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.
| Edition : | Vol. - No. |
| File Size : | 1
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| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 9 |
| Published : | 06/17/2004 |
