MATHEMATICAL-MODELING AND SIMULATION OF AN INDUSTRIAL-SCALE FLUIDIZED-BED REACTOR FOR ANAEROBIC WASTE-WATER TREATMENT - SCALE-UP EFFECT ON PH-GRADIENTS

A mathematical model of anaerobic wastewater treatment in an industria l scale fluidized bed reactor (FBR) is presented together with simulat ion results for reactors in lab-scale (11) and industrial scale (500 m (3)). The model was developed to study the effect of scale up on the a naerobic wastewater treatment in FBRs by examining the interactions be tween biological degradation and the physico-chemical environment upon the outcome of this process. Material balance equations for substrate s and products in gas and liquid phase are basis of the model. Hereby, the following effects were taken into account: biological degradation steps, convection and dispersion, chemical equilibria and calcium car bonate precipitation under consideration of ion activities. Model exte nsions are discussed, for example the calcium carbonate precipitation and the pH-dependency of degradation reactions. Simulation results sho w the strong impact of reactor performance on axial pH-gradients and t hus on process stability in dependence of reactor scale. In this conte xt the crucial role of the precipitation reaction together with the su bstrate degradation und carbon dioxide production reactions on local p s-values in the system is illustrated. (C) 1997 IAWQ. Published by Els evier Science Ltd.