Identifying leverage points using material flow analysis to circularise resources from urban wastewater and organic waste

• Published in: Journal of environmental management 2024-10, Vol.369, p.122215, Article 122215
• Main Authors: Hatley, Gregory A., Pahlow, Markus, Bello-Mendoza, Ricardo, Gutiérrez-Ginés, Maria J.
• Format: Article
• Language: English
• Subjects: Circular economies; Material flow analysis; New Zealand; Nitrogen - analysis; Organic waste; Phosphorus - analysis; Substance flow analysis; Waste Disposal, Fluid - methods; Wastewater; Wastewater - analysis
• ISSN: 0301-4797; 1095-8630; 1095-8630
• DOI: 10.1016/j.jenvman.2024.122215

Anthropogenic systems are synonymous with linear economies that cause widespread resource waste and environmental degradation. Urban areas are hotspots for this behaviour due to their high population density and resource consumption. Changing this situation is limited by the lack of a holistic but sufficiently detailed understanding of system units where resource waste occurs. The objectives of this study were: (1) to develop and apply a model of the material and substance (nitrogen, phosphorus, and carbon) flows of organic waste and wastewater systems at a local scale, taking Christchurch, New Zealand, as a study case, and (2) to identify leverage points within the system to achieve resource circularisation. Results show that groundwater, infiltrated water, and industrial wastewater are the predominant material flows into the system. Nitrogen and phosphorus inputs predominantly come from food products, detergents, green waste, and industrial wastewater. The Christchurch wastewater system is a prime example of a linear economy, where ∼66 % of the nitrogen and ∼63 % of the phosphorus entering the wastewater system is discharged to the ocean. Leakage from the water supply system reduces water resource efficiency, while water infiltration into the wastewater network inflates the quantity of wastewater treated at the centralised treatment plant, limiting nutrient recovery. In the compost facility, 86 % of the waste is composted, with 33% of the nitrogen and all the phosphorus exiting as compost, while ∼66 % of the nitrogen treated exits through volatilisation. The remaining 14 % of the organic waste entering the treatment plant is deemed unsuitable for composting and is landfilled. The material and substance flow analysis allowed the identification of flows with leverage points in the system where there are opportunities to reduce, reuse, or recover materials and substances to encourage circularisation. These flows include food products, detergents, unsuitable materials for composting, domestic water supply leakages, wastewater network infiltration, and wastewater treatment plant's nutrient recovery. •Material and substance flows for Christchurch wastewater and organics are detailed.•67 %, 63 %, and 12 % of N, P, and C entering CWWTP were discharged into the ocean.•Water infiltration accounted for 46 % of water entering CWWTP in 2018.•53 % and 59 % of N and C entering the compost facility were lost as gas products.•Sub-system material flow analysis provides le