pH-Dependent Ozonation of Diclofenac: Molecular Insights and Implications for Water Quality and Nature-Based Water Reuse Systems

Natalia Villota (), Unai Duoandicoechea and Enzo Valentin Tosi-Zarate
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Natalia Villota: Department of Environmental and Chemical Engineering, Faculty of Engineering Vitoria-Gasteiz, University of the Basque Country UPV/EHU, 01006 Vitoria-Gasteiz, Spain
Unai Duoandicoechea: Department of Environmental and Chemical Engineering, Faculty of Engineering Vitoria-Gasteiz, University of the Basque Country UPV/EHU, 01006 Vitoria-Gasteiz, Spain
Enzo Valentin Tosi-Zarate: Department of Environmental and Chemical Engineering, Faculty of Engineering Vitoria-Gasteiz, University of the Basque Country UPV/EHU, 01006 Vitoria-Gasteiz, Spain

Clean Technol., 2025, vol. 7, issue 2, 1-17

Abstract: Diclofenac (DCF), a widely consumed non-steroidal anti-inflammatory drug, presents significant environmental challenges due to its persistence and toxicity in aquatic ecosystems. This study investigates the pH-dependent ozonation of DCF in aqueous media, focusing on degradation kinetics, transformation pathways, and effects on key water quality indicators. Ozonation experiments were conducted across a broad pH range (2.0–13.0), using a multi-scale analytical approach combining UV/Vis spectroscopy, colorimetry, turbidity, and aromaticity measurements. The results show that pH strongly influences DCF degradation efficiency: acidic conditions favor selective reactions with molecular ozone, while an alkaline pH enhances non-selective oxidation via hydroxyl radicals. Spectroscopic analyses revealed the progressive breakdown of aromatic structures, the transient formation of quinonoid and phenolic intermediates, and eventual mineralization to inorganic by-products such as nitrate. Low-pH conditions also induced turbidity due to precipitation of neutral DCF species. These findings underline the importance of pH control in optimizing ozonation performance and minimizing toxic by-products. Furthermore, this study proposes ozonation as a viable pre-treatment step within Nature-Based Solutions (NBSs), potentially improving the performance of downstream biological systems such as constructed wetlands. The results contribute to the development of integrated and sustainable water treatment strategies for pharmaceutical contaminant removal and water reuse.

Keywords: ozonation; diclofenac degradation; advanced oxidation processes; pH-dependent transformation; pharmaceutical pollutants; water quality (search for similar items in EconPapers)
JEL-codes: Q2 Q3 Q4 Q5 (search for similar items in EconPapers)
Date: 2025
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