Application of Photocatalytic Falling Film Reactor to Elucidate the Degradation Pathways of Pharmaceutical Diclofenac and Ibuprofen in Aqueous Solutions

Ali Mahyar,Khalid M. Omer,Siegfried Mueller,Kosar Hikmat Hama Aziz,Hans Miessner,Detlev Moeller

doi:10.3390/coatings9080465

Abstract

Diclofenac (DCF) and ibuprofen (IBP) are common pharmaceutical residues that have been detected in the aquatic system. Their presence in the aquatic environment has become an emerging contaminant problem, which has implications for public health. The degradation pathway and identification of transformation products of pharmaceutical residues are crucial to elucidate the environmental fate of photocatalytic decomposition of these pollutants in aqueous media. The degradation process might lead to creation of other possible emerging contaminates. In this study, the degradation of DCF and IBP in aqueous solutions was investigated. To this end, coated TiO2 on a Pilkington Active glass was used as a photocatalyst under UVA illumination, in a planar falling film reactor. Pilkington ActivTM glass was used as a photocatalyst and a falling liquid film generator. Degradation kinetics of both pharmaceuticals followed a pseudo-first-order model. The transformation products of both diclofenac and ibuprofen during the degradation process were detected and identified with gas chromatography–mass spectrometry (GC–MS) and ion chromatography. The results showed that the mineralization rate of both pharmaceuticals through photocatalysis was very low. Low chain carboxylic acids, such as formic, acetic, oxalic, malonic, and succinic acids were the main by-products. A pathway of DCF and IBP degradation was proposed.

Highlights

Pharmaceutical wastes such as anthropogenic contaminants often cannot be removed using conventional wastewater treatment and accumulate in aquatic media [1,2]
Despite the large variety of photocatalysts reported in literature, which showed a capability for decomposing and mineralizing various organic pollutants, the TiO2 anatase/rutile heterostructure as a photocatalyst has been successfully commercialized and its use is widespread
When a semiconductor is illuminated with light of sufficient energy (>band gap energy) it produces highly reactive species like hydroxyl and superoxide radicals, which can cause a photocatalytic degradation of pollutants

Summary

Introduction

Pharmaceutical wastes such as anthropogenic contaminants often cannot be removed using conventional wastewater treatment and accumulate in aquatic media [1,2]. The accumulation of pharmaceuticals in aquatic environment, even in low concentrations, can be harmful for human health and aquatic life, resulting in a serious environmental problem [7,8]. Coatings 2019, 9, 465; doi:10.3390/coatings9080465 www.mdpi.com/journal/coatings (NSAIDs) that have been detected in water environment at low concentrations (ng/L to μg/L) [4,9,10,11]. NSAIDs are considered to be one of the most frequently detected pharmaceuticals in aquatic systems, including surface and ground water [12,13]. Advanced oxidation processes (AOPs) have attracted significant attention in the field of water treatment, due to its high removal efficiency and environmental compatibility [14]. Various AOPs have been successfully applied for environmental remediation [15,16]

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