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Kinetics of surface water desalination by neutralization dialysis (ND) was studied in a three-compartment stack with ion-exchange membranes, and the process feasibility was evaluated. The pH and the ionic conductivity of a model saline solution (0.02 M NaCl) were measured during different ND operations in batch mode. The influence of the flow rate, the solution concentration in the alkali and acid compartments was investigated. It was found that, at the beginning of the operation, the ion-exchange kinetics was mainly controlled by the membrane diffusion. The maximal fluxes of exchanging ions (Jmax) (Na+ and H+ across CMX membrane, and Cl− and OH− across AMX membrane) were theoretically evaluated. The calculated and the experimentally measured fluxes at the beginning of batch operation were close. However, after some minutes of solution desalination, the salt concentration decreased, which involved diffusion boundary layer controlled kinetics. Hence, with time, the fluxes decreased and were considerably smaller than Jmax. The increase/decrease in the acid and alkali solution concentration resulted in corresponding increase/decrease in the ion-exchange rate. Recommendations have been provided to reduce the desalination duration.

For about 60 years, it is known that “limiting current” density does not really limit the current density in electrodialysis (ED). The use of intensive currents allows one to decrease the area of expensive ion-exchange membranes, hence to obtain more compact ED plants with lower investment costs. However, in practice overlimiting currents are applied solely in electrodeionization, and not in conventional ED devices. In literature (H. Strathmann [1]), overlimiting current density operation ED is considered as being under ongoing research and development. Where is the research today? What is the actual understanding of overlimiting mass transfer processes in membrane systems? As far as electroconvection is involved as a major mechanism of overlimiting transfer, what could bring specific knowledge and practice acquired in nano- and microfluidics into desalination? Can overlimiting ED be economically advantageous? Is there an alternative for classical ED devices applied? This review is intended to give some responses to these questions.

A technique to test electrodialysis (ED) stacks designed to desalt dilute solutions is developed. The technique permits obtaining reproducible data on laboratory and medium-scale units useful for predicting mass transfer characteristics of large ED stacks. Quasi-steady state of desalination process is the main condition to obtain such data. This state can be attained by applying recycling hydraulic modes and special devices to maintain constant pH, or pH and concentration of the feed solution. To obtain data for scaling, it is necessary to apply a fixed voltage on the stack and to use a constant flow rate of the feed solution during the experiment, the feed solution concentration may vary with the time. Specifications of the stacks studied, rational hydraulic and electrical modes of testing are considered.

A mathematical model of the competitive electro-transport of two counter-ions through an ion exchange membrane based on the Nernst-Planck and Poisson equations is developed. A three-layer system is considered: the membrane and two adjacent diffusion layers. Concentration profiles in the three layers, effective transport numbers as functions of the current and current-voltage characteristics are calculated. Deviation from the local electroneutrality in space charge region near the depleted solution/membrane interface is taken into account. It is shown that the space charge region grows with the voltage applied. However the fluxes of the competitive counter-ions at over-limiting currents are determined by their transfer through the electroneutral part of the depleted diffusion layer.

A modified static method for investigation of CO32−, HCO3− and OH− ions sorption by anion-exchange membranes was developed. The ion-exchange equilibrium coefficient in the system of the Russian commercial anion-exchange membrane MA-41 in sodium carbonate/hydrocarbonate solutions within pH range from 8.3 to 10.8 is found. This value is calculated by two methods: taking into account or not the hydrolysis reactions of carbonate in the equilibrium solution and the sorption of OH− ions by the membrane. The ion exchange coefficient valueKHCO3−CO32− is 9.

Facilitated transport of amino acid zwitterion (S) through sulfonic plane and tubular cation-exchange membranes (CEM) in a reactive form H + is studied. This transport uses the ability of a non-charged species S to combine with H + in order to form a counter-ion SH + in the membrane. A theoretical model of the facilitated transport taking into account effect of the diffusion layers adjoining the membrane is developed. It is illustrated by the experimental results of α-alanine (Ala) and phenylalanine (Phe) transport through plane Nafion® 117 and Nafion® 120 membranes (Du Pont de Nemours), Ala transport through a plane CRP membrane (Rhone Poulenc®), and Ala transport through a tubular Nafion® 811X.

In order to provide drinking water for the population of the Aral region, the electrodialysis (ED) process was selected for desalting well waters containing up to 15 g/L of salts. Two new designs of electrodialysers were developed for adapting the process at the scale of a little village. Experimental tests were conducted in the Aral region. ED has been proved to solve effectively the problem of provision of the Aral region population with drinking water as well as partially demineralised water for irrigation and drinking water for animals. Our cost estimate of drinking water production made from the results of an ED plant exploitation at the Bozoi village in Kazakhstan (capacity is 10 m 3 / h, raw water TDS is 12.9 g/L) gives 1.2 and 0.3 US$ per m 3 when the energy cost is 0.13 and 0.02 US$/kWh, respectively, or 0.1 and 0.025 US$ per kg eliminated salts for the same energy cost values.

Salt and H+(OH−) ion fluxes, the resistivity of desalted solution as well as pH changes are studied in a desalination compartment containing a monolayer of ion-exchange bed (IEB). The influence of anion-exchanger volume fraction in the IEB on the fluxes and the desalted solution characteristics are discussed. The optimum value for the IEB composition is found for the case of Russian commercial ion-exchange membranes and resins.

The analysis of electrodialysis water desalination costs was made. Application of the hydrodynamic convective-diffusion model permitted to determine optimum parameters of an “ideal” process in a desalination channel with smooth-wall ion-exchange membranes without a spacer. The method of mathematical simulation based on a regression of experimental data is applied for cost estimation of the process at optimum operating parameters.

The diffusion boundary layer (DBL) arisingat an electrode or an ion-exchange membraneaffects significantly the mass transfer in electro-chemical systems. There is a great interest in lit-erature as for determination of DBL parametersand development of the real meaning of thisconcept [1]. In this paper, the chronopotentiom-etry is applied to determine the DBL thickness das a function of the time and the applied currentdensity near a CM2 cation-exchange membraneseparating two identical KCl solutions undernatural convection, the membrane being invertical position.

The purpose of the work presented is the investigation of electrodialysis apparatuses of two types differing by demineralization chambers construction only. These are pilot apparatuses based on Russian membranes: cation exchange MK-40 and anion exchange MA-40.

A method to forecast behavior of electrodialyzers with long demineralization channels is suggested. It is based on the data obtained using a laboratory cell or an apparatus with short demineralization channels of similar construction. The results are presented as dimensionless parameters.