THE ROLE OF BIOFILM GROWTH IN BACTERIA-FACILITATED CONTAMINANT TRANSPORT IN POROUS-MEDIA

Groundwater contaminants adhered to colloid surfaces may migrate to gr eater distances than predicted by using the conventional advective-dis persive transport equation. Introduction of exogenous bacteria in a bi oremediation operation or mobilization of indigenous bacteria in groun dwater aquifers can enhance the transport of contaminants in groundwat er by reducing the retardation effects. Because of their colloidal siz e and favorable surface conditions, bacteria can be efficient contamin ant carriers. In cases where contaminants have low mobility because of their high partition with aquifer solids, facilitated contaminant tra nsport by mobile bacteria can create high contaminant fluxes. In this paper, we developed a methodology to describe the bacteria-facilitated contaminant transport in a subsurface environment using the biofilm t heory. The model is based on mass balance equations for bacteria and c ontaminant. The contaminant is utilized as a substrate for bacterial g rowth. Bacteria are attached to solid surfaces as a biofilm. We invest igate the role of the contaminant adsorption on both biofilm and mobil e bacteria on groundwater contaminant transport. Also, the effect of b acterial injection on the contaminant transport is evaluated in the pr esence of indigenous bacteria in porous media. The model was solved nu merically and validated by experimental data reported in the literatur e. Sensitivity analyses were conducted to deduce the effect of critica l model parameters. Results show that biofilm grows rapidly near the t op of the column where the bacteria and contaminant are injected, and is detached by increasing fluid shear stress and re-attach downstream. The adsorption of contaminant on bacterial surfaces reduces contamina nt mobility remarkably in the presence of a biofilm. The contaminant c oncentration decreases significantly along the biofilm when contaminan t partition into bacteria. Bacterial injection and migration in subsur face environments can be important in bioremediation operations regard less of the presence of indigenous bacteria.