The metropolitan area of Barcelona is of high residential intensity (more than 5,000 inhabitants/km2), generating a large quantity of waste on a daily basis. This waste comprises approximately 36% organic matter, which by means of separate waste collection is less contaminated by other impurities. For this reason the city would be a perfect location for the use of anaerobic digestion as a system to dispose of organic waste. This would enable the city not only to produce clean energy, but it would also be able to reduce the odours involved in treating such a large quantity of waste.