Effects of fundamental differences between batch and miscible displacement techniques on sorption distribution coefficient

Abstract

A circulation-through-column (CTC) technique was developed and employed to evaluate the in¯uence of fundamental differences between batch and miscible displacement (MD) techniques on the value of the sorption distribution coef®cient (K). Batch, MD, and CTC experiments were conducted to determine sorption equilibrium parameters for dimethylphthalate (DMP), diethylphthalate (DEP), and dipropylphthalate (DPP) using two natural soil samples with 0.36 and 1.48% organic carbon. Batch sorption isotherms of DMP and DEP were linear while that of DPP was nonlinear. Batchdetermined K values for the compounds were 30 to 170% higher than the corresponding values obtained from breakthrough curves (BTCs) generated through MD experiments. Similarities between values of K derived from batch and CTC techniques suggest that underestimation of K determined from BTCs is not due to fundamental differences between batch and MD techniques. The extent of deviation between the K values determined by batch and MD experiments was inversely related to the value of K. This was well explained by a ®xed percent reduction in the retardation coef®cient determined from solute BTCs, suggesting a possible leftward shift of these curves.

Ability of Single-Rate Models to Predict Solute Distribution Coefficients in Systems with Heterogeneous Sorption Kinetics

“…Several studies have reported discrepancies between the K values of organic compounds determined by batch and column techniques. In most cases, the batch-determined values were higher than their column-determined counterparts (Bilkert and Rao 1985;Celorie et al 1989;Gaber et al 1992;Piatt et al 1996;Maraqa et al 1998Maraqa et al , 2011Maraqa 2001a;Thorbjarnarson and Mackay 1994b;MacIntyre et al 1991;Carmichael et al 1999;Bouchard et al 1988;Perillo et al 1998;Thomsen et al 1999;Kazemi et al 2008;Hanna et al 2012). The level of discrepancy between the batch-and column-determined K varies from slight differences (Bouchard et al 1988;Celorie et al 1989;Maraqa et al 1998;Maraqa 2001a) to differences that reached orders of magnitude (Piatt et al 1996).…”

“…This method was used by Maraqa (2001a) for the determination of K for few phthalate esters. Results obtained by this method were found to be comparable to those obtained from batch isotherm experiments Maraqa (2001a).…”

“…This method was used by Maraqa (2001a) for the determination of K for few phthalate esters. Results obtained by this method were found to be comparable to those obtained from batch isotherm experiments Maraqa (2001a). The method, however, is more difficult to conduct than the batch experiment since it requires a separate column run to generate each data point on the sorption isotherm curve.…”

“…Results from batch and column methods are generally more accurate in predicting contaminant movement. For the column method, K is calculated from the retardation factor, which is typically determined either by moment analysis of breakthrough curves (BTCs) (Thorbjarnarson and Mackay 1994a;Piatt et al 1996;Maraqa et al 1998;Maraqa 2001a) or by curve fitting a transport model to the breakthrough data. Both equilibrium (Gaber et al 1992) and nonequilibrium (Ptacek and Gillham 1992; Thorbjarnarson and Mackay 1994b;Maraqa et al 1998;Pot et al 2005;Dousset et al 2007;Maraqa et al 2011) transport models have been used for such a purpose, but the latter are more appropriate to use in many situations (Brusseau and Rao 1989).…”

Simulação do transporte e da sorção de imazaquin em colunas de solo

“…No caso do imazaquin, a sua difusão em partículas minerais do solo não pode ser completamente descartada. A molécula apresenta dois grupos funcionais ionizáveis: um grupo carboxílico (ácido, pK a = 3,8) e um grupo quinolina (básico, pk a = 2,0) (Stougaard et al, 1990 (Gonzalez & Ukrainczyk, 1999;Maraqa, 2001). Esta discrepância tem sido atribuída a diversos fatores: (a) no deslocamento miscível, o contato entre o soluto e o sorvente é menor, quando comparado ao método "batch"; (b) o tempo para promover o equilíbrio químico geralmente é menor no deslocamento miscível.…”