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

A circulation-through-column (CTC) technique was developed and employed to evaluate the influence of fundamental differences between batch and miscible displacement (MD) techniques on the value of the sorption distribution coefficient (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. Batch-determined 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 fixed percent reduction in the retardation coefficient determined from solute BTCs, suggesting a possible leftward shift of these curves.