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CONTENTS
Volume 4, Number 3, July 2013
 

Abstract
The present study is devoted to the validation of a new method for in line electrokinetic characterisation of deposits on membrane surfaces. This method is based upon simultaneous measurements of transversal streaming potential and permeates flux at constant pressure before and during the deposit formation. Dead-end filtration experiments were conducted with negative flat membranes forming a narrow slit channel, negative hollow fiber membranes and mono-dispersed suspensions of (negatively charged) polystyrene latex and (positively charged) melamine particles at various concentrations. It was observed that the overall streaming potential coefficient increased in absolute value with the deposited latex quantity, whereas it decreased and changed of sign during the filtration of melamine suspensions. By considering a resistance-in-series model, the streaming potential coefficient of the single deposit (SPd) was deduced from the electrokinetic and hydraulic measurements. The independence of SPd with respect to growth kinetics validates the measurement method and the reliability of the proposed procedure for calculating SPd. It was found that SPd levelled off much more quickly when filtration was performed through the slit channel. This different behaviour could result from a non-uniform distribution of the deposit thickness along the membrane given that the position of measuring electrodes is different between the two cells.

Key Words
electrokinetics; streaming potential; particles; latex; melamine; cakes; fouling; dead-end filtration; hollow fibers

Address
1 Yannick Lanteri: Institut Europeen des Membranes, 34095 Montpellier cedex 5, France;
2 Wael Ballout, Patrick Fievet, Sebastien Deon: Institut UTINAM, Universite de Franche-Comte, 25030 Besancon cedex, France;
3 Anthony Szymczyk: Universite de Rennes 1, Institut des Sciences Chimiques de Rennes, 35042 France;
4 Patrick Sauvade: Degremont Technologie - AQUASOURCE, 31029 Toulouse, France

Abstract
A membrane bioreactor (MBR) with sludge retention time (SRT) of 300 days was maintained for over 2 years. Polypropylene microfiltration (MF) membrane with pore size of 0.2

Key Words
long SRT; MBR; membrane fouling; solutes; suspended solids

Address
Darren Delai Sun and Shushu Liu: School of Civil and Environmental Engineering, Nanyang Technological University, Singapore 639798

Abstract
The application of ultrafiltration operation to the dialysis in countercurrently parallel-flow rectangular membrane modules was investigated. The assumption of uniform ultrafiltration flux was made for operation with slight concentration polarization and declination of transmembrane pressure. Considerable improvement in mass transfer is achievable if the operation of ultrafiltration is applied, especially for the system with low mass transfer coefficient. The enhancement in separation efficiency is significantly increased with increasing ultrafiltration flux, as well as with increasing the volumetric flow rates. Furthermore, increasing the volumetric flow rate in retentate phase is more beneficial to mass transfer than increasing in dialysate phase.

Key Words
mass transfer; dialysis; ultrafiltration; countercurrently parallel-flow; rectangular membrane module

Address
Ho-Ming Yeh and Chien-Yu Chen: Energy and Opto-Electronic Materials Research Center, Department of Chemical and Materials Engineering, Tamkang University, Tamsui, Taipei County, 251, Taiwan

Abstract
Laboratory tests were performed to determine the efficiency of dye solution desalination by electrodialysis. The study involved anionic dye and mineral salt recovery by obtaining two streams from a salt and dye mixture . dye-rich solution and salt solution. A standard anion-exchange and cation-exchange membranes or monovalent selective anion-exchange membranes were used in the ED stack. It was found that the separation efficiency was strongly dependent on the dye molecular weight. The best results for standard ion-exchange membranes were achieved for the desalination of Direct Black solution. Furthermore, the obtained results implied that the application of monovalent selective anion-exchange membranes improved the recovery of dye and salt solutions — the dye concentration in the diluate remained constant irrespective of the molecular weight of anionic dyes, whereas the salt recovery remained very high (99.5%).

Key Words
dye; mineral salt; electrodialysis; monovalent selective anion-exchange membrane

Address
Katarzyna M. Majewska-Nowak: Wroclaw University of Technology, Wyb. Wyspianskiego 27, 50-370 Wroclaw, Poland

Abstract
The maximum current density that can be achieved in bipolar membrane electrodialysis is limited by the sharp increase in resistance that is experienced when the water content at the membrane interface is not adequately replenished and the membranes dry out. In this paper we show how the water content near the interface depends on the properties of the membranes. A water retaining parameter is introduced, which characterizes the thermodynamic properties of the membrane material and may be used to guide the choice of polymers for mitigation of the dry-out problem.

Key Words
bipolar membrane; dry-out; current-voltage curve; electro-osmosis; water absorption

Address
1 Ora Kedem: Weizmann Institute of Science, Rehovot 76100, Israel;
2 Andrea Ghermandi: Dept. of Natural Resources and Environmental Management, University of Haifa, 31905 Haifa, Israel;
3 Rami Messalem: Zuckerberg Inst. for Water Research, Ben Gurion University of the Negev, 84105 Beer-Sheva, Israel


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