoic acid (DHA), when compared to mediums containing glucose and commercial YE.