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Methane gas production in MSW landfills and its migration are well documented in the literature. Maximizing methane yield per unit refuse mass and minimizing its migration are beneficial for energy recovery purposes. This research project was based on suppressing methane generation in landfills, and its production in a controlled external reactor. Three different systems of simulated sanitary landfills were constructed at West Virginia University. System 1 simulated a conventional sanitary landfill. In System 2, leachate was recycled, and its pH was controlled by adding caustic. In System 3, anaerobic digestion supernatant was added to MSW to provide nutrients and bacterial seed. Leachate was treated in a hybrid upflow fixed film anaerobic reactor (FBR). The aim in system 3 was to separate the anaerobic digestion phases between the landfill simulator (acid-producing reactor) and the FBR (methane-producing reactor). Phase separation in system 3 was difficult to achieve, because methanogenic microorganisms were protected in microenvironments within the refuse. Acid addition to leachate combined with high recirculation rates controlled methane production but failed to stop it. Leachate was aerated to raise the dissolved oxygen concentration and oxidation-reduction potential. Aerated leachate was recirculated through refuse to obtain limited aerobic conditions. Recirculation of aerated leachate with low pH and total alkalinity concentration suppressed methane production in the landfill simulator when the concentration of readily available and easily biodegradable organic matter in leachate was low. As the concentration of soluble, easily biodegradable organics was increased by adding glucose, aerated leachate recirculation failed to suppress methane gas production. Cumulative methane produced during 426 days of monitoring was 941 {dollar}\\ell{dollar} CH{dollar}\\sb4{dollar} in System 1 (approximately 16 {dollar}\\ell{dollar}/kg dry waste), 6371 {dollar}\\ell{dollar} CH{dollar}\\sb4{dollar} in System 2 (approximately 106 {dollar}\\ell{dollar}/kg dry waste) adjusted for methane potential lost in wasted leachate, and 1618 {dollar}\\ell{dollar} CH{dollar}\\sb4{dollar} in System 3 (approximately 26.9 {dollar}\\ell{dollar} CH{dollar}\\sb4{dollar}/ kg dry waste) adjusted for methane potential lost and added to the system. Recirculation of neutralized leachate enhanced methane production rate and cumulative volume produced after 426 days of operation. Phase separation was difficult to achieve. Recirculation of aerated leachate did not suppress methane when soluble, easily biodegradable organics were readily available in landfill.