Contents lists available at ScienceDirect Desalination journal homepage: www.elsevier.com/locate/desal Effect of operational conditions on post-treatment of RO permeate of geothermal water by using electrodeionization (EDI) method Samuel Bunani a,b,c , Müşerref Arda a , Nalan Kabay a,⁎ a Department of Chemical Engineering, Ege University, Izmir, Turkey b Department of Chemistry, Ege University, Izmir, Turkey c Department of Chemistry, University of Burundi, Bujumbura, Burundi ARTICLE INFO Keywords: Arsenic Boron Electrodeionization (EDI) Geothermal water Ion exchange Reverse osmosis (RO) Ultrapure water ABSTRACT With the growing of electronics, semiconductors, food and pharmaceutical manufactures, the need of water quantity with high purity is increasing. The water quality needed should be with high electrical resistance and free of weakly ionized dissolved species. Integration of separation processes such as reverse osmosis (RO) and electrodeionization (EDI) was proven to be successful to produce water with high quality. This paper is about the applicability of EDI method for post-treatment of RO permeate of geothermal water. For this purpose, the effects of process parameters such as feed flow rate, electrical potential applied, type of ion exchange membranes, and cell number on reduction of electrical conductivity and the contents of boron, silicon and arsenic in EDI product water were investigated. In addition, pseudo first order and pseudo second order kinetics models, infinitive solution volume (ISV) and unreacted core (UCM) models were applied to determine the rate controlling steps of the removal of electrical conductivity and boron by EDI process. Obtained results revealed that a EDI product water containing ˂0.20 mg B/L, ˂0.05 mg Si/L and ˂0.10 μg As/L was produced using a multi-cell EDI in which ion exchange resins in mixed bed configuration is placed between Neosepta CMX-AMX ion exchange membrane pair. These results were obtained when the optimum flow rate of 1.08 L/h and electrical potential of 20 V were applied to multi-cell EDI. At the optimal operational conditions, boron removal was found to be governed by second order kinetic model and the determining steps were film diffusion and liquid film according to ISV and UCM models, respectively. It was observed that thick ion exchange membranes were better than thin ion ex- change membranes for polishing RO permeate of geothermal water by using EDI process. 1. Introduction Various modern industrial applications require water quality free of weakly ionized species. The commonly concerned species vary from one industry to another. Generally, water purity preferred in most of the industrial applications is water with high electrical resistance and without silica, boron and arsenic contents. In electronics industry, silica is reported to have an impact of the material used, device performance and final product yielded [1,2]. Lower reliability of the oxide of the thermal growth, phosphor silica fog, voltage threshold variation and plasma breakdown are the drawbacks of using water containing silica in electronic industries [3]. The quality of the electronic tubes and solid state circuits is affected by silica present in water used in the manu- facturing process. Because of its toxicity, arsenic is rigorously restricted in drinking water and food. Arsenic exists in different compartments of the environment in the form of inorganic and organic arsenics. The arsenic toxicity depends of the form in which it is present, the concentration level and the time of exposure. Inorganic arsenic com- pounds such found in water are more toxic than organic arsenic com- pounds such present in seafood. Arsenic and boron are considered as doping impurities added in silicon to control the electrical conductance of semiconductors. Although boron as one of the p-type impurities in silicon, it provides positively-charged holes to the valence band of semiconductors, much of it is reported to invert the n-type impurities in silicon and has an impact on concentration of carriers [3]. Therefore, ultrapure intended for use in various industrial applications should be free of silica, boron and arsenic. Traditional separation methods reported for removal of these spe- cies from water are coagulation and electro-coagulation processes [4,5], adsorption [6,7], mixed bed ion exchange (IEX) [8–10], elec- trodialysis (ED) [11–13] and reverse osmosis (RO) [14–17]. However, a single method is not able to remove boron, silica and arsenic to the desired level for ultrapure water grade. Combination of two or more methods is the only choice to reduce these species at ultrapure water http://dx.doi.org/10.1016/j.desal.2017.10.032 Received 18 July 2017; Received in revised form 24 September 2017; Accepted 18 October 2017 ⁎ Corresponding author. E-mail address: nalan.kabay@ege.edu.tr (N. Kabay). Desalination xxx (xxxx) xxx–xxx 0011-9164/ © 2017 Elsevier B.V. All rights reserved. Please cite this article as: Bunani, S., Desalination (2017), http://dx.doi.org/10.1016/j.desal.2017.10.032