Automated control of bioreactors: An hardware-in-the-loop proof of concept test towards an experimental facility

Ensuring controlled environmental conditions during bacterial growth in a bioreactor is often crucial for the success of an experiment or to grant efficiency in an industrial procedure. For instance, in some experiments, temperature, oxygen and pH levels should be kept constant to achieve a good yield. Commercial bioreactors commonly provide proprietary automation systems for the regulation of some of the above mentioned variables, but the possibility to personalize the control algorithm, to jointly control multiple variables or to modify the control task, is usually rather limited. To surpass this limitation we aim to build an Arduino-based bioreactor, controlled by a PC and capable of running customized, possibly advanced, control algorithms. As a preliminary step toward this goal, in this contribution we present the design of a simple Arduino-based reactor for the control of the concentration of a substance (coffee) in a tank, by automatically pumping a concentrated solution of the same substance or pure water. The optimal command of the pumps is computed with a nonlinear model predictive control (MPC) by using a model of the mass balance occurring within the reactor. The controller is implemented in Simulink. The system is tested via hardware-in-the-loop (HIL) simulation. The controller proved to be able to drive the simulated concentration of caffeine to the desired value, and it was verified that the pumps were correctly commanded. Similarly, sensor readings were also successfully transferred to the Simulink scheme. Future experiments with the physical system will complete the validation and demonstrate the possibility of creating controller prototypes in Matlab for this toy problem.