RESEARCH ARTICLE Removal of anionic surfactant sodium dodecyl benzene sulfonate (SDBS) from wastewaters by zero-valent iron (ZVI): predominant removal mechanism for effective SDBS removal Akari Takayanagi 1 & Maki Kobayashi 1 & Yoshinori Kawase 1 Received: 22 November 2016 /Accepted: 20 January 2017 # Springer-Verlag Berlin Heidelberg 2017 Abstract Mechanisms for removal of anionic surfactant sodium dodecyl benzene sulfonate (SDBS) in wastewaters by zero- valent iron (ZVI) were systematically examined. The contribu- tions of four removal mechanisms, i.e., reductive degradation, oxidative degradation, adsorption, and precipitation, changed significantly with solution pH were quantified and the effective removal of SDBS by ZVI was found to be attributed to the adsorption capability of iron oxides/hydroxides on ZVI surface at nearly neutral pH instead of the degradation at acidic condi- tion. The fastest SDBS removal rate and the maximum TOC (total organic carbon) removal efficiency were obtained at pH 6.0. The maximum TOC removal at pH 6.0 was 77.8%, and the contributions of degradation, precipitation, and adsorp- tion to TOC removal were 4.6, 14.9, and 58.3%, respectively. At pH 3.0, which is an optimal pH for oxidative degradation by the Fenton reaction, the TOC removal was only 9.8% and the con- tributions of degradation, precipitation, and adsorption to TOC removal were 2.3, 4.6, and 2.9%, respectively. The electrostatic attraction between dodecyl benzene sulfate anion and the iron oxide/hydroxide layer controlled the TOC removal of SDBS. The kinetic model based on the Langmuir-Hinshelwood/Eley- Rideal approach could successfully describe the experimental results for SDBS removal by ZVI with the averaged correlation coefficient of 0.994. ZVI was found to be an efficient material toward the removal of anionic surfactant at nearly neutral pH under the oxic condition. Keywords Zero-valent iron . Anionic surfactant . Iron oxides/ hydroxides . Adsorption . Solution pH Introduction Surfactants have been widely used in many industries such as textiles, food, cosmetics, and pharmaceuticals, and they consist mainly of three types, i.e., anionic, non-ionic, and cationic. Anionic surfactants constitute about 60% of the total surfactant production (Karray et al. 2016). The discharge of surfactants from industrial and domestic activities causes crucial water pol- lution since they are relatively resistant to degradation (Lechuga et al. 2016; Jardak et al. 2016). Surfactants have been generally removed by activated sludge treatments, which are unable to remove surfactants completely. Various chemical treatments such as coagulation (Beltran-Heredia et al. 2009), photocatalytic oxi- dation (Lea and Adesina 1998; Eng et al. 2012; Ono et al. 2012), and ozonation (Uchiyama et al. 2007) have been applied as ter- tiary treatments (Panizza et al. 2013). Zero-valent iron (ZVI) particulate being an environmental- ly friendly material has received wide attention because of its effectiveness in a variety of wastewater treatment applications (Yan et al. 2010; Guan et al. 2015; Lefevre et al. 2016; Ali et al. 2012). ZVI particulate is non-toxic, abundant, and inex- pensive, and furthermore, its easy recycling by magnetism is one of the advantages of the ZVI treatment. It should be point- ed out that ZVI application often suffers from restraints such as large amount of iron sludge production and constrained operating pH (Guan et al. 2015). It has been generally accept- ed that four mechanisms, i.e., reductive degradation, oxidative degradation, adsorption, and precipitation, are responsible for removal of pollutants by ZVI (Fu et al. 2014; Sun et al. 2015). ZVI particulate in aqueous solutions has a core-shell structure consisting of a metallic iron core covered by a thin iron oxide/ Responsible editor: Guilherme L. Dotto * Yoshinori Kawase ykawase@toyonet.toyo.ac.jp; ynkawase@gmail.com 1 Research Center for Biochemical and Environmental Engineering, Department of Applied Chemistry, Toyo University, Kawagoe, Saitama 350-8585, Japan Environ Sci Pollut Res DOI 10.1007/s11356-017-8493-8