【正文】 teins, carbohydrates and lipids which are further hydrolyzed to yield biomonomers like amino acids, sugars, and high molecular fatty acids. Amino acids and sugars are converted into either intermediate byproducts (. propionic, butyric and other volatile acids) or directly fermented to acetic acid. High molecular fatty acids are oxidized to intermediate byproducts and hydrogen. Methane and carbon dioxide generation occurs primarily through acetate cleavage. Methane is also produced through carbon dioxide reduction with a land?ll environment, methane generation from the latter route is often limited by the lack of hydrogen which is consumed by sulfate reducers (Kasali, 1986). Qualitatively, land?ll gas is highly dependent on the deposition stage within the land?ll (Rovers and Farquhar, 1973。 Mosey, 1983。 McCarty 1981。 Zehnder, 1978。 Nozhevnikova et al., 1992。 Carr and Cossu, 1990). Therefore, landfills will continue to be the most attractive disposal route for solid waste. Indeed, depending on location, up to 95% of solid waste generated world wide is currently disposed of in landfills (Bingemer and Crutzen, 1987。 Environmental Impacts of Solid Waste Landfilling Abstract:Inevitable consequences of the practice of solid waste disposal in landfills are gas and leachate generation due primarily to microbial deposition, climatic conditions, refuse characteristics and landfilling operations. The migration of gas and leachate away from the landfill boundaries and their release into the surrounding environment present serious environmental concerns at both existing and new facilities. Besides potential health hazards, these concerns include, and are not limited to, fires and explosions, vegetation damage, unpleasant odors, landfill settlement, ground water pollution, air pollution and global warming. This paper presents an overview of gas and leachate formation mechanisms in landfills and their adverse environmental impacts, and describes control methods to eliminate or minimize these impacts. Keywords: landfill, solid waste disposal, biodegradation, gas and leachate generation, environmental impacts, control methods Solid waste disposal in landfills remains the most economic form of disposal in the vast majority of cases (Thompson and Zandi, 1975。 Rushbrook, 1983。 Cossu, 1989。 Gendebien et al., 1992). Alternatives to landfilling are considered as volume reduction processes because they produce waste fractions ( and slag from bustion processes that represent the second leading method of waste disposal) which ultimately must be landfilled (Emberton and Parker, 1987). Resorting to landfills is not limited to the disposal of municipal solid waste, but it icludes most other industrial wastes. For instance, nearly 80% of hazardous wastes generated in the . is dumped in landfills (Eichenberger et al., 1978). Solid waste position varies substantially with socioeconomic conditions, location, Most anic materials are biodegredable and can be broken down into simpler pounds by aerobic and anaerobic microanisms, leading to the formation of gas and leachate. The following sections provide an overview of the mechanisms of gas and leachate formation in land?lls, their environmental impacts, and appropriate control methods to eliminate or minimize these impacts. 2. Land?ll Gas Formation Mechanisms At the time of waste deposition in a land?ll, oxygen is present in the void space, giving rise to aerobic deposition during which biodegradable anic materials react quickly with oxygen to form carbon dioxide, water, and other byproducts (. bacterialcells). Carbon dioxide is produced in approximate molar equivalents to the oxygenconsumed. Oxygen depletion within the land?ll marks the onset of the anaerobic depositon phase. Although a land?ll ecosystem undergoes an initial short aerobicdeposition phase, the subsequent anaerobic phase is the dominant phase in its age and the more important one from the perspective of gas formation. Much of what is known or assumed concerning anaerobic processes in land?lls has primarily e from work with anaerobic digesters. Microbial populations in both environments appear to be similar however, the major di?erence is that the substrates may vary in their relative content of fat, protein, and carbohydrates, and conversely to land?lls, the environment in anaerobic digesters is well controlled and often under optimal conditions. Investigators have recognized several major steps to describe the anaerobic deposition phase during which anic materials are converted to methane and carbon dioxide (Alexander, 1971。 Wolfe, 1979。 Zehnder et al.,1982。 Archer and Robertson, 1986。 Rees, 1980。 Barlaz et al.,1989c). Under a stabilized methanogenic condition which is the stage of interest from a bene?cial recovery perspective, methane and carbon dioxide are by far the two principal ponents of land?ll gas and form more than 90% of the total gas and oxygen are normally present i