Ozonation of Spent Reactive Dye-Baths: Effect of HCO3-/CO32- Alkalinity

Abstract

The effect of carbonate and bicarbonate alkalinity (soda ash buffer as 5,180 mg/L HCO3- alkalinity at pH 7 and as 5,100 mg/L CO32- alkalinity at pH 12) on the ozonation of reactive vinylsulphone dyestuffs in a simulated spent dye-bath has been studied at varying pHs. Adsorbable organic halogen (AOX) formation due to the high chloride content of the effluent and detoxification, which was evaluated in terms of the relative toxicity index Itox determined from the ED50 values for the marine photobacteria Vibrio fischeri, were also evaluated. Highest total organic carbon (56%), chemical oxygen demand (44%), and UV254 (77%) removals were achieved at pH 7 in the presence of HCO3- alkalinity. The fastest decolorization was observed for the case pH 2, the first order decolorization rate constant found as k620=0.16min-1, closely followed by the pH 12 case with soda ash (k620=0.12min-1) case. No positive correlation was evident between AOX, whose maximum value (=1.3 mg/L) appeared after 40 min ozonation at pH 7 and ...