TRANSPORT OF BACTERIA DURING UNSTEADY UNSATURATED SOIL-WATER FLOW

Transport of bacteria in porous media has been a subject of great interest in recent years because of its importance in many areas. However, there is a lack of quantitative experimental data on bacterial movement through porous media. Column experiments were carried out to obtain experimental data needed to test the conceptual and mathematical approaches used to describe bacterial transport. Constant-head horizontal infiltration experiments were carried out with bacterial suspensions and three different sand materials. Bacteria were suspended in various solutions: distilled water to which tritium was added (34 MBq L-1), CaCl2 solution at each of two different concentrations (25 and 3 mmol L-1), or KCl solution (75 mmol L-1). In all experiments, bacterial profiles were found to scale in terms of the well-known similarity variable, lambda, defined as distance divided by the square root of time. Compared with Cl- and tritium, the bacterial movement was retarded and the retardation was attributed to the adsorption of bacteria onto the sand surfaces. The ionic strength of the suspending solutions and the soil surface properties were found to affect bacterial transport. A quasi-analytical model was derived for bacterial adsorption and transport during unsaturated unsteady soil water flow for conditions in which the sole mechanism of retention is adsorption. The position of the retarded bacterial concentration fronts were predicted using the model together with independently measured batch adsorption data. The agreement between measured and predicted bacterial concentration fronts was very good for four out of five sets of experiments.