Photolysis and TiO2-catalysed degradation of diclofenac in surface and drinking water using circulating batch photoreactors

Abstract

Environmental context. Diclofenac, a common non-steroidal anti-inflammatory drug, is not completely removed from surface and drinking water by conventional treatment methods. Consequently, this drug is present in the aquatic environment and has been subsequently linked to toxic effects on organisms. We show that photolysis and TiO 2 -catalysed degradation in circulating batch reactors efficiently results in diclofenac removal under a variety of conditions. These photochemical methods thus may lead to more effective water treatment processes.Abstract. The occurrence of diclofenac (DCF) as an emerging pollutant in surface waters and drinking water has been attributed to elevated global consumption and the inability of sewage treatment plants to remove DCF. In this study, DCF spiked drinking water and river water was subjected to photolysis and TiO 2 photocatalytic treatments in a circulating laboratory-scale (immersion-well) and a demonstration-scale loop reactor (Laboclean). The operational parameters for the immersion-well reactor were optimised as follows: TiO 2 P25 loading, 0.1 g L À1 ; natural pH, 6.2; initial concentration, 30 mg L À1 ; water type, distilled water. Complete DCF removal was realised within 15 min under the optimised conditions using the immersion-well reactor. Sunlight-mediated photochemical degradation required a prolonged exposure period of up to 360 min for complete DCF removal. DCF in distilled and drinking water was efficiently degraded in the larger Laboclean reactor. Differences were, however, observed based on their pseudo-first-order rate constants, which implies that the water matrix has an effect on the degradation rate. Six major photoproducts, 2-(8-chloro-9H-carbazol-1-yl)acetic acid, 2-(8-hydroxy-9H-carbazol-1-yl)acetic acid, 2,6-dichloro-N-o-tolylbenzenamine, 2-(phenylamino)benzaldehyde, 1-chloromethyl-9H-carbazole and 1-methyl-9H-carbazole, generated from TiO 2 photocatalysis of DCF were identified by liquid chromatography-mass spectrometry (LCMS) and Fourier transform-ion cyclotron resonance-mass spectrometry (FT-ICR-MS). This work has shown that photocatalytic degradation kinetics of DCF are dependent on both the geometry of the photoreactor and the nature of the water matrices.

Photodegradation of diclofenac in wastewaters

“…4. In agreement with several investigations [6,[22][23][24][25] Carbazole was identified as the main by-product of the DCF photolysis.…”

“…3. Moreover the persistence of the carbazole-1-acetic acid to the direct photolysis was highlighted, as reported by Lekkerkerker-Teunissen et al [21] and Kanakaraju et al [24].…”

Photo-oxidation of three major pharmaceuticals in urban wastewater under artificial and solar irradiations

“…On the one hand, this is much faster than another study conducted on fixed TiO2 and pharmaceuticals initial concentrations of 5 mg/L which needed 50 and 70 h for the complete removal of DCF in wastewater effluent and deionized water, while did not fully degrade CBZ and even IBU, in both waters, after 100 h of experiment [24]. On the other hand, this is much slower than the 30 min observed in distilled water with P25 Aeroxide TiO2 and 30 mg/L DCF initial concentration [84] but his study used a very powerful MP 500W mercury lamp. The degradation profiles were similar in both waters, showing the same global behavior and mechanisms in action, which seemed independent of the matrix containing the target molecules.…”

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

“…Diclofenac (DCF) and ibuprofen (IBP) are highly consumed pharmaceuticals and are typical representatives of analgesic non-steroidal anti-inflammatory pharmaceutical compounds (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].…”