Process waste into valuable industrial inputs or consumer products; distribute processed waste to users.
🍏 💧 Biogas from organic materials
Residual organic and food wastes can offer a quasi-renewable and low-carbon source of energy. By processing organic wastes, often under high temperatures, pressures and in the absence of oxygen, organic wastes can be transformed into fuels, which can be used for heating, electricity generation, as well as transportation. A variety of technologies have been developed to generate biogas from organic materials, for example, anaerobic digestion. Such facilities can vary in scale from single units that can process the waste of a single building or neighbourhood, to large-scale facilities that can process the majority of the organic wastes generated from the entire city.
Cities have a key role to support the utilisation of organic materials as biofuels due to their close oversight and influence on the urban waste management system. In particular, cities can support the financing of large-scale facilities to help to overcome the investment costs, as well as develop relationships with businesses to operate such facilities.
🚌 Cycled materials for mobility infrastructure
Globally, 13% of global resources consumed relate to mobility. This includes transport infrastructure, from roads, to rail, to cycle routes (<a href="https://ellenmacarthurfoundation.org/circular-economy-opportunity-and-benefit-factsheets">Ellen MacArthur Foundation). Virgin materials sourced to build mobility infrastructure often include cement and asphalt, which are responsible for a significant portion of global greenhouse gas emissions (cement—a constituent component of concrete—is responsible for an estimated 8% of global greenhouse gas emissions) (<a href="https://www.bbc.co.uk/news/science-environment-46455844">BBC).
The materials that are required for the construction of transport infrastructure can be sourced from residual materials, to offset the demand for virgin resources. Construction techniques that utilise residual material are often less intensive in relation to greenhouse gas emissions, and can help to lower the material footprint of mobility infrastructure. A range of residual materials can be used within mobility infrastructure. These can come from conventional materials, such as cycled concrete and other stones and aggregate. As well as other residual materials such as plastics and rubber from end of life tyres.
Local governments can support the cycling of materials for mobility infrastructure by mandating a certain proportion of recycled material input in tenders for new developments or renovations of existing infrastructure. For example, criteria could stipulate that all residual materials within renovations must be cycled back into the project, for example as aggregate. Alternatively, criteria could stipulate a minimum proportion of material inputs from cycled sources, or ban the landfilling of certain residual materials. Collaboration and engagement with local businesses can help local governments to identify the most appropriate criteria that the local market is able to satisfy, and support the most effective transition towards a more circular economy.
💧 Recovery of nutrients and chemicals from wastewater and sludge
Much of the wastewater generated by homes, industries, and businesses must be treated before it is released back into the environment. This is because it contains nutrients and other substances that can be harmful to the environment and human health, as well as to aquatic fauna and flora. These nutrients can cause oxygen depletion in water bodies, beach closures and contamination of drinking water. However, if the nutrients are recovered, they can often be put to beneficial use.
For instance, biorefineries use wastewater as a source of raw materials, generating products of value from waste nutrients and simultaneously producing clean water for reuse or discharge. Nutrients such as nitrogen and phosphorus can be converted into environmentally friendly fertilisers, and used for ecological restoration and agricultural purposes. Biosolids from wastewater can be used as fuel for heating, replacing fossil fuels and reducing the amount of biosolids sent to landfill.
Local governments have an important role to play in providing pipes, water management and treatment infrastructure to ensure that water is safely handled. They can also play a role in monitoring privately run facilities to ensure compliance with environmental performance standards. Finally, cities can connect stakeholders to match supply and demand for non-potable water, energy and nutrients recovered from wastewater.
🚌 Recycling of vehicle components
The most common and visible problems associated with vehicle use and transportation in cities are road accidents, air pollution, or traffic congestion. However, vehicles also present a problem at the end of their life. They continue to take up space in landfill (although sometimes in a compacted form), and even if fossil fuel vehicles are phased out, the shift to electric vehicles in the short term could lead to more internal combustion engine vehicles being scrapped, and to a mountain of battery waste in the longer term.
High-value reuse, and recycling of vehicles and their components, is key to a sustainable future of mobility. When reuse is not an option, advanced recycling technologies can extract valuable raw materials, such as lithium and cobalt, before batteries are disposed of. This would not only reduce the burden on incinerators and landfills, but could provide a new, local and circular source of critical materials for the automotive industry.
Although only few initiatives exist at the municipal level to support high-value reuse and recycling of vehicle components, many initiatives are being supported at national level and businesses are taking the lead in implementing pilot projects across Europe. In the future, local governments could support the recycling of materials by implementing environmental standards for pollution reduction, dismantling, crushing and shredding of vehicles, as well as financial incentives (such as tax rebates and subsidies.) for remanufacturing of cars and part recovery. Alternatively, cities could ban the landfilling of scrap metals and batteries without any previous treatment. Collaboration and engagement with local businesses can help local governments to accelerate research and disseminate knowledge about circular economy approaches to end-of-life vehicle management.
🏢 Disassembly, selective deconstruction and demolition of buildings and infrastructure
Buildings and infrastructures often include many types of components and materials used in ways that make disassembly or repurposing difficult. Some of the barriers can be solved by integrating circular concepts over the entire lifecycle of buildings and infrastructures. Flexible and modular design facilitates repurposing in response to changing needs over the life of a building and supports lifetime extension, as modular constructions are often easier to renovate. Design for disassembly (DfD) enables deconstruction instead of demolition at the end of life and recovery of high value components and materials such as doors, flooring, windows and other elements before demolition. Selective demolition, finally, allows to retain the structural integrity of a building while refurbishing it for new uses. These practices not only increase the material reused and value recovered at the end-of-life of buildings, but are often labour-intensive, creating more jobs than conventional demolition. As such, they can spur local innovation and industry, preserve local character and heritage of buildings, while reducing landfill costs and limiting the need for virgin and often carbon-intensive materials.
City governments can promote the adoption of these practices by providing locally appropriate guidance on flexible and modular design, design for disassembly and selective demolition, and including these principles in their procurement guidelines. They can also enable such practices through end-of-life standards and regulation. Additionally, they can undertake a cost-benefit analysis of deconstruction, building material reuse and DfD in the city compared to demolition and new build. This type of analysis can encourage circular approaches and help cities set targets for construction and demolition, waste minimisation and material reuse in their plans, as well as standardise design for modularity and disassembly. Finally, cities can create enabling conditions for the upscaling of such solutions by supporting digital tools such as material passports and Building Information Modelling (BIM).
For these strategies to be successful, the city can take an active role in awareness building and demonstrating circular approaches in city owned buildings. It is also important to involve relevant stakeholders in the planning and implementation of building deconstruction and disassembly. Cities need to involve and support collaboration among representatives of their planning and construction departments, and representatives of property developers, construction companies, neighbourhood groups, deconstruction companies, and recycling and waste management companies.