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Electropermutation assisted by ion-exchange textile: removal of nitrate from drinking water
KTH, School of Engineering Sciences (SCI), Mechanics.
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Increased levels of nitrate in ground water have made many wells unsuitable as sources for drinking water. In this thesis an ion-exchang eassisted electromembrane process, suitable for nitrate removal, is investigated both theoretically and experimentally. An ion-exchange textile material is introduced as a conducting spacer in the feed compartment of an electropermutation cell. The sheet shaped structure of the textile makes it easy to incorporate into the cell. High permeability and fast ion-exchange kinetics, compared to ion-exchange resins, are other attractive features of the ion-exchange textile.

A steady-state model based on the conservation of the ionic species is developed. The governing equations on the microscopic level are volume averaged to give macro-homogeneous equations. The model equations are analyzed and relevant simplifications are motivated and introduced. Dimensionless parameters governing the continuous electropermutation process are identified and their influence on the process are discussed. The mathematical model can be used as a tool when optimising the process parameters and designing equipment.

An experimental study that aimed to show the positive influence of using the ion-exchange textile in the feed compartment of an continuous electropermutation process is presented. The incorporation of the ion-exchange textile significantly improves the nitrate removal rate at the same time as the power consumption is decreased. A superficial solution of sodium nitrate with a initial nitrate concentration of 105 ppm was treated. A product stream with less than 20 ppm nitrate could be obtained, in a single pass mode of operation. Its concluded from these experiments that continuous electropermutation using ion-exchange textile provides an interesting alternative for nitrate removal, in drinking water production. The predictions of the mathematical model are compared with experimental results and a good agreement is obtained.

Enhanced water dissociation is known to take place at the surface of ion-exchange membranes in electromembrane processes operated above the limiting current density. A model for this enhanced water dissociation in presented in the thesis. The model makes it possible to incorporate the effect of water dissociation as a heterogeneous surface reaction. Results from simulations of electropermutation with and without ion-exchange textile incorporated are presented. The influence of the water dissociation is investigated with the developed model.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006.
Series
Trita-MEK, ISSN 0348-467X ; 2006:10
Keyword [en]
Ion-exchange textile, Ion-exchange membrane, Electropermutation, Electroextraction, Electrodialysis, Electrodeionisation, Modeling, Conducting spacer, Nitrate removal, Water treatment, Water dissociation
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-3992OAI: oai:DiVA.org:kth-3992DiVA: diva2:10291
Public defence
2006-06-08, D3, Lindstedtsvägen 5, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101118Available from: 2006-05-23 Created: 2006-05-23 Last updated: 2010-11-18Bibliographically approved
List of papers
1. Nitrate Removal by Continuous Electropermutation Using Ion-Exchange Textile: I. Modeling
Open this publication in new window or tab >>Nitrate Removal by Continuous Electropermutation Using Ion-Exchange Textile: I. Modeling
2006 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 153, no 4, D51-D61 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents a steady-state model of the feed compartment of an electropermutation cell, used for nitrate removal, with ion exchange textiles incorporated as a conducting spacer. In the model the ion-exchange textile is treated as a porous medium and volume averaging is applied to obtain a macrohomogeneous two-phase model. The ion-exchange between the two phases is modeled assuming that the rate-determining step is the mass-transfer resistance on the liquid side of the phase interface. Analysis of the model equations reveals appropriate simplifications. The influence of the governing dimensionless numbers is investigated through simulations based on the model.

Keyword
high-resistivity water, electrodialysis, membranes, electrodeionization, transport, anions, beds
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-5790 (URN)10.1149/1.2170597 (DOI)000235723600039 ()2-s2.0-33644814154 (Scopus ID)
Note
QC 20101115Available from: 2006-05-23 Created: 2006-05-23 Last updated: 2017-12-14Bibliographically approved
2. Nitrate Removal by Continuous Electropermutation Using Ion-Exchange Textile: II. Experimental Investigation
Open this publication in new window or tab >>Nitrate Removal by Continuous Electropermutation Using Ion-Exchange Textile: II. Experimental Investigation
2006 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 153, no 4, D62-D67 p.Article in journal (Refereed) Published
Abstract [en]

Water with nitrate concentrations above 100 ppm has been treated with continuous electropermutation which partially substitutes the nitrate with chloride. The performance of a textile anion exchanger as conducting spacer in the feed compartment of an electropermutation cell was investigated. Experiments with and without textile are compared and the influence of the textile is discussed. The process could, using the textile, successfully treat feed water with 105 ppm nitrate to produce a water with less than 25 ppm nitrate. The importance of establishing a good contact between the membranes and the textile spacer was pointed out. The experimental results were compared to model predictions and a good agreement was found.

National Category
Natural Sciences
Identifiers
urn:nbn:se:kth:diva-5791 (URN)10.1149/1.2170659 (DOI)000235723600040 ()2-s2.0-33644803700 (Scopus ID)
Note

QC 20141127

Available from: 2006-05-23 Created: 2006-05-23 Last updated: 2017-12-14Bibliographically approved
3. A Model for the Enhanced Water Dissociation On Monopolar Membranes
Open this publication in new window or tab >>A Model for the Enhanced Water Dissociation On Monopolar Membranes
2009 (English)In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 54, no 11, 2983-2991 p.Article in journal (Refereed) Published
Abstract [en]

A model for the enhanced water dissociation that takes place at the solution/membrane interface in electromembrane processes is presented. The mechanisms behind the enhanced water dissociation are poorly understood and therefore a semi-empirical approach is suggested. The enhanced water dissociation is introduced as a heterogeneous surface reaction similar to the well established Butler–Volmer law for electrode reactions. In the model there are two parameters that need to be determined through experiments. A 1D diffusion boundary layer problem is presented and solved in order to show that a sufficient rate of water dissociation can be obtained with the model. The advantage of the presented model is that it can easily be incorporated into simulations of electromembrane processes such as electrodialysis, electrodeionization and electropermutation. The influence of the enhanced water dissociation on these processes can then be studied.

Keyword
Electromembrane processes, Water dissociation, Simulations, Ion-exchange membranes, Water treatment
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-5792 (URN)10.1016/j.electacta.2008.12.025 (DOI)000265342100006 ()2-s2.0-61849101879 (Scopus ID)
Note
Ändrad från submitted till published 20101118. QC 20101118Available from: 2006-05-23 Created: 2006-05-23 Last updated: 2017-12-14Bibliographically approved
4. Modeling Continuous Electropermutation with Effects of Water Dissociation Included
Open this publication in new window or tab >>Modeling Continuous Electropermutation with Effects of Water Dissociation Included
2010 (English)In: AIChE Journal, ISSN 0001-1541, E-ISSN 1547-5905, Vol. 56, no 9, 2455-2467 p.Article in journal (Refereed) Published
Abstract [en]

The repeating unit consisting of a cell pair of one concentrate and one feed compartment of an electropermutation stack is modeled. Both the feed and the concentrate compartments are filled with an ion-exchange textile material. Enhanced water dissociation taking place at the surface of the membrane is included in the model as a hetrogeneous surface reaction. Results from simulations of nitrate removal for drinking water production are presented and comparisons with previous experimental results are made. The influence of both conductive and inert textile spacers on the process is investigated via simulations

Keyword
ion exchange, mathematical modeling, membrane separations, electrochemistry, simulation, process
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-5793 (URN)10.1002/aic.12139 (DOI)000280826600021 ()2-s2.0-78650448074 (Scopus ID)
Note
ändrad från submitted till published 20101118. QC 20101118Available from: 2006-05-23 Created: 2006-05-23 Last updated: 2017-12-14Bibliographically approved

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