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.