Reactive Pathways, Inorganic-Ion Effects, and Water-Matrix Impacts in Peracetic Acid Activation by an Ordinary Steel-Copper Galvanic Cell for Organic Pollutant Removal

Peracetic acid (PAA) activation by macroscopic galvanic materials offers a low-complexity alternative to soluble-metal dosing and engineered nanocatalysts. This study investigates reactive pathways and water-matrix effects during PAA activation by an ordinary steel-copper galvanic cell using Sunset Yellow FCF (SSY) as a model contaminant. Under the reference conditions ([SSY]0 = 5 mg/L, [PAA]0 = 0.13 mM, natural initial pH ≈ 4.5, 400 rpm), approximately 95% SSY decolorization was observed within 5 min, and decolorization was near complete within 9 min. PAA alone produced no measurable decrease in SSY concentration during the same experimental period, confirming that direct decolorization by unactivated PAA was negligible under the investigated conditions. Cu/PAA alone produced no measurable decrease in SSY absorbance at 482 nm, demonstrating that copper alone did not appreciably activate PAA under the investigated conditions. When considered together with established Fe-Cu galvanic behavior, this result supports a predominantly cathodic role for copper in the coupled system; however, the extent of any copper-induced enhancement of steel dissolution was not quantified. Strong inhibition by TEMPO and ascorbic acid, combined with weaker responses to tert-butanol and nitrobenzene, was consistent with a major contribution from PAA-derived organic-radical chemistry and argued against freely diffusing HO• as the dominant oxidant. Br− markedly promoted SSY chromophore disappearance, whereas NO2−, HCO3−, and CO32− strongly inhibited the process. Without deliberate pH adjustment, final decolorization was approximately 5.5%, 9%, and 43% in Zamzam water, tap water, and seawater, respectively. Adjustment to pH 3 increased decolorization to approximately 86% in Zamzam water and 61% in tap water, whereas seawater remained strongly inhibitory, with approximately 37–38% decolorization. These percentages quantify the loss of absorbance at 482 nm and do not establish complete molecular degradation or mineralization. The results demonstrate that galvanic PAA activation is governed jointly by Fe-mediated activation, reactive-species chemistry, pH/alkalinity, and non-additive water-matrix effects.