Waste-to-Energy in a Circular Economy: Assessing the Energy Recovery Potential and Economic and Environmental Optimal Pathways

Abstract

The circular economy continues to gain traction in the political agenda for a competitive and climateneutral economy. In this context, the prevention, re-use, and recycling of municipal solid waste (MSW) are at the top of the waste policy. Meanwhile, energy recovery from MSW, or waste-to-energy (WTE), seems to have received rather scarce attention despite the dual benefit of avoiding landfilling and providing a domestic energy source. However, an increased circularity of materials will have broad implications on the WTE sector that remain poorly understood. The goal of this thesis is to assess the energy recovery potential of MSW and the economic and environmental optimal WTE pathways within the context of an increasingly circular economy. To achieve this goal, new tailored tools capable of tackling the complexity of MSW and anticipating system-wide consequences have been developed. First, a material flow analysis (MFA) model is applied to quantify the energy recovery potential of MSW under future scenarios of increased separate collection and recycling. Secondly, the MFA approach is combined with life cycle assessment (LCA) to quantitatively evaluate the potential environmental consequences of phasing-out MSW incineration. Finally, building on the previous tools and mathematical programming, a multi-period optimization framework is developed to determine time-dependent waste treatment capacities and flows according to economic and climate objectives and subject to waste availability and composition, system constraints and restrictions, and policy targets. Focusing on the case study of Madrid, it has been found that a higher separate collection and recycling of MSW do not compromise the energy recovery potential. This relatively low impact can be attributed to inefficiencies in separate collection and the limited efficiency of materials recovery at automatized sorting facilities. Overall, the future availability and characteristics of feedstocks are found adequate to sustain the operation of large-scale incineration and anaerobic digestion (AD) WTE facilities. Within this context, phasing-out the existing incineration facility in Madrid could reduce some of the environmental impacts, including climate change impacts, human toxicity, and ecotoxicity, at the expense of jeopardizing the realization of the 10% landfill target by 2035. In fact, the optimization results reveal that a more intensive use of incineration will be necessary to achieve this landfill target. Based on the work presented in this thesis, envisioning a future with a relevant role for WTE appears highly likely even within the context of an increasingly circular economy.