Assessing the temperature effect on the kinetics of a hydrogenotrophic methanogenic culture using a novel headspace-free methodology

Accurately determining the biological activity of hydrogenotrophic microbial cultures independently of potential gas-liquid mass transfer limitations for hydrogen is important but is challenging. In this work, a novel methodology called Pressurized Headspace-Free Hydrogen Uptake Rate (PHF-HUR) is presented and validated. The methodology consists on first saturating a microbial culture bubbling pure H2 under selected pressures in a 120 mL stirred batch bioreactor equipped with a dissolved H2 probe. Secondly, the decrease of the dissolved H2 concentration under headspace-free conditions is monitored in real-time. Hydrogen profiles under headspace-free conditions are used to calculate the HUR and to assess the microbial activity and related kinetics. A mixed culture was characterized at different temperatures ranging from 27 °C to 70 °C using this methodology. Modelling of hydrogen uptake rate was conducted using Monod and Moser kinetic equations, the latter providing a better fit of the experimental data. In the novel PHF-HUR methodology, hydrogen uptake increased with temperature reaching 773 mmolH2·gVSS−1·d−1 at 65 °C, but was nil at 70 °C. The half-saturation concentration for the methanogens was also temperature dependent, ranging from 4.3·10−3 mM H2 at 27 °C to 6.9·10−2 mM at 65 °C. Results indicate the potential of the novel methodology to accurately determine the biological kinetics of hydrogenotrophic methanogens without gas-liquid mass transfer limitations.