Dynamical modelling of an anaerobic digestion fluidized bed reactor

One of the main difficulties in modelling a Fluidized Bed Biofilm Reactor (FBBR) is to take into account hydraulic phenomena (such as bed expansion) and its interactions with the biological variables. In this paper, we shall present a dynamical model of the process, analyse the stability of the hydrodynamics and illustrate its performances in simulation, A key feature of the model is that it combines mass balance of the process components with momentum balance equations in order to emphasise the different hydrodynamics of the liquid phase and of the solid phase, and the interactions between both phases, The model derivation finally leads to a set of partial differential equations (PDE), This model is intended to be used as a basis for the derivation of controllers and for dynamical simulation. (C) 1997 IAWQ. Published by Elsevier Science Ltd

Asymptotic observers as a tool for modelling process dynamics

This paper deals with the dynamical modelling of processes with a special emphasis on wastewater treatment. Dynamical process modelling is usually derived from mass balance considerations and results in models which contain two types of terms representing the hydrodynamics and transport dynamics, and the conversion due to the involved (bio)chemical reactions involved, respectively. The conversion terms are indeed generally speaking the products of two terms:a yield coefficient and a reaction rate (strictly speaking, the kinetics). The latter usually concentrates a predominant part of the model uncertainty, The bioprocess model building exercise is usually global in the sense that it concerns all the terms involved in the model. In addition to the inherent bioprocess modelling difficulties (model complexity, data scarcity), this makes the interpretation of the model identification results difficult if not questionable. In this paper it is suggested how to use asymptotic observers to model and validate reaction schemes independently of the reaction kinetics. The results will be illustrated with two wastewater treatment processes : an activated sludge process and a detoxification reactor. (C) 1997 IAWQ. Published by Elsevier Science Ltd