Wat. Res. Vol. 35, No. 18, pp. 4370–4378, 2001 r 2001 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0043-1354/01/$-see front matter PII: S0043-1354(01)00176-2 SONOCHEMICAL DECOMPOSITION OF DIBENZOTHIOPHENE IN AQUEOUS SOLUTION IL-KYU KIM, CHIN-PAO HUANG* and PEI C. CHIU Department of Civil and Environmental Engineering, University of Delaware, Newark, DE 19716, USA (First received 1 March 2000; accepted in revised form 1 March 2001) AbstractFDibenzothiophene is decomposed rapidly by sonication in aqueous solution. Decomposition of dibenzothiophene follows a first-order reaction kinetics. The rate constant was found to increase with increasing ultrasonic energy intensity, temperature, and pH and decrease with increasing initial dibenzothiophene concentration. The activation energy was 12.6kJ/mol in the temperature range of 15–501C, suggesting a diffusion-controlled reaction. Hydroxydibenzothiophenes and dihydroxydiben- zothiophenes were identified as reaction intermediates. It is proposed that dibenzothiophene is oxidized by OH radical to hydroxy-dibenzothiophenes and then to dihydroxy-dibenzothiophenes. Kinetic analysis suggests that approximately 72% of the dibenzothiophene decomposition occurred via OH radical addition. A pathway and a kinetic model for the sonochemical decomposition of dibenzothiophene in aqueous solution are proposed. r 2001 Elsevier Science Ltd. All rights reserved Key wordsFsonochemical, ultrasound, dibenzothiophene, advanced oxidation process, hydroxy radical INTRODUCTION Polycyclic aromatic sulfur hydrocarbons (PASHs) are a group of toxic and/or mutagenic compounds (Eastmond et al., 1984; Pelroy et al., 1983; Karcher et al., 1981; McFall et al., 1984) which are abundant in petroleum and coal tars. These compounds are also present in wastewaters from petroleum and coal liquefaction industries (Smith et al., 1978). PASHs were found to bioconcentrate more significantly than sulfur-free polycyclic aromatic compounds (Dillon et al., 1978; Vassilaros et al., 1982) and have been shown to accumulate in sediments (Boehm et al., 1982), plants and animal tissues (Ogata and Fujisa- wa, 1985). These PASHs are among the most refractory compounds in the residuals at contaminated sites (Teal et al., 1978; Berthou et al., 1981; Boehm et al., 1982). In addition, the conventional activated sludge process does not effectively degrade these toxic compounds (Petrasek et al., 1983). The low biode- gradability of PASHs suggests that physical–chemi- cal methods may be more effective for degrading PASHs in wastewaters. Over the past several years, there has been an increasing interest in use of sonochemical irradiation to treat organic contaminants in aqueous solutions (Kotronarou et al., 1991; Gondrexon et al., 1993; Huang and Hao, 1994; Hoffmann et al., 1996; Hua and Hoffmann, 1996, 1997; Petrier et al., 1998; Kang and Hoffmann, 1998; Kang et al., 1999; Weavers et al., 1998, 2000; Colussi et al., 1999; Destaillats et al., 2000; Zhang and Hua, 2000; Beckett and Hua, 2000). Sonochemical decomposition of organic pol- lutants is resulted from the formation and collapse of high-energy cavitation bubbles. Upon collapse, the solvent vapor is subjected to the enormous increases in both temperature (upto 50001K) and pressure (up to several thousand atm) (Mason and Lorimer, 1988). Under such extreme conditions the solvent molecules undergo homolytic bond breakage to generate radicals. When water is sonicated, H . and HO . are produced (Riesz et al., 1990), the latter is a strong oxidizing agent (E o h ¼ 2:33 V) and can react with organic pollutants. Alternatively, organic com- pounds in the vicinity of a collapsing bubble may undergo pyrolytic decomposition due to the local high temperature and pressure (Suslick, 1986). Much research has been conducted to assess the sonochemical destruction of aromatic compounds in water. Petrier et al. (1998) showed that 44% of the carbon atoms in chlorobenzene were mineralized and recovered as CO and CO 2 within 120min. Kotronar- ou et al. (1991) reported that 90% of p-nitrophenol was degraded within 140min, primarily by denitra- tion. Nagata et al. (1996) showed that 95% of hydroxybenzoic acids were decomposed within an hour and suggested that the decomposition of *Author to whom all correspondence should be addressed. Tel.: +1-302-831-8428; fax: +1-302-831-3640; e-mail: huang@ce.udel.edu 4370