INVESTIGATING THE INFLUENCE OF INCOMPLETE SEPARATION OF SEDIMENT AND WATER ON EXPERIMENTAL SORPTION COEFFICIENTS OF CHLORINATED BENZENES

The influence of incomplete separation of water and sediment in batch sorption experiments was investigated with five chlorinated benzenes (sediment/water ratios between 0.25 and 50 g/L). Only the sorption coefficients of the most hydrophobic chemical, hexachlorobenzene, decreased with increasing sediment/water ratios. This decrease is assumed to be caused by an increasing amount of sediment that was not separated from the aqueous phase. To quantify this incomplete water/sediment separation, the unseparated sediment fraction, called the third phase, was analyzed in suspension water. For this purpose the apparent enhanced solubilities of hexachlorobenzene and two polychlorinated biphenyls were determined in the suspension water. Solubilities of these compounds were found to be considerably enhanced (up to about 8 times). In addition, turbidity, dry weight, and dissolved organic carbon (DOC) measurements were used to quantify the third phase. On the basis of these third-phase analyses, experimental sorption coefficients of hexachlorobenzene were corrected for third-phase influence, where the apparent solubility measurements were the most successful.