Online Optimization of Microbial Electrolysis Cells

In this chapter, two Extremum Seeking Control (ESC) strategies are presented to maximize the hydrogen production rate of a Microbial Electrolysis Cell (MEC). First, a model-free ESC strategy based on a simple sliding mode controller, with the input-output map gradient as a sliding variable, is proposed to online maximize the MEC productivity by using the dilution rate as a manipulated variable. Next, the model of the MEC is considered to calculate the input-output gradient to offline solve an optimization problem. The maximum HPR computed is then used as a reference by a Super-Twisting controller to compute the optimum dilution rate to track the MEC productivity to its maximum value. Both algorithms are proposed in discrete time to be easily implemented in digital systems such as microcontrollers, DSP, or FPGA. The results of both gradient-based optimization strategies are compared by simulations considering an uncertainty parameter framework in the MEC model.