Production of non-methane organic compounds during refuse decomposition in a laboratory-scale land®ll The presence of non-methane organic compounds (NMOCs) in land®ll gas is well documented. However, there is little understanding of the degree to which the production of NMOCs should be attributed to the volatilization of household hazardous waste as opposed to intermediates of the anaerobic decomposition of the major cellulosic components of municipal solid waste. The objectives of this study were: (1) to compare the NMOC yields for decomposed refuse, fresh residential refuse, and a synthetic refuse; and (2) to evaluate the source of NMOCs emitted during refuse decomposition. Replicate 2-l reactors were ®lled with shredded residential refuse expected to contain household hazardous waste, synthetic refuse containing no hazardous constituents, and control reactors with decomposed refuse only. Anaerobic decomposition of each refuse was initiated with a seed of decomposed refuse, and the reported methane and NMOC yields were corrected for that attributable to the seed. The NMOC yields from the seed, synthetic refuse, and residential refuse were comparable (0.62 to 1.01 3 10 ±4 g NMOC (dry g) -1 , suggesting that the volatilization of hazardous organic compounds is not the sole source of NMOCs in land®ll gas and that anaerobic biodegradation intermediates also contribute to NMOCs. Clark L. Thomas Morton A. Barlaz Department of Civil Engineering, Box 7908, North Carolina State University, Raleigh, NC 27695±7908, USA Keywords Ð Hazardous wastes; land®ll gases; land®lls; methane; municipal solid wastes; non-methane organic compounds; refuse Corresponding author: Morton A. Barlaz, Department of Civil Engineering, Box 7908, North Carolina State University, Raleigh, NC 27695±7908, USA. email: barlaz@eos.ncsu.edu Received April 1998, accepted in revised form 15 January 1999 Introduction Land®ll gas contains methane and carbon dioxide, which are the major endproducts of refuse decomposition in land®lls. It also contains trace amounts of multiple organic constituents, including benzene, toluene, xylene, and chlorinated aliphatics (Pohland & Harper 1986; Reinhart 1993; US EPA 1995). The presence of trace amounts of organic compounds in land®ll gas is suspected to originate from the presence of household hazardous waste (HHW) in municipal solid waste (MSW), the disposal of hazardous waste by small-quantity generators, and illegal disposal (Reinhart 1993). Components of MSW that contain trace amounts of organic constituents include paint and paint remover (toluene and xylene), motor oil and gasoline (benzene and ethylbenzene), tire sealant (perchlor- oethene), and glues (trichloroethene) (Reinhart 1993). Vinyl chloride, which is often present in land®ll gas, likely results from the reductive dehalogenation of chlorinated organic compounds. In this process, a chlorinated organic compound serves as an electron acceptor and the chloride moiety is replaced by a hydrogen, forming a less chlorinated and more reduced intermediate (Mohn & Waste Manage Res 1999: 17: 205±211 Printed in UK ± all rights reserved Copyright # ISWA 1999 Waste Management & Research ISSN 0734±242X 205