AWWA ACE60029

N-Nitrosodimethylamine (NDMA) is one of the disinfection byproducts of concern for systems that chloraminate. NDMA has been shown to form preferentially with chloramine than with free chlorine when diallyldimethylammonium chloride (DADMAC) cationic polymer was used as a treatment coagulant aid. DADMAC is used nationwide for coagulation. East Bay Municipal Utility District (EBMUD) has extensively tested the conditions under which NDMA was formed at the treatment plants and minimized its formation (Wilczak et al, 2003a). Literature references report that under acidic conditions NDMA may form upon the contact of dimethylamine (DMA) or certain tertiary amines with nitrite, which is of concern because nitrite is often present in chloraminated distribution systems that nitrify, and amine precursors may occur in DADMAC cationic polymer. However, this reaction was deemed unlikely under typical water treatment pH conditions. Mechanistic studies reported in the literature suggest that the main pathways of NDMA formation under conditions of water treatment and distribution would be a reaction between amine precursors and monochloramine, as well as a reaction between DMA, nitrite and the hypochlorous acid. Bench tests indicated that NDMA was not a DADMAC polymer contaminant and did not form in the presence of polymer and ammonia, nitrite and nitrate. It was, therefore, unlikely that nitrification would contribute to NDMA formation when DADMAC was the only significant NDMA precursor (Wilczak et al, 2003a). A nitrification monitoring program was conducted in the distribution system to confirm the effect of nitrification on NDMA levels. Includes 8 references, tables, figures.