Influence of the permeate flux on continuous biohydrogen production, permeability, and granulation in a dynamic membrane bioreactor

•H2-producing dynamic membrane was established on meshes sized 220 and 444 μm.•The influence of permeate flux was observed as an influential parameter for H2-production.•The highest average permeate flux was observed at 233 ± 12 L/m2/h at 3 h HRT.•Startup of dynamic membrane bioreactor with Clostridium butyricum DSM 10702.•Dominant species were Clostridium pasteurianum and Ethanoligenens harbinense. This study examined the effect of the high permeate flux on continuous biohydrogen production using dynamic membrane bioreactor (DMBR). A lab-scale DMBR was equipped with polyester mesh having two pore sizes, 220 μm and 444 μm, to avoid washout and membrane fouling, respectively. The DMBR was continuously fed with 20 g glucose/L at a hydraulic retention time of 3 h, while the permeate flux increased from 116 to 291 L/m2.h over 58 days, under non-sterile conditions. The highest average hydrogen production rate, hydrogen yield, and daily hydrogen production were observed as 21.7 ± 1.7 L H2/L/d, 1.41 ± 0.05 mol H2/mol hexoseconsumed, and 184.0 ± 9.3 L H2/d, respectively, at the permeate flux of 233 ± 12 L/m2.h, with an average permeability for 444-μm mesh was 25.42 L/m2.h/kPa at an average transmembrane pressure (TMP) of 9 ± 1.2 kPa. Higher permeate flux (≥291 ± 14 L/m2.h) caused severe biomass washout, while lower permeate flux (≤175 ± 9 L/m2.h) resulted in excessive cake layer along with the increased H2 consuming pathways. At the optimum permeate condition, H2-producing granules were formed, which were with an average size of 1875 μm and a size distribution of 1150–2580 μm for 60% of the volume fraction. Although the reactor was inoculated with Clostridium butyricum DSM 10702, the dominant microbial species became Clostridium pasteurianum and Ethanoligenens harbinense as it was operated under non-sterile conditions.