In this paper the biogas flow rate and the dilution rate are taken, respectively, as the regulated and manipulated variables to optimize biogas production of an Anaerobic Digestion plant. Based on a simple validated model of the Microalgae Anaerobic Digestion (MAD*), a Feedback Linear Control is synthesized. The control law is then applied on a more complex anaerobic digestion model combined to its reduced model considered an observer of the unmeasured states. The closed-loop performances are studied by the operational stability of the controller response, on the one hand, and it robustness against parametric uncertainties, on the other hand. The obtained results may be useful in industrial process applications.