Dynamic operation of anaerobic digestion plants requires sophisticated monitoring and control for effective performance. This article evaluates different simplifications of the Anaerobic Digestion Model No. 1 (ADM1), highlighting:

• The manual algebraic assessment proved effective for ADM1-R4 and simplified ADM1-R3.
• The algebraic approach, however, was found insufficient for larger models.
• A geometric approach employed with the STRIKE_GOLDD toolbox confirmed observability for more complex models using two different algorithms.

These findings are crucial for designing robust state observers and enhancing parameter estimation and advanced control mechanisms based on ADM1 models. The approach shows promise for improving oversight and management of anaerobic digestion processes in agricultural settings, which could further enhance productivity and environmental sustainability.