An experimental application of extremum seeking control to cultures of the microalgae Scenedesmus obliquus in a continuous photobioreactor

Summary The cultivation of microalgae in photobioreactors (PBRs) is important in various sectors such as food, bioenergy, pigments, and cosmetics. Productivity optimization can be achieved without the need for a dynamic process model using model‐free extremum seeking control (ESC). This article explores the use of ESC to drive the productivity of a continuous PBR to optimal or suboptimal setpoints. The latter can be achieved by estimating on‐line the gradient of a measurable performance index using a recursive least squares estimator and by regulating this gradient to a specific value (zero corresponding to the optimum) using the dilution rate as a manipulated variable. Experimental results for the cultivation of the microalgae Scenedesmus obliquus in a lab‐scale flat‐panel PBR are discussed. They show the fast convergence of ESC and its robustness towards environmental perturbations, such as changes in the incident light intensity.