Towards optimal trade-offs between material and energy recovery for green waste

D.A.M. Inghels, Wout Dullaert, R. Heijungs, El Houssaine Aghezzaf

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Abstract

Green waste is a type of biomass consisting mainly of grass, leaves and fresh prunings originating from gardens and parks. It can be used as feedstock for composting, or for energy recovery. The EU Waste Directive 2008/98/EC advocates composting to prevent waste. This directive allows green waste to be used for (renewable) energy valorization only if a better overall environmental outcome can be demonstrated. In this paper, we propose an assessment procedure based on examining the Pareto front of optimal trade-off combinations for maximizing composting and energy recovery of green waste while minimizing environmental impact and minimizing particulate matter emission. The Pareto optimal front is determined by solving a multi-objective
optimization problem using the ε-constraint method. Previous research on green waste valorization using Life Cycle Analysis (LCA) shows that either energy recovery or composting is the preferred option depending on how environmental impact is assessed. In contrast to the full assignment to one of these recovery methods produced by LCA, we demonstrate, using the case of green waste valorization in the Netherlands and Belgium, that the proposed assessment procedure provides optimal solutions in a range between full allocation to
compost or energy recovery. The proposed methodology supports the selection of optimal solutions taking the decision makers’ preference into account that allows complying with Directives that have opposite goals on green waste valorization. Finally, computational results show that the assessment of the “better environmental outcome” requested by the EU waste Directive 008/98/EC is influenced by the life cycle impact categories and the policy makers references with respect to the valorization options taken into account. Since the EU waste Directive 2008/98/EC does not specify how to execute the outcome assessment of valorization alternatives, this can lead to ambiguity.
Original languageEnglish
Pages (from-to)100-111
Number of pages12
JournalWaste Management
Volume93
Early online date24 May 2019
DOIs
Publication statusPublished - 15 Jun 2019

Keywords

  • Decision support tool
  • Multiple objective linear programming
  • green waste valorization
  • material conservation
  • waste-to-energy

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