Understanding the Assisting Role of PMS in Low Current Electrochemical Processes for Degradation of Antibiotics

Electro-activated persulfate has displayed good performance in the oxidation of antibiotic pollutants in wastewater. However, high power consumption and the introduction of excessive sulfate ions hinder the application of this technology. This research provided a novel strategy for the applications of small power supply and simple devices in antibiotic pollutant treatment. It has been confirmed that sulfate radical ( SO4 center dot-) could be generated at the boron-doped diamond (BDD) anode in both low and high current conditions. This study proposed a novel low current density electrochemical technology assisted by peroxymonosulfate (PMS) for the degradation of antibiotics. Adding 1 mg/L PMS at current density as low as 1.25 mA/cm(2) increased the electro-oxidation rates of ciprofloxacin 5-fold from 1.92 +/- 0.67 h(-1)to 9.70 +/- 0.10 h(-1). According to the Butler-Volmer equation, the introduction of PMS changed the mechanism of electrode reactions, thermodynamic properties of the system therefore changed. The electron spin resonance (ESR) test has confirmed that hydroxyl radical (center dot OH) SO4 center dot-, and singlet oxygen (O-1(2)) are all generated in low current electrochemical systems. Quenching experiments illustrate that both radical and nonradical ways play essential roles in electro-oxidation processes. The contribution rates of center dot OH, SO4 center dot- and O-1(2) were 15.6%, 33.2%, and 40.5%, respectively. An oxidation peak was observed in cyclic voltammetry (CV) around +1.2 V, indicating that PMS electrolyte may drive oxidation at this potential. Besides, the reaction pathways of ciprofloxacin were speculated. Four transformation pathways including stepwise piperazine ring cleavage, OH/F substitution, cyclopropane ring cleavage, and decarboxylation were proposed for ciprofloxacin degradation.

Automated summary

This study proposed a novel low current density electrochemical technology assisted by peroxymonosulfate (PMS) for the degradation of antibiotics. It has been confirmed that sulfate radical ( SO4 center dot-) could be generated at the boron-doped diamond (BDD) anode in both low and high current conditions. The reaction pathways of ciprofloxacin were also speculated.