초록
<P><B>Abstract</B></P> <P>Hydrogen is a strong inhibitor of dark fermentation. We aimed at directly correlating the hydrogen production by <I>Thermotoga neapolitana</I> with the supersaturation of hydrogen in the liquid phase (H<SUB>2aq</SUB>), which is often disregarded. Different agitation speeds, biogas recirculation and bubble induction by AnoxK™ K1 carrier were tested to prevent the supersaturation of H<SUB>2aq</SUB>. At 100 rpm agitation, the H<SUB>2aq</SUB> was 29.7 (±1.4) mL/L, which is 3-times higher than 9.7 mL/L, i.e. the equilibrium concentration given by Henry's law. Increasing the agitation speed up to 600 rpm reduced the H<SUB>2aq</SUB> until 8.5 (±0.1) mL/L in 2 h and increased the hydrogen production rate (HPR) from 39 (±2) mL/L/h at 0 rpm to 198 (±4) mL/L/h at 600 rpm. Similar to 600 rpm, biogas recirculation and the presence of K1 carrier at 200 rpm maintained the H<SUB>2aq</SUB> below the equilibrium concentration. This study demonstrates the reciprocal influence of HPR and H<SUB>2aq</SUB> and revealed an inverse nonlinear correlation between the two parameters. Therefore, we conclude that an adequate gas-liquid mass transfer, efficiently provided by biogas recirculation or the presence of solid materials (e.g. a biomass carrier), is essential to remove H<SUB>2</SUB> from the liquid phase and prevent H<SUB>2</SUB> supersaturation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> An inverse nonlinear correlation was found between HPR and H<SUB>2aq</SUB>. </LI> <LI> The equilibrium between H<SUB>2aq</SUB> and HPR depends on the gas-liquid mass transfer. </LI> <LI> Agitation at 100 rpm resulted in a supersaturation of H<SUB>2aq</SUB> up to 29.7 (±1.4) mL/L. </LI> <LI> Gas recirculation and K1 carrier led to the lowest H<SUB>2aq</SUB>, i.e. 5.8 (±0.5) mL/L. </LI> <LI> K1 carrier induced H<SUB>2</SUB> bubble formation reducing H<SUB>2aq</SUB> by about 50% in the first 15 h. </LI> </UL> </P>