Karine Arrhenius

Suitability of different containers for the sampling and storage of biogas and biomethane for the determination of the trace-level impurities - A review

The traceable and accurate measurement of biogas impurities is essential in order to robustly assess compliance with the specifications for biomethane being developed by CEN/TC408. An essential part of any procedure aiming to determinate the content of impurities is the sampling and the transfer of the sample to the laboratory. Key issues are the suitability of the sample container and minimising the losses of impurities during the sampling and analysis process. In this paper, we review the state-of-the-art in biogas sampling with the focus on trace impurities. Most of the vessel suitability studies reviewed focused on raw biogas. Many parameters need to be studied when assessing the suitability of vessels for sampling and storage, among them, permeation through the walls, leaks through the valves or physical leaks, sorption losses and adsorption effects to the vessel walls, chemical reactions and the expected initial concentration level. The majority of these studies looked at siloxanes, for which sampling bags, canisters, impingers and sorbents have been reported to be fit-for-purpose in most cases, albeit with some limitations. We conclude that the optimum method requires a combination of different vessels to cover the wide range of impurities commonly found in biogas, which have a wide range of boiling points, polarities, water solubilities, and reactivities. The effects from all the parts of the sampling line must be considered and precautions must be undertaken to minimize these effects. More practical suitability tests, preferably using traceable reference gas mixtures, are needed to understand the influence of the containers and the sampling line on sample properties and to reduce the uncertainty of the measurement.

Development of Analytical Methods to Gain Insight into the Role of Terpenesin Biogas Plants

Terpenes have been shown to be the dominant VOCs present in biogas mostly in plants where food wastes are digested. In particular, p-cymene and D-limonene have been reported to represent up to 90% of all VOCs in the biogas. A number of problems have been linked to terpenes in biogas plants, including odor problems, indoor air quality issues at workplaces and operational problems. In order to study the faith of terpenes, there is a need to develop robust analytical methods to quantify terpenes in all the flows at biogas plants including substrates, gas, and water samples. In this study, reliable analytical methods for the detection and quantification of terpenes in these flows are presented. The methods have a common final step consisting of a TD-GC-MS/FID analysis using Tenax TA for the trapping of terpenes. The methods were then applied to some samples taken at a biogas plant where food waste is digested. The results show that D-limonene was the dominant terpene in the substrate whereas p-cymene was dominant in biogas and process water.