In this work the degradation of aqueous solutions of reactive azo-dyes is reported using a combined reductive/advanced oxidative process based in the H2O2/zero-valent iron system. At optimized experimental conditions (pH 7, H2O2 100 mg L-1, iron 7 g L-1) and using a continuous system containing commercial iron wool, the process afforded almost total discolorization of aqueous solutions of three reactive azo-dyes (reactive orange 16, reactive black 5 and brilliant yellow 3G-P) at a hydraulic retention time of 2.5 min. At these conditions the hydrogen peroxide is almost totally consumed while the released total soluble iron reaches a concentration compatible with the current Brazilian legislation (15 mg L-1).

The toxic character of organochloride compounds, their habitual presence in many industrial effluents, and mainly the low efficiency of the current remediation processes, are important aspects that have been promoted to study new degrading technologies. Among the great number of new physical and chemical alternatives, the photochemical and electrochemical processes have been played an important role, mainly due to their high degradation capacity through relatively low-cost procedures. In these contexts biological processes, the use of white-rot fungi, or even ligninolytic enzymes produced from them, are also very promising alternatives. However, the necessity of long reaction time and the high cost of the enzyme production process are some of the drawbacks that difficult the definitive consolidation of these processes.