Waste that cannot be reduced, reused, or recycled can be used for energy recovery. Modern waste-to-energy plants handle a waste problem and produce electricity and heat to nearby cities. The best and most modern systems work with an energy efficiency of nearly 100 percent through advanced technology. The impact of these plants on the local environment is minimal through the advanced use of filters and other technologies to such an extent that they can even be located in the centre of large cities, as is seen in Copenhagen, Denmark.