Interrelationships between bioreactor volume, effluent recycle rate, temperature, pH, %H2, hydrogen productivity and hydrogen yield with undefined bacterial cultures

Simultaneous achievement of high volumetric productivities (HP = 231.3 mmol H2/L/h) and high hydrogen yields (HY = 3.55 mol H2/mol glucose) was obtained by increasing the temperature to 70 °C and by reducing the total bioreactor system volume (V) to 5.74 L and increasing the degassed effluent recycle rate (Fer) to 3.2 L/min, giving a V/Fer value of 1.8 min. The bioprocess involved the recycling of degassed effluent at a high flow rate through a quasi-stationary fluidized granular bed. In this process the rate of physical removal of H2 trapped in the bulk liquid phase surrounding the fluidized granules reduced the thermodynamic constraints preventing the simultaneous achievement of high HPs and high HYs in the anaerobic fluidized granular bed bioreactor. Energy balance analysis showed that with heat recycling the bioreactor system could achieve a net positive volumetric energy output of 11.76 W/L at an energy efficiency of 49.3%.