Reductive dehalogenation of trichloroethylene by zero-valent iron and multiphase transport model

Reductive dehalogenation of trichloroethylene (TCE) using zero-valent iron was studied. Laboratory studies were carried out to get an insight into the mechanism of the reaction and thereby improve the rate of degradation. The rate of reaction was found to be independent of the initial concentration of TCE. initial pH had an insignificant effect on the degradation process. Surface area of the metal was found to be a critical parameter in the reductive dehalogenation. A two-fold increase in the rate constant was observed when the particle size was decreased by a factor of 2.5. In order to increase the relative abundance of active sites on the iron surface, the metal was treated with chloride before reaction. Pretreatment of the iron surface with chloride ions significantly increased the initial reaction rate. This was corroborated further by the surface analysis of structure of iron using Atomic Force Microscopy.; A kinetic model was developed to predict the behavior of such a two-phase reactive system. The model was verified using the experimental results and data from the literature. The model was also used to investigate the effect of different variables on the system. These variables are very difficult to achieve through intricate experimental analysis. The general model developed can be easily modified to take into account the system-dependent conditions. The sorption of TCE onto the iron molecule was included in the model by introducing a new concept of 'fractional active site concentration'.; To better understand the fate and transport of volatile organic contaminants in the subsurface environment, a model was developed using the Least Squares Finite Element Method to simulate multiphase, multicomponent transport in porous media. This method is superior for advection-dominated problems. The LSFEM always results in a symmetric and positive definite matrix. One-dimensional and two-dimensional immiscible problems were solved to study he applicability of the LSFEM in subsurface transport. The use of upstream weighting, which often leads to the smearing of the front and may cause grid orientation effects, was found be unnecessary for the example problems studied. The Symmetric Positive Definite (SPD) feature of the LSFEM makes it an attractive method for predictive simulation of subsurface movement of both immiscible and miscible contaminants. vement of both immiscible and miscible contaminants.