KNOWLEDGE-BASED CONTROL APPLIED TO FIXED-BED PULSED BIOREACTORS

In this work, an expert system was developed and applied for on-line c ontrol and supervision of ethanolic fermentation by immobilized Saccha romyces cerevisiae in a fixed-bed pulsed bioreactor of 1.2 l of workin g volume. A number of experiments with different substrate concentrati ons (75, 100, 150 and 200 g/l) and hydraulic residence times (2.4, 1.2 and 0.8 h) were carried out. Knowledge-based computer-aided supervisi on of this process involves accurate on-line measurement of the releva nt process variables (temperature, pH, flow rate, carbon dioxide produ ction, etc.). Carbon dioxide production was used for the estimation of the ethanol productivity. The analysis of the measured data allowed t o detect states or trends that may be indicative of process or system failures, providing advices and/or alarms. The results showed the reli ability of the control system. In previous works, it was proven that p ulsing the feed stream highly improves the productivity of fermentatio n processes carried out in fixed-bed bioreactors [14, 15, 16]. The amp litude and frequency of the pulsation, which is a key factor in the pe rformance of a pulsed feed bioreactor [13], was selected by the contro l system by using an algorithm allowing the ethanol productivity to be optimized. The pulsation frequency which maximizes the ethanol produc tivity, presents a high dependency on the hydraulic residence time and the feeding substrate concentration. When increasing the substrate co ncentration the optimum pulsation frequency also increases; when incre asing the hydraulic residence time the optimum pulsation frequency dec reases.