Composting and organic waste stabilization are aerobic processes and a large fraction of the degradable organic carbon in the treated material is converted into CO2, which is not counted as anthropogenic emission because it is of biogenic origin. On the other hand, these processes release CH4 by anaerobic sections of compost/stabilized
organic waste, that are less than 1% of the initial carbon content; they also produce emissions of N2O in a range that varies fromless than 0.5%e5% of the initial nitrogen content (IPCC, 2006). As proposed by the 2006 IPCC methodology, we have chosen emissions factors equal to 0.05 g CH4/kg of organic waste and 0.30 g N2O/kg of
organic waste treated in composting and selection plants. To determine emissions from the fossil carbon fraction of the waste burned in the incinerator, we used CO2 emissions detected by continuous site-specific measures (SIENA AMBIENTE S.p.A, 2012); the CO2 generated by the combustion of the non-fossil carbon fraction was subtracted (Table S.10 in the Supplementary on-line material). Anthropogenic emissions from natural gas used to maintain the combustion temperature in furnaces was also subtracted from the measured tons of CO2 released by incineration (Nate S.4 in the Supplementary on-line material). Emissions due to natural gas combustion in the incinerator must be calculated separately in order to avoid double-accounting.