초록
<P><B>Abstract</B></P> <P>This study focused on the supersaturation of hydrogen in the liquid phase (H<SUB>2aq</SUB>) and its inhibitory effect on dark fermentation by <I>Thermotoga neapolitana cf. capnolactica</I> by increasing the agitation (from 100 to 500 rpm) and recirculating H<SUB>2</SUB>-rich biogas (GaR). At low cell concentrations, both 500 rpm and GaR reduced the H<SUB>2aq</SUB> from 30.1 (±4.4) mL/L to the lowest values of 7.4 (±0.7) mL/L and 7.2 (±1.2) mL/L, respectively. However, at high cell concentrations (0.79 g CDW/L), the addition of GaR at 300 rpm was more efficient and increased the hydrogen production rate by 271%, compared to a 136% increase when raising the agitation to 500 rpm instead. While H<SUB>2aq</SUB> primarily affected the dark fermentation rate, GaR concomitantly increased the hydrogen yield up to 3.5 mol H<SUB>2</SUB>/mol glucose. Hence, H<SUB>2aq</SUB> supersaturation highly depends on the systems gas-liquid mass transfer and strongly inhibits dark fermentation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> H<SUB>2</SUB> supersaturates in the liquid phase at 100 rpm despite hyperthermophilic conditions. </LI> <LI> High H<SUB>2aq</SUB> concentrations directly inhibit the specific rates of dark fermentation. </LI> <LI> H<SUB>2</SUB> supersaturation and H<SUB>2</SUB> production rate depend on the gas-liquid mass transfer. </LI> <LI> H<SUB>2</SUB>-rich biogas recirculation is an effective method to prevent H<SUB>2</SUB> supersaturation. </LI> <LI> Gas recirculation increased the hydrogen production rate by 271%. </LI> </UL> </P>