URBAN - Urban metabolism for the urban century

Like organisms, cities need energy, water, and nutrients, and they need to dispose of wastes and byproducts in ways that are viable and sustainable over the long run. This notion of "urban metabolism" is a model for looking systematically at the resources that flow into cities and the wastes and emissions that flow out from them-to understand the environmental impacts of cities and to highlight opportunities for efficiencies, improvements, and transformation.

http://phys.org/news/2013-01-urban-metabolism-century.htm