BACKGROUNDSeveral pretreatment methods at lab-scale have been developed to inactivate methane-producing and hydrogen-consuming microorganisms. The need to obtain a hydrogen-producing inoculum by a more practical method is still necessary. The objective of this study was to evaluate the adaptation of anaerobic granules to suppress the methanogenic activity for hydrogen production. RESULTSPreliminary tests in discontinuous operation indicated that methanogenic bacteria were hardly suppressed. The continuous adaptation of the granules, at pH of 4.5 and HRT of 5.5 h, produced hydrogen and successfully suppressed the methanogenic activity. An even distribution of -polysaccharides and cells was observed when the adapted granules were stained with fluorescent molecular tags. The reactor productivity was 71 6 mL-H-2 L-reactor(-1) h(-1) with a yield of 2.6 +/- 0.2 mol H-2 mol(-1) glucose. CONCLUSIONHydrogen was produced from methanogenic granules. The continuous strategy successfully suppressed the methanogenic activity of the seeded granules and the hydrogen production was stable. The high yield and even distribution of cells suggests that the continuous adaptation generated a more active biomass due to an improved mass transfer present in the process. (c) 2013 Society of Chemical Industry