The aim of the present study was to evaluate the influence of the recirculation rate on the efficiency of a 1,000-L pilot anaerobic sequencing batch biofilm reactor (ASBBR) treating effluent from a small dairy plant over a long-term period (570 days). Three opera-tional conditions were studied, in which recirculation rates were varied, resulting in upflow velocities of 0.2, 3.8, and 6.4 m h −1 and the cycle time of 48 h. The biomass was immobilized on plastic supports containing polyurethane foam. The organic loading rate varied according to the operations occurring in the dairy plant. After system stabil-ity had been verified, temporal profiles of the substrate and metabolite concentrations were obtained, allowing kinetic parameter inference. Sludge samples from the inoculum and from the reactor were analyzed through microscopic examination, molecular biology analyses, and specific me-thanogenic activity assays. The average efficiencies of or-ganic matter removal were 82±11, 84±9, and 87±9 % at velocities of 0.2, 3.8, and 6.4 m h −1 , respectively. Micro-scopic examinations indicated that the fluorescent microor-ganisms decreased throughout the experiment, and they were not detected in the last condition. Homoacetogenesis was inferred as a possible pathway for H 2 removal and for maintenance of the methanogenic process. Specific methan-ogenic activity increased throughout the monitoring period. It was possible to conclude that the ASBBR was efficient, robust, and reliable in treating dairy effluents under the conditions used.