and;Occurrence;first identified NDMA
formation potential from chlorination of
dimethylamine polymers and recommends
that dosage rates of such polyelectrolytes be
minimized to be consistent with turbidity and
other water quality objectives. Occurrence
and;Formation;of;Nitrogenous;Disinfection
By-Products advises utilities to especially
minimize the use of coagulation polymers
featuring tertiary amines. Since these polymers
are thought to be removed by filtration, an
alternative or additional precaution is to
hold off adding chlorine or chloramine until
the filter effluent. Strategies;for;Minimizing
Nitrosamine;Formation;During;Disinfection
proposes the use of membrane technologies
for separation to reduce the need for polymers
and thus help eliminate this nitrosamine
precursor source. Also, as stated in the
previous section, certain anion exchange
resins used to remove inorganic contaminants
and NOM have been found to serve as
precursors for nitrosamines. “Anion Exchange
Resins as a Source of Nitrosamines and
Nitrosamine Precursors,” will investigate this
further and identify treatment schemes and
conditions to be avoided in order to prevent
nitrosamine precursors from leaching.
In addition to minimizing N-DBP
precursors, removal of precursors is an
option for controlling N-DBPs. Strategies
for;Minimizing;Nitrosamine;Formation
During;Disinfection recommends that
utilities consider treating water sources with
slow sand filtration, artificial groundwater
recharge, or riverbank filtration, all of
which have been found to reduce levels
of nitrosamine precursors. Besides the
removal of nitrosamine precursors, these
treatment steps have the added benefit of
reducing concentrations of nitrosamines
already present in surface waters. Biological
filtration is also capable of removing
significant levels of HNM precursors and
aldehyde precursors for CNXs, according to
Occurrence;and;Formation;of;Nitrogenous
Disinfection;By-Products. While neither
study showed coagulation or lime softening
to be efficient at removing nitrosamine
precursors, Occurrence;and;Formation
of;Nitrogenous;Disinfection;By-Products
found these treatment options capable of
removing approximately 30% of precursors
for CNXs and HANs. This study also
found lime softening capable of removing
approximately 30% of HNM precursors.
However, conventional treatment processes
do not remove HNM precursors from
water, according to a nearly complete
project, “Exploring Formation and
Control of Emerging DBPs in Treatment
Facilities: Halonitromethanes and Iodo-trihalomethanes.”
Another option for minimizing N-DBP
formation is pre-oxidation of precursors.
In Strategies;for;Minimizing;Nitrosamine
Formation;During;Disinfection,
laboratory-scale experiments as well as
full-scale tests at several water utilities
proved that oxidation is an efficient tool
for removal of nitrosamine precursors.
Reduction in NDMA formation rates
of greater than 90% were observed
after pre-ozonation as well as after
pre-chlorination. Likewise, Occurrence
and;Formation;of;Nitrogenous
Disinfection;By-Products found
application of chlorine or ozone upstream
of chloramine will hinder nitrosamine
formation. It also found free chlorine
will rapidly destroy CNXs. However, in
this same study, pre-oxidation with chlorine
promoted the formation of regulated DBPs
and HANs. While pre-oxidation with ozone
promoted the formation of HNMs and
CNXs, HNMs and CNXs can be removed
by biological filtration.
In addition, pre-ozonation can increase
bromate formation, and, as stated in
