Structural Modifications to Quaternary Ammonium Polymer Coagulants to Inhibit N-Nitrosamine Formation.
Quaternary ammonium cationic polymers, such as poly(diallyldimethylammonium chloride) (polyDADMAC) and epichlorohydrin-dimethylamine (Epi-DMA), are commonly used by water utilities to enhance removal of particles and dissolved organic matter (DOM) from raw waters. Unfortunately, chloramination of waters treated with quaternary ammonium polymers leads to the formation of carcinogenic N-nitrosodimethylamine (NDMA). In this study, two approaches were developed to modify polyDADMAC and Epi-DMA to inhibit N-nitrosamine formation. The first approach involved treatment of polymers with methyl iodide (MeI), an alkylating agent, to convert polymer-bound tertiary amine groups to less chloramine-reactive quaternary ammonium groups. The second approach involved synthesis of polymers bearing less chloramine-reactive quaternary ammonium groups with dipropylamino (DPA) substituents. Treatment with MeI reduced NDMA formation from polymers by ∼75%, while synthesis of DPA-based polymers eliminated NDMA formation and formed N-nitrosodipropylamine, which is 10-fold less carcinogenic than NDMA, at 20-fold lower yields. Bench-scale jar tests demonstrated that both MeI-treated and DPA-based polymers achieved similar removal of particles and DOM as the original polyDADMAC and Epi-DMA at both low and high doses, but formed significantly less N-nitrosamines. This work demonstrates two approaches for modifying quaternary ammonium cationic polymers, which may enable water utilities to meet potential future regulations on N-nitrosamines while maintaining polymer usage to meet existing regulations.
Department of Civil and Environmental Engineering, Syracuse University , 151 Link Hall, Syracuse, New York 13244, United States.|Department of Civil and Environmental Engineering, Stanford University , 473 Via Ortega, Stanford, California 94305, United States.|National Science Foundation Engineering Research Center for Re-Inventing the Nation's Urban Water Infrastructure (ReNUWIt), 473 Via Ortega, Stanford, California 94305, United States.
Teng
T
Zeng
Department of Chemistry, Stanford University , 333 Campus Drive, Stanford, California 94305, United States.
Russell Jingxian
RJ
Li
Department of Civil and Environmental Engineering, Stanford University , 473 Via Ortega, Stanford, California 94305, United States.|National Science Foundation Engineering Research Center for Re-Inventing the Nation's Urban Water Infrastructure (ReNUWIt), 473 Via Ortega, Stanford, California 94305, United States.
William A
WA
Mitch
D064751:Ammonium Compounds; D004128:Dimethylnitrosamine / Q000737:chemistry; D009602:Nitrosamines / Q000737:chemistry; D011108:Polymers / Q000737:chemistry; D018508:Water Purification
D064751:Ammonium Compounds; D009602:Nitrosamines; D011108:Polymers; D004128:Dimethylnitrosamine