Degradation of wastewater from terephthalic acid manufacturing process by ozonation catalyzed with Fe2+, H2O2 and UV light: Direct versus indirect ozonation reactions

In this work, terephthalic acid wastewater containing a very high chemical oxygen demand (COD = (35.0 +/- 1.8) g L-1) and possessing a dark reddish brown color (platinum cobalt unit = 1400) with a pH 8.5 discharged from a terephthalic acid manufacturing plant was treated by ozonation catalyzed with Fe2+, H2O2 and UV light. To arrive at an efficient Fe2+, H2O2 and UV catalyzed ozone system (O-3/H2O2/Fe2+/UV), the individual methods, viz., ozone alone (O-3), UV assisted ozonation (O-3/UV), H2O2 and UV assisted ozonation (O-3/H2O2/UV), and Fe2+ catalyzed ozonation (O-3/Fe2+) were studied to evaluate their effectiveness in decomposing the COD concentration and the three major toxic organic components, namely, terephthalic acid (TPA), isophthalic acid (IPA) and benzoic acid (BA) present in the wastewater. The first-order kinetic rate constant for the COD removal process was evaluated for comparison. The O-3/H2O2/Fe2+/UV combined catalytic system showed highest oxidizing power amongst the tested methods with better COD degradation degree as high as 90% at 240 min, and TPA, IPA and BA present in TPA wastewater completely destroyed within 150 min. In order to assess the contribution to the overall COD elimination by the direct molecular oxidation and the indirect free radical oxidation, degradation studies were carried out for all the five optimized systems with tert-butyl alcohol as the (OH)-O-center dot scavenger. Individual contributions of the two pathways to the overall global oxidation were quantified in terms of the process rate constant: and the performance evaluation of the different ozonation systems was analyzed. Finally, the potentiality of the O-3/H2O2/Fe2+/UV process as a promising pre-treatment stage to obtain more easily biodegradable molecules with lower toxicity for the subsequent anaerobic digestion of the TPA wastewater was demonstrated. (C) 2009 Elsevier B.V. All rights reserved.