Water Research 253 (2024) 121227 Available online 30 January 2024 0043-1354/© 2024 Published by Elsevier Ltd. Electrochemical arsenite oxidation for drinking water treatment: Mechanisms, by-product formation and energy consumption E. Kraaijeveld a, * , S. Rijsdijk a , S. van der Poel b , J.P. van der Hoek a , K. Rabaey c , D. van Halem a a Faculty of Civil Engineering and Geosciences, Delft University of Technology, Stevinweg 1, 2628 CN Delft, the Netherlands b Dunea, Utility for drinking water and nature conservancy, Plein van de Verenigde Naties 11-15, 2719 EG Zoetermeer, the Netherlands c Department of Biotechnology, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, Ghent 9000, Belgium A R T I C L E INFO Keywords: Arsenic Groundwater THMs Bromate ABSTRACT The mechanisms and by-product formation of electrochemical oxidation (EO) for As(III) oxidation in drinking water treatment using groundwater was investigated. Experiments were carried out using a fowthrough system, with an RuO 2 /IrO 2 MMO Ti anode electrode, fed with synthetic and natural groundwater containing As(III) concentrations in a range of around 75 and 2 μg/L, respectively. Oxidation was dependent on charge dosage (CD) [C/L] and current density [A/m 2 ], with the latter showing plateau behaviour for increasing intensity. As(III) concentrations of <0.3 μg/L were obtained, indicating oxidation of 99.9 % of infuent As(III). Achieving this required a higher charge dosage for the natural groundwater (>40 C/L) compared to the oxidation in the syn- thetic water matrix (20 C/L), indicating reaction with natural organic matter or other compounds. As(III) oxidation in groundwater required an energy consumption of 0.09 and 0.21 kWh/m 3 , for current densities of 20 and 60 A/m 2 , respectively. At EO settings relevant for As(III) oxidation, in the 30–100 C/L CD range, the for- mation of anodic by-products, as trihalomethanes (THMs) (0.11–0.75 μg/L) and bromate (<0.2 μg/L) was investigated. Interestingly, concentrations of the formed by-products did not exceed strictest regulatory stan- dards of 1 μg/L, applicable to Dutch tap water. This study showed the promising perspective of EO as electro- chemical advanced oxidation process (eAOP) in drinking water treatment as alternative for the conventional use of strong oxidizing chemicals. 1. Introduction Electrochemical water treatment technologies have been gaining considerable interest in recent years, providing a promising alternative to conventional chemical-driven processes. Electrochemical oxidation (EO), being one of the electrochemical technologies of interest, has shown potential to replace the use of (strong) oxidizing chemicals such as KMnO 4 , HOCl, H 2 O 2 /UV and O 3 , for removal of organics and micropollutants, and for disinfection purposes (Bergmann and Koparal, 2005; Najafnejad et al., 2023; Radjenovic et al., 2011; Rajab et al., 2015). While a range of EO techniques exists, anodic oxidation (AO) is arguably considered most popular and applicable from a practical perspective (Moreira et al., 2017). In AO, contaminants are oxidized following two main pathways; (1) direct surface oxidation by electron transfer, and (2) indirect oxidation by generated oxidizing agents. With the latter being split up in; (2.1) indirect oxidation by OH radicals attached to and/or in close vicinity of the electrode’s surface, and (2.2) indirect oxidation by generated oxidizing agents from ions available in the bulk solution (e.g. chlorine from chloride) (Panizza and Cerisola, 2009) (Fig. 1). Innovation in AO mostly focusses on the selection and improvement of electrode materials, with boron doped diamond (BDD) and mixed metal oxide (MMO) based electrodes being favoured due to their stability and broad availability (Moreira et al., 2017; Najafnejad et al., 2023). Interestingly, the use of RuO 2 /IrO 2 -coated Titanium (Ti) MMO electrodes is gaining preference over BDD electrodes due to relatively low production costs and process scalability. However, the active behaviour and the low chlorine evolution overpotential of the MMO electrodes has a signifcant downside related to the potential formation of unwanted chlorinated by-products (Radjenovic et al., 2011). While AO has extensively been studied for the removal of (in)organic trace contaminants and disinfection purposes (e-disinfection), limited attention is given to groundwater-based drinking water treatment. Due to its carcinogenic nature, the presence of arsenic, and especially its * Corresponding author. E-mail address: e.kraaijeveld98@gmail.com (E. Kraaijeveld). Contents lists available at ScienceDirect Water Research journal homepage: www.elsevier.com/locate/watres https://doi.org/10.1016/j.watres.2024.121227 Received 23 August 2023; Received in revised form 24 December 2023; Accepted 28 January 2024