Enhanced decolorization and mineralization of Metanil Yellow dye by combined ferrate (VI) and plasma-activated water

Metanil Yellow (MY), a toxic and persistent azo dye, poses significant environmental challenges in wastewater treatment. This study explores the degradation and mineralization of MY using ferrate (Fe (VI)) alone and in combination with plasma-activated water (PAW). Optimal decolorization occurred at pH 7 with a second-order rate constant (kapp) of 93.73 M⁻¹·s⁻¹. An [MY]:[Fe (VI)] molar ratio of 1:8 ensured complete dye removal, while increasing the temperature to 45°C enhanced degradation kinetics (kapp = 193.65 M⁻¹·s⁻¹) with an activation energy of 52.86 kJ/mol. Despite high decolorization, Fe (VI) alone achieved limited mineralization (11–14%), indicating the presence of persistent intermediates. Computational toxicity estimation (USEPA TEST software) confirmed the formation of less toxic degradation products. To improve treatment performance, a hybrid Fe (VI)–PAW system was introduced, significantly enhancing decolorization (up to 95%) and mineralization (up to 35%). The synergistic effect factor (SEF) exceeded 1.0, especially in sequential Fe (VI)–PAW application. These results highlight the potential of the Fe (VI)–PAW process as an efficient and environmentally friendly advanced oxidation strategy for dye-contaminated wastewater.