The Study Of Heavy Metal Removal By Biosorption

With the fast development of mining, metallurgy, metal plating and petrochemical industries, a great deal of wastewater containing the excessive dangerous heavy metal ions was released. These heavy metals cause serious threat to environment and human for their extreme toxicity. Conventional heavy metal wastewater treatments have chemical precipitation, adsorption, chemical oxidation-reduction, ion exchange, membrane separation, and solvent extraction, etc. But these methods have several disadvantages including high-energy requirements, incomplete metal removal, and high capital investment and running costs. In recent years, biosorption is an emerging technology to remove metals from solution, with its rich source of raw materials, low cost and no secondary pollution. For the treatment of low concentrate heavy metal wastewater, it has broad prospects.In this paper, the biosorbent of activated sludge and biofilm have been studied for the adsorption of zinc(Ⅱ) and copper(Ⅱ) from water, respectively. The biosorption processes were studied through batch experiments with regard to the effects of pH, contact time, biomass dose, and initial metal ions concentration. In addition to this, the isotherms, kinetics and thermodynamics of the biosorption were also studied. The result provided theoretical foundation for the practical application of the heavy metal wastewater treatment.In the experiment of biosorption of zinc(Ⅱ) on the dried activated sludge, the pH of the aqueous phase strongly affects the biosorption capacity. It was concluded that the adsorption capacity is favoured by an increase of pH, and the optimum pH was 5. The equilibrium of biosorption was reached within 3h. The zinc removal efficiency increased with increase in adsorbent dosage. The metal adsorption capacity increased while the removal efficiency of zinc(Ⅱ) decreased with an increase in initial zinc ion concentration. The equilibrium data were modeled by the Langmuir and Freundlich models. The results demonstrate that the Langmuir model fits better than the Freundlich model for the adsorption equilibrium data in the examined concentration range of 0-200 mg/L, and the maximum adsorption capacity was 17.86 mg/g. The kinetic data were tested using the pseudo first-order and second-order models, and the results show that the kinetics of the biosorption of zinc was better described with second-order kinetics. Fourier transform infrared spectral analysis (FT-IR analysis) showed that the dominant mechanism of zinc(Ⅱ) biosorption onto the dried activated sludge was the bind between amide groups and zinc ions. The group of-OH also involved in zinc binding to some extent.In the experiment of biosorption of copper(Ⅱ) onto the biofilm, the pH of solution was one of the most important parameters affecting metal ion sorption. The copper adsorption capacity increased when solution pH increased, and the optimum pH value was obtained at pH 5.0. The equilibrium occurred within 3h. The biosorption capacity of copper(Ⅱ) increased, and the biosorption efficiency decreased when the initial concentration of copper ions increased. It was shown that the uptake amount of copper ions increased with increasing temperature from 25 to 45℃. The removal efficiency of copper(Ⅱ) increased while the metal adsorption capacity decreased with an increase in the dosage of the adsorbent. Langmuir model gave the best satisfactory correlation coefficients for the concentration of 0-200 mg/L, and the maximum biosorption capacity was found to be 36.36 mg/g. The kinetics followed the pseudo-second-order rate equation. The thermodynamics constants showed that biosorption of copper(Ⅱ) was the endothermic and spontaneous process.