Full Description

Pilot and bench testing conducted at the East Bay Municipal Utility District (District) indicated that cationic treatment polymer, diallyldimethylammonium chloride (DADMAC), was the only significant source of N-nitrosodimethylamine (NDMA) precursors in tested waters. The levels of NDMA formed increased with higher cationic polymer doses and longer contact times with the chloramines. Higher NDMA levels were measured with preammoniation or simultaneous addition of chlorine and ammonia, whereas free chlorine contact time for three to four hours prior to chloramination resulted in lower NDMA levels. Application of nonionic flocculant or filter aid may lower NDMA concentrations in chloraminated-finished water, possibly due to better residual cationic polymer removal during sedimentation and filtration. Intermediate ozonation and peroxone process did not increase NDMA formation but rather appeared to lower the overall levels. Similar levels of NDMA were formed in test waters when either alum or ferric chloride was used as the primary coagulant. Filtration rate variations between 3 and 6 gpm/sf through anthracite/sand filter media did not impact NDMA formation. Recycled filter backwash supernatant was a significant source of NDMA precursors, possibly due to residual cationic polymer contained in this stream. It is unknown to what extent this recycled stream may impact finished water NDMA levels; presumably the majority of recycled polymer is removed by clarification and filtration. Includes 15 references, tables, figures.

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Edition: Vol. - No. Published: 06/16/2002 Number of Pages: 18File Size: 1 file , 570 KB