Irreversible sorption of benzene in sandy aquifer materials

Abstract

Abstract:Hydrocarbon compounds in aquifers are generally known to show a retardation effect due to sorption onto the surfaces of solid particles. In this study, we investigated the effect of sorption on the transport of benzene in sandy aquifer materials by conducting batch and column tests for both sandy aquifer materials and sandy materials to which had been added 0Ð5% powdered activated carbon. The batch test was conducted by equilibrating dry materials with benzene solutions of various initial concentrations, and by analysing the concentrations of benzene in the initial and equilibrated solutions using high-performance liquid chromatography (HPLC). The column test was performed to monitor the concentrations of effluent versus time, known as a breakthrough curve (BTC). We injected KCl and benzene solutions as tracers into the inlet boundary as two different types of square pulse and step, and monitored the effluent concentrations at the exit boundary under a steady-state condition using an electrical conductivity meter and HPLC. Simulation of benzene transport was performed using the convective-dispersive equation model with the distribution coefficients obtained from the batch test and the transport parameters of the conservative solute KCl from the column test. The observed BTCs of KCl and benzene for pulse injection showed that the arrival times of the peaks of both tracers coincided well, but the relative peak concentration of benzene was much lower than that of KCl. Comparison of the simulated and observed BTCs showed a great discrepancy for all cases of injection mode and material texture, indicating the absence of retardation effect. These results reveal that the predominant process affecting the benzene transport in the sandy aquifer materials is an irreversible sorption rather than retardation. This tentative conclusion was verified by simulation of benzene transport using an irreversible sorption parameter that led to a good agreement between the simulated and observed BTCs.

Analysis of benzene transport in a two-dimensional aquifer model

“…These values are considerably different from the results of Priddle and Jackson (1991), who reported from a laboratory column experiment that benzene was retarded 14Ð3 times relative to a conservative tracer. However, they were slightly overestimated compared to the results of Baek et al (2003), who found that no benzene retardation occurred during transport through sandy aquifer materials. Despite the same aquifer materials being used in the two laboratory aquifer model tests, the discrepancy between the results from this study and Baek et al (2003) can be attributed to the effect of flow velocity on the benzene retardation.…”

“…Mass reduction of hydrocarbon compounds by volatilization was also reported by Chiang et al (1989) and Lahvis et al (1999), who observed volatilization along with biodegradation of BTX compounds in a shallow aquifer and at gasoline spill sites, respectively. Recently, mass reduction by irreversible sorption was also reported by Baek et al (2003), who investigated the irreversible sorption of benzene using a column approach, showing that a significant amount of the added benzene was not desorbed from the same sandy material. Thus, volatilization coupled with irreversible sorption can be major processes affecting the fate of aqueous benzene during transport through the aquifer materials.…”

“…The advective-dispersive transport equation (Zheng, 1992) for a reactive solute in a saturated flow regime showing retardation and decay, such as any loss from irreversible sorption (Baek et al, 2003) and/or volatilization, can be written as:…”

“…Very recently, Baek et al (2003) reported the occurrence of irreversible benzene sorption in sandy aquifer materials, and Kim et al (2004) determined laboratory-scale dispersivities from two-dimensional KCl plume data obtained from the same aquifer model. Hence, following the previous study of Kim et al (2004), we further investigated the fate and transport of aqueous benzene by conducting a two-dimensional plume test in the same aquifer model.…”

Volatilization of benzene from gasoline: the effect of ethanol blends

“…Baek et al [14] studied the benzene sorption in sand and conducted a test to verify the influence of Plexiglass ® in the results. In a separate experiment concentrations of benzene solution were measured with time for glass and Plexiglass containers under a closed system.…”