Power Input and Oxygen Transfer in Fed-Batch Penicillin Production Process

Abstract

Fed-batch experiments in a 20 lfermentor utilizing Penicillium chrysogenum IFO 8644 were conducted using a medium containing sucrose and com steep liquor as main components. The runs were interrupted at different stages of the process-24, 48, 72, 96 and 120 hand broths were transferred to an agitated vessel. Power consumption under gassed and ungassed broths and volumetric oxygen transfer coefficient, kLa. were measuredfor various agitation speeds and aeration rates. The rheological characteristics of each broth were also determined. Power number-modified Reynolds number plots were similar to those for other non-Newtonian fluids. Michel and Miller correlation was applied for predicting gassed power drawn for all broths. A general correlation for kLa, as a function of operating variables and apparent viscosity for broths of different cultivation ages was obtained. The penicillin production process is a classical example of a fermentation process producing highly VISCOUS non-Newtonian fluids [1] and dcmanding large oxygen amounts. The penicillin broth rheological characteristics can be represented fairly well by the "power law" as a pseudoplastic fluid. Bongenaar et al [2.] observed that conventional rheometers are not appropriate to determine these characteristics and proposed the utilization of a turbine viscometer for such suspensions. Calderbank and Moo-Young [l] utilized the concept of average shear rate around an impeller in the laminar flow region and showed that it is proportional to the shaft agitation spccd. Concerning power consumption in gassed systems, Taguchi and Miyamoto [~I working with pseudoplastic Endomyces sp. broths in a wide range of fennentor volumes verified the validity of the correlation proposed by Michel and Miller lSi] for Newtonian flUIds. Ogut and Hatch lli] studied the effect of the rheological characteristics of various fluids on kLa. Based on Cooper's correlation. Their results indicated that, for Ne\\10nian fluids the effect of P gN L was significant, while for non-Ne\\10nian fluids this term had only slight dfect On the other hand the superficial vclocity, v S ' affected kLa of both types of fluids. Zlokarnik [2] originally working with aqueous solutions, in cylindrical agitated vessels, proposed a correlation based on dimensionless groups, relating volumetric mass transfer coefficient with operation variables and the flUid kinematic viscosity as follows: 157 (I) Mention should be made here that this relationship is valid for the penicillin femlentation broth as it is a non-coalescent fluid. Recently, studies on rheological characteristics of filamentous mierorganisms broths were presented by Allen and Robinson [.l.Q] where rheological properties, measured by diffen;nt methods, are related to eell mass concentration. These workers point out that, in spite of its importance, there are only few studies attempting to quantify the relationship between transport process and rheological properties of fermentation broths. On the other hand, operating parameters, such as agitation speed, may also have a direct influence on penicillin productivity. and not just as a consequence of their interaction with rheology and transport properties. For instance, Smith and Lilly [Ul examined the effect of agitation speed on penicillin productivity suggesting that there is a zone around the impeller in whieh mycelia may be damaged, impairing the production rate In this work the power requirements and the kL a dependence on operating variables and apparent viscosity were examined in broths of fed batch penicillin fermentation process during 120 hours.