Comparison of Cadmium, Lead, and Nickel Tolerance and Removal by Free and Immobilized Soil Bacterial Isolates

Abstract

Heavy metal bioremediation is of utmost importance today in the world. The use of immobilized bacteria cells in matrices such as agarose. alginate and agar-agar have been observed to improve cell stability and removal efficiencies in the removal of heavy metals. This study observed the tolerance and removal efficiencies of ten bacterial isolates in agarose, alginate, agar-agar, and free cells to cadmium, nickel, and lead. Tolerance indices for isolates in media containing nickel ranged from 0.20 to 16.43, 1.48 to 15.88, 0.68 to 2.76, and 0.70 to 0. 97 for agarose, agar-agar, alginate, and free cells respectively. In media containing lead, the tolerance index ranged from 0.27 to 8.77, 0.50 to 6.77, 0.21 to 0.94, and 0.75 to 1.36 for agarose, agar-agar, alginate, and free cells respectively. In media containing cadmium, the tolerance index ranged from 0.02 to 3.09, 0.03 to 0.43, 0.04 to 0.22, and 0.26 to 0.88 for agarose, agar-agar, alginate, and free cells respectively. Removal percentage of isolates in immobilized cells across nickel, lead, and cadmium ranged from 82.5% to 98.5%, 56.03% to 92%, and 82.47% to 96.23% respectively. The significantly high removal percentage of the isolates in immobilized cells emphasizes the capacities of immobilized bacteria cells in the bioremediation of heavy metals. This shows that cell immobilization enhanced the metal removal efficiencies of the bacterial strains by enabling better control over cell retention and activity during remediation. Thus, further research can be carried out in the future.