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N-Nitrosodimethylamine (NDMA) is one of the disinfection byproducts of concern forsystems that chloraminate. NDMA has been shown to form preferentially withchloramine than with free chlorine when diallyldimethylammonium chloride (DADMAC)cationic polymer was used as a treatment coagulant aid. DADMAC is used nationwidefor coagulation. East Bay Municipal Utility District (EBMUD) has extensively tested theconditions under which NDMA was formed at the treatment plants and minimized itsformation (Wilczak et al, 2003a). Literature references report that under acidicconditions NDMA may form upon the contact of dimethylamine (DMA) or certain tertiaryamines with nitrite, which is of concern because nitrite is often present in chloraminateddistribution systems that nitrify, and amine precursors may occur in DADMAC cationicpolymer. However, this reaction was deemed unlikely under typical water treatment pHconditions. Mechanistic studies reported in the literature suggest that the mainpathways of NDMA formation under conditions of water treatment and distribution wouldbe a reaction between amine precursors and monochloramine, as well as a reactionbetween DMA, nitrite and the hypochlorous acid. Bench tests indicated that NDMA wasnot a DADMAC polymer contaminant and did not form in the presence of polymer andammonia, nitrite and nitrate. It was, therefore, unlikely that nitrification would contributeto NDMA formation when DADMAC was the only significant NDMA precursor (Wilczak etal, 2003a). A nitrification monitoring program was conducted in the distribution systemto confirm the effect of nitrification on NDMA levels. Includes 8 references, tables, figures.

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Edition: Vol. - No. Published: 06/17/2004 Number of Pages: 9File Size: 1 file , 240 KB