Incinerator ash is made up of the particles that are left over after waste is burned in an incinerator. Waste plants that use incineration burn a wide range of municipal wastes and can contain glass, brick, rubble, sand, grit, metal, stone, concrete, ceramics and fused clinker as well as combusted products such as ash and slag.
The ash removed from the furnace, and large objects, such as stones, bricks and metals are screened out and are recycled where possible. The remaining ash must then be characterized by the plant operator as either hazardous or non-hazardous and taken off site. Non-hazardous waste can be processed into a secondary aggregate and used in cement-bound materials. Hazardous waste must be disposed of in a hazardous waste landfill or go for further treatment.
The most likely reason for incinerator ash to be classified as hazardous is excessive levels of lead, copper and nickel. These metals can be toxic to plants, invertebrates and fish if significant amounts get onto land or into waterways surrounding the industrial plant.