Degradative removal of diclofenac from wastewater - Statistical and analytical approaches to understand degradation pathways

In environmental management area, quality of water is a major growing concern with the emerging contaminants such as pesticides and pharmaceuticals likely to be present at low concentrations in water bodies, thereby potentially harming the ecosystem and human health. Diclofenac (DCF), a commonly used drug, has been found in wastewater, surface water, and drinking water sources, whose elimination can be a challenge issue. This study investigates the elimination of DCF by the photochemical method from aqueous media using short-wavelength radiation and hydrogen peroxide. A statistical approach is used to optimize and evaluate the effects of experimental parameters on the degradation of DCF. A quadratic model was proposed to predict the response to variations in three key parameters viz., initial DCF concentration, pH of the solution, and H₂O₂ concentration. The suggested model shows a high coefficient of determination (R² = 0.9961), indicating that observed data is replicated by modelled data. The findings suggest that pH of the solution is the most significant factor affecting the degradation process. Furthermore, a strong interaction between initial concentrations of DCF and hydrogen peroxide is observed. Complete degradation of DCF is achieved within 90 min under the optimal conditions (pH = 4, [DCF]₀ = 20 mg L⁻¹, and [hydrogen peroxide]₀ = 600 mg L⁻¹). This is the first of its kind of study to identify the reaction intermediates using the solid phase extraction (SPE), a pre-concentration step via evaporation with a gentle stream of nitrogen, and direct infusion high-resolution mass spectrometry (DI-HRMS) to detect trace level reaction intermediates. The study follows the United Nations SDGs # 7 program dealing with clean water production. The possible degradation pathways of DCF are proposed.