identify the best quenching approach for
chloraminated DBP samples but no final
recommendation could be made.
The study found that the direct reaction of
monochloramine with dissolved organic
matter (DOM) is the major pathway for HAA
formation during chloramination and that
when preformed chloramine is used, 80%
of the DBPs are in the form of DXAAs. The
study determined that formation was much
slower than reported in previous studies,
but no kinetic equations were developed.
Wastewater was looked at as a possible
source of DBPs and precursors for systems
that use river water downstream from
a wastewater discharge. Contribution
of Wastewater to DBP Formation
(2008, order #91206/project #2948)
found that high levels of ammonia in
wastewater upon disinfection results in
chloramination and formation of HAAs
and N-nitrosodimethylamine (NDMA). The
river ecosystem promotes the degradation
of each DBP in different ways; HAAs are
biodegraded, NDMA is photolyzed, and
THMs are volatilized. Wastewater plants
that nitrify well have lower ammonia
levels and when disinfected, form higher
levels of THMs. As human sources do not
contribute significantly to humic material,
much of the halogenated DBP precursors
in the wastewater effluent originate from
disposal of drinking water with high NOM.
Nitrogenous DBPs were a different matter
and are discussed in the unregulated/
emerging DBP section of this issue.
A lot of research has been published on
DBP formation mechanism, reactivity, and
control at the treatment plant, but very
little was known about fate and transport
of precursors through the watershed to
the plant intake. Long-Term Variability
of BDOM and NOM as Precursors in
Watershed Sources (2007, order #91186/
project #2868) examined the fate and
transport of DBP precursors in watersheds.
It studied the generation of DOC at the water
source and its cycling in the ecosystem.
The project conducted a survey of over 500
utilities concerning their DBP and precursor
(TOC and DOC) data collection. Most of the
utilities had extensive data on precursors.
One of the most surprising results was that
THM and HAA precursor levels were very
uniform across the continent. Bench-scale
experiments were conducted with real leaf
litter biodegradation. The experiments
showed that significant DOC was leached
in 24 hours from pine, maple, and oak
material, while SUVA levels increased after
81 days of biodegradation in all species.
Two watersheds were analyzed over several
seasons. The data showed that precursor
level actually decreased with increasing
TOC. This, along with rain event data,
showed that the first flush was generally
high in TOC, but low in reactive precursors.
Younger TOC that has not undergone
biodegradation is not as reactive as aged
TOC and tends to form less DBPs.
A quantitative model was developed and
calibrated. It had parameters for many
different classes of NOM such as proteins,
sugars, lignins, etc. The model accounted
well for actual DBP formation. It predicted
that biodegradation would increase precursor
levels and that tannins and lignins would be
the most reactive for THM formation.
A large survey of utilities was compiled into
a database to look for temporal and spatial
variations. Generally, TOC levels increased
in more populated areas and decreased
in rural locations, however, there was no
strong, consistent correlation. Wetlands
were shown to be a major contributor to