Multi-faceted rotating arc discharge plasma for efficient textile dye removal in wastewater: Performance, energy efficiency, and degradation pathways

Synthetic dyes in textile wastewater pose severe environmental risks due to their toxicity and resistance to biodegradation. This study investigates a multi-faceted rotating arc discharge (MFRAD) plasma system for dye-contaminated wastewater treatment, focusing on performance, energy efficiency, energy cost estimation, and degradation mechanisms. Methyl Orange (MO) and Crystal Violet (CV), including their binary mixture, were selected as representative pollutants commonly found in textile effluents. Rapid decolorization was achieved, with removal efficiencies of 95.8% for CV, 97.6% for MO, and 88.5% for the mixed solution within 60 min. Total organic carbon reduction of up to 90–95% confirmed substantial mineralization. The maximum energy efficiency reached 16.45 g/kWh, corresponding to the lowest energy cost of 0.255 $/m 3 for CV at 15 min. Across all tested conditions, the electrical energy cost ranged from 0.255 to 1.036 $/m 3 of treated wastewater. Reactive species analysis using scavengers demonstrated the dominant roles of ozone and hydroxyl radicals in CV and mixed dye degradation, while hydrogen peroxide contributed significantly to MO removal. High-Performance Liquid Chromatography–Mass Spectrometry (HPLC-MS) analysis identified key intermediates and revealed degradation pathways involving demethylation, hydroxylation, azo bond cleavage, and aromatic ring opening. Plasma treatment also resulted in increased conductivity and decreased pH due to the formation of nitrate and nitrite species, reflecting the contribution of reactive nitrogen pathways. The results demonstrate that MFRAD plasma provides an effective, energy-efficient approach for recalcitrant dye removal, with promising potential for industrial wastewater treatment, particularly for complex dye mixtures.