Sustainable Brackish Desalination Management: Oxidative Removal of Antiscalants and Scale-Forming Constituents From Desalination Concentrate
Brackish water desalination has become increasingly important in arid inland regions for sustainable water supplies, but the management of desalination brine waste is costly. In particular, the presence of oversaturated calcium as scale-forming compounds in the brine is the most important factor limiting the recovery of water. Removal of these antiscalants from the brine can induce the precipitation of oversaturated scale-forming substances, enable additional water recovery from RO concentrate, and reduce the risk of eutrophication after brine disposal. This study investigated the impact of photochemical degradation of three widely used antiscalants, i.e., nitrilotri-methylenephosphonic acid (NTMP), ethylenediaminetetra-methylenephosphonic acid (EDTMP) and diethylenetriaminepentakis-methylphosphonic acid (DTPMP) with hydrogen peroxide and persulfate as the photo-oxidants and on inducing the precipitation of calcium sulfate. Results showed that the antiscalants could be effectively degraded at the optimized conditions. DTPMP degrades much slower compared to NTMP and EDTMP with all the oxidants in this study. DTPMP also has much higher inhibition capacity in delaying the precipitation of gypsum. The degradation byproduct generated by the oxidation of DTPMP are likely responsible for the higher inhibition capacity in delaying the precipitation. Among the oxidants tested, persulfate shows the highest degradation rate of all the antiscalants tested. It was also observed that induction time depends on the extent of UV exposure. This study shows an effective way to increase the water recovery in desalination concentrate with the help of a UV/oxidant-assisted removal of TDS and thereby employing a secondary RO.