Model-based control of a fedbatch biodegradation process by the control Lyapunov function approach

Abstract

A strategy based on a kinetic model was developed to control a fedbatch process for phenol degradation by means of the feeding pattern. Biodegradation of phenol by acclimated activated sludge was modeled by the Haldane equation. This model was considered as the control system and the feeding flow (Q) to the reactor as the input. The Control Lyapunov Function (CLF) approach was used to synthesize the controller, which was applied in open loop. A feeding strategy and a fedbatch cycle, consisting of 4h of filling, 6h of aeration, 0.58h of settling and 0.03h of drawing, were obtained by simulation. The kinetic model and the control strategy were validated experimentally in a fedbatch cycle, and the performance of the latter was compared with that of a non-controlled cycle. The model allowed to predict adequately both the phenol and the biomass concentrations during the culture. The control of the process resulted in a lower hydraulic retention time (21.28h) than that of the non-controlled cycle (47.62h). Higher applied and phenol mass loads (1.13g phenolL−1d−1 and 4.82gphenolg−1TSSd−1, respectively) could also be obtained in the controlled cycle. Further, the phenol mass load was higher than that reported in other processes even though any online monitoring was carried out. This is the first reported use of the CLF approach to biodegradation processes, and it is our view that it could be applied to other phenolic wastewater treatment systems lacking of real-time monitoring.