Modeling and control of dissolved oxygen concentration in the fermentation of Glucose to Gluconic Acid
Fermentation systems are often highly nonlinear, with poorly understood dynamic behaviour of the reactor. In this work, mathematical modeling of the fermentation process based on aeration rate control was performed in a semi-batch airlift loop bioreactor. The bioconversion of glucose to gluconic acid by the Aspergillus niger strain was considered in an oxygen consuming system in the liquid phase. The proper kinetic model for the bioconversion of glucose to gluconic acid was investigated using experimental data from a 40 dm3 reactor. Kinetic parameter estimation was used from the literature. The model was validated by experimental data and was compared with the Monod kinetic model. The comparison showed that the Contois kinetic model was in a better agreement with the experimental data of dissolved oxygen concentration (DO) than the Monod kinetic model. An optimal substrate-to-microorganism concentration ratio of 55 was suggested by applying the model, which led to achieving the maximum conversion of glucose to gluconic acid. The conventional PID controller with fixed parameters obtained from the Ziegler-Nichols tuning method was used to control the dissolved oxygen concentration at a constant level of 2 mg/dm3, which was important for microorganism survival and growth.