| As an advanced absorbent, biological absorbent which has been proved to be engineering feasible and economical beneficial, has an extensive vista of research and large advantages in the treatment of wastewater that contains heavy metals.An SBR reactor was used to discuss the feasibility and utility of heavy metal biosorption by activated sludge in the treatment of desulfurization wastewater which contains traces of heavy matals. The biosorption capacities of activated sludge towards Cr(Ⅲ), Cd(Ⅱ) and Pb(Ⅱ) in the desulfurization wastewater were observed. In this study, the influences of different hydraulic retention times(HRT), MLSS, initial concentrations of heavy metals and pH on the heavy metal biosorption process were assessed and an optimum operation condition of heavy metal biosorption by activated sludge process were obtained. The research results are as follows:(1) HRT=16h is an optimum operation time for sufficient biosorption and at the same time non-desorption towards heavy metals, the biosorption efficiency is at its best with a value of 71 %.(2) When the concentrations of activated sludge (MLSS) are 5000～5500 mg/L, the metal biosorption capacity of activated sludge reaches a highest value, with COD removal rate of 88.7% and Cr (Ⅲ) removal rate of 70%.(3) when the initial Cr(Ⅲ) concentrations are 1～600μg /L, the capacity and efficiency of Cr biosorption are increasing constantly with the increase of initial Cr(Ⅲ) concentrations and reaches an extreme of 85% by biosorption efficiency at the Cr(Ⅲ) concentration of 600μg /L. However, the biosorption efficiency of Cr begins to drop when the initial Cr(Ⅲ) concentrations are 600～1000μg/L while the biosorption capacity remains to increase. The biosorption efficiency lowered to 78% at the initial Cr(Ⅲ) concentration of 980μg/L.(4) pH values influence heavy metal biosorption by activated sludge most. When pH<4, the out-lowered pH leads to the death of activated sludge; when pH>7, biosorpation capacity is affected by reducing the adsorption points and weakening the adsorption capability of points.In the experiment, pH=6 is optimal for heavy metal biosorption of activated sludge with the biosorption capacity and biosorption efficiency of 12.82μg/g and 72.3 %, respectively.(5) Heavy metals compete for binding sites of activated sludge in case that several metals are contained. This competition leads to the inhibition of heavy metal biosorption, and the biosorption capacity of target ions will be lowered. The Cr(Ⅲ) removal rates are lowered to 44% and 63%, compare to the condition of only existing Cr(Ⅲ),which are fell by 41% and 22%, when Pb (Ⅱ) and Cd (Ⅱ) are added to the system, respectively. The existence of Pb (Ⅱ) and Cd (Ⅱ) affects the biosorption of activated sludge towards Cr(Ⅲ).(6) Simulate the heavy metal biosorption of activated sludge using Langmuir and Freundlich adsorption models. It's obtained that Cd(Ⅱ) and Pb(Ⅱ) biosorptions fit Langmuir adsorption model and Cr(Ⅲ) biosorption fits Freundlich adsorption model. The metal-sludge affinity order is obtained as follow: Pb(Ⅱ)>Cd(Ⅱ)>Cr(Ⅱ).(7) An SBR activated sludge process is practical for heavy metal treatment in full-scale desulfurization wastewater to the discharge standard abroad. In this study, the main heavy metals in the desulfurization wastewater such as Cd2+, Cr3+, Hg2+, Pb2+ and Zn2+ are treated to 21μg /L, 17μg /L, 8μg /L, 13μg /L and 215μg /L, resbectively, which are all lower than the discharge standard abroad.(8) Through the research on microorganism of activated sludge, founding that the Epistylis Vrceolata played a major role in the absorption of heavy metal by activated sludge. At the same time there are a lot of Protozoans and Epigenetic animals exist in the activated sludge, it will reduce the amount of sludge theoretically and able to achieve the objective of reducing.
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