Enhancement of hydrogen production using untreated inoculum in two-stage food waste digestion

•H2 production could be enhanced using untreated inoculum.•Significant H2 yield was achieved by selecting a high F/M ratio.•H2 producers could be enriched with a slight addition of inoculum.•Two-stage showed a more stable methane production than single-stage process.•Overall energy yield was improved by two-stage process. This research investigated the possibility to enhance H2 production using untreated inoculum in a two-stage hydrogen-methane process from food waste. Batch experiments were conducted to evaluate the H2 production efficiency at different F/M ratios (ranging from 1:1 to 64:1). The results showed that when a proper F/M ratio was selected, significant H2 production was feasible to be achieved even inoculated with untreated anaerobic sludge. Among the F/M ratios studied, maximum H2 yield (217.98 mL H2 g VS−1 FW) was found in the digester at the F/M of 64:1, which was 93.75 times higher than that of the digester at the F/M of 1:1. Higher hydrogen yield was achieved at the greater F/M ratio, due to the enrichment of the H2 producing bacteria and the reduction of the antagonistic bacteria. The two-stage process allowed more stable methane production and higher overall energy yield compared to the single-stage process.