Treatment of model inland brackish groundwater reverse osmosis concentrate with electrodialysis—Part I: sensitivity to superficial velocity

The objective of this research was to investigate the sensitivity of electrodialysis performance to variations in hydraulic flow when treating brackish water reverse osmosis (BWRO) concentrate waste. A synthetic BWRO concentrate from Arizona of 7890mg/L total dissolved solids was prepared with poly-phosphonate antiscalants, and desalinated with a laboratory-scale electrodialyzer with 10 cell-pairs and a transfer area of 64cm2 per membrane. Flow, pressure, conductivity, temperature, and pH were measured continuously, and periodic process samples were analyzed by ion chromatography and inductively coupled plasma-optical emission spectrometry for anion and cation concentrations, respectively. The BWRO concentrate was successfully treated with a stack voltage application of 1.0V/cell-pair and current densities less than 280A/m2 for salinity removal ratios up to 99% (without precipitation). The superficial velocities were controlled in a range of 1.2 to 4.8cm/s, which corresponded to Reynolds numbers of 10 to 40. This paper shows the polarization parameter (ranging from 2.0 to 3.6A/m2 per meq/L) as a function of Reynolds number and removal ratio, and, at maximum sensitivity, the polarization parameter was proportional to Reynolds number raised to the 0.132 power.