A comparative study of adsorption of perfluorooctane sulfonate (PFOS) onto granular activated carbon, ion-exchange polymers and non-ion-exchange polymers
Introduction
Perfluorooctane sulfonate (PFOS) is an anthropogenic organic pollutant, which is recognized as an emerging problem in water environment due to its persistence, bio-accumulation, long range transportation and toxic effects. PFOS was categorized as persistent organic pollutants (POPs) in the 4th meeting of the conference of the parties to the Stockholm Convention in May 2009 (Earth Negotiations Bulletin, 2009). From the available literature, tap water and surface water samples in several countries were found to be contaminated with PFOS (Fujii et al., 2007, Lien et al., 2008, Jin et al., 2009; Quinete et al., 2009). For example in Osaka (Japan), PFOS concentration in portable tap water varies from 0.16 ng L−1 to 22.00 ng L−1 (Takagi et al., 2008). Also there is a positive correlation between the PFOS concentration in raw water and tap water samples suggesting minimum removal efficiency at conventional water purification systems (Fujii et al., 2007, Takagi et al., 2008).
Since the conventional techniques are not sufficient to treat PFOS, different alternative treatment techniques have been suggested. The methods that have been already tested are UV–visible light irradiation (Hori et al., 2004), photochemical decomposition with persulfate ions () (Hori et al., 2005), membrane process (Tang et al., 2006) and sonochemical degradations (Moriwaki et al., 2005).
It has been demonstrated in many cases that, adsorption is an effective and economical method to remove many polar organic pollutants from water. However most of these researchers have focused on industrial wastewater where PFOS concentration is in μg L−1 level. Few researchers have reported the effectiveness of some anion-exchange synthetic polymers (Yu et al., 2009) and activated carbon (Schaefer, 2006; Yong et al., 2007; Ochoa-Herrera and Sierra-Alvarez, 2008; Yu et al., 2009) to eliminate PFOS in environmental water. The published data on adsorption of PFOS onto non-ion-exchange synthetic polymer materials is still not available.
The objectives of this study were to investigate and to compare the sorption behaviors of PFOS on ion-exchange and non-ion-exchange commercial adsorbents including activated carbon at low equilibrium concentration (<1 μg L−1). In this study, the sorption kinetics and sorption isotherms of PFOS for Dowex polymers (DowV493, DowL493 and DowMarathonA), Amberlite polymers (AmbXAD4 and AmbIRA400) and Filtrasorb 400 (GAC) were studied in detail.
Section snippets
PFOS and adsorbents
PFOS (98%) was purchased from Wako Chemicals (Japan). Ion-exchange polymers, non-ion-exchange polymers and Filtrasorb 400 (GAC) were purchased from Dow Chemicals (USA) and Sigma Aldrich (USA).
Adsorbent pretreatment
Prior to the use in the sorption experiment, synthetic polymers were first washed in deionized water to remove dirt and then dried at 50 °C until reached constant weight. Similarly, the coal-based activated carbon of Filtrasorb 400 was first rinsed with deionized water for several times and then washed in 80
Sorption isotherms
Most of the polymers tested in this study are widely used in water and wastewater treatment, particularly for organics. The adsorptive capacities of six polymers at a low concentration (100 ng L−1) were calculated by fitting the experimental data to Freundlich models. Freundlich equation is an empirical relationship describing the adsorption of solutes from a liquid to a solid surface. It is widely applied to describe adsorption process for many compounds onto heterogeneous surfaces, including
Conclusions
The adsorption of PFOS onto ion-exchange polymers, non-ion-exchange polymers and GAC was demonstrated in this study. Synthetic polymer materials were identified as better filter materials (in terms of adsorption capacity) to eliminate PFOS in water at low concentration (1 μg L−1). The magnitude of Kf decreases in the following order: Ion exchange polymers > non-ion-exchange polymers > GAC, but at further low equilibrium concentration (100 ng L−1) non-ion-exchange polymers showed higher adsorption
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(2009) - Earth Negotiations Bulletin, 2009. Published by the International Institute for Sustainable Development (IISD), vol....