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Available onlineKeywords: Silicate-deposits Landfill gas Biogas Municipal solid waste Digester Combustion engine a b s t r a c tThe objectives of this study were to compare composition and morphological characteristics of the deposits forming in engines operated with biogas from anaerobic digesters and from landfills. Engine deposit samples were collected from biogas to energy facilities in Florida, USA. The deposit samples were analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Similarities and differences between the deposit samples collected from the engines operated with biogas from anaerobic digesters and biogas from landfills were analyzed in terms of chemical composition and morphology. The sample obtained from the anaerobic digester gas did not contain potassium while calcium and zinc were present at a higher ratio. Relatively high levels of carbon were present in the crystalline deposits forming during the combustion of biogas. C:O:Si ratios were about 5:7:1 in the deposits obtained from the engines operated with biogas from the anaerobic digesters and 2:3.5:1 in the deposits from the engines operated with landfill gas. In general, the silicon content from deposits found in facilities utilizing biogas from anaerobic digesters was lower than those operated with landfills gas. The difference was made up with higher phosphorus, sulfur and calcium content in the deposits from the engines operated with digester gas.

E v a lu a tio n of a F u ll-S c a le W a te r-B a s e d S c ru b b er fo r R e m o v in g S ilo x a n e s fro m D ig e s te r Gas: A C ase S tudySharon C. Surita1 *, Berrin Tansel2A B S T R A C T : Siloxanes are becoming more prominent in digester gas at water resource recovery facilities because of their wide use in personal care products. This study evaluates a full-scale water-based scrubber operating in a water resource recovery facility (Miami, FL). The digester gas is used for energy generation due to its high methane content. During energy generation, siloxanes are converted to silicates and Silicon Dioxide (Si02), which leave deposits on engine components. Trimethylsilanol (TMSOH), Octamethyltrisiloxane (L3), Hexamethylcyclotrisiloxane (D3), Octamethylcyclotetrasiloxane (D4), Decamethylcyclopentasiloxane (D5), and Dodecamethylcyclohexasiloxane (D6) were detected in the digester gas. D4 and D5 were present at the highest concentrations, 5000 and 1800 pg/ m3, respectively. Sampling results have indicated that scrubbers employed for hydrogen sulfide (H2S) removal at the facility do not provide effective removal of siloxanes due to their high Henry's Constant. Post scrubber treatm ent is needed to remove siloxanes from the digester gas prior to combustion. Water Environ. Res., 87, 444 (2015).