Saturated Output-Feedback control of continuous anaerobic digestors

The saturated Output-Feedback (OF) control problem for a class of four-state anaerobic digestors with volatile fatty acids (VFAs) measurement is addressed. The reactor must operate about an optimal steady-state, with maximum VFA consumption, that is locally stable but not structurally unstable. The problem is addressed as an interlaced control-observer design within a geometric control framework in the light of passivity, observability, and bifurcation properties. The result is a saturated linear PI OF controller with global robust stability conditions in terms of control gains and limits. The proposed approach is illustrated with a representative case example through numerical simulations.