Integrated nanofiltration cascades with low salt rejection for complete removal of pesticides in drinking water production

In this study, the aim is to remove micropollutants (pesticides) from water completely while removing only a small fraction of salts. To achieve the latter, loose commercial nanofiltration (NF) membranes were selected (Desal51HL, N30F and NF270). To realize a high removal of organic compounds, combined with a low salt rejection, cascades of NF stages are proposed. Experiments with pesticides (aldrin, atrazine, bentazone, dieldrin, and propazine) and NaCl confirmed that a nearly complete rejection of pesticides is possible, depending on specific properties of the solutes such as molecular size and chemical structure (e.g. hydrophobicity). Salt rejection was highly dependent on the specifications of the membrane and on the ion charge, and ranged from low to high values. Through modeling based on transport equations and mass balances, it was shown that the separation was significantly improved by adopting the principle of an integrated cascade of NF membranes.