Competitive Effects of Cu~(2+) and Cd~(2+) on the Biosorption of Pb~(2+) by Activated Sludge

[Objective] Batch experiments were conducted to assess the competitive effects of Cu2+ and Cd2+ on the biosorption of Pb2+ ions by fresh activated sludge.[Method] The biosorption capacity of Pb2+ was studied for single,binary and ternary solutions at different initial concentrations and pH values.[Result] The biosorption capacity was significantly affected by contact time,pH value and initial ion concentration.The single heavy metal biosorption experiments data was fitted to two isotherm models of Langmuir and Freundlich,respectively,the Langmuir isotherm model gave better fit for the experimental data.The maximum Pb2+ biosorption capacity was 186.81 mg/g in the single metal biosorption conditions,while the data decreased to 138.94 mg/g by adding 30 mg/L Cu2+ and raised to 214.58 mg/g by adding 30 mg/L Cd2+.In the preference experiment study,the initial adsorption mole numbers of Pb2+ and Cu2+ were nearly the same,but desorption of Cu2+(0.300 mmol/L) seemed to be more easier than Pb2+(0.089 mmol/L) after adding the second heavy metal.[Conclusion] Low concentration of Cd2+ in the binary system may promote the biosorption of Pb2+ by activated sludge,but have adverse effects at higher concentration.In spite of low or high concentration,Cu2+ restrains the biosorption of Pb2+ with more obvious effects.Comparison between biosorption of Pb2+ and Cu2+ by fresh activated sludge in the binary solution could lead to the conclusion that the biosorbent has better preference of Pb2+ to Cu2+.