Full Description

Cationic polymer doses were reduced at two East Bay Municipal Utility District(EBMUD) treatment plants based on prior work conducted at the District indicating thatthe diallyldimethylammonium chloride (DADMAC) cationic polymer was a significantsource of N-nitrosodimethylamine (NDMA) precursors. Recycled filter backwashsupernatant was a significant source of NDMA precursors, possibly due to residualcationic polymer. When filtered water was chloraminated with chlorine and ammoniaadded simultaneously (in batch samples), elevated NDMA concentrations were formedduring recycle. When filtered water was free chlorinated first (in batch samples) thisrecycle stream did not form increased NDMA concentrations. Distribution systemmonitoring trends were consistent with expectations based on prior experimental results.NDMA concentrations in the chloraminated distribution system decreased when thecationic polymer doses at two treatment plants were decreased. Out of five distincttreatment and distribution service areas operated by the District, the lowest concentrationsof NDMA were observed in the service areas that receive water coagulated at lowpolymer doses, without the input of filter backwash recycle.Ammonia, nitrite and nitrate did not form NDMA with DADMAC; a chloramine residualwas necessary for significant levels of NDMA to be formed. This would indicate thatnitrification in the distribution system is not likely to contribute to NDMA formation forthe current precursor material. Includes 6 references, tables, figures.

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Edition: Vol. - No. Published: 06/15/2003 Number of Pages: 11File Size: 1 file , 320 KB