Effects of initial lactic acid concentration, HRTs, and OLRs on bio-hydrogen production from lactate-type fermentation

► The effects of initial lactic acid concentration, OLRs, HRTs on hydrogen production at pH 4.5 were evaluated. ► Even though lactate was one of the major VFAs, hydrogen production was feasible via the continuous operation. ► Cumulated butyric acid by high OLR on continuous hydrogen production decreased hydrogen production efficiency. ► HRT should be determined with soluble metabolite concentration, OLR, and avoiding wash-out of the bacteria.