Hiroshi Yamaguchi*, Eiichi Shibuya*, Naoki Furuno*, Shouichi Suda*, Atsushi Morishige*, Kiyoshi Uyama**, Nakamichi Yamasaki*** and Mamoru Nishioka***

*NKK Corporation
**NKK Plant Engineering Co.
***Faculty of Science, Kochi University

+ Correspondence should be addressed to Hiroshi Yamaguchi
(1-1, Minamiwatarida-cho, Kawasaki-ku, Kawasaki 210 Japan)

Abstract

In order to reduce the toxicity of Municipal Solid Waste Incinerator (MSWI) fly ash containing polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), well-known as highly toxic organic pollutants, fly ash was hydrothermally treated. Under hydrothermal conditions, concentration of PCDDs and PCDFs decreased due to dechlorination reaction. This reaction occurred more effectively with high temperature and the existence of alkaline ingredients and/or methanol in solvent. Even at 373 K, which is relatively lower than the operating temperatures of thermal decomposition technique, the dechlorination reaction took place. PCDDs/PCDFs decomposed almost completely and toxicity of treated ash decreased to 0.03ng-TEQ/g at 573K for 20min with the solvent of 1N NaOH solution and methanol. Estimated activated energy for the reaction, assuming that the whole of PCDDs/PCDFs was one chemical species, was about 13kcal/mol and reaction rate constant k was expressed as k = 2.27X104exp{-13.2/ (RT) }.

Key words: municipal solid waste incinerator, fly ash, PCDDs, PCDFs, hydrothermal treatment, decomposition, dechlorination