Pretreatment of Textile Dye Carriers with Ozonation and Enhanced Ozonation

Abstract

The chemical treatability of a nonbiodegradable textile dye carrier by single ozonation and ozonation enhanced by ferrous iron salt (FeSO4 · 7H2O) and granular activated carbon (GAC) addition has been reported. First, the single effects of Fe2+ and Fe3+ salts (100–1,000 mg L-1 at pH = 11) and GAC (1–10 g L-1 at pH = 3) addition have been examined to explain their effects in combination with ozone. Thereafter, t he investigated pollutant has been subjected to oxidative treatment via direct ozonation at pH = 3 (the natural pH of carrier added textile dye-baths) to reduce its chemical oxygen demand (COD) and thereby to improve its biodegradability in terms of the 5-day biochemical oxygen demand (BOD5), which is a useful sum parameter for biological treatability evaluation. A kinetic study was also conducted in which time-dependent changes in COD as well as in outlet partial ozone pressure have b een measured throughout the ozonation process. These have been used to determine kCOD, the bimolecular reaction rate constant for COD abatement that has been found as 81 M-1 min-1 . Finally, it could established that the addition of only 1 mM (56 mg L-1) Fe2+ considerably enhanced COD abatement, speculatively by acting as a redox catalyst, whereas the effect of GAC was rather additive. The biodegradability of the textile dye c arrier (initial BOD5 ≈ 0) increased to 70, 109, and 140 mg L-1 after oxidative treatment with O3, Fe(II)/O3, and GAC/O3, respectively, supporting the possibility of chemical pretreatment with enhanced ozonation process at reasonable ozone doses (0.7 mgO3 mg L -1 CODo).