An optimal control strategy for a gas phase bioreactor for the biodegradation of para-xylene

A methodology to formulate a "smart" control strategy for optimization of a gas phase bioreactor is developed and implemented to maximize the performance of the bioreactor system. The performance objective of the control policy was to biodegrade the maximum amount of p-xylene from the gas stream treated by the reactor within the run time. A bioreactor with a novel design configuration was used to treat a gaseous feed mixture of air and para-xylene. The feed stream is transported radially through an annular sand packing where the microorganism Pseudomonas putida ACTCC 23973 was immobilized. P-putida degraded the toxic para-xylene in the gas stream producing carbon dioxide and water. The development of the control algorithm was based on Optimal Control Theory. The objective functional consisted of a penalty function which represented the biodeactivation of the column. Biodeactivation was correlated with the toxicity effects of p-xylene loading. The control algorithm was developed and the control system was simulated by a numerical iterative technique in conjunction with the finite difference method Theoretical optima and the control strategy were tested by experiment. Experimentally obtained data of the average removal of p-xylene were compared with the simulated values. Within the tested operating regimes, the developed dynamic optimal control strategy was successfully demonstrated by maximizing the removal of p-xylene fed into the reactor. For feed concentration with 100 ppm of p-xylene the removal improved by 80%, and at feed concentration of 50 ppm the improvement was 20% compared to the experimental runs without any controls implemented. The investigation successfully demonstrates a viable methodology to develop a dynamic optimal control technique for a defined objective and the applicability of the control strategy to a gas phase bioreactor.