Biosorption Kinetics of Various Metals by Aerobic Granules

Biosorption of Cd2+ by Aerobic Granules

It can be seen from Figs 11.1 and 11.2 that the proposed kinetic model (equation (11.9)) can provide a satisfactory description for the cadmium biosorption data obtained at various initial cadmium and aerobic granules concentrations, indicated by a coefficient of correlation greater than 0.91. Figure 11.1 shows the biosorption profiles of cadmium at different initial cadmium concentrations (C0), indicating that about 50% of the amount of adsorbed cadmium at equilibrium was removed in the first 1 h of the test,

100 150 200 Contact time (min)

Fig. 11.2. Biosorption profiles of Cd2+ at different initial aerobic granules concentrations, while initial Cd2+ concentration was kept at 100mg/l. The model prediction is shown by a solid curve (Liu et al., 2003a).

100 150 200 Contact time (min)

Fig. 11.2. Biosorption profiles of Cd2+ at different initial aerobic granules concentrations, while initial Cd2+ concentration was kept at 100mg/l. The model prediction is shown by a solid curve (Liu et al., 2003a).

and the biosorption equilibrium was gradually achieved in 3 h. When the initial granules concentration was constant, the increased Cd2+ concentration led to an increase in the Cd2+ uptake capacity from 38.2 mg Cd2+/g granules at 10mg/l Cd2+ to 99.8 mg Cd2+/g granules at 150mg/l Cd2+. These seem to imply that the initial Cd2+ concentration has a significant influence on its biosorption by aerobic granules, i.e. biosorption process would slow down when the initial metal concentration is low. Scott and Karanjkar (1992) also reported that when the cadmium concentration increased from 25 to 500 mg/l, the corresponding time required to achieve the equilibrium of biosorption by Enterobater aerogens decreased accordingly.

Figure 11.2 shows the biosorption profiles of cadmium at different initial aerobic granules concentrations (X0), while the initial cadmium concentration was fixed at 100 mg/l. The cadmium biosorption could reach equilibrium within 4 h at all X0 studied. It should be realized that the cadmium uptake capacity by aerobic granules tend to decrease with increasing initial aerobic granules concentration.

Biosorption of Cu2+ by Aerobic Granules

Figure 11.3 shows the biosorption profiles of copper at different initial copper concentrations with a fixed granules concentration of 100 mg/l, while Fig. 11.4 displays the biosorption behaviors of copper at different initial granules concentration with a constant initial copper concentration of 100 mg/l. It can be seen that for both cases, the predictions by equation (11.9) are in good agreement with the experimental data, indicated by a correlation coefficient greater than 0.93.

It appears from Figs 11.3 and 11.4 that the patterns of copper biosorption by aerobic granules are similar to those of cadmium biosorption at various initial metal ions and aerobic granules concentrations. At the constant initial aerobic granules concentration, the increase in the Cu2+ concentration led to an increase in the Cu2+ biosorption capacity from 8.65 mg Cu2+/g granules at 2 mg/l Cu2+ to 29.8 mg Cu2+/g granules at 100 mg/l Cu2+. It seems that the Cu2+ biosorption capacity by aerobic granules is related to initial Cu2+ concentration, while at a fixed initial Cu2+ concentration, an increase of initial aerobic granules concentration would result in a decline in the Cu2+ uptake capacity by aerobic granules.

0 30

100 150

Contact time (min)

Fig. 11.3. Biosorption profiles of Cu2+ at different initial Cu2+ concentration with a constant initial aerobic granules concentration of 100 mg/l. The model prediction is shown by a solid curve (Xu, 2006).

A A

A A

A

A

—A-A

k

—ft-a—

o

r / — w

100 150 200 Contact time (min)

100 150 200 Contact time (min)

Fig. 11.4. Biosorption profiles of Cu2+ at different initial aerobic granules concentrations with a constant initial Cu2+ concentration of 100 mg/l. The model prediction is shown by a solid curve (Xu, 2006).

Compared with cadmium biosorption by aerobic granules, the copper removal by aerobic granules is a fast process, e.g. about 50% of the amount of adsorbed copper at equilibrium was removed in the first half hour of contact, and the equilibrium was attained after two hours of contact. Meanwhile, Fig. 11.4 reveals that the uptake of copper at higher initial copper concentrations was faster than that observed at the lower initial copper concentrations, e.g. at an initial copper concentration of 2mg/l, the time required to attain the biosorption equilibrium was about two hours, however the copper biosorption can reach the equilibrium within one hour at an initial copper concentration of 100mg/l.

Biosorption ofZn 2+ by Aerobic Granules

The biosorption profiles of zinc at different initial zinc concentrations (Co) and aerobic granules concentrations (X0) were illustrated in Figs 11.5 and 11.6, respectively. It can be seen that the proposed model (equation (11.9)) can fit those biosorption data well, indicated by a correlation coefficient greater than 0.88. It can be seen that the zinc biosorption by aerobic granules could reach the equilibrium within one hour. Compared to the

Contact time (min)

Fig. 11.5. Biosorption profiles of Zn2+ at different initial Zn2+ concentrations with a constant initial aerobic granules concentration of 100mg/l. The model prediction is shown by a solid curve (Liu et al., 2002).

Contact time (min)

Fig. 11.5. Biosorption profiles of Zn2+ at different initial Zn2+ concentrations with a constant initial aerobic granules concentration of 100mg/l. The model prediction is shown by a solid curve (Liu et al., 2002).

Contact time (min)

Contact time (min)

Fig. 11.6. Biosorption profiles of Zn2+ at different initial granules concentrations with a constant Zn2+ concentration of 100mg/l. The model prediction is shown by a solid curve (Liu et al., 2002).

Fig. 11.6. Biosorption profiles of Zn2+ at different initial granules concentrations with a constant Zn2+ concentration of 100mg/l. The model prediction is shown by a solid curve (Liu et al., 2002).

biosorption of cadmium and copper, it seems that the zinc uptake by aerobic granules is a faster process.

Was this article helpful?

0 0

Post a comment