By Pete Harrison and Peter Henderson
"These are the three giant stomachs of Lille."
Amid the hum of machinery and warm odour of putrefying autumn leaves, official Pierre Hirtzberger is explaining how three giant fermenters can convert household food waste, trimmings from parks and gardens and the slops from school and hospital canteens into enough methane gas to power about a third of the buses in the French city.
"The process is exactly the same as in the stomach of a cow," he said, gesturing towards three biodigesters which each hold 20 000 cubic metres of rotting liquefied waste.
Much of it will just be plain boring "The objective is to fuel 100 of Lille's buses on this biogas, out of a total fleet of 350," Hirtzberger, head of the city's urban waste research and development, told Reuters.
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From San Francisco to Malmo, Sweden, cities around the globe are preparing for a new imperative: to accommodate the mass of world population growth and thrive, without further accelerating the release of carbon dioxide that threatens their existence.
With half the world's population already living in cities and the urban population projected to reach almost five billion by 2030, it is not just growth that puts them in the front line of climate change.
Even if populations escaping drought migrate to urban centres, the fact that 60 percent of the world's 39 largest metropolises are located in coastal areas puts the cities themselves at risk in future centuries, from rising seas.
Unsold sandwiches, cavity insulation
'Potentially, one could run the entire bus system with biogas' Sunshine, tech creativity and a clued-in population help widen the range of options for places like San Francisco - the first city to make it a crime not to compost food and waste in city bins, in a bid to cut landfill use to zero.
Plenty of money on top of abundant sun are allowing Abu Dhabi to showcase a futuristic eco-city: Masdar City is a vision of solar panels powering pilotless taxis and trams and feeding desalinated water to citizens and its verdant palms.
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