Membrane-free dissolved hydrogen monitoring in anaerobic digestion.

Dissolved hydrogen (dH 2) is an important parameter in anaerobic digestion (AD) processes, in particular in a two-stage operation mode encompassing separate hydrolytic/acidogenic and methanogenic stages. Then, monitoring of dH 2 as a substrate of hydrogenotrophic methanogenesis is essential to avoid feast and famine conditions. Despite its significance, there is currently a lack of established monitoring systems which are capable of reliably measuring dH 2 concentrations in culture broth. To address this challenge, we propose a novel measurement system, which is based on the membrane-free extraction of hydrogen in an extraction chamber and the subsequent analysis by a metal-oxide (MOX) gas sensor. The response time of the MOX sensor lies in the range of seconds, while the entire measurement process completes within a total processing time of about 70 min). This study explores the measurement performance of the dH 2 sensor in the hydrolytic/acidogenic and methanogenic stage during lab-scale anaerobic digestion. The measurement principle was consistently applied for over three months. During this period, the methanogenic stage was partly sparged with gaseous hydrogen to monitor the dH 2 response afterwards. The dH 2 sensor responded reliably to these and other dynamic changes. Depending on the process conditions, concentrations between < 10 and > 4,000 Pa were detected, corresponding to dH 2 concentrations of < 0.074 to > 30 µmol L⁻¹. The findings demonstrated the importance of dH 2 monitoring and show that it facilitates the control of H 2 addition, thereby preventing both under- and oversupply during methanogenesis. [Display omitted] • Quantification of dissolved hydrogen with metal-oxide sensor. • Measurement range and long-term stability suitable for anaerobic fermentation broth. • Reliable detection of dissolved H 2 concentrations during H 2 feeding. • Insights into microbial uptake of hydrogen in anaerobic culture broth. • Flexible production of biogas and carboxylic acids in two-stage anaerobic digestion. [ABSTRACT FROM AUTHOR]