Trace contaminants in biogas: Biomass sources, variability and implications for technology applications

Biogas represents a renewable and controllable energy source. Although predominantly composed of methane and carbon dioxide, it also contains various trace contaminants that can be detrimental to the technologies used for its conversion. The aim of this work is to comprehensively explore trace contaminants in biogas. The assessment employs a two-level approach: an extensive literature review on biogas trace contaminants, complemented with on-site analyses from real-scale biogas plants to enhance and validate the literature findings. The biogas contaminants – sulphur compounds, siloxanes, halocarbons and aromatic compounds – are quantified and categorised into four distinct groups: landfill gas, agricultural gas, gas derived from the organic fraction of municipal solid waste (OFMSW), and gas from wastewater (WWTP). This study also provides contaminant effects and required thresholds for different biogas conversion technologies, including internal combustion engines, upgrading to biomethane, and innovative solid oxide fuel cells (SOFCs). The two-level analysis reveals significant variability in contaminant levels across different biogas sources, with H2S being the most prevalent contaminant, averaging between 181 (WWTP) and 901 ppm (landfill gas). Other sulphur compounds show the highest average concentration in biogas from OFMSW (98 ppm), followed by agricultural and landfill gases. Siloxanes are typically more abundant in biogas from WWTP (2.55 ppm), while landfill gas exhibits the highest average concentrations of halocarbons and aromatic compounds (6 ppm and 109 ppm, respectively). Moreover, this study highlights the need for in-depth measurements of contaminants for highly sensitive technologies, such as SOFCs, to properly design tailored contaminant removal solutions.