Hydrogen peroxide enhanced Cu(II)/peroxymonosulfate system for naproxen degradation in natural water matrix and simultaneously reduced the formation potential of halogenated by-products

The susceptibility to the natural water matrix and the risk-generating halogenated by-products in the Cu(II)/peroxymonosulfate system heavily restricted its practical application. This study first demonstrated hydrogen peroxide (H2O2) could remarkably improve the anti-interference capacity of the Cu(II)/peroxymonosulfate system in the natural water matrix through promoting the copper species cycle [Cu(II)/Cu(I)]. A complete naproxen (NPX) removal was achieved at pH 10.0 for 180 s with the H2O2/Cu(II)/peroxymonosulfate system, and the degradation rate of NPX was 28 times greater than its counterpart without H2O2·H2O2 functioned as an electron donor to reduce Cu(II) to Cu(I), while the formed Cu(I) preferentially interacting with peroxymonosulfate to generate reactive species. Several reactive species, including Cu(III), •OH and SO4•−, participated in NPX degradation, while Cu(III) primarily contributed to NPX abatement. The NPX abatement in the H2O2/Cu(II)/peroxymonosulfate system was strongly pH-dependent, with weakly alkaline circumstances being more beneficial to its removal. Additionally, Cl−, H2PO42− and humic acid in the natural water matrix had the slight impact on NPX elimination with the H2O2/Cu(II)/peroxymonosulfate system, whereas H2PO42− and humic acid strongly suppressed NPX elimination in the Cu(II)/peroxymonosulfate system. Furthermore, the generation of halogenated by-products could be suppressed in treating halide-containing wastewater with the H2O2/Cu(II)/peroxymonosulfate system. To sum up, this research offered a new strategy to strengthen the anti-interference capacity of the Cu(II)/peroxymonosulfate system and simultaneously inhibiting halogenated by-product production. The finding should be important for studying the synergistic effect of dual oxidants in treating Cu(II)-containing wastewater.