BACKGROUND The aim of the present research was to provide a strategy for the start-up of upflow anaerobic sludge blanket (UASB) reactors treating sugar cane vinasse, with emphasis on the relevant sulfur compounds along the reactor height. To this end, a laboratory-scale UASB reactor was started up and its performance under the applied conditions was studied. RESULTS Biomass was able to assimilate organic loading rates from 3 to 10 kg chemical oxygen demand (COD) m(R)(-3) d(-1), reducing VFAs accumulation, while increasing biogas production rate (BPR) from 0.92 to 4.12 m(3) m(R)(-3) d(-1). The COD and sulfate (SO42-) were mainly removed in the reactor bed, showing homogenous distribution in the blanket and settler zones. However, from bottom to top of the reactor, a slight decrease of total and free sulfide concentrations was observed, indicating that the sludge bed in the UASB reactor was exposed to H2S concentrations higher than those measured in the reactor effluent. CONCLUSIONS During 54 days, the development of macroscopic granules, the COD removal efficiency, the BPR and the CH4 content proved good indicators to monitor the start-up period. Further research will be needed for strategy validation in pilot and full-scale UASB reactors treating vinasse. (c) 2019 Society of Chemical Industry