Estimation of global warming emissions in waste incineration and landfilling: An environmental forensic case study

Abstract

Anthropogenic emissions of greenhouse warming gases (GWG) to the atmosphere are thought to contribute to the Earth’s global warming. Among different waste management options, incineration is often considered one of the most effective and environmentally protective as demonstrated by many Life Cycle Assessment analysis. Nonetheless, depending on previous treatments that a waste may receive, such as mechanical biological treatment (MBT), landfilling could offer better possibilities than incineration in terms of GWG emissions thanks to carbon sequestration according to the “Carbon Sink” principle. The latter refers to any process that avoids the emission of GWG, for example, the biogenic carbon that is not dissimilated and remains permanently stored in a landfill, avoiding its emission to the atmosphere. The current study presents a forensic case study of municipal solid waste management in Italy; it aims at assessing the GWG [i.e., methane, carbon dioxide (CO2), and nitrous oxide] released to the atmosphere by two different scenarios of a waste flow processed in a MBT: incineration with energy recovery and landfill disposal with gas recovery. For each scenario, total fluxes of GWG are estimated as the sum of: 1) emissions during waste refinery to produce refuse-derived fuel; 2) indirect emissions associated to transport; 3) process or treatment emissions derived from the waste itself (direct emissions) and from the fuel used for its treatment prior to disposal; 4) disposal emissions that result from the ultimate disposal of the waste; 5) emissions avoided as a result of useful energy or materials recovery; 6) stored or sequestered emissions due to short-cycle carbon locked up in the landfill and prevented from being returned to the atmosphere as CO2 for longer than 100 years. Carbon sink is a fundamental phenomenon to be accounted in the study, given that, without considering it, the GWG in the landfill would considerably change (from –33.9 kg CO2/t DF to 250.3 kg CO2/t DF, DF being the dry fraction from the MBT process). According to the composition of waste and to the plant engineering for the treatment/disposal destinations assumed, landfilling results the better option in term of GWG emissions. It is worth mentioning that not only GWG should be considered in the evaluation of waste management options. Nonetheless, the results from the present study provide useful information to prove that a waste management option (landfilling), that a priori could appear less sustainable, represents, instead, an optimal solution.