Valorizing Cr(III) in a Microwave-Assisted Fenton-like System for Sustainable Dye Degradation and Resource-Efficient Wastewater Treatment

Abstract

One of the major environmental challenges today is the effective removal of synthetic dyes from industrial wastewater. The current study developed a Fenton-like oxidation system mediated by Cr(III) and assisted by microwave radiation at 2.45 GHz to rapidly degrade Rhodamine B (RhB). The process achieved 98% RhB degradation in 90 s under ideal batch conditions, which included a pH of 6, 0.5 mM Cr(III), 19.4 mM H₂O₂, 0.07 mM RhB, and 520 W of microwave power. Total organic carbon analysis indicated that the system achieved 55% mineralization of RhB. The hydroxyl radical was identified by fluorescence spectroscopy as the primary reactive oxygen species in this process, and UV–visible studies examined degradation kinetics. Major intermediates, including oxalic acid, methanediol, and phthalic acid, were identified by GC–MS/MS. In comparison to RhB, toxicity evaluations using the EPA’s TEST software revealed that more than 80% of the degradation products were less toxic, nonbioaccumulative, and nonmutagenic. The process capitalizes on the circular reuse of Cr(III), a common industrial waste component, as a catalytic agent. Microwave irradiation improved reaction kinetics, expanded the pH range, and lowered energy input. Additionally, transient Cr(VI) formation provided a secondary catalytic cycle without persistent toxicity. Although moderate levels of Cr(VI) were observed after multiple reuse cycles (25 mg L^–1), these can be mitigated through post-treatment reduction, ensuring compliance with discharge regulations. These results position the Cr(III)-MW-Fenton system as a rapid, energy-efficient, and environmentally safe method for sustainable wastewater treatment.