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 thermo-
philic 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/m3 d based
on the feed COD load and hydrogen UASB volume, the produced gas from the hydrogen UASB unit mainly
contained H2 and CO2 which provided the maximum hydrogen yield (54.22 ml H2/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 H2 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