least one dissociation constant (pKa) (for example,
sulfamethoxazole has two, pKa1 = 1.7, pKa2=
5.6). By modifying the pH of the solution and
surpassing the pKa value, the charge of the target
compound can be changed in order to enhance
rejection [68]. In the study by Nghiem et al. [74],
carbamazepine, with a pKa of 2.3, became negatively
charged when the experiment was conducted
at pH 8.0. Drewes et al. [68] proved that
non-ionic compounds were inconsistently removed
even in the presence of natural organic
matter (NOM), illustrating that the negative
charge of NOM is insufficient to cause an effect
or compensate for the neutral property of the
target compound. However, at the test pH, rejection
for both sulfamethoxazole and ibuprofen was
increased as the compounds became negatively
charged causing electrostatic interaction and
repulsion mechanisms.