Biological methanation using a tubular foam bioreactor
Hoda Khesali Aghtaei, Max-Planck-Institute for Dynamics of Complex Technical Systems, Magdeburg, Germany
Flash Presentation: Chemical & Biological (Re-)Synthesis
Video Conference Room (BigBlueButton): https://bbb.mpi-magdeburg.mpg.de/meeting/SmartPSE2022-Aghtaei
Abstract: Microbial communities, including methanogenic archaea can be applied for the conversion of H2 and CO2 to CH4. Regarding process performance, the transfer of H2 from the gas phase into the aqueous solution is the rate-limiting factor. H2 diffusivity can be controlled by pressure, gas holdup, and gas-liquid interfacial area. Tubular (plug flow) reactors with small diameter tubing could increase the gas holdup without intensive stirring and prevent the mixing of the gaseous substrates and product as in the headspace of the CSTR. Furthermore, by the addition of a foaming agent to the liquid medium, the stability of gas bubbles in the tubing could be improved to maintain a large interfacial area. In this study, a mesophilic tubular methanation reactor(40 °C; tubing with 12 m length, 4 mm inner diameter) was established. It showed a productivity of 1.8 VCH4/VR/day and CH4 content of 80 %. The addition of Pluronic F-68 as foaming agent increased the productivity to 16.7 VCH4/VR/day with a CH4 content of 92 %. The process was challenged by implementing a discontinuous feeding regime using H2 for one week (12 h per day nominal feeding, 12 h with 10% of nominal feeding). Interestingly, a fast recovery of the process to continuous conditions was observed. In particular, the methane production rate recovered nearly completely after the starvation periods. Finally, the productivity was increased to 31.5 VCH4/VR/day by operation under thermophilic conditions (55 °C). Both, addition of the foaming agent and the increased temperature challenged the microbial community used as biocatalyst. Some adaptations were required to stabilize the process under this new condition. In contrast, the discontinuous feeding regime did not require any adaptation phase and was tolerated without loss in process performance. The observed productivity and robustness of biological methanation in tubular foam reactors may allow its application for storage of excess electrical power as CH4 in the gas grid.