Sorption and Transport Behaviour of Hydrophobic Organic Compounds in Soils and Sediments of Bangladesh and Their Impact on Groundwater Pollution : Laboratory Investigations and Model Simulations

Abstract

*** Zugleich als Dissertation an der Univ. Tübingen erschienen, 2002 *** This thesis focuses on the elucidation of the sorption and related transport processes controlling the fate of hydrophobic organic compounds (HOCs) (contaminants and pesticide) in the subsurface environment. For a variety of organic compounds (phenanthrene, 1,2-DCB, TCE and carbofuran) batch and column experiments were carried out with different geosorbents (deltaic, floodplain and residuum soils, aquifer sediments and peat) to simulate the effect in Bangladesh top soils and sediments and the ultimate impact on groundwater. Overall, the results reported here so far indicate that sorption in these samples for the chemicals investigated is dominated by the partitioning processes. A nonlinear type sorption isotherm is described by the combination of the partitioning and pore-filling mechanisms. The solubility normalized Freundlich model predicts an inverse linear relationship between the sorption coefficient measured at a given relative concentration vs. S which facilitate the prediction of sorption of a variety of pollutants based on measured data of one probe compound. An effect of preferential solute transport coupled with diffusion into the surrounding matrix region has been examined by conducting macropore flow column experiments. A new analytical solution was developed to model the breakthrough curves. The model accounts for advection in the macropore region, diffusion into the matrix region and linear sorption in both regions. From the experimental results and the model assumptions it was concluded that sorption equilibrium was not achieved during matrix diffusion at the time scale of the macropore flow experiment. The combination of batch and column experimental results together with materials (solids) and environmental properties and a use of solute transport model, can provide tools for cost-effective soil and groundwater risk assessment.

*** Published as printed thesis at Tuebingen University, 2002 ***