Siloxanes, which are found in small fractions in the biogas from anaerobic digesters and landfills, interfere with the operation of biogas-to-energy systems.  During biogas combustion, siloxane oxidation products form either white crystalline or amorphous deposits on engine components (engine heads and spark plugs,) depending on the combustion temperature. The purpose of this study is to evaluate the economic impacts on landfill gas-to-energy systems when operators have to manage the operational challenges of siloxanes in biogas. Economic analyses were performed to compare the costs of the increased maintenance needed to remove the deposits from the engine components vs. the costs to install a carbon adsorption system.  The maintenance costs increased with biogas capacity up to about 600 acfm and declined for larger facilities.  Biogas samples were collected from a landfill and from an anaerobic digester. Siloxane levels were analyzed by assembling four carbon sorbent tubes in series.  The adequacy of capturing siloxanes using the single-tube sampling method was evaluated, as well as the recommended sampling conditions (0.2 L/min gas flow rate for 30 minute sampling time.) Carbon sorbent tubes in series can be an appropriate component of biogas sampling standard operating procedure and a way to determine siloxane levels in biogas. Careful implementation of appropriate QA/QC procedures for biogas sampling and analyses of selected low molecular weight siloxanes (up to D4) is required. The single sorbent tube sampling method was adequate only for trimethylsilanol and L2.  D5 has significantly lower affinity for sorption, therefore, single tube sampling may not be an adequate method for determining overall siloxane levels in biogas.

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