H2-rich biogas recirculation prevents hydrogen supersaturation and enhances hydrogen production by Thermotoga neapolitana cf. capnolactica

This study focused on the supersaturation of hydrogen in the liquid phase (H-2aq) and its inhibitory effect on dark fermentation by Thermotoga neapolitana cf. capnolactica by increasing the agitation (from 100 to 500 rpm) and recirculating H-2-rich biogas (GaR). At low cell concentrations, both 500 rpm and GaR reduced the H-2aq 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-2aq primarily affected the dark fermentation rate, GaR concomitantly increased the hydrogen yield up to 3.5 mol H-2/mol glucose. Hence, H-2aq supersaturation highly depends on the systems gas-liquid mass transfer and strongly inhibits dark fermentation. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.