Contribution and Removal of Watershed and Cationic Polymer N-Nitrosodimethylamine Precursors

N-nitrosodimethylamine (NDMA) is a disinfection by-product formed when chloramines react with watershed-derived or water treatment polymer-derived precursors. The authors examined the sorption potential of both precursor groups to powdered and granular activated carbon (PAC and GAC). AC reduced NDMA formation potential (NDMAFP) by 30–80 % when only watershed precursors were present. Polydiallyldimethyl ammonium chloride (polyDADMAC)-derived precursors were not removed well by AC. Seven samples of polyDADMAC from across the United States produced 47 ± 3 ng NDMAFP/mg active polymer after coagulation and settling, which is about one-third of the NDMAFP formed in ultrapure water. Ultrapure water was the same as that used for the polyamine testing. Polyamine (340 ng/mg) formed NDMA when diluted in ultrapure water with chloramines, but the precursors were effectively removed by AC. PolyDADMAC use always increased the NDMAFP of the settled water regardless of dose; this suggests that the optimum dose should be based on turbidity removal with consideration for balancing NDMA formation