Evaluation of nanofiltration for disinfection by-products control in drinking water treatment

DBP control by nanofiltration was studied. Nine DBPs including THMs were selected as target compounds. Reagent DBPs and DBPs formed as a result of chlorination of NOM contained in river water, were applied to nanofiltration to examine DBPs removal. Humic acid was used to investigate DBP precursor control. Nanofiltration was conducted for about one day for each experiment using two 2-inch membrane modules. NF showed high performance for DBP precursor removal but little effect on the removal of DBPs themselves, especially THMs. In the experiment of DBP precursors removal, rejections were 98 to 100 percent for most of the DBPFPs. For NOM in river water, rejections of THMFPs were 96 to 99 percent. This shows nanofiltration is effective even at low concentrations of NOM. Nanofiltration can remove almost all organic substances with the apparent molecular weight of greater than 2,000 daltons. Molecular weight distribution patterns of the permeate were different depending on NF. THMs showed decreasing rejection as filtration proceeded because of adsorption on the membrane surface. THM rejections at 24 hours after filtration started were about 10 and 30 percent in Module-A and B, respectively. Haloacetic acids showed relatively higher rejections. It is recommended, from the viewpoint of THM control, that NOM removal using NF is much preferable to the removals of THM, formed by chlorination, using NF.