10th International Symposium on Process Systems Engineering - PSE2009 Rita Maria de Brito Alves, Claudio Augusto Oller do Nascimento and Evaristo Chalbaud Biscaia Jr. (Editors) © 2009 Elsevier B.V. All rights reserved. Heterogeneous aerobic ofilm actor dels Application to UASB, EGSB and AFB actors Mauren Fuentes, Pío A. Aguirre and Nicolás J. Scenna INGAR Instituto de Desarrollo y Diseño (CONICET-UTN)-Avellaneda 3657 (3000) Santa Fe, Argentina Abstract In a previous work, a methodology developed for modeling anaerobic fluidized bed (AFB) reactors was presented. The aim of this work is to extend this methodology for modeling upflow anaerobic sludge blanket (UASB) and expanded granular sludge bed (EGSB) reactors, and compare and discuss model hypotheses and simulation results. A set of experimental data obtained by Kato et al. (2003), during the start-up of a bioreactor operating as UASB and EGSB reactor configurations, is used for model validation. A good agreement was obtained among experimental and predicted values. A simulation-based sensitivity analysis of model parameters such as the specific rate of granule rupture and the axial dispersion coefficient is performed. A decrease in the granule diameter is predicted for values of the specific rate of granule rupture higher than 1×10 -7 m s 2 kg -1 . At low values of the axial dispersion coefficient, a decrease in the bioreactor efficiency is predicted. Simulation results are more sensitive when the bioreactor operates with a UASB configuration. Keywords: dynamic modeling and simulation, anaerobic biofilm reactors: UASB, EGSB and AFB, three-phase (solid-liquid-gas) systems. 1. Introduction Anaerobic reactors based on biofilm development such as UASB, EGSB and AFB reactors have become popular high-rate wastewater treatment systems. The anaerobic digestion is a multi-step process consisting of hydrolysis of complex organic substrates such as proteins, lipids, and carbohydrates into soluble amino acids, fatty acids, and sugars followed by the fermentation to acetate, formate, hydrogen, and carbon dioxide, which are finally utilized by methanogenic microorganisms to form methane. There are clear differences between UASB and AFB reactors, e.g. the former is based on the ability of microorganisms to form dense aggregates by autoimmobilization, and operates at a lower fluid superficial velocity than the second one, which is loaded with inert support particles for biofilm attachment. The conception of the EGSB reactor can be considered as an improvement of the UASB reactor. Inside the EGSB reactor, the higher upflow velocities, which are caused by a high recycle rate and a high height/diameter ratio, cause the sludge expansion through the whole reactor thus improving its contact with the effluent and reduce the unit dead volume. A better understanding of the microbial and hydraulic mechanisms that regulate the system has contributed to the development of more compact and efficient units. The heterogeneous sludge distribution in UASB reactors does not make easy the application of most mathematical models developed for completely mixed anaerobic digestion systems, since these models assume homogeneous biomass distribution and hydrodynamic pattern within the reactor. The UASB reactor has being modeled as a Mo Re Bi An Re 297