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CONTENTS
Volume 2, Number 3, July 2011
 

Abstract
Membrane processes are major breakthrough for the removal of organic pollutants in water remediation. The separations of solutes depend on nature of the membranes and solutes. The separation performance depends on the nature of the solutes (i.e., molecular volume, polarity, and hydrophobicity) for the same membrane. As 4-chlorophenol is of more dipolemoment compared to 2-chlorophenol, the orientation of the molecule enables it pass through the pores of the membrane, which is of negatively charged and thus separation order follows: 2-chlorophenol > 4-chlorophenol. Hydrophobicity factor also supports the order. Addition of sodium dodecyl sulfate (SDS) to chlorophenol solution shows remarkable increase in separation performance of the membrane. The improvement in separation is 1.8 and 1.5 times for 4- and 2- chlorophenol consecutively in case of 0.0082 M SDS (1cmc = 0.0082 M) in the solution. 4-chlorophenol has better attachment tendency with SDS because of its relatively more hydrophobic nature and thus reflects in performance i.e. the separation performance of 4-chlorophenol with SDS through the membrane is better compared to 2-chlorophenol.

Key Words
thin film composite; membrane; surfactant; chlorophenol; hydrophobicity

Address
Reverse Osmosis Discipline, Central Salt and Marine Chemicals Research Institute
(Council of Scientific and Industrial Research), G. B. Marg, Bhavnagar-364021, Gujarat, India

Abstract
Membrane distillation process was used for desalination of hot (333 K) geothermal water, which was applied in the plant producing heating water. The investigated water contained 120 g salts/dm3, mainly NaCl. The mineral composition was studied using an ion chromatography method. The obtained rejection of solutes was closed to 100%, but the small amounts of NH3 also diffused through the membrane together with water vapour. However, the composition of obtained distillate allowed to use it as a makeup water in the heating water system. The geothermal water under study was concentrated from 120 to 286 g NaCl/dm3. This increase in the solution concentration caused the permeate flux decline by a 10-20%. The geothermal water contained sulphates, which was subjected to two–fold concentration to achieve the concentration 2.4-2.6 g SO4 2−/dm3 and the sulphates then crystallized in the form of calcium sulphate. As a results, an intensive membranes scaling and the permeate flux decline was observed. The XRD analysis indicated that beside the gypsum also the NaCl crystallites were deposited on the membrane surfaces. The fresh geothermal water dissolved the mixed CaSO4 and NaCl deposit from the membrane surface. This property can be utilized for self-cleaning of MD modules. Using a batch feeding of MD installation, the concentration of geothermal water was carried out over 800 h, without significant performance losses.

Key Words
membrane distillation; geothermal water; desalination

Address
West Pomeranian University of Technology, Szczecin, Institute of Chemical Technology and Environment Engineering, ul. Pulaskiego 10, 70-322 Szczecin, Poland

Abstract
The air gap membrane distillation (AGMD) process was applied for water desalination. The main objective of the present work was to study the heat and mass transfer mechanism of the process. The experiments were performed on a flat sheet module using aqueous NaCl solutions as a feed. The membrane employed was hydrophobic PTFE of pore size 0.22

Key Words
AGMD; desalination; heat transfer coefficient; mass transfer coefficient; temperature polarization coefficient

Address
Bhausaheb L. Pangarkar:Sir Visvesvaraya Institute of Technology, University of Pune, Chincholi, Nashik, 422 101, India
Mukund G. Sane:National Chemical Laboratory, Pune, India

Abstract
Ultrafiltration is an emerging technology for drinking water treatment because it produces better water quality as compared with conventional treatment systems. More recently, the combination of UF technology with other processes in order to improve its performance has been observed. These associations aim to maximize the contaminants removal and reduce membrane fouling. The operational performance of contaminants removal and water production of two UF pilot plants was compared. The first plant (Guarapiranga) was fed with raw water and the second plant (ABV) with pre-treated water by the coagulation, flocculation and sedimentation processes at Alto da Boa Vista WTP (Sao Paulo, Brazil). Both units operated continuously for approximately 2,500 hours, from September/2009 to January/2010. The results showed that the ABV UF pilot plant was able to operate at higher specific fluxes (6.2 L.d−1.m−2.kPa−1 @ 25oC) than Guarapiranga (3.1 L.d−1.m−2.kPa−1 @ 25oC). However, the number of chemical cleanings conducted in both pilot units during the considered operation period was the same (4 chemical cleanings for each plant), which shows that the pre-treatment reduced the membrane fouling. The water quality at ABV for all the variables analyzed was better, but the feed water quality was also better due to pretreatment. The rejection values for the different contaminants were higher at Guarapiranga mainly because of a pollution load reduction after pretreatment at ABV. Even with the better performance of the ABV UF pilot plant, it is necessary to take into consideration the complexity of the complete treatment system, and also the costs involved in the construction and operation of a full-scale treatment unit.

Key Words
ultrafiltration; drinking water treatment; pretreatment; performance comparison; pilot plant

Address
Escola Politecnica da Universidade de Sao Paulo. Hydraulic and Sanitary Engineering Department, Sao Paulo, Brazil

Abstract
The electric transport of the mixture of hydrochloric and phosphoric acids through strong base (Neosepta ACM) and weak base (Selemion AAV) anion-exchange membranes was investigated. The instantaneous efficiency of HCl removal from the cathode solution, CECl, with and without H3PO4 was determined. It was found that CECl was 0.8-0.9 if the number of moles of elementary charge passed through the system, nF, did not exceed ca. 80% of the initial number of HCl moles in the cathode solution, nCl,ca,0. The retention efficiency of H3PO4 in that range was close to one. The transport of acid mixtures was satisfactorily described by a model based on the extended Nernst-Planck and Donnan equations for nF not exceeding nCl,ca,0. Among the tested model parameters, most important were: concentration of fixed charges, the porosity-tortuosity coefficient, and the partition coefficient of an undissociated form of H3PO4. For the both membranes, the obtained optimal values of fixed charge concentration, , were up to 40% lower than the literature values of obtained from the equilibrium measurements. Regarding the H3PO4 equilibria, it was sufficient to consider H3PO4 as a monoprotic acid.

Key Words
anion-exchange membrane; hydrochloric acid; phosphoric acid; extended Nernst-Planck equation; current efficiency; electrodialysis

Address
Faculty of Chemistry, Nicolaus Copernicus University, 7 Gagarin St., 87-100 Toru , Poland


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