Rapid tetracycline degradation by a hydroxylamine/chloride- enhanced zero-valent copper/peroxydisulfate system under near- neutral conditions

Abstract Limited copper(I) availability constrains peroxydisulfate (PDS) activation by zero-valent copper (Cu⁰). This study evaluates the combined effects of hydroxylamine (HA) and chloride by comparing matched Cu⁰/PDS control systems and relating tetracycline (TC) removal to measured copper(I) concentrations and PDS consumption. At an initial pH of 5.0, TC removal after 10 min was 11.1% without either additive, 63.8% with HA, 23.8% with chloride and 86.2% with both; the combined-system apparent rate constant was 0.2119 min⁻¹. PDS consumption was 6%, 34%, 13% and 54%, respectively. These concurrent trends are consistent with complementary HA-assisted copper(I) regeneration and chloride-mediated stabilization, although they do not directly resolve individual copper(I) complexes or quantify an interaction between the additives. Electron paramagnetic resonance spectroscopy and quenching tests support radical involvement and possible reactive chlorine participation, without establishing copper(III) as the dominant oxidant. TC removal was 68.6% at initial pH 7.0, 77.1% in tap water and 67.7% in surface water. Total organic carbon removal was only 5.7% after 10 min, indicating limited mineralization. Alkaline precipitation and filtration reduced total dissolved copper from 7.16 to 0.673 mg/L. The study links combined-additive enhancement to copper(I) availability and oxidant consumption while identifying mineralization and copper management as limitations requiring further evaluation.