TRANSPORT OF REACTIVE COLLOIDS AND CONTAMINANTS IN GROUNDWATER - EFFECT OF NONLINEAR KINETIC INTERACTIONS

Transport of reactive colloids in groundwater may enhance the transpor t of contaminants in groundwater. Often, the interpretation of results of transport experiments is not a simple task as both reactions of co lloids with the solid matrix and reactions of contaminants with the so lid matrix and mobile and immobile colloids may be time dependent and nonlinear. Further colloid transport properties may differ from solute transport properties. In this paper, a one-dimensional model for coup led colloid and contaminant transport in a porous medium (COLTRAP) is presented together with simulation results. Calculated breakthrough cu rves (BTC's) during contamination and decontamination show systematica lly the effect of nonlinear and kinetic interactions on contaminant tr ansport in the presence of reactive colloids, and the effect of colloi d transport properties that differ from solute transport properties. I t is shown that in case of linear kinetic reactions, the rate of excha nge of mobile and immobile colloids have a large impact on the shape o f BTC's even if the solid matrix is saturated with respect to colloids . BTC's during the contamination and decontamination phase have identi cal shapes in this case. Moreover, the slow reactions of contaminants and colloids may lead to unretarded breakthrough of contaminants. Inde pendent of reaction rates, nonlinear reactions lead to BTC's that are steeper during contamination than in the linear case. A characteristic aspect of nonlinear sorption is that shapes of BTC's differ during th e contamination and decontamination phase. It has been observed that s hapes of some of the simulated adsorption and desorption curves are si milar as shapes found in experiments reported in literature. This stre sses the importance of incorporating both kinetics and nonlinearity in models for coupled colloid and contaminant transport and the capabili ty of COLTRAP to interpret experimental results. Finally, to figure ou t whether nonlinear processes play a role, it is very important to con sider both contamination and decontamination in transport experiments. (C) 1998 Elsevier Science B.V. All rights reserved.