Effect of temperature on continuous fermentative hydrogen production from Laminaria japonica by anaerobic mixed cultures

•H2 production was achieved at 35, 50 and 65°C using Laminaria japonica as feedstock.•A highest H2 yield of 61.3±2.0mL H2/g TS was observed at mesophilic condition.•Reduced microbial diversity was found with an increase of temperature.•Highest total cellulase activity was monitored at mesophilic condition. The temperature effect on continuous dark fermentative hydrogen production from non-pretreated Laminaria japonica was investigated in the present study. In a preliminary step, the fermentors were continuously operated as an inoculation process at three different temperatures, 35, 50 and 65°C, to respectively represent mesophilic, thermophilic, and hyperthermophilic conditions. An optimization process was subsequently conducted with a range of organic loading rate (OLR) and cultivation pH. Among the various operation conditions, the maximum H2 yield, 61.3±2.0mL H2/g TS, was observed under a mesophilic condition at OLR of 3.4g COD/L/d and pH 5.5. From a PCR-DGGE analysis, it was found that an increase of temperature can reduce the microbial diversity and change the predominant species. Finally, total cellulase activity was measured, to investigate the effect of temperature on hydrolysis of L. japonica. The highest cellulase activity was 0.19±0.02 FPU/mL, observed at 35°C, coinciding with the maximum H2 yield.