GHG emissions are classified into direct and indirect, depending on the origin. Direct emissions take place in the sites considered (geographical criteria), and indirect emissions occur outside the disposal plants (responsibility criteria). Anaerobic degradation of organic matter in landfills, combustion of waste, bio-oxidation of
organic wastes in composting and selection plants provide direct emissions. Direct emissions also derive from fossil fuels used for heating, machinery, transport of materials and energy production within the plants. Electricity imported from the national grid and fossil fuels used to transfer wastes from one plant to another (the
distance between two plants and a consumption of 2.5 km/L of diesel used by trucks were considered) make up indirect emissions. The amount of treated wastes and the other activity data of the eight solid waste disposal plants are shown in Tables S.1eS.8 of the Supplementary on-line material. To estimate CH4 emissions from decomposition of biodegradable matter in landfills, we used the IPCC Waste Model (IPCC, 2006),
which considers the production of biogas generated by a widerange of waste types, characterized by specific decomposition parameters Table S.9 and Note S.3 in the Supplementary on-line material). The biogas recovery plants installed in the three land- fills capture up to 85% of the methane produced, as confirmed by Oonk and Boom (1995).