Abstract
The paper aimed at the evaluation of the batch electrodialysis (ED) run in the course of treatment and desalination of various aqueous mixtures containing both mineral (sodium fluoride, sodium chloride) and organic substances (dyes or humic acids). The commercial ED stack (PCCell Bed) equipped with standard anion-exchange and cation-exchange membranes or monovalent selective anion-exchange membranes was used. The ED experiments were performed at a constant current density (1.56 or 1.72 mA/cm 2 ). The mechanism of ion migration as well as membrane deposition for variable solution composition and various membrane types was analyzed The calculated mass balance and electrical energy demand for each ED run were helpful in evaluating the membrane fouling intensity. It was found that the presence of organic substances in the treated solution had a minor impact on energy consumption, but rather strongly affected chloride flux. The extent of organics deposition was significantly lower for monovalent selective anion-exchange membranes than for classic anion-exchange membranes.
Highlights
Membrane technology is being increasingly used in the treatment of natural water as well as industry wastewater
The chloride flux decreased from 780 mmol/m2h for solution containing only Cl- and low amount of F- ions (5 mg F-/dm3) to 330 mmol/m2h for solution supplemented with humic acids (5 mg HA/dm3) and high concentration of F- ions (200 mg F-/dm3)
It seems that the effect of increasing content of fluoride on chloride migration through the anion exchange membranes is much greater than the presence of organic matter
Summary
Membrane technology is being increasingly used in the treatment of natural water as well as industry wastewater. Most of the currently conducted studies are focussed on water reuse and reducing pollution impact on the environment. The electrodialysis (ED) seems to be very viable technology for simple treatment and desalination of polluted natural and process water. Electromembrane processes offer a great opportunity to the recovery of valuable substances, separate charged components from neutral substances, and fractionation of mono- and multi-valence ions of the same sign. These unique advantages make the electrodialysis very attractive in view of environmental and economic benefits. The mechanism of mass transport through the specially designed ion-exchange membranes becomes more complex than through the classic ion-exchange membranes, especially when multicomponent solutions are treated by ED
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