was used with the same monovalent-selective CEM. To avoid F(I)-related limitations, fluoride-free solution was used to simulate PIWAA pre-treated for F(I) removal. Previous studies and current industrial practice indicate effective F(I) removal in PIWWA treatment by, for example, adsorption on silicate-bearing materials. Omitting F(I) allowed the use of a standard 0.45 mm spacer rather than the special-grade 1 mm spacer. To minimize P transport, the feed pH was lowered to 1.5, with (note that F(I) removal was shown to reduce PIWAA pH, thus no acid addition is required). Under these conditions and with the modified stack, the current density (Figure ) was higher than that achieved in the low-recovery experiments (Figure ), despite the higher voltage of the latter (18 V vs. 4 V).