Conference Agenda

A non-convex metafrontier approach is proposed to study the temporal evolution and the productivity change in the water usage efficiency of 91 countries for the period 2015-2020. A circular three-stage Network Data Envelopment Analysis (NDEA) model is considered. The non-radial Directional Distance Function is used to compute the system efficiency as well as that of the three stages. Three sets of NDEA models are solved: contemporaneous group, intertemporal group and intertemporal metafrontier. The corresponding Malmquist index and its decomposition into efficiency change, best practice gap change and technology gap change is computed for each country and averaged for each world region. The results found indicate that water usage inefficiency seems to be limited to a relatively small number of countries and is due to shortfalls in the gross value added and treated municipal wastewater dimensions. The inefficiency in gross value added actually shows an upward trend. The inefficiency in the water withdrawal and treated municipal wastewater dimensions have remained approximately constant during this period while the inefficiency in produced municipal wastewater have decreased slightly. As regards productivity change, most regions had a negative evolution during this period. Central Asia and Middle East-Western Asia are the exception to this trend and their productivity improvement is mostly due to an improvement in their best practice gap and, to a lesser extent, in their technology gap ratios.

The recycling of mixed plastic waste poses challenges for the realization of a circular economy. Specifically, for polystyrene in application within composite thermal building insulation, no recycling systems are yet in place to close material loops due to long product life cycles, material compositions that impede conventional recycling methods, and chemical recycling technologies with low TRL. To cope with increasing volumes of this polystyrene waste in the future, thorough ex-ante planning of reverse logistics networks is necessary for efficiently integrating promising chemical recycling processes, given the waste material’s geographical dispersion and uncertainties regarding future return quantities per region and regulatory changes.

We aim to develop a decision support system to find optimal and robust long-term pathways and strategies for regulating and implementing sustainable recycling systems for polystyrene waste from building insulation that are economically viable. We design corresponding reverse logistics networks, accounting for uncertain polystyrene waste quantities and regulatory requirements through scenario-based robust optimization. Minimizing the expected regret in a strategic multi-period planning horizon, we integrate strategic decisions, such as technology selection of (novel) recycling options, location and capacity decisions, and tactical decisions such as material transformation and transportation.

Through our model, we mitigate the risk of developing cost-ineffective network configurations, ensure scalability to handle potential waste volumes, and address regulatory compliance. Using an application-based case study within the WSS founded research project catalaix, our study provides valuable insights for decision-makers seeking optimal strategies to manage mixed plastic waste through chemical recycling amidst uncertain developments, ultimately advancing sustainable waste management.

The valorization of brownfields presents a significant challenge in urban redevelopment, as decisions in this domain involve a trade-off between environmental sustainability and financial feasibility. Our study, focusing on three sites in Switzerland, introduces a comprehensive framework integrating operations research methodologies to optimize the rehabilitation process of such sites. Within this framework, we identify key cost components related to transportation and rehabilitation expenses, which include routing, vehicle, tool, material, inventory, and recycling costs. Our framework evaluates various scenarios to find the most efficient strategy while considering (i) spatial, i.e., the location of sites and recycling facilities, (ii) technical, i.e., the quality of the material that is being recycled, and (iii) financial, i.e., budget, constraints. The scenarios are also evaluated with respect to their environmental impact: CO2 emissions, energy and water consumption are taken into account so that extra-financial factors play roles in decision-making. Evaluating options such as demolition, recycling, and upcycling for materials like cement, timber, concrete, and metal, we aim to provide actionable insights for sustainable redevelopment. The results of this research help us to propose incentives for circular economy practices in construction and promote sustainability, thus supporting a shift toward more environmentally conscious and economically viable approaches. Our interdisciplinary decision-making process addresses operational challenges and highlights the societal, economic, and environmental benefits of circular economy principles in construction.