The objective of this study was to investigate the separate hydrogen and methane productions from cassava wastewater by using a two-stage upflow anaerobic sludge blanket (UASB) system under thermophilic operation. Recycle ratio of the effluent from methane bioreactor-to-feed flow rate was fixed at 1: 1 and pH of hydrogen UASB unit was maintained at 5.5. At optimum COD loading rate of 90 kg/m(3) d based on the feed COD load and hydrogen UASB volume, the produced gas from the hydrogen UASB unit mainly contained H-2 and CO2 which provided the maximum hydrogen yield (54.22 ml H-2/g COD applied) and specific hydrogen production rate (197.17 ml/g MLVSS d). At the same optimum COD loading rate, the produced gas from the methane UASB unit mainly contained CH4 and CO2 without H-2 which were also consistent with the maximum methane yield (164.87 ml CH4/g COD applied) and specific methane production rate (356.31 ml CH4/g MLVSS d). The recycling operation minimized the use of NaOH for pH control in hydrogen UASB unit. (C) 2014 Elsevier Ltd. All rights reserved.