Biogas sequestration from the headspace of a fermentative system enhances hydrogen production rate and yield

Total pressure (TP) affects the level of dissolved hydrogen gas in the fermentation medium leading to metabolic shifts in mixed microbial-culture-based systems. In this study, the effect on hydrogen production rate and yield was investigated at different TP of a hydrogen-producing system using a microbial non-sterile culture previously heat-treated. Four continuous stirred-tank reactors (CSTR) were operated in parallel on a mineral salts-molasses medium (21 g-COD. L −1 ) at 35 °C, pH 5.5 and hydraulic retention time (HRT) of 6 h. The TP was set at 80 kPa (R1), 100 kPa (R2), 120 kPa (R3) and 140 kPa (R4) for which reactor performances were estimated at steady-state conditions. As the increase of TP consequently increased the partial pressure of hydrogen ( pH2 ), the hydrogen production rate (HPR) and yield (HY) were consistently negatively influenced. The highest HPR and HY (406.1 ± 36.8 mL-H 2 h −1 ; 4.51 molH 2 mol −1 suc eq. ) were achieved at low pressure conditions (80 kPa). The composition of the microbial community mainly represented by species from Sporolactobacillus and Clostridium genera, did not change with the increase and/or decrease of the TP, indicating a regulation at cellular but not population level.