Treatment of model inland brackish groundwater reverse osmosis concentrate with electrodialysis — Part III: Sensitivity to composition and hydraulic recovery

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Electrodialysis has an advantage in concentrate treatment because the waste concentration factor increases linearly with removal ratio, Sodium concentration (mg/L) Calcium concentration (mg/L) Chloride concentration (mg/L) resistance of 2 Ω·cm2, the resistance from two membranes would represent 14% of the cell-pair resistance. Thus, it is assumed that the majority of the voltage loss is due to diffusion potentials and liquid junction potentials [20,21]. Again, the specific energy consumption was proportional to the concentration of ionic content removed from the diluate (i.e., ~ 0.03 kWh/m3 per Volt/cell-pair applied per meq/L separated), as shown in Fig. 9. Furthermore, for these test conditions, the specific energy of Stage B (D0 = 4.0x, C0 = 7.4x) was nearly identical to the specific energy of Stage A (D0 = 4.0x, C0 = 4.0x), which indicates that the electrical resistance of the concentrate cell is a relatively insignificant fraction of the total resistance. Recognizing that the specific energy is correlated with the operating cost of an ED system, it is important to note that, at some point, the energy required to concentrate a solution by ED would be greater than the energy required by a thermal process (20-40 kWh/m3 [26]), which is relatively insensitive to salinity. Furthermore, the specific energy shown here could be reduced by two-thirds, simply by applying one-third the voltage (i.e., 0.5 V/cell-pair), as shown in Part II [2] of this series.