Electrochemical process combined with UV light irradiation for synergistic degradation of ammonia in chloride-containing solutions

Abstract

Active chlorine radicals a b s t r a c tAn electrochemical process combined with ultraviolet light irradiation (UPE) using nonphotoactive dimensionally stable anodes (DSAs) like RuO 2 /Ti and IrO 2 /Ti in the presence of chlorides was investigated for ammonia degradation. In this process, the in situ electrogenerated active chlorine and in situ photogenerated chlorine radicals were responsible for the high efficiency of ammonia degradation. More than 97% of ammonia was converted to nitrogen and a significantly synergistic effect was confirmed. Compared with the single electrochemical (E) and photochemical (P) process, the degradation rates of ammonia and the average current efficiencies (ACEs) of the UPE process increased by 1.5 and 1.7 times using RuO 2 /Ti and IrO 2 /Ti electrodes, respectively. On the basis of the linear voltammograms, Electrochemical Impedance Spectra (EIS), UV-vis spectra, Electron Spin Resonance (ESR) analysis and a series of experiments designed, the synergistic mechanism was investigated. In addition, this unique process succeeded in transferring the reaction from the electrode surface to the bulk of the solution compared with the conventional photoelectrocatalytic (PEC) process. The loss of chloride decreased from 21.0% to 7.2% and the recycle of chloride was accelerated in the UPE process. Finally the effects of initial pH, current density and ammonia-nitrogen concentration were discussed. Results indicated that pH and ammonia concentration exerted little influences on the degradation rates and current density was the ''rate-determining'' factor. ª 2009 Elsevier Ltd. All rights reserved. IntroductionAmmonia, as one of the major nitrogen-containing pollutants, is a source of nutrients that may accelerate the eutrophication and algal growth in natural water (Feng et al., 2003;Nemoto et al., 2006). The abatement of ammonia in wastewater discharged has become a prime issue of environmental control. High concentrations of ammonia in wastewater effluents deplete dissolved oxygen, reduce chlorine disinfection efficiency, and exhibit acute toxicity to aquatic life. There are several methods for ammonia removal from water and wastewater, including biological process (Kalyuzhnyi et al., 2006), ammonia stripping (Bonmati and Flotats, 2003), ion exchange (Lin and Wu, 1996), breakpoint chlorination (Thomas et al., 1972), photocatalysis (Zhu et al., 2005) and electrochemical process (Chiang et al., 1995;Kim et al., 2006;Wang et al., 2006). Electrochemical method for the advanced treatment of ammonia in the wastewater has attracted a great deal of * Corresponding author. Tel.: þ86 10 62849151; fax: þ86 10 62923558. E-mail address: jhqu@rcees.ac.cn (J. Qu).A v a i l a b l e a t w w w . s c i e n c e d i r e c t . w a t e r r e s e a r c h 4 3 ( 2 0 0 9 ) 1 4 3 2 -1 4 4 0

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