• Monochloramination alone did not form
any measurable HNMs.
• Chlorination did not form significant
amounts of HNMs even in the presence
of bromide. However, the presence of
nitrite significantly increased HNM
concentrations during chlorination.
• For all cases, HNM formation increased
with pH, and treated water had higher
brominated HNM species as compared to
the raw water.
• Conventional treatment processes did not
remove HNM precursors from water.
• Trihalogenated HNMs were the major
HNM species formed above the method
reporting limits (MRLs).
For I-THMs, the results obtained so far
show that chlorinating prior to ammonia
addition may not always result in lower
I-THM concentrations than preformed
chloramines, which simulate the addition
of chlorine and ammonia at the same
location in practice. On the contrary,
prechlorination increased I-THM formation
under some circumstances. Therefore,
prechlorination strategy requires a
balanced and water specific approach to
control both I-THMs and regulated THMs.
For preformed chloramination, the results
demonstrated that I-THM formation
depends on the ratio of iodide to dissolved
organic carbon (I-/DOC) and characteristics
of NOM. I-THM species formed when the
I-/DOC ratio was high, and more I-THM
formation was observed in waters with
low specific ultraviolet absorption (SUVA)
than high SUVA. Therefore, higher I-/DOC
ratios will be necessary in high-SUVA
waters for I-THM formation to occur. For
prechlorination followed by ammonia
addition, Cl /DOC ratio was found to be
one of the critical parameters to control
both the extent of THM and I-THM
formation and the ratio of THMs to I-THMs
ratio to control both the concentrations
of THMs and I-THMs will need to be
determined for specific source waters.
Research on I-THM formation and
speciation is ongoing. When the study is
complete, the results will provide a wide
range of greatly needed information to
the drinking water community about the
occurrence, formation, and control of
HNMs and I-THMs. The water industry can
then use the results to develop strategies to
control the formation of HNMs and I-THMs.
The final report is expected to be published
in early 2010. For more information
about the study, contact Alice Fulmer at