A closed-loop controller for optimizing nitrogen removal in a microalgal outdoor pond
Résumé
Microalgae based processes are often seen as a promising technology to produce renewable energy under the form of lipids or, when coupled with anaerobic digestion, methane. However, it has been shown that an economical and environmental sustainable process must be coupled with a wastewater treatment procedure providing the nitrogen and phosphorus which will support the microalgal growth. The microalgal plant of the future is therefore both dedicated to biomass production and to inorganic nitrogen and phosphorus removal. Managing such a plant is however difficult due to its nonlinear and complex character. In this paper, we propose a model based control strategy for optimizing nitrogen removal in a microalgae open pond (raceway). Our objective is to determine an optimal dilution rate strategy ensuring a maximal transformation of inorganic nitrogen into biomass by regulating the efficiency of light absorption in the microalgae culture. The resulting controller provides satisfactory results in comparison to the optimal open loop solution.