Importance of Sorption Kinetics in the Partitioning of Organic Pollutants from a Point Source onto Suspended Sediments in the Transverse Mixing Zone

Sorption kinetics for pollutants onto suspended sediments with respect to particle size and onto dissolved organic carbon (DOC) which reversibly partitions on sediments was incorporated into a finite difference sediment transport model. The model for transport with sorption kinetics was developed for the bound to naturally occurring DOC, bound to sediments, and free aqueous pollutant concentrations in the ideal case of a rectangular channel with a steady uniform flow, to evaluate the importance of the formulation of sorption kinetics on the transport of hydrophobic non-ionic organics in the transverse mixing zone of a stream with a point source. Four formulations for partitioning were compared: 1) kinetics for rapid and slow types of kinetically controlled sorption sites, 2) instantaneous equilibrium for the rapid sorption site, 3) overall instantaneous sorption equilibrium, and 4) overall equilibrium without DOC. The common equilibrium models cannot correctly predict the phase distribution of pollutants. The full kinetic description is most important in predicting distributions of the more hydrophobic species, in the transverse mixing zone, and in fast streams.