Resistance of microorganisms to hydrodynamic stress

Methods of investigation and representative experimental results for the effects of mechanical forces, such as those that occur during stirring, pumping, and aeration, on the production of microbial metabolites and the growth of microorganisms are discussed. The sensitivity of the organisms depends on the stability of the cell wall and its morphology. For a given stirrer speed, raising the viscosity of the nutrient solution magnifies the symptoms of damage. With methane-producing microorganisms, growth and the production of methane are affected in the same manner. Physiological stress, e.g., due to the absence of essential nutrients, is additive in effect to mechanical stress. The power dissipated per unit volume is suggested as a criterion for scale-up and for the transfer of experience gained with one type of flow system, e.g., jet flow, to another, e.g., a stirred tank.