Journal of Hazardous Materials 167 (2009) 959–965 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat Kinetic study of electrolytic ammonia removal using Ti/IrO 2 as anode under different experimental conditions Yan Liu a , Liang Li b , Ramesh Goel b,∗ a Department of Environmental Science and Engineering Fudan University 220 Handan Road, Shanghai 200433, China b Department of Civil & Environmental Engineering 122 S. Central Campus Drive University of Utah Salt Lake City, Salt Lake City 84112 UT, United States article info Article history: Received 30 September 2008 Received in revised form 20 January 2009 Accepted 20 January 2009 Available online 30 January 2009 Keywords: Ammonia Electrolytic oxidation Hydroxyl radical Current intensity Wastewater abstract This study reports electrolytic degradation and kinetic modeling of electrolytic degradation of ammo- nia using Ti/IrO 2 . The experimental and modeling results are compared with those previously obtained using Ti/RuO 2 anode. Synthetic solution containing predetermined ammonia concentration and the raw municipal wastewater collected after the aerobic or the anaerobic treatment were used in different sets of experiments. The experimental conditions varied for electrolytic degradation of ammonia present in the synthetic feed were initial chloride concentration, initial pH and applied current density. The results show that the ammonia removal followed pseudo zero-order kinetics. The current density (j) and the initial Cl - concentration ([Cl - ]) affected the constant of the pseudo zero-order kinetics, expressed as k Ti/IrO 2 = 0.0020[Cl - ]j+0.4848 and k Ti/RuO 2 = 0.0026[Cl - ]j - 0.7417. The ammonia removal rate averaged at 8.5 using Ti/IrO 2 and was comparable to the rate (11.7 mg N L -1 h -1 ) obtained using Ti/RuO 2 anode, at 15.4 mA cm -2 current density, 300 mg L -1 Cl - and pH of 7. Higher current density and as well as the chlo- ride concentration resulted in greater ammonia degradation. On the other hand, pH did not seem to have any effect on electrolytic degradation of ammonia. More than 95% ammonia degradation in municipal wastewater effluents collected after aerobic or anaerobic treatment was achieved. The ammonia nitrogen in the electrolytically treated wastewater effluents collected at the end of aerobic and anaerobic envi- ronments were 0.9, 0.5 mg N L -1 using Ti/IrO 2 and 0.5, 0.2 mg N L -1 by using Ti/RuO 2 anodes, respectively. Published by Elsevier B.V. 1. Introduction Ammonia nitrogen present in liquid waste generated from var- ious sources is detrimental to the water quality of surface waters. Being an essential nutrient, ammonia nitrogen enhances the growth of algae in the surface water, thus causing eutrophication and other environmental concerns [1]. The most commonly used methods to remove ammonia nitrogen from liquid waste are air stripping, biological nitrification, electrolysis, break point chlorination and chemical precipitation [2,3]. Among these, biological oxidation of ammonia to nitrate has wide spread application and is the most commonly used method of ammonia removal from wastewaters. Biological oxidation of ammonia to nitrate is a two-step process and is employed worldwide currently using different reactor con- figurations. More and more attention has been given to the removal of ammonia from wastewater especially when the purpose is to obtain treated wastewater of reusable quality. In this context, electrolytic ∗ Corresponding author. Tel.: +801 581 6110; fax: +801 585 5477. E-mail address: rgoel@civil.utah.edu (R. Goel). oxidation of ammonia directly to nitrogen gas has a great poten- tial of application and has attracted a great interest in recent times for the advance treatment of wastewater [4–8], because it is a simple technology with low maintenance and the by products of electrolytic ammonia oxidation, which is nitrogen in most of the cases, are harmless and do not require further treatment. Direct conversion of ammonia nitrogen to gaseous nitrogen also alleviates the need of complex wastewater flow regimes which are gener- ally required in biological conversion of ammonia to nitrogen gas through biological nitrification and denitrification. Direct oxidation of ammonia nitrogen to gaseous nitrogen have been already demonstrated for tannery wastewater [9,10], power plant effluents [11], municipal discharges [12], landfills leachate [13,14], and sludge digester effluent [15]. Addition of sodium chlo- ride to form hypochlorous acid (HOCl) during the electrolysis of ammonia has been also investigated in a number of research efforts in which case the concentration of chloride ranged from 4800 to 6600 mg L -1 [11,12]. Several factors including current density [5,11,13], pH [5,11,13], Cl - concentration in the feed solution [5,10,11–13] and electrode material, especially anode, can affect electrolytic ammonia degra- dation efficiency. Among these, anode material is critical and 0304-3894/$ – see front matter. Published by Elsevier B.V. doi:10.1016/j.jhazmat.2009.01.082