Formation of NDMA in Chloraminated Water Coagulated with DADMAC Cationic Polymer

Abstract

Cationic treatment polymer, diallyldimethylammonium chloride (DADMAC), was the only significant source of N‐nitrosodimethylamine (NDMA) precursors in tested waters at the East Bay Municipal Utility District. NDMA concentrations increased with higher cationic polymer doses and longer chloramine contact times. Recycled filter backwash supernatant was a significant source of NDMA precursors, possibly because of residual cationic polymer. Higher NDMA levels were formed with pre‐ammoniation or simultaneous addition of chlorine (Cl2) and ammonia (NH3), whereas free Cl2 contact time prior to chloramination resulted in lower NDMA concentrations with less dependence on polymer dose. NH3, nitrite, and nitrate did not form NDMA with DADMAC; chloramine was necessary to form significant levels of NDMA. NDMA concentrations in the chloraminated distribution system decreased when the cationic polymer doses at two treatment plants were decreased. The lowest concentrations of NDMA were observed in the service areas that received water that was coagulated at low polymer doses and did not contain recycled filter backwash water.