The composting plant at Bordo Poniente, one of the garbage dump facilities in Mexico City, processes daily around 2,500 metric tons of organic garbage in open windrow piles, generating around 1000 m3 of leachates each day. These effluents are characterized by a high organic matter content, that varies from  90 g COD/L for leachates characterized during the rainy season to 119 g COD/L for the dry season ones. A two-phase acidogenic-methanogenic anaerobic system was implemented for the treatment of these effluents diluted with municipal wastewater to attain feeding concentrations from 4.9 to 26.5 g COD/L. A maximum formation rate of 0.306 g VFACOD/L-d and organic matter conversion to VFA of 76.3% were attained in the acidogenic reactor, as well as small amounts of hydrogen in the biogas. This pre-treated effluent was fed to the methanogenic reactor, which attained a methane productivity of 6.4 L CH4/L-d equivalent to 390 kW-h per m3 of raw treated leachate or 3.2 kW-h per kg treated COD. The acidogenic-methanogenic system maintained a removal efficiency of 95.3% showing to be a suitable technology for the environmental impact reduction of this effluent and for biofuels production.