Abstract: The present invention relates to a thermal treatment device comprising a primary chamber (204) for receiving waste material (230) to be combusted, the primary chamber having a hearth (207), a transport system (206) arranged for transportation of waste material across the hearth, a mixing chamber (220) in fluid communication with the primary chamber (204); a secondary chamber (208) in fluid communication with the mixing chamber (220), and material introducing means (229) for introducing waste material (230) into the primary chamber, wherein the material introducing means (229) comprises a valve (202) for controlling air flow there-through.