A generic and systematic procedure to derive a simplified model from the anaerobic digestion model No. 1 (ADM1)

•We introduce the hydrolysis stage and the ammonium dynamics into the AM2 model.•A generic and systematic state-association approach is proposed.•The new proposed model AM2HN is calibrated.•The AM2HN model gives an accurate description of the dynamics of the ADM1 model.•The AM2HN is robust with regard to moderate variations in the influent composition. The anaerobic digestion model No.1 (ADM1) developed by the IWA Task Group for mathematical modelling of anaerobic digestion processes Batstone et al. [1] is a structural model which describes the main biochemical and physicochemical processes. For such purposes, other models have been proposed to describe anaerobic processes with a reduced set of parameters, state variables and processes. Among them, the anaerobic model No. 2 (AM2) proposed by Bernard et al. [2] which describes the degradation of soluble organic compounds, appears as a model well-suited for control and optimization applications. In this work, we aimed at obtaining a model of reduced dimensions on the basis of which to synthesize regulators or observers with guarantees of performance, stability and robustness. Specifically, our contribution is twofold. First, a modified version of the AM2 is proposed while preserving the simplicity of the new model “AM2HN”. Second, we propose a systematic and generic state association procedure in order to obtain such a simplified model from any validated ADM1. Simulations and comparisons with the predictions of the ADM1 for a case study involving the anaerobic digestion of waste sludge are presented along with satisfactory results.