The desorption of chlorobenzenes from heterogeneous suspended solid mixtures and sediments at nonequilibrium conditions was investigated, using a gas purge method. This technique offers the possibility to measure equilibrium and rate data from adsorbent suspensions, without phase separation. The desorption patterns were interpreted and fitted in terms of multiple box models. The results show that when the equilibration time for sediment suspensions contaminated in the laboratory is longer, desorption is slower. At nonequilibrium conditions, the more hydrophobic chlorobenzenes are released faster than the less hydrophobic ones.
For ten suspended solid samples the model parameters were related to adsorbent characteristics, such as organic matter, phytoplankton and clay content by means of correlation analysis, and compared to similar desorption data for algal cultures obtained in earlier studies in our laboratory. It was found that all desorption data could be described with a two-compartment desorption model. The partition coefficient was proportional to the content of organic matter, which in turn was mainly determined by the concentration of phytoplankton in the samples. The desorption rate was positively correlated with the phytoplankton content as well. This suggests that phytoplankton cells form an easily accessible fraction of the total adsorbent.