City-Level Decoupling-Full Report

City-Level Decoupling: Urban resource flows and the governance of infrastructure transitions

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5.3.3. Re-use wastes

'Biomimetic systems' are closed-loop lifecycles where outputs and by-products become inputs for something else, where 'waste equals food'. 97 Achieving a circular metabolism at the scale of the city is challenging due to the many different resources and wastes that circulate through it, so it requires connecting complex webs of interdependency. This may be where nature has the most to teach; everything alive is part of multiple complex webs of predator/prey, waste/ fertilizer, parasite/host, symbiant, and scavenger, only a few of which have precise equivalents in modern cities. 98 Biomimicry or biomimetic design provide the potential for buildings and cities to act “…as closed-loop ecosystems that, like a forest or savanna, draw their energy from the elements and produce no net waste - and perhaps even improve the surrounding environment." 99 'Recycling' runs the risk of being limited to the separation and collection of household packaging wastes, but can include considering all 'waste' generated by urban production and consumption activities as valuable inputs to useful processes. Even the built fabric of the city has potential to be re-used as buildings are retrofitted instead of being replaced, salvaged bricks and other materials from demolitions are re-used as inputs into construction, and rubble is processed for use in road surfacing and other projects. Although an emphasis on recycling is perhaps more applicable to saturated cities in

Human settlements have always generated waste. The metabolism of a typical modern city can be described as 'linear' in that it extracts resources from beyond its boundaries, makes use of them within its boundaries to support urban activities, and then deposits the resulting wastes in high concentrations back onto the external environment. 92 In this way, the modern city’s metabolism is fundamentally different to the circular metabolismthat of a natural ecosystem which produces no waste and survives off its immediate environment. 93 Modern cities require a continuous supply of resource inputs and an unlimited capacity of nature to absorb the concentrated wastes they produce. Returning to forms of more circular, location- specific urban metabolisms is increasingly recognized as necessary if cities are to survive a future of resource limitations and climate uncertainty. 94 Ravetz explains that “...a city or region which contains its own eco-cycles would tend to be less vulnerable and damaging, or more ’sustainable'....” 95 Growing cities have traditionally expanded the boundaries of the hinterlands on which they depend for survival as a means of accommodating growth, but green cities show signs of a trend toward re-localisation and attempts to create more autonomous circular or 'closed-loop' metabolisms. 96

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