Nitroimidazoles adsorption on activated carbon cloth from aqueous solution R. Ocampo-Pérez a , F. Orellana-Garcia a , M. Sánchez-Polo a,⇑ , J. Rivera-Utrilla a , I. Velo-Gala a , M.V. López-Ramón b , M.A. Alvarez-Merino b a Departamento de Química Inorgánica, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain b Departamento de Química Inorgánica y Orgánica, Facultad de Ciencias Experimentales, Universidad de Jaén, 23071 Jaén, Spain article info Article history: Received 10 January 2013 Accepted 25 March 2013 Available online 2 April 2013 Keywords: Adsorption Nitroimidazole Activated carbon cloth Real water Kinetics abstract The objective of this study was to analyze the equilibrium and adsorption kinetics of nitroimidazoles on activated carbon cloth (ACC), determining the main interactions responsible for the adsorption process and the diffusion mechanism of these compounds on this material. The influence of the different opera- tional variables, such as ionic strength, pH, temperature, and type of water (ultrapure, surface, and waste), was also studied. The results obtained show that the ACC has a high capacity to adsorb nitroim- idazoles in aqueous solution. Electrostatic interactions play an important role at pH < 3, which favors the repulsive forces between dimetridazole or metronidazole and the ACC surface. The formation of hydrogen bonds and dispersive interactions play the predominant role at higher pH values. Modifications of the ACC with NH 3 ,K 2 S 2 O 8 , and O 3 demonstrated that its surface chemistry plays a predominant role in nitro- imidazole adsorption on this material. The adsorption capacity of ACC is considerably high in surface waters and reduced in urban wastewater, due to the levels of alkalinity and dissolved organic matter present in the different types of water. Finally, the results of applying kinetic models revealed that the global adsorption rate of dimetridazole and metronidazole is controlled by intraparticle diffusion. Ó 2013 Elsevier Inc. All rights reserved. 1. Introduction Nitroimidazoles are the most widely used pharmaceuticals to treat infections in humans and animals caused by anaerobic and protozoan bacteria, such as Trichomonas vaginalis and Giardia lamb- lia [1]. Among nitroimidazoles, only five are useful as antibacterial and antiparasitic drugs [2,3]. Metronidazole (MNZ) is used in hu- man, and dimetridazole (DMZ) is applies to animals. Metronida- zole is the most widely used nitroimidazole. It is one of the 100 most commonly prescribed drugs in the USA [4] and one of the 10 most frequently administered drugs during pregnancy [5]. Moreover, MNZ is the only nitroimidazole included in the WHO list of essential drugs. This has produced an accumulation of these drugs in the animal organism, in fish-farm waters, and especially in the effluents from meat industries [6–8]. Nitroimidazoles have high water solubility, low biodegradabil- ity [9], and high toxicity [10,11] and show mutagenic and carcino- genic characteristics [2]. These characteristics make nitroimidazoles potentially dangerous compounds because of their persistence in water, which favors their bioaccumulation. Accord- ing to the International Agency for Research on Cancer, there is suf- ficient evidence to consider MNZ as a potentially carcinogenic substance [12]. For all these reasons, nitroimidazoles are consid- ered emerging water micropollutants. Adsorption on carbon materials, one of the oldest water treat- ment technologies has been recognized by the U.S. Environmental Protection Agency as one of the best methods available to remove organic and inorganic compounds from water intended for human consumption [13–22]. The value of activated carbons in this field resides in the chemical and textural properties of their surfaces. However, this technology is not very widely used to treat wastewa- ter and industrial effluents, mainly because of their high organic matter content. Importantly, some experimental parameters of activated carbon adsorption remain unknown, and the mecha- nisms involved in each system have yet to be elucidated. This knowledge is essential for optimizing the use of activated carbon in water treatments. Nitroimidazole adsorption on granular activated carbon (GAC) has not been extensively studied in the literature. In previous works, Méndez-Díaz et al. [23] investigated the adsorption kinetics of four nitroimidazoles (DMZ, MNZ, ronidazole, and tinidazole) on three activated carbons (C, S, and M) and reported that the time to reach equilibrium was 60 h. The nitroimidazole adsorption rate in- creased in the order C < S < M, which was attributed to the hydro- phobicity values of these activated carbons. Rivera-Utrilla et al. [24,25] studied the behavior of activated carbons with different chemical and textural characteristics in nitroimidazole adsorption in static and dynamic regime in ultrapure, surface, ground, and 0021-9797/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jcis.2013.03.038 ⇑ Corresponding author. Fax: +34 958243856. E-mail address: mansanch@ugr.es (M. Sánchez-Polo). Journal of Colloid and Interface Science 401 (2013) 116–124 Contents lists available at SciVerse ScienceDirect Journal of Colloid and Interface Science www.elsevier.com/locate/jcis