Degradation of ronidazole by electrochemically simultaneously generated persulfate and ferrous ions

Nitroimidazoles are found in pharmaceuticals and personal care products (PPCPs) and, when discharged into the environment, have adverse effects on human health and survival. Advanced oxidation technologies (AOTs) based on persulfate (PS) can rapidly and efficiently degrade organic pollutants via strong oxidizing radicals under activation conditions. This study investigated the degradation of ronidazole (RNZ) by indirect electrolytic generation of PS and its activator, ferrous ion (Fe²⁺). An electrochemical system was developed, with a high concentration of PS generated at the anode while the activator Fe²⁺ was produced at the cathode. It showed that ammonium polyphosphate (APP) could effectively promote the electrolysis of PS. A high current efficiency (88%) at the anode could be obtained after 180 min at a high current density (300 mA cm^-2). However, Fe²⁺ was inhibited at the cathode due to material control. The degradation of RNZ in the Fe²⁺/PS system generated from the electrochemical system was also explored. Increasing PS concentration and Fe²⁺/PS ratio were beneficial to the RNZ degradation. In homogeneous reactions, the degradation efficiency of RNZ could be improved by decreasing the Fe²⁺ addition rate through a peristaltic pump. Five intermediates were also detected and the degradation pathways were proposed. These findings provide a new method and mechanism for rapid and efficient degradation of RNZ.