Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur Capacitive deionization for simultaneous removal of salt and uncharged organic contaminants from water Yaal Lester a , Evyatar Shaulsky b , Razi Epsztein c , Ines Zucker d,e, ⁎ a Environmental Technologies, Department of Advanced Materials, Azrieli College of Engineering, Jerusalem 9103501, Israel b Department of Chemical and Environmental Engineering, Yale University, New Haven, CT 06520-8286, USA c Faculty of Civil and Environmental Engineering, Technion – Israel Institute of Technology, Technion City, Haifa 32000, Israel d School of Mechanical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978, Israel e Porter School of Environmental Studies, Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel ABSTRACT Capacitive deionization (CDI) has been solely employed for the removal of charged ions from water, showing limited feasibility compared to other conventional technologies such as reverse osmosis (RO). In this work, we propose to use CDI with activated carbon electrodes for simultaneous removal of inorganic salt and trace organic contaminants (TOrCs). This approach is based on the inherent sorption potential of activated carbon CDI electrodes towards organic species. We show that salt removal by CDI is only slightly affected by the presence of different TOrCs (bisphenol A, carbamazepine, estrone, and phentoxifylline). Sorption and removal of TOrCs (taking place concomitantly) was most effective for the hydrophobic compounds (bisphenol A and estrone) and was not affected by the presence of salt or the applied electric field. Sequential desorption of salt and TOrCs into two separated streams was achieved by short-circuiting the two electrodes and washing the electrodes with water and ethanol, respectively. Notably, the described process produces separate waste streams for salts (i.e., water) and organics (i.e, ethanol), which can facilitate their disposal or further treatment. Altogether, the study shows the high potential of the proposed CDI application, which may be valuable for treating water or wastewater streams contaminated with both salt and TOrCs. 1. Introduction Capacitive deionization (CDI) belongs to the class of electro- chemical desalination techniques, with potential applications for water and wastewater treatment [1,2]. In a typical CDI process, the treated (salt-containing) water flows through oppositely-charged porous elec- trodes; salt ions are then extracted by the applied electric field and adsorbed onto the electrode porous surface. Once the electrodes are saturated, they undergo desorption and regeneration by applying zero electrical potential or reverse electric field [3]. Large number of studies were conducted over the last decades on CDI processes, ranging from fundamental mechanistic evaluation (e.g. [4]), electrodes synthesis and optimization [5,6,7], and assessment of different potential applications (e.g. [8]). Presently, it is arguable whether CDI can compete with other common techniques for seawater desalination—such as reverse osmosis (RO) and thermal dis- tillation—mainly due to its higher energy consumption at elevated salt concentration [9,10]. As a consequence, the majority of recent studies focuses on CDI application for brackish-water desalination with total dissolved solids (TDS) of approximately 10,000 mg L -1 with marginal advantages compared to other technologies [11,12]. A review by AlMarzooqi et al. [13] evaluated the energy demand of CDI for brackish-water desalination to be in the range of 0.10–2.03 kWh m -3 , which is seemingly competitive with RO desalination [14]. However, the values provided in the review were mostly calculated for small-scale systems (labs or pilots), and scale-up typically decreases the process efficiency [11]. For example, Welgemoed and Schutte [3] ap- proximated the specific energy requirement for brackish-water desali- nation (TDS ∼ 1000 mg L -1 ) by an industrial-type CDI system to be six times higher than that of a laboratory-type module (0.1 kWh m -3 versus 0.6 kWh m -3 ). Hence, it is now becoming more acceptable that CDI cannot compete with RO, even for brackish-water desalination. This assumption was more recently confirmed by Qin et al. [10], which determined that RO is significantly more efficient than CDI for brackish-water desalination, using system-scale models for comparing the two technologies over a wide range of operating conditions. To become competitive and cost-effective, CDI must be employed in alternative applications, rather than desalination, where it is advanta- geous. Examples for such potential applications include the removal or recovery of industrial wastewater contaminants [15], the selective re- moval of nutrients (e.g., nitrate and phosphate) (e.g. [16]) and heavy metals [17], and water softening [18,19,20]. In fact, water softening by https://doi.org/10.1016/j.seppur.2019.116388 Received 4 October 2019; Received in revised form 30 November 2019; Accepted 4 December 2019 ⁎ Corresponding author at: School of Mechanical Engineering, Faculty of Engineering, and Porter School of Environmental Studies, Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel. E-mail address: ineszucker@tauex.tau.ac.il (I. Zucker). Separation and Purification Technology 237 (2020) 116388 Available online 05 December 2019 1383-5866/ © 2019 Elsevier B.V. All rights reserved. T