| dc.description.abstract | N-nitrosodimethylamine (NDMA), a probable human carcinogen disinfection by-product, has been
detected in chloraminated drinking water systems. Understanding its formation over time is important
to control NDMA levels in distribution systems. The main objectives of this study were to investigate the
role of chloramine species (i.e., monochloramine and dichloramine); and the factors such as pH, sulfate,
and natural organic matter (NOM) influencing the formation of NDMA. Five NDMA precursors (i.e.,
dimethylamine (DMA), trimethylamine (TMA), N,N-dimethylisopropylamine (DMiPA), N,N-dimethylbenzylamine (DMBzA), and ranitidine (RNTD)) were carefully selected based on their chemical
structures and exposed to varying ratios of monochloramine and dichloramine. All amine precursors
reacted relatively fast to form NDMA and reached their maximum NDMA yields within 24 h in the
presence of excess levels of chloramines (both monoe and dichloramine) or excess levels of dichloramine
conditions (with limited monochloramine). When the formation of dichloramine was suppressed
(i.e., only monochloramine existed in the system) over the 5 day contact time, NDMA formation from
DMA, TMA, and DMiPA was drastically reduced (~0%). Under monochloramine abundant conditions,
however, DMBzA and RNTD showed 40% and 90% NDMA conversions at the end of 5 day contact time,
respectively, with slow formation rates, indicating that while these amine precursors react preferentially
with dichloramine to form NDMA, they can also react with monochloramine in the absence of
dichloramine. NOM and pH influenced dichloramine levels that affected NDMA yields. NOM had an
adverse effect on NDMA formation as it created a competition with NDMA precursors for dichloramine.
Sulfate did not increase the NDMA formation from the two selected NDMA precursors. pH played a key
role as it influenced both chloramine speciation and protonation state of amine precursors and the
highest NDMA formation was observed at the pH range where dichloramine and deprotonated amines
coexisted. In selected natural water and wastewater samples, dichloramine led to the formation of more
NDMA than monochloramine. | |
