Determination of bacterial mass recovery in iron-coated sand: Influence of ionic strength

Column experiments were performed in this study to investigate the influence of ionic strength on the mass recovery of Escherichia coli in iron-coated sand. The first set of the experiments was performed in the coated sand under various NaCl concentrations. The second experiments were carried out in the coated sand under various NaCl concentrations with a fixed phosphate concentration. Bacterial mass recoveries were quantified from breakthrough curves. The mass recoveries were compared with those obtained from the experiments in quartz sand under the same ionic strength/composition. Experimental results show that the mass recovery in quartz sand decreased from 76.7 to 9.2% with increasing effective ionic strength (I(e)) from 0 to 149.4 mM using NaCl. In the coated sand, however, the mass recovery remained constant in the range between 2.7 and 3.7% even though I(e) increased in the same range. This indicates that bacterial adhesion to the coated sand may not be affected by ionic strength in the presence of NaCl. Results also illustrate that the mass recovery in quartz sand decreased from 64.7 to 13.3% with increasing I(e) from 0.97 to 149.6 mM using NaCl under a fixed phosphate concentration (0.97 mM as I(e)). In the coated sand, the mass recovery increased sharply to 58.5% in 0.97 mM phosphate concentration compared to the case in deionized water (3.0%). This indicates that in the coated sand bacterial mass recovery can increase due to the presence of phosphate. In addition, the mass recovery in the coated sand decreased from 58.5 to 6.7% with increasing I(e) from 0.97 to 149.6 mM using NaCl under a fixed phosphate concentration (0.97 mM as I(e)). This demonstrates that bacterial adhesion to the coated sand may be influenced by ionic strength in the presence of phosphate.