(Figure 1). Chlorine was more effective in
the pH range of 8 to 9 and in warmer water.
Ozone and MPUV were more effective at
higher pH levels.
RBF, PAC, and GAC removed watershed-
(wastewater) derived precursors. Low
doses of PAC (e.g., 5–10 mg/L) were often
effective. RBF, PAC, and GAC removed
NDMA FP better than that of the bulk dissolved organic carbon (DOC) or UV at 254
nm (UV254) (Figure 2). PAC removed, in limited tests, polyamine-derived precursors,
but did not remove polyDADMAC-derived
precursors. GAC did not appear to be effective at removing polyDADMAC-derived
precursors. Thus, polymer management
and the use of alternative polymers must
also be considered.
Biofiltration sometimes removed
NDMA precursors, but more often, it
raised the NDMA FP. This suggests that
bacteria sloughed off the biofilter and/
or their soluble microbial products may
be a source of precursors. Magnetic ion
exchange (MIEX) resin removed some
wastewater-derived precursors, but was
also a source of precursors.
THE BENCH-, PILOT-, and full-scale studies provided important information on
the control of nitrosamine formation.
This information was used to develop a
decision tree to guide utilities through
nitrosamine control strategies. Moreover,
the information in this project should
help regulators in developing standards
Utilities should conduct initial studies on the occurrence of nitrosamines in
their finished waters. If significant levels
are present, FP and SDS tests should be
conducted to determine the source(s) of
precursors, the efficacy of existing treatment and disinfection processes, and the
ability of modifications in treatment and/
or pre-oxidation on nitrosamine control.
However, strategies to control nitrosa-
mines must be balanced with the forma-
tion of other DBPs. Moreover, unintended
consequences must be considered. This
project, along with other Water Research
Foundation studies, will help determine
cost-effective methods for utilities to con-
trol nitrosamine formation.
More information about this project
was presented in a WRF webcast on
March 18, 2015. The webcast is available
on the WRF website.
Figure 2. DOC, UV254, and NDMA FP breakthrough in GAC packed beds using blended surface water (SW) and secondary wastewater
( WW) (GAC820 [bituminous] [¯ for 10% SW + 90% WW; R for 50% S W + 50% W W; £ for 90% SW + 10% WW] or HD3000