One of the largest waste water treatment centres in Holland is Waternet, which alone serves the city of Amsterdam, i.e. 1 million citizens. Every year, through anaerobic digestion, it obtains 11 million m3 of biogas, which is used to generate electricity and produce biomethane. The heat produced by the cogeneration plant and by the incinerator which burns the residual sludge is used for the district heating system of the city, whereas the biomethane is made available to all the population by means of the neighbouring service station.