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.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 570 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 18 |
| Published : | 06/16/2002 |
