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Xiong L.,Peking University | Xiong L.,The Key Laboratory of Water and Sediment science | Yang Y.,Peking University | Mai J.,Peking University | And 8 more authors.
Chemical Engineering Journal | Year: 2010

Calcined titanate nanotubes were synthesized with hydrothermal treatment of the commercial TiO2 (Degussa P25) followed by calcination. The morphology and structures of as-prepared samples were investigated by transmission electron microscopy, X-ray diffraction and N2 adsorption/desorption. The samples exhibited a tubular structure and a high surface area of 157.9 m2/g. The adsorption of methylene blue onto calcined titanate nanotubes was studied. The adsorption kinetics was evaluated by the pseudo-first-order, pseudo-second-order and Weber's intraparticle diffusion model. The pseudo-second-order model was the best to describe the adsorption kinetics, and intraparticle diffusion was not the rate-limiting step. The equilibrium adsorption data were analyzed with three isotherm models (Langmuir model, Freundlich model and Temkin model). The best agreement was achieved by the Langmuir isotherm with correlation coefficient of 0.993, corresponding to maximum adsorption capacity of 133.33 mg/g. The adsorption mechanism was primarily attributed to chemical sorption involving the formation of methylene blue-calcined titanate nanotubes nanocomposite, associated with electrostatic attraction in the initial bulk diffusion. © 2009 Elsevier B.V. All rights reserved.

Zhao B.,Peking University | Zhao B.,The Key Laboratory of Water and Sediment science | Zhao H.,Peking University | Zhao H.,The Key Laboratory of Water and Sediment science | And 2 more authors.
Chemical Engineering Journal | Year: 2010

Donnan dialysis is an ion exchange membrane process driven by an electrochemical potential gradient that is capable of removing ionic contaminants from water. To better understand and simulate arsenate (As(V)) removal by Donnan dialysis, a simple model focusing on intermembrane ionic diffusion at steady state was developed based on the Nernst-Planck equation in this study. Using experimental data from independent ion exchange reaction experiments and dialysis experiments, the self-diffusion coefficient of As(V) in the anion exchange membrane was calculated. This value was on the order of 10-8 m2 h-1 and related to the system pH and membrane type. The As(V) removal by Donnan dialysis (feed solution: 1 L, 1.3 × 10-2 mol As m-3 (1000 μg As L-1) with 10 mol m-3 NaCl; stripping solution: 1 L, 100 mol m-3 NaCl) was conducted with different types of membrane at different system pH. At the end of the 12-h dialysis, the removal efficiency was lowest (35%) for the heterogeneous membrane at pH 4.5 and highest (95%) for the homogeneouse membrane at pH 9.2. Higher ion-membrane affinity, higher intermembrane ionic mobility, and thinner membrane thickness facilitated the As(V) transfer according to the model results. Using the calculated membrane phase self-diffusion coefficients and the corresponding distribution coefficients of As(V) between the membrane and the solution, the present model successfully predicted the As(V) removal profiles of different dialytic conditions. © 2010 Elsevier B.V. All rights reserved.

Wang Y.,Beijing Normal University | Wang Y.,The Key Laboratory of Water and Sediment science | Shen Z.,Beijing Normal University | Shen Z.,The Key Laboratory of Water and Sediment science | And 2 more authors.
Chemosphere | Year: 2010

The erbium (Er)-chitosan-fluorine (F) modified PbO2 electrode was prepared by electrodeposition method, and its use for adsorption and electrochemical degradation of 2,4-dichlorophenol (2,4-DCP) in aqueous solution was compared with F-PbO2 and Er-F-PbO2 electrodes in a batch experiment. The electrodes were characterized by scanning electron microscopy, X-ray diffraction and cyclic voltammetry. Degradation of 2,4-DCP depending on Er and chitosan contents was discussed. The results showed that Er2O3 and chitosan were scattered between the prevailing crystal structure of β-PbO2 and thus decreased the internal stress of PbO2 film. Prior to each electrolysis, the modified PbO2 anode was first pre-saturated with 2,4-DCP solution for 360 min to preclude the 2,4-DCP decrease due to adsorption. Among the electrodes examined in our study, the highest adsorption and electrochemical degradation for 2,4-DCP and TOC removals that are due to oxidation and adsorption of the organic products onto the chitosan was observed on Er-chitosan-F-PbO2 electrode. At an applied current density of 5 mA cm-2, the removal percentages of 2,4-DCP and TOC (solution volume: 180 mL, initial 2,4-DCP concentration: 90 mg L-1) were 95% after 120 min and 53% after 360 min, respectively. At Er amount of 10 mM in the precursor coating solution, the degradation and mineralization removal for 2,4-DCP on the Er-F-PbO2 electrode reached a maximum. At chitosan amount of 5 g L-1, the highest TOC removal on the Er-chitosan-F-PbO2 electrode was observed. Intermediates mainly including aliphatic carboxylic acids were examined and a possible degradation pathway for 2,4-DCP in aqueous solution involving dechlorination and hydroxylation reactions was proposed. © 2010 Elsevier Ltd. All rights reserved.

Sun J.-J.,Peking University | Sun J.-J.,The Key Laboratory of Water and Sediment science | Zhao H.-Z.,Peking University | Zhao H.-Z.,The Key Laboratory of Water and Sediment science | And 4 more authors.
Electrochimica Acta | Year: 2010

To exploit the outstanding ability of carbon nanotubes to facilitate electron transfer in a microbial fuel cell (MFC) system, multi-wall carbon nanotube (MWNT) and polyeletrolyte polyethyleneimine (PEI) were employed to modify carbon paper (TP) electrode utilizing a layer-by-layer (LBL) assemble technique for the first time, and the performance of the modified electrode as an anode in MFC was investigated. This modification strategy ensured a relatively high content of MWNTs within the polymer matrix. IR and cyclic voltammetry (CV) demonstrated the uniform formation of a polyethyleneimine/MWNT multilayer composite on the TP surface. The SEM profiles presented a three-dimensional MWNTs interwoven network surface structure with a large accessible surface area. Electrochemical impedance spectroscopy (EIS) measurements confirmed that the existence of polyelectrolyte/MWNT multilayers decreased the interfacial charge transfer resistance from 1163 to 258 Ω. With the modified anode, the MFC produced a higher power density with 20% enhancement comparing to the bare TP anode. The MWNT-based LBL self-assembled electrode is promising for the electricity production by MFC. © 2010 Elsevier Ltd. All rights reserved.

Miao C.,Peking University | Miao C.,The Key Laboratory of Water and Sediment science | Ni J.,Peking University | Ni J.,The Key Laboratory of Water and Sediment science | Borthwick A.G.L.,University of Oxford
Progress in Physical Geography | Year: 2010

The Yellow River basin contributes approximately 6% of the sediment load from all river systems globally, and the annual runoff directly supports 12% of the Chinese population. As a result, describing and understanding recent variations of water discharge and sediment load under global change scenarios are of considerable importance. The present study considers the annual hydrologic series of the water discharge and sediment load of the Yellow River basin obtained from 15 gauging stations (10 mainstream, 5 tributaries). The Mann-Kendall test method was adopted to detect both gradual and abrupt change of hydrological series since the 1950s. With the exception of the area draining to the Upper Tangnaihai station, results indicate that both water discharge and sediment load have decreased significantly (p<0.05). The declining trend is greater with distance downstream, and drainage area has a significant positive effect on the rate of decline. It is suggested that the abrupt change of the water discharge from the late 1980s to the early 1990s arose from human extraction, and that the abrupt change in sediment load was linked to disturbance from reservoir construction. © The Author(s) 2010.

Zhu Y.,Shaoxing University | Zhu Y.,The Key Laboratory of Water and Sediment science | Zhu Y.,Peking University | Zhu H.,Shaoxing University | And 4 more authors.
World Journal of Microbiology and Biotechnology | Year: 2014

In order to improve the efficiency of biotransformation of saponins in Dioscorea zingiberensis to diosgenin, a new enzymatic model was developed to investigate the mechanism of the metabolic systems. Four main saponin hydrolases (E1, E2, E3 and E4) were purified from Trichoderma reesei. Using progracillin as substrate, the enzymatic hydrolysis experiments with E1, E2, E3 and E4 were carried out respectively. Saponin concentrations during each biotransformation reaction were constructed with a kinetic model consisting of a few Michaelis-Menten equations. During biotransformation, C-26 glycoside and C-3 terminal glycoside were cleaved sequentially from saponins by E1, E2, E3 and E4. Then C-3 terminal rhamnoside and C-3 glycoside were released from the aglycone stepwisely by E2 and E3, to yield diosgenin. E2 and E3 were the key enzymes in the system, and cleavage of the C-3 glycoside from saponins was the rate-limiting step in the biotransformation process. The proposed enzymatic model might be used to analyze the mechanism for biotransformation of saponins to diosgenin. © 2013 Springer Science+Business Media Dordrecht.

Zhu Y.,The Key Laboratory of Water and Sediment science | Zhu Y.,Peking University | Huang W.,CAS Chengdu Institute of Biology | Ni J.,The Key Laboratory of Water and Sediment science | Ni J.,Peking University
Journal of Cleaner Production | Year: 2010

This study proposes a new approach for diosgenin production from Dioscorea zingiberensis C. H. Wright tubers with respect to resources utilization and clean production. This process consisted of two successive parts, i.e., recovery of starch from raw material, and microbial hydrolysis of the residue to produce diosgenin by Trichoderma reesei. In the first step, about 75.4% of hemicellulose and 98.0% of starch were removed from the tubers. In the second step, about 90.2% of diosgenin was released from saponins by T. reesei at 30 °C, at an aeration of 0.80 vvm and agitation rate of 300 rpm in a 5.0 L bioreactor. Significant reduction of pollutant production was detected by replacing the traditional approach with the proposed new method. About 99.2% of reducing sugar, 99.4% of chemical oxygen demand, 99.2% of total organic carbon, 100% of SO42-, and 100% of acid was reduced in the new processing wastewater. © 2009 Elsevier Ltd. All rights reserved.

Zhao H.-Z.,Peking University | Zhao H.-Z.,The Key Laboratory of Water and Sediment science | Sun J.-J.,Peking University | Sun J.-J.,The Key Laboratory of Water and Sediment science | And 2 more authors.
Carbon | Year: 2010

To gain insights into the direct electron transfer (DET) mechanism of multi-walled carbon nanotubes (MWCNTs), we investigated the conformational changes that occur in proteins when they interact with MWCNTs. We used glucose oxidase (GOD) as an example. Using cyclic voltammetry measurements, the GOD that was immobilized on the MWCNT-modified carbon paper electrode exhibited apparent direct electrochemistry compared to that on the bare electrode without MWCNTs. The structural transformation of GOD upon adsorption on the MWCNTs was characterized spectrally. GOD was not denatured, and only small shifts of the wavenumber of the β-sheet structure were observed. There was a consistent tendency for the amount of α-helix to decrease and the β-sheet to increase. The α-helix content dropped from 21.2% to 19.6% as measured using Fourier transform infrared spectroscopy and from 27.1% to 25.9% as measured using circular dichroism. The reduction in the amount of α-helix led to a less shielded GOD active site and weakened the resistance of the electron transfer. These MWCNT-induced conformational changes could account for the DET between GOD and the MWCNT-modified electrode surface. © 2009 Elsevier Ltd. All rights reserved.

Wang Z.,The Key Laboratory of Water and Sediment Science | Ye Z.,The Key Laboratory of Water and Sediment Science | Zhang M.,The Key Laboratory of Water and Sediment Science | Zhang M.,University of Science and Technology of China | Bai X.,Lanzhou University
Process Biochemistry | Year: 2010

The combined process of immobilized microorganism-biological filter was used to degrade TNT in an aqueous solution. The results showed that the process could effectively degrade TNT, which was not detected in the effluent of the system. GC/MS analysis identified 2-amino-4,6-dinitrotoluene (2-A-4,6-DNT), 4-amino-2,6-dinitrotoluene (4-A-2,6-DNT), 2,4-diamino-6-nitrotoluene (2,4-DA-6-NT) and 2,4-diamino-6-nitrotoluene (2,6-DA-4-NT) as the main anaerobic degradation products. In addition, the Haldane model successfully described the anaerobic degradation of TNT with high correlation coefficients (R2 = 0.9803). As the electron donor, ethanol played a major role in the TNT biodegradation. More than twice the theoretical requirement of ethanol was necessary to achieve a high TNT degradation rate (above 97.5%). Moreover, Environment Scan Electron Microscope (ESEM) analysis revealed that a large number of globular microorganisms were successfully immobilized on the surface of the carrier. Further analysis by Polymerase Chain Reaction (PCR)-Denaturing Gradient Gel Electrophoresis (DGGE) demonstrated that the special bacterial for TNT degradation may have generated during the domestication with TNT for 150 days. The dominant species for TNT degradation were identified by comparing gene sequences with Genebank. © 2010 Elsevier Ltd. All rights reserved.

Tan Y.,The Key Laboratory of Water and Sediment science | Ji G.,The Key Laboratory of Water and Sediment science
Bioresource Technology | Year: 2010

Status of, and changes in, the bacterial communities at two acclimation stages (with- and without-ultrasound) in a small 70 °C ultrasound-enhanced anaerobic reactor for treating carbazole-containing wastewater reactor were analyzed by PCR-DGGE and real-time PCR techniques. PCR-DGGE results indicated that a large number of bands occurred in the whole sludge samples. Pseudomonas sp., Comamonas sp., and Diaphorobacter sp. were identified as being able to utilize carbazole as a carbon source, survive in an anaerobic and ultra-high-temperature environment and become dominant bacterial taxa during the with-ultrasound stage in the reactor. Total bacterial density in the with-ultrasonic stages was 10 × higher than in the without-ultrasonic treatment. The proportion of Pseudomonas was relatively stable at 0.13%-0.15% in both acclimation stages, which indicates that Pseudomonas can flourish and promote carbazole degradation either with or without-ultrasound. These studies provide information on carbazole degradation under ultra-high-temperature conditions in an anaerobic environment. © 2009 Elsevier Ltd. All rights reserved.

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