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

Danilo Bertagna Silva,Sandra Babić,Bruna Babić,Gianluigi Buttiglieri,Danijela Ašperger

doi:10.3390/nano12020295

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.

Highlights

Published: 17 January 2022Water scarcity across the globe demands an effort to find efficient and sustainable treatments that will allow its safe reuse [1,2]
The degradation depends on: (1) the types and amount of available oxidative species; (2) the pharmaceutical active compounds (PhACs)’ respective reactivity with each of the generated oxidative species [5]; (3) the interaction between the PhACs and the catalyst surface [56]; (4) the ionic state of each PhAC in solution; (5) PhAC absorption spectrum and quantum yield for a given wavelength [57,58]
A design of experiments approach involving multiple parameters was able to quantify the significance of different individual and combined effects on kinetic rate constants, effluents’ total organic carbon abatement, and toxicity levels

Summary

Introduction

Published: 17 January 2022Water scarcity across the globe demands an effort to find efficient and sustainable treatments that will allow its safe reuse [1,2]. PhACs may end up in waterbodies, persist in the environment and bio-accumulate, causing diverse sorts of endocrine disruptions in aquatic life, even at very small concentrations (ng/L, μg/L) [7,8]. Among possible water treatment solutions, advanced oxidation processes (AOPs) have shown a high degradation potential due to the formation of reactive oxygen species (ROS), especially the hydroxyl radical ( OH), which are able to oxidize persistent pollutants [10,11,12]. These processes are highly energy-demanding [13]. Photocatalysis using TiO2 has been investigated in depth in previous decades due to its capacity for generating radicals in water using only light—be it solar or artificial—but real-life applications have rarely

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