Pretreatment of textile dye carriers with ozonation and enhanced ozonation

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, the 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 been measured throughout the ozonation process. These have been used to determine k_COD, 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 carrier (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 COD₀).