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

Abstract

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.