Effects of Intrusion on Disinfection Byproduct Formation in Intermittent Distribution Systems

Intermittently operated distribution
systems serve over one billion
people and may be impacted by the intrusion of contaminated waters
carrying disinfection byproduct (DBP) precursors. The impact of intrusion
on the formation of 19 DBPs was evaluated in an intermittent water
system supplied by deep aquifers in Dhaka, Bangladesh. Untreated piped
water samples were collected from residential taps and chlorinated
under controlled conditions. Chloride, dissolved organic carbon, and
the artificial sweetener sucralose were measured as indicators of
intrusion. Most piped water samples had low concentrations of DBPs
and indicators; however, a subset had higher levels of DBPs and indicators,
suggesting the intrusion of contaminated water into the distribution
system, particularly during the rainy season. Piped water samples
with evidence of intrusion typically formed higher concentrations
of haloacetaldehydes and haloacetonitriles when chlorinated, which
greatly increased the calculated cytotoxicity. DBP formation and calculated
cytotoxicity in piped water samples impacted by intrusion were comparable
to those in piped water samples supplied by horizontal and vertical
recharge-impacted groundwaters, yet lower than piped surface waters
from other regions of Dhaka. The results demonstrated that intrusion
can increase DBP formation in an unpredictable fashion, highlighting
the need to sample from many locations in intermittent water systems
to accurately evaluate DBP exposure risk.