The influence of various factors on aqueous ozone decomposition by granular activated carbons and the development of a mechanistic approach P.M. Alva´rez a, * , J.F. Garcı ´a-Araya a , F.J. Beltra´n a , I. Gira´ldez a , J. Jaramillo b , V. Go´ mez-Serrano b a Departamento de Ingenierı´a Quı´mica y Energe´tica, Universidad de Extremadura, Badajoz 06071, Spain b Departamento de Quı´mica Inorga´ nica, Universidad de Extremadura, Badajoz 06071, Spain Received 22 December 2005; accepted 10 March 2006 Available online 5 May 2006 Abstract The decomposition of aqueous ozone in the presence of various granular activated carbons (GAC) was studied. The variables inves- tigated were GAC dose, presence of tert-butyl alcohol (TBA), aqueous pH as well as textural and chemistry surface properties of GAC. All the GAC tested enhanced the rate of ozone decomposition to some extent. From the analysis of experimental results it was deduced that ozone transformation into HO radicals mainly occurred in the liquid bulk through a radical chain reaction initiated by OH  and HO  2 ions. Hydroperoxide ions arise from the formation of H 2 O 2 on surface active sites of GAC and its further dissociation. No direct relationship between textural properties of GAC and the rate of ozone decomposition was found. However, a multiple regression anal- ysis of data revealed that basic and hydroxyl surface oxygen groups (SOG) of GAC favor the kinetics of the ozone decomposition pro- cess. It is thought that these groups are the active sites for ozone transformation into H 2 O 2 . Repeated used of GAC in ozonation experiments resulted in loss of basic and hydroxyl SOG with formation of carboxyl, carbonyl and lactone-type groups. Then, pre-ozon- ation of GAC reduces its ability to enhance the aqueous ozone transformation into hydroxyl radicals. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Activated carbon; Oxidation; Reaction kinetics; Surface oxygen complexes 1. Introduction Catalytic ozonation is a promising technology for the effective removal of water and wastewater contaminants that are refractory to conventional oxidation treatments. The main advantages of the catalytic processes with respect to traditional non-catalytic ozonation are better ozone uti- lization, increased contaminant removal efficiency and greater degree of organic matter mineralization [1]. Heter- ogeneous catalytic ozonation, though less studied than the homogeneous processes, is more attractive since oxidation efficiency and selectivity can be improved by proper selec- tion or modification of the catalysts. Moreover, when a homogeneous catalysts is used (i.e., metal ion) an addi- tional separation process is required to remove the toxic metal ions from the treated water. The use of a solid as cat- alyst overcomes this problem as it can be easily recovered from the aqueous medium. In addition to metal based heterogeneous catalysts (metal oxides and metals or metal oxides on supports) the use of different types of activated carbons to promote ozone reactions in water has arisen a great deal of interest in the last few years. Thus, some dissolved organic water pollutants have been effectively transformed into final products (CO 2 and H 2 O) through ozone reactions enhanced by powered and granular activated carbons e.g., [2–8]. The effect of the presence of activated carbon 0008-6223/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2006.03.016 * Corresponding author. Tel./fax: +34 924 289385. E-mail address: pmalvare@unex.es (P.M. Alva´rez). www.elsevier.com/locate/carbon Carbon 44 (2006) 3102–3112