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3.5. Pulsed Electric Field Application and Influences on Membrane Phenomena 3.5.1. Principle of Pulsed Electric Field The pulsed mode is a non-stationary regime applying a hashed current (Figure 12) or voltage: Membranes 2020, 10, 221 19 of 72 for a defined time, the system is under the influence of a constant current/voltage (Pulse lapse—Ton), then the current/voltage is turned off for a fixed time (Pause lapse—Toff). Pulsed electric field (PEF) procedure consists in application of consecutive pulse and pause lapses (Ton/Toff) of constant duration. procedure consists in application of consecutive pulse and pause lapses (Ton/Toff) of constant duration. The application of PEF in electrodialysis was first proposed by Karlin and Kropotov in 1995 [98]. The application of PEF in electrodialysis was first proposed by Karlin and Kropotov in 1995 [98]. Figure 12. Principle of pulsed electric field (PEF) and effect on concentration polarisation. CEM: Figure 12. Principle of pulsed electric field (PEF) and effect on concentration polarisation. CEM: cation-exchange membrane; DBL: diffusion boundary layer. cation-exchange membrane; DBL: diffusion boundary layer. 3.5.2. Advantages and Limitations 3.5.2. Advantages and Limitations PEF has numerous advantages such as (1) suppression of concentration polarization phenomenon, PEF has numerous advantages such as (1) suppression of concentration polarization (2) decrease in water dissociation, (3) enhances demineralization process rate and reduce system phenomenon, (2) decrease in water dissociation, (3) enhances demineralization process rate and resistance, (4) increases the current efficiency and consequently decrease the relative energy reduce system resistance, (4) increases the current efficiency and consequently decrease the relative consumption, (5) enhances transfer of charged biomolecules (organic acid, amino acids, etc.), energy consumption, (5) enhances transfer of charged biomolecules (organic acid, amino acids, etc.), (6) effectiveness against fouling, (7) induces a selective ion migration according to the pulse/pause (6) effectiveness against fouling, (7) induces a selective ion migration according to the pulse/pause combination used and (8) simplicity of equipment, which makes integration of such approach into combination used and (8) simplicity of equipment, which makes integration of such approach into industrial scale easy and inexpensive but it also currently presents some limitations. industrial scale easy and inexpensive but it also currently presents some limitations. First, the positive influence of PEF was found in terms of decrease in concentration polarization First, the positive influence of PEF was found in terms of decrease in concentration polarization phenomenon and consequently decrease in water dissociation [51,54,99,100]. During each pause phenomenon and consequently decrease in water dissociation [51,54,99,100]. During each pause time, time, the concentration polarization decreases until it eventually disappears (Figure 12). This time, the concentration polarization decreases until it eventually disappears (Figure 12). This time, necessary for the disappearance of the boundary layer, is called transition time and makes it possible necessary for the disappearance of the boundary layer, is called transition time and makes it possible to return to an initial state of concentration similar to that of the homogeneous solution (Figure 12). to return to an initial state of concentration similar to that of the homogeneous solution (Figure 12). It mainly depends on the diffusion of ions through the membranes and in the boundary layer, It mainly depends on the diffusion of ions through the membranes and in the boundary layer, the ion the ion concentration as well as the voltage applied to the system [54,99]. Hence, removing the concentration as well as the voltage applied to the system [54,99]. Hence, removing the concentration concentration polarization phenomenon increases the efficiency of the current and therefore of the polarization phenomenon increases the efficiency of the current and therefore of the energy energy consumed during the process [99]. Recently, the scientific community has gained a better consumed during the process [99]. Recently, the scientific community has gained a better understanding of the phenomena involved during the pauses in PEF electrodialysis. After pausing understanding of the phenomena involved during the pauses in PEF electrodialysis. After pausing the system, a low electrical resistance is achieved because of the restitution of ions in the depleted the system, a low electrical resistance is achieved because of the restitution of ions in the depleted layer at the diluate membrane interface. The re-application of a voltage after each pulse promotes electroconvective vortices (ECVs) that translates into current surges [101]. The electroconvection affects turbulence, even at low Reynolds numbers [78]. ECVs promote the transfer of ions onto the surface of the membranes [51], making it possible to work in overlimiting current conditions under negligible water dissociation [64,65]. It was also proven that mass transfer could be intensified severalPDF Image | Electrodialytic Processes
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