لخّصلي

Biosorption study

From Table 2 the biosorption of Pb by S. oneidensis decreased with the increasing of the incubation period for all concentrations.Hence, the percentage removal of metal is dependent on the initial metal concentration forsolutions.And this agrees with Giri (2012), who reported that, maximum removal of As (III and Cr (VI) by living cells of B. cereus took place within a few minutes and equilibrium is reached at 30 min.From the results of present study S. oneidensis was able to absorb higher concentration of Pb than Cd, Banik et al., (2013) reported that Pb does not create any extraordinary toxicity to microorganisms which accumulate Pb through the general biosorption process.The change in the rate of removal with time might be due to the fact that initially all sorbent sites are vacant, and the solution concentration gradient was high, but as time passes, the number of sites on the sorbent filled up and the sorbet also increases.The high absorption.

Biosorption study

From Table 2 the biosorption of Pb by S. oneidensis decreased with the increasing of the incubation period for all concentrations. The high absorption. was 51.06% at concentration 50 mg L¹ for 2h of incubation, while the lowest absorption was 14.00% at concentration 5 mg L for 48h of incubation. Thebiosorption of Cd has the same approach of Pb, in

which the absorption decreased with the increasing

of the incubation period. The highest absorption was 42.64% at concentration 5 mg L, for 2h of incubation and the lowest was 10.41% at concentration 50 mg L¹, for 48h of incubation. The change in the rate of removal with time might be due to the fact that initially all sorbent sites are vacant, and the solution concentration gradient was high, but as time passes, the number of sites on the sorbent filled up and the sorbet also increases. At equilibrium, when all the sites are filled the rate of biosorption is equal to the rate of desorption. So, after equilibrium, it is found that there was no further increase in the removal of metal ion with increases in contact time. And this agrees with Giri (2012), who reported that, maximum removal of As (III and Cr (VI) by living cells of B. cereus took place within a few minutes and equilibrium is reached at 30 min. From the results of present study S. oneidensis was able to absorb higher concentration of Pb than Cd, Banik et al., (2013) reported that Pb does not create any extraordinary toxicity to microorganisms which accumulate Pb through the general biosorption process. The high percentage of Pb sorption was 51.06%, while it was 42.64% for Cd. The results also showed that the biosorption rate of Pb increases with the increase of the concentration for all times. This would suggest that the ratio of initial metal ion concentration to fractional surface area for absorption of metal ions is relatively high. Hence, the percentage removal of metal is dependent on the initial metal concentration forsolutions. Statistically the data showed significant (P>0.05) differences in biosorption for both metals as related to the time and concentration