Removal of miconazole from water by O3, UV/H2O2 and electrochemical advanced oxidation: Real-time process monitoring and degradation pathway elucidation

The occurrence of azole drugs in the environment is of growing concern due to their ecological toxicity as well as their potential role in the emergence of drug-resistant fungal strains. In this study, the degradation of miconazole (MCZ), a persistent antifungal agent, was studied using ozonation, photodegradation and electrochemical advanced oxidation processes. The elimination of MCZ was evaluated in deionized water (DIW) as well as simulated wastewater (SWW) matrices. Under optimal conditions, the results for DIW indicate that MCZ is highly degradable by ozonation (pH 3, 41.6 mg L-1 O3 dose, 5 min reaction time) and electrochemical (pH 3, 0.05 M Na2SO4, 10 mA, 180 min reaction time) processes, resulting in 98 % and 94 % removal, respectively. The photodegradation process (2.5 mg L-1 H2O2, 24,000 J m- 2 UV dose) resulted in 80 % removal. Additionally, matrix effects in SWW were observed due to the presence of scavenging species. The ozonation and electro-chemical reactors were coupled with an online liquid chromatography system for automated sampling. By-products, formed due to incomplete oxidation, were elucidated by liquid chromatography in combination with high-resolution mass spectrometry (LC-HRMS). The main degradation routes include hydroxylation, dehalogenation, intramolecular cyclization and imidazole ring-opening mechanisms. Preliminary ecological toxicity estimations revealed the formation of intermediates that were less toxic than MCZ, potentially increasing the biodegradability of the processed waters. Finally, the automated process analytical technology via online sampling from the reactor can provide a diagnostic tool for real-time process monitoring during the advanced treatment of reclaimed waters.