Waste-to-energy incineration plants as greenhouse gas reducers: a case study of seven Japanese metropolises.

Municipal solid waste (MSW) incineration is a greenhouse gas (GHG) emitter; however, if GHG reductions, achieved by accounting for waste-to-energy, exceed GHG emissions, incineration can be considered as a net GHG reducer. In Japan, only 24.5% of MSW incineration plants perform energy recovery despite 80% of MSW being incinerated; therefore, there is great potential to extract more energy from MSW. In this study, the factors that should be considered to achieve net GHG reductions from incineration were analysed from a life cycle perspective. These considerations were then applied to the energy supply requirements in seven Japanese metropolises. Firstly, the carbon footprints of approximately 1500 incineration plants in Japan were calculated. Then, the incineration plants with negative carbon footprint values were classified as net GHG reducers. Next, the processes that contribute to the carbon footprint were evaluated, and two processes-plastic burning and electricity savings-were found to have the greatest influence. Based on the results, the energy supply requirements were analysed and discussed for seven metropolises (Sapporo, Tokyo, Nagoya, Osaka, Kobe, Takamatsu and Fukuoka) taking into account the energy demands of households. In Kobe, 16.2% of the electricity demand and 25.0% of the hot water demand could be satisfied by incineration to realise a net GHG reducer, although urban design for energy utilisation would be required.