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Several international reports have pointed that 2.3 billion people are living in regions with absolute water scarcity, despite the availability of a surface water source that can be treated to become drinkable. We, thus, suggest to apply a new technique, called neutralization dialysis (ND). We described this technique meant to desalinate real brackish water in previous papers. The ND is a low energy intensive technique and is easy to implement even in isolated locations. Kinetics of reconstituted and brackish waters desalination by ND were studied in a three-compartment stack (acid, saline, and alkali compartments) with Neosepta® AMX and CMX ion-exchange membranes, and the process feasibility was evaluated. Brackish water samples were taken from the city of Gabes in the south of Tunisia and analysed in different terms. The pH and the ionic conductivity kinetics were measured in the saline solution during different ND operations for five different solutions: CaCl2, Na2SO4, MgSO4, the mixture of these three salts (which are used to have, by themselves, a reconstructed water very close to the reconstituted water), and Gabes brackish water. The correlation of ion transport through the cation- and the anion-exchange membranes was investigated. This work has shown that the desalination kinetics is similar in the cases of Na2SO4 and MgSO4 solutions, while it is different in the case of CaCl2. We found out that the time dependence of pH for the reconstituted and the real waters during desalination is quasi-similar. However, the conductivity evolution for both solutions is different. The values of ion charge (monovalent/divalent) and concentration in the feed solution have an impact on the ion-exchange rate. The total cost of Gabes brackish water desalination by the ND process (stopped at conductivity of 1 mS cm–1) was estimated at 1.90 $/m3. [ABSTRACT FROM AUTHOR]

The broad possibilities of electrochemical impedance spectroscopy for assessing the capacitance of interphase boundaries; the resistance and thickness of the foulant layer were shown by the example of AMX-Sb membrane contacted with red wine from one side and 0.02 M sodium chloride solution from the other side. This enabled us to determine to what extent foulants affect the electrical resistance of ion-exchange membranes, the ohmic resistance and the thickness of diffusion layers, the intensity of water splitting, and the electroconvection in under- and over-limiting current modes. It was established that short-term (10 h) contact of the AMX-Sb membrane with wine reduces the water-splitting due to the screening of fixed groups on the membrane surface by wine components. On the contrary, biofouling, which develops upon a longer membrane operation, enhances water splitting, due to the formation of a bipolar structure on the AMX-Sb surface. This bipolar structure is composed of a positively charged surface of anion-exchange membrane and negatively charged outer membranes of microorganisms. Using optical microscopy and microbiological analysis, it was found that more intense biofouling is observed on the AMX-Sb surface, that has not been in contacted with wine. [ABSTRACT FROM AUTHOR]

The use of enzymatic agents as biological solutions for cleaning ion-exchange membranes fouled by organic compounds during electrodialysis (ED) treatments in the food industry could be an interesting alternative to chemical cleanings implemented at an industrial scale. This paper is focused on testing the cleaning efficiency of three enzyme classes (β-glucanase, protease, and polyphenol oxidase) chosen for their specific actions on polysaccharides, proteins, and phenolic compounds, respectively, fouled on a homogeneous cation-exchange membrane (referred CMX-Sb) used for tartaric stabilization of red wine by ED in industry. First, enzymatic cleaning tests were performed using each enzyme solution separately with two different concentrations (0.1 and 1.0 g/L) at different incubation temperatures (30, 35, 40, 45, and 50 °C). The evolution of membrane parameters (electrical conductivity, ion-exchange capacity, and contact angle) was determined to estimate the efficiency of the membrane′s principal action as well as its side activities. Based on these tests, we determined the optimal operating conditions for optimal recovery of the studied characteristics. Then, cleaning with three successive enzyme solutions or the use of two enzymes simultaneously in an enzyme mixture were tested taking into account the optimal conditions of their enzymatic activity (concentration, temperatures, and pH). This study led to significant results, indicating effective external and internal cleaning by the studied enzymes (a recovery of at least 25% of the electrical conductivity, 14% of the ion-exchange capacity, and 12% of the contact angle), and demonstrated the presence of possible enzyme combinations for the enhancement of the global cleaning efficiency or reducing cleaning durations. These results prove, for the first time, the applicability of enzymatic cleanings to membranes, the inertia of their action towards polymer matrix to the extent that the choice of enzymes is specific to the fouling substrates. [ABSTRACT FROM AUTHOR]