Kosuke SAWADA Degradation Behavior of Municipal Solid Waste in Simulated Landfill Column Reactors Hideki HARADA, Akiyoshi OHASHI Degradation behaviors of MSW based on the mass balances of carbon and nitrogen were studied using by simulated landfill column reactor at three different conditions. The first column was adjusted to completely anaerobically, the second was upper-aerobically and the third was semi-aerobically. In addition, microbial community responsible for methane emission were identified and quantified by direct FISH count. According to the 428 days experiments, similar pattern was observed during acid production phase (the first 150 days), whereabouts 13% and 40% of carbon and nitrogen was washed out as leachate. On the other hand, from the 150 day downward a distinct behavior was observed from each reactor, 1) anaerobic reactor, methane production was slowly and VFA was accumulated, 2) upper-aerobic reactor, 1.3�}0.2�~109 cells/g-dry-waste of methane oxidizing bacteria was quantified in the upper layer, 3) semi-aerobic reactor, the lowest concentration of organic matters in leachate and highest greenhouse gas emission was obtained. Consequently, the results of initial degradation behavior suggested that enlarge of aerobic area was effective for reduction of organic matter concentration in leachate as well as methane emission.