ADAPTIVE ONLINE OPTIMIZING CONTROL FOR LACTIC-ACID FERMENTATION

The adaptive on-line optimization strategy was applied for continuous lactic acid fermentation. The control objective was to maximize the lactate production rate while keeping the lactate concentration at a specified value. The control task was divided into two. The task of the upper layer in the hierarchical control scheme was to search for the optimal operating point for cell concentration, while the task of the lower layer was to make the cell and lactate concentrations follow the respective set points which were either specified or given from the upper layer. The cell and lactate concentrations were either measured on-line or estimated every 2 min. The bioreactor was equipped with a hollow-fiber module, and control was implemented by manipulating the draw-off rate through the filter and the bleed stream flow rate in an on-off manner. It was experimentally shown that productivity as high as 20 kg/m3.h could be attained and maintained for about 40-50 h when the lactate concentration was kept at either 20 kg/m3 or 30 kg/m3.