Composition and source identification of deposits forming in landfill gas (LFG) engines and effect of activated carbon treatment on deposit composition Orhan Sevimo  glu a, * , Berrin Tansel b a Fatih University, Department of Environmental Engineering, 34500 Buyukcekmece, Istanbul, Turkey b Florida International University, Civil and Environmental Engineering Department, Miami, FL, USA article info Article history: Received 21 November 2012 Received in revised form 5 May 2013 Accepted 8 May 2013 Available online 13 June 2013 Keywords: Landfill gas Siloxanes Motor oil Gas engines Combustion Energy Activated carbon treatment abstract Compositions of deposits forming on engines parts operated with landfill gas (LFG) were analyzed. The deposit compositions were compared before and after the installation of activated carbon system for treatment of LFG. Deposits forming on the spark plugs had significantly higher levels of calcium, chro- mium, and nickel in comparison to those forming on the engine heads. The LFG contained about 9.5  0.4 mg/m 3 total siloxanes, majority of which were octamethylcyclotetrasiloxane (D4) (5.0  0.2 mg/ m 3 ), decamethylcyclopentasiloxane (D5) (2.9  0.1 mg/m 3 ) and hexamethyldisiloxane (L2) (1.6  0.1 mg/ m 3 ). The samples collected from the engine heads before the activated carbon treatment of LFG had significantly high levels of silicon (149,400  89,900 mg/kg) as well as calcium (70,840  17,750 mg/kg), sulfur (42,500  11,500 mg/kg), and zinc (22,300  7200 mg/kg). After the activated carbon treatment, silicon levels decreased significantly; however, deposits had higher sulfur content (104,560  68,100 mg/ kg) indicating that the activated carbon released some sulfur during treatment. The analyses indicate that zinc and calcium originated from the additives in the lube oil while lead, aluminum, copper, nickel, iron, chromium were due to the engine wear. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction In internal combustion engines, knocking is an operational concern. It is caused by the resonation of the piston, connecting rod and bearings when multiple flame fronts collide. The unstable combustion pattern caused by multiple flame fronts, with only one being initiated by the spark plug, increases the cylinder pressure rapidly causing spontaneous burning and release of energy. The sharp edges of the engine parts are prone to super heating, hence, accumulation of deposits (Selim, 2004). In gas engines operated with landfill gas (LFG), electricity is produced by burning landfill gas. In addition to methane (CH 4 ) and carbon dioxide (CO 2 ), landfill gas contains small amounts of im- purities such as hydrogen sulphides, mercaptans, halogenated hy- drocarbons and siloxanes (Eklund et al., 1998; Allen et al., 1996) and trace metals (Suzuki et al., 2002). Volatile methyl siloxanes (VMS) have been reported to have adverse effects on utilization of LFG (Ohannessian et al., 2008; Ajhar et al., 2010; Appels et al., 2008; Gaur et al., 2010; Rasi et al., 2010, 2011). Also, presence of trace metals in LFG (i.e., Se, Te, Hg, Pb, As, Sn, Sb, Bi, Cl, S, Mg, Cu, Zn) has been reported in the literature (Glindemann et al., 1996; Feldmann and Hirner, 1995; Thorburn et al., 1979; Badjagbo et al., 2010). During the combustion process, deposits form due to oxidation of metals present in the landfill gas or in the engine oil (Naja et al., 2011; Demirbas, 2005). Over time, small amounts of lube oil can leak into the combustion chamber and burn with the LFG (Diaby et al., 2009). Lube oil contains small amounts of metals which are converted to metal oxides during the combustion process (Maryutina and Soin, 2009; Jorand et al., 2000). Dimkovski et al. (2011) have reported that the higher concentrations of sulfur and calcium in deposits forming in the honing grooves of truck engines could be due to a detergent additive in the motor oil. Presence of siloxanes in LFG can also result in deposit formation on the engine parts (Arnold and Kajolinna, 2010; Goossens, 1996). Siloxanes contain silicon atoms attached to organic chemical units (e.g., methyl group) (Huppmann et al., 1996). When siloxanes are burned in the combustion chamber, they are converted into sili- cates (SiO 2 or SiO 3 )(Dewil and Appels, 2006). Activated carbon treatment has been effective for removing siloxanes from LFG (Schweigkofler and Niessner, 2001; Shin et al., 2002; Finocchio et al., 2009; Matsui and Imamura, 2010. Silicates and metal oxides which deposit on the functional components of gas engines (i.e., spark plugs and engine heads) * Corresponding author. Tel.: þ90 212 866 33 00x5599. E-mail address: sevimoglu@gmail.com (O. Sevimo glu). Contents lists available at SciVerse ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman 0301-4797/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jenvman.2013.05.029 Journal of Environmental Management 128 (2013) 300e305