Abstract
The focus of this study was to investigate the efficacy of applying boron-doped diamond (BDD) electrodes in an electrochemical advanced oxidation process, for the removal of the target compound diclofenac (DCF) in different water matrices. The reduction of DCF, and at the same time the formation of transformation products (TPs) and inorganic by-products, was investigated as a function of electrode settings and the duration of treatment. Kinetic assessments of DCF and possible TPs derived from data from the literature were performed, based on a serial chromatographic separation with reversed-phase liquid chromatographyfollowed by hydophilic interaction liquid chromatography (RPLC-HILIC system) coupled to ESI-TOF mass spectrometry. The application of the BDD electrode resulted in the complete removal of DCF in deionized water, drinking water and wastewater effluents spiked with DCF. As a function of the applied current density, a variety of TPs appeared, including early stage products, structures after ring opening and highly oxidized small molecules. Both the complexity of the water matrix and the electrode settings had a noticeable influence on the treatment process’s efficacy. In order to achieve effective removal of the target compound under economic conditions, and at the same time minimize by-product formation, it is recommended to operate the electrode at a moderate current density and reduce the extent of the treatment.
Highlights
The growing consumption of pharmaceuticals worldwide is resulting in an increasing threat to human health and the aquatic environment, as many of these polar and semi-polar micropollutants are not removed, or only incompletely removed, by traditional biological treatment technologies in wastewater treatment plants [1]
The aim of the present study was to investigate the efficiency of boron-doped diamond (BDD) in a worst-case scenario, in order to highlight the effects of varied electrode conditions and water composition on the degradation of DCF, and at the same time the formation of transformation products (TPs) as well as inorganic by-products
Results from the present study revealed that the application of the BDD electrode is effective in the removal of DCF from water matrices of different compositions
Summary
The growing consumption of pharmaceuticals worldwide is resulting in an increasing threat to human health and the aquatic environment, as many of these polar and semi-polar micropollutants are not removed, or only incompletely removed, by traditional biological treatment technologies in wastewater treatment plants [1]. Among the large variety of pharmaceutical compounds present in the environment, the non-steroidal anti-inflammatory drug diclofenac (DCF) is one of the most-consumed substances; the annual intake worldwide is estimated to exceed 1000 tons [6]. The annual consumption of DCF per capita varies between 195 and 940 mg [5]. At a pH value above its pKa of 4.0–4.5, the carboxyl group of DCF dissociates and the molecule becomes negatively charged, exhibiting a lower tendency to adsorb into sludge (Log kD : 1.2–2.1). DCF is only moderately biodegradable under suboxic and anoxic conditions (kbiol : ≤ 0.1 L/g·day) [5,6,7]
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