Abstract: “Through the incorporation of a solid-liquid separator in the form of 11.6 L settling column bacteria granular bed wash out was prevented for a 5.0 L thermophilic bioreactor system operated at high volumetric biomass densities, low hydraulic retention times and high degassed effluent recycle rates. Stability of the bioreactor operation in terms of volumetric hydrogen productivity (L H2/L/h), %H2 content and pH maintenance was readily maintained for 50 days. While volumetric hydrogen productivity increased with bacterial biomass density, both hydrogen yield (mol H2/mol glucose) and specific hydrogen productivity (L H2/g/h) declined with increasing biomass density”

Keywords: Biohydrogen production, Expanded bed, Bacterial granules, Biomass density, Effluent recycling, Thermophilic.