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Volume 1, Number 1, January 2010
Abstract
Membrane distillation process was used for purification of pre-treated natural water (tap water). The rejection of inorganic and organic compounds in this process was investigated. The obtained rejection of inorganic solutes was closed to 100%, but the volatile organic compounds (VOCs) diffused through the membrane together with water vapour. The content of trihalomethanes (THMs) in the obtained distillate was two-three fold higher than that in the feed, therefore, the rejection of the total organic compounds present in the tap water was reduced to a level of 98%. The intensive membranes scaling was observed during the water separation. The morphology and composition of the fouling layer was studied using scanning electron microscopy coupled with energy dispersion spectrometry. The influence of thermal water pre-treatment performed in a heat exchanger followed by filtration on the MD process effectiveness was evaluated. This procedure caused that significantly smaller amounts of CaCO3 crystallites were deposited on the membrane surface, and a high permeate flux was maintained over a period of 160 h.
Key Words
membrane distillation; water treatment; hydrophobic membrane; desalination.
Address
Marek Gryta; West Pomeranian University of Technology, Szczecin Institute of Chemical Technology and Environment Engineering, ul. Pulaskiego 10, 70-322 Szczecin, Poland
Abstract
The performance of an electrodialyzer for concentrating seawater is predicted by means of a computer simulation, which includes the following five steps; Step 1 mass transport; Step 2 current density distribution; Step 3 cell voltage; Step 4 NaCl concentration in a concentrated
solution and energy consumption; Step 5 limiting current density.
The program is developed on the basis of the following assumption; (1) Solution leakage and electric current leakage in an electrodialyzer are negligible. (2) Direct current electric resistance of a membrane includes the electric resistance of a boundary layer formed on the desalting surface of the membrane due to concentration polarization. (3) Frequency distribution of solution velocity ratio in desalting cells is equated by the normal distribution. (4) Current density i at x distant from the inlets of desalting cells is approximated by the quadratic equation. (5) Voltage difference between the electrodes at the entrance of desalting cells is equal to the value at the exits. (6) Limiting current density of an electrodialyzer is defined as average current density applied to an electrodialyzer when current density reaches the limit of an ion exchange membrane at the outlet of a desalting cell in which linear velocity and electrolyte concentration are the least. (7) Concentrated solutions are extracted from concentrating cells to the outside of the process.
The validity of the computer simulation model is demonstrated by comparing the computed results with the performance of electrodialyzers operating in salt-manufacturing plants. The model makes it possible to discuss optimum specifications and operating conditions of a practical-scale electrodialyzer.
Key Words
ion exchange membrane; electrodialysis; seawater concentration; energy consumption; salt production.
Address
Yoshinobu Tanaka; IEM Research, 1-46-3 Kamiya, Ushiku-shi, Ibaraki 300-1216, Japan
Abstract
Using a conventional two-compartment cell with stirrers the separation of an aqueous solution of HCl-NiCl2 by an anion-exchange membrane Neosepta-AFN was investigated. The dialysis process was characterized by the permeability coefficient of the membrane towards to Cl? ions. This quantity was determined by the numerical integration of equations, which describe the time dependence of the total concentration of Cl? ions in compartment initially filled with stripping agent (water), combined with an optimizing procedure. The analysis of the experimental results showed that this permeability coefficient is a satisfactory characteristic for the process studied. It can be graphically correlated with the initial acid and initial salt concentrations in the compartment initially filled with acid+salt mixture.
Key Words
batch dialysis; hydrochloric acid; nickel chloride; permeability of membrane; anion-exchange membrane.
Address
Zdenk Palaty and Helena Bendova; Institute of Environmental and Chemical Engineering, Faculty of Chemical Technology, University of Pardubice, Studentska 573, 532 10 Pardubice, Czech Republic
Abstract
In this study, response surface methodology (RSM) was performed in NF membrane process to evaluate the separation efficiency of membrane in the removal of salt and reactive dye by varying different variables such as pressure, temperature, pH, dye concentration and salt concentration. The significant level of both the main effects and the interaction were observed by analysis of variance (ANOVA) approach. Based on the statistical analysis, the results have provided valuable information on the relationship between these variables and the performances of membrane. The rejection of salt was found to be greatly influenced by pressure, pH and salt concentration whereas the dye rejection was relatively constant in between 96.22 and 99.43% regardless of the changes in the variables. The water flux on the other hand was found to be affected by the pressure and salt concentration. It is also found that the model predictions were in good agreement with the experimental data, indicating the validity of these models in predicting membrane performances prior to the real filtration process.
Key Words
nanofiltration; membrane; response surface methodology; salt rejection; dye removal.
Address
W. J. Lau and A. F. Ismail; Advanced Membrane Technology Research Centre (AMTEC), Faculty of Chemical and Natural Resources Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia
Abstract
The aim of this work is to analyse and discuss the use of the Economic Evaluation and of some new \"metrics\" for an appropriate valuation of membrane operations in the logic of Process Intensification. In particular, the proposed approach has the goal to show how the utilized indicators can drive to the choice of the most convenient process. Although in this work the planned procedure is applied, as a case study, to the membrane-based systems for boron and arsenic removal from waters, the suggested approach can be generally applied to any other process of interest.
Key Words
sustainability; process intensification strategy; metrics; cost.
Address
Francesca Macedonio* and Enrico Drioli; Department of Chemical Engineering and Materials, University of Calabria,Via P. Bucci Cubo 44/A, 87030 Arcavacata di Rende (CS), Italy
Institute on Membrane Technology, ITM-CNR, c/o University of Calabria, Via P. Bucci Cubo 17/C, Arcavacata di Rende (CS), Italy
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Surface modification of polypropylene membrane to improve antifouling characteristics in a submerged membrane-bioreactor: Ar plasma treatment
Jin Zhou, Wei Li, Jia-Shan Gu and Hai-Yin Yu
Abstract;
Full Text (5753K)
Abstract
To improve the antifouling characteristics of polypropylene hollow fiber microporous membranes in a submerged membrane-bioreactor for wastewater treatment, the surface-modification was conducted by Ar plasma treatment. Surface hydrophilicity was assessed by water contact angle measurements. The advancing and receding water contact angles reduced after the surface modification, and hysteresis between the advancing and receding water contact angles was enlarged after Ar plasma treatment due to the increased surface roughness after surface plasma treatment. After continuous operation in a submerged membrane-bioreactor for about 55?h, the flux recovery after water cleaning and the flux ratio after fouling were improved by 20.0 and 143.0%, while the reduction of flux was reduced by 28.6% for the surface modified membrane after 1min Ar plasma treatment, compared to those of the unmodified membrane. Morphological observations showed that the mean membrane pore size after Ar plasma treatment reduced as a result of the deposition of the etched species; after it was used in the submerged membrane-bioreactor, the further decline of the mean membrane pore size was caused by the deposition of foulants. X-ray photoelectron spectroscopy and infrared spectroscopy confirmed that proteins and polysaccharide-like substances were the main foulants in the precipitate.
Key Words
antifouling characteristics; polypropylene microporous membrane; Ar plasma treatment; submerged membrane-bioreactor; membrane surface modification; wastewater treatment.
Address
Jin Zhou, Wei Li, Jia-Shan Gu and Hai-Yin Yu; College of Chemistry and Materials Science, Anhui Key Laboratory of Functional Molecular Solids, Anhui Key Laboratory of Molecule-based Materials, Anhui Normal University, Wuhu 241000, China
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Editors-in-Chief
