Quantitative longitudinal assessment of volatile organic silicon compounds in biogas from landfills and wastewater treatment plants

Extensive use of organic silicon compounds in consumer products has led to their presence in landfills and wastewater treatment plants (WWTPs), hindering energy production from waste-derived biogas. This work broadly characterized the scope and scale of volatile silicon species in biogas by consolidating global data from the literature and applying statistical analysis. The current work also includes original data from two United States (US) Midwest landfills for a period of two years. The data from the literature showed siloxanes are present at similar levels worldwide in landfills and WWTPs, with no clear trends over time. Most of the data in the literature were from European countries, with fewer data from US and Asian countries. Statistical analysis shows that trimethylsilanol (TMSO) correlated well with the total siloxane content of landfill biogas (R² = 0.96), and decamethylcyclopentasiloxane (D5) correlated well with the total siloxane content of WWTP biogas (R² = 0.95). The strong correlations identified in the current work suggest TMSO and D5 can serve as sentinel species for total siloxane content monitoring. Results from sampling the Midwest landfill sites showed similar species and concentration trends as found with the literature data, except for octamethyltrisiloxane (L3). The new quantitative results on local and global siloxane trends provide a foundation of biogas characteristics that may be helpful for species measuring and monitoring, gas clean-up development, and resource recovery. The results also underscore the need for additional data from diverse sources to assess challenges and enable solutions for waste-derived biogas systems.