Trash can be burned at very high temperatures in incinerators (some of which are designed to also generate electricity), but in some facilities, fuel oil must be added to the mix for more complete combustion. In modern facilities, cleaning systems remove particulates, sulfur, and nitrogen pollutants, as well as toxic pollutants like mercury and dioxins. The ash is considered toxic waste and must be buried in the hazardous waste landfills. Municipal solid waste, medical waste, and some hazardous waste are incinerated in the United States.