CONTAMINANT TRANSPORT IN GROUNDWATER IN THE PRESENCE OF COLLOIDS AND BACTERIA

Abstract

Colloids and Bacteria (microorganisms) naturally exist in groundwater aquifers and can significantly impact contaminant migration rates. During the past decade, a significant effort has been devoted to studying separately either colloids- or bacteria­ associated contaminant transport, but the combined effect of both colloids and bacteria has not been thoroughly explored. In addition, many of the previous studies are restricted to one-dimensional analysis. In the present study, a conceptual model is first developed to account for the different physiochemical and biological processes, reaction kinetics, and different transport mechanisms of the combined system (contaminant-colloids-bacteria). The mass balance equations are numerically solved for two-dimensional groundwater systems using a third-order, total variance­ diminishing scheme (TVD) for the advection terms. The TVD scheme significantly reduces numerical dispersion. The model is tested against experimental data and the results are favorable. The model is used to investigate the effects of various reaction rates and parameter values on the transport of contaminant in the combined system. The model is also used to investigate the hypothesis of using colloids as retarding agents in a bioremediation process. The analysis shows that the contaminant transport is more sensitive to reaction rates that govern colloid transport than to those governing bacterial transport. !tis also found that accounting for biological processes like bacterial growth and decay, bacterial chemotaxis, and bacterial lysing are essential for a successful bioremediation modeling. The model further illustrates that using colloids with a high affinity to the soil particles factor can help immobilize contaminant plumes and thereby can maximize the benefits of remediation efforts of groundwater contaminated aquifers.