Group Contribution Method for Predicting Equilibria of Nonionic Organic Compounds between Soil Organic Matter and Water

摘要

Soil organic matter (SOM) is known to be responsible for nonionic organic compound sorption in water-saturated soil, but the equilibria and kinetics of this process are not fully understood. Since the kinetics depend on the equilibrium driving force, understanding the equilibrium solubility of organic compounds in SOM is particularly important. This work describes a method of predicting SOM-water partition coefficients for nonionic organic compounds based on the UNIFAC-type models. Partition coefficients are calculated from the predicted activity coefficients of organic compounds in water and in SOM phases. A model humic acid molecule is used to represent SOM as a polymeric phase, and the ELBRO-FV model is applied to predict SOM-solute activity coefficients. This method resulted in partition coefficients that were within 1 order of magnitude of experimental values for most compounds studied. Chlorinated compounds do not seem to be modeled well by this method, and predictions may be in error by an order of magnitude. Using data ratherthan UNIFAC predictions for the water phase activity coefficients improved the predictions to within a factor of 3 of the experimental values for all compounds where activity data was available.