TRANSPORT OF BACTERIA IN AN AQUIFER SAND - EXPERIMENTS AND MODEL SIMULATIONS

Experiments were carried out to determine the breakthrough of bacteria through a saturated aquifer sand at three flow velocities and three c ell concentrations. Bacteria were either suspended in deionized water or 0.01 mol L(-1) NaCl solution. Bacterial transport was found to incr ease with flow velocity and cell concentration but was significantly r etarded in the presence of 0.01 mol L(-1) NaCl. A mathematical model b ased on the advection-dispersion equation was formulated to describe b acterial transport and retention in porous media. The transport equati ons for bacteria were solved using the finite difference Crank-Nicolso n scheme combined with Newton-Raphson iterations. The best fit of the numerical model to the experimental data was obtained using the downhi ll simplex optimization technique to minimize the sum of the squares o f deviations between model predictions and experimental data by varyin g three parameters. This numerical model was found to describe the exp erimental data very well under all the experimental conditions tested. An alternative model (also based on the advection-dispersion equation ) was tested against all the experimental data sets, but it did not re present the experimental data as well as the model proposed in this pa per.