Kinetics of decolorization and mineralization of reactive azo dyes in aqueous solution by the UV/H 2O 2 oxidation

Abstract

The photodegradation of three non hydrolysed reactive azo dyes (Reactive red 120, Reactive black 5, Reactive yellow 84) in aqueous solution was investigated in a laboratory-scale batch photoreactor equipped with an immersed low-pressure mercury lamp. Six different doses of hydrogen peroxide, at constant initial concentration of the substrate (100 mg/l) were used. The pseudo-first order rate constants have been calculated from the experimental kinetic curves, for the three azo dyes. These rate constants have extreme values of the order of 0.1 min −1 at a H 2O 2 dose of 24.5 mmol/l. The effectiveness of the UV/H 2O 2 process has been evaluated by the degree mineralization of the total organic carbon (TOC), as a complementary indicator of the treatment efficiencies. Our results confirm the suitability of the UV/H 2O 2 process as a textile wastewater pre-treatment step, once optimum operating conditions and cost effectiveness of the method are established.