At first glance a bus in Lille, northern France, is just like any other. It is not running later, or with fewer seats. It is not slower, either, but there is one big difference: it runs on biogas. This is a natural gas produced by the fermentation of organic animal or vegetable matter.Lille has France’s only biogas fuel facility, and Europe’s biggest. Organic refuse represents around a quarter of all household waste. It is collected and brought to a special centre where it is digested in reactors that artificially reproduce the rotting and fermentation process that normally happens in the open air. Project manager Pierre Hirtzberger explained: “All of the organic matter that arrives here is pulped, prepared and then pushed into three digesters – which are closed volumes – where the bacteria works at turning the matter into biogas. So the degradation is natural and all we are doing is reproducing, in an accelerated process and in a closed area, something that normally takes place naturally in the environment.” Opposite the centre is a bus station where other official vehicles can also come to fuel up with biogas at prices equivalent to diesel. It is a promising experiment, and the city of Lille is thinking about applying it elsewhere. “We hope very soon to be able to inject this biogas into the natural gas pipelines since, actually, our biogas once purified is a clone of natural gas which can totally substitute for all natural gas usage whether it be for fuel for transport, or heating,” adds Hirtzberger. Half of the world’s population lives in cities where pollution is extremely heavy. The world’s urban population will be five billion strong in 20 years, underlining the importance of such initiatives.