PERFORMANCE OF A MULTISTAGE FERMENTOR WITH CELL FILTERING AND RECYCLING FOR CONTINUOUS ACETIC ACID PRODUCTION

Abstract

The steady-state performance of a multistage fermentor with cell filtering through a membrane and recycling of concentrated cells is studied numerically for continuous production of acetic acid. The tanks-in-series odel is used to describe the flow behaviour of culture broth in the multistage fermentor. Kinetic expressions and parameter values are taken from the literature. The effects of the total number of stages, the dilution rate, the bleed ratio, the recycle ratio and the feed concentrations as operating conditions on fermentor characteristics such as the concentrations of total and viable cells as well as substrate and product in each stage, the cell viability, the acetic acid productivity and the substrate conversion were examined under the conditions of equal tank volumes and a recycle ratio equal to or greater than one. An increase in the number of stages and decreases in the bleed and recycle ratios and in the feed concentration of product enhance the productivity. The relations between the maximum productivity and the corresponding optimum dilution rate and between the corresponding outlet concentrations of the four components and the optimum dilution rate are presented as figures. Equations for the average cell viability and the critical dilution rate causing cell washout are also obtained. Furthermore, the minimum feed concentration of substrate for its complete consumption is mentioned. Compared to a single tank fermentor, staging and cell recycle increase substrate utilisation and acetic acid productivity. The computed performance of the fermentor configuration proposed in this study is sufficiently promising for the continuous production of acetic acid that it should now be checked experimentally.