The influence of mixing intensity as well as physical and chemical parameters on the cells of different microorganisms and the biosynthesis process is examined in this paper. Some reactions of cells effecting mixing intensity are described, such as retarded biomass growth, changes in aggregation and mutual arrangement of cells, morphological changes of cells and decreasing of biological activity, caused by an increased intensity of turbulence (turbohypobiosis). Several methods for investigating the local energy in reactors are compared. It is concluded that conventional methods of hydrodynamic analysis do not always allow valid results for the optimization of the mixing regime to be obtained; practically any system requires its own optimization to achieve the maximum yield. To prevent possible adverse effects of micromixing, while simultaneously employing the positive effects, the developers of a new biotechnological process should perform a whole range of experiments (for process optimization) varying temperature, pH and other factors, as well as aeration and mixing intensity simultaneously with medium composition.
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.
Abstract:The present review describes the influence of different types of mixing systems under excess turbulence conditions on microorganisms. Turbohypobiosis phenomena were described by applying a method for measurement of the kinetic energy of flow fluctuations based on the piezoeffect. It can be assumed that the shear stress effect (the state of turbohypobiosis) plays a role mainly when alternative mechanisms in cells cannot ensure a normal physiological state under stress conditions. Practically any system (inner construction of a bioreactor, culture and cultivation conditions, including mixing) requires its own optimisation to achieve the final goal, namely, the maximum product and/or biomass yields from substrate (Y P/S or/and Y X/S ), respectively. Data on the biotechnological performance of cultivation as well as power input, kinetic energy (e) of flow fluctuations, air consumption rate, rotational speed, tip speed, etc. do not correlate directly if the mixing systems (impellers-baffles) are dissimilar. Even the widely used specific power consumption cannot be relied upon for scaling up the cultivation performance using dissimilar mixing systems. A biochemical explanation for substrate and product transport via cell walls, carbon pathways, energy generation and utilisation, etc. furnishes insight into cellular interactions with turbulence of different origin for different types of microorganisms (single cells, mycelia forming cells, etc.
Authors have studied the dependence of the physiological and biochemical characteristics of lysine producers Brevibacteriuni flawurn on medium stirring intensity upon constant PO, during fermentation processes. Various factors affecting the rate of biochemical reactions in cells upon a changeable intensity of medium stirring in apparata with turbine stirrers; oxygen mass transfer intensity in the system; stirring characteristics in the fermenter; biochemical changes in the cells due to gradients of energy introduced by the stirrer in the fermenter, etc. have been studied. A comparison of the experimentally established values, characterizing macrostirring ( e ) and microstirring (KR), with the physiological and chemical characteristics of bacteria during fermentation made us suppose that the character of the kinetic energy distribution in the volume of fermenter is one of the factors regulating bacterial metabolism. Besides, there exists the value ecrit, upon which there can be observed essential changes of the physiological and biochemical properties of the cells. The effect of medium flows upon the cells is characterized by index Fstress, which takes into account both, the possible presence of the cells in the zone with e 2 eCrit, and the degree of medium flow and cell interaction, numerically equal to value (e -ecrit)O.s.
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