The research study hereby is aimed at the characterization of the hydrodynamics and kinetics of an upflow anaerobic fixed-bed reactor used in the secondary treatment of slaughterhouse wastewater. Hydrodynamics was determined by means of impulse tracer trials and by calculating residence time distribution curves at different volumetric flow rates. At high flow rates (110-204 mL/min), the reactor showed a plug flow behavior with axial dispersion and interactions with dead zones; nonetheless, at low volumetric flow rates (2.29-27.90 mL/min), the dispersion and interaction with dead zones increased, and short circuits appeared behaving as a stirred reactor. In this study, the hydrodynamics and kinetics results were combined with flow pattern description models (stirred tank, plug flow, stirred tank reactors in series and dispersion models) in order to assess organic matter removal efficiency as chemical oxygen demand at the anaerobic reactor. The comparison of the first-order kinetic constants obtained experimentally and the kinetics constants from the models allowed the obtaining of the anaerobic reactor's hydrodynamics and kinetic characterization. Optimal operating conditions and design parameters such as average residence time and efficiency, by taking into account reactor and wastewater characteristics were determined. (C) 2011 Elsevier B.V. All rights reserved.