Simultaneous effect of macromixing and micromixing on growth processes

Abstract Interaction of macromixing and micromixing in microbiological flow reactors based on a kinetic model of the Michaelis‐Menten type has been treated by considering two general types of flow systems: the system of n continuous stirred‐tank reactors in series (n‐CSTR's in series) and the series combination of a plug‐flow reactor and a continuous stirred‐tank reactor. Systematic schemes to describe the micromixing conditions of a reactor system are presented. Additional micromixing states are considered besides those proposed by Kramers and those proposed by Zwietering if the systems are employed as empirical models of a flow system. When the number of stirred‐reactor units in the system of n‐CSTR's in series is small, micromixing has a significant effect on the growth processes. As the number of reactor units increases, the micromixing effect on the growth processes decreases. The effect of micromixing is also important for a system described by a series combination of a plug‐flow reactor and a continuous stirred reactor. In addition, the exit concentrations from the system having the same residence time distribution and the same degree of segregation may be different from each other. Information obtained in this study is pertinent in the design of biological flow reactors and sewage treatment systems.