Transport and retention of Escherichia coli in a mixture of quartz, Al-coated and Fe-coated sands

摘要

Transport and retention of Escherichia coli through the mixture of quartz, Al-coated and Fe-coated sands was examined using column experiments to investigate the effect of geochemical heterogeneity on bacteria transport. The first set of the experiments was performed in quartz, Al-coated and Fe-coated sand mixtures (coated sand: 0, 5, 10, 25, 50, 100%) to examine the influence of positively-charged sand grains on bacteria transport. The second experiments were carried out to observe the impact of pH (range 6.74-8.21) on bacteria transport in the mixture of quartz 50% and Fe-coated sand 50%. The third experiments were conducted to analyse the effect of ionic strength (0, 50, 100, 200 mM) on bacteria transport in the mixture of quartz 50% and Al-coated sand 50%. The first experiments show that bacterial mass recoveries were in the range of 3.6-43.4%, decreasing nonlinearly as the content of Al- and Fe-coated sands increased. In the second experiments, the bacterial mass recoveries were in the range of 35.5-79.2%, increasing linearly as the solution pH increased. In the third experiments, the mass recovery was 3.4% at 0 mM. As the ionic strength increased to 50mM, the mass recovery decreased to 0%. When the ionic strength increased further to 100 and 200 mM, no bacterial mass was recovered as in the case of 50 mM. It indicates that in the mixed medium of quartz 50% and Al-coated sand 50% both positive (increment of bacterial adhesion) and negative (decrement) effects of ionic strength may be counterbalanced, minimizing the impact of ionic strength on the bacterial adhesion. This study helps to understand the role of metal oxides and solution chemistry in the transport of bacteria in geochemically heterogeneous media..