  Dynamic operation of anaerobic digestion plants requires advanced process
monitoring and control. Different simplifications of the Anaerobic Digestion
Model No. 1 (ADM1) have been proposed recently, which appear promising for
model-based process automation and state estimation. As a fundamental
requirement, observability and identifiability of these models are analyzed in
this work, which was pursued through algebraic and geometric analysis. Manual
algebraic assessment was successfull for small models such as the ADM1-R4 and
simplified versions of the ADM1-R3, which were derived in this context.
However, for larger model classes the algebraic approach showed to be
insufficient. By contrast, the geometric approach, implemented in the
STRIKE_GOLDD toolbox, allowed to show observability for more complex models
(including ADM1-R4 and ADM1-R3), employing two independent algorithms. The
present study lays the groundwork for state observer design, parameter
estimation and advanced control resting upon ADM1-based models.
