Treatment of brackish water inland desalination brine via antiscalant removal using persulfate photolysis

Abstract

Brine disposal is a challenging issue for brackish water desalination in inland regions. This study developed an ultraviolet-driven persulfate oxidation pre-treatment (UV/PS) followed by chemical demineralization (CDM) and microfiltration to effectively treat brackish water desalination brine, specifically by degrading the antiscalant during UV/PS and precipitating scale-forming calcium from the brine during CDM. To optimize calcium removal kinetics, the effects of the persulfate dose and UV irradiation time during UV/PS were investigated and softening by NaOH and lime during CDM was evaluated. The UV/PS pre-treatment successfully eliminated the scale inhibition effect of the antiscalant, resulting in an enhanced chemical demineralization performance. A few minutes of CDM operating time was sufficient to remove more than 85% of total calcium from the brine due to the fast sedimentation of calcium precipitates. Moreover, compared to a control (no pre-treatment), the subsequent microfiltration (MF) membrane fouling potential was reduced by 80%. Overall, the application of the UV/PS-CDM-MF combined process has the potential to remove more than 90% of calcium from the brackish desalination brine, and consequently recover a significant amount of fresh water (>90%) from the brine. Results from this study point to the UV/PS-CDM process as a promising brine treatment technology to remove scale-forming precursors and improve water recovery.