Emission of methane into the atmosphere from landfills in the former USSR

The annual production of solid domestic wastes by population of big cities of the USSR is about 37.5 million tons. The main method of disposal is burial in designated landfills. In the USSR large landfills occupy an area of more than 140,000 hectares. It has been calculated that the mass of the landfill deposits generating methane is today about 600 million tons. The studies carried out using geophysical, isotopic, and microbiological methods at different landfills of the Moscow region have shown that the emission of methane and other gases from the surface of landfills into the atmosphere is extremely irregular and considerably less than their generation in the anaerobic zone. The most important factors determining methane emission are the thickness of the layer of buried refuse, the heterogeneity of the deposit body, and the microbiological oxidation of gases in the upper aerated ground layer. It has been shown that the temperature in the anaerobic zone of big landfills is relatively constant and in most cases is 25–35°C. Methanogenesis often is most intensive in the upper part of anaerobic zone where the content of organic matter is rather high. The stable carbon isotope composition of the biogas generated from landfills is characteristic of the methanogenesis from organic wastes and depends on the concentration of organic matter and the age of the landfill. At first a lighter gas is generated and then a heavier one as the substrate is depleted. In the upper aerated ground layer of the landfill, about 1 meter in depth, methane, hydrogen, and carbon monoxide (CH 4, H 2, CO) are oxidized intensively. The number of bacteria oxidizing these gases reaches 10 11 cells per gram of wet refuse. In this case the stable isotope composition of methane becomes heavier and, of carbon dioxide, lighter. It has been shown that at small landfills methane can be oxidized completely in aerobic zones. The gas-oxidizing ability of the microflora of the aerated ground layer of a landfill decrease considerably in the cold season of the year. The methane emission from landfills located in the USSR is estimated at 1.2 – 2.4 billion cubic meters per year. About two-thirds comes from the European part of the country. Effective methods of decreasing methane emission into the atmosphere are the extraction of biogas from big landfills and the maintenance of good aeration of the upper ground layer at the small ones.