and high concentrations of P (~5.25 g L -1 ), Na + (~1.9 g L -1 ), and SO4 2-(~0.72 g L -1 ), with lower concentrations of Mg 2+ (~0.2 g L -1 ), Ca 2+ , K + (both ~0.13 g L -1 ), and Cl -(~0.08 g L -1 ; Table and Figure , B). To assess mineral precipitation during concentration of the diluate, PHREEQC software (sit.dat database) was used to simulate the gradual concentration of the diluate through the removal of aliquots of H2O. Even after removing 95.5% of the water (i.e., a 22-fold concentration), the saturation indices (defined as the log of the ion activity product over the solubility constant) of all possible solid phases were negative, suggesting no scaling risk. Ca-P and Mg-P minerals were undersaturated due to the low pH, and gypsum was nearest saturation with a saturation index of -0.09 (Supplementary Information). This simulation thus suggest that a high permeate recovery ratio can be attained by RO without scaling, owing to the removal of most sulfate species by the upstream ED. Laboratory-scale filtration experiments were undertaken with synthetic water simulating a concentrated ED diluate to investigate the feasibility of the RO step. Two types of experiment were undertaken 24 :