Fuzzy-Decision-Making Problem of L-Lysine Production

A fuzzy-decision-making procedure is applied to find the optimal feed policy of a fed-batch fermentation process for L-lysine production in a stirred tank bioreactor from Brevibacterium flavum 22LD. The policy consists of a feed flow rate, feed concentration of glucose and threonine, and fermentation time. In this paper the fermentation process is formulated as a general multiple objective optimization problem. By using an assigned membership function for each of the objectives, the general multiple objective optimization problem can be converted into a maximizing decision problem. In order to obtain a global solution, a method of fuzzy sets theory is introduced to solve the maximizing decision problem. This method allows direct determination of the optimization problem solution. The applied multiple objective optimization of the process has shown a vast increase of its productivity and decrease of the glucose and threonine concentration at the end of the process.