Catalytic and noncatalytic oxidations of diluted (0.5 g/L) aqueous azo dye (Orange II) solutions were performed at temperatures from 180 to 240℃ and oxygen partial pressure of 10 bar. The catalyst consisted of alumina and copper and zinc oxides.Dye-decay curves indicate that nearly complete removal of Orange II was achieved after 10 mm at 240℃ in experiments without the catalyst while only about 3 min was needed in the presence of the catalyst at 180℃. The TOC removal rates were found lowerthan those of the dye, thus implying the formation of intermediate products that are more resistant to further oxidation to carbon dioxide. On the basis of concentration-time behavior and the intermediate products identified, it is concluded that bothcatalytic and noncatalytic oxidations of Orange II obey a parallel consecutive reaction pathway involving free radicals. Aerobic biodegradability of Orange II solutions treated by catalytic and noncatalytic oxidation processes increases with time. Theratio of BOD{sub}5/COD vs temperature exhibited a slight maximum at about 200℃ in the case of noncatalytic oxidation. The results of this investigation indicate that intermediate product distribution plays a dominant role in biodegradability: thesolutions treated by catalytic oxidation were found to be more amenable to aerobic biodegradation, simply because smaller quantities of intermediate products were formed in this process.
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