OZONE, HYDROGEN-PEROXIDE OZONE AND UV OZONE TREATMENT OF CHROMIUM-COMPLEX AND COPPER-COMPLEX DYES - DECOLORIZATION AND METAL RELEASE

Metal-complex azo dyes constitute a significant fraction of the dyes used in the textile industry and exhibit properties such as superior light- and wash-fastness. While effluent color is not always regulated, the textile finishing industry often decolorizes wastewater using processes including chemical oxidation. In this study, the use of ozone, hydrogen peroxide/ozone and UV/ozone oxidant systems was examined for treatment of two common metal-complex (premetalized) dyes. Acid Black 52 (chromium) and Direct Blue 80 (copper). Oxidant dosages required for decolorization of these dyes were determined. The effect of bicarbonate alkalinity on the ozonation and the hydrogen peroxide/ozone processes also was examined. Results from analyses using high performance liquid chromatography with pose-column derivatization showed that inorganic copper was readily released during decolorization of Direct Blue 80 using ozonation or advanced oxidation. This release of inorganic copper is significant because it may affect the toxicity of a treated wastewater. The release of chromium from Acid Black 80's ligand structure was examined using ion exchange with strong base anion (SBA) and strong acid cation (SAC) exchange resins. The results indicate that oxidative decolorization did not result in appreciable Cr(III) in solution. Oxidation by ozone or hydrogen peroxide/ozone did cause chromium species to undergo anionic exchange reactions, however whether the resulting chromium was complexed with organic molecules as Cr(III) or whether it existed as an anionic Cr(VI) species (e.g., CrO4-2, HCrO4-, or Cr2O7-2) was not determined conclusively and is currently under examination.