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A Laboratory Study of Bacteria-Facilitated Cadmium Transport in Alluvial Gravel Aquifer Media

^a Institute of Environmental Science & Research Ltd, PO Box 291 81, Christchurch, New Zealand
^b Animal and Food Science Division, Lincoln University, PO Box 84, Canterbury, New Zealand

View larger version (35K): [in a new window]   Fig. 1. Results of batch experiments on Cd adsorption onto bacteria surface: effect of (a) solution pH, (b) adsorption time, (c) bacterial concentration, (d) bacterial cell size, (e) Cd concentration, and (f) surface charge of the bacterial cells.

View larger version (19K): [in a new window]   Fig. 2. Cadmium–Bacillus subtilis adsorption isotherms. Observed data are in dots and Freundlich function–simulated data are in dashed lines.

View larger version (25K): [in a new window]   Fig. 3. Results of column experiments on Cd transport with Bacillus subtilis spore input concentrations of (a) 9 x 104 colony-forming units (cfu)/mL, pH = 7.0; (b) 7 x 105 cfu/mL, pH = 7.7; and (c) 5.6 x 107 cfu/mL, pH = 7.0. The spores were introduced after about 5 pore volumes injection of Cd and Br.

View larger version (26K): [in a new window]   Fig. 4. Results of column experiments on Cd transport with Escherichia coli input concentrations of (a) 5 x 103 colony-forming units (cfu)/mL, pH = 7.5; (b) 1.6 x 105 cfu/mL, pH = 7.0; and (c) 3.7 x 107 cfu/mL, pH = 7.0. Escherichia coli were introduced after about 5 pore volumes injection of Cd and Br.

View larger version (31K): [in a new window]   Fig. 5. Observed (dots) and CXTFIT-simulated (dashed line) Br concentrations from the equilibrium model. For Cd + Bacillus subtilis experiments: (a) input concentration (c0) = 9 x 104 colony-forming units (cfu)/mL, pH = 7.0; (b) c0 = 7 x 105 cfu/mL, pH = 7.7; and (c) c0 = 5.6 x 107 cfu/mL, pH = 7.0. For Cd + Escherichia coli experiments: (a) c0 = 5 x 103 cfu/mL, pH = 7.5; (b) c0 = 1.6 x 105 cfu/mL, pH = 7.0; and (c) c0 = 3.7 x 107 cfu/mL, pH = 7.0.

View larger version (27K): [in a new window]   Fig. 6. Observed (dots) and CXTFIT-simulated (dashed line) bacteria concentrations. Bacteria were introduced after about 5 pore volumes injection of Cd and Br. For Cd + Bacillus subtilis experiments: (a) input concentration (c0) = 9 x 104 colony-forming units (cfu)/mL, pH = 7.0; (b) c0 = 7 x 105 cfu/mL, pH = 7.7; and (c) c0 = 5.6 x 107 cfu/mL, pH = 7.0. For Cd + Escherichia coli experiments: (a) c0 = 5 x 103 cfu/mL, pH = 7.5; (b) c0 = 1.6 x 105 cfu/mL, pH = 7.0; and (c) c0 = 3.7 x 107 cfu/mL, pH = 7.0.

View larger version (34K): [in a new window]   Fig. 7. Observed (dots) and CXTFIT-simulated (dashed line) Cd concentrations from the two-site adsorption–desorption nonequilibrium model for the individual portions. The shaded lines show model fitting for the whole breakthrough curves. For Cd + Bacillus subtilis experiments: (a) input concentration (c0) = 9 x 104 colony-forming units (cfu)/mL, pH = 7.0; (b) c0 = 7 x 105 cfu/mL, pH = 7.7; and (c) c0 = 5.6 x 107 cfu/mL, pH = 7.0. For Cd + Escherichia coli experiments: (a) c0 = 5 x 103 cfu/mL, pH = 7.5; (b) c0 = 1.6 x 105 cfu/mL, pH = 7.0; and (c) c0 = 3.7 x 107 cfu/mL, pH = 7.0.