Piston‐flow reactor model for continuous industrial fermentations

Although the piston‐flow (tubular) fermentor would provide operational difficulties, it is of significance for the analysis of mixing imperfections, for the analysis of a large number of stirredtank fermentors operated in series, and for the possibility of more efficient operation than the stirred tank. The basic kinetics of microbial growth are reviewed, noting that the reaction order varies during the course of reaction from autocatalytic first to ordinary first order; the equations describing effluent micro‐organism and limiting substrate concentrations for a stirred‐tank fermentor operated with recycle are reviewed. A rigorous analysis of the piston‐flow fermentor is given, for the first time, by means of a combination of the equations of microbial growth with a mathematical description of the hydraulic regime. A quantitative comparison is made between the two basic reactor types: the type of fermentor used depends on the objective of the process; if the objective is the reduction in effluent concentration of the limiting substrate, the piston‐flow fermentor provides more efficient operation. High recycle and concentration factors are of greater benefit to the piston‐flow unit, which becomes more efficient from the point of view of both objectives.