Dry Anaerobic Digestion Modelling: Parameter Sensitivity Hassen Benbelkacem,* Julien Bollon, Rémy Gourdon and Pierre Buffière Laboratoire de Génie Civil et d'Ingénierie Environnementale, Université de Lyon, INSA‐LYON, 20 Avenue Albert Einstein F‐69621, Villeurbanne Cedex, France A model dedicated to dry anaerobic digestion process was previously developed. This model was based on the ADM1 model and modified to take into account the specificity of dry anaerobic media. The objective of the work presented here was to study the sensitivity to the model of 2 parameters. The first parameter (k L a) was related to mass transfer of the biodegradation products (CH 4 , CO 2 ,H 2 ) from liquid phase to gas phase. Two gas production behaviours were pointed out, depending on k L a value and corresponding to limiting or non‐limiting transfer rate. A k L a value of 5 d 1 marked the transition. The second parameter (k m X) was linked to biological kinetic reactions. The sensitivity of k m X was important: a variation of 10 % of its value affected clearly the kinetic consumption of the substrate. A method to determine those parameters was presented. This method was then used to determine both biological kinetic parameter and mass transfer coefficient from batch experimental data of methane production with acetate as organic substrate at two different moisture contents. Keywords: modelling, dry anaerobic digestion, model sensitivity, kinetic parameter, mass transfer INTRODUCTION D ry anaerobic digestion is a particularly attractive technolo- gy for the treatment of biowaste and residual municipal solid waste. Even if, in 2010, dry digestion processes accounted for 60 % of the digestion European capacity, [1] high‐ solid anaerobic digestion (AD) is a less mature technology than wet AD and it can suffer from biological, physical and chemical problems due to excessive amounts of solids. Indeed, at such high solids content (more than 20 %), many questions arise in terms of rheological behaviour, chemical equilibriums and mass transfer. The mass transport of soluble and particulate compounds within a high‐solid anaerobic digester is totally misunderstood. Biological reactions induced by the microorganisms are sensitive to their local environments; however, because of the low water content and the poor mixing efficiency within a high‐solid digester, soluble com- pounds are transported by diffusive convection, thereby creating the potential for pockets of local environment (pH, VFAs, dissolved H 2 and CO 2 …) which can inhibit the biological activity and more precisely the methanogenic stage. As a consequence, high‐solid AD can thus be driven by local mass transfer phenomena. Diffusive transport is strongly related to the porosity and the viscosity of the media and, thus, to the global water content. Only a recent paper determined experimentally the diffusion coefficients in high‐solid digested media by using an innovative experimental method where iodide was used as a soluble tracer. [2] Abbassi‐Guendouz et al. [3] have also shown that physical limitation related to liquid/gas mass transfer can affect the global anaerobic digestion performance for high solids content. The effect of the total solids (TS) content on AD performances was experimentally investigated in a batch reactor (TS ranging from 10 to 35%). An inhibition of methanogenic step was observed for high solids content (>30 % TS). Many models have been proposed for wet digestion but ADM1 was the most used since it was settled in 2002. [4] ADM1 is a very complete and complex biological model that introduces many physical and biochemical phenomena. However, ADM1 does not seem to be adapted to dry digestion media, in particular because of the singular properties of dry media in terms of biological kinetics and mass transfer. A previous article detailed the main modifica- tions applied to ADM1 to adapt to dry conditions. [5] It was shown that the model calibration with the fitting of biochemical parameters only was not sufficient for the full understanding of the observed experimental data, especially at high solids content. This is the reason why the liquid to gas mass transfer was believed to be limiting in such cases. It is the purpose of the present paper to study the sensitivity of the model. Two parameters related respectively to mass transfer and biological kinetic reaction were then tested. A method to determine those parameters was presented and used for batch experimental data of methane production with acetate as organic substrate at two different moisture contents. MODEL DESCRIPTION The model presented was based on the ADM1 model, originally developed for liquid‐phase anaerobic digestion. [4] The ADM1 is a structured biological model that simulates the major conversion mechanisms of complex organic substrates into biogas and degradation by‐products. 24 state variables and 19 reactions (4 hydrolysis steps, 8 substrate uptake reactions, and 7 microbial growth reactions) are involved. The ADM1 model has been modified to take into account the specificity of dry anaerobic digestion processes. This kinetic model is developed for a homogeneous (completely mixed) system and its structure was already presented in a previous paper. [5] The main differences are detailed here. Main Modifications to ADM1 Four main modifications have been made:  Disintegration, hydrolysis and acidogenesis steps were gath- ered in a single step (called DHA). This step was modelled by a first‐order kinetic expression. *Author to whom correspondence may be addressed. E‐mail address: hassen.benbelkacem@insa-lyon.fr Can. J. Chem. Eng. 9999:1–5, 2014 © 2014 Canadian Society for Chemical Engineering DOI 10.1002/cjce.22089 Published online in Wiley Online Library (wileyonlinelibrary.com). VOLUME 9999, 2014 THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING 1