Performance of Streptomyces rimosus biomass in biosorption of heavy metals from aqueous solutions

The removal of heavy metals by Streptomyces rimosus has been the subject of many investigations. This review paper focuses on the removal of heavy metals from aqueous solution through Streptomyces rimosus, produced from pharmaceutical industry as solid waste, as adsorbent, and discusses the effect of various process parameters like pH, temperature, metal concentration etc., on the metal removal efficiency of this bacterium. The paper also evaluates the different kinetic, equilibrium, and thermodynamic models used in Streptomyces rimosus sorption of heavy metals. Biomass characterization and sorption mechanisms as well as elution of metal ions are also discussed. The literature revealed that Streptomyces rimosus had a good affinity for binding lead and iron compared with other heavy metals. The adsorption of heavy metals is well described by Langmuir isotherm, which expresses the existence of monolayer adsorption. The kinetic data followed both pseudo first order and pseudo second order models. Thermodynamic studies showed spontaneous and exothermic nature of the sorption processes in most case. Dilute acids (HCl and H2SO4) are quite effective in desorption of heavy metals. Ion exchange played the chief role in the adsorption mechanism of metal, and carboxyl groups are mainly involved in this mechanism.