Contribution and removal of watershed and cationic polymer N-nitrosodimethylamine precursors

N-nitrosodimethylamine (NDMA) is a disinfection by-product formed when chloramines react with precursors derived from watersheds or water treatment polymers. The authors examined the sorption potential of both precursor groups to powdered and granular activated carbon (PAC and GAC). Activated carbon reduced the formation potential (FP) of NDMA by 30 to 80% when only watershed precursors were present. Polydiallyldimethyl-ammonium chloride (polyDADMAC) precursors were not removed well by activated carbon. 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 (> 18.2 MΩ-cm) water. Polyamine (340 ng/mg) formed NDMA when diluted in ultrapure water with chloramines, but the precursors were effectively removed by activated carbon. 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.