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Influence of liquid-phase hydrogen on dark fermentation by Thermotoga neapolitana

Dreschke, Gilbert, Papirio, Stefano, Lens, Piet N.L., Esposito, Giovanni
Renewable energy 2019 v.140 pp. 354-360
Thermotoga neapolitana, agitation, biogas, biomass, fermentation, hydrogen, hydrogen production, liquids, mass transfer
Hydrogen is a strong inhibitor of dark fermentation. We aimed at directly correlating the hydrogen production by Thermotoga neapolitana with the supersaturation of hydrogen in the liquid phase (H2aq), which is often disregarded. Different agitation speeds, biogas recirculation and bubble induction by AnoxK™ K1 carrier were tested to prevent the supersaturation of H2aq. At 100 rpm agitation, the H2aq 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 H2aq 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 H2aq below the equilibrium concentration. This study demonstrates the reciprocal influence of HPR and H2aq 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 H2 from the liquid phase and prevent H2 supersaturation.