Biosorption of lead, copper and cadmium by biomass of Pseudomonas aeruginosa PU21

In this study, the biosorption kinetics of lead (Pb), copper (Cu) and cadmium (Cd) ions on the biomass of Pseudomonas aeruginosa PU21 (Rip64) was investigated. Effects of environmental factors and growth conditions on the biosorption were studied. Efficiency of metal ion recovery from metal-loaded biomass and subsequent regeneration of the biosorbent were also determined. The results show that, at pH 5.5, the resting cells were able to uptake up to 110 mg Pb/g dry cell, and the inactivated cells can adsorb 70 mg Pb/g dry cell. Biomass of P. aeruginosa PU21 (Rip64) had lower adsorption capacities for Cu and Cd ions than for lead ions. The resting cells had the maximum uptake of 23 mg Cu/g dry cell (at pH 5.0) and had 58 mg Cd/g dry cell (at pH 6.0). The saturation uptake capacities of inactivated cells were 19 mg Cu/g dry cell (at pH 5.0) and 43 mg Cd/g dry cell (at pH 6.0). The resting cells held optimal Pb adsorption capacity at the early stationary phase, whereas the best uptake of cadmium was observed with the cells which were of exponential growth phase. The growth phase exhibited no effects on the adsorption of Cu, however. The increase in mercury concentration (from 0 to 50 mg Hg²⁺/litre) in the growth media did not significantly affect the adsorption capacities of Pb²⁺, Cu²⁺ and Cd²⁺. However, the saturation uptake capacity and metal-cell affinity tended to increase as pH increased, until metals precipitated as metal hydroxides when the pH exceeded some threshold values. Adjusting the pH value to about 2.0 resulted in 98, 98 and 82% recovery of Pb, Cu and Cd, respectively. The biomass resulted from desorption processes was able to retain approximately 80% of original adsorption capacity for Pb and Cu with four repeated adsorption and recovery runs. Regeneration of biomass appears to enhance the uptake capacity of Cd by nearly 35% after four adsorption/desorption cycles.