Evaluation of a material hub as a circular waste management strategy

A case in Haarlem municipality

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Dutch municipalities face the waste management problem of assets which are reaching their end of life cycle. This is why, they investigate ways to effectively tackle this issue, by simultaneously complying with the goal imposed by the Dutch government about 100% circular construction sector by 2050. As a preparatory step in the transition towards Circular Economy (CE) in the Netherlands by 2050 and the forecasted changing regulations in waste management, a material hub is deemed as a solution to the waste management concern on the level of municipalities. For this reason, the Dutch public authorities are searching a unified framework to evaluate the impact of the material hub as a circular waste management strategy. The main objective of this study is to create a decision-making tool from the municipalities’ perspective to explore the circumstances under which the material hub can contribute to circularity objectives in waste management domain, given the increased cost incurred, and assess the future feasibility of the material hub. In order to achieve the above-stated objective, this research, first, introduces the concepts of circular waste management practices in the Netherlands and the material hubs based on the academic evidence and exploratory discussions with relevant professionals. Moreover, it entails literature review of recent publications relevant to waste management models and specifically Reverse Logistics (RL) models. Second, this study describes the conceptual framework of the defined problem: • by categorising all the construction and demolition waste (CDW) into fifteen material clusters that reflect sufficiently the various waste streams in municipalities • by translating circularity in this context • by configuring a RL supply chain which is universally applicable for the fifteen material clusters. Third, the methodology used to provide a solution to the postulated problem is formulated together with simplifications for transforming the actual problem into optimization model. Fourth, the real-life problem is simulated in a mathematical model, which is then tested in the municipality of Haarlem. Fifth, the data for this case, which is either gathered or generated and inserted as model inputs, is summarised. In data generation, various scenarios of supply-demand ratio of returned materials are used. Sixth, the model results are evaluated in order to determine whether the material hub can lead to economical and circular objectives. Finally, conclusions are drawn about circumstances under which the material hub is financially viable investment for the Haarlem municipality. The cost effectiveness of the material hub is determined by two criteria. The first one is that investment in the material hub as waste management practice could evoke cost savings for the municipality in comparison with the current strategy. This is achieved by giving a new purpose to returned materials and avoiding buying all materials needed in new construction projects. The second financial criterion is the required storage capacity of the material hub. The outputs of the model for different scenarios lead to the conclusion that these two financial criteria can be fulfilled when the supply is higher than demand for returned materials. More specifically, it is concluded that in scenarios with supply-demand ratio of 2:1 and 3:1, cost savings can reach 2.5-3.6% and 10.8-12% respectively compared to the current situation. In parallel, circular objectives are realised within the aforementioned scenarios. It is identified that the optimal objective values (minimum cost, maximum circularity and minimum CO2 emissions) are not obtained simultaneously in one scenario. Subsequently, the optimal solution is determined depending on the focus of the decision-makers in the municipality. Furthermore, it should be commented that even though financial and circular goals are accomplished under the specific circumstances, the cost savings are deemed relatively low considering the initial effort and time of building a material hub. Another implication from the model results is that only limited quantity of returned materials is actually stored at the material hub. This is in contradiction with the intended basic function of the material hub as storage facility.