Critical analysis of some concepts proposed in ADM1

The Anaerobic Digestion Model No. 1 (ADM1) has been developed by the expert task group of the IWA to establish a common platform for simulation of a wide variety of anaerobic degradation processes. It enables comparison of different methods and parameter values for description of specific sub-processes, with the methods and default values proposed by the task group. This will hopefully stimulate a more structured discussion on anaerobic digestion modelling compared to the recent past, when many different researchers developed a slightly different model and it remained largely unclear what could, and what could not be compared. In this paper we take the liberty to criticize some aspects of ADM1 and its implementation, as we think they represent concepts that are too easily extrapolated from activated sludge models. The specific subjects discussed here are the COD-based description of the reaction stoichiometry (i), the widely adopted use of a constant value for the solid retention time high-rate anaerobic bioreactors (ii), and the kinetic description of the acetogenic reactions as proposed in ADM1 (iii).