Investigation of volatile methyl siloxanes in biogas and the ambient environment in a landfill.

Landfill biogas is a potential alternative for fossil fuel, but the containing impurities, volatile methyl siloxanes (simplified as siloxanes), often cause serious problems in gas turbines when applied to generate electricity. In this research, a collecting and analyzing method based on solvent adsorption and purge and trap-gas chromatography-mass spectrometry was established to determine the siloxanes in biogas from a landfill in Jinan, China, and adjacent ambient samples, such as soil, air, and leachate of the landfill. The results showed that, octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5) accounted for 63% of total siloxanes; and without considering D4 and D5, the order of detected siloxanes in concentration was found relating to Gibbs free energies of molecules, namely that higher abundant siloxane (except for D4 and D5) usually had lower Gibbs free energy. Additionally, the mass ratio between D4 and octamethyltrisiloxane (L3) in the biogas varied with different garbage age in landfills, possibly revealing the breaking-down of larger siloxane molecules with time. The samples, which were collected from environmental samples adjacent to the landfill, such as soil, water, and air, presented much higher siloxane level than urban or rural area away from landfills. The current H2S scrubber of the landfill biogas could decrease the total siloxanes from 10.7 to 5.75 mg/m3 due to Fe2O3 and a refrigerant drier in a purification system and cyclic siloxanes were more easily removed than linear ones.