The biosorption of Pb(II), Zn(II) and Ni(II) from industrial wastewater using Stenotrophomonas maltophilia and Bacillus subtilis was investigated under various experimental conditions regarding pH, metal concentration and contact time. The optimum pH values for the biosorption of the three metals were in the range 5.0-6.0, while the optimal contact time for the two bacterial species was 30 min. Experimental data was analyzed using Langmuir and Freundlich isotherms; the former had a better fit for the biosorption of Pb(II), Zn(II) and Ni(II). The maximum adsorption uptakes (qmax) of the three metals calculated from the Langmuir biosorption equation for S. maltophilia were 133.3, 47.8 and 54.3 for Pb(II), Zn(II) and Ni(II), respectively, and for B. subtilis were 166.7, 49.7 and 57.8 mg/g, respectively. B. subtilis biomass was more favorable for the biosorption of Pb (II) and Ni (II), while S. maltophilia was more useful for the biosorption of Zn (II).
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