Waste Reduction Strategies: A Different Perspective on Waste Flow Modeling and its Application to Concrete and Phosphorus

Changing consumption patterns and global population growth lead to ever-increasing waste generation. Human activity and waste generation are irrevocably linked, and the current situation thus calls for a more circular approach to waste management, where wastes become new resources. Industrial ecology offers a variety of waste reduction-favoring concepts. As a first step this project identifies waste-preventing, waste-reducing, end of pipe (EOP) waste management approaches and legislation as classification categories for waste management strategies. Although, according to the waste hierarchy, waste prevention is the most preferable waste management approach, it is the least implemented. To facilitate the identification of waste prevention and reduction potentials, a special waste flow diagram from the waste management perspective is elaborated. The model tends to visualize all waste flows, including by-product valorization along a product's life cycle through the choice of a thematic-geographic system boundary. In a further step the applicability of the waste flow model is tested for concrete-related wastes and phosphorus (P) flows in wastes. The quantification of concrete waste flows for the city of Zurich shows that recycling is well implemented, whereas preferable waste management strategies, prevention and reduction of waste, are hardly put into practice. Scenario modeling is used to show the benefits of these techniques and the comparative LCA for different construction methods and materials identifies waste prevention as most beneficial option. For P, the waste flow model is applied to test its ability to detect P recovery potentials, however no new findings in terms of P-recovery potential are identified. The most compelling result regarding phosphorus is found in the extension to the initial investigation, the mass flow analysis for a wet-chemical and a thermochemical P-recovery procedure from sewage sludge ashes. The analysis shows that for EOP waste technologies, the material output can be bigger than the input due to the extended use of additives. Although all generated by-products can, in this case, be valorized by other industrial activities, this finding highlights the need for more waste prevention-oriented waste management strategies, thus avoiding the necessity to generate high by-product flows in the first place.