The application of thermal plasma to waste treatment may be a possible method for treating various kinds of hazardous waste through volume reduction and detoxification. The vitrified slag's safety test was performed. The leaching tests of the solution of pH 2 to 6 were examined. The leaching solution was analyzed by ICP-MS and by its conductivity. At pH 4, the leaching limit was satisfactory. The concentration of non-organic material in the sludge was not enough to cause vitrification. The properties of the slag were affected by differences in the cooling methods. The water-cooled slag showed good elution proof. The slag vitrified by thermal plasma was non-hazardous and was not contaminated with heavy metals. This slag exhibited sufficient strength to be utilized, e.g., as a fill for a roadbed material, as a component in asphalt mixtures, in concrete structures, and in secondary products interlocking materials of blocks.