Chemical Engineering Journal 142 (2008) 161–167 Volatilization reduction of monoaromatic compounds in nonionic surfactant solutions Huan-Ping Chao a , Jiunn-Fwu Lee b,∗ , Chung-Kung Lee c , Fu-Chang Huang d , Gurusamy Annadurai b a Department of Bioenvironmental Engineering, Chung Yuan Christian University, Chung-Li 32023, Taiwan b Graduate Institute of Environmental Engineering, National Central University, Chung-Li 32001, Taiwan c Green Environment R&D Center and Department of Environmental Engineering, Vanung University, Chung-Li 32061,Taiwan d Department of Civil and Environmental Engineering, Nanya Institute of Technology, Chung-Li 32091, Taiwan Received 2 October 2006; received in revised form 29 October 2007; accepted 19 November 2007 Abstract Changes in the overall mass transfer coefficient (K OL ) of several volatile organic compounds (VOCs) in surfactant (Triton X-100, Triton X-305, and Triton X-405) solutions are investigated. Different surfactant concentrations, from below to above the critical micelle concentration (CMC), are used to examine the possible inhibition effects on the volatilization of VOCs. The volatilization reduction (or the decrease in the K OL value) of the monoaromatic solutes from the surfactant solutions is considered to be a result of the effects of solubility enhancement and gas–liquid interface hindrance. For the solubility enhancement effect, the extent of volatilization reduction would generally be larger when a surfactant contains less polar ethylene oxide (EO) and when a monoaromatic compound has lower water solubility. On the other hand, gas–liquid interface hindrance may inhibit the volatilization of VOCs due to the aggregation of surfactants at the interface. Both the two-film and surface-depletion rate-limiting (SDRL) models are applied to elucidate the volatilization reduction of VOCs in surfactant solutions. © 2007 Elsevier B.V. All rights reserved. Keywords: Volatilization rate; Volatilization reduction; Surfactants; Solubility enhancement; Interface hindrance 1. Introduction A significant volume of aqueous effluents containing syn- thetic VOCs is generated by the large number of wastewater treatment plants (WWTPs). The release of these VOCs from wastewater into the surrounding environment has caused increasing concern about their toxic effects on human health. Over the past decades, numerous researchers have developed a series of models to predict the fate of organic compounds in WWTPs [1–4]. For these proposed models, however, the changes in the volatilization rates of the organic compounds accompanying with the variation in the environmental condi- tions are poorly clarified. One well-known example is that the effects of surfactants in the wastewater on the volatilization of organic solutes are rarely investigated [5–7]. Since the surfac- ∗ Corresponding author. Tel.: +886 3 4227171x34658; fax: +886 34226742. E-mail address: jflee@ncuen.ncu.edu.tw (J.-F. Lee). tants are often found in the WWTPs, a comprehensive study for the effects of surfactants on the volatilization of VOCs is nec- essary to develop a more accurate model to predict the fate of VOCs in the surfactant solutions. In general, the existence of surfactants in the solution can enhance the apparent solubility of the organic compounds [8,9], which in turn gives a significant inhibition on the volatilization of VOCs. In addition to the solubility enhancement, however, there are other factors that could also reduce the volatilization of the solutes in surfactant solutions. One recognized property of surfactants is that they can aggregate at the gas–liquid inter- face and may also hinder the volatilization of organic solutes from surfactant solutions [5]. In this study, effects of non- ionic surfactants with different EO number on the K OL values of organic solutes with comparable Henry’s law constant (H, dimensionless) and different water solubility are investigated. The relative suppressing effect of different surfactants on the organic solute volatilization via the solubility enhancement and interface hindrance are discussed. Both the two-film and the 1385-8947/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2007.11.020