Dioxins are eliminated from soot by conversion into oil and water. A gas stream of smoke and dioxin-entraining ash is passed through a curtain of water in a separator to separate the dioxin-entraining ash from the gas stream. The ash-water mixture is separated by a centrifuge, the separated ash is mixed with water and the mixture is again separated by a centrifuge into ash and an emulsion-like oil-water mixture in which dioxins are dissolved. This separated ash is also washed with water and the various wash waters and the dioxin-containing oil-water mixture are admixed and electrolyzed in a primary electrolyzer equipped with a carbon anode and a stainless steel cathode to decompose the dioxin components. The remaining aqueous liquid is electrolyzed in a secondary electrolyzer with an aluminum anode and a stainless steel cathode to generate hydrogen by electrolysis of water and metal hydroxides by electrolysis of aluminum.