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In order to elucidate the potential mechanisms involved in the biosorption of metal ions, atomic force microscopy (AFM) and Fourier transform infrared (FT-IR) spectroscopy were used to characterize the interaction between Pb 2+ and Bacillus cereus. AFM imaging of the biomass surfaces exposed to different concentrations of lead ions solution showed a major morphological change occurred after Pb 2+ biosorption. The FT-IR spectra indicated the binding characteristics of the lead ions involved the carboxyl, hydroxyl and amino groups in the biomass. Equilibrium biosorption experiments of Pb 2+ were carried out to investigate the effects of pH values and the initial metal concentrations. The experimental isotherm data were then modeled using Langmuir, Freundlich, and Redlich-Peterson isotherm equations. As a result, the Redlich-Peterson model yielded the best fit of experimental data. Kinetics experiments showed the biosorption was a rapid process and the pseudo-second-order model was successfully applied to predict the rate constant of biosorption.

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The Yellow River in winter as source water is characterized as high alkalinity, low temperature and low particle concentrations, which have brought many difficulties to water treatment plants. This study fully examines the optimized coagulation process of the Yellow River by conventional and pre-polymerized metal coagulants, pH adjustment and polyelectrolytes as the primary coagulants or coagulant aids. For all the metal coagulants, polyaluminum chlorides are superior to traditional metal coagulants due to their stable polymeric species and low consumption of alkalinity. The removal of natural organic matter by monomeric metal coagulants can be improved through pH adjustment, which is in accordance with the higher concentration of polymeric species formed at corresponding pH value. With the addition of polyelectrolytes as coagulant aids, the coagulation performance is significantly improved. The effective removal of dissolved organic matter is consistent with high charge density, while molecular weight is relatively important for removing particles, which is consistent with polyelectrolytes as primary coagulants. These results suggest that the coagulation mechanisms in the removal of dissolved organic matter and particles are different, which may be exploited for optimized coagulation for the typical source water in practice.

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The release and transport of heavy metals (Ni, Cr, Cu and Pb) from Liangshui River sediments into the overlying water column during the resuspension event were determined using an annular flume with a velocity ranging from 0.15 to 0.35 m/s. It is shown that the suspended particulate matters (SPM) increased as much as nearly 25 times from 165 to 4220 mg/L as the velocity increased. Heavy metals showed an increase in dissolved phase as the velocity increased due to their desorption from the SPM. Acid-soluble heavy metals increased as the velocity increased, indicating that part of the heavy metals transformed from stable phase to labile phase during resuspension. Heavy metal concentrations in the SPM on volume normalization increased by approximately 2-6 times. However, on the mass weighted basis they decreased, approaching the bulk-sediment contents at high velocity, due to the "particle concentration effect". The distribution coefficients (K D ) of heavy metals were higher at slower velocity during the sediment resuspension, which could be attributed to the decrease of fine particles (silt/clay fraction) during resuspension.heavy metals, sediment resuspension, suspended particulate matters, acid-soluble heavy metals, annular flume Citation:Huang J Z, Ge X P, Yang X F, et al. Remobilization of heavy metals during the resuspension of Liangshui River sediments using an annular flume. Chin Sci Bull, 2012, 57: 35673572,

a b s t r a c tInteractions of silica microspheres were examined by light scattering in presence of alum and polyaluminum chloride (PACl) with various OH/Al ratios. The coagulation behaviors were investigated using different coagulant dosages at constant pH (6.5) and salt concentration (0.01 mol/L). Based on the measurement of size distribution and zeta potential, charge neutralization was proposed to be the primary coagulation step for all the coagulants while other distinct coagulation steps were also involved depending on in situ formed or preformed hydrolyzing products. Precipitate coverage and sweep flocculation were induced for alum, contrasted to polycation patch and bridge aggregation for PACl. Based on simplified DLVO theory, particle aggregation was explained in terms of interaction forces. It was demonstrated that PACl outperformed alum in particle agglomeration at lower concentration (1-2 mol/L), owing mainly to the considerable energy barrier reduction and deeper secondary minimum at longer distance induced by high positive polycations. The role of secondary minimum was found to be significant when secondary depth exceeded 12 kT. The interaction energy calculations coincided well with coagulation result for PACl, especially PACl22 with high content Al 13 . However, other interaction forces prevailed over the electrical repulsion for alum and PACl containing other aluminum species.