Performance of TiO2/UV-LED-Based Processes for Degradation of Pharmaceuticals: Effect of Matrix Composition and Process Variables

Abstract

Ultra-violet light-emitting diode (UV-LED)-based processes for water treatment have shown the potential to surpass the hurdles that prevent the adoption of photocatalysis at a large scale due to UV-LEDs’ unique features and design flexibility. In this work, the degradation of five EU Watch List 2020/1161 pharmaceutical compounds was comprehensively investigated. Initially, the UV-A and UV-C photolytic and photocatalytic degradation of individual compounds and their mixtures were explored. A design of experiments (DoE) approach was used to quantify the effects of numerous variables on the compounds’ degradation rate constant, total organic carbon abatement, and toxicity. The reaction mechanisms of UV-A photocatalysis were investigated by adding different radical scavengers to the mix. The influence of the initial pH was tested and a second DoE helped evaluate the impact of matrix constituents on degradation rates during UV-A photocatalysis. The results showed that each compound had widely different responses to each treatment/scenario, meaning that the optimized design will depend on matrix composition, target pollutant reactivity, and required effluent standards. Each situation should be analyzed individually with care. The levels of the electrical energy per order are still unfeasible for practical applications, but LEDs of lower wavelengths (UV-C) are now approaching UV-A performance levels.

Evaluation of the Degradation Performance of Pharmaceuticals in Environmental Water by Multi-wavelength UV Irradiation and the Estimation of their Degradation Pathways

“…However, they did not investigate which wavelength is favorable in the UV-C and did not attempt to compare the results of UV combined irradiation to the degradation [17]. For the matrices' effect on the degradation efficiencies of pharmaceuticals in water, Bertagna Silva et al [19] also used UV-A and UV-C with TiO 2 catalytic reaction, and UV-A photocatalysis was more effective than those in UV-C. Also, UV-C photocatalytic reaction was hindered by the screening effect of the catalyst and low concentration of matrices in tap water such as bicarbonate and nitrate ions. Also, it is reported that pharmaceutical degradation efficiency was suppressed in the wastewater effluent due to the presence of NO 3 − and humic acid compared to pure water using UV-LED combined with TiO 2 and/or chlorine [17,18].…”