Original Article | 2005, Vol.27, No.5, pp. 1057-1064
Optimal feed rate profiles for fed-batch culture in penicillin production
Wanwisa Skolpap, Jeno M. Scharer, Peter L. Douglas and Murray Moo-Young
pp. 1057 - 1064
Abstract
The fed-batch optimization of penicillin productivity was applied as an example of optimization algorithm verification. The objective function of this problem was to optimize penicillin productivity by determination of feed rate trajectory. This study compared the optimized results derived from the proposed algorithm and from the iterative dynamic programming. Three decision variables for the proposed algorithm comprised ts (switching time from exponential to linear feeding schedules), K (constant in feed rate equation), and ε (a multiplier on substrate requirement). Estimation of this set of decision variables employed Markov chain Monte Carlo procedures (the Gibbs parameter sampling and the Metropolis-Hasting algorithm) using an originally given set of initial values. The optimization procedure was divided into two time periods as follows: i) the time period of exponential feeding policy, t < ts and ii) the time period of linear feeding schedule, t > ts. The calculation procedure of the first period of fermentation time had been proposed by integrating Pontryagin’s optimum principle and Luedeking-Piret equation. The feed rate profile during the later period was obtained from the direct substitution of desired substrate requirement derived from Monod equation. The optimal feed-rate profile corresponded to the values of decision variables as follows [ts K ε] = [35.937 0.096 2.087]. The proposed algorithm was appropriate for the determination of optimal feed-rate trajectories in any fed-batch problems provided that the product formation rate agrees with a Luedecking-Piret model.
