With a population of nearly 20 million and counting, Sao Paolo is the largest city in Brazil and the eighth largest in the world. And as its population grows, so too does its waste.  

For nearly three decades, the huge Bandeirantes landfill site took half of Sao Paulo's rubbish. But now the site has been grassed over and given a new lease of life: as a source of power for the city.

The Landfill Gas to Energy Project based at Bandeirantes collects gases such as methane, released by decomposing rubbish, and turns them into biogas, which is used to generate electricity.

Since the project started in 2004, it is estimated that it has prevented the net release of 7.4 million tonnes of greenhouse gases.