The Effects of Salt Concentration on the Rejection of Pharmaceutically Active Compounds by Nanofiltration Membranes

While traces of pharmaceuticals have been found in the environment, the pharmaceutical industry produces waste streams high in pharmaceutically active compounds concentration along with other components such as salts. This work investigated the removal of three common pharmaceuticals, carbamazepine, ibuprofen, and diclofenac, at concentrations found in the pharmaceutical industry, under different monovalent salt concentrations of sodium chloride using a commercially available nanofiltration membrane. The influence of a monovalent salt concentration and temperature on the removal were determined. Pharmaceutical rejection was found to be dependent on the compounds' molecular weights, charge, and hydrophobicity. Diclofenac and ibuprofen rejections were found to be high (90-99%) and (85-96%) respectively, and the rejection increased with increasing salt concentration. Meanwhile, moderate retention values were found for the neutral carbamazepine (65-77%) and these values decreased with increasing salt concentration, and also decreased with increasing temperatures. A threshold salt concentration was found at which these effects were buffered or even reversed.