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

The steady-state performance of a multistage fermenter with cell filte ring through a membrane and recycling of concentrated cells is studied numerically for continuous production of acetic acid. The tanks-in-se ries model is used to describe the flow behaviour of culture broth in the multistage fermenter. 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 co ncentrations as operating conditions on fermenter 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 product ivity 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 r ecycle ratios and in the feed concentration of product enhance the pro ductivity. The relations between the maximum productivity and the corr esponding optimum dilution rate and between the corresponding outlet c oncentrations of the four components and the optimum dilution rate are presented as figures, Equations for the average cell viability and th e critical dilution rate causing cell washout are also obtained, Furth ermore, the minimum feed concentration of substrate for its complete c onsumption is mentioned. Compared to a single tank fermenter, staging and cell recycle increase substrate utilisation and acetic acid produc tivity. The computed performance of the fermenter configuration propos ed in this study is sufficiently promising for the continuous producti on of acetic acid that it should now be checked experimentally.