Monitoring of gas composition in a laboratory biogas plant using cavity enhanced Raman spectroscopy.

Biogas production from organic raw materials is a highly complex biotechnological process. The responsible anaerobic fermentation process is difficult to measure due to its multi-stage nature. Still, optimization of biogas production and the development of robust and efficient process management strategies require continually updated information about the process. Hence, the development of a comprehensive sensor system with high temporal resolution is key to further advancement in biogas technology. Here, we demonstrate a gas sensor based on cavity enhanced Raman spectroscopy for biogas monitoring. Online detection of all gas components of a biogas mixture enables a comprehensive quantification. In addition, robust calibration routines facilitate the adaptation of the sensor for biogas monitoring. A simulated concentration course of a typical fermentation process with defined gas mixtures consisting of CH4, CO2, N2, O2 and H2 showed reliable results for all relevant biogas components for varying concentration ranges from ppm to 100 vol%. The response time of 5 seconds allows online detection and - as a consequence - real time information is obtained about the biogas composition. A laboratory biogas reactor was designed to operate biogas production on a miniaturized scale and analyze it using the Raman gas sensor. The developed sensor enables the observation of methane production throughout the first 24 h of the fermentation process. The obtained results show the suitability of cavity enhanced Raman spectroscopy as a gas sensor to monitor the entire process of biogas production. As this strategy would allow the process to be manipulated and optimized according to the current state, it is of great biotechnological interest.