Effect of dye auxiliaries on the kinetics of advanced oxidation UV/H 2 O 2 of Acid Orange 7 (AO7)

BACKGROUND: The effect of four dye‐auxiliary chemicals, typically employed in acid dyeing, on the performance of UV/H 2 O 2 decolouration of the model non‐biodegradable dye C.I. Acid Orange 7 (AO7) was investigated. The initial concentration of AO7 was 0.150 g L −1 , while the concentration of the auxiliary compounds (NaCl, Na 2 SO 4 , Na 2 CO 3 and CH 3 COOH) was varied in the range 1–10 g L −1 . RESULTS: The negative influence of the presence of the dye‐auxiliary compounds studied on the decolouration rate of AO7 decreased in the following order: CH 3 COOH > Na 2 SO 4 > NaCl > Na 2 CO 3 . Results were quantified in terms of the observed kinetic rate constant, k obs (s −1 ), of AO7 decolouration as a function of dye auxiliary chemical concentration. The decolouration rate of AO7 decreased as the concentration of dye‐auxiliary compound increased in the range 1–5 g L −1 , while higher concentrations had a minor effect. Upon addition of 5 g L −1 of CH 3 COOH, NaCl and Na 2 SO 4 , the kinetic rate constant decreased by 39%, 30% and 12%, respectively. CONCLUSIONS: It was concluded that the presence of NaCl, Na 2 SO 4 and above all of CH 3 COOH should be considered in the design of the treatment of real dye‐bath effluents by UV/H 2 O 2 . Copyright © 2008 Society of Chemical Industry