Mathematical model of a parallel plate ammonia electrolyzer for combined wastewater remediation and hydrogen production Ali Estejab, Damilola A. Daramola, Gerardine G. Botte * Center for Electrochemical Engineering Research, Department of Chemical and Biomolecular Engineering, Stocker Center 165, Ohio University, Athens, OH 45701, United States article info Article history: Received 3 December 2014 Received in revised form 4 March 2015 Accepted 15 March 2015 Available online 24 March 2015 Keywords: Ammonia electrolysis Water deammonification Hydrogen production Wastewater remediation Waste-energy recovery Water-energy nexus abstract A mathematical model was developed for the simulation of a parallel plate ammonia electrolyzer to convert ammonia in wastewater to nitrogen and hydrogen under basic conditions. The model consists of fundamental transport equations, the ammonia oxida- tion kinetics at the anode, and the hydrogen evolution kinetics at the cathode of the electrochemical reactor. The model shows both qualitative and quantitative agreement with experimental measurements at ammonia concentrations found within wastewater (200e1200 mg L 1 ). The optimum electrolyzer performance is dependent on both the applied voltage and the inlet concentrations. Maximum conversion of ammonia to nitrogen at the rates of 0.569 and 0.766 mg L 1 min 1 are achieved at low (0.01 M NH 4 Cl and 0.1 M KOH) and high (0.07 M NH 4 Cl and 0.15 M KOH) inlet concentrations, respectively. At high and low concentrations, an initial increase in the cell voltage will cause an increase in the system response e current density generated and ammonia converted. These system responses will approach a peak value before they start to decrease due to surface blockage and/or depletion of solvated species at the electrode surface. Furthermore, the model predicts that by increasing the reactant and electrolyte concentrations at a certain voltage, the peak current density will plateau, showing an asymptotic response. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Ammonia electrolysis is undergoing development as a viable technology for wastewater remediation (Boggs and Botte, 2009; Botte, 2010; Kim et al., 2006; Reyter et al., 2010). NH 3 and other nitrogen compounds in water can cause eutrophi- cation which endangers aquatic life (Feng et al., 2003). On the other hand, ammonia is a good source of hydrogen for energy generation (Boggs and Botte, 2010; Botte, 2012a, b, c; Cooper and Botte, 2006; Muthuvel and Botte, 2009; Vitse et al., 2005). Using an electrolytic cell, ammonia is oxidized at the anode and water is reduced at the cathode for an overall reaction that produces benign nitrogen and useful hydrogen according to Equations (1)e(3) (Diaz and Botte, 2012): Anode : 2NH 3 ðaqÞþ 6OH  /N 2 ðgÞþ 6H 2 O þ 6e  Eº ¼0:77V vs: SHE (1) * Corresponding author. Tel.: þ1 740 593 9670; fax: þ1 740 593 0873. E-mail address: botte@ohio.edu (G.G. Botte). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/watres water research 77 (2015) 133 e145 http://dx.doi.org/10.1016/j.watres.2015.03.013 0043-1354/© 2015 Elsevier Ltd. All rights reserved.