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FIGURE 17.4 Biosorption isotherms of Co2+, Ni2+, and Cr3+ onto P. aeruginosa. The biomass was contacted with metal solution for 10 h at 25°C and 180 rpm in shaking incubator.

that metal uptake by P. aeruginosa was a chemically equilibrated and saturated mechanism. When experimental data were applied to adsorption models such as Langmuir and Freundlich, the data were found to fit in the Langmuir isotherm model reasonably. From the result, the maximum amounts of metals taken up by P. aeruginosa were 188.7 |mol Co2+/g dry weight; 166.7 |mol Ni2+/g dry weight; and 149.3 |mol Cr3+/g dry weight.

17.3.2 Comparing Metal Capacity

Uptake of toxic metal ions may contribute to the detoxification of polluted environments. Therefore, the investigation of the metal capacity of bacteria is fundamental for the field application of biosorption because it gives information about the removal efficiency of metal ions in the process [33]. As a necessary factor for the design of equipment, the metal capacity of bacteria is usually used by the parameter rmax. Table 17.1 shows the maximum metal capacities reported in literature by bacteria.

17.3.3 Influence of Environmental Conditions

In the biosorption process, many environmental factors can influence the metal capacity of bacteria due to the change of bacterial surface properties and the characteristics of metal-bearing streams such as a variable pH and competing ions.

17.3.3.1 Bacterial Growth Phase

The physiological changes between the exponential and stationary phases are often reported to be significant so that cells in the stationary phase have distinct characteristics. When Arthrobacter, for example, reached the stationary phase, t its factor changed from rod to coccoid [26]. Thus, the cell growth phase can be an important factor that affects metal sorption.

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