**3. Results and discussion**

#### **3.1 Binding capacities of native and modified** *d. innoxia*

Figure 1 illustrates a sequential 50-mL exposure of 0.1mM Zn2+, Ni2+, and Cd2+ to the native *D. innoxia*. Figure 2 shows the sequential 50-mL exposures of 0.2mM Zn2+, Ni2+, and Cd2+ to the modified biomaterial. Table 2 lists the observed binding capacities for the three metals to the modified *D. innoxia* reported in moles metal bound per gram of biomaterial for each replicate. The capacities reported are mass balance capacities, as the column effluent was monitored.

Simple statistical analysis using a t-test confirms the binding capacity of each metal to the biomaterial was decreased as expected. The position of the metal in the sequence was similarly indicated as affecting capacities in both the native and the modified biomaterial materials. Further statistical analysis indicated that not only the position in the sequence but

**2.4 Frontal affinity chromatography with inductively coupled plasma atomic emission** 

This technique has been described in detail elsewhere (Williams and Rayson, 2003). Briefly, the biomass packed column, having been exposed to 20 mL of 1.0M HCl to remove any metals remaining on the biomaterial (effluent monitored by ICPAES), was exposed to 5 mL of 16 M, distilled-deionized water. The influent was a metal-ion solution, 0.1mM-0.2mM, made from the nitrate salt of Cd2+, Ni2+, or Zn2+. Initially, the influent metal ion

Each influent was pumped through a column using a peristaltic pump (Rainin) at the rate of ~1.0 mL min-1 to a cross-flow type nebulizer and Scott-type double-pass spray chamber of the ICP-OES spectrometer (Jarrell-Ash, AtomComp700). The biomaterial in each column was exposed to each metal solution for 50 minutes. The effluent was monitored and resulting break-through curves were recorded for each metal ion (Figures 1A-C). Following exposure to the column, bound metal ions were stripped from the column using each of two exposures to a 1.0 M HCl solution. The first 150-second (~2.5 mL) exposure removed approximately 98% of the metal ions on the column (Figure 1D). The second 20 minute (~20 mL) exposure removed the remaining 2%. This was followed by a 5 minute (~5 mL) rinse with distilled deionized water to return the pH to f the biomaterial to that of the natural water (~6.2). Influent pH was not buffered to a predetermined pH to more accurately

With a three metal system there are six combinations that the metals can be sequentially exposed to the biomaterial (CdZnNi, CdNiZn, NiCdZn, NiZnCd, ZnCdNi, and ZnNiCd) and all six were performed on each column. Specifically, the ZnNiCd sequence involved exposure of a column packed with a biosorbents to a 0.20 mM Zn2+solution for 50 minutes (Figure 1A). The influent was changed to a 0.20 mM Ni2+ solution for another 50 minutes (Figure 1B). Similarly, a 0.20 mM Cd2+ solution was pumped through the same column for an additional 50 minutes (Figure 1C). The column was then exposed to 1.0 M HCl for 2.5

Simultaneous exposure of the three metals at the same molar concentration was also undertaken for each column with both the native (Figure 2) and modified (not shown) biomaterials. All determinations were performed in triplicate with three separate columns

Figure 1 illustrates a sequential 50-mL exposure of 0.1mM Zn2+, Ni2+, and Cd2+ to the native *D. innoxia*. Figure 2 shows the sequential 50-mL exposures of 0.2mM Zn2+, Ni2+, and Cd2+ to the modified biomaterial. Table 2 lists the observed binding capacities for the three metals to the modified *D. innoxia* reported in moles metal bound per gram of biomaterial for each replicate. The capacities reported are mass balance capacities, as the column effluent was

Simple statistical analysis using a t-test confirms the binding capacity of each metal to the biomaterial was decreased as expected. The position of the metal in the sequence was similarly indicated as affecting capacities in both the native and the modified biomaterial materials. Further statistical analysis indicated that not only the position in the sequence but

emulate conditions of a natural water supply within a remediation application.

and 20 minutes to remove all bound metal ions (Figure 1D).

**3.1 Binding capacities of native and modified** *d. innoxia*

packed with each individual biosorbent.

**3. Results and discussion** 

monitored.

**detection** 

concentration increased as a step function.

the history of exposure appears to impact apparent steady state binding metal ion capacities of the biomaterial.

Fig. 1. Effluent profiles resulting from solutions of (A) 0.2mM Zn2+ (), (B) followed by 0.2 mM Ni2+ (□), followed by 0.2mM Cd2+() pumped through a column packed with chemically modified *D. innoxia*.(D) Effluent profile of first 1.0M HCl wash of the metal-laden material.
