Dichloroacetic acid degradation employing hydrogen peroxide and UV radiation Cristina S. Zalazar, Marisol D. Labas, Rodolfo J. Brandi, Alberto E. Cassano * INTEC (Universidad Nacional del Litoral and CONICET), Gu ¨ emes 3450. (3000) Santa Fe, Argentina Received 5 January 2006; received in revised form 14 June 2006; accepted 16 June 2006 Available online 14 August 2006 Abstract The degradation reaction of dichloroacetic acid employing H 2 O 2 and UVC radiation (253.7 nm) has been studied in a well mixed reactor operating inside a recycling system. It has been shown that in an aqueous solution no stable reaction intermediates are formed and, at every time during the reaction, two mols of hydrochloric acid are formed for every mol of dichloroacetic acid that is decomposed and, in the same way, there is a paired agreement between the calculated TOC concentration corresponding to the unaltered dichloro- acetic acid and the experimental values measured in the solution. On this basis and classical references from the scientific literature for the H 2 O 2 photolysis, a complete reaction scheme, apt for reaction kinetics mathematical modeling and ulterior scale-up is proposed. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Advanced oxidation technologies; Dichloroacetic acid mineralization; Effects of operating variables; Reaction paths 1. Introduction Water pollution remains a problem of general concern creating a demand for technological solutions. Nowadays, various Advanced Oxidation Technologies (AOTs) are in the process of development or already available in compe- tition with older and established methods. One of the main advantages of the former methods are their destructive potential, transforming most organic pollutants in harm- less chemicals such as carbon dioxide, water and halide ions or equivalent inorganic acids (mineralization). The vast majority of these processes have in common that as a result of the intervention of the employed active agent, the generation of one or more highly reactive inter- mediate species is produced, the hydroxyl radical ( Å OH) being the most relevant. Different technological ways are in use to introduce the required energy; among them, the UV radiation is one of the most widely practiced. These oxi- dation mechanisms are known to decompose a broad family of organic compounds. In most cases their ability to destroy the contaminants and do it with almost no selectivity consti- tutes one noticeable, advantageous feature (Pulgarı ´n et al., 1999; Kitis et al., 2000; Aceituno et al., 2002; Mohey El-Dein et al., 2003). A special attraction is also the pos- sibility of using, in some cases, these AOTs to reduce the toxicity of contaminated waters up to the point where they can be combined with the more economical biological treatments to complete the proposed purification (Pulgarı ´n et al., 1999). UV radiation in homogeneous or pseudo-homogeneous processes can be combined with ozone (UV/O 3 ) and with hydrogen peroxide (UV/H 2 O 2 ). Also, H 2 O 2 can be used in association with ozone (H 2 O 2 /O 3 ). Considering design, operation and maintenance characteristics, UV/H 2 O 2 is the simplest of all them (Hu ¨gul et al., 2000). In fact, H 2 O 2 is very soluble in water, easy to transport and its oxi- dation potential is very similar to the one of ozone (Alfano et al., 2001). According to Stefan et al. (1996) the main advantages of the UV/H 2 O 2 method are: (i) high rates of pollutant 0045-6535/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2006.06.044 * Corresponding author. Tel.: +54 342 4559176; fax: +54 342 4511087. E-mail address: acassano@ceride.gov.ar (A.E. Cassano). www.elsevier.com/locate/chemosphere Chemosphere 66 (2007) 808–815