Experimental and modeling studies of the fate of organic contaminants in the presence of alfalfa plants

Abstract

Experimental investigations were carried out in the laboratory to study the impact of vegetation in bioremediating soil and groundwater contaminated with hazardous organic substances. A chamber consisting of two U-shaped channels, each 1.8 m in length, 10 cm in width, and 35 cm in depth, was set up. The channels were packed with fine sandy soil collected from near a landfill. Alfalfa plants were grown in the channels under laboratory conditions for nearly two years. The water fed to the plants in one channel was contaminated with toluene solution at saturated concentrations at 26°C. Plants in the other channel were fed with water contaminated with phenol solution at 500 ppm (v/v). The contaminant concentrations in the groundwater were monitored at sampling wells located along each of the channels. The influent and effluent flow rates from each channel were recorded daily. Evapotranspiration significantly influenced the fate of the pollutants. Dispersion and adsorption processes in the channel were studied separately, by introducing bromide tracer as a broad pulse into the toluence fed channel, and by observing the washout of toluene and phenol contaminants following a feed step change to pure water. Tracer studies indicated that short-circuiting at the U-bend of the channel was quite significant. Previously developed models which described the fate of contaminants in variably-saturated soils in the presence of vegetation are employed to simulate the fate of these hazardous organic substances in the laboratory chamber.