A study of anaerobic digestion of piggery wastewater was carried out in a laboratory-scale sludge bed reactor as a secondary treatment. The effect of organic volumetric loading rates (B-V) in the range of 1.0-8.1 g TCOD/l d on the process performance was evaluated. The best results were obtained at B-V equal to or lower than 4 g TCOD/1d. At higher Bv values, the removal efficiency of the process decreased suddenly. A linear relationship was found between the effluent SCOD and the TVFA/alkalinity ratio (P). A relationship was found among the different operational variables (B-V, removal efficiency, effluent soluble COD, Soluble COD removal rate (R), retention factor (phi), specific microbial growth rate (mu), methane production rate per volume of reactor and per volume of waste treated-Q(M) and q(M), respectively) and the corresponding regression equations were obtained. An increase of B-V determined a decrease of removal efficiency, phi and q(M) and an increase of effluent soluble COD, mu, R and Q(M). The value of the maximum specific microbial growth rate (mu(M)) determined through the equation that correlated B-V and mu was found to be 0.19 d(-1). This value was of the same magnitude as those reported in other works of anaerobic digestion of piggery waste. (C) 2004 Elsevier Ltd. All rights reserved.