Comparison of the TOC removal efficiencies of the simultaneous and sequential nZVI/H2O2 processes at various H2O2 doses revealed that the sequential process had higher removal efficiency. Specifically, an approximately 10–15% enhancement in TOC removal efficiency was obtained by application of the sequential nZVI and H2O2 process. It is estimated that the sequential Fenton like reaction is more effective because nZVI is added to the pre-reduced azo dye the azo dye is converted into smaller molecules that are easier to degrade as nZVI is oxidized into Fe2+ and then OH radicals are generated by dosing H2O2.