Biosorption of some heavy metal ions by local isolate of Zoogloea ramigera
Fourteen isolates of Zoogloea ramigera have been successfully isolated from organically polluted wastewater. The isolates were screened for their tolerance to three heavy metals (Cadmium, Chromium and Nickel) using plate diffusion method. Some of the isolates showed relatively high tolerance to the tested metals, while others showed a relatively low tolerance. These results are approved by a quantitative assessment when both tolerant and non-tolerant isolates grown in liquid media supplemented with different metal ion concentrations. A relationship between tolerance and Cd2+ uptake was demonstrated using tolerant and non-tolerant isolates. The optimal conditions for Cd2+ biosorption were characterised. The highest Cd2+ uptake (16.3 mg.g-1biomass) was obtained at pH 7.0 using biomass concentration of 1 g.l-1 from Cd2+ solution of 25 mg.l-1. The bound Cd2+ ions could be released by different washing agents, among them 10 mM HCl, which was found to be the best desorbent agent. The washing step has released the bound metal and allowed the biosorbent (Z6) again to be available for new treatment, at least for three sorption–desorption cycles.
Keywords: biosorption, heavy metals, tolerance, Zoogloea ramigera, wastewater treatment, water pollution, cadmium, chromium, nickel, metal ion concentrations