Laboratory study of intrinsic degradation of organic pollutants in compacted clayey soil

This thesis examines the intrinsic biodegradation of selected organic pollutants under diffusive transport in laboratory compacted clayey soil. A series of 16 cells containing clayey soil were placed in contact with an essentially constant source solution consisting of a synthetic blend of volatile fatty acids (VFAs), BTEX and chlorinated aliphatic solvents. Results from the tests indicate that as they diffuse through the soil, most of the pollutants tested degrade slowly but steadily in the soil, even under adverse conditions imposed by compaction and flow limitations. The process is modeled as diffusion coupled with linear sorption and first order biological decay. Estimates of the intrinsic degradation rates for selected chemicals under diffusive transport through the clay under laboratory conditions are given in this thesis.; Separate series of diffusion-degradation tests were performed with Keele Valley Landfill leachate with an emphasis on the fate of dichloromethane alone. These tests provide additional evidence of dichloromethane degradation in the compacted soil plugs. Very fast anaerobic degradation of dichloromethane is also observed in the batch tests with the Keele Valley Landfill leachate.; Diffusion coefficients are obtained from independent short-term tests with the same soil and solution medium. Batch equilibrium tests are performed in order to obtain the sorption coefficients for the chemicals. The diffusion and linear sorption coefficients deduced for the 11 pollutants examined are also presented. Results from the short-term tests are in excellent agreement with those obtained for modeling of the long-term intrinsic degradation under diffusive transport. The impact of VFAs, dichloromethane, benzene and xylenes on an aquifer under a hypothetical landfill was modeled using the values of diffusion, sorption and degradation coefficients determined in the experiments. The results of the transport simulation for a simple barrier with primary and secondary leachate collection system and clay liner indicate that intrinsic degradation could significantly reduce contamination of underlying groundwater.