Abstract
Decomposition and detoxification of 2, 4, 5-trichlorophenoxyacetic acid (2, 4, 5-T) and 2, 4-dichloro-phenoxyacetic acid (2, 4-D) as organochlorinated agricultural chemicals and dioxins in fly ash were examined using supercritical water oxidation (SCWO) . The decomposition efficiencies of chlorinated herbicides were more than 99.99% at the conditions of 600°C, 25 MPa, 30 min and an excess hydrogen peroxide ratio of 1.4 (for 2, 4, 5-T) and 1.1 (for 2, 4-D) . The decomposition products of 2, 4-D for SCWO, supercritical water hydrolysis and pyrolysis at 600°C and 30 min were compared. SCWO did not produce any organic products. On the other hand, phenol and other compounds were formed using supercritical water hydrolysis, and polycyclic aromatic compounds along with phenol and others were generated using pyrolysis. For the decomposition of dioxins with SCWO, the decomposition efficiency of each homologue increased along with increased reaction temperature and pressure. Furthermore, there was the possibility that highly toxic tetra- and penta-chlorinated dioxins re-mained as stable intermediates after treatment. More than 99.999% of all kinds of dioxin homologues were decomposed at 600°C, 25 MPa, 30 min and an excess hydrogen peroxide ratio of 10000.
